U.S. patent application number 12/811845 was filed with the patent office on 2010-11-04 for lash adjuster.
Invention is credited to Eiji Maeno, Katsuhisa Yamaguchi, Makoto Yasui.
Application Number | 20100275865 12/811845 |
Document ID | / |
Family ID | 40912706 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100275865 |
Kind Code |
A1 |
Yasui; Makoto ; et
al. |
November 4, 2010 |
LASH ADJUSTER
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.
Inventors: |
Yasui; Makoto; ( Shizuoka,
JP) ; Yamaguchi; Katsuhisa; ( Shizuoka, JP) ;
Maeno; Eiji; ( Shizuoka, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
40912706 |
Appl. No.: |
12/811845 |
Filed: |
January 26, 2009 |
PCT Filed: |
January 26, 2009 |
PCT NO: |
PCT/JP2009/051171 |
371 Date: |
July 7, 2010 |
Current U.S.
Class: |
123/90.54 |
Current CPC
Class: |
F01L 1/22 20130101; F01L
1/181 20130101; F01L 2305/00 20200501; F01L 1/185 20130101; F01L
1/143 20130101 |
Class at
Publication: |
123/90.54 |
International
Class: |
F01L 1/22 20060101
F01L001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2008 |
JP |
2008-016111 |
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.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] This invention relates to a lash adjuster mounted in an
engine valve gear.
[0003] 2. Background Art
[0004] 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).
[0005] 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.
[0006] 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.
[0007] 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).
[0008] 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).
[0009] 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).
[0010] 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.
[0011] 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
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] An object of the present invention is to provide a lash
adjuster of which the adjusting screw can rotate smoothly.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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
[0027] FIG. 1 is a front view of a valve gear including a lash
adjuster according to a first embodiment of the present
invention.
[0028] FIG. 2 is an enlarged sectional view of a portion of the
valve gear where there is the lash adjuster.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] FIG. 10 is a front view of a valve gear including a lash
adjuster according to a second embodiment of the present
invention.
[0037] 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
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] The operation of the lash adjuster 1 is now described.
[0049] When the cam 6 is rotated by the engine and the cam lobe 6a
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.
[0050] When the cam 6 further rotates and the cam lobe 6a 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.
[0051] In a strict sense, when the cam lobe 6a 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 6a has moved past the roller 11
and until the cam lobe 6a 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.
[0052] 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
6b of the cam 6 and the roller 11.
[0053] Conversely, when the contact surfaces of the valve 4 and the
valve seat 10 become worn, even while the base circle 6b 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 6a 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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).
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
* * * * *