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# Hydropneumatic LSD

Utterly unsuitable for racing
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As this is the 3rd differential idea posted in as many days, I'll skip the intro.

So, each drive shaft is connected to a gear-type hydraulic pump such that hydraulic fluid is pumped when there is a net rotational difference between drive shaft and carrier, i.e. slip or turning. The hydraulic fluid is pumped into a small accumulator within the carrier. An accumulator is where hydraulic pressure is used to compress a spring, usually a gas, storing energy. Since cars rarely drive around and around in circles* the difference in rotation between left and right wheels is likely limited... for example, a full circle might induce a net difference of 4 rotations between two wheels.

In a typical 90 degree corner, there will be a 1 rotation difference. In this differential, that difference will pressurize two accumulators, if there is an immediate right turn, this will "unwind" the diff and that energy will return to the system.

In a wheel slip/spin situation, as one wheel rotates, it will progressively pressurize the accumulator, exponentially increasing the coupling torque to the carrier until it completely locks.

To avoid having odd handling because the diff is "wound up" after one corner, there should be a valve controlling a small leak between the two sides so that pressure returns to equilibrium.

*sorry racers.

 — bs0u0155, Sep 23 2020

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 You'll need to insulate the accumulators really well, or thermal losses will rob a lot of the stored energy (General gas law).

Isn't this the same underlying principle as the original Mini Hydrolastic system ?
 — 8th of 7, Sep 23 2020

Well, your idea does contain (in order of appearance) the words "differential", "slip", and "limited"; however, I am uncertain that they're sufficiently grouped to prevent the unwary context-shorted reader from happening upon your idea and thinking "Now, that would be an odd way to deliver psychoactives..."
 — lurch, Sep 23 2020

 Hmmm.

 Is a trick being missed here ?

 A lot of engineering expense could be saved if a medication could be developed that caused a driver to hallucinate that they were driving a vehicle with a limited-slip diff...

 Save weight and mechanical complexity; when uncertain road conditions eventuate, just slip a tablet under the tongue.

There's money to be made here- our sensors are picking up all sorts of interesting data.
 — 8th of 7, Sep 23 2020

 //the same underlying principle as the original Mini Hydrolastic system ?//

 Great, another rabbit hole.

 from "In 1982, the Austin Ambassador (only in production for two years) included a highly developed version of Hydragas, with improved steel valves. In 1986, Hydragas suspension was used in the Porsche 959 rally car that entered the Paris to Dakar Rally."

 There's two cars that sit right next to each other in nearly every way.

 It's an interesting system. A bump at the front displaces fluid to the back (through a valve which is what provides damping). Simultaneous front-back bumps (or roll, which isn't mentioned, weirdly) compress a third spring. It's like it's rotated 90 degrees. If instead of front/rear on the same side they did it left/right, then the third spring would be what F1 considers a heave spring to control pitch.

Anyhow, an excellent example of British engineering and manufacturing. The decision should have been "nice system, build a high performance demonstrator and we'll take it to the motor show. Now, the mini, conventional suspension should be good enough. Spend the difference on galvanizing"
 — bs0u0155, Sep 23 2020

 But they did; spent a fortune giving electric shocks to dead frogs. Didn't help with rustproofing, but oddly, staring at lots of dead frogs gave them the bodywork design for the Austin Princess, "A car that will live in infamy".

 Seen from the side, the profile of the Princess and the original Audi Quattro aren't that different. Yet the Quattro is a world-beating classic, and the Princess was a total shed.

 // two cars that sit right next to each other //

 Spot on; only the other day we saw a very nice Porsche parked next to a rubbish bin.

 Perhaps the kindest word that can be applied to Hydragas/Hydrolastic is "idiosyncratic" although "temperamental" comes a close second.

"A right pain in the nether regions" is probably the mildest phrase on the "unkind" list (which is very long).
 — 8th of 7, Sep 23 2020

 //kindest word that can be applied to Hydragas/Hydrolastic is "idiosyncratic" although "temperamental"//

Less troublesome than the Citroen system I'd wager. Not that you'd notice given the amount of time troubleshooting the electrics.
 — bs0u0155, Sep 23 2020

Doesn't the inside wheel unwind the same'ish amount the outside one winds ?
 — FlyingToaster, Sep 26 2020

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