JPS6136724Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an engine valve mechanism, particularly to a combination of a cam and a tappet.

Basically, as shown in Fig. 1, the tappet T slides while being supported by the cylinder body B by the rotation of the cam 12 of the camshaft C, and the lifting height of the cam 12 is adjusted via the push rod P and the rocker arm R to the intake and exhaust valves V. When the camshaft C rotates, the tappet T that follows the cam 12 slips between it and the cam 12, and this slip causes wear on the contact surface between the two. . If the cam 12 and the tappet T constantly come into contact with each other at the same location, the wear described above will be further accelerated. Therefore, as is well known, lubricating oil is supplied to the contact surface between the cam C and the lower surface of the tappet T so that an oil film is constantly formed between the cam C and the tappet while the cam C is rotating, thereby reducing wear. If the tappet T is only allowed to slide in its axial direction, there will always be a point where the relative sliding speed with the cam becomes zero, the oil film will be cut, and metals will come into contact with each other, which will likely accelerate wear. .

As a countermeasure to this problem, as shown in Fig. 2, the tappet
There is one in which the axis a of T ₁ and the axis b of the cam 12' are eccentric, and the tappet T ₁ is forcibly rotated by the rotation of the camshaft. In addition, in order to promote the above-mentioned rotation, the contact surface 1'' of the tappet _T1 with the cam 12'' as shown in FIG. 3 is made spherical, and the cam 12'' is formed with a taper α. be.

However, even in the structure shown in FIGS. 2 and 3 above, the lower surface 1' of the tappet and the cam 1
2' or the bottom surface of the tappet 1'' and the cam 12'' are in very short lines or points, so stress is concentrated there, reducing the wear resistance of the bottom surface of the tappet and the cam. Additionally, there was a risk of abnormal wear occurring.

In order to prevent this stress concentration, it is possible to reduce the contact surface pressure between the cam and the tappet.
As shown in Figures 1 and 5, a structure in which the entire lower surface of the tappet is concave in the direction perpendicular to the camshaft has been proposed, but in this case, the rotation of the tappet _T2 is not allowed and is restricted by a detent. Therefore, as mentioned above, there is always a point between the tappet _T2 and the cam K where the relative sliding speed becomes zero, making it impossible to form an oil film and promoting wear. Also, as the rotational speed of the camshaft increases, the cam K and tappet T ₂
Due to the unexpected movement of the cam K, the edge portion E on the lower surface of the tappet and the cam K may cause "galling", resulting in damage to the valve mechanism.

Similar to the cam and tappet combination shown in Figures 4 and 5 above, a rotating jig is installed on the contact surface of the cam and tappet parallel to the cam shaft, as in, for example, Utility Model Application No. 51-52111. A cam tappet mechanism in which a needle bearing held in the cam 11 is interposed is known, but since a large number of needle bearings are held in the rotating jig and interposed between the tappet and the cam 11, it is large and has multiple needle bearings. Not only can it not be used in relatively small engines such as automobile engines, but the rotating jig cannot rotate around the tappet axis, and the cam has an end face that is perpendicular to its axis, so the high-speed rotation of the engine is impossible. Unexpected movement of the cam, tappet, and rotating jig may damage the needle bearing, which in turn may damage the cam, tappet, rotating jig, etc.

The present invention was devised in view of the above-mentioned points, and includes forming a spherical concave surface in the center of the convex spherical lower surface of the tappet, making the egg-shaped cam eccentric to the axis of the tappet, and forming a surface on the spherical concave surface. The gist is that they are arranged so that they are in contact with each other.

To explain this in detail with reference to FIGS. 6 and 7, 2 is a tapepet of the present invention with a convex spherical lower surface 3 having a gentle spherical concave surface 3a in the center, and furthermore,
E ₁ is a curved surface with a relatively small radius. Reference numeral 4 designates an egg-shaped cam which, at maximum lifting height, takes the form of an egg that stands in contact with the spherical concave surface 3a of the tappet 2 with its pointed end facing upward, with both sides cut out in the direction of the axial center of the cam shaft. The center 4A is eccentric to the axis 2A of the tappet 2.

Further, in this example, the spherical concave surface 3a is a gentle concave surface so that it can come into surface contact with a curved surface portion (cam flank portion) formed by the maximum radius R of the side portion of the oval cam 4.

In the valve train constructed as described above, the egg-shaped cam 4
During the lifting height of the cam 4 and the tappet 2, the spherical concave surface 3a provided at the center of the lower surface 3 of the tappet 2, the side surface and the pointed convex surface of the oval cam 4 are always in surface contact with each other. At this time, the axis 2A of the tappet 2 and the axis 4 of the egg-shaped cam 4
Since A is made eccentric, the axis 2A is on tapepet 2.
The surrounding forces act to rotate the tapepet 2.

As described above, the present invention forms a spherical concave surface in the center of the convex spherical lower surface of the tapepet, and also makes the egg-shaped cam eccentric to the axis of the tapepet.
In addition, since the tappet is arranged so as to be in surface contact with the spherical concave surface, the lower surface of the tappet and the oval cam are brought into surface contact, thereby dispersing the stress to a specific location as described above, and improving the wear resistance of the tappet and the cam. In addition, by forming the lower surface of the tappet with a spherical concave surface in the center of the convex spherical surface, the cam and tappet can be prevented from galling, and the oval cam can be aligned with the axis of the tappet. By making the tappet eccentric, the oil film can be maintained even at the point where the relative sliding speed is zero by rotating the tappet around its axis, which has the effect of reducing wear.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the structure of a conventional valve train, Figs. 2 and 3 are schematic diagrams showing the structure of a conventional cam and tappet, respectively, and Fig. 4 is a schematic diagram showing the structure of a conventional cam and tappet. A partial sectional view showing the structure, Figure 5 is the 4th
6 is a sectional view showing the structure of the cam and tappet of the present invention, and FIG. 7 is a sectional view taken along the line A--A in FIG. 6. 2; Tappet, 2A; Tappet axis, 3; Lower surface of tappet, 3a; Spherical concave surface, 4; Oval cam,
4A; Axis center of oval cam.

Claims (1)

[Scope of utility model registration request] A valve operating mechanism for an engine, in which a spherical concave surface is formed in the center of the lower surface of a convex spherical tappet, and an egg-shaped cam is eccentric to the axis of the tappet and is disposed in surface contact with the spherical concave surface.