GB2436359A

GB2436359A - Chain drive assembly

Info

Publication number: GB2436359A
Application number: GB0601845A
Authority: GB
Inventors: Gregory Portier; Christian Poiret; Emmanuel Desmarchelier; Nicholas Dogimont; Adrien Catheline
Original assignee: Schaeffler Chain Drive Systems SAS; Renold PLC
Current assignee: Schaeffler Chain Drive Systems SAS
Priority date: 2006-01-31
Filing date: 2006-01-31
Publication date: 2007-09-26
Anticipated expiration: 2026-01-31
Also published as: GB2436359B; GB0601845D0

Abstract

A chain drive assembly comprises at least one sprocket and an inverted tooth silent chain. Some teeth 61 of the sprocket at random locations having their leading flanks modified (as shown in fig 12) such that the initial point of contact with a tooth of a chain is lower than for a standard sprocket tooth 60 (also see figures 13a and b). The arrangement is such that the pin hole centre of the meshing link plate does not rise above the pitch line PL of the chain during the initial phases of meshing. This reduces chordal action and vibrations during meshing and serves to reduce the overall noise associated with impacts of the chain link and sprocket teeth. The inner flanks of the chain teeth are designed to have a specific curvature for improved meshing (fig 7). The shape of the pin holes is configured for controlled and supported pivoting of the link plates during meshing (figs 9 and 10).

Description

A CHAIN DRIVE ASSEMBLY

The present invention relates to a chain drive assembly comprising a chain and at least one sprocket. It particularly, but not exclusively, relates to a power transmission chain drive assembly in a vehicle that uses an inverted tooth or silent chain in order to transmit power from an internal combustion engine to the vehicle transmission.

An inverted tooth chain comprises a plurality of link plates that are interconnected by pins and that are designed to mesh with teeth defined on the peripheries of rotary drive sprockets so as to transmit torque and power between rotating shafts. In the context of an internal combustion engine such a chain can be used as a power transmission chain and/or a timing chain. In the former application a chain is typically used to transfer power from the engine to the vehicle transmission or is employed in the transfer case to split power transmission between the front and rear axles of a four-wheel drive vehicle. In the latter application the chain ensures that rotation of the crankshaft of an internal combustion engine is synchronised with rotation of the camshaft to ensure that the movement of valves on the camshaft is in an accurate timed relationship with the movement of the pistons on the crankshaft. It is well recognised in the industry that inverted tooth chains have the capacity to transmit high power and torque in relatively confined areas with high efficiency.

An inverted tooth or silent chain generally comprises a plurality of inner articulating link plates each of which has a sprocket-engaging edge that defines a pair of teeth separated by a crotch. The teeth of the sprocket are received in the crotch of the links such that the flanks of the sprocket teeth are in driving engagement with the inside and/or outside flanks of the link teeth so as to transmit the torque of the sprocket to the chain. The contours of the link teeth flanks are carefully designed to ensure smooth and progressive engagement on meshing with the sprocket so that there is a gradual assumption of the load. Guide links, which do not provide driving contact with the sprocket teeth, are positioned on the flanks and/or in the centre of the chain and serve to maintain the lateral position of the chain on the sprocket. The link plates are interconnected by transverse pins that are received in aligned apertures. The inner link plates are designed to articulate on the pins whereas the guide link plates are fixed to the pins by means of a press-fit or friction fit or the like. Power transmission chains of the kind described above generally have rocker joint pins whereby adjacent link plates are interconnected by a pair of pins that occupy the same hole in each plate. The pins have facing arcuate surfaces that allow for rolling engagement during articulation of the chain. During chain articulation, the two profiled pivots roll against each other smoothly, removing the sliding friction that occurs with single pin joints and other pintle chain formats, as well as contributing to less wear elongation. The design also serves to reduce the effect of chordal action (described below) whereby the chain pitch increases slightly as the links articulate.

It is well established that chains with rocker joint pins are able to withstand the relatively high tensile loading applied in power transmission applications. However, in view of the loads that the chain is to withstand it is particularly important to ensure that the engagement between the pins and the edges of the pin holes in the link plates is such that stress concentrations are avoided.

One of the main considerations in the design of inverted tooth silent chains is the noise created by meshing of the teeth of the chain links with the sprocket. The impact of the chain link teeth on the sprocket happens rapidly during meshing and attempts have been made to control the action.

The meshing process is also complicated by what is known as "chordal action" or the "polygonal motion" whereby the chain links move relative to the sprocket teeth during meshing and unmeshing. The movement arises from the fact that the pitch line of the chain comprises a plurality of straight lines or chords that combine to form part of a polygon rather than a circle (as would be the case for a flexible belt). This means that the distance of the chain pin to the centre of the sprocket of an unmeshed chain link fluctuates as it approaches the meshing point. This rapid and uncontrolled movement of the chain links can add to the impact noise. For a chain comprising identical inner links the impact noise is repeated at a frequency related to the speed of rotation of the drive. Sprockets for inverted tooth drives have involute teeth and the teeth of the link plates, whose outer flanks are oriented at a predetermined angle (e.g. degrees), engage between sprocket teeth such that both teeth flanks make contact.

In a conventional inverted tooth silent chain drive, such as that shown in figures 1 to 4, when the taut side of the chain loop 10 (only part of which is shown in the figures) starts to mesh with the driving sprocket lithe first point of impact P1 is between the inside flank 12 of the link plate 13 and the involute sprocket tooth 14, as the profile of this flank extends beyond the outside flank 15 of the adjacent link plate 16 (see figure 2). As the sprocket 11 rotates (clockwise in the direction of figures 2 to 4) during the early stages of meshing of the link plate 13 and the sprocket 11, the centre of the leading pin hole 17 in the link plate 13 temporarily rises above the pitch line PL of the chain, which is effectively a tangent to the pitch diameter PD of the sprocket 11, before dropping again. This polygonal motion is a cause of noise and occurs just before the meshing contact transfers from the inside flank 12 of the tooth of a chain link plate 13 to the outside flank 15 of the overlapping link plate 16 (as shown by reference P2 in figure 3). Thereafter, as the chain link 13 fully engages with the sprocket 11 (figure 4), the contact (indicated at points P3 and P4) with the sprocket only occurs at the outside flank 15 of the link teeth. Thus noise is generated not only by the two part engagement of a given link plate with the sprocket tooth but also by the polygonal motion vibration.

There have been several different approaches to reducing meshing noise in a chain drive assembly. One approach is to provide the chain with at least two different link plate shapes and to interleave the link plates in a random configuration such that the frequency of engagement between the link plates and the sprocket varies as the chain meshes. This serves to disperse the noise over a range of frequencies such that the overall noise level is reduced. US 4,342,560 describes one example of this approach in which some link plates are designed to engage drivingly with the sprocket with their outside tooth flanks and others are designed to engage with their inside tooth flanks. The links are arranged such that there is a random pattern of engagement as the chain meshes with the sprocket, thereby reducing the noise level. In US 4,832,668 a similar result is achieved by varying the curvature of the inside flanks of the teeth. US 5,453,059 discloses the idea of using links of different or unequal pitch lengths randomly arranged along the chain length to modify the noise pattern. The disadvantage of such chain designs is that chain assembly is complicated by the provision of at least two different link plate types and the need to arrange them in predetermined patterns along the chain.

An alternative approach to noise reduction is to modify the roots and/or teeth of the sprocket with which the chain meshes. The chain drive assembly described in US Patent No. 3,495,468 uses this approach and provides for a driven sprocket in which all of the sprocket teeth are relieved on the trailing flank (rather than the leading flank that serves to make driving contact with the link teeth) so as to provide for a smooth and shorter path to the root for the tips of the link teeth during meshing.

The idea is to prevent the tip of the link teeth from contacting the top of the sprocket teeth on chain elongation as this impedes desirable random root contact that serves to break up the mesh frequency and disperses the resultant noise over a range of frequencies. The diameter of the non-relieved roots is such that the tips of the link plate teeth make contact therewith. Similarly US Patent No. 3,377,875 describes a random engagement sprocket in which random teeth have material removed from the trailing flank such that they are of reduced circumferential width so as to render them inactive. In this drive assembly contact between the sprocket root and the tips of the chain link teeth serves to guide the meshing engagement. US Patent No. 4,168,634 describes a random engagement driven sprocket featuring a combination of teeth modified on the trailing flank so as to be of reduced circumferential width and random root relief. Again the teeth are designed to make contact with the sprocket roots. The arrangement is designed such that the tips of the chain link teeth contact the (unrelieved) sprocket roots without any contact occurring between the chain link teeth flanks and the sprocket teeth flanks.

It is an object of the present invention to provide for an inverted tooth chain, sprocket and drive assembly that has reduced noise levels in operation in comparison to a conventional drive by providing for a smooth meshing engagement between the chain links and the sprocket.

According to a first aspect of the present invention there is provided a chain drive assembly comprising an inverted tooth chain and a toothed sprocket, the chain having a plurality of links arranged into rows across the chain and interleaved, the links being interconnected by transverse pins that pass through aligned apertures in the links, the links comprising articulating links having a peripheral inner surface facing the sprocket during meshing and an outer peripheral surface distal to the sprocket, the inner surface of the links defining a pair of teeth configured to mesh with the sprocket, the sprocket having a main body from which extend a plurality of spaced teeth, and roots defined between said sprocket teeth, each sprocket tooth having a leading flank that first makes contact with a meshing flank of a link tooth during meshing of an articulating link with the sprocket, the sprocket having a plurality of first sprocket teeth with relieved leading flanks at least at the tips thereof and being disposed randomly amongst second sprocket teeth having leading flanks of a different profile, the relieved flanks of the first teeth being designed to ensure that the initial point of contact of a chain link during meshing is lower down the leading flank of a first tooth than for a second tooth, the teeth of the chain links not contacting the sprocket roots during meshing with the sprocket.

The different leading flank profiles provide at least two different tooth profiles such that that the distance between the centre of the sprocket and the initial meshing point of a link for a first sprocket tooth is shorter than that for a second tooth. It will be appreciated that the leading flanks of the second teeth may have no relief in comparison to a conventional sprocket tooth or may have less relief than that of the first teeth.

The relieved tips of the leading flanks of the first sprocket teeth may be provided by an arcuate profile of one or more arc portions or by one or more straight line profiles or a combination thereof. The first teeth may define a different pressure angle to the second teeth. The arrangement is such that the centre of the apertures of a link does not rise above the pitch line of the chain on initial meshing contact with a first tooth of the sprocket. The relief may be provided additionally on the trailing flank of the first teeth.

The sprocket teeth profiles are such that when a link is completely meshed, whether with a first or second sprocket tooth, the centres of the link apertures occupy the pitch diameter of the sprocket.

The links may be interconnected by a pair of pins passing through each set of aligned apertures, the pins each having an arcuate rocker surface, the rocker surfaces abutting one another such that during articulation of the links the rocker surfaces roll over each other.

The meshing flank of the chain link may be defined on the inside or outside of the link tooth.

A pair of sprockets is preferably provided, one being a driving sprocket and the other being a driven sprocket, one or both of the sprockets has said first teeth with relieved leading flanks.

The chain link may have a pair of teeth separated by a crotch, each tooth having an inside flank adjacent to the crotch and an outside flank distal from the crotch, the first point of contact between the sprocket teeth and a meshing chain link teeth being made with an inside flank of a tooth of chain link.

The skilled reader will appreciate that the pitch of a chain is the distance between the centres of the link apertures that the pins occupy. The pitch diameter of sprocket and chain assembly is recognised in the field as the circle traced by the path of the chain pin centers as the chain travels around the sprocket. The pitch line of the chain is a line occupied by the apertures of the links of the chain in an unmeshed part of the chain and is substantially at a tangent to the pitch diameter of the assembly.

According to a second aspect of the present invention there is provided a sprocket for a chain drive assembly in which a chain of articulating inverted tooth links meshes with the sprocket, the sprocket comprising a main body from which extend a plurality of spaced teeth and roots defined between said sprocket teeth, each sprocket tooth having a leading flank that is designed to make initial contact with a meshing flank of a chain link tooth during meshing of the chain link with the sprocket, the sprocket having a plurality of first sprocket teeth with relieved leading flanks at least at the tips thereof and being disposed randomly amongst second sprocket teeth having leading flanks with profiles that differ from those of the first teeth, the relieved flanks being designed to ensure that, in use, the initial point of contact of the chain link during meshing is lower down the leading flank of a first tooth than for a second tooth.

According to a third aspect of the present invention there is provided An inverted tooth silent chain comprising a plurality of interleaved articulating inner link plates interconnected by transverse pins, the inner link plates each defining a pair of teeth separated by a crotch, each tooth having inner flanks adjacent said crotch and outer flanks, the inner and outer flanks of a given tooth being separated by a tooth tip, the inner flanks having a convex arcuate surface comprising at least two portions, a first portion adjacent to said tip having a first radius of curvature and a first arc length and a second portion between said first portion and said crotch having a second radius of curvature and a second arc length, the first radius of curvature being less than the second radius of curvature and the first arc length being greater than the second arc length.

There may be provided a pair of pins in each set of aligned apertures, the pins each having an arcuate rocker surface, the rocker surfaces abutting one another such that during articulation of the links the rocker surfaces roll over each other.

The convex arcuate surface of the inner flank may have further portions, each portion having a different radius of curvature and arc length, the radii of curvature increasing from portion to portion in the direction from tooth tip to crotch and the arc length curvature decreasing in that direction.

According to a fourth aspect of the present invention there is provided an inverted tooth silent chain comprising a plurality of interleaved links each having a pair of teeth for meshing with a sprocket and a pair of apertures, the links being interconnected by pairs transverse rocker pins that pass through aligned apertures in overlapping links, the rocker pins each having an arcuate rocker surface, the rocker surfaces of each pair being in abutment and designed to rock over each other during articulation of the links, and an arcuate seat surface opposite the rocker surface for abutment with a corresponding surface defined by an aperture of the link plate, the radius of curvature of the seat surface being less than that of the rocker surface, arcuate apices flanking the rocker surface and a rectilinear portion interconnecting each arcuate apex with the seat surface.

The arcuate apices may have the same radius of curvature, which may be less than that of the seat surface. The radius of curvature of the arcuate apex may be less than half that of the seat surface. The centre of curvature of the seat surface may be outside the pin whereas the centres of curvature of the seat surface and apices are inside the surface defined by the pin.

According to a fifth aspect of the present invention there is provided an inverted tooth silent chain comprising a plurality of interleaved links each having a pair of teeth for meshing with a sprocket and a pair of apertures, the links having an upper surface, a lower surface that defines the teeth and side flanks that interconnect the upper and lower surfaces, the links being interconnected by pairs transverse rocker pins that pass through aligned apertures in overlapping links, the rocker pins each having an arcuate rocker surface, the rocker surfaces of each pair being in abutment and designed to rock over each other during articulation of the links, the link apertures being generally ovate in shape and being defined by a continuous surface, each surface comprising a seat portion disposed nearest to the side flanks of the link and having a first radius of curvature and for abutment with a seat surface of the same radius of curvature defined by a surface of one of the pins, an opposite central arcuate portion having a second radius of curvature that is smaller than the first radius of curvature, a pair of side arcuate portions that flank the central arduate portion and which have a third radius of curvature substantially equal to the first radius of curvature, and opposed upper and lower arcuate portions having a fourth radius of curvature and being disposed between the seat surface and the central arcuate portion.

The upper and lower arcuate portions may be flanked on each side by rectilinear portions of the surface and the fourth radius of curvature may be greater than the first radius of curvature. The fourth radius of curvature may be less than the second radius of curvature.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a front view of a prior art inverted tooth silent chain shown engaged with part of a sprocket; Figures 2 to 4 are enlarged front views of the prior art silent chain of figure 1 showing the meshing of a given link with teeth of a sprocket (shown in fragment); Figure 5 is a partially sectioned front view of an inverted tooth chain of the present invention; Figure 6 is a partially sectioned plan view of the chain of figure 5; Figure 7 is a front view of an inner link plate of the chain of figure 5, illustrating the curvature of the inside tooth flank and the profile of the pin hole; Figure 8 is an end view of the pin illustrating its profile; Figures 9 and 10 are front views of two chain links in the chain illustrating movement of the rocker joint pins during pivoting of the chain links; Figure 11 shows a sprocket of the chain drive assembly of the present invention, with some of the sprocket teeth having a modified profile; Figure 12 shows in more detail the profile of a modified tooth of the sprocket of figure 11; Figures 13a and 13b are illustrations providing a comparison of the meshing of the chain of figures 5 to 10 with a conventional sprocket and the random modified sprocket of figures 11 and 12; Figure 14 shows two graphs comparing the loads on the links of a conventional inverted tooth chain used with a standard sprocket and with the random modified sprocket of figures 11 and 12; Figure 15 shows a chain drive assembly of the present invention comprising a standard inverted tooth chain meshing with two random modified sprockets according to figure 11 and provides a key to some of the notation used for the graphs of figure 14; and Figure 16 are graphs that illustrate the noise patterns for a conventional inverted tooth chain used on a conventional sprocket and a random modified sprocket in accordance with the present invention.

Referring now to figures 5 to 10 of the drawings, the exemplary inverted tooth silent drive chain has a plurality of interleaved inner chain link plates 30 flanked by outer guide link plates 31 on each side. The overlapping links are interconnected by pairs of rocker joint pins 32, 33 that pass transversely across the chain through aligned pin holes 34, 35 in the plates, one of the rocker joint pins 32 being longer than the other 33 so that it passes through an aperture 36 in the guide link plates 31 on each side.

The guide link plates 31 are very similar to those described in European Patent No. 1072816 and are designed to prevent lateral movement of the chain when meshed with a sprocket. Each of the plates 31 has two apertures 36 disposed symmetrically about a centre line of the link plate that are each designed to receive the longer of the rocker pins 32 of each pair in a fixed engagement such as an interference or press fit or by riveting the end of the pin. The upper edge of the guide plate has a concave arcuate recess 37 disposed in the region between the pin apertures 36 and which meets with convex curved edges 38 that in turn run into a lower edge 39.

Each inner link plate 30 (seen most clearly in figure 7) has an upper edge 41 that is substantially planar and a lower edge 42 that defines a pair of teeth 43 separated by a crotch 44, each tooth having inner and outer flanks 45, 46. There are again two spaced pin apertures 34, 35 disposed symmetrically about a centre line CL that bisects the crotch 44 and the upper edge 41. These apertures 34, 35 differ in profile to those of the guide link 31. In use the chain is formed into an endless loop that is wrapped around a pair of toothed sprockets, one being a drive sprocket and the other being driven. The lower edge 42 of each inner link 30 faces inwardly with respect to the sprocket such that the teeth 43 engage with the sprocket periphery.

As best seen in figure 7, the outer flanks 46 of the inner link plates 30 each define a substantially planar edge that merges with an arcuate tooth tip 47 of radius RI and arc length Li that in turn merges with the inside flank 45 of the tooth 43. The outer flanks 46 subtend an angle of 600 between them, as is conventional The inside flank 45 of the tooth 43 comprises a smooth continuous convex surface that is defined by a plurality of arcuate portions each having a predetermined radius of curvature R2, R3, R4, R5 and a predetermined arc length L2, L3, LA, L5. The portions are arranged such that their arc lengths L2, L3, L4, L5, decrease in the direction from the tip 47 to the crotch 44 of the link plate and their radii R2, R3, R4, R5 increase in that direction.

The radius Ri of the tip 47 is less than the next arc length R2 and the arc length is longer than L2.

The pin apertures 34, 35 (best seen in figure 7) of the inner link plates 30 are identical but are a mirror image of each other about the centre line (CL) of the link plate. Each aperture 34, 35, shown most clearly in figure 7, is generally ovate and is defined by a continuous surface that can be viewed as comprising several portions. A seat surface 48 of radius R6 is defined at a portion of the aperture that is furthest from the centre line CL and closest to the outer periphery of the link plate 30. This surface is designed to receive a corresponding exterior surface portion of the short rocker pin 33 and is flanked by two divergent rectilinear portions 49 on each side that each merge with upper and lower arcuate portions 50, 51 at the opposed top and bottom portions of the aperture 34, 35, each having a radius R7. On the side of the aperture opposite the seat surface 48 there is a central arcuate portion 52 of radius R8 that is flanked on each side by upper and lower arcuate stop surfaces 53, 54 of smaller radius R9, which is substantially identical to the radius of the seat surface 48. These stop surfaces 53, 54 are connected to the upper and lower arcuate portions 50, 51 by rectilinear portions 55. It will be noted that in accordance with its generally ovate shape, the end of the aperture 34, 35 that includes the seat surface 48 is slightly narrower that its opposite end.

Each of the pins 32, 33 has an identical cross-section with the outer surface (see figure 8) having a profile that approximates to a D-shape. The two major surfaces comprise a rolling surface 56 with a shallow convex curvature of radius RiO and a back surface 57 having a convex curve of much smaller radius Ri 1. The rolling surface 56 is flanked at each end by arcuate apices 58 of a smaller radius R12 and each of these apices merges with upper and lower short rectilinear surfaces 59, 60 that each converge towards the back surface 57. The radius Ri I of the back surface 57 is designed to be identical to that (R6) of the seat surface 48 and the two stop surfaces 53, 54 of the pin aperture 34, 35.

The rolling contact of the rolling surfaces 56 of the two rocker joint pins 32, 33 during pivoting of adjacent inner link plates 30 is illustrated in figures 9 and 10.

The long pin 32 in disposed inboard of the short pin 33 in the aligned apertures 34', of a left hand plate 30 (shown in solid line) and a right hand plate 30' (shown in dotted line) that is disposed behind and is offset therefrom along the length of the chain. The two pins 32, 33 pass through aligned apertures 34', 35 in overlapping portions of the plates 30, 30' and are arranged such that their rolling surfaces 56 are in contact with one another. When the two plates 30, 30' are under tension and in a straight line as shown in figure 9, the back surface 57 of the short pin 33 is seated against the complementary seat surface 48 of the aperture 35 of the left hand plate 30 such that it is prevented from rolling movement relative thereto. The back surface 57 of the long pin 32 is similarly received by the seat surface 48' of the right hand link plate 30'. With the pins 32, 33 thus seated the stresses imparted by the tension force that is transmitted along the chain under load are reduced as far as possible, thereby improving the load capacity of the chain. At this point the back surface 57 of the long pin 32 abuts the lower arcuate stop surface 54 of the aperture 35 in the left hand link but is clear of the upper stop surface 53 to accommodate rolling movement of the two pins. The same can be said of the back surface 57 of the short pin 33 in relation to the corresponding surfaces 53', 54' of the aperture 34' in the right hand link 30'. As the chain links wraps around the sprocket (not shown in figures 9 or 10) and the link plates 30, 30' pivot with respect to the other, the long pin 32 rotates with the right hand link 30' by virtue of it being carried by the seat surface 48' and its rolling surface 56 rolls over that 56 of the short pin 33 to the position shown in figure 10.

This movement of the long pin 32 carries it clear of the lower stop surface 54 and into contact with the upper stop surface 53 of the link 30. Similarly the lower stop surface 54' of the pin aperture 34' in the righthand link 30' moves clear of the back surface 57 and lower arcuate apex 58 of the short pin 33. The configuration of the pins 32, 33 and pin apertures 34', 35 provides for controlled and supported pivoting of the inner chain link plates 30, 30'. It also ensures that during engagement of the link plate teeth 43 with the sprocket teeth the position of the plate 30 in relation to the theoretical pitch diameter of the sprocket can be carefully controlled as will be described in more detail below.

A sprocket for use with the chain described above is shown schematically in figure 11. It is to be appreciated that such a sprocket can be used with a conventional inverted tooth chain with improved noise and wear reduction. The sprocket has a plurality of peripheral sprocket teeth some of which (labelled 60) are of conventional involute shape (where the pressure angle of the tooth is 30 ) and others (denoted by reference numeral 61) at random locations around the sprocket wheel have a modified profile that is shown more clearly in figure 12. Each tooth 60, 61 has a leading flank that first makes contact with the teeth of a link plate during meshing and a trailing flank, the direction of rotation being shown by the arrow.

The modified profile of the tooth 61 is shown in figure 12 in dotted line with the profile of a conventional sprocket tooth 60 shown in solid line. The modification is provided on the leading flank 62 of the tooth. However, it is to be appreciated that the modification can be made to both flanks of the sprocket tooth 61. In the exemplary embodiment shown the modification is provided by removing material from the tip of the leading flank 62 of a tooth to leave an arcuate profile and a modified pressure angle of 31.5 . This modified flank 62' ensures that the point of initial contact between the chain link plate tooth 43 and the leading flank 62' of the sprocket tooth 61 occurs at a position lower down the flank. The modification can be achieved by using a involute tooth profile of a different size to the rest of the (unmodified) sprocket teeth 60 e.g. by adopting a profile that is one down the range of standard involute tooth profiles such as one with a pressure angle of 31 5O as opposed to 3 0 However, the modification of the tooth can be achieved in any convenient manner provided that material is removed from the tip of flank 62 so that the first contact point of the meshing chain link plate is lower down the tooth flank that for a conventional sprocket. For example, the modified profile can be a straight line, an arcuate surface comprising at least one radius or an involute.

The meshing of the inverted tooth chain described above with a conventional sprocket and with a modified tooth of the sprocket of figure 11 is illustrated in figures 13a and 13b respectively. When the meshing link 30 of the chain engages with a tooth 14 of a conventional sprocket 11 although there is improved sliding contact with the sprocket tooth 14 profile in view of the shape of the inside flank 45 of the link teeth 43, the plate 30 lifts temporarily at the very commencement of meshing such that the centre C of the pin hole 35 rises above the pitch line PL (which is effectively a tangent to the pitch diameter PD) by a distance H (figure 13a) in the same manner as a conventional IT chain on a conventional sprocket as described in relation to figures 2 to 4. However, when the sprocket of figure 11 is used the initial contact point is lower down the leading flank 62 of a modified tooth such that the pin hole 35 centre C does not rise above the pitch line PL. This configuration provides for a reduction in the vibration of the link plates immediately prior to meshing. When the chain link plate is fully meshed with the sprocket 11, the pin hole centres 34, 35 are located on the pitch diameter PD. The meshing of the chain link plate with the randomly located modified teeth 61 as well as standard teeth 60 provides a number of different backlash impact noise frequencies during operation of the chain drive thereby attenuating the overall noise amplitude levels.

It is to be appreciated that the modified teeth may have more two different profiles to increase number of impact frequencies.

It will also be appreciated that the chain link plate teeth 43 do not make contact with the roots defined between the sprocket teeth 60, 61 and are therefore not supported by the sprocket roots during meshing.

The chain impact force on the random modified sprocket is much lower than in other sprockets such as those described in US 4, 168,634. The chain impact force is not along a vertical line.

The improvement in noise reduction provided by a random modified tooth sprocket is illustrated by the graphs of figures 14 and 16. The top graph A of figure 14 shows the chain load fluctuations along a length of endless loop chain using conventional sprockets and an IT chain driven at 1500 rpm. The plot shows the result of tests performed on a chain drive assembly comprising a 72-link chain of pitch 9.525mm and a pair of identical standard 36 tooth sprockets, both of conventional design. The x-axis gives a stationary "observation" location around the endless loop chain in the manner of a Eulerian co-ordinate and through which the chain links pass as the drive rotates. The positions are annotated in the key provided in figure 15. The driving sprocket is shown on the left, the driven sprocket on the right and both rotate in the clockwise direction such that the taut side of the chain is at the bottom and the slack side is at the top. There are six observation positions per link and the plots in figure 14 show the maximum load at each position during a full rotation of the chain.

It will be observed that the taut side of the chain is represented by locations 216 to 431 whereas the slack side of the chain is represented by positions 0 to 216 and this is illustrated by the greater load on these link positions as shown in the graph. The second graph B shows the results of the same test applied to a chain drive assembly comprising the same conventional IT chain and two sprockets with random modified teeth 61 in accordance with the present invention. The sprockets again had 36 teeth with 16 of modified profile and 20 of standard involute profile. In each case a load of 1 093Nm was applied to the chain (equivalent to 2000kgf) for the particular sprocket and chain combination. It can be seen from the graphs that the load is greatest at the links of the chain that mesh with the driving sprocket and those immediately behind in the taut section of the chain. It will be appreciated by a comparison of the two plots A and B that the maximum load values for the random sprocket chain drive oscillates with a smaller amplitude and at a lower absolute value compared to the conventional drive. The random modified tooth sprocket thus affords a lower load fluctuation on the chain links.

The graphs of figure 16 illustrate the amplitude and orders of the resonant noise frequencies of the two chain drive assemblies of figure 14. The plots show the spectra of the instantaneous torsional acyclism of the driven sprocket measured over two revolutions.

Acyclism is defined by: where 0 is the instantaneous driven sprocket angle, c is the angular speed (constant in this case), t is the time and Oo is the value of 0 at t=O.

Acyclism is a parameter commonly used in vibro-acoustic analysis of power trains and is particularly relevant to power trains where the torsional load fluctuates.

Acyclism is a measure of the torque fluctuations and therefore the fluctuation impact forces of the chain link plates on the sprocket. It is therefore a good empirical indication of the noise radiated by the drive assembly.

It can be seen from the first graph A that the acyclism (and therefore noise) peak occurs at a single frequency for the standard sprocket. The second graph B illustrates that with the modified sprocket the drive assembly has several acyclism peaks but each peak has a significantly lower amplitude. Thus the noise generated by the inventive drive assembly is much reduced in amplitude in comparison to a standard drive assembly through having been spread over a number of noise frequencies.

Claims

CLAIMS

A chain drive assembly comprising an inverted tooth chain and a toothed sprocket, the chain having a plurality of links arranged into rows across the chain and interleaved, the links being interconnected by transverse pins that pass through aligned apertures in the links, the links comprising articulating links having a peripheral inner surface facing the sprocket during meshing and an outer peripheral surface distal to the sprocket, the inner surface of the links defining a pair of teeth configured to mesh with the sprocket, the sprocket having a main body from which extend a plurality of spaced teeth, and roots defined between said sprocket teeth, each sprocket tooth having a leading flank that first makes contact with a meshing flank of a link tooth during meshing of an articulating link with the sprocket, the sprocket having a plurality of first sprocket teeth with relieved leading flanks at least at the tips thereof and being disposed randomly amongst second sprocket teeth having leading flanks of a different profile, the relieved flanks of the first teeth being designed to ensure that the initial point of contact of a chain link during meshing is lower down the leading flank of a first tooth than for a second tooth, the teeth of the chain links not contacting the sprocket roots during meshing with the sprocket.

2. A chain drive assembly according to claim 1, wherein the relieved tips of the leading flanks of the first sprocket teeth are provided by one or more arcuate profiles.

3. A chain drive assembly according to claim 1 or 2, wherein the first teeth define a different pressure angle to the second teeth.

4. A chain drive assembly according to claim 1, 2 or 3, wherein the articulating links each have first and second apertures, a first aperture being disposed above a first link tooth that first contacts a sprocket tooth during meshing, wherein the centre of the first aperture does not rise above the pitch line of the chain on initial meshing contact with a leading flank of a first tooth of the sprocket.

5. A chain drive assembly according to any preceding claim, wherein when a link is completely meshed with a first or second sprocket tooth the centres of the link apertures occupy the pitch diameter of the sprocket.

6. A chain drive assembly according to any preceding claim, wherein the second sprocket teeth are of conventional design having flanks with a conventional involute profile.

7. A chain drive assembly according to any preceding claim, wherein the trailing flank of at least some of the first teeth of the sprocket is also relieved.

8. A chain drive assembly according to any preceding claim comprising a pair of sprockets, one being a driving sprocket and the other being a driven sprocket, wherein one or both of the sprockets has said first teeth with relieved leading flanks.

9. A chain drive assembly according to any preceding claim, wherein the pair of teeth of each link are separated by a crotch, each tooth having an inside flank adjacent to the crotch and an outside flank distal from the crotch, the first point of contact between the sprocket teeth and a meshing chain link teeth being with an inside flank of a tooth of chain link.

10. A chain drive assembly according to any preceding claim, wherein the links each define a pair of teeth separated by a crotch, each tooth having inner flanks adjacent said crotch and outer flanks, the inner and outer flanks of a given tooth being separated by a tooth tip, the inner flanks having a convex arcuate surface comprising at least two portions, a first portion adjacent to said tip having a first radius of curvature and a first arc length and a second portion between said first portion and said crotch having a second radius of curvature and a second arc length, the first radius of curvature being less than the second radius of curvature and the first arc length being greater than the second arc length.

11. A chain drive assembly according to claim 10, wherein the convex arcuate surface of the inner flank has further portions, each portion having a different radius of curvature and arc length, the radii of curvature increasing from portion to portion in the direction from tooth tip to crotch and the arc length decreasing in that direction.

12. A chain drive assembly according to any preceding claim, wherein the links are interconnected by a pair of pins passing through each set of aligned apertures, the pins each having an arcuate rocker surface, the rocker surfaces abutting one another such that during articulation of the links the rocker surfaces roll over each other.

13. A chain drive assembly according to claim 12, each link having a pair of apertures, the rocker pins having an arcuate seat surface opposite the rocker surface for abutment with a corresponding surface defined by the aperture of the link plate, the radius of curvature of the seat surface being less than that of the rocker surface, arcuate apices flanking the rocker surface and a rectilinear portion interconnecting each arcuate apex with the seat surface.

14. A chain drive assembly according to claim 13, wherein the arcuate apices have the same radius of curvature.

15. A chain drive assembly according to claim 14, wherein the radius of curvature of the arcuate apices is less than that of the seat surface.

16. A chain drive assembly according to claim 14 or 15, wherein the radius of curvature of the arcuate apex is less than half that of the seat surface.

17. A chain drive assembly according to any one of claims 13 to 16, wherein the centre of curvature of the seat surface is disposed outside of the pin whereas the centres of curvature of the seat surface and apices are disposed inside the area occupied by the pin.

18. A chain drive assembly according to any one of claims 12 to 17, wherein the link apertures are generally ovate in shape and are defined by a continuous surface, said surface comprising a seat portion disposed nearest to the side flanks of the link, the seat surface having a first radius of curvature and configured for abutment with a seat surface of the same radius of curvature defined by a surface of one of the pins, an opposite central arcuate portion having a second radius of curvature that is smaller than the first radius of curvature, a pair of side arcuate portions that flank the central arcuate portion and which have a third radius of curvature substantially equal to the first radius of curvature, and opposed upper and lower arcuate portions having a fourth radius of curvature and being disposed between the seat surface and the central arcuate portion.

19. A chain drive assembly according to claim 18, wherein the upper and lower arcuate portions are flanked on each side by rectilinear portions of the surface.

20. A chain drive assembly according to claim 18 or 19, wherein the fourth radius of curvature is greater than the first radius of curvature.

21. A chain drive assembly according to claim 18, 19 or 20, wherein the fourth radius of curvature is less than the second radius of curvature.

22. A sprocket for a chain drive assembly in which a chain of articulating inverted tooth links meshes with the sprocket, the sprocket comprising a main body from which extend a plurality of spaced teeth and roots defined between said sprocket teeth, each sprocket tooth having a leading flank that is designed to make initial contact with a meshing flank of a chain link tooth during meshing of the chain link with the sprocket, the sprocket having a plurality of first sprocket teeth with relieved leading flanks at least at the tips thereof and being disposed randomly amongst second sprocket teeth having leading flanks with profiles that differ from those of the first teeth, the relieved flanks being designed to ensure that, in use, the initial point of contact of the chain link during meshing is lower down the leading flank of a first tooth than for a second tooth.

23. A sprocket according to claim 22, wherein the relieved tips of the leading flanks of the first sprocket teeth are provided by one or more arcuate profiles.

24. A sprocket according to claim 22 or 23, wherein the first teeth define a different pressure angle to the second teeth.

25. A sprocket according to claim 22, 23 or 24, wherein the second sprocket teeth are of conventional design having flanks with a conventional involute profile.

26. A sprocket according to any one of claims 22 to 25, wherein the relief is provided additionally on a trailing flank of at least some of the first teeth of the sprocket.

27. An inverted tooth silent chain comprising a plurality of interleaved articulating inner link plates interconnected by transverse pins, the inner link plates each defining a pair of teeth separated by a crotch, each tooth having inner flanks adjacent said crotch and outer flanks, the inner and outer flanks of a given tooth being separated by a tooth tip, the inner flanks having a convex arcuate surface comprising at least two portions, a first portion adjacent to said tip having a first radius of curvature and a first arc length and a second portion between said first portion and said crotch having a second radius of curvature and a second arc length, the first radius of curvature being less than the second radius of curvature and the first arc length being greater than the second arc length.

28. An inverted tooth silent chain according to claim 27, wherein the convex arcuate surface of the inner flank has further portions, each portion having a different radius of curvature and arc length, the radii of curvature increasing from portion to portion in the direction from tooth tip to crotch and the arc length decreasing in that direction.

29. An inverted tooth silent chain according to claim 27 or 28, further comprising a pair of rocker pins in each set of aligned apertures, the pins each having an arcuate rocker surface, the rocker surfaces abutting one another such that during articulation of the links the rocker surfaces roll over each other.

30. An inverted tooth silent chain according to claim 29, each rocker pin having an arcuate seat surface opposite the rocker surface for abutment with a corresponding surface defined by an aperture of the link plate, the radius of curvature of the seat surface being less than that of the rocker surface, arcuate apices flanking the rocker surface and a rectilinear portion interconnecting each arcuate apex with the seat surface.

31. An inverted tooth silent chain according to claim 30, wherein the arcuate apices have the same radius of curvature.

32. An inverted tooth silent chain according to claim 31, wherein the radius of curvature of the arcuate apices is less than that of the seat surface.

33. An inverted tooth silent chain according to claim 31 or 32, wherein the radius of curvature of the arcuate apex is less than half that of the seat surface.

34. An inverted tooth silent chain according to any one of claims 30 to 33, wherein the centre of curvature of the seat surface is disposed outside of the pin whereas the centres of curvature of the seat surface and apices are disposed inside the area occupied by the pin.

35. An inverted tooth silent chain according to any one of claims 28 to 34, wherein the link apertures are generally ovate in shape and are defined by a continuous surface, each surface comprising a seat portion disposed nearest to the side flanks of the link and having a first radius of curvature and for abutment with a seat surface of the same radius of curvature defined by a surface of one of the pins, an opposite central arcuate portion having a second radius of curvature that is smaller than the first radius of curvature, a pair of side arcuate portions that flank the central arcuate portion and which have a third radius of curvature substantially equal to the first radius of curvature, and opposed upper and lower arcuate portions having a fourth radius of curvature and being disposed between the seat surface and the central arcuate portion.

36. An inverted tooth silent chain according to claim 35, wherein the upper and lower arcuate portions are flanked on each side by rectilinear portions of the surface.

37. An inverted tooth silent chain according to claim 35 or 36, wherein the fourth radius of curvature is greater than the first radius of curvature.

38. An inverted tooth silent chain according to claim 35, 36 or 37, wherein the fourth radius of curvature is less than the second radius of curvature 39. An inverted tooth silent chain comprising a plurality of interleaved links each having a pair of teeth for meshing with a sprocket and a pair of apertures, the links being interconnected by pairs transverse rocker pins that pass through aligned apertures in overlapping links, the rocker pins each having an arcuate rocker surface, the rocker surfaces of each pair being in abutment and designed to rock over each other during articulation of the links, an arcuate seat surface opposite the rocker surface for abutment with a corresponding surface defined by an aperture of the link plate, the radius of curvature of the seat surface being less than that of the rocker surface, arcuate apices flanking the rocker surface and a rectilinear portion interconnecting each arcuate apex with the seat surface.

40. An inverted tooth silent chain according to claim 39, wherein the arcuate apices have the same radius of curvature.

41. An inverted tooth silent chain according to claim 40, wherein the radius of curvature of the arcuate apices is less than that of the seat surface.

42. An inverted tooth silent chain according to claim 40 or 41, wherein the radius of curvature of the arcuate apex is less than half that of the seat surface.

43. An inverted tooth silent chain according to any one of claims 39 to 42, wherein the centre of curvature of the seat surface is outside the pin whereas the centres of curvature of the seat surface and apices are inside the surface define by the pin.

44. An inverted tooth silent chain comprising a plurality of interleaved articulating links each having a pair of teeth for meshing with a sprocket and a pair of apertures, the links having an upper surface, a lower surface that defines the teeth and side flanks that interconnect the upper and lower surfaces, the links being interconnected by pairs transverse rocker pins that pass through aligned apertures in overlapping links, the rocker pins each having an arcuate rocker surface, the rocker surfaces of each pair being in abutment and designed to rock over each other during articulation of the links, the link apertures being generally ovate in shape and being defined by a continuous surface, each surface comprising a seat portion disposed nearest to the side flanks of the link and having a first radius of curvature and for abutment with a seat surface of the same radius of curvature defined by a surface of one of the pins, an opposite central arcuate portion having a second radius of curvature that is smaller than the first radius of curvature, a pair of side arcuate stop portions that flank the central arcuate portion and which have a third radius of curvature substantially equal to the first radius of curvature, and opposed upper and lower arcuate portions having a fourth radius of curvature and being disposed between the seat surface and the central arcuate portion.

45. An inverted tooth silent chain according to claim 44, wherein the upper and lower arcuate portions are flanked on each side by rectilinear portions of the surface.

46. An inverted tooth silent chain according to claim 44 or 45, wherein the fourth radius of curvature is greater than the first radius of curvature.

47. An inverted tooth silent chain according to claim 44, 45 or 46, wherein the fourth radius of curvature is less than the second radius of curvature.

48. An inverted tooth silent chain according to any one of claims 44 to 47, wherein each rocker pin has an arcuate seat surface opposite the rocker surface for abutment with the seat portion of the link aperture surface, the radius of curvature of the seat surface of the pin being less than that of the rocker surface, arcuate apices flanking the rocker surface and a rectilinear portion interconnecting each arcuate apex with the seat surface.

49. An inverted tooth silent chain according to claim 48, wherein the side arcuate stop portions of the surface defining the aperture comprise first and second stop portions, whereby as the chain links pivot with respect to the other, a first of the pins rotates with a link by virtue of it being carried by a seat surface thereof and the rocker surface of the first pin rolls over the rocker surface of the other pin, this movement carries the pin clear of a first stop surface and into contact with a second stop surface.

50. An inverted tooth silent chain according to claim 45 wherein the rectilinear portions are divergent from the central arcuate portion.