Hydraulic Steering?
Discussion
rockin said:
DoubleD said:
What is there to like or dislike about a handbrake?
Electric systems,- No "just on" position
- No control over release. Often slow to release.
- Brake switch in a different position in every car
- Some switches push to apply brake, some switches pull to apply brake
- Some cars have a hold function, some don't. Many different hold systems
- Some cars have automatic hill hold, some don't. Rarely does hill hold manage to spot a hill.
- Can't release brakes without battery connected
- Can't release brakes with a flat battery.
Toltec said:
Not Porsche, but an interesting view of why BMW steering isn't as 'good' as it used to be-
https://blog.caranddriver.com/steer-me-feel-me-exp...
TL:DR Core customers prefer isolated steering.
You might as well ask why Porsche still don't do an affordable 911 that is a real sports car as opposed to the GT it has turned into. I've been doing some research into 911s recently and it seems people have been bemoaning the loss of the raw feeeling of the car since it went water cooled. At the same time it is acknowledged that it has also become a technically much better car.
God that is painful to read, a man in his position seemingly sympathetic to the masses who want lifeless steering.https://blog.caranddriver.com/steer-me-feel-me-exp...
TL:DR Core customers prefer isolated steering.
You might as well ask why Porsche still don't do an affordable 911 that is a real sports car as opposed to the GT it has turned into. I've been doing some research into 911s recently and it seems people have been bemoaning the loss of the raw feeeling of the car since it went water cooled. At the same time it is acknowledged that it has also become a technically much better car.
Unfortunately it’s not just mundane BMWs that are affected by this. Why does a brand new a Porsche 911 have less steering feedback and precision than a 10 year old 1.8 Mondeo with 100k on the clock? It’s embarrassing.
Edited by SkinnyPete on Monday 19th February 23:12
SkinnyPete said:
God that is painful to read, a man in his position seemingly sympathetic to the masses who want lifeless steering.
Unfortunately it’s not just mundane BMWs that are affected by this. Why does a brand new a Porsche 911 have less steering feedback and precision than a 10 year old 1.8 Mondeo with 100k on the clock? It’s embarrassing.
We had it right from the late 90's to the late 00's. When we improved from the god awful steering on the MK5 Escort, and had some absolute crackers like the MK1 Focus and the E46 3 Series, can't go without mentioning the 306 either. Who knows, maybe we're in the early 90's period for EPAS, maybe we'll get to a period where steering becomes amazing again. Unfortunately it’s not just mundane BMWs that are affected by this. Why does a brand new a Porsche 911 have less steering feedback and precision than a 10 year old 1.8 Mondeo with 100k on the clock? It’s embarrassing.
Edited by SkinnyPete on Monday 19th February 23:12
Max_Torque said:
Er, it can, and it does!
With hydraulic steering, there is a small hydraulic ram mounted concentrically to the rack bar, and as the rack moves left / right it moves with it.
Connected to the (rotating) steering column is an OPEN SPOOL (and that bit's important) proportional valve. When you apply torque to the handwheel, the rotary valve, which has a small torsion bar in it it) deflects, and opens up the ports to the cylinder, allowing oil pressure to be applied to one side of the ram. The more torque you put in, the more pressure is applied. The clever bit is two fold. When the rack moves, the torque falls, meaning the torsion bar twist automatically reduces, and so assistance pressure tails off, unless you keep moving the handwheel as the rack actually moves. But because it is an open spool valve, no system pressure is built up when you are not applying torque to the handwheel, hence the rack ism broadly speaking, pretty free to move, with just a small amount of damping from having to pump the hydraulic fluid out of the ram.
EPAS is very different. A large electric motor is geared directly to the rack, with a reasonably high gear ratio. That means as the rack moves, even a tiny amount, the motor must rotate. So what you say, well, the motors rotating inertia is referenced to the rack via the gear ratio, so that inertia appears to be large, meaning there is a large damping force resisting free movement of the rack. Early systems, with big motors and low power struggled to control their own inertia, leading to flat, lifeless steering feel. Later EPAS systems, with much more power and much smarter control electronics can now negate their own inertia (by applying electric power to spin up the motor at the same speed the rack is moving, so the motor doesn't act as a damper to free movement
I wonder if you could use something similar to the magnetic drive pumps as a torque amplifier for steering. Instead of fixed magnets the outer shell would have electromagnets and there would be two counter-rotating shells driven by a normal electric motor. By applying current to the drive shells you induce a torque in the shaft in the direction you want.With hydraulic steering, there is a small hydraulic ram mounted concentrically to the rack bar, and as the rack moves left / right it moves with it.
Connected to the (rotating) steering column is an OPEN SPOOL (and that bit's important) proportional valve. When you apply torque to the handwheel, the rotary valve, which has a small torsion bar in it it) deflects, and opens up the ports to the cylinder, allowing oil pressure to be applied to one side of the ram. The more torque you put in, the more pressure is applied. The clever bit is two fold. When the rack moves, the torque falls, meaning the torsion bar twist automatically reduces, and so assistance pressure tails off, unless you keep moving the handwheel as the rack actually moves. But because it is an open spool valve, no system pressure is built up when you are not applying torque to the handwheel, hence the rack ism broadly speaking, pretty free to move, with just a small amount of damping from having to pump the hydraulic fluid out of the ram.
EPAS is very different. A large electric motor is geared directly to the rack, with a reasonably high gear ratio. That means as the rack moves, even a tiny amount, the motor must rotate. So what you say, well, the motors rotating inertia is referenced to the rack via the gear ratio, so that inertia appears to be large, meaning there is a large damping force resisting free movement of the rack. Early systems, with big motors and low power struggled to control their own inertia, leading to flat, lifeless steering feel. Later EPAS systems, with much more power and much smarter control electronics can now negate their own inertia (by applying electric power to spin up the motor at the same speed the rack is moving, so the motor doesn't act as a damper to free movement
ETA: Steering torque seems to be 20Nm maximum so using a magnetic torque converter to couple an electric motor to the steering shaft may work. If the coupling force is controlled using electro magnets rather than permanent magnets the level of assistance can be controlled quickly without needing to vary the motor speed rapidly so its inertia becomes less of an issue. As the coupling force is controlled feedback would not be directly afected by the inertia of the motor. I'd put the permanent magnets on the motor side and the electro-magnets on the steering shaft as connecting the power would not need slip rings then.
ETA2: Patent using a linear motor in the rack itself - https://patents.google.com/patent/US20110153159
Edited by Toltec on Tuesday 20th February 11:08
Edited by Toltec on Tuesday 20th February 11:31
aaron_2000 said:
Interesting, from the experience I've had with all 3, I've found unassisted is a bit of a ball ache until you learn to drive around it, I found cars with EPAS just too disconnected and light, the sweet spot for me was on the 00's cars with PAS, the E46, E60, Focus, Ka/Fiesta and cars of the like. I've never driven any new hot hatch, although I've driven the 340i which suffers from horrid steering, it's so artificial, light and disconnected that it isn't that enjoyable in the corners for me.
Yes, very interesting! I had a P6 Rover 3500S with no PAS and it really was a PITA - heavy at lower speeds and exceedingly vague above 30 mph due to the woolly steering box! Whereas the MKII Granada with HPAS and rack and pinion that I bought afterwards felt like a go-kart by comparison.
I currently have an E46 with HPAS, and it's heavier (and no better) than the EPAS on my E86 - but that certainly isn't too light.
I'm sure it varies from car to car - it's surely all about what the manufacturer specifies?!
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