TABLE OF CONTENTS This case study shows how the gear ratios of a manual gear box can he optimized to improve the fuel economy of a passenger car. This analysis is purely academic because it completely neglects all drivability issues and only focuses on the fuel economy of a vehicle that follows the MVEG-95 driving profile.
Nevertheless, it is instructive because it shows how a numerical parametric optimization problem can be defined and solved using a quasistatic problem formulation. The software tools used in this example are the QSS toolbox in conjunction with numerical optimization routines provided by Matlab/Simulink. This approach is quite powerful and can be used to solve non-trivial problems.
The powertrain of the light-weight vehicle analyzed in Sects. 3.3.2 and 3.3.3 includes a standard five-speed manual gear box. The ratios of these five gears are chosen according to the approach introduced in Sect. 3.2.2 and satisfy the usual requirements with respect to acceleration performance, towing capability, etc.
These gear ratios do not yield the smallest possible fuel consumption when the vehicle is following the MVEG-95 test cycle and it is clear that there is a different set of gear ratios that improve the vehicle's fuel economy. However, it is not clear at the outset what gear ratios are optimal and - more importantly - what gains in fuel economy may be expected in the best case. These two questions can be answered using the approach shown below.
The...
