Off Road Traction Control

[dewy721]

Sure thing. No problem.

The overall concept of ABS (Or even ABS w/traction control) is pretty simple.

The MICRO-CONTROLLER that makes up the 'brain' of the ABS/TC system performs a really simple task.

Logic examples:
Rudimentary ABS(only) logic.

• Compare frequency of each wheel.


• If any ONE wheel frequency reads 10% less than the other wheels; A wheel has locked up! Apply GLOBAL brake modulator valve. (ie. pump da brakes!

Basic ABS+TC logic.

• Compare frequency of each wheel.


• If any ONE wheel frequency reads 10% LESS than the fastest wheel; A wheel has locked up! Apply GLOBAL brake modulator valve.


• If any ONE wheel freq. reads 10% GREATER than the slowest wheel; A wheel spin has occurred! Apply TC (aka. throttle limiter).

More advanced systems have stuff like:

• Front/Rear modulator valves, very common in pickup trucks.


• Independent modulator valves, sport/luxury cars.


• Wheel speeds are averaged instead of absolute measurements. ie. Cadillac.


• Steering angle + skid + out-of-control = engine deration + intelligent brake modulation to re-orient vehicle to road.  ie. Cadillac.


• Multi-stage or even pwm'd engine deration. ie. Various supercars.


• Active TC/Steer angle torque steering. ie.Think top tier rally cars that have a ballistic guidance TC.


• ABS/TC + ABS + ABS + ABS... system linking. ie. Combination Tractor/Trailer(s) or 'Road Trains'.


• ABS/TC networks with sequential braking. ie. High-speed rail transit, some modern freight trains.

I think that's about it. (As far as I know of that is.)

[jetboy]

Just came across this thread looking for something else.  Wanted to throw out a comment to make sure you're aware that this will never provide similar traction to a real mechanical locking differential.

The reason for this is because of the significant difference between static and kinetic friction.  With a mechanical locking diff. both axles (left and right side) spin at exactly the same speed.  This means the tire contact with the surface is the same and before you begin to slip you will reach maximum static friction on both surfaces even though one side may only be 50% of the force of the other.  A slip sensing system like all electronic systems requires one tire to break static friction before the system can identify where to apply the brake.  This means that before the system can even generate a signal to operate, you've already lost a significant portion of your available force from the tire/surface interface.   

To give an example, lets say you are on a surface that has a static friction coefficient of 10 units and a kinetic friction coefficient of 1 unit on one side and 20 and 5 on the other. (a 10:1 ratio isn't unusual - think snow for example). We'll ignore the weight on each side and just consider it 1 unit.  With a full locking differential you could reach the full 20 plus the 10 in static - 30 units of fwd force.  With your system at best you'll reach the 10 unit of forward force per side and the first tire will spin after reaching the limit.  Then, unless your system can actually perfectly match wheel speed, you will get - at most - 21 units of forward force.  With an open diff you'd max out at something like 20 units, but once you slip that would drop to 1 unit of force.   So clearly traction control offers a benefit. 

It should simply be recognized before you start this that you will not be building something as good as a full mechanical locking differential.

Good luck with the project!

[robotteck]

I do agree, it will not be as good as a locking differential. The vehicle we be utilizing this system in a <5 mph range, so I proposed the traction control would have time to interact with the loss of traction. Also, I have further ideas, like the ability to brake one tire at a time to help position or spin the vehicle on a trail.

Instead of controlling the ABS, I saw these hydraulic eBrakes, or turning brakes that could be actuated for controlling the brakes while not interfering with any existing system.

Thanks for the input.

[jetboy]

I think it's a very interesting project.  Just commented because I wanted to make sure you weren't thinking this was going to provide similar function for less $.  A really basic locker can be had for around $200 and a Toyota E-locker can be had for around $400 plus some retrofit time and a bit of wiring, and I'm not sure you can build something for less.  But I'm all for fun projects and trying new things.

I think the hydraulic brake boosters would be a better option.  I'd suspect that the e-brake mechanism would simply be too slow to be of much use.  Nearly instantaneous operation can help stop you from losing whatever momentum you have at the time.   So the faster the better.