h a l f b a k e r yCompound disinterest.
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Torque steer is an annoying side effect of having a large amount of torque driving the front wheels. It can be largely remedied with a limited slip differential, equal length half shafts, and changes to suspension settings, but it never be completely eliminated.
So torque steer is essentially a tug
of war between you and the steering rack. Problem is, if the steering rack is trying to change the direction with more force than you are applying to the steering wheel, you also have the power steering working against you. I propose a very simple solution: the steering column turns a worm gear right or left, which moves a gear that it is in contact with clockwise or counterclockwise (which is then converted back into left/right with bevel gears). The worm gear acts as a one-way power transmitting system (the gear cannot rotate the worm), and with this system power steering can easily overcome the added resistance of the steering column trying to move against the worm gear (without it actually working against you). Basically, it means that you can easily change the direction of the car, and the direction won't change unless input is applied from the steering wheel.
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Wouldn't this destroy any sense of "steering feel"? Probably only people who like driving would care about steering feel, but they are also the only ones who would notice torque steer. |
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Regardless, this is one of the many reasons I (and the rest of the car-loving world) drive a RWD car. And FWD is pretty much neering the end of its days anyway now that AWD is taking over as the drivetrain-to-have. |
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[DIYmatt], don't you think it's the motor car itself that is pretty much neering the end of its days anyway now, and that walking and bicycling and pack animals will soon be taking over? |
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Torque steer is the result of compromises in the suspension geometry. If the steer axis (kingpin axis) passes through the centre of the contact patch (where the tyre meets the ground), then the driving thrust has no moment about the steer axis and there is no torque steer. |
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A properly designed FWD suspension can virtually eliminate torque steer. Torque steer is most commonly seen in 'sports' versions of cars which were designed to have less power and narrower tyres. |
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For various reasons, the geometry does not have this characteristic, known a zero scrub radius. Also wide tyres may grip at one side better than the other, due to camber angle changes, road surface changes etc. |
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Many vehicles already use a worm gear to operate steering (Landrovers and VW beetles are well-known examples). If the worm drive has a reasonable ratio, it will give just as much feedback as a rack and pinion. |
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Worm gears in adjuster mechanisms etc. usually have a very high reduction ratio. It is that which prevents motion feedback, as the friction between the rubbing surfaces exceeds the rotary moment at the worm. |
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A worm drive will still give force feedback (it will be harder to turn the wheel against the effect of torque steer). Force feedback is increased by the addition of friction. |
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Not needed, and wouldn't work. |
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[DIYMatt] couldn't agree with you more about AWD, but in this system you could very easily have passive feedback. the shaft that goes from steering column to worm gear can also be connected from worm gear back to shaft with a clutch in between. when the clutch is engaged, the rack can spin the worm gear itself so feedback occurs. when the clutch is disengaged, the worm gear is not affected by the rack, other than increased friction to turn it. |
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Also, I know worm gears are used on older style steering systems, usually recirculating ball, but this would effectively combine a worm gear with rack and pinon steering, which is a better overall design than recirculating ball. And while the force needed to overcome the friction due to torque steer will be greater than no friction, variable power steering assist can account for it, while it cannot account for torque steer usually (unless a complicated system is employed a la Lexus) due to it causing an actual direction change. And the worm gear can still have a very low gear ratio with the reduction coming from the bevel gears. |
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My idea still might not be geat, but just saying. |
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Among the requirements for a steering system is simplicity. As the series of links between the drivers hands and the contact patches becomes longer and more complex, feedback is dulled and the opportunity for failure is increased. |
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A worm drive in series with a rack and pinion is worse than either setup on it's own, inheriting all the friction and backlash of both. |
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Adding more shafts and clutches is just asking for trouble. |
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The solution is to design the suspension correctly in the first place, not to try fixing the prblem with another gadget. |
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Electrical power steering uses this setup anyway. The problem is (as mentioned above) that it removes a lot of the feedback from the steering wheel, and whilst electronics are being developed to try and bring some of that back, it's a case of artificially recreating the tugs and nuances from the road upstream of the worm gear. |
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that lack of feedback is a real killer. I'd rather have torque steer that I can feel than a "dead wheel". |
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The passive feedback system I proposed with the clutch would allow for feedback for conditions other than heavy throttle. It would however add complexity, as noted. |
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