SECTION 2 STRUCTURE AND FUNCTION
Group 1 Pump Device -------------------------------------------------------------------------------------------------- 2-1
Group 2 Main Control Valve ----------------------------------------------------------------------------------------- 2-6
Group 3 Swing Device -------------------------------------------------------------------------------------------------- 2-30
Group 4 Travel Device --------------------------------------------------------------------------------------------------- 2-40
Group 5 RCV Lever ------------------------------------------------------------------------------------------------------ 2-46
Group 6 RCV pedal ------------------------------------------------------------------------------------------------------ 2-53
Group 7 Brake pedal (valve) ---------------------------------------------------------------------------------------- 2-54
Group 8 Gear box --------------------------------------------------------------------------------------------------------- 2-56
Group 9 Steering valve ------------------------------------------------------------------------------------------------- 2-59
Group 10 Axle ----------------------------------------------------------------------------------------------------------------- 2-61
SECTION 2 STRUCTURE AND FUNCTION
GROUP 1 HYDRAULIC PUMP
1. GENERAL
This is a variable displacement double-piston pump for discharge with equal displacements from one
cylinder block. This pump is so compact as to appear a single pump though this is actually a double
pump.
Because this pump has one swash plate, the tilting angle is the same for two pumps. Tilting of the
pump changes in response to the total pressure of P1 + P2. Namely, the output is controlled to the
constant value so that the relationship between the discharge pressure and flow rate Q becomes
constant, (P1 + P2) * Q =Constant.
The third pump and pilot pump can be connected to the same shaft via a coupling.
A1 A2
A1G A2G A3G PPG
R1 A1 A2 A3 A4
ENG
S1
PPG Hydraulic circuit
R1 A3
A1G A2G
A4 A3G S1 555W92MP01
Description of the ports
Port Name Bore
S1 Suction port SAE 1 1/2 (standard)
A1, A2 Discharge port PF 1/2
A3 Discharge port PF 1/2
A4 Discharge port PF 1/4
A1G, A2G Gauge port PF 1/4 with quick coupler
A3G Gauge port PF 1/8 with quick coupler
PPG Gauge port PF 1/4 with quick coupler
R1 Air bleeder port M10×1.0 with bleeder valve
2-1
2. PRINCIPAL COMPONENTS AND FUNCTIONS
1 2 5 8
3 6 4 7
55W72MP02
1 Drive shaft 5 Control spring
2 Hanger 6 Control piston
3 Rotary group 7 Gear pump
4 Cover 8 Housing
SPECIFICATIONS
● Capacity : 2×25+16.2+6.5 cc/rev
● Rated oil flow : 2×60+38.9+15.6 ℓ /min
● Rated pressure : 2×220+200+30 kgf/cm2
This is a variable displacement double-piston pump for discharge with two equal displacements
from one cylinder block. Because this is one rotary group, there is only one suction port.
The oil is divided into two equal flows by the control plate in the cover and directed to two
discharge ports provided in the cover.
The discharge pressure directed to the control piston tilts the hanger by overcoming the spring
force.
Since the piston stroke changes according to the tilting angle of the hanger, the flow can be
changed.
The simultaneous tilting angle constant-output control method is employed.
The third pump and pilot pump can be connected to the same shaft via a coupling.
2-2
1) PRINCIPLE OF OPERATION
(1) Function of pump
Piston α
Lower dead point
Hanger
Cylinder block (Swash plate)
Control plate
Discharge port
P1
P2
Upper dead point
Discharge
process
Suction process
Suction port
R5572SF03
The cylinder block is connected via spline and can rotate together with the drive shaft.
The piston assembled into the cylinder block performs reciprocal operation while following the
swash plate on the hanger.
The piston moves in a direction to increase the displacement during a stroke from the lower to the
upper dead points. The oil flows from the suction port via a port plate into the cylinder block
(suction process).
During a stroke from the upper to the lower dead points, the piston moves in a direction to
decrease the displacement. The oil is discharged to the discharge port (discharge process).
The displacement can be changed by changing the tilting of the hanger (swash plate).
The oil sucked through the port in the cylinder block is discharged from the discharge port in the
port plate.
The oil sucked through the port on the outside of the cylinder block is discharged from the
discharge port on the outside of the port plate.
2-3
2) CONTROL FUNCTIONS
Spring A Spring B
D D
Hanger Piston
P1
A+B
P
Piston P3
pressure
A
Total
Piston for
P3 shift
Shifting line
Piston
P2
Pi
Q max Section D-D
Flow rate
55W72MP04
The discharge pressures P1 and P2 are directed to the pistons of equal area act on the hanger.
The spring is provided to act against the discharge pressure. When the oil pressure acting on the
piston is less than the installation load of the spring A (outer spring), the hanger is fixed to the
maximum tilting position. When the oil, pressure acting on the piston exceeds the installation load
of the spring A the hanger is tilted and kept tilted at a position where the oil pressure is balanced
with the spring force. (Region A in the middle of the figure above)
When the oil pressure acting on the piston rises further to reduce the tilting angle, the spring B
which has been inactive up to now becomes active.
To overcome the spring force of two springs, the oil pressure must be higher and the shifting line
becomes more steep. (Regions A + B in the middle of the figure above)
When the P3 oil pressure acts on the shift piston, the control shifting line is shifted.
2-4
3) CONTROL / ADJUSTMENT PROCEDURE
(1) Loosen the hexagonal nut.
(2) Tighten or loosen the adjusting screw to set the power shifting line.
Spring seat Cover
Adjusting screw
Tighten
Total pressure
P (P1+P2)
Loosen
Nut
Q max
Flow rate
Tighten Loosen
R5572SF05
2-5
