[Vwdiesel] something worth trading the A4 in for

[Kurt Nolte]

"Power robbing transmission" my boot! Typical manual transmission is 95% 
efficient, and improves prime mover efficiency by allowing it to operate 
within its peak efficiency and power bands more of the time.

You could drive a normal car without a transmission, but you'd need a 
single step-down (or really tiny wheels) and some way to decouple the 
engine from the wheels while stopped. These two alone would introduce 
the same level of power loss as a gear-gear transmission/differential 
and dry clutch. Electric motors, granted, get around the decoupling 
necessity.

Oh, and your engine would need to be able to produce 100% of the hp 
necessary to begin accelerating the vehicle's mass at low RPM points, as 
opposed to being able to wind it out to its peak HP point to do your 
standing acceleration.

In other words, you'd need a V8 to move a Rabbit around.

Even  electric motors have peak efficiency bands, outside of which the 
efficiency can drop off fairly sharply in some cases. Also, though they 
tend to have very flat torque curves, torque only equals horsepower when 
multiplied by the RPM and divided by 5252 (if you're in hp and ft-lbs).

So your 1000 ft-lbs of torque out of that Tango is that and only that at 
0RPM. No horsepower, but it's putting down 1k ft-lbs. You start getting 
into fractional hp when you start rotating.

Assuming it keeps that 1k torque rating throughout it's power band, it's 
laying down 114hp @ the ~600 rpm that a typical wheel needs to turn to 
maintain 60mph. That's massively oversized for such a tiny little car, 
and running it a partial load reduces efficiency.

You could get that same 1k ft-lbs starting off torque by taking an 
engine that produces, say, 200ft-lbs throughout it's range (~23hp at 
around 600rpm, or enough hp to keep the average sedan rolling at 60mph) 
and gearing it down 5:1, which would increase your torque five fold 
while rotating the wheel 1/5 as fast as the motor.

Get out of your RPM range, you change to a 4:1, or 3 or 2:1. Even 1:1 @ 
600, if you'd like. You lose ~5% through the drivetrain, so... you'd 
have 22hp at the wheels.

Zing, that's some power-robbing right there. Whooo. In exchange you now 
operate your electric motor at its peak efficiency, you need less 
overall system voltage, you have a smaller motor/controller package, and 
you reduced weight.

Yeah, I get kinda annoyed here.

-Kurt

mikitka wrote:
> Not a VW but still say this is an awesome commuter vehicle for those only
> driving up to 40 miles one way.
>
> http://www.commutercars.com/
>
>
>
> Acceleration and top speed:
>
> With over 1,000 ft-lbs. of torque, the Tango can accelerate from zero to
> over 130 mph in one gear. Without needing an energy-robbing transmission or
> differential, it accelerates from zero to 60 mph in about 4 seconds and
> finishes the standing 1/4 mile in about 12 seconds at over 100 mph.
>
> Nick
>
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