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| Illustration 1 | g00999554 |
Brake retarder circuit | |
The components of the retarder circuit are the Power Train/Chassis Electronic Control Module (Power Train/Chassis ECM), the Engine Electronic Control Module (Engine ECM), the retarder lever switch, the automatic retarder switch, the front service brake and retarder oil pressure switch, the rear service brake and retarder oil pressure switch, the retarder supply solenoid valve for the front brakes, the retarder supply solenoid valve for the rear brakes, the retarder control solenoid valve for the front brakes, the retarder control solenoid valve for the rear brakes and the engine speed sensor.
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| Illustration 2 | g00995567 |
Front view of cab (front cover plate removed) (1) Power Train/Chassis ECM | |
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| Illustration 3 | g00997864 |
Cab (2) Retarder lever switch | |
With the key start switch in the ON position, 24 volt power is supplied from the batteries via circuit breaker #12 to the retarder lever switch and the Power Train/Chassis ECM.
Power Train/Chassis ECM (1) has inputs that determine the output to the retarder supply solenoid valves and the retarder control solenoid valves. Retarder lever switch (2) is an input to the Power Train/Chassis ECM. The retarder lever switch sends a Pulse Width Modulated (PWM) signal to the Power Train/Chassis ECM. The Power Train/Chassis ECM controls the retarder solenoid valves proportionally to the retarder lever position.
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| Illustration 4 | g00997866 |
Rear view of engine (3) Engine speed sensor | |
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| Illustration 5 | g00999555 |
Typical example of a retarder control valve (4) Rear service brake and retarder oil pressure switch (5) Front service brake and retarder oil pressure switch (6) Retarder supply solenoid valve for the rear brakes (7) Retarder supply solenoid valve for the front brakes (8) Retarder control solenoid valve for the front brakes (9) Retarder control solenoid valve for the rear brakes | |
If the service brakes are applied the rear service brake and retarder oil pressure switch (4) and front service brake and retarder oil pressure switch (5) close contacts when the retarder is active. This signal is sent to the Power Train/Chassis ECM. This signal causes retarder operation to be cancelled when the service brake is applied.
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| Illustration 6 | g00997867 |
Dash panel (10) Automatic retarder switch | |
Engine speed sensor (3) is an input to the Power Train/Chassis ECM. The engine speed sensor sends an inductive pulse signal for engine rpm to the Power Train/Chassis ECM. The Power Train/Chassis ECM uses the engine speed signal to calculate at what point the retarder must operate.
When automatic retarder switch (10) is in the ON position the automatic retarding system will operate. When the engine speed has reached 2160 rpm, the Power Train/Chassis ECM will pulse the retarder solenoid valves.
This retarding pulse is used to bring the oil pressure within the braking system up to operating pressure. If the engine speed increases from 2160 rpm to 2450 rpm, the automatic retarding system applies the service brakes. The engine rpm will be limited to 2160 rpm and below.
When the throttle position sensor is moved past 60 percent of the sensors travel range and the engine speed exceeds 2450 rpm, the engine over speed function operates. The Power Train/Chassis ECM energizes the retarder solenoid valves. The service brakes will apply and the fuel rack setting will decrease, until the engine speed has decreased below 2450 rpm.
The Power Train/Chassis ECM can be programmed to limit the ground speed from 0 km/h to 60 km/h. The Power Train/Chassis ECM can be programmed to limit the transmission gear shifting from FIRST gear to FOURTH gear, depending on the operators requirements.
The retarder lever position switch sends a (PWM) signal to the Power Train/Chassis ECM. When the retarder lever is in the OFF position, an 83 percent duty cycle signal is sent from the retarder lever position switch to the Power Train/Chassis ECM. When the retarder lever is in the fully ON position, a 13 percent duty cycle signal is sent from the retarder lever position sensor to the Power Train/Chassis ECM. The Power Train/Chassis ECM then operates the retarder solenoid proportionally.
Reference: For more information on the retarder system, refer to Systems Operation, Testing and Adjusting, "Power Train Electronic Control System" for the machine that is being serviced.