Typical steering ratios

[MedievalMan]

As part of the knowledge I need for the torque limits for a hardware-in-the-loop simulation of an electric power steering system, I would like to know what typical steering ratios (ratio of how far you turn the steering wheel to how far the wheels turn) are for small-large sized sedan vehicles.

Intuitively from driving experience, I know that some cars have much different ratios than others.

From literature I've read so far, I've read that 50-100 Nm are typical maximums for road torque applied to the rack from the wheels (the counter torque increasing the higher degree of turn) (this is for small cars).

My question, then is

1) what amount of torque does this apply to the pinion shaft, which would depend on the steering ratio, from my understanding.

2) Are there any chapters of books that might be good reading on this matter? Or webpages/any other techincal reference for that matter.

Thanks in advance,

Matt Lawson

 

[GregLocock]

SWA/toe is typically between 10 and 20, on centre. Lock to lock is typically 800-1000 degrees, and typically gives around 35-40 degrees of toe.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MedievalMan]

I'm not sure what you mean exactly. Could you elaborate?

Thanks again,

Matt Lawson

 

[GregLocock]

elaborate what?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MedievalMan]

"SWA/toe is typically between 10 and 20, on centre. Lock to lock is typically 800-1000 degrees, and typically gives around 35-40 degrees of toe."

I take this to mean steering wheel angle / toe angle is typically between 10 and 20 degrees, on center.

I'm not sure how this relates to the torque on the pinion shaft.

Right now running Carsim, it seems to be in the 10-20 Nm range during typical driving conditions (road reaction torque on steering/pinion shaft), although previous work amplified this by a gear ratio of 16, though I can't find any reason why.

That doesn't seem right intuitively: Carsim already factors in the steering ratio, and 160-320 Nm of road reaction torque on the steering wheel shaft seems a bit high to me.

I apologize if my terminology/understanding is not up to par.

Thanks

Matt Lawson

 

[GregLocock]

You asked a question, I answered it exactly. Your lack of understanding is NOT my problem.

So, you asked for a ratio. I defined the ratio. The steering wheel angle divided by the change in toe is between 10 and 20, on centre. At full lock the road wheels attain a toe of 35-45 degrees, and the lock to lock SWA is typically 800-1000 degrees.

Your carsim results are completely ridiculous. I suggest you go and drive a car and make some estimates or measurements of your own. You could have answered your own question by 5 minutes work in the car park, hence my lack of patience.


The book you need is

http://www.amazon.com/gp/product/07...104-4241930-5757563?s=books&v=glance&n=283155

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

The load applied will be controlled by the driver.

The wheel will pull out of his grip if the load exceeds his strength.

In very fast manoeuvres the rate of change in SWA is also dependant on drivers strength to overcome inertia, self centring and friction in the system.

I agree with Greg re method. Turn the wheel, count the turns, convert to degrees. Measure resultant angle at wheels. Not exactly complicated.

Converting drivers maximum possible strength to force at any point in the system is simple high school physics and math. Safety factors and effect of dynamics is more complex I am sure. Someone with experience in the field may be prepared to offer advice in that regard. This might include the people who will be designing the front suspension of the car this steering box is going into.

Regards

eng-tips, by professional engineers for professional engineers
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[MedievalMan]

Thanks for the help guys.

Matt