[Magna]

BMW offers two kinds of steering assist. I read that on the 4.6is X5 there's speed sensitive steering which I think makes more sense since you need assist when the car is going slow. But on the 3 series, the steering assist is engine-speed sensitive. Is engine-speed sensitive easier to manufacture or is easier regarding maintenance?

 

[Nick325xiT 5spd]

I don't know, but I wish I could turn it off above 5MPH. There is absolutely no need for it, aside from parking.

Nick

 

[Kaz]

Most cars with variable assist use engine speed. I've heard that with many cars assist is tied to engine speed so much so that it affects steering at the track, when you tend to run higher RPMs when there's less boost.

Its probably easier to design engine speed-dependent systems since the PS pump runs off the engine (though it turns more at higher speeds, giving more boost... anyhow...).

Now that electrically driven PS pumps are starting to come out (MINI, and I believe the Insight), changing this to vehicle speed should be easy.

I will say that my car's PS is far less speed-sensitive than most Japanese cars I've driven.

 

[bmw325]

yep-- engine speed steering is cheaper and simpler. I guess it works to some extend-- although it doesn't help too much when you're crusing in the US at around 70mph turning 3k rpm. I don't think you can really notice a boost difference until over 4k-- and no one in the US is cruising at that speed. I'd imagine this type of system would feel less "linear" since everytime the car revs and shifts the steering is going to go from heaver to ligher at the same road speed. I've never really noticed much difference-- except when I had the car in Germany-- I did notice that power steering was reduced at 5k rpm (when i was cruising at 125mph).

I've actually noticed that most Japanese manufaturers use acutal speed sensitive steering (and have for quite some time).

BMW calls this system "servotronic" and reserves to for the 5 and 7 series. It seems like it would be a pretty obvious way to address all of the steering effort controversey. My dad has an e38 7 series with this--and the steering feels light as a feather at parking speeds. Then again, its pretty light at highway speeds too (it also has recirculating ball steering) so that may have something to do w/ the overal light feeling.

I bet (but I'm not sure) that on the E65 you can adjust the boost t your preferences-- I know that on the M5 pressing the sport button makes the steering firmer.

In conclusion the only "advantage" to engine speed sensitve steering is that its cheaper to make.

 

[Emission]

Now that electrically driven PS pumps are starting to come out (MINI, and I believe the Insight), changing this to vehicle speed should be easy.

Kaz is right, most manufacturers are going towards (future) electric pumps and accessories not belt driven. This will make the speed sensitive steering easy to make... and maybe it will trickle down to the 3-series!

 

[guzplace]

Is it true that japanese cars .. like Hondas had this vehicle speed sensitive steering since ages and BMW just added it to its line ......!!!