EPS System Description
System Outline
This vehicle is equipped with electrical power steering (EPS). The driver's steering force is assisted by an electric motor at the steering gearbox, instead of an engine-driven oil pump to generate oil pressure, so the EPS system improves engine efficiency.
The EPS control unit monitors and controls the EPS motor's assisting force to match driving conditions.
- Low vehicle speeds: High power assist (for easy handling)
- High speed driving: Low power assist (for stable driving)
- Low speed to high speed driving: Change smoothly from high assist to low assist
EPS Control
The EPS control unit calculates the assistance torque based on the steering torque signal and the vehicle speed signal, and activates the motor to assist the steering force. To protect the system, the EPS control unit reduces motor current when repeated extreme steering force, such as turning the steering wheel continuously with the vehicle stopped or holding the steering at the lock position (full right or left). Also, the EPS control unit assists the steering force when the EPS control unit receives the steering assist request from the driving support system.
Steering Wheel Return Control
The steering wheel return control controls the return speed of the steering wheel based upon the steering angle and the vehicle speed. This control is responsible for the returning the steering wheel to the neutral position.
Integrated Dynamics System
The steering feel is changed by the integrated dynamics system mode.
'19-21
| EPS System | Integrated Dynamics System Mode | |||
|---|---|---|---|---|
| SNOW | COMFORT | SPORT | SPORT+ | |
| Steering Effort | Same as SPORT. | Lightest effort level of all the modes, light parking lot efforts for easy maneuvering. | Sporty and direct steering effort character for all vehicle speeds. | Heaviest efforts of all modes. More direct steering feel than sport mode. |
'22-23
| EPS System | Integrated Dynamics System Mode | |||
|---|---|---|---|---|
| SNOW | COMFORT | NORMAL | SPORT | |
| Steering Effort | Same as NORMAL. | Lightest effort level of all the modes, light parking lot efforts for easy maneuvering. | Sporty and direct steering effort character for all vehicle speeds. | Heaviest efforts of all modes. More direct steering feel than normal mode. |
Straight Driving Steering Assist
Steering effort is detected and reduced by applying EPS motor assist when driving on a sloped road. This control will return to normal when no longer driving on a sloped road. This function only operates when the cruise control is on and the speed is set.
Assist image
Motion Adaptive - EPS Control
Overview
The motion adaptive - EPS control performs the steering torque correction control coordinated with VSA system for stabilizing the vehicle when the steering is unstable. The EPS system determines the state of the vehicle based on the data calculated by the VSA modulator-control unit, and the data from the yaw rate signal and the acceleration signal. When the system determines that the vehicle behavior is abnormal, the EPS control unit calculates the correction current based on the vehicle behavior and corrects the steering torque. The motion adaptive - EPS control is stopped in the event of failure in the VSA system.
Mitigates Oversteer Control
When oversteer occurs, it compensates for steering torque to steer in the countersteer direction, and enhances vehicle control with suppression control of oversteer by the VSA system.
Mitigates Understeer Control
When understeer occurs, it compensates for steering torque to prevent steering wheel from turning too much with suppression control of understeer by the VSA system and prevents turning radius increase by maintaining the tire grip.
Stabilizes Braking on Road Surfaces With Different Friction Coefficients Control
When the vehicle behavior is abnormal while braking on an uneven road surface, it compensates for steering torque to enhance vehicle control.
EPS Motor Control Circuit
The EPS motor control circuit is composed of the main CPU, the sub CPU, the field-effect transistor (FET) drive circuit, the FET, the relay drive circuits, the power relay, the fail-safe relays, the electric current detection circuit, and the EPS motor. With the signal from the input sensor, the CPU calculates and duty cycle outputs the appropriate three-phase current for the FET drive circuit. This operation is duty controlled.
Failsafe
The EPS control unit diagnoses and monitors the motor system, the torque sensor system, the power supply system, the communication system, and the CPU. When a failure is detected, the EPS indicator comes on and the unit takes one of the following failsafe actions:
- Stop assist
- Limit assist
- Start alternative assist (limited control)