http://www.forbes.com/feeds/ap/2007/...ap4086947.html

The hybrid electric propulsion system is not enough. All of the vehicle systems including power steering, need to be optimized. The electric powered, AC compressor is another brilliant advance. As for a '8 percent' fuel improvement by switching to an electric power steering, that seems a little bit of a stretch.

Bob Wilson

 

This thing stuck me entirely differently, as I have been disagreeing with another poster at Prius Chat about whether Toyota ought to be (even) asked to pay for post-warranty failures in the PS system.

Electrical PS depends on some sort of torque sensor to determine how much (and in what direction) to add electrical assist. Toyota initially did that with potentiometers on a rubber plate. The problem was that potentiometers get noisy, and because assist may be needed 'promptly', only so much filtering can be done in the time domain. After paying for replacements under (and perhaps beyond) warranty, Toyota decided to use Hall Effect sensors instead. Whether or not led to this change by NHW11 problems (whiney NHW11 drivers), they have now got a system that works well and can make them lots of money in the future.

I do not know how much energy can be saved by electrical assist PS. Its major strength may be that it allows freedom in designing 'auto-stop' and hybrid vehicles. Toyota and other manufacturers will no doubt continue to use these systems.

DAS

 

lets not forget honda. my 2000 insight has had electric power steering since it was a baby.

 

Could it be that the 8%, is due to the fact that the electric power steering can be turned 'off' when not needed? I mean when no steering boost is required like when at highway speeds?

 

Doug's comment got me thinking about the last bastion of hydraulic fluid, the brakes. There will always be a need for highly reliable, mechanical brakes but it isn't clear that it has to be hydraulic operated. Before hydraulic brakes, they were mechanical and though hydraulic brakes were an improvement, it may be time for this last bastion to be replaced by electrically operated brakes.

Two approaches come to mind: directly actuated shoes and 4-wheel motor/generators. Of the two, I like the 4-wheel drive solution since it also provides improve drive as well as braking. However, directly actuated shoes would also work by elimination of hydraulic lines and advanced traction control.

For those worried about reliability, truck air brakes offer a solution. Truck brakes have a spring that is 'unloaded' by air pressure, much like trains. When the pressure is reduced, the spring actuates the brakes. The failure mode is to apply the brakes. A similar, magnetic latch could be used in an electro-mechanical brake. Loss of power would simply release the spring to apply the brakes and stop the vehicle.

Hydraulic brakes have an 80 year history but electronics and stolid state control have reached a point where designers may be able to do better.

Bob Wilson

 

Would not a spring only offer a fixed deceleration rate? Basically, the strength of the spring?

BTW, going off on a tangent... My Mustang has hydraulic assist power brakes. There is no large vacuum "disc" sitting behind the master cylinder. Instead the "power" comes from the power steering pump, which has been renamed due to its now dual purpose.

Anyway, I wonder if on the hybrids they could replace the electric vacuum pump (you know, that thing you hear when you open door), with something more direct like they did with the power steering. And if so, would it be better?

 

So, it's 'too 20th century' to continue to use non-compressible fluid for pressure transfer?

Apologies for not considering Honda Insight for electrical steering. Now that you mention it, I'd like to know how their torque sensor works.

Have been grumbling for years about the belt-driven engine coolant pump, but there it remains...

DAS

 

The HCH II's steering is electric, too, of course, and I can't believe how good it feels. Always the right level of boost, and you can never feel the thing working. The steering is just *there*, rock solid. It will definitely be interesting to see how it does long-term.

I was actually really concerned about electric power steering because reports on, for example, BMW's variable-ratio electric suggested way too much computer interference that would change boost levels/steering ratio at the wrong times. Absolutely no such problems with the Honda system.

Cheers -
Doug

 

That's about double everything I've seen on it.

Peace,

Martin

 

I've not seen an electric power steering application that "turns off". You either have electric power steering or you have hydraulic power steering. The fuel savings comes from reduced mass and from reduced friction losses. Neither of those is gonna get you near 8%.

The additional benefits of EPS have not yet been widely experienced. Well, maybe the Lexus LS450 with the autonomous parking system would be an exception. There are several safety related technologies that help keep drowsy / distracted drivers from straying out of their lanes that will rely on electric power steering as a base technology. Eventually, autonomous driving will take electric power steering to a new level. Honda already has some vehicles (in the UK I think?) that experiment with semi-autonomous driving.

Peace,

Martin