ESP function: Braking

The brakes are applied through ESP control of the pump motor, pressure increase and pressure relief valves, as well as the inlet and outlet valves in the hydraulic unit. This allows the braking force for each wheel to be controlled individually. The ESP control module receives information from the brake pressure sensor and uses this information to control brake pressure on each wheel in relation to the braking force applied by the driver. A wheel regulated by ESP in controlled using the ESP criteria.

Both front and rear wheels are connected to the pressure increase and pressure relief valves in the hydraulic unit, which allows each wheel to be controlled independently.

Friction is estimated by calculating drive wheel torque during acceleration (which is a function of the engine torque) or braking (which is a function of braking force).

If performing evasive action during emergency braking, the vehicle can be maneuvered by regulating the braking pressure applied by the driver using the control module and pump. The applied braking force on each wheel can therefore be above or below force requested by the driver.

Braking distance is given priority when braking in a straight line while stability is given priority during evasive action. ESP modulation can occur with or without the driver applying the brake pedal.

During ESP modulation, the control module starts the pump which remains running during the entire modulation cycle. At the same time, the pressure relief valve is closed in order to allow pressure build-up. Pressure is built up through the opening of the pressure increase valve, which supplies the pump with brake fluid.

The control module closes the pressure increase valve when a pre-set pressure is reached. The control module regulated pressure by opening of the pressure increase valve, closing the pressure increase and pressure relief valves to maintain pressure and opening the pressure relief valve in order to lower the pressure. The inlet and outlet valves are activated for individual wheel control.

The valves are activated with a pulse train, during which the time corresponds to a pressure increase or pressure decrease. Excess brake fluid remaining when the pressure relief valve opens is returned to the master cylinder.

The ESP function controls one to three wheels simultaneously.