Department Of Mechanical And Automobile Engineering CYLINDER DEACTIVATION 1 2 Sanchit Tandon , Swati Bhardwaj 09-ITMG-1517-AU Automobile Engineering Abstract:
The four stroke Spark Ignition (SI) engine’s P– V diagram contains two main parts. They are the high pressure loop (compression – combustion combustion – expansion) expansion) and the low pressure (exhaust-intake) loops. The main reason for efficiency decrease at part load conditions for these types of engines is the flow restriction at the cross sectional area of the intake system by partially closing the throttle valve, which leads to increased pumping losses. This can be rectified by implementation of cylinder deactivation in four cylinder IC engine by developing proper control system. Cylinder deactivation is considered as a very promising technology for reducing emissions and fuel consumption. Keywords: SI engine, Part load, Pumping loss, Pressure loop, Cylinder Deactivation .
1. INTRODUCTION:
The non renewable energy sources such as fossil fuels like petrol, diesel, etc. are continuously under depletion. Even though the renewable energy sources exist, the utilization of such energy resources is very low due to high cost involved in utilization of such resource. Hence the fossil fuel must be effectively utilized. The internal combustion engine has been the predominant power plant in the automobile for nearly a century. Although a century of development has lead to a highly refined technology, there is still some opportunity for further fuel efficiency gains [1]. The four stroke SI engine is a widely applied power source in transportation and other power generation units. However, with the increasing number of such applications, air pollution caused by exhaust emissions has become of primary significance due to its environmental impact. During the past forty years, with the pressure of governmental policies and enormous research activity in this area, the emission (NOx, CO and HC) levels have been decreased significantly. In the future, a considerable decrease in emission levels due to further improvement in engine technology is expected. Reducing the fuel consumption and related CO2 emission is increasingly important these days. Typically, internal combustion engines operate more efficiently when the engine load is high [1-3]. However in daily life, most of the time the engine is operated in lower efficiency region. Better matching of real engine load with optimum engine load can be obtained by applying cylinder deactivation. By deactivation of cylinder, the load of the still activated cylinder is increased with improved efficiency. Thomas Tsoi-Hei Ma used a multi-cylinder spark ignition internal combustion engine having two groups of cylinders, and developed disabling means for selectively deactivating one group of cylinders by cutting off its fuel supply while continuing to receive air. The exhaust system includes an NOx trap to store NOx gases while the exhaust gases contain excess air. During part load operation, the engine is run with one bank of cylinders disabled most of the time during 1|Page
Department Of Mechanical And Automobile Engineering which NOx gases are stored in the NOx trap. In order to permit the trap to be regenerated or purged periodically, both bank are fired at is the same time for short intervals to supply a stoichiometric or reducing mixture to the exhaust system. Michael Ralph Foster et al., invented a controller and cylinder deactivation system to regenerate an exhaust after treatment device for a multicylinder engine that operates primarily at an air/fuel ratio that is lean of stoichiometric [2]. The invention uses the cylinder deactivation system to control temperature and air/fuel ratio of an exhaust gas feed stream going into an after treatment device. The invention also increases the amount of fuel delivered to each non-deactivated cylinder by an amount sufficient to maintain operating power of the engine. The regeneration action includes desorbing NOx from a NOx adsorber catalyst, desulfating the NOx adsorber catalyst, and purging a diesel particulate trap. Tyler M. Nester et al., designed, implemented and tested crankshaft-mounted pendulum absorbers used for reducing vibrations in a variable displacement engine [3]. The engine can run in V8 and V4 modes, and without absorbers it experiences significant vibration levels, especially in V4 idle. The absorbers are tuned to address the dominant second order vibrations, and are slightly overtuned to account for nonlinear effects. The absorbers were designed to replace the large counterweights at the ends of the crankshaft, and thus serve for both balancing and vibration absorption. The engine was placed in a vehicle and tested for vibration levels at idle under various load conditions, and these results were compared with results obtained from a similar vehicle without absorbers. The tests demonstrate that these absorbers offer an effective means of vibration attenuation in variable displacement engines. Wang Y et al., implemented model-based control methodology utilizes position feedback, a nonlinear observer that provides virtual sensing of the armature velocity and current, and cycle to cycle learning for actuating electromechanical valve actuator [4]. An electro mechanical valve actuator model was developed and experiments were used to identify unknown model parameters and functions and to validate the model predictions. Osman Akin Kutlar et al., investigated the methods for increasing efficiency at part load conditions and their potential for practical use [5]. M. Sellnau et al., designed a 2-step variable valve actuation system and integrated on a 4-valve-per-cylinder 4.2 litre inline-6 engine and also used simulation tools to develop valve lift profiles for high fuel economy and low NOx emissions. A 2-step valvetrain mechanism was developed that features hydraulically-actuated switchable rocker arms and hydraulic lash adjusters. The engine management system was modified for control and calibration of 2-step VVA, and to realize the full fuel economy potential of the system. Cylinder deactivation is one of the technologies that improve fuel economy, the objective of which is to reduce engine pumping losses under certain vehicle operating conditions. When operating at part load the throttle restricts the airflow into the engine, reducing the volumetric efficiency, and as a result the air pressure in the intake manifold falls significantly below atmospheric pressure. In order to draw air from the manifold into the cylinder, the piston is required to do work against the manifold depression and this is termed pumping work
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Department Of Mechanical And Automobile Engineering Pumping Losses
Full load
Part load
FIG-1 Schematic diagram showing throttle valve position and P-V diagram for full load condition and part load condition [1]
2. HISTORY
For long, cylinder deactivation is considered as a very promising technology for reducing emissions and fuel consumption. Apparently already in 1905, at the beginning of the internal combustion engine revolution, cylinder deactivation was used in the Sturtevant 38/45 six. The first mass production attempt of engines with cylinder deactivation was by GM in 1981 with the Cadillac Eldorado V8-6-4. As the name suggests, the V8 engine was capable of deactivating 2 or 4 cylinders. The technology was used for only one model year and due to electronic problems, only after 120000 produced engines, the technology went out of production. More recently, in 1998, DaimlerChrysler re-introduced the cylinder deactivation technology (named Active Cylinder Control) on their 5.0L V8 and 6.0L V12 engines, used by Mercedes-Benz. The system is able to deactivate 4 respectively 6 cylinders. Honda is applying their so called Variable Cylinder Management since 2005 on their 3.5L V6 gasoline engine range, where one cylinder bank of 3 cylinders can be deactivated. A clear trend is that the most attempts with deactivation are done with a cylinder count of 6 or more. One exception is Mitsubishi, who presented a 1.6L 4 cylinder in-line engine, equipped with cylinder deactivation in 1992. The engine never went into production.
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Department Of Mechanical And Automobile Engineering 3. CYLINDER DEACTIVATION ACTUATION MECHANISM
Cylinder deactivation is simply keeping the intake and exhaust valves closed through all cycles for a particular set of cylinders in the engine Depending on the design of the engine, valve actuation is controlled by different methods 3.1 For pushrod designs — when cylinder deactivation is called for — the hydraulic valve lifters are collapsed by using solenoids to alter the oil pressure delivered to the lifters. In their collapsed state, the lifters are unable to elevate their companion pushrods under the valve rocker arms, resulting in valves that cannot be actuated and remain closed. 3.2 For overhead cam designs , generally a pair of locked-together rocker arms is employed for each valve. One rocker follows the cam profile while the other actuates the valve. When a cylinder is deactivated, solenoid controlled oil pressure releases a locking pin between the two rocker arms. While one arm still follows the camshaft, the unlocked arm remains motionless and unable to activate the valve.
FIG-3 Overhead Cam Design [7]
3.3 For camless engine i.e. engines with electromechanical valves is controlled with the help of ECU. Implementing the cylinder deactivation technology in camless engines is easy but the programming of the microprocessor is done carefully so as to take care of the opening time of the electromechanical valves. The system is very complex.
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Department Of Mechanical And Automobile Engineering 4. WORKING PRINCIPLE
Cylinder deactivation is realized by deactivating (closing) the valves and blocking injector or ignition (Otto-engine) signals. Current cylinder deactivation systems use a mechanical valve train, where a hydraulic control element is used to prevent the cam followers from actuating the valve. Figure 4a shows a mechanical/hydraulic deactivation mechanism used by General Motors. Future camless valve train systems, figure 4b, simplify cylinder deactivation by keeping the valves closed. By closing the valves the cylinder is being used as an‖air spring‖. This air spring performs a periodical compression and expansion cycle, which eliminates the pumping losses (apart from blowby). There are three moments to start the deactivation, before the exhaust stroke, after the intake stroke and after the exhaust stroke. Deactivation before the exhaust stroke results in hot exhaust gases being trapped inside the cylinder. This keeps the cylinder warm and according to [3] this high
(a) (b) FIG 4: (a) Cylinder deactivation by deactivating the pushrod [8] (b) Electromechanical valves system concept [8]
Temperature has advantages regarding thermal efficiency. The consequence of this timing is a higher compression end pressure. Deactivation after the intake stroke results in near ambient temperature and pressure conditions. Compression end pressure will consequently be lower. Deactivation after the intake stroke leads to even lower compression end pressures. Blow-by effects and cylinder wall heat transfer will eventually level the cylinder pressure and cylinder temperature.
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Department Of Mechanical And Automobile Engineering 5. ADVANTAGES OF CYLINDER DEACTIVATION
The major advantage of cylinder deactivation is increased fuel efficiency (10-20%).Cylinder deactivation also results in decreased emissions from deactivated cylinders. This technology increases the breathing capability of the engine, thereby reducing power consumed in suction stroke. Changes in engine friction or reduced energy consumption because of deactivated valve. Less fuel consumption during engine idling. Cylinder deactivation also improves the performance of exhaust control system. 6. GAPS IN CYLINDER DEACTIVATION TECHNOLOGY
There are several constraints that limit the use of cylinder deactivation Deactivating cylinders can cause change in engine balancing which can lead to very violent vibration and increased noise levels. Increased cost of manufacturing - deactivation will reduce the operating cost but the cost of the additional parts or the deactivation components like electronic control module and the complexity in the design will increase the cost. The unbalanced warm-up and cooling of engine components, which could lead to thermal stresses. Increased emissions and fuel consumption when cooled down cylinders are active again. Overall increase in weight. Complexity of system makes maintenance difficult.
7. CONCLUSION
In summary, the benefit of cylinder deactivation is threefold. The deactivated cylinders operate as an air spring and therefore do not require pump work, apart from a marginal loss caused by blow-by and heat transfer. Power normally needed to operate the valves is not needed for the deactivated cylinders (holds for both cam driven and camless valvetrain). Therefore the engines mechanical loss is reduced. The third and main benefit is a result of the higher engine load, which results in less pumping losses. Due to limitations the benefit and effect of Cylinder deactivation on engine efficiency will be reduced. With an effective Noise Vibration Harness suppression method the engines’ efficiency and deactivation time could be increased, resulting in reduced fuel consumption.
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Department Of Mechanical And Automobile Engineering REFERENCES
[1] Ma Thomas Tsoi-Hei, ― Engine with cylinder deactivation‖, U.S. Patent No. 6,023,929. [2] Foster Michael Ralph, Foster Matthew G, Price Kenneth S, ―Engine cylinder deactivation to improve the performance of exhaust emission control systems‖, U.S. Patent No. 6,904,752 B2. [3] Nester Tyler M, Haddow Alan G, Shaw Steven W, ―Vibration reduction in a variable displacement engine using pendulum absorbers‖, SAE Paper 2003-01-1484. [4] Wang Y, Megli T, Haghgooie M, ―Modeling and Control of Electromechanical Valve Actuator‖, SAE Paper 2002-01-1106. [5] Kutlar Osman Akin, Arslan Hikmet, Calik Alper Tolga, ―Methods to improve efficiency of four stroke, spark ignition engines at part load‖, Energy Conversion and Management 46(2005) 3202 – 3220, Elsevier Science Publishers. [6] Sellnau M, Kunz T, Sinnamon J, Burkhard J, ―2-step Variable Valve Actuation: System Optimization and Integration on an SI Engine‖, SAE Paper 2006-01-0040. [7] www.Google/images.com [8] www.Scribd.com
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