789D and 789D XQ Off-Highway Truck Air System and Brakes: Retarder Control Valve - Automatic

Location of the automatic retarder control valve

The system for the Automatic Retarder Control (ARC) is designed to modulate the brakes of a truck during the descent of a grade. The ARC modulates the brake system in order to maintain a constant engine speed. The ARC reduces the effort that is required by the operator in order to maintain a constant engine speed during downhill operation. The Automatic Retarder Control valve is located on the inside of the left frame rail.

The Engine is Running and the Switch for the Automatic Retarder Control (ARC) is in the OFF Position

(1) Spool (2) Accumulator (3) Supply solenoid valve (4) Check valve(5) Parking brake release pump

Supply from parking brake release pump (5) flows across check valve (4). Flow then enters the Automatic Retarder Control Valve. Hydraulic flow is stopped because spool (1) is in the blocked position. Hydraulic flow is then directed to accumulator (2) in order to charge accumulator (2) to the parking brake release system pressure. Hydraulic flow is also routed through supply solenoid valve (3) in order to apply pilot pressure. This will keep spool (1) in the blocked position.

The Engine is Running and the Switch for the Automatic Retarder Control (ARC) is in the ON Position

(1) Spool (3) Supply solenoid valve (6) Control solenoid valve (7) Control solenoid(8) Supply solenoid

The Brake ECM supplies current to supply solenoid (8) which shifts Supply Solenoid Valve (3) in order to open the left side of the Spool to tank. This will direct pump supply oil to the right side of spool (1). Spool (1) will shift to the left in order to allow pump supply oil to flow to control solenoid valve (6). The Brake ECM will send varying levels of current to control solenoid (7). This will modulate the spool within the proportional valve. This is dependent on the brake requirements for the Automatic Retarder Control Valve. When control solenoid (7) is energized, the pin moves to the right and pushes against the ball. The ball blocks the pump supply oil from flowing to the drain. Pressure increases in the chamber to the left of spool (1) in order to move spool (1) to the right. When spool (1) moves to the right, pump supply oil flows to the service brakes. In order to maintain the correct brake pressure, the Brake ECM will open the oil drain port. Also, the Brake ECM will close the oil drain port, as needed.

The Engine is Off and the Switch for the Automatic Retarder Control (ARC) is in the OFF Position

(1) Spool (2) Accumulator (3) Supply solenoid valve (6) Control solenoid valve (7) Control solenoid (8) Supply solenoid (9) Purge solenoid(10) Purge solenoid valve

All the current that is supplied by the Brake ECM is removed from supply solenoid (8) and control solenoid (7). This causes supply solenoid valve (3) to shift and all pilot pressure that is acting on spool (1) is routed back to the tank. Current is supplied from the Steering Bleed Control to purge solenoid (9) which shifts purge solenoid valve (10). This allows the pressure within accumulator (2) to drain from accumulator (2) and back to the tank.

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789D and 789D XQ Off-Highway Truck Air System and Brakes: Retarder Control Valve - Automatic 2013-01-25T20:31:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown