MossRoad
Super Moderator
- Joined
- Aug 31, 2001
- Messages
- 58,182
- Location
- South Bend, Indiana (near)
- Tractor
- Power Trac PT425 2001 Model Year
Think of it this way...
On a normal HST tractor, the engine turns a pump that provides hydraulic juice to ONE hydraulic motor. That motor turns a shaft that turns a gear box that has 2 or three ranges. The output shaft of that gear box turns a differential, which turns the wheels. By using your foot to vary the amount of juice that gets from the pump to the motor the speed of the motor is varied. This is done because when you push the pedal, the angle of the swash plate changes in the variable volume pump. Low angle = high torque and vice versa. Where the gear box comes in is just like gears in a car. You can have a low range with massive torque and low top speed, say 0-4MPH. A middle range with less torque and more top speed, say 0-8MPH. And a gutless high range with very little torque but very high speed, like you would want for road travel, say 0-18MPH. You can feather that high range with the softest foot all you want, but you will have no guts behind it because the gearing is too high.
On a Power Trac, the engine turns a pump that provides hydraulic juice directly to all FOUR wheel motors. There is no gear box or range selector and no differential(s). Operation with your foot is the same... low speed = high torque and vice versa.
My PT425 is listed as 0-8MPH. If they would use different wheel motors(one's with lower RPM but same hydraulic flow), I could have way more torque, but way less top speed. Good for excavating, bad for mowing the lawn. So, they had to come to a compromise between low end torque and top end speed by selecting the proper pump and motor that would give the optimum performance for MOST jobs the machine is used for. There is some torque sacrificed and some top end sacrificed in this setup.
You can let off on the pedal to give it maximum torque, but a normal tractor will have more torque in low range. You can also mash the pedal down for top speed, but a normal tractor will have more top speed in high range.
With that said, I think the Power Trac system is a very good blend of what I would compare to the low and mid ranges of a normal tractor. I really like it. There are few times I wish I had more low end torque. On a machine that weighs only 1500 pounds with operator, I lose traction before I lose power. Although this afternoon I had plenty of traction and torque... I spun the left front tire off it again. So much so that I blew it halfway off the rim, all the wire came out of the sidewall, and the inner tube was bulging all over the place. I almost made it back to the garage on the inner tube, but the wires popped the tube, so I had to go in reverse by skidding along on the bucket. New tire and tube will have to be purchased tomorrow.
How could they add two ranges to their setup? I'm not sure if I would want it, but I can think of a couple.
1. Two speed wheel motors. Although this has been discussed, I don't see how you could get all four wheel motors to be in the same 'gear' at any given time. Maybe someone could explain that.
2. Two speed pump. That would seem more logical. Log splitters use two speed pumps. High speed until enough force builds up to kick it over to low speed with massive torque. Of course, I know doodly beans about hydraulic motors, so maybe someone could explain that one as well.
3. Differentials and gear boxes. BOOOO! /forums/images/graemlins/mad.gif Nobody wants to go back to differentials. You'd need positraction or lockers and that would tear up the turf. Remember, the Power Trac never tears up the turf and we like that! /forums/images/graemlins/grin.gif
OK. Any other thoughts about how to get HI/LOW ranges out of these beasts? Do we really want HI/LOW ranges? Do we like it just the way it is? Should I convert to the new wheel motors, or is it not that big of a deal? I need to test drive one of the new ones to compare it to my green machine of 2001 and see just how much of a difference it makes. /forums/images/graemlins/wink.gif
On a normal HST tractor, the engine turns a pump that provides hydraulic juice to ONE hydraulic motor. That motor turns a shaft that turns a gear box that has 2 or three ranges. The output shaft of that gear box turns a differential, which turns the wheels. By using your foot to vary the amount of juice that gets from the pump to the motor the speed of the motor is varied. This is done because when you push the pedal, the angle of the swash plate changes in the variable volume pump. Low angle = high torque and vice versa. Where the gear box comes in is just like gears in a car. You can have a low range with massive torque and low top speed, say 0-4MPH. A middle range with less torque and more top speed, say 0-8MPH. And a gutless high range with very little torque but very high speed, like you would want for road travel, say 0-18MPH. You can feather that high range with the softest foot all you want, but you will have no guts behind it because the gearing is too high.
On a Power Trac, the engine turns a pump that provides hydraulic juice directly to all FOUR wheel motors. There is no gear box or range selector and no differential(s). Operation with your foot is the same... low speed = high torque and vice versa.
My PT425 is listed as 0-8MPH. If they would use different wheel motors(one's with lower RPM but same hydraulic flow), I could have way more torque, but way less top speed. Good for excavating, bad for mowing the lawn. So, they had to come to a compromise between low end torque and top end speed by selecting the proper pump and motor that would give the optimum performance for MOST jobs the machine is used for. There is some torque sacrificed and some top end sacrificed in this setup.
You can let off on the pedal to give it maximum torque, but a normal tractor will have more torque in low range. You can also mash the pedal down for top speed, but a normal tractor will have more top speed in high range.
With that said, I think the Power Trac system is a very good blend of what I would compare to the low and mid ranges of a normal tractor. I really like it. There are few times I wish I had more low end torque. On a machine that weighs only 1500 pounds with operator, I lose traction before I lose power. Although this afternoon I had plenty of traction and torque... I spun the left front tire off it again. So much so that I blew it halfway off the rim, all the wire came out of the sidewall, and the inner tube was bulging all over the place. I almost made it back to the garage on the inner tube, but the wires popped the tube, so I had to go in reverse by skidding along on the bucket. New tire and tube will have to be purchased tomorrow.
How could they add two ranges to their setup? I'm not sure if I would want it, but I can think of a couple.
1. Two speed wheel motors. Although this has been discussed, I don't see how you could get all four wheel motors to be in the same 'gear' at any given time. Maybe someone could explain that.
2. Two speed pump. That would seem more logical. Log splitters use two speed pumps. High speed until enough force builds up to kick it over to low speed with massive torque. Of course, I know doodly beans about hydraulic motors, so maybe someone could explain that one as well.
3. Differentials and gear boxes. BOOOO! /forums/images/graemlins/mad.gif Nobody wants to go back to differentials. You'd need positraction or lockers and that would tear up the turf. Remember, the Power Trac never tears up the turf and we like that! /forums/images/graemlins/grin.gif
OK. Any other thoughts about how to get HI/LOW ranges out of these beasts? Do we really want HI/LOW ranges? Do we like it just the way it is? Should I convert to the new wheel motors, or is it not that big of a deal? I need to test drive one of the new ones to compare it to my green machine of 2001 and see just how much of a difference it makes. /forums/images/graemlins/wink.gif
