Puzzled

[Tony]

We are lead to believe that ABS and Traction control are dependant on the rolling radius of the wheel, and the ABS ring indicates a potential hazard dependant on the pules electronically, so i wonder this..

 

 

 

Since during any turn each wheels rotates at a different speeds through their axis how does the TC or ABS know what's happening unless you brake harshly on that turn.

 

Also did you know that on a Tractor Trailer during a 45 degree turn the rotation forces the rear inner wheels to rotate backwards

[scorps]

Also did you know that on a Tractor Trailer during a 45 degree turn the rotation forces the rear inner wheels to rotate backwards

 

Rear steering axles are used to cancel this problem out.

[Tony]

Also did you know that on a Tractor Trailer during a 45 degree turn the rotation forces the rear inner wheels to rotate backwards

 

Rear steering axles are used to cancel this problem out.

They do now but the diff still rotates the inner to some extent?..Admittedly the scrub is reduced but nevertheless interesting to watch especially if the tyre is on your foot

[IanF]

We are lead to believe that ABS and Traction control are dependant on the rolling radius of the wheel, and the ABS ring indicates a potential hazard dependant on the pules electronically, so i wonder this..

 

 

 

Since during any turn each wheels rotates at a different speeds through their axis how does the TC or ABS know what's happening unless you brake harshly on that turn.

 

 

Isn't the target slip for both ABS and Traction control about 20%?

 

If your vehicles track is 1.4 metres then this would imply that the turning circle has to be less than 16metres before either the ABS or the TC would consider the "slip" needs correcting.

 

I've just realized that I don't know what the minimum turning circle is for my car! I wouldn't be surprised if it was similar to 16m. Which means that even on full lock the TC and ABS systems wont be fooled. Not that it has TC.

 

I think that the ABS system on my car doesn't operate below 5mph but I'm not certain of this. If this is common practice then this is another strategy that the control unit has to avoid operating during manoevering.

[Tony]

We are lead to believe that ABS and Traction control are dependant on the rolling radius of the wheel, and the ABS ring indicates a potential hazard dependant on the pules electronically, so i wonder this..

 

 

 

Since during any turn each wheels rotates at a different speeds through their axis how does the TC or ABS know what's happening unless you brake harshly on that turn.

 

 

Isn't the target slip for both ABS and Traction control about 20%?

 

If your vehicles track is 1.4 metres then this would imply that the turning circle has to be less than 16metres before either the ABS or the TC would consider the "slip" needs correcting.

 

I've just realized that I don't know what the minimum turning circle is for my car! I wouldn't be surprised if it was similar to 16m. Which means that even on full lock the TC and ABS systems wont be fooled. Not that it has TC.

 

I think that the ABS system on my car doesn't operate below 5mph but I'm not certain of this. If this is common practice then this is another strategy that the control unit has to avoid operating during manoevering.

20% seems generous.. i will check.. whatever your theory satisfies. The image i posted can you see something Geometrically wrong with it

[Mark H.]

My cars turning circle is 9.8M iirc, although it has a little help from the rear .

[Tony]

My cars turning circle is 9.8M iirc, although it has a little help from the rear .

 

You are to close to deny the answer... The problem with the image is the destination displayed for the lock angle of the inner wheel.

 

By degrees the lock angle will always conclude at the rear thrust centre. this is the Ackerman pivotal axis.

 

Even if the thrust position is incorrect the steering axis must follow the same centre of rotation.... this by measurement displays handling issues, like steering centre and over/under-steer.

[Tony]

We are lead to believe that ABS and Traction control are dependant on the rolling radius of the wheel, and the ABS ring indicates a potential hazard dependant on the pules electronically, so i wonder this..

 

 

 

Since during any turn each wheels rotates at a different speeds through their axis how does the TC or ABS know what's happening unless you brake harshly on that turn.

 

 

Isn't the target slip for both ABS and Traction control about 20%?

 

If your vehicles track is 1.4 metres then this would imply that the turning circle has to be less than 16metres before either the ABS or the TC would consider the "slip" needs correcting.

 

I've just realized that I don't know what the minimum turning circle is for my car! I wouldn't be surprised if it was similar to 16m. Which means that even on full lock the TC and ABS systems wont be fooled. Not that it has TC.

 

I think that the ABS system on my car doesn't operate below 5mph but I'm not certain of this. If this is common practice then this is another strategy that the control unit has to avoid operating during manoevering.

Bump:

The 'slip' i assume we are talking pneumatic and 'brake away' forces?

[IanF]

Bump:

The 'slip' i assume we are talking pneumatic and 'brake away' forces?

 

 

slip ratio = (speed of roadwheel/ vehicle speed) -1.

 

+ve slip = accelerating. -ve slip = decelerating.

 

 

I found a reference that indicates that ABS systems work by calculating the rate of change of wheel speed. If this is the case, then ABS wont operate under the rolling turn in the first post, as this is a steady state condition.

 

Using rate of change of wheel speed would make my earlier statement that ABS has a target slip as part of its control strategy incorrect. There is an optimum slip for both braking and accelerating but the ABS doesn't have to care about optimum slip to function. The same isn't true for TCS though. The book indicates that Traction Control is more complex than ABS and that the control system has to adapt its target slip values to different road conditions and to allow for the negative effect that slip has on cornering. (negative unless your aim is drifting that is). One of the strategies used by the TCS designers to cope with different raod conditions is a driver selectable off switch LOL.

 

 

[bTW How do I post pictures? I could then post the graph showing how friction varies with slip from the book]

 

reference : An introduction to modern vehicle design editor Julian Happian-smith. chapter 11: control systems in automobiles. graphs taken from Chowanietx and Jurgen 1995)

[Tony]

Bump:

The 'slip' i assume we are talking pneumatic and 'brake away' forces?

 

 

slip ratio = (speed of roadwheel/ vehicle speed) -1.

 

+ve slip = accelerating. -ve slip = decelerating.

 

 

I found a reference that indicates that ABS systems work by calculating the rate of change of wheel speed. If this is the case, then ABS wont operate under the rolling turn in the first post, as this is a steady state condition.

 

Using rate of change of wheel speed would make my earlier statement that ABS has a target slip as part of its control strategy incorrect. There is an optimum slip for both braking and accelerating but the ABS doesn't have to care about optimum slip to function. The same isn't true for TCS though. The book indicates that Traction Control is more complex than ABS and that the control system has to adapt its target slip values to different road conditions and to allow for the negative effect that slip has on cornering. (negative unless your aim is drifting that is). One of the strategies used by the TCS designers to cope with different raod conditions is a driver selectable off switch LOL.

 

 

[bTW How do I post pictures? I could then post the graph showing how friction varies with slip from the book]

 

reference : An introduction to modern vehicle design editor Julian Happian-smith. chapter 11: control systems in automobiles. graphs taken from Chowanietx and Jurgen 1995)

 

Excellent information..... The picture posting issue is temporarily suspended due to malicious coding targeting many forums, Scarface the (Boss) is addressing this as we speak.