I want to replace the LSHT drive motors on my 2006 t300 with 75cc EDC S90 pumps coupled to some torque hubs for many reasons that makes it worth some extra trouble. Sauer Danfoss said the pumps could be used as motors if I pulled out the charge pumps. But its up to me to ensure I take into consideration the following: 1) As far as the charge pump size, that involves a bunch of factors. First, did the motors you are replacing have loop flushing? How do you plan to flush the loops to control heat in your circuit? The amount of loop flush will affect the size of charge pump required. 2) Consider the system protection type that is in the pump used as a motor. If you have pressure limiters they could cause the pump to stroke or destroke depending on the operating condition and pressures. You need to make sure you understand how that will work in all machine modes. 3) You need to make sure you understand the potential failure modes. The OEM drive pumps are 55cc s90's that will stay for now until upgrade them to same 75cc s90's. #2 doesn't seem like a big deal. If my figuring is correct I'll have about 3 times the original tractive force before the limiters kick in to protect the pump.... If that would even happen on the 75cc drive side and not 55cc pump side first. And the use as drive motors is going to be much more intermittent then the OEM 55cc pumps driving them, so if the 55cc's are keeping themselves cool from the factory, the 75cc's probably aren't generating much more heat then the oem drive motors they are replacing. The only issue I can think of is if I have the drive motors just barely stroked(small displacement) and I head down a steep hill with a heavy load. I am often driving off of cliffs that I am unable to drive back up. I have no clue about #1 What do you guys think, should this be plug and play once i pull the charge pumps? Is there anything else to consider? I can make them fit and cut my own sprockets or modify oem ones. Parking Brake: The hold back(w/out the parking brake) of the oem system is almost sufficient. If anything it just creeps, i'm guessing this has to do with the loop flushing??? Should I try to utilize the 75cc s90 on the drive side as a quasi parking brake? If not I have another plan that is simple and safe.
The park brake is in the drive motors, if you replace the motors, you will not have park brakes. The stock motors do have case drain back to the sump. The machine monitors charge pressure. If you change out the hydrostat out and do not have a simalr charge pressure, the machine will go into shutdown. That will take some electrical engineering to get around. If you are so dissapointed in this machines performance, I think you are throwing good money after bad. Buy a different machine.
Thanks for the input. I like the rest the architecture of the t300, and all the machines have their quirks. Ok, i'll take care of the park brake. My neighbor is an electrical engineer, he is currently building me a wireless RC controller for some of my machines, so I can deal with the charge pressure issue if it arises. But the motors aren't generating the charge pressure, the only thing they can be contributing to that is backpressure, if anything. I guess the main question is how do I accommodate loop flushing to keep the circuit cool when the motors aren't turning but the pumps are? I see 2 options. Use the edc on the motor(75cc pump) to return it to neutral when i'm not traveling so that the charge flow from the oem pumps(55cc) just pass thru the motor(75ccpump). Is there any reason that wouldn't work? Otherwise I have the external charge pump filtration ports and other charge pump ports to work with.
Do the oem drive motors have a loop flushing valve in them?
When the motor is not turning, the pumps are not pumping. Yeah they are turning, but no flow is created. The hydrostat has a small charge pump built into it. I talked with the saleman if he ever heard of your complaint. He said a few guys have said that when going up against a Deere CT332, but nothing else. I use to work for Deere and could buy that. The Deeres have an outer plantery where the bobcat has no gear reduction. I don't think you would gain what you want out these bigger pumps and motors. Flow equals speed, not power. A stock T300 can already build up to 5000 psi. So you put higher flow pumps, it should go faster, but most likly won't have any more power. You said you had some torque hubs in mind, but do the calculations work out that this thing would haul ass while still being able to push moutains?
The drive motors have "engineered leakag". A line goes from the motor, to the cas drain filter and back to sump.
A premium hydrostatic transmission should have variable pumps and motors, imho. The bobcat motors are fixed. To answer your question, yes the numbers work. I'll have more speed or more power, esp at lower engine rpm, just not at the same time without an engine upgrade, but that is all i need. Theres a chart on one of the forums, t300 is at the bottom of the competition at about 6-7k lbs tractive effort and the Tak is at the top with about 13,000lbs. I researched it a couple years ago, and its very hard to find bobcat publishing these specs. I would think from the specs i just pulled on their drive motors that they should be able to produce a little more the what i saw on that chart 6-7k, but not by much. But its definitely common knowledge that bobcat, t300 particularly, loses in this department. It doesn't really matter, i just know what i need. All that matters is if i start tearing tracks in two or destroying the rear idler- then i'll back off a little or get better tracks/idler bearings. "The drive motors have "engineered leakag". A line goes from the motor, to the cas drain filter and back to sump. " A guy that rebuilds these bobcat(rexroth) motors also said they didn't have a loop flushing valve in them. But according to the data tag on it thats not true. More Thoughts: The OEM motor is a Rexroth: MCR10F1120F250z32B5M1L/48SF4P0S0395H 1120 cc 10L/min flushing And unknown special order features.(SO395) Nom Output @250bar(3625.9psi)= 4010Nm (2957.6 ft-lbs) Max Output@400bar(5801psi)=6420Nm(4885.2 ft-lbs) Max Seed 150rpm The Planetary Hub I want to replace the oem motor with is: 34.6:1 Ratio Nom Output=5270.7Nm (3887.5 ft-lbs) Max Output=10541.5Nm (7775 ft-lbs) Max Input = 4500rpm Max Output= 150rpm (per mfg spec) Here is the 75cc pump specs that I would like to try to run as a motor behind the planetary hub: Flow @ Rated speed=270L-m (71gpm) Torque @ Max Displacement= 1.19 Nm/bar Min Input Speed=500 Rated Speed=3600 Max Speed=3950 Max Working Pressure=450bar (6525psi) Max Pressure=480bar (6960psi) Max Low Loop=45bar (650psi) Min Low Loop=10bar (145psi) Loop Flushing the OEM pumps that were flushing out the oem motors: I would use a auxillary loop flushing valves. Sun Hydraulics makes them. Or i could just use a standard relief block. Control Pressure: I could tap charge pumps on the oem pumps to derive my charge/control flow for operating the new motor(s90 pump). But I not sure it would be enough flow, and I risk the oem pumps. So I would probably opt for either a separate aux pump(since the pressure/flow is small, or tapping into the work function gear pumps on the machine and using a regulator. Loop Flushing the new motors(s90 pumps) Do you think I need additional loop flushing to keep these cool, even if the oem pumps are loop flushing? There would be some flow out the case drain. If so, then I would use the sun loop flushing valve. If you need a separate valve for each pump. Pump vs Motor Control Conflicts: I would keep the motor(s90pump) stroked fully, until I want to speed it up and would destroke it with an input from the operator. So the only conflict I can see there is if I have it destroked for more speed and I increase the load on it and spike the pressure to the point of it trying to destroke itself thru the multifunction valve, meanwhile I am trying to stroke it and I’m not sure what the net effect would be. But I could just back of the drive controls to reduce the pressure I’m putting to it so the multifunction valve will close and I can then stroke it for more power- not a big deal with this machine, and probably avoidable all together with just a few minutes of learning to operate it. Are there any other features that a motor would have that the pump won’t? Any guesses on what the output torque of the pump would be when used as a motor? I’m still studying this. Any input is appreciated. Pics always help. 1)oem motor tag 2)OEM motor 3)Actual machine 4)Sauer Danfoss’s suggested s90 use diagram 5)My modified version using the pump as a motor and pulling from the oem pump charge circuit to control the motor(but I don’t think I want to do that)