Tensioner for Internal Combustion Engine
Field of the invention
The present invention relates to a tensioner for an internal combustion engine and more particularly to a tensioner for applying tension to a bendable, transmission member in the internal combustion engine.
Background of the invention
In internal combustion engines, transmission member such as a chain/cam chain is used for transmitting rotation from a crankshaft to one or more valve-operating the camshafts. During transmitting the rotation from the driving shaft to a driven shaft i.e. from the crankshaft to one or more valve-operating the camshafts, the chain/cam chain elongates due to the effect of thermal expansion and results in to slackening of chain and the like.
In order to prevent the slackening, the use of tensioner's known in the prior art. The tensioner is placed in proximity to the chain within the engine which applies force on the chain and tightens the same.
The tensioner is one of the most important parts of chain transmission system of the engine. The tensioner is a mechanical part which applies positive force on slack side of the chain through a chain guide. The retraction end of tensioner guided at chain guide which is opposite end of pivot of chain guide. As the chain elongates due to thermal expansion, the tensioner applies force on chain and tightens the same.

Description of the prior art
Specifically, figure 1 shows a cam tensioner used in the internal combustion engine, in accordance with prior art. The cam tensioner includes a spring (5) assembled in the housing (2), in between a flange (3c) of a screw (3) and bottom end of the housing (2). Upper end of the spring (5) is arrested in a slot (3c) of the screw (3) while the lower end of the spring (5) is arrested in slot of the housing (2).
As the screw (3) rotates the number of turns of the spring (5) increases and proportionally inner diameter of the spring (5) decreases. As the spring (5) lies between the flange (3c) of the screw (3) and bottom end of the housing (2), there is limited space available for the spring (5) to fit in between flange (3 c) and the housing. Accordingly, the spring (5) generates limited force and torque as the spring (5) has limitation of number of turns and inner diameter of spring within limited space available for the spring (5) within the housing (2). The spring (5) develops more stresses, and has factor of safety against failure less than "2" at fully wounding condition. Factor of safety means ratio of allowable stress value of material to the actual working stress developed in the spring (5) during operation of tensioner.
Hence, the tensioner of the prior art becomes complicated for making closed slot portion in housing to arrest fixed end of said spring.
Accordingly, there exists a need to provide tensioner for cam chain in the internal combustion engine which overcomes above-mentioned drawbacks.

Objects of the invention
An object of the present invention is to provide a tensioner with increased factor of safety while a spring is in full wound condition.
Yet another object of the present invention is to provide a tensioner with no limitation of spring length to achieve desired load in the tensioner.
Summary of the invention
Accordingly, the present invention provides a tensioner capable of applying tension to a bendable, transmission member in an internal combustion engine. The tensioner comprises cylindrical hollow housing having closed bottom end and open top end. Further, the tensioner comprises a screw configured in the housing from the open top end. The screw includes a flange adapted on lower portion thereof, Furthermore, the tensioner comprises a plunger configured at lower end of the screw. The screw is capable of being rotated so as to push/reciprocate the plunger in forward direction. Moreover, the tensioner comprises a spring wound over the plunger passing over the flange of the screw and a spacer mounted in-between the plunger and inner diameter of the spring. Upon rotating the screw, the rotary motion of the screw is converted into linear motion of the plunger. The rotary movement of the plunger restricted within the housing and the spring moves over the screw thereby decreasing limitation of spring length and total number of coil of the spring to achieve desired load.
Brief description of drawings

Figure 1 shows a cross sectional view of a tensioner of the prior art; and
Figure 2 shows a cross sectional view of a tensioner, in accordance with the present invention.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
The present invention provides a tensioner (alternatively referred as a small throat cam chain tensioner). The tensioner fulfills higher load requirement thereby ensuring minimum factor of safety "2" for stresses development in a spring in fully wound condition of the tensioner.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.
Referring now to figure 2, there is shown a tensioner (100) capable of applying tension to a bendable, transmission member in the internal combustion engine, in accordance with the present invention. The tensioner (100) is generally mounted on an engine block in a two wheeler such as motorcycle, scooter and moped. During transmitting rotation from a driving shaft to a driven shaft i.e. from a crankshaft to one or more valve-operating the camshafts, a chain/cam

chain elongates due to thermal expansion. The tensioner (100) is placed in proximity to the chain within the engine which applies force on the chain and tightens the same.
The tensioner (100) comprises a cylindrical hollow housing (10), a screw (20), a plunger (30), a spring (40), and a spacer (50).
The cylindrical hollow housing (10) includes a closed bottom end and open top end. In preferred embodiment, the cylindrical hollow housing (10) is made of metal having good strength. The screw (20) is configured in the housing (10) from the open top end, such that the screw (20) can be rotated within the housing (10). In an embodiment, the open top end of the housing (10) is provided with threads configured within internal diameter thereof for receiving the screw (20) rotatably therein. In preferred embodiment, the screw (20) is made of suitable metal.
The screw (20) includes a flange (22) adapted on lower portion thereof. Specifically, the flange (22) is skirt like portion extending from lower portion of the screw (20). Further, the plunger (30) is configured at lower end of the screw (20). Specifically, when the screw (20) is rotated, the plunger (20) is pushed/reciprocated in forward direction. In an embodiment, the screw (20) and the plunger (30) have same thread specifications. Further, the plunger (30) is guided within the housing by a guiding means (32) made up of plastic.
Furthermore, the spring (40) is wound over the plunger (30). The spring (40) also known as torsion spring (40) has upper fixed end (42) fixed in a slit (12a) of the hollow cylindrical housing (10) and the lower floating end (44) fixed in a slot (24) of the screw (20).

In preferred embodiment of the present invention, the inner diameter of the spring (40) is larger than the diameter of the flange (22). This allows the spring (40) to pass over the flange (22) of the screw (20) within the housing (10). More space available for the spring (40) allows using the spring (40) of more length as compared to springs of the prior art. More the length of the spring (40), more would be the turns thereof thereby having more stored energy. Thus the spring (40) generates higher force and torque due to more stored energy. As the length of spring (40) is more, the spring stores more energy as there is no limitation of number of turns of the spring upon applying higher force.
Specifically, the spacer (50) is incorporated in-between the plunger (30) and inner diameter of the spring (40). In an embodiment, the spacer (50) has inner diameter greater than outer diameter of the flange (22). The spacer (50) prevents tangling of the spring (40) within the housing (10) and allows the spring (40) to wound properly over the plunger (30). In preferred embodiment, the spacer (50) sits on the opposite face of the flange (22) of the screw (20). Specifically, the spacer (50) has a closed bottom end with hole for screw accommodation.
When the screw (20) is rotated; the rotary motion of the screw (20) is converted into linear motion of the plunger (30). As the rotary movement of the plunger (30) is restricted within the housing (10), the spring (40) moves over the screw (20) thereby decreasing limitation of spring (40) length and total number of coil of the spring (40) to achieve the desired load.
Advantages of the invention

1. In the tensioner (100), there is no space limitation for the spring.
2. In the tensioner (100), as the spring (40) size is more, less stress is developed at higher force.
3. The tensioner (100) provides factor of safety of minimum 2 in full wound condition of the spring (40).
4. The tensioner (100) does not require special construction of a slot within housing for spring (40) end fitment.
5. The tensioner's (100) casting construction is simple.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We Claim;
1. A tensioner capable of applying tension to a bendable, transmission
member in the internal combustion engine, the tensioner comprising:
a cylindrical hollow housing having closed bottom end and open top end;
a screw configured in the housing from the open top end, the screw having a flange adapted on lower portion thereof;
a plunger configured at lower end of the screw, the screw capable of being rotated so as to push the plunger in forward direction;
a spring wound over the plunger and passing over the flange of the screw;
a spacer placed on opposite face of the flange and being incorporated in-between the plunger and inner diameter of the spring, wherein the spring is having inner diameter greater than the outer diameter of spacer thereby allowing the spring to expand over the screw that decreasing limitation of spring length and total number of coil of the spring to achieve desired load.
2. The tensioner as claimed in claim 1, wherein the screw and the plunger have same thread specifications.
3. The tensioner as claimed in claim 1, wherein movement of the plunger is guided and/or restricted within the housing by guiding means such as bearing made up of plastic.
4. The tensioner as claimed in claim 1, wherein the spring has an upper fixed end fastened through/in a slit of the hollow cylindrical housing.

5. The tensioner as claimed in claim 1, wherein the spring has a lower floating end fastened through/in a slot of the flange of the screw.