The description of the parking brake system assumes that the decel/brake pedal is fully released.
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| Illustration 1 | g03713478 |
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(1) Parking brake solenoid valve
(2) Parking brake switch (3) Spring (4) Piston (5) Brake pack (6) Hystat override solenoid valve (7) Brake pack (8) Piston (9) Spring (10) Electronic Control Module (ECM) (11) Display (12) Charge pump (13) Servo valve (14) Servo valve | |
Note: Parking brake switch (2) is a momentary switch.
When the parking brake is ON, parking brake switch (2) completes the circuit between ground and the normally open contact. The completed circuit results in a signal of 0 V to ECM (10).
ECM (10) also sends a signal of 0 V to hystat override solenoid valve (6). The return signal flows through the coil of hystat override solenoid valve (6) to ECM (10).
Since the signal through the coil of hystat override solenoid valve (6) is 0 V, hystat override solenoid valve (6) shifts upward. Pilot oil from charge pump (12) is blocked by hystat override solenoid valve (6). Pilot oil from servo valve (13) and servo valve (14) flows back to the hydraulic tank.
ECM (10) sends out a data signal to display (11). The data signal indicates that the parking brake is in the ON position and the display turns on the parking brake indicator.
ECM (10) sends a signal of 0 V to parking brake solenoid valve (1). The return signal flows through the coil of parking brake solenoid valve (1).
Since the signal through the coil of parking brake solenoid valve (1) is 0 V, parking brake solenoid valve (1) shifts upward. Pilot oil from charge pump (12) is blocked at parking brake solenoid valve (1). Oil from piston (4) and piston (8) flows to parking brake solenoid valve (1). The oil flows through parking brake solenoid valve (1) back to the hydraulic tank. As the oil flows from piston (4), spring (3) forces piston (4) against brake pack (5). As the oil flows from piston (8), spring (9) forces piston (8) against brake pack (7). Then, the brakes are engaged.
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| Illustration 2 | g03713150 |
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(1) Parking brake solenoid valve
(2) Parking brake switch (3) Spring (4) Piston (5) Brake pack (6) Hystat override solenoid valve (7) Brake pack (8) Piston (9) Spring (10) Electronic Control Module (ECM) (11) Display (12) Charge pump (13) Servo valve (14) Servo valve | |
Note: Parking brake switch (2) is a momentary switch.
When the parking brake is ON, parking brake switch (2) completes the circuit between ground and the normally connected contact. The completed circuit results in a signal of 0 V to ECM (10).
While in neutral and pressing the parking brake switch (2) in order to disengage the parking brake, the ECM (10) sends a signal of 12 V to hystat override solenoid valve (6). The return signal flows through the coil of hystat override solenoid valve (6) to ECM (10).
As the signal flows through the coil of hystat override solenoid valve (6), hystat override solenoid valve (6) shifts downward. Pilot oil from charge pump (12) flows to hystat override solenoid valve (6). The oil flows from hystat override solenoid valve (6) to servo valve (13) of the rear piston pump and servo valve (14) of the front piston pump.
ECM (10) sends out a data signal to display (11). The data signal indicates that the parking brake is in the OFF position and the display turns off the parking brake indicator.
When the machine is placed in a FORWARD or REVERSE position and the parking brake is OFF, ECM (10) sends a signal of 12 V to parking brake solenoid valve (1). The return signal flows through the coil of parking brake solenoid valve (1) to ECM (1).
As the signal flows through the coil of parking brake solenoid valve (1), parking brake solenoid valve (1) is shifted downward. Pilot oil from charge pump (12) flows to parking brake solenoid valve (1). The oil flows from parking brake solenoid valve (1) to piston (8). The oil overcomes the force of spring (9) and the oil forces piston (8) to move downward from brake pack (7). Then, the right piston motor is free to rotate.
The oil also flows to piston (4). The oil overcomes the force of spring (3) and the oil forces piston (4) to move upward from brake pack (5). Then, the left piston motor is free to rotate.
The description of the service brake system assumes that the parking brake switch is in the OFF position and the direction/speed control lever is in the FORWARD position. For additional information regarding the power train system, refer to Systems Operation, "Power Train Hydraulic System".
The Service Brake Pedal Released.
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| Illustration 3 | g03713551 |
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(1) Parking brake solenoid valve
(6) Hystat override solenoid valve (10) Electronic control module (ECM) (15) Decel/brake pedal sensor (16) Service brake switch | |
When the service brake pedal is fully released, pedal position sensor (15) sends a pulse width modulated signal to ECM (10).
Since ECM (10) registers the signals as the release of the service brake pedal, ECM (10) does not modify any signals to the servo valve (13) and servo valve (14) of the pumps or to the servo valves of the motors. Also, ECM (10) does not modify any signals to parking brake solenoid valve (1) or to hystat override solenoid valve (6). Refer to "Parking Brake (OFF)" for additional information regarding the operation of parking brake solenoid valve (1) and of hystat override solenoid valve (6).
The Service Brake Pedal Is Partially Depressed
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| Illustration 4 | g03713724 |
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(10) Electronic control module (ECM)
(13) Servo valve (14) Servo valve (15) Decel/brake pedal sensor (17) Servo valve (18) Servo valve (19) Left track travel motor (20) Right track travel motor (21) Right track piston pump (22) Left track piston pump | |
As you start to depress the service brake pedal, the duty cycle of the pulse width modulated signal from pedal position sensor (15) decreases. The signal flows from pedal position sensor (15) to ECM (10).
As ECM (10) interprets the decreased duty cycle, ECM (10) modifies the signals to the servo valve (13) and servo valve (14) of the pumps and to the servo valve (17) and servo valve (18) of the motors. ECM (10) starts to decrease the duty cycle of the pulse width modulated signals to servo valve (18) and to servo valve (17). As the duty cycles of the signals decrease, left track travel motor (19) and right track travel motor (20) 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, ECM (10) starts to decrease the duty cycle of the pulse width modulated signals to servo valve (13) and to servo valve (14). As the duty cycles of the signals decrease, right track piston pump (21) and left track piston pump (22) start to destroke and the machine continues to slow down until the pumps reach zero angle.
The Service Brake Pedal Is Fully Depressed
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| Illustration 5 | g03713746 |
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(3) Spring
(4) Piston (5) Brake pack (7) Brake pack (8) Piston (9) Spring (10) Electronic control module (ECM) (12) Charge pump (15) Decel/brake pedal sensor (16) Service brake switch | |
When the service brake pedal is fully depressed, pedal position sensor (15) sends a pulse width modulated signal to ECM (10). When ECM (10) receives a signal with a duty cycle between 35% and 31%, ECM (10) interprets the signal as full depression of the decel/brake pedal.
Also, when the service brake pedal is fully depressed, service brake switch (16) closes the circuit between ground and the normally closed connection.
ECM (10) modifies the signals to the piston motors and deenergizes the override valve in order to return the piston motors to the maximum displacement. Also, ECM (10) modifies the signals to the piston pumps in order to return the piston pumps to zero angle.
Also, when the decel/brake pedal is fully depressed, service brake switch (16) closes the circuit between ground and the normally open contact. ECM (10) also interprets this signal as full depression of the decel/brake pedal.
ECM (10) sends a signal of 0 V to parking brake solenoid valve (1).
Since the signal to parking brake solenoid valve (1) is 0 V , parking brake solenoid valve (1) shifts upward. Pilot oil from the charge pump (12) is blocked at parking brake solenoid valve (1). Oil from piston (4) flows through the drain line back to the hydraulic tank. As the oil flows from piston (4), spring (3) forces piston (4) against brake (5). As the oil flows from piston (8), spring (9) forces piston (8) against brake (7). Then, the brakes are engaged.
ECM (10) sends out a data signal to display. The data signal indicates that the parking brake switch is in the ON position and the display turns on the parking brake indicator.