[androdev]

TL;DR: Power steering pump is at max load under full lock + car is stationary. Avoid it for mechanical empathy as 90% lock with slow rolling car is nearly as effective in turning as full lock + stationary.

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Got my car dropped at home after a visit to the A.S.S and I was reversing my car to park it in the garage. When the steering wheel was in full-lock position, the steering wheel was pushing back to turn in the other direction by few degrees as if there is a spring recoiling. I have been doing this parking routine almost daily for the last 5 years and never experienced this push back. I tried full-lock few more times and each time I was getting the recoil, interestingly it was happening only while reversing and when the car is not rolling.

I called the service adviser to report the problem and wondering if the driver who dropped the car damaged front suspension bits by hitting a speed bump very hard. SA promised a call back from the breakdown person and got a call to inform that this happens at times if the pressure build up is in excess and not to keep the steering in full lock position continuously, especially when the car is stationary. It builds peak pressure under full-lock and car is stationary.

Googled a bit and that seems to be the general consensus. Ease off the steering wheel a bit after full lock (better yet stop before reaching full lock). Don't keep it in full lock for long duration. Keep the car rolling slightly to cut down load on steering (static vs rolling friction) not to mention tire wear while turning a stationary tire.

It is possible that my power steering is dropping subtle hints about an upcoming expense, but let's hope for the best.

[greenhorn]

I have noticed, especially at U turns that when when the car is stationary, the wheel does not turn fully at full lock. once you start moving, if you keep it at full lock, its turns a bit further. Not sure if this is good or bad

also, I assume this is for HPS (since you mentioned a pump). Does this apply for EPS also ?

[androdev]

Originally Posted by greenhorn

also, I assume this is for HPS (since you mentioned a pump). Does this apply for EPS also ?

Hey good point, and my post is probably not useful after all given that most modern cars come with EPS without any pump nonsense. My post is about Mercedes S class (w221) which uses EHPS (some hybrid type with electric motor and pump) and I am not sure what other cars in India use hydraulic based steering.

[amit_purohit20]

The noise of my hydraulic pump in the car changes when its in full lock condition. I can hear and feel that, although its not easily audible. Its a clear cut sign of strain on the complete hydraulic system.

[Motard_Blr]

All hydraulic systems come equipped with a pressure relief valve to avoid just the problem that is mentioned here. The prv is usually a spring-loaded valve that opens at a preset pressure to prevent damage to the hydraulic circuit. That preset pressure is usually a bit higher than the maximum system pressure so the load on the pump and engine or motor at the prv pressure is higher than usual but usually not much higher.

The hybrid electric hydraulic power steering pump was used by German car manufacturers as a means to reduce fuel consumption since the pump only runs when needed and at the speed required. A conventional engine driven hydraulic pump runs at a fixed proportion of engine speed. It would need to be designed for the most extreme situation of low engine speed but high load, such as a fully loaded car trying to park. Since this situation happens only for very short periods, the pump output in almost all other cases is much more than required and this is why they have such a big impact on fuel consumption.

[Jeroen]

Originally Posted by amit_purohit20

The noise of my hydraulic pump in the car changes when its in full lock condition. I can hear and feel that, although its not easily audible. Its a clear cut sign of strain on the complete hydraulic system.

What you hear is the pressure valve opening and the hydraulic fluid bypassing the steering rack so to speak. No big worries as it is supposed to work like this under full lock. Nothing to worry about strain on the system

Jeroen

[Sutripta]

What is frowned upon is sawing away at the steering wheel with the car stationary. Power steering masks the effort and thus the forces at play.

Regards
Sutripta

[headers]

Originally Posted by androdev

Hey good point, and my post is probably not useful after all given that most modern cars come with EPS without any pump nonsense. My post is about Mercedes S class (w221) which uses EHPS (some hybrid type with electric motor and pump) and I am not sure what other cars in India use hydraulic based steering.

EHPS works as EPS at low speeds and HPS above a preset speed.

It is advised not to keep the steering locked to any side while parking, at least in older generation cars.

Dunno about W221 though..

[Motard_Blr]

Originally Posted by headers

EHPS works as EPS at low speeds and HPS above a preset speed.

...

Could you explain how this works? My understanding of its working principle is different. Am I mistaken?

Edit: I checked and my understanding is correct.
See: http://en.volkswagen.com/en/innovati...volenkung.html

http://www.nissan-global.com/EN/TECH...IEW/ehpss.html

[a4anurag]

While reading through this thread, felt like checking the load conditions on the power steering motor when rotated at stand-still position.

Took out the OBD-II reader and recorded the data. Here is what I observed.

Car in question is a 2013 Maruti Swift ZDi that gets a EPS (So slightly OT for this thread).

At idle (I mean no load on steering wheel)


Load on the motor while rotating the steering wheel slowly


Holding the steering wheel at full lock

Also here is a video showing the same

Load on EPS motor when steering wheel is rotated while car is standstill

[bowser]

I noticed an interesting bit written in the owner's manual of my 1st gen Honda City that comes equipped with hydraulic power steering. See the notice in the bottom right corner of the page:



It says one should not turn the steering wheel all the way to avoid damage.

[honeybee]

With hydraulic power steering, it is advised to avoid lock to lock turns as much as possible to avoid damage to the pump.

So I would assume with a running engine, keeping the wheels turned full lock would be bad as it will increase wear and tear of the pump/steering.

However with the engine switched off, this should not be a problem - obviously :-).

No such zanzat with electronic power steering.

[headers]

Even while engine switched off, there is the mechanical load which is supported by the hydraulic steering, so I'd refrain!!

[Jeroen]

Originally Posted by headers

Even while engine switched off, there is the mechanical load which is supported by the hydraulic steering, so I'd refrain!!

How does that work then. With the engine off there is no hydraulic pressure.

Although the manufacturers do warn against full lock, I don't see an immediate concern, unless you do it an awful lot or keep the full lock on for a prolonged period of time. The hydraulic pump has a pressure relief valve and that will open on full lock. On most it produces a specific noise. The issue is not so much the pressure as the heat building up. If you go full lock, back of a hair and the noise will disappear.
Jeroen

[rahul4640]

Originally Posted by honeybee

With hydraulic power steering, it is advised to avoid lock to lock turns as much as possible to avoid damage to the pump.

Though I am sure that lock to lock turns harms the hydraulic power steering system, I somehow guess it does more harm to the oil seals than the pump. Experts may give detailed opinions.