What is CMS? How it works System Configuration Warning Devices Collision Avoidance Maneuvers Conclusions

Honda Motor: Science & Education. Trends in Japan 2003

Autoweb.com.au: Honda Develops New Collision Avoidance Safety System. 2003

Francois Granet, Rosella Picado, Lauren Smith: Longitudinal Avoidance. 2003

CMS is the world's first Collision Mitigation Brake System (CMS). The technology predicts rear-end collisions and assists brake operation to reduce the impact.

CMS anticipates a collision based on driving conditions, distance to the vehicle ahead and relative speeds. It then uses visual and audio warnings to prompt the driver to take preventative action and also initiates braking if the driver fails to respond to the warnings.

First, the radar measures the distance between the car and other vehicles up to 100 meters ahead and any differences in speed, and an onboard computer judges the risk of a collision based on this information and on data about the course of the car.

Then if the system judges that there is a risk of a crash, such as when the car gets too close to the vehicle in front, it alerts the driver by sounding an alarm and lighting up a “BRAKE” warning on the dashboard. This is the first warning stage, aimed at alerting the driver to the danger and encouraging the driver to slow down.

The system works in conjunction with the "E-Pretensioner" seatbelt retraction system. If the car continues to get closer to the other vehicle and the computer decides that it will be hard to avoid a collision, it tightens the seatbelt more firmly and applies the brakes forcibly and hard.

The CMS has three staged modes:

An audible warning, An audible warning, light braking and light seat-belt

retraction. An audible warning, strong braking and strong seat-belt

retraction.

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, the ECU calculates the likelihood of a collision, and warns the driver, and in some cases activates the braking function.

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.

“Figure: Autoweb.com.au, CAS 2003”

Visual head-up displays: warnings are displayed on the windshield in the driver's field of view.

Audio/Voice signals: auditory signals appear to be less intrusive on driving tasks.

Headway distance control: the system warns the driver whenever his/her car is following the leading car too closely

Hazard warning: the system warns the driver of an object within its projected path, so that the driver has sufficient time to avoid a crash.

Automatic vehicle control: the system controls the vehicle's brakes and steering wheel

Sensors fulfill the tasks of headway control and obstacle detection, which are the basis of Collision Avoidance Systems (CAS) Sensing.

SensorSensing Range 

Resolution Directional

ity Response

Time Cost  Size 

Ultrasonics  10 m. (max)  10 mm.  30 deg. (min) speed of sound  $15 

30 mm. diameter 

Passive Infrared  10 m. (max)  poor  90 deg.  1 sec.  under $10 

20 mm. square 

Laser radar (lidar) 

100 m. (max), 0.5 m. (min)  1 mm. (min)  1 deg. 

fast (10 msec.)  over $50 

50 mm. x 100 mm. 

FMCW Radar  150 m.  10 mm. 2 deg. or wider  fast (1 msec)  over $200 

250 mm. x 150 mm. 

Impulse Radar  50 m. (max)  10 mm.  25 deg.  Fast (1 msec)  over $100 

250 mm. x 100 mm. 

Capacitive  2 m. (max)  10 mm. 90 deg. Or

wider  fast (1 msec)  $1  small Vision Systems  100 m.  poor  good  100 msec.  Over $200 

40 mm. x 100 mm. 

Table 2 Sensor Devices' Measures of Performance

Source: Stobart and Upton, 1995

Sensing range: the maximum range over which the

technique can be used  Resolution: the relative change in distance that can be

measured  Directionality: the width of the beam over which the

sensor is sensitive  Response time: how quickly the sensor can respond to a

change in distance 

Automatic braking systems can detect an obstacle and bring the car to a complete halt just before impact. The technology has reached the level where the systems can even detect the speed of a vehicle in front, compare it with the speed of the user's car, and stop the car to avoid an accident. Honda and Toyota are applying and testing these Automatic braking systems nowadays and will continue improving this type of technology.