use power steering line to drive other components

[schiao]

Is it legal to use power steering supply line to run a hydraulic motor before entering steering gear on a bus? Or to split the line to run a hyd motor as for another option? I'd appreciate any helpful input here.

 

[GregLocock]

I suggest you install a second p/s pump and run an independent circuit. I know this is not what you were hoping for.

In the automotive world (I'm not so sure about buses) P/s pumps are selected by capacity, at a particualr speed, often idle.

If the pump is not big enough, or you divert some of the fluid elsewere, then typically your driver will experience 'catch-up', where the steering wheel goes very heavy as he turns it as the pump tries to catch up.

However, on some pumps there is a bypass, used when the engine is running fast and the steering isn't moving. This returns oil direct to the reservoir, Perhaps you could pick up that feed and use it for something else.

Messing with the steering makes me very nervous. Cheers

Greg Locock

 

[patprimmer]

I agree with Greg.

Power steering pumps are carefully matched to steering requirements, and on many cars, even with everything exacty stock, if you really get into it on tight winding roads, you can easily get ahead of the PS.

I have also had experience replacing a power steering box from an identical model designation (bothToyota Soarer MZ20), but slightly newer car (1988 vs 1989).

I found that I also needed to swap pumps to overcome heavy steering while parking and catch up when cornering. Regards
pat

 

[schiao]

Thank you all so much for your input. Actually I'm the advocate for setting up a second hydraulic pump dedicated for purposes other than power steering (ex. PTO). My reason is for safety. I would not risk the safety by introducing a component that may become a failure point for the power steering line. My co-worker, on the other hand, insists it's a great idea to run a hydraulic motor with the existing pump before entering the steering gear. Since everything is connected in one line, flow rate should not be affected as long as the pump rotates at the required speed, overall pressure drop will be increased which obviously means the pump has to do more work. Conceptually a series circuit like that should work. Also, it is not a problem for me to spec a pump with a higher flow rate if a parallel circuit is considered. But my major concern is the safety and I hope someone would know a regulation that addresses that issue so I could use it for my argument.

 

[Slowzuki]

Milemarker hydraulic winches use the vehicles power steering pump to drive the winch. The US military uses them on humvees. The winch obviously would not operate during road type driving.

Three types of setups I know of people using:

From the bypass on the PS spool to the motor spool on the winch to reservoir. It is simplest method but can overheat the fluid when winching + steering. The other problems listed above can occur too.

On some vehicles a flow priority valve is installed to shut the flow to the winch off immediately when steering occurs, there would be 2 returns to the reservoir

Last some people use are a simple selector to choose PS or winch operation.

I hope this helps.
Ken

 

[Chumley]

I wouldn't do it. Some vehicles use a single piston type
pump with dual circuits which operate at substantially
different pressures and flow rates that power multiple
servos. For example, my Audis use this system which is
made by ZF, a German company. One pump circuit powers the
rack and pinion, the other powers the hydraulic brake
booster for the power brakes. Both circuits are
independent but use a common reservoir and fluid.

In a single stage pump system with multiple parallel type
hydraulic circuits, the servo that requires the least
pressure has the possibility of consuming a majority of the
flow unless you regulate the pressure/flow somehow. If one
unit fails, you'll lose hydraulic assist in the other
servos in the same circuit unless you use some type of
pressure accumulator.

See this link:

http://www.zf.com/defaultz.asp?lang=1

Here's a link to the type of dual circuit hydraulic pump I
referenced

http://catalog.eautopartscatalog.co...e=AU&model=200-T-001&category=M&part=P/S+Pump

You may have to copy and paste the URL to complete it.
Then click the thumbnail to see a larger picture.

Hope this helps.

Chumley

 

[jons999]

Toyota and other manufacturers have in the past used the power steering pump to run the engine cooling fan. I believe GM had a hydroboost system that incorporated the power steering into the braking system. You might research these systems and see what sort of design elements were incorporated into these systems.

-Jon

 

[puginfo]

>>> Hi Mates, i need yr expertise to sort of attach a pulley of 75mm versus the original 140mm diam. to the same OE ps pump. Theoretically, it should make the pump spin about twice as fast as well. Would someone help me understand the implications of running it twice as fast?

Would the OE pressure hoses be up to handling the new press?
Would the pump bearing take the revs (but now without the belt tension load on it)?
Is there a pressure relieve valve built in it to cater for all this?
Power ram seals?
Steering control valve seals?

I intend to run the pump some 10" away from the main belt driveline using a pipe and shaft config. due to space unvailability. So the pump will be attached on the rear end of shaft so it sees no belt tension at all. This would be similar to the eaton's long nose s/c drive assy'. Pls f/back on this and thks.

cheers
Ganesan

 

[patprimmer]

I am sure that at least some factors are dependant on individual pump design, for instance, will you generate cavitation at the pump inlet port. This depends on how close the pump runs to cavitation at it's original design speed. Also the ultimate pressure developed might depend on the presence and design of pressure releif valves.

Regards
pat

 

[puginfo]

>>> Thks Pat. This pump is probably made by ZF systems and looks the same as the one used in volvo's. Don't have any data on it but can describe the structure but need help in understanding what's it doing in my pug405. Its a vane type, 2.5ins diam cast body, sealed (no joints on body), has a sub body-0.75ins diam right atop the main(for valving i suppose) just next to the pulley but placed 90deg of the main shaft centerline. One end of the sub body is the press output treads and somewhere in the middle it has a low press input fluid tube.

Are the external power ram typed systems different from the power ram built into the rack types? Where would pressure relieve be done then?

Still not very clear of how this thing should be put together. In any case, would an oriface (a pipe diam reducer) placed inside the high pressure metal pipe be of any use in reducing the system pressure developed by higher rpms?

cheers
Ganesan

 

[patprimmer]

Sorry Ganesan

I am not a steering systems expert, so I am not familiar with many details on various pumps.

I base my comments on the 3 times I have adapted the wrong pump to steering box when doing engine swaps, and more general work with fuel pumps in mechanical FI systems, speed boat water pumps, and when modifying oil pumps for hotrodded engines, and a fairly comprehensive broad band knowlege of applied physics.

The orifice will not necessarily reduce pressure, it will reduce flow. This may reduce pressure if some oil is bleeding of, so the input to output ratio changes, but will only slow the rate of buildup if flowing into a closed pipe.

The best way to control pressure is with a pressure relief valve that will bypass oil back to the reseviour at a certain pressure. This obviously needs to be sized correctly, and should be adjustable

Regards
pat

 

[Slowzuki]

Generally steering pumps are positive displacment pumps so putting an orifice in is a bad idea. Sizing the pump correctly is a better idea. An orifice will simply heat the oil, if it raises the pressure to the point where the relief valve operates continuously, you are throwing away power, and will generate a lot of heat. Most likely you would cook the fluid in minutes.

A steering valve bypasses fluid so the pump just circulates under no load conditions.
Ken

 

[puginfo]

>>> Thks guys. Further checking did reveal that it has a pressure relieve built in at 80bar. Also, someone had pointed out that the max pressure of such a system only happens when the rack is on an full lock where the power ram had stopped.

Ken, you had pointed out sizing the pump as important. But this is the very same system we are talking about, with the only difference being the pulley diam. I wasn't sourcing to fit a diff pump from some other model. I guess if a small diam pulley was used, then the 80bar bypass trigger would happen much earlier in the rev range than usual thus increasing the fluid temp. Would an inline oil cooler keep things together? On which line should this cooler be inserted?

cheers and thks
Ganesan

 

[patprimmer]

I would put the cooler on the return line, or low pressure line.
Less chance of leaks, less chance of bursting a cooler

Regards
pat

 

[JayMaechtlen]

"Capacity" will appear to double, or nearly so, if the pump speed is doubled.

After all- this is positive displacement pump, meaning a certain volume per PUMP REVOLUTION.

May need pressurized reservoir to avoid cavitation?
Maybe want larger hoses to and from the ram?

and very good sized cooler...





Jay Maechtlen