Variable valve mechanism of internal combustion engine

#1. Field of the Invention

#The present invention relates to a variable valve mechanism of an internal combustion engine, which controls valve timing and valve lift of the engine in accordance with an operating condition of the engine.

#2. Description of Related Art

#FIG. 1 is a schematic view of a variable valve mechanism which is a first embodiment of the present invention;

#FIG. 2 is a sectional view taken along the line II—II of FIG. 1;

#FIG. 3 is a graph showing acceleration of first, second and third connecting pins employed in the mechanism of the first embodiment;

#In order to clarify the task of the present invention, a related variable valve mechanism shown in Japanese Laid-open Patent Application 11-141321 will be briefly described with reference to FIG. 15 of the accompanying drawings.

#As shown in FIG. 15, the variable valve mechanism generally comprises a drive shaft 51 rotated together with a crankshaft (not shown) of an internal combustion engine, a swing cam 53 rotatably disposed on the drive shaft 51 to actuate intake (or exhaust) valves 52, a control shaft 54 extending in parallel with the drive shaft 51 and a link mechanism for linking the drive shaft 51 and the swing cam 53 through the control shaft 54. The link mechanism comprises a first eccentric cam 55 fixed to the drive shaft 51 and a ring-shaped link (or ring-link) 56 rotatably disposed on the first eccentric cam 55. A second eccentric cam 57 is fixed to the control shaft 54, and a rocker arm 58 is rotatably disposed on the second eccentric cam 57. A projected end of the ring-link 56 and one end of the rocker arm 58 are pivotally connected through a first connecting pin 61, and the other end of the rocker arm 58 and the swing cam 53 are pivotally connected through a rod-shaped link (or rod-link) 59. That is, the other end of the rocker arm 58 and one end of the rod-link 59 are pivotally connected through a second connecting pin 62 and the other end of the rod-link 59 and the swing cam 53 are pivotally connected through a third connecting pin 63. Denoted by 57a is a center of the second eccentric cam 57, about which the rocker arm 58 swings. Denoted by numeral 54a is a center of the control shaft 54. Thus, when, under operation of the associated engine, the control shaft 54 is rotated to a certain angular position, the center 57a of the second eccentric cam 57 is displaced relative to the center 54a of the control shaft 54 thereby to change the lifting characteristic of the intake valves 52. For achieving a smoothed pivoting between the mutually connected elements (viz., 56 and 58, 58 and 59, or 59 and 53), the first, second and third connecting pins 61, 62 and 63 are each arranged to show a free rotation relative to both the mutually connected elements. That is, each connecting pin 61, 62 or 63 is rotatable to both the mutually connected elements associated thereto. This means that there is inevitably defined a radial clearance between the pin 61, 62 or 63 and an inner wall of a cylindrical bore formed in each of the mutually connected elements.

#However, as is known, determining ideal dimensions of such radial clearance is very difficult and at least troublesome. In fact, if the dimensions are not properly made, out-of alignment between the mutually connected elements tends to occur, which may cause an undesirable unsymmetrical wear of a bearing portion such as the portion indicated by the arrow 64.