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Discussion Starter #1
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.
 

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Discussion Starter #3
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?
 

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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=hp&ei=LQvaXJjvLr_J0PEP0qq9iA4&q=explain+hydrostatic+transmission&oq=explain+hydrosta&gs_l=psy-ab.1.7.0l9j0i22i30.1321.12839..17458...0.0..1.2714.16951.5-2j12j0j1j2......0....1..gws-wiz.....0..35i39j0i131j0i10j0i20i263.35H4v29ncNY

Neat Video of how it works;https://www.youtube.com/watch?v=qxZFSNITK-c
 

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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.
.................................
:bigthumb:

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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Discussion Starter #6
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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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”?
 

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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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Discussion Starter #10
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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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.
It is the engine that can't keep up. You are trying to suddenly move a heavyweight object. When this happens you are spiking the pressure in the system. The pump and motor are loading up to a point that the engine is trying to stall. The pump may have also bypassed to relief for a second or two to dump off pressure. Once the load is shed by relief the engine can then keep up.
It is much easier to bring an object to top speed that is already rolling than to suddenly move it at full power from a dead start.

Sent from my LGL52VL using Tapatalk
 

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Discussion Starter #12
That makes sense, and meshes with my experience. Thank you.
 

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A hydra-static transmission consisted of at least a variable angle swash-plate piston pump and a fixed angle swash-plate piston motor.

If the pump swash plate is straight, no flow occurs. As the control lever is pushed and the pump swash plate begins to angle, the pistons will forces oil out the ports to the motor causing the motor to turn.

When the pump swash plate is at a slight angle, the hydra-static transmission will produce large amounts of torque, low speed with minimal input HP.

When the pump swash plate is at a high angle, the hydra-static transmission will produce lower torque, high speed and requires more input HP.

Here is a video that sort of explains it.

https://www.youtube.com/watch?v=qxZFSNITK-c


So, what is happening in your scenarios. When you push the forward propel pedal all the way down in hi-range, the hydra-static transmission is trying to speed up quickly due to the high flow of hydraulic oil which cause high pressure to build in the system which will cause the system to go on relief. Now, going on relief doesn't mean the tractor stops, the system is just dumping off some flow to maintain the relief pressure, hence the slower speed up of the tractor.

In scenario 2, you are slowly increasing the angle of the swash plate which gradually increase the flow, allowing the tractor to gain momentum normally without suddenly trying to gain momentum. This allows the system pressure to stay within its working range and no flow is lost over the relief.

The engine is powerful enough to power the hydra-static system on relief. Proof is this. If you try to propel up a fairly steep hill in hi-range and hold the propel pedal down too far, the tractor will stop and the propel system will go on relief and not be able to overcome the weight of the tractor trying to climb the hill.

So, the moral to the story is, if you are in hi-range and need more torque, back off on the propel pedal. If you still need more torque, use low range. If you want more speed, use high range and gradually push the propel pedal down. Truthfully, it is always best to slowly engage the propel pedals, forward and reverse.
 

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All very good info and good read.

Ray_PA. I want to go home and test out the more torque in high with less pedal. I’m curious about that now. Mainly because I had a 1025 and just recently got a 2025. I haven’t really put the 2025 to work but just driving around and moving a few things I feel the 1025 would work circles around the 2025 in high gear. Maybe it’s the tires or geared different or combinations.
 

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All very good info and good read.

Ray_PA. I want to go home and test out the more torque in high with less pedal. I’m curious about that now. Mainly because I had a 1025 and just recently got a 2025. I haven’t really put the 2025 to work but just driving around and moving a few things I feel the 1025 would work circles around the 2025 in high gear. Maybe it’s the tires or geared different or combinations.
I believe the 2025R has larger tires, correct? The larger tires, in the end, will increase the gear ratio. This will cause more speed and less torque.

Now, I don't know if JD uses the same differential ratios in the 2025 as they do in the 1025. Many have said, the 1025R and the 2025R have the same drive train, I don't know that for sure. If that is actually the case, then the 2025R, with the larger diameter tires, with the propel pedals full depressed, will have higher speed but less torque at the wheels, both in low and high range.

Now, if you back off on the propel pedal on the 2025R, the system will also develop allot of wheel torque, albeit, if they are equal, the 1025R will develop more wheel torque than the 2025R.

I know that sounds bad but it isn't, as the limitations of any tractor in low range isn't that they do not have enough wheel torque or engine HP, it is traction. Getting the HP and wheel torque to the ground without spinning the wheels is the real issue.

So, the 2025R will actually be better at getting the HP and torque to the ground because it is heavier.
 
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