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Hydraulics Design: Bobcat T300 HACK: Using Pumps as drive motors. LoopFlushing,etc

Discussion in 'Heavy Equipment' started by LoadTest, Jun 4, 2012.

  1. LoadTest

    LoadTest Junior Member
    Messages: 1

    I want to replace the LSHT drive motors on my 2006 t300 with 75cc EDC S90 pumps coupled to some torque hubs. The t300s are hard on drive motors, have about half the drawbar pull of the competition to begin with, and are slow. 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 i'm wanting to use as drive motors, probably with a hybrid powerplant.

    #2&#3 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