This is true, but I don't think the car uses the y-axis accelerometer to measure vehicle acceleration (change in the car's speed). They have an imu that measures vehicle dynamics. Otherwise they would have difficulty bringing the car to a a a stop consistently as the slope of the road changed. If you were on a 20 percent downhill grade, the y-axis accelerometer would read 0.0 gs if you weren't impeding the car's acceleration with the brakes (ignoring drag for the moment), but the car's speed would be increasing at 0.2gs, like when you are in freefall toward the earth. Your speed is increasing, but you don't feel the acceleration (see vomit comet). Now you put the car in drive, but don't apply the accelerator. The car will start to apply regen, but that is limited to 0.2g. The car stops accelerating so the speed remains constant, and the y-axis accelerometer reads -0.2g. If the car only used the y-axis accelerometer, it would assume it was slowing down, but it wouldn't until the bottom of the hill.Going downhill causes the accelerometer to measure deceleration, not uphill. Think about it. If you’re at a stop on a steep decline, gravity is pulling you forward against your seatbelt, exactly like braking would on level ground. On a steep incline, gravity is pushing you back in the seat just like acceleration.
Last edited: