Stability System

Stability system





Traction Control function
Monitors and controls wheel spin in the driving wheels at lower speeds in order to increase forward movement. If a wheel starts to spin that wheel is automatically braked so that the drive power is transferred to the other wheel. Activated only at speeds up to approximately 40 km/h (25 mph). When the traction control has been activated it can be used up to 80 km/h (50 mph). Traction control can be likened to an electronic limited slip differential.
Traction control is always connected after starting but can be deactivated using a switch. If the driver depresses the brake when the system is operating the function is deactivated.
The control module monitors how hard the traction control is working and calculates theoretical brake temperature. If there is a risk of the brakes overheating the function is deactivated. At the same time the warning lamp and a diagnostic trouble code is stored. When the brakes have cooled the warning lamp goes out and the function is reactivated, but the diagnostic trouble code (DTC) is still stored in the memory.

Note! This diagnostic trouble code (DTC) can also be stored if the brakes have had to work hard.

In cars with Traction control the ABS hydraulic modulator contains the following components: hydraulic valve (1), solenoid valve (2), and a by-pass valve (3), 2 of each, 1 per circuit.
There is a central valve in the hydraulic cylinder primary cylinder. The valve is normally open and ensures that the pump receives sufficient brake fluid during traction control (TC) operation.
The function is similar to the TRACS in the X70.

Traction control control
If for example the front wheels have a tendency to spin when the car is driven off the following occurs:
- The solenoid valves (2) close and block the connection between the pump pressure side and the master cylinder
- The inlet valve (C1) for the left front wheel closes so that that wheel cannot brake.
- The pump starts and then runs constantly during operation.
- The pump takes brake fluid from the master cylinder via the hydraulic valve (1) and pumps the brake fluid to the right front wheel.
- The wheel is braked to the same speed as the left front wheel and drive is split between the wheels.
- The control module then controls the wheel spin (braking power) by closing /opening the inlet valves (C4) and the outlet valve (D4).
When the control is stopped the pump is switched off, the solenoid valves (2) opens and the in- and outlet valves resume the position for normal braking.
Control is stopped if:
- Wheelspin stops, for example because of increased friction between the road surface and the tires.
- There is a risk of the brake discs overheating.
- Braking takes place (the brake pedal is depressed, signal from the stop (brake) lamp switch).
In addition the pressure from the master cylinder hydraulic valve (1) is shut off and the pump can no longer receive brake fluid from the master cylinder.
The pump motor is controlled with a signal which has a fixed frequency but a variable pulse width. This means that the engine speed (RPM) and sound vary during traction control.
Because the pump supplies more brake fluid than is normally required for control there are two by-pass valves (3) which open at a certain pressure. When the valves open the brake fluid is released back to the brake fluid reservoir via the master cylinder.





Stability Control function
Monitors and controls wheel-spin in the drive wheels at all speeds to improve the cars traction and stability.
If one or both of the drive wheels begins to spin (rotates faster than the rear wheels), an order is sent to the engine control module (ECM) to limit the engine torque.
Id deactivated if the driver depresses the brake pedal.
The function is similar to the DSA S/V 40.

Note! The Stability control function cannot be ordered separately, but is part of Stability traction control (STC).

Stability and Traction Control (STC) function
STC = Traction control + Stability control
Stability and traction control (STC) maximizes the cooperation between the traction control and stability control depending on the circumstances and driving conditions.
Is deactivated if the driver depresses the brake pedal.
The activation/deactivation switch is on the dashboard.
Standard/option depending on market.

Diagnostics, fault-tracing
The diagnostic functions are similar to the X70. The diagnostic trouble codes appear to be different depending on function and car type.