Exhaust emissions from a vehicle under road driving condition is affected by the control state of ECU (Engine Control Unit). This control state highly depends on the driving force of the vehicle. The driving force is nearly equal to the driving resistance, which is the sum of the acceleration resistance, the air resistance, the rolling resistance and the gradient resistance. Although it is essential to take an accurate measurement of the road gradient, it is quite difficult to evaluate the gradient resistance in testing on-road driving.
In this study, the measurement methods of the road gradient and the altitude with GPS, gyro sensor and height sensor are reported. The road gradient under the on-road driving condition is evaluated by the combination of measuring the pitch angle with the gyro sensor and measuring the vehicle gradient with the two height sensors. Verifying of this method, the altitude of the driving test route is also evaluated.
From the measurement values of height sensors, the gradient of vehicle was obtained. Then, the road gradient is obtained by taking account of this vehicle gradient to insure the accuracy of gradients. This method has a high repeatability, and yet is able to solve an inaccuracy problem associated in conventional measurement method of road gradient and altitude.