does anyone have experience with unbalanced tires driving the Prius at about 100 km/h? Unbalanced tires with a car without steerings aids can be feeled at the driving wheel. What about the Prius with "steering by wire" and less mechanical contact?
the prius does not steer by wire, there is electric power assistance
AFAIK there are no steer-by-wire cars are there? it seems a safety feature that should be left in - redundancy in case of total electronic failure.
If a tyre was unbalanced, at 100 Km/h wouldn't it produce a shake that could be felt through the car body as a whole, especially on a good road? The Prius is generally smooth-running, although its suspension is quite firm, more EUian (and JPian?) than USian, and might let you feel such movements. (AFAIK, the trade-off benefit of firmer suspension is better road-holding. Have we an expert?)
Andrew Stephenson schrieb:
Hello Andrew my question is when you have an unbalanced tire if one can feel it at the steering wheel, since Prius has no mechanical contact with the wheels, the Prius (and some other Toyota cars) use "steering by wire", e.g. the steering wheel sensor drives an electric motor, hence there is no mechanical contact to the front wheels.
Fly by wire aircraft use "stick shakers" to provide ersatz mechanical feedback to the pilot. Unless the Prius were similarly equipped with a mechanical device to provide steering feedback one would not feel the shaking of an unbalanced tire... er, tyre through the steering wheel. It would, however, communicate vibration to the body through the suspension.
I doubt such a device exists on the Prius since some drivers have complained about the lack of such feedback, e.g. "floaty" steering.
-- Mike Harris Austin TX
I am pretty sure that Toyota does not currently produce any "steer by wire" vehicles.
Note that "steer by wire" means that there is no mechanical connection between the steering wheel and the steering rack, which is connected to the front wheels.
Electric power steering (which the Prius and the 2007 LS 470 have) means that the power steering pump is driven by an electric motor, not a belt-driven pulley, but there is still a steering shaft connecting the steering wheel to the steering rack. In the the Prius and 2007 LS, the steering wheel is connected to a steering shaft which is connected to a steering rack which is connected to the rack ends, which are connected to the front wheels.
As "mr cheerful" pointed out, the Prius _does_ have a mechanical connection between the steering and road wheels. Power steering simply reinforces the driver's efforts. If it fails, the driver can still haul at the wheel and thus steer the car.
AFAIK, this arrangement is commonplace in modern cars.
Even the top-posters? ;-) I shall, of course, go and eat worms.
Does the Prius have a hydraulic pump? I used to own a Saturn Vue that had "electric" power steering. There was no hydraulic pump. An electric motor was connected directly to the sterring shaft and provided the assist. I assume this is what the Prius does as well, but since I have not actually wokred on a Prius, I can't be sure. The electric power sterring in the Vue was mostly devoid of feel, but I got used to it. It wasn't nearly as dead feeling as the power steering from a early 70's Chrysler product.
My Saturn Vue was this way as well. It still had a conventional rack and pinion steering system, the "electric" part was just an assist. This is not a true fly by wire system. I do have three farm tractors that have "fly by hydraulic" sterring systems. There is no mechnical link between the steering wheel and the front wheels. The front wheels are moved solely by hydraulic cylinders that are activated by steering wheel movement.
Good question, I do not know how the power steering in a Prius works. I had assumed, perhaps incorrectly, that it had a hydraulic pump that was driven by an electric motor, like the MR2 had. Perhaps someone with a Prius can ansewer?
The hydraulic steering systems sound like the setup that some larger forklifts have, where the hydrostatic drive pump also provides steering and other duties.
AIUI Prius' steering servo is electric, as you speculate. There may be a hydraulic component, as another post suggested. Toyota do caution (in line with IIRC Ray's counsel) against holding the wheel hard over for too long, lest it overheat things.
The steering itself is very gentle and easy. But the suspension is, as I posted previously, "live" in the EUian/JPian manner and transmits road bumpiness more than a USian-style car would.
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