By George S. Bower
Traction Motor Uprate
An analysis was conducted to predict what traction motor uprate would be needed to get quicker acceleration times for the ELR (or Volt Super Sport please).
A computer simulation was written in Microsoft Excel with Visual Basic to predict 0-60 mph times as a function of traction motor size.
Input to the model comes as: 1) torque speed map for the traction motor (MGB) and 2) drag characteristic
A scaler on the torque speed map was included so the map could be scaled up and the improved acceleration times observed for various motor uprates.
The motor map used is presented here.
It is a Delco Remy HVH250 (thanks tboult). This map was scaled to the Volt’s motor rating of 368 Nm and 111 Kw rating as the baseline and then with uprates of 20 percent and 40 percent. Looking at the Delco Remy link, there are some interesting data relative to 60-second peak loads and performance at voltages as high as 700V so perhaps a voltage increase is in the cards for ELR.
The results of the study are shown in figure 2
The baseline Volt acceleration time is 8.8 seconds. A 20 percent increase in torque drops the time to 7.3 seconds and a 40 percent increase in torque drops the 0-60 time to 6.2 seconds This is my estimate of where ELR will end up … not quite as quick as the Tesla Model S but still lots of fun. (The 60-kwh Model S 0-60 MPH time is 5.9 seconds as shown here.
I can say this because, as a Volt owner, the Volt is already extremely fun to drive with an 8.5 second 0-60 time so 6.2 seconds would be a blast – especially with traction control off!
Therefore, a 150-Kw traction motor is my estimate for MGB. Some of this uprate could come from the 60-second peak load and/or a voltage increase.
What does this mean about battery sizing? We are pretty sure that GM has an improved battery waiting in the wings. This new battery will have a higher kwh/lb rating and also will have a higher power (C) rating.
As shown in figure 3 the increase to 150 Kw motor should be easily attainable with the new battery. The Volt is currently running 6.9C which is not that aggressive. An increase to 9.4C should be a piece of cake.
Since we are expecting a higher kwh/lb rating for this new battery, we can expect an improvement in range, or if we hold the range to the existing 40 miles then we would see a reduction in pack weight.
In addition to the potential weight savings in the battery, we could also see some select use of composites or aluminum resulting in additional weight savings.
Note that these potential weight reductions are NOT included in the 0-60 MPH acceleration times so every pound we take out of the existing Volt weight gets us closer to the Model S bogey.
But what of the ICE? If we scale the existing ICE up by the same 1.4 scaler that we came up with for the traction motor, we would have a 70 Kw ICE. However a somewhat larger ICE could be justified due to the performance orientation of ELR.
ICE uprate is summarized in figure 4.
I see direct injection and variable valve timing for ELR but we will NOT see a turbo version as suggested in the past by our good friend Statik (Jay Cole) as shown here.
Super Sport Mode
Even with a 100-Kw ICE, we have an ICE that is smaller than the 150 Kw traction motor so in order to support the 150 Kw traction motor we need to supplement with batter power.
Proposed here is an addition of super sport mode for ELR.
In super sport mode the battery buffer is increased from the current 0.5 kwh to perhaps 1 kwh or more as shown in figure 6 and more time is spent in series mode.
While operating in super sport mode gives us some nice performance, unfortunately it is not all that efficient from a fuel consumption point of view as explained here so we want to use this super sport mode sparingly.
We select super sport mode when we want more performance but at the expense of MPG. When operating in normal mode ELR reverts to “eco minded” ways of the current Volt engaging power split whenever possible and minimizing battery charging with the ICE.
A summary of predictions for ELR is presented in figure 7
ELR will be an extremely fun vehicle to drive with acceleration times approaching Model S but requiring only minor modifications to the Voltec drive train. Plus we have retained all the efficiency of the basic Volt … Assuming we can keep our finger of the
Super Sport Mode button
Cheers Volt Heads!
This entry was posted on Thursday, October 11th, 2012 at 5:55 am and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.