PRE-CRASH SAFETY SYSTEM


  1. FUNCTION OF MAIN COMPONENTS

    Item Function
    Combination Meter Sub-assembly PCS Warning Light

    • Illuminates or flashes to warn the driver in accordance with signals from the seat belt control ECU or driving support ECU assembly.

    • Illuminates or flashes when the system is malfunctioning or temporarily disabled.
    Millimeter Wave Radar Sensor Assembly Radiates millimeter wave radar forward, uses the reflected millimeter waves for detecting the presence of a vehicle ahead, the vehicle-to-vehicle distance, and the relative speed, and then transmits this information to the driving support ECU assembly.
    Front Seat Outer Belt Assembly Seat Belt Motor Retracts the seat belt in accordance with signals received from the seat belt control ECU.
    Front Seat Inner Belt Assembly (for Driver) Buckle Switch Detects the condition (verifies if the belt is fastened) of the driver seat belt and transmits a signal to the seat belt control ECU.
    Front Seat Inner Belt Assembly (for Front Passenger) Buckle Switch Detects the condition (verifies if the belt is fastened) of the front passenger seat belt and transmits a signal to the seat belt control ECU.
    Driving Support ECU Assembly Makes judgments on whether a collision is possible based on the information received from the millimeter wave radar sensor assembly. It then outputs a seat belt operation signal and brake assist standby request signal and pre-crash brake request signal if required.
    Seat Belt Control ECU Receives a seat belt operation request signal from the driving support ECU assembly or skid control ECU and operates the seat belts.
    Headup Display Unit (Combination Meter Mirror ECU)* Displays a warning message on the windshield to inform or warn the driver of the system condition in accordance with signals from the driving support ECU assembly.
    Brake Booster Pump Assembly Receives an operation signal from the skid control ECU and generates hydraulic pressure for brake control.
    Brake Booster with Master Cylinder Assembly Master Cylinder Pressure Sensor Detects the master cylinder pressure and transmits a signal to the skid control ECU.
    Skid Control ECU

    • Receives a brake assist standby request signal from the driving support ECU assembly and switches the brake assist to standby mode. When a stop light switch signal is input, it activates the brake assist.

    • Receives a pre-crash brake request signal from the driving support ECU assembly, and then applies the brakes.

    • Determines if the brakes have been applied suddenly through signals received from the master cylinder pressure sensor, and outputs a seat belt operation signal to the seat belt control ECU.

    • Determines that the vehicle is out of control or that the brakes have been applied and outputs a seat belt operation signal to the seat belt control ECU.

    • Transmits vehicle speed signals to the driving support ECU assembly.
    Stop Light Switch Detects if the brake pedal is depressed and transmits a signal to the skid control ECU.
    Stop Light Control ECU Assembly Receives a stop light turn on request signal from the skid control ECU, and turns on the stop lights.
    Speed Sensor Detects speed of each wheel and transmits the signals to the skid control ECU.
    Yawrate Sensor Detects the yaw rate and lateral/longitudinal deceleration of the vehicle and transmits the signal to the skid control ECU and the driving support ECU assembly.

    Spiral Cable with Sensor Sub-assembly

    - Steering Angle Sensor

    		 Detects the angle and direction of steering and transmits a signal to the skid control ECU and the driving support ECU assembly.
    Pre-crash System Cancel Switch Assembly Disables the pre-crash brake operation when the switch is turned on. The PCS warning light illuminates to show that the pre-crash brake operation is disabled.
    Skid Control Buzzer Assembly Sounds to warn the driver in accordance with signals from the skid control ECU.

    *: Models with Headup Display

  2. OPERATING CONDITION


    1. Operating Conditions

      Operating Conditions

      When the driving support ECU assembly determines the high possibility of a collision, or an unavoidable collision with an obstacle in front of the vehicle.

      The pre-crash seat belt also operates under the following conditions:


      • When the brakes are suddenly applied.


      • When the system determines a loss of vehicle control.

    2. The following pre-crash safety system controls are performed under the following conditions.

      Control Condition
      Pre-crash Seat Belt (Situation 1)

      • Front seat belt is buckled.


      • Vehicle speed is approximately 30 km/h (19 mph) or above.


      • Brakes are suddenly applied, or front or rear wheel skid tendency is detected.
      Pre-crash Seat Belt (Situation 2)

      • Front seat belt is buckled.


      • Vehicle speed is approximately 5 km/h (3 mph) or above.


      • Oncoming vehicle or an obstacle relative speed is approximately 30 km/h (19 mph) or above.
      Pre-crash Brake Assist

      • Vehicle speed is approximately 30 km/h (19 mph) or above.


      • Oncoming vehicle or an obstacle relative speed is approximately 30 km/h (19 mph) or above.


      • Brake pedal is depressed.
      Pre-crash Brake

      • Pre-crash brake operation has not been disabled using pre-crash system cancel switch assembly.


      • Vehicle speed is approximately 15 km/h (10 mph) or above.


      • Oncoming vehicle or an obstacle relative speed is approximately 15 km/h (10 mph) or above.

  3. SYSTEM CONTROL


    1. Loss of Vehicle Control

      (1) While the vehicle is traveling at approximately 30 km/h (19 mph) or more, the skid control ECU determines if skid recovery will be difficult based on the signals from the steering angle sensor, yawrate sensor and speed sensors.
      (2) The skid control ECU sends a seat belt operation request signal to the seat belt control ECU.
      (3) The seat belt control ECU determines the seat belt motor operating conditions based on this signal and seat belt buckle switch signals. Then, it retracts the slack in the seat belts by operating the seat belt motors.
      (4) The seat belts return to a normal state when the relevant conditions of the vehicle have stabilized.
      A00512ME02

    2. Sudden Braking

      (1) While the vehicle is traveling at approximately 30 km/h (19 mph) or more, the skid control ECU can determine a sudden braking condition based on the signals from the master cylinder pressure sensor, stop light switch and speed sensors.
      (2) At this time, the skid control ECU outputs a seat belt operation request signal to the seat belt control ECU.
      (3) The seat belt control ECU determines the seat belt motor operating conditions based on this signal and seat belt buckle switch signals. Then, it retracts the slack in the seat belts by operating the seat belt motors.
      (4) The seat belts return to normal when the vehicle stops and the brake pedal is released.
      A0051B4E02

    3. High Possibility of Collision or Unavoidable Collision

      (1) The driving support ECU assembly determines that the possibility of a collision is high based on the signals received from the millimeter wave radar sensor assembly, steering angle sensor, speed sensor and yawrate sensor.
      (2) The driving support ECU assembly transmits a PCS warning display request signal to the combination meter sub-assembly and a skid control buzzer assembly request signal to the skid control ECU.
      (3) The driving support ECU assembly outputs a pre-crash brake assist request signal to the skid control ECU. Upon receiving this signal, the skid control ECU switches the brake assist to the standby condition and sounds the skid control buzzer assembly to warn the driver. At this time, the skid control ECU activates pre-crash brake assist when the brake pedal is depressed by the driver.
      (4) The driving support ECU assembly determines that an unavoidable collision condition exists based on the signals received from the millimeter wave radar sensor assembly, speed sensor, steering angle sensor and yawrate sensor.
      (5) The driving support ECU assembly outputs a seat belt operation request signal to the seat belt control ECU and a pre-crash brake request signal to the skid control ECU.
      (6) The seat belt control ECU determines the seat belt motor operation condition based on this signal and the seat belt buckle switch signal, and retracts the slack in the seat belts by operating the seat belt motors. At the same time, the skid control ECU decreases the vehicle speed by activating the brake actuator and brake booster pump assembly to perform a pre-crash brake operation, activates the stop light control relay to turn on the stop lights, and sounds the skid control buzzer assembly to warn the driver.
      (7) If no collision occurs, the seat belts and brake assist will return to their normal states.
      A0050R6E02

  4. FUNCTION


    1. Warning displayed in combination meter sub-assembly


      1. The combination meter sub-assembly uses the PCS warning light and buzzer to provide the driver with pre-crash safety system warnings and indications.

      2. If the driving support ECU assembly determines that the possibility of a collision is high, it sends a signal to the combination meter sub-assembly. Upon receiving this signal, the combination meter sub-assembly operates the PCS warning light.

  5. CONSTRUCTION


    1. Millimeter Wave Radar Sensor Assembly


      1. The millimeter wave radar sensor assembly consists of a millimeter wave radar circuit, signal processing circuit and CPU.

      2. The millimeter wave radar outputs waves when the vehicle speed is above 0 km/h (0 mph), and not when the vehicle speed is at 0 km/h (0 mph). The millimeter wave radar uses frequencies in the 76 GHz band.

      3. The reception antennas receive the millimeter wave radar waves that have been reflected.

      4. The signal processing circuit detects the distance, relative speed, and the direction of the object by generating millimeter wave radar waves and calculating the signals received by the reception antennas. Then, it transmits this information to the driving support ECU assembly.

        A00513JE01
        Text in Illustration
        *1 Millimeter Wave Radar Sensor Assembly - -
        *a Detection Distance: Approximately 150 m (490 ft.) *b Horizontal Angle: Approximately 20°
        *c Vertical Angle: Approximately 8° *d Signal Processing Circuit
        *e Millimeter Wave Radar Circuit - -

      5. The distance to the object, azimuth and relative speed are calculated from the information that is provided by the reflection millimeter wave radar as described below.

        Item Calculation Method
        Distance Calculated from the length of time that has elapsed from the time the waves of the millimeter wave radar have been emitted, until the waves reflected by the millimeter wave radar are received. The detection distance is approximately 150 m (490 ft.).
        Azimuth Calculated from the angle of the waves reflected by the millimeter wave radar that have been received. The detection angle has a horizontal angle of approximately 20° and a vertical angle of approximately 8°.
        Relative Speed Calculated by utilizing the changes (Doppler effect*) that occur in the frequencies of the reflected millimeter wave radar waves.

        Tech Tips

        *: The Doppler effect causes the observer to perceive the radio waves emitted by a moving object to be a higher frequency as it approaches, and to be a lower frequency as it recedes. This phenomenon is created because when an object is located far away, the radio waves are perceived at higher frequency than those of the radio source.

        A0050ZXE34

        Tech Tips


        • Millimeter wave radar uses an extremely high frequency band between 30 GHz and 300 GHz, with an extremely short wavelength between 1 and 10 mm (0.04 to 0.40 in.) in a vacuum. The millimeter wave radar sensor of the pre-crash safety system uses frequencies in the 76 GHz band.

        • Millimeter wave radar is less affected by weather conditions such as rain, fog, or snow, and provides excellent characteristics for recognizing objects. Therefore, it is well suited to the pre-crash safety system and the dynamic radar cruise control system.

        • An SST is used if radar axis adjustment is needed. For details, refer to the Repair Manual.

        A0050QJE34

    2. Warning Indication


      1. The combination meter assembly uses the headup display, PCS warning light and buzzer to provide the driver with pre-crash safety system warnings and indications.

      2. If the driving support ECU assembly determines that there is a possibility of a collision, it sends a signal to the combination meter assembly. Upon receiving this signal, the combination meter assembly indicates a warning using the headup display, PCS warning light and skid control buzzer assembly. Details are indicated below.

        When there is a high possibility of a collision
        Headup Display PCS Warning Light Skid Control Buzzer Assembly
        A0051D3 Flashes Sounds Continuously
        When there is a high possibility of a collision
        Headup Display PCS Warning Light Skid Control Buzzer Assembly
        A0050VT Flashes Sounds Continuously

      3. When the system is not available, the following warning occurs to warn the driver.

        When a system malfunction is detected
        Warning Detail Master Warning Light PCS Warning Light Buzzer DTC
        Check PCS system The seat belt control ECU or the driving support ECU assembly detects a system malfunction. Illuminates Flashes Sounds once

        Repair is required

        DTCs are stored
        PCS system is not currently available

        • The seat belt control ECU or the driving support ECU assembly determines any of the following conditions exists:


          • Dirty millimeter wave radar sensor assembly

          • Poor weather condition

          • Overheated seat belt control ECU

        After the condition has been resolved, the system will operate normally.

        		 - Illuminates - -

  6. DIAGNOSIS


    1. Initial Check


      1. The seat belt control ECU performs an initial check on the system for approximately 3 seconds after the power switch has been turned on (IG).

    2. Monitor Function


      1. After completing the initial check, the pre-crash safety system becomes ready to operate. During this time, the seat belt control ECU periodically monitors the system for any malfunctions.

    3. Diagnostic Trouble Code (DTC)


      1. If the seat belt control ECU or the driving support ECU assembly detects a malfunction in the pre-crash safety system, it stores a 5 digit Diagnostic Trouble Code (DTC) in memory.