U.S. patent application number 09/970510 was filed with the patent office on 2002-02-14 for tensioner for applying tension to force transmitting member.
This patent application is currently assigned to NHK Spring Co., Ltd.. Invention is credited to Kaibuki, Tomokazu, Takamura, Noritoshi.
Application Number | 20020019281 09/970510 |
Document ID | / |
Family ID | 14455562 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019281 |
Kind Code |
A1 |
Takamura, Noritoshi ; et
al. |
February 14, 2002 |
Tensioner for applying tension to force transmitting member
Abstract
This tensioner comprises a casing, a first shaft member
rotatably stored in the casing so as to be restrained from moving
in its axial direction, a second shaft member in screwed engagement
with the first shaft member, and a spring for applying a turning
force to the first shaft member. The second shaft member is
restrained from rotating relatively to the casing and allowed to
move in the axial direction. An axial load from a force
transmitting member, such as a chain or belt, acts on the first
shaft member. An end face of the first shaft member touches a
receiving surface of the casing across a washer. The end face
receives the axial load that acts on the second shaft member. The
flatness of at least the end face of the first shaft member is
adjusted to 15 .mu.m or less.
Inventors: |
Takamura, Noritoshi;
(Aiko-gun, JP) ; Kaibuki, Tomokazu; (Komagane-shi,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN &
LANGER & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
NHK Spring Co., Ltd.
10, Fukuura 3-chome
Yokohama-shi
JP
236-0004
|
Family ID: |
14455562 |
Appl. No.: |
09/970510 |
Filed: |
October 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09970510 |
Oct 4, 2001 |
|
|
|
PCT/JP00/02458 |
Apr 14, 2000 |
|
|
|
Current U.S.
Class: |
474/101 ;
474/109 |
Current CPC
Class: |
F16H 2007/081 20130101;
F16H 7/08 20130101; F16H 2007/0891 20130101 |
Class at
Publication: |
474/101 ;
474/109 |
International
Class: |
F16H 007/08; F16H
007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 1999 |
JP |
11-107298 |
Claims
What is claimed is:
1. A tensioner for applying tension to a force transmitting member,
comprising: a casing; a first shaft member rotatably stored in said
casing so as to be restrained from moving along an axis; a second
shaft member in screwed engagement with said first shaft member,
movable in the direction of the axis, restrained from rotating
relatively to said casing, and subjected to a load in the direction
of the axis from the force transmitting member; and a spring stored
in said casing and capable of applying turning force to said first
shaft member, wherein a slit extending in the diametrical direction
of said first shaft member is formed in an end face of said first
shaft member, said end face touching a receiving surface of said
casing directly or across a washer and receiving said load acting
on said second shaft member, the flatness of the end face of said
first shaft member ranging from 1.5 .mu.m to 15 .mu.m.
2. A tensioner according to claim 1, wherein said end face of said
first shaft member is formed having a chamfer portion on the outer
peripheral edge thereof, the flatness of the whole end face except
the chamfer portion being 15 .mu.m or less.
3. A tensioner according to claim 1, wherein the flatness of an
annular portion of said end face extending in the circumferential
direction thereof is 15 .mu.m or less.
4. A tensioner according to claim 1, wherein the surface roughness
of the end face of said first shaft member ranges from 1.5 .mu.m to
5 .mu.m.
5. A tensioner according to claim 2, wherein the surface roughness
of the end face of said first shaft member ranges from 1.5 .mu.m to
5 .mu.m.
6. A tensioner according to claim 3, wherein the surface roughness
of the end face of said first shaft member ranges from 1.5 .mu.m to
5 .mu.m.
7. A tensioner according to claim 1, wherein said washer is
provided between the end face of said first shaft member and the
receiving surface of said casing.
8. A tensioner according to claim 1, wherein said end face of said
first shaft member is directly in contact with the receiving
surface of said casing.
9. A tensioner according to claim 1, wherein said end face of said
first shaft member is formed having a recess in the central part
thereof, the flatness of an annular portion around said recess
being 15 .mu.m or less.
10. A tensioner according to claim 1, wherein said end face of said
first shaft
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation Application of PCT Application No.
PCT/JP00/02458, filed Apr. 14, 2000, which was not published under
PCT Article 21(2) in English.
[0002] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 11-107298,
filed Apr. 14, 1999, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a tensioner for applying a
given tension to a force transmitting member such as a camshaft
driving chain or timing belt of an engine mounted in a vehicle,
e.g., a four-wheeler, two-wheeler, etc.
[0005] 2. Description of the Related Art
[0006] A tensioner is used to keep a chain and timing belt under a
substantially fixed tension even if they are stretched or worn to
be slackened during use. A conventional prevalent tensioner
comprises a casing, a first shaft member having an external thread
portion, a second shaft member having an internal thread portion in
mesh with the external thread portion of the first shaft, a spring
for urging the first shaft member in a first rotating direction, a
bearing for restraining the second shaft member from rotating, etc.
When the first shaft member is rotated in the first direction by
means of the aforesaid spring, the second shaft member moves in the
axial direction. The first shaft member is stored in the casing,
and an end face of the first shaft member is in contact with the
inner surface (receiving surface) of the casing.
[0007] This tensioner urges the first shaft member in the first
rotating direction by means of a repulsive force (elastic energy)
the aforesaid spring accumulates when it is twisted in the
direction opposite to the first rotating direction. Urged by its
own turning torque, the second shaft member moves in the direction
to project from the casing. The distal end of the second shaft
member directly or indirectly pushes a force transmitting member
such as a chain or timing belt.
[0008] If the tension of the chain or timing belt increases as an
engine rotates at high speed, for example, a force that pushes back
the second shaft member is augmented. In this case, the second
shaft member is pushed back into the casing, resisting the sum
total of torques, mainly including the urging force of the
aforesaid spring, frictional resistance between the aforesaid
external and internal thread portions, and frictional resistance
between the end face of the first shaft member and the casing.
Based on these torques, the tensioner can apply a fixed tension to
the chain or timing belt.
[0009] The second shaft member of the tensioner described above is
expected to be able to advance and retreat smoothly depending on
the tension of the chain or timing belt. In the conventional
tensioner, however, frictional torque between the end face of the
first shaft member and the receiving surface of the casing
sometimes vary substantially. Thus, there is a problem that the
second shaft member cannot advance and retreat smoothly. When the
engine is in a low-speed rotation zone for idling operation or the
like, in particular, the return characteristic of the second shaft
member may be poor, or the initial characteristics of the tensioner
may be unstable if the tensioner is a brand-new one having just
started to be used. Accordingly, measures are taken to optimize the
lead angle of each of the aforesaid thread portions and adjust the
spring constant of the aforesaid spring. Despite these measures,
however, there still remain problems that the initial
characteristics of the tensioner are subject to substantial
fluctuations and that the change of the frictional resistance is
great.
BRIEF SUMMARY OF THE INVENTION
[0010] Accordingly, the object the of the prevent invention is to
provide a tensioner designed so that its initial characteristics
can be stabilized, change in its characteristics during operation
can be reduced, and optimum specifications can be set corresponding
to an engine in which it is attached.
[0011] In order to achieve the above object, a tensioner of the
present invention comprises a casing, a first shaft member
rotatably stored in the casing so as to be restrained from moving
along an axis, a second shaft member in screwed engagement with the
first shaft member, movable in the direction of the axis,
restrained from rotating relatively to the casing, and subjected to
a load in the direction of the axis from a force transmitting
member, and a spring stored in the casing and capable of applying
turning force to the first shaft member, characterized in that an
end face of the first shaft member touches a receiving surface of
the casing directly or across a washer and receives the load acting
on the second shaft member, the flatness of at least the end face
of the first shaft member being 15 .mu.m or less.
[0012] In the tensioner of this invention, the axial load from the
force transmitting member, e.g., a chain or timing belt, applied to
the tensioner is supported by the receiving surface of the casing
through the medium of the end face of the first shaft member. Since
the flatness of the end face of the first shaft member is 15 .mu.m
or less, the first shaft member can rotate smoothly. As the first
shaft member rotates, the second shaft member smoothly moves in the
axial direction with respect to the casing, so that the return
characteristic of the second shaft member is improved.
[0013] In the present invention, the end face of the first shaft
member may be formed having a chamfer portion on the outer
peripheral edge thereof, the flatness of the whole end face except
the chamfer portion being 15 .mu.m or less. As the first shaft
member rotates around the axis with respect to the receiving
surface of the casing, in this invention, the whole end face
smoothly slides with respect to the casing, so that a stable return
characteristic can be obtained.
[0014] In the present invention, the flatness may be adjusted so
that the flatness of an annular portion of the end face extending
in the circumferential direction thereof is 15 .mu.m or less. As
the first shaft member rotates around the axis with respect to the
receiving surface of the casing, in this invention, the annular
portion of the end face extending in the circumferential direction
smoothly slides, so that a satisfactory return characteristic can
be enjoyed.
[0015] Preferably, in the present invention, the surface roughness
of the end face of the first shaft member should be 5 .mu.m or
less. According to this invention, the first shaft member can
rotate more smoothly, so that a satisfactory return characteristic
can be enjoyed.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0016] FIG. 1A is a sectional view showing a tensioner according to
a first embodiment of the present invention;
[0017] FIG. 1B is a partial sectional view of an engine showing an
example of usage of the tensioner shown in FIG. 1A;
[0018] FIG. 2 is a diagram showing results of measurement of
variation in the flatness of the end face of a first shaft member
of the tensioner according to the aforesaid embodiment;
[0019] FIG. 3 is a bottom view showing measuring positions for the
flatness of the end face of the aforesaid shaft member;
[0020] FIG. 4 is a diagram showing the relationship between the
flatness and squareness of the end face of the aforesaid shaft
member;
[0021] FIG. 5 is a diagram showing the relationship between the
flatness of the end face of the aforesaid shaft member and the
return torque of the tensioner;
[0022] FIG. 6 is a diagram showing the relationship between the
flatness of the end face of the aforesaid shaft member and the
return travel of the tensioner;
[0023] FIG. 7A is a diagram showing the relationship between the
torque and return travel of the tensioner of the aforesaid
embodiment;
[0024] FIG. 7B is a diagram showing the relationship between the
torque and return travel of a conventional tensioner;
[0025] FIG. 8 is a diagram showing the relationship between the
working time and return operation torque of the tensioner of the
aforesaid embodiment and the conventional tensioner;
[0026] FIG. 9 is a diagram showing the relationship between the
surface roughness of the end face of the first shaft member and the
return travel of the tensioner of the aforesaid embodiment and the
conventional tensioner;
[0027] FIG. 10 is a diagram showing results of measurement of the
flatness of the end face of the first shaft member in the
conventional tensioner;
[0028] FIG. 11 is a partial sectional view of a tensioner according
to a second embodiment of the present invention;
[0029] FIG. 12 is a partial sectional view of a tensioner according
to a third embodiment of the present invention;
[0030] FIG. 13 is a partial sectional view of a tensioner according
to a fourth embodiment of the present invention;
[0031] FIG. 14 is a partial sectional view of a tensioner according
to a fifth embodiment of the present invention;
[0032] FIG. 15 is a partial sectional view of a tensioner according
to a sixth embodiment of the present invention;
[0033] FIG. 16 is a sectional view of a pull-type tensioner
according to a seventh embodiment of the present invention;
[0034] FIG. 17 is a partial sectional view of a tensioner according
to an eighth embodiment of the present invention; and
[0035] FIG. 18 is a partial sectional view of a tensioner according
to a ninth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] A first embodiment of the present invention will now be
described with reference to FIGS. 1A to 9.
[0037] FIG. 1A shows a push-type tensioner according to the first
embodiment of the present invention. This tensioner is used in a
power transmission mechanism 101 of an automotive engine 100 shown
in FIG. 1B, for example. The power transmission mechanism 101
transmits the rotary motion of the engine 100 to a camshaft 103 by
means of an endless force transmitting member 102, such as a timing
belt or chain. This tensioner is mounted in a given position on the
engine 100, and pushes the force transmitting member 102 in the
direction indicated by arrow V by means of a thrust, which will be
mentioned later.
[0038] The tensioner shown in FIG. 1A comprises a casing 1, a first
shaft member 2, and a cylindrical second shaft member 3. The first
shaft member 2 is held in the casing 1. The rear end portion of the
second shaft member 3 is inserted in the casing 1. The front end
portion of the second shaft member 3 projects outward from the
casing 1.
[0039] A cavity portion 1a for the insertion of the first and
second shaft members 2 and 3 is formed in the casing 1. An opening
1b is formed in the front end portion of the casing 1, and the
second shaft member 3 is designed to advance and retreat along its
axis X from the opening 1b. An opening 1c is also formed in the
rear end portion of the casing 1. A stopper 14 for locking and
stopping the first shaft member 2 from rotation as required can be
inserted into the opening 1c. A slit 23 is formed in the rear end
portion of the first shaft member 2. The first shaft member 2 can
be locked and stopped from rotation as the distal end of the
stopper 14 is inserted into the slit 23. When the tensioner is
worked, the stopper 14 is removed from the slit 23 of the shaft
member 2.
[0040] An external thread portion 21 is formed on the front part of
the first shaft member 2. An internal thread portion 13 is formed
on the inner peripheral surface of the hollow second shaft member
3. By mating the internal thread portion 13 and the external thread
portion 21 with each other, the first and second shaft members 2
and 3 can be joined together for relative rotation and screwed
advance in the direction of the axis X. Usually, these thread
portions 13 and 21 have a lead angle wider than those of
conventional threads, and multiple threads such as triple threads
are used for them.
[0041] The first and second shaft members 2 and 3 joined in this
manner are inserted into a torsion spring 5. The spring 5 extends
along the axis X of the shaft members 2 and 3. One end portion 5a
of the spring 5 is inserted in the slit 23 of the first shaft
member 2. The slit 23 extends in the direction of the axis X of the
shaft member 2. The other end portion 5b of the spring 5 is
anchored to the casing 1 or a bearing 6 that is attached to the
casing 1. Thus, the opposite end portions 5a and 5b of the spring 5
are anchored to the shaft member 2 and the casing 1, respectively.
The tip of a jig (e.g., screwdriver) for rotation is inserted into
the slit 23, and the first shaft member 2 is rotated around the
axis X. Thereupon, the spring 5 is twisted to store energy (torque)
that urges the shaft member 2 to rotate in the opposite
direction.
[0042] The bearing 6 is provided on the front end portion of the
casing 1. This bearing 6 is fixed to the casing 1 by means of a
fixing member such as a ring spring 7. A noncircular slide hole 6a
is formed in the bearing 6. The second shaft member 3 is passed
through the slide hole 6a. The outer peripheral surface of the
second shaft member 3 is formed having a noncircular shape
corresponding to the slide hole 6a of the bearing 6. As the second
shaft member 3 is fitted in the slide hole 6a of the bearing 6, the
second shaft member 3 is restrained from rotating with respect to
the casing 1. A cap 8 is attached to the front end of the second
shaft member 3. This cap 8 touches the timing belt or chain (shown
in FIG. 1B) for use as the force transmitting member 102 directly
or indirectly across an intermediate portion.
[0043] If the first shaft member 2 is rotated in a second direction
to twist the spring 5, the elastic energy of the spring 5 causes
the first shaft member 2 to rotate in a first direction. This
rotation is transmitted to the second shaft member 3 via the thread
portions 13 and 21. Since the bearing 6 restrains the second shaft
member 3 from rotating, the turning force of the first shaft member
2 is converted into a propulsive force in the direction of the axis
X of the second shaft member 3. Accordingly, the second shaft
member 3 advances in the direction to project from the casing
1.
[0044] On the other hand, a load Z from the force transmitting
member 102, formed of the timing belt or chain, is applied to the
second shaft member 3 and presses the second shaft member 3 in the
direction of the axis X. As this pressing force is transmitted to
the first shaft member 2 via the thread portions 13 and 21, the
first shaft member 2 rotates in the second direction, resisting the
urging force of the spring 5. The rotation in this direction pushes
back the second shaft member 3 into the casing 1. By these motions,
the tension of the force transmitting member 102 can be kept
substantially constant.
[0045] A large-diameter portion 28 having a diameter larger than
that of the thread portion 21 is formed on the rear end portion of
the first shaft member 2. A receiving surface 19 of the casing 1
that is formed around the opening 1c adjoins an end face 22 of the
large-diameter portion 28. A washer 9 in the form of a bottomed
ring (or cup) is located between the receiving surface 19 and the
end face 22 of the first shaft member 2. The end face 22 of the
first shaft member 2 is in contact with the bottom surface or a
contact surface 9a of the washer 9. The aforesaid load Z that is
applied to the second shaft member 3 is supported on the receiving
surface 19 of the casing 1 through the end face 22 of the first
shaft member 2 and the washer 9.
[0046] Since the washer 9 is interposed between the end face 22 of
the first shaft member 2 and the receiving surface 19 of the casing
1 according to this embodiment, the receiving surface 19 of the
casing 1 can be prevented from wearing. Accordingly, a lightweight
metal, such as aluminum alloy, can be used for the casing 1. The
washer 9 is formed of low-carbon steel or a material that is
obtained by plating the surface of steel with a hard metal, and it
is made as flat as possible for the following reason.
[0047] A chamfer portion 2c is formed on the outer peripheral edge
of the end face 22 of the first shaft member 2. The flatness of the
whole end face 22 of the first shaft member 2 except the chamfer
portion 2c is adjusted to 15 .mu.m or less, and preferably to 10
.mu.m or less. Here the flatness implies the height of waviness
(height of waviness in the direction of the axis X) of the end face
22.
[0048] FIG. 2 shows results of measurement of the flatness of the
end face 22 of the first shaft member 2 of the tensioner according
to this embodiment by means of an optical shape measuring device.
The flatness was measured by scanning lines T-T, D-D and S-S shown
in FIG. 3 with the measuring head of the measuring device.
Characteristic curves a, b and c shown in FIG. 2 represent the
degrees of flatness measured along lines T-T, S-S and D-D,
respectively. As seen from FIG. 2, the flatness according to this
embodiment is within the range of 5 .mu.m or less.
[0049] Since the flatness is improved in this manner, the whole end
face 22 except the chamfer portion 2c can securely uniformly touch
the contact surface 9a of the washer 9. In this case, the whole end
face 22 uniformly receives the load Z, so that the load Z can be
prevented from being locally unevenly distributed. If the load Z is
a small load that acts when the engine rotates at low speed, as
mentioned later, therefore, the first shaft member 2 can smoothly
rotate resisting the urging force of the spring 5. Thus, the second
shaft member 3 can smoothly return to the interior of the casing 1,
so that the return characteristic of the tensioner is improved.
[0050] The operation of the tensioner according to this embodiment
will now be described in accordance with data.
[0051] FIG. 10 shows results of measurement of the flatness of the
end face of a first shaft member used in a conventional tensioner
by means of the aforesaid measuring device. The measured
conventional tensioner is constructed in the same manner as the one
shown in FIG. 1 except for the flatness of the end face. In FIG.
10, characteristic curves a', b' and c' correspond to the
characteristic curves a, b and c in FIG. 2, respectively. In FIG.
10, characteristic curves d' represents the degree of flatness
measured along line L-L of FIG. 3. The flatness of the conventional
end face shown in FIG. 10 is 22.5 .mu.m or more. If the value of
flatness of the end face is so large as in this conventional case,
the frictional force (friction torque) increases locally, since the
load Z that acts on the end face is locally unevenly distributed.
In this case, the small load Z cannot cause the first shaft member
to rotate, so that the return characteristic of the shaft member
worsens.
[0052] FIG. 4 shows the relationship between the flatness (height
of waviness) of the end face 22 of the first shaft member 2 and the
squareness of the end face 22 to the axis X of the shaft member 2.
If the flatness is 15 .mu.m or less, the squareness to the axis X
is low. If the squareness is low, the whole area of the end face 22
can securely touch the contact surface 9a of the washer 9, so that
the whole end face 22 can uniformly receive the load Z. Thus, the
return characteristic of the second shaft member 3 is improved
further. If the flatness and squareness of the end face 22 of the
first shaft member 2 are lowered, the return characteristic of the
second shaft member 3 can be improved further.
[0053] FIG. 5 shows the relationship between the flatness of the
end face 22 of the first shaft member 2 and the torque of return
operation of the second shaft member 3 obtained when the load Z is
applied. It can be seen that if the flatness is 15 .mu.m or less,
the required torque for the return operation is stabilized at a
small value of about 8 kgf.multidot.mm or below, and the second
shaft member 3 can satisfactorily perform the return operation.
[0054] FIG. 6 shows results of measurement of the return travel of
the tensioner attached to a hydraulic vibration testing machine
under conditions that the input load for low-rotation operation of
the engine is simulated. In FIG. 6, the axis of abscissa represents
the flatness of the end face 22 of the first shaft member 2. It is
understandable that if the flatness is 15 .mu.m or less, the return
travel is evidently greater and the second shaft member 3 operates
more smoothly than in the case where the flatness exceeds 15
.mu.m.
[0055] FIGS. 7A and 7B show the relationships between the torque
produced by the load Z and return travel (strokes) of the second
shaft member 3. FIG. 7A shows the characteristics of tensioner of
this embodiment, while FIG. 7B shows the characteristics of the
conventional tensioner. In the case of the conventional tensioner,
there is a spot G where the torque locally increases, and the
second shaft member cannot smoothly return at the spot G. On the
other hand, the tensioner of the embodiment of the present
invention has characteristics such that the torque smoothly changes
to ensure a smooth return operation.
[0056] FIG. 8 shows the change of the return operation torque
compared with the working time of the tensioner. In FIG. 8, full
lines Ml represent the characteristics of the tensioner of the
foregoing embodiment, and broken lines M2 represent the
characteristics of the conventional tensioner. While variation
H.sub.2 of the return operation torque of the conventional
tensioner is great, variation H.sub.1 of the return operation
torque of the tensioner of this embodiment is very small.
[0057] Thus, the conventional tensioner has a high initial return
torque that it sometimes requires a running-in or the like. On the
other hand, the tensioner of this embodiment can smoothly perform
the return operation from the start of use.
[0058] FIG. 9 shows the relationship between the surface roughness
of the end face 22 of the first shaft member 2 and the return
travel of the second shaft member 3. Here the surface roughness is
an arithmetic roughness that is based on Japanese Industrial
Standards (JISBO601) and concerned with a plurality of measuring
points that exist within a reference length on a surface as an
object of measurement. For example, ten-point mean roughness (Rz)
is a value in micrometers (.mu.m) indicative of the difference
between the average of the greatest to fifth-greatest top heights
and the average of the greatest to fifth-greatest bottom heights
that are obtained at the individual measuring points.
[0059] In FIG. 9, black circles represent results of measurement on
the tensioner according to the foregoing embodiment, while white
circles represent results of measurement on the conventional
tensioner. In the tensioner of the foregoing embodiment, the
flatness of the end face 22 of the first shaft member 2 varies
within the range from 8.2 .mu.m to 13.8 .mu.m. In the conventional
tensioner, on the other hand, the flatness of the end face varies
within the range from 18.9 .mu.m to 26.2 .mu.m.
[0060] As shown in FIG. 9, the flatness itself of the end face of
the conventional tensioner is poor even though its surface
roughness is 10 .mu.m or less, so that its return travel is
unstable and limited. According to the tensioner of the embodiment
of the present invention, on the other hand, the return travel is
stable and substantial. In the case of the embodiment where the
surface roughness and flatness are 5 .mu.m or less and 15 .mu.m or
less, respectively, in particular, the return travel is very stable
and large.
[0061] According to the foregoing embodiment, the flatness of the
whole end face 22 of the first shaft member 2 is 15 .mu.m or less.
In carrying out this invention, however, the flatness of an annular
portion in the circumferential direction of the end face 22 may be
adjusted to 15 .mu.m or less. In the characteristic curves a, b and
c of FIG. 2, those portions which are situated substantially at
equal distances from the center (near a 4,500-.mu.m point on the
axis of abscissa) of the end face 22 toward the outer periphery of
the end face 22 are at equal heights. More specifically, the
flatness varies under the level of 15 .mu.m in the annular portion
along the circumferential direction of the end face 22. As the
portion along the circumferential direction of the end face 22 is
thus adjusted to the precise flatness (15 .mu.m or less), various
parts in the circumferential direction can equally touch the
contact surface 9a of the washer 9. Thus, the annular portion can
uniformly receive the load Z. Even if the load Z is small,
therefore, the first shaft member 2 can smoothly rotate when the
load is applied to it. Thus, the return characteristic of the
second shaft member 3 can be improved.
[0062] FIG. 11 shows a part of a tensioner according to a second
embodiment of this invention. FIG. 12 shows a part of a tensioner
according to a third embodiment of this invention. For these
embodiments, common numerals for the foregoing first embodiment
refer to common portions that are also used in the tensioner
according to the first embodiment, and a description of those
portions is omitted. In the tensioner of the second embodiment
shown in FIG. 11, an end face 22 of a first shaft member 2 is
brought directly into contact with a receiving surface 19 of a
casing 1 without providing the aforesaid washer between the end
face 22 and the receiving surface 19. In the tensioner of the third
embodiment shown in FIG. 12, a ring-shaped washer 15 is located
between an end face 22 of a first shaft member 2 and a receiving
surface 19 of a casing 1. The end face 22 of the first shaft member
2 is in contact with the washer 15. In the second and third
embodiments, the return characteristics of the tensioners can be
improved in the same manner as in the first embodiment by adjusting
the flatness of the whole area of the end face 22 or an annular
portion along its circumferential direction to 15 .mu.m or
less.
[0063] FIGS. 13 to 15 show further embodiments of the present
invention, individually. For these embodiments, common numerals for
the foregoing first embodiment refer to common portions that are
also used in the tensioner according to the first embodiment, and a
description of those portions is omitted. In a fourth embodiment
shown in FIG. 13, a relatively great chamfer portion 37 is formed
on the outer peripheral edge of an end face 22 of a large-diameter
portion 28 of a first shaft member 2. This chamber portion 37 is
formed by obliquely cutting the outer peripheral edge of the end
face 22 at an angle of about 45.degree.. The substantial area of
the end face 22 is reduced by a margin for the formation of the
chamfer portion 37. Further, a ring-shaped washer 15 is provided
between the end face 22 and a receiving surface 19 of a casing 1.
The washer 15 has the form of a protrusion that is in contact with
the whole area of the end face 22 except the chamfer portion 37 of
the first shaft member 2. The return characteristic of this
tensioner can be improved by adjusting the flatness of the portion
of the end face 22 in contact with the washer 15 to 15 .mu.m or
less.
[0064] In a fifth embodiment shown in FIG. 14, a protrusion 38 is
formed integrally on the rear end of a large-diameter portion 28 of
a first shaft member 2. This protrusion 38 is located in an opening
1C of a casing 1 in a manner such that it penetrates a ring-shaped
washer 15. An end face 22 of the first shaft member 2 is in contact
with the washer 15 at its annular portion except the protrusion 38.
The return characteristic of this tensioner can be improved by
adjusting the flatness of the portion of the end face 22 in contact
with the washer 15 to 15 .mu.m or less.
[0065] In a sixth embodiment shown in FIG. 15, a recess 39 is
formed in the central part of an end face 22 of a large-diameter
portion 28 of a first shaft member 2. The end face 22, having the
recess 39 therein, is in contact with a ring-shaped washer 15 at
its annular portion except the recess 39. The return characteristic
of this tensioner can be improved by adjusting the flatness of the
portion of the end face 22 in contact with the washer 15 to 15
.mu.m or less. The washer 15 is in the form of a ring corresponding
to the portion of contact with the end face 22.
[0066] FIG. 16 shows a pull-type tensioner according to a seventh
embodiment of the present invention. A first shaft member 2 of this
tensioner includes a distal end portion 24 projecting toward a
chain guide 17, an intermediate portion 25 formed integrally with
the distal end portion 24, and a large-diameter rear end portion 26
formed integrally on the rear side of the intermediate portion 25.
The distal end portion 24 is inserted in a cylindrical second shaft
member 3. An external thread portion 21 is formed on the outer
peripheral surface of the distal end portion 24. The external
thread portion 21 is in mesh with an internal thread portion 13
that is formed on the inner surface of the second shaft member 3.
The distal end portion 24 and the second shaft member 3 are
inserted in a spring 5 in a manner such that the shaft members 2
and 3 are in screwed engagement with each other. The chain guide 17
is attached to a chain (not shown) for use as a force transmitting
member. One end portion 5a of the torsion spring 5 is anchored to
the intermediate portion 25 of the first shaft member 2. The other
end portion 5b of the torsion spring 5 is anchored to a casing 1 or
a bearing 6.
[0067] The spring 5 urges the first shaft member 2 in a first
rotating direction. Its urging force acts in a direction such that
the second shaft member 3 is drawn into the casing 1. The pull-type
tensioner is completed in this manner. The distal end portion of
the second shaft member 3 is coupled to the chain guide 17 by means
of an arm 35. An input load Z from the chain guide 17 acts in a
direction such that the second shaft member 3 is drawn out of the
casing 1 along its axis X.
[0068] The rear end portion 26 of the first shaft member 2 is in
the form of a flange having a diameter greater than that of the
intermediate portion 25. Formed in the casing 1 is a ring-shaped
extending portion 31 that can support the rear end portion 26. A
washer 16 in the form of a bottomed ring is located between the
extending portion 31 and the rear end portion 26. The rear end
portion 26 of the first shaft member 2 has an end face 22 that
touches the washer 16.
[0069] In this embodiment, the flatness of the whole end face 22 or
an annular portion along the circumferential direction is adjusted
to 15 .mu.m or less. By doing this, the first shaft member 2 of the
pull-type tensioner can rotate smoothly even though the input load
Z is small. In this case, the return characteristic of the second
shaft member 3 is also improved.
[0070] FIG. 17 shows an eighth embodiment of this invention. An end
face 2d of a first shaft member 2 of this tensioner is formed of a
spherical surface. A washer 9' that is touched by this end face
(spherical surface) 2d has a contact surface 9a' that is inclined
like a cone. In the case of this embodiment, the same effects of
the foregoing embodiments can be produced by adjusting the flatness
of at least an annular portion in the circumferential direction of
the end face 2d that is in contact with the washer 9' to 15 .mu.m
or less.
[0071] FIG. 18 shows a ninth embodiment of this invention. An end
face 2e of a first shaft member 2 of this tensioner is formed of a
tapered conic surface. A washer 9' that is touched by this end face
(conic surface) 2e has a contact surface 9a' that is inclined like
a cone. In the case of this embodiment, the same effects of the
foregoing embodiments can be produced by adjusting the flatness of
at least an annular portion in the circumferential direction of the
end face 2e that is in contact with the washer 9' to 15 .mu.m or
less.
[0072] In each of the embodiments described above, the flatness of
the end face of the first shaft member is adjusted to 15 .mu.m or
less. In carrying out the present invention, the flatness of the
surface of the washer that is touched by the end face of the first
shaft member or the receiving surface of the casing, like that of
the end face of the first shaft member, may be adjusted to 15 .mu.m
or less. By doing this, the return characteristic of the tensioner
can be improved further.
[0073] As is evident from the above description, the present
invention is suitably applicable to a tensioner for applying
tension to a force transmitting member such as a camshaft driving
chain or timing belt of an engine mounted in a vehicle, e.g., a
four-wheeler, two-wheeler, etc.
[0074] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *