Hydraulic vehicle drive

Go to one of these web sites and look at their Hydrastatic drive systems.:

http://www.sauer-danfoss.com/Products/products_hydrostatics.html

http://hydraulics.eaton.com/products/trans_main.htm

There are others you could find by searching Google/

They also have all the sizing information you need.

I hope you have deep pockets. To get the job done right you need an experienced hydraulic person to design your circuit. They charge $100-150/hour for their time and you are probably looking at 30-50 hours.

Thanks bud!

I have already started the ckt designing myself. I am pretty decent with regular ckts I make but we typically use fixed displacement gear pumps. Now i am learning the variable systems.

You can use fixed displacement gear pumps with hydraulic control valves and by-pass circuits, which is esentially what a hydrostatic transmission is with everything built-in.

I have toyed with the idea of building an off-road vehicle with four hydraulic motors on four wheels for several years with the flow rate being controlled to each motor as a function of steering wheel position, which is not a trivial problem as each wheel moves at a different rate when direction is not straight ahead.

I too have toyed with a similar idea but to reduce the complexity of the hydraulic drive, I considered steering the rear wheels as well as the front. The forward and rear wheels on each side would be driven with a series circuit since they will travel at the same speed. In this way, you only have to differentiate two speeds instead of four. I planned on using the front ends of two front wheel drive donor cars with the steering rack and all. The costs of the hydraulic pump and motors are my main stumbling blocks. My plan would be to mount the hydraulic motors to the chassis and use the shorter axle shafts on both sides to reduce the width of the vehicle somewhat. Most front wheel drive cars have different length drive axles. Plus, I'd rather not have all that unsprung weight hanging on the wheels. Linking the forward and aft steering racks with a good solid connection does present some challenges. Build the chassis as a watertight "tub", large tires, and hmmmmm . . . an amphibious vehicle anyone? (I know, I can buy a six wheeled, skid steering version of that, but anyone can do that :o)

You wrote: "The forward and rear wheels on each side would be driven with a series circuit since they will travel at the same speed."

Almost, but not quite, for a front-end-steered vehicle. I had considered four-wheel-steered vehicle with equal angles of steering angle for each side, which will result in front to rear wheels traveling at the same speed. I even considered locking the rear wheel steering for higher-speed driving for that type vehicle, but when turning tight curves with the rear steering locked, there will be skidding on at least one tire.

When "toying" with all the ideas, I even considered a mode whereby front and rear steering can be independent of each other by adding a second steering wheel. Things got complicated when that was considered, and I haven't yet given up on working out the control system details, but I probably will save that for "Phase II."

They are the same because I described a four-wheeled steering scenario.

I would restrict my concept to slower, rock crawling speeds. No drifting the rear-end out on fire roads, flat-tracking, etc.

I didn't mean to give you the impression that I didn't agree with you -- I guess I wasn't clear with what I wrote . . .

I did notice that you said the wheel speed would be the same for a 4-wheel steered vehicle. I was merely commenting that the wheel speed on each side is close to the same for a front-end-only-steered vehicle, but not quite.

Guest wrote (in the #6 spot): "You will need an engine with at least 72 horse power to drive the pumps and transmission etc."

I don't like to get picky all the time, but power is torque times speed. Theoretically, a 1 HP engine will do the job 72 times slower.

Its done on mining equipment all the time.

All the major hydraulic equipment manufacturers have parts and components for this.

You will need an engine with at least 72 horse power to drive the pumps and transmission etc.

Save your self a lot of headaches and use a single gear pump or vane pump driven off the flywheel with a rubber coupler with 2 open center valves with a 3 section flow divider instead to feed the drive transmission and steering.

Section one of the flow divider feeds oil to the transmission for drive power to the wheel motors, section two goes to the power steering, section three goes to the accessory function which must have an open center valve controlling the accessory circuit.

The flow divider must be plumbed in an open center configuration and only this way.