柴油机可变阀液压升降系统的设计【中文7120字】
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柴油机可变阀液压升降系统的设计【中文7120字】,柴油机,可变,液压,升降,系统,设计,中文
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Journal of Mechanical Science and Technology 29 (4) (2015) 17991807/content/1738-494xDOI 10.1007/s12206-015-0352-2Design of a variable valve hydraulic lift system for diesel engineZhilong Hu1, Yong Gui2, Min Xu1, Kangyao Deng1, Yi Cui1,* and Jiayong Dou31Key Laboratory for Power Machinery & Engineering of State Education Ministry, Shanghai Jiao Tong University, Shanghai, 200240, China2Hudong Heavy Machinery Co. Ltd., Shanghai, 200120, China3China North Engine Research Institute, Tianjin, 300405, China(Manuscript Received March 15, 2014; Revised September 22, 2014; Accepted December 28, 2014)- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -AbstractA continuous variable valve lift (VVL) mechanism for a diesel engine is proposed in this research. The hydraulic mechanism, which consists of a driving plunger, a driven plunger, a hydraulic cylinder, and a hydraulic oil tank, is the key part of the VVL mechanism. Simulation is conducted to study the relationship between maximum valve lift and rotation angle of driving plunger. Calculation results indicate that the maximum valve lift decreases with increasing rotation angle. A prototype was manufactured and successfully tested in a single-cylinder diesel engine. The experiments, which were conducted at different rotation angles of the driving plunger, validate the accuracy of the calculation results. The difference between experimental valve lift curve and cam lift curve is considered the result of oil leakage. Rotating the driving plunger is an effective method to regulate valve lift. Working stability of the VVL mechanism is validated through a multi-cycle operation. Experimental results indicate that the VVL mechanism is effective and reliable for realizing continuous VVL in engines.Keywords: Diesel engine; Hydraulic mechanism; Throttle-less; Variable valve lift- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -1. IntroductionThe problems of energy shortage and pollution control along with increasingly stringent emission regulations have led to the development of variable valve technology to de- crease fuel consumption and engine emissions. Several origi- nal equipment manufacturer companies have considered ap- plying variable valve actuation (VVA) mechanisms in their new generation vehicles 1, 2.The present valve control system consists of two parts, namely, the variable valve timing (VVT) mechanism and the variable valve lift (VVL) mechanism. Torque curve, brake power curve, and indicator power curve can be improved by controlling valve timing 3-5. The throttle valve of gasoline engine can be removed by introducing a VVT system, which decreases pumping loss significantly. Considerable research indicates that fuel consumption of engines under a light or a moderate load can be decreased by 10%-15% 6, 7. In addi- tion, VVT can be used to control the maximum temperature in the cylinder and the amount of residuals, which are both use- ful for decreasing engine emissions 8, 9.VVL also plays an important role in engine performance 10, 11. Combining VVL and exhaust turbo-charging offers a*Corresponding author. Tel.: +86 21 34206861, Fax.: +86 21 34206589 E-mail address: ycui Recommended by Associate Editor Kyoung Doug Min KSME & Springer 2015considerable potential to improve both low-end torque and maximum engine power. For diesel engines, a small valve lift at a low engine speed increases the negative pressure in cylin- der and intake eddy, which are both beneficial for improving fuel-air mixing and fuel economy and increasing torque in low speed. A large valve lift in high engine speed increases the charging efficiency, which is beneficial for improving power performance of engines at high speed. In addition, if a multi- cylinder engine is operated at low load, then the valve lift of a few cylinders could be reduced to zero to realize cylinder de- activation technology. This approach effectively decreases fuel consumption.Therefore, variable valve technology is desirable with the development of engine technology. Numerous valve control systems have been proposed, and a few of these systems have been demonstrated in engines 12-15. Variable valve tech- nology has a few disadvantages, including complicated struc- tures, complex control process, and need for extra energy. These shortcomings restrict the application of variable valve technology in engineering.A simple and effective VVL mechanism is proposed in this research. A prototype was manufactured and successfully tested in a single diesel engine. The VVL mechanism has no complicated structures, and only minor changes are made in the existing engine to realize continuous VVL. This paper describes the continuing development progress of the VVL lift1800 Z. Hu et al. / Journal of Mechanical Science and Technology 29 (4) (2015) 17991807(a) VVL mechanism(a) In the oil drain process(b) In the beginning of valve opening Fig. 2. Profile chart of hydraulic mechanism.(b) Hydraulic actuator Fig. 1. Structure of the VVL mechanism.mechanism. The design features and operation of the mecha- nism are explained. The effectiveness and reliability of the VVL mechanism were verified through an experiment on the single diesel engine.2. Description of the VVL mechanismThe structure of the VVL mechanism is shown in Fig. 1. The driving mechanism of the valve is essentially similar to that of a customary engine with valves and cams. However, the present system has a hydraulic mechanism, which is the key part for controlling valve lift.The hydraulic mechanism mainly consists of a driving plunger connected to the rocker arm, a driven plunger con- nected to a valve, a hydraulic cylinder filled with hydraulic oil, and a small hydraulic oil tank that affords hydraulic oil that is necessary in the oil return process and conserves oil drained from the hydraulic cylinder in the oil drain process Fig. 1(b).Two holes are present in the middle position of the hydrau-lic cylinder, which is symmetric about the axis of the hydrau- lic cylinder. The two holes are defined as drain holes and are connected to the hydraulic oil tank by an oil pipe.Two oblique sections exist at the bottom of the driving plunger, which is also symmetric about the axis of hydraulic cylinder.Both driving plunger and driven plunger are assembled in the hydraulic mechanism (Fig. 2).In the beginning of the valve opening process, the rocker arm pushes the driving plunger to move downward. Hydraulic oil is discharged from drain holes until the drain holes are sealed by the driving plunger completely. Then, cylinder in- ternal hydraulic pressure rises rapidly, and the valves are pushed open by the high pressure of residual hydraulic oil in the cylinder. Given that hydraulic oil is incompressible, resid- ual hydraulic oil could be considered a connector that transfers force applied by driving plunger. The maximum valve lift is controlled by the amount of oil that is leaked from the hydrau- lic cylinder. The amount of leaked oil is determined by the location of the driving plunger at the time drain holes are sealed completely.Revolving the driving plunger is a simple method of chang-Z. Hu et al. / Journal of Mechanical Science and Technology 29 (4) (2015) 17991807 1801y z - d - a(a) 0(c) 20(b) 10(d) 30Fig. 4. Description of curves A and B.The origin of coordinate is defined as the intersection point of the axis and bottom cross section of the driving plunger.X axis is parallel with the axis of drain holes.Z axis is parallel with the axis of the driving plunger. Y axis is defined according to the right-hand rule.Curves A and B meet at a point when drain holes are sealed completely by the driving plunger (Fig. 3). Therefore, whether the drain holes are sealed completely can be determined by the cross point number of curves A and B. If curves A and B have a unique cross point, then the drain holes are sealed com- pletely.As assumed, if the driving plunger is revolved around the axis bydegrees, then moving the curve B by a mm to allow only a unique cross point between curves A and B (or drain holes remain sealed completely) is necessary.Fig. 3. Profile chart of hydraulic mechanism at different rotation angles of driving plunger.ing the relative location between the driving plunger and the hydraulic cylinder at the time drain holes are sealed com- pletely (Fig. 3). Therefore, the maximum valve lift is con-The problem of solving the maximum valve lift at different angles is changed to the problem of solving the intersection point of curves A and B.Equations of working curve A at different rotation angles are expressed as Eqs. (1) and (2):trolled by the rotation angle of driving plunger around the axis of the driving plunger. is defined as the rotation angle of the driving plunger around the axis. The rotation angle of thex2 y2 ( D )22cos y - sin x - (D - f ) / 2 z - d 0 .(1)(2)driving plunger at the position of Fig. 3(a) is 0. h 23. Research on motion regularity of valve3.1 Calculation research on the change rule of maximum valve liftEquations of working curve B at different displacement aare expressed as Eqs. (3) and (4):Definition of working curve (Fig. 4):Working curve A is defined as the intersection curve of the oblique section and the outer cylindrical surface of the drivingx2 y2 ( D)2222 ( d )2(3)(4)plunger.Working curve B is defined as the intersection curve of the inner cylindrical surface of the drain hole and the inner cylin- drical surface of the hydraulic cylinder.Definition of coordinate system (Fig. 4): 2 2where D and D are the external diameter of the driving plunger and internal diameter of the hydraulic cylinder, re- spectively; d is the internal diameter of the drain hole; f is the1802 Z. Hu et al. / Journal of Mechanical Science and Technology 29 (4) (2015) 17991807Table 1. Geometric parameters of hydraulic mechanism.Parameters Program dataMaximum cam lift ( Lm ax ) 8.927 mmExternal diameter of driving plunger ( D ) 9 mmInternal diameter of hydraulic cylinder ( D ) 9 mmInternal diameter of drain hole ( d ) 3 mmMinimum distance of two oblique sections ( f ) 3 mmHeight of oblique section ( h ) 8 mmPressure of hydraulic oil 1 barHydraulic oil Lubricating oilFig. 5. Definition of geometric parameters.minimum distance of two oblique sections, and h is the height of the oblique section. The external diameter of the driving plunger D and internal diameter of hydraulic cylinder D are assumed to be equal. All the parameters are defined in Fig. 5, and the specifications are shown in Table 1.The maximum valve lift ( Lmax ) is equal to the difference between the initial maximum valve lift ( Lm ax ) and value of a.Fig. 6. Cam profile of a single diesel engine.Fig. 7. Calculation results on a and maximum valve lift.the shape of working curve A can be used to regulate the change characteristic of maximum valve lift with rotation angle. Thus, regulating the curve of maximum valve lift is the best for different engines.The calculation results indicate that rotating the driving plunger is an effective method of regulating valve lift. In addi- tion, this plunger can realize continuous variation of maxi- mum valve lift.3.2 Experimental validation of the VVL mechanismLmax Lm ax - a (5) A prototype was built and tested in a single-cylinder diesel engine to verify the principle of the VVL mechanism. Thewhere Lm ax is defined as the initial maximum valve lift at highest speed of the diesel engine is 1500 r/min. The assembly 0 , which is equal to the maximum cam lift. The cam pro-file of a single diesel engine is shown in Fig. 6.The calculation results on a and maximum valve lift at dif- ferent rotation angles of the driving plunger are shown in Fig.7. The value of a increases with increasing rotation angle .By contrast, the maximum valve lift decreases with increasing rotation angle . If the driving plunger is rotated from 0 to 90, the maximum valve lift decreases from a maximum value of 8.927 mm to a minimum value of 0.927 mm. The change rate of maximum valve lift increases with increasing rotation angle because of the shape of the working curve A. Therefore,of the VVL mechanism is shown in Fig. 8 and has been de- scribed in detail in the previous sections. The VVL system was mounted in a single diesel engine and driven by the cam of the diesel engine. The valve motion was measured by using a displacement sensor. To rotate the driving plunger easily, a rotating control part is designed at the top of the driving plunger (Fig. 8). The rotation degree of the driving plunger is controlled by revolving the rotating control part. In the ex- periment, the driving plunger is rotated manually. A driving mechanism could be mounted to rotate the driving plunger if necessary.Z. Hu et al. / Journal of Mechanical Science and Technology 29 (4) (2015) 17991807 180310864200 20 40 60 80 100Rotation Angle(j) /deg(a) Assembly drawing of the VVL system(b) Drawing of the VVL system(c) Hydraulic mechanism Fig. 8. Experimental VVL system apparatus.To validate the accuracy of the calculation results on the changing rule of maximum valve lift, an experiment was con- ducted at four different rotation angles of the driving plunger ( = 0, 30, 50, 65) and a constant engine speed of 800 rpm. Fig. 9 shows a comparison of the calculation and experiment results on maximum valve lift. From this figure, the experimental maximum valve lift decreases with increas- ing rotation angle. This result is consistent with the calculation results. However, a difference is observed between the ex- perimental and calculation results. This difference is probablyFig. 9. Comparison of calculation and experiment results on maximum valve lift.due to the leakage of hydraulic oil from gaps, such as the gap between the outer wall of the driving plunger and the inner wall of the hydraulic cylinder. Notably, when drain holes are sealed by the driving plunger completely, hydraulic oil is still drained from the gaps, which decreases the available lift of the valve. However, such a small decrease in the available valve lift is acceptable.Fig. 10 shows the test results of valve motion at different ro- tation angles of the driving plunger (= 0, 30, 50) and constant engine speed (n = 800 r/min). All shapes of the valve lift curves are similar to those of conventional valve trains, which suggests that good performance can be expected in different rotation angle operations Fig. 10(a). Figs. 10(b) and(c) show the valve velocity and acceleration at different rota- tion angles of the driving plunger, respectively.Fig. 11 shows a comparison of cam lift curve and valve lift curve at a rotation angle of = 0 degree and engine speed of 800 r/min. This figure shows a small delay in the phase of the experimental valve lift curve and a decrease in the maximum valve lift. The change rule of experimental curve of valve lift is consistent with cam lift curve. The difference between ex- perimental valve lift curve and cam lift curve is defined as lift loss, which is considered the result of oil leakage. The maxi- mum lift loss is approximately 0.795 mm. The leakage prob- lem can be solved by improving the precision of hydraulic system components. The reason for the phase of experimental valve lift curve delays compared with cam lift curve will be discussed in the following analysis on the effect of engine speed on valve lift curve.3.3 Analysis on working stability of the VVL mechanismValve lift curves of multi-cycles are analyzed to validate the working stability of the VVL mechanism. Fig. 12 shows the valve lift curves of ten cycles at different rotation angles of the driving plunger ( 0 , 30, 50) and constant engine speed (800 r/min). This figure shows that all the shapes of the valve lift curves for different rotation angles are consistent with the valve lift curve of the single cycle introduced in the previous analysis. A small variation is observed between the maximumcalculation experimentMaximumValveLift (mm)1804 Z. Hu et al. / Journal of Mechanical Science and Technology 29 (4) (2015) 179918078.204 mm7.087 mm5.23 mmn=800r/min0 degree 30 degree 50 degreen=800r/min0 degree30 degree50 degreeValve Lift (mm)Valve Lift /mm10886 64 42200 50 100 150 200Cam Angle(deg)00 1000 2000 3000 4000 5000 6000 7000C rank A ngle (C A ) A TD C(a) Rotation angle 0(a) Valve lift at different rotation angles of driving plunger80. 30. 2 60. 1 40. 0 2- 0. 1 0- 0. 2- 0. 30 20 40 60 80 100 120 140 160 180Cam angle(deg)0 1000 2000 3000 4000 5000 6000 7000C rank A ngle (C A ) A TD C(b) Rotation angle 30(b) Valve velocity at different rotation angles of driving plunger 60. 01540. 0100. 00520. 0000- 0. 005- 0. 010- 0. 0150 20 40 60 80 100 120 140 160 180Cam angle (deg)0 1000 2000 3000 4000 5000 6000 7000Crank Angle (CA ) ATDC(c) Rotation angle 50Fig. 12. Valve lift curve of multi-cycles at different rotation angles of(c) Valve acceleration at different rotation angles of driving plungerFig. 10. Valve lift, velocity, and acceleration curves at different rota- tion angles of driving plunger.10864200 50 100 150 200Cam Angle(deg)Fig. 11. Comparison of cam lift curve and valve lift curve.driving plunger and constant e
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