GENERAL INFORMATION

An active stability control (ASC) system incorporates a traction control (TCL) function and a stability control function. This system have the following features.

note

The active stability control system (ASC) has the traction control (TCL) function and the stability control function. By the integrated control with the anti-lock brake system (ABS), the system stabilises the vehicle attitude and at the same time secures the driving force.

When the TCL function detects the slip of driving wheel (eg. during startup on slippery road), it automatically applies the braking force to the slipping driving wheel. At the same time, TCL function reduces the engine output and prevents the wheel spin when it determines that the engine torque is too high for the road surface friction coefficient.
When the stability control function determines that the vehicle is in a critical state, it reduces the engine output and applies brake force to four wheels independently to control the vehicle behaviour, avoiding the critical state.
Ensuring braking performance and improvement in service quality by fail-safe function during ASC system malfunction
If an emergency brake is determined by the brake pedal depression speed and force, the brake assist will be activated to enhance the braking force which the driver produces.
An emergency braking signalling system (ESS) ^*1 will flash the hazard warning lamp more quickly while heavy braking is applied.
A Hill Start Assist (HSA) ^*2 will prevent the vehicle from moving backwards during uphill starting.
The Forward Collision Mitigation System (Low speed range) (FCM-LS), which reduces the damage of collision or avoids collision at risk of a rear end collision is considered, has been employed.^*3
The Radar sensing misacceleration Mitigation System (RMS) (Forward), which prevents sudden acceleration by detecting a forward vehicle or obstacle during a stop or low-speed running to reduce the damage at collision, has been employed.^*3

note

^*1: ESS (Emergency Stop signal System)
^*2: HSA (Hill Start Assist function)
^*2: FCM-LS and RMS, refer to the GROUP 54A - FCM-LS.

CONSTRUCTION DIAGRAM

MAIN COMPONENTS AND FUNCTIONS

Name of part		Number	Functional description
Sensor	Wheel speed sensor	1	Outputs the frequency signal in proportion to the rotation speed of each wheel to ASC-ECU.
	Magnetic encoder for wheel speed detection	2	The wheel speed sensor is a pulse generator. When the magnetic encoder for wheel speed detection (a plate on which north and south pole sides of the magnets are arranged alternately) rotates, it outputs frequency pulse signal in proportion to each wheel speed.
	Stop lamp switch	3	Outputs the signal indicating whether the brake pedal is depressed or not to ASC-ECU.
	G & yaw rate sensor	4	Is integrated in the ASC-ECU, detects the yaw rate and longitudinal and lateral acceleration of a vehicle, and sends a signal to the ASC-ECU.
	Steering wheel sensor	5	Detects the steering angle of the steering wheel, and outputs signal to ASC-ECU via the CAN bus line.
	Brake fluid pressure sensor	6	Integrated into the hydraulic unit, and outputs the signal for the brake fluid pressure in the master cylinder to ASC-ECU.
	ASC OFF switch	7	Sends a signal to the ASC-ECU to turn on and off the active stability control and traction control (engine control only).
	FCM-LS OFF switch <Vehicles with FCM-LS>	8	Sends the FCM-LS OFF switch signal to the ASC-ECU.
Actuator	Hydraulic unit	9	Drives the solenoid valve using the signal from ASC-ECU, and controls the brake fluid pressure for each wheel.
	ABS warning lamp	10	Informs the driver of the system status by illuminating, flashing, or turning off the ABS warning lamp according to the signal from ASC-ECU.
	Brake warning lamp	11	Used as the brake warning lamp for the parking brake, brake fluid level, and EBD control. Informs the driver of the system status by illuminating or turning off the brake warning lamp according to the signal from ASC-ECU.
	ASC indicator lamp	12	Depending on the signal from the ASC-ECU, the indicator lamp informs the driver of the system status by flashing when the system is in operation and by illuminating when the system is abnormal.
	ASC OFF indicator lamp	13	Informs the driver of the system shutdown by illuminating by the signal from ASC-ECU.
	Stop lamp relay	14	Illuminates the stop lamps when a stop lamp illumination request signal is sent from the ASC.
Diagnosis connector		15	Sets the diagnosis code and establishes the communication with M.U.T.-III.
Engine-ECU		16	Controls the engine output based on the signal from ASC-ECU.
CVT-ECU		17	CVT-ECU performs integrated control with ASC-ECU. Output the gear position to ASC-ECU.
ETACS-ECU		18	Relays a signal from the stop lamp switch and the back up lamp switch to the ASC-ECU.
ASC control unit (ASC-ECU)		19	Controls the actuators (hydraulic unit) based on the signals sent from sensors.
			Controls the self-diagnostic function and fail-safe function.
			Controls diagnostic function (Compatible with M.U.T.-III).
FCM-ECU <Vehicles with FCM-LS>		20	Informs the ASC-ECU how the FCM-LS works.

SCHEMATIC DIAGRAM

SENSOR

G & YAW RATE SENSOR

The G & yaw rate sensor is integrated in the ASC-ECU, and detects the yaw rate and longitudinal and lateral acceleration of a vehicle.

STEERING WHEEL SENSOR

The steering wheel sensor is attached to the column switch, and detects the rotational angle of the steering wheel.

ASC OFF SWITCH

The ASC OFF switch is installed on the side air outlet (driver’s side). ASC functions can be disabled by pressing this switch for 3 seconds (The HSA and BA (Brake Assist) function operates even when the ASC system is turned OFF with the ASC OFF switch). Pressing this switch again resumes the ON status. As a countermeasure for the stuck of the ASC OFF switch, pressing the ASC OFF switch for 15 seconds resumes the system to the ON status.
When the ignition switch is turned from "LOCK" (OFF) to ON position, ASC functions are constantly in the ON status.

ASC OFF SWITCH OPERATION AND SYSTEM OPERATION

ASC OFF switch operation	TCL		Stability control	HSA	BA	FCM-LS
ASC OFF switch operation	Brake control	Engine control	Stability control	HSA	BA	FCM-LS
Not operated	Enabled	Enabled	Enabled	Enabled	Enabled	Enabled
Operated (Press and hold for 3 seconds)	Prohibited	Prohibited	Prohibited	Enabled	Enabled	Prohibited

note

The stability control is available when the vehicle speed is 15 km/h or more.

ACTUATOR

HYDRAULIC UNIT

The hydraulic unit incorporates the ABS control and ASC control. The cut valve, pressure relief valve, suction valve, G & yaw rate sensor and pressure sensor have been added to the unit for the ASC control.

note

For the internal hydraulic circuit of the hydraulic unit.

STOP LAMP RELAY

When the FCM-LS triggers automatic braking, the ASC-ECU will activate the stop lamp relay to illuminate the stop lamps.

ASC INDICATOR LAMP, ASC OFF INDICATOR LAMP

The ASC system illuminates or flashes the ASC indicator lamp or ASC OFF lamp in the following operation patterns, and informs the driver of the ASC system status.
ASC indicator lamp

Flashes at 4 Hz while the stability control or the TCL is in progress.
Illuminates when the stability control, the TCL or the HSA is disabled.

ASC OFF indicator lamp

Illuminates when the ASC-OFF switch is operated to disable the stability control and the TCL. Also illuminates when the stability control or the TCL is disabled.

ASC indicator lamp, ASC OFF indicator lamp illumination and flashing patterns

Status		ASC indicator lamp	ASC OFF indicator lamp
Normal	Normal	-	-
	Stability control operated	Flashing (4 Hz)	-
	TCL operated	Flashing (4 Hz)	-
	HSA operated	-	-
ASC is disabled by ASC OFF switch	ASC disabled	-	Illuminates
Abnormal	Stability control malfunction	Illuminates	Illuminates
	TCL malfunction	Illuminates	Illuminates
	HSA malfunction	Illuminates	-
	FCM-LS malfunction	Illuminates	-

ASC-ECU

This ECU incorporates the ABS function, EBD function, stability control function, and TCL 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.

Hill START ASSIST (HSA) FUNCTION

A Hill Start Assist (HSA) will prevent the vehicle from moving backwards during uphill starting.

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 & 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 shift lever operation to the shift position other than the uphill direction driving is detected (Forward uphill driving: shift position "Reverse", Reverse uphill driving: shift position other than "Reverse") <M/T>.
The shift lever operation to the shift or selector position other than the uphill direction driving is detected (Forward uphill driving: shift or selector position other than "D"^*, Reverse uphill driving: shift or selector position other than "R"). <Vehicles with CVT>
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.

*: When uphill driving, if shift position is "N" position, HSA function is operated

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.

BRAKE ASSIST (BA) CONTROL

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 ASC indicator lamp illuminates.

Brake assist operation

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 and G & yaw rate sensor) have been replaced with new ones, calibration must be performed using M.U.T.-III*.

note

M.U.T.-III uses the ABS data list.
*: For calibration, refer to Workshop Manual.