Accident avoidance system (VDIM) explained - GreenHybrid

stevenvillatoro · #1 (**permalink**) 06-25-2006, 01:52 PM

I found this informative post on edmunds.com, compiled by 'kdhspyder,' and thought it might be of interest to some:

The TCH has the next generation accident avoidance system that many of the Lexus's also have. It's acronym is VDIM. It's a more integrated approach to the 5 main active safety features; ABS, EBD, BA, VSC, TRAC ( alphabet soup ) and the electric steering.

ABS: It's well-known and standard in most vehicles now. It pumps the brakes electronically faster than a human can when there is a risk of the brakes locking up.

EBD: ( Electronic Brakeforce Distribution ) From the load on the vehicle ( passengers and cargo ) sensors determine how to balance the brake pressure in order to give the best braking performance. With just the driver in the vehicle on a straight stop most of the pressure would be directed to the front. With a full load the pressure would be directed more evenly front and back.

BA: ( Brake Assist ) By the manner in which one hits the brake pedal the computer senses whether this is a 'normal' stop or a 'panic' stop. In a 'panic' stop the full force of the brakes are applied even if the brake pedal isn't pushed all the way to the lowest point, a shorter-legged driver for example.

VSC: ( Vehicle Stability Control ) This is the most recent advancement in active accident avoidance systems which the IIHS and the EURO/NCAP are both advocating be the next safety feature to be made standard on all vehicles. The yaw sensors in the vehicle 'keep an eye out' for situations where the vehicle seems to be going in a direction other than where the driver intended. It commonly is explained as helping to minimize understeer and oversteer in order to keep the vehicle on track. This link from the European insurance institute is a great visual explanation:

Euro/NCAP Click on 'Recommendation' then 'See Stability Control in Action'

Essentially VSC senses when the vehicle seems out of control and will take the throttle away from the driver ( slow down even if your foot is on the gas pedal ) and apply the brakes selectively in order to bring the vehicle back into the intended direction. It will not keep a sleeping or drunk or inattentive driver from simply driving off the road.

TRAC: ( Traction Control ) It senses when there is a significant difference in the rotation of the wheels on one side of a vehicle as opposed to the other. When this difference is sensed the brakes are applied to slow the faster spinning wheel. Imagine if one side of your car was going 60 while the other was going 80.

All the foregoing are well-known throughout the world. All or some of these active safety features are on almost all vehicles now.

VDIM: ( Vehicle Dynamics Integratred Managment ) This is the Toyota/Lexus advancement that incorporates the electric steering into the equation. When an out of control situation is detected the steering is made harder ( retarded ) in the direction which will worsen the situation and made easier in the direction which will improve the situaiton.

This Lexus link gives a good explanation Lexus VDIM

An example:
On an icy/newly plowed right exit ramp off an Interstate with a sharp right turn, suddenly the back end of your vehicle is beginning to whip around out of control ( oversteer ). The yaw sensors in the VSC system sense loss of control ( not the intended dirction ). The vehicle is throttled down, more pressure is applied to the rear left brake more forcefully and steering to the right is hindered, which would exacerbate the out of control situation, while steering to the left is assisted ( into the direction of the skid ) to bring the vehicle back on course.