GB2323893A

GB2323893A - Chain guide assembly for an ic engine providing vibration damping

Info

Publication number: GB2323893A
Application number: GB9804407A
Authority: GB
Inventors: Tomokazu Kaido; Fumiaki Oba
Original assignee: Tsubakimoto Chain Co
Current assignee: Tsubakimoto Chain Co
Priority date: 1997-03-31
Filing date: 1998-03-02
Publication date: 1998-10-07
Anticipated expiration: 2018-03-02
Also published as: GB2323893B; JPH10274298A; GB9804407D0

Abstract

A chain guide assembly comprises a chain guide 1 having at each end a mounting hole 6 for securing the guide 1 to an engine block 4 by shoulder bolts 5 passing through the holes 6 and an elastic buffer 7 interposed between the bolt 5 and the hole 6 to isolate one from the other thus providing vibration damping and reduced noise. At the peripheral edge of the hole 6 an annular groove 8 may be provided to receive the buffer 7. In a second embodiment (figure 2) the peripheral edge may be chamfered to form a tapered surface and in a third embodiment (figure 3) an annular groove, for receiving the buffer 7, is provided part way down the hole 6.

Description

CHAIN GUIDE ASSEMBLY The present invention relates to a structure for mounting a chain guide to, for example, a mounting surface of an engine block. The invention is particularly useful where the coefficient of linear expansion of the mounting surface and that of the chain guide are different from one another.

In a conventional chain drive system used for an engine or the like, as shown in FIG. 4, a chain A3 is entrained between a driving-side sprocket Al and a driven-side sprocket A2, and a chain guide A4 for preventing vibration of the chain A3 during travel of the chain is disposed outside a chain portion serving as a tension side, while a tensioner unit A5 for eliminating the slack of the chain A3 is disposed outside a chain portion serving as a slack side.

The tensioner unit A5 comprises a tensioner lever A8 which is pivotably mounted on one end side thereof on a mounting surface A6 such as an engine block through a pivot pin A7, and a tensioner A9 which urges the opposite end side of the tensioner lever A8 toward the chain A3. With the urging force of the tensioner A9, a shoe face A10 of the tensioner lever A8 pushes a side face on the slack side of the chain A3, thereby imparting a moderate tension to the chain to prevent the chain from becoming loose.

Further, the chain guide A4 comes into sliding contact with the outer side face of the chain A3 to prevent vibration of the chain while the chain is travelling. For the reduction of resistance and vibratory noise generated upon such sliding contact with the chain A3, the chain guide A4 is formed of a resin material, usually nylon.

As shown in FIG. 5, a large-diameter portion A13 of a shoulder bolt A12 is inserted into a mounting hole All formed in both longitudinal end portions of the chain guide A4, while a screw threaded portion A14 of the shoulder bolt is brought into engagement with a screw threaded hole A15 formed in the mounting surface A6 such as an engine block.

In this way the chain guide A4 is mounted to the mounting surface A6.

In this case, due to a difference in the coefficient of linear expansion between the mounting surface A6 and the resinous chain guide A4, a rise in the temperature of the mounting surface A6 causes a discrepancy between the spacing of both mounting holes All at both ends of the chain guide A4 and the spacing of the shoulder bolts A12 clamped to the mounting surface A6 through those mounting holes. For absorbing this discrepancy, the inner diameter of each mounting hole All formed in the chain guide A4 is set somewhat larger than the outer diameter of each large-diameter portion A13 of the shoulder bolt A12 to form a gap S between the two.

The conventional chain guide referred to above involves the problem that a striking sound generated between the chain and the chain guide is propagated through the shoulder bolts to various components, including the engine block, on the mounting surface side. Moreover, since there is a gap between each mounting hole of the chain guide and the large-diameter portion of the shoulder bolt inserted therein, the chain guide may vibrate while the chain travels, resulting in collision of the outer peripheral surface of the large-diameter portion with the inner peripheral surface of the mounting hole and consequent generation of noise.

Propagation of the sound generated on the chain guide side to the mounting surface side through the shoulder bolts will cause resonance of components low in rigidity such as a chain cover and a head cover, with consequent generation of a loud noise. According to the prior art, for example the shape of such low-rigidity components is modified to prevent the resonance, thus giving rise to the problem that the manufacturing cost of those components It is therefore an object of the present invention to solve the abovementioned problems of the prior art and provide a chain guide mounting structure capable of cutting off the transfer to the mounting surface of a striking sound generated between the chain and the chain guide and capable of preventing the generation of noise which is ascribable to vibration of the chain guide.

According to the present invention, in order to achieve the abovementioned object, there is provided a chain guide assembly comprising a chain guide having at each end a mounting hole, the guide being secured to a mounting surface by a respective shoulder bolt passing through each mounting hole with a mounting portion of the bolt in the mounting hole and a screw threaded portion in a tapped hole in the mounting surface, and the inner diameter of the mounting hole being larger than the outer diameter of the mounting portion; and an elastic buffer member interposed between the outer peripheral surface of the mounting portion of the bolt and the inner peripheral surface of the mounting hole to isolate the outer and inner peripheral surfaces from each other.

When the chain comes into sliding contact with the chain guide during travel of the chain, the annular gap between the inner peripheral surface of each of the mounting holes and the outer peripheral surface of the mounting portion of the shoulder bolt is maintained by the elastic buffer member, so that the striking sound generated between the chain and the chain guide during travel of the chain is absorbed by the elastic buffer member and the transfer thereof to the mounting surface is thus prevented.

Moreover, the vibration of the chain guide resulting from sliding contact of the chain guide with the travelling chain is damped by the elastic buffer member, and the collision between the inner peripheral surface of the mounting hole and the outer peripheral surface of the large-diameter portion caused by vibration of the chain guide is avoided by the elastic buffer member disposed between the inner and outer peripheral surfaces, whereby the generation of a collision noise is prevented.

Further, in the event there occurs a discrepancy between the centre-to centre distance of the mounting holes at both end portions of the chain guide and the centre-to-centre distance of the two shoulder bolts due to a rise in temperature of the mounting surface during travel of the chain, the elastic buffer member deforms itself elastically, whereby the discrepancy can be absorbed.

In the accompanying drawings: FIGS. 1 to 3 are similar sectional views of part of a chain guide assembly according to three embodiments of the present invention; FIG. 4 is a plan showing an example of a conventional chain guide of the kind to which the invention is applicable; and, FIG. 5 is a view as seen in the arrowed direction X-X in FIG. 4.

As shown in FIG. 1, which corresponds to the section of Fig. 5, but is a sectional view of a chain guide assembly according to the first embodiment of the present invention, the chain guide 1 is formed by molding using a resin material low in friction and high in strength, such as nylon. One end face of the chain guide 1 is formed as a shoe face 3 for sliding contact with a chain 2. Further, one side face of the chain guide 1 is abutted against a mounting surface 4 formed in an engine block.

In the mounting surface 4 is formed a tapped hole 4A, and a screw threaded portion 5A of a shoulder bolt 5 is brought into engagement with the tapped hole 4A, whereby the end face of a mounting portion 5B of the bolt 5 is fixed in abutment with the mounting surface 4. The diameter of the mounting portion 5B is larger than that of the screw threaded portion 5A.

The large-diameter portion 5B of the bolt 5 is inserted into a mounting hole 6 formed in the chain guide 1. The inner diameter of the mounting hole 6 is slightly larger than the outer diameter of the large-diameter portion 5B of the bolt 5, and the length L of the large-diameter portion SB is slightly larger than the width W of the chain guide 1.

A flange portion 5D having an outer diameter larger than the inner diameter of the mounting hole 6 is formed between the large-diameter portion 5B of the shoulder bolt 5 and a head portion 5C thereof, whereby the chain guide 1 is held on the large-diameter portion 5B.

An annular groove 8 for fitting therein of an annular elastic buffer member 7 is formed in the peripheral edge portion of the mounting hole 6 of the chain guide 1 on the flange portion 6D side. The elastic buffer member 7 is made of rubber and its inner peripheral surface is in close contact with the outer peripheral surface of the large-diameter portion 5B of the shoulder bolt 5, with an annular gap S being formed between the mounting hole 6 of the chain guide 1 and the large-diameter portion SB.

FIG. 2 shows the second embodiment in which the portions represented by the same reference numerals as in Fig. 1 are constructed as in Fig. 1.

In this second embodiment, on the side opposed to the flange portion 5D of the shoulder bolt 5, the peripheral edge portion of a mounting hole 6A formed in a chain guide 1A is chamfered to form a tapered surface 8A, and an elastic buffer member 7A formed of rubber and having a tapered surface as an outer peripheral surface conforming to the tapered surface 8A is fitted on the tapered surface 8A.

With the shoulder bolt 5 fixed to the mounting surface 4, the elastic buffer member 7A is pressed by the flange portion 5D, so that the tapered surface at an outer peripheral surface thereof is pushed against the tapered surface 8A of the peripheral edge portion of the mounting hole 6A formed in the chain guide lA and the elastic buffer member 7A is slightly deformed elastically. Consequently, the inner peripheral surface of the elastic buffer member 7A comes into close contact with the outer peripheral surface of the shoulder bolt 5, thereby centering the mounting hole 6A of the chain guide 1A with respect to the shoulder bolt 5, with formation of an annular gap S between the mounting hole 6A and the large diameter portion 5B.

Fig. 3 shows the third example in which the portions represented by the same reference numerals as in FIG. 1 are constructed as in FIG. 1.

In this third embodiment, an annular groove 8B for fitting therein of an annular elastic buffer member 7B made of rubber is formed in the inner peripheral surface of a mounting hole 6B made in a chain guide 1B. The annular groove 8B is U-shaped in section, which is open to the inner peripheral surface side of the mounting hole 6B. The outer peripheral surface of the elastic buffer member 7B is fitted in and fixed to the annular groove 8B, while the inner peripheral surface thereof comes into close contact with the outer peripheral surface of the large-diameter portion 5B of the shoulder bolt 5, to form an annular gap S between the large-diameter portion 5B and the mounting hole 6B.

In this third embodiment, the annular groove 8B is formed in the inner peripheral surface of the mounting hole 6B at a position located axially part way along the mounting hole, so there is no fear of falling off of the elastic buffer member 7B even if the member is mounted beforehand in the annular groove 8B of the mounting hole 6B prior to mounting the chain guide lB to the mounting surface 4 with the shoulder bolt 5. This brings about the advantage that the assembling work can be done efficiently.

Although in each of the above embodiments only one elastic buffer member is disposed between the mounting hole of the chain guide and the shoulder bolt, plural such elastic buffer members may be provided in the axial direction.

Although in each of the above embodiments the annular groove and the tapered surface for fitting therein and positioning the annular elastic buffer member are formed on the chain guide side, a modification may be made such that an annular groove is formed in the outer peripheral surface of the large-diameter portion of the shoulder bolt and an elastic buffer member is fitted therein with its outer peripheral surface in close contact with a smooth inner peripheral surface of the mounting hole formed in the chain guide.

Further, between the inner peripheral surface of the mounting hole of the chain guide and the outer peripheral surface of the large-diameter portion of the shoulder bolt there may be arranged a plurality of elastic buffer members spaced in the circumferential direction. For example, there may be adopted a structure in which several rectilinear grooves such as key ways are formed axially in the outer peripheral surface of the shoulder bolt or in the inner peripheral surface of the mounting hole so as to be spaced from one another in the circumferential direction, and elastic buffer members each having such width and length as conform to each of those rectilinear grooves are fitted in the grooves, to prevent direct contact of the inner peripheral surface of the mounting hole with the outer peripheral surface of the shoulder bolt.

According to the chain guide mounting structure of the present invention, since an elastic buffer member is disposed between the mounting hole of the chain guide and the shoulder bolt inserted through the mounting hole, a striking sound generated between the chain and the chain guide during travel of the chain is absorbed by the elastic buffer member and hence the transfer of the striking sound to the mounting surface side can be prevented. Besides, in the event a rise in temperature of the mounting surface during travel of the chain causes a discrepancy between the centre-to-centre distance of the mounting holes at both end portions of the chain and the centre-to-centre distance of the two shoulder bolts due to the difference in the coefficient of linear expansion between the chain guide and the mounting surface, the elastic buffer member deforms itself elastically, whereby the discrepancy can be absorbed.

Moreover, the vibration of the chain guide induced by sliding contact thereof with the chain during travel of the chain is damped by the elastic buffer member, and since an annular gap is ensured by the elastic buffer member between the outer peripheral surface of the shoulder bolt and the inner peripheral surface of the mounting hole, collision between such outer and inner peripheral surfaces is avoided even upon vibration of the chain guide, whereby the generation of a collision noise can be prevented.

Further, it is not necessary to enhance the rigidity of components located on the chain guide mounting surface side. By merely adding the elastic buffer member to a conventional chain guide and making a minute modification of the mold for the chain guide it is made possible to prevent the generation of noise from the chain guide and attain a great reduction of cost.

Claims

1. A chain guide assembly comprising a chain guide having at each end a mounting hole, the guide being secured to a mounting surface by a respective shoulder bolt passing through each mounting hole with a mounting portion of the bolt in the mounting hole and a screw threaded portion in a tapped hole in the mounting surface, and the inner diameter of the mounting hole being larger than the outer diameter of the mounting portion; and an elastic buffer member interposed between the outer peripheral surface of the mounting portion of the bolt and the inner peripheral surface of the mounting hole to isolate the outer and inner peripheral surfaces from each other.

2. An assembly according to claim 1, wherein the elastic buffer member is annular.

3. An assembly according to claim 2, wherein the elastic buffer member is located axially part way along the mounting hole.

4. An assembly according to any one of the preceding claims, wherein the diameter of the mounting portion is greater than that of the tapped portion.

5. A chain guide assembly, substantially as described with references to Figs. 1 to 4 of the accompanying drawings.