973D Track-Type Loader Power Train Brake System Caterpillar


Brake System
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973D Track-Type Loader Power Train [KENR6524]
POWER TRAIN
DRIVE GP-FINAL
PL61 Pipelayer Systems Final Drive
973D Track-Type Loader Power Train Brake System
1.1. Parking Brake System
2.2. Parking Brake Switch in the OFF Position
3.2. Parking Brake Switch in the ON position
4.1. Service Brake System
5.2. The Service Brake Pedal Released.
6.2. The Service Brake Pedal Is Partially Depressed
7.2. The Service Brake Pedal Is Fully Depressed

Parking Brake System

The description of the parking brake system assumes that the service brake pedal is fully released.

Parking Brake Switch in the OFF Position

The parking brake solenoid is energized when the NEUTRAL interlock is not active and the transmission control lever is in any of the following positions:

  • FORWARD

  • REVERSE




Illustration 1g01949229

(1) Speed sensor

(2) Motor solenoids

(3) Oil from hydraulic return manifold to the parking brake actuators

(4) Brakes

(5) Piston

(6) Oil from hydraulic return manifold to the parking brake actuators

(7) Left side motor

(8) Right side motor

(9) Hydraulic return manifold

(10) Spring

(11) Parking brake solenoid

(12) Oil cooler

(13) Oil to hydraulic tank

(14) Oil passage from the right side drive loop

(15) Transmission NEUTRAL interlock solenoid

(16) Oil to the right and left hydrostatic drive pumps

(17 ) Machine ECM

(18) Parking Brake Switch

When parking brake switch (18) is in the OFF position, parking brake switch (18) completes the circuit between wire F780-PK and wire 200-BK. The completed circuit results in a signal of 0 volts to ECM (17) at pin 33 and a open circuit of 13V at pin 34 of the J1 connector.

When the transmission lever is shifted from NEUTRAL to either FORWARD or REVERSE, ECM (17) sends a signal of 24 volts from pin 6 of the J2 connector. The signal flows through wire A958-WH to solenoid valve (11) . The signal flows through the coil of solenoid valve (11) through wire F761-BR to ECM (17) through pin 4 of the J2 connector.

As the signal flows through the coil of solenoid valve (11) , solenoid valve (11) is shifted downward. Pilot oil from the charge pump is routed through the right hydrostatic pump (14) . The oil flows from solenoid valve (11) through line (3) to line (6) . The right and left piston motors are free to rotate.

Oil from solenoid (15) flows through line (13) back to the hydraulic tank.

Parking Brake Switch in the ON position




Illustration 2g01949230

(1) Speed sensor

(2) Motor solenoids

(3) Oil from hydraulic return manifold to the parking brake actuators

(4) Brakes

(5) Piston

(6) Oil from hydraulic return manifold to the parking brake actuators

(7) Left side motor

(8) Right side motor

(9) Hydraulic return manifold

(10) Spring

(11) Parking brake solenoid

(12) Oil cooler

(13) Oil to hydraulic tank

(14) Oil passage from the right side drive loop

(15) Transmission NEUTRAL interlock solenoid

(16) Oil to the right and left hydrostatic drive pumps

(17 ) Machine ECM

(18) Parking Brake Switch

When parking brake switch (18) is in the ON position, parking brake switch (18) completes the circuit between wire 419-YL and wire 202-BK. The completed circuit results in a signal of 0 volts to ECM (17) at pin 34 and an open circuit of 13V at pin 33 of the J1 connector.

ECM (17) sends a signal of 0 volts from pin 6 of the J2 connector. The signal flows through wire F761-BR to solenoid valve (11) . The signal flows through the coil of solenoid valve (11) through wire A958-WH to ECM (17) through pin 4 of the J2 connector.

Since the signal through the coil of solenoid valve (11) is 0 volts, solenoid valve (11) shifts upward. Oil from the charge pump is passed through the right hydrostatic pump (14) . The oil is blocked at solenoid valve (11) . Oil from pistons (5) flows through line (6) . The oil from line (6) flows through solenoid (11) . The oil flows through line (13) back to the hydraulic tank. As the oil flows from piston (5) , spring (10) forces piston (5) against brake (4) . Then, the brakes are engaged.

Service Brake System

The description of the service brake system assumes that the parking brake switch is in the OFF position and the transmission control lever is in any of the following positions:

  • FORWARD

  • NEUTRAL

  • REVERSE

For additional information regarding the power train system, refer to Systems Operation, "Power Train Hydraulic System".

The Service Brake Pedal Released.




Illustration 3g01985214

The Service brake pedal released.

(1) Oil cooler

(2) Brake release regulator (if equipped)

(3) Manual brake release valve (if equipped)

(4) Implement pumps

(5) Hand pump (if equipped)

(6) Check valve (if equipped)

(7) Tank

(8) Right charge pump

(9) Charge relief valve

(10) Breather assembly

(11) Drain

(12) Temperature sensor

(14) Right pump filter and bypass switch

(15) Hystat crossover relief valve

(16) Servo valve

(17) Right hystat piston pump

(18) Engine

(19) Right hystat motor controller

(20) Right hystat piston motor

(21) Brake

(22) Speed sensor

(23) Motor relief valve (if equipped)

(24) Electronic Pressure Override (EPOR)

(25) Left hystat piston motor

(26) Left hystat motor controller

(27) Left hystat piston pump

(28) Servo valve

(29) Accumulator

(30) Left pump filter and bypass switch

(31) Left charge pump

(32) Return manifold

(33) Transmission NEUTRAL interlock solenoid

(34) Parking brake solenoid

(35) Cooler bypass

(P1) Test port for the left hystat charge pressure

(P2) S·O·S sampling port

(P3) Test port for the right hystat charge pressure

(R3) Test port for the case pressure

(R4) Test port for the parking brake pressure

(R6) "mB" test port for left hystat pump

(R7) "mA" test port for right hystat pump

(R8) "mA" test port for left hystat pump

(R9) "mB" test port for right hystat pump

The following items are only present if the machine is equipped with a Steel Mill Arrangement:

  • Brake release regulator (2) (if equipped)

  • Manual brake release valve (3) (if equipped)

  • Hand pump (5) (if equipped)

  • Check valve (6) (if equipped)

  • Motor relief valve (23) (if equipped)

Since the ECM registers the signals as the release of the service brake pedal, the ECM does not modify any signals to the servo valves of the pumps or to the servo valves of the motors. Also, the ECM does not modify any signals to solenoid valve (34) .

The Service Brake Pedal Is Partially Depressed




Illustration 4g01949234

The service brake pedal is partially depressed.

(16) Servo valve

(17) Right hystat piston pump

(20) Right hystat piston motor

(25) Left hystat piston motor

(27) Left hystat piston pump

(28) Servo valve

(36) Servo valve

(37) Servo valve

As you start to depress the service brake pedal, the duty cycle of the pulse width modulated signal from pedal position sensor increases. The signal flows from the pedal position sensor to the ECM.

As the ECM interprets the increased duty cycle, the ECM modifies the signals to the servo valves of the pumps and to the servo valves of the motors. The ECM starts to decrease the duty cycle of the pulse width modulated signals to servo valve (36) and to servo valve (37) . As the duty cycles of the signals decrease, piston motor (20) and piston motor (25) start to upstroke and the machine begins to slow down.

When the piston motors reach the maximum displacements and you continue to depress the service brake pedal, the ECM starts to decrease the duty cycle of the pulse width modulated signals to servo valve (16) and servo valve (28) . As the duty cycles of the signals decrease, right piston pump (17) and left piston pump (27) start to destroke and the machine continues to slow down until the pumps reach zero angle.

The Service Brake Pedal Is Fully Depressed




Illustration 5g01949240

The service brake pedal is fully depressed.

(17) Right hystat piston pump

(21) Brake

(34) Parking brake solenoid

(35) Cooler bypass

(38) Piston

(39) Spring

(40) Line

(41) Line

When the service brake pedal is fully depressed, the pedal position sensor sends a pulse width modulated signal to the ECM . When the duty cycle is greater than the calibrated detent point, the ECM interprets the signal as full depression of the service brake pedal.

The ECM modifies the signals to the piston motors in order to return the piston motors to the maximum displacement. Also, the ECM modifies the signals to the piston pumps in order to return the piston pumps to zero angle.

The ECM sends a signal of 0 volts from pin 6 of the J2 connector. The signal flows through wire A958-WH to solenoid valve (34) .

Since the signal to solenoid valve (34) is 0 volts , solenoid valve (34) shifts upward. Charge oil from the right hystat pump (17) is blocked at solenoid valve (34) . Oil from pistons (38) flows through line (40) . The oil flows through line (40) through solenoid valve (34) . The oil flows from solenoid (34) through line (41) to the hydraulic tank. As the oil flows from pistons (38) , springs (39) force pistons (38) against brakes (21) . Then, the brakes are engaged.

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