Honda Develops World's First 'Collision Mitigation Brake System'(CMS) for Predicting Rear-end Collisions and Controlling Brake Operations

May 20, 2003, Japan


Tokyo, May 20, 2003 - Honda Motor Co., Ltd., announced today it has developed the world's first Collision Mitigation Brake System (CMS), which predicts rear-end collisions and assists brake operation to reduce impact on occupants and vehicle damage. This system determines the likelihood of a collision based on driving conditions, distance to the vehicle ahead, and relative speeds, and uses visual and audio warnings to prompt the driver to take preventative action. It can also initiate braking to reduce the vehicle's speed. The new system will be installed in the new Inspire scheduled for release in June of this year, in combination with the "E-Pretensioner," which retracts the seatbelt in anticipation of impact. 

The CMS and E-Pretensioner use a millimeter-wave radar to detect vehicles ahead within a range of 100 meters, and then calculate the distance between the vehicles, the relative vehicle speeds, and the anticipated vehicle path to determine the likelihood of a collision. If the system determines that a collision is likely, it sounds a buzzer and provides a tactile warning, tightening the seatbelt to prompt the driver to take preventative action. The system also incorporates a number of functions to reduce impact on occupants in the event an impact is unavoidable, including a brake assist function that compensates for insufficient pedal pressure to reduce the speed of impact and seatbelt control that increases seatbelt tension to hold the driver more securely in place. 

Honda considers safety as one of the most crucial issues automakers face, and as such has long been active in the fields of driver safety education, active safety (preventing collisions), and passive safety (minimizing injury in the event of a collision). In addition, Honda has been promoting research and development of 'Honda Pre-crash Safety Technologies,' which are designed to predict collisions and minimize impacts. CMS and the E-Pretensioner, which warn the driver of impending collisions and reduce impact when collisions are unavoidable, represent the first stage in the practical application of these technologies.

Outline of CMS and E-Pretensioner Operations

  • 1.Primary warning
    When there is a risk of collision with the vehicle ahead or if the distance between the vehicles has become too short, an alarm sounds, and the message "BRAKE" appears on the multi-information display in the instrument panel, prompting the driver to take preventative action.
  • 2.Secondary warning
    If the distance between the two vehicles continues to diminish, CMS applies light braking, and the E-Pretensioner retracts the seatbelt gently two or three times, providing the driver with a tactile warning. At this point, if the driver applies the brakes, the system interprets this action as emergency braking, and activates the brake assist function to reduce impact speed.
  • 3.Collision damage reduction
    If the system determines that a collision is unavoidable, the E-Pretensioner retracts the seatbelt with enough force to compensate for seatbelt slack or baggy clothing, providing even more effective driver retention than conventional seatbelt pretensioners, which only begin to operate once the collision has occurred. The CMS also activates the brakes forcefully to further reduce the speed of impact. The E-Pretensioner is designed to operate whenever the driver brakes suddenly and the brake assist functions, tightening the seatbelt to secure the driver even if the CMS has not prediced a collision.

CMS & E-Pretensioner System Configuration

  • Millimeter-wave radar
    Detects vehicles within a range of about 100 meters ahead, in a 16-degree arc.
  • Sensors
    The system determines driving conditions using a range of sensors that detect factors such as yaw rate, steering angle, wheel speed, and brake pressure.
  • CMS Electronic Control Unit (ECU)
    Based on distance to the vehicle ahead and relative speed obtained from radar information, and on the anticipated vehicle path as determined based on sensor information, the ECU calculates the likelihood of a collision, and warns the driver, and in some cases activates the braking function. The ECU exchanges information as required with the E-Pretensioner, the Variable Signal Analyzer (VSA) and the Meter Unit (see below).
  • VSA-ECU integrated hydraulic unit
    Receives information from the various sensors, and sends this information to the CMS ECU and other control units. Also controls the brake hydraulic unit to activate the brakes based on instructions from the CMS ECU.
  • E-Pretensioner ECU
    Sends instructions to the motorized E-Pretensioner to retract the seatbelt, based on braking instruction signals from the CMS ECU and electronically controlled brake assist signals.
  • E-Pretensioner
    Retracts the seatbelt using an internal motor, based on instructions from the E-Pretensioner ECU. Used in combination with conventional pretensioners.
  • Meter unit 
    Receives signals from the CMS ECU, and warns the driver of potential danger using a buzzer and a visual warning 
CMS & E-Pretensioner System Operation
CMS & E-Pretensioner System Overview