JPH0210292B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an engine valve spring used, for example, in an engine of an automobile or the like. [Prior Art] Valve springs for engines tend to be used at high vibration frequencies depending on the engine speed, and the stress amplitude generated in the valve springs when the cam is driven is also quite large. Conventionally, valve springs are generally used which are coiled from a material having a longitudinally uniform cross-sectional shape.
Also, recently, in order to reduce the height of the spring,
Valve springs with a so-called oval cross section have also been seen. However, the stress waveform of a coil spring that is repeatedly compressed in a high frequency range, such as an engine valve spring, exhibits a rather special behavior compared to a general coil spring (for example, a coil spring for vehicle suspension). The curve shown in Figure 7 shows the change in stress when the cam is driven by engine rotation, whereas the curve shows the change in stress that occurs when a displacement equivalent to the valve lift is statically applied to the valve spring. It represents.
Here, τ ₀ is the static stress amplitude between the installed state of the valve spring and when the valve is opened, τ _c is the maximum stress amplitude in the stress waveform when driving the cam, and τ _s is the stress amplitude of the surge wave immediately after the valve is closed. shall be. Further, the values obtained by dividing the above τ _c and τ _s by τ ₀ are set as α _c and α _s , respectively. These α _c and α _s values increase as the engine speed increases, especially when the valve spring is surging. FIG. 8 shows strain gauges attached to four locations in the axial direction of the valve spring to measure changes in dynamic stress in the valve spring when the cam is driven. In the figure, changes in dynamic stress at each part are organized by the ratios α _c and α _s of dynamic stress amplitude to static stress amplitude. As can be seen from the figure, the rate of increase in α _c and α _s is not constant in the winding direction (axial direction) of the coil, and the rate of increase is low at the center of the spring (second winding), and increases toward the end of the winding. The rate of increase in α _c and α _s is high. FIG. 9 shows stress waveforms measured at the four positions of the valve spring when the engine speed was 5000 rpm. From the figure, it can be seen that the stress amplitude is small in the center of the spring, and that the change in stress amplitude becomes more severe as it approaches the winding ends. [Problems to be Solved by the Invention] In recent years, as engines have become more powerful and rotated at higher speeds, there has been a strong desire to reduce the weight of valve train systems. Among valve train parts, valve springs have a large influence, but
With current valve springs, it is difficult to further reduce weight and contact length, and it is also impossible to reduce stress during surging. However, as mentioned above, in engine valve springs used at relatively high frequencies, there are two types of stress amplitude: the dynamic stress amplitude that appears when the cam is driven, and the static stress that appears when a displacement equivalent to the valve lift is applied statically. There is a large difference between the actual stress amplitude and the actual stress amplitude. That is, in the current valve spring, when the valve spring is actually used in a cam-driven state, the stress amplitude at the center portion of the spring is smaller than that at the end portions, so there is a margin for durability.
In other words, the durability is not uniform in the axial direction of the spring, and it cannot be said that the material is used effectively enough in the center of the spring. [Means for Solving the Problems] The present invention is directed to valve springs, which are coil springs that are used under severe dynamic stress amplitude. This was based on the discovery that the stress amplitude in the middle part of the longitudinal direction is small. Therefore, the gist of the present invention is to determine the required wire diameter D based on the static stress when a load is applied to this valve spring in a range extending from the end of the effective part of the spring wire to at least 0.75 turns. In addition to providing standard diameter portions at both ends, a central small diameter portion having a wire diameter d smaller than the wire diameter D of the standard diameter portions at both ends is provided in the longitudinally intermediate portion of the wire. Wire diameter d
The ratio (d/D) of the wire diameter D of the standard diameter portion at both ends is
0.80 to 0.96, and the wire diameter is gradually decreased from the standard diameter portions at both ends to the small diameter portion at the center. Furthermore, the wire diameter of valve springs used in automobile engines is usually 5.0 mm or less, and they are always used to the maximum amplitude, so the stress conditions are lower than that of suspension springs, etc., which are used with a mixture of large and small amplitudes. strict.
The present invention provides a coil spring having a shape suitable for a valve spring used under such severe conditions. [Function] In the valve spring of the present invention, the diameter of the strands becomes thinner toward the central small diameter portion of the spring. The stress in the center small diameter part is statically higher than that of conventional springs, but in actual use as the engine rotates (when driven by a cam), the stress amplitude in the center of the spring is small, so the durability under actual use is low. The durability is uniform in the axial direction of the coil, and it can demonstrate the same durability as current products. Furthermore, for spring specifications with the same spring constant, etc., the product of the present invention can reduce the effective number of turns compared to conventional valve springs, making it possible to reduce weight and shorten the contact length. Furthermore, the reduced contact length has the effect of reducing the weight of the engine's valve train and other parts, thereby increasing the engine speed limit. Additionally, the natural frequency is increased compared to conventional valve springs. That is, when driven by a cam, the dynamic stress generated in the valve spring becomes particularly high during surging, but surging of the valve spring occurs when the harmonic frequency of the cam lift matches the natural frequency of the valve spring. In general, the amplitude of the harmonics of the cam lift decreases as the order of the harmonics increases, so an increase in the natural frequency of the valve spring will cause surging to occur on the side of higher harmonics with smaller amplitudes. This is advantageous in reducing stress increase. [Example] Fig. 1 shows a valve spring 1 of equal pitch. This valve spring 1 is made by coiling a spring wire 2 having a circular cross section as illustrated in FIG. In this embodiment, the inner diameter of the coil is constant. In addition, in FIG. 2, the wire diameter is drawn thicker than the actual length compared to the length of the strand 2 for easy understanding. The strand 2 has a central small diameter portion 3 having the smallest strand diameter at its longitudinal center portion. Both end portions 4 and 5 of the wire 2 have wire diameters larger than the central small diameter portion 3 by a predetermined length l ₁ . These both ends 4,
5 are each of equal diameter over a length l ₁ . The wire diameters of both end portions 4 and 5 may be the same as that of a conventional valve spring having a spring constant equivalent to that of the product of this embodiment (see Table 1 below). That is, the wire diameter D of both ends 4 and 5
is set to a necessary wire diameter value based on the static stress when a load is applied to the valve spring 1, as in the conventional case. Therefore, in this specification, both ends 4 and 5 of the wire diameter D are also referred to as both end standard diameter parts. Above central small diameter part 3 and both ends (standard diameter part) 4, 5
There are tapered portions 7 and 8 in which the wire diameters gradually decrease toward the central small diameter portion 3. Although the tapered portions 7 and 8 of this embodiment have a linear taper shape in which the wire diameter changes uniformly, any other taper shape may be used. Note that the absolute value of the stress generated in the valve spring 1 reaches its maximum value around the 0.75th turn from the end of the effective part of the spring, so the wire diameter for about one turn from the end of the effective part may be the same as that of the end (l ₁ = end winding of the terminal + approximately one winding of the effective part). Further, the ratio of the maximum material diameter D to the minimum material diameter d is suitably d/D=0.80 to 0.96. According to research conducted by the present inventors, when d/D is smaller than 0.80, static stress in the small diameter portion 3 becomes too high, causing problems such as fatigue and durability. Furthermore, if it exceeds 0.96, the intended purpose of the present invention cannot be achieved. The valve spring 1 having the above structure is attached to the valve 10 of an engine via a retainer 11 as shown in FIG. 3, for example, and is driven by a rocker arm 13 as the cam 12 rotates. Table 1 below shows the specifications of the product of this example, which has the same spring constant, coil inner diameter, and load when installed and when opening the valve as the conventional (current) valve spring. The inner diameter of both coils is 25.2mm. (In the same table, τmax
is the maximum stress, τ is the average stress, and τa is the stress amplitude) In the valve spring 1 of this embodiment, the wire diameter d of the central small diameter portion 3 is smaller than the wire diameter of the current spring. If left as is, the spring constant will drop. Therefore, in this embodiment, the effective number of turns is reduced in order to keep the spring constant constant, and as a result, the contact length can be shortened.

【table】

〔Effect of the invention〕

According to the present invention, it is possible to reduce the weight, shorten the contact length, and increase the natural frequency while maintaining the same durability as conventional valve springs.

[Brief explanation of drawings]

Fig. 1 is a side view of a valve spring showing an embodiment of the present invention, Fig. 2 is a developed view of the strands of the valve spring shown in Fig. 1, and Fig. 3 is a part of an engine showing an example of how the valve spring is used. 4 is a side view of a valve spring showing another embodiment of the present invention, FIG. 5 is a developed view of the strands of the valve spring of FIG. 4, and FIG. It is a development view of the wire of the valve spring showing an example. Fig. 7 is a diagram comparing the static stress amplitude and dynamic stress amplitude of the valve spring, and Fig. 8 is a diagram showing the relationship between the dynamic stress amplitude ratios α _c and α _s of the valve spring and the engine rotation speed. FIG. 9 is a diagram of stress waveforms measured at four locations on the valve spring. DESCRIPTION OF SYMBOLS 1... Valve spring, 2... Spring wire, 3... Central small diameter part, 4, 5... End part, 7, 8... Taper part, 1
0... Valve.

Claims (1)

[Claims] 1. An engine valve spring made by coiling a spring wire, which is based on the static stress when a load is applied to the valve spring in a range of at least 0.75 turns from the end of the effective part of the wire. In addition, a standard diameter section at both ends with the required diameter D of the strand is provided, and a central small diameter section having a strand diameter d smaller than the strand diameter D of the standard diameter section at both ends is provided in the longitudinally intermediate portion of this strand. A section is provided, and the wire diameter d of this central small diameter section is
The ratio (d/D) of the wire diameter D of the standard diameter portion at both ends is
A valve spring for an engine, characterized in that the diameter of the strands is 0.80 to 0.96 and gradually decreases from standard diameter portions at both ends toward a small diameter portion at the center.