Valve Mechanism and Mechanical Lash Adjuster

Abstract

A valve mechanism is provided with a cam, a valve urged in a valve closing direction by a valve spring, a rocker arm, and a lash adjuster. The lash adjuster may include a plunger to which a pressing force of the cam and an urging force of the valve spring are transmitted through the rocker arm, a housing that forms a thread engagement portion, and a compression coil spring urging the plunger in the extension direction. The thread engagement portion may be such that a load acting on the plunger in the plunger extension or contraction direction causes sliding rotation in the thread engagement portion to be suppressed, and such that a lateral load acting on the plunger causes the suppression of sliding rotation to be relieved.

1 . A valve mechanism comprising: a cam rotating in conjunction with rotation of an engine output shaft; a shaft end portion of a valve urged in a valve closing direction by a valve spring; a power transmitting member interposed between the shaft end portion of the valve and the cam to transmit a pressing force of the cam to the shaft end portion of the valve as a valve opening force; and a mechanical lash adjuster linked to the power transmitting member and adjusting a valve clearance between the cam and the power transmitting member, wherein
 the mechanical lash adjuster includes   a plunger that is brought into contact with the power transmitting member and to which the pressing force of the cam and an urging force of the valve spring are transmitted through the power transmitting member,   a plunger engaging member that is put into thread engagement with the plunger to form a thread engagement portion cooperating with the plunger to extend and contract the plunger based on rotation relative to the plunger and that is retained non-rotatably in a circumferential direction of the thread engagement portion, and   a compression coil spring associated with the plunger and the plunger engaging member and urging the plunger in a direction in which the power transmitting member comes into contact with the cam, and wherein   the thread engagement portion is set such that when a load acts on the plunger in one of extension and contraction directions of the plunger, slide rotation of the plunger relative to the plunger engaging member is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion and that when a lateral load acts on the plunger to cause a swing of the plunger relative to the plunger engaging member, the suppression of the slide rotation is relieved.   
     
     
         2 . The valve mechanism according to  claim 1 , wherein
 a torsion spring is associated with the plunger and the plunger engaging member so that the plunger is urged in a relative rotational direction for extension from the plunger engaging member.   
     
     
         3 . The valve mechanism according to  claim 2 , wherein
 the compression coil spring and the torsion spring are constituted as a plunger spring by one spring member.   
     
     
         4 . The valve mechanism according to  claim 2 , wherein
 the compression coil spring and the torsion spring are separately independently provided as a plunger spring.   
     
     
         5 . The valve mechanism according to  claim 1 , wherein,
 the plunger engaging member is a cylindrical housing retained by a cylinder head, wherein   the plunger has one end of the plunger as a contact end for the power transmitting member and is arranged such that one end side of the plunger projects from the housing while the other end side of the plunger other than the one end side is housed in the housing, and wherein   the thread engagement portion is constituted by a male thread formed on an outer circumferential surface of the plunger and a female thread formed on an inner circumferential surface of the housing and screwed with the male thread.   
     
     
         6 . The valve mechanism according to  claim 1 , wherein,
 the thread engagement portion is set such that due to a lead angle and a flank angle of thread ridges of the threads constituting the thread engagement portion, when a load acts on the plunger in one of extension and contraction directions of the plunger, slide rotation of the plunger relative to the plunger engaging member is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion and that when a lateral load acts on the plunger to cause a swing of the plunger relative to the plunger engaging member, the suppression of the slide rotation is relieved.   
     
     
         7 . A mechanical lash adjuster comprising:
 a plunger;   a plunger engaging member put into thread engagement with the plunger to form a thread engagement portion cooperating with the plunger to extend and contract the plunger based on rotation relative to the plunger; and   a compression coil spring associated with the plunger and the plunger engaging member and urging the plunger in a direction in which the plunger is extended relative to the plunger engaging member, wherein   the thread engagement portion is set such that when a load acts on the plunger in one of extension and contraction directions of the plunger, slide rotation of the plunger relative to the plunger engaging member is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion and that when a lateral load acts on the plunger to cause a swing of the plunger relative to the plunger engaging member, the suppression of the slide rotation is relieved.   
     
     
         8 . The mechanical lash adjuster according to  claim 7 , wherein
 a torsion spring is associated with the plunger and the plunger engaging member so that the plunger is urged in a relative rotational direction for extension from the plunger engaging member.   
     
     
         9 . The mechanical lash adjuster according to  claim 8 , wherein
 the compression coil spring and the torsion spring are constituted as a plunger spring by one spring member.   
     
     
         10 . The mechanical lash adjuster according to  claim 8 , wherein
 the compression coil spring and the torsion spring are separately independently provided as a plunger spring.   
     
     
         11 . The mechanical lash adjuster according to  claim 7 , wherein
 the plunger engaging member is a cylindrical housing, wherein   the plunger is arranged such that one end side of the plunger projects from the housing while the other end side of the plunger other than the one end side is housed in the housing, and wherein   the thread engagement portion is constituted by a male thread formed on an outer circumferential surface of the plunger and a female thread formed on an inner circumferential surface of the housing and screwed with the male thread.   
     
     
         12 . The mechanical lash adjuster according to  claim 7 , wherein
 the mechanical lash adjuster is used in a valve mechanism including a cam rotating in conjunction with rotation of an engine output shaft, a shaft end portion of a valve urged in a valve closing direction by a valve spring, and a power transmitting member interposed between the shaft end portion of the valve and the cam to transmit a pressing force of the cam to the shaft end portion of the valve as a valve opening force, for adjusting a valve clearance between the cam and the shaft end portion of the valve, wherein   the plunger is brought into contact with the power transmitting member and arranged such that the pressing force of the cam and an urging force of the valve spring are transmitted through the power transmitting member, and wherein   the plunger engaging member is retained non-rotatably in a circumferential direction of the thread engagement portion in the valve mechanism.   
     
     
         13 . The mechanical lash adjuster according to  claim 7 , wherein the thread engagement portion is set such that due to a lead angle and a flank angle of thread ridges of the threads constituting the thread engagement portion, when a load acts on the plunger in one of extension and contraction directions of the plunger, slide rotation of the plunger relative to the plunger engaging member is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion and that when a lateral load acts on the plunger to cause a swing of the plunger relative to the plunger engaging member, the suppression of the slide rotation is relieved.