Hydraulic motor circuit?

[scgargoyle]

For too many reasons to explain here, I want to repower a golf cart, using a gas engine and hydraulic drive. The plan is basically to have a pump mounted on the engine, go through a valve that will adjust speed (flow) and go to a hydraulic motor driving the wheels. Is there a valve that will control both speed and direction? Preferably something that stays where you put it, so I don't have to hold my hand on it all the time. How big a reservoir do I need? What about a cooler? I'm thinking maybe 10-15 hp, and a top speed of 10-15 mph. Anyone know a bit about this? I know just enough to be dangerous LOL!

[dynasim]

Most cheaper pumps are positive displacement, which means that the speed of the motor will be directly related to the speed of drive.


Most HST drives use a variable displacement pump, which is much more expensive.

A normal valve with a bypass(open center) could conceivably work, but it would be tough to implement effectively(in my opinion).

Chris

[scgargoyle]

So- if I use a positive displacement pump, I can control speed with the throttle, like a mechanical drive? Is there a simple valve I can use to simply change direction? I saw a valve designed to control the speed of a hydraulic motor, but I don't think it had any way to reverse direction.

[Soundguy]

You could use a DA and plumb it that way.. perhaps a valve with detents.. however.. there are special concerns for using motors so that you don't cause shock loads when you center the spool.

You may also want to add in a 'clutch'.. IE.. a valve to sump that bypasses the spool so that you can leave the engine idled up if you need it.. etc.

I've not seen and DA spools that were friction loaded to leave them variably open.. though I'm sure you could rig up some linkage to the valve using perhaps a marine throttle setup..

soundguy

[Harry c]

Originally Posted by scgargoyle

So- if I use a positive displacement pump, I can control speed with the throttle, like a mechanical drive?
Is there a simple valve I can use to simply change direction? I saw a valve designed to control the speed of a hydraulic motor, but I don't think it had any way to reverse direction.

Yes, with a positive displacement pump the engine speed will directly control the vehicle speed just like a mechanical drive. Remember though, you can't stop without disengaging the hydraulic valve or killing the engine. If you use a regular 4 way valve it will lock the wheels when you shift to neutral. See below.
Yes, you need a bi-directional MOTOR Valve I haven't looked, but I would guess a hydraulic posthole digger among other things would use this type valve. They are available. A motor valve lets the motor coast to a stop when you shift to the neutral position. A regular 4 way would lock the wheels when you shift to neutral.

Another option you might consider if you're using a fairly small engine: Drive the pump with a centrifugal clutch like the ones used on go-karts. You can let off the gas and come to a stop without touching a valve. Then just hit the gas and off you go again. Stop completely before moving the control valve from forward to neutral or reverse and you can use any old 4 way valve with detents in both directions (or just make your own detents...Bungee cord maybe?) instead of a harder to find motor valve. The downside to this is you have essentially a one speed transmission. You do have forward, reverse and neutral though.

If you can find a variable displacement pump you have infinitely variable speeds and reduction ratio when needed. Actually, you have a hydrostatic transmission.

[HarryVanderpool]

All you need is a Bi-directional proportional flow control valve and amplifier.
Let me reword that:
All you need is about $1400.00
Your foot pedal will actuate a 5K potentiometer that will signal a small amplifyer. A toggle switch selects forward or reverse.
There is a pot on the amplifyer for ramp speed to smooth things out.
Here's what I have used:

Proportional Control Valves - Bosch Rexroth Corp.

[scgargoyle]

I'm a pretty skilled scavenger, so once I figure out what I need, I'll start shopping around. Looking through catalogs, there are pretty reasonable ($70) speed controls for hydraulic motors. The excess dumps back into the tank. I just haven't found any that work both ways, although I can find a DA valve with a neutral center for forward and reverse. I think neutral center is the right term- it allows the hydraulic motor to freewheel in neutral, so it doesn't lock up. I have a really sweet liquid cooled 13 Hp Honda I might use, although it's more power than I need. Any idea what size reservoir I should plan on? How much heat am I going to generate driving around all day at a swap meet?