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Old 23rd August 2006, 04:48   #1
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Exclamation No power assistance from EPS at high speeds - Why ?

Got the following info related with EPS from the Zen website

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The ZEN LXi is a vehicle especially meant to provide Superior Control at all speeds through its special electronic power steering. The electronic power steering vis a vis the ordinary hydraulic power steering available in other small cars has a computer controlled mechanism which provides low maintenance costs, less load on engine (2%) as well as no oil leakage's.

Its greatest strength though lies on the fact that it provides virtually no power assistance at high speeds(unlike the other ordinary power steering) and hence provides safety.
My question is that why there is no power assistance at high speeds from EPS ?

What will be the after-effect if there is a need for quick manoeuver of the car at high speeds ? Will the car lose it control in the absence of traction control ?
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Old 23rd August 2006, 07:34   #2
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Power assisted steering is dangerous on high speeds. Cozes when in speed a slight turn (which will be much softer due to power steering) can cause the vehicle to loose control and may be difficult avoid disaster. This is the reason the other safety features have been added to the high end vehicles. (ABS, EBD, Etc)

At high speeds the steering power control should shut off making the steering hard as per speed to manage the drive.

The need for power steering is on the low speed and usually in city driving where you may need to drive vehicle at low speed and on most turns.

The super cars like Ferrari, the Lamb .., does not come with Power steering installed in it.
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Old 23rd August 2006, 08:18   #3
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Mithun, PS is more required at slower speeds, esp in city driving conditions. To understand this, try to see the effect of the steering at low speeds and high speeds - but pls try in a ground.

Also, at higher speeds, you would not be doing too much turning.
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Old 23rd August 2006, 09:48   #4
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The reason was obvious, I feel. You dont want to taste a tree at 120 kmph because ur power steering was super responsive.
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Old 23rd August 2006, 10:19   #5
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Quote:
Will the car lose it control in the absence of traction control ?
Firstly, There is a difference between ESP and EPS. ESP is "Electronic Stability Program" which is traction control. EPS is "Electronic Power Steering".

Its a good thing that EPS switches off at high speeds else the steering will be too sensitive and light. Very dangerous at high speeds. Most cars have a speed-sensitive power steering, which makes the steering harder as speeds go up.
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Old 23rd August 2006, 11:53   #6
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Quote:
Originally Posted by mithun
Got the following info related with EPS from the Zen website



My question is that why there is no power assistance at high speeds from EPS ?

What will be the after-effect if there is a need for quick manoeuver of the car at high speeds ? Will the car lose it control in the absence of traction control ?
all designed for your safety my friend
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Old 24th August 2006, 20:55   #7
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Smile Power steering!!

Mithun, I feel the most important time when one needs power steering is during parking and turning at very low speeds. Power steering controlled via EPS, is a kind of intelligent system, which nearly shuts down power assist to steering when on higher speeds.

This enhances our safety actually. I drive the Alto that has powersteering, and I recently drove a Zen without power steering. The steering is hard in the beginning but on the drive i feel its better without power steering because it gives a good feel when turning as well.

I believe the feel should be lessened as it happens with EPS so that turning effort is there during higher speeds than just a light wriggle with a finger which can prove quite fatal at times.
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Old 24th August 2006, 21:09   #8
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Correct me if im wrong,but eps depends on the revs you are pulling rather than your speed.I say this coz in the baleno while revving at around 5500rpm while becomes quite difficult to turn.Try it and see....you might feel a difference even at 4k rpm

I could be wrong though.

binz

Last edited by binz : 24th August 2006 at 21:11.
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Old 24th August 2006, 21:24   #9
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Quote:
Originally Posted by binz
Correct me if im wrong,but eps depends on the revs you are pulling rather than your speed.I say this coz in the baleno while revving at around 5500rpm while becomes quite difficult to turn.....
binz
Binz, you have started another great topic. Thats something I never thought about. Yes it should be the rews i guess or some intelligent system to tell what rews and which gear the vehicle is on and then decide the feel!!

Not too sure, will try on Alto and see, it has some kind of intelligent system I guess.
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Old 24th August 2006, 23:45   #10
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as far as i remember the eps shuts off at around 60 coz it is only needed at speeds below that in the city but at higher speeds its not needed and cause damage to you and your car!
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Old 25th August 2006, 17:27   #11
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The Eletric power steering is completely speed dependant and not rev dependant at all.

The steering only feels hard when you rev, perhaps psychology... I dunno, but I really don't see the use of RPM to decide steering assistance.. Else, a car with tall gearing which could hit 60kph at 2000rpm in fifth and 40 kph in 1st at around 4000rpm would have it's power steering switch on and off as the driver rises or drops revs...

The electric power steering also has a direct drive mechanism; Even when the engine is switched off and assist from the electric motor is not available, the steering can be turned just like a regular rack and pinion.. Which is not the case with the hydraulic system.

Thus, when the speeds exceed 60kph or any other speed decided by the manufacturer, the steering is essentially direct.
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Old 25th August 2006, 17:58   #12
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Quote:
Originally Posted by binz
Correct me if im wrong,but eps depends on the revs you are pulling rather than your speed.I say this coz in the baleno while revving at around 5500rpm while becomes quite difficult to turn.Try it and see....you might feel a difference even at 4k rpm

I could be wrong though.

binz
I don't think that the EPS depends upon the revs. It is dependent on the speed. e.g. in NHC the EPS turns off at the speed of 30kmph.
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Old 25th August 2006, 18:37   #13
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Quote:
Originally Posted by pastmaster
The steering only feels hard when you rev, perhaps psychology...

I dunno, but I really don't see the use of RPM to decide steering assistance.. Else, a car with tall gearing which could hit 60kph at 2000rpm in fifth and 40 kph in 1st at around 4000rpm would have it's power steering switch on and off as the driver rises or drops revs...
I know my car and i know that when i hit 5500rpm the steering becomes hard.Nothing psychological about that.

I agree with your second point though.Steering should depend on speed and not upon revs because at 100kmph in 5th gear,the revs will be at around 3-4k rpm and if the steering depended on that,potential disaster.

Just stating what happens in the baleno(hydraulic power steering).Eps in the NHC and swift is completely different.
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Old 25th August 2006, 19:00   #14
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Quote:
Originally Posted by pastmaster
The electric power steering also has a direct drive mechanism; Even when the engine is switched off and assist from the electric motor is not available, the steering can be turned just like a regular rack and pinion.. Which is not the case with the hydraulic system.

Thus, when the speeds exceed 60kph or any other speed decided by the manufacturer, the steering is essentially direct.
I think you mean there is no Cut-Off mechanism in the Hydraulic system. Even in the hydraulic power steering systems, you could turn the steering like regular rack & pinion if the hydraulic system fails. That's why it is called "Power Assisted Steering" really... it will be very hard to turn the steering without the boost though....
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Old 25th August 2006, 22:41   #15
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It doesn't shut off.. ...
it is speed sensitive.. and thats it.
Try switching off the engine at 80+... and you will still feel the sudden power loss in the steering.

It can not be rpm sensitive... else while doing 120... if I go into neutral.. .. I'll most probably fly off the road.

Its not just EPS... but some hydraulic steerings too are speed sensitive.
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