Hydrostatic drive discussion

[Zico]

I came across this interesting video of a hydrostatic 2wd yamaha R1, a hydraulic system developed by Ohlins http://www.youtube.com/watch?v=5TrvXwoGKKU It looks very simple, light and efficient.

I know its quite popular among enthusiasts in the US for DIY motorcycle conversions for just rear wheel drive and they use it in various types of farm machinery, and military offroad machines, It got me wondering about any possible use for it in road cars, what the pros and cons would be verses a conventional 4wd system.

What format would it work best in? Im thinking Rear engine/Rear wheel drive with hydrostatic linked fronts. The drive to each wheel could be controlled by a valve linked to the steering. Im not sure how the weight would compare, unsprung weight, the cost, reliability etc etc..

Thoughts?

[phoenix]

The first thing that springs to mind are the power losses; converting the output power of the engine into an hydraulic pressure and then back again into a mechanical drive will, I am sure, involve losses; or to put it another way, it can't be 100% efficent.

So, a neat solution in some circumstances, but probably not where competition where classes are based on engine capacity.

[GORDON STREETER]

Lots of farm machinery have run this system for years and one main problem apart from the power loss would be the heat generated. The type of things like hydrostatic drive hedge mowers and Sambrons have massive tanks to try and keep the temperature down and even then the oil can boil.

[R59]

Providing you can manage traction, hydrostatic drive can produce some dramatic accelleration (and decelleration too!).

You have the engine running at peak power, and the hydrostatic motors drive each wheel. You then apply maximum thrust!! Believe me, it's very quick indeed!

I remember trying a International Hydro 84 a lot of years ago, throttle fully open, drive from "halt" to "full" in one swift movement, 0-20mph in *cough*.
It'd also do 20-0 in *ouch*

As for motorsport use - not much really. That tractor was only 80hp, but had a transmission oil capacity near on 35gallons.

Our combine harvesters are all hydrostatic drive, and they carry a good 45gallons of fluid, with large coolers to cope.

The best method of transferring power is a mechanical gearbox, with big fat straight teeth, and no transfer of axis. IE: transverse engines, however the packaging & weight distribution issues offset that benefit dramatically, hence a 90degree turn of axis works best for balance.