POWER STEERING SYSTEM


  1. FUNCTION OF MAIN COMPONENTS

    Component Function
    Steering Sensor Detects the steering direction and angle of the steering wheel assembly.
    Speed Sensor Detects the wheel speed of each of the 4 wheels.
    Rack and Pinion Power Steering Gear Assembly Steering Torque Sensor Detects the amount of twist of the torsion bar. Based on the torque applied to the torsion bar, the sensor creates an electrical signal, and sends this signal to the power steering ECU.
    Reduction Mechanism Reduces the speed of the power steering motor and transmits the rotation of the power steering motor to the rack shaft.
    Power Steering ECU with Motor Assembly Power Steering Motor Generates power assist in accordance with a signal received from the power steering ECU.
    Rotation Angle Sensor Sends the rotation angle of the power steering motor to the power steering ECU.
    Power Steering ECU Operates the power steering motor to provide power assist based on the signals received from various sensors and ECUs.
    ECM Sends the engine speed to the power steering ECU.
    Skid Control ECU Assembly
    • Outputs the vehicle speed signal.

    • Requests steering torque assist during cooperative control.

    FR Steering Control ECU*1 Sends the target front wheel turning angle signal to the power steering ECU.
    RR Steering Control ECU*1 Outputs the rear wheel turning angle signal.
    Absorber Control ECU Outputs the damping force control mode signal.
    Air Conditioning Amplifier Assembly Receives a signal from the power steering ECU to limit electrical usage.
    Driving Support ECU Assembly*2 Outputs collision avoidance support signals.
    Forward Recognition Camera*2 Sends steering assistance request signals to the power steering ECU.
    Combination Meter Assembly Power Steering Warning Light (Red Indicator) Illuminates to alert the driver when the power steering ECU detects a malfunction in the EPS system which results in a loss of steering assist torque.
    Power Steering Warning Light (Yellow Indicator) Illuminates to alert the driver when the power steering ECU detects a malfunction in the EPS system which limits the steering assist torque.
    Multi-information Display Displays a warning message to inform the driver of a malfunction in the EPS system.
    Master Warning Light
    • Illuminates when the warning message is displayed on the multi-information display.

    • Illuminates when the power steering warning lights is illuminated.

    Buzzer Sounds to warn the driver of a malfunction in the EPS system.

    *1: Models with LEXUS Dynamic Handling (LDH) system

    *1: Models with pre-collision system

  2. SYSTEM CONTROL


    1. The power steering ECU calculates the steering assist force based on steering torque information from the steering torque sensor, vehicle speed information from the skid control ECU assembly and information from each ECU and controls the power steering motor to generate the required steering assist torque.

    2. The EPS system consists of the control functions listed below:

      Control Outline
      Steering Assist Control Basic Control Calculates the assist current required based on the steering torque value and the vehicle speed and operates the power steering motor.
      Compensation Control Compensates with a force, according to the driver's steering maneuver, improving the comfort of steering.
      Sport Mode Control When drive mode Sport S+ is selected, the power steering ECU switches to assist characteristics with higher steering responsiveness than Normal mode to achieve a more direct steering feeling.
      Brake Control System Cooperative Control Receives requests from the skid control ECU assembly and performs steering assist control in accordance with the operating condition of the brake control system. This facilitates the steering operation of the driver, achieving a high level of vehicle stability.
      Lane-keeping Assist System Cooperative Control If the power steering ECU determines that the vehicle may deviate from its lane or the lane keeping assist function operates while the lane departure alert function and lane keeping assist system are operating, it provides steering assist according to signals from the forwrd recognition camera.
      Power Supply Voltage Drop Control When the power steering ECU detects a power supply voltage drop, it sends a load control demand to the air conditioning amplifier assembly in order to limit electrical usage.
  3. FAIL-SAFE


    1. If the power steering ECU detects a malfunction in the EPS system, the power steering ECU illuminates the power steering warning light (red indicator*1 and yellow indicator*2) and master warning light, displays the warning message on the multi-information display, and sounds the buzzer to alert the driver of the malfunction.

      Tech Tips

      *1: Illuminates when a malfunction which results in a loss of steering assist torque.

      *2: Illuminates when a malfunction which limits the steering assist torque.

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

  4. DIAGNOSIS


    1. The power steering ECU will also store a Diagnostic Trouble Code (DTC). The DTC can be accessed through the use of the Global TechStream (GTS). For details, refer to the Repair Manual.