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 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 in order to fully engage the brakes. When the parking brake switch is OFF, high-pressure oil fully releases the brakes. The parking brake switch can be used when the machine is moving and the brakes will be fully applied.
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| Illustration 1 | g03717460 |
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(1) Housing
(2) Stationary ring gear (3) Friction discs and brake plates (4) Housing (5) Brake piston (6) Belleville spring (7) Carrier (8) Chamber (9) Chamber (10) Belleville spring (11) Brake piston (12) Friction discs and brake plates (13) Retainer (14) Hub (15) Steering differential and brake (16) Planetary gears and brake | |
The brakes are included in two different components of the machine.
One component, which is located on the left side of the machine, is the steering differential and brake (15). The other component, which is located on the right side of the machine, is the planetary gears and brake (16).
The brakes are used to stop the machine. The brakes do not assist in the steering of the machine.
The brakes have main components: hub (14), carrier (7), brake pistons (5) and (11), retainer (13), stationary ring gear (2), Belleville springs (6) and (10), housings (1) and (4) and friction discs and brake plates (3) and (12).
The brakes are engaged by Belleville springs (6) and (10). The brakes are released by pressure oil from the brake control valve. The operator controls the brake control valve with a service brake foot pedal.
During movement of the machine, pressure oil is sent through passages in brake housings (1) and (4) to chambers (8) and (9). Since the brakes are held in the released position, the outer axle shafts rotate freely.
When the service brake pedal is pushed, pressure oil to chambers (8) and (9) is stopped. The chambers are opened to the drain.
Belleville springs (6) and (10) then push brake pistons (5) and (11) against friction discs and brake plates (3) and (12). Friction discs and brake plates (3) and (12) stop the rotation of the following power train components: hub (14), carrier (7) and the outer axle shafts.
The machine stops. The engine is in torque converter stall condition.
Operation of the Brake Control Valve
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| Illustration 2 | g03377059 |
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Parking brake OFF (1) From pump (2) To / From left-hand brake (3) Pressure tap (B) (4) To / From right-hand brake (5) To tank (6) Brake dump solenoid (7) Proportional brake solenoid (8) Service brake switch (9) Service brake pedal sensor (10) Park brake switch (11) Power train ECM | |
The brake control valve is installed on the top of the bevel gear case. The brake control valve is controlled by power train ECM (11). Power train ECM (11) responds to the operator movement of the service brake pedal and to the position of the parking brake switch.
The brake control valve contains parking brake solenoid (6) and brake proportional solenoid (7). The park brake solenoid is either full ON or full OFF. The brake proportional solenoid is a modulating valve. Parking brake solenoid (6) is controlled by either parking brake switch (10) or service brake switch (8) through power train ECM (11). Service brake switch (8) is at the end of the travel of the service brake pedal.
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 switch (8).
Proportional brake solenoid (7) is controlled by power train ECM (11). This solenoid sets the pressure in the brake control valve. Power train ECM (11) determines the current to proportional brake solenoid (7) by the position of service brake pedal sensor (9).
The accumulator piston reduces fluctuations in pilot pressure. The accumulator piston accumulates oil at pump pressure. The pressure in 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
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| Illustration 3 | g03379639 |
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Service Brakes Released (1) From pump (2) To / From left-hand brake (3) Pressure tap (B) (4) To / From right-hand brake (5) To tank (6) Brake dump solenoid (7) Proportional brake solenoid (8) Service brake switch (9) Service brake pedal sensor (10) Park brake switch (11) Power train ECM | |
When the operator releases the service brake pedal, service brake pedal sensor (9) sends a signal to power train ECM (11). Power train ECM (11) increases the current to proportional brake solenoid (7). 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 in order to allow pump oil to flow to brake lines (2) and (4). The pressure releases the brakes.
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| Illustration 4 | g03666733 |
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Service Brakes Engaged (1) From pump (2) To / From left-hand brake (3) Pressure tap (B) (4) To / From right-hand brake (5) To tank (6) Brake dump solenoid (7) Proportional brake solenoid (8) Service brake switch (9) Service brake pedal sensor (10) Park brake switch (11) Power train ECM | |
Note: Illustration 4 shows 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 the service brake pedal toward the floor, service brake pedal sensor (9) sends a signal to power train ECM (11). Power train ECM (11) decreases the current to proportional brake solenoid (7). 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 in order to relieve oil pressure in brake lines (2) and (4) 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 (8) sends a signal to power train ECM (11). Power train ECM (11) then sends a current to energize brake dump solenoid (7). Brake dump solenoid (7) allows any remaining pump pressure to flow to the drain. The reducing spools move in order to drain brake lines (2) and (4). The brakes fully engage.
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| Illustration 5 | g03666734 |
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Parking brake ON (1) From pump (2) To / From left-hand brake (3) Pressure tap (B) (4) To / From right-hand brake (5) To tank (6) Brake dump solenoid (7) Proportional brake solenoid (8) Service brake switch (9) Service brake pedal sensor (10) Park brake switch (11) Power train ECM | |
Note: The parking brake may be engaged when the machine is moving.
When parking brake switch (10) is ON, brake dump solenoid (6) is energized. The parking brake valve allows all pilot oil to drain. The reducing spools shift in order to drain brake lines (2) and (4). The brakes fully engage.
Neutral default strategy is a feature that is programmed into the machine transmission control module. 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" that is in this module for additional information about neutral default strategy.