FORM 2
THE PATENT ACT 1970
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The Patents Rules, 2003
COMPLETE SPECIFICATION
1. TITLE OF THE INVENTION
THRUST BEARING FOR TENSIONER
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2. APPLICANT . j
(a) NAME: ADVIK HI-TECH PVT LTD |
(b) NATIONALITY: Indian Company
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Plot No. B-5. Chakan Industrial Area,
(c) ADDRESS: ' '
j Phase II. Village Vasuli. Taluka Khed,
j District Pune, Pin Code-410501,State
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j Maharashtra, Country India.

TECHNICAL FIELD
[001] The present invention relates to a tensioner that imparts a predetermined tensile force to a force transmitting member such as a chain or timing belt that drives a camshaft of an engine mounted in a vehicle for e.g. four wheeler automobile or a two wheeled vehicle.
BACKGROUND ART
[002] A tensioner is used in order to maintain a substantially fixed tensile force on a chain or timing belt. even if slackness develops in the chain or a timing belt due to stretching or wear during use. A conventional tensioner shown in Figure 5 consists of a case 101. a rotary member 1.02 having a male screw portion 102a. a pressing member 103 having a female screw portion 103a that screws together with the male screw portion 102a of the rotary member 102. a spring 104 that urges the rotary member 102 in a first rotary direction, a bearing 109 in order to restrain rotation of the pressing member 103. and the like. When the rotary member 102 is rotated in the first direction by the spring 104. the pressing member 103 moves in an axis line direction. The rotary member is stored in the case 101. and an end surface 102b of the rotary member 102 is rotatably supported by a bearing surface 101b of the case 103.
[003] The tensioner urges the rotary member 102 in the first rotary direction by means of repulsive force that accumulates when the spring 104 twists in a direction by means of a repulsive force that accumulates when the spring 104 twists in a direction that is opposite to the first rotary direction. A rotary torque of the rotary member 102 moves the pressing member 103 in an axis line direction projecting from the case 101 .A distal end of the pressing member 103 directly or indirectly pushed the force transmitting member such as the chain or the timing belt. Further, when the tensile force of the chain or the timing belt increases, a force pushing back the pressing member 103 increases. In this case, the pressing member 103 is pushed back in the axis line direction toward an inner portion of

the case 101. resisting a sum total of torques mainly including an urging screw portion 102a and the female screw portion 103a. and a frictional resistance between the end surface 102b of the rotary member 102 and the bearing surface 101b of the case 101. The tensioner can impart a fixed tensile force to the chain or the timing belt based on those toques and the like.
[004] The frictional torque between the end surface 102b of the rotary member 102 and the bearing surface of the case 101 largely fluctuates in the conventional tensioner. and large changes in performance arise. For example: the return characteristics of the pressing member 103 may become poor and the initial characteristics may become unstable.
[005] In view of those points, an object of the present invention is to provide a tensioner in which a bearing is provided in an end portion contact surface of a bearing surface of a case that supports an end portion of a rotary member, or in a bearing surface of the case, and in which changes in performance are prevented by setting the initial surface precision of the end portion contact surface of the bearing to the same order as the surface roughness after use, and leveling the contact surface with high precision, the tensioner of a quality having performance that is further stabilized than a conventional tensioner.
DISCLOSURE OF THE INVENTION
[006] According to the present invention- there is provided a tensioner which converts a rotary force of a rotary member into an impulsive force in an axis line direction of a pressing member, the tensioner including: a case: the rotary member rotatably received in the case in a state where a movement in the axis line direction is restrained; the pressing member which is threaded!)' engaged with the rotary member, which is movable in the axis line direction, whose rotation with respect to the case is restrained, and on which a load from a force transmitting member acts in the axis line direction: and a spring which is stored in an upper portion of the case, and which imparts the rotary force to the rotary member characterized in that: an end portion of the rotary member is rotatably supported

by a bearing surface of the case ; the end portion of the rotary member receives the load that acts on the pressing member; and a precision of a contact surface of the thrust member that contacts the end portion of the rotary member is set such that a surface roughness is less than or equal to Ra 3.2
[007] A frictional torque between the end portion of the rotary member and the bearing surface of the case thus decreases and thus becomes constant, the initial characteristics stabilize, changes in characteristics over time during use become smaller, and the performance characteristics are stabilized over a long period of time.
[008] Further, the tensioner of the present invention is a tensioner which converts a rotary force of a rotary member into an impulsive force in an axis line direction of a pressing member, the tensioner including: a case; the rotary member rotatably received in the case in a state where a movement in the axis line direction is restrained; the pressing member which is threadedly engaged with the rotary member, which is movable in the axis line direction, whose rotation with respect to the case is restrained, and on which a load from a force transmitting member acts in the axis line direction; and a spring which is stored in an inner portion of the case., and which imparts the rotary force to the rotary member, characterized in that an end portion of the rotary member receives the load that acts on the pressing member, and a precision of a contact surface of the bearing surface that contacts the end portion of the rotary member is such that a surface roughness is less than or equal to Ra 3.2
[009] In addition, the tensioner according to the present invention is characterized in that the bearing is a closed end cylindrical member, or the bearing is a circular base plate having pre-defined thickness and being hollow at the center.
[010] Actions and effects similar to the aspect of the present invention described above are also provided by the tensioner according to the present invention.
Thus, in the tensioner according to the present invention, by setting the precision of the contact surface of the thrust member supporting the rotary member, which

contacts the rotary member end portion such thai the surface roughness is less .than or equal to Ra 3.2. In addition, rotary sliding between the end surface of the rotary member and the bearing surface of the case is made satisfactory. Therefore. there is little reduction in the tensile force overtime with use and characteristics can be kept stable over a long period of time.
BRIEF DESCRIPTION OF DRAWINGS
[011] Fig.l shows sectional view of spiral tensioner
[012] Fig.2 shows detailed view of thrust member
[013] Fig.3 shows sectional view of torsion tensioner
[014] Fig.4 shows front and side view of thrust member
DESCRIPTION OF THE DRAWINGS
[015] Figure 1 shows a sectional view of the spiral tensioner. Spiral tensioner mentioned consists of parts namely case 1. screw 2, nut 3, retainer 4, spring 5, cap 6, clip 7. stopper 8 and thrust member 9. Screw 1 is threadedly engaged with the nut 2. Rotary motion of the screw 2 is converted into linear motion of the nut 3. Retainer 5 acts as a guide to ensure linear motion of the nut .3. Cavity portion for inserting the screw 2 and the nut 3 is formed in the inner portion of the case 1. An open portion is formed into the back end portion of the case. Stopper 8 provided has an elongated portion that fits in the slit provided in the screw 2. Stopper 8 is used to provide rotary motion to the screw 2. The screw 2 and the nut 3 in the attached state are inserted into the spring 5.. The spring 5 extends in a direction along the axis line X of the screw 2 and the nut 3 and one end portion, of the spring is inserted into the slit of the screw 2. Another end portion of the spring is latched to the case 1. Both end portions of the spring are thus latched to the screw and the case respectively. The retainer 4 is provided in the front end ■portion of the case 1. A fixing member such as a clip 7 for example fixes retainer 6 to the case 3. A cap 6 is attached to the front end of the nut 3. The cap 6 contacts the timing belt or the chain used as the force transmitting member directly or indirectly through a

relay member. When the screw 2 is made to rotate in a second direction and the spring 5 is twisted, elastic energy in the spring 5 causes the screw 2 to rotate in the first direction. This rotation is transmitted to the nut 3 through the screw portions and the retainer 6 restricts the rotation of the nut 3. The nut 3 thus advances in a direction projecting from the case 1. On the other hand, a load Z applied from the force transmitting member such as timing belt or a chain acts on the nut 3 and pushes the nut in the axis line X direction. This pushing force is transmitted to the screw 2 and the screw 2 thus resists an urging force of the spring 5 and rotates in the second direction. By the screw 2 rotating in this direction, the nut 3 is pushed
back within the case 1. The tensile force of the force transmitting member can be
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kept nearly constant by this motion.
[016] A closed end cylinder like shown in Fig 2 this embodiment for the thrust member 9. The load Z that acts on the nut 3 supports the bearing surface of the case 1 through the end surface of the screw 2 and the closed, end cylinder. The base surface of the cylinder that is the contact surface of the end surface of the screw 2, is polished precisely so that the surface roughness is less than or equal to Ra 3.2. Further as shown in Figure 2 the thickness of the base of the thrust member can be 4 mm or less than that. Also the thickness of the side portions of the thrust member can be 4 mm or less than that. Base of the thrust member is convex having an angle of at least 1 degree so that the screw contacts on the outer edges of the thrust member.
[017] Tensioner as described in Figure 3 is sectional view of torsional tensioner. Torsional tensioner consists of case 1, screw 2, nut 3, retainer 4. spring 5. cap 6. circlip 7. stopper 8 and thrust washer 9. The tensioner consists of screw 2 having its thread ensased with the nut 3. Retainer 4 acts as a auide to ensure linear motion of the nut 3. Cavity portion for inserting the screw 2 and the nut 3 is formed in the inner portion of the case 1. An open portion is formed into the back end portion of the case. Stopper 8 is used to provide rotary motion to the screw 2. The screw 2 and the nut 3 in the attached state are inserted into the spring 5. The spring 5 extends in. a direction along the axis line X of the screw 2 and the nut 3

and one end portion of the spring is inserted into the slit of the screw 2. Both end portions of the spring are thus latched to the screw and the case respectively. The retainer 4 is provided in the front end portion of the case 1. A fixing member such as a clip 7 for example fixes retainer 6 to the case 1. A cap 6 is attached to the front end of the nut 3. The cap 6 contacts the timing belt or the chain used as the force transmitting member directly or indirectly through a relay member. When the screw 2 is made to rotate in a second direction and the spring 5 is twisted. elastic energy in the spring 5 causes the screw 2 to rotate in the first direction. This rotation is transmitted to the nut 3 through the screw portions and the retainer 6 restricts the rotation of the nut 3. The nut 3 thus advances in a direction projecting from the case 1. On the other hand, a load Z applied from the force transmitting member such as timing belt or a chain acts on the nut 3 and pushes the nut in the axis line X direction. This pushing force is transmitted to the screw 2 and the screw 2 thus resists an urging force of the spring 5 and rotates in the second direction. By the screw 2 rotating in this direction, the nut 3 is pushed back within the case 1. The tensile force of the force transmitting member can be kept nearly constant bv this motion.
[018] Figure 4 shows front view and side view of the thrust member 9 used in Torsional lensioner. The thickness of the thrust member can be 4 mm or less.

CLAIMS
1) A tensioner that converts a rotary force of the screw into an impulsive force in
an axis line direction of a nut, the tensioner comprising:
a case;
screw being rotatably received in the case in such a state that movement
thereof in the axis line direction is caused to be restrained;
the nut being threadedly engaged with the screw, said nut being movable in
the axis line direction, and rotation thereof with respect to the case being
caused to be restrained, and on said nut a load from a force transmitting
member is adapted to act in the axis line direction; and
a spring being stored in an inner portion of the case, which imparts the rotary
force to the screw;
characterized in that:
an end portion of the screw is rotatably supported by the thrust member placed
in the case;
the end portion of the screw receives the load that acts on the nut; and a
precision of the contact surface of the thrust member that contacts the end
portion of the screw is set such that a surface roughness is less than or equal to
Ra.3.2.
2) A tensioner as claimed in Claim 1. wherein the thrust member is one of a closed end cylinder circular plate being hollow at the center.
3) A tensioner as claimed in Claim 1, wherein the thickness of the base of the thrust member varies from is less than or equal to 4 mm.
4) A tensioner as claimed in Claim 1. wherein the thickness of the side portions of the thrust member varies from is less than or equal to 4 mm.
5) A tensioner as claimed in Claim 1, wherein the thrust member is made of steel formed by cold rolling, forging, machining or metal injection molding.
6) A tensioner as claimed in Claim 1, wherein the bottom surface of the thrust member forms a convex shape having an angle of at least 1 degree from the vertical plane with respect to the cylindrical part cenlerline.

7) A tensioner that converts a rotary force of the screw into an impulsive force in
an axis line direction of a nut, the tensioner comprising:
a case;
screw being rotatably received in the case in such a state that movement
thereof in the axis line direction is caused to be restrained;
the nut being threadedly engaged with the screw, said nut being movable in
the axis line direction, and rotation thereof with respect to the case being
caused to be restrained, and on said nut a load from a force transmitting
member is adapted to act in the axis line direction; and
a spring being stored in an inner portion of the case, which imparts the rotary
force to the screw;
characterized in that:
an end portion of the screw is rotatably supported by the thrust member placed
in the case;
the end portion of the screw receives the load that acts on the nut; and a
precision of the contact surface of the thrust member that contacts the end
portion of the screw is set such that a surface roughness is less than or equal to
Ra3.2.
8) A tensioner as claimed in Claim 7, wherein the thrust member is a flat circular plate having hole at the center and thickness of the plate is 4 mm or less.
9) A tensioner as claimed in Claim 7, wherein the thrust member is made of steel formed by cold rolling, forging, machining or metal injection molding.
10) A tensioner as claimed in Claim 1. wherein the thrust member forms a convex surface having an angle of at least 1 degree.