My Vision of Gen 2.0 Volt

By George S. Bower

Let’s start by addressing the two biggest problems with the current Volt design:

1) Price is too high
2) Interior room is too low

Price

We simply go after the two most expensive parts of the current car:

1) The battery
2) the 4ET50 transmission

The battery cost problem will solve itself. Time and higher production rates will bring the cost down. Volt AER is already ideally suited to cover over 80 percent of the driving public. That is the one beauty of the current Volt design philosophy: Don’t make the battery any larger than required. Keep the cost down.

The Volt’s 4ET50 transmission is a complicated device. It contains a planetary gear set, three clutches and a final gear reduction set as shown below.

 

The advantage of the 4ET50 transmission is that it allows the Volt to operate in two modes during extended range mode: pure series and power link. The advantage of power link is that it increases mpg in extended-range mode by mechanically connecting the internal combustion engine (ICE) to the wheels. This mechanical link increases mpg in extended-range (ER) mode on the order of 7-10 percent as described in the analysis presented here http://gm-volt.com/2012/08/24/pure-series-e-rev-in-search-of-the-holy-grail/ .

The brilliance of the Voltec design is that it has a battery just big enough to cover the average daily driving distance of most drivers (40 miles). Keeping the pack as small as possible keeps the electric vehicle cost down.

We have data from the Volt fleet at Voltstats http://www.voltstats.net/ that shows that the median fleet MPG is 171 MPG and that the median %EV is 80%. Some drivers never even use the range extender.

So why have tons of money tied up in a complicated transmission?

Answer is: There is no reason.

The effect of going to pure series should be much less than 7-10% on a fleet basis. Since 80% of fleet driving is in electric mode, the 7-10% penalty on fuel consumption for going pure series would be reduced by at least half. A 3.5% penalty on fleet MPG would only reduce fleet MPG from 171 MPG to 165 MPG….a negligible amount and not worth the extra expense of the 4ET50 transmission.

The Key is the Spark EV Coaxial gearbox

The beauty of the Spark EV’s gearbox is in its simplicity.

 

GM pulled a very special trick when they designed the Spark EVs gearbox. They reduced the amount of gear reduction needed in the transmission by going to a higher torque motor. Gear reduction is only approximately 3/1 in the Spark coaxial unit versus 6/1 in the Volt. This eliminates the extra reduction downstream of the PG set shown in figure 2.

Going to the Sparks coaxial gearbox instead of the current 4ET50 transmission would significantly reduce the cost of Gen 2.0 Volt.
But what of the ICE? Simple solution is to go to an aluminum block 3-cylinder non-turbocharged unit reducing cost and weight and size of the ICE.
In order to integrate the coaxial gearbox and the 3 cylinder ICE with generator GM would need to redesign the transaxle case.

How do we fix the problem with too little interior room?

Simple … put the batteries in the floor like all the other serious EV manufacturers do, namely Tesla (Model S), Nissan (Leaf), and BMW (i3). This issue was addressed in a previous article presented here so I will not go into detail on that subject.

Conclusion

In order to lower cost and increase interior room GM should make the following changes in Gen 2.0:

1) Put the batteries in the floor.
2) Go to a pure series configuration: eliminate the 4ET50 transmission and go with the Spark EV coaxial unit married to an aluminum block 3 cylinder ICE driving a generator.

This approach opens the door to a CUV design which is always being requested by Volt fans here.

Source: GM-Volt.com