Brake ECM System
The brake electronic control module (ECM) controls the following braking functions:
- Service braking
- Secondary braking
- Park braking
- Manual retarding
- Automatic retarder control (ARC)
- Traction control system (TCS)
The brake ECM also performs monitoring of the system and diagnostic warnings through the graphical display module.
Note: The park brakes are spring-applied. The park brakes are released by brake oil pressure that is stored in the secondary brake accumulator. The brake oil pressure in the secondary brake accumulator is developed when the engine is running.
The park brakes will engage when any of the following conditions are met:
- Keyswitch is in the OFF position.
- Direction/speed control is in the PARK position.
- The brake oil pressure from the secondary brake accumulator is exhausted.
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| Illustration 1 | g02160432 |
Diagram of the components on the brake ECM | |
Service Brake Control
Service braking is performed by pedals which are located on the floor of the cab. The ECM determines whether the service brakes should engage for the function of ARC or TCS.
Note: The service brakes are applied by brake oil pressure that is stored in the service brake accumulator. The brake oil pressure in the service brake accumulator is developed when the engine is running. The service brakes are released by spring pressure.
Note: Allow the engine to run for 45 seconds before depressing the service brake pedal or moving the direction/speed control out of PARK. This action will allow the brake accumulators to charge and provide full braking capacity.
During normal operation, depress service brake control pedal to engage the service brakes. Use the service brakes for reducing ground speed or for stopping the machine.
The pedal is fully variable. The amount of force that is applied to the brakes is proportional to the amount of force that is applied to the pedal.
Note: Repeated engagement of the service brakes on downgrades may cause excessive wear and overheating of the service brakes. Refer to Operation and Maintenance Manual, "Retarding".
Secondary Brake Control
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To avoid the possibility of a unexpected machine movement when parking on a slope, always block the wheels securely before leaving the machine unattended. If the secondary brake system is required in order to stop the machine, do not operate the machine until a complete check has been made of the entire braking system and until all necessary repairs have been made. |
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The secondary brake pedal is located on the floor of the cab. To modulate the secondary brakes, the operator presses the secondary brake pedal. Pressing the secondary brake pedal causes the brake ECM to modulate pressure to the spring-applied brake pack through use of the secondary brake valve.
Note: The secondary brake system utilizes the park brake system to apply braking force to the rear wheels. This system also utilizes the front service brake system to apply braking force to the front wheels.
In case of failure of the service brakes, depress secondary brake control pedal to engage the secondary brake system. The amount of force that is applied to the brakes is proportional to the amount of force that is applied to the pedal.
To obtain the maximum available braking force to the machine in an emergency stop condition, apply both the service and secondary brake control pedals simultaneously.
Park Brake Control
Note: The park brake is used for parking the truck and is applied by placing the direction/speed lever in the PARK position. Do not use the retarder levers for parking the truck.
Park brake control is performed by the brake ECM. The park brake is a spring-applied brake and does not release if hydraulic brake pressure is lost. The park brakes are released by brake oil pressure that is stored in the secondary brake accumulator. The brake oil pressure in the secondary brake accumulator is developed when the engine is running.
The park brakes will engage when any of the following conditions are met:
- Keyswitch is in the OFF position.
- Direction/speed control is in the PARK position.
- The brake oil pressure from the secondary brake accumulator is exhausted.
Following is the operation of the park brake:
- The operator places the shift lever in PARK position.
- The brake ECM receives the shift lever position from the transmission ECM.
- The brake ECM completely turns off the secondary brake valve.
- This action engages the spring-applied park brakes.
| Park Brake Indicator - When the park brakes are applied, the park brake indicator will illuminate. |
Front Brake Disable Switch
The front brakes and the rear brakes are applied when the service brake pedal is depressed. Front brake disable switch allows the front brakes to be deactivated. If the front brakes are used continuously for an extended time, the front brakes can overheat. Under normal circumstances, the front brake disable switch should be in the OFF position.
| ON Position - When the top half of the front brake disable switch is depressed, only the rear brakes are applied when the service brake pedal is depressed. |
Note: When the top half of the front brake disable switch is depressed, the bottom symbol illuminates to indicate the deactivation of the front brakes.
| OFF Position - When the bottom half of the front brake disable switch is depressed, the following occurs: |
- The front and rear brakes will be applied when the service brake pedal is depressed.
Note: When the bottom half of the front brake disable switch is depressed, the top symbol illuminates to indicate the activation of the front brakes.
Manual Retarding Control
Manual retarding is performed with a lever located on the steering column. Manual retarding is performed by energizing the enable solenoid valve and then modulating the left and right proportional solenoid valves.
Automatic Retarder Control
Automatic retarding is performed by energizing the enable solenoid valve and then modulating the left and right proportional solenoid valves. ARC can work with the compression brake, which is controlled by the engine ECM.
Traction Control System
Traction control is performed by energizing the enable solenoid valve and then modulating the proportional solenoid valve for the side that is slipping. TCS is activated based on the steering angle of the front wheels, determined by the left steering cylinder position sensor.
Diagnostic Capabilities
The ECM also provides enhanced diagnostics. These diagnostics are available by using onboard memory. Onboard memory stores the diagnostic codes for retrieval at the time of service. Service personnel can use the Caterpillar Electronic Technician (Cat ET) service tool for troubleshooting.