homemade tractor project

[aspenelm]

I am building a tractor using 3/4 ton 4wd GM truck drivetrain (wheels,tires, axles,4 speed manual transmission, and transfer case) and a small isuzu c223 diesel. After using my neighbors kubota 4wd hydrostatic tractor with a loader I have decided on a hydraulic drive. Usage is primarily as a utility tractor to spread gravel, move dirt, raise and move heavy items, mowing, etc... I have a rough design worked out in CAD (sketchup). I also have a topic on machinebuilders.net and would like to get additional input here.

Goals:
-Size/weight roughly comparable to ford 9n and similar tractors, wag is 2500-3500lbs
-4wd
-loader with 1500+ lbs capacity
-top speed of 10-15mph in highest gear
-cat 1 implements
-low cost ($2500 ballpark)
-rear pto (hydraulic)

I have a lot of questions about sizing the hydraulic motors and pump for this application. I will give a rundown of what is my idea so far. There will be a two hydraulic motors, one for drive propulsion and the other for the pto. A hydraulic pump will be installed on the engine to supply hydraulic pressure. The drive motor will be direct coupled to the input of the transmission (the rest of the drivetrain is all mechanical). The engine I have is rated 58hp@4300rpm and 98lb.ft.@2200rpm. At lower rpms, I am going to assume it will produce around 25-40hp@1800-2000rpm.

1) Can one large pump supply the needs for all the hydraulics (loader, pto, and drive)? Is that the best solution?
2) Do I want variable displacement pump or a variable displacement motor? what does a fixed displacement motor torque curve look like in regards to flow,pressure,rpm and torque.
3) What kind of pressures and flow do I want? is this for the entire hydraulic system or is each circuit treated separately (drive,loader,pto)
4) are there some online resources to get me up to speed on this area?

Thanks, Jim.

 

[jimgerken]

I can't answer any of your more technical questions, but I have an opinion on the number of pumps. I would use three. One for motivation, one for steering and one for hydraulics (implements and loader). That is how a hydrostatic tractor is set up. You don't want one circuit reaching its strength limits (like the loader lifting a bit more than its max) or stroke limits, and opening the relief valve and then you can't steer and you can't move. And etc. I assume they would be three different sizes. Possibly a multi-section pump would be easier to drive from the engine output shaft, as opposed to trying to mechanically link and drive three seperate pumps. I would guess they all can share the same main resevoir and maybe even the same cooler. Independent filters on the inputs to the pumps is needed I think. And each will have its own relief valve. Good luck, sounds like an ambitious project. Your hydraulics budget will very quickly approach/exceed the $2500 low budget figure, in my experience. Teach yourself to fabricate hard line for hydraulic routing, I bet its cheaper and will be longer-lasting maybe. That hydraulic PTO is going to kill your budget. Try to find a way to drive it mechanically.

 

[Renze]

I would at least use that old 4 speed for PTO, it saves you some bucks. Does that old truck has powersteering you can transplant ?

You definately need to have at least 2 circuits, the hydrostatic tranny must work totally independent from anything else.
You can use the power steering pump for the 3pt lift and external outlets, but then make sure that the oil is directef through the power steering first. since power steering orbitrols are proportional, they will split off the oil flow they need and leave the rest to your loader valve. When you dont steer very fast, there will be enough flow to do both at the same time. When you do steer fast, the hydraulics have to wait till the steering gives the oil flow back.


Hydraulic components are expensive: I'd use a tried and tested Hydramatic auto tranny instead of a home made HST if you want to keep within your budget. they are scarce in Europe, but i think on your side of the pond, there must be plenty on wreckyards.

Tractor use will double the duration factor of the trannies duty, compared to automobile use... but if you put an Isuzu motor in front of it at 1/4 its designed max power, overheating wont be such a big issue and it will last quite a while, i think.

 

[aspenelm]

Thanks for the response.

Separate circuits makes a lot of sense. Yes, budget is a concern, I can go higher but am shooting for this target. I am also doing this for fun and for welding time. I don't have a good feel for how much the peripheral hydraulic stuff like valves, lines, tanks, filters, etc... will end up costing but I know they are expensive. I will try to source surplus or used stuff where possible.

So far, I have $400 in the entire 4wd driveline, the diesel engine, 2x6 tubing for the frame, tires and wheels. That leaves me $2k for hydraulics and miscellaneous stuff. There is a pto motor I want to use for $280, rated output is 25hp and 750rpm continuous. Just bolt in on, a lot easier than mechanical setup and it is reversible. The drive motor will be around $300 from the same source. The pumps have me confused. I would imagine for the pto circuit I could use a fixed displacement pump since it tends to be constant speed. Steering will just use the power steering pump that is already on the engine.

I found a hydrostatic motor and pump sizing guide from eaton's library. Need to work through the equations.

I am using the specifications from kubotas 4wd l3240/l3540 series tractors as a guide. If only I could find out what kind of pumps/motors they use and their specs.

Some more questions:
what kind of drawbar pull is typical for these tractors?
what percentage of engine hp should I dedicate to each circuit? or can they overlap? how much can I expect to lose to inefficiency?

As you can tell I am new to tractors, I have driven a few but never owned one larger than a garden tractor.

 

[dfkrug]

Jim, you have a very ambitious project ahead of you. Go for it.

An HST tractor usually uses a main hyd pump for implements and either
a flow-divider for the PS or another smaller pump on the same
shaft. The HST uses a "charge" pump, which provides hyd flow
to a variable displacement pump, which is controlled by a pedal-
operated "swash plate" to vary its displacement. Flow from THAT
pump goes to a hyd motor that looks similar to the variable displacement
pump. That motor drives the gearbox.

If you go with fixed disp pump AND motor for the drive, you COULD vary
your wheel speed by varying your hyd pump flow with changes in engine RPM. You do not have a large engine RPM range to work with however.
I do not know what is available in the variable displacement motor area....White Hyd has an extensive web site you might want to look at.
I have had a hard time getting their distributors to get back to me with
any hyd motor quotations. I use the White Hyd motors for hyd PHDs.

If you do find a solution in the area of variable disp hyd pumps and/or
motors, let us know.

Consider this: Use the PS setup from the donor car or another
vehicle. That's a fairly low press/low volume belt driven unit that
could be separate from other hydraulics. Use a separate pump, also
driven off a belt on the front of the engine, to run the hyd motor of
your PTO. Finally, use a trans that fits your donor engine to drive
a separate transfer case (or 2). An auto tranny would work well here.
Dual transfer cases may be the economical way to get ultra-low
gearing in addition to the 4WD.

 

[aspenelm]

renze we must have posted at the same time.

I don't have the transmission that went with the isuzu motor. Not sure what bellhousing they use. I suppose I could find a matching automatic. Probably will need a second transmission to get the gearing low enough. I will have to change my current layout to fit the space for two transmissions + transfer case. But this is probably the easiest and cheapest route. I am going to give this some more thought, I really wanted the effortless forward/reverse movement.

also, will I need a clutch between all these pumps? or is there a relief type valve I can plumb in to reduce resistance when starting the engine.

 

[MikesTractor]

This project sounds very interesting. I'm looking forward to seeing the completed "tractor".

I have to agree with the rest that you need seperate hydraulic circuits. There are several ways to do each one. The power steering could run off an existing engine mounted pump, or it could steal a couple of gallons of flow from the main pump by using a Priority Flow Divider. This would be a dedicated flow and would remain constant. This would allow you to have power steering at all times. The rest of the flow would go to the loader/rear lift/aux. outlets.

You don't need a clutch for the pumps. At engine start up, there shouldn't be any hydraulic load on the system.

So, when do we load dirt?

Mike

 

[aspenelm]

dfkrug, thanks for the explanation about the HST tractor. this is going to show how little I know about hydraulics.

with the fixed disp pump and drive motor, varying the engine speed to vary ground speed makes sense. but I am wondering if at engine idle and lower rpms, the hydraulic pto pump/motor (coupled via belts to engine pullies) would not be getting the rpms needed to make enough power. I would have this problem with the automatic transmission as well. I think I will need a constant engine speed or close to it.

Can speeds be varied with a valve or divertor type thing? Something that adjusts the flow rate going to a motor.

 

[aspenelm]

This project sounds very interesting. I'm looking forward to seeing the completed "tractor".

I have to agree with the rest that you need seperate hydraulic circuits. There are several ways to do each one. The power steering could run off an existing engine mounted pump, or it could steal a couple of gallons of flow from the main pump by using a Priority Flow Divider. This would be a dedicated flow and would remain constant. This would allow you to have power steering at all times. The rest of the flow would go to the loader/rear lift/aux. outlets.

You don't need a clutch for the pumps. At engine start up, there shouldn't be any hydraulic load on the system.

So, when do we load dirt?

Mike

Loading dirt will probably come next year. I would like to get the tractor built by late fall. The loader comes after that.

I will use the existing engine mounted pump for the steering. Not sure if I'll use a rack and pinion or standard truck PS.

I am curious why my neighbors HST tractor has a clutch that you press in before starting. What about in cold temps? I would prefer a clutchless setup if possible.

 

[dfkrug]

...with the fixed disp pump and drive motor, varying the engine speed to vary ground speed makes sense. but I am wondering if at engine idle and lower rpms, the hydraulic pto pump/motor (coupled via belts to engine pullies) would not be getting the rpms needed to make enough power. I would have this problem with the automatic transmission as well. I think I will need a constant engine speed or close to it.

Can speeds be varied with a valve or divertor type thing? Something that adjusts the flow rate going to a motor.

Yes, you would not be running your engine at low RPMs, except when you
are not asking any power of it. I know that I can get enough power delivered
to my hyd PHD by varying my eng RPM from 1500-2100. That does give
a useful range of final auger speeds, but your project would require multiple
gear ranges IMO.

Mikestractor is right, no clutches for the hyd pumps. The hyd motors and
valves I have owned all have or have as an option, relief valves. If you
have them on the valves or motors, you don't need them on the pump,
in general. (In my limited experience.)

You would likely be using open center valves, which can be feathered
for some limited flow control, but I do not think it would be steady enough
to run the driveline. Also if you force hyd fluid thru narrow restrictions,
it gets hot. Fast. Then again, there are all sorts of valves....

Have you also considered an hyd motor at every corner? This is how the
CADLoader from CADPlans works. You can find blders of that machine
on places like machinebldrs network. They have worked out the control
issues, too. The hydraulics are quite a bit of $.