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Hydrostatic drive efficency


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#1 DH1 ONLINE  

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Posted April 05, 2011 - 04:57 PM

OK here's a question for those who know and if I knew the answer I wouldn't be asking the question.

How efficient is a Hydrostatic drive system in delivering power?

My understanding is basically a gas or diesel engine drives a hyd pump that supply's fluid pressure through control vales and hoses to a hyd motor that drives the trany, moves the tractor.

So if an engine has 10hp or 20hp, whatever # you want to use, at the crankshaft then how much HP is at the Hyd motor's shaft?

10hp in how much out?

#2 olcowhand ONLINE  

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Posted April 05, 2011 - 05:43 PM

My understanding is basically a gas or diesel engine drives a hyd pump that supply's fluid pressure through control vales and hoses to a hyd motor that drives the trany, moves the tractor.

So if an engine has 10hp or 20hp, whatever # you want to use, at the crankshaft then how much HP is at the Hyd motor's shaft?

10hp in how much out?


What you described is hydraulic drive, not hydrostatic. Hydrostatic involves a piston pump with variable flow rate, and a fixed displacement piston motor. Hydraulic drive is a fixed displacement gear pump, with a valve to vary the amount of oil to flow to the gear motor in order to change speed.
With hydrostatic the power loss is somewhere around 20% give or take, depending on particular unit. So a 10hp engine can only put about 8hp to the ground, maybe a tad more.
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#3 NUTNDUN OFFLINE  

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Posted April 05, 2011 - 06:24 PM

I was going to say it would be at least a 15% - 20% loss. Dan hit the nail on the head with his description :D
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#4 DH1 ONLINE  

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Posted April 05, 2011 - 08:18 PM

What you described is hydraulic drive, not hydrostatic. Hydrostatic involves a piston pump with variable flow rate, and a fixed displacement piston motor. Hydraulic drive is a fixed displacement gear pump, with a valve to vary the amount of oil to flow to the gear motor in order to change speed.
With hydrostatic the power loss is somewhere around 20% give or take, depending on particular unit. So a 10hp engine can only put about 8hp to the ground, maybe a tad more.


So which of those 2, Hydrostatic vs Hydraulic in general would be more efficient in terms of delivering power?

#5 olcowhand ONLINE  

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Posted April 05, 2011 - 08:26 PM

So which of those 2, Hydrostatic vs Hydraulic in general would be more efficient in terms of delivering power?


I had to look up hydraulic drive efficiency, but after finding this here: The Next Challenge For the Maintenance Department
It would appear hydrostatic wins by a good margin over gear hydraulic pump drive. Hydraulic loses 40 to 50% to hydrostatic loss of around 20%.
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#6 DH1 ONLINE  

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Posted April 05, 2011 - 08:37 PM

I had to look up hydraulic drive efficiency, but after finding this here: The Next Challenge For the Maintenance Department
It would appear hydrostatic wins by a good margin over gear hydraulic pump drive. Hydraulic loses 40 to 50% to hydrostatic loss of around 20%.


Then I guess that's why they use Hydrostatic over Hydraulic drive.
And I guess that's why Hydro's in general don't do so well in pulling tractors, a strong Hydro pulling tractor needs a more powerful engine.

I see in your link they mention pump losses and motor losses is that the case here with Hydrostatic drive?
Is the 20% loss total or for each pump+motor?

#7 olcowhand ONLINE  

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Posted April 05, 2011 - 08:41 PM

Yes, the losses is for the entire system, pump & motor, plus valve losses & such. Hydrostatic might even go down to 75% efficiency, but still way ahead of hydraulic drive.
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#8 DH1 ONLINE  

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Posted April 05, 2011 - 08:46 PM

OK no more questions I found out what I wanted to know. Thanks

#9 middleageddeere OFFLINE  

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Posted April 06, 2011 - 05:53 AM

How do those numbers compare to loss on gear drives?

#10 TUDOR OFFLINE  

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Posted April 06, 2011 - 06:23 AM

How do those numbers compare to loss on gear drives?


Efficiency ratings of hydraulic pumps and motors.

Piston - 90%
Vane - 85%
Gear - 75 -80%

For a pump/ motor combination

- Piston to Piston (.9 x .9) - 81%
- Vane to Vane (.85 x .85) - 72%
- Gear to Gear (.8 x .8 best case) -64%
- Gear to Gear (.75 x .75 worst case) - 56%
- Piston to Gear (.9 x .8 MF12H) - 72% or 68% using the lower number , but Sundstrand has pretty good equipment.

Wear can change things , but these are the theoretical numbers used for basic design of a system.
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#11 IamSherwood OFFLINE  

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Posted April 06, 2011 - 07:50 AM

I had to look up hydraulic drive efficiency, but after finding this here: The Next Challenge For the Maintenance Department
It would appear hydrostatic wins by a good margin over gear hydraulic pump drive. Hydraulic loses 40 to 50% to hydrostatic loss of around 20%.


That's quite a loss in the hydraulic system. Had know idea.

#12 olcowhand ONLINE  

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Posted April 06, 2011 - 08:58 AM

I knew Tudor would have all the figures! Thanks Tudor!

#13 NUTNDUN OFFLINE  

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Posted April 06, 2011 - 10:10 AM

How do those numbers compare to loss on gear drives?


I am not real sure but I think the gear drives can range from 5% - 10% loss depending on how efficient they are. The more gears, bearings and shafts that the power gets transmitted through more loss there will be. Would be great to know what the efficiency loss would be say per gear tooth width, bearing surface area and what not. I am sure the figures are out there somewhere but I don't know the mathematical equations to figure it all out :D

#14 JD DANNELS OFFLINE  

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Posted April 06, 2011 - 10:26 AM

Not to be argumenitive but with that considered. What makes the Case/Ingersoll Gt's Hydralic Drive so admired and apreciated?

#15 olcowhand ONLINE  

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Posted April 06, 2011 - 10:31 AM

Not to be argumenitive but with that considered. What makes the Case/Ingersoll Gt's Hydralic Drive so admired and apreciated?


One is the fact they still make them as strong built as in the olden days. The other (my opinion anyway) is because they are so unique in their drive design.




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