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Budget4x4
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I used to do a lot of agricultural work and have on numerous occations fitted an hydrolic P.T.O to prevent snagging on very tight turns and gradients.. Just wondering if such a thing is possible on a road legal car.. My RR clasic sits 4" higher than it should and is on its 12th or so front prop due to the strops snapping and dropping axle away from chassis.. Has anyone attempted this for an off roader? The lift angle would become infinate if fitted..

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I used to do a lot of agricultural work and have on numerous occations fitted an hydrolic P.T.O to prevent snagging on very tight turns and gradients.. Just wondering if such a thing is possible on a road legal car.. My RR clasic sits 4" higher than it should and is on its 12th or so front prop due to the strops snapping and dropping axle away from chassis.. Has anyone attempted this for an off roader? The lift angle would become infinate if fitted..

By Hydraulic PTO you mean... fitting a hydraulic pump to your transfer box output and a motor to your dif and connecting them via flexy hose?

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By Hydraulic PTO you mean... fitting a hydraulic pump to your transfer box output and a motor to your dif and connecting them via flexy hose?

Man, you're going to need some flow (and pressure) to get 60 or 70 horses to a diff at speed, not to say a fairly big oil cooler!

On this thread, why bother with the diffs at all? Why not independently motor each wheel with a flow splitter and a flow restricted pressure relief between the pairs (fronts, rears and front to back) to mimic an LSD?

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Man, you're going to need some flow (and pressure) to get 60 or 70 horses to a diff at speed, not to say a fairly big oil cooler!

On this thread, why bother with the diffs at all? Why not independently motor each wheel with a flow splitter and a flow restricted pressure relief between the pairs (fronts, rears and front to back) to mimic an LSD?

Whats an LSD?

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Limited Slip Differential

Google is your friend!

You swines, I've got the maths goin' on now ...

The torque required at each wheel to shift a two tonne car up a 45 degree slope assuming only two number 1 metre diameter (39 inch) wheels on the ground (something of a worst case ...) is half a half a half of 2000 x 9.81, or about 2450Nm, which is 245DaNm. For this you'd need a 800cc/rev motor running at 210 bar . Since one rev of our wheel is pi x d, one rev is 3.14 metres. My example motor does 300 rpm flat out, which equals 942m / min or 56 kph (35 mph). In doing so, one motor uses 300 x 800 cc of oil, or 240 l/min. You would need four motors, so 960 l/min at 56kph. Assuming you can find a 210 bar pump that will run at 4000 rpm, it would need to displace 240 cc/rev at full speed (I can't), or lower if you don't mind crawling along ... I suppose you could stack two 120cc pumps or better four 60cc pumps , which would work, and then you wouldn't the flow splitters either.

(The LSD comment was that you'd have to allow the wheels to rotate a little independently to mimic a diff, so if you linked the relevant pairs with a flow restricted connection you'd get a limited slip diff effect for free. Closing the link would "lock the diff".)

Cor, I feel better now :wacko: must be the LSD wearing off ...

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A company i work for has designed and built such a system for passenger cars, but using lots of electronics to control the hydraulics:

http://www.artemisip.com/appli_auto_transm.htm

The car has no gearbox. The pump is bolted directly to the rear of the engine. I've been "round the block" in the car and the performance is pretty impressive.

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There have been plenty of hydrostatic drive builds, but there are always compromises which can defeat the object.

As the maths above shows, it's very hard to achieve enough flow to move at road speed yet enough torque to crawl at off-road speeds. When you're pumping 240l/m by the general rule of thumb you'll be needing about 200L of oil in a tank and be having quite a job keeping it all cool. A motor on each wheel means a lot of hoses and valves, and those valves need to be variable to allow reasonable control. You need some way of making sure all the wheels go at the right speed at the right time, and what to do about corners.

Hydrostatic quickly becomes slow, heavy, and hot. That's not to say it doesn't have advantages, a lot of very good industrial & agri stuff uses it, but none of it is then capable of cruising up the motorway at 70mph.

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I think the electronic control gear (valves etc) is the stuff that Artemis has the patents on, and what makes the difference between what you describe, and a workable vehicle transmission. I'm not totally clued up on the hydraulics, but if you take a look on their website it shows some of the tech.

http://www.artemisip.com/technology.htm

They've had the 530i round millbrook proving ground, including at motorway speeds, and it whooped the manual box on fuel consumption across the board, even in a steady state cruise.

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The Artemis setup does look very good, I'd be interested to see if it works long-term. However, what's being described here is a more traditional hydrostatic setup as I imagine the Artemis setup would be beyond the average DIY wallet and complexity.

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