FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
1. TITLE OF THE INVENTION
SURFACE ROUGHNESS OF SCREW USED IN TENSIONER
2. APPL1CANT
(a) NAME: ADVIK HI-TECH PVT LTD
(b) NATIONALITY: Indian Company
(c) ADDRESS; Plot No. Bo. Chakan Industrial AreaPhase II, Village Vasuli. Taluka Khed.
District Pune Pin Code-410501 .State
Maharashtra. Country India. 1 TECHNICAL FIELD OF THE INVENTION
[001] The present invention relates to a tensioner for applying pre-determined tension to a force transmitting member such as camshaft driving chain or timing belt of an engine mounted in a vehicle e.g, a four wheeler, two wheelers, etc.
BACKGROUND OF THE INVENTION
[002] A conventional tensioner consists of a thrust member interposed between the end face of the screw and the casing. The thrust member supports the rotation of the end face of the screw. As shown in Figure 1, the prior art describes an angle of 0.5 degree or less between the end surface of the screw and the inner bottom surface of the thrust member. The contact radius r which contacts the thrust member by the outer peripheral part of the screw determines the torque which is largely stable at the beginning. However, if the thrust member is abraded out bv use or wear and tear, the angle between the end surface of the screw and bottom inner surface of the thrust member will become zero. As the angle will become zero, there will be more contact between the end surface of the screw and the inner bottom surface of the thrust member. This will result in high friction between the screw and the thrust member. As a result, the torque required to overcome the friction will be more and hence the thrust of the nut on the cam chain will reduce and a cam chain sound may be generated.
DISCLOSURE OF THE INVENTION
[003] it is an object of the invention to overcome the problems associated with the prior art.
[004] The present invention consists of a tensioner having a bottomed cylindrical thrust member which is inserted in the casing of the tensioner. The cylindrical thrust member supports the end face of the screw. The end surface of the screw contacts the thrust- member which is inclined in an axial direction inner side 0.5 to 1.5 degree and is carried out concave from the vertical plane with respect to a screw centerline. The bottom surface of the thrust member is 1 degree or less from the vertical plane with respect to a cylindrical part centerline, inclined on the axial direction on the outer side and carried out in convex shape.
[005] Since the end surface of the screw is carried out concave while the inner bottom surface of the thrust member is carried out convex, the inner bottom surface of the thrust member is always touched by outer peripheral part of the screw. The surface roughness of the contact surface of end face of the screw is maintained equal to or less than Ra 3.2. on account of which the friction torque is reduced. Hence, the thrust of the tensioner can be maintained uniformly and the tension of the transmission band can be kept constant. Hence, even when the rotation force of the screw is low, the generation of the cam chain sound can be prevented.
DESCRIPTION OF DRAWINGS
[006] Fig. 1 describes a sectional view of thrust member of conventional tensioner.
[007] Fig.2 describes a sectional view of the screw and thrust member after abrasion arises by use of tensioner.
[008] Fig.3 describes a sectional view of the tensioner assembly.
[009] Fig.4 describes an expanded sectional view of the screw and the thrust member of the present invention.
[010] Fig.5 describes a side view made into the partial cross section of the base end part of the screw of the tensioner.
DETAILED DESCRIPTION OF DRAWINGS
[011] Figure 1 illustrates a sectional view of the thrust member 8 of a conventional tensioner. It illustrates an angle of 0.5 degree or less between the end surface of the screw 2 and the inner bottom surface of the thrust member 8.

[012] Figure 2 illustrates a. sectional view of the screw 2 and thrust member 8 afier abrasion of the arises by use of tensioner. As seen in the figure, the abrasion results in contact of the end face of the screw with the inner bottom surface of the thrust member 8. This results in high friction when torque is applied to the screw.
[013] Figure 3 illustrates a sectional view of the tensioner assembly
List of element in the tensioner assembly are as follows:
1.Casing
2.Screw
3.Nut
4.Spring
5.Stopper
6.Circlip
1.Bearing
8.Thrust Member
9.Cap Element
[014] Figure 4 describes an expanded sectional view of the screw 2 and the thrust member 8 of the present invention. The bottom surface of the thrust member 8 is 1 degree or more from the vertical plane with respect to a cylindrical part centerline. inclined on the axial direction on the outer side and carried out in convex shape.
[015] Figure 5 describes the end surface of the screw 2 contacts the thrust member 8 which is inclined in an axial direction inner side 0.5 to 1.5 degree and is carried out concave from the vertical plane with respect to a screw 2 centeriine. The contact radius r and the surface roughness of the contact surface of the end face of the screw determines the torque required to overcome the frictiona! force between the end face of the screw 2 and the thrust member -8. Since, the surface roughness of the contact surface of the end face of the screw 2 is maintained at a value less than or equal to Ra 3,2. the friction torque is reduced.

CLAIMS
!. A tensioner for applying tension to a force transmitting member comprising: a casing;
a screw rotatably stored in said casing so as to be restrained from moving along an axis:
a nut in screwed engagement with said screw, 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 torque to said screw; and a spring stored in said casing and capable of applying torque to said screw, wherein a slit extending in the diametrical direction of said screw is formed in an end face of said screw, said end face touching a receiving surface of said casing directly or across a thrust member and receiving said load acting on said nut, wherein the end surface of the screw contacting the thrust member is 1 degree or more and is carried out concave from the vertical plane with respect to a screw center!ine.
2. A tensioner as claimed in claim I, wherein the surface roughness of the end face of the screw is less than or equal to Ra 3.2