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Old 30th November 2006, 05:09   #1
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Arrow Know your power steering

It's a known fact that a typical hydraulic power steering system is continually placing a small load on the engine, even when no steering assist is required. And also the EPS system only needs to draw electric power when steering assist is required, no extra energy is needed when cruising, improving fuel efficiency. And Electric power steering (EPS) is mechanically simpler than a hydraulic system, meaning that it should be more reliable and is capable of self-diagnosing faults by monitoring the system's input and output.

I've also heard that HPS contains more number of internal components and it's architecture is pretty complex. Does it mean that HPS in cars like Santros will be a headache in the long run ? Does HPS requires maintenance in the long run ?

Then why Hyundai is still sticking to the HPS ? Is it due to the cost factor ?

Can someone please point any other differences between EPS & HPS ?
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Old 30th November 2006, 18:14   #2
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In layman's terms, Hydraulic power steering works by oil pump pressure and EPS works form the electric motor that draws power from the battery and some power from the engine as well.

Some differences that I know:

1. EPS is safer as it deactivates after a certain speed (60km/hour in Maruti cars). My Alto's steering is hard after 55 kms/hr. HPS continues to work which could be unsafe as turning the steering even lightly may cause the car to oversteer. But I think there is a safey device for HPS as well.

2. HPS since it runs on servo, the oil level has to be maintained for better steering feel. EPS requires no such maintainence. However, the motor has to be checked at regular intervals.

3. HPS can be used on all sizes of cars. But EPS are usually limited to small cars. But our own Honda City uses EPS.

4. I beleive EPS cars (Technically) should get better FE cause there is no or minimal effort from the engine.

I read in one report that my consulting company produces that there is new system called Electric-hydraulic or something where a combination of both is used. As I am not an engineer, I am not able to exactly understand how it works. I guess a electric motor will give the hydraulic power to the steering.

Last edited by mail4ajo : 30th November 2006 at 18:15.
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Old 30th November 2006, 18:31   #3
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Quote:
Originally Posted by mail4ajo View Post
1. EPS is safer as it deactivates after a certain speed (60km/hour in Maruti cars). My Alto's steering is hard after 55 kms/hr. HPS continues to work which could be unsafe as turning the steering even lightly may cause the car to oversteer. But I think there is a safey device for HPS as well.
If that was true most of the high-end cars would today be crashing backwards into trees on account of sudden oversteer. Nowadays most cars have Speed-sensitive HPS which varies the amount of assistance depending on th speed of the vehicle, meaning that at high-speeds the assistance is close to or absolutely nil. This is designed purely to keep the car's handling safe & predictable.

Quote:
Originally Posted by mail4ajo View Post
2. HPS since it runs on servo, the oil level has to be maintained for better steering feel. EPS requires no such maintainence. However, the motor has to be checked at regular intervals.
IMHO good steering systems oil level rarely gets low so no problems there unless you have a leak in the system.

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Originally Posted by mail4ajo View Post
4. I beleive EPS cars (Technically) should get better FE cause there is no or minimal effort from the engine.
Yes, but the difference is very small & hardly noticeable.

Quote:
Originally Posted by mail4ajo View Post
I read in one report that my consulting company produces that there is new system called Electric-hydraulic or something where a combination of both is used. As I am not an engineer, I am not able to exactly understand how it works. I guess a electric motor will give the hydraulic power to the steering.
Yes new Hydro-Electric steering systems are being introduced on many cars worldwide.

Main grime of people especially enthusiasts world over with EPS has been that it robs you of the feel that a good HPS system provides you with. For eg. WagonR has a pretty dead steering feel. This is a stumbling block that has not yet been solved by the creators of the EPS.

Last edited by iraghava : 30th November 2006 at 18:39.
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Old 30th November 2006, 18:43   #4
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Quote:
Originally Posted by iraghava View Post
Yes new Hydro-Electric steering systems are being introduced on many cars worldwide.
Raghava, do you have any info or links I can read on this system? I am not able to locate our company report on that. But I know companies like Audi, VW and Mazada is offering this on some models.

Actually this happens to be a favourite topic for me.
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Old 30th November 2006, 18:44   #5
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Quoted by Iraghav---"If that was true most of the high-end cars would today be crashing backwards into trees on account of sudden oversteer. Nowadays most cars have Speed-sensitive HPS which varies the amount of assistance depending on th speed of the vehicle, meaning that at high-speeds the assistance is close to or absolutely nil. This is designed purely to keep the car's handling safe & predictable."

Dear Iraghav,
In 1982, I had a brand new Beemer 730i and they already HAD a speed sensitive power steering then i.e 24 years back. They were first introduced I think in 1975 by Porsche.

Last edited by scooby05 : 30th November 2006 at 18:45.
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Old 30th November 2006, 18:51   #6
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Dear Iraghav,
In 1982, I had a brand new Beemer 730i and they already HAD a speed sensitive power steering then i.e 24 years back. They were first introduced I think in 1975 by Porsche.
So I wasn't wrong after all. There is a safety device on HPS. Was HPS invented by BMW or Chrysler? I read somewhere it was jointly developed.
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Old 30th November 2006, 19:00   #7
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Thsi thread might be of some use here :-)

http://www.team-bhp.com/forum/techni...-steering.html (How good is electronic power steering?)
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Old 1st December 2006, 05:30   #8
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Quote:
Originally Posted by scooby05 View Post
Quoted by Iraghav---"If that was true most of the high-end cars would today be crashing backwards into trees on account of sudden oversteer. Nowadays most cars have Speed-sensitive HPS which varies the amount of assistance depending on th speed of the vehicle, meaning that at high-speeds the assistance is close to or absolutely nil. This is designed purely to keep the car's handling safe & predictable."

Dear Iraghav,
In 1982, I had a brand new Beemer 730i and they already HAD a speed sensitive power steering then i.e 24 years back. They were first introduced I think in 1975 by Porsche.

It may have been available on the Beemer (I always thought that it was a Beamer). But what about cars in India today. My brother says that his Corsa which has a HPS is not speed sensitive and the over steer can be scary at high speeds. Is that a stray incident? Or is it that most of the low end cars do not come with speed sensitive HPS?

Sharath
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Old 5th December 2006, 05:17   #9
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Quote:
Originally Posted by iraghava
For eg. WagonR has a pretty dead steering feel. This is a stumbling block that has not yet been solved by the creators of the EPS.
Are you saying that even the WagonR LX which is not having a PS has a dead steering feel ?

Quote:
Originally Posted by mail4ajo
HPS can be used on all sizes of cars. But EPS are usually limited to small cars.
Would you please explain the reason behind why HPS (and not EPS) is used in high-end cars ?
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Old 5th December 2006, 10:09   #10
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If I remember correctly, in last months overdrive, there was this review of a new Merc (dont remember exactly but I think it was the new S-Class). It seems it has the EPS in the previous model but because of customer feedback this was replaced by HPS in the latest model. I think the report said that the customers didnt like the feel of EPS.
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Old 5th December 2006, 15:52   #11
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Quote:
Originally Posted by mithun View Post
Are you saying that even the WagonR LX which is not having a PS has a dead steering feel ?
No I am saying WagonR which has an EPS steering has a dead steering feel. Never driven a manual steering WagonR.
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Old 5th December 2006, 17:45   #12
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Quote:
Originally Posted by mithun View Post
Would you please explain the reason behind why HPS (and not EPS) is used in high-end cars ?
I am not sure about HIGH END cars, But in heavy vechicles HPS is more used perhaps due to the weight and effort required to turn the car. HPS uses a hydraulic pump whereas EPS uses motors.

Last edited by mail4ajo : 5th December 2006 at 17:47.
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Old 31st March 2007, 05:55   #13
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Does the EPS systems provide variable load assistance which adjusts the assistance required according to the vehicle load since the steering becomes heavy when there is full load in the vehicle ?
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Old 31st March 2007, 07:34   #14
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I agree with what Iraghava said. An Estilo that I drove which had EPS lacked feel. It was a lot easier to turn the wheel that the Santro but I only enjoyed this while parking it. On the road you reallly need to get some sort of feedback. The EPS feels far too light atleast on the Estilo.
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Old 1st April 2007, 14:53   #15
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I agree to what AJO said. But EPS does not deactivate after 55-60 kmph, but decreases the sensitivity of the steering.. And it will make a big hole in your pocket if the EPS is damaged. My friend had this problem and he removed the EPS and is driving like normal. While HPS is complex, it is okay to use. We can get it right even some problem occurs to it. We need to change the hydraullic oil in regular intervals. Even Mercs uses HPS, so i think HPS is better.
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