Automatic valve clearance adjuster

Abstract

An automatic valve clearance adjuster comprising an internally screw-threaded housing ( 1 ); an externally screw-threaded screw member ( 3 ) extending within the housing; the screw thread ( 4 ) of the screw member ( 3 ) having an external form which is complementary to the thread form of the internal thread ( 2 ) of the housing and fits therein with a predetermined axial clearance, the thread being trapezoidal in form, symmetrical in axial cross-section and exhibiting equal frictional resistance against movement in both axial directions; wherein the flank angles, helix angle and number of starts of the screw thread are selected to ensure that the screw member will rotate and advance axially out of the housing solely under the influence of an axial force on its end within the housing; and the emerging end ( 7 ) of the screw member is adapted to work in conjunction with an adjacent component to receive therefrom a frictional resistance to rotation.

1 . An automatic valve clearance adjuster comprising an internally screw-threaded housing ( 1 ); an externally screw-threaded screw member ( 3 ) extending within the housing; the screw thread ( 4 ) of the screw member ( 3 ) having an external form which is complementary to the thread form of the internal thread ( 2 ) of the housing and fits therein with a predetermined axial clearance, the thread being trapezoidal in form, symmetrical in axial cross-section and exhibiting equal frictional resistance against movement in both axial directions; wherein the flank angles, helix angle and number of starts of the screw thread are selected to ensure that the screw member will rotate and advance axially out of the housing solely under the influence of an axial force on its end within the housing; and the emerging end ( 7 ) of the screw member is adapted to work in conjunction with an adjacent component to receive therefrom a frictional resistance to rotation.  
     
     
         2 . An automatic valve clearance adjuster according to  claim 1  wherein the flanks of each thread on the screw member and in the housing are inclined at an angle of 30° to the perpendicular to the axis of the screw thread.  
     
     
         3 . An adjuster according to  claim 1  or  claim 2  wherein the energising end of the screw member is adapted to contact said adjacent component in one of:—
 (a) a circular line  
 (b) an annular area  
 (c) an area of the curved surface of a thin conical frustum, and  
 (d) an area of the curved surface of a thin slice of a sphere.  
 
     
     
         4 . An adjuster according to  claim 3  wherein, in the case of contact with said adjacent component in b, c or d, the area of contact approximates to line contact.  
     
     
         5 . An adjuster according to  claim 3  or  4  wherein the diameter of said contact line or area is greater than the mean diameter of the screw thread in the adjuster.  
     
     
         6 . An adjuster according to any one of the preceding claims comprising spring means acting on the screw member to urge it to advance axially out of the housing.  
     
     
         7 . An adjuster according to  claim 6  wherein said spring means acts on the end of the screw member within the housing through a ball-ended member.  
     
     
         8 . An adjuster according to any of  claims 1  to  5  wherein said screw member is adapted to be acted on by oil pressure to urge it axially out of the housing.  
     
     
         9 . An adjuster according to  claim 6  or  claim 7  wherein there is provided abutment means operable between the screw member and the housing when the screw member is screwed into the housing to an inner position, whereby frictional forces can be established between the screw member, housing and abutment means sufficient to retain the screw member in said inner position against the action of the spring means.  
     
     
         10 . A valve clearance adjuster comprising a housing having an internal screw thread, a screw member extending into the housing from an open end thereof and having an external screw thread engaging the thread within the housing, and spring means acting on the screw member in the direction of its longitudinal axis; the co-operating screw threads of the screw member and housing being of such a configuration that the screw member will rotate and advance out of the housing under the influence of the spring means; wherein there is provided abutment means operable between the screw member and the housing when the screw member is screwed into the housing to an inner position, whereby frictional forces can be established between the screw member, housing and abutment means sufficient to retain the screw member in said inner position against the action of the spring means.  
     
     
         11 . An adjuster according to  claim 9  or  claim 10  wherein said abutment means comprises a shoulder formation inside the housing and engageable by an innermost end face of the screw member.  
     
     
         12 . An adjuster according to  claim 11  wherein said shoulder is afforded by the housing.  
     
     
         13 . An adjuster according to  claim 11  wherein said shoulder is afforded by a member disposed within the housing.  
     
     
         14 . An adjuster according to  claim 9  or  claim 10  wherein the screw member has an abutment formation engageable with an end face of the housing.  
     
     
         15 . An adjuster according to  claim 14  wherein said formation comprises a collar provided on the screw member beneath a head part thereof.  
     
     
         16 . An adjuster according to  claim 15  wherein said collar provides for holding the screw member for screwing it into the housing.  
     
     
         17 . An adjuster according to any one of  claims 9  to  16  wherein the screw member is adapted to be engaged by a tool for screwing it into the housing and causing said abutment means to be brought into operation.  
     
     
         18 . The combination of an adjuster according to  claim 17  and said tool engageable therewith.  
     
     
         19 . The combination according to  claim 18  wherein said tool is frictionally engageable with said head portion of the screw member.  
     
     
         20 . A valve operating mechanism including an automatic valve clearance adjuster according to any one of  claims 1  to  17  interposed between respective components of the mechanism for taking up clearances therebetween.  
     
     
         21 . An internal combustion engine including a number of valve operating mechanisms according to  claim 20 .  
     
     
         22 . An automatic valve clearance adjuster substantially as hereinbefore described with reference to FIGS.  5  to  7  or FIG. 17 of the accompanying drawings.  
     
     
         23 . Any novel feature or novel combination of features described herein and/or in the accompanying drawings.