Trying to understand power steering hydraulics

[me3@neuralfibre.com]

I am thinking about Hydraulic winches, and realised my understanding of power steering is somewhat limited.

From what I understand
A power steering pump is a positive displacement pump (generally vane style) whose displacement is proportional to RPM. It has a fixed output pressure limited by a relief valve.
So it will pump x l/min depending on RPM, at a constant pressure (provided there is some flow restriction that limits flow to less than x)

Now this where I am confused.
When cruising in a straight line, the power steering unit must allow the fluid to bypass the box and simply circulate, so the pressure in the line would be minimal. Otherwise the load would be constant, and the relief valve would be open all the time, this would waste power. It is also proved by when you hit the steering lock, you hear the engin RPM drop from idle. This indicates the bypass flow is being blocked and the flow is being forced into the box to turn the wheels. As they won't move, the pressure ramps up and cracks the relief valve.

SO
If the flow bypasses the box most of the time and simply circulates, how does a hydraulic winch "borrow" the fluid to drive it? It would have to have solenoids that disconnected the power steering totally. I know there is some type of tricky box to handle this, but can't figure out how it works.

Are there any knowledgable types here? :)

Thanx
Paul

[chimpboy]

I wish I had time to write up a 10 page outline of how I think it works, but instead here's http://auto.howstuffworks.com/steering4.htm

In answer to your specific question, the fluid is always circulating under pressure from the pump, through the lines, and back to the pump again. When you are not steering, it passes through the steering box without doing any work. Thus there is still hydraulic fluid flow for the hydraulic winch to tap into. The winch just intrudes into that flow and depletes some of the pressure, then lets the fluid continue on its way to the steering box and back to the pump. Does that make sense?

[me3@neuralfibre.com]

No, because if it's just circulating and not under pressure, then it can't do any work.
If it is under pressure, then it would be "loaded" all the time, and hitting the steerin stop would make no difference.
And the T peices are not electrical solenoids, so they can't "redirect" the flow.

Paul

[chimpboy]

No, because if it's just circulating and not under pressure, then it can't do any work.
If it is under pressure, then it would be "loaded" all the time, and hitting the steerin stop would make no difference.
And the T peices are not electrical solenoids, so they can't "redirect" the flow.

Paul

It leaves the pump at pressure, and that pressure does work if it hits resistance in the fluid circuit.

When you hit the steering stop, what you are hearing is a relief valve. On the other hand, when you aren't steering the fluid just goes straight back to the pump without losing much pressure since it's not doing any work on the way.

I didn't say anything about redirecting. The winch doesn't redirect the fluid away from the steering, it just sits inline with the steering, so the fluid goes pump -> winch -> steering -> pump instead of pump -> steering -> pump.

I am not sure what you mean by '"loaded" all the time'; I think there's something basic about this that you have misunderstood but I am not sure what.

[me3@neuralfibre.com]

The line from the pump to the box is the pressure side.
The line from the box to the pump is the return (not pressurised)

If there is flow across a pressure drop then there is power being used.

You are right, it is the relief valve, the valve in the pump because the flow is being restrictied by the box and hitting the max pressure, workin the pump hard, and needing relief to stop overpressure.

The question is what happens when the steering wheel is not moving. I would bet the line from the pump to the box is not under pressure, just has a constant flow(depending on RPM)

Remember, it's positive displacement. If this is the case, where does the winch get it's "presssure" from.

I *think* it must block the line to the power steer and divert the fluid though it's own plumbing.

I haven't even got into the logic of the hydrailic flow within the winch yet.

Paul

[chimpboy]

When the steering wheel is not moving, the hydraulic fluid flows through the steering box doing no work and heads straight back to the pump.

When the winch is deactivated the fluid flows freely through it to the steering box. When the winch is activated the flow goes through the hydraulic motor in the winch to do work... but it still continues on (on the "low pressure" side of the winch) to the steering before making its way back to the pump. In other words the line between the winch and the steering could be considered "low pressure" or "high pressure" depending on whether you are steering at the time.

It's always a single circuit of fluid from the pump back to the pump again, and on the way the fluid can be forced to do work in the winch, the steering, or both.

I'm scratching my head a bit as I am not sure what aspect of this is confusing you!

[me3@neuralfibre.com]

What forces the fluid to go through the winch, rather than simply passing through the bypass cct in the power steering?

(I know the answer is the T peices, but they must be more than that to have that effect)

Paul

[chimpboy]

What forces the fluid to go through the winch, rather than simply passing through the bypass cct in the power steering?

(I know the answer is the T peices, but they must be more than that to have that effect)

Paul

I don't know how your winch is wired up but IIRC a hydraulic winch is normally hooked up as follows:

power steering pump -> winch -> steering box -> pump. A handle on the winch switches between a bypass mode and an operation mode.

How is your setup hooked together... where are these T pieces?

[me3@neuralfibre.com]

I dont have one, looking on web.

Evil plan is to buy a haydraulic winch and parallel in a second pump to increase flow. I need to understnd the flow and bypass behavior to work this out however.

The Milemarker and TJM Ox are descripbed quite differently to what you describe.

Paul

[STIKA]

what exactly are you trying to achieve

[me3@neuralfibre.com]

A cheap and bodgy winch that never gets hot, melts plasma and pulls fast and hard. (or maybe that is me that is pulling fast and hard...)

In theory a hydraulic winch meets all these except for speed. If I candouble the fluid flow, I can double the speed. A second ps pump is easy to add.
BUT
I need to understand ps hydraulic flow to knwo the impacts. Done wrong would result in fuel economy going to crap and ps pump working all the time.

These systems are not as simple as it might appear.

http://en.wikipedia.org/wiki/Hydraulic_ ... c_circuits

The "redirection" valves are part of it
So is the control maifold flow rates
So is the braking behaviour using the valves
So is fuel economy as the flow should "bypass" when not under load.

Paul

[STIKA]

what about any restrictions in the winch itself

and to get rid of the heat you need a large oil resiviour with cooling

[ISUZUROVER]

A cheap and bodgy winch that never gets hot, melts plasma and pulls fast and hard. (or maybe that is me that is pulling fast and hard...)

In theory a hydraulic winch meets all these except for speed. If I candouble the fluid flow, I can double the speed. A second ps pump is easy to add.
BUT
I need to understand ps hydraulic flow to knwo the impacts. Done wrong would result in fuel economy going to crap and ps pump working all the time.

These systems are not as simple as it might appear.

http://en.wikipedia.org/wiki/Hydraulic_ ... c_circuits

The "redirection" valves are part of it
So is the control maifold flow rates
So is the braking behaviour using the valves
So is fuel economy as the flow should "bypass" when not under load.

Paul

Have a read of this link. I would suggest a dedicated PTO hydraulic motor.
phttp://www.outerlimits4x4.com/viewtopic.php?t=51126

[chimpboy]

I dont have one, looking on web.

Evil plan is to buy a haydraulic winch and parallel in a second pump to increase flow. I need to understnd the flow and bypass behavior to work this out however.

The Milemarker and TJM Ox are descripbed quite differently to what you describe.

I've seen an Ox in real life and from what I can read the milemarker is as I described it. It's also the only logical configuration I can think of.

[me3@neuralfibre.com]

OK - figured part of it.
Winch goes in SERIES with the PS box, not parallel like I thought. I was basing this on the comments re "redirecting fluid flow when steering is required".

So that's one thing down.

So I wonder what the stock LC PS box would think of having twice the fluid shoved through it? Would it flow that much though it's bypass?

I would love the know the standard flow rate of the integrated Toyota pump. I would bet it's the same on all the diesels, including the 4cyl.

Paul

[me3@neuralfibre.com]

A cheap and bodgy winch that never gets hot, melts plasma and pulls fast and hard. (or maybe that is me that is pulling fast and hard...)

In theory a hydraulic winch meets all these except for speed. If I candouble the fluid flow, I can double the speed. A second ps pump is easy to add.
BUT
I need to understand ps hydraulic flow to knwo the impacts. Done wrong would result in fuel economy going to crap and ps pump working all the time.

These systems are not as simple as it might appear.

http://en.wikipedia.org/wiki/Hydraulic_ ... c_circuits

The "redirection" valves are part of it
So is the control maifold flow rates
So is the braking behaviour using the valves
So is fuel economy as the flow should "bypass" when not under load.

Paul

Have a read of this link. I would suggest a dedicated PTO hydraulic motor.
phttp://www.outerlimits4x4.com/viewtopic.php?t=51126

Which would be wonderful if I had a PTO option.... (did mention that too)

[me3@neuralfibre.com]

what about any restrictions in the winch itself

and to get rid of the heat you need a large oil resiviour with cooling

Discussions on the web indiate the vavle pack with the milemarker is a restriction after 17L/min. The danfoss motor will go much much more, it'll just turn faster, provided you dont excedd it's max pressure.

I have no idea how many L/min or operating pressure for the PS in the cruiser. Someone must have a contact that would have this spec somewhere???

And not to be picky, but resovoirs dont get rid of heat, they jsut store it. The crusier already has a PS cooler from memory - a loop of pipe near the front ncrossmember. If that's not enough I'll plumb in a small auto trans cooler. I don't think heat will be a massive problem as hydraulic efficiency if very good, and being incompressible there is no "latent heat" properties.

Paul

[STIKA]

[
And not to be picky, but resovoirs dont get rid of heat, they jsut store it. The crusier already has a PS cooler from memory - a loop of pipe near the front ncrossmember. If that's not enough I'll plumb in a small auto trans cooler. I don't think heat will be a massive problem as hydraulic efficiency if very good, and being incompressible there is no "latent heat" properties.

Paul[/quote]

you may have to re-think that comment a larger volume of oil will take longer to heat up. How much oil does this sysytem hold??

i not talking about a 1/2 litre resovoir! for a kick ass winch you will need 20litres +

if you want it to pull harder and faster you will generate more heat so the volume of oil/resovoir and cooling will all be relevant

Why are you after speed?

[chimpboy]

OK - figured part of it.
Winch goes in SERIES with the PS box, not parallel like I thought. I was basing this on the comments re "redirecting fluid flow when steering is required".

So that's one thing down.

It's what I was trying to tell you all along, sheesh.

[cooter]

both winch and box have a onen centre valve and both work exactly the same as each other apply load by restricting flow the box does so by turning the rotary spool valve via a torsion bar system and the winch by a solenoid operated inline spool valve quite simple really
as for pumps i would recomend aquiring a vickers style truck ps pump and an external reservoir may be able to find ya one cheapish

[me3@neuralfibre.com]

[
And not to be picky, but resovoirs dont get rid of heat, they jsut store it. The crusier already has a PS cooler from memory - a loop of pipe near the front ncrossmember. If that's not enough I'll plumb in a small auto trans cooler. I don't think heat will be a massive problem as hydraulic efficiency if very good, and being incompressible there is no "latent heat" properties.

Paul

you may have to re-think that comment a larger volume of oil will take longer to heat up. How much oil does this sysytem hold??

i not talking about a 1/2 litre resovoir! for a kick ass winch you will need 20litres +

if you want it to pull harder and faster you will generate more heat so the volume of oil/resovoir and cooling will all be relevant

Why are you after speed?[/quote]


That's like saying I should run a 44 drum in the back to cool the 1HZ - they got rid of that motor cooling technique about 75 years ago and went to radiators - found them more useful.

[me3@neuralfibre.com]

both winch and box have a onen centre valve and both work exactly the same as each other apply load by restricting flow the box does so by turning the rotary spool valve via a torsion bar system and the winch by a solenoid operated inline spool valve quite simple really
as for pumps i would recomend aquiring a vickers style truck ps pump and an external reservoir may be able to find ya one cheapish ;)

Sweet - you seem to know all the right words.
It's all scheming at this stage to work out if it is practical.
I would like to parallel the pumps as it would make the best use of the least resources, and I reckon I can grab a belt driven pump pretty easily from some wreck. What I am unsure of is what will happen to the PS box when I try and shove twice the flow through it? Will the open centre still pass this much flow, or will the restriction build pressure until the relief valve opens, and costs me $$$ in fuel economy pushing all the time.
I doubt spinning the pump will hurt fuel economy much, as it's just recirculating, but pushing under full load cerainly will.

Do you know any numbers on different PS pump flow rates?
Can you tell me what happens if you shove more flow through a stock PS Box?

Thanx
Paul

[me3@neuralfibre.com]

OK - figured part of it.
Winch goes in SERIES with the PS box, not parallel like I thought. I was basing this on the comments re "redirecting fluid flow when steering is required".

So that's one thing down.

It's what I was trying to tell you all along, sheesh.

Sorry, I'm not always good with big words :(

[chimpboy]

If you are planning to run two pumps, the best way to go would probably be to run one through the power steering and the other (the big one) through the winch..? Saves a lot of headaches and complexity of trying to run two pumps in to one pipe.

Just a thought.

[me3@neuralfibre.com]

If you are planning to run two pumps, the best way to go would probably be to run one through the power steering and the other (the big one) through the winch..? Saves a lot of headaches and complexity of trying to run two pumps in to one pipe.

Just a thought.

That defeats the whole purpose. The reason hydraulic winches are slow is because of limited flow rates. The P/S pumpt spends 98% of it's time doing nothing, and *should* have about the right pressure ratings, but it's flow is limited. Makes sense to use it, and supplement it with another pump.

[1MadEngineer]

If you are planning to run two pumps, the best way to go would probably be to run one through the power steering and the other (the big one) through the winch..? Saves a lot of headaches and complexity of trying to run two pumps in to one pipe.

Just a thought.

That defeats the whole purpose. The reason hydraulic winches are slow is because of limited flow rates. The P/S pumpt spends 98% of it's time doing nothing, and *should* have about the right pressure ratings, but it's flow is limited. Makes sense to use it, and supplement it with another pump.

dude you need to do a lot more research and a lot less talking!

then you would know that PS pumps flow approx 5L/min and between 900-1100psi

[me3@neuralfibre.com]

If you are planning to run two pumps, the best way to go would probably be to run one through the power steering and the other (the big one) through the winch..? Saves a lot of headaches and complexity of trying to run two pumps in to one pipe.

Just a thought.

That defeats the whole purpose. The reason hydraulic winches are slow is because of limited flow rates. The P/S pumpt spends 98% of it's time doing nothing, and *should* have about the right pressure ratings, but it's flow is limited. Makes sense to use it, and supplement it with another pump.

dude you need to do a lot more research and a lot less talking!

then you would know that PS pumps flow approx 5L/min and between 900-1100psi

This is my research

Do the numbers you quoted apply at 800 or 8000RPM?
Is this the same for the 1HZ as it is for a Jeep that most of the Milemarker discussions circulate around?
Will doubling the flow rate bother the stock PS Box?

I don't know anyone that can answer these questions, hoping someone on here knows, or knows someone.

Paul

[rvh96]

I think if you tried to double flow though the steer box it would just build up pressure and probably blow a hose or seal. to increase flow in any hydralic system you will have to run larger pipes and hose but in would still be restricted in the box oil ways and valves

[Ruffy]

That defeats the whole purpose. The reason hydraulic winches are slow is because of limited flow rates. The P/S pumpt spends 98% of it's time doing nothing, and *should* have about the right pressure ratings, but it's flow is limited. Makes sense to use it, and supplement it with another pump.

dude you need to do a lot more research and a lot less talking!

then you would know that PS pumps flow approx 5L/min and between 900-1100psi

This is where this needs to end. Mr nueralfibre you DO NOT have enough knowledge of hydraulics to be doing this. You can't simply make a hydraulic motor work harder and faster by increasing the flow.

Hydraulics are very similar to steam power. Do you know when a traction engine makes it greatest amount of torque?
Hydraulics are complex. You can have fast or you can have torquey. Fast and torquey is not a simple thing. I can guaruntee you that two power steering pumps in parallel or series will not achieve what you are claiming it will. In order for an hydraulic system to create pressure it needs a restiction. The greater the restriction the greater the pressure but the slower the flow so less speed. It's not just a matter or increasing the flow.
Do yourself a favour and do a WHOLE lot more research before you start spending money.
Dan

[me3@neuralfibre.com]

That defeats the whole purpose. The reason hydraulic winches are slow is because of limited flow rates. The P/S pumpt spends 98% of it's time doing nothing, and *should* have about the right pressure ratings, but it's flow is limited. Makes sense to use it, and supplement it with another pump.

dude you need to do a lot more research and a lot less talking!

then you would know that PS pumps flow approx 5L/min and between 900-1100psi

This is where this needs to end. Mr nueralfibre you DO NOT have enough knowledge of hydraulics to be doing this. You can't simply make a hydraulic motor work harder and faster by increasing the flow.

Hydraulics are very similar to steam power. Do you know when a traction engine makes it greatest amount of torque?
Hydraulics are complex. You can have fast or you can have torquey. Fast and torquey is not a simple thing. I can guaruntee you that two power steering pumps in parallel or series will not achieve what you are claiming it will. In order for an hydraulic system to create pressure it needs a restiction. The greater the restriction the greater the pressure but the slower the flow so less speed. It's not just a matter or increasing the flow.
Do yourself a favour and do a WHOLE lot more research before you start spending money.
Dan

Dan, very sorry, but your own statements indicate your knowledge is flawed. If you dont liek the thread, don't read it, but I'll keep tossing ideas out until I can find an expert, and then I'll keep goign casue I want to cut corners and do it cheap.

Steam is a compressible gas. Hydraulic fluid is incompressible and with a positive displacement flow pump the flow will NOT change, nor will the speed of the motor regardless of load (assuming the pump drive is capable). Pressure will increase until it reaches the systems relief valve pressure.

Now, heaps of looking on others who have modified Milemarker winches indiate the Danfoss motors on them are suitable for flow rates up to around 60L/min. The valve pack will only cope with about 17l/min.

The real questions circulate around what the impacts to the vehicle power steering is.

Thank you for your input Dan, but you did nothing to further the knowledge of this group. Nor did you help by making decisions on what I will and will not do with my equipment and my time.

Paul