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Electric power steering



 
 
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  #1  
Old May 25th 09, 02:15 PM posted to rec.autos.tech
Don Stauffer
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Posts: 278
Default Electric power steering

I understand electric power steering is coming (actually, I have it on
my Prius), because it is supposed to be more energy efficient. Is a
generator that much more efficient than a hydraulic pump, or is it that
there is energy going into turning the belt and pump even when not
pumping against pressure?
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  #2  
Old May 25th 09, 05:20 PM posted to rec.autos.tech
Mike Walsh[_3_]
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Posts: 42
Default Electric power steering


Electric power steering is used on the Prius because electricity is the only power available when the engine is not running. Drive by wire electric steering is more energy efficient but is not as reliable as hydraulic assist because if the electric steering fails you have no steering at all. Using electric assist would be more reliable than drive by wire and probably more efficient than hydraulic assist because the hydraulic pumps turns fastest at highway speed when you need it the least. I don't know if the Prius uses electric assist or true drive by wire steering.

Don Stauffer wrote:
>
> I understand electric power steering is coming (actually, I have it on
> my Prius), because it is supposed to be more energy efficient. Is a
> generator that much more efficient than a hydraulic pump, or is it that
> there is energy going into turning the belt and pump even when not
> pumping against pressure?


--
Mike Walsh
  #3  
Old May 25th 09, 10:28 PM posted to rec.autos.tech
Ashton Crusher[_2_]
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Posts: 2,874
Default Electric power steering

On Mon, 25 May 2009 08:15:56 -0500, Don Stauffer
> wrote:

>I understand electric power steering is coming (actually, I have it on
>my Prius), because it is supposed to be more energy efficient. Is a
>generator that much more efficient than a hydraulic pump, or is it that
>there is energy going into turning the belt and pump even when not
>pumping against pressure?


Both
  #4  
Old May 26th 09, 11:21 PM posted to rec.autos.tech
Clive[_2_]
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Posts: 262
Default Electric power steering

In message >, Mike Walsh
> writes
>
>Electric power steering is used on the Prius because electricity is the
>only power available when the engine is not running. Drive by wire
>electric steering is more energy efficient but is not as reliable as
>hydraulic assist because if the electric steering fails you have no
>steering at all. Using electric assist would be more reliable than
>drive by wire and probably more efficient than hydraulic assist because
>the hydraulic pumps turns fastest at highway speed when you need it the
>least. I don't know if the Prius uses electric assist or true drive by
>wire steering.
>
>Don Stauffer wrote:
>>
>> I understand electric power steering is coming (actually, I have it on
>> my Prius), because it is supposed to be more energy efficient. Is a
>> generator that much more efficient than a hydraulic pump, or is it that
>> there is energy going into turning the belt and pump even when not
>> pumping against pressure?

>

Here in England, your "Drive by Wire" is prohibited. In the event of a
total power failure all controls have to be manually usable, so both
steering and brakes have to be usable without the engine's assistance.
--
Clive
  #5  
Old May 27th 09, 01:28 AM posted to rec.autos.tech
Scott Dorsey
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Posts: 3,914
Default Electric power steering

Clive > wrote:
>>

>Here in England, your "Drive by Wire" is prohibited. In the event of a
>total power failure all controls have to be manually usable, so both
>steering and brakes have to be usable without the engine's assistance.


The Prius system is legal under those requirements, as much as a hydraulic
assist is. You _can_ drive a car with hydraulically-assisted power steering
that has failed. It's no fun, but you can control it enough to get it off
the road. The same is the case with the electrically assisted system.

That said.... with a car as small as the Prius, the real solution would
seem to be rear wheel drive and manual steering. No reason to make things
more complicated than they have to be, and I commute every day in a car
with manual steering and it's just fine.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #6  
Old May 27th 09, 05:31 AM posted to rec.autos.tech
P.V.
external usenet poster
 
Posts: 14
Default Electric power steering

"Mike Walsh" > kirjoitti viestissä
...
>
> Electric power steering is used on the Prius because electricity is the
> only power available when the engine is not running. Drive by wire
> electric steering is more energy efficient but is not as reliable as
> hydraulic assist because if the electric steering fails you have no
> steering at all. Using electric assist would be more reliable than drive
> by wire and probably more efficient than hydraulic assist because the
> hydraulic pumps turns fastest at highway speed when you need it the least.
> I don't know if the Prius uses electric assist or true drive by wire
> steering.
>


AFAIK, drive-by-wire steering (i.e. no mechanical link) is not in use in any
current cars, at least not in models in production. I don't know whether it
would be too expensive or just impossible to implement it to be sufficiently
reliable to be road legal.

Electric power steering means what you call electric assist, just like
hydraulic power steering means hydraulic assist. Both power steering methods
have the mechanical link, so when either of them stops working (e.g. due to
failure in hydraulic pump or electricity) there's still steering, it's just
harder because it's no longer assisted by power steering.

P.V.

  #7  
Old May 27th 09, 05:33 PM posted to rec.autos.tech
Mike Walsh[_3_]
external usenet poster
 
Posts: 42
Default Electric power steering



Scott Dorsey wrote:
>
> Clive > wrote:
> >>

> >Here in England, your "Drive by Wire" is prohibited. In the event of a
> >total power failure all controls have to be manually usable, so both
> >steering and brakes have to be usable without the engine's assistance.

>


There has been much written about drive by wire steering and brakes, but I have not seen either. Drive by wire throttle is common in the United States for emission control. The throttle is completely controlled by a computer and there is no mechanical link between the gas pedal and the throttle body.

--
Mike Walsh
  #8  
Old May 27th 09, 05:56 PM posted to rec.autos.tech
Steve[_1_]
external usenet poster
 
Posts: 3,043
Default Electric power steering

Don Stauffer wrote:
> I understand electric power steering is coming (actually, I have it on
> my Prius), because it is supposed to be more energy efficient. Is a
> generator that much more efficient than a hydraulic pump, or is it that
> there is energy going into turning the belt and pump even when not
> pumping against pressure?


In general, electrical conversion (alternator/motor/wiring) is
significantly more efficient than a hydraulic system of the same
size/weight/cost. You can make hydraulics a bit more efficient by very
precise machining, removing as much compliance from the tubing as
possible, electronic controls, etc., but it hits a point of diminishing
returns and there is always the frictional loss of pumping fluid around
when its not being used for assist.

 




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