Electric PAS pumps

[richardw]

I have recently seen a hydraulic PAS pump mounted remotely instead of being powered by the engine. I’d like to start a discussion on the pros, cons and feasibility of this approach. There seem to be quite a few systems that have been fitted to production vehicles. One I have seen available secondhand for around £170 is from a Citroen Saxo, but I’m unsure how to assess its suitability. At least it only has two wires rather than anything more complex looking at speed sensors etc.

I’m keen on making my engine as efficient as possible by removing any unnecessary power drain such as the PAS pump when it is not needed. I believe the electric pump gets around this.

Cheers, Richard

[Pete Boole]

I used the Saxo pump on my track day Excel - worked perfectly. I'm not sure how much more efficient it would make your car as the alternator has to work harder - the pumps draw quite a bit of current.

Pete

[richardw]

Thanks Pete - good to know the Saxo pump works. I think it will use less energy as the pump will only cut in when needed rather than all the time - if I’m right! Anyway a lot less costly than an electric pas conversion and easier to fit.

Cheers, Richard

Edit: just found this article which explains the efficiencies that can be gained: https://pmmonline.co.uk/technical/elect ... explained/

[rbgosling]

Also, I wouldn't go with full-electric PAS anyway, it would numb the steering feel. The fact that Lotus have stuck with hydraulic PAS for the Emira (with an electric pump - the Mercedes engine doesn't have anywhere to mount an engine-driven pump!) against any electric PAS they could have found tells you all you need to know.

[DavidOliver]

The steering when used needs an immediate response. I assume the electric pump would need to be working before the steering was activated.
Also when you use the steering generally you are not on full throttle to obtain maximum power.
And what is the total weight of an electric system compared to normal hydraulics, maybe more ?

Dave the cog

[rbgosling]

What David says it true, that the pump needs to be running prior to the steering input. However, an engine-driven pump is being driven at engine speed - when you are going flat out the pump is being driven far faster than it needs to be, so that is wasted energy. Equally, when you are parking your car the engine is slow yet the demand for PAS is high, so the pump is sized for that scenario and is pumping harder than necessary the rest of the time. An electric pump (well, at least this Saxo option that doesn't vary with car speed or anything) will pump at the same speed all the time, it'll still be wasteful but should be less wasteful.

Dunno whether it is bound to be heavier - yes, there is an electric motor to include in the package. But on the other hand the pump side may not need to be so massive, as its size can be optimised to the motor speed rather than having to work over the full range of engine speeds. My guess is it'll still be a bit heavier!

[Pete Boole]

There are two types of this pump as well - one with an integral reservoir and one with a remote reservoir - the remote type makes installation slightly more flexible.

I'll see if I can find my pump and weigh it - perhaps someone can do the same with with a standard pump - then we can compare weights.

Pete

[TrevorK]

I don’t see how a saving of 0.3l/100km is equivalent to 3.75mpg. I think the author of that article needs to revisit that.

If the electric pump just keeps the system pressure topped up, the system should respond instantly. My MR2 has electrically-powered hydraulic power steering and is very responsive. The complications of measuring steering angle and road speed to vary the assistance under different conditions sound like something to avoid.

[rbgosling]

I don’t see how a saving of 0.3l/100km is equivalent to 3.75mpg. I think the author of that article needs to revisit that.

Depends on what your starting point is! If your baseline fuel consumption is 4.9 l/100km (57.65 mpg) then an improvement to 4.6 l/100km gives 61.41 mpg, which is the improvement quoted. Sadly, our Lotus are doing about half this on their good days.

[bash]

Im no electrical expert but I presume maximum current draw would only be when worked hard like parking ? and, could the voltage be varied to give less assistance on the move.
Bash