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| Illustration 1 | g03832782 |
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(1) Proportional brake solenoids
(2) Brake dump solenoid (B1) Pressure port for the right brake (B2) Pressure port for the left brake | |
The brake control valve is mounted on the top of the main case. The control valve contains two proportional brake solenoids (1). One proportional solenoid controls the pressure that is allowed to reach the right brake. The second proportional solenoid controls the oil that is allowed to reach the left brake. The control valve also contains an ON/OFF solenoid (2). The brake control valve is operated electrically by the power train electronic control module (ECM). The ECM responds to the operator movement of the brake pedals and to the position of the parking brake switch.
When the operator pushes either brake pedal toward the floor, the position sensor sends a signal to the power train ECM. The power train ECM decreases the current to the appropriate proportional brake solenoid (1). The amount of current that is sent to the solenoid is directly proportional to the position of the brake pedal.
When the operator pushes either service brake pedal past the detent point, the ON/OFF solenoid (2) is energized. The ON/OFF solenoid (2) allows any remaining brake pressure to flow to the drain. The brakes fully engage.
The brakes are engaged with spring force. Hydraulic pressure is required to disengage the brakes. If hydraulic pressure is lost, the brakes will fully engage due to the action of the spring force.
Oil flow to the brake control valve comes from the power train oil pump. Part of the oil from the power train oil pump flows to the brake control valve. Part of the oil flows to the modulating valves for the transmission. This flow is described in the section on the power train hydraulic system.
A calibration procedure is used in order to adjust the settings for the brake pressure.