Power steering - What systems are people using?
Discussion
In an "off road" application, more system inertia may be a good thing! (as it will help prevent the wheel getting knocked out of your grasp on big impacts to the front wheels, and also damp out some of the "chatter" from broken surfaces at high speed ;-) Also, when off road, most rapid handwheel inputs are not occurring under a high lateral load (generally corrections on "slippy" surfaces etc, more like in gravel rallying etc)
stevieturbo said:
Build the PAS pump onto another stage of the dry sump pump lol
If i had any extra space around the oil pump i would do just that!stevieturbo said:
I wonder for the crappy electrohydraulic....could you somehow have an accumulator to store pressure so there would always be sufficient power for those fast times ?
As mentioned previously, the issue is that PAS is "open spool". When no steering assistance is required (ie most of the time) the fluid flows freely to and from the rack and hence there is no pressure built up to "store". The only time you have pressure is when you are requesting assistance, and at that point you might not want to loose any flow, depending on the rack velocity at the time. Hence a system to control a valve to let fluid flow into and out of a pressure accumulator would be quite complex and difficult to optimise, and suffer from being heavy, bulky and "finite" (ie it could only add an extra flow boost for a fixed max period, and would take time to recharge) Better to just fit a bigger (or second) pump!
Max_Torque said:
^^^^ Running "closed spool" with that Moog valve i assume?
Has to be really or we'd need to run a seperate hydraulic circuit just for the PAS. Is there a reason you can't go closed spool for your application? Maybe 16K€ of Parker pump would be over the top but there are a few options which are much cheaper as a hydraulic power source that would be suitable, or the older spec 6500RPM input speed Parker pumps are quite cheap and plentiful now and you could move your gearbox control to hydraulic at the same time....The RX8 'lecy power rack looks like it might be a possible solution:
Looks like effectively an "Linear" brushed DC motor on the end of the rack, so easy to drive. I imagine it's pretty heavy mind, but all the weight is about as low as it can go in the chassis.
But it's got a quite slow ratio at 16.4:1 (when installed in an Rx8, obviously different length steering arms on the uprights will change that in "non RX8" applications)
Looks like effectively an "Linear" brushed DC motor on the end of the rack, so easy to drive. I imagine it's pretty heavy mind, but all the weight is about as low as it can go in the chassis.
But it's got a quite slow ratio at 16.4:1 (when installed in an Rx8, obviously different length steering arms on the uprights will change that in "non RX8" applications)
Max_Torque said:
I could do just that, but it would be a major revision of the cars systems tbh! Looking for a simpler option ;-)
Pneumatics for show, Moogs for a pro. Go on you know you want to really. I'll permanently lend you a 6.5K RPM IS pump if you go for it..... you could do active ride then as well 
Max_Torque said:
annodomini2 said:
Rack drive units tend to have major installation issues in cars not designed for them.
Care to expand on that^^^ ??They also tend to be for heavier cars 1600kg+ (in general).
Max_Torque said:
annodomini2 said:
How heavy is the car?
Pretty much 960kg before we get in it.How about Fiesta Mk7 Column drive unit?
annodomini2 said:
Column drive should be fine for that weight, unless you're running 3/4 turn lock to lock?
How about Fiesta Mk7 Column drive unit?
Oh i see, i was not thinking about the "Physical packaging" issues, but obviously there would have to be room to fit what ever solution i decided to use!How about Fiesta Mk7 Column drive unit?
Can't run with a column motor as i don't have any space around the column, and i hate how it puts lots of mass up high!
The latest ZF Servolectric Paraxial unit is ~1kW, with a brushless DC motor and belt drive into a ball screw directly on the rack bar. Looks petty chunky, but i'm wondering about taking it's internals (pinion, rack,motor,ballscrew) and putting them into a custom casing to fit:
I seen a GM car with a motor directly on the column...but this was installed right at the very base of the column, inside the cabin
It was a spaceframe, carbon bodied race car ( Andrew Gallachers Focus )
Not sure which vehicle this was from though
gotta love google images sometimes. Maybe an adaptation of this ?
http://autoinformed.com/wp-content/uploads/2011/10...
http://plugincars.790831.n2.nabble.com/Electric-Po...
http://electricpowersteering.net/automotive-power-...
It was a spaceframe, carbon bodied race car ( Andrew Gallachers Focus )
Not sure which vehicle this was from though
gotta love google images sometimes. Maybe an adaptation of this ?
http://autoinformed.com/wp-content/uploads/2011/10...
http://plugincars.790831.n2.nabble.com/Electric-Po...
http://electricpowersteering.net/automotive-power-...
Basically, anything mounted to the steering column is a no go. Because of the front mid engine location, the column threads it's way past the engine and ancillaries, missing by about 5mm max in most places!
I also don't really like the idea of having the motor on the column, much better to put the load where it's needed right into the rack bar, like we all did with conventional hydraulic PAS!
Those powered columns from that "electric power steering" company look, er, extremely weedy. Probably alright for a shonky "hot rod" that doesn't really need to go around corners, but not for a proper competition car. They also make no mention of their system fail safes / diagnostics etc, which is a tad worrying considering the safety critical application.......
I also don't really like the idea of having the motor on the column, much better to put the load where it's needed right into the rack bar, like we all did with conventional hydraulic PAS!
Those powered columns from that "electric power steering" company look, er, extremely weedy. Probably alright for a shonky "hot rod" that doesn't really need to go around corners, but not for a proper competition car. They also make no mention of their system fail safes / diagnostics etc, which is a tad worrying considering the safety critical application.......
Max - you need to consider the fact that a hydraulic pas rack will have a torsion shaft which transmits torque to the pinion and operates the spool valve that controls the assistance. If the assistance is removed, the torsion bar transmits torque, but it is unlikely to be sized for infinite life unassisted. If you were to reuse the rack with epas, you would want to use a far thicker version that was sized to have infinite life.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff