POWER STEERING SYSTEM


  1. FUNCTION OF MAIN COMPONENTS


    1. The main components of the EPS system are as follows:

      Component Function
      Power Steering ECU Assembly Power Steering ECU Actuates the power steering motor mounted on the steering column assembly to provide power assist, based on the signals received from various sensors and ECUs.
      Power Steering Motor Generates assist torque in accordance with a signal received from the power steering ECU.
      Rotation Angle Sensor (Built in Power Steering Motor) Outputs the rotation angle of the power steering motor to the power steering ECU.
      Electric Power Steering Column Sub-assembly Torque Sensor Detects the amount of twist of the torsion bar. Based on the torque that is applied to the torsion bar, the sensor creates an electrical signal, and outputs this signal to the power steering ECU.
      Reduction Mechanism Reduces the speed of the power steering motor through the use of a worm gear and a wheel gear and transmits it to the column shaft.
      Brake Booster with Master Cylinder Assembly Skid Control ECU

      • Sends the vehicle speed signal to the power steering ECU assembly.

      • Requests steering torque assist during steering cooperative control.
      Air Conditioning Amplifier Assembly Receives a signal from the power steering ECU to limit electrical use.
      Power Management Control ECU Transmits the ready status signal to the power steering ECU assembly.
      Combination Meter Assembly P/S Warning Light

      • Illuminates to alert the driver when the power steering ECU assembly detects a malfunction in the EPS system.

      • If the power steering ECU assembly detects low auxiliary battery voltage, it will illuminate the P/S warning light.

      • When the power switch is turned on (IG), the P/S warning light illuminates in order to check the warning light circuits. When the system enters the READY ON state, the warning light turns off.
      Buzzer Sounds to warn the driver of a malfunction in the system.
      Clearance Warning ECU Assembly* Requests steering torque assist during steering cooperative control.

      *: Models with TOYOTA parking assist-sensor system

  2. SYSTEM CONTROL


    1. The EPS system has the following controls:

      Control Outline
      Basic Control Based on the driver's input torque signal, the motor current and motor control device are controlled to achieve the target assist power.
      Compensation Control Assist power is adjusted to improve steering feeling according to the steering operation.
      Electric Load Control Prevents a reduction of assist torque if the auxiliary battery voltage decreases.
      Cooperative Control Brake Control System The power steering ECU assembly performs cooperative control with the skid control ECU in order to control the steering assist torque in accordance with information received from the skid control ECU. This facilitates the steering operation of the driver, thus realizing a high level of vehicle stability.
      TOYOTA Parking Assist-sensor System* When the vehicle is parked in a garage, the TOYOTA parking assist-sensor system assists steering in accordance with the signal from the clearance warning ECU assembly.

      *: Models with TOYOTA parking assist-sensor system

    2. Electric Load Control


      1. When the power steering ECU assembly detects a decrease in auxiliary battery voltage it transmits the electric load control signal to the air conditioning amplifier assembly in order to limit electrical usage.

      2. The air conditioning amplifier assembly limits operation of the rear window defogger until the power steering ECU assembly releases the limitation demand.

  3. FAIL-SAFE


    1. If the power steering ECU assembly detects a malfunction in the EPS system, the power steering ECU assembly illuminates the P/S warning light and sounds the buzzer to inform the driver.

    2. If a system malfunction occurs, the power steering ECU assembly changes control mode to fail-safe mode. For details, refer to the Repair Manual.

  4. DIAGNOSIS


    1. The power steering ECU assembly also stores Diagnostic Trouble Codes (DTCs). The DTCs can be accessed through the use of the Global TechStream (GTS). For details, refer to the Repair Manual.