travel pump

[MossRoad]

I've got some pretty good slopes on our other property. Some of them I cannot climb with the mower in float because the wheels start spinning. I can lift the mower off the ground a bit, transferring its weight to the front tires of the tractor and gain huge amounts of traction, but even with that, I still get to a point that the tires will spin in lose soil or wet grass. Even if one starts spinning, some of the others still have traction and I can keep going up that hill.

Another example is when I back drag a ball diamond. I use the large material bucket. I tip the bucket down and push up on the joystick until the front tires are off the ground. I step on the reverse pedal. The front tires spin a bit, but the rears pull me right along. If all four wheel motors where in parallel, I think the front tires would just sit there spinning with no power to the rears.

That's why I think, that with all four wheel motors in parallel, you will have excellent torque until one slips just a bit. Then all fluid will immediately go to the spinning wheel, which will spin faster, which will suck more fluid, which will make it spin even faster, which will suck even more fluid, etc.... until you let off the pedal and the wheel stops spinning. Then we will probably be at a stop, on an incline, where starting takes huge amounts of traction to get moving up hill again. One of the wheels is more likely to slip when starting on an uphill than when already moving.

However, with that said, no one would learn anything without experimentation. I'll refrain from further comment, as, after re-reading my posts, I sound like a broken record. /forums/images/graemlins/tongue.gif I hope it works for you and I end up eating crow /forums/images/graemlins/blush.gif. It would be really cool if we could make this modification for a few hundred bucks and have switchable power. I wait with anticipation(which little smiley face is for anticipation, anyhow?).

 

[ClintBlake]

Stray, Kent,

Hang in there, I think you are right on the money about halving the speed but doubling the torque. With my 422 and loaded tires, I can't get it to spin a tire unless I am on a slippery surface. I do however frequently run out of steam when trying to climb a hill or crawl out of a gully. With the proper valves, you could easily switch to "high range" if traction became a problem much the same as you start off in second gear when driving on snow or mud.

I have heard, many times, the argument that letting off on the treadle increases torque to the wheels. It sounds good, but never seems to work for me. With mine, the more I push down on the treadle, the more climbing power it seems to have right up to the point where it bogs or stalls the engine. If replumbing the wheel motors really does work, Stray will be my hero for a long time.

 

[stray]

Am i hearing that your tractor never stalls out it just spinns the wheels? Does that 3 horse power make that much difference? My 2003 422 PT acts just like ClintBlake explained. /forums/images/graemlins/confused.gif

 

[blackwell]

Some older PT's had a two speed mode, hi/low selector lever near the right foot and larger machines selected with electric valve. One problem with a pure parallel circuit, if one wheel gets light or off the ground, it takes all the flow and you stop moving. PT used a divider/combiner to help solve this problem but it has limited value since they are only efficent in one flow range and they are hard to switch in and out of the circuit. For those who want to run at half top speed and twice the torque, change the wheel motors to ones with twice the displacement.
Good luck,
EB

 

[stray]

It’s good to here from you on this blackwell. You most likely have more experience on PT’s than all of us combined. If one would change the motors they wouldn’t even need to go to twice the size motor to get the torque needed and could still maintain a decent top end speed. One would need to spend around $1500. Not to bad to make the little tractor exactly what you want and need (one attachment can cost this). The question most would have is what size do I have now and what do I need. Can you help here?

For now I’m still pursuing the high low mode. Cost being one reason and because I do traverse long distances, keeping the high speed. I don’t what to do anything that will keep the normal mode from being anything less than what it is now. When I’m going up a steep hill, 4 feet are planted firmly on the ground in a place I know the tractor will stall I want to be able to switch and go. I guess it is kinda like moss said it is time for me to quit talking and do it. I just have a little more research to do.

 

[MossRoad]

<font color="blue"> Am i hearing that your tractor never stalls out it just spinns the wheels? </font>

I've only killed the engine once that I can recall and that was slamming into a hidden treestump in a pile of sand. I don't recall ever hearing the reliefs open, either. Maybe I am not beating on the unit as much as the rest of the folks. Maybe it is the turf tires. All I know is the thing spins tires when pushing up against imovable objects, or, for instance, skimming sod off the ground. As the bucket gets fuller and heavier, the tires will start to spin before the unit will lose any power.

 

[MossRoad]

I didn't say you should quit talking. I said I'd quit talking. Ooops, I talked! /forums/images/graemlins/tongue.gif

 

[keeney]

You build a hydraulic "posi-trac" mechanism for parallel wheel motors not by bypassing the spinning wheel in a parallel circuit, but by limiting how much fluid is allowed to flow through it or constricting the flow.

There are hydraulic valves that can control the flow to stay below a set maximum. You would need one in series with each motor. You would need the bi-directional versions of these flow valves. Set each to 4 GPM and then the spinning wheel can only dump a max of 4GPM while the pressure would be maintained to the other wheels. Note that the power would be dissapated in the flow valve as heat, so your oil cooling system needs to be designed according to how much wheel slippage you expect.

Another alternative is similar to traction control on a car - apply some kind of brake to the spinning wheel applied by electronics and a wheel speed sensor.

Another alternative is to parallel up four smaller variable pumps, one for each wheel with the control circuits linked together.

Another alternative is to use mechanicl flow dividers to force the flow to be split between the wheels. There are flow dividers that are actually made out of two hydraulic motors connected to the same shaft - they are forced to spin at the same rate, and thus the flow is the same through both motors. One end is connected in parallel to the pump, and the other is connected to the two wheels that it is desired to control. This would be the same as locking the axels toghether. You could add a cross-over between the two sides with a flow valve or orifice and then you would simulate a limited-slip differential.

- Rick

 

[KentT]

I've discussed this possible mod in about 3 different topics -- I want to close the loop on this topic also, since it may mislead someone in the future.

I've abandoned the plan to replumb my PT-425s system from 2 series circuits to 4 parallel circuits... not because of any theoretical issue in doing so -- I still think that replumbing would double the torque and halve the speed.

I've had to abandon it because I do NOT have White CE Model 230 14.2ci wheel motors that are rated for up to 3000 PSI. Instead I have White RS Model 141 12.5ci wheel motors that are rated to 1500 PSI (continuous). My old wheel motors would not handle doubling the pressure in the system. I am now looking at installing larger displacement wheel motors (18ci or larger) that can increase the torque without replumbing the system.

 

[johara1]

KentT, you are right again,the big wheel motors are the answer.i now mow up a 3 to 1 slope and i don't spin the front tires, it seems to put more power to the rear. the tractor doesn't want to lift the front end when pushing the mower in float up hill.........jim