Automatic Stability Control (ASC-EZA)

INTRODUCTION




Automatic Stability Control (ASC) - EZA has been developed for use with 4 cylinder vehicles. EZA is a German acronym, translated to English it means "Individual cylinder fade-out". Design criteria for the system was to develop an ASC system that was both reliable and inexpensive. The EZA system fills these requirements.

The system continues to provide traction control through rear brake regulation. The major difference is in the engine control side of the system. EZA uses ignition timing control and individual cylinder canceling to provide torque reduction for stability control.

ASC-EZA was developed in conjunction with Teves to operate with the Bosch M5.2 engine management system and Teves hydraulic control. The use of individual cylinder canceling allows for the elimination of the throttle control and the components involved with it.

EZA joins the other ASC systems already in use to provide the high degree of traction and stability control.

OVERVIEW OF ASC SYSTEMS






ASC OVERVIEW





The basic concept of providing optimum traction and stability at the rear wheels remains unchanged for the EZA system. The ability to control the vehicle while driving is lost as a result of excessive wheel spin or slip. Automatic Stability Control (ASC) - EZA ensures that the maximum amount of lateral locating forces exist for the prevailing driving conditions and road surface, the same as other traction control systems currently in use.

Additionally an electronic slip control system is able to react quicker than the driver when driving situations change and the vehicle is in danger of losing traction or stability.

Wheel slip is determined from the wheel speed sensor inputs. Any time the rear wheels exceed the critical values for slip or spin, ASC regulation will activate to restore stability or the lost traction. This is carried out by the control module signaling the DME M5.2 control module over CAN or the hydraulic unit to reduce the power applied to the rear wheels.

The ASC-EZA limits the drive torque applied to the rear wheels through:

^ The engine control module by retarding the ignition timing
^ The engine control module by canceling individual cylinders
^ The hydraulic unit by applying the rear brakes.

The EZA system includes the MSR function that limits the engine drag torque affect on decel. Engine drag torque is reduced by the EZA through:

^ Regulation of the engine's idle control valve and canceling decel fuel cut - off.

ASC - EZA COMPONENTS
Control Module





The EZA system uses the 42 pin Teves "Mark IV - G" control module. As with other Automatic Stability Control (ASC) systems, the EZA control electronics are combined in the ABS module. The ABS/ASC -EZA system also uses redundant processing to ensure reliable operation. The location of the control module is in the passenger side kick panel.

Inputs from the four wheel speed sensors are processed by the control electronics. If the threshold values for wheel slip occur, the module will activate ASC regulation.

Hydraulic Unit





The hydraulic unit is the same component used on the Teves Automatic Stability Control (ASC)+T system in the M50/M52 equipped E36. It incorporates four inlet and four outlet solenoids to regulate the flow of brake fluid to the brake calipers.

The hydraulic unit also houses the changeover solenoid valve, the intake (suction) valve and the return pump and motor.

Wheel Speed Sensors





Inductive pulse type sensors are used on the EZA system to provide the wheel speed input to the control module.

Tandem Master Cylinder





The master cylinder is the same as the one used on the E36 ASC+T system. It incorporates the central valves that allows brake fluid to be drawn from and returned to the master cylinder making the "Mark IV - G" a closed system.

ASC-EZA OPERATION
The parameters for Automatic Stability Control (ASC) control remain the same for the EZA system as other slip control systems. The critical values for wheel slip are programmed in the control module. The inputs from the wheel speed sensors are monitored and compared with these values. If the values for wheel slip are exceeded, ASC regulation is activated.
As with other systems, the EZA systems operates on both the select high and select low regulating principles. The determining factors for select high or low regulation is based on the degree of slip and road speed of the vehicle.




From a stand still up to approximately 25 MPH, the emphasis is on traction. Stability is not a critical issue so the control module will use select high as its regulation factor. With select high, both rear brake and engine torque control are used to restore traction. However, the emphasis is placed on the rear brake control to eliminate the wheel spin.





At speeds above 25 MPH, the control module will use select low as its regulation factor. The vehicle's stability is now the governing factor. Greater emphasis is placed on reducing the engine output torque. With select low, rear brake regulation can still be used up to a road speed of approximately 50 MPH. Above 50 MPH only engine regulation is used to control wheel slip.

REAR BRAKE REGULATION





Operation of the EZA traction control is the same as the Teves Automatic Stability Control (ASC)+T system currently in use on the E36s. The inlet and outlet solenoids in the hydraulic unit are regulated by the control module to provide the - Pressure Build, Pressure Hold and Pressure Drop cycles needed to pulse the rear brakes.

The return pump in the hydraulic unit supplies the volume of brake fluid needed to apply the brakes.
The changeover valve is used to isolate the rear brake circuits so that ASC regulation at the rear does not effect the front brakes.

The Intake (or suction) valve is hydraulically controlled. It is held open by a spring to supply the hydraulic unit's return pump with brake fluid during ASC regulation.
The valve is closed by hydraulic pressure when the brake pedal is depressed.

Pressure Build





The inlet valves are open and the outlet valves are closed in pressure build.
Brake pressure is supplied by the return pump to the brake calipers for the pressure build phase of regulation.

Pressure Hold





During pressure hold, the inlet valves are powered closed. The outlet valves remain closed and pressure is held in the brake calipers.

Pressure Drop





The outlet valves are powered open during pressure drop and the inlet valves remain powered closed.

The brake fluid is pumped through the inlet valve circuit for continued regulation If regulation is complete the brake fluid is returned through the open changeover valve in the hydraulic unit and the central valve in the master cylinder.

ENGINE TORQUE CONTROL

Engine output torque reduction is a function of both the EZA and DME control modules. The EZA control module makes the determination that power reduction is required and the DME carries out the request for torque reduction. The major difference with the EZA system is the elimination of the throttle control for torque reduction.





Retarding the ignition timing is the main control request utilized by the EZA for reducing the engine's output torque.

Additionally, the control module can request DME to selectively cancel fuel injectors to further reduce the power output if required.





There are limits to retarding the timing based on the exhaust gas temperature in front of the catalytic converter. If the temperature goes too high, damage can result to the catalytic converter.

The exhaust gas temperature in front of the catalytic converter is calculated by the EZA control module based on the intake air temperature, engine temperature and ignition timing.





This temperature factor is taken into account when the processor determines that power reduction is called for. If the calculated temperature is below the threshold limit, the EZA will call for retarding the timing to reduce the output power.

If the calculated temperature is to high, the EZA will go the an acceptable limit on timing retard and selectively cancel injectors to reduce the power.





In practical application, the EZA uses a combination of retarded timing and cylinder shut down to bring the wheel slip under control

MSR REGULATION





The EZA system is equipped with the MSR function. The purpose of MSR is to reduce the engine braking effect on deceleration. Drag torque or engine braking can adversely effect stability by causing the rear wheels to stop or slip and lose traction. This effect is most noticeable at high engine RPMs in low gears with low frictional coefficients.

The EZA system detects a high drag torque condition from the wheel speed sensor inputs. When the front wheels are turning faster than the rear and the rear wheels are about to stop or slip.
To counteract the drag torque, the EZA control module signals the DME control module to:

^ Cancel the decel fuel cut off
^ Open,the idle control valve slightly

The engine's braking effect is reduced and the stability of the vehicle is improved.

During MSR control, neither ignition timing retard nor cylinder cancellation are activated.

MSR regulation is only activated above approximately 12 MPH. This prevents MSR from activating when the vehicle is cornering at low speeds.

EZA - DME/EGS INTERFACE





The EZA system uses the CAN Bus for communication between the DME and EGS control modules.

Any request for engine torque reduction or drag torque reduction are passed over the CAN line and processed by the DME.

The DME supplies the EZA module with the air temperature, engine temperature and the ignition timing signal for its processing requirements.

If the vehicle is equipped with an automatic transmission, the shift intervention signal is also passed over the CAN line to the EGS control module. This signal prevents the transmission control module from shifting gears during ASC regulation to further improve stability.

ABS - ASC WARNING LAMPS





Both warning lamps are controlled by the ABS/EZA control module. When the ignition is switched ON, the control module performs a "SELF CHECK" of its internal electronics as well as various input signals and output controls. If any defects are detected, either one or both lamps will remain illuminated.

A fault that affects the operation of both systems will cause both lamps to stay ON. For example a wheel speed sensor fault will cause both the ABS and ASC functions to go off - line. A fault that only affects ASC will only cause the ASC function to go off - line and only the ASC lamp will remain ON. For example a fault with the CAN line would only affect ASC operation.

The same applies if the vehicle is being driven when a fault occurs, If it affects both systems, both lamps will illuminate, or only the ASC lamp will illuminate with a fault that affects only ASC control.

If the ASC is switched OFF manually, the ASC lamp will illuminate to indicate that the system is shut down.

DIAGNOSIS AND TROUBLESHOOTING





The ASC - EZA system is connected to the diagnostic link. Use the fault symptom troubleshooting procedures of the diagnosis software in the DIS.