2428123 - E7023 ESP - Description

Description

The electronic anti-lock brake system (ABS) governs braking pressure sent to the wheels and prevents loss of grip under all tyre and road surface conditions.On the most extensive version the ABS control unit also includes the ESP (Electronic Stability Program) and ASR (Anti Slip Regulation) functions as well as the HBA (Hydraulic Brake Assist) and HH functions (Hill Holder)The ESP system acts on the engine and brakes to generate a stabilising torque when the ABS sensors detect conditions that could lead to the vehicle slipping.

The ESP system includes the following specific components over and above those of the ABS:

• a sensor which detects the steering wheel position (steering sensor in the electric power assisted steering control unit);
• a sensor which detects the vehicle's rotation around the vertical axis and side acceleration (centrifugal force) (yaw sensor);
• a sensor which measures the pressure in the ABS hydraulic unit (incorporated in the ABS control unit)

The ESP system is always connected to the ASR system.The ASR system increases vehicle stability and active safety by controlling drive wheel slip. If slip is caused by excessive power transmission, it cuts in to reduce engine power through communication with the engine management control unit. if slip is detected at a single wheel, the system cuts in to brake the slipping wheel by acting on the modulation solenoid.The ASR comes on automatically whenever the engine is started: the system can be deactivated by operating the 'ASR OFF' button in the control panel in the centre of the dashboard.When the system is off, an LED on the button comes on at the same time as a warning light on the control panel.The ESP function, on the other hand, comes on automatically when the vehicle is started up and cannot be switched off.The Hill Holder system is designed to assist the driver during hill starts. The HH automatically delivers enough brake torque to hold the car so that the clutch is not fully released and the engine torque is high enough to start the car comfortably.

The HH activates automatically when the brake pedal is pressed under the following circumstances:

• vehicle speed equal to zero, gradient greater than 2% and clutch pedal pressed.

When the brake pedal is released, the Hill Holder maintains the brake system under pressure for 2 seconds without altering the other conditions to give the driver time to move his or her foot from the brake pedal to the accelerator pedal without the vehicle moving backwards and without the use of the parking brake.Once the accelerator has been pressed, the Hill Holder keeps the car still for an additional 10 seconds or until engine torque is high enough to move the car.The H.B.A. system aids the driver during emergency stops when the brake pedal is applied quickly and maintenance load is low; the system intervenes when the pressure gradient exceeds a certain threshold (fast application of brake pedal - emergency stop) multiplying the braking pressure at the wheels applied by the driver to maximize deceleration.ASR/ESP warning light: the warning light flashes when the system cuts in to notifiy the driver that the ASR system has cut in due to road surface grip conditions.When th econtrol unit detects an error in the ASR function or the ESP function, it lights up the warning light constantly.HH warning light: the warning light comes on when the system cuts in to notifiy the driver that the HH system has cut in due to road surface grip conditions.The warning light comes in in fixed mode when the control unit detects an error in the HH function. As far as the ABS function only is concerned,  See E7020  ABS . For more details  Characteristic of working principle 3350  DRIVE CONTROL' .