HEATED STEERING WHEEL SYSTEM


  1. FUNCTION OF MAIN COMPONENTS

    Component Function
    Steering Wheel Assembly Thermostat Stops current flow in the heater wire when the steering wheel assembly surface temperature exceeds a threshold.
    Heater Wire Increases the steering wheel assembly surface temperature using power supplied by the steering wheel heater control assembly.
    Thermistor Sends a steering wheel assembly surface temperature signal to the steering wheel heater control assembly.
    Steering Wheel Heater Control Assembly Performs heated steering wheel control according to signals from the air conditioning amplifier assembly and thermistor.
    Air Conditioning Amplifier Assembly Sets the target temperature of the heater wire according to the target outlet temperature and outputs a heated steering wheel control request signal to the steering wheel heater control assembly.
    Radio Receiver Assembly Outputs information that was set on the display screen of the multi-display to the air conditioning amplifier assembly.
    Remote Touch (Remote Operation Controller Assembly) Used to operate the display screen of the multi-display.
    Multi-display

    Used to set the control mode on the display screen.


    • Switches the target temperature (LO or HI) when in MANUAL mode.

    • Switches AUTO mode on and off.

    • Switches the Lexus Climate Concierge on and off.

  2. SYSTEM CONTROL


    1. MANUAL Mode


      1. When the control mode is set on the screen of the multi-display while the engine switch is on (IG), the steering wheel heater control assembly supplies an electric current to the heater wire according to signals from the air conditioning amplifier assembly. As a result, the heater wire is heated to heat the steering wheel.

      2. The steering wheel heater control assembly detects the temperature of the heater wire via the thermistor* and controls the amount of electric current supplied to the heater wire to maintain the steering wheel surface at the set temperature

        MANUAL Mode Set Temperature (Thermistor Detection Temperature)
        LO 38°C +/- 2°C
        HI 42°C +/- 2°C

        Tech Tips

        *: An element that uses a semiconductor whose electrical resistance changes significantly in response to slight changes in temperature (the resistance is high at normal temperatures, but it decreases as the temperature increases).

      3. When the heater wire temperature increases to approximately 55°C or higher, the thermostat* stops supplying electric current to the heater wire. When the heater wire temperature increases to approximately 40°C, the thermostat starts supplying electric current again.

        Tech Tips

        *: This is a temperature adjustment device which automatically controls a heat source by using a switch based on bimetal and shape-memory alloy.

    2. AUTO Mode


      1. When the engine switch is on (IG), the air conditioning amplifier assembly automatically determines the heated steering wheel system operation according to the target outlet temperature of the air conditioning system. The air conditioning amplifier assembly determines the target temperature of the heater wire according to the target outlet temperature and controls the supply of electric current to the heater wire in the steering wheel heater control assembly to maintain the target temperature.

  3. FAIL-SAFE


    1. When a system malfunction occurs, the steering wheel heater control assembly stops the supply of electric current to the heater wire to ensure safety in accordance with the fail-safe function. For details, refer to the Repair Manual.