e-hydrostatic transmission question
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    mike01's Avatar
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    e-hydrostatic transmission question

    I have a question that is best asked by comparing two scenarios. This is primarily about e-hydros, but may also apply to regular hydros.

    Scenario 1:
    You open the throttle all the way, then put it in high, then floor the forward pedal like an on/off switch. The engine RPMs drop, the tractor starts to move, the engine RPMs climb, and eventually you get up to your top speed. This takes place on flat, paved ground.

    Scenario 2:
    Same as above, except that you don't floor the pedal, you press it and gradually but quickly move it all the way forward. The tractor accelerates to its top speed a lot faster than in Scenario 1.

    What exactly is going on between the engine and the e-hydro transmission that causes the above to happen? In Scenario 1, something is being overwhelmed and forced to play catch up. Is it the engine or the transmission, and what exactly is going on?

    Thanks in advance for your help in understanding this.
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    It is done thru Fluid Flow Gearing. It does create heat in the process like slipping a manual clutch. The main Gearing is done thru Manual Gears and Hydro(Fluid)Drive with out a mechanical connection.

    What is a hydrostatic system?
    A hydraulic drive system is a quasi-hydrostatic drive or transmission system that uses pressurized hydraulic fluid to power hydraulic machinery. The term hydrostatic refers to the transfer of energy from pressure differences, not from the kinetic energy of the flow.
    Last edited by JD4044M; 05-13-2019 at 07:03 PM.
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    mike01's Avatar
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    Quote Originally Posted by JD4044M View Post
    It is done thru Fluid Flow Gearing by a Torque Converter. It does create heat in the process like slipping a manual clutch. The main Gearing is done thru Manual Gears and Hydro(Fluid)Drive with out a mechanical connection.

    What is a hydrostatic system?
    A hydraulic drive system is a quasi-hydrostatic drive or transmission system that uses pressurized hydraulic fluid to power hydraulic machinery. The term hydrostatic refers to the transfer of energy from pressure differences, not from the kinetic energy of the flow.
    So can you use the above to explain what's happening in scenario 1 and not happening in scenario 2?
    2019 X758, 54" Autoconnect deck
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    JD4044M's Avatar
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    There are guys on here that are better with words but it has to do with Engine RPM compared to pump Flow/PSI. The gearing is in the fluid flow ratio till you get up to speed and can let off on the pedal some. So speed is controlled with fluid flow(Pedal) more HP needs More Fluid Flow @ Higher PSI to get to top speeds faster. Setting the RPMs is for using the engine at a performance setting for max usable working HP. The Pedal is for controlling fluid flow off the pump the engine spins inside the transmission area. Only so many HP so to get things going the fluid ratio flow changes so the engine can keep up the RPMs on the pump. Like slipping the manual clutch in a truck to get going RPMs High but still going slow.


    Here is a search that has a ton of information on it.https://www.google.com/search?source...63.35H4v29ncNY

    Neat Video of how it works;https://www.youtube.com/watch?v=qxZFSNITK-c
    Last edited by JD4044M; 05-13-2019 at 07:30 PM.
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    Quote Originally Posted by JD4044M View Post
    There are guys on here that are better with words but it has to do with Engine RPM compared to pump Flow/PSI. The gearing is in the fluid flow ratio till you get up to speed and can let off on the pedal some. So speed is controlled with fluid flow(Pedal) more HP needs More Fluid Flow @ Higher PSI to get to top speeds faster. Setting the RPMs is for using the engine at a performance setting for max usable working HP. The Pedal is for controlling fluid flow off the pump the engine spins inside the transmission area. Only so many HP so to get things going the fluid ratio flow changes so the engine can keep up the RPMs on the pump. Like slipping the manual clutch in a truck to get going RPMs High but still going slow.
    .................................


    or

    trying to take off in 4th gear manual transmission. is your example 1. with gas pedal pressed to the floor and hoping your vehicle will take off without dropping a clutch or transmission.

    That is my take.
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    Let me narrow it down to a more specific question...

    Is it the engine that can't keep up with the transmission's demands when you floor the pedal, or the transmission not being able to keep up with the sudden torque from the engine?
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    Little bit of both tractors are not race cars so they don't put waste 400-600 hp to smoke the tires off with way more then needed just to do 100 mph. Race Cars have it for how fast you can get there. It is a balance thing Engine HP and Transmission Gearing. More power with faster acceleration means a bigger tractor with more HP.
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    Quote Originally Posted by mike01 View Post
    Let me narrow it down to a more specific question...

    Is it the engine that can't keep up with the transmission's demands when you floor the pedal, or the transmission not being able to keep up with the sudden torque from the engine?
    In high range if the transmission went into relief you would definitely hear it. It is an unmistakable squeal.

    Another thing that affects things is whether load match is turned on. Normally it is enabled.
    Loadmatch has the effect of electronically letting off the pedal when when the engine is bogging down.
    Works pretty well in conjunction with the ethrottle feature.

    If anything is playing catch-up, it’s the engine. The transmission can’t. It either spins or goes into relief.

    Did you test drive an e-hydro machine and make this observation, or is this purely another “thought exercise”?
    Last edited by arlen; 05-13-2019 at 10:42 PM.
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    Quote Originally Posted by mike01 View Post
    I have a question that is best asked by comparing two scenarios. This is primarily about e-hydros, but may also apply to regular hydros.

    Scenario 1:
    You open the throttle all the way, then put it in high, then floor the forward pedal like an on/off switch. The engine RPMs drop, the tractor starts to move, the engine RPMs climb, and eventually you get up to your top speed. This takes place on flat, paved ground.

    Scenario 2:
    Same as above, except that you don't floor the pedal, you press it and gradually but quickly move it all the way forward. The tractor accelerates to its top speed a lot faster than in Scenario 1.

    What exactly is going on between the engine and the e-hydro transmission that causes the above to happen? In Scenario 1, something is being overwhelmed and forced to play catch up. Is it the engine or the transmission, and what exactly is going on?

    Thanks in advance for your help in understanding this.
    I am going to assume this is with a computer controlled power train. Much like my Duramax powered truck, in scenario 1, the PCM senses a massive change in power requirements and starts to defuel the tractor so power doesn't hit in a one big shock. This is the OEM trying to save the tractor (or in my case my truck) from itself. I can't floor my truck and hope for instant power, I have to roll the throttle on for a quick acceleration. Same thing here with your scenario. For whatever reason the OEM doesn't want the tractor to go from full stop to full go all at once, most likely to reduce the stress on the components in the drive train.

    I can understand the OEM's desire. My JD 400 GT doesn't have any such programmed controls and if I slam the hydro lever forward it will pull the front wheels, even with my plow mounted on the front! I am pretty sure that sudden shock to the power/drive train doesn't do it any favors and the OEM is looking to reduce that kind of stress.
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    In my experience, increasing HP (specifically via a turbo) makes the hesitation in Scenario 1 better (less hesitation). That doesn't quite mesh with the above answers, unless turbo lag is responsible.
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