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.
EPS Control
The EPS control unit calculates the assisted 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 is 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 neutral position.
End Brake Control
The end brake control is a system that electrically absorbs the load before the rack reaches to the end stopping position in order to reduce the hitting sound when hitting the rack end and enhance of the steering feeling. This system will be done by detecting the rack position from the rotation of the EPS motor and reducing the motor rotation at the near of the rack end. Immediately after disconnecting the 12 volt battery terminal, the end brake control will not work because the rack position information is erased. It will start to work by learning the steering angle neutral position.
Integrated Dynamics System
The steering effort is changed by the integrated dynamics system. When the integrated dynamics system is in the INDIVIDUAL mode, the EPS system can be customized separately by the INDIVIDUAL settings.
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 the vehicle is 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 the VSA system to stabilize 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 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, the EPS system suppresses it by compensating the steering torque to steer in the countersteer direction. In addition to that, the VSA system works with the EPS system to enhance vehicle control.
Mitigates Understeer Control
When understeer occurs, the EPS system suppresses it by compensating for steering torque which prevents the steering wheel from turning too much. In addition to that, the VSA system works with the EPS system to prevent an increase in turning radius by maintaining 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.
Driver Attention Monitor Function
Overview
To help avoid a crash or collision due to drowsiness or fatigue, the driver attention monitor function can prompt the driver to take a break.
System Description
The driver attention monitor function analyzes steering inputs to determine if the vehicle is being driven in a manner consistent with drowsiness or inattentive driving behavior based on the steering angle and the yaw rate when the vehicle speed is above a set point. If the system detects driver drowsiness or inattention, the driver attention monitor function warns the driver to take a break by showing a message on the multi-information display (MID) and/or vibrating the steering wheel.
Operation Conditions
The driver attention monitor function operates under these conditions:
- Vehicle speed is 25 - 112 mph (40 - 180 km/h).
- The EPS system, the SRS, and/or the transmission system does not have a malfunction.
Function Prohibition
The driver attention monitor function is not activated under these conditions:
- Driving duration is less than 30 minutes.
- Driving on rough roads.
- Driving in a strong side wind.
- Active driving situation (changing the traffic lane or the vehicle speed).
- Driving with the LKAS activated.
Attention Level Reset
The driver attention monitor function resets the attention level displayed on the multi-information display (MID) if these conditions are detected:
- The vehicle is turned to the OFF (LOCK) mode.
- The driver releases the seat belt and opens the driver's door with the vehicle in the ON mode.
Steering Angle Detection
The EPS control unit calculates the steering angle from the motor angle sensor value.
Steering Angle Neutral Position Learning
The EPS control unit learns the steering angle neutral position to detect an initial steering angle when turning the vehicle to the ON mode. The steering angle neutral position learning is classified into initial learning and the regular learning.
Initial Learning
The initial learning is performed automatically when the vehicle is driven after steering angle neutral position is cleared. When the EPS control unit judges that the vehicle is going straight based on each sensors signals, the steering angle neutral position is learned. For more details of the learning procedure, refer to the Steering Angle Neutral Position Learning - Refer to: Steering Angle Neutral Position Learning or EPS Control Unit Update .
The steering angle neutral position is cleared whenever you do any of these actions:
- The power supply voltage for the EPS control unit is decreased greatly, or 12 volt battery terminal is disconnected from the 12 volt battery.
- Replacing or removing the EPS motor/control unit.
- When a failure that cannot calculate the steering angle occurs in the EPS system.
Regular Learning
The regular learning corrects the neutral position gap that occurs due to normal wear and tear of the vehicle and changes in the wheel alignment while driving.
Learning using the HDS
The VSA sensor neutral position memorization for the VSA system is performed using the HDS, the steering angle neutral position is cleared and overwritten.
Failsafe
The EPS control unit diagnoses and monitors the motor system, torque sensor system, power supply system, communication system, and 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
Redundancy of EPS System
Due to giving a redundancy to EPS system, the torque sensor, the motor drive circuit, and the motor are consist of two systems. For the torque sensor and the EPS motor angle sensor, the CPU uses the system 1 in normal condition. If the failure is occurred in the part of the system 1, the CPU will use the sensor in the system 2 instead. And for the motor drive circuit (FET driver, three-phase inverter) and the motor, the CPU uses both system 1 and 2 in normal condition. If the failure is occurred in either system 1 or 2, the CPU will use either normal system. In these situations, the EPS indicator goes on, but the EPS control is continued.