Deceleration levels of vehicle during uphill/downhill braking 2

[elogesh]

Hi,

During downhill braking/uphill braking, as per the mathematical calculation, depending upon the slope angle, the deceleration will decrease of increase as sin(theta) component of vehicle weight.


Is there a mechanism which will ensure the max. deceleration level of vehicle in downhill/uphill braking as it is in plain road!!

Thanks,
Elongo

 

[SuperSalad]

I would suspect tire traction and road interface to be your limiting factor. You can always just stop the wheels from spinning.

Andrew H.

http://www.mototribology.com

 

[Compositepro]

That is what traction control is for.

 

[MikeHalloran]

Elongo, all of the above answers are absolutely correct.

I suspect that none of them actually answers the question you intended to ask.

But you have gathered a knowledgeable crowd, who probably could be a lot more helpful if you would expand a bit on what, exactly, you are trying to figure out.

We cannot see what is right in front of you, so it's up to you to paint an illuminative word picture of your problem.

Do not be afraid to use more words, or to attach or embed an illustration or photograph.


Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Achieving Equal stopping distance when going downhill as on the level?

If available tire traction on the hill and the level is equal, I don't think so.

 

[BrianPetersen]

If the slope is steep enough and slippery enough, the vehicle will accelerate downhill!

https://www.youtube.com/watch?v=0BhhsEuYXZQ

 

[LionelHutz]

What Tmoose posted - you'll never have the same braking distance going downhill as level ground with the same traction.

Uphill is a different story and it should be fairly easy to achieve an even better braking distance than level ground with the same traction.

 

[Lou Scannon]

No guesswork about it, it's simple Newtonian physics. The acceleration of gravity times the sine of the slope (0 degrees being horizontal) is superimposed on the braking deceleration going uphill, and subtracted from the braking deceleration going downhill. Meanwhile, the normal force between the tires and the road is multiplied by the cosine of the slope, so the available traction is falling off sharply as the slope increases beyond say, 30 degrees. Also to be considered with extreme slopes is the height of the vehicle's centre of gravity above the vehicle's footprint, as weight transfer will become a significant factor. Eventually, the line of action of the C of G will fall outside the wheelbase and the vehicle will lift the front or rear wheel(s), depending on the case, and may start to somersault, downhill, of course.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[GregLocock]

Perhaps somebody with an AP grasp of classical mechanics could define under what conditions a car could stop more quickly downhill than on the level. The problem is that in the limiting case, off a cliff, it doesn't decelerate at all, the reverse in fact.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[IRstuff]

Can't happen because that part of the braking force that has to overcome g*sin(theta) takes away from the total deceleration.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[Tmoose]

Hi Greg, I'm thinking a modification of Hemi's response provides one example of the possibility of quicker stopping on a modest downhill, if I'm allowed to use real tire "friction" characterics instead of Fsmax = μs η .

 

[Lou Scannon]

In answer to the OP, matching the level case going uphill is no problem. Going downhill, reverse thrust is one solution.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[elogesh]

In the past, we did virtual simulation of vehicle on plain roads. It involves standard set of static load cases along vertical direction (Bump/Rebound), longitudinal (Braking/acceleration) + self weight, Lateral (cornering) + self-weight,pot-holes,etc for strength assessment of structural members. In one of our internal reviews there was direction to include strength assessment during uphill/downhill braking.

In plain road condition, max braking deceleration(in terms of g) * safety margin considered for the calculation. In FE analysis, reaction due to braking applied as inertial acceleration on the whole structure with minimum support condition on the tire patch.

For uphill/downhill braking, similar to the discussion happened over here, there was an internal discussion, whether to consider the values accounting sin(slope) or plain road values. Hence posted this query...

Meanwhile from internal vehicle testing team got the communication that the effect of slope has to be accounted.Hence with that we proceeded with the calculation.Hope, I clarified the details.

Kindly consider this post as closed.

Once again thanks to the members responded to this post.