HOT AND COLD


While it sounds technical, “linear extrapolation” is a simple method of predicting results by extending a trendline beyond verified test data. While this has worked fairly well for almost 50 years, the standard may no longer be as valuable as it once was. (See “What Is Linear Extrapolation,” Page 77)


Many ground vehicles within the U.S. Army’s fleet are either newly introduced or have undergone significant modernization in the last several years. Specifically, the vast majority of the fleet no longer uses mechanically controlled powertrains, but are now operating on electronically controlled powertrains. Te differ- ence between mechanical and electronic control is best explained by an example. In the years before electronic control gradually took over virtually all of the vehicles on American highways, it was not uncommon to see overheated cars, hoods open and steam pouring out, on the side of the road during the hottest months of summer. Tat is nearly nonexistent today. Te differ- ence is electronic control. Te engine is controlled by a computer that employs algorithms that prevent the vehicle from going past certain thresholds.


When linear extrapolation is applied to electronically controlled powertrains, the results suffer from significant error or may be invalid entirely. Linear extrapolation has limited uses where it can be trusted, and electronically controlled powertrains is not one of them.


Everyone who has ever tried investing knows that drawing a trendline on past financial data doesn’t account for all—or even


any—of the economic variables that will set future pricing. Like the stock market, electronically controlled powertrains operate on complex algorithms that are influenced by too many variables to trust linear extrapolation.


BEHIND THE SCENES IN ELECTRONICALLY CONTROLLED POWERTRAINS In order to achieve goals such as better fuel economy, increased power output, reduced emissions and enhanced diagnos- tic information, the heavy-duty truck industry transitioned to electronically controlled powertrains starting in the 1990s. Eventually, this transition also reached military vehicles as new vehicles were introduced or older vehicles were modernized.


Although electronically controlled powertrains often have multi- ple controllers, the two most common types are the engine control module (ECM) and the transmission control module (TCM). Tese two controllers are programmed to work in harmony to produce the optimized response of a vehicle based on criteria such as driver demand, road grade, vehicle load, ambient temperature, elevation and other factors.


To account for all of the combinations of conditions, these controllers have complex algorithms that usually have upwards of a million lines of software code.


While the driver interfaces with these controllers through the simple and singular input of the accelerator pedal, a network of feedback sensors is providing data to those controllers such as


TEMPERATURE EXTREMES


It can be a challenge to find environments suitable for testing certain Army vehicles, which require exposure to both extreme heat and cold. (Photos by Getty Images)


76


Army AL&T Magazine


Fall 2022


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