[ausev] Clutch-less Porsche 914

[Rob]

Gary - you're taking my response more seriously than I intended :P

Yes.  My cut off in independent of the controller, so it does provide the
safety needed.  That is specifically part of EVA's design pattern to address
your exact concern.

-----Original Message-----
From: gary [mailto:gkrysztopik at satx.rr.com] 
Sent: Thursday, December 04, 2008 3:03 PM
To: rob at zehicle.com; AustinEV News Announcements and General Discussion
Subject: Re: [ausev] Clutch-less Porsche 914



> I have this stick between the seats in my car and if I move it into a 
> middle position, it disengages the transmission.  It NEUTRALizes the 
> power train.
>   
- that works well in some situations, but I doubt you'd be able to shift 
it out of gear under inadvertent full power.  I'm not saying that 
everyone should always leave the clutch in otherwise it won't be a safe 
conversion.  I just wanted to point out that it's not a bad thing to 
leave the clutch in and that it actually provides - another level - of 
safety.  Yes it weighs more, the adapter has to be more precise and it's 
another item that will wear out.  As in most decisions, there are both 
pro's and cons and it's beneficial to consider as many of both as 
possible before making a decision.
> I also use a high-pedal relay so that my controller is unpowered when 
> my foot is off the accelerator.
>   
- by unpowered do you mean that it opens the main contactor or does it 
tell a possibly toasted controller to turn off?  If it's independent of 
a possible failure mode then it's redundant and it's good.  If it goes 
to the controller then it might just make sure that the controller will 
not turn on if the pedal is depressed (not sure how yours works) and 
this is also a good safety feature.  There are different failures that 
can happen in different modes of operation.  A good design practice is a 
Failure Modes and Effects analysis where each failure mode and it's 
effect is considered.  If it's likely to fail, and it creates an unsafe 
condition then it should be at the top of the list.  If it's not likely 
to fail and the resulting effect is minor, then it's at the bottom of 
the list.  There's also the case where it's not likely to fail, but if 
it did it would be really bad.  Some form of redundant safety feature 
(it's extremely unlikely that two different things will fail at the same 
time) should be used for the big items.  Some examples would be the main 
contactor failing either open or closed, in either a driving mode or 
while it's parked.  If it gets stuck closed when you're driving, the 
controller still controls and it's no big deal.  When you go to shut it 
off, it would be nice if there was an indication that it didn't shut off 
so you can fix it.  If it gets stuck closed and then you go to work on 
the car then it could be a big deal if you don't check the voltage 
first.  So maybe you want to put an LED or DVM on the input to the 
controller, or maybe you want to put a "danger - high voltage" sticker 
there as a reminder to check it with a meter before touching it.  If the 
contactor fails open when driving - no big deal unless you are pullling 
out in front of another car.  If these were low-reliability items you 
might want to put two in parallel (just an example - I think they are 
fairly high-reliability and not likely to drop out while energized).  If 
it fails open when you're working on it - no big deal.  Same exercise 
with the controller and all other parts.  It's worth going through this 
thought process to see if there are ways to make it safer and more reliable.
> Sorry Gary, but I just don't buy the safety argument for the clutch in 
> this case.
>
>   
- that's ok, I'm not trying to sell it.  Either method in an EV is 
better than any in an ICE   ;<}

gary