# hydraulic direct drive



## major (Apr 4, 2008)

alexis.marcil said:


> Hi, I wonder why I don't find any info on using an electric motor to power an hydraulic pump and then a hydraulic motor that is direct drive into a differential?
> 
> It would eliminate the transmission, controller, and allow the motor to always work in the prime range...
> 
> ...


Hi alexis,



> Hydraulics are powerful and reliable.


 And heavy, and leaky, and inefficient, and noisy.

The one type of vehicle which comes to mind which uses electrohydraulic drive and is battery powered is the scissors lift. So yes, it is a valid means of vehicle propulsion. However, it is far from ideal for most battery powered vehicles. I think you have some misconceptions about prime working range for electric motors. Electric motors in conjunction with modern speed controllers work very well over a wide range of speed and power.

Hydraulics bring nothing to the table for most EVs. Hydraulics can offer advantage for certain applications and are utilized in those cases.

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

There is one case. Lawn tractors with hydrostatic drives are most easily converted by using a shunt motor. They are already designed to work with a constant rpm, so with a shunt motor (runs at constant rpm) your "controller" is just a switch. This makes for a very cheap and easy conversion. You don't care as much about efficiency in this case (range is less of an issue when you are never more than 100 meters from a plug). That extra hydraulic step just wastes energy. BTW I might be doing this myself soon, the gas motor on my lawn tractor just died.

Like major says, you'd never do a fresh design this way, it only works because if it is already there and the easiest route.


alexis.marcil said:


> Hi, I wonder why I don't find any info on using an electric motor to power an hydraulic pump and then a hydraulic motor that is direct drive into a differential?
> 
> It would eliminate the transmission, controller, and allow the motor to always work in the prime range...
> 
> ...


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## tom_001 (Mar 19, 2011)

Personaly I'v only seen that kind of drive on boats, mostly medium foil catamarans where weight distribution is a probablem and the drive out is in a hard to reach place. On a side knote yamaha ttr 600 belgarda (hell of a bike) and the WR were made (tested?) in a two wheel drive virsion using a hydraulic hub motor on the front driven by the final drive.


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## poprock (Apr 29, 2010)

Basically, what you are suggesting would be like removing the Kubota diesel from a 743 Bobcat and replacing it with an equivalent electric.


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## oldchuck (Jul 5, 2011)

poprock1 said:


> Basically, what you are suggesting would be like removing the Kubota diesel from a 743 Bobcat and replacing it with an equivalent electric.


Yes, exactly. I run a 44 hp Kubota tractor with an HST and find the HST much more desirable than a gear box. I would really like a battery powered tractor of about the same size and functionality. Of course, you can't buy one anywhere so I would have to make one. The simplest route I can think of is find an HST tractor with a blown engine and figure out how to put an electric drive for the HST pump. Could I maybe get some opinions?


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## Beemer (Jun 2, 2011)

All the detractions mentioned of hydraulic drives is, I'm sorry, garbage.

A good example that proves otherwise is the Honda DN-01.


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## major (Apr 4, 2008)

Beemer said:


> All the detractions mentioned of hydraulic drives is, I'm sorry, garbage.
> 
> A good example that proves otherwise is the Honda DN-01.


Hi Beemer,

The Honda DN-01 did not use an electric motor. How does it prove anything relevant to the original question? 


alexis.marcil said:


> ....why I don't find any info on using an *electric motor* to power an hydraulic pump and then a hydraulic motor that is direct drive into a differential?


Regards,

major


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## Beemer (Jun 2, 2011)

major said:


> Hi Beemer,
> 
> The Honda DN-01 did not use an electric motor. How does it prove anything relevant to the original question?
> 
> ...


Everything!

I've not confused a clonking low torque half litre V twin from electric. I've proved the viability of hydraulic transmissions!

Hydraulic drives can be very compact, fully variable, easily reversible, quiet, efficient and reliable. Even supply wheel braking!

A Standard car wheel does around 750 rpm at 70 mph and motors rarely over 4k rpm - not an issue.

Further advantages can be shaft free all wheel drive; if the lines are kept short and a reasonable bore. This would create/release more space for batteries.

The advantage will be from pressure related control to keep the electric motor unloaded at start. Many motors like the Netgain have a sweet spot around 2,500 to 3,500 rpm between lowest operating temperature and efficiency.

I've already looked into this and cannot see why such a "box" cannot be designed a little less compact than a standard clutch bolted to the motor face. The downside is what is available are created as disparate parts, non unit construction and price.

http://www.surpluscenter.com/hydraulic.asp?catname=hydraulic

http://www.industrial-gear-repairs.co.uk/carter.htm

Non hydraulic
http://www.industrial-gear-repairs.co.uk/kopp.htm


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## Woodsmith (Jun 5, 2008)

oldchuck said:


> Yes, exactly. I run a 44 hp Kubota tractor with an HST and find the HST much more desirable than a gear box. I would really like a battery powered tractor of about the same size and functionality. Of course, you can't buy one anywhere so I would have to make one. The simplest route I can think of is find an HST tractor with a blown engine and figure out how to put an electric drive for the HST pump. Could I maybe get some opinions?


If you can find out the flow rate and pressure of the original pump you could look for an electro-hydraulic pump from a forklift. They have pumps to operate the lift rams and the steering and would give a self contained motor and pump set up that just needs plumbing in.

I have just taken apart such a pump to rebuild the motor to use in my Dad's electric cart project.
It is only the steering pump so a bit on the small side for your project.


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## oldchuck (Jul 5, 2011)

Thank you Woodsmith. I have read your tractor thread and found it very interesting. You are clearly an expert salvage engineer, skill I think that will be in great demand going forward. I am not nearly as talented or skilled.

I don't believe I could possibly get what I want starting from scratch. My plan, my hope, is to find a tractor with a blown engine but otherwise intact. It would already be set up with intact hydraulic systems for transmission (HST) and supplementary loops for things like loader, backhoe, three point hitch, and other things that I am now using all the time. Tractor hydraulics get pretty complicated. I'm thinking I would be able to simply fit an electric motor shaft to the pump and throw a bunch of batteries where the engine used to be. Simple, yeah. I'm sure it will present plenty of difficulties that I don't yet understand. First step is to find that magical fully functional tractor except a bad engine. Cheap.


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## Woodsmith (Jun 5, 2008)

Yes, that is the simplest method to get the tractor working and everything functional.

If the pump is easily parted from the engine, ie belt drive or a simple two part coupling, then you can swap a motor straight in. The altenative of swaping for a motor and pump unit would require a bit more work in coupling hydraulic hoses and the associated risks of contamination, leaks and damage.

First job is to find your tractor and see what it has on it. It may even be worth buying a running tractor, so you can see that it all does work properly first, and then selling the working engine.

One thing you may save on is the controller. The motor may be able to work quite happily just on or off. The money saved can go towards a huge contactor instead!


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## Beemer (Jun 2, 2011)

Woodsmith said:


> Yes, that is the simplest method to get the tractor working and everything functional.
> 
> If the pump is easily parted from the engine, ie belt drive or a simple two part coupling, then you can swap a motor straight in. The altenative of swaping for a motor and pump unit would require a bit more work in coupling hydraulic hoses and the associated risks of contamination, leaks and damage.
> 
> First job is to find your tractor and see what it has on it. It may even be worth buying a running tractor, so you can see that it all does work properly first, and then selling the working engine.


I agree.
Also the 2nd hand/scrap route should be the cheapest. However, if you want new, look here.
http://www.surpluscenter.com/hydraulic.asp?catname=hydraulic.

Electric motors have similar revs and torque to that of a diesel. It's good to note the available torque. A lot of "gas" drives are often found to be lacking. 


Not knowing your equipment. Do you need anything but direct drive for a tractor?


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## oldchuck (Jul 5, 2011)

Variable engine rpms does make a difference with an HST, both with speed and torque. I think I would need to have an electric motor that does the same thing. Engine rpms don't make so much difference with the other hydraulic functions. 

The one item that is not hydraulic but some kind of gearing off the engine is the PTO, the power take off which is essential for a lot of rear mounted attachments. It seems to gear down about 4-1.

Nothing will happen on this project until at least winter. Hopefully by then we'll have the tractor barn, greenhouse, big solar PV array project finished. Then we'll have a place to work and the power to run EVs.


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## pengyou (Nov 21, 2012)

Sorry to revive an old thread...but has anyone seen this: 

http://ecomodder.com/forum/showthread.php/170-mpg-hydraulic-drive-car-12648.html

http://www.scientificamerican.com/article.cfm?id=hydraulic-hybrid-vehicle


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## Beemer (Jun 2, 2011)

pengyou said:


> Sorry to revive an old thread...but has anyone seen this:
> 
> http://ecomodder.com/forum/showthread.php/170-mpg-hydraulic-drive-car-12648.html
> 
> http://www.scientificamerican.com/article.cfm?id=hydraulic-hybrid-vehicle


Oh no need to apologise for opening an old thread. The offence is taken when people talk of 170mpg but the ruddy thing simply does not exist!
The (especially) electric car industry is simply full of these projects. Most hope for some non-returnable Gov't backed funds to "look into the viability of". Steer clear.

Straight off. It makes no sense for hydraulic transmission on long pipelines where a shaft is far more efficient.


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