[ausev] extraneous parts

[jefoy at mindspring.com]

Without knowing how big an issue it really is, one potential downside to keeping the flywheel is the motor staying at relatively high RPM while shifting. Picture the Nissan commercial about "shift shock". With an ICE, there is natural braking due to compression and a good driver will develop a feel for how long the clutch needs to stay depressed so the RPM is fairly well matched before engaging the clutch in the next gear. Without the natural braking, the motor takes a long time to spin down when selecting a higher gear so there is the need to "slip" the clutch more to make the transition smooth.

As someone else suggested, you can have the flywheel machined to reduce the mass and thereby reduce the inertia. You might also find an aluminum "racing" flywheel that will fit but be prepared to spend ~$150 or more. 

One concept that might work is to look at a racing transmission like a Brinn. These are typically very light and only have two gears, low and direct drive. Applications are limited to rear wheel drive vehicles. The same would be true of the old Generic Motors powerglide automatic. It has two speeds, low and direct and there are kits to eliminate the torque converter. This has the added advantage that it is a planetary gear box and would not require a clutch for shifting. 

Come to think of it, that might be something else to look into, use an automatic transmission but eliminate the torque converter. It would require an external hydraulic pump to actuate the brake bands (or clutches) but it could be direct coupled.

Jack

-----Original Message-----
>From: Mark Farver <mfarver at mindbent.org>
>Sent: Mar 2, 2007 3:50 PM
>To: AustinEV News Announcements and General Discussion <ausev at austinev.org>
>Subject: Re: [ausev] extraneous parts
>
>TERRY KING wrote:
>> I've read that most EVs are typically kept in 2nd or 3rd gear all the 
>> time except when reversing. Has this been your experience or is it 
>> helpful to "downshift" in order to negociate a hill?
>Downshifting to climb a hill may be necessary, it depends a gear ratio, 
>speed, and the overall power of your system.  For example, the MR2, with 
>a 1000amp controller, has met only one hill in Austin it couldn't climb 
>in third (the several hundred foot climb up to Alaric's apartment off 
>HWY 360).   Actually, it climbed just fine, but it required excessive 
>currents and I downshifted to avoid overheating the motor.
>
>I usually leave second only for burnouts.  Third is good up to about 
>70mph before the motor starts to reach its RPM redline.  Torque and 
>acceleration are lousy at high RPM, but efficiency is great.  At freeway 
>speeds it is sometimes necessary to upshift to 4th to get enough 
>acceleration to pass (this is backwards from an ICE)
>
>On a lower power or heavier car, like the Henney or Roy's Geo with its 
>400amp controller, you find yourself shifting the car pretty much 
>exactly like you would in an ICE.  The exception: in an ICE for maximum 
>efficiency you try to upshift quickly, in an EV you want to linger in 
>the lower gear until acceleration falls off or you reach redline, then 
>upshift.
>
>> Are undo forces also placed on the electric motor's shaft because the 
>> forces applied in using the clutch in an EV are now applied to the 
>> armature. Has premature wear ever happened to armature bearings due 
>> to  these thrust loads?
>Technically, yes.  The armature bearings are not rated for thrust 
>loads.  However, an EV spends so little time with the clutch depressed, 
>its not an issue.  In fact, I know only one EV user that has required a 
>bearing replacement on his motor, and that was because of poor alignment 
>of the adapter.  (The Advanced DC motors that are the most common for 
>use in an EV use very standard and inexpensive bearings which are fairly 
>easy to replace.)
>
>Far more annoying is the pilot bearing/bushing on some (rear wheel 
>drive) vehicles.  The bearing is usually embedded into the end of the 
>crackshaft.  This means the adapter has to be thicker to give enough 
>space for the bearing to sit in front of the motor shaft, or the motor 
>shaft must be bored out for the bearing.  (Or you can cut it off and 
>take your chances, but on many vehicles this will cause a nasty vibration)
>
>
>> My goal is to lighten the car as much as possible.
>It is a good goal to have, but it is very hard to make a significant 
>dent in the vehicles weight without major surgery, most of it is in 
>parts that are not readily replaceable.  Your best bet is to start with 
>a lightweight vehicle.
>
>Mark Farver
>
>
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