Influence of the final drive ratio on the consumption of passenger cars under real driving conditions

The predetermined gear shift points in the type approval test for the European Union (NEDC - New European Driving Cycle) influence the technical design of today's vehicles with manual transmission significantly. Most manufacturers select a long total gear ratio to achieve fuel savings by down speeding. The effects of the final drive ratio on improving fuel consumption in real customer driving, and subjectively perceivable longitudinal dynamics have hardly been considered so far. This paper studies the effect of varying the final drive of a vehicle on its fuel consumption and the driving experience in daily driving. Therefore we analyze two vehicles with different drive trains (Diesel and Gasoline) firstly with their initial and secondly with a modified final drive by applying (a) legally stipulated driving cycles, a aggregated daily driving cycle and (b) constant driving on a chassis dynamometer as well as (c) real driving situations. We quantify the impact of varying the final drive ratios on the fuel consumption in several driving cycles: the NEDC, the Worldwide Harmonized Light-Duty Vehicles Test Procedure (WLTC) and a highly dynamic driving cycle (HDDC), which corresponds to more dynamic driving behavior. Thus this HDDC comprises various route profiles depending on the driver type (city driver, commuter, long-distance driver). Additionally we carried out constantly driving phases at different velocities utilizing a chassis dynamometer to quantify consumption influences. Real driving situations complement these chassis dynamometer testing and enables evaluation of the effects of a higher final drive on the longitudinal driving dynamics in an objective (driving maneuvers) and a subjective manner (comprehensive volunteer study). The final drive has a large influence on the consumption in the NEDC for vehicles with a manual transmission. Real drivers on the other hand, only have a very small consumption advantage with a long total gear ratio. The real consumption effects are clearly better represented by the WLTP. Besides, through the use of shorter final drives the customer-relevant driving dynamics can be significantly improved.