Investigation into the trade-off between the part-load fuel efficiency and the transient response for a highly boosted downsized gasoline engine with a supercharger driven through a continuously variable transmission

Adam T J M Rose, Sam Akehurst, Chris J Brace

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Abstract

Downsizing is an established trend in the development of passenger car engines. However, the benefits of an improved fuel economy are often obtained at the expense of the engine’s dynamic response (owing to increasing demands on the boosting system) and, consequently, the vehicle driveability. The use of a continuously variable transmission in the supercharger driveline offers increased control flexibility over the air path, which could allow more suitable calibrations to be developed. This paper gives details of a co-simulation-based investigation into the trade-off between the steady-state part-load fuel efficiency and the resulting tip-in transient response for a highly boosted downsized gasoline engine. The engine was a 2.0 l in-line four-cylinder unit, designed to replace a 5.0 l, naturally aspirated V8, equipped with a positive displacement supercharger in a sequential series arrangement with a fixed-geometry turbocharger with an external wastegate. The supercharger can be de-clutched and bypassed, and therefore three separate supercharger engagement regimes were investigated for part-load operation, defined as follows: with the supercharger disengaged and bypassed; with the supercharger engaged with a fixed drive ratio; with the supercharger engaged using a variable ratio (i.e. through a continuously variable transmission). For each of these supercharger engagement regimes, design-of-experiments and optimisation techniques were used to find the best settings for the key engine control parameters such as the intake and exhaust valve timings and the exhaust gas recirculation rate. Using these calibrations as a starting point, the transient performance was then assessed in fixed-speed tip-in simulations. The trade-off situation was found to be highly complex; identifying the best overall balance of the steady-state efficiency and the dynamic performance requires a subjective assessment. However, the continuously variable transmission does provide the best potential for dynamic response combined with a satisfactory fuel economy. It is suggested that the most suitable solution would be to have multiple user selectable calibrations, such as the ‘economy’ and ‘sport’ modes used on many modern vehicles.
LanguageEnglish
Pages1674-1686
Number of pages13
JournalProceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering
Volume227
Issue number12
Early online date16 Sep 2013
DOIs
StatusPublished - Dec 2013

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Superchargers
Transient analysis
Gasoline
Engines
Calibration
Fuel economy
Dynamic response
Exhaust gas recirculation
Passenger cars
Engine cylinders
Sports
Design of experiments
Geometry

Cite this

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title = "Investigation into the trade-off between the part-load fuel efficiency and the transient response for a highly boosted downsized gasoline engine with a supercharger driven through a continuously variable transmission",
abstract = "Downsizing is an established trend in the development of passenger car engines. However, the benefits of an improved fuel economy are often obtained at the expense of the engine’s dynamic response (owing to increasing demands on the boosting system) and, consequently, the vehicle driveability. The use of a continuously variable transmission in the supercharger driveline offers increased control flexibility over the air path, which could allow more suitable calibrations to be developed. This paper gives details of a co-simulation-based investigation into the trade-off between the steady-state part-load fuel efficiency and the resulting tip-in transient response for a highly boosted downsized gasoline engine. The engine was a 2.0 l in-line four-cylinder unit, designed to replace a 5.0 l, naturally aspirated V8, equipped with a positive displacement supercharger in a sequential series arrangement with a fixed-geometry turbocharger with an external wastegate. The supercharger can be de-clutched and bypassed, and therefore three separate supercharger engagement regimes were investigated for part-load operation, defined as follows: with the supercharger disengaged and bypassed; with the supercharger engaged with a fixed drive ratio; with the supercharger engaged using a variable ratio (i.e. through a continuously variable transmission). For each of these supercharger engagement regimes, design-of-experiments and optimisation techniques were used to find the best settings for the key engine control parameters such as the intake and exhaust valve timings and the exhaust gas recirculation rate. Using these calibrations as a starting point, the transient performance was then assessed in fixed-speed tip-in simulations. The trade-off situation was found to be highly complex; identifying the best overall balance of the steady-state efficiency and the dynamic performance requires a subjective assessment. However, the continuously variable transmission does provide the best potential for dynamic response combined with a satisfactory fuel economy. It is suggested that the most suitable solution would be to have multiple user selectable calibrations, such as the ‘economy’ and ‘sport’ modes used on many modern vehicles.",
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