Modeling the Effects of Transmission Gear Count, Ratio Progression, and Final Drive Ratio on Fuel Economy and Performance Using ALPHA

Abstract

The Advanced Light-Duty Powertrain and Hybrid Analysis (ALPHA) tool was created by EPA to evaluate the Greenhouse Gas (GHG) emissions of Light-Duty (LD) vehicles [1]. ALPHA is a physicsbased, forward-looking, full vehicle computer simulation capable of analyzing various vehicle types combined with different powertrain technologies. The software tool is a MATLAB/Simulink based desktop application. The ALPHA model has been updated from the previous version to include more realistic vehicle behavior and now includes internal auditing of all energy flows in the model [2]. As a result of the model refinements and in preparation for the mid-term evaluation (MTE) of the 2022-2025 LD GHG emissions standards, the model is being revalidated with newly acquired vehicle data. This paper presents an analysis of the effects of varying the absolute and relative gear ratios of a given transmission on carbon emissions and performance. Energy-based methods of selecting absolute gear ratios are considered and the effects of alternative engine selections are also examined. An algorithm is presented for automatically determining ALPHAshift parameter sets based on the selected engine and transmission combination. It is observed that no single ratio progression optimizes fuel consumption for all applications, however, fuel consumption is also relatively insensitive to progression which implies a fixed set of ratios can still be used for a range of applications without necessarily compromising consumption. The energy-based ratio analysis may prove useful in determining the optimal overall top gear ratio for a given engine-vehicle combination and also helps to explain the relative insensitivity to ratio progression. Individual performance metrics can show high sensitivity to ratio progression, final drive ratio and shift calibration, in particular 30-50 and 50-70 MPH passing times.

A heuristic synthesis of multistage planetary gearbox layout for automotive transmission

“…In recent articles, it can be found object-oriented gear ratio selection is gaining the traction in vehicle transmission design. 7 Here, except reverse gear and direct drive seven speed ratios need to be determined. The value of the teeth number is selected based on the International Organization for Standardization standard.…”

“…The findings show that the planetary gears with large number of ratios can reduce the fuel consumption and NO x emission but simultaneously large apart speed ratios can reduce the driving comfort. 6,7 The transmission control unit (TCU), during gear shifting, should synchronize the engagement and disengagement of clutch for shift control. 8 In manual transmission, the discontinuity of power during gear shifting creates a jerk and causes the passenger discomfort.…”

Estimating GHG Reduction from Combinations of Current Best-Available and Future Powertrain and Vehicle Technologies for a Midsized Car Using EPA’s ALPHA Model

“…ALPHA estimates four different performance metrics when driving each vehicle package over a performance drive cycle (0-60 mph time, 30-50 mph time, 50-70 passing time, and ¼ mile time). For this standard car matrix analysis for this paper we settled with summing four performance metrics and comparing it to the sum of the performance metrics of the baseline vehicle (a 2008-era Camry) [7] [8].…”

“…To assure that the engine in each vehicle package in the standard car matrix maintains neutral performance, the engine displacement is adjusted so the vehicle package's performance metric sum falls reasonably close to the performance of the baseline vehicle. The approach taken for resizing the vehicle package's engine to maintain neutral performance this paper is to approximate the power at the wheels using iterative calculation rather than using iterative simulation which would provide a more realistic result while also increasing the simulation time, perhaps significantly [8]. For this reason the performance is not quite held perfectly neutral, however the results are still quite reasonable, typically within 3.5% of the baseline.…”

Improving Car Fuel Efficiency by Optimising Transmission Parameters

“…The engine operates in the traction mode 47.7% of the total travel time. 38.7% of this time is accompanied by the acceleration processes [8]. Slowing down and operating the engine without a load with the clutch disengaged takes 13.3% and 39% of the driving cycle time, respectively.…”