SECTION 3

COMPONENT OPERATION

—CONTENTS—
Group 1 Pump Device Group 5 Travel Device
Outline .....................................................T3-1-1 Outline .....................................................T3-5-1
Main Pump ...............................................T3-1-2 Travel Reduction Gears ............................T3-5-2
Regulator .................................................T3-1-5 Travel Motor .............................................T3-5-3
Pilot Pump..............................................T3-1-20 Travel Brake Valve ...................................T3-5-8
N Sensor (Engine Speed Sensor) ...........T3-1-20 Parking Brake.........................................T3-5-10
Pump Delivery Pressure Sensor .............T3-1-20
Pump Control Pressure Sensor ..............T3-1-20 Group 6 Signal Control Valve
Outline .....................................................T3-6-1
Group 2 Swing Device Pilot Port ..................................................T3-6-2
Outline .....................................................T3-2-1 Shuttle Valve ............................................T3-6-4
Swing Reduction Gear..............................T3-2-2 Shockless Valve .......................................T3-6-6
Swing Motor .............................................T3-2-3 Pump 1 and Pump 2 Flow Rate
Swing Parking Brake ................................T3-2-4 Control Valves ........................................T3-6-8
Valve Unit .................................................T3-2-6 Bucket Flow Rate Control Valve
Control Spool, Flow Combiner Valve
Group 3 Control Valve
Control Spool, Swing Parking Brake
Outline .....................................................T3-3-1
Release Spool ......................................T3-6-10
Hydraulic Circuit .......................................T3-3-8
Flow Combiner Valve..............................T3-3-12 Group 7 Others (Upperstructure)
Main Relief Valve....................................T3-3-14 Pilot Shut-Off Valve ..................................T3-7-1
Overload Relief Valve .............................T3-3-16 Solenoid Valve Unit ..................................T3-7-2
Regenerative Valve ................................T3-3-18 Torque Control Solenoid Valve, Pump 2
Anti-Drift Valve .......................................T3-3-20 Flow Rate Control Solenoid Valve ...........T3-7-4
Flow Rate Control Valve .........................T3-3-22 Pilot Relief Valve ......................................T3-7-6
Auxiliary Flow Combining Valve and EC Motor ..................................................T3-7-6
Bypass Shut-Out Valve .........................T3-3-24
Group 8 Others (Undercarriage)
Group 4 Pilot Valve Swing Bearing ..........................................T3-8-1
Outline .....................................................T3-4-1 Center Joint..............................................T3-8-2
Operation .................................................T3-4-2 Track Adjuster ..........................................T3-8-3

1F1T-3-1
(Blank)

1F1T-3-2
 COMPONENT OPERATION / Pump Device
OUTLINE

The pump device consists of the main pump and pilot

pump.
The main pump is a bent-axis type variable
displacement axial plunger pump. Pump 1 (6) and
pump 2 (1) are integrated as two units in one housing.
Pilot pump (4) is a gear pump and located in the
housing.
Pump delivery pressure sensors (7 and 8), pump
control pressure sensors (2 and 3), and N sensor are
provided to control pump and valve operations.

4
3

5
2

6
T1F1-01-02-003

8 7

1 - Pump 2 3 - Pump 1 Control Pressure 5 - N Sensor 7 - Pump 1 Delivery Pressure

Sensor Sensor
2 - Pump 2 Control 4 - Pilot Pump 6 - Pump 1 8 - Pump 2 Delivery Pressure
Pressure Sensor Sensor

T3-1-1
 COMPOMRNT OPERATION / Pump Device
MAIN PUMP

The main pump supplies pressure oil to actuate the Drive disc (1) of pump 2 is connected to drive disc (2)
hydraulic components such as motors or cylinders. of pump 1 and drive disc (10) of pilot pump (8) via
The main pump consists of pump 1 and pump 2. The gears (6 and 7) of the drive disc. Therefore, when drive
engine torque is transferred to drive disc (1) of pump 2. disc (1) rotates, drive discs (2 and 10) together to
Drive disc (1) is connected to cylinder block (5) via deliver the hydraulic oil. Pumps 1 and 2 are equipped
seven plungers (4) so that drive disc (1) and cylinder with regulator (9) which controls the flow rate.
block (5) rotate together. When cylinder block (5) is
rotated, plungers (4) oscillate in the cylinder block,
suctioning and delivering hydraulic oil.

9
2 8

10
6

1 4 5

T165-03-01-012

T1F1-03-01-001

1 - Drive Disc (Pump 2) 5 - Cylinder Block 7 - Gear 9 - Regulator

2 - Drive Disc (Pump 1) 6 - Gear 8 - Pilot Pump 10 - Drive Disc (Pilot Pump)
4 - Plunger

T3-1-2
 COMPOMRNT OPERATION / Pump Device
Operational Principle

Engine torque is transferred to the shaft and the

seven plungers, causing the cylinder block to rotate
while sliding along the valve plate surface. The
plungers oscillate in the cylinder block bores to
alternately draw and deliver hydraulic oil.

Plunger

Valve Plate

Shaft

Cylinder Block

T105-02-03-002

T3-1-3
 COMPOMRNT OPERATION / Pump Device
Increasing and Decreasing Flow Rate

Changing inclination of cylinder block (3), causes

plunger (2) stroke to increase or decrease depending
on the slant angle which in turn controls the main
pump flow rate. Up-down movement of servo piston
(6) changes inclination of cylinder block (3). Servo
piston (6) is interlocked with valve plate (4) via rod (5).
The one end of cylinder block (3) is kept in contact
with the surface of valve plate (4) and slides along it.

Maximum Displacement Angle:

3
̔

3 6

5
T105-02-03-021

Minimum Displacement Angle (Operable Limit Angle):

T1F1-03-01-001
̔

T105-02-03-022

2 - Plunger 4 - Valve Plate 5 - Rod 6 - Servo Piston

3 - Cylinder Block

T3-1-4
 COMPOMRNT OPERATION / Pump Device
REGULATOR

The regulator regulates the main pump flow by pilot

pressures to keep the pump driving power below the
engine output. Pumps 1 and 2 are each provided with 1
a regulator.
The regulator includes spring 1 (1), spring 2 (4), spring
3 (6), spring 4 (7), spring 5 (8), piston 1 (2), piston 2 (3), 2
control piston (5), servo piston (9), and rod (10).
The regulator opens or closes a circuit to large
chamber (12) by pilot pressures in order to move servo
3
piston (9) and rod (10) up and down, which changes
the pump inclination angle to control the pump delivery
flow. 4

10

11

12

T1F1-03-01-004

1 - Spring 1 4 - Spring 2 7 - Spring 4 10 - Rod

2 - Piston 1 5 - Control piston 8 - Spring 5 11 - Small Chamber
3 - Piston 2 6 - Spring 3 9 - Servo piston 12 - Large Chamber

T3-1-5
 COMPOMRNT OPERATION / Pump Device
Regulator Control Functions
The regulator has the following four control functions:

• Control by Pump Control Pressure

The pump flow control valve housed in the signal
Flow
control valve controls the pump control pressure Rate (Q)
Pi according to control lever stroke. By Pi, the
regulator increases or decreases the pump
delivery flow.
As the control lever is shifted, Pi increases to let
the regulator increase the pump delivery flow. As
the control lever is returned to neutral, Pi
decreases to let the regulator reduce the pump
delivery flow.
0 Pump Control Pressure (Pi)

• Control by Pressure of Own Pump or Companion

Pump
The regulator is subjected to the delivery pressure
Pd1 of the own pump and the delivery pressure
Pd2 of the companion pump. When the average
pressure of both Pd1 and Pd2 exceeds the preset
P-Q curve, the regulator works to decrease the Flow Pressure Increase
delivery flow from both the pumps according to Rate (Q)
the P-Q curve. This protects the engine from Flow Decrease
overloading.
The P-Q curve is preset on both the pumps, so
the delivery flow from both the pumps becomes
almost the same. Therefore, one pump, when
subjected to a higher pressure, will be loaded
more, and vice versa. The total output of both the
pumps becomes almost equal to the engine 0 Pressure (P)
output. This is called the Summation Control.

• Control by Pilot Pressure at Torque Control

Solenoid Valve
MC (Main Controller) operates based on the
target engine speed and actual engine speed, and
sends signals to the torque control solenoid valve.
By these signals, the torque control solenoid valve
transmits the torque control pilot pressure Pps to Flow
the regulator. Rate (Q)
The regulator, when subjected to Pps, decreases
the pump delivery flow. (Speed Sensing (Power
Decrease) Control, and Slow Speed Torque
Increase Control)
(Refer to the CONTROL SYSTEM section.)

0 Pressure (P)

T3-1-6
 COMPOMRNT OPERATION / Pump Device

• Control by Pilot Pressure at Flow Control Solenoid Flow

Valve Rate (Q)
(Pump 2 only)
MC, when receiving signals from the work mode
switch, pressure sensor (auxiliary) or attachment
mode switch (option), sends signals to the
maximum pump flow control solenoid valve.
By these signals, the maximum pump flow control
solenoid valve decreases the pump control
pressure Pi for maximum pump delivery flow 0 Pressure (P)
control. This is called the Maximum Pump Flow
Control.
(Refer to the CONTROL SYSTEM section.) Flow
Rate (Q)

0 Pump Control Pressure (Pi)

Pi Pps Pd2

Pd1

Dr

Min.

Displacement
Angle
Max.

T1F1-03-01-003

Pd1 -Pump 1 Delivery Pressure Pi - Pump Control Pressure

(Self Delivery Pressure)
Pd2 -Pump 2 Delivery Pressure Pps -Torque Control Pressure
Dr - Return to Hyd. Oil Tank

T3-1-7
 COMPOMRNT OPERATION / Pump Device
Control by Pump Control Pressure

• Flow Increase Control

1. When a control lever is operated, the flow rate
Flow
control valve in the signal control valve is shifted, Rate (Q)
increasing pump control pressure Pi.
2. When a total force of Pi, spring 2 (4), spring 4 (7)
and spring 5 (8) exceeds a spring force of spring 1
(1), piston 1 (2) moves up.
3. By this movement, a passage at the notch B
opens in control piston (5) to connect the large
chamber of servo piston (9) to the hydraulic oil
tank.
4. The small chamber of servo piston (9), in which 0 Pump Control Pressure (Pi)
Pd1 is always applied, moves down in the flow
increase direction.
5. Servo piston (9) actuates the valve plate via rod
(10) to increase the inclination angle of the
Pi
cylinder block and the delivery flow.
6. As servo piston (9) moves down, a total spring
force of spring 4 (7) and spring 5 (8) is decreased,
which serves to press the piston 1 (2) up.
Pd1
1
7. Servo piston 1 (2) moves down to a level where 2
the total spring force of spring 4 (7) and spring 5
(8), and a spring force of spring 1 (1) are
balanced.
8. By this movement, a passage at the notch B
closes in control piston (5) to disconnect the large B 5
chamber to the hydraulic oil tank. 4
Movement of servo piston (9) stops, and the flow 7,8
increase control is completed. Dr
10
Min.
9
Displacement
Angle
Max.

T1F1-03-01-003

1- Spring 1 7- Spring 4
2- Piston 1 8- Spring 5
4- Spring 2 9- Servo Piston
5- Control Piston 10 - Rod

Pd1 -Pump 1 Delivery Pressure Pi - Pump Control Pressure

(Self Delivery Pressure)
Dr - Return to Hyd. Oil Tank

T3-1-8
 COMPOMRNT OPERATION / Pump Device

1 1

Pi Pi

2 2

4 4

5 5

B B

7
8 8

Dr Dr

9 9

10
10

Self Delivery Pressure Self Delivery Pressure

Small Chamber Small Chamber

Large Chamber Large Chamber

T1F1-03-01-007 T1F1-03-01-008

T3-1-9
 COMPOMRNT OPERATION / Pump Device
• Flow Decrease Control
1. By returning the control lever to neutral, the flow
rate control valve housed in the signal control Flow
valve is shifted to reduce the pump control Rate (Q)
pressure Pi.
2. As a result, piston 1 (2) and control piston (5)
move down by a spring force of spring 1 (1).
3. By this movement, a passage at the notch A
opens to apply Pd1 to the large chamber.
4. Pressures in the large and small chambers are
equalized, because Pd1 is always applied in the
small chamber of servo piston (9). 0 Pump Control Pressure (Pi)
Servo piston (9) moves up (in the flow reduction
direction) due to a difference in sectional area
between large and small chambers.
5. Servo piston (9) actuates the valve plate via rod Pi
(10) to reduce the inclination angle of the cylinder
block and the pump delivery flow.
6. When servo piston (9) moves up, a total spring
force of spring 4 (7) and spring 5 (8) is increased, Pd1
1
which serves to press piston 1 (2) up. 2
7. As a result, servo piston 1 (2) moves up to a level
where a total spring force of spring 4 (7) and
spring 5 (8), and a spring force of the spring 1 (1) A
are balanced. 5
8. At this time, a passage at the notch A closes in
4
control piston (5) to disconnect the large chamber
7,8
to the hydraulic oil tank. Dr
Movement of servo piston (9) stops, and the flow 10
Min.
decrease control is completed.
9
Displacement
Angle
Max.

T1F1-03-01-003

1- Spring 1 7- Spring 4
2- Piston 1 8- Spring 5
4- Spring 2 9- Servo Piston
5- Control Piston 10 - Rod

Pd1 -Pump 1 Delivery Pressure Pi - Pump Control Pressure

(Self Delivery Pressure)
Dr - Return to Hyd. Oil Tank

T3-1-10
 COMPOMRNT OPERATION / Pump Device

1 1

Pi Pi

2 2

4 4

5 5

A A

7
7

8 8

Dr Dr

9 9

10
10

Self Delivery Pressure Self Delivery Pressure

Small Chamber Small Chamber

Large Chamber Large Chamber

T1F1-03-01-016 T1F1-03-01-009

T3-1-11
 COMPOMRNT OPERATION / Pump Device
Control by Delivery Pressure of Own Pump or
Companion Pump

• Flow Decrease Control

1. When the pump is loaded, Pd1 (pump 1 delivery
Flow
pressure) or Pd2 (pump 2 delivery pressure) is Rate (Q)
increased.
(Pump control pressure Pi is applied in operation.)
2. Pd1 or Pd2 acts on piston 2 (3) to move it down.
When Pd1 or Pd2 exceeds a total spring force of
spring 2 (4), spring 4 (7) and spring 5 (8), piston 2
(3) presses the control piston (5) down.
3. As a result, a passage at the notch A opens to
apply Pd1 to the large chamber.
4. Pressures in the large and small chambers are 0 Pressure (P)
equalized, because Pd1 is always applied in the
small chamber.
Servo piston (9) moves up (in the flow decrease Pi Pd2
direction) due to a difference in sectional area
between large and small chambers.
5. Servo piston (9) actuates the valve plate via rod
(10) to reduce the inclination angle of the cylinder 1
Pd1
block and the pump delivery flow. 2
6. When servo piston (9) moves up, a total spring
force of spring 4 (7) and spring 5 (8) is increased,
which serve to press the piston 2 (3) up.
A 3
7. As a result, servo piston 2 (3) moves up to a level
where a total spring force of spring 4 (7) and 5
spring 5 (8), and a total force of Pd1 and Pd2 are 4
balanced. 7,8
Dr
8. At this time, a passage at the notch A closes in
10
control piston (5) to shut off a circuit to the large Min.
chamber. 9
Movement of servo piston (9) stops, and the flow Displacement
Angle
decrease control is completed. Max.

T1F1-03-01-003

1- Spring 1 7- Spring 4
2- Piston 1 8- Spring 5
3- Piston 2 9- Servo Piston
4- Spring 2 10 - Rod
5- Control Piston

Pd1 -Pump 1 Delivery Pressure Dr - Return to Hyd. Oil Tank

Pd2 -Pump 2 Delivery Pressure Pi - Pump Control Pressure

T3-1-12
 COMPOMRNT OPERATION / Pump Device

1 1

Pi Pi

2 2
Pd2 3 Pd2 3
Pd1 4 Pd1 4

5 5

A A

7
7

8 8

Dr Dr

9 9

10
10

Self Delivery Pressure Self Delivery Pressure

(Pd1 or Pd2) (Pd1 or Pd2)

Small Chamber Small Chamber

Large Chamber Large Chamber

T1F1-03-01-010 T1F1-03-01-011

T3-1-13
 COMPOMRNT OPERATION / Pump Device
• Flow Increase Control
1. When the load to the pump is reduced, Pd1
(pump 1 delivery pressure) or Pd2 (pump 2
delivery pressure) is reduced, which serves to
lower piston 2 (3).
(Pump control pressure Pi is applied in operation.) Flow
Rate (Q)
2. Thus, the force that lowers piston 2 (3) is reduced.
Piston 2 (3) and control piston (5) moves up by a
total spring force of spring 2 (4), spring 4 (7) and
spring 5 (8).
3. By this movement, a passage at the notch B
opens in the control piston 5 to connect the large
chamber of servo piston (9) to the hydraulic oil
tank.
4. Servo piston (9) moves down (in the flow increase 0 Pressure (P)
direction), because Pd1 is always applied in the
small chamber of servo piston (9).
5. Servo piston (9) actuates the valve plate via rod
Pi Pd2
(10) to increase the inclination angle of the
cylinder block and the delivery flow.
6. As servo piston (9) moves down, a total spring
force of spring 4 (7) and spring 5 (8) is decreased,
Pd1
1
which serves to move piston 2 (3) up. 2
7. As a result, servo piston 2 (3) moves down to a
level where a total spring force of the spring 4 (7)
and spring 5 (8), and a total force of Pd1 and Pd2
are balanced. 3
8. By this movement, a passage at the notch B B 5
closes in control piston (5) to disconnect the large 4
chamber of servo piston (9) to the hydraulic oil 7,8
tank. Dr
Movement of servo piston (9) stops, and the flow 10
Min.
increase control is completed. 9
Displacement
Angle
Max.

T1F1-03-01-003

1- Spring 1 7- Spring 4
2- Piston 1 8- Spring 5
3- Piston 2 9- Servo Piston
4- Spring 2 10 - Rod
5- Control Piston

Pd1 -Pump 1 Delivery Pressure Dr - Return to Hyd. Oil Tank

Pd2 -Pump 2 Delivery Pressure Pi - Pump Control Pressure

T3-1-14
 COMPOMRNT OPERATION / Pump Device

1 1

Pi Pi

2 2
Pd2 3 Pd2 3
Pd1 4 Pd1 4

5 5

B B

8 8

Dr Dr

9 9

10 10

Self Delivery Pressure Self Delivery Pressure

(Pd1 or Pd2) (Pd1 or Pd2)

Small Chamber Small Chamber

Large Chamber Large Chamber

T1F1-03-01-011 T1F1-03-01-013

T3-1-15
 COMPOMRNT OPERATION / Pump Device
Control by Pilot Pressure at Torque Control
Solenoid Valve

• Flow Decrease Control

1. The torque control solenoid valve is operated by
Flow
signals from MC (Main Controller), and the torque Rate (Q)
control pilot pressure Pps is increased.
2. Pps, Pd1 and Pd2 act on piston 2 (3) to lower
piston 2 (3).
3. When a total force of Pps, Pd1 and Pd2 exceeds
a total spring force of spring 2 (4), spring 4 (7) and
spring 5 (8), control piston (5) moves down.
4. By this movement, a passage at the notch A
opens to apply Pd1 to the large chamber.
5. Pressures in the large and small chambers are 0 Pressure (P)
equalized, because Pd1 is always applied in the
small chamber of servo piston (9).
Servo piston (9) moves up (in the flow decrease
direction) due to a difference in sectional area
Pi Pps Pd2
between large and small chambers.
6. As a result, servo piston (9) actuates the valve
plate via rod (10) to reduce the inclination angle of
the cylinder block and the pump delivery flow.
Pd1
1
7. As servo piston (9) moves up, a total spring force 2
of piston 4 (7) and spring 5 (8) is increased to
press piston 2 (3) up.
8. Piston 2 (3) moves up to a level where a total
spring force of spring 4 (7) and spring 5 (8), and a A 3
total force of Pps, Pd1 and Pds2 are balanced. 5
9. By this movement of piston 2 (3), a passage at the 4
notch A closes to shut off a circuit to the large 7,8
chamber. Dr
Movement of servo piston (9) stops, and the flow 10
Min.
decrease control is completed. 9
Displacement
Angle
Max.

T1F1-03-01-003

1- Spring 1 7- Spring 4
2- Piston 1 8- Spring 5
3- Piston 2 9- Servo Piston
4- Spring 2 10 - Rod
5- Control Piston

Pd1 -Pump 1 Delivery Pressure Pi - Pump Control Pressure

Pd2 -Pump 2 Delivery Pressure Pps -Torque Control Pressure
Dr - Return to Hyd. Oil Tank

T3-1-16
 COMPOMRNT OPERATION / Pump Device

1 1

Pi Pi

Pps Pps
2 2
Pd2 3 Pd2 3
Pd1 4 Pd1 4

5 5

A A

8
8

Dr Dr

9 9

10
10

Self Delivery Pressure Self Delivery Pressure

(Pd1 or Pd2) (Pd1 or Pd2)

Small Chamber Small Chamber

Large Chamber Large Chamber

T1F1-03-01-010 T1F1-03-01-014

T3-1-17
 COMPOMRNT OPERATION / Pump Device
Control by Pilot Pressure at Flow Control
Solenoid Valve Flow
Rate (Q)
• Maximum Flow Control
1. The maximum pump flow rate limit solenoid valve,
provided in the pump control pressure Pi circuit, is
operated by signals from MC.
2. The maximum pump flow rate limit solenoid valve,
like a pressure-reducing valve, regulates the
pump control pressure Pi.
3. Piston 1 (2) moves up when a total force of pump 0 Pressure (P)
control pressure, spring 2 (4), spring 4 (7) and
spring 5 (8) exceeds a spring force of spring 1 (1).
4. By this movement, a passage at the notch A Flow
opens to apply Pd1 to the large chamber. Rate (Q)
5. Pressures in the large and small chambers are
equalized, because Pd1 is always applied in the
small chamber of servo piston (9).
Servo piston (9) moves up (in the flow decrease
direction) due to a difference in sectional area
between large and small chambers.
6. Servo piston (9) actuates the valve plate via rod
(10) to reduce the inclination angle of the cylinder
0 Pump Control Pressure (Pi)
block and the pump delivery flow.
7. As servo piston (9) moves up, a total spring force
of spring 4 (7) and spring 5 (8) is increased to
press piston 1 (2) up.
Pi
8. Piston 1 (2) moves up to a level where a total
spring force of spring 4 (7) and spring 5 (8), and a
spring force of spring 1 (1) are balanced.
9. By this movement of piston 1 (2), a passage at the 1
notch A closes to shut off a circuit to the large Pd1
2
chamber.
Movement of servo piston (9) stops, and the flow
reduction control is completed.
10. The maximum flow is kept below normal flow, A
because the pump control pressure is limited. 5
4
7,8
Dr
10 Min.
9
Displacement
Angle
Max.

T1F1-03-01-003

1- Spring 1 7- Spring 4
2- Piston 1 8- Spring 5
4- Spring 2 9- Servo Piston
5- Control Piston 10 - Rod

Pd1 -Pump 1 Delivery Pressure Pi - Pump Control Pressure

(Self Delivery Pressure)
Dr - Return to Hyd. Oil Tank

T3-1-18
 COMPOMRNT OPERATION / Pump Device

1 1

Pi is limited by
maximum pump
flow control
solenoid valve
Pi

2 2
3 3
4 4

5 5

A A

7
7

8
8

Dr Dr

9 9

10

10

Self Delivery Pressure Self Delivery Pressure

Small Chamber Small Chamber

Large Chamber Large Chamber

T1F1-03-01-010 T1F1-03-01-015

T3-1-19
 COMPOMRNT OPERATION / Pump Device
PILOT PUMP
Inlet Port
Drive gear is driven by the engine via the transmission
Drive Gear
which in turn rotates driven gear as they are meshed Driven Gear
together.
The teeth of gear are filled with the hydraulic oil from
the inlet. The hydraulic oil drains from the outlet port
along the inner of housing.

Outlet Port

T137-02-03-005
N SENSOR (ENGINE SPEED SENSOR)
4 5
The N sensor detects the engine speed, which is used
to control various operations. The N sensor is located
close to the transmission teeth so that the sensor
converts the number of teeth passing by the sensor
into pulse signals, effectively sensing the engine
speed.
T107-07-02-054
1 - Coil 4 - Output Terminal
2 - Magnet 5 - Output Terminal
3 - Disc Drive (Gear)

PUMP DELIVERY PRESSURE SENSOR 3

This sensor detects the pump delivery pressures,

which are used to control various operations. When oil
pressure is applied onto diaphragm (9), the diaphragm
T107-02-03-020
is deformed. The deformation of the diaphragm is
detected as electrical signals.

6 - Ground 8 - Power Source (5V)

7 - Output 9 - Pressure Receiving Area
(Diaphragm)

PUMP CONTROL PRESSURE SENSOR 6 7 8 9

T157-02-03-010

This sensor detects the pump control pressures, which

are used to control various operations. When oil
pressure is applied onto diaphragm (10), the
diaphragm is deformed. The deformation of the
diaphragm is detected as electrical signals.

10 - Pressure Receiving Area 12 - Output

(Diaphragm) T176-03-01-023
11 - Ground 13 - Power Source (5V) 10 11 12 13

T3-1-20
 COMPONENT OPERATION / Swing Device
OUTLINE

The swing device consists of the valve unit, swing mo- The swing reduction gear converts the swing motor
tor, and swing reduction gear. The valve unit prevents output into slow large torque to rotate the shaft.
cavitation in the swing circuit from occurring and pro- Thereby, the upperstructure is rotated.
tects the circuit from being overloaded. The swing mo-
tor is a swash plate type axial plunger motor with a
built-in swing parking brake. The swing motor is driven
by pressure oil delivered from the pump, and drives the
swing reduction gear.

Valve Unit

Swing Motor

Swing Reduction
Gear

T178-03-02-001

T3-2-1
 COMPONENT OPERATION / Swing Device
SWING REDUCTION GEAR

The swing reduction gear is a two stage reduction The shaft meshes with the swing bearing internal gear
planetary gear type. The ring gear is formed on the secured to the undercarriage, causing the upperstruc-
internal surface of the housing so that they are inte- ture to rotate.
grated. As the housing is bolted on the upperstructure,
the ring gear doesn’t rotate. The swing motor shaft
rotates the first stage sun gear. Then, its torque is
transmitted to the second stage sun gear via the first
stage planetary gear and carrier. The second stage
sun gear rotates the shaft via the second stage plane-
tary gear and carrier.

Swing Motor Shaft

First Stage Sun Gear

First Stage Planetary Gear
First Stage Carrier
Ring Gear
Second Stage Sun Gear
Second Stage Planetary Gear
Second Stage Carrier

Shaft

T178-03-02-006

T3-2-2
 COMPONENT OPERATION / Swing Device
SWING MOTOR

The swing motor consists of the swash plate, rotor, When pressure oil is supplied from the pump, the
plungers, valve plate, housing and swing parking brake pressure oil pushes the plungers. Since the swash
(springs, brake piston, plates, friction plates, and plate is inclined, the shoes on top of the plungers slide
switch valve). The rotor in which the plungers are in- along the swash plate, causing the rotor and shaft to
serted is splined onto the shaft. rotate. The shaft tip end is splined into the first stage
sun gear in the swing reduction gear so that shaft rota-
tion is transmitted to the swing reduction gear.

Spring
Valve Plate
Brake Piston

Rotor Plate

Housing
Friction Plate
Shoe
Plunger

Retainer
Swash Plate

Shaft

T178-03-02-002

T3-2-3
 COMPONENT OPERATION / Swing Device
SWING PARKING BRAKE

The swing parking brake is a wet-type multi-disc brake.

The brake is released when brake release pressure
enters into the brake piston chamber (negative brake
type). Brake release pressure is supplied from the pilot
pump only when a front attachment and/or swing op-
eration is made. During operations other than swing
and/or front attachment or while the engine is stopped,
brake release pressure is returned to the hydraulic oil
tank so that the brake is automatically applied by
spring.

Releasing Brake: Applying Brake:

1. When the swing and/or front attachment control 1. When the swing and/or front attachment control
levers are operated, the swing parking brake re- levers are released, the swing parking brake re-
lease spool in the signal pilot pressure control lease spool in the signal pilot pressure control
valve is shifted. Thereby, the pilot pressure oil valve is returned to neutral so that the pilot pres-
from the pilot pump is routed to port SH. sure routed to port SH is reduced.
2. Pilot pressure at port SH pushes to open the 2. Therefore, the check valve is closed, allowing
check valve and flows into the brake piston brake release pressure to flow into the swing mo-
chamber. tor housing through the orifice.
3. Then, the brake piston is raised, breaking contact 3. Consequently, spring force is applied to plates
between the plates and friction plates so that the and friction plates which are meshed with the
brake is released. outer diameter of the rotor and inner diameter of
the housing respectively via the brake piston.
Then, the rotor outer diameter is held with friction
force. While the engine is stopped, no pilot pres-
sure is routed to port SH, allowing the brake to be
automatically applied.

Spring

Brake Piston

Orifice

Friction Plate Check Valve

Port SH
(Brake Release
Pressure)
Plate

Brake Piston Chamber

T178-03-02-003

T3-2-4
 COMPONENT OPERATION / Swing Device
(Blank)

T3-2-5
 COMPONENT OPERATION / Swing Device
VALVE UNIT

The valve unit consists of the make-up valves and the

relief valves. The make-up valves prevents cavitaion in
the circuit. The relief valves prevent surge pressure
and overloads in the circuit. Relief Valve

Make-Up Valve
During swing stop operation, the swing motor is
Make-Up Valve
driven by inertia force of the upperstructure. The mo-
tor is rotated by inertia force more than by pressure
oil delivered from the pump, causing cavitation to de-
velop in the circuit. To prevent cavitation, when pres-
sure in the swing circuit is reduced more than the re- Port C
turn circuit (port C) pressure, the poppets are opened
so that hydraulic oil is drawn into the circuit from the
Control Valve
hydraulic oil tank to compensate for the lack of oil in
the circuit.
T107-02-04-013

Control Valve

Poppet

Make-Up Valve Make-Up Valve

Port C

Relief Valve T178-03-02-004

T3-2-6
 COMPONENT OPERATION / Swing Device
Relief Valve
During starting or stopping swing operation, oil pres-
sure in the swing circuit becomes high. The relief
valve prevents the circuit pressure from rising higher
than the set-pressure.

Low Pressure Relief Operation (Shock Reducing Func- High Pressure Relief Operation (Overload Prevention):
tion): 1. After the piston is moved full stroke, the spring is
1. Pressure at port HP (swing circuit) is routed into compressed so that the circuit pressure is in-
oil chamber C through the poppet orifice. creased to the set-pressure.
2. Pressure oil in oil chamber C is further routed into 2. If pressure in port HP increases more than the
oil chambers A and B via passages A and B re- spring set-pressure, the poppet is unseated, caus-
spectively. ing pressure oil to flow to port LP from port HP.
3. The pressure receiving area in oil chamber B is 3. When pressure in port HP is reduced to the speci-
larger than oil chamber A so that the piston moves fied level, the poppet is seated by spring force.
to the left.
4. As long as the piston keeps moving, a pressure
difference is developed between the front and the
rear of the poppet. When this pressure difference
is increased more than spring force, the poppet is
unseated, allowing pressure oil to flow to port LP.
5. When the piston is moved full stroke, the pressure
difference between the front and the rear of the
poppet disappears, causing the poppet to be
seated.

Poppet Orifice Spring Passage A Passage B Piston

HP

LP

Oil Chamber C Oil Chamber B T178-03-02-005

Oil Chamber A

T3-2-7
 COMPONENT OPERATION / Swing Device
(Blank)

T3-2-8
 COMPONENT OPERATION / Control Valve
OUTLINE

The control valve controls oil pressure, flow rate, and The spool arrangements are as follows from the
oil flow direction in the hydraulic circuit. The major machine front side.
parts of the control valve are the main relief valve, 4-Spool Side: Right Travel, Bucket, Boom 1, Arm 2
overload relief valves, flow combiner valve, anti-drift 5-Spool Side: Left Travel, Auxiliary, Boom 2, Arm 1,
valves, flow rate control valve, regenerative valve, aux. Swing
flow combining valves, bypass shut-out valve, and
spools. Each spool is operated by the pilot oil pressure.

Swing
Arm 1
Boom 2
Auxiliary
Left Travel

Arm 2

Boom 1
5-Spool Side
Bucket

Right Travel

T176-03-03-035
Machine Front
4-Spool Side

T3-3-1
 COMPONENT OPERATION / Control Valve
Component Layout

Travel Motor (Left) Travel Motor (Right)

1 2 3 4 5 6 7 8 9 10

35 Bucket Cylinder
12
34
13
33
32
14
Arm Cylinder 15
31
Boom Cylinder
30
16
29
17
28

Swing Motor

18
27
19
20
21

Main Pump

26 25 24 23 22
T1F1-03-03-001
1 - Load Check Valve (Travel 10 - Bucket Flow Rate Control 20 - Load Check Valve (Arm 2 28 - Overload Relief Valve
Tandem Circuit) Valve (Poppet Valve) Tandem Circuit) (Arm: Bottom Side)
2 - Load Check Valve (Travel 12 - Overload Relief Valve 21 - Bypass Shut-Out Valve 29 - Overload Relief Valve
Parallel Circuit) (Bucket: Rod Side) (Arm: Rod Side)
3 - Check Valve (Main Relief 13 - Overload Relief Valve 22 - Check Valve (Orifice) (Arm 30 - Arm Anti-Drift Valve (Check
Circuit) (Bucket: Bottom Side) 2 Parallel Circuit) Valve)
4 - Main Relief Valve 14 - Load Check Valve (Boom 1 23 - Load Check Valve (Arm 1 31 - Arm Anti-Drift Valve
Parallel Circuit) Parallel Circuit) (Selector Valve)
5 - Check Valve (Main Relief 15 - Boom Regenerative Valve 24 - Load Check Valve (Arm 1 32 - Load Check Valve (Boom 2
Circuit) Tandem Circuit) Parallel Circuit)
6 - Flow Combiner Valve 16 - Overload Relief Valve 25 - Load Check Valve (Swing 33 - Aux. Flow Rate Control
(Boom: Bottom Side) Circuit) Valve (Poppet Valve)
7 - Check Valve (Flow 17 - Overload Relief Valve 26 - Arm Regenerative Valve 34 - Aux. Flow Rate Control
Combining Circuit) (Boom: Rod Side) (Selector Valve) Valve (Selector Valve)
8 - Aux. Flow Combining Valve 18 - Boom Anti-Drift Valve 27 - Arm Regenerative Valve 35 - Load Check Valve (Bucket
(Check Valve) Parallel Circuit)
9 - Bucket Flow Rate Control 19 - Boom Anti-Drift Valve
Valve (Selector Valve) (Selector Valve)

T3-3-2
 COMPONENT OPERATION / Control Valve

16
26

29

18, 19
5

21
12
9, 10
Machine Front

T176-03-03-038

30, 31

33, 34

28

Machine Front

8 17 T176-03-03-036

13
6 35 7

T3-3-3
 COMPONENT OPERATION / Control Valve

Travel Motor (Left) Travel Motor (Right)

1 2 3 4 5 6 7 8 9 10

35 Bucket Cylinder
12
34
13
33
32
14
Arm Cylinder 15
31
Boom Cylinder
30
16
29
17
28

Swing Motor

18
27
19
20
21

Main Pump

26 25 24 23 22
T1F1-03-03-001
1 - Load Check Valve (Travel 10 - Bucket Flow Rate Control 20 - Load Check Valve (Arm 2 28 - Overload Relief Valve
Tandem Circuit) Valve (Poppet Valve) Tandem Circuit) (Arm: Bottom Side)
2 - Load Check Valve (Travel 12 - Overload Relief Valve 21 - Bypass Shut-Out Valve 29 - Overload Relief Valve
Parallel Circuit) (Bucket: Rod Side) (Arm: Rod Side)
3 - Check Valve (Main Relief 13 - Overload Relief Valve 22 - Check Valve (Orifice) (Arm 30 - Arm Anti-Drift Valve (Check
Circuit) (Bucket: Bottom Side) 2 Parallel Circuit) Valve)
4 - Main Relief Valve 14 - Load Check Valve (Boom 1 23 - Load Check Valve (Arm 1 31 - Arm Anti-Drift Valve
Parallel Circuit) Parallel Circuit) (Selector Valve)
5 - Check Valve (Main Relief 15 - Boom Regenerative Valve 24 - Load Check Valve (Arm 1 32 - Load Check Valve (Boom 2
Circuit) Tandem Circuit) Parallel Circuit)
6 - Flow Combiner Valve 16 - Overload Relief Valve 25 - Load Check Valve (Swing 33 - Aux. Flow Rate Control
(Boom: Bottom Side) Circuit) Valve (Poppet Valve)
7 - Check Valve (Flow 17 - Overload Relief Valve 26 - Arm Regenerative Valve 34 - Aux. Flow Rate Control
Combining Circuit) (Boom: Rod Side) (Selector Valve) Valve (Selector Valve)
8 - Aux. Flow Combining Valve 18 - Boom Anti-Drift Valve 27 - Arm Regenerative Valve 35 - Load Check Valve (Bucket
(Check Valve) Parallel Circuit)
9 - Bucket Flow Rate Control 19 - Boom Anti-Drift Valve
Valve (Selector Valve) (Selector Valve)

T3-3-4
 COMPONENT OPERATION / Control Valve

F Cross Section A
E 4
D
C
B

5
A
3

34

7 8

6
T176-03-03-035
T176-03-03-002

Cross Section C
Cross Section B Bucket Auxiliary
Travel (Right) Travel (Left)

12

1 10 33

9 34

2 13

T176-03-03-003 T176-03-03-004

T3-3-5
 COMPONENT OPERATION / Control Valve

Travel Motor (Left) Travel Motor (Right)

1 2 3 4 5 6 7 8 9 10

35 Bucket Cylinder
12
34
13
33
32
14
Arm Cylinder 15
31
Boom Cylinder
30
16
29
17
28

Swing Motor

18
27
19
20
21

Main Pump

26 25 24 23 22
T1F1-03-03-001
1 - Load Check Valve (Travel 10 - Bucket Flow Rate Control 20 - Load Check Valve (Arm 2 28 - Overload Relief Valve
Tandem Circuit) Valve (Poppet Valve) Tandem Circuit) (Arm: Bottom Side)
2 - Load Check Valve (Travel 12 - Overload Relief Valve 21 - Bypass Shut-Out Valve 29 - Overload Relief Valve
Parallel Circuit) (Bucket: Rod Side) (Arm: Rod Side)
3 - Check Valve (Main Relief 13 - Overload Relief Valve 22 - Check Valve (Orifice) (Arm 30 - Arm Anti-Drift Valve (Check
Circuit) (Bucket: Bottom Side) 2 Parallel Circuit) Valve)
4 - Main Relief Valve 14 - Load Check Valve (Boom 1 23 - Load Check Valve (Arm 1 31 - Arm Anti-Drift Valve
Parallel Circuit) Parallel Circuit) (Selector Valve)
5 - Check Valve (Main Relief 15 - Boom Regenerative Valve 24 - Load Check Valve (Arm 1 32 - Load Check Valve (Boom 2
Circuit) Tandem Circuit) Parallel Circuit)
6 - Flow Combiner Valve 16 - Overload Relief Valve 25 - Load Check Valve (Swing 33 - Aux. Flow Rate Control
(Boom: Bottom Side) Circuit) Valve (Poppet Valve)
7 - Check Valve (Flow 17 - Overload Relief Valve 26 - Arm Regenerative Valve 34 - Aux. Flow Rate Control
Combining Circuit) (Boom: Rod Side) (Selector Valve) Valve (Selector Valve)
8 - Aux. Flow Combining Valve 18 - Boom Anti-Drift Valve 27 - Arm Regenerative Valve 35 - Load Check Valve (Bucket
(Check Valve) Parallel Circuit)
9 - Bucket Flow Rate Control 19 - Boom Anti-Drift Valve
Valve (Selector Valve) (Selector Valve)

T3-3-6
 COMPONENT OPERATION / Control Valve

Boom 1 Boom 2
Cross Section D

19
16

18

14 32

15

17

T176-03-03-005
Cross Section E Cross Section F
Arm 2 Arm 1 Swing

31
29
26
30

25
20 23

22
24
27

28 21
T176-03-03-007

T176-03-03-006

T3-3-7
 COMPONENT OPERATION / Control Valve
HYDRAULIC CIRCUIT

Main Circuit
The pressure oil from main pump 1 flows to the 4-
spool side control valve and the pressure oil from
main pump 2 flows to the 5-spool side control valve.
Both right and left main circuits are provided with the
parallel circuits, making combined operations
possible. The boom and arm circuits are provided
with the flow combining circuits so that the pressure
oil from main pump 1 and 2 can be supplied together
to each cylinder when a single operation is made.

The main relief valve is located in the main circuit

(between the pumps and actuators), preventing the
oil pressure in the main circuit from increasing over
the set-pressure during operation (when any control
lever is operated).
The overload relief valves are located in the boom,
arm, and bucket circuits (between the control valve
and actuators), preventing the surge pressure from
being developed by external loads in the actuator
circuits and from increasing over the set-pressure
while the control levers are in neutral.

T3-3-8
 COMPONENT OPERATION / Control Valve

Travel Motor (Left) Travel Motor (Right)

Main Relief Valve

5-Spool Side 4-Spool Side

Auxiliary

Bucket
Cylinder

Overload
Relief Valve
Arm
Cylinder Overload
Relief Valve

Swing Motor

Boom
Cylinder

Flow Combining
Circuit

5-Spool Side
Parallel Circuit Pump 2 Pump 1

T1F1-03-03-032

T3-3-9
 COMPONENT OPERATION / Control Valve
Pilot Pressure Operation Circuit External Pilot Oil Pressure Control Circuit
The pilot pressure oil (shown by figure letters) from • The arm regenerative valve (selector valve) is
the pilot valve is routed to the spool end faces in the shifted by the pilot pressure oil from solenoid
control valve, moving the spools. Besides moving valve unit (SC).
the spools, the pilot pressure oil operates the control • The flow combiner valve is shifted by the pilot
valve at the same time in the following operations: pressure oil from the flow combiner control spool
• When arm roll-in operation (4) is made, the pilot in the signal control valve.
pressure oil moves the spools and shifts the arm • The bucket flow rate control valve is shifted by the
anti-drift valve selector valve. pilot pressure oil from the bucket flow rate control
• When boom lower operation (2) is made, the pilot valve control spool in the signal control valve.
pressure oil moves the spools and shifts the boom • The aux. flow combining valve and bypass shut-
anti-drift valve selector valve. out valve are shifted by the pilot pressure oil from
As the air bleed circuit is provided in the upper auxiliary pilot valve.
section of the control valve so that any air trapped in • The aux. flow rate control valve is shifted by the
the control valve will automatically be bled. pilot pressure oil from the aux. flow rate control
solenoid valve.
(Refer to the SYSTEM / Control System group.)

T3-3-10
 COMPONENT OPERATION / Control Valve
Pilot Pressure Oil from Flow Combiner Valve
Control Spool in Signal Control Valve

Aux. Flow Combining Valve Pilot Pressure Oil from Aux. Pilot Valve

Flow Combiner Valve Pilot Pressure Oil from Bucket

Flow Rate Valve Control Spool in
Signal Control Valve

10
11
9
12

Bucket Flow
Rate Control
Valve
Pilot
Pressure Oil
8
from Aux.
Flow Rate 7
Control
Solenoid
Valve

Aux. Flow
Rate Control 2
Valve 1
1

Arm Anti-
Drift Valve

Boom Anti-
4 Drift Valve
3
Pilot Pressure 3
Oil from
Solenoid Valve
Unit (SC)
Pilot
Arm Pressure
Regenerative Oil from
Valve 6 Aux. Pilot
(Selector Valve) 5 Air Bleed Circuit Valve

Bypass Shut-Out Valve

T1F1-03-03-025
1 - Boom Raise 4 - Arm Roll-In 7 - Bucket Roll-In 10 - Left Travel Reverse
2 - Boom Lower 5 - Left Swing 8 - Bucket Roll-Out 11 - Right Travel Forward
3 - Arm Roll-Out 6 - Right Swing 9 - Left Travel Forward 12 - Right Travel Reverse

T3-3-11
 COMPONENT OPERATION / Control Valve
FLOW COMBINER VALVE

1. Normally, the pressure oil from pump 1 pushes

the check valve through hole B so that the check
valve is seated.
2. When the front attachment and/or travel function
is operated, the right travel pilot pressure oil shifts
the flow combiner control spool in the signal
control valve, causing the pilot pressure oil to shift
the flow combiner valve spool.
3. Then, the pressure oil from pump 1 enters hole A,
unseats the check valve, and flows into the left
travel spool.
4. Accordingly, the pressure oil from pump 1 is
routed to both the right and left travel spools at the
same time, allowing the pressure oil from pump 2
to flow to the front attachment and swing spools.
Therefore, even if travel and front
attachment/swing functions are operated at the
same time, the machine can travel straight.

Travel Motor (Left) Travel Motor (Right)

Flow Combiner Valve Pilot Pressure from Flow

Combiner Valve Control
Spool in Signal Control Valve

Pump 1 T176-03-03-026

T3-3-12
 COMPONENT OPERATION / Control Valve
When Neutral: When Operating:

To Hydraulic Oil Tank

To Hydraulic Oil Tank

To Left Travel Check Valve To Left Travel

Spool Check Valve
Spool
Hole B

Pressure Oil Pressure Oil

from Pump 1 from Pump 1
Hole A Hole A

Spool Spool

Pilot Pressure
Oil from Flow
To Flow Combiner Valve
Combiner Valve Control Spool
Control Spool

T176-03-03-008
T176-03-03-009

T3-3-13
 COMPONENT OPERATION / Control Valve
MAIN RELIEF VALVE

The main relief valve prevents the oil pressure in the

main circuit from rising higher than the set-pressure
while operating the actuators such as the motors and
cylinders. Thereby, oil leakage from hoses and pipe
joints and damage to the actuators are prevented.

Operation
1. The oil pressure in port HP (main circuit) acts on
the pilot poppet through orifice A in the main
poppet and orifice B in the seat.
2. When the oil pressure in port HP increases more
than the spring B set-force, the pilot poppet is
unseated, allowing the pressure oil to flow to port
LP (hydraulic oil tank) through passage A and
around the outer diameter of the sleeve.
3. At this time, a pressure difference arises between
port HP and the spring chamber due to orifice A.
4. When this pressure difference increases more
than the spring A set-force, the main poppet is
unseated, causing the pressure oil in port HP to
flow to port LP.
5. Thereby, the main circuit pressure is reduced.
6. When the main circuit pressure is reduced to the
specified pressure, the main poppet is closed by
spring A.

T3-3-14
 COMPONENT OPERATION / Control Valve
When Normal:

Main Poppet Orifice A Orifice B Seat Passage A Spring B

HP

LP T176-03-03-010
Sleeve Spring Chamber Spring A Pilot Poppet

When Relieving:

Main Poppet Orifice A Orifice B Seat Passage A Spring B

HP

LP T176-03-03-011
Sleeve Spring Chamber Spring A Pilot Poppet

T3-3-15
 COMPONENT OPERATION / Control Valve
OVERLOAD RELIEF VALVE
(with Make-Up Function)

The overload relief valves are located in the boom, arm,

and bucket circuits. The overload relief valve prevents
each actuator circuit pressure from rising excessively
when the actuators are moved by external loads. In
addition, when the actuator circuit pressure is reduced,
draws the hydraulic oil from the hydraulic oil tank to
prevent the occurrence of cavitation (make-up
function).

Relief Operation
1. The oil pressure in port HP (actuator circuit) acts
on the pilot poppet through orifice A in the main
poppet and orifice B in the seat.
2. When the oil pressure in port HP increases more
than the spring B set-force, the pilot poppet is
unseated, allowing the pressure oil to flow to port
LP (hydraulic oil tank) through passage A and
around the outer diameter of sleeve.
3. At this time, a pressure difference arises between
port HP and the spring chamber due to orifice A.
4. When this pressure difference increases more
than the spring A set-force, the main poppet is
unseated, causing the pressure oil in port HP to
flow to port LP.
5. Thereby, the actuator circuit pressure is reduced.
6. When the actuator circuit pressure is reduced to
the specified pressure, the main poppet is closed
by spring A.

Make-Up Operation
1. When the oil pressure in port HP (actuator circuit)
is reduced lower than the oil pressure in port LP
(hydraulic oil tank), the make-up valve is moved to
the left.
2. Then, the hydraulic oil in port LP flows to port HP,
preventing cavitation.
3. When the oil pressure in port HP increases more
than the specified pressure, the make-up valve is
closed by spring C.

T3-3-16
 COMPONENT OPERATION / Control Valve
When Normal: Sleeve Make-Up Valve Main Orifice A Orifice B Passage A Spring B
Poppet Seat

HP

LP T176-03-03-012
Spring C Spring Chamber Spring A Pilot Poppet

When Relieving: Sleeve Main Orifice A Orifice B Passage A Spring B

Poppet Seat

HP

LP T176-03-03-013
Spring Chamber Spring A Pilot Poppet

When Operating Make-Up: Make-Up Valve

HP

LP T176-03-03-014
Spring C

T3-3-17
 COMPONENT OPERATION / Control Valve
REGENERATIVE VALVE

The regenerative valves are located in the boom lower

and arm roll-in, accelerating the cylinder operating
speeds, preventing the cylinders from making a pose
in movement, and improving machine controllability.

NOTE: Operational principles of each regenerative

valve are almost identical. Therefore, the
bucket regenerative valve is used as an
example.

Operation
1. When the boom is lowered, the return oil from the Pressure Oil
from Pump 1
cylinder bottom side (the rod side in case of the Boom 1 Spool Boom Cylinder
arm cylinder) is routed the check valve via anti-
drift valve and hole A on the spool.(Refer to T3-3-
20 as for the operation of the anti-drift valve.)
2. At this moment, when the oil pressure in the
cylinder rod side ( the bottom side in case of the
arm cylinder) is lower than the bottom side, the
check valve is unseated.
3. Then, the return oil from the cylinder bottom side
flows into the rod side so that the return pressure
oil is regenerated, increasing the cylinder
operating speed.
4. When the cylinder is fully stroked or digging loads
increase, the oil pressure in the cylinder bottom Check Valve Anti-Drift Valve
circuit increases, causing the check valve to seat (Check Valve)
T1F1-03-03-027
so that regeneration is stopped. From Boom 2
Spool
(Pressure Oil
from Pump 2)

NOTE: Arm Regenerative Valve (Selector Valve)

Operation
The arm regenerative valve (selector
Valve) is shifted by the pilot pressure oil
from solenoid valve unit (SC) so that the
return oil circuit from the cylinder rod side to
the hydraulic oil tank is blocked. Then, the
return oil from the arm cylinder rod side is
combined with the pressure oil from the
pump and is routed to the arm cylinder
bottom. Refer to the SYSTEM / Control
system group.)

T3-3-18
 COMPONENT OPERATION / Control Valve
When Operating:

Boom 1 Boom 2
Spool Spool

Boom
Cylinder

Anti-Drift Valve
(Check Valve)

Hole A

Check
Valve

T1F1-03-03-016

T3-3-19
 COMPONENT OPERATION / Control Valve
ANTI-DRIFT VALVE

The anti-drift valves are located in the boom cylinder

bottom and arm cylinder rod side circuits to reduce the
cylinder drift.

NOTE: The boom and arm anti-drift valves are

identical in construction.

Blocking Operation Boom Cylinder

1. When the control lever (the spool) is in neutral,
the anti-drift valve (selector valve) is not shifted.
2. Therefore, the pressure oil in the boom cylinder
bottom (arm cylinder rod side) is applied to the
anti-drift valve check valve via the control valve.
3. Consequently, the check valve is seated, blocking
the return oil circuit from the cylinder so that the
cylinder drift is reduced.

Releasing Operation
1. When rolling the arm in or lowering the boom, the
pressure oil from the pilot valve shifts the anti-drift T176-03-03-028
Anti-Drift Valve Anti-Drift Valve
valve (selector valve). (Selector Valve) (Check Valve)
2. The hydraulic oil in the check valve spring
chamber is returned to the hydraulic oil tank via
the orifice in the Selector valve. Pressure Oil To Hydraulic
3. Accordingly, the check valve is unseated, allowing from Pump 1 Oil Tank Boom Cylinder
the return oil from the boom cylinder bottom side
(arm cylinder rod side) to flow to the spool.

From Pilot
Valve

To Hydraulic
Oil Tank

T176-03-03-029
Anti-Drift Valve Anti-Drift Valve
(Selector Valve) (Check Valve)

T3-3-20
 COMPONENT OPERATION / Control Valve
When Blocking:

Drain

Boom
Cylinder

To Pilot
Valve

Selector Valve
Sleeve

Spring B
Seat

Spring A

Check Valve

To Spool

T176-03-03-017
When Releasing:
Drain

Boom
Cylinder

From Pilot
Valve

Selector Valve
Sleeve

Pressure Spring B
Oil from
Seat
Pump
Spring A

Check Valve

To Spool

T176-03-03-018

T3-3-21
 COMPONENT OPERATION / Control Valve
FLOW RATE CONTROL VALVE

The flow rate control valve is located in the bucket and

auxiliary circuits. When a combined operation is made,
the flow rate control valve restricts the oil flow so that
the other actuators are given priority to operate.

NOTE: The bucket flow rate control valve restricts

the bucket circuit oil flow when the bucket,
boom raise and arm roll-in operations are
made simultaneously. The auxiliary flow
rate control valve restricts the auxiliary
circuit oil flow when a combined operation
with the auxiliary and other front attachment To Hydraulic
Poppet Valve Pressure Oil
is made. The bucket flow rate control valve from Pump 1 Oil Tank
is used here as an example.

When bucket (auxiliary) single operation is made:

1. The pressure oil from pump 1 acts on the check
valve in the poppet via port P1. Selector
Bucket
2. Normally, the selector valve is kept open so that Valve
Cylinder
the pressure oil from pump 1 unseats the check
valve and flows into the main spool through the
selector valve.
3. Thereby, the poppet valve is opened, allowing the
pressure oil to flow to the bucket spool.

When the combined operation of the bucket Pilot Pressure T176-03-03-030

(auxiliary), boom raise, and arm roll-in is made: from Bucket Flow
1. When the boom raise and arm roll-in functions are Rate Control Pressure Oil To Hydraulic
Valve from Pump 1 Oil Tank
operated simultaneously, the selector valve is
Poppet Valve
shifted so that the bucket flow rate control valve in
the signal control valve is shifted by the boom
raise pilot pressure.
2. Then, the oil pressure behind the poppet valve Selector
increases, and the force to close the poppet valve Valve Bucket
appears. Cylinder
3. Consequently, the opening clearance of the
poppet valve is reduced so that oil flow to the
bucket spool is restricted, allowing the pressure
oil to be routed to the high pressure side of the
boom raise circuit.

T176-03-03-031

T3-3-22
 COMPONENT OPERATION / Control Valve
When Normal Operation:

Poppet Check Valve Spring A

Spring B

To Main Spool

To Hydraulic
Oil Tank

Pressure Oil Selector

from Main Valve
Pump 1

Boom Raise
Pilot Pressure

To Main Spool

T176-03-03-019
Plug 2

When Oil Flow is Restricted:

Poppet Check Valve Spring A

Spring B

To Main Spool

To Hydraulic
Oil Tank

Selector
Pressure Oil Valve
from Main
Pump 1

Boom Raise
Pilot Pressure

To Main Spool

T176-03-03-020
Plug 2

T3-3-23
 COMPONENT OPERATION / Control Valve
AUX. FLOW COMBINING VALVE AND Single Operation
BYPASS SHUT-OUT VALVE When a single aux. pilot valve operation is made, the
aux. flow combining valve allows the pressure oil
The aux. flow combining valve and the bypass shut-out from pump 1 to flow to the aux. spool together with
valve are located in the upper reaches of the 4-spool the pressure oil from pump 2, increasing the
side and in the lower reaches of the 4-spool side attachment operating speed.
respectively. The aux. flow combining valve and the 1. When an aux. pilot valve is operated, the pilot
bypass shut-out valve operate differently depending on pressure oil is routed to port SM and port SJ so
whether a single or combined operation is made. that both the aux. flow combining valve and
bypass shut-out valve are shifted.
2. When the bypass shut-out valve is shifted, the
neutral circuit in the 4-spool side is blocked.
3. At this moment, the aux. flow combining valve is
also shifted, allowing the pressure oil from the 4-
spool side (pump 1) to flow to the aux. spool via
the aux. flow combining valve.
4. Consequently, the pressure oil from pump 1
merges with the pressure oil from pump 2 so that
the attachment operating speed is increased.

Pilot Pressure from

Signal Control Valve Aux. Pilot Valve
Aux. Flow Combining
Aux. Flow
Solenoid Valve
Combining Valve

Port SN Port SM

Attachment
Neutral Circuit

Auxiliary

Port SJ

Bypass Shut-Out Valve

4-Spool Side
5-Spool Side

Pump 2 Pump 1

T176-03-03-033

T3-3-24
 COMPONENT OPERATION / Control Valve
When Neutral:
Aux. Flow Combining Valve
Bypass Shut-Out Valve
Port SN

Spring B
To Aux. Spring Spool 4-Spool Side
Spool Neutral Circuit
Check Valve

Pressure
Oil from
Pump 1

Spool
Return to
Hydraulic
Oil Tank

Spring A

Port SM Port SJ T176-03-03-022

T176-03-03-021

When Operating:

Port SN
Spring Spool 4-Spool Side
Spring B Neutral Circuit
To Aux.
Spool Check Valve

Pressure
Oil from
Pump 1

Return to
Spool Hydraulic
Oil Tank

Spring A
Port SJ T176-03-03-024

Port SM

T176-03-03-023

T3-3-25
 COMPONENT OPERATION / Control Valve
Combined Operation
When the aux. pilot valve and the boom, arm, bucket, Aux. Flow Combining Valve
or travel functions are operated simultaneously, the
Port SN
aux. flow combining valve is not shifted. Thereby, the
specified operating speed of the boom, arm, bucket,
Spring B
or travel function is ensured. To Aux.
1. When the aux. pilot valve is operated, the pilot Spool
pressure oil is routed to port SM on the aux. flow Check Valve
combining valve. Pressure
2. When the boom, arm, bucket, or travel is Oil from
operated at the same time, the pilot pressure oil Pump 1
from the signal control valve is routed to port SN.
3. The pressure oil from port SM acts on the aux.
flow combining valve spool toward opening
direction. The pressure oil from port SN and Spool
spring A act toward the closing direction.
4. Since the force to close the spool is larger than
that to open the spool, the spool is kept closed.

Spring A

Port SM

T176-03-03-037

T3-3-26
 COMPONENT OPERATION / Pilot Valve
OUTLINE

The pilot valve controls the pilot oil pressure by which The reducing valves in both the front attachment /
the control valve spools are operated. swing and travel pilot valves are identical construction
Two types of the standard pilot valves are located on except for the pusher moving cam.
this machine. Both have four oil ports. One type is
used for the front attachment / swing function control.
Another is used for the travel function control. Optional
type has two oil ports.
• Travel Pilot Valve
• Front Attachment / Swing Pilot Valve 1 Right Travel Reverse
Port ISO Control 2 Right Travel Forward
H Pattern 3 Left Travel Forward
No. Pattern
1 Bucket Roll-Out ұ 4 Left Travel Reverse
2 Boom Lower ұ
Right
3 Bucket Roll-In ұ Hydraulic P T
Symbol
4 Boom Raise ұ
1 Right Swing Arm Roll-In
2 Arm Roll-Out Right Swing
Left
3 Left Swing Arm Roll-Out
1 3 2 4
4 Arm Roll-In Left Swing
T105-02-07-020

Hydraulic P T
Symbol

1 3 2 4
T105-02-07-020
T

3 4

2 1
1
T178-03-04-002

P
T178-03-04-001

T3-4-1
 COMPONENT OPERATION / Pilot Valve
OPERATION
Spool (6) head comes in contact with the upper face of
spring guide (3) which is kept raised by return spring
(5).

Neutral (Output Diagram: A to B):

1. When neutral, spool (6) totally blocks the pressure
oil in port P (from the pilot pump).The output port E F
is opened to port T (hydraulic oil tank) through the
passage in spool (6). Therefore, the oil pressure
in the output port (to the control valve) is equal to D
that in port T. Pilot
Pressure
2. When the control lever is slightly tilted, cam (1) is
tilted, moving pusher (2) downward. Then, pusher
(2) pushes return spring (5) downward with spring C
guide (3). At this time, as the oil pressure in the
output port is equal to that in port T, spool (6) A B
moves downward while keeping the under face of Lever Stroke
the spool head in contact with spring guide (3). T522-02-05-001

3. This status continues until hole (7) on spool (6) is

opened to port P.

T3-4-2
 COMPONENT OPERATION / Pilot Valve
Front Attachment / Swing Pilot Valve

1 1

2 2

6
3 3 Port T

4 4
7
5 5 Port P

6 Output Port
6

Port T Port T

7 Port P 7 Port P

Output Port T178-03-04-005

Output Port T178-03-04-007

Travel Pilot Valve

1 1

2 2 Port T

7
Port P
3 3 6

4 4
5 Output Port
5
6
Port T Port T
6
Port P Port P
7 7

Output Port T178-03-04-006

Output Port T178-03-04-011

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

T3-4-3
 COMPONENT OPERATION / Pilot Valve
During Metering or Decompressing (Output
Diagram: C to D)
1. When the control lever is further tilted to move E F
pusher (2) downward more, hole (7) on spool (6)
is opened to port P, the allowing the pressure oil in
D
port P to flow into the output port.
Pilot
2. The oil pressure in the output port acts on the Pressure
bottom face of spool (6) so that spool (6) is
pushed upward.
C
3. However, until the upward force acting on the
bottom face of spool (6) overcomes balance
spring (4) force, balance spring (4) is not A B
Lever Stroke
compressed. Then, spool (6) is not raised,
allowing the oil pressure in the output port to T522-02-05-001

increase.
4. As the oil pressure in the output port increases,
the force to push spool (6) upward increases.
When, this force overcomes balance spring (4)
force, balance spring (4) is compressed so that
spool (6) is moved upward.
5. As spool (6) is moved upward, hole (7) is closed
so that the pressure oil from port P stops flowing
into the output port, stopping the pressure oil in
the output port to increase.
6. As spool (6) is moved downward, balance spring
(4) is compressed, increasing the spring force.
Therefore, the oil pressure in the output port
becomes equal to the oil pressure acting on the
bottom face of spool (6) being balanced in
position with the spring force.

T3-4-4
 COMPONENT OPERATION / Pilot Valve
Front Attachment / Swing Pilot Valve

1 1

2 2

3 3

4 4

5 5

6 6

Port T Port T

7 Port P 7 Port P

Output Port T178-03-04-008 Output Port T178-03-04-009

Travel Pilot Valve

1 1

2 2

3 3

4 4
5 5
6 6
Port T Port T

Port P Port P
7 7

Output Port T178-03-04-012 Output Port T178-03-04-013

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

T3-4-5
 COMPONENT OPERATION / Pilot Valve
Full Stroke (Output Diagram: E to F)
1. When the control lever is fully stroked, pusher (2)
is moved downward until pusher (2) in the front E F
attachment / swing pilot valve comes in contact
with the casing shoulder, or cam (1) on the travel
D
pilot valve comes in contact with the casing. Pilot
2. At this moment, the bottom of pusher (2) directly Pressure
pushes spool (6). Therefore, even if the oil
pressure in the output port increases further, hole
C
(7) on spool (6) is kept open.
3. Consequently, the oil pressure in the output port is
equal to the oil pressure in port P. A B
Lever Stroke
T522-02-05-001
NOTE: Total lever strokes for the front attachment
and swing controls are determined by
stroke dimension (E) of pusher (2). Total
lever stroke for the travel control is
determined by stroke dimension (E) of cam
(1).

T3-4-6
 COMPONENT OPERATION / Pilot Valve

Front Attachment / Swing Pilot Valve

2 2

4
5

6
Port T

7 Port P

T178-03-04-010
Output Port T178-03-04-005

Travel Pilot Valve

1
1

E
2

4
5
6
Port T

Port P
7

T178-03-04-006
Output Port T178-03-04-014

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

T3-4-7
 COMPONENT OPERATION / Pilot Valve
(Blank)

T3-4-8
 COMPONENT OPERATION / Travel Device
OUTLINE

The travel device consists of travel motor, the travel

reduction gear, and the sprocket.

Travel Motor

Travel Reduction Gear

Sprocket

T165-03-05-006

T3-5-1
 COMPONENT OPERATION / Travel Device
TRAVEL REDUCTION GEARS

The travel reduction gears are second stage planetary Since second stage carrier (2) of the reduction gear
gear type. and holder (9) of the travel motor are integrated within
The travel motor rotates shaft (6) and this driving force a monoblock, second stage carrier (2) is held
is transmitted to second stage carrier (2) and ring gear stationary.
(1) through first stage planetary gear (5), first stage As ring gear (1) is bolted to sprocket (8), they all rotate
carrier (4), second stage sun gear (3) and second together.
stage planetary gear (7).

1 2 3 4 5

1 2 3 4

6
6
5

Second First
Stage Stage

8 7 T165-03-05-008

T165-03-05-003
9 7

1 - Ring Gear 4 - First Stage Carrier 6 - Shaft 8 - Sprocket

2 - Second Stage Carrier 5 - First Stage Planetary Gear 7 - Second Stage Planetary 9 - Holder (Travel Motor)
Gear
3 - Second Stage Sun Gear

T3-5-2
 COMPONENT OPERATION / Travel Device
TRAVEL MOTOR

The travel motor is a variable-displacement swash Rotor (7) is splined to shaft (5) and friction plate (2).
plate-type motor which includes parking brake (Wet- Each plunger (6) is fitted to a shoe (3) by a ball socket
single-disc negative type). joint.
The main parts of the motor are valve plate (8), rotor Shoe (3) moves, sliding along swash plate (4).
(7), plungers (6), shaft (5), swash plate (4), piston (9),
brake piston (1), and friction plate (2).

1 2 3 9

8 7 6 5 4

T165-03-05-002

1 - Brake Piston 4 - Swash Plate 6 - Plunger 8 - Valve Plate

2 - Friction Plate 5 - Shaft 7 - Rotor 9 - Piston
3 - Shoe

T3-5-3
 COMPONENT OPERATION / Travel Device
Pressure oil routed to port a1 (1) of valve plate (8) acts As rotor (3) rotates, plungers (7) move to port a1 (1)
on plungers (7) in one half of rotor (3), pushing them side one by one, returning oil to the hydraulic oil tank
against swash plate (4). As the swash plate surface is via port a2 (2).
slanted against the plungers, shoes (6) slide along Travel direction (forward or reverse) is determined by
swash plate (4), rotating rotor (3) and shaft (5). which of the valve plate ports (port a1 or a2) the
pressure oil from the pump is supplied to.

1 3 4

2 8 7 6

T135-03-04-004

1 - Port a1 3 - Rotor 5 - Shaft 7 - Plunger

2 - Port a2 4 - Swash Plate 6 - Shoe 8 - Valve Plate

T3-5-4
 COMPONENT OPERATION / Travel Device
(Blank)

T3-5-5
 COMPONENT OPERATION / Travel Device
Travel Speed Selection

Piston (1) is located next to swash plate (3). The 3. The motor plungers push swash plate (3) down,
angle of swash plate (3) is changed by making the surface (A) of swash plate (3) come in
extending/retracting piston (1) so as to change the contact with the casing surface. In this position,
travel speed mode. the displacement angle of swash plate (3) is at the
maximum angle, allowing the motor plungers to
• Slow Speed reciprocate in maximum stroke, thus achieving
1. When the slow speed travel mode is selected, the the slow speed travel mode.
main controller (MC) does not send a control
signal to the solenoid valve unit (SI). For this
reason, the pilot pressure used for travel mode
change is not routed to port PS (4). As a result,
spool (5) is held to the left side by spring (6).
2. Pressure oil from high pressure side motor port a2
(7) or a1 (8) is blocked by spool (5), draining oil in
the two-speed control piston chamber via spool
(5).
6 4 5 6

T165-03-05-005

Surface (A)

3
2 7 8

Top View of Swash Plate Surface (B) Valve Plate

T165-03-05-010

1 - Piston 3 - Swash Plate 5 - Spool 7 - Port a2

2 - Steel Ball 4 - Port PS 6 - Spring 8 - Port a1

T3-5-6
 COMPONENT OPERATION / Travel Device

• Fast Speed
1. With the fast speed travel mode selected, the 3. Then, piston (1) pushes swash plate (3), making
main controller (MC) send a control signal to the the surface (B) of swash plate (3) come in contact
solenoid valve unit (SI) when traveling under light with the casing surface. In this position, the
loads. Pilot pressure SH used for travel mode displacement angle of swash plate (3) is at the
change is then routed from port PS (4), moving minimum angle, allowing the motor plungers to
spool (5) to the right. reciprocate in minimum stroke, thus achieving the
2. Pressure oil from high pressure side motor port a2 fast speed travel mode.
(7) or a1 (8), routed via spool (5), acts on piston
(1).

6 4 5 6

T165-03-05-007

Surface (A)

3
2 8
7
Top View of Swash Plate Valve Plate

Surface (B) T165-03-05-011

1 - Piston 3 - Swash Plate 5 - Spool 7 - Port a2

2 - Steel Ball 4 - Port PS 6 - Spring 8 - Port a1

T3-5-7
 COMPONENT OPERATION / Travel Device
TRAVEL BRAKE VALVE

The travel brake valve is located on the motor head of OVERLOAD RELIEF VALVE (9):
each travel motor. Prevents overload and surge pressure in the motor
The travel brake valve consists of the following valves: circuit.

COUNTERBALANCE VALVE: TRAVEL MOTOR SWASH ANGLE CONTROL VALVE

Ensures smooth starts and stops, and prevents (10):
overrunning when traveling down slopes. Activated by pilot pressure from the solenoid valve unit
(SI). Routes the travel motor driving pressure to the
CHECK VALVE (2): two-speed control piston.
Ensures smooth starts and stops, and prevents
cavitation from occurring in the motor circuit by
functioning together with counterbalance valve.

From Control Valve To Control Valve

1 2 3 4 5 6

9 8 10 7

T165-03-05-004
1 - Orifice 4 - Port P1 7 - Port a2 10 - Overload Relief Valve
2 - Check Valve 5 - Port P3 8 - Port a1 11 - Travel Motor Swash Angle
Control Valve
3 - Spool 6 - Port P2
(Counterbalance Valve)

T3-5-8
 COMPONENT OPERATION / Travel Device
Travel Operation Circuit Protection

1. When pressure oil from the control valve is routed 1. If pressure in the circuit exceeds the setting
to port P1 (4), it is then routed to motor port a1 (8) pressure of overload relief valve (9), the valve
after opening check valve (2). opens to relieve peak pressure to the lower
2. On the other hand, return oil from the travel motor pressure side to protect the motor from
returns to motor port a2 (7) but does not flow overloading.
further as it is blocked by the other check valve 2. This valve also functions to release shock
(2). pressure caused by inertial force that develops
3. As supply oil at port P1 (4) increases, it is then when the motor stops.
routed to the left end of spool (3) via orifice (1), 3. When the motor sucks oil as it may happen when
shifting spool (3) to the right. descending, check valve (2) opens to prevent
4. Consequently, return oil from the motor port starts cavitation in the circuit from occurring.
to flow into port P2 (6) via a notch on spool (3),
allowing the travel motor to rotate.
5. When the travel levers are returned to the neutral Shuttle Function
position, spool (3) is returned to the original
position by the spring, blocking the motor circuit to 1. When spool (3) is moved from its neutral position,
stop motor rotation. port P1 (4) or port P2 (6) is connected to parking
brake release port P3 (5), routing pressure oil to
the parking brake chamber to release the parking
Descending Operation brake.
2. When the travel motor stops rotating, spool (3) is
1. When the machine travels down a slope, the returned to the neutral position, closing port P3 (5).
travel motors are forcibly driven by the machine Then, oil in the parking brake chamber is drained
weight so that the motor sucks oil like a pump. to the drain port, activating the parking brake.
2. When the motor sucks oil, the oil pressure at port
P1 (4) and the left end of spool (3) decreases,
moving spool (3) to the left to restrict the return oil
flow.
3. For this reason, the pressure at motor port a2 (7)
rises to brake (slow) motor rotation.
4. As the motor rotation is slowed, the pressure at
port P1 (4) rises, moving spool (3) to the right.
Repetition of this return oil restriction and
unrestriction (hydraulic braking) prevents the
machine from overrunning.

T3-5-9
 COMPONENT OPERATION / Travel Device
PARKING BRAKE

The parking brake is a negative-type brake which is When the parking brake releasing:
released when oil pressure acts on parking brake 1. When operating the travel lever, the pressure oil
chamber M. The parking brake is always automatically from the main pump flows into the travel motor
applied except for travel operation. port (P1 or P2) via the control valve.
2. Pressure oil form the travel motor port (P1 or P2)
The friction plate is connected to the rotor by a spline is routed to parking brake chamber M via the
coupling. When the spring pushes the piston, the parking brake release port P3.
piston comes in contact with the friction plate, applying 3. This pressure oil frees the piston to the left from
the parking brake. the friction plate, releasing the parking brake.
(Refer to the shuttle function on the previous
page.)

When the parking brake operation:

1. When returning the travel lever to neutral, the
counterbalance spool is returned to its neutral
position, closing the parking brake release port
P3.
2. As parking brake chamber M is connected to the
drain line.
3. The piston is slowly moved to the right by the
spring the until it makes contact securely with
friction plate, applying the parking brake.

Port P3 Spring Piston M Friction Plate Rotor

T165-05-04-009

T3-5-10
 COMPONENT OPERATION / Signal Control Valve
OUTLINE

The signal control valve is provided in the pilot circuit

between the pilot valve and the control valve and con-
trols the pilot signal pressure used to regulate the
pumps and various kinds of valves.
The major components of the signal control valve are,
shuttle valves, shockless valve, pump 1 flow rate con-
trol valve, pump 2 flow rate control valve, flow com-
biner valve control spool, bucket flow rate control valve
control spool, and swing parking brake release spool.

Pilot Valve Side

T178-03-06-016
Cross Section A-A

Shockless Valve

Auxiliary Bucket Flow Rate Control Valve

Pump 1 Flow Rate Control Valve Pump 2 Flow Rate Control Valve

Swing Parking Brake Flow Combiner Valve Control Spool

Release Spool

T178-03-06-002

T3-6-1
 COMPONENT OPERATION / Signal Control Valve
PILOT PORT

Pilot Valve Side

Port Name Connecting to Note
Port A Right Pilot Valve Boom Raise Pilot Pressure
Port B Right Pilot Valve Boom Lower Pilot Pressure
Port C Left Pilot Valve Arm Roll-Out Pilot Pressure
Port D Left Pilot Valve Arm Roll-In Pilot Pressure
Port E Left Pilot Valve Left Swing Pilot Pressure
Port F Left Pilot Valve Right Swing Pilot Pressure
Port G Right Pilot Valve Bucket Roll-In Pilot Pressure
Port H Right Pilot Valve Bucket Roll-Out Pilot Pressure
Port I Travel Pilot Valve Left Travel Forward Pilot Pressure
Port J Travel Pilot Valve Left Travel Reverse Pilot Pressure
Port K Travel Pilot Valve Right Travel Forward Pilot Pressure
Port L Travel Pilot Valve Right Travel Reverse Pilot Pressure
Port M Auxiliary Pilot Valve Auxiliary Open Pilot Pressure
Port N Auxiliary Pilot Valve Auxiliary Close Pilot Pressure
Port SA Pump 1 Regulator Pump 1 Control Pressure
Port SB Pump 2 Regulator Pump 2 Control Pressure
Port PI Pilot Shut-Off Valve Primary Pilot Pressure
Port PH Pilot Shut-Off Valve Primary Pilot Pressure (Heating Circuit)
Port SH Swing Parking Brake Brake Release Pressure
Port DF Hydraulic Oil Tank Returning to Hydraulic Oil Tank

Control Valve Side

Port Name Connecting to Note
Port 1 Control Valve Boom Raise Pilot Pressure
Port 2 Control Valve Boom Lower Pilot Pressure
Port 3 Control Valve Arm Roll-Out Pilot Pressure
Port 4 Control Valve Arm Roll-In Pilot Pressure
Port 5 Control Valve Left Swing Pilot Pressure
Port 6 Control Valve Right Swing Pilot Pressure
Port 7 Control Valve Bucket Roll-In Pilot Pressure
Port 8 Control Valve Bucket Roll-Out Pilot Pressure
Port 9 Control Valve Left Travel Forward Pilot Pressure
Port 10 Control Valve Left Travel Reverse Pilot Pressure
Port 11 Control Valve Right Travel Forward Pilot Pressure
Port 12 Control Valve Right Travel Reverse Pilot Pressure
Port 13 Control Valve Auxiliary Open Pilot Pressure
Port 14 Control Valve Auxiliary Close Pilot Pressure
Port SE ӸӸӸ Plug
Port SM Hydraulic Oil Tank Returning to Hydraulic Oil Tank
Port SN ӸӸӸ Plug
Port SP Solenoid Valve Unit Returning to Hydraulic Oil Tank
Port SL Control Valve Flow Combiner Valve Control Pressure
Port SK Control Valve Bucket Flow Rate Control Valve Control Pressure

T3-6-2
 COMPONENT OPERATION / Signal Control Valve

Pilot Valve Side

PH
C
A

E
M
D
H
B
F
SB
PI G

Pilot Valve Side

K N

I
SH
J

DF

SA L
T178-03-06-016

Control Valve Side

SM
3

1 5

13
2 4
SK
SE
8
Pressure Sensor (Swing)

14
Control Valve Side
7
9
6
10

SN
SL
11

Pressure Sensor (Travel) 12 SP T178-03-06-015

T3-6-3
 COMPONENT OPERATION / Signal Control Valve
SHUTTLE VALVE

The shuttle valve selects the pilot pressure used to

perform each operation and routes it to the corre-
sponding flow rate control valves and/or control spools.
The flow rate control valves and/or control spools cor-
responding to each operation are as follows:

Pump 1 Flow Pump 2 Flow Flow Combiner Bucket Flow Swing Parking
Rate Control Rate Control Valve Control Rate Control Brake Release
Valve Valve Spool Valve Control Spool
Spool
Boom Raise { { - - {
Boom Lower { { - - {
Arm Roll-In { { - { {
Arm Roll-Out { { - - {
Bucket Roll-In { - - - {
Bucket Roll-Out { - - - {
Right Swing - { - - {
Left Swing - { - - {
Right Travel { - { - -
Left Travel - { - - -
Auxiliary - { - - {

Left Right 5 6 7 8 9
Travel Travel Swing Arm Boom Bucket 10
1 2 3 4 11
12
13

14 15 16 17

T178-03-06-001

Pump 1 Flow Pump 2 Flow Bucket Flow Flow Combiner Swing Parking
Rate Control Rate Control Rate Control Valve Control Brake Release
Valve Valve Valve Control Spool Spool
Spool

T3-6-4
 COMPONENT OPERATION / Signal Control Valve

Pilot Valve Side

T178-03-06-016

Cross Section B-B

9
5
8
7
16

17

15
13
11
14

6 10
12
3
1
4

2
T178-03-06-009

1 - Left Travel 6 - Boom/Arm/Bucket/Right 11 - Boom/Arm/Bucket 16 - Swing/Auxiliary

Travel
2 - Left Travel/Right Travel 7 - Boom/Arm 12 - Boom/Arm/Bucket/ 17 - Auxiliary
ŅSwing/Auxiliary
3 - Right Travel 8 - Boom 13 - Arm/Boom
Raise/Swing/Auxiliary
4 - Boom/Arm/Bucket/ Right 9 - Arm/Boom Raise 14 - Bucket
Travel
5 - Arm 10 - Boom/Arm/Bucket/Left 15 - Swing
Travel/Swing

T3-6-5
 COMPONENT OPERATION / Signal Control Valve
SHOCKLESS VALVE

The shockless valve is provided in the boom raise cir-

cuit and functions during boom lowering operation.

During Boom Raising Operation:

1. The boom raise pilot pressure is routed from port
A and acts on the spool.
2. Immediately after the operation is started, the low
pilot pressure oil flows to port 1 via clearance C
between the spool and the housing, and inner
passage 2.
3. The set-force of spring A is weaker than that of
spring B. Therefore, when the pilot pressure in-
creases, the spool is moved to the left.
4. As the spool is moved to the left, port A is con-
nected to port 1, increasing the pressure in port 1
so that the spool in the control valve is moved.

During Boom Lowering Operation (Shock Reduc-

ing Operation)
1. When the boom is lowered, the return oil from the
boom raise spool in the control valve is routed to
port 1.
2. Since the spool blocks the oil passage between
port 1 and port A, the return oil cannot flow directly
to port A.
3. Port 1 is connected to spring A side via inner pas-
sage 1 and to the oil chamber via inner passage
2.
4. The pressure oil in the oil chamber flows out of
clearance C between the spool and the housing,
reducing the pressure in the oil chamber. Then,
the spool is moved to the right by the pressure in
the spring A side. Thereby, clearance C between
the spool and the housing is closed, blocking the
pressure oil flow.
5. When clearance C is closed, the pressure in the
oil chamber increases, moving the spool to the left.
Therefore, clearance C is opened again, allowing
the pressure oil to flow to port A.
6. As operations in steps (4 and 5) are repeated, the
pressure oil is gradually returned to port A so that
the control spool returns slowly.

T3-6-6
COMPONENT OPERATION / Signal Control Valve

Pilot Valve Side

Port A
Inner Passage 1 C Spool Spring B

Spring A Inner Passage 2 Oil Chamber

Port 1
T178-03-06-013
Control Valve Side

T3-6-7
 COMPONENT OPERATION / Signal Control Valve
PUMP 1 AND PUMP 2 FLOW RATE CON-
TROL VALVES

The pump flow rate control valve delivers the pump

control pressure Pi to the pump regulator in response
to the pilot oil pressure from the pilot valve.

1. The pilot pressure from the pilot valve is routed

into the spring chamber side in either the pump 1
or pump 2 flow rate control valve after being se-
lected by the shuttle valves in the signal control
valve.
2. Then, the spool is moved to the right, causing the
primary pilot pressure to flow in either port SA or
SB.
3. Therefore, the pressure in port SA or SB in-
creases.
4. The oil pressure in port SA or SB acts on the right
end of the spool. Thus, the spool is moved back to
the left until the pressure force in port SA or SB
balances with the pilot pressure force in the spring
chamber so that the pressure in port SA or SB
stops increasing.

NOTE: The pump 1 flow rate control valve oper-

ates when the boom (raise or lower), arm
(roll-in or out), bucket (roll-in or out), auxil-
iary, and travel (right) functions are oper-
ated. The pump 2 flow rate control valve
operates when the boom (raise or lower),
arm (roll-in or out), swing (right or left), and
travel (left) functions are operated.

T3-6-8
COMPONENT OPERATION / Signal Control Valve

Port SA, SB
Spring Spool

Primary Pilot Pressure

Pilot Pressure

Shuttle Valve

T178-03-06-017

T3-6-9
 COMPONENT OPERATION / Signal Control Valve
BUCKET FLOW RATE CONTROL VALVE
CONTROL SPOOL, FLOW COMBINER
VALVE CONTROL SPOOL, SWING PARK-
ING BRAKE RELEASE SPOOL
Bucket Flow Rate Control Valve Control Spool:
NOTE: The three captioned spools are identical in To Hydraulic Boom Raise Control
Oil Tank Pilot Pressure
operational principle. Spool Spring

The bucket flow rate control valve control spool is

shifted by the arm roll-in control pilot pressure, allowing
the boom raise pilot pressure to flow to the bucket flow
rate control valve in the control valve.
The flow combiner valve control spool is shifted by the T178-03-06-014
right travel pilot pressure, allowing the primary pilot Arm Roll-In To Bucket Flow Rate
pressure to flow to the flow combiner valve in the con- Pilot Pressure Control Valve
trol valve.
The swing parking brake release spool is shifted by the Flow Combiner Valve Control Spool:
To Hydraulic Primary Pilot
boom, arm, bucket, or auxiliary pilot pressure, allowing Oil Tank Pressure
the primary pilot pressure to flow to the swing motor. Spool Spring

T178-03-06-014
Right Travel To Flow Combiner
Pilot Pres- Valve
sure
Swing Parking Brake Release Spool:
To Hydraulic Primary Pilot
Oil Tank Pressure
Spool Spring

T178-03-06-014
Pilot To Swing
Pressure Parking Brake

T3-6-10
 COMPONENT OPERATION / Others (Upperstructure)
PILOT SHUT-OFF VALVE

The pilot shut-off valve is a manual-operated switch

valve. The spool in the pilot shut-off valve is rotated by
moving the pilot control shut-off lever to turn on or off
the pilot oil flow to the pilot valves.

• When Pilot Control Shut-Off Lever is in LOCK

Position.
The pilot shut-off valve is set in the OFF position.
The pressure oil from the pilot pump does not flow Section Z-Z
into the pilot valves, but it is routed to the signal
control valve. The pilot oil on the pilot valve side is
routed to the hydraulic tank. The pilot valve are
operated, as the control levers are operated.

• When Pilot Control Shut-Off Lever is in UNLOCK

Position
The pilot shut-off valve is set in the ON position. The
pressure oil from the pilot pump to flow into the pilot
valves as the drain circuit is blocked. If the control
lever is operated, the pilot valve works.
To Signal From Pilot
Control Valve Valve T178-03-07-002

A2 A1
Z

T1 T2 A3 A4 T4

T3 P

A5 T178-03-07-003

A1 - Right Pilot Valve A4 - Signal Control Valve T1 - Travel Pilot Valve T - Hydraulic Oil Tank
(Port PH)
A2 - Travel Pilot Valve A5 - Signal Control Valve T2 - Left Pilot Valve
(Port PI)
A3 - Left Pilot Valve P - Primary Pilot Pressure T3 - Right Pilot Valve

T3-7-1
 COMPONENT OPERATION / Others (Upperstructure)
SOLENOID VALVE UNIT

The solenoid valve unit functions to control the control

valve and travel motor swash angle control valve by
signals from the main controller (MC).
The solenoid valve unit consists of two proportional
solenoid valves (SC) and (SI). (Refer to the Control
System Group in the SYSTEM Section.)

SC : Controls the arm regenerative valve located in the

control valve.
SI : Controls the travel motor swash angle.

SC SI T176-03-07-002

T3-7-2
 COMPONENT OPERATION / Others (Upperstructure)
Proportional Solenoid Valve

Upon receiving an electric current signal from the MC,

the proportional solenoid valve outputs the hydraulic
pressure proportional to the degree of the electric
current.

• When not energized (In neutral): Because of the pressure receiving area difference
The spring pushes the spool to the right, between two step parts (a), the pressure at port S
connecting output port S to tank port T. acts as a force to push the spool to the right. As
the pressure at port S increases, the force to push
• When energized: the spool to the right also increases. When this
The solenoid pushes the spool to the left for a force overcomes the force to push the spool to the
distance proportional to the electric current left by the solenoid, the spool moves back to the
flowing through the solenoid. The pilot oil from right side, closing the passage between output
port (P) flows into output port S, increasing the port S and port P. As a result, the pressure
pressure at output port S. The pressure at port S increase at port S stops.
acts on step parts (a) on the spool. (See detail
“a.”)

Spool Spring Solenoid

T S P

a
T107-02-07-005

T3-7-3
 COMPONENT OPERATION / Others (Upperstructure)
TORQUE CONTROL SOLENOID VALVE,
PUMP 2 FLOW RATE CONTROL SOLE-
NOID VALVE

The torque control solenoid valve and the pump 2 flow

rate control solenoid valve are placed at the top of the
pilot filter.

ST: Controls the pump regulator.

(Speed Sensing Control)
SB: Controls the pump regulator.
(Pump 2 Flow Rate Control) SB

ST
• The torque control solenoid valve supplies torque
control pressure Pps to the regulators of pump 1 and
pump 2, reducing the pump delivery flow.
• The pump 2 flow rate control solenoid valve reduces
the pump control pressure to the regulator of pump 2, Pilot Filter
controlling the maximum limit of the pump 2 delivery
flow. T1F1-01-02-004

Operation:
1. In the neutral position, port P is connected to the
output port via the notch on the spool.
2. When the current from MC (Main Controller) flows
to the solenoid, the solenoid pushes spring 1.
3. As spring 1 pushes the spool, the output port is
connected to port T via the notch on the spool, re-
ducing the pressure in the output port.
4. The left diameter (A) is larger than the right di-
ameter (B) of the spool notch, so the spool is
moved back to the left.
5. When the notches on the spool and the sleeve
come in contact with each other, the spool stops
moving and the pressure in the output port stops
decreasing.

T3-7-4
 COMPONENT OPERATION / Others (Upperstructure)
When Neutral:

Solenoid Spring 1 Spring 2 Sleeve Spool

T176-03-01-030

A Port P Port T B

Output Port

When in Operation:

Solenoid Spring 1 Spring 2 Sleeve Spool

T176-03-01-031

A Port P Port T B

Output Port

T3-7-5
 COMPONENT OPERATION / Others (Upperstructure)
PILOT RELIEF VALVE

The pilot relief valve has a pilot filter incorporated.

The pilot relief valve functions to regulate the pilot
pump pressure oil routed to port P to a set constant
pressure.

Pilot Relief
Valve

Pilot Filter

T1F1-01-02-004

EC MOTOR
Output Output Worm
The EC motor is used to control the engine speed. A Gear Shaft Gear
worm gear is incorporated into the EC motor to prevent
a loss of synchronism from occurring. The EC sensor
is provided to detect the degrees of the EC motor
rotation to calculate the governor lever position. (Refer
to the Control System Group in SYSTEM Section.)

Motor

Sensor EC Worm
Gear Sensor Wheel

T157-02-05-018

T3-7-6
 COMPONENT OPERATION / Others (Undercarriage)
SWING BEARING

The swing bearing supports the upperstructure and The internal gear of inner race (3) engages with the
allows the upperstructure to rotate smoothly. The output shaft of the swing reduction gear.
bearing is a single-row shear ball-type bearing,
comprising outer race (1), inner race (3), balls (6),
supports (5), and seals (2) and (4). Outer race (1) is
bolted to the upperstructure and inner race (3) is
bolted to the undercarriage.

T135-03-02-001

1 - Outer Race 3 - Inner Race 5 - Support 6 - Ball

2 - Seal 4 - Seal

T3-8-1
 COMPONENT OPERATION / Others (Undercarriage)
CENTER JOINT

The center joint is a 360° rotating joint. When the Hydraulic oil flows to the right and left travel motors
upperstructure is rotated, the center joint avoids via the spindle and the oil ports of the body. The seals
twisting of hoses and allows the hydraulic oil to flow prevent oil leaks between the spindle and body into
smoothly to the travel motors. The spindle is attached adjacent passages.
to the upperstructure and the body is bolted to the
swing center of the undercarriage.

Left Travel Right Travel Left Travel Right Travel

Motor (Reverse) Motor (Forward) Motor (Forward) Motor (Forward)

Left Travel Left Travel Right Travel

Right Travel Motor (Reverse)
Motor (Forward) Motor (Reverse)
Motor (Reverse)
Spindle

Pilot Pressure Pilot Pressure

for Travel Mode Control Drain for Travel Mode
Control

Body

Drain

Drain Seal

Drain

: Forward
: Reverse
: Pilot Pressure
for Travel Mode Control

T157-03-02-004

T3-8-2
 COMPONENT OPERATION / Others (Undercarriage)
TRACK ADJUSTER

The track adjuster located on the side frame is

composed of spring (5) and adjuster cylinder (6).
Spring (5) absorbs loads applied to the front idler.
Adjuster cylinder (6) adjusts track sag.

• Grease is applied through grease fitting into

chamber (a) of adjuster cylinder (6) as illustrated
below. The pressure of the grease pushes piston
rod (8) out and decreases track sag.
1
• To increases track sag, loosen valve (1) 1 to 1.5 Grease Fitting
turns counterclockwise to release grease from
the track adjuster cylinder through the grease
discharge hole.

CAUTION: Do not loosen valve (1) quickly

or loosen too much since high-pressure
grease in the adjusting cylinder may spout
out.
Loosen carefully, keeping body parts and
Grease Discharge Hole
face away from valve (1).
Never loosen grease fitting.
M104-07-119

1 2 3 4 a
5 6 7 8

W178-03-04-002

1 - Valve 3 - Washer 5 - Spring 7 - Flange

2 - Nut 4 - Spacer 6 - Adjuster Cylinder 8 - Piston Rod

T3-8-3
 COMPONENT OPERATION / Others (Undercarriage)
(Blank)

T3-8-4