HDC minimum target speeds (Brakes)

Minimum target speed The minimum target speed depends on which gear is engaged. Reduced minimum target speeds are employed for some gears if rough terrain or sharp bends are encountered while already travelling at the normal minimum target speed. If loss of traction makes it impossible to maintain the minimum target speed, the SLABS ECU temporarily increases the minimum target speed to maintain stability, then restores the normal minimum target speed when traction improves.

HDC minimum target speeds

Fade out To provide a safe transition from active braking to brakes off, the SLABS ECU invokes a fade out strategy if it detects any of the following during active braking: l A system fault. l The conditions for HDC are no longer being met. l Possible brake overheat.

The fade out strategy increases the target speed at a low constant acceleration rate, independent of actual throttle position. This results in the braking effort being gradually reduced and then discontinued. The SLABS ECU operates warning indications during fade out that are dependent on the cause.

Fade out warning indications

Clutch disengagement/neutral selection During active braking, if the SLABS ECU detects the clutch is disengaged or neutral is selected, it flashes the HDC information warning lamp and sounds the audible warning continuously to indicate that conditions for HDC are no longer being met. Initially, the SLABS ECU also fixes the target speed to the applicable minimum target speed, but if the condition continues for approximately 60 seconds the SLABS ECU invokes fade out.

Brake overheat prevention To prevent the brakes overheating, the SLABS ECU monitors the amount of active braking employed and, from this, estimates brake temperature. If the SLABS ECU estimates the brake temperature has exceeded a preset limit, it flashes the HDC fault warning lamp and sounds the audible warning continuously, to indicate that HDC should be deselected to allow the brakes to cool. If active braking continues and the SLABS ECU estimates that brake temperature has increased to an unacceptable level, fade out is employed and HDC is disabled. After fade out, the audible warning is discontinued but the HDC fault warning lamp continues to flash, while HDC is selected, until the SLABS ECU estimates brake temperature to be at an acceptable level. This calculation continues even if the ignition is turned off, so turning the ignition off and back on will not reduce the disabled time. When the SLABS ECU estimates the brake temperature to be acceptable, it extinguishes the HDC fault warning lamp and illuminates the HDC information warning lamp to indicate that HDC is re-enabled. The disabled time is dependent on vehicle speed; typical times at constant vehicle speeds are as follows: