PRE-CRASH SAFETY SYSTEM


  1. FUNCTION OF MAIN COMPONENTS

    Item Function
    Combination Meter 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.
    Multi-information Display Displays a warning message to inform or warn the driver of the system condition in accordance with signals from the seat belt control ECU or driving support ECU assembly.
    Master Warning Light Illuminates to warn the driver in accordance with signals from the seat belt control ECU or driving support ECU assembly.
    Buzzer Sounds to warn the driver in accordance with signals from the seat belt control ECU or driving support ECU assembly when the system is malfunctioning.
    Millimeter Wave Radar Sensor 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 Side)

    		 Buckle Switch Detects the condition (verifies if the belt is fastened) of the driver seat belt and transmits a signal to the airbag sensor assembly.

    Front Seat Inner Belt Assembly

    (for Passenger Side)

    		 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.
    Airbag Sensor Assembly Transmits the condition (fastened or unfastened) of the driver seat belt to the seat belt control ECU.
    Driving Support ECU Assembly Makes judgments on whether a collision is unavoidable based on the information received from the millimeter wave radar sensor. 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.
    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 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 Assembly Detects if the brake pedal is depressed and transmits a signal to the skid control ECU.
    Stop Light Control Relay* Receives a stop light turn on request signal from the skid control ECU, and turns on the stop lights.
    Speed Sensors 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 with Sensor Cable 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 Brake Cancel Switch* 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 Pre-crash Brake

  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. Controls on the pre-crash safety system area 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 (4 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 brake cancel switch.


      • 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.

      *: Models with Pre-crash Brake

  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.
      A004V9CE04

    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.
      A004V1TE03

    3. High Possibility of Collision or Unavoidable Collision (Models without Pre-crash Brake)

      (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, steering angle sensor, speed sensor and yawrate sensor.
      (2) The driving support ECU assembly transmits a BRAKE! warning display request signal to the combination meter assembly and a skid warning buzzer 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 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, 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.
      (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.
      (7) If no collision occurs, the seat belts and brake assist will return to their normal states.
      A004V1PE03

    4. High Possibility of Collision or Unavoidable Collision (Models with Pre-crash Brake)

      (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, steering angle sensor, speed sensor and yawrate sensor.
      (2) The driving support ECU assembly transmits a BRAKE! warning display request signal to the combination meter assembly and a skid warning buzzer 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 to warn the driver. At this time, the skid control ECU activates the 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, 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 booster pump assembly and brake actuator and operating the pre-crash brake, activates the stop light control relay to turn on the stop lights, and sounds the skid control buzzer to warn the driver.
      (7) If no collision occurs, the seat belts and the brake assist will return to their normal states.
      A004V8KE03

  4. FUNCTION


    1. Warning messages displayed in combination meter assembly and multi-information display


      1. The combination meter assembly uses the master warning light, PCS warning light, buzzer and multi-information display 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 assembly. Upon receiving this signal, the combination meter assembly indicates a warning on the multi-information display, operates the PCS warning light and sounds the skid control buzzer. Details are indicated below.

        When there is a high possibility of a collision
        Multi-information Display Master Warning Light PCS Warning Light Buzzer*
        BRAKE ! - Flashes sounds

        Tech Tips

        *: Skid control buzzer

      3. 2 types of warning messages are used for the pre-crash safety system, as described below. The pre-crash safety system will not operate when these messages appear in the combination meter assembly.

        Multi-information Display Detail Master Warning Light PCS Warning Light Buzzer DTC
        Check PCS System This message appears when the seat belt control ECU or driving support ECU assembly detects a system malfunction. Illuminates Flashes Sounds Once X
        PCS temporarily not available

        • This message appears when the seat belt control ECU determines the following conditions:


          • Dirty front millimeter wave radar sensor

          • Poor weather conditions

          • Overheated seat belt control ECU

        After these conditions have been resolved, the system will operate normally.

        		 - Turns On - -

        • X: Repair is required/DTCs are stored

        • -: Repair is not required/DTCs are not stored

  5. CONSTRUCTION


    1. Millimeter Wave Radar Sensor


      1. The millimeter wave radar sensor 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.

        A004V2JE03
        Text in Illustration
        *1 Millimeter Wave Radar Sensor - -
        *a Detection Distance: Approximately 150 m (490 ft.) *b Horizontal Angle: About 20°
        *c Vertical Angle: About 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 about 20° and a vertical angle of about 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 of higher frequencies as it approaches, and to be of lower frequencies at it recedes. This phenomenon is created because when an object is located far away, the radio waves are perceived at higher frequencies than those of the radio source.

        A004V3UE33

        Tech Tips

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

  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 detects a malfunction in the pre-crash safety system, it stores a 5 digit Diagnostic Trouble Code (DTC) in memory.