Chain drive with a combination rail

Abstract

A chain drive for an internal combustion engine, comprises a driving sprocket, at least one driven sprocket, a drive chain coupling the sprockets, a pivotably supported tensioning rail which is pressed against one of the spans of the drive chain, and a slide rail which abuts on another of the spans of the drive chain, wherein the slide rail and the tensioning rail have a common base body, which is arranged such that it is pivotable about a common pivot axis, and the arcuate portion of a slide surface of the slide rail, which comes into contact with the drive chain during operation, has an axis of curvature or axes of curvature, and the arcuate portion of a slide surface of the tensioning rail, which comes into contact with the drive chain, has an axis of curvature or axes of curvature.

Claims

1. A chain drive for an internal combustion engine, comprising a driving sprocket, at least one driven sprocket, a drive chain coupling the sprockets, a pivotably supported tensioning rail which is pressed against one of the spans of the drive chain, and a slide rail which abuts on another of the spans of the drive chain, wherein the slide rail and the tensioning rail have a common base body, which is arranged such that it is pivotable about a common pivot axis, and an arcuate portion of a slide surface of the slide rail, which comes into contact with the drive chain during operation, has an axis of curvature or axes of curvature, and an arcuate portion of a slide surface of the tensioning rail, which comes into contact with the drive chain, has an axis of curvature or axes of curvature, and the distance of the axis of curvature which is associated with the slide rail or the averaged distance of the axes of curvature which are associated with the slide rail to the pivot axis of the base body is smaller than a distance of the axis of curvature which is associated with the tensioning rail or an averaged distance of the axes of curvature which are associated with the tensioning rail to the common pivot axis of the common base body, wherein a distance of the axis of curvature which is associated with the slide rail or an averaged distance of the axes of curvature which are associated with the slide rail to the common pivot axis of the common base body is smaller than 6 times a chain pitch of the drive chain.

2. The chain drive according to claim 1, wherein the tensioning rail is pressed against a tight span of the drive chain and wherein the slide rail abuts on a slack span of the drive chain.

3. The chain drive according to claim 1, wherein the common base body comprises a long support section associated with the tensioning rail and a shorter support section associated with the slide rail.

4. The chain drive according to claim 1, wherein the arcuate shape of the slide rail and the distance of the axis of curvature which is associated with the slide rail or the averaged distance of the axes of curvature which are associated with the slide rail are chosen such that a change of the effective length of a slack span taking place during operation is a maximum change of 0.3 times the chain pitch.

5. The chain drive according to claim 1, wherein two driven sprockets are provided, which are positioned such that, between the two driven sprockets, a tight span of the drive chain is deflected by more than 80 by means of the tensioning rail, the support section of a common base body associated with the tensioning rail extending in an arcuate shape around the driving sprocket in spaced relationship therewith.

6. The chain drive according to claim 5, wherein in an area of the tight span between the driving sprocket and a driven sprocket of the two driven sprockets that is most remote from the common pivot axis of the common base body, a chain tensioner is arranged, which presses against a free end portion of the support section associated with the tensioning rail.

7. The chain drive according to claim 6, wherein a further slide rail is provided as an integral component of the chain tensioner, said slide rail abutting on the tight span between the driving sprocket and the driven sprocket that is most remote from the common pivot axis of the common base body.

8. The chain drive according to claim 5, wherein the driving sprocket is configured to drive a crankshaft, the driven sprocket of the two driven sprockets that is located closest to the common pivot axis is configured to drive a shaft of an oil pump, and the other driven sprocket is configured to drive a shaft of a mass balancer.

9. The chain drive according to claim 1, wherein the distance of the axis of curvature which is associated with the slide rail or the averaged distance of the axes of curvature which are associated with the slide rail to the common pivot axis of the common base body is smaller than 4.5 times the chain pitch of the drive chain.

10. The chain drive according to claim 1, wherein the arcuate shape of the slide rail and the distance of the axis of curvature which is associated with the slide rail or the averaged distance of the axes of curvature which are associated with the slide rail are chosen such that a change of the effective length of a slack span taking place during operation is a maximum change of 0.16 times the chain pitch.

11. The chain drive according to claim 1, wherein two driven sprockets are provided, which are positioned such that, between the two driven sprockets, a tight span of the drive chain is deflected by more than 90 by means of the tensioning rail, a support section of the common base body associated with the tensioning rail extending in an arcuate shape around the driving sprocket in spaced relationship therewith.

12. A combination rail for a chain drive, comprising a common base body, a first, long slide section to be associated with a tensioning rail, and a second, short slide section to be associated with a slide rail, wherein the common base body defines a common pivot axis for the slide sections, the first long slide section is configured such that it is adapted to be brought into contact with a tight span of the chain drive, and the second short slide section is configured such that it is adapted to be brought into contact with a slack span of the chain drive, wherein the second short slide section to be associated with the slide rail is arranged in the area of the common pivot axis, the second short slide section, which is adapted to be brought into contact with a drive chain during operation, having a curvature axis or curvature axes whose distance to the common pivot axis or whose averaged distance to the pivot axis is smaller than 6 times the chain pitch of the drive chain of the chain drive.

13. The combination rail according to claim 12, wherein the common base body together with the slide sections is produced integrally as a single-component part.

14. The combination rail according to claim 12, wherein the first long slide section to be associated with the tensioning rail is configured in an arcuate shape such that the drive chain of the chain drive is deflectable by more than 80 between two driven sprockets of the chain drive.

15. The combination rail according to claim 12, wherein the second short slide section to be associated with the slide rail comprises an effective slide surface having a length that is 5 times shorter than a length of the effective slide surface of the first long slide section to be associated with the tensioning rail.

16. The combination rail according to claim 12, wherein the first long slide section to be associated with the tensioning rail is configured in an arcuate shape such that the drive chain of the chain drive is deflectable by more than 90 between two driven sprockets of the chain drive.

17. The combination rail according to claim 12, wherein the second short slide section to be associated with the slide rail comprises an effective slide surface having a length that is 6 times shorter than a length of the effective slide surface of the first long slide section to be associated with the tensioning rail.

18. A combination rail for a chain drive, comprising a common base body, a first, long slide section to be associated with a tensioning rail, and a second, short slide section to be associated with a slide rail, wherein the common base body defines a common pivot axis for the slide sections, the first long slide section is configured such that it is adapted to be brought into contact with a tight span of the chain drive, and the second short slide section is configured such that it is adapted to be brought into contact with a slack span of the chain drive, wherein the second short slide section to be associated with the slide rail is arranged in the area of the common pivot axis, the second short slide section, which is adapted to be brought into contact with a drive chain during operation, having a curvature axis or curvature axes whose distance to the common pivot axis or whose averaged distance to the pivot axis is smaller than 4.5 times the chain pitch of the drive chain of the chain drive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, an embodiment of the present invention will now be explained in more detail making reference to the drawings, in which:

(2) FIG. 1 shows a front view of a chain drive according to the present invention,

(3) FIG. 2 shows a perspective front view of the combination rail according to FIG. 1,

(4) FIG. 3 shows a perspective rear view of the combination rail according to FIG. 1,

(5) FIG. 4a shows a perspective view of the chain drive for illustrating the principle of the embodiment shown in FIG. 1,

(6) FIG. 4b shows a perspective view of the chain drive for illustrating the principle of the embodiment shown in FIG. 1 and

(7) FIG. 5 shows a schematic sketch of the chain drive for illustrating the ideal case.

DETAILED DESCRIPTION

(8) The chain drive 1 shown in FIG. 1 is shown without the internal combustion engine and without the associated fasteners for the sake of simplicity. This chain drive is an oil pump drive and a mass balancer drive for such an internal combustion engine.

(9) The chain drive 1 substantially comprises a driving crankshaft sprocket 2, an oil pump sprocket 3, a mass balancing sprocket 4, a drive chain 5 coupling the sprockets 2, 3, 4 to one another, a chain tensioner 6 and a combination rail 7. The crankshaft sprocket 2 is connected to the crankshaft of the internal combustion engine, which is not shown, and is in mesh with the outer side of the drive chain 5. When the internal combustion engine is in operation, the crankshaft sprocket 2 rotates clockwise and is in mesh with the inner side of the drive chain. In the normal mounting condition of the internal combustion engine, the oil pump sprocket 3 is arranged below the crankshaft sprocket 2 and within an area delimited by the drive chain 5. Other than the crankshaft sprocket 2, around which the drive chain 5 is wrapped over an angle that is slightly larger than 90, the oil pump sprocket 3 has wrapped the drive chain 5 therearound over an angle of almost 180. The mass balancing sprocket 4 drives a mass balancing weight 8, which has a vibration-reducing effect and which counteracts in the manner known the unbalances induced by the crankshaft. The drive chain 5 is also wrapped around the mass balancing sprocket 4 over an angle of almost 180. The chain tensioner 6 is arranged within an area delimited by the drive chain 5. In the drawing, it is shown in its locked position. As soon as it has been unlocked, its tensioning piston 9 presses against the combination rail 7. The chain tensioner housing 10 is secured to the engine block by fasteners that are not shown. The lower end of the chain tensioner housing 10 has mounted thereon a slide rail 11, which defines a unit together with the chain tensioner 6 and which abuts on the inner side of the drive chain 5 between the crankshaft sprocket 2 and the mass balancing sprocket 4.

(10) The drive chain 5 shown is a roller chain with alternate inner and outer chain links having a conventional structural design and a pitch T. Alternatively, also a bush chain may be used. In addition to the sections of the drive chain 5 which are fully (without entering and exiting sections) in mesh with the sprockets 2, 3, 4, three sub-strands are obtained. These sub-strands are the slack span 12 extending between the crankshaft sprocket 2 and the oil pump sprocket 3, the comparatively long tight span 13 extending between the oil pump sprocket 3 and the mass balancing sprocket 4 and the comparatively short tight span 14 extending between the mass balancing sprocket 4 and the crankshaft sprocket 2.

(11) In the following, the combination rail 7 will now be explained in more detail with the aid of FIGS. 2 and 3.

(12) The combination rail 7 is arranged within an area delimited by the drive chain 5 and comprises a common base body 15 provided with a pivoting eye 16 on the lower end thereof, said pivoting eye 16 being used for receiving therein a pivot pin connected to the engine block. The main axis of the pivoting eye 16 is to be equated with the pivot axis S of the combination rail 7. The base body 15 is subdivided into a longer support section 17 of arcuate shape and a short support section 18. The combination rail 7 is a combination of a pivotably arranged tensioning rail, which is mainly defined by the longer support section 17, and a slide rail, which is mainly defined by the shorter support section 18. The shorter support section 18 is located in the area of the pivoting eye 16, whereas the long support section 17 mainly extends away from this pivoting eye 16. The base body 15 is provided with a truss structure. On the back of the base body 15, at the end located remote from the pivoting eye 16, there is a press-on area 19 onto which the end face of the tensioning piston 9 of the chain tensioner 6 presses during operation. The base body 15 is configured integrally and represents a single-component part. This means that the press-on sides of the respective support sections 17, 18 are provided with a long slide section 20 and a short slide section 21. The respective slide sections 20 and 21 define an arcuate slide surface 20.1 and a slide surface 21.1, which are directed away from one another and which each abut on the inner side of the drive chain. The slide surface 21.1 to be associated with the slide rail is configured straight and flat, respectively, in the thickness direction of the combination rail 7 and has, at least in the section which enters into contact with the drive chain during operation, a circular curvature with a radius of curvature R in a simplified manner. Due to the straight and flat shape of the slide surface 21.1, also a curvature axis A.sub.G can be taken into account for observation. This curvature axis A.sub.G is shown in FIG. 4a, so is the circle of curvature K.sub.G associated therewith. The curvature axis A.sub.G extends perpendicular to the image plane and the circle of curvature K.sub.G characterizes the circular curvature of the slide surface 21.1. This observation does not take into account the radii of the roundings at the ends of the slide section 21, since these roundings are not intended to enter into contact with the drive chain 5.

(13) The slide section 20 comprises a subdivided slide surface 20.1. In this area 22 no contact with the drive chain 5 occurs. This has friction-reducing reasons. The remaining sections of the slide surface 20.1 have three different curvatures, and, consequently, different circles of curvature K.sub.S1, K.sub.S2, K.sub.S3 and curvature axes A.sub.S1, A.sub.S2, A.sub.S3 are here to be determined (cf. also FIG. 4b). Also in this case, radii of the roundings at the ends of the slide section 20 as well as the recessed roundings in the area 22 are of no importance for the observation. In order to actually allow tensioning of the drive chain 5 by means of the combination rail 7, so as to compensate for a stretch of the drive chain 5 during operation, the pivot axis S (cf. FIG. 5) is arranged in displaced relationship with the curvature axes A.sub.S1, A.sub.S2, A.sub.S3 of the slide surface 20.1. For simplified observation, a respective distance V.sub.1, V.sub.2, V.sub.3 from the pivot axis S to the curvature axes A.sub.S1, A.sub.S2, A.sub.S3 of the slide surface 20.1 is determined and divided by the number (here 3) of the distances V.sub.1, V.sub.2, V.sub.3 or curvature axes A.sub.S1, A.sub.S2, A.sub.S3 to be taken into account in the present context, so as to obtain an averaged distance.

(14) The distance V of the pivot axis S from the curvature axis A.sub.G is shown in FIG. 4. The distance V is chosen such that, in the present case, it is smaller than 3 times the chain pitch T (according to definition smaller than 6 times, preferably smaller than 4.5 times the chain pitch T). In addition, the distance of the pivot axis S to the slide surface 21.1 is smaller than the radius of curvature R of the circle of curvature K.sub.G. If the combination rail 7 is now pivoted clockwise due to stretching of the drive chain 5 during operation, this will, of course, also influence the routing of the slack span 12. The slide section 21 is pivoted slightly away from the drive chain 5. The influence is, however, comparatively small due to the geometrical conditions chosen. In the present case, the effective length of the slack span 12 changes only very slightly during operation, viz. less than 0.16 times the chain pitch T (according to definition not more than 0.3 times the chain pitch T, preferably not more than 0.16 times the chain pitch T), the influence on the angle of rotation being thus only small. What changes predominantly is the length of the tight span 13 because the averaged distance of the curvature axes to the pivot axis S, related to the slide surface 20.1, is much larger. Moreover, the effective slide surface (i.e. the length from the area where the chain enters up to the area where the chain exits the slide surfaces 20.1 and 21.1, respectively) is more than 5 times longer in the case of the slide surface 20.1 than the effective length of the slide surface 21.1 (according to definition 5 times longer, preferably 6 times longer). Therefore, the length compensation is mainly caused by the slide section 20.

(15) Furthermore, it should be stated that the slide section 20 is configured in an arcuate shape such that the drive chain 5 is deflected between the exit end on the mass balancing sprocket 4 and the meshing end on the oil pump sprocket 3 by an angle of more than 90 (according to definition more than 80, preferably more than 90). Due to this fact and due to the fact that the base body 15 does not have its full height over the main part of its length, said full height existing in the area of the slide section 21, the resultant chain drive 1 is, on the whole, narrow and requires little space. Due to the arrangement of the combination rail 7, the resulting from the slight pivotal displacement of the support section 18 representing the slide rail can be more than compensated for. The combination rail 7 is easy to produce because it only necessitates the use of a single tool. Fastening is reduced to a single swivel mounting by means of the pivoting eye 16. An additional fastening of the slide rail can be dispensed with. This leads to distinct cost advantages and to simplified mounting.

(16) Making reference to FIG. 5, the aimed-at ideal case, which, however, can only be used when admissible installation space conditions are given, will now additionally be discussed. In this ideal case, the pivot axis S and the curvature axis A.sub.G of the slide rail are congruent. Hence, a correspondingly smaller circle of curvature K.sub.G will be used. If the combination rail 7 now pivots about the pivot axis S, this will no longer have any influence whatsoever on the guide track of the slack span 12. Only the slide surface 21.1 will be slightly displaced, but this does not have any effect on the guide track. The complete pivoting distance is then provided by the slide section 20. The two routings of the drive chain 5, in the new condition as well as after chain stretch, are shown in FIG. 5. It can also be seen that there will be no change in the tight span 14. In practice, a compromise, similar to FIG. 5, will, however, have to be made, and this means that a slight change in the routing of the slack span 12 will have to be accepted.

LIST OF REFERENCE NUMERALS

(17) 1 chain drive 2 crankshaft sprocket 3 oil pump sprocket 4 mass balancing sprocket 5 drive chain 6 chain tensioner 7 combination rail 8 mass balancing weight 9 tensioning piston 10 chain tensioner housing 11 slide rail 12 slack span 13 long tight span 14 short tight span 15 base body 16 pivoting eye 17 short support section 18 long support section 19 press-on area 20 slide section 21 slide section 20.1 slide surface 21.1 slide surface 22 area A.sub.G curvature axis A.sub.S1, A.sub.S2, A.sub.S3 curvature axis K.sub.G circle of curvature K.sub.S1, K.sub.S2, K.sub.S3 circle of curvature R radius of curvature S pivot axis T chain pitch V distance V.sub.1, V.sub.2, V.sub.3 distance angle