Application study of new algorithm for valve piston extreme gap analysis

Liu Fang, The fields enter the garden, Tao Lifang, Liu Jianhua

Pick want:Based on the motion rules of valves and pistons and the assembly error of manufacturing, a new algorithm for ultimate motion gap between valves and pistons was constructed, and theExcelsoftware, Valve piston clearance analysis program was prepared。Taking a gasoline engine as an example, a calculation and analysis were carried out. The analysis results show that the dimensional tolerance of the parts is、Manufacturing assembly errors and other factors have a great impact on the results。

Keywords:Valve; piston; clearance; calculation method

lead Word

Valves and pistons are important components to achieve engine performance. The combination of the valve opening and the reciprocating movement of the piston achieves the performance of the engine^[1]. When the engine is working, both the valve and the piston move in accordance with certain rules. When the piston moves upward from the bottom dead center and reaches the top dead center, if the valve is still in a large open state, the valve will hit the piston.^[2]，Causes valve breakage^[3], In order to make the valve and the piston move smoothly, there must be sufficient clearance between the piston and the valve.

The traditional analysis method of valve piston gap includes using formulas to solve the problem.CAESoftware analysis. Grey Yongyin^[4]And Chen Wenbi^[5]By constructing a mathematical model of engine valve piston gap calculation, the smaller distance between the valve and the piston is obtained by solving the simplified equation. This mathematical model solution process is complex and cumbersome, including a large amount of mathematical theoretical knowledge, making this analysis method difficult to generalize. Shi Yuchun et al.^[6]Through mathematical modeling,4G15VThe valve piston of the model diesel engine has a small motion gap, and explains that the errors between theory and actual situations come from the manufacturing tolerances of the cam, thermal deformation of parts, etc.

along withCAEThe wide application of analysis software, the above problems have been solved well and the results have been significant.^[7-11]. Wang Dongyu et al.[7]useAdamsThe software built a model of the entire crankshaft system, timing system and air distribution system, and applied the gap analysis function in the software to obtain a smaller motion gap between the piston and the valve. However, the pre-processing of this method often takes up a lot of time, resulting in design engineers being unable to analyze and optimize the design scheme in a timely and efficient manner; in addition, with the division of enterprise functions, many designers do not have the experience of simulation calculations, design andCAEData exchange between them greatly reduces work efficiency.

In view of the above shortcomings, this paper corrects the method of calculating the ultimate motion gap of the valve piston, and adds factors such as dimensional tolerance, processing and assembly error; and is based onExcelWith powerful computing functions, the valve piston clearance analysis and calculation program is designed with a good user interface, simple operation and powerful function, and realizes analysis automation. The designer only needs to check the input data to obtain the calculation and analysis results, which not only reduces the designer's requirements for simulation capabilities, but also greatly shortens the design cycle.

1 Construction of analysis method

The main factors affecting valve piston clearance^[12]There are: valve lift and valve inclination, piston motion equation, related parts size, limit tolerance and thermal deformation, cam manufacturing tolerance, assembly tolerance of transmission chain and transmission error.

1.1 Establishment of mathematical models

1) According to the picture1, the piston motion equation can be established asx=f（φ),inφIt is the crankshaft angle. Assuming that the piston starts to move from the top dead center, the crank radius isR, the connecting rod length isL, obtain the piston's motion equation^[13]：

（1）

2) Valve lifth=g（φ）。

3) When the valve is closed, the nominal distance between the valve top and the piston avoidance pitHl , including cylinder gasket thickness, valve pit depth, and distance from the upper surface of the piston to the surface of the cylinder.

4) Dimensional tolerances and thermal deformation of each associated moving partsDl。

5) Total tolerance for manufacturing assembly transfer phaseA, the manufacturing error of the cam and the assembly error of the camshaft and the crankshaft will be reflected in the front or rear hysteresis of the valve phase.

6) Valve phase adjustment angled, when the phase is pre-hysteresis, take a positive value, and when the phase is post-hysteresis, take a negative value.

Valve and piston clearance:

（2）

Where:bIt is the valve inclination angle; when calculating the gap between the intake valve and the pistonATake the right plan When calculating the gap between exhaust valve and pistonATake negative.

1.2 ExcelImplementation

existExcelIn this paper, different types of input parameters are classified, and the valve piston gap calculation formula is solved through powerful calculation functions;ExcelDrawing function, displays the calculated results, obtains various data on valve lift and small valve piston clearanceMin.c, as shown in the picture2Shown.

Using an analysis program can omit modeling time and reduce the analyst's requirements for simulation analysis and computing capabilities. In the early stage of product development, design engineers only need to collect relevant input data and input it into the program to obtain the required results, so that they can devote their main energy to solution optimization^[14]。

2 Computation example

2.1 Known conditions

1) A two-cylinder four-stroke gasoline engine with a stroke of34.5 mm, connecting rod length43 mm；2) Valve lift is shown in the figure3；3) The piston is at the top dead center (TDC) When the top surface of the cylinder body to the top surface of the piston is2 mm；4) The thickness of the cylinder gasket is0.75 mm, the valve pit is deep0 mm；5) The distance between the lower point of the valve closing moment and the bottom of the cylinder head1 mm；6) The total dimensional tolerance of each associated moving parts is0.821 mm；7) The total deviation of manufacturing and assembly phase is controlled in4.5°Inside the crankshaft angle.

2.2 Calculation results and analysis

In calculation analysis control, set the size+The analysis and calculation of phase tolerances take into account the impact of dimensional tolerances and phase tolerances of manufacturing and assembly transmissions on valve piston clearance. picture4Give the valve-The motion relationship diagram of the piston and the motion clearance diagram of the valve piston.

picture5Given a smaller valve piston clearance value, it can be seen that after the valve reaches the upper dead point5.75°Cam angle (camdeg) When the valve piston gap is smaller, the valve piston clearance is1.48 mm, meet design requirements.

In many previous research on valve piston clearance, the influence of dimensional tolerance and phase tolerance of manufacturing and assembly transmission has been ignored. In fact, according to the dimension chain tolerance theory^[15]It can be seen that the dimensional tolerance of the system and the phase tolerance of the manufacturing and assembly transmission will inevitably affect the original valve piston movement trajectory, thereby affecting the valve piston movement clearance. The impact of different parameters on smaller valve piston gaps is now explained based on the calculation results.

Figure 6 Calculation results without parameters

picture6The calculation results of different parameters are given, and the impact of different parameters on smaller valve piston gap can be obtained. From the figure, we can see that when the influence of dimensional tolerance and phase tolerance is not taken into account, the nominal value is obtained.Min.c = 2.67 mm, this calculation result is the theoretical result obtained by the current traditional calculation method. Considering the impact of dimensional tolerances separately, we can obtainMin.c = 1.85 mm; Consider phase tolerance separately to obtainMin.c = 2.30 mm; Taking into account the influence of all parameters, we can obtainMin.C=1.48mm。

From the picture6middle4Comparison of the results shows that the influence of dimensional tolerance is (2.67-1.85）=0.82 mm, the influence value of phase tolerance is (2.67-2.30）= 0.37 mm, the influence value of the total tolerance is (0.82+0.37）=1.19 mm. It can be seen that the dimensions and phase tolerances have significant impact on the valve piston gap and cannot be ignored.

Figure 7 Calculation results under different nominal distances

picture7The calculation results under different nominal distances are given, and it can be seen that the nominal distance is3.75 mmReduced to2.1 mmWhen nominal valueMin.c = 1.02 mm. According to the value recommended by the design company, the nominal value of smaller valve piston gap is1 mm, from the calculation results, it can be seen that when the size and phase tolerance are taken into account, the smaller valve piston gap value is-0.17 mm, it can be seen that under this working condition, the valve will hit the piston.

3 in conclusion

1) By analyzing the influencing factors of valve piston gap, a calculation valve is proposed-The new algorithm for piston gap, considering the tolerances of related parts, the manufacturing tolerances of cam and the crankshaft-Factors such as cam assembly transmission errors make this calculation method faster.

2)useExcelWith powerful calculation and drawing functions, the valve piston clearance calculation and analysis program is designed, which can greatly improve working efficiency.

3) Through the calculation and analysis of a certain engine, the program intuitively shows the dimensional tolerance and phase tolerance factors for smaller valves.-The impact contribution value of piston gap provides a theoretical basis for designers to conduct data analysis and optimization solutions.

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