Abstract:
In a mechanism for actuating valves of an internal combustion engine, in place of a conventional coil spring, a holding member formed at least partly like a leaf spring is used to hold resiliently a plurality of rocker arms in position. The holding member together with a rocker shaft is fixed to a support member, for example, by means of a bolt. A holding portion of the holding member can be formed at one end or both ends of a body portion of the holding member.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a structure for fitting rocker arms in a mechanism for actuating valves of an internal combination engine. 
     In general, there are two valves for each cylinder: an intake or inlet valve and an exhaust valve. The intake valve opens during the intake stroke to admit the air-fuel mixture into the cylinder. The exhaust valve opens during the exhaust stroke to permit the burned gases to be exhausted from the cylinder. A mechanism for actuating the valves is related to a crankshaft so as to cause the valves to open and close with the proper relationship to the piston strokes. In the past, various types of valve-actuating mechanisms have been used for internal combustion engines. For example, a side-valve type, over-head valve type and over-head-camshaft type are well known. 
     FIG. 1 shows an example of conventional overhead camshaft type mechanism. A camshaft 2 is located near a cylinder head 1 and rotates in response to rotation of a crank shaft (not shown). A cam 3 is attached to the camshaft 2 in such a way that it can actuate rocker arms 4 so that the rocker arms move reciprocatively. The rocker arms 4 further actuate intake and exhaust valves 5, 6 so that the valves 5, 6 can open and close during reciprocating action of a piston (not shown). 
     As shown in FIG. 2, each rocker arm 4 has a boss portion 4&#39; rotatably set onto a rocker shaft 7 which is mounted through a bracket 9 to a support member 8 fixed to the cylinder head 1. The bracket 9 is fixed to the support member 8, for instance, by means of a bolt. 
     In the illustrated conventional mechanism, two rocker shafts 7 are used. One rocker shaft 7a is equipped with a rocker arm 4a for the intake valve 5. The other rocker shaft 7b is equipped with another rocker arm 4b for the exhaust valve 6. The length of the bracket 9 in the axial direction of the rocker shaft is predetermined in such a manner that the rocker arms 4 can fittably contact both ends of the bracket 9 whereby the position of the rocker arms 4 can be properly located. In order to prevent the rocker arms 4 from moving out of position, also, the rocker shafts 7 are inserted into coil springs 10 between the rocker arms 4 and the brackets 9&#39; adjacent thereto. Thus, the rocker arms 4 are pressed against the ends of the brackets 9&#39;. 
     However, in such a conventional mechanism for securing the rocker arms 4, before the rocker shafts 7 are fixed to the support member 8, it is necessary to assemble in order the rocker arms 4, coil springs 10 and brackets 9 onto the rocker shafts 7. For such a reason, the assembling efficiency is extremely low. In addition, the brackets 9, coil springs 10 and others are required to be used for the purpose of holding the rocker arms 4 in position. As a result, many parts must be used and the production costs increase. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a mechanism for actuating valves such as inlet and exhaust valves includes a special member for holding a plurality of rocker arms by its biasing force. Such a holding member is formed at least partly like a leaf spring and used in place of a conventional coil spring and other related parts in order to resiliently hold the rocker arms in position. The holding member has a holding portion at one end or each end of a body portion thereof. The body portion is to be fixed to a support or mounting member together with a rocker shaft, for instance, by means of a bolt. 
     Therefore, it is a main object of the present invention to provide a mechanism for actuating valves of an internal combustion engine in which rocker arms can be easily assembled. 
     A further object of the present invention is to provide a mechanism for actuating valves in which the number of required parts can be decreased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof when read in conjunction with the accompanying drawings in which: 
     FIG. 1 is a sectional view showing a conventional structure for securing rocker arms; 
     FIG. 2 is a plane view showing the conventional structure shown in FIG. 1; 
     FIG. 3 is a perspective view showing a holding member according to a preferred embodiment of the present invention; 
     FIG. 4 is a perspective view showing a part of a rocker shaft according to the present invention; 
     FIG. 5 is a plane view showing a structure for securing rocker arms according to the present invention; 
     FIG. 6 shows a vertical section of the central portion of the structure shown in FIG. 5; 
     FIG. 7 is a sectional view taken along the line II--II in FIG. 5; 
     FIG. 8 is a plane view showing a further embodiment of the present invention; 
     FIG. 9 shows a lateral section of an essential portion of the embodiment shown in FIG. 8; 
     FIG. 10 is a schematic view showing a holding member according to another embodiment of the present invention; and 
     FIG. 11 is a perspective view of the holding member shown in FIG. 10. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 shows a holding member 20 according to a preferred embodiment of the present invention. The holding member 20 is made of a spring material in a plate-shape. The holding member 20 includes a trapezoidal body portion 21 open at its bottom, a pair of holding portions 22 formed at both ends of the body portion 21 for holding resiliently the rocker arms 4 under pressure by the biasing force thereof, and a fitting or fixing portion 23 formed on the center of the body portion 21 in which a stepped portion 23a and a through hole 23b for a bolt are formed. The holding portions 22 may be formed by bending vertically both ends of the body portion 21. Each of holding portions 22 includes a pair of receiving pieces 22a for the rocker arms 4. The length l&#39; between a pair of receiving pieces 22a is predetermined. Also, a pair of pressing pieces 22b are joined by way of a connecting piece 22c to the ends of the body portion 21 in such a way that the pressing pieces 22b can face toward the receiving pieces 22a in the axial direction of the rocker shafts 7. Each connecting piece 22c is formed substantially in a U-shape or the like to be arranged over the boss portion 4&#39; of each rocker arm 4. The distance l&#34; between the receiving pieces 22a and the pressing pieces 22b is slightly shorter than the thickness of the boss portion 4&#39; of the rocker arm 4 so that the rocker arms can be held resiliently under pressure by means of the pressing pieces 22b and the receiving pieces 22a. The pressing piece 22b has at its underside portion a notched portion 22b&#39; for the rocker shaft 7. 
     As shown in FIG. 4, the rocker shaft 7 has a notched portion 7c on which the stepped portion 23a of the fitting portion 23 of the holding member 20 is mounted, and a through hole 7d corresponding to the through hole 23b of the fitting portion 23. The reference 7&#39; designates an oil passage formed in the axial direction of the rocker shaft 7. 
     FIGS. 5 through 7 illustrate how the rocker arms 4 are assembled with other related parts. First of all, the rocker shafts 7 are rotatably inserted into the rocker arms 4. A pair of rocker arms 4 are set to be resiliently held by the holding portions 22 of the holding member 20 under pressure. Next, the body portion 21 of the holding member 20 is set on the rocker shaft 7. The fitting portion 23 is mounted on the notched portion 7c of the rocker shaft 7 so that they are located in position. The bolt B is inserted into both through-holes 23b, 7b and then screwed to the support or mounting member 8 as best shown in FIG. 6. 
     Although in the shown embodiment the holding member 20 is manufactured by a press method to be a plate-like member made of a spring or elastic material as a whole, the present invention is not limited to such a mode. For example, the body portion 21, the receiving piece 22a and the pressing piece 22b can be separately formed of a rigid material in a plate-shape and joined with each other by means of the connecting piece 22c made of a resilient or elastic material. 
     When the connecting piece 22c is formed like a leaf spring, its characteristic frequency can be higher than that of the conventional coil spring 10 so that the rocker arms 4 can be prevented from breaking due to the engine resonance. 
     As the coil spring 10 is omitted, according to the present invention, no member covers partly the rocker shafts 7 within the ranges designated by the reference L. As shown in FIGS. 8 and 9, the holding member 20 is arranged in such a manner that the front end portion of the rocker arms 4b attached onto one rocker shaft 7b is positioned near the other rocker shaft 7a, and a small opening 7a&#39; is formed in the other rocker shaft 7 to be connected with the oil passage 7&#39; within the ranges L of the other rocker shaft 7a. The small opening 7a&#39; faces a portion of the rocker arm 4b which the cam 3 engages, so that the lubricating oil sprayed through the small opening 7a&#39; can lubricate the cam face of the cam 3. By doing so, no opening for lubricating oil need be formed in the cam 3 and the rocker arms 4. As a result, the strength of the cam 3 and the rocker arms 4 can be remarkably increased. 
     FIGS. 10 and 11 show a holding member according to a further embodiment of the present invention. A holding member 20&#39; is substantially the same as a half part of the holding member 20 shown in FIG. 3. That is, a holding portion 22 is formed only at one end of the body portion 21. Like members or portions are designated by the same references in FIGS. 3 and 11. Such a type of holding member 20&#39; is suitable for holding a rocker arm 4 placed at an end of the rocker shaft 7. 
     As can be seen from the foregoing, according to the present invention, only the rocker arms can be attached to the rocker shafts when they are assembled at a first stage. Thus, by adjusting the position of the holding member, the rocker arms can be precisely positioned. It results in the remarkable improvement of the assembling efficiency. Also, as the number of parts to be assembled can be decreased, the production costs can be decreased.