Electronic Stability Program (ESP) is an auxiliary function to enable the vehicle to stabilize while the vehicle is running, stopping or turning.
ESP consists of the following functions:
Antilock brake system (ABS)
This function prevents wheel locking which may occur when the brake is applied suddenly or on slippery roads. With this function, as the vehicle is kept in the stable state and wheels unlocked, the driver can avoid any obstacle by turning the steering wheel.
Electronic brake force distribution (EBD)
This function distributes braking force of front and rear wheels properly according to the vehicle load condition.
The braking force of the front and rear wheels is controlled for the optimum effect to secure the maximum braking force regardless of the load.
Traction Control
This function controls the engine and brake to prevent the driving wheels from spinning at the time of starting and accelerating.
When the ESP control module detects wheel spinning, using information from the yaw rate sensor and wheel speed sensor, it lower the engine torque by closing the electronic controlled throttle and controlling ignition. At the same time, braking is applied to the spinning wheel.
Stability Control
This function controls the vehicle in the stable state by controlling the engine and braking so as to prevent the vehicle from over-steering or under-steering while turning.
When under-steering occurs, this function lowers the engine torque and applies braking to the inner rear wheel in the vehicle forward direction, so as to prevent the vehicle from moving outward.
When over-steering occurs, this function applies braking to the outer front wheel in the vehicle forward direction so as to prevent the vehicle from moving inward.
The ESP system is equipped with a Traction Control Support System (TCSS) OFF switch.
The traction control function in the ESP system can be stopped and resumed by the TCSS OFF switch.
The traction control function resumes automatically when ignition switch is turned to the OFF position once and then to ON.
ESP control module / hydraulic unit
The control module receives signals from each wheel speed sensor, TCSS OFF switch, brake master cylinder pressure sensor (7), steering angle sensor and yaw rate sensor. Based on these signals as information, the control module judges the vehicle conditions and controls the brake hydraulic pressure by combining the ON/OFF operation of the solenoid in the hydraulic unit and the pump motor operation.
The hydraulic unit contains an inlet solenoid valve (8) and an outlet solenoid valve (9) for each wheel as well as a cut solenoid valve (10) and a low pressure solenoid valve (11) for each hydraulic unit system, together with a master cylinder pressure sensor, pump motor (6).
The hydraulic pressure control is operated in 3 modes, pressure increase, pressure holding and pressure reduction.
- Pump motor:
The pump motor turns on and applies pressure to each brake when braking is activated in the traction control and stability control state. When in the pressure reduction mode, it causes the brake fluid in the reservoir (12) to return to the master cylinder (1).
- Brake master cylinder pressure sensor:
The brake master cylinder pressure sensor detects the brake hydraulic pressure in the primary piping when the brake is applied in normal conditions. Also, it detects the pump motor driving state when the brake is applied in the traction control and stability control state.
- Inlet solenoid valve:
In the ABS, traction control and stability control state, the inlet solenoid valve is activated in the pressure holding and pressure reduction modes to open the fluid passage. This restricts any increase of the hydraulic pressure applied to the brake caliper.
- Outlet solenoid valve:
In the ABS, traction control and stability control state, the outlet solenoid valve is activated in the pressure reduction mode to open the fluid passage, thereby lowering the hydraulic pressure in the brake caliper.
- Cut solenoid valve:
As the brake is applied in the traction control and stability control state, the cut solenoid valve is activated to close the fluid passage, thereby causing the hydraulic pressure generated by the pump motor to apply to the brake caliper.
- Low pressure solenoid valve:
As the brake is applied in the traction control and stability control state, the low pressure solenoid valve is activated to open the fluid passage from the master cylinder to the pump motor.
- 1. Brake master cylinder
- 2. Brake caliper (right front)
- 3. Brake caliper (left front)
- 4. Brake drum (right rear)
- 5. Brake drum (left rear)
- 6. Control module pump motor
- 7. Brake master cylinder pressure sensor
- 8. Inlet solenoid valve
- 9. Outlet solenoid valve
- 10. Cut solenoid valve
- 11. Low pressure solenoid valve
- 12. Brake master cylinder reservoir
Steering angle sensor
The steering angle sensor is assembled with the contact coil as a unit and mounted to the steering column. Detecting the angle as the steering wheel is turned, the steering angle sensor sends the information to the ESP control module.
Yaw rate / G sensor
- The yaw rate / G sensor consists of the yaw rate sensor (angular velocity in the vehicle turning direction) and right / left G sensor (acceleration in right-left direction).
- The sensor detects the angular velocity in the vehicle turning direction and movement in the right-left direction, and sends the information to ESP control module.
- The sensor is mounted under the centre console box.
TCSS OFF switch
The TCSS OFF switch is a momentary contact type, and is attached to the instrument panel.
The TCSS OFF light in the display illuminates and informs the driver that the traction control function has been switched off.