Allison 3000/4000 Product Families - Retarder

Retarder - Fleets

The Allison output Retarder is available as an optional feature for most 3000 and 4000 Product Families Transmissions.

Retarders assist the vehicle braking system, extend service brake life and improve braking control.

The Retarder rotor is physically connected to the Transmission output shaft.

When the Retarder is applied, the Retarder housing is charged with Transmission fluid which slows the vaned rotor.

The initial charge of fluid is provided by an externally-mounted accumulator.
When the Retarder is turned off, the fluid in the Retarder housing is evacuated and the Retarder no longer slows the Transmission output.

Retarder application increases Transmission fluid temperature, and the vehicle cooling system must be designed to dissipate this heat.

Allison offers Transmission fluid coolers specifically designed to aid the cooling system when vehicles utilize retarder-equipped Transmissions.

Various Retarder capacities and control systems are available.

Retarder capacity is an indication of the Retarder’s slowing capability and is determined by electronic controls programming.

Additional Operator controls may or may not be included, depending on the configuration.

Specific input and output features are available (and sometimes required) for Retarder system integration.

Retarder-equipped Transmissions utilize an expanded capability TCM.

These TCMs include a Retarder mode shift calibration to command downshifts at higher speeds than normal closed throttle downshift points, which can improve cooling performance.
The Retarder mode shift calibration is automatically activated when the TCM commands retarder apply.

A). Retarder Control - Hydraulics

The PCS5 solenoid, SS2 accumulator solenoid, and retarder flow valve work together to control fluid flow in and out of the Retarder.

When the Retarder is not applied, lube pressure (10-40 kPa/ 1-6 psi) enters the Retarder cavity through the Retarder flow valve.

When applied, the PCS5 solenoid energizes and strokes the regulator valve and the relay valve against spring pressure.

Main pressure flows through the relay valve and strokes the Retarder flow valve against spring pressure.
The SS2 solenoid energizes and directs vehicle air to the accumulator, which strokes to charge fluid through the flow valve and into the Retarder cavity.

The PCS5 solenoid modulates, based on operator and controls input, to adjust the level of retardation by controlling the amount of main pressure entering the Retarder cavity.

Fluid exiting the Retarder is monitored by the Retarder temperature sensor which can signal the TCM to reduce Retarder application if temperature limits are exceeded.

B). Retarder Control - Electronics

The Retarder electronic apply system provides a way for the Operator to request a desired level of retardation.

Configurations vary, but typical operation includes an Operator request being translated into an electronic signal by a Retarder resistance module.
This electronic signal is evaluated by the TCM in conjunction with other input data which defines the current operating status of the Transmission and vehicle.
Based on these criteria, the TCM determines if and how the Retarder should be applied.

Allison Tech Data provides details on available system configurations and Operator controls.

The system can be configured to apply the Retarder using only TCM and resistance module logic, other than the Retarder Enable switch, the Operator does not control Retarder application.

A Retarder foot pedal may be utilized to allow the Operator infinitely-variable levels of retarder apply.

A Retarder hand lever can be integrated to enable up to 6 levels of Retarder application, from 17-100 percent apply.

The system can be integrated with pressure switches in the vehicle air brake system.

Various combinations of all these options may be utilized to fully adapt the Retarder system to the vehicle and its intended use.

Some electronic control inputs and outputs are utilized for Retarder applications.

Retarder Enable (Input Z) provides the required signal activated by the Operator Retarder Enable switch.

Anti-Lock Brake Response (Input Y) disengages the Transmission lockup clutch, modifies the Transmission downshift schedule, and can disengage the retarder when the ABS is active.

Service Brake Status (Input AA) allows the retarder to apply even if the Throttle Position Signal has failed, a loss of throttle signal causes the TCM to react as if the Engine is at full throttle, which prevents Retarder application.

Retarder On Indicator (Input Z and Output Q) is used to illuminate the vehicle brake lights when the Retarder is applied, this output can also illuminate a dash light indicating the Retarder is applied.

Sump/Retarder Temperature Indicator (Output B) can illuminate a dash light or warning alarm if an overtemperature condition exists, this warning also indicates the Transmission controls are restricting Transmission and Retarder operation.

The Transmission controls also offer two features for integrating Retarder operation with Cruise Control, one feature cancels the Retarder when cruise is active, and the other cancels cruise if a specific level of retardation is requested.

C). Diagnostics

A variety of Retarder-related DTCs are included in the Troubleshooting Manual.

Allison DOC® includes data related to Retarder configuration and performance.

A pressure tap is available for checking Retarder apply pressure.

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