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Application of GPS receiver to road tests of automobile

Sar H., Pokorski J., Fundowicz P., Reński A.

Journal of KONES

2013

Vol. 20, No. 3

359--366

The article presents the assessment of the possibilities of applying GPS receiver for the measurement and acquisition of the longitudinal velocity of automobile in the investigations of longitudinal dynamics of automobile. For many years for the measurement of the longitudinal velocity Correvit-L sensors are applied. Major simplification of the measurement of the velocity with the GPS receiver, compared with correlational-optical sensors Correvit-L is giving the possibility to faster prepare the automobile for examinations. The more so as only recently GPS receivers with 10 Hz sampling rate are available. In the paper is shortly described the software specially designed for the measurements that makes it possible to simultaneously measure both the longitudinal velocity signal from GPS receiver and from Correvit-L sensor in real time. Furthermore, the application of the measurement of the velocity is presented on the basis of such road tests as the attempt of accelerating through the following gears, the attempt of free deceleration and the attempt of braking according to ECE 13 Regulation. On the basis of the mentioned manoeuvers the characteristics of the vehicle’s acceleration and dynamic coefficient, rolling and air drag coefficient and the braking deceleration were determined. The paper shows also some problems connected with applying GPS receiver to measure longitudinal velocity of the automobile.

Determination of air drag coefficient of a car by means of coasting

Münch K.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

2012

z. 5/91

27--32

The air drag coefficient will usually determined by wind tunnel experiments. The boundary conditions are fixed and reproducible. The costs of wind tunnel experiments are high and connected with a significant effort. Influence of the “moving street” during the experiment is only difficult to simulate, frequently done by means of a moving belt between the wheels of the car. Therefore at the lab of Thermo-and Fluiddynamics at the Cologne Institute for Automotive Engineering a new test procedure for determination of the air drag coefficient has been developed. A serial production car “Seat Ibiza ST” was tested unchanged and with modified under surface by means of coasting. The car was accelerated up to 120 km/h on a test track (2 km). The deceleration curve due to friction and air drag was measured by a GPS tracking system. By means of a general accepted evaluation procedure (NEDC-coasting) the drag was able to determine. A separation between friction based drag and aerodynamic drag is possible. The measurements indicate a good accuracy. The mistake is less than 5 % related to the origin drag coefficient. Unfortunately the boundary condition must not be changed during the test. That means, that the weather has to be stable, dry, not windy during the tests. An unusable procedure for industrial kind of work with a given time schedule. Therefore wind tunnel tests are still necessary.