Can someone explain why the steering is engine speed sensitive? It seems like it should be vehicle speed sensitive.

(Just kidding, of course I'm not going to give you $20 for answering my question. Because I know the satisfaction of enlightening thousands of forum members is reward enough. )

P.S. - post # 200! I thought it would feel different.

 

my guess is that since the steering pump is connected to the crank via a belt, the faster the engine goes, the faster the pump turns and then the assist is...

...nevermind, I have know idea what Im talking about.

 

rpgonzales you really cracked me up on this one and I needed it Thanks.

 

Should be road speed sensitive steering, must be a typo like when they said the closest you can get to driving a formula car without putting on nomex. You know a typo like saying it would have the best interior in the industry.

 

Classic!

Thanks also!

 

I've never seen a power steering system which was engine speed sensitive, only vehicle speed sensitive. (If the former were the case, you could conceivably rev the engine to 3000 RPM and effectively have no power steering with the car sitting still.)

In short, speed-sensitive power steering adjusts the flow of high-pressure fluid as needed in proportion to the car's speed. At higher speed, power steering is not required as much, so less fluid is pumped through the system.

This link covers how steering works quite nicely.

 

I am pretty sure that 'engine speed sensative steering' is not a typo. I think rpgonzalez pretty much got it right. The power steering used a pump that is powered by the engine. If the pump was not engine speed sensative, then it would put out more pressure when the engine was running at high rpms. I am thinking that this type of power steering just keeps the assistance constant across all rpm ranges. A non speed sensative system would be easier to turn if you were sitting still at 5k rpms, than at idle.

The only vehicle speed sensative power steering systems that I have heard of are either computer controlled pumps, or an electric motor. I would assume that both of these would be pretty costly over the engine speed sensitive steering, which could be purely mechanical.

Take a closer look at the howstuffworks article, and pay attention to the 'future of power steering section'

 

I also wondered about this. I don't think it's a mistake, because they are pretty careful about these things (except for screen savers, maybe ) and if it was actually vehicle speed sensitive (which is what you want) they would probably say so. Could it be that a side effect of how the system works (e.g. engine-driven booster pump) has been turned into a "feature"?

Engine-speed sensitive steering doesn't sound very good to me; do I want ultra-boosted steering (that typically gives less road feel) when I'm screaming near redline in 2nd coming into a corner so that I can power out of it nicely? Don't think so.

Maybe this would be a good question for ZISME to take to the Nissan engineers. (Which would be a helluva lot better than my wild speculation in this post. Like rpgonzalez says, I have no idea what I'm talking about! )

 

Could it be that while the RPM's higher, the less the power steering is?

 

Well, at least I don't feel so dumb now.

zPilott, your explanation makes sense. I guess it's one of those "features" that is standard on most modern cars ( ?). Was probably a big deal on Mercedes or Chryslers 20 years ago. It's good for the marketing types to list on the features sheet, but not of much consequence to a buyer. Unless, of course, it DIDN'T have engine-speed sensitive steering.

Maybe someone should come up with a better name, like HyperSteer® or UltraSteer 9000© or HydraEngiSteer™!

 

Hmmm. I'm not sold yet. More research needed...

All cars today have a power steering pump driven off the main crank. So in effect, we all have some form of engine-speed sensitive effect on the existing power steering system in our cars. The torsion bar detects torque on the steering column and permits the flow of higher-pressure fluid as needed.

The part I have a difficult time with is the concept of an RPM-based variable steering assist system. 3000 RPM in first gear is a LOT slower than 3000 in 6th gear, and I would think I'd need a lot less power-assist in 6th.

Hmmm. Perhaps an argument can be made that the system provides a higher level of power assist below a certain engine RPM threshold (something low, like 1500 RPM perhaps).

I'll keep digging and report back...

 

OK, I did some additional research on the topic.

BMW and Mazda both use RPM-sensitive power steering instead of vehicle-speed sensitive PS.

The rationale seems to follow as such:
1. RPM-based PS systems are more cost-effective. The pump is driven off the main crank, and as such the proportioning valve is simpler to implement.
2. RPM-based PS systems appear to have less of an assist range than the speed-based systems. One can interpret that as saying there's really not that dramatic a difference at higher or lower vehicle speeds.

In short, this seems to be a tried-and-true technology that other manufacturers have used with success. I'll try to get more technical info from my mechanic as time permits.

(Still waiting to get a reasonable answer on the variable valve timing system in the VQ engine...)

 

Cool. Thanks for the research NSANY.

 

Should be, otherwise, a twitch of the steering wheel could send you into the weeds or into another lane. That is steering "feel" and at higher speed the less power you want in steering; otherwise, it would be very easy to turn the wheel too much, overcorrect, and you're in the weeds again. I hate the steering of cars that can turned lock-to-lock with one finger sitting still. That car is dangerous at highway speeds because you are always correcting, not connecting to the road and they are very dangerous in crosswinds. How can you say, older models of the Lincoln Town car?

 

Makes me think of the older cars. The wipers were engine-speed sensitive since they were vacuum-operated. When the engine slowed down (e.g., at a red light), so did the wipers. When you sped away - and the window got wetter - the wipers sped up to clear the rain quicker. Guess those cars were just ahead of their time!

WayneTN