Cylinder Deactivation
From c,mm,n
The following text is the summary of a graduation thesis by Gilbert Peters. He graduated in february 2007 on this study about cylinder deactivation at the Eindhoven University of Technology.
Abstract
The project ”car of the future” is a project aimed at designing a sustainable passenger car for the year 2020. Sustainability is a very broad topic, which reaches further than fuel economy and exhaust emissions. The ”car of the future” uses a modularity concept to maximize the sustainability aspect of the vehicle in a broad sense. The modularity concept makes it possible to use different powertrains, creating the opportunity to adapt the vehicle to the availability of fuels, or adapt the powertrain to the demands of the user in the future. The desire for flexibility justifies the choice for an internal combustion engine as primary mover, because it can be adapted to a large variety of fuels with more or less modifications to its construction.
Reducing the fuel consumption and the related CO2 emissions is increasingly important these days. Increasing the powertrain efficiency is therefor one of the major goals within the project ”car of the future”. Typically, internal combustion engines operate more efficiently when the engine load is high. Engine load during daily traffic however is typically low, resulting in sub-optimal fuel consumption. Better matching of the real engine load with the optimal engine load can be obtained by applying cylinder deactivation. By deactivation of cylinders the load of the still activated cylinder is increased with improved efficiency as a consequence.
Cylinder deactivation increases the torsional vibrations of the engine because of the reduced combustion interval and increased combustion peaks. Currently, cylinder deactivation is used on multicylinder engines, V12, V8 or V6, where the torsional vibrations do not cause much of a problem due to the still acceptable combustion intervals and combustion peaks during deactivation. In Europe, the majority of passenger cars use a 4 cylinder engine, therefor the research has been focussed on the vibrational powertrain behavior of four cylinder engines using cylinder deactivation. The goal of this research is therefor:
”Determine the influence of cylinder deactivation on a 4-cylinder engine, regarding the vibrational behavior of the powertrain.”
In order to analyze the effect of cylinder deactivation on powertrain dynamics, the important criteria regarding powertrain vibrations are analyzed. The important criteria regarding powertrain comfort which are studied are ”engine shake”, ”gear rattle” and ”vehicle shuffle”. Vibrations can be suppressed or damped by using for instance a torsion damper (TD) or an integrated starter alternator damper (ISAD), which can apply a positive or negative torque to the crankshaft. The ISAD system is herein preferred because it makes other powertrain functions possible, like regenerative braking, boosting and start/stop function.
The powertrain with all its components are modeled, in order to analyze the effect of cylinder deactivation on the powertrain dynamics. These models describe the engine dynamics, manual transmission, driveshafts, wheels and vehicle. The powertrain can be equipped with a torsion damper or ISAD system. Both powertrains are compared by analyzing the frequency responses of both powertrains. Both powertrains show different eigenfrequencies, which can interfere with the engines’ excitation frequency. Interference of the eigenfrequencies with the excitation frequencies can cause resonances. Analysis will show which powertrain is best suited in combination with cylinder deactivation.
During deactivation the deactivated cylinders are being used as an ”air spring”. The valves of the deactivated cylinder are kept closed, to minimize the pump work by this cylinder. The trapped air in the cylinder will periodical complete a compression cycle, followed by an expansion cycles. The timing of valve closing influences the torque caused by the ”air spring”. Three different valve timings are being discussed, serving as a starting point for further research.
Deactivation of cylinders leads to increased powertrain vibrations. These vibrations are the cyclic speed fluctuation, primary transmission shaft acceleration, longitudinal vehicle acceleration and powertrain unit acceleration. The influence of the engine speed, engine load and gear ration on these vibrations are studied. The ISAD system can be used as a passive damper to reduce the vibrations caused by cylinder deactivation. Simulation results show how effective this damping system is.
