| |
| Illustration 1 | g01285424 |
|
Retarder Hydraulic Control Valve (1) Retarder (2) Oil from torque converter relief valve (3) Oil to retarder oil cooler (4) Oil to transmission lubrication (5) Retarder spool port (6) Oil supply port (7) Spring (8) Solenoid (9) Solenoid valve (10) Control spool (11) Chamber (12) Drain port (13) Spool (14) Pressure test points | |
The retarder hydraulic control valve receives oil from the torque converter (2). In normal operation, the oil from torque converter (2) is fed through retarder oil cooler (3) and back to the retarder hydraulic control valve. The oil is then sent as lubricant for the transmission.
When the retarder is selected, oil pressure from the actuation for the retarder control valve moves spool (13) downward. The oil from torque converter (2) is diverted to retarder (1). From the retarder, the oil is then sent to retarder oil cooler (3) via the retarder hydraulic control valve. Oil that returns from retarder oil cooler (3) is split and a portion of the oil is sent to the transmission for lube. The rest of the oil is sent to the retarder inlet.
The different degrees of retardation are determined by the position of spool (13). The position of the spool is determined by the pressure of the oil that is supplied by the actuation of the retarder control valve.
The actuation of the retarder control valve is controlled by solenoid (8).
Oil is supplied by the transmission pump to oil supply port (6). A pilot pressure is allowed through control spool (10) to chamber (11). The oil in chamber (11) is allowed to flow to drain port (12) by solenoid valve (9).
When the retarder is selected, solenoid valve (9) blocks the oil in chamber (11) and the pressure of the oil rises. As the pressure of the oil in chamber (11) rises, control spool (10) moves to the left against spring (7). Oil in oil supply port (6) is able to flow to retarder spool port (5). Pressure in the retarder spool port moves the spool in the retarder hydraulic control valve downward. The oil from torque converter relief valve (2) is allowed to flow to the retarder. When the pressure on the spool in the retarder hydraulic control valve reaches the same pressure as the oil in chamber (11) control spool (10) is moved back to the right by spring (7). This blocks the supply of oil to the spool in the retarder hydraulic control valve. As the pressure on the spool drops, control spool (10) moves back to the left. This allows more oil from the oil supply port to flow to the retarder hydraulic control valve. Thus, the pressure on the spool is modulated at the same pressure as the oil in chamber (11).
The solenoid on the actuation of the retarder control valve is activated by a PWM signal from the ECM. The electrical current that is supplied to solenoid (8) is balanced against the pressure of the oil in chamber (11). The current is adjustable in order to control the pressure of the oil in chamber (11). The pressure of the oil in chamber (11) regulates the pressure that acts on spool (13) in the retarder hydraulic control valve. This determines the position of the spool. This allows varying degrees of retardation to be achieved.