JP2000034906A - Cam-follower device for valve system of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure durability of a roller by regulating a maximum value of tensile stress acting on an inside diameter of a roller according to rotation of a cam shaft to a specified value or below. SOLUTION: This device is fixed to a member receiving movement of a cam 2 such as a locker arm 3 in a state that a shaft 5 is laid between a pair of supporting wall parts 4, 4. Around this shaft 5, a bearing steel roller 6 such as an SUJZ is freely rotatably supported via a radial roller bearing 9. A maximum value of tensile stress acting on an inside diameter part of the roller 6 is regulated to 25 kgf/mm2 or below according to rotation of a cam shaft 1. Therefore, generation of damage of a crack can be prevented in the roller 6 before an engine reaches a maximum life (about traveling distance 2 million km). Because this maximum value is quantitatively regulated, a design by which sufficient durability can be secured can be easily performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The cam follower device for an engine valve operating mechanism according to the present invention is incorporated in an engine valve operating mechanism to reduce the friction of the valve operating mechanism to reduce the fuel consumption rate during engine operation. It is intended to reduce the amount.

[0002]

2. Description of the Related Art For the purpose of reducing friction inside an engine and reducing a combustion consumption rate, a portion that converts rotation of a camshaft synchronized with a crankshaft into reciprocating motion of an intake valve and an exhaust valve is provided. It is common practice to incorporate a cam follower device for an engine valve train. FIG.
Reference numerals 2 to 2 denote cam followers for a valve operating mechanism of an engine described in Japanese Utility Model Laid-Open No. 3-108806.

A rocker arm 3 is provided opposite to a cam 2 fixed (generally integrally formed) to a camshaft 1 which rotates in synchronization with a crankshaft of an engine, and receives a movement of the cam 2. I have. One end of the rocker arm 3 (the left end in FIGS. 1 and 2) has a pair of support walls 4,
4 are provided at an interval from each other. A hollow or solid shaft 5 made of steel is bridged between the pair of support walls 4. Without quenching both ends of this shaft 5,
When the shaft 5 is fixed as it is, the unhardened portion is swaged toward the inner peripheral surfaces of the through holes 7 formed in the pair of support walls 4. As described above, a roller 6 is rotatably supported around a shaft 5 extending between the pair of support walls 4, 4. The outer peripheral surface 6a of the roller 6 2 is in contact with the outer peripheral surface 2a.

According to the cam follower device for an engine valve operating mechanism configured as described above, the rocker arm 3 and the cam 2
And the frictional force acting between them can be reduced, and the fuel consumption rate during engine operation can be reduced. The cam follower device for the valve train of the engine is made of a cam 2
The camshaft 1 is made of cast iron or bearing steel, and the roller 6 and the shaft 5 are made of bearing steel such as high carbon chromium bearing steel such as SUJ2. This is generally done from the aspect of suppression.

In order to further reduce the frictional force, as shown in FIG. 3, a plurality of rollers (needle) 8, 8 are provided between the outer peripheral surface of the shaft 5 and the inner peripheral surface of the roller 6, The roller 6 is rotatably supported around the shaft 5 by a radial roller bearing 9. As described above, in the case of the cam follower for the valve operating mechanism of the engine in which the roller 6 is supported by the radial roller bearing 9 with respect to the shaft 5, a part of the inner diameter surface of the roller 6 during the operation of the engine is as follows. For that reason, a large tensile stress is applied.

That is, when the engine is operating, the outer peripheral surface 2a of the cam 2 is
(FIG. 1 to 2), F _c becomes radial load is applied.
During operation of the engine, the rollers 8 revolve around the shaft 5 while rotating by the rotation of the rollers 6. Accordingly, the portion a in FIG. 3 which is on the opposite side of the inner peripheral surface of the roller 6 just where the radial load _Fc is applied,
There may be a portion between the rollers 8 adjacent to each other in the circumferential direction. In this state, a large tensile stress is repeatedly applied to the portion on the inner diameter side of the roller 6 in the portion a.

[0007]

In order to ensure the durability of the roller 6 constituting the cam follower device for the valve operating mechanism of the engine, it is necessary to reduce the tensile stress applied to the inner diameter side portion of the roller 6. It is necessary to secure a wall thickness in the diametrical direction or a length in the axial direction. On the other hand, reducing the inner diameter of the roller 6 to increase the wall thickness is limited in terms of securing the load capacity of the radial roller bearing 9 that supports the roller 6. Increasing the outer diameter of the roller 6 not only hinders downsizing of the engine, but also increases the inertial mass of the portion that reciprocates during rotation, and prevents high output due to high speed of the engine. Is not preferred. Further, increasing the length in the axial direction also causes an increase in the size of the engine.
There is a limit.

[0008] On the other hand, heretofore, it has not been known about the numerical value of the above-mentioned tensile stress that can ensure sufficient durability for practical use. For this reason, at present, the shape and dimensions of the roller 6 that can secure the durability of the roller 6 constituting the cam follower device for the valve operating mechanism of the engine are determined by trial and error. Thus, in the method of determining the shape and dimensions of the roller 6 by trial and error, the design of the cam follower device for the valve train of the engine becomes complicated. The cam follower device for an engine valve train of the present invention has been invented in view of such circumstances.

[0009]

The cam follower device for the valve operating mechanism of the engine according to the present invention is the same as the cam follower device for the valve operating mechanism of the engine which has been conventionally known, as shown in FIG.
-3. That is, a member that receives the movement of the cam 2 such as the rocker arm 3 provided opposite to the cam 2 fixed to the camshaft 1 that rotates in synchronization with the crankshaft of the engine has a pair of support walls 4, 4 are formed at intervals. The shaft 5 is fixed between the pair of support walls 4 in a state of being bridged. A roller 6 made of bearing steel such as SUJ2 is rotatably supported around the shaft 5 via a radial roller bearing 9. In particular, in the cam follower device for the valve operating mechanism of the engine of the present invention, the maximum value of the tensile stress acting on the inner diameter portion of the roller 6 with the rotation of each camshaft 1 is set to 25 kgf / mm ² or less. Regulating.

[0010]

In the case of the cam follower for the valve train of the engine according to the present invention, the maximum value of the tensile stress acting on the inner diameter of the roller 6 is regulated to 25 kgf / mm ² or less. It is possible to prevent the roller 6 from being damaged, such as cracks, before the engine reaches its maximum possible life (running distance of about 2 million km). Moreover, the maximum value, which is the allowable value of the tensile stress, is
Since the regulation is performed quantitatively, it is possible to easily design a cam follower device for an engine valve operating mechanism having sufficient durability.

Next, the maximum value of the tensile stress is set to 25 kg.
The reason for restricting f / mm ² or less will be explained. SUJ2 which is the most common bearing steel for forming the roller 6
(High carbon chromium bearing steel) The hardness of the test piece (HR _c62 ) required for the roller 6 was increased to prepare a test piece, and various magnitudes of tensile stress (pulsating stress) were applied to the test piece. When added, the relationship between the number of repetitions until damage such as cracks occur in each test piece and the tensile stress applied repeatedly is:
As shown in FIG. On the other hand, when the maximum service life of the engine is assumed to be about 2 million km, the number of repetitions of the tensile stress applied to the roller 6 is 1.8 × 10 ⁹ times (3000 rpm.
10000hr). Assuming a safety factor of less than 40% with respect to this value, the value of the above-mentioned tensile stress in which no damage occurs until the number of repetitions of about 2.5 × 10 ⁹ times, as shown in FIG.
Thus, a value of 25 kgf / mm ² was determined.

[0012]

EXAMPLE An experiment conducted to confirm the effect of the present invention will be described. In the experiment, the width B and the outer diameter D of the roller 6 were determined.
8 kinds of test pieces were prepared by changing the ratio B / D in the range of 0.1 to 0.8 in increments of 0.1.
It was assembled into a test device that operates in the same way as the cam follower device for the actual valve train of the engine, and was subjected to an acceleration test. Test time is 10,000 hours, engine speed is 9000
rpm (the rotational speed of the camshaft was 4500 rpm), and the radial load with which the cam 2 pressed the roller 6 was 300 kgf.

FIG. 5 shows the results of an experiment conducted under such conditions. In FIG. 5, the horizontal axis represents the ratio B / D of the width B and the outer diameter D of the roller 6, and the vertical axis represents the ratio under the above experimental conditions.
The values of the tensile stress applied to the inner diameter portion of each test piece are shown. The difference in the value of the tensile stress is caused by the difference in the ratio B / D. Also, the circles shown in FIG.
A mark in which no damage such as a crack was generated even after the accelerated test was shown, and a mark x indicates that damage was generated. From experiments conducted under such conditions, it was confirmed that sufficient durability could be ensured if the tensile stress was regulated to 25 kgf / mm ² or less.

[0014]

Since the present invention is constructed and operates as described above, it is possible to easily design a cam follower device for an engine valve operating mechanism capable of securing sufficient durability.

[Brief description of the drawings]

FIG. 1 is a partially cutaway plan view of a cam follower device for a valve train of an engine.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a partial cross-sectional view of a cam follower device for a valve train of an engine to which the present invention is applied.

FIG. 4 is a diagram showing the relationship between the number of repetitions until damage such as cracks occur in a test piece made of bearing steel and the tensile stress applied repeatedly.

FIG. 5 is a diagram showing the results of an experiment performed to confirm the effects of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Camshaft 2 Cam 2a Outer peripheral surface 3 Rocker arm 4 Support wall part 5 Shaft 6 Roller 6a Outer peripheral surface 7 Through hole 8 Roller (needle) 9 Radial roller bearing

Claims (1)

[Claims] A cam fixed to a camshaft that rotates in synchronization with a crankshaft of an engine, and a pair of members provided opposed to the cam and receiving the movement of the cam and formed at an interval. A support wall portion, a shaft fixed in a state of being bridged between the pair of support wall portions, and rotatably supported around the shaft via a radial roller bearing;
In a cam follower device for an engine valve operating mechanism comprising a roller made of bearing steel, the maximum value of the tensile stress acting on the inner diameter portion of the roller with the rotation of each of the camshafts is reduced to 25 kgf / mm ² or less. A cam follower device for an engine valve train characterized by the restriction.