Quote:
Originally Posted by John in Santa Cruz
um, Super Duty's have gone to drive-by-wire steering? really? so if you have a electrical power loss, you have no steering at all??
the steering in my 2002 Super Duty is conventional mechanical steering box with a hydraulic booster. I thought the variable assist just changed the amount of power assist with the speed.
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Variable boost has been available for a long time, with hydraulic power steering. It requires no extra parts if the boost is either electrohydraulic (electric motor run hydraulic pump) or simply electric.
Loss of assist is not such a big deal - if the engine stops or there is a leak you lose assist with the entirely mechanical and hydraulic system, and that's rarely an issue. With an electrically boosted system you might be able to steer on battery power if the engine stops but the ignition is still on.
No system in production is fully steer-by-wire; even the ones which work that way at times mechanically lock up when power is lost so there is still steering.
Varying the steering ratio (how much the front wheels steer per turn of the steering wheel) is very different from varying the steering boost (how much steering force is applied per unit of torque applied to the steering wheel). It looks like I misread the original post, seeing only the effort reduction and not the ratio change. Good catch, John.
Quote:
Originally Posted by John in Santa Cruz
hmm, this says its entirely inside the steering wheel, that a motor in the wheel changes the ratio. that suggests the steering shaft is still mechanical, but it also suggests that a truck without the adaptive steering simply won't have that fancy steering wheel. |
Actually changing the ratio doesn't make sense, because there there is no gearbox in the steering wheel, let alone a variable-ratio gearbox; however, that's the terminology used in
Ford's official description. What this describes is that the motor in the steering wheel turns the steering column shaft more or less than the wheel turns, which makes mechanical sense but is a little scary to me... although less scary than the systems from other manufacturers that actually disconnects the wheel from the column to make it steer-by-wire. Ford's explanation:
Quote:
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... adaptive steering can add or subtract rotations to driver input at the steering wheel. Up to one full revolution can be saved at low speeds when steering lock-to-lock.
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This will not decrease effort at low speeds when the extra movement is added, so there is probably a coordinated boost change.
Ford's system (at least for other models) appears to just shift the relative position of the wheel and shaft. The motor in any system like this would need to drive through a worm gear so that it locks when power is lost or the computer fails and the system essentially disappears; fortunately, it appears from
images found in a web search that this is how it is built, and that worm gear pair is the "gear unit" in Ford's description, providing both the locking and 48:1 gear reduction.
The description by Car&Driver in a
2014 article about new features for 2015 noted that it would be available through Ford's car and light truck line - SuperDuty got it for 2017.
By the way, this system is built by Takata for Ford. Yes, that's the same company responsible for the defective airbags which have resulted in many millions of vehicles (from many manufacturers) being recalled.
That would certainly be additional hardware, and not just a programming feature - US$1000 isn't surprising for a system like that, although it is mechanically pretty simple. I'm not sure if I would like it, but if I did (based on test driving), the price would probably be acceptable. It would be strange that the steering wheel position no longer consistently indicates the front wheel steering angle; obviously they will have been careful to ensure that straight ahead on the wheel is still straight ahead in the steering.
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