What is CMS?CMS is the worlds first Collision MitigationBrake System (CMS). The technology predictsrear-end collisions and assists brake operation toreduce the impact.CMS anticipates a collision based on drivingconditions, distance to the vehicle ahead andrelative speeds. It then uses visual and audiowarnings to prompt the driver to take preventativeaction and also initiates braking if the driver failsto respond to the warnings.
How it Works?First, the radar measures the distance between the car andother vehicles up to 100 meters ahead and any differencesin speed, and an onboard computer judges the risk of acollision based on this information and on data about thecourse 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 firstwarning stage, aimed at alerting the driver to the dangerand 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.
CMS configuration:Millimeter-wave radar: Detects vehicles within a rangeof about 100 meters ahead, in a 16-degree arc.Sensors: The system determines driving conditions using arange of sensors that detect factors such as yaw rate,steering angle, wheel speed, and brake pressure.CMS Electronic Control Unit (ECU): Based on distanceto the vehicle ahead and relative speed obtained from radarinformation, the ECU calculates the likelihood of acollision, and warns the driver, and in some cases activatesthe braking function.
E-Pretensioner ECU: Sends instructions to the motorizedE-Pretensioner to retract the seatbelt, based on brakinginstruction signals from the CMS ECU and electronicallycontrolled brake assist signals.E-Pretensioner: Retracts the seatbelt using an internalmotor, based on instructions from the E-Pretensioner ECU.Used in combination with conventional pretensioners.Meter unit: Receives signals from the CMS ECU, andwarns the driver of potential danger using a buzzer and avisual warning.
“Figure: Autoweb.com.au, CAS 2003”
CMS Warning DevicesVisual head-up displays: warnings are displayed on thewindshield in the drivers field of view.Audio/Voice signals: auditory signals appear to be lessintrusive on driving tasks.
CMS Collision Avoidance Maneuvers:Headway distance control: the system warns the driverwhenever his/her car is following the leading car toocloselyHazard warning: the system warns the driver of an objectwithin its projected path, so that the driver has sufficienttime to avoid a crash.Automatic vehicle control: the system controls thevehicles brakes and steering wheel
Precise breaks Actuator Systems depend a lot on sensors:Sensors fulfill the tasks of headway control andobstacle detection, which are the basis of CollisionAvoidance Systems (CAS) Sensing.
Table 2 Sensor Devices Measures of Performance Sens ing D irectio nal R es po ns e Sens o r R es o lutio n C o s t Size R ange ity Time speed of 30 mm. Ultrasonics 10 m. (max) 10 mm. 30 deg. (min) sound $15 diameter Passive 20 mm. Infrared 10 m. (max) poor 90 deg. 1 sec. under $10 square Laser radar 100 m. (max), fast (10 50 mm. x 100 (lidar) 0.5 m. (min) 1 mm. (min) 1 deg. msec.) over $50 mm. 2 deg. or 250 mm. x 150 FMCW Radar 150 m. 10 mm. wider fast (1 msec) over $200 mm. Impulse 250 mm. x 100 Radar 50 m. (max) 10 mm. 25 deg. Fast (1 msec) over $100 mm. 90 deg. Or Capacitive 2 m. (max) 10 mm. wider fast (1 msec) $1 small Vision 40 mm. x 100 Systems 100 m. poor good 100 msec. Over $200 mm. Source: Stobart and Upton, 1995
Indicators:Sensing range: the maximum range over which thetechnique can be usedResolution: the relative change in distance that can bemeasuredDirectionality: the width of the beam over which thesensor is sensitiveResponse time: how quickly the sensor can respond to achange in distance
ConclusionAutomatic braking systems can detect an obstacle andbring the car to a complete halt just before impact. Thetechnology has reached the level where the systems caneven detect the speed of a vehicle in front, compare it withthe speed of the users car, and stop the car to avoid anaccident. Honda and Toyota are applying and testing theseAutomatic braking systems nowadays and will continueimproving this type of technology.