ASC-ECU

This ECU incorporates the ABS function, EBD function, stability control function, TCL function, BA control function and HSA function.
The hydraulic units of the ASC systems employ the automatic pressurisation function. These systems also incorporates G and yaw rate sensor, steering wheel sensor, and master cylinder pressure sensor.

STABILITY CONTROL DESCRIPTION

ASC-ECU detects vehicle movement based on information from various sensors and calculates a model of ideal vehicle movement. ASC-ECU compares the actual vehicle movement with the ideal vehicle model, and manages the brake of the specific wheel so that the actual vehicle movement gets close to the ideal vehicle mode. It also controls the understeer or oversteer condition by creating the yaw moment in the vehicle.

Example of Stability Control function

The Stability Control manages the vehicle attitude by creating a yaw moment from altering the balance between the cornering force and each wheel’s braking mechanism.

Example of the effect of control

For example, on a slippery surface, if the vehicle tends to be under-steered contrary to the driver’s intention, a yaw moment (a rotational moment) is created to restrain the under-steering by increasing the rear-inside braking force. On the other hand, when the vehicle tends to be oversteered, a yaw moment (a restorative moment) is created to restrain the oversteering by increasing the front-outside wheel braking force. Furthermore, when it is determined that the vehicle is over-speeding, safe and stable cornering is enabled by deceleration from reducing the engine output.

Joint control

ASC-ECU transmits data necessary for control of ABS and TCL, performing joint control.

Control system	Control content
ABS	Even during ABS operation, ABS performance is improved from the joint operation of the stability control.
TCL	During acceleration, engine output is governed through joint operation with stability control.

Example of TCL function

When the driving wheels slip on the slippery road surface, TCL applies the brake automatically, sends the signal requesting engine speed reduction to the engine-ECU, and prevents the loss of the driving force resulting from the slippage of the driving wheel.

BRAKE ASSIST (BA) CONTROL

Operation description

If an emergency brake is determined by the brake pedal depression speed and force, the brake assist works to increase the braking force the drivers produce. [The braking force is not increased more than the brake performance (the friction force between the road surface and the tyres).]
The brake assist is completed when the brake pedal is released or the vehicle is stopped.

Fail-safe function

The brake assist mechanism does not work when the ABS warning lamp illuminates.

Brake assist operation

HILL START ASSIST (HSA) FUNCTION

A HSA will prevent the vehicle from moving backwards during uphill starting. (This system operates only during uphill driving forwards or backwards).
System configuration

When the vehicle has completely stopped on a steep uphill by the service brake, ASC-ECU judges whether or not start the HSA function control in accordance with the signals (ETACS-ECU, CVT-ECU, G and yaw rate sensor, brake fluid pressure sensor, engine-ECU, wheel speed sensor).

HSA function state transition diagram (Overview)

note

ASC-ECU judges the inclination angle of the slope according to the G and yaw rate sensor output.
When either of the following conditions is satisfied, the mode is shifted to the forcible termination mode, and HSA function control is terminated.

The parking brake operation is detected.
The selector lever operation to the selector position other than the uphill direction driving is detected (Forward uphill driving: selector position other than "D", Reverse uphill driving: selector position other than "R").
The accelerator pedal and brake pedal are depressed at the same time.
The wheel speed sensor pulse is generated (When the vehicle moved)
The engine is stopped by engine stall, etc.

HSA function control activated

ASC-ECU judges that the HSA operation condition is satisfied. When the driver releases the brake pedal, ASC-ECU maintains the brake wheel cylinder pressure and waits.

FLUID PRESSURE HOLD MODE

By closing the cut valve, ASC-ECU maintains the brake wheel cylinder pressure of the time when the brake pedal is depressed, to prevent the vehicle from moving backward.

START MODE

ASC-ECU releases the brake wheel cylinder pressure maintained by the cut valve, depending on the engine torque generated by depressing the accelerator pedal.

FORCIBLE TERMINATION MODE

ASC-ECU immediately releases the brake wheel cylinder pressure maintained by the cut valve and terminates HSA function control.

FAIL-SAFE AND DIAGNOSTIC FUNCTIONS

ASC-ECU constantly monitors the input and output signals. If an error is detected in the system, ASC-ECU sends a fail signal and the corresponding indicator lamp is illuminated or blinks. Various controls are processed depending on the cause of malfunction as shown below.
ASC-ECU has the following functions for easier system checks.

Diagnosis code set
Service data output
Actuator test
Freeze frame data output

All the above items can be diagnosed using M.U.T.-III.

CALIBRATION

After the steering wheel sensor and hydraulic unit (integrated with ASC-ECU, G and yaw rate sensor) have been replaced with new ones, calibration must be performed using M.U.T.-III.