> And a yoke requires progressive steering which is impractical without steer-by-wire.
But also look at Citroën's DIRAVI system, used on the CX, SM, and some XMs. There's no direct mechanical link between the steering wheel and the rack when the system is pressurised. When you turn the wheel a kind of dogbone link thing pushes a spool valve one way or the other allowing hydraulic fluid to push the rack along, which pushes the other end of the link back to shut the fluid off again.
So far, so similar to the Danfoss valve in a conventional power-assisted steering system, except that uses a rotary valve and a big torsion spring in the steering rack (that's why your steering wheel feels springy with the engine off).
But DIRAVI is fully powered with no mechanical link, so how do you get increasing resistance with increasing speed? Well, there's a governor on the gearbox that allows hydraulic fluid into a little cylinder that pushes a spring-loaded roller against a heart-shaped cam attached to the steering wheel shaft. This will try to spring back to the middle, and the faster you go the harder it springs back. At 70mph you can barely move the steering wheel, but it will flick a large heavy car from lane to lane with fingertip pressure.
You have to get used to this and for the first few miles you'll be zig-zagging down the road like you're tacking a dinghy, but after that you'll get used to just thinking about your right pinky finger being a gram heavier and going round a corner. I've driven some seriously high-end sports cars with legendary handling and performance and they feel pretty rough and tractory now ;-)
If the pressure fails of course then there's no powered steering (notice I say powered, not power-assisted), although in practice what tends to happen is that the "resistance" part goes first giving you very sensitive steering.
What happens once there's no pressure is that the steering wheel moves about 20° before you run the valve to its end and then the dogbone pushes directly on the drive gear for the rack. So the steering is very loose and wobbly but you can at least steer well enough to get it out of the parking space and into the workshop. You still have brakes for an hour or so if the pump belt breaks, and enough steering to get safely to the side of the road, or at least out of the fast lane.
In the 1960s they had a prototype Citroën DS controlled by a joystick using pretty much the same setup (hydraulic valve to push the rack around, heart-shaped cam to apply resistance). Apparently it was very comfortable and natural to drive but ultimately a bit to weird even for Citroën.
Not a scrap of electronics in it, unless you count the pressure switch and dashboard lightbulb.
I had the hydraulic pump belt break when I was about 30 or 40 miles from home, and of course I had a water pump belt and an alternator belt, but not the hydraulic pump belt.
The brake and regulator accumulators were both nice and new though so the "low brake pressure stop immediately" warning only came on about two or three miles from home (once there's no pressure at all, there's no brakes at all, but this is pretty difficult to achieve in practice) and I just had to cope with the twitchy steering through the difficult part - driving through town at 15-20mph in rush hour traffic anyway.
It would only be overengineered if it was not necessary, and once you drive one you'll realise that all cars should have it.
You can actually get pretty close with electric power steering but that's a lot more involved than a few dozen incredibly finely machined parts and a bunch of thin oil at 180 times atmospheric pressure.
But also look at Citroën's DIRAVI system, used on the CX, SM, and some XMs. There's no direct mechanical link between the steering wheel and the rack when the system is pressurised. When you turn the wheel a kind of dogbone link thing pushes a spool valve one way or the other allowing hydraulic fluid to push the rack along, which pushes the other end of the link back to shut the fluid off again.
So far, so similar to the Danfoss valve in a conventional power-assisted steering system, except that uses a rotary valve and a big torsion spring in the steering rack (that's why your steering wheel feels springy with the engine off).
But DIRAVI is fully powered with no mechanical link, so how do you get increasing resistance with increasing speed? Well, there's a governor on the gearbox that allows hydraulic fluid into a little cylinder that pushes a spring-loaded roller against a heart-shaped cam attached to the steering wheel shaft. This will try to spring back to the middle, and the faster you go the harder it springs back. At 70mph you can barely move the steering wheel, but it will flick a large heavy car from lane to lane with fingertip pressure.
You have to get used to this and for the first few miles you'll be zig-zagging down the road like you're tacking a dinghy, but after that you'll get used to just thinking about your right pinky finger being a gram heavier and going round a corner. I've driven some seriously high-end sports cars with legendary handling and performance and they feel pretty rough and tractory now ;-)
If the pressure fails of course then there's no powered steering (notice I say powered, not power-assisted), although in practice what tends to happen is that the "resistance" part goes first giving you very sensitive steering.
What happens once there's no pressure is that the steering wheel moves about 20° before you run the valve to its end and then the dogbone pushes directly on the drive gear for the rack. So the steering is very loose and wobbly but you can at least steer well enough to get it out of the parking space and into the workshop. You still have brakes for an hour or so if the pump belt breaks, and enough steering to get safely to the side of the road, or at least out of the fast lane.
In the 1960s they had a prototype Citroën DS controlled by a joystick using pretty much the same setup (hydraulic valve to push the rack around, heart-shaped cam to apply resistance). Apparently it was very comfortable and natural to drive but ultimately a bit to weird even for Citroën.
Not a scrap of electronics in it, unless you count the pressure switch and dashboard lightbulb.