spring is to ensure that the valve and the valve seating timely close contact, to prevent jitter valve gadget engine vibration occurs, destroying its sealability.
a valve spring between the trailing end of the tool describes a spring seat
of the valve spring of the cylinder head and the valve stem. Valve spring function is guaranteed to close with the valve seat or the valve seat when the valve close fit, and to overcome the inertia force when the valve opening of the valve means to produce, so that the drive member is always controlled by the cam without departing from each other.
Multi-valve spring made of high quality alloy steel, and heat treated to increase their fatigue strength. In order to avoid corrosion of the spring, the spring should be galvanized surface phosphide. Both end surfaces of the spring must be polished and is perpendicular to the axis of the spring, the spring in order to prevent the work generated skew.
Multi-valve spring is a cylindrical helical spring. When the valve spring is equal to or into its operating frequency an integer multiple of the natural frequency of the valve spring will increase the chances of breaking the occurrence of resonance. In order to prevent the occurrence of resonance can be variable pitch spring, most of the engine with dual spring concentrically mounted. Inner and outer opposite handedness two springs, outer spring stiffness than the springs. Double SpringNot only can prevent the resonance, the spring length can be shortened. And wherein a spring break, the other can continue to work the spring, the valve does not fall into the cylinder.
2. Design of valve spring
based sauce valve spring and the cam designs, of equal importance to the performance of the engine system. Functions to prevent the valve spring comprises a valve at an air pressure jump away from the valve seat floating load, and a control valve motion in order to avoid the separation valve mechanism. Cam valve spring design stress impact, friction and spring valve mechanism flutter. An engine valve spring is generally closed at both ends of a helical compression spring ring opening. Most engines given the stiffness of the spring, although some use variable stiffness spring. For lower speed diesel engines is concerned, the use of a single spring design requirements is usually sufficient, but sometimes requires the use of a damping spring or tape spring double spring design, to reduce the severity of the valve spring chatter. Valve spring design is a very complex task. It can serve as an example to illustrate the principles of the engine system design, twenty or reason. Firstly, the spring design method shows no link between the gauge member system parameters and design parameters. Second, the analytical method of spring design shows a design for the same problem, there are two different mathematical construction methods: one is a deterministic solution to deal with, the other is as an optimization problem to solve. Mathematically configuration optimization problem, the objective function and the constraint functions are explicit functions listed as an example. Note that, (e.g., cycle performance, the design of the cam, valve means kinetics) in other areas of the engine system design. Function for optimizing the configuration of a generally more complex implicit function. Third, the analytical method of spring design gives an example design using a graphical method to construct parametric sweep the value of the design of FIG. A typical view of these parameters can be handled Sichuan multidimensional design problems in the diesel engine system design often encountered.
In the valve spring design, known in the input data includes the following: ① maximum valve lift; ② a given length of a spring is mounted; ③ desired spring preload; the desired spring rate ④. Note that, the spring stiffness and preload of the system-level engine design parameters, need to meet the maximum allowable stress of the spring force and the cam, the exhaust valve does not jump floating, valve mechanism does not fly off requirements. There is a strong interaction between the design of the valve spring cam design. If it is difficult to find a solution on the spring design, it is necessary to modify the input data.
In the valve spring design, the following parameters are calculated output data: ① basic or separate spring design parameters (i.e., the spring average diameter of the spring coil wire diameter, the working number of coils); ② derived design parameters (consisting of e.g. a spring the gap between the free length, the maximum length of compression, compaction length, the coil, when the physical gap between the maximum compression coil spring and the natural frequency of chatter vibration order, maximum spring carrier profile, to the maximum force of the torsion spring). The basic design parameters determine the spring stiffness of the spring.
Some limited output parameter design constraints. For example, mounting length and the average diameter of the spring packed by space constraints. The maximum spring compression in the spring and the length of the compaction torsion spring fatigue life, strength, and the maximum allowable stress limit by restricted stress. Constraints on the spring chatter protection is achieved by the clearance control entity and the natural frequency of the spring. Flutter order of spring means than the operating frequency of the natural frequency of the engine the spring. In order to ensure that the spring is not running, where a strong flutter. The natural frequency of the valve spring is generally should be at least 13 times the operating frequency of the engine, i.e. desired order of the spring 13 is higher than the flutter. Spring natural frequency analysis shows that if one of the dominant spring for cam profile harmonic response is very sensitive, then the trend is definitely flutter present. In this case, it is necessary to design modified cams or springs. Variable stiffness sometimes be used to change the frequency or nested springs spring to help alleviate flutter.
spring design is a multidimensional parameter of no problem juice may be processed by a graphical way to check the sensitivity parameter trends. Valve spring setTotal optimization is to maximize the natural frequency of the spring, the spring in order to reduce vibration, while the following restrictions conditions: ① the spring preload and spring rate of the engine valve systems required; ② the maximum allowable stress of the spring; ③ appropriate entities to control the gap spring flutter.
3. Step valve spring design
did not count the valve spring is a complex system design issues. Good spring design to minimize friction and wear in the valve train. Will now be a parametric sensitivity analysis based on the configuration of the valve spring design approach design is summarized as follows:
(1) Step 1 downhill running performance of the vehicle and engine braking by analyzing, determining flying off valve mechanism speed target in order to determine the valve spring preload and spring rate required;
(2) step 2 valvetrain established kinetic model to accurately predict flying off, and the evaluation of the in-cylinder pressure recompressed Effect of fly off;
(3) step 3 by different values of the spring preload and spring rate value calculating parametric sweep, build parameters FIG valve mechanism kinetics, to examine their distribution of gas the impact of institutional vibration. In FIG we need to draw the plunger force, acceleration and the spring valve train deceleration versus crank angle, in order to display the design margins flying off, thereby enabling convenient selection step 4 and the spring preload and wisely having a desired spring rate target;
(4) step 4 based on a static force balance exhaust gate valve head, calculate the required spring preload to prevent the exhaust valve float skips. Selected spring preload of the exhaust valve with and without the engine exhaust brake, andUsed in step 3 in FIG design parameters selected spring rate matching;
(5) Step 5 design parameters for parametric sweep value calculation, using the graphical design methods designed as a spring configured parametric sensitivity Design Fig. Select the average diameter, number of coils and wire diameter of the coil springs, torsion springs while satisfying the design constraints of stress, the natural frequency, the coil gap and the like. Or optimization methods can also be solved directly analytical formula.
4. A method of breaking valve spring
Because the torsion-spring valve when working on it so that the stress distribution is not uniform circular cross-section. From an origin near the center of the edge points, gradually increasing stress, the maximum surface stress suffered. For each point on the surface, the inner surface of the stress positive maximum, and by the plane stress. For this reason, once the valve spring surface defects, i.e., defects located at the greatest possible stress concentration, leading to early fracture of the spring.