Sizing a Hydrostatic Transmission

Mtjohnso

Member
I have an old dozer made by the Windolph Corp in Portland Oregon in the 50s.
Originally this unit had a Wisconsin TF (14 0r 16 HP) with a Crosley 3 speed transmission.
The Transmission had a 3.29 to 1 ratio in 1st, 1.72 to 1 in 2nd and 1 to 1 in 3rd.
The Wisconsin engine and transmission were removed and replaced with a Duetz F2L511 diesel engine and a hydraulic pump and a hydraulic motor.
The problem is that the dozer has a lot of torque and is very slow moving. So I have been reading and asking questions and pondering of what can I do to make this a little closer to speed selection and gear choices of what was there originally.
One thought is to install a hydrostatic transmission. I have done much looking on line, ebay and other places trying to figure out what would be best.
Since the original motor only produced 16 horse power at best, then the thought is that the Hydrostatic would not need to be that beefy.
So how does one determine what size and specs one needs for a hydrostatic transmission? Then where to find one that is somewhat economical. Not a lot of room between motor and rear housing assembly. So the smaller the better or maybe the shorter the better.
Thoughts? What would you do?
Marvin Johnson
 
Food for thought - transmissions need to be sized for TORQUE, not horsepower. Horsepower does the work, but torque makes it go. Diesel engines in general put out way more torque than comparable gas engines - even of the same horsepower. There is also the vibration issue to be reckoned with. Choose carefully, lest you have to choose again.
 
You already have a hydrostatic trans mission of sorts. The best setup would be a variable displacement pump with a fixed drive motor. Tell us more about what you have and we can point you in the right direction.

HP=GPM*PSI/1714
 
There are several equations you need to be familiar with when dealing with hydrostatic drives. Two of the more basic ones are:

GPM=RPM*displacement/231 (displacement is cubic inches)

and

torque=PSI*displacement/6.28 (torque is in-lb and displacement is cubic inches)

Using these equations you can determine the maximum flow rate from your pump at full displacement then the resulting motor speed. By knowing your relief valve setting you can then determine the motor torque.

Moresmoke noted the HP=GPM*PSI/1714 relationship which is also important. This comes into play because you want a system that can move enough oil at a high enough pressure to fully load your engine. Your available 16hp would not be usable if you're blowing over relief when only pulling 10hp from the engine.

If you currently have a fixed displacement motor the main thing to understand is that you essentially have a single speed transmission. Regardless of the displacement of the hydrostatic pump the resulting maximum motor torque will be the same so the chosen motor size becomes a compromise between speed and torque. There is really nothing you can do with this setup to duplicate the speed and torque range that a multi-speed transmission provides. The only way this can be overcome is with a variable displacement motor or inserting a multi-range gearbox between the fixed motor and drive axle.
 
Adapting a 3 speed transmission (like a Volvo stick shift from about 1960) so it was driven backward to make it a overdrive, then driving the pump with that setup, gives increased speed. Using a higher displacement pump, and the 3 speed on the output to the final drive with the motor driving the 3 speed (as designed input to output would also work. Those tranmissions were short. Jim
 
I have a small rubber tired articulating loader and its powered by a hydraulic motor works great,bought a replacement motor from Surplus tractor last year for around
$200.Of course you'll need some type of hydraulic pump to drive it.
 
Somebody erred in the hydraulic motor specs and maybe the pump. The motor needs to have less displacement per revolution to increase rpms but this will reduce torque. However it sounds like there is surplus torque at the moment.
Will the engine lug down when driving the hydraulic pump?
What size of pump on the 16HP motor? If it's a 2500psi system the pump should be good for 10gpm.
 

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