Diesel Data: Automotive Repair
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Failure Modes Trouble Shooting ACE


Failure Modes
Failures where the vehicle can still be driven safely are indicated by the ACE warning lamp illuminating continuously with an amber colour. The amber warning lamp will remain illuminated until the ignition is turned off. For all faults the warning lamp will only illuminate again if the fault is still present. Failures which require the driver to stop the vehicle immediately are indicated by the ACE warning lamp flashing with a red colour and an audible warning. All faults are recorded by the ACE ECU and can be retrieved with diagnostic equipment.
The following tables show the type of system failures and their effects on the system operation. Torsion bar 'floppy' means that fluid is allowed to circulate freely through the system. With no pressure in the actuators the torsion bar will have no effect on vehicle roll. 'Locked bars' means that all pump flow is directed through the valve block and returns to the reservoir. Both DCV's close and fluid is trapped in the actuators but can flow from one actuator to the other via the valve block. In this condition the torsion bar will perform similar to a conventional anti-roll bar, resisting roll but still allowing the axles to articulate.





Acceleration Sensors





Pressure Transducer





Road Speed Signal





Engine Speed Signal





Reverse Gear Signal





Ignition ON Signal





Pressure Control Valve Failure





Directional Control Valves

Operation





Hydraulic Circuit Diagram

Vehicle Not Moving
When the engine is running and the vehicle is not moving, both DCV's are closed, locking fluid in each side of the actuator pistons. The hydraulic pump draws fluid from the reservoir and passes it at very low pressure to the valve block. Because both DCV's are closed, after the fluid passes through the high pressure filter, it is directed through the pressure control valve to the reservoir. The pressure control valve is open fully to allow the full flow to pass to the reservoir. The DCV's will remain closed until the ECU detects a need to operate.

Vehicle Moving And Turning Left
When the vehicle is turning left, the accelerometers detect the cornering forces applied and transmit signals to the ECU. The ECU determines that an opposing force must be applied to the torsion bars to counter the cornering forces. The ECU supplies a current to the solenoid of the DCV2. Simultaneously, a current is sent from the ECU to the pressure control valve which operates to restrict the flow of fluid returning to the reservoir.
The restriction causes the hydraulic pressure in the system to rise and the pressure is sensed by the pressure transducer which sends a signal to the ECU. The ECU determines from the inputs it receives what pressure is required and adjusts the pressure control valve accordingly.
The pressure in the system is applied to the annulus of each actuator, applying an opposing force to the torsion bar and minimising the cornering effect on the vehicle and maintaining the vehicle attitude. The fluid displaced from the full area of the actuator is returned to the reservoir via the valve block.
As the cornering force is removed when the vehicle straightens up, the ECU opens the pressure control valve to reduce the pressure in the system. The fluid bleeds from the actuator back into the system as the cornering force is reduced, removing the force from the torsion bar. When the vehicle is moving in a straight line DCV 2 closes.

Vehicle Moving And Turning Right
When the vehicle is turning right, the accelerometers detect the cornering forces applied and transmit signals to the ECU. The ECU determines that an opposing force must be applied to the torsion bars to counter the cornering forces. The ECU supplies a current to the solenoid of the DCV1. Simultaneously, a current is sent from the ECU to the pressure control valve which operates to restrict the flow of fluid through the by-pass gallery.
The restriction causes the hydraulic pressure in the system to rise and the pressure is sensed by the pressure transducer which sends a signal corresponding to the pressure to the ECU. The ECU determines from the inputs it receives what pressure is required and adjusts the pressure control valve accordingly.
The pressure in the system is applied to the full area of each actuator, applying an opposing force to the torsion bar and minimising the cornering effect on the vehicle and maintaining the vehicle attitude. The fluid displaced from the annulus of the actuator is returned to the reservoir via the valve block.
As the cornering force is removed when the vehicle straightens up, the ECU opens the pressure control valve to reduce the pressure in the system. The fluid bleeds from the actuator back into the system as the cornering force is reduced, removing the force from the torsion bar. When the vehicle is moving in a straight line the DCV 1 closes.

Vehicle Moving In A Straight Line
The ECU is constantly monitoring the signals received from the accelerometers and operates the DCV's and pressure control valve to maintain the vehicle attitude when the vehicle is moving.

Off-Road Driving
Off -road detection is achieved by the ECU by monitoring the signals from the upper and lower accelerometers for varying degrees of body movement. Off -road driving generates differing signals to the accelerometers which in turn produce differing outputs due to their vertical separation and the location of the roll center of the vehicle. The two signals are passed through a filter to remove any offset caused by the vehicle leaning or the terrain. The ECU then uses this signal to calculate the percentage of road roughness.
Below 25 mph (40 km/h) the percentage of road roughness calculated is used by the ECU to limit the operation of the ACE system. The system is completely inoperative at speeds below 2 mph (3 km/h). At speeds above 25 mph (40 km/h) the system disables the percentage road roughness signal and full ACE system assistance is restored.

Side Slope Detection
The ECU uses side slope detection when the upper and lower accelerometers detect an average acceleration of more than ± 0.2 g and a road speed of less than 25 mph (40 km/h).
When side slope is detected both DCV's close to provide a 'locked bars' condition. This condition increases stability and gives a consistent vehicle response. As the road speed increases up to 25 mph (40 km/h), the level of average lateral acceleration must also increase and be maintained for the system to recognize that the vehicle is on a side slope. If the side slope angle is steep and the road speed is low, the ECU will detect the side slope in a short time.
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