US20100275865A1

US20100275865A1 - Lash adjuster

Info

Publication number: US20100275865A1
Application number: US12/811,845
Authority: US
Inventors: Makoto Yasui; Katsuhisa Yamaguchi; Eiji Maeno
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 2008-01-28
Filing date: 2009-01-26
Publication date: 2010-11-04
Also published as: DE112009000091T5; WO2009096353A1; JP2009174488A

Abstract

A lash adjuster includes a nut member inserted in a receiving hole formed in the top surface of a cylinder head, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with an internal thread on the inner periphery of the nut member, and a return spring biasing the adjusting screw. The adjusting screw has an end protruding from the nut member and pivotally supporting an arm of a valve gear. The adjusting screw is a solid member. A spring seat is disposed between the adjusting screw and the return spring and kept in point contact with the end of the adjusting screw inserted in the nut member. The spring seat is axially slidably fitted in the inner periphery of the nut member, thereby keeping the adjusting screw and the spring seat coaxial with each other.

Description

BACKGROUND OF THE INVENTION

1. Technical Field
This invention relates to a lash adjuster mounted in an engine valve gear.
2. Background Art
Known valve gears for moving a valve provided at an intake port or an exhaust port of an engine include one comprising an arm pivotable about one end thereof and adapted to be pushed down at its central portion, thereby pushing down a valve stem at the other end (swing arm type valve gear), one comprising an arm pivotable about its central portion and adapted to be pushed up by a cam at one end thereof, thereby pushing down a valve stem at the other end (rocker arm type valve gear), and one comprising a valve lifter vertically movably supported and adapted to be pushed down by a cam, thereby pushing down a valve stem (direct type valve gear).
In these valve gears, gaps between their component parts may change due to differences in thermal expansion between component parts, which may cause noise and compression leakage. Also, when the sliding parts of the valve gear become worn too, gaps between component parts of the valve gear may change, which may also cause noise.
In order to prevent such noise and compression leakage, ordinary valve adjusters include a lash adjuster for absorbing gaps between component parts of the valve gear.
One known lash adjuster used in a swing arm type valve gear comprises a nut member inserted in a mounting hole formed in the top surface of a cylinder head, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude upwardly from the nut member, the adjusting screw pivotally supporting the arm of the valve gear with its end protruding from the nut member (JP Patent Publication 2005-273510A).
One know lash adjuster used in a direct type valve gear comprises a lifter body vertically slidably inserted in a guide hole formed in a cylinder head, a nut member fixed to the lifter body so as to be vertically movable together with the lifter body, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude downwardly from the nut member, the adjusting screw pressing the valve stem of the valve gear with its end protruding from the nut member (JP Patent Publication 2003-227318A).
One known lash adjuster used in a rocker arm type valve gear comprises a nut member inserted in a mounting hole formed in the bottom surface of the arm which pivots as the cam rotates, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude downwardly from the nut member, the adjusting screw pressing the valve stem of the valve gear with its end protruding from the nut member (JP Patent Publication 2006-132426A).
In these lash adjusters, the external thread of the adjusting screw and the internal thread of the nut member have a serration-shaped section such that their pressure flanks for receiving pressure when a load is applied that tends to push the adjusting screw into the nut member having a greater flank angle than their clearance flanks. Thus, as the cam rotates and the load is applied that tends to push the adjusting screw into the nut member, the pressure flank of the external thread of the adjusting screw is supported on the pressure flank of the internal thread of the nut member, so that the adjusting screw is axially fixed in position.
If gaps between component parts of the valve gear change due e.g. to thermal expansion of the valve gear, the adjusting screw move axially in the nut member while rotating, thus absorbing change in gaps between component parts of the valve gear.

SUMMARY OF THE INVENTION

With the lash adjuster disclosed in each of Patent documents 1 and 3, since the return spring is in direct contact with the end of the adjusting screw inserted in the nut member, there is the possibility that the adjusting screw may not be smoothly movable axially while rotating due to the friction between the adjusting screw and the return spring.
With the lash adjuster disclosed in Patent document 2, a spring seat is disposed between the adjusting screw and the return spring to prevent friction between the adjusting screw and the return spring. This return spring has a convex spherical surface kept in point contact with the adjusting screw.
The adjusting screw of this lash adjuster is a hollow member having an opening at its end inserted in the nut member. The spring seat is fitted in the adjusting screw so as to be rotatable relative to the adjusting screw, thereby keeping the adjusting screw and the spring seat coaxial with each other.
But with this lash adjuster, since the spring seat is fitted in the inner periphery of the adjusting screw, the outer periphery of the spring seat tends to contact the adjusting screw, which may in turn make smooth rotation of the adjusting screw impossible due to friction between the contact surfaces of the spring seat and the adjusting screw.
An object of the present invention is to provide a lash adjuster of which the adjusting screw can rotate smoothly.
In order to achieve this object, a solid member is used as the adjusting screw, a spring seat is disposed between the adjusting screw and the return spring so as to be kept in point contact with the end of the adjusting screw inserted in the nut member, and the spring seat is axially slidably fitted in the inner periphery of the nut member, thereby keeping the adjusting screw and the spring seat coaxial with each other.
If the spring seat is fitted in the internal thread on the inner periphery of the nut member, the fitting surface of the spring seat fitted in the internal thread preferably has an axial length longer than the pitch of the internal thread.
The spring seat may comprise a cylindrical portion fitted in the inner periphery of the nut member, and an end portion kept in point contact with the end of the adjusting screw inserted in the nut member, with the return spring inserted in the cylindrical portion of the spring seat.
One of the contact surfaces of the adjusting screw and the spring seat may be a convex spherical surface and the other of the contact surfaces may be a flat surface; one of these contact surfaces may be a convex spherical surface and the other of the contact surfaces may be a concave spherical surface; or one of these contact surfaces may be a convex spherical surface and the other of the contact surfaces may also be a convex spherical surface.
With the lash adjuster according to the present invention, since the spring seat is fitted in the inner periphery of the nut member, the outer periphery of the spring seat is kept out of contact with the adjusting screw, so that there is no friction between the outer periphery of the spring seat and the adjusting screw. Also, even though the outer periphery of the spring seat contacts the inner periphery of the nut member, this does not hinder rotation of the adjusting screw, so that the adjusting screw can rotate smoothly.
Since the fitting surface of the spring seat fitted in the inner periphery of the nut member has an axial length that is longer than the pitch of the internal thread on the inner periphery of the nut member, the fitting surface is guided by the internal thread over the entire circumference thereof. Thus, the spring seat can be diametrically positioned stably compared to a lash adjuster of which the fitting surface has an axial length shorter than the pitch of the internal thread.
With the arrangement in which the spring seat comprises a cylindrical portion fitted in the inner periphery of the nut member, and an end portion kept in point contact with the end of the adjusting screw inserted in the nut member, with the return spring inserted in the cylindrical portion of the spring seat, since the fitting surface of the spring seat fitted in the inner periphery of the nut member diametrically overlaps with the return spring, it is possible to reduce the axial length of the lash adjuster.
With the arrangement in which one of the contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other is a flat surface, the contact surfaces can be formed easily at a low cost.
With the arrangement in which one of the contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other is a concave spherical surface, the spring seat is less likely incline, so that the contact position between the adjusting screw and the spring seat stabilizes.
With the arrangement in which one of the contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other is also a convex spherical surface, it is possible to reduce the friction between the contact surfaces to an extremely low level, thus further reducing the resistance to rotation of the adjusting screw.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a valve gear including a lash adjuster according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a portion of the valve gear where there is the lash adjuster.

FIG. 3 is an enlarged sectional view of a modification in which one of the contact surfaces of the adjusting screw and the spring seat shown in FIG. 2, i.e. the contact surface of spring seat is replaced by a concave spherical surface.

FIG. 4 is an enlarged sectional view of a modification in which one of the contact surfaces of the adjusting screw and the spring seat shown in FIG. 2, i.e. the contact surface of the adjusting screw is replaced by a flat surface, and the contact surface of the spring seat is replaced by a convex spherical surface.

FIG. 5 is an enlarged sectional view of a modification in which one of the contact surfaces of the adjusting screw and the spring seat shown in FIG. 2, i.e. the contact surface of the spring seat is replaced by a convex spherical surface.

FIG. 6 is an enlarged sectional view of a modification in which the spring seat shown in FIG. 2 is replaced by a spring seat comprising a cylindrical portion fitted in the inner periphery of the nut member, and an end portion kept in point contact with the end of the adjusting screw inserted in the nut member.

FIG. 7 is an enlarged sectional view of a modification in which one of the contact surfaces of the adjusting screw and the spring seat shown in FIG. 6, i.e. the contact surface of spring seat is replaced by a concave spherical surface.

FIG. 8 is an enlarged sectional view of a modification in which one of the contact surfaces of the adjusting screw and the spring seat shown in FIG. 6, i.e. the contact surface of the adjusting screw is replaced by a flat surface, and the contact surface of the spring seat is replaced by a convex spherical surface.

FIG. 9 is an enlarged sectional view of a modification in which one of the contact surfaces of the adjusting screw and the spring seat shown in FIG. 6, i.e. the contact surface of the spring seat is replaced by a convex spherical surface.

FIG. 10 is a front view of a valve gear including a lash adjuster according to a second embodiment of the present invention.

FIG. 11 is a front view of a valve gear including a lash adjuster according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a valve gear including the lash adjuster 1 according to the first embodiment of the present invention. This valve gear includes a valve 4 for an intake port 3 formed in a cylinder head 2 of an engine, a valve stem 5 connected to the valve 4, and an arm 7 that pivots as a cam 6 rotates.
The valve stem 5 extends upwardly from the valve 4 and is slidably inserted through the cylinder head 2. An annular spring retainer 8 is fixed to the outer periphery of the valve stem 5 at its upper portion. A valve spring 9 is mounted between the bottom surface of the spring retainer 8 and the top surface of the cylinder head 2. The valve spring 9 biases the valve stem 5 upwardly through the spring retainer 8, thereby seating the valve 4 on a valve seat 10.
The arm 7 has one end thereof supported by the lash adjuster 1 and the other end in contact with the top end of the valve stem 5. The arm 7 carries at its central portion a roller 11 kept in contact with the cam 6, which is located over the arm 7.
As shown in FIG. 2, the lash adjuster 1 comprises a tubular nut member 13 received in a receiving hole 12 formed in the top surface of the cylinder head 2, an adjusting screw 16 having an external thread 15 on its outer periphery at its lower portion which is in threaded engagement with an internal thread 14 formed on the inner periphery of the nut member 13, a return spring 17 biasing the adjusting screw 16, and a spring seat 18 disposed between the return spring 17 and the adjusting screw 16.
The external thread 15 and the internal thread 14 have an asymmetrical serration-shaped section along the axis such that their pressure flanks 19 for receiving pressure when a load is applied that tends to push the adjusting screw 16 into the nut member 13 having a greater flank angle than their clearance flanks 20.
The return spring 17 has its bottom end supported on the bottom 21 of the nut member 13 and presses the adjusting screw 16 at its top end, thereby biasing the adjusting screw 16 in the direction to protrude upwardly from the nut member 13.
The adjusting screw 16 is a solid member, and has a convex spherical surface 22 at its end inserted in the nut member 13. The spring seat 18 has a flat surface 23 that is in contact with the convex spherical surface 22. The convex spherical surface 22 of the adjusting screw 16 and the flat surface 23 of the spring seat 18 are in point contact with each other at a point located on the rotation axis of the adjusting screw 16.
The spring seat 18 is axially slidably fitted in the internal thread 14 on the inner periphery of the nut member 13, and thus remains coaxial with adjusting screw 16. The surface 24 of the spring seat 18 that is fitted in the internal thread 14 is a cylindrical surface of which the axial length is longer than the pitch of the internal thread 14.
The spring seat 18 is formed with a protrusion 25 that is fitted in the inner periphery of the end portion of the return spring 17. By fitting the protrusion 25 in the return spring 17, the return spring 17 and the spring seat 18 are kept coaxial with each other. If as shown, the return spring 17 is a conical coil spring of which the diameter increases toward the bottom 21 of the nut member 13, such a return spring 17 is less likely to buckle, which increases reliability of the return spring 17.
The end 26 of the adjusting screw 16 protruding from the nut member 13 is fitted in a recess 27 formed in the bottom surface of the arm 7 at the one end, thus supporting the arm 7 so as to be pivotable about the protruding end 26.
The operation of the lash adjuster 1 is now described.
When the cam 6 is rotated by the engine and the cam lobe 6 a of the cam 6 presses down the arm 7, the valve 4 separates from the valve seat 10, thus opening the intake port 3. At this time, force acts on the adjusting screw 16 that tends to push in the adjusting screw 16. But due to the frictional resistance between the external thread 15 of the adjusting screw 16 and the internal thread 14 of the nut member 13, the adjusting screw 16 is prevented from rotating, so that the adjusting screw 16 is axially fixed in position.
When the cam 6 further rotates and the cam lobe 6 a moves past the roller 11, the valve stem 5 rises under the biasing force of the valve spring 9, until the valve 4 is seated on the valve seat 10 and the intake port 3 is closed.
In a strict sense, when the cam lobe 6 a of the cam 6 presses down the arm 7, slight slip occurs between the pressure flank 19 of the external thread 15 and the pressure flank 19 of the internal thread 14. But after the cam lobe 6 a has moved past the roller 11 and until the cam lobe 6 a again contacts the roller 11, since a load tending to push in the adjusting screw 16 is removed, the adjusting screw 16 returns to the original position under the biasing force of the return spring 17.
When the distance between the cam 6 and the arm 7 increases due to differences in thermal expansion between component parts of the valve gear such as the cylinder head 2, valve stem 5 and arm 7 while the engine is running, the adjusting screw 16 moves in the protruding direction while rotating under the biasing force of the return spring 17. Thus, a gap never forms between the base circle 6 b of the cam 6 and the roller 11.
Conversely, when the contact surfaces of the valve 4 and the valve seat 10 become worn, even while the base circle 6 b of the cam 6 is in contact with the roller 11, the biasing force of the valve spring 9 continuously acts on the adjusting screw 16 as a load tending to push in the adjusting screw 16. Thus, due to slight slip that occurs between the external thread 15 and the internal thread 14 every time the cam lobe 6 a contacts the roller 11, the adjusting screw 15 is gradually pushed into the nut member, and the valve stem 5 gradually moves up, thus preventing formation of a gap between the contact surfaces of the valve 4 and the valve seat 10.
With this lash adjuster 1, since the spring seat 18 is fitted in the inner periphery of the nut member 13, the outer periphery of the spring seat 18 is kept out of contact with the adjusting screw 16, so that there is no friction between the outer periphery of the spring seat 18 and the adjusting screw 16. Also, even though the outer periphery of the spring seat 18 contacts the inner periphery of the nut member 13, this does not hinder rotation of the adjusting screw 16, so that the adjusting screw 16 can rotate smoothly.
With this lash adjuster 1, since the fitting surface 24 of the spring seat 18 has an axial length that is longer than the pitch of the internal thread 14 on the inner periphery of the nut member 13, the fitting surface 24 is guided by the internal thread 14 over the entire circumference thereof. Thus, the spring seat 18 can be diametrically positioned stably compared to a lash adjuster of which the fitting surface 24 has an axial length shorter than the pitch of the internal thread 14.
With this lash adjuster 1, since the adjusting screw 16 is a solid member, its rigidity is high compared to the adjusting screw of a lash adjuster which is a hollow member having an opening at its end inserted in the nut member. Thus, if the external thread 15 on the outer periphery of the adjusting screw 16 is formed by rolling, the external thread 15 is less likely to be an incomplete thread.
In this embodiment, of the contact surfaces on the adjusting screw 16 and the spring seat 18, the contact surface on the adjusting screw 16 is the convex spherical surface 22 and the contact surface on the spring seat 18 is the flat surface 23. But instead, as shown in FIG. 4, the contact surface on the adjusting screw 16 may be a flat surface 28 and the contact surface on the spring seat 18 may be a convex spherical surface 29. By forming a convex spherical surface on one of the contact surfaces of the adjusting screw 16 and the spring seat 18 and forming a flat surface on the other, the contact surfaces can be easily formed at a low cost.
Alternatively, of the contact surfaces of the adjusting screw 16 and the spring seat 18, as shown in FIG. 3, the contact surface on the adjusting screw 16 may be a convex spherical surface 30 and the contact surface on the spring seat 18 may be a concave spherical surface 31 having a larger radius of curvature than the convex spherical surface 30. With this arrangement, the spring seat 18 is less likely to incline, which stabilizes the contact position between the adjusting screw 16 and the spring seat 18. Similarly, the contact surface on the spring seat 18 may be a convex spherical surface (not shown) and the contact surface on the adjusting screw 16 may be a concave spherical surface (not shown).
Further alternatively, of the contact surfaces of the adjusting screw 16 and the spring seat 18, as shown in FIG. 5, the contact surface on the adjusting screw 16 may be a convex spherical surface 32 and the contact surface on the spring seat 18 may also be a convex spherical surface 33. With this arrangement, it is possible to reduce the friction between the contact surfaces of the adjusting screw 16 and the spring seat 18 to an extremely low level, thus further reducing the resistance to rotation of the adjusting crew 16.
In the above embodiment, the solid spring seat 18 is fitted in the inner periphery of the nut member 13 while being kept in point contact with the end of the adjusting screw 16 inserted in the nut member 13. But instead of this spring seat 18, a spring seat 36 shown in FIG. 6 may be used, which comprises a cylindrical portion 34 fitted in the inner periphery of the nut member 13, and an end portion 35 kept in point contact with the end of the adjusting screw 16 inserted in the nut member 13, with the return spring 17 inserted in the cylindrical portion 34 of the spring seat 36. With this arrangement, since the fitting surface 37 of the spring seat 36 fitted in the inner periphery of the nut member 13 diametrically overlaps with the return spring 17, it is possible to reduce the axial length of the lash adjuster 1.
Preferably, as shown in FIG. 6, the fitting surface 37 has an axial length that is larger than twice the pitch of the internal thread 14 With this arrangement, irrespective of the axial position of the spring seat 36, the fitting surface 37 of the spring seat 36 is always guided by the internal thread 14 at two or more axially spaced points. This makes the spring seat 36 less likely to incline, thus stabilizing the contact position between the adjusting screw 16 and the spring seat 36.
When the spring seat 36 comprising the cylindrical portion 34 and the end portion 35 is used too, as shown in FIGS. 6 and 8, one of the contact surfaces of the adjusting screw 16 and the spring seat 36 may be a convex spherical surface 38 and the other may be a flat surface 39 so that the contact surfaces can be easily formed at a low cost. Alternatively, as shown in FIG. 7, one of the contact surfaces may be a convex spherical surface 40 and the other may be a concave spherical surface 41. With this arrangement, by the contact between the convex spherical surface 40 and the concave spherical surface 41, it is possible to prevent inclination of the spring seat 36. Further, as shown in FIG. 9, one of the contact surfaces may be a convex spherical surface 42 and the other may also be a convex spherical surface 43. With this arrangement, it is possible to reduce the friction between the contact surfaces of the adjusting screw 16 and the spring seat 36 to an extremely low level, thus further reducing the resistance to rotation of the adjusting crew 16.
FIG. 10 shows a valve gear including the lash adjuster 51 according to the second embodiment of the present invention. As with the first embodiment, this valve gear includes a valve 54 provided at an intake port 53 of a cylinder head 52, and a valve stem 55 connected to the valve 54. The valve stem 55 extends upwardly from the valve 54. A spring retainer 56 is fixed to its upper portion. The valve spring 57 biases the spring retainer 56 upwardly, thereby seating the valve 54 on a valve seat 58.
The lash adjuster 51 comprises a lifter body 60 vertically slidably inserted in a guide hole 59 formed in the cylinder head 52, a nut member 61 vertically movable together with the lifter body 60, an adjusting screw 64 having an external thread 63 on the outer periphery thereof which is in threaded engagement with an internal thread 62 formed on the inner periphery of the nut member 61, a return spring 65 biasing the adjusting screw 64, and a spring seat 66 disposed between the adjusting screw 64 and the return spring 65.
The lifter body 60 comprises a tubular portion 67 and an end wall 68 closing the top end of the tubular portion 67. A hard shim 69 is fixed to the top surface of the end wall 68. A cam 70 is in contact with the shim 69. The nut member 61 is integrally formed at the central portion of the end wall 68, and has its top end closed by the shim 69.
The external thread 63 and the internal thread 62 each have a pressure flank for receiving pressure when a force is applied that tends to push the adjusting screw 64 into the nut member 61, the pressure flank having a larger flank angle than the clearance flank.
The return spring 65 has its top end supported by the shim 69 and presses at its bottom end the adjusting screw 64 through the spring seat 66, thereby biasing the adjusting screw 64 in the direction to protrude downwardly from the nut member 61. The end of the adjusting screw 64 protruding from the nut member 61 presses the top end of the valve stem 55.
The adjusting screw 64 is a solid member having a convex spherical surface at its end inserted in the nut member 61. The spring seat 66 has a flat surface that contacts the convex spherical surface. The adjusting screw 64 is in point contact with the spring seat 66 at the center of rotation of the adjusting screw 64.
The spring seat 66 is axially slidably fitted in the inner periphery of the nut member 61, so that the adjusting screw 64 and the spring seat 66 remain coaxial with each other. The surface of the spring seat 66 fitted in the internal thread 62 is a cylindrical surface having an axial length longer than the pitch of the internal thread 62. The spring seat 66 comprises a cylindrical portion 71 fitted in the inner periphery of the nut member 61, and an end portion 72 kept in point contact with the end of the adjusting screw 64 inserted in the nut member 61, with the return spring 65 inserted in the cylindrical portion 71.
With this lash adjuster 51, as in the first embodiment, since the spring seat 66 is fitted in the inner periphery of the nut member 61, the outer periphery of the spring seat 66 is kept out of contact with the adjusting screw 64, so that there is no friction between the outer periphery of the spring seat 66 and the adjusting screw 64. Also, even though the outer periphery of the spring seat 66 contacts the inner periphery of the nut member 61, this does not hinder rotation of the adjusting screw 64, so that the adjusting screw 64 can rotate smoothly.
With this lash adjuster 51, since the fitting surface of the spring seat 66 has an axial length that is longer than the pitch of the internal thread 62 on the inner periphery of the nut member 61, the fitting surface of the spring seat 66 is guided by the internal thread 62 over the entire circumference thereof. Thus, the spring seat 66 can be diametrically positioned stably compared to a lash adjuster of which the fitting surface has an axial length shorter than the pitch of the internal thread 62.
With this lash adjuster 51, since the adjusting screw 64 is a solid member, its rigidity is high compared to the adjusting screw of a lash adjuster which is a hollow member having an opening at its end inserted in the nut member. Thus, if the external thread 63 on the outer periphery of the adjusting screw 64 is formed by rolling, the external thread 63 is less likely to be an incomplete thread.
In this embodiment, of the contact surfaces on the adjusting screw 64 and the spring seat 66, the contact surface on the adjusting screw 64 is a convex spherical surface and the contact surface on the spring seat 66 is a flat surface. But instead, as in the first embodiment, the contact surface on the adjusting screw 64 may be a flat surface and the contact surface on the spring seat 66 may be a convex spherical surface. Alternatively, one of the contact surfaces of the adjusting screw 64 and the spring seat 66 may be a convex spherical surface and the other may be a concave spherical surface, or one of these contact surfaces may be a convex spherical surface and the other may also be a convex spherical surface.
In this embodiment, in order to reduce the axial length of the lash adjuster 51, the spring seat 66 is used which comprises the cylindrical portion 71 fitted in the inner periphery of the nut member 61, and the end portion 72 kept in point contact with the end of the adjusting screw 64 inserted in the nut member 61, with the return spring 65 inserted in the cylindrical portion 71 of the spring seat 66. But instead, as in the first embodiment, a solid spring seat (not shown) may be fitted in the inner periphery of the nut member 61 and kept in point contact with the end of the adjusting screw 64 inserted in the nut member 61.
In this embodiment, the nut member 61 and the lifter body 60 are integrally formed. But the nut member 61 may be a member separate from the lifter body 60 and fixed to the lifter body 60. What is important is that the nut member is vertically movable together with the lifter body when the lifter body moves vertically.
FIG. 11 shows a valve gear including the lash adjuster 81 according to the third embodiment of the present invention. This valve gear includes a valve 84 provided at an intake port 83 of a cylinder head 82 of an engine, a valve stem 85 connected to the valve 84, and an arm 87 pivotally supported about a pivot shaft 86. The valve stem 85 extends upwardly from the valve 84, and has a spring retainer 88 fixed to its upper portion. A valve spring 89 biases the spring retainer 88 upwardly, thereby seating the valve 84 on a valve seat 90.
The arm 87 has its central portion pivotally supported by the pivot shaft 86. The arm 87 carries at one end thereof a roller 92 kept in contact with a cam 91 so that the arm 87 pivots as the cam 91 rotates. The lash adjuster 81 is mounted to the other end of the arm 87.
The lash adjuster 81 comprises a nut member 93, an adjusting screw 94, a return spring 95, and a spring seat 96 disposed between the adjusting screw 94 and the return spring 95. The nut member 93 is inserted in a hole 97 extending vertically through the arm 87. The adjusting screw 94 has an external thread 99 on its outer periphery that is in threaded engagement with an internal thread 98 formed on the inner periphery of the nut member 93.
The nut member 93 has a top end protruding from the top surface of the arm 87, and a tubular cap 100 having a closed top end is fitted on and fixed to the protruding top end portion of the nut member 93. The cap 100 engages the top edge of the hole 97, thereby preventing the nut member 93 from separating downwardly from the hole 97. The nut member 93 has a flange 101 at its bottom end which is in abutment with the bottom surface of the arm 87, and configured to receive upward force applied to the nut member 93.
The external thread 99 and the internal thread 98 each have a pressure flank for receiving pressure when a force is applied that tends to push the adjusting screw 94 into the nut member 93, the pressure flank having a larger flank angle than the clearance flank.
The return spring 95 has its top end supported by the cap 100 and presses at its bottom end the adjusting screw 94, thereby biasing the adjusting screw 94 in the direction to protrude downwardly from the nut member 93. The end of the adjusting screw 94 protruding from the nut member 93 is pressed against the top end of the valve stem 85.
The adjusting screw 94 is a solid member having a convex spherical surface at its end inserted in the nut member 93. The spring seat 96 has a flat surface that contacts the convex spherical surface. The adjusting screw 94 is in point contact with the spring seat 96 at the center of rotation of the adjusting screw 94.
The spring seat 96 is axially slidably fitted in the inner periphery of the nut member 93, so that the adjusting screw 94 and the spring seat 96 remain coaxial with each other. The spring seat 96 comprises a cylindrical portion 102 fitted in the inner periphery of the nut member 93, and an end portion 103 kept in point contact with the end of the adjusting screw 94 inserted in the nut member 93, with the return spring 95 inserted in the cylindrical portion 102.
With this lash adjuster 81, as in the first embodiment, since the spring seat 96 is fitted in the inner periphery of the nut member 93, the outer periphery of the spring seat 96 is kept out of contact with the adjusting screw 94, so that there is no friction between the outer periphery of the spring seat 96 and the adjusting screw 94. Also, even though the outer periphery of the spring seat 96 contacts the inner periphery of the nut member 93, this does not hinder rotation of the adjusting screw 94, so that the adjusting screw 94 can rotate smoothly.
With this lash adjuster 81, since the adjusting screw 94 is a solid member, its rigidity is high compared to the adjusting screw of a lash adjuster which is a hollow member having an opening at its end inserted in the nut member 93. Thus, if the external thread 99 on the outer periphery of the adjusting screw 94 is formed by rolling, the external thread 99 is less likely to be an incomplete thread.
In this embodiment, of the contact surfaces on the adjusting screw 94 and the spring seat 96, the contact surface on the adjusting screw 94 is a convex spherical surface and the contact surface on the spring seat 96 is a flat surface. But instead, as in the first embodiment, the contact surface on the adjusting screw 94 may be a flat surface and the contact surface on the spring seat 96 may be a convex spherical surface. Alternatively, one of the contact surfaces of the adjusting screw 94 and the spring seat 96 may be a convex spherical surface and the other may be a concave spherical surface, or one of these contact surfaces may be a convex spherical surface and the other may also be a convex spherical surface.
In this embodiment, in order to reduce the axial length of the lash adjuster 81, the spring seat 96 is used which comprises the cylindrical portion 102 fitted in the inner periphery of the nut member 93, and the end portion 103 kept in point contact with the end of the adjusting screw 94 inserted in the nut member 93, with the return spring 95 inserted in the cylindrical portion 102 of the spring seat 96. But instead, as in the first embodiment, a solid spring seat may be fitted in the inner periphery of the nut member 93 and kept in point contact with the end of the adjusting screw 94 inserted in the nut member 93.
In any of the above embodiments, any of the adjusting screws 16, 64 and 94, as well as any of the nut members 13, 61 and 93 and any of the spring seats 18, 36, 66 and 96 may be made of a ferrous material, with their surfaces subjected to carburization, carbonitriding or soft nitriding to increase their durability.

Claims

1. A lash adjuster comprising a nut member inserted in a receiving hole formed in a top surface of a cylinder head and having an internal thread on its inner periphery, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with the internal thread of the nut member and a return spring biasing the adjusting screw in a direction to protrude upwardly from the nut member, said adjusting screw having an end protruding from the nut member and pivotally supporting an arm of a valve gear, wherein said adjusting screw is a solid member, that the lash adjuster further comprises a spring seat disposed between the adjusting screw and the return spring and kept in point contact with an end of the adjusting screw inserted in the nut member, and the spring seat is axially slidably fitted in the inner periphery of the nut member, thereby keeping the adjusting screw and the spring seat coaxial with each other.

2. A lash adjuster comprising a lifter body vertically slidably inserted in a guide hole formed in a cylinder head, a nut member vertically movable together with the lifter body and having an internal thread on its inner periphery, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with the internal thread of the nut member, and a return spring biasing the adjusting screw in a direction to protrude downwardly from the nut member, said adjusting screw having an end protruding from the nut member and pressing a valve stem of a valve gear, wherein said adjusting screw is a solid member, the lash adjuster further comprises a spring seat disposed between the adjusting screw and the return spring and kept in point contact with an end of the adjusting screw inserted in the nut member, and that the spring seat is axially slidably fitted in the inner periphery of the nut member, thereby keeping the adjusting screw and the spring seat coaxial with each other.

3. A lash adjuster comprising a nut member inserted in a receiving hole formed in a bottom surface of an arm that pivots as a cam rotates and having an internal thread on its inner periphery, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with the internal thread of the nut member, and a return spring biasing the adjusting screw in a direction to protrude downwardly from the nut member, said adjusting screw having an end protruding from the nut member and pressing a valve stem of a valve gear, wherein said adjusting screw is a solid member, the lash adjuster further comprises a spring seat disposed between the adjusting screw and the return spring and kept in point contact with an end of the adjusting screw inserted in the nut member, and that the spring seat is axially slidably fitted in the inner periphery of the nut member, thereby keeping the adjusting screw and the spring seat coaxial with each other.

4. The lash adjuster of claim 1 wherein the spring seat has a fitting surface axially slidably fitted in the internal thread on the inner periphery of the nut member, said fitting surface having an axial length longer than a pitch of the internal thread.

5. The lash adjuster of claim 1 wherein the spring seat comprises a cylindrical portion fitted in the inner periphery of the nut member, and an end portion kept in point contact with the end of the adjusting screw inserted in the nut member, and wherein the return spring is inserted in the cylindrical portion of the spring seat.

6. The lash adjuster of claim 1 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is a flat surface.

7. The lash adjuster of claim 1 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is a concave spherical surface.

8. The lash adjuster of claim 1 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is also a convex spherical surface.

9. The lash adjuster of claim 2 wherein the spring seat has a fitting surface axially slidably fitted in the internal thread on the inner periphery of the nut member, said fitting surface having an axial length longer than a pitch of the internal thread.

10. The lash adjuster of claim 3 wherein the spring seat has a fitting surface axially slidably fitted in the internal thread on the inner periphery of the nut member, said fitting surface having an axial length longer than a pitch of the internal thread.

11. The lash adjuster of claim 2 wherein the spring seat comprises a cylindrical portion fitted in the inner periphery of the nut member, and an end portion kept in point contact with the end of the adjusting screw inserted in the nut member, and wherein the return spring is inserted in the cylindrical portion of the spring seat.

12. The lash adjuster of claim 3 wherein the spring seat comprises a cylindrical portion fitted in the inner periphery of the nut member, and an end portion kept in point contact with the end of the adjusting screw inserted in the nut member, and wherein the return spring is inserted in the cylindrical portion of the spring seat.

13. The lash adjuster of claim 2 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is a flat surface.

14. The lash adjuster of claim 3 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is a flat surface.

15. The lash adjuster of claim 2 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is a concave spherical surface.

16. The lash adjuster of claim 4 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is a concave spherical surface.

17. The lash adjuster of claim 2 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is also a convex spherical surface.

18. The lash adjuster of claim 3 wherein one of contact surfaces of the adjusting screw and the spring seat is a convex spherical surface and the other of the contact surfaces is also a convex spherical surface.