I drive a petrol-powered Renault Grand Scenic III, and it’s not what you’d call overpowered in any way, shape or form. It has a handy display that lets you know when to change up and down, which I thought had to do with how many revs the engine was doing, but I noticed that at comparable speeds, but different inclines, the car wants me to change down when the going gets tough. Which makes sense, but how does it know that it’s struggling? It seems crazy to me that the combustion cycle could be monitored to such a degree.
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Cars are controlled by things known as maps. A simple map is a 2D lookup table of precomputed values like a spreadsheet – with one parameter on the x and another on the y. An example would be the car knows how much fuel its currently using, and how fast the engine is going. With this it can plug that into two maps and work out engine power and engine efficiency. It can then look at another map and work out if for the given power requirements another engine speed gives better efficiency, this can be translated to a gear recommendation.
These maps are prepopulated by engineers in a test environment so the car never has to do complex combustion calculations. Choosing the correct maps to use is an art as well as a science – 5 dimensional maps are not uncommon, so it gets quite complicated for the engineer doing the calibration!
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