Chain transmission device for driving camshafts

Abstract

A chain transmission device for driving camshafts includes a chain including a loose side chain portion, and the chain is trained around the crank sprocket and the cam sprockets. A chain guide is mounted on the outer side of the loose side chain portion so as to be pivotable about one of the two end portions of the chain guide, and the chain guide has a plurality of rotatable rollers. An adjustment force is applied to the other of the two end portions of the chain guide by a chain tensioner such that the chain guide is biased toward the chain, so that the rollers of the chain guide can guide the chain by rolling. The winding angle of the portion of the chain located on the outer periphery of the roller located closest to the crank sprocket is set to be 170 degrees or greater so as to reduce noise.

Claims

1. A chain transmission device for driving a camshaft, the device comprising: a crank sprocket to be mounted to a crankshaft; a cam sprocket to be mounted to the camshaft; a chain including a loose side chain portion, the chain being trained around the crank sprocket and the cam sprocket; and a chain guide mounted on an outer side of the loose side chain portion so as to be pivotable about one of two end portions of the chain guide, the chain guide having a plurality of rotatable rollers, wherein the chain guide is configured such that when an adjustment force is applied to the other of the two end portions of the chain guide by a chain tensioner such that the chain guide is biased toward the chain, the rollers of the chain guide can guide the chain by rolling, and wherein one of the rollers is located closest to the crank sprocket, and a winding angle of a portion of the chain located on an outer periphery of the one of the rollers is set to be 170 degrees or greater.

2. The chain transmission device according to claim 1, wherein winding angles of portions of the chain located on respective outer peripheries of the others of the rollers are set to be 170 degrees or greater.

3. The chain transmission device according to claim 1, wherein the chain further comprises a tension side chain portion, wherein the chain transmission device further comprises a fixed chain guide mounted on an outer side of the tension side chain portion, the fixed chain guide including a plurality of rotatable rollers configured to guide a movement of the tension side chain portion, and wherein winding angles of portions of the chain located on respective outer peripheries of the rollers of the fixed chain guide are set to be 170 degrees or greater.

4. The chain transmission device according to claim 2, wherein the chain further comprises a tension side chain portion, wherein the chain transmission device further comprises a fixed chain guide mounted on an outer side of the tension side chain portion, the fixed chain guide including a plurality of rotatable rollers configured to guide a movement of the tension side chain portion, and wherein winding angles of portions of the chain located on respective outer peripheries of the rollers of the fixed chain guide are set to be 170 degrees or greater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a chain transmission device for driving camshafts according to an embodiment of the present invention.

(2) FIG. 2 is an enlarged sectional view illustrating the vicinity of the crank sprocket of FIG. 1.

(3) FIG. 3 is a sectional view taken along line III-III of FIG. 2.

(4) FIG. 4 is a view illustrating the winding angle of the portions of a chain located on the respective outer peripheries of rollers.

(5) FIG. 5 is a graph of an experimental result showing the relationship between a noise and the winding angle of the chain.

DETAILED DESCRIPTION OF THE INVENTION

(6) The chain transmission device for driving camshafts according to the embodiment of the present invention will now be described with reference to FIGS. 1 to 3. As illustrated in FIG. 1, this chain transmission device includes a crank sprocket 2 attached to an end portion of a crankshaft 1, cam sprockets 4 attached to end portions of respective camshafts 3, and a timing chain 5 trained around the crank sprocket 2 and the cam sprockets 4. With this arrangement, the rotation of the crankshaft 1 is transmitted to the camshafts 3 so as to rotate the camshafts 3.

(7) As the timing chain 5, a roller chain or a silent chain is used.

(8) The crankshaft 1 rotates in the direction indicated by the arrow in FIG. 1. Due to the rotation of the crankshaft 1, the timing chain 5 (hereinafter, simply referred to as chain) moves in the direction indicated by the arrows in FIG. 1. At this time, the portion of the chain 5 moving upwardly becomes loose, and the portion of the chain 5 moving downwardly becomes tensioned. These portions are therefore called loose side chain portion 5a and tension side chain portion 5b, respectively. A tension-adjusting chain guide A.sub.1 for adjusting the tension of the chain 5 is provided on one side of the loose side chain portion 5a. A movement-guiding chain guide A.sub.2 for guiding the movement of the chain 5 is provided on the other side of the tension side chain portion 5b.

(9) As illustrated in FIGS. 1 to 3, the tension-adjusting chain guide A.sub.1 includes a curved guide base 20 having opposed side plates, and elongated in the direction in which the chain 5 moves. A plurality of roller receiving recesses 21 are formed in the convex curved surface of the guide base 20, namely, its surface opposed to the chain 5 so as to be spaced apart from each other in the longitudinal direction of the guide base 20. The tension-adjusting chain guide A.sub.1 further includes roller shafts 22 each having both ends supported by the respective opposed side plates of the guide base 20, between which side plates the roller receiving recesses 21 are formed, and rollers 23 rotatably supported by the respective roller shafts 22.

(10) The guide base 20 is made of a synthetic resin having sufficient oil resistance, weather resistance, and strength, such as polyamide 46 (PA46) or polyamide 66 (PA66).

(11) The roller shafts 23 are made of SUJ2 or SC material. Heat treatment is performed to the roller shafts 23 so as to increase their hardness, thereby increasing their wear resistance. As such heat treatment, though bright quenching is used in this embodiment, high frequency quenching, carburizing and quenching, or carbonitriding may be used.

(12) The rollers 23 are roller bearings each including a shell-type outer race 24 formed by drawing a metal plate such as SPC or SCM, a plurality of roller elements 25 mounted inside of the outer race 24, and a retainer 26 retaining the roller elements 25.

(13) With the tension-adjusting chain guide A.sub.1 arranged along the direction in which the loose side chain portion 5a moves, the upper end portion of the guide base 20 is supported by a fulcrum shaft 10 protruding from an engine block such that the chain guide A.sub.1 is pivotable about the fulcrum shaft 10, and an adjustment force is applied to the lower end portion of the chain guide A.sub.1 remote from the fulcrum shaft 10 by a chain tensioner 11 such that the chain guide A.sub.1 is biased toward the loose side chain portion 5a. Therefore the chain guide A.sub.1 can guide the loose side chain portion 5a by rolling the rollers 23 kept in contact with the loose side chain portion 5a.

(14) The movement-guiding chain guide A.sub.2 is substantially identical in structure to the tension-adjusting chain guide A.sub.1, but differs from the chain guide A.sub.1 only in that a guide base of the chain guide A.sub.2 has a shape different from that of the guide base 20 of the chain guide A.sub.1. Therefore, as for the elements of the chain guide A.sub.2 corresponding to those of the chain guide A.sub.1, the same reference numerals used in the chain guide A.sub.1 are used, and their description is omitted.

(15) With the movement-guiding chain guide A.sub.2 arranged along the direction in which the tension side chain portion 5b moves, the upper and lower end portions of the chain guide A.sub.2 are fixed in position by the fastening of respective bolts 12 screwed into the engine block, so that the chain guide A.sub.2 can guide the movement of the chain 5 by its rollers 23.

(16) The chain 5, guided by the rollers 23 of the tension-adjusting chain guide A.sub.1 and the rollers 23 of the movement-guiding chain guide A.sub.2, linearly moves between the adjacent rollers 23 of the chain guides A.sub.1 and A.sub.2, but moves while curving at the positions of the chain 5 coming into contact with the respective rollers 23 so as to collide against the outer peripheries of the rollers 23, thereby generating noise. In order to reduce such noise, the winding angles illustrated in FIG. 2 of the portions of the chain 5 located on the respective outer peripheries of all of the rollers 23 are set to be 170 degrees or over in this embodiment.

(17) By setting the winding angle of the portions of the chain 5 located on the respective outer peripheries of all of the rollers 23 to be 170 degrees or greater as described above, since the chain 5 moves substantially linearly, the force of the chain 5 colliding against the respective outer peripheries of the rollers 23 is weakened, thus making it possible to reduce noise.

(18) By setting the winding angle to be large, specifically, 170 degrees or greater, the loads applied to the respective rollers 23 from the chain 5 are made small, so that the chain 5 and the outer races 24 are less likely to wear.

(19) When the torque of the crank sprocket 2 changes due to the explosion of the engine, the tension of the chain 5 changes, so that the chain 5 flaps. At this time, the roller 23 of the chain guide A.sub.1 located closest to the crank sprocket 2 is likely to be affected by the flapping of the chain 5, so that noise is likely to occur especially at this roller 23.

(20) Therefore, by setting only the winding angle of the portion of the chain 5 located on the outer periphery of the roller 23 of the chain guide A.sub.1 located closest to the crank sprocket 2 to be 170 degrees or over, too, it is possible to very effectively reduce noise.

DESCRIPTION OF REFERENCE NUMERALS

(21) A.sub.1: chain guide A.sub.2: chain guide 2: crank sprocket 4: cam sprocket 5: timing chain (chain) 11: chain tensioner 23: roller (roller bearing)