Hydraulic design

[RPW]

Ok, a simple design question. If you were to design a hydraulic motor system to drive a simple cart such as a UTV which type of pump would you choose? Fixed displacement or variable? And why? What I'm looking at is a simple method of driving a UTV. Currently I'm looking at a using 18HP vertical shaft motor driving a 10gpm pump through a valve assemby to control direction of the hydraulic motor which will drive a belt to the drive shaft. This is a design that maximize the use of parts on hand. Speed will be controlled by the speed of the engine. What I'm not sure of is when brake is applied will pressure build up in the system to the point of stopping the engine?

Thanks.

 

[J_J]

The best you can do with a 18 HP engine is 9 GPM @3000 psi

That is what you have to work with.

These variable speed pumps, pump about 6 GPM, @3000 psi and then you need a hyd motor for the wheels.

http://www.surpluscenter.com/item.asp?item=9-7686&catname=hydraulic

 

[Zebrafive]

As far as pressure build up you need a relief valve. Your pump may have one built in or your control valve, if not you need to add one.

 

[oldnslo]

Fixed displacement pump requires some form of valving to allow starting and stopping smoothly. It will also some what limit your drive spped and torue available to the drive wheels. reason being you are pumping a fixed flow that consumes a given amount of power.

Variable pumps I.e. an HST provides infinite speed adjustments so you can adjust speed to match engine power. These are more expensive to purchase but will provide a more versatile drive system

Other option is variable speed belt drive like on snowmobiles.

 

[RPW]

That's what I thought I'd need (relief valve). As far as gpm I for use a value of 10th nut less wouldn't hurt me as this UTV is for a ranch vehicle just to do carry tools and maybe something for the grandkids to use.

 

[ch47dpilot]

Little expensive but this maybe the easiest option Surplus Center - ZTR LEFT/RIGHT TRANSAXLE ASSEMBLY

 

[RPW]

I looked into those (ZTR drives) and if I was building from scratch i would have looked more closely but what I'm working with is an old ezgo workhorse utv. the existing motor and all hardware under the seat had been removed so all I have is the rear axle with variable pulley. I looked into replacing with what's suppose to go there, looked at making it totally electric or the hydraulic method. From a $$$$ perspective the hydraulic was the least costly mainly because I already have a 18HP engine and a hydraulic motor so all I need is hoses which I have some but not all and an electric valve (F/R) and pump. Fabrication isn't a problem. The hydraulic route also allows me to make a hydraulically actuated dump bed at a later date. Based on some excellent comments I need to verify the bypass valve in the the F/R solinoid.

 

[Leejohn]

Why don't you just get a 90 deg gear box from a old mower deck and hook up the old drive sheave. You do have to know the offset for the drive and driven, then the belt should not be to hard to fit one. When running wide open the belt should be all the way up on the drive and all the way down in the driven. That should give you the length you need.

 

[oldnslo]

I looked into those (ZTR drives) and if I was building from scratch i would have looked more closely but what I'm working with is an old ezgo workhorse utv. the existing motor and all hardware under the seat had been removed so all I have is the rear axle with variable pulley. I looked into replacing with what's suppose to go there, looked at making it totally electric or the hydraulic method. From a $$$$ perspective the hydraulic was the least costly mainly because I already have a 18HP engine and a hydraulic motor so all I need is hoses which I have some but not all and an electric valve (F/R) and pump. Fabrication isn't a problem. The hydraulic route also allows me to make a hydraulically actuated dump bed at a later date. Based on some excellent comments I need to verify the bypass valve in the the F/R solinoid.

What size is your motor? This will dictate to certain extent what size pump you can use.

 

[J_J]

He wants to use an 18 HP engine he already has, but that is not really enough HP in my opinion.

His 18 HP at 3600 rpm can only power a pump, .7 cu in, pumping about 9 GPM at 3000 psi.

Could do something like this or better.