ABS/TCS/VDC

ABS (Anti Block System) was originally invented for airplane, because keeping weight balance in airplane is very hard because of long wing span if skidding happens at the tires during landing or taxing. Now, most of the vehicles are equipped with this ABS device and this helps quite a lot for safe driving.

 

Slip Ratio

When drivers pushed brake pedal, the pedal forces are converted into hydraulic forces and again it applied on the brake pad in the wheel. The optimal performance of brake is decided on how fast the vehicle can be stopped (stop time and distance), and again this stop distance is dependent on the friction coefficient between road surface and tire. By measurement we know that the relationship between friction coefficient and slip ratio in rotational direction and radial direction shows like the graph below.

 

 

 

Because the friction coefficient comes to the maximum value when the slip ratio is close to 20%, it is important to keep the slop ratio in this range to take the optimal performance of the brake system. Now, the question is how can we keep this optimal value of slip ratio by pumping brake pedal in a panic situation.

 

Pressure Modulation

When drier quickly and firmly applied the brakes and holds pedal down, the brakes not equipped with ABS will almost immediately lock the wheels. Then the vehicle slides rather than rolls to a stop. During this time the driver has big difficulties to control vehicle because it skids and almost out of control. The important thing is that the driver should release pedal if the wheel speed slip ration comes more than 20% and press again.  But this is hard to learn and even the brake system characteristic is different from car to car. Therefore, we have assigned this repetitive pressure application and release action to the device (ABS) which is composed of some electronic and hydraulic components.

 

 

 

TCS (Traction Control System)

Automotive engineers use the technology and hardware of ABS to control tire traction and vehicle stability. ABS is pumping and release pressure to stop the vehicle in an optimal manner, but for traction control, the system reduces the wheel speed by applying braking pressure if the wheel starts to spin. Of course it is not enough to reduce only the wheel speed, the torque from engine should be reduced at the same time by decreasing injected fuel amount or retarding ignition timing in case of gasoline engine.

 

VDC (Vehicle Dynamic Control)

This system is being called as several other names, now ESC (Electronic Stability Control) is the most commonly used name than VDC which is the very first name when Bosch has invented this system.

 

 

The fast moving brake system can also be used to keep the vehicle stand stable by applying braking force at one or more wheels independently. By doing this, this system can help prevent skid, swerves and rollover accidents. The most important sensor for this function is so-called “Yaw” sensor which can measure vehicle spin or swerves.  Based on the signal from this “yaw” sensor and wheel speed sensor the ESC control unit decides how much pressure should be applied on which wheel and how long.

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