U.S. patent application number 12/811225 was filed with the patent office on 2010-11-18 for lash adjuster.
Invention is credited to Eiji Maeno, Katsuhisa Yamaguchi, Makoto Yasui.
Application Number | 20100288219 12/811225 |
Document ID | / |
Family ID | 40901036 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100288219 |
Kind Code |
A1 |
Yasui; Makoto ; et
al. |
November 18, 2010 |
LASH ADJUSTER
Abstract
A lash adjuster is provided of which the return spring is never
compressed excessively when the adjusting screw is pushed into the
nut member, and of which the external thread on the outer periphery
of the adjusting screw can be formed easily by rolling. The lash
adjuster 1 includes a nut member 12 having an internal thread 13,
an adjusting screw 15 having an external thread 14 on its outer
periphery which is in threaded engagement with the internal thread
13, and a return spring 17 biasing the adjusting screw 15 in the
direction to protrude from the nut member 12. The adjusting screw
15 pivotally supports an arm 7 of a valve gear at its end
protruding from the nut member 12. The adjusting screw 15 has at
its portion protruding from the nut member 12 a stopper portion 23
having a larger diameter than the inner diameter of the nut member
12. By supporting the stopper portion 23 on the open end of the nut
member 12, it is possible to restrict the movement of the adjusting
screw 15 when the adjusting screw 15 is pushed into the nut member
12.
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: |
40901036 |
Appl. No.: |
12/811225 |
Filed: |
January 16, 2009 |
PCT Filed: |
January 16, 2009 |
PCT NO: |
PCT/JP2009/050534 |
371 Date: |
June 30, 2010 |
Current U.S.
Class: |
123/90.53 |
Current CPC
Class: |
F01L 2303/00 20200501;
F01L 1/185 20130101; F01L 1/22 20130101; F01L 1/462 20130101; F01L
1/053 20130101; F01L 3/08 20130101; F01L 1/0532 20130101; F01L
2305/00 20200501; F01L 1/181 20130101; F01L 1/143 20130101 |
Class at
Publication: |
123/90.53 |
International
Class: |
F01L 1/14 20060101
F01L001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 22, 2008 |
JP |
2008-011409 |
Dec 22, 2008 |
JP |
2008-325682 |
Claims
1. A lash adjuster comprising a nut member (12) having an internal
thread (13) on its inner periphery, an adjuster screw (15) having
an external thread (14) on its outer periphery which is in threaded
engagement with the internal thread (13), and a return spring (17)
biasing the adjusting screw (15) in a direction to protrude from
the nut member (12), wherein an axial load that tends to push the
adjusting screw (15) into the nut member (12) is received by
pressure flanks (18) of the external thread (14) and the internal
thread (13), characterized in that the adjusting screw (15) has a
stopper portion (23) at its portion protruding from the nut member
(12), said stopper portion (23) having a diameter larger than the
inner diameter of the nut member (12), wherein the nut member (12)
has an open end configured to support the stopper portion (23),
thereby restricting movement of the adjusting screw (15) when the
adjusting screw (15) is pushed into the nut member (12).
2. The lash adjuster of claim 1 wherein the stopper portion (23)
has a tapered surface (24) on its outer periphery which is
configured to abut a tapered surface (25) formed on the open end of
the nut member (12).
3. The lash adjuster of claim 1 wherein the stopper portion (23)
has a flat surface (26) on its outer periphery which extends
perpendicular to an axial direction and configured to abut a flat
surface (27) formed on the open end of the nut member (12) so as to
extend perpendicular to the axial direction.
4. The lash adjuster of claim 1 wherein the stopper portion (23)
comprises a snap ring (28) fitted on the outer periphery of the
portion of the adjusting screw (15) protruding from the nut member
(12).
5. The lash adjuster of claim 1 wherein the return spring (17) is a
compression spring that applies an axial force to the adjusting
screw (15) that tends to push the adjusting screw (15) out of the
nut member (12), and wherein the external thread (14) and the
internal thread (13) have a serration-shaped section with their
pressure flanks (18) having a larger flank angle than their
clearance flanks (19).
6. The lash adjuster of claim 1 wherein the return spring (17) is a
torsion spring that applies torque to the adjusting screw (15) that
tends to push the adjusting screw (15) out of the nut member (12),
and wherein the external thread (14) and the internal thread (13)
are serration-shaped threads, trapezoidal threads or triangular
threads.
7. The lash adjuster of claim 6 wherein the torsion spring is one
of a torsion coil spring, a spiral spring and a volute spring.
8. The lash adjuster of claim 1 wherein the nut member (12) is
inserted in a receiving hole (11) formed in a top surface of a
cylinder head (2), and wherein the adjusting screw (15) pivotally
supports an arm (7) of a valve gear at its end protruding from the
nut member (12).
9. The lash adjuster of claim 1 wherein the nut member (41) is
fixed to a lifter body (40) vertically slidably inserted in a guide
hole (39) formed in a cylinder head (32), and wherein the adjusting
screw (44) presses a valve stem (35) of a valve gear at its end
protruding from the nut member (41).
10. The lash adjuster of claim 1 wherein the nut member (73) is
inserted in a receiving hole (76) formed in a bottom surface of an
arm (67) that pivots as a cam (71) rotates, and wherein the
adjusting screw (74) presses a valve stem (65) of a valve gear at
its end protruding from the nut member (73).
11. The lash adjuster of claim 1 wherein the adjusting screw (15)
comprises a pivot member (15A) axially slidably inserted in the nut
member (12), an externally threaded member (15B) supporting an end
of the pivot member (15A) located in the nut member (12) and having
said external thread (14) on its outer periphery, and an elastic
member (15C) disposed between the pivot member (15A) and the
externally threaded member (15B).
12. The lash adjuster of claim 11 wherein the pivot member (15A)
has a square hole (96) formed in its end located in the nut member
(12), and wherein the externally threaded member (15B) has a square
shaft (97) engaged in said square hole (96), whereby the pivot
member (15A) and the externally threaded member (15B) are rotatable
together due to the engagement of the square shaft (97) in the
square hole (96).
Description
TECHNICAL FIELD
[0001] This invention relates to a lash adjuster mounted in an
engine valve gear.
BACKGROUND ART
[0002] 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).
[0003] 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.
[0004] 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.
[0005] 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 (Patent documents 1 and
4).
[0006] 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 (Patent
document 2).
[0007] 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 (Patent
documents 3 and 4).
[0008] In Patent documents 1-3, the return spring is a coil spring
that applies an axial force to the adjusting screw that tends to
move the adjusting screw in the direction to protrude from the nut
member. In Patent document 4, the return spring is a torsion spring
that applies torque to the adjusting spring that tends to move the
adjusting screw in the direction to protrude from the nut
member.
[0009] In these lash adjusters, as a cam rotates and a load that
tends to push the adjusting screw into the nut member is applied,
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.
[0010] If the relative position between the arm and the valve stem
changes due e.g. to thermal expansion of the valve gear, according
to the degree of change in the relative position, the adjusting
screw axially moves in the nut member while rotating, thereby
absorbing gaps between component parts of the valve gear.
Patent document 1: JP Patent Publication 2005-273510A Patent
document 2: JP Patent Publication 2003-227318A Patent document 3:
JP Patent Publication 2006-132426A Patent document 4: JP Utility
Model Publication 64-34407
DISCLOSURE OF THE INVENTION
Object of the Invention
[0011] With these types of lash adjusters, in an ordinary
situation, only slight slip occurs between the external thread of
the adjusting screw and the internal thread of the nut member. But
if abnormal loads or vibrations act on the adjusting screw due to
over-speed of the engine, if the frictional resistance between the
pressure flanks decreases due to wear of the external thread and
the internal thread, or if the adjusting screw is suddenly and
rapidly pushed in due to sudden thermal expansion of the valve
gear, unnecessarily large slip may occur between the external
thread of the adjusting screw and the internal thread of the nut
member.
[0012] As a result, the adjusting screw is markedly pushed into the
nut member, which may cause breakage of the return spring due to
over-compression or separation of the arm.
[0013] One way to prevent the return spring from being excessively
compressed and broken when the adjusting screw is pushed into the
nut member would be to provide a tubular extension at the end of
the adjusting screw located in the nut member so as to surround the
return spring. The extension restricts the movement of the
adjusting screw by abutting the bottom of the nut member. But with
this arrangement, since the tubular extension of the adjusting
screw is low in rigidity, when the external screw is formed on the
outer periphery of the adjusting screw by rolling, the external
screw tends to be formed incompletely.
[0014] An object of the present invention is to provide a lash
adjuster of which the return spring is never compressed excessively
when the adjusting screw is pushed into the nut member, and of
which the external thread on the outer periphery of the adjusting
screw can be formed easily by rolling.
Means to Achieve the Object
[0015] In order to achieve this object, the adjusting screw is
provided with a stopper portion at its portion protruding from the
nut member, the stopper portion having a diameter larger than the
inner diameter of the nut member. The stopper portion abuts an open
end of the nut member, thereby restricting movement of the
adjusting screw when the adjusting screw is pushed into the nut
member.
[0016] The stopper portion may have a tapered surface on its outer
periphery which is configured to abut a tapered surface formed on
the open end of the nut member. With this arrangement, when the
adjusting screw is pushed into the nut member, the tapered surfaces
contact each other, thereby preventing inclination of the adjusting
screw. This helps the adjusting screw to protrude smoothly
thereafter.
[0017] Alternatively, the stopper portion may have a flat surface
on its outer periphery which extends perpendicular to the axial
direction and configured to abut a flat surface formed on the open
end of the nut member so as to extend perpendicular to the axial
direction. With this arrangement too, when the adjusting screw is
pushed into the nut member, the flat surfaces contact each other,
thereby preventing inclination of the adjusting screw, which helps
the adjusting screw to protrude smoothly thereafter.
[0018] The stopper portion may be integrally provided at the
portion of the adjusting screw protruding from the nut member, or
may be a separate member from the adjusting screw. In the latter
case, such a separate stopper member may be a snap ring fitted on
the outer periphery of the portion of the adjusting screw
protruding from the nut member.
[0019] This invention is applicable to a lash adjuster wherein the
return spring is a compression spring that applies an axial force
to the adjusting screw that tends to push the adjusting screw out
of the nut member. In this case, the external thread and the
internal thread may have a serration-shaped section with their
pressure flanks having a larger flank angle than their clearance
flanks.
[0020] This invention is also applicable to lash adjuster wherein
the return spring is a torsion spring that applies torque to the
adjusting screw that tends to push the adjusting screw out of the
nut member. In this case, the external thread and the internal
thread may be serration-shaped threads, trapezoidal threads or
triangular threads. The torsion spring may be one of a torsion coil
spring, a spiral spring and a volute spring.
[0021] This invention is applicable e.g. to the following lash
adjusters.
1) A lash adjuster wherein the nut member is inserted in a
receiving hole formed in a top surface of a cylinder head, and
wherein the adjusting screw pivotally supports an arm of a valve
gear at its end protruding from the nut member. 2) A lash adjuster
of any wherein the nut member is fixed to a lifter body vertically
slidably inserted in a guide hole formed in a cylinder head, and
wherein the adjusting screw presses a valve stem of a valve gear at
its end protruding from the nut member. 3) A lash adjuster wherein
the nut member is inserted in a receiving hole formed in a bottom
surface of an arm that pivots as a cam rotates, and wherein the
adjusting screw presses a valve stem of a valve gear at its end
protruding from the nut member.
[0022] The adjusting screw may comprises a pivot member axially
slidably inserted in the nut member, an externally threaded member
supporting an end of the pivot member located in the nut member and
having the external thread on its outer periphery, and an elastic
member disposed between the pivot member and the externally
threaded member.
[0023] In this case, the pivot member preferably has a square hole
formed in its end located in the nut member, and the externally
threaded member preferably has a square shaft engaged in the square
hole, whereby the pivot member and the externally threaded member
are rotatable together due to the engagement of the square shaft in
the square hole. With this arrangement, since the externally
threaded member can be rotated by rotating the pivot member, the
externally threaded member can be easily mounted in the nut
member.
ADVANTAGES OF THE INVENTION
[0024] With the lash adjuster according to this invention, when the
adjusting screw is pushed into the nut member, the stopper portion
abuts the open end of the nut member, thereby restricting movement
of the adjusting screw. This prevents over-compression of the
return spring.
[0025] With this lash adjuster, since the stopper member for
restricting the movement of the adjusting screw is provided at the
portion of the adjusting screw protruding from the nut member, it
is not necessary to provide a tubular extension for restricting the
movement of the adjusting screw by abutting the bottom member at
the end of the adjusting screw located in the nut member. Thus, the
external thread on the outer periphery of the adjusting screw can
be formed easily by rolling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a front view of a valve gear including a lash
adjuster according to a first embodiment of the present
invention.
[0027] FIG. 2 is an enlarged sectional view of the lash adjuster
shown in FIG. 1, showing the state in which its adjusting screw is
pushed in.
[0028] FIG. 3 is an enlarged sectional view of a modification of
the lash adjuster shown in FIG. 2.
[0029] FIG. 4 is an enlarged sectional view of a further
modification of the lash adjuster of FIG. 2.
[0030] FIG. 5 is an enlarged sectional view of a still further
modification of the lash adjuster of FIG. 2.
[0031] FIG. 6 is a front view of a valve gear including a lash
adjuster according to a second embodiment of the present
invention.
[0032] FIG. 7 is a front view of a valve gear including a lash
adjuster according to a third embodiment of the present
invention.
[0033] FIG. 8 is an enlarged view of a modification of the return
spring shown in FIG. 2.
[0034] FIG. 9 is an enlarged view of a modification of the return
spring shown in FIG. 6.
[0035] FIG. 10 is an enlarged view of a modification of the return
spring shown in FIG. 7.
[0036] FIG. 11 is an enlarged sectional view of a lash adjuster
according to a fourth embodiment of the present invention.
[0037] FIG. 12 is an enlarged sectional view of a modification of
the return spring shown in FIG. 11.
[0038] FIG. 13 is an enlarged sectional view of a further
modification of the return spring shown in FIG. 11.
[0039] FIG. 14 is an enlarged sectional view of a still further
modification of the return spring shown in FIG. 11.
[0040] FIG. 15 is a sectional view taken along line XV-XV of FIG.
14.
DESCRIPTION OF THE NUMERALS
[0041] 1. Lash adjuster [0042] 2. Cylinder head [0043] 7. Arm
[0044] 11. Receiving hole [0045] 12. Nut member [0046] 13. Internal
thread [0047] 14. External thread [0048] 15. Adjusting screw [0049]
15A. Pivot member [0050] 15B. Externally threaded member [0051]
15C. Spring washer [0052] 17. Return spring [0053] 18. Pressure
flank [0054] 19. Clearance flank [0055] 23. Stopper portion [0056]
24, 25. Tapered surface [0057] 26, 27. Flat surface [0058] 28. Snap
ring [0059] 31. Lash adjuster [0060] 32. Cylinder head [0061] 35.
Valve stem [0062] 39. Guide hole [0063] 40. Lifter body [0064] 41.
Nut member [0065] 42. Internal thread [0066] 43. External thread
[0067] 44. Adjusting screw [0068] 45. Return spring [0069] 51.
Stopper portion [0070] 61. Lash adjuster [0071] 65. Valve stem
[0072] 67. Arm [0073] 71. Cam [0074] 73. Nut member [0075] 74.
Adjusting screw [0076] 75. Return spring [0077] 76. Receiving hole
[0078] 77. Internal thread [0079] 78. External thread [0080] 82.
Stopper portion [0081] 91. Lash adjuster [0082] 94, 95. Flat
surface [0083] 96. Square hole [0084] 97. Square shaft
BEST MODE FOR EMBODYING THE INVENTION
[0085] 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.
[0086] 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.
[0087] As shown in FIG. 2, the lash adjuster 1 comprises a tubular
nut member 12 received in a receiving hole 11 formed in the top
surface of the cylinder head 2, an adjusting screw 15 having an
external thread 14 on its outer periphery at its lower portion
which is in threaded engagement with an internal thread 13 formed
on the inner periphery of the nut member 12, a bottom member 16
fixed to the bottom end of the nut member 12, and a return spring
17 mounted between the adjusting screw 15 and the bottom member
16.
[0088] The external thread 14 and the internal thread 13 each have
a pressure flank 18 for receiving an axial load that tends to push
the adjusting screw 15 into the nut member 12, and a clearance
flank 19, and have a serration-shaped section with the pressure
flank 18 having a larger flank angle than the clearance flank
19.
[0089] The return spring 17 is a compression coil spring having its
bottom end supported on the bottom member 16 and applying at its
top end an axial force to the adjusting screw 15 through a spring
seat 20 that tends to protrude the adjusting screw 15 upwardly from
the nut member 12. The end portion of the adjusting screw 15 that
is inserted in the nut member 12 has a tubular shape, and receives
the spring seat 20.
[0090] The end of adjusting screw 15 protruding from the nut member
12 is engaged in a recess 21 formed in the bottom surface of the
arm 7 at one end thereof. The arm 7 is thus pivotally supported
about the protruding end of the adjusting screw 15. The bottom
surface of the arm 7 at the other end is in contact with the top
end of the valve stem 5. The arm 7 carries at its mid-portion a
roller 22 that is in contact with the cam 6, which is located over
the arm 7.
[0091] The portion of the adjusting screw 15 protruding from the
nut member 12 has a stopper portion 23 having a diameter larger
than the inner diameter of the nut member 12. As shown in FIG. 2,
the stopper portion 23 has a tapered surface 24 on its outer
periphery which is adapted to abut a tapered surface 25 formed at
the open end of the nut member 12 when the adjusting screw 15 is
pushed into the nut member 12, thereby restricting the movement of
the adjusting screw 15.
[0092] The operation of the lash adjuster 1 is now described.
[0093] 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 15 that tends to push in the adjusting
screw 15. But due to the frictional resistance between the external
thread 14 of the adjusting screw 15 and the internal thread 13 of
the nut member 12, the adjusting screw 15 is prevented from
rotating, so that the adjusting screw 15 is axially fixed in
position.
[0094] When the cam 6 further rotates and the cam lobe 6a moves
past the roller 22, 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.
[0095] 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 18 of
the external thread 14 and the pressure flank 18 of the internal
thread 13. But after the cam lobe 6a has moved past the roller 22
and until the cam lobe 6a again contacts the roller 22, since a
load tending to push in the adjusting screw 15 is removed, the
adjusting screw 15 returns to the original position under the
biasing force of the return spring 17.
[0096] 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 15 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 22.
[0097] 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 22, the biasing force of the valve
spring 9 continuously acts on the adjusting screw 15 as a load
tending to push in the adjusting screw 15. Thus, due to slight slip
that occurs between the external thread 14 and the internal thread
13 every time the cam lobe 6a contacts the roller 22, 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.
[0098] As discussed above, in an ordinary situation, only slight
slip occurs between the external thread 14 of the adjusting screw
15 and the internal thread 13 of the nut member 12. But if abnormal
loads or vibrations act on the adjusting screw 15 due to over-speed
of the engine, if the frictional resistance between the pressure
flanks 18 decreases due to wear of the external thread 14 and the
internal thread 13, or if the adjusting screw 15 is suddenly and
rapidly pushed in due to sudden thermal expansion of the valve
gear, unnecessarily large slip may occur between the external
thread 14 of the adjusting screw 15 and the internal thread 13 of
the nut member 12.
[0099] As a result, the adjusting screw 15 is markedly pushed into
the nut member 12. But as shown in FIG. 2, when the adjusting screw
15 is pushed in a certain distance, the stopper portion 23 abuts
the open end of the nut member 12, thus preventing any further
movement of the adjusting screw 15, and thus preventing breakage of
the return spring 17 due to over-compression or separation of the
arm 7.
[0100] When abnormal loads or vibrations or sudden thermal
expansion of the valve gear disappears, the adjusting screw 15 is
moved in the protruding direction under the biasing force of the
return spring 17, and the lash adjuster returns to normal.
[0101] With this lash adjuster 1, since the adjusting screw 15 has
a stopper portion 23 at its portion protruding from the nut member
12, it is not necessary to provide a tubular extension for
restricting the movement of the adjusting screw 15 by abutting the
bottom member 16 at the end of the adjusting screw 15 located in
the nut member 12. Thus, the external thread 14 on the outer
periphery of the adjusting screw 15 can be formed easily by
rolling.
[0102] With this lash adjuster 1, when the adjusting screw 15 is
pushed into the nut member 12, the tapered surface 24 on the outer
periphery of the stopper portion 23 abuts the tapered surface 25
formed at the open end of the nut member 12, thereby preventing
inclination of the adjusting screw 15 by the contact of the tapered
surfaces 24 and 25. This helps the adjusting screw 15 to protrude
smoothly thereafter.
[0103] As shown in FIG. 3, the stopper portion 23 may have on its
outer periphery a flat surface 26 perpendicular to the axial
direction and configured to abut a flat surface 27 formed on the
open end of the nut member 12 so as to be perpendicular to the
axial direction when the adjusting screw 15 is pushed into the nut
member 12. With this arrangement too, it is possible to prevent
inclination of the adjusting screw 15 when the adjusting screw 15
is pushed into the nut member 12 by the contact of the flat
surfaces 26 and 27, thus helping the adjusting screw 15 to protrude
smoothly thereafter.
[0104] In the above embodiment, the stopper portion 23, which has a
larger diameter than the inner diameter of the nut member 12, is
integrally provided at the portion of the adjusting screw 15
protruding from the nut member 12. But instead, the stopper portion
23 may be a separate member from the adjusting screw 15. For
example, such a separate stopper member 23 may be a snap ring 28
fitted around the portion of the adjusting screw 15 protruding from
nut member 12, as shown in FIG. 4.
[0105] In the above embodiment, the portion of the adjusting screw
15 having the external thread 14 on the outer periphery is integral
with its portion protruding from the nut member 12. But as shown in
FIG. 5, the adjusting screw 15 may comprise a body 15b having the
external thread 14 on the outer periphery, and a head 15a separate
from the body 15b and protruding from the nut member 12. In this
case, the head 15a may be slidably inserted in the nut member 12,
and an engaging member 29 may be provided at the open end of the
nut member 12 to prevent separation of the head 15a from the nut
member 12 by engaging the head 15a.
[0106] FIG. 6 shows a valve gear including the lash adjuster 31
according to the second embodiment of the present invention. As
with the first embodiment, this valve gear includes a valve 34
provided at an intake port 33 of a cylinder head 32, and a valve
stem 35 connected to the valve 34. The valve stem 35 extends
upwardly from the valve 34, and has a spring retainer 36 fixed to
its upper portion. A spring retainer 36 biases the spring retainer
36 upwardly, thereby seating the valve 34 against a valve seat
38.
[0107] The lash adjuster 31 comprises a lifter body 40 vertically
slidably inserted in a guide hole 39 formed in the cylinder head
32, a nut member 41 vertically movable together with the lifter
body 40, an adjusting screw 44 having an external thread 43 on the
outer periphery thereof which is in threaded engagement with an
internal thread 42 formed on the inner periphery of the nut member
41, and a return spring 45 biasing the adjusting screw 44 in the
direction to protrude downwardly from the nut member 41.
[0108] The lifter body 40 comprises a tubular portion 46 and an end
wall 47 closing the top end of the tubular portion 46. A hard shim
48 is fixed to the top surface of the end wall 47. A cam 49 is in
contact with the shim 48. The nut member 41 is integrally formed at
the central portion of the end wall 47, and has its top end closed
by the shim 48.
[0109] The external thread 43 and the internal thread 42 each have
a pressure flank for receiving an axial load tending to push the
adjusting screw 44 into the nut member 41, and a clearance flank,
and have a serration-shaped section, with the pressure flank having
a larger flank angle than the clearance flank.
[0110] The return spring 45 is a compression spring having its top
end supported by the shim 48 and applying at its bottom end an
axial force to the adjusting screw 44 through a spring seat 50 that
tends to push the adjusting screw 44 downwardly out of the nut
member 41. The end of the adjusting screw 44 protruding from the
nut member 41 is pressed against the top end of the valve stem 35.
The end of the adjusting screw 44 located in the nut member 41 has
a tubular shape in which the spring seat 50 is received.
[0111] The adjusting screw 44 has at its portion protruding from
the nut member 41 a stopper portion 51 having a larger diameter
than the inner diameter of the nut member 41. When the adjusting
screw 44 is pushed into the nut member 41, the stopper portion 51
restricts the movement of the adjusting screw 44 by abutting the
open end of the nut member 41. The stopper portion 51 can be formed
by rolling simultaneously with the external thread 43.
[0112] As with the first embodiment, with this lash adjuster 31, in
an ordinary situation, only slight slip occurs between the external
thread 43 of the adjusting screw 44 and the internal thread 42 of
the nut member 41. But if abnormal loads or vibrations act on the
adjusting screw 44 due to over-speed of the engine, or if the
frictional resistance between the pressure flanks decreases due to
wear of the external thread 43 and the internal thread 42,
unnecessarily large slip may occur between the external thread 43
of the adjusting screw 44 and the internal thread 42 of the nut
member 41.
[0113] As a result, the adjusting screw 44 is markedly pushed into
the nut member 41. But when the adjusting screw 44 is pushed in a
certain distance, the stopper portion 51 abuts the open end of the
nut member 41, thus preventing any further movement of the
adjusting screw 44, and thus preventing breakage of the return
spring 45 due to over-compression.
[0114] With this lash adjuster 31, since the stopper portion 51 for
restricting the movement of the adjusting screw 44 is provided at
the portion of the adjusting screw 44 protruding from the nut
member 41, it is not necessary to provide a tubular extension for
restricting the movement of the adjusting screw 44 by abutting the
shim 48 at the end of the adjusting screw 44 located in the nut
member 41. Thus, the external thread 43 on the outer periphery of
the adjusting screw 44 can be formed easily by rolling.
[0115] In this embodiment, the nut member 41 and the lifter body 40
are integrally formed. But the nut member 41 and the lifter body 40
may be separate members with the nut member 41 fixed to the lifter
body 40. In either case, it is important that the nut member 41
move vertically together with the lifter body 40 when the lifter
body 40 is vertically moved.
[0116] FIG. 7 shows a valve gear including the lash adjuster 61
according to the third embodiment of the present invention. This
valve gear includes a valve 64 provided at an intake port 63 of a
cylinder head 62 of an engine, a valve stem 65 connected to the
valve 64, and an arm 67 pivotally supported about a pivot shaft 66.
The valve stem 65 extends upwardly from the valve 64, and has a
spring retainer 68 fixed to its upper portion. A valve spring 69
biases the spring retainer 68 upwardly, thereby seating the valve
64 on a valve seat 70.
[0117] The arm 67 has its central portion pivotally supported by
the pivot shaft 66. The arm 67 carries at one end thereof a roller
72 kept in contact with a cam 71 so that the arm 67 pivots as the
cam 71 rotates. The lash adjuster 61 is mounted to the other end of
the arm 67.
[0118] The lash adjuster 61 comprises a nut member 73, an adjusting
screw 74 and a return spring 75. The nut member 73 is inserted in a
hole 76 extending vertically through the arm 67. The adjusting
screw 74 has an external thread 78 on its outer periphery that is
in threaded engagement with an internal thread 77 formed on the
inner periphery of the nut member 73.
[0119] The nut member 73 has a top end protruding from the top
surface of the arm, and a tubular cap 79 having a closed top end is
fitted on and fixed to the protruding top end portion of the nut
member 73. The cap 79 engages the top edge of the hole 76, thereby
preventing the nut member 73 from separating downwardly from the
hole 76. The nut member 73 has a flange 80 at its bottom end which
is in abutment with the bottom surface of the arm 67, and
configured to receive upward force applied to the nut member
73.
[0120] The external thread 78 and the internal thread 77 each have
a pressure flank for receiving an axial load tending to push the
adjusting screw 74 into the nut member 73, and a clearance flank,
and have a serration-shaped section, with the pressure flank having
a larger flank angle than the clearance flank.
[0121] The return spring 75 is a compression spring having its top
end supported by the cap 79 and applying at its bottom end an axial
force to the adjusting screw 74 through a spring seat 81 that tends
to push the adjusting screw 74 downwardly out of the nut member 73.
The end of the adjusting screw 74 protruding from the nut member 73
is pressed against the top end of the valve stem 65.
[0122] The adjusting screw 74 has at its portion protruding from
the nut member 73 a stopper portion 82 having a larger diameter
than the inner diameter of the nut member 73. When the adjusting
screw 74 is pushed into the nut member 73, the stopper portion 82
restricts the movement of the adjusting screw 74 by abutting the
open end of the nut member 73. The stopper portion 82 can be formed
by rolling simultaneously with the external thread 78.
[0123] As with the first embodiment, with this lash adjuster 61, in
an ordinary situation, only slight slip occurs between the external
thread 78 of the adjusting screw 74 and the internal thread 77 of
the nut member 73. But if abnormal loads or vibrations act on the
adjusting screw 74 due to over-speed of the engine, or if the
frictional resistance between the pressure flanks decreases due to
wear of the external thread 78 and the internal thread 77,
unnecessarily large slip may occur between the external thread 78
of the adjusting screw 74 and the internal thread 77 of the nut
member 73.
[0124] As a result, the adjusting screw 74 is markedly pushed into
the nut member 73. But when the adjusting screw 74 is pushed in a
certain distance, the stopper portion 82 abuts the open end of the
nut member 73, thus preventing any further movement of the
adjusting screw 74, and thus preventing breakage of the return
spring 75 due to over-compression.
[0125] With this lash adjuster 61, since the stopper portion 82 for
restricting the movement of the adjusting screw 74 is provided at
the portion of the adjusting screw 74 protruding from the nut
member 73, it is not necessary to provide a tubular extension for
restricting the movement of the adjusting screw 74 by abutting the
cap 79 at the end of the adjusting screw 74 located in the nut
member 73. Thus, the external thread 78 on the outer periphery of
the adjusting screw 74 can be formed easily by rolling.
[0126] In the first embodiment, a compression spring is used as the
return spring 17 for biasing the adjusting screw 15 in the
direction to protrude upwardly from the nut member 12, a torsion
coil spring may used instead as shown in FIG. 8.
[0127] In FIG. 8, the return spring 17 has its bottom end engaged
in an engaging hole 83 formed in the bottom member 16, and its top
end engaged in an engaging hole 84 formed in the adjusting screw
15. Thus this return spring applies torque to the adjusting screw
15 that tends to push the adjusting screw out of the nut member 12
by its torsional deformation.
[0128] In the second embodiment too, as shown in FIG. 9, a torsion
coil spring may be used as the return spring 45 for biasing the
adjusting screw 44 in the direction to protrude downwardly from the
nut member 41.
[0129] In FIG. 9, the return spring 45 has its top end engaged in
an engaging hole 85 formed in the shim 48 and its bottom end
engaged in an engaging hole 86 formed in the adjusting screw 44.
Thus this return spring applies torque to the adjusting screw 44
that tends to push the adjusting screw out of the nut member 41 by
its torsional deformation. The external thread 43 on the outer
periphery of the adjusting screw 44 and the internal thread 42 on
the nut member 41 are both vertically symmetrical trapezoidal
thread.
[0130] In the third embodiment too, as shown in FIG. 10, a torsion
coil spring may be used as the return spring 75 for biasing the
adjusting screw 74 in the direction to protrude downwardly from the
nut member 73.
[0131] In FIG. 10, the return spring 75 has its top end engaged in
an engaging hole 87 formed in the cap 79 and its bottom end engaged
in an engaging hole 88 formed in the adjusting screw 74. Thus this
return spring applies torque to the adjusting screw 74 that tends
to push the adjusting screw out of the nut member 73 by its
torsional deformation. The external thread 78 on the outer
periphery of the adjusting screw 74 and the internal thread 77 on
the nut member 73 are both vertically symmetrical triangular
thread.
[0132] FIG. 11 shows a valve gear including the lash adjuster 91
according to the fourth embodiment of this invention. Elements
corresponding to those of the first embodiment are denoted by
identical numerals and their description is omitted.
[0133] The adjusting screw 15 comprises a pivot member 15A axially
slidably inserted in the nut member 12, an externally threaded
member 15B supporting the end of the pivot member 15A located in
the nut member 12 and having an external thread on its outer
periphery, and a spring washer 15C disposed between the pivot
member 15A and the externally threaded member 15B. The spring
washer 15C may be a disk spring washer or a wavy washer.
[0134] An annular anti-separation member 92 is fitted on the open
end of the nut member 12 through which the pivot member 15A
extends. The pivot member 15A is formed with an annular groove 93
at its portion extending through the open end of the nut member 12.
The anti-separation member 92 is engaged in the annular groove 93,
thereby preventing separation of the pivot member 15A from the nut
member 12.
[0135] At its portion protruding from the nut member 12, the pivot
member 15A has a stopper portion 23 having a diameter larger than
the inner diameter of the nut member 12. The stopper portion 23 has
a flat surface 94 formed on its outer periphery to extend
perpendicular to the axial direction. When the pivot member 15A is
pushed into the nut member 12, the flat surface 94 is configured to
abut a flat surface 95 formed on the anti-separation member 92
provided at the open end of the nut member 12 to extend
perpendicular to the axial direction, thereby restricting the
movement of the pivot member 15A.
[0136] The pivot member 15A is formed with a square hole 96 in the
center of its end inserted in the nut member 12. The externally
threaded member 15B is formed with a square shaft 97 engaged in the
square hole 96. Thus, when the pivot member 15A is rotated, the
pivot member 15A and the externally threaded member 15B rotate
together due to the engagement of the square shaft 97 in the square
hole 96.
[0137] The return spring 17 is a torsion coil spring having its
bottom end engaged in an engaging hole 98 formed in the bottom
member 16, and its top end engaged in an engaging hole 99 formed in
the externally threaded member 15B. The return spring 17 thus
applied torque to the externally threaded member 15B that tends to
push the pivot member 15A out of the nut member 12 due to its
torsional deformation.
[0138] With this lash adjuster 91, when the adjusting screw 15 is
pushed into the nut member 12, the stopper portion 23 abuts the
anti-separation member 92 at the open end of the nut member 12,
thus restricting the movement of the adjusting screw 15. This
prevents breakage of the return spring 17 due to
over-compression.
[0139] With this lash adjuster 91, since the stopper portion 23 for
restricting movement of the adjusting screw 15 is provide at the
portion of the pivot member 15A protruding from the nut member 12,
it is not necessary to provide a tubular extension at the end of
the externally threaded member 15B located in the nut member 12 for
restricting the movement of the adjusting screw 15 by abutting the
bottom member 16. Thus, the external thread 14 on the externally
threaded member 15B can be formed easily by rolling.
[0140] With this lash adjuster 91, when the engine is stopped in a
high-temperature state, and differences in shrinkage appear between
component parts of the valve gear when the engine cools down
subsequently, the spring washer 15C between the externally threaded
member 15B and the pivot member 15A is compressed, thereby
absorbing such differences in shrinkage. Thus, when the engine is
restarted, no gap forms between the valve 4 and the valve seat 10
due to differences in shrinkage. This prevents compression
leakage.
[0141] With this lash adjuster 91, since the pivot member 15A and
the externally threaded member 15B are adapted to rotate together
due to the engagement of the square shaft 97 in the square hole 96,
it is possible to rotate the externally threaded member 15B by
rotating the pivot member 15A. Thus, compared to an arrangement
having no square shaft 97 and the square hole 96, the externally
threaded member 15B can be easily mounted in the nut member 12.
[0142] In this embodiment, the elastic member disposed between the
pivot member 15A and the externally threaded member 15B is the
spring washer 15C. But the spring washer 15C may be replaced by a
different elastic member (such as a compression coil spring).
[0143] If a torsion coil spring is used as the return spring 17, it
may be a tubularly wound member as shown in FIG. 11, or may be a
conically wound member as shown in FIG. 12.
[0144] Also, the return spring 17 may be a torsion spring other
than a torsion coil spring (such as a spiral spring or a volute
spring).
[0145] The return spring 17 in FIG. 13 is a spiral spring
comprising a spirally wound thin sheet. This return spring 17 has
its radially outer end rotationally fixed to the bottom member 16
of the nut member 12 and its radially inner end engaged in a slit
formed in a protrusion 100 formed on the end of the externally
threaded member 15B located in the nut member 12. The return spring
17 thus applies torque to the externally threaded member 15B that
tends to push the pivot member 15A out of the nut member 12 due to
its torsional deformation. The external thread 14 on the outer
periphery of the externally threaded member 15B and the internal
thread 13 on the inner periphery of the nut member 12 are
vertically symmetrical triangular threads.
[0146] The return spring 17 in FIGS. 14 and 15 is a volute spring
comprising a helically wound thin sheet. This return spring 17 has
its radially outer end rotationally fixed to the bottom member 16
of the nut member 12 and its radially inner end engaged in a slit
formed in a protrusion 101 formed on the end of the externally
threaded member 15B located in the nut member 12. The return spring
17 thus applies torque to the externally threaded member 15B that
tends to push the pivot member 15A out of the nut member 12 due to
its torsional deformation. The external thread 14 on the outer
periphery of the externally threaded member 15B and the internal
thread 13 on the inner periphery of the nut member 12 are
vertically symmetrical trapezoidal threads.
* * * * *