Why does one need a compushift?

[GBMUD]

OK, so the conventional wisdom is that one needs a Compushift to make a D2 auto box work in a Defender, but why? It clearly works without one in a Discovery, I assume with it's own ECU or is it controlled by something else? (the BECM?) If the gearbox controller is looking for some inputs not present in a Defender, what is it looking for and can one not just feed it some suitable inputs - throttle position, speed, driver's hair colour etc.?

Thanks for any ideas

Chris

[sean f]

Not sure about the Disco 2 but I assume it is a similar system (in theory) to the P38.

In that case it has its own auto box controller but this is linked with the BECM for inputs such as road speed, brakes and the engine management system etc, I don't know if it is possible to replicate these input directly with out a lot of knowledge. I assume if it was that simple then the likes of Ashcroft wouldn't sell a relatively expensive Compushift to do it for you.

[simonr]

I can't imagine it would be that complicated. I've looked at similar for a Suzuki box - which has sensors for input speed, output speed and road speed plus 5 solenoid valves to control the gear & TC lockup. Replacing it with a uControlller would be easy. I cant imagine a LR box is much more complex?

Si

[sean f]

I can't imagine it would be that complicated. I've looked at similar for a Suzuki box - which has sensors for input speed, output speed and road speed plus 5 solenoid valves to control the gear & TC lockup. Replacing it with a uControlller would be easy. I cant imagine a LR box is much more complex?

Si

Not that complicated for you but beyond the ability of normal people!.

X-shift coming up?, if you could make something which would work of the shelf for cheaper than a Compushift there is likely to be a market. I have a fully working P38 (HP24) box sat on the drive if you want something to play with.

[Bowie69]

Megashift has already been done on a P38 box

Well, the same box as a P38, albeit in a BMW of some flavour.

[simonr]

I've been thinking about it while driving home!

The Suzuki Vitara box it the only one I have experience of. As I said it has an input for the engine speed, the speed of the input to the box and the output / road speed. Because of the slippage in the torque converter, the frequency difference between the engine rpm and the box input is proportional to torque. The ECU would also know the throttle position (for kick-down).

The Suzuki box has one solenoid valve for park, reverse and TC lockup then two valves for the three gears - one or the other or both to select (I presume).

Jthe disco box would take a little reverse engineering, but I dare say someone will know the wiring and which combos of valves do what. Then it would not be much more than a map of torque against speed against gear / solenoid combo. Then settings for the speed that the TC locks up, a separate map for low range (perhaps to ramp up the engine braking by locking the TC when you take your foot off the throttle while you are still moving.

Inputs for 'manual' override and sequential shift would be easy.

It's all within the capability of a simple micro controller - though for reliability I might be tempted to use three in a majority vote configuration. This way it will carry on working if one of the three processors gets confused / crashes, it just does what the majority of processors thinks ought to be happening. Add a watchdog timer / reboot and it should be fairly bomb proof.

I'd really like to have a go. Not so much to compete with compushift but more about hacking a bit of hardware to do something cool!

Si

[LandyManLuke]

For what it's worth, I've been looking in to doing exactly this, but for the Toyota box often fitted to the 1UZFE V8 fitted to Lexus LS400s. There are 2 solenoids to select gears, using binary combinations, as well as a solenoid to lock the TC up, and another solenoid to modulate the hydraulic pressure, so that the pressure can be dropped whilst shifting to make sure shifts are smoother, reducing shock loads in the transmission.

It's a definite contender for a uC project

[Dave W]

Or just use a MegaShift because the hardware, firmware and the software to configure and tune your gear changes are already available for free or very cheaply (in the case of the hardware). Like any open source project, the more people that use it and adapt it to their gearbox the easier it is for others to follow.

[simonr]

Or just use a MegaShift

Thanks Dave - saves me a project!

Si

[RangeyRover]

I agree that megashift should be the controller, but there is a ton of work to work out what the shift solenoids should be doing.

What compushift are selling is that knowledge, as well as the hardware.

As always, if someone is prepared to share or acquire the knowledge by monitoring an existing box for voltages and PWM rates then the job becomes much easier.

The Howto is here New transmission with megashift

The control isnt very difficult, monitoring to find the details needs a working vehicle and patience.