| Abstract [eng] |
The goal of this research project is to determine a passenger vehicles' acceleration and top speed change in response to the change in the ratio of the final drive gearing coefficient. To accomplish this, the following tasks had to be completed: analysis of the transmission types, their construction and the operation of the final drive assembly, performing a numerical analysis and comparing it to dynamic real world test results using a “BMW (E36) 318is” as the test subject. The car chosen for this research is a “BMW (E36) 318is” due to its classical arrangement comprised of a front mounted four cylinder petrol engine and rear wheel drive. The analysis of the final drive gearing in such arrangement is easier, due to the transmission being separate from the rear mounted differential assembly. By changing the differential housings which have different internal gearing, their effect on the vehicle's acceleration and top speed could be observed and compared to the calculations of expected values. The research was started by gathering and analyzing material about the power delivery chain in the manual transmission vehicle model to develop a familiarity with the components: flywheel, clutch, transmission and integrated subframe final drive assembly. In regards to the available final drive assemblies, four differential housings were chosen with the following internal gearing configurations to conduct this study: 2.79:1 – the lowest one, available from the factory in the diesel powered vehicles known for their high torque. 3.15:1 – the gear set mostly found in the high powered petrol engine cars. 3.45:1 – the gear set that came standard with the chosen test vehicle. 4.10:1 – the gear set used for the least powerful petrol engines, usually coupled with automatic transmissions. Changing the differential therefore changes the gearing of the final drive assembly and provides a change in vehicle dynamics. After conducting the gathering and analysis of the available information from the data-sheets and literal documentation, practical tests were conducted using a “DL1” data collection tool to capture the information about the response of the car with all four aforementioned differentials. Using the “Analysis V8” software with the said tool, the top speed and acceleration for each gear and all four differentials were determined, alongside the engine RPM for 50 km/h and 90 km/h for different gears. Finally the theoretical calculations for the top speed at max engine in every gear were calculated. They were correlated with the observed values for our measurements, including the top RPM for each gear and the engine RPM for 50 km/h in 3'rd gear, 50 km/h and 90 km/h in 4th gear, 90 km/h in 5th gear. The observations conclude that increasing the ratio of the gear set in the differential leads to a quicker accelerating vehicle, but it negatively affects the comfort and fuel consumption. The best gear set ratio for fuel economy and acceleration for our test vehicle was determined to be the factory 3.45:1 although with increased driving speed (above 90km/h) fuel economy and comfort are reduced. For users who spend most of their commute at highway speeds, it would be recommended to switch their final drive assembly to the one with the ratio of 2.79:1 for increased comfort and decreased fuel consumption. The conducted research is unique in terms of applicability. A user could tailor their car to their needs in regard to the expected driving conditions based on this research. Also- the calculated and observed data have a very close correlation, therefore a calculated final drive ratio selection could be trusted to have the expected result on the vehicle. |
