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Suggested Improvements to the Volt's Power Flow screen

1631 Views 4 Replies 3 Participants Last post by  jcramer
I bought a pre-owned 2015 Volt Base with 18,400 miles on it three weeks ago, and I like it very much. At first, I was fascinated by the Power Flow screen, and I kept it on all the time I was driving. However, my enthusiasm for the Power Flow display lasted only about two days. It provides a lovely qualitative cartoon of the energy flow of the Volt, but it lacks any quantitative information about that process. After a few days, watching the little arrows move back and forth was no longer interesting. The Power Flow display could be improved in future Volt generations (or even with Gen 1 and 2 software upgrades) by giving the viewer more information about where the energy is going and how it is being used. Consider the following:

Data values that the Volt is continuously measuring are: (1) the vehicle speed (in miles/hour, convertible to feet/second), and (2) the power flowing between the battery and the propulsion system (in kilowatts, convertible to foot-pounds/second). Dividing the power in foot-pounds/second by the speed in feet/second gives the instantaneous thrust in pounds. This thrust is the force at any instant that is applied through the tires to drive the Volt forward or to decelerate it.

By observing changes with time in the speed of the Volt, the system could monitor the acceleration of the vehicle. A good estimate of the mass of the vehicle can then be derived by observing the thrust needed to provide several independent standing-start accelerations. In particular, if F1 and F2 are the thrusts needed to produce accelerations a1 and a2, then the effective mass M of the Volt would be M = (F1-F2)/(a1-a2). In hilly locations like Seattle, this mass estimate will have to be averaged because uphill or downhill slopes will affect the value. It might take some processing to derive an accurate estimate of the vehicle mass, but it should be a constant and should be accurately estimated in a few minutes of driving.

The thrust has three components, (1) the drag due to the friction in the tires and mechanical system, (2) the force due to air resistance, and (3) the force that produces the instantaneous acceleration. Knowing the mass and acceleration, the acceleration-dependent force could be removed, leaving the combined friction plus air resistance force in pounds. Since the Volt's speed is known, the dependence of that combined force on speed could be used to extract the force due to air resistance and the coefficients of its velocity dependence. (I won’t go into how to do that, but it’s simple algebra.)

These three force components could then be multiplied by the instantaneous speed to give the three power flow components, providing separate power flows (converted back to kilowatts) (1) due to mechanical friction, (2) due to air resistance, and (3) due to acceleration. The Power Flow display could display these three power component values, as well as the net energy going into these three processes (in kW-hrs) since the last charge. Having this information available would be very useful to many Volt owners, because they could directly observe the separate energy consumption effects of tire changes, driving style and mode, and high-speed driving.
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Yes, and I keep that on display on my Volt's main screen. But if it's too distracting, they can look at when they will need their next oil change instead.

But wouldn't they like to see a 3-section pie chart showing where their energy is going?
You do have the instantaneous KW power values on the main screen showing where power is flowing. And some folks think that is too distracting.
The comment of edk-austin prompted me to consider that, without involving the inscrutable GM Engineers, I could make a video recording in my own Volt of the Driver Information Center display with the Select set to Power Gauge. Assuming video included a clock display ticking off the seconds, I’d have a recording of the Volt’s speed and power consumption/regeneration vs. time.

Then, if I drove a “calibration run” involving some varying standing start accelerations on level ground and some freeway driving at a pre-selected set of speeds up to 70 mph, I’d have the information I mentioned in my post. Then, using Mathematica, I could analyze that data to extract the mass of the vehicle (to check against the Volt's known “curb weight”), the velocity and velocity-squared coefficients of the Volt’s air resistance, and the coefficient of friction associated with energy loss due to friction from the tires and the power train. These quantities should be constants, or at least values that should not change much from one day to the next. This could be checked with several such runs. If it worked, we’d have a more precise way of determining the effect of tires and the effect of Normal vs. Sport driving.

Thanks edk-austin. Maybe in my “copious free time” I’ll do this and report back.
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