Power steering - What systems are people using?
Discussion
If you have power steering on your kit or modified car, what systems are you using?
The "Corsa" electric column motor system seems popular but i don't think it's performance (power, inerta etc) is very good by modern standards, but it has the benefit of working with pretty much any steering rack!
Guess most people just use the std engine driven PAS pump and what ever rack they find that fits etc?
The "Corsa" electric column motor system seems popular but i don't think it's performance (power, inerta etc) is very good by modern standards, but it has the benefit of working with pretty much any steering rack!
Guess most people just use the std engine driven PAS pump and what ever rack they find that fits etc?
On my mk2 Granada with the 24v lump fitted, I went over to a Saxo/106 electric hydraulic pump.
Works perfectly fine for pretty much all conditions and the weight of the steering is almost bang on the same as the old 2.8 engine driven pump.
The only short comings of it are when trying to go from one direction to the other at low engine speeds, as the alternator can't quite give enough output to keep up with the pump.
But, the system is essentially 4wires and the 2 main hydraulic lines to plumbin. And there's no steering column modifying needed to fit either
Works perfectly fine for pretty much all conditions and the weight of the steering is almost bang on the same as the old 2.8 engine driven pump.
The only short comings of it are when trying to go from one direction to the other at low engine speeds, as the alternator can't quite give enough output to keep up with the pump.
But, the system is essentially 4wires and the 2 main hydraulic lines to plumbin. And there's no steering column modifying needed to fit either
The saxo pump, which is actually just a standard "hydraulic power pack" from the Canadian firm HPI is ok for small light cars with low ratio racks, but it struggles for larger cars with "faster" racks that require a much higher oil flow rate. I found it had massive hydraulic lag when i tried one on my car (which to be fair, has a high volume ram and is just 1.5 turns LtL). Peak hydraulic power is only around 450W, which is low.
The corsa column driver has the advantage of being on the column (fairly obviously!) and so it's input rate is constant (pretty much how fast a human can turn a wheel) whereas systems that apply the assistance to the rack bar will have a variable velocity depending on the pinion ratio and steering arm effective length on the uprights etc! In this case, the low power of the system means that assistance falls with handwheel rate, but at least there are no hydraulic effects to cause additional resistance (for a hyraulic system, the ram on the rack turns into a PUMP if when the flow rate exceeds that of the pump...) On the "motor on column" systems the issue is the mechanical inertia of the motor is coupled to the column, which tends to damp the steering response,making the steering feel unresponsive, and unless you clutch that motor to the column,that inertia is there the entire time, even when no assistance is being delivered (ie driving in a straight line)
The corsa column driver has the advantage of being on the column (fairly obviously!) and so it's input rate is constant (pretty much how fast a human can turn a wheel) whereas systems that apply the assistance to the rack bar will have a variable velocity depending on the pinion ratio and steering arm effective length on the uprights etc! In this case, the low power of the system means that assistance falls with handwheel rate, but at least there are no hydraulic effects to cause additional resistance (for a hyraulic system, the ram on the rack turns into a PUMP if when the flow rate exceeds that of the pump...) On the "motor on column" systems the issue is the mechanical inertia of the motor is coupled to the column, which tends to damp the steering response,making the steering feel unresponsive, and unless you clutch that motor to the column,that inertia is there the entire time, even when no assistance is being delivered (ie driving in a straight line)
I'm looling to improve the linearity of the assistance on my rally car at all handwheel rates, expecially on big fast "oh s**t" moments when you need to use a lot of lock very quickly. At the moment the system weights up unacceptably.
I use a LHD GrpA/WRC Escort Cossie rack,which has a modified pinion/bar to achieve both a variable ratio and a faster one (compared to the std road cosworth rack).
As far as i can tell it uses the std sierra/escort housings and power ram:
I have no idea if the spool valve has been re-profiled, there is certainly a good chance that it has.
I power it with a TRW Gen2 EHPAS pump running with vehicle and handwheel rate based pump speed control:
but although this is one of the most powerful pumps available (1kW) it still struggles to keep up with the flow demands of the rack in-extremis ;-(
I use a LHD GrpA/WRC Escort Cossie rack,which has a modified pinion/bar to achieve both a variable ratio and a faster one (compared to the std road cosworth rack).
As far as i can tell it uses the std sierra/escort housings and power ram:
I have no idea if the spool valve has been re-profiled, there is certainly a good chance that it has.
I power it with a TRW Gen2 EHPAS pump running with vehicle and handwheel rate based pump speed control:
but although this is one of the most powerful pumps available (1kW) it still struggles to keep up with the flow demands of the rack in-extremis ;-(
Simple answer after some friends experience.
It seems that all of these electric, electrohydraulic look and sound nice on paper.
Maybe even sound nice on the internet...and cruising about, leisurely tracks etc....yup all good.
But once you actually need to steer, or have big grippy tyres and work the steering hard. It does seem all of the above systems seriously struggle.
I know two friends have recently switched back to a simple reliable mechanical pump because of the above failings. They had been using electro-hydraulic
Really..modern mechanical pumps are small, they're light, they're reliable...and usually already bolted to the engine you're using.
WTF change it !
It seems that all of these electric, electrohydraulic look and sound nice on paper.
Maybe even sound nice on the internet...and cruising about, leisurely tracks etc....yup all good.
But once you actually need to steer, or have big grippy tyres and work the steering hard. It does seem all of the above systems seriously struggle.
I know two friends have recently switched back to a simple reliable mechanical pump because of the above failings. They had been using electro-hydraulic
Really..modern mechanical pumps are small, they're light, they're reliable...and usually already bolted to the engine you're using.
WTF change it !
Options seem to be:
1) beef up the current EHPAS pump (fit larger pump gears, modify current shunts etc)
2) Modify the rack to have a smaller dia power ram (not that easy) (less total assistance, but available over a wider range of rack velocities)
3) change to an aftermarket "race" style race and use an external power ram and spool assy
4) Move to completely electric steering, using the rack off something like the new M3 that has a beefy electric rack (also, an 'lecy RX8 rack looks like it might be modifyable, as the power electronics look to be separate)
1) beef up the current EHPAS pump (fit larger pump gears, modify current shunts etc)
2) Modify the rack to have a smaller dia power ram (not that easy) (less total assistance, but available over a wider range of rack velocities)
3) change to an aftermarket "race" style race and use an external power ram and spool assy
4) Move to completely electric steering, using the rack off something like the new M3 that has a beefy electric rack (also, an 'lecy RX8 rack looks like it might be modifyable, as the power electronics look to be separate)
I`ve had 3 gm power steering columns fail,2 on Corsas and the other,same setup on an Agila.
The Corsas systems had just stopped working completely and with the massive gearing between column and motor winding that motor over at any speed using the column took some serious heft.
the Agila was also dead and even heavier but inspection revealed the main power plug had been unplugged.
When we plugged it back in the steering wheel spun to full left lock in around half a second,vibrating and shaking the whole column upon stopping.
We un plugged it and set the wheels straight then plugged it back in,it happened again.
At the third try I attempted to hold the steering wheel,not a chance.
I always assumed that upon failure these things should just shut down leaving heavy but safe-ish steering.
It seems that is not always the case,
scary stuff at anything over 2mph,I would imagine.
How about a booster tank for the hydraulics they are used for lifting gear,etc.
A small tank inline that stores fluid,pressurised during normal pumping.
when the system back-pressure reaches a set amount the same valve releases that stored pressurised fluid back in to the system to assist.
The Corsas systems had just stopped working completely and with the massive gearing between column and motor winding that motor over at any speed using the column took some serious heft.
the Agila was also dead and even heavier but inspection revealed the main power plug had been unplugged.
When we plugged it back in the steering wheel spun to full left lock in around half a second,vibrating and shaking the whole column upon stopping.
We un plugged it and set the wheels straight then plugged it back in,it happened again.
At the third try I attempted to hold the steering wheel,not a chance.
I always assumed that upon failure these things should just shut down leaving heavy but safe-ish steering.
It seems that is not always the case,
scary stuff at anything over 2mph,I would imagine.
How about a booster tank for the hydraulics they are used for lifting gear,etc.
A small tank inline that stores fluid,pressurised during normal pumping.
when the system back-pressure reaches a set amount the same valve releases that stored pressurised fluid back in to the system to assist.
shoehorn said:
How about a booster tank for the hydraulics they are used for lifting gear,etc.
A small tank inline that stores fluid,pressurised during normal pumping.
when the system back-pressure reaches a set amount the same valve releases that stored pressurised fluid back in to the system to assist.
Unfortunately PAS racks are "open spool" ie they have flow but no pressure when not servoing the rack, hence there is no pressure to store!A small tank inline that stores fluid,pressurised during normal pumping.
when the system back-pressure reaches a set amount the same valve releases that stored pressurised fluid back in to the system to assist.
I had a quick look at the calibration of the TRW EHPAS pump i'm using by pulling out the contents of the controller EEPROM and the characteristic tables for pump speed (and hence flow rate) are easy to spot!
Basically there are 6 different 5x5 tables for pump speed vs vehicle speed and handwheel rate, i imagine they are used for different driving "modes" in the donor car (eco, sport, etc).
However, all are quite similar, and all have the same maximal pump speed, currently 237 out of a possible max speed of 255. That suggests there might be a bit of pump speed headroom availible to get a little bit more flow but not a lot (assuming sufficient battery voltage is availible)
I'd also imagine there's a memory checksum in there somewhere so it won't be quite straight forward to change those characteristic tables!
Probably better to try to modify the gear pump for more flow at the same speed and modify the motor current shunts to "fool" the controller into not spotting the extra load current instead.
Hi Max,my company converts commercial vehicles into,water filtration units,generators,pumping platforms,winching drums etc.
I will try to use mechanical-hydraulic set ups where possible as Most of our vehicles end up in places like Libya and Egypt so electric is best avoided.
I have utilised some Hydra Products 24volt 3Kw uints to raise and rotate a 3 1/2 ton platform where mechanical drive is impossible and have been more than satisfied with the units abilities.
They build a 12 volt 1.8 KW unit @ <220 bar and 25 Lpm.
they are based in Gloucester.
A booster tank could be a solution ,the previous poster has the right idea but it would need a slightly different set up at the pump and would require some tricky fine tuning.
I will try to use mechanical-hydraulic set ups where possible as Most of our vehicles end up in places like Libya and Egypt so electric is best avoided.
I have utilised some Hydra Products 24volt 3Kw uints to raise and rotate a 3 1/2 ton platform where mechanical drive is impossible and have been more than satisfied with the units abilities.
They build a 12 volt 1.8 KW unit @ <220 bar and 25 Lpm.
they are based in Gloucester.
A booster tank could be a solution ,the previous poster has the right idea but it would need a slightly different set up at the pump and would require some tricky fine tuning.
Edited by dickkark on Tuesday 9th September 00:32
Max_Torque said:
Options seem to be:
1) beef up the current EHPAS pump (fit larger pump gears, modify current shunts etc)
2) Modify the rack to have a smaller dia power ram (not that easy) (less total assistance, but available over a wider range of rack velocities)
3) change to an aftermarket "race" style race and use an external power ram and spool assy
4) Move to completely electric steering, using the rack off something like the new M3 that has a beefy electric rack (also, an 'lecy RX8 rack looks like it might be modifyable, as the power electronics look to be separate)
Max i have the simplest and cheapest answer for you. GO TO THE GYM! 1) beef up the current EHPAS pump (fit larger pump gears, modify current shunts etc)
2) Modify the rack to have a smaller dia power ram (not that easy) (less total assistance, but available over a wider range of rack velocities)
3) change to an aftermarket "race" style race and use an external power ram and spool assy
4) Move to completely electric steering, using the rack off something like the new M3 that has a beefy electric rack (also, an 'lecy RX8 rack looks like it might be modifyable, as the power electronics look to be separate)
Didn't the old TCA Tuscan racers try to install power steering but it was costing them too much and thus went back to manual racks.
Max, whats do the WRC teams use?
Max_Torque said:
stevieturbo said:
WTF change it !
Quite simply because there was no easy position in which to fit a FEAD driven pump on my engine / install! Otherwise i would have just fitted a decent modern, variable displacement mech pump and been done with it like you say ;-)stevieturbo said:
Some PAS pumps these days are very very compact.
I'd find it impossible to believe one couldnt be squeezed in somewhere.
Job done.
Well, i agree, sort of!I'd find it impossible to believe one couldnt be squeezed in somewhere.
Job done.
The lhs of the engine is totally full of exhaust, turbo, wastegate and ALS valving etc, and it's pretty dam hot that side of the engine, so that would be EXTREMELY difficult to try.
The rhs of the engine is full of throttle, plenum, water pump, alternator and drysump pump.
Two options exist probably:
1) Move to a 'lecy water pump, fit PAS pump in space currently occupied by mech water pump. Unfortunately, as i'm sure you know, i'm really rather not keen on 'lecy water pumps ;-)
2) Fit pump "backwards" on front of engine somehow (space currently occupied by oil laminover and rad / IC exit shrouding etc, run off back of belt using std "front of belt" type pump. Possible, but will require the most complex mounting bracket in the history of such brackets, and i think belt wrap will be extremely marginal at high pump torque (back of belt is an issue for this obviously, as without the grooves it does not have the geometrical loading advantage of the V groove side!)
Edited by anonymous-user on Tuesday 9th September 13:33
Think i'm going to try a "quick and dirty" high flow mod on my spare TRW 'lecy pump. Luckily the gear pump driven by the motor is pretty modular (i'm sure they will do models with different volume flow) and it looks like by taking two of these parts, milling off the opposite ends of the centre housing and the gears, i can make a Frankenpump that has around 30% more volumetric flow rate per revolution than the std pump, but still fit back into the unit!
Currently not sure how i am going to re-join the gears, either i'll TIG em together or drill and pin/press fit them somehow. I imagine it'll whine a bit, but if it proves the point i'd then just get some proper new gears hobbed out!
I think also i can lower the pressure relief valve setting a bit (std is 120bar apparently, although i haven't measured it) to reduce the motor load in extremis, as i currently have plenty of actual assistance at low rack velocities. If i drop the pmax to 80bar, i think peak motor load will be very similar (need to go do some hydraulic calcs to check!)
Currently not sure how i am going to re-join the gears, either i'll TIG em together or drill and pin/press fit them somehow. I imagine it'll whine a bit, but if it proves the point i'd then just get some proper new gears hobbed out!
I think also i can lower the pressure relief valve setting a bit (std is 120bar apparently, although i haven't measured it) to reduce the motor load in extremis, as i currently have plenty of actual assistance at low rack velocities. If i drop the pmax to 80bar, i think peak motor load will be very similar (need to go do some hydraulic calcs to check!)
chuntington101 said:
Max i have the simplest and cheapest answer for you. GO TO THE GYM!
er, have you seen the cost of gym membership these days!! WAY more than buying a new PAS system....... ;-)chuntington101 said:
Max, whats do the WRC teams use?
FEAD driven "std" mech pumps (std parts, modified pressure relief and/or delivery volume control valves)I had similar issues. In my case I didn't want to use an engine pump as the engine is tightly packaged in the back and the steerings at the front. I've seen a couple of fire where power steering fluid has hit the exhaust which also put me off.
I tried the pug pump, crude and too slow.
Used the astra electro/hydraulic, not too bad but a little slow.
For the last 7 years I've used a Corsa column onto a custom rack 1.8 lock to lock 16" chunky tyres. I does need extra cooling for my use, I cool the ECU and motor but not sure the motor needs it. I find I have more than enough feel, to be honest I think the best test is that I can do an event and think afterwards that I never thought about the steering.
I tried the pug pump, crude and too slow.
Used the astra electro/hydraulic, not too bad but a little slow.
For the last 7 years I've used a Corsa column onto a custom rack 1.8 lock to lock 16" chunky tyres. I does need extra cooling for my use, I cool the ECU and motor but not sure the motor needs it. I find I have more than enough feel, to be honest I think the best test is that I can do an event and think afterwards that I never thought about the steering.
I'm not that keen on the corsa power column for my application tbh. it's relatively lower powered, puts the weight up high, adds bulk to the steering column area (where, due to my front mid engine position i don't have a lot of space anyway, and adds significant inertia to the system.
In your application, on low friction but bumpy surfaces i can see how it works, but for my car, pushing big slicks with lots of castor and camber on dry tarmac, i think it will struggle more than my current system tbh (it is less powerful than what i currently have)
In your application, on low friction but bumpy surfaces i can see how it works, but for my car, pushing big slicks with lots of castor and camber on dry tarmac, i think it will struggle more than my current system tbh (it is less powerful than what i currently have)
Max_Torque said:
I'm not that keen on the corsa power column for my application tbh. it's relatively lower powered, puts the weight up high, adds bulk to the steering column area (where, due to my front mid engine position i don't have a lot of space anyway, and adds significant inertia to the system.
In your application, on low friction but bumpy surfaces i can see how it works, but for my car, pushing big slicks with lots of castor and camber on dry tarmac, i think it will struggle more than my current system tbh (it is less powerful than what i currently have)
I can't comment on the relative power, I can see your point on inertia. I can't sense it I can see how it may show in a more refined set up.In your application, on low friction but bumpy surfaces i can see how it works, but for my car, pushing big slicks with lots of castor and camber on dry tarmac, i think it will struggle more than my current system tbh (it is less powerful than what i currently have)
A contemporary has adapted the unit to fit direct to his rack, partly for packaging and partly to reduce the number of joints after the 'power' unit.
Edited by C Lee Farquar on Wednesday 10th September 06:36
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