ROAD GRADE AND VEHICLE PARAMETER ESTIMATION FOR LOGITUDINAL CONTROL USING GPS.

Abstract

This paper demonstrates two methods for obtaining an estimate of road grade using a Global Positioning System (GPS) system on a ground vehicle. In the first method, two antennae are used to directly measure the attitude of the vehicle in the pitch plane; in the second method, the ratio of vertical to horizontal velocity at a single antenna is used to estimate road grade. Both methods are implemented experimentally and their relative sensitivities to corruption by vehicle pitch and bounce motion characterized. The resulting grade measurements are then used together with engine torque information to produce estimates of mass, rolling resistance and aerodynamic drag from a simple longitudinal force balance. The resulting mass estimation consistently converged to within f 2 YO of the true vehicle mass. Another variable that has a profound effect on vehicle performance is the road grade. Modest road grades may prove to be quite a challenge for vehicles with low power- to-weight ratio such as ab:omated commercial heavy vehicles. Figure 1 shows the relative capability of a heavy truck engine and the demands from grade and aerodynamics as a function of speed. At highway speeds (about 20 ds), a typical commercial heavy vehicle has little capability for acceleration in reserve since most of the engine output must go to counteract aerodynamic drag and rolling resistance. A 4% road grade can be a severe loading to such vehicle:<. This is why, in most cases, heavy vehicles have to slow down considerably going up steep grades, sacrificing speed in order to get more power from engine.