Hydrostatic Drive!!!!!

[jhellwig]

I did some minor searching and cam up with nothing.

What is the rpm's that the drive shaft would turn around highway speeds? I don't need anything exact just a range would be good.


I am pondering a hydrostatic drive system for a truck. It seams in my mind that it would be possible. Probaly not the most cost effective thing in the world but the upsides to it would make it awsome. Eliminate the tranny, tcase, and drive shafts.

I know there are hydralic motors out there that would be able to transmit all the power you would need at the axel but I am not sure weather or not they would run at the appropriate speed.


I duno, just some thoughts and ponderings. Probaly wouldn't be feasable.

What is everyone elses thought on the idea?

 

[BigOrange90Jimmy]

welcome to the world of the infinite gear ratio

i've thought of doing something similar.

was talking to an old timer who works on farm equipment about it and he said that anything is possible.

the only downside to it was the size of the hydro motor needed to turn the input.....plus the amount of hose needed, hydro tank, HUGE AS HELL cooler, and the $$$$pump$$$$

we decided the best thing to do is to have the hydro motor turn the input of the transfer case. that way you have an exact 50/50 torque split and it's further upstream so a smaller motor and pump could be used.

 

[diesel4me]

rpms....

The driveshaft turns the same RPM as the motor when the tranny is in the highest gear(unless its an overdrive tranny)..dont know how a hydrostatic setup would work in a truck like a full size GM,but thats what bucket loaders and bobcats and other industrial machines use,so I guess it will work--probably waste a lot of fuel though...you'll need a good sized pump I'd assume..

I'd like to make a hydrostatic tranny for a go cart or mini bike by using a hydraulic pump and a motor--I think it would work good,and it would be possible to have forward and reverse!..and no chains or clutches to screw up too,and no tranny or gears needed either....I did see a mini bike that had 2 gm power steering pumps on it---one used as a pump,the other coupled to it to work as a hydraulic motor!--it did work,but it wasn't powerful enough to climb a hill... ..a guy was riding it around at a swap meet I went to a few years ago..

I've seen old "Pennsylvania" lawn tractors that had a narrowed 50's plymouth
rear axle in them,with a big sprocket where the U-joint normally would go,coupled by chain to a hydralic motor to drive it,the engine only drove a hydraulic pump,all the attachments like the mower deck were hydro!--my friend had one,he used to pull cars and trucks in and out of his garage with it when swapping motors or scrapping them--it was very powerful--I thought it worked a lot better than the junk hydrostatic transaxles they put in riding mowers nowadays..never understood why more aren't made that way..TOO rugged maybe.??

 

[jhellwig]

Well, size isn't that big of a problem. I some motor that will put out more than enough torque (biggest was just short of 2000 ftlbs.) that were only about 6x6x6 inches.

At just under 700 ft.lbs. the motor needs 20 gpm and only run at 220 rpm. That is a ton of power ina small package. That is also a fixed displacement pump.

The 20 gpm would be the hard part. That is alot, but that goes without saying. It would just take a massive resivor for it and a huge cooler. That would be alot of dead weight but if you plaud around with bigger coolers and smaller resivors you might be able to make something that is acceptible.


Going with one motor in the center would be good but it kinda defeats the purpose. If you went that route all you would gain is unlimited gearing wich isn't that big of an advatage over and auto trans for the cost.

 

[jhellwig]

The driveshaft turns the same RPM as the motor when the tranny is in the highest gear(unless its an overdrive tranny).

Doh! I should have known that. Now that you mention it.


A simple 1:10 ratio gearing off the motor would work necely to get it into an acceptable range of speed. Plus those motors had a realy low stall rpm (1rpm is what their stall torque was rated at). If a person was to go with a variable dissplacement motor you could greatly lower you gpm for highway use while still being able to get the high torque for trail.


Also with it turning such low rpms you could use a much higher axel ratios thus obtaining a stronger pinion.

 

[ntsqd]

Bigest problem with hydrostatic drive has been touched on, the need for a BIG cooler. To go slow isn't too difficult. It's when you want to go hiway speeds that things get ugly.

I think a hydro drive light weight buggy would be really cool! I doubt I'll ever build one though. It would have a looonnggggg project list in front of it.

 

[jhellwig]

Speed wouldn't be an issue. If you had a motor that only operated at 200 rpm all you need is a 1:10 gearing and you got that ability to run at highway speeds and with the low stall of 1 rpm you could still crawl it. Also with a variable dissplacement pump, when you are going at high speeds your flow would be low because you don't need as high of torque. Thus you will be making more heat at your lower speeds. A cooler roughly the size of a normal radiator and the same thinkness would be more than enough to cool the system. Combines have coolers about that size and you would be looking at less fluid flow than what they require.