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Product: TRACK-TYPE TRACTOR
Model: D8R TRACK-TYPE TRACTOR DWJ
Configuration: D8R TRACK-TYPE TRACTOR DWJ00001-UP (MACHINE) POWERED BY
C15 Engine

Systems Operation
D8R and D8T Track-Type Tractors Machine Systems
Media Number -M0079658-02 Publication Date -01/04/2019 Date Updated -15/04/2019

i07926359

Brake System
SMCS - 4061; 4250; 4251; 4267; 7000

The brake system includes a left brake, a right brake, and a brake control valve. The brakes
are used as both service brakes and parking brakes.

When the brakes are used as service brakes, the brake control valve modulates the pressure
of the oil that is sent to the left and right brakes in proportion to the position of the brake
pedal. This modulation allows the brakes to be controlled proportionally from zero
engagement to full engagement.

When the brakes are used as parking brakes, the brake control valve works as an ON/OFF
valve. When the parking brake switch is ON, the parking brake solenoid valve will drain all
oil to the left and right brakes to engage the brakes fully. When the parking brake switch is
OFF, high-pressure oil fully releases the brakes. This braking mode cannot be used when the
machine is moving.

Brake Components
Illustration 1 g06000910
Brake Assemblies
(1) Retainer
(2) Hub
(3) Discs and Plates
(4) Piston
(5) Housing
(6) Belleville Springs
(7) Chamber
(30) Hub
(31) Housing
(32) Retainer
(33) Discs and Plates
(34) Piston
(35) Belleville Spring
(36) Chamber

The brakes are included in two different components of the machine.

One component, which is on the left side of the machine, is called the steering differential
and brake. The other component, which is on the right side of the machine, is called the
planetary gears and brake.

The brakes are used to stop the machine. The brakes do not assist in the steering of the
machine.

The brakes are engaged by belleville spring (35) and (6). The brakes are released by
pressure oil from the brake control valve. The operator controls the brake control valve
with the service brake pedal.
Because hydraulic pressure is required to disengage the brakes, the brakes fully engage in
the case of lost hydraulic pressure.

During movement of the machine, pressure oil is sent through a passage in housing (31) and
housing (5). The oil flows to chamber (36) and (7). The pressure holds the service brake in
the released position. This pressure allows hub (30), hub (2), and the outer axle shafts to
turn.

When the brake pedal is depressed, chamber (36) and chamber (7) is open to the drain and
the pressure oil is released. The release of the pressure allows belleville springs (35) and (6)
to push piston (34) and (4) against the disc and plates (33) and (3).

The friction between the disc and plates stops the rotation of hub (30), hub (2), and the
outer axle shafts. The machine comes to a stop.

Operation of the Brake Control Valve

Illustration 2 g06008504
(11) Proportional brake solenoid
(12) To/From left brake
(13) Brake dump solenoid
(14) Pump supply oil
(15) To/From right brake
(16) Park brake switch
(17) Power train ECM
(18) To tank
(19) Service brake switch
(20) Service brake pedal sensor
(BB) Cutaway Section
(CC) Component Surface
(FF) Activated Components
(GG) Tank Pressure
(KK) High Pressure
(LL) First Pressure Reduction
(RR) Pilot Pressure
The brake control valve is installed on the top of the bevel gear case. The brake control
valve is controlled by power train ECM (17). Power train ECM (17) responds to the operator
movement of the service brake pedals and to the position of the parking brake switch.

The brake control valve contains brake dump solenoid (13) and brake proportional
solenoids (11). The park brake solenoid is either full ON or full OFF. The brake proportional
solenoids are modulated. Parking brake dump solenoid (13) is controlled by either parking
brake switch (16) or service brake switches (19) through power train ECM (17). Service
brake switches (19) are at the end of the travel of the service brake pedals.

One pump input is used for both the left brake and the right brake. The brake pressure in
each brake is controlled by reducing spools.

In addition, the brake control valve includes a shutoff valve. If the pressure from the pump
input drops suddenly, the shutoff valve gradually drains the brake pressure. This shutoff
valve prevents sudden brake engagement due to an electrical failure. At the same time, the
operator can rapidly apply the brakes because of service brake switches (19).

Proportional brake solenoids (11) are controlled by power train ECM (17). This solenoid sets
the pressure in the brake control valve. Power train ECM (17) determines the current to
proportional brake solenoids (11) by the position of service brake pedal sensors (20).

The accumulator pistons reduce fluctuations in pilot pressure. The accumulator pistons
accumulate oil at pump pressure. The pressure in the brake control valve moves the
accumulator piston. The movement increases the supply of oil to the reducing spool.
Fluctuations in pump pressure due to the movement of the reducing spool is reduced. Also,
a supply of oil is provided for the operation of shutoff valve.

The brake control valve is supplied by the transmission charging section of the power train
oil pump.

Service Brake and Parking Brake Operation

Service Brakes Released
Illustration 3 g06013543
Service brake OFF
(11) Proportional brake solenoid
(12) To/From left brake
(13) Brake dump solenoid
(14) Pump supply oil
(15) To/From right brake
(16) Park brake switch
(17) Power train ECM
(18) To tank
(19) Service brake switch
(20) Service brake pedal sensor
(BB) Cutaway Section
(CC) Component Surface
(FF) Activated Components
(GG) Tank Pressure
(KK) High Pressure
(LL) First Pressure Reduction
(RR) Pilot Pressure
When the operator releases the service brake pedal, service brake pedal sensor (20) sends a
signal to power train ECM (17). Power train ECM (17) increases the current to proportional
brake solenoids (11). The amount of current that is sent to the solenoid is inversely
proportional to the position of the service brake pedal.

The increased current increases pump pressure to the reducing spools. The reducing spools
move to allow pump oil to flow to brake lines (12) and (15). The pressure releases the
brakes.

Service Brakes Engaged

Illustration 4 g06013556
Service brake ON
(11) Proportional brake solenoid
(12) To/From left brake
(13) Brake dump solenoid
(14) Pump supply oil
(15) To/From right brake
(16) Park brake switch
(17) Power train ECM
(18) To tank
(19) Service brake switch
(20) Service brake pedal sensor
(BB) Cutaway Section
(CC) Component Surface
(FF) Activated Components
(GG) Tank Pressure
(KK) High Pressure
(LL) First Pressure Reduction
(RR) Pilot Pressure

Note: Illustration 4shows the service brakes when the brakes are partially engaged. The
following text explains the engagement of the service brakes from zero engagement to full
engagement.

When the operator pushes either service brake pedal toward the floor, service brake pedal
sensor (20) sends a signal to power train ECM (17). Power train ECM (17) decreases the
current to proportional brake solenoid (11). The amount of current that is sent to the
solenoid is inversely proportional to the position of the brake pedal.

The decreased current reduces pump oil pressure to the reducing spools. The reducing
spools move to relieve oil pressure in brake lines (12) and (15) by partially opening the
brake circuits to the drain.

When the operator pushes the service brake pedal all the way to the floor, service brake
switch (19) sends a signal to power train ECM (17). Power train ECM (17) then sends a
current to energize brake dump solenoid (13). Brake dump solenoid (13) allows any
remaining pump pressure to flow to the drain. The reducing spools move to drain brake
lines (12) and (15). The brakes fully engage.

Parking Brake Engaged

Illustration 5 g06025692
Parking brake ON
(11) Proportional brake solenoid
(12) To/From left brake
(13) Brake dump solenoid
(14) Pump supply oil
(15) To/From right brake
(16) Park brake switch
(17) Power train ECM
(18) To tank
(19) Service brake switch
(20) Service brake pedal sensor
(BB) Cutaway Section
(CC) Component Surface
(FF) Activated Components
(GG) Tank Pressure
(KK) High Pressure
(LL) First Pressure Reduction
(RR) Pilot Pressure
Note: The parking brake may be engaged when the machine is moving.

When parking brake switch (16) is ON, brake dump solenoid (13) is energized. The parking
brake valve allows all pilot oil to drain. The reducing spools shift to drain brake lines (12)
and (15). The brakes fully engage.

Neutral Default Strategy

Neutral default strategy is a feature that is programmed into the transmission control
module of the machine. Neutral default strategy will prevent movement of the machine or
damage to the transmission when the transmission is in neutral and the transmission ECM
expects that one or more components in the transmission control are failed. See
Specifications, Systems Operation, Testing and Adjusting, "Transmission" located in this
module for additional information about neutral default strategy.

Effective with 579-0224 Power Train Software Gp Three

Additional Power Train Features Were Added
Two-stage Engine Speed Limit

A two-stage engine speed limit that is commanded during forward to reverse and neutral to
reverse shifts. The two-stage speed limit will command 1500 rpm initially during forward to
reverse and neutral to reverse shift and then drop down to 1200 rpm, if necessary, to allow
the transmission clutches to lock up.

A Brake Based Torque Limit

A Brake Based Torque Limit (BBTL) that initiates an engine torque limit when the brakes
are applied in reverse. The BBTL activation will cause the engine stall speed in reverse to be
reduced to approximately 1150 rpm.

In Gear Slip Detect

In Gear Slip Detect (IGSD) that drastically limits engine torque when transmission slip is
detected in reverse. IGSD uses measured transmission speeds to compare the measured
gear ratio relative to the expected gear ratio. If the measured gear ratio and expected gear
ratio do not match a torque limit is sent to the engine to allow the transmission clutches to
lock up. When IGSD activates, the engine stall speed in reverse will measure approximately
1000 rpm.

A new operator notification to indicate Service Brake Abuse (SBA) is occurring has also been
introduced. SBA activates when the service brakes are applied while the decelerator pedal
is depressed less than 40 percent, the transmission selector is in reverse gear, and there has
been no machine movement or shift in progress for two seconds. This code is identified as
an EID 60020 "Service Brake Misuse".

Prior to this point, the transmission slip count matrix has been one means of identification
of clutch health. From this point forward, the following applies to this matrix:

Activation of IGSD will increment the slip count matrix. Activation of IGSD in reverse
will increment the slip count matrix and also be accompanied by an engine torque
limit (as described above). Activation of IGSD in forward will increment the slip count
matrix but will not be accompanied by a torque limit.
 Activation of IGSD in forward is not necessarily a bad sign in and of itself. Speed
sensor noise near zero machine speed has been known to contribute to false positive
IGSD events in forward gears, most frequently with heavy brake usage. If slip events
are observed in forward gears, and multiple SBA warnings have also been logged, the
likely cause of the IGSD events in forward are due to speed sensor noise and likely not
real slip events. If slip events are observed in forward with no or very few SBA
warnings logged, more investigation is warranted as these events are likely real slip
events. These will also be accompanied by the EID 60020 "Service Brake Misuse" codes.

Observing slip counts in reverse is a more concerning scenario. Slip counts in reverse
indicate that IGSD has been triggering, meaning that the two stage speed limit and the
BBTL have been unsuccessful in locking up and or keeping the transmission clutches
locked up.

If a large number of slip events in reverse are observed along with multiple 585–2 and
673–2 diagnostic codes logged at the same time, it will be critical to troubleshoot the
machine further to understand what is causing probable transmission clutch slip
events. These would also be accompanied by the EID 60020 "Service Brake Misuse"
codes.

Brake Touch-up Calibration

The brakes are spring-applied. The brakes are hydraulically released. Brake touch-up
pressure is the highest pressure that can still be overcome by the springs. At this pressure,
the springs are still able to apply the brakes to overcome the torque that is generated by the
drive train. Brake touch-up pressure varies slightly on each tractor.

The Brake Touch-up Calibration can be accessed through Cat Advisor or Cat Electronic
Technician. The Brake Touch-up Calibration can be performed to affect the feel of the
service brakes.

The Brake Touch-up Calibration is used to set a calibration value. This calibration value is
used to create a pedal modulation map that is used by the ECM. The pedal modulation map
is divided into the following three segments: engagement, modulation and fully applied.
During the engagement segment of pedal travel, the brakes gradually apply from zero drag
to a moderate amount of drag. This segment of pedal travel can be used for fine controls
such as inching. As the operator continues to depress the brake pedal, the modulation
segment is encountered. During the modulation segment, the brake drag gradually
increases from a moderate amount of drag. The last segment of brake pedal travel that is
encountered is the fully applied segment. During this segment, the brake drag continues to
increase until the end of the pedal travel. At the end of the pedal travel, the pedal contacts
the secondary dump solenoid which allows the brake pressure to drop to zero.

The calibration value establishes the beginning of the engagement segment. The calibration
value can be adjusted to meet individual operator preferences. Decreasing the calibration
value will engage the brakes earlier. Then more of the pedal travel is available for
modulation. If the calibration value is increased, the brake engagement is later but there is
less modulation after engagement.

See Specifications, Systems Operation, Testing and Adjusting, "Calibration" located in this
module for additional information about the Brake Touch-up Calibration.

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