4-Wheel Drive - Hydraulic skid steering

[BeardofZeus]

Hi Everyone,

I'm very new to hydraulics so please forgive me if my question is very basic.

I have a "tractor" that has hydraulic motors at each wheel. Each side has the front and rear motors setup in parallel with a 50/50 divider (

https://www.surpluscenter.com/item.asp?item=9-1048-C&catname=hydraulic)

that is supposed to allow equal flow to the front a back wheels. Steering works via valves by the operator that change the pressure going to each side resulting in skid steering.

Now on our latest revision we've added a tank-track to each side (chains going all the way around both tires coupling them together) so that it can have better traction. We're finding now that the wheel couplers are breaking where they before the tank track they weren't.

Trying to diagnose the problem, we're trying to figure out if it's hydraulics related or just that the couplers are under-designed for the forces we've been putting through them.

So because the wheels are now coupled together externally via the tank track, is there fighting between the motors if they're not spinning perfectly at the same rate or does this setup account for that?

Appreciate the help!

- Mike

 

[hydtools]

Are the tracks installed tight or loose? You may be adding a bending load that was not there without the track.

Ted

 

[BeardofZeus]

Tight enough to wrap and grip around the rubber of the wheels, so yes this may be one of the possibilities as well, I'll check into this tomorrow.

So then is the hydraulic setup ok you think in terms of the wheels forcing the motors or basically always turn at the same speed regardless of flow to each?

 

[hydtools]

Knowing no more, I would suspect mechanical problem rather than hydraulic. With the track the pair of wheels must turn at the same speed regardless of the accuracy of the flow splitter. Seems no different than without the track and travelling on a hard, non-skid surface.

Ted

 

[MikeHalloran]

The track enforces equal wheel speed much more accurately than the flow splitter ever could. I.e., the flow splitter and the track are fighting for dominance; remove the splitter.


Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Remove the splitter if you will always have the tracks installed. Otherwise you will not have all wheel drive without the tracks, the least loaded wheel will abosorb all the flow.

More common skidsteer drive is one motor for each side driving through a chain to both wheels on each side. The chain drive times the wheels and after-market over-the-tire tracks do not cause problems. No flow splitter.

Ted

 

[BeardofZeus]

Ok so on another one we've removed that divider valve and just have a T junction. The idea being that we'd like to use two smaller motors on each side vs one larger one.

Thoughts?

 

[kcj]

Are these wheels and motors exactly the same?
If not, you may have 'recirculating power', where the tracks equalize speed in ft/min at the rim of the wheels, and the flow divider equalizes flow or shaft rotation at the motor output, but the two may not be the same. Then one or the other must slip or create high forces to get the two synchronized.

I would not think the spool divider is that accurate, but it might be. Or, maybe the spool dividere is solid but is metering 48/52 instead of 50/50

Since the tracks equalize the wheel speeds, you don't need two devices doing the same thing. Pitch the divider if the tracks on or it.

There can be just a few hp or low torque going into a drive, but the connected path can produce very large torques in the components themselves, and break parts.

Search on foursquare gearbox testing: 4 gearboxes can be tested at very large torques internally, but only driving the arrangement with 10 or 20 hp.

Also steel wheel track or crane drives that use wheels on a rail. The drive into the first wheel from gearbox may use a much smaller roller chain than the chain between the two wheels.

 

[BeardofZeus]

Appreciate all the input from you guys. Yes it does seem then that it is our mechanical linkage that was under designed. The tracks were supposed to be removable (up to the user) so we'll try and come up with a configuration that allows you to choose to use the splitter or not with some quick-connects or something similar.

Man this forum is awesome. I've never posted but used it as a resource before and indeed the expert knowledge here is great! Hopefully I can contribute back in some of the other areas.

Thanks!
- Mike

 

[EngineerTex]

The easiest way to select between splitter vs non-splitter mode is simply to have a ball valve that connects the two downstream sides of the flow divider together. Turn it one way and flow is divided, turn it the other and the flow is free to follow whatever path it wants. You would eliminate your proposed quick disconnects and whatnot.

Engineering is not the science behind building. It is the science behind not building.