Mechanical tensioner with damping feature

A mechanical tensioner for a traction drive element is provided. It includes a housing with a bore having an open end and a closed bottom. A plunger having a first end is located in the bore. The first end of the plunger has a tapered slot or tapered opening defined therein forming a hollow wall portion of the plunger. The hollow wall portion is discontinuous in a circumferential direction. A wedge insert is located at least partially in the slot or opening. The wedge insert has an outer surface with a contact area that is complementary to the tapered slot or tapered opening. A spring is located between the wedge insert and closed bottom of the housing. The spring forces the wedge insert into the tapered slot or tapered opening with an increase in force as the plunger is depressed into the bore in the housing. This forces the hollow wall portion outwardly in order to provide a friction damping feature that increases with the distance that the plunger is depressed.

BACKGROUND

The present invention relates to the field of tensioning devices for traction drive elements, such as chains or belts, and in particular is directed to tensioning devices used in connection with tensioning the timing chain or belt for an internal combustion engine.

Chain tensioners for traction drive elements for a timing chain or timing belt drive are known and are also used in connection with traction drive elements for various auxiliary units, such as the generator, power steering pump, air conditioning pump as well as other auxiliary units commonly used on internal combustion engines. The know devices, for example such as shown in U.S. Pat. No. 5,720,683 or U.S. Pat. No. 6,406,391 utilize a plunger located within the bore of a fixed housing which acts on a tensioning shoe to press against the inner or outer run of a traction drive element in order to reduce slack and/or skipping of the traction element on a sprocket or toothed pulley. These known devices utilize a spring in order to press the plunger and associated tensioning shoe toward the tension element. However, they generally lack damping features in order to more effectively attenuate vibrations.

Other known tensioners utilize a ratcheting device in connection with the plunger in order to prevent return motion of the plunger once it has extended past an additional detent or notch on the ratchet. Prior art examples include U.S. Pat. No. 7,513,843 and U.S. Pat. No. 7,455,606.

Additionally, other tensioning devices utilize a blade or leaf spring in connection with the tensioning shoe in order to provide the tensioning function, for example as shown in U.S. Pat. No. 6,609,986 and U.S. Pat. No. 5,797,818.

None of these devices provide a controlled damping feature that allows for improved functioning of the tensioning device so that it not only reduces slack in the traction element, but further dampens vibrations.

SUMMARY

A mechanical tensioner for a traction drive element is provided. It includes a housing with a bore having an open end and a closed bottom. A plunger having a first end is located in the bore. The first end of the plunger has a tapered slot or tapered opening defined therein forming a hollow wall portion of the plunger. The hollow wall portion is discontinuous in a circumferential direction. A wedge insert is located at least partially in the slot or opening. The wedge insert has an outer surface with a contact area that is complementary to the tapered slot or tapered opening. A spring is located between the wedge insert and closed bottom of the housing. The spring forces the wedge insert into the tapered slot or tapered opening with an increase in force as the plunger is depressed into the bore in the housing, forcing the hollow wall portion outwardly in order to provide a friction damping feature that increases with the distance that the plunger is depressed.

Other aspects of the invention are defined below and in the claims and have not been repeated in the for the sake of brevity. Those skilled in the art will recognize that one or more of the features can be used alone or in combination in order to provide a damping feature in a plunger-type mechanical tensioner for a traction drive element that is simple to assemble and of low cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Certain terminology is used in the following description for convenience only and is limiting. The words “front,” “rear,” “upper” and “lower” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to the directions toward and away from the parts referenced in the drawings. A “traction drive element” refers to a belt or chain that extends between pulleys or sprockets, respectively, to transfer rotary force. A reference to a list of items that are cited as “at least one of a, b or c” (where a, b or c represent the items being listed) means any single one of the items a, b or c, or combinations thereof. The terminology includes the word specifically noted above, derivatives thereof and words of similar import.

The present invention provides a mechanical tensioner10,110, shown inFIGS. 2 and 5that is used for tensioning a traction drive element, for example a timing belt or timing chain of an internal combustion engine. A prior art tensioner is shown inFIG. 1that includes a tension shoe1that is mounted on a pivot axle2for pivoting relative to a base3. A spring element4is arranged between the tension shoe1and the base element3and is supported with one end on the base element and the other end forcing the tension shoe1against the traction drive element5. Other arrangements are known in which the spring element linearly displaces a tension shoe as opposed to pivotable displacement.

In the first embodiment of the present invention, shown inFIGS. 2-4, the tensioner10is shown without the tension shoe and with a housing12which can be an integral part of or inserted into a base element, such as the base element3shown inFIG. 1. Housing12includes a bore14having an open end16and closed bottom18. The housing12can be made of deep drawn sheet metal which is inserted into a polymeric or metal base3or can be formed integrally with a base having connection points for connection to the block or an auxiliary bracket of an internal combustion engine or other device where a mechanical tensioner is required.

A plunger20having a first end22is located within the bore14. The first end22of the plunger20has tapered slot or tapered opening24defined therein forming a hollow wall portion26at the first end22of the plunger20. In the first embodiment shown inFIGS. 2-4, a tapered opening24is provided and the hollow wall portion26forms a sleeve28having at least one axially extending slot30defined therein. In the preferred embodiment there are four axially extending slots30, as shown inFIG. 3, which are spaced apart generally equally in a circumferential direction. These slots30preferably extend up to the base32of the tapered opening24.

As shown inFIG. 2, in the first preferred embodiment of the mechanical tensioner10, the tapered opening24defines an angle α with respect to a longitudinal axis34of the plunger20which is in the range about 5° to about 45°. More preferably, α is in the range of about 10° to 25°. In one preferred embodiment, the angle α is preferably about 15°.

The plunger20can be made from a metallic or polymeric material. It can also be formed as a deep drawn sheet metal part with the tapered opening24being formed in a separate step after the formation of the plunger body. The slots30are preferably also formed in a separate step and, based on the separation between the segments of the sleeve28due to the slots30, allow the segments of the hollow wall portion26to be elastically deflectable in an outward direction.

Still with reference toFIGS. 2-4, a wedge insert40is located at least partially in the tapered slot or opening24. In the first preferred embodiment shown inFIGS. 2-4, the tapered opening24is preferably conical in form and the wedge insert40has an outer surface42with a contact area that is complementary to the tapered opening24. Thus, the wedge insert40preferably has a frustoconical form as shown most clearly inFIG. 4. A coating can be provided on the outer surface42of the wedge insert40or on the tapered surface of the opening24in order to adjust the amount of friction generated. Alternatively, or in addition, the material selection and finish for both the plunger20and the wedge insert40can take into account the respective coefficients of friction.

A spring50is located between the wedge insert40and the closed bottom18of the housing12. The spring50is preferably a compression spring, although other types of springs could utilized, if desired. Friction pads or a friction coating44are preferably located on an outer surface of the hollow wall portion26that is slidingly engaged in the bore14of the housing12.

In use, the mechanical tensioner10provides a damping function in that any inward force on the plunger20compresses the spring50which forces the wedge insert40into the tapered opening24, expanding the segmented sections (separated by the slots30) of the hollow wall portion26outwardly against the inside of the bore14. The amount of damping can be controlled depending upon the spring constant as well as the type of friction coating or pads44utilized. The greater the displacement of the plunger20, the more force that is applied by the spring50to the wedge insert40which creates a greater damping effect.

Referring toFIGS. 5-7, second embodiment of the mechanical tensioner110is shown. The second embodiment of the mechanical tensioner110is similar to the mechanical tensioner10and the same reference numbers increased by 100 have been used to identify similar elements. In this case, the primary difference between the mechanical tensioner110and the mechanical tensioner10is that the wedge insert140has a trapezoidal wedge shaped as shown inFIGS. 6 and 7, with two generally planar wedge surfaces142instead of having a frustoconical shape. A tapered slot124is provided instead of the tapered opening24, and the tapered slot124extends radially across an entire width of the plunger120. The hollow wall portion126is formed as two separate halves divided by the slot124.

The mechanical tensioner110functions in the same manner as the mechanical tensioner10in that as a force is applied to the plunger220, the wedge insert140is forced into the tapered slot124by the spring150forcing the two segments of the hollow wall portion126outwardly in order to create greater friction against the walls of the bore114and provide controlled damping for the plunger120. A friction coating or friction pads144may also be provided on an outer surface of the hollow wall portion126which slidingly engages in the bore114of the housing112.

The amount of damping provided by the mechanical tensioners10,100can be varied or adjusted based on changes in a number of factors, including the spring constant of the springs50,150, the angle α, the use and/or type of the frictions pads or coating44, the material selection and finish for the slidingly mating parts, as well as the thickness of the hollow wall portion26,126and/or number of slots30.

Those skilled in the art will appreciate that various other modifications can be made to the mechanical tensioner10,110described above which would still fall within the scope of the present invention which is defined by the appended claims.