EV Conversion - Part 5


03/07/10 - Well, at last I got around to re-installing the clutch on my Daihatsu HiJet micro-van conversion.

I've done around 6k miles in the 12 months since I converted it by removing the 1300cc petrol ICE and replacing it with a Netgain Impulse 9" DC series motor, 120V of Thundersky LiFePO4 LFP160's (38 cells) and a Belktronix 500A integrated drive system (recently upgraded to 800A).  The drive from motor to gearbox was via a home-made coupler consisting of a taper-lock hub mounted to the remains of a clutch plate, retaining the spring shock absorbers.  Now, maybe my van has a dog of a synchro gearbox and maybe all those other potential manual EV donors out there don't need their clutch, but I suspect my van is about average in this respect and so I would heartily recommend any would-be converter keeps their clutch if they can.

Initially, I thought I could live without the clutch and I guess if I were only using it around town when I could leave it in 2nd gear all the time (max speed, around 45MPH) I probably could.  But, living, as I do, out in the wilds of the Hertfordshire countryside and having a 20 mile commute, it became painfully clear quite quickly that basically... I missed my clutch too much - or at least I convinced myself that I did and wanted to find out one way or the other.  Why...?

Well for 4 reasons, as follows:-

1/  It can be used to disconnect the motor very easily and effectively in a runaway motor situation.

2/  It allows MUCH faster acceleration as you do not have to wait (3 seconds or so in my van) for the motor to slow down to match its speed to the gear you want to change up to.

3/  It makes changing down easier as you do not have to try to raise the motor speed up to match the gear you are changing down to, particularly difficult when negotiating a bend or junction where you have to steer, brake and change gear in a short space of time - and when you can't hear the motor, it doesn't help!

What follows is how we used a piece of 6mm mild steel plate turned down on a lathe into a light-weight ‘flywheel’ for my existing EV.  The fly wheel is more accurately a clutch driving plate, as there is no function for the traditional ICE flywheel in an EV.  This is because the ICE flywheel is designed to have significant weight - 10kg or so in van’s case - which has considerable momentum when rotating.  This is needed to allow the pistons in an ICE time between power strokes to do all the other things they need to do without the engine stopping. 

An EV has no jerky pistons and hence does not need a flywheel.  In fact the clutch for an EV needs to be light as possible - just enough to be strong enough not to fail under the high centripetal forces created when rotating at speed (up to 5000rpm) - the pressure plate helps here, of course.  Otherwise the motor loses efficiency by wasting energy accelerating the weight of the clutch up as the vehicle accelerates.  Equally it makes changing gear slower as the inertia of the clutch causes it to slow down more slowly.  The alternative to making a new driving plate is to turn down the existing one.  This may be quicker but some standard ICE flywheels are made of cast iron and therefore are a lot more brittle than mild steel. Consequently, removing metal from these can have disastrous consequences when spun up.

So having taken out the old direct drive coupling yesterday, replaced it with the home made clutch - all of which went fantastically smoothly, thanks to my extremely talented and helpful friend Ade, the ex-toolmaker.  I drove it to work and back yesterday evening, 40 miles of mixed driving, and it is marvelous!

So anyone out there reading this who wants to know if they should keep their clutch or go clutch-less, the answer is KEEP IT!

This photo shows the assembled clutch ready for attaching to the gear box.

So, what’s involved?  Firstly, the most important factor (after strength) is concentricity ie keeping the axes of all the parts in the same place and parallel.  If you don’t mount, for example the pressure plate concentrically with the driven plate (clutch disc), then the clutch will vibrate which, if mild, is just annoying but if bad can lead to premature motor bearing wear and other nasty things. 

We mounted the pressure plate on the original flywheel but separated them with a few mm of washers and then turned down the outer edge of the original, balanced pressure plate so it had a very sharp corner on it.  You can see this on the picture above (without the washers).

Then we mounted the plate on the taper-lock hub with a spacer to bring the face of the driven plate slightly proud of hub face to allow for a little clearance of the driven plate. Next we cut a  25mm wide groove in the face of the ‘flywheel’ about 0.5mm deep, leaving a 1mm lip right on the outer edge (it is just visible on the photo, below - right). 

The pressure plate sits in the groove centering it nicely.  There is very little vibration in the finished article - with no additional balancing performed - due, I am sure, to this detail.

Next Page...


23Mar11 - How it can all go horribly wrong.  The deice on the left is a Watt-Hour meter (a recent addition)  and on the right, a timer (been in use like this for 18 months).  I used these to control the charger in the van and clearly the Wh meter (despite being rated for 15A) has not taken well to having even 10A though it for 4 hours or so.  Or it could have just been down to dirty contacts...  Fortunately the plastic was good quality, fire suppressing type and not cheapo stuff that could have torched the van.