Anyone tried converting the hydraulic latch to something using non-leaky electricity?

To begin with, who's idea was it to fit a hydraulic sieve to the header bar of my convertible anyway. Do you know how long it took me to strip the centre console out, dismantle the radio, the heater controls and the switches in between, then clean all the gooey hydraulic oil out of them and then refit it all. AND that's before I've even got anywhere near replacing the faulty "centre console and dash panel oil delivery system", sorry, I mean roof latch parts.

I've been thinking, and doing some research. The BMW's use a motor and lead screw, with limit switches, instead of the hydraulic cylinder in the roof latch. With the advent of DIY 3D printers, every good techie hobby shop is selling lead screws and motors. (type lead screw into ebay for examples).

The theory goes, that a lead screw, motor and nut, (with limit switches), could replace the latch cylinder. I'm thinking the solenoids on the hydraulic pump will have the required signals for triggering the close and open. The pipes to the header rail can then be sealed off at the pump (or looped together?) to take them out of use. (then the old leaky pipes can be pulled out, be chopped into small pieces, crushed under foot, then be taken out to the garden and ceremoniously set fire to)

FYI... Here's the BMW version.



BMW Roof Latch lead screw



And this is the sort of lead screws and nuts you can get from ebay...


Lead screws and nuts

It doesn't look like rocket science to use a lathe to machine up some end mounts, and an adapter for the lead screw nut. Then add some simple electrics and a DC geared motor with some limit switches. If you wanted to go really tech, you could have an Arduino (tiny DIY computer) control a stepper motor for even better automated control.

Is this an idea, or the ravings of a lunatic that's losing the plot??

 

That is exactly what I have been thinking about doing to my latch for all the reasons you have listed. Plus an electric motor and screw makes more sense. I was thinking of a lower mounted motor and running the spinning cable through one of the existing hydraulic lines terminating at a worm gear and screw combo at the latch. Makes me wish I had never gotten rid of my 'Capsela' motor and gear toy.

 

If you decide to go for it, please keep us posted here. An affordable electric motor solution that takes the green shower out of the equation would be the most appropriate improvement to these cars that has been attempted to date....

 

Good idea, but I just use the wrench.

 

I think the main challenge is to get enough torque in such a device to fit in the small space available in the header. The hydraulic actuator is quite small.

The 2007 and later redesigned XK uses an electric linear actuator, which is basically a manufactured and packaged version of the motor and screw, but there is more space reserved for it.

 

Hmm... so other people have been thinking of it too.

I must admit, I misread Magnum454's message and quite liked the idea of a roof wench.

WhiteXKR, I think you've hit the main issue, and I'm going to have to set up some trials to see what forces are involved. The BMW unit uses a remote motor, a bit like 03 XKR suggested in order to get the power and space.

These lead screws come in many different pitches, common options seem to be anywhere from 1mm up to 8mm per turn. There's a real trade-off to be figured out between the amount of force available and the number of turns (and therefore the time) it takes for the latch to work.

Since mine leaked even before I got the car, I don't know how long the latch takes from the moment the roof hits it, can anyone enlighten me??

Once I've got the force needed, and the time needed, I can work out the pitch of the screw and the motor power needed. Then I'm handing it over to my 'senior engineer', Jack, who's 86, got time on his hands, and is an ex aircraft engineer that is very handy with a lathe and mill that are sitting unused in his garage. Useful... :-)

Watch this space for the first two prototype failures!!

 

Keep us posted!

If you are successful and do not want to sell kits yourself, I might be interested in licensing the design to make it available to my customers.

 

Very cool project.

One potential complication, or at least a constraint to be aware of: there are timeouts in the system. Closing the latch at completion of raising the top is the operation most likely to cause trouble, as it requires the most force. After X seconds of trying, if the relevant position sensor does not indicate "top closed" the system will stop. I never measured the value of X but some rough numbers for starters ...

- Time to open the latch or to close it, other than at completion of raising the top: about 1 to 2 seconds.
- Time to close the latch at completion of raising the top: lots of variables, and variation car to car, but up to maybe 4 or 5 seconds in my experience.
- Timeout when trying to close the latch. I have only a vague memory on this. Just a SWAG ... 10 seconds or so.

Good luck with this project!


Edit: the above needs some clarifying. By "system stops" I meant the system stops running the hydraulic pump. But also ... even if the latch were then closed by some external agent (manual, electric motor ...) the "raise top" cycle would not resume ... the rear windows would not raise. Again, this is from memory; haven't poked at this in a while, but pretty sure.

 

Howdy folks:
A few years back, I posted the question of possibly replacing the latch lines with steel brake lines. If I remember correctly, Gus replied that the latch ram unit had to pivot. This pivoting may be a concern in an electric conversion.

 

Thanks guys, some much needed information there. I'm going to see if I can find/buy/beg/borrow a spare header rail from somewhere for experimenting with. I can't really leave my car in the driveway with no header rail or latch in it.

There's nothing too frightening that I can see yet. But hey, the control system might just object in some way I haven't though yet. What makes me a little more confident is that the manual process works perfectly well.

 

Good luck!!! You likely could sell some of these if you get this working. Tops have been a constant problem with this car.

 

My top is working perfect, new lines and everything! But... I would more interested in a manual override for the latching mechanism. It's the week point in all these cars.

If a beautiful well crafted lever could be put in instead of using the hex key, I would totally rock it! It would be worth it just for the piece of mind..

 

A manual method has been worked out. See "manual latch" link below.

 

I think I posted virtually the identical sentiment maybe 7 years ago after I purchased my vehicle.

Doug