Abstract
Based on the analysis of the working profiles of internal combustion (IC) engines, a case-emphasized propulsion method is generalized to improve vehicle fuel efficiency. With this method, the ratio of the most-used speed to the most-desired speed of an IC engine is employed to control the engine to always run at its optimal working state with an efficient single-stage gear transmission. Examples of the propulsion method with different brands of IC engines in the market place demonstrate the potential that this method could reduce engine fuel consumption up to 5 ~ 39 %. A conceptual design of n-ratio automatic single-stage gear transmission is then developed to implement the case-emphasized propulsion method in a general way. Not only can such a design execute the proposed propulsion method well as an almost continuous variable transmission, but it can also increase the propulsion efficiency about 8 ~ 18 % if it is applied to replace the traditional automatic transmissions or continuously variable transmissions (CVTs) in vehicle drivetrains.
Highlights
Because of the shortage of crude oil and the concern of environment, the automotive industry is required to ramp up production of more fuel-efficient vehicles on a tight timeline
To ensure that an internal combustion (IC) engine can constantly perform in the optimal working state, it is necessary to know the general relationships of the engine speed versus its fuel consumption and the engine speed versus its output torque
It should be emphasized that the fuel consumption curve developed with either the full-load or the part-load tests can only be used for the case which has the same working condition and load as the tests; otherwise, the profile of tests can only be used as a rough reference
Summary
Because of the shortage of crude oil and the concern of environment, the automotive industry is required to ramp up production of more fuel-efficient vehicles on a tight timeline. They indicated that a continuously variable transmission (CVT) allowed a drivetrain controller the freedom to develop a required output power at a range of engine torque and speed conditions This flexibility can be used to maximize fuel efficiency. & It is noted that the prior arts were developed with the concept to approach the optimal fuel efficiency by controlling the IC engine to run in the RPM range around the maximum power since the range is close to the congregation of the minimum fuel consumption Such a concept may not always work because of the following reasons:The torque decreases with the increase of speed after the maximum torque is reached. It is necessary to comprehensively understand the IC engine working properties to conduct further development
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