Is there a link between fuel consumption and power steering? I ask because I noticed a big difference in fuel consumption betwee two base model Toyota Yaris's. Yaris S - no power steering - 54 mpg. Yaris T2 - power steering - 48 mpg.
A Yaris S is an older version? Perhaps this gave better results because the engine is run in? I experienced around 28mpg when I first got my Celica VVTi, after several months I started to get around 34-35mpg doing the same journey to work.
PAS does make a noticable difference to power and fuel consumption. You have to run a load of hydraulic gear to run the assistance, and it's running all the time. FIAT have moved to electric power steering to reduce fuel consumption.
Yup; power steering does sap power - I just happen to have figures for the Ford Ka wearing 165/60/14 tyres, with and without PAS (using the same final drive ratio):
Note that these models were not available in the UK (the data uses the taller final drive ratio, and all PAS-equipped Kas use the shorter final drive, and non-PAS Kas use 165/65/13 wheels and tyres).
Electric power steering systems are more efficient, which is why a whole bunch of manufacturers use this system these days (hydraulic units are always driven, electric systems are only driven when needed).
Accepting that I know precious little about PAS - but,
Since its (almost) impossible to drive a car in an absoloutely straight line (which is the only condition where I can see that electric PAS would switch off), would this therefore not create a situation where it will be constantly switching in and switching out? I appreciate there will be some hysteresis within the system to compensate for the straight ahead situation, but in a realistic, non-motorway, situatuon, this isn't going to be the case.
Therefore, with an electric system, there's going to be even higher maintenance (because - one day - that ever-so-important-relay will fail).
So, the owner/driver scores from lower purchase costs/running costs, and gets lumbered with higher maintenance costs (which *ALWAYS* increase through time).
To be fair though, its been my experience that belts fail, motors burn out - but pumps run forever!
Yes. However, I'm quite certain that the electric motor is designed to only cut in when needed, and is probably load sensing (or perhaps only when speed is above 20 mph or something) - so when you turn the wheel on a main road it doesn't kick in.
They can overheat, however, and then you lose all assistance! :(
The Citroen Xantia and C5 both have hyrdaulic suspension. The Xantia has a hydraulic pump run all of the time off the engine, the C5 has an electrically driven hydraulic pump. I was thinking that this had been changed from the Xantia to the C5 to reduce fuel consumption but didn't think that it made that much difference in any case.
The PAS pump in a hydraulic system runs whenever the engine is running, if it's variable output it could do this fairly efficiently. The electrical systems only consume power when being used where as the hydraulic will always consume some power even when not being used.
Pumps don't last very long when somebody forgets to check the fluid level and it runs dry...
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