Discussion
buggalugs said:
You're talking like there isn't anything to go wrong with conventional PAS systems either, rubber couplings, valves, hydraulics, bits of metal made by the lowest bidder.
Bottom line is that if you're going to jump in a metal box and do 70mph then at some point you have to start trusting the people who made it.
Of course there is. But if the PAS fails, you've still got a steering rack to rely on. Steering does work without PAS, you know? Bottom line is that if you're going to jump in a metal box and do 70mph then at some point you have to start trusting the people who made it.
I knew the mechanics failing point would come up... It's a lot easier to maintain and check mechanical components. You mostly get warnings, such as clunks and bangs, or not operating quite like they should before they completely fail. With electronics though, all it takes is for a bit of solder on a circuit to crack, a design fault, a wire to snap etc, and the component is useless.
Plus you can't really inspect the electrical components. Are you going to strip down the motors, relays, wiring looms, ECUs, etc every year to inspect them for wear? Or maybe just throw them in the bin and replace as part of the service? With mechanical components, you can check for simple things like play, breakdown in the material, leaking fluids, etc.
BriC175 said:
But 'trust' isn't enough. End of the day, things go wrong. They might work 99.9% of the time as intended, but I wouldn't want to be in the car, travelling around a sweeping bend on the motorway at 70+mph, when all of a sudden, the steering fails due to a breakdown in an electrical component, or even a design fault (which would lead to recalls.. fine for most, but not for the poor sod who found the fault).
Things like Servo assistance, ABS, PAS, ESC, etc are all fine, as there is a mechanical back up. Completely removing mechanical back up seems like a silly idea, and one that I don't see catching on.
Have a friend pull your PAS fuse on that 70mph sweeping bend and see how well you can maintain your line with no assistance. For added fun, repeat with a 7 stone woman. For bonus points, disconnect the vacuum hose from your brake servo and try stopping from that speed in a hurry.Things like Servo assistance, ABS, PAS, ESC, etc are all fine, as there is a mechanical back up. Completely removing mechanical back up seems like a silly idea, and one that I don't see catching on.
Cars are already heavily reliant on assistance systems and a major electrical failure now is capable of causing a loss of control or crash.
sjg said:
BriC175 said:
But 'trust' isn't enough. End of the day, things go wrong. They might work 99.9% of the time as intended, but I wouldn't want to be in the car, travelling around a sweeping bend on the motorway at 70+mph, when all of a sudden, the steering fails due to a breakdown in an electrical component, or even a design fault (which would lead to recalls.. fine for most, but not for the poor sod who found the fault).
Things like Servo assistance, ABS, PAS, ESC, etc are all fine, as there is a mechanical back up. Completely removing mechanical back up seems like a silly idea, and one that I don't see catching on.
Have a friend pull your PAS fuse on that 70mph sweeping bend and see how well you can maintain your line with no assistance. For added fun, repeat with a 7 stone woman. For bonus points, disconnect the vacuum hose from your brake servo and try stopping from that speed in a hurry.Things like Servo assistance, ABS, PAS, ESC, etc are all fine, as there is a mechanical back up. Completely removing mechanical back up seems like a silly idea, and one that I don't see catching on.
Cars are already heavily reliant on assistance systems and a major electrical failure now is capable of causing a loss of control or crash.
FBW steering would.
BriC175 said:
Things like Servo assistance, ABS, PAS, ESC, etc are all fine, as there is a mechanical back up. Completely removing mechanical back up seems like a silly idea, and one that I don't see catching on.
Completely agree that, with no mechanical backup, you're in a lot of trouble if a fuse blows, ECU dies, etc. Planes have 3 of most things, partly for that reason. Not sure how they'd ever make that particularly safe in a car.But, having said that, if your electric power steering suddenly decides you need maximum clockwise assistance, or your ESP decides it's detected oversteer and applies the front right brake hard, then you're probably going to crash... Even with mechanical backup, I think we've already reached the point where if electronic systems don't fail safe, then they could cause a crash.
It's just that they probably prevent more crashes than they're going to cause.
Have none of you lot ever driven a tractor? Hydraulic steering, no feedback, no bumpstops on the steering wheel. Now that is interesting to thread roads with! Admittedly, being able to twirl the wheels from lock to lock with a flick of the wrist is useful in a field, but at speed, among traffic, not fun.
The system could use brake yaw (via the ESP system) to steer if the steering system fails. And unlike a conventional mechanical only system, it can easily self diagnose any issues in real time and at all times. (Whereas the mech system relies on the driver or the "once-a-year" MOT man, and neither of those are exactly foolproof..........)
Ok, loss of steering culd be bad, very bad but I suspect in reality it is very very unlikely, the system will be controlled by the ecu which will check every time the car is started and will constantly monitor stuff, if a fault is detected it will alert you via the instruments, very unlikely it just cuts out and leaves you with no steering, probably as likely as a ball joint, rack, pas pump breaking. We rely on tyres that explode and we lose steering but we have accepted that risk already, this is a new one where I think the perceived risk is much greater than the actual risk and probably less than the normal mode failures we accept as part of driving.
In most situations if you did lose steering totally, along with whatever failsafe is employed then you would slow the car with the brakes, most of the time you would be travelling at a suitable speeds and not leaning on the cornering abilities, it has the potential for disaster of course but I suspect most failures will be inconvenient but uneventful.
I dont think the manufacturers wwould be touting this without being sure it can be safe and reliable, it will need extensive testing and approval but I really think it could work.
In most situations if you did lose steering totally, along with whatever failsafe is employed then you would slow the car with the brakes, most of the time you would be travelling at a suitable speeds and not leaning on the cornering abilities, it has the potential for disaster of course but I suspect most failures will be inconvenient but uneventful.
I dont think the manufacturers wwould be touting this without being sure it can be safe and reliable, it will need extensive testing and approval but I really think it could work.
The Nissan system as linked has three ECUs - it would take all three to fail for the clutch in the steering column to need to be engaged.
If it's like the ones in aircraft, the ECUs monitor each other, and if one doesn't agree with the other two, it flags a warning and gets ignored (and possibly restarted).
If it's like the ones in aircraft, the ECUs monitor each other, and if one doesn't agree with the other two, it flags a warning and gets ignored (and possibly restarted).
sjg said:
Have a friend pull your PAS fuse on that 70mph sweeping bend and see how well you can maintain your line with no assistance. For added fun, repeat with a 7 stone woman. For bonus points, disconnect the vacuum hose from your brake servo and try stopping from that speed in a hurry.
Cars are already heavily reliant on assistance systems and a major electrical failure now is capable of causing a loss of control or crash.
I have driven cars that were designed for PAS when the PAS wasn't working numerous times. Mainly when being towed. It really isn't that bad, and becomes less of an issue as the speed increases. If the servo doesn't work, it's harder to brake, but certainly not impossible. I'd be interested to see if it actually significantly increases the braking distance to be honest, as I know that if I felt my servo is dead (and you can feel it), I'd put a lot of my force into the brake pedal. Cars are already heavily reliant on assistance systems and a major electrical failure now is capable of causing a loss of control or crash.
Max_Torque said:
The system could use brake yaw (via the ESP system) to steer if the steering system fails.
But would it not just progressively straighten the steering? Again, I go back to my example of travelling at 70+mph around a sweeping bend on the motorway... That wouldn't be much use! J4CKO said:
very unlikely it just cuts out and leaves you with no steering...
...In most situations if you did lose steering totally, along with whatever failsafe is employed then you would slow the car with the brakes, most of the time you would be travelling at a suitable speeds and not leaning on the cornering abilities...
Again, using my example above, it wouldn't be much use. ...In most situations if you did lose steering totally, along with whatever failsafe is employed then you would slow the car with the brakes, most of the time you would be travelling at a suitable speeds and not leaning on the cornering abilities...
I'm all for progression and I'm not the sort of person that complains about change just for complainings sake, as I realise that without change, we'd still be stuck in caves. But, as with everything, you need to draw the line somewhere. Sure, it does offer some advantages, such as making for easier packaging and less steering feedback (if you'd consider that an advantage?), but IMO it provides very little advantage for huge engineering costs and risk.
kambites said:
It's a clutched steering column as an active fail-safe. Which presumably also needs to be activated by the computer that they're worried about failing. 
Er, no. You do realise that "fail-safe" means literally that. It fails (when removing the computer control, electrical power etc) safe, which means that the clutch engages and you can still steer.
kambites said:
Big Fat Fatty said:
How does the system work in aircraft, is it just the landing gear or is it connected to the control surfaces while in the air as well?
I think some modern passenger planes have no physical link between the cockpit controls and any of the fight surfaces. Works like this:
Pilot moves the stick etc.
signal goes to the FCC (Flight Control Computer)
FFC sends signal to the control surface actuator
Actuator moves the control surface.
Yes aircraft have multiple redundant backup systems to, I would imagine civil aircraft are atleast tripple redundant (needs citation) because if it had only one system and it failed the aircraft cannot be flown as there are no mechanical controls, on a fighter jet the pilot ejects - in an airliner...
And as another poster stated the regular control cables are quite thin, I watched The Plane Crash last week (ch 4) and was amazed at how thin the control cables actually are!
There is no reason why a system like this on a car (not a joystick controller but full drive by wire) should be unsafe, the firmware would have to be tested to a very high level because it is a safety critical component.
Most cars these days have no mechanical link between the throttle pedal and the throttle body and other than the characteristic lag you get (can be dialed out with a decent re-map) there are no real issues with this system.
The only problem I can think of with a system like this is the loss of steering feel, which is a major part of driving, it lets you know all sorts of details about the road surface. But you can be that they will counter this with, it will have artificial feedback!
sjg said:
Have a friend pull your PAS fuse on that 70mph sweeping bend and see how well you can maintain your line with no assistance. For added fun, repeat with a 7 stone woman. For bonus points, disconnect the vacuum hose from your brake servo and try stopping from that speed in a hurry.
Cars are already heavily reliant on assistance systems and a major electrical failure now is capable of causing a loss of control or crash.
Above 70 mph the power assistance is pretty irrelevant. My car turns the electro hydraulic system off at those speeds. Cars are already heavily reliant on assistance systems and a major electrical failure now is capable of causing a loss of control or crash.
DaveCWK said:
Above 70 mph the power assistance is pretty irrelevant. My car turns the electro hydraulic system off at those speeds.
At 70mph there should be no problems controlling a car with non-functional PAS. Parking and taking sharp corners at low speeds is another matter entirely!Gassing Station | General Gassing | Top of Page | What's New | My Stuff