OM3232 8/11 Operator Cab And Controls - Section 32 Page 32-3 DYNAMIC RETARDING Dynamic retarding is a braking torque (not a brake) produced through electrical generation by the wheelmotors when the truck motion (momentum) is the propelling force. Dynamic Retarder/Service Brake Pedal Retarder/service brake pedal (2, Figure 32-1) is a single foot-operated pedal that controls both retarding and service brake functions. The first portion of pedal travel commands retarding effort through a rotary potentiometer. The second portion of pedal travel modulates service brake pressure directly through a hydraulic valve.
Thus, the operator must first apply and maintain full dynamic retarding in order to apply the service brakes. Releasing the pedal returns the brake and retarder to the OFF position. For normal truck operation, dynamic retarding should be used to slow and control truck speed . Dynamic retarding is available in FORWARD/ REVERSE at all truck speeds above 0.5 kph (0.3 mph). However, as the truck speed slows below 5 kph (3 mph), the available retarding force may not be effective. Use the service brakes to bring the truck to a complete stop. When the pedal is partially depressed, the dynamic retarding is actuated.
As the pedal is further depressed to where dynamic retarding is fully applied, the service brakes (while maintaining full retarding) are actuated through a hydraulic valve which modulates pressure to the service brakes. Completely depressing the pedal causes full application of both dynamic retarding and the service brakes. Indicator light (8, Figure 32-9) on the instrument panel will illuminate, and an increase in pedal resistance will be felt when the service brakes are applied. Dynamic retarding will not hold a stationary truck on an incline. Move the directional control lever to PARK or use the wheel brake lock for this purpose.
When in NEUTRAL, dynamic retarding is available only when truck speed is above 5 kph (3 mph). When dynamic retarding is in operation, engine rpm will automatically go to an advance retard speed setting. This rpm will vary depending on temperature of several electrical system components. Dynamic retarding will be applied automatically if the speed of the truck obtains the maximum speed setting programmed in the control system software. For normal truck operation, dynamic retarding should be used to slow and control the speed of the truck.
Service brakes should be applied only when dynamic retarding requires additional braking force to slow the truck speed quickly or when bringing the truck to a complete stop. The grade/speed retard chart should always be used to determine safe downhill speeds. Refer to Grade/ Speed Retard Chart on the following page. Throttle/Accelerator Pedal Throttle/accelerator pedal (3, Figure 32-1) is a foot- operated pedal which allows the operator to control engine rpm. It is used by the operator to request torque from the motors when in FORWARD or REVERSE. In this mode, the propulsion system controller commands the correct engine speed for the power required.
In NEUTRAL, this pedal controls engine speed directly.