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Engineering 2013 5 245 250 doi 10 4236 eng 2013 53035 Published Online March 2013 http www scirp org journal eng Gear Drive Mechanism for Continuous Variable Valve Timing of IC Engines Osama H M Ghazal 1 Mohamad S H Dado 2 1 Mechanical Engineering Department Applied Science Private University Amman Jordan 2 Mechanical Engineering Department The University of Jordan Amman Jordan Email hamzy211 dado ju edu jo Received December 18 2012 revised January 15 2013 accepted January 23 2013 ABSTRACT Continuous variable valve actuating CVVA technology provides high potential in achieving high performance low fuel consumption and pollutant reduction To get full benefits from CVVT various types of mechanisms have been proposed and designed Some of these mechanisms are in production and have shown significant benefits in improving engine performance In this investigation a newly designed gear drive mechanism that controls the intake valve opening IVO and closing IVC angles is studied The control scheme is based on maximizing the engine brake power P and specific fuel consumption BSFC at any engine speed by continuously varying the phase between the cam shaft angle and the crank shaft angle A single cylinder engine is simulated by the LOTUS software to find out the optimum phase angle for maximum power and minimum fuel consumption at a given engine speed The mechanism is a plane tary gear drive designed for precise and continuous control This mechanism has a simple design and operation condi tions which can change the phase angle without limitation Keywords Mechanism Design Planetary Gear Variable Valve Timing Spark Ignition Engines Performance 1 Introduction In internal combustion engines variable valve timing VVT also known as Variable valve actuation VVA is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine 1 6 The VVT system allows the lift duration or timing in vari ous combinations of the intake and or exhaust valves to be changed while the engine is in operation which have a significant impact on engine performance and emissions In a standard engine the valve events are fixed so per formance at different loads and speeds is always a com promise between drivability power and torque fuel economy and emissions An engine equipped with a variable valve actuation system is freed from this con straint allowing performance to be improved over the engine operating range 7 10 Some types of variable valve control systems optimize power and torque by varying valve opening times and or duration Some of these valve control systems optimize performance at low and mid range engine speeds Others focus on enhancing only high rpm power Other systems provide both of these benefits by controlling valve timing and lift There are many ways in which this can be achieved ranging from mechanical devices to hydraulic pneumatic and camless systems 11 14 Hydraulic sys tem suffer from many problems including viscosity change of the hydraulic medium due to the temperatures change the liquid tends to act like a solid at high speed and hydraulic systems must be carefully controlled which require the use of powerful computers and very precise sensors Pneumatic system utilizing pneumatics to drive the engine valves would in all probability not be feasible because of their complexity and the very large amount of energy required for compressing the air Camless system or free valve engine uses electromagnetic hydraulic or pneumatic actuators to open the poppet valves instead Common problems include high power consumption accuracy at high speed temperature sensitivity weight and packaging issues high noise high cost and unsafe operation in case of electrical problems Multiair system or Uniair is an electro hydraulic variable valve actuation technology controlling air intake without a throttle valve in petrol or diesel engines The system allows optimum intake valve opening schedules which gives full control over valve lift and timing 2 Continuous Variable Valve Timing CVVT First The CVVT system offers a unique ability to have C op yrigh t 20 13 S ciRes ENG O H M GHAZAL M S H DADO 246 independent control of the intake and exhaust valves in an internal combustion engine 15 17 For any engine load criteria the timing of intake and exhaust can be inde pendently programmed and the engine s performance could be optimized under all conditions However if valve timing could be controlled independent of crank shaft rotation then a near infinite number of valve timing scenarios could be accommodated which would dra matically improve fuel economy and emission levels of an automobile These systems are used in several automo biles with gasoline engine like Toyota Nissan Honda and others In 2010 Mitsubishi developed and started mass production of its 4N13 1 8 L DOHC I4 world s first passenger car diesel engine that features a variable valve timing system One of the high effective mechanisms proposed for controlling variable valve timing is planetary gear me chanism The planetary gearbox arrangement is an eng ineering design that offers many advantages One ad vantage is its unique combination of both compactness and outstanding power transmission efficiencies A ty pical efficiency loss in a planetary gearbox arrangement is only 3 per stage This type of efficiency ensures that a high proportion of the energy being input is transmitted through the gearbox rather than being wasted on me chanical losses inside the gearbox Another advantage of the planetary gearbox arrangement is load distribution Because the load being transmitted is shared between multiple planets torque capability is greatly increased The more planets in the system the greater load ability and the higher the torque density The planetary gearbox arrangement also creates greater stability due to the even distribution of mass and increased rotational stiffness Hence in this work we will present a new design of planetary gear drive mechanism for Continuous variable valve timing IC engine 3 The Gear Drive Mechanism Design After the text edit has been completed the paper is ready for the template Duplicate the template file by using the save as command and use the naming convention pre scribed by your journal for the name of your paper In this newly created file highlight all of the contents and import your prepared text file You are now ready to style your paper 3 1 A Description The proposed gear drive mechanism is designed by Prof M Dado from mechanical engineering department at the University of Jordan This mechanism guarantees a pre cise and continuous camshaft phasing for intake and ex haust valves in internal combustion engine The phase angle between the camshaft and crankshaft changes re lated to engine s speed which improve engine s per formance and emissions The mechanism shown in Figure 1 is a planetary gear train system consisting from an external sun gear 3 planetary gears 2 carried by two planet arms 1 and an internal ring gear 4 with external worm teeth meshing with a worm gear 5 which is connected to a stepper motor interfaced to the engine computer control system When the stepper motor shaft is stationary which is the prevailing case the ring gear is also stationary This yields a constant speed ratio between the crank shaft and the camshaft A rotation of the stepper motor shaft leads to the rotation of the ring gear resulting in additional rotation for the planetary gears and the external sun gear and the camshaft This additional rotation results in phase change between the crank shaft and the cam shaft 3 2 Mechanism Installation The mechanism is operated by planetary gear train to continuously and precisely change the phase angle be tween camshaft and crank shaft The internal ring gear has an external worm tooth so it can acts like a worm wheel It trains with the worm The mechanism is operated by planetary gear train to continuously and precisely change the phase angle between camshaft and gear The four identically planetary gears are meshing with the ring gear and the sun gear and they are carried by the two arms The mechanism Figure 2 is installed to the internal combustion engine as follows The mechanism is carried by bearing in such way that the camshaft 6 and the sun gear shaft are coaxial and then shafts are connected by the Figure 1 The components of the mechanism Cop yrigh t 20 13 S ciRes ENG O H M GHAZAL M S H DADO 247 Figure 2 The mechanism installation spline coupling 7 One of the planet arms 1 is con nected with the crank shaft 9 by chain or timing belt 8 The worm gear shaft is connected mechanically with a stepper motor The stepper motor is equipped with sensors and power supply which are connected to the CPU to control the motion of the worm gear 3 3 The Method of Operation The method of the mechanism operation is easy and sim ple and it s described below 1 When the stepper motor shaft is stationary which is the prevailing case the ring gear is also stationary The rotation of the arm by the crank shaft causes the rotation of the ring according to the equation 4 3 1 1 T T 1 1 where 3 the speed of the sun gear 3 which is also the speed of the camshaft 1 the speed of the arm 1 T 1 and T 4 are the number of teeth of the sun gear and the number of internal teeth for the ring gear respectively The relationship between the number of teeth for the sun gear planetary gears and internal ring gear is 43 2 TTT 2 2 where T 2 the number of teeth for the planetary gears 2 2 When the stepper motor have a signal from the CPU it will rotate according to the required shift angle resulting in the rotation of the worm gear 5 which will cause the rotation of the ring gear and consequently an additional rotation of the planetary gears 3 This rotation resulting in additional rotation for the sun gear which is connected with the camshaft according to the following equation 35 3 46 TT TT 5 3 where 3 the shift angle for the camshaft 5 the angle of rotation for the worm gear T 5 T 6 the number of teeth for worm gear and external teeth for the ring gear respectively 4 The arm will not be affected by this rotation because it is coupled to the crankshaft 5 The additional rotation for the sun gear which is connected to the camshaft results in phase change between camshaft and crank shaft of value 1 3 4 The Advantages of the Mechanism The main advantages of the above mechanism over other mechanisms can be summarized as follows 1 The change in the phase angle is constrained to the motion of the stepper motor which can be controlled with accuracy up to 1 8 degrees for each step with zero over shoot This value will be smaller for the camshaft de pending on the gear teeth numbers 2 The worm gear which is connected to the stepper motor and meshing with ring gear offers a self locking mechanism for ring gear That will guarantee a constant speed ratio between the camshaft and crank shaft for specific phase angle which is necessary for good engine operation 3 In this mechanism there is no limitation for phase angle changing value except the limitation imposed by the engine s performance envelop 4 Cam Phasing Optimization Maximizing Power Output In this work the optimum values for intake and exhaust valve timing have been calculated to maximize brake power These values were used to calculate and compro mise the brake power and fuel consumption for different engine s speeds and compression ratios For the purpose of analyzing the engine characteristics the dimensions were considered with Lotus Engineering Software The Lotus Engine Simulation and analysis program is an in house code developed by LOTUS ENGINEERING Company since the late 1980 s Validation of global per Cop yrigh t 20 13 S ciRes ENG O H M GHAZAL M S H DADO Cop yrigh t 20 13 S ciRes ENG 248 which means that one revolution of the arm results in 4 revolutions of the camshaft and the sun gear This re quires keeping the velocity ratio between crankshaft and the arm equals two to obtain the velocity ratio between the camshaft and the crankshaft equals two which is neces sary for four stroke IC engine operation formance parameters of power volumetric efficiency and fuel consumption has been performed on a wide range of current production engines The simulation model of 4 cylinder engine Figure 3 has been built to find out the optimum phase angle for maximum power The engine geometry data and valve timings are as shown in Table 1 Input data such as inlet pressure temperature equivalence ratio are also intro duced for all runs Also the required exit data such as the back pressure are given The calculations were carried out for the default and optimum values of valve timing which are given in Table 2 The optimization engine variable is to find the maximum brake power output The speed is varied from 1000 6000 rpm The effects of optimum valve timings values and default values on the brake power and for different compression ratio CR are illus trated in Table 3 and Figure 4 through 6 On the other hand the relationship between the stepper motor angle and camshaft angle is obtain from Equation 3 35 5 35 3 46 7 5 NN NN 6 That mean when the stepper motor and worm gear rotates 7 5 degrees the camshaft rotates one additional degree The dimensions of the mechanism can be found as fol lowing we assume that planetary gear sun gear and ring gear are helical gears with helical angle 30 and module m 1 mm and the face width f 20 mm In addition the worm teeth has lead angle 10 and axial pitch p 2 mm From these assumptions we find out that the diameter of the mechanism are not more than 150 150 50 mm so it can be installed in engine room eas ily 5 The Application of the Mechanism Example The data given in Table 2 were used to calculate the re quired values of shift angle for worm gear To illustrate the work of the above mentioned mechanism we have made the following assumptions 6 Conclusion 3256 20 20 2 45 TTTT 4 A planetary gear drive mechanism is designed and im plemented to optimize the performance of a four stroke single cylinder engine The mechanism precisely and continuously changes the phase angle between the cam shaft and crank shaft angles The effect of optimizing the phase angle at a given speed on the brake power is From Equations 1 and 2 we get 4 31 20 2 20 60 and 4 T 5 Figure 3 The simulation model of IC engine O H M GHAZAL M S H DADO 249 Table 1 Base engine geometry fuel is gasoline C 8 H 18 Type of engine 4 stroke Bore 82 mm Stroke 80 mm No of cylinders 4 Compression ratio 8 14 Inlet throat dia 26 5 mm Exhaust throat dia 22 5 mm Max valve lift 8 mm IVO angle bTDC 10 deg IVC angle aBDC 66 deg EVO angle bBDC 38 deg EVC angle bTDC 38 deg Speed 1000 6000 rpm Table 2 Optimum values of valve timing for maximum power and different speeds Valve timings Inlet valve timing Exhaust valve timing Speed rpm Open bTDC Close aBDC Open bBDC Close aTDC 1000 25 30 55 32 2000 33 37 65 39 3000 44 43 70 45 4000 49 47 70 51 5000 51 50 70 53 6000 57 60 70 57 Table 3 a Brake power for optimum and default values of valve timing for different speeds b Brake power for op timum and default values of valve timing for different speeds a CR 8 CR 10 Speed rpm Opti Def incre Opti Def incre 1000 3 73 2 78 34 4 1 2 98 37 2000 7 8 6 09 28 8 35 6 52 28 3000 11 7 9 37 25 12 56 10 05 25 4000 15 31 12 4 23 16 47 13 38 23 5000 18 56 15 2 22 20 07 16 43 22 6000 21 39 17 7 21 23 22 19 13 21 b CR 12 CR 14 Speed rpm Opti Def incre Opti Def incre 1000 4 21 3 11 35 4 3 3 24 33 2000 8 76 6 8 29 9 07 7 06 28 3000 13 1 10 5 25 13 69 10 91 25 4000 17 3 14 0 23 18 01 14 58 24 5000 21 1 17 3 22 22 02 17 97 23 6000 24 5 20 2 22 25 62 21 03 22 Figure 4 The effect of optimum valve values and default values on brake power CR 8 a b Figure 5 a The effect of optimum valve values and default values on brake power CR 10 b The effect of optimum valve values and default values on brake power CR 12 Figure 6 The effect of optimum valve values and default values on brake power CR 14 Cop yrigh t 20 13 S ciRes ENG O H M GHAZAL M S H DADO 250 appreciable The increase of the brake power ranges be tween 21 and 35 depending on the engine speed and compression ratio as indicated in Table 3 This increase is large at low engine speed and drops as the engine speed increases It could be concluded that the implementation of the proposed mechanism in four stroke engines im proves the engine performance and efficiency REFERENCES 1 S Bohac and D Assanis Effects of Exhaust Valve Tim ing on Gasoline Engine Performance and Hydrocarbon Emissions SAE Technical Paper No 2004 01 058 2004 2 T H Ma Effect of Variable Engine Valve Timing on Fuel Economy SAE Technical Paper No 880390 1988 3 C Gray A Review of Variable Engine Valve Timing SAE Technical Paper No 880386 1988 4 T Ahmad and M A Theobald A Survey of Variable Valve Actuation Technology SAE Technical Paper No 891674 1989 5 T Dresner and 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