SPROCKET ASSEMBLY

Abstract: A quiet drive sprocket assembly (14) for driving an endless chain assembly (20) for propelling a vehicle (10) includes a housing (22), which is mountable to the power drive system (12) of the vehicle (10), and a plurality of replaceable tooth structures (42) which are secured to the housing (22). The housing (22) includes a hub portion (26) having a cushion band (70) and spaced apart parallel flanges (28,30). Each tooth structure (42) is in contact with the band (70) and is secured to the flanges (28,30) by a plurality of retaining pins (44). Each tooth structure (42) is resiliently isolated from the hub (26) by the cushion band (70) and from adjoining teeth structures (42) by non-metallic pads (48,50).

Description: This invention relates generally to a drive sprocket assembly for a track-laying vehicle and more particularly to a resilient drive sprocket assembly having a plurality of individually replaceable tooth structures with each tooth structure being resiliently isolated from adjacent tooth structures and preferably also from a drive sprocket support hub. Earthmoving and construction vehicles, which have endless self-laying track chain assemblies for support and propulsion, generally utilize a sprocket wheel to engage and drive the track chain. Several different types of sprocket wheels have been used in the past, including a single wheel member having a plurality of integral teeth, a circular support member for supporting wheel segments, each segment having several teeth, and hub members accommodating a plurality of separate individual teeth. One type of drive sprocket having a plurality of separate, individual teeth bolted to a hub portion is disclosed in US-A-2,365,544. In that patent, the teeth are fulcrumed to the hub portion somewhere near the middle of the teeth so that the teeth can rotate in either direction about the fulcrum. Resilient means are provided to return the teeth to their original no load position. This arrangement is intended to make the teeth self-adjusting to accommodate variations in the track chain. Another type of sprocket having separate, individual teeth secured to a hub is shown in US-A-3,996,814. That patent discloses a plurality of link members secured together around the circumference of a hub. The links are keyed longitudinally and laterally on the hub. Each link carries one or more separate teeth projecting radially outwardly. Still another type of sprocket assembly with replaceable teeth is shown in US-A-4,522,611. That patent discloses a generally cylindrical sprocket hub equipped with a plurality of L-shaped pockets in the periphery of the hub. A replaceable tooth, having a partial T-shaped inner end, is intended to be received within each of the L-shaped pockets and locked in place by wedge lock means which operate against the T-shape of the tooth. Each of the above-noted sprocket assemblies provides individual replaceable drive teeth. However, such sprocket assemblies appear to be quite complicated and costly and utilize intricately formed pieces. All of them would seem to be ineffective or quite limited in their ability to reduce noise levels during driving operation against an endless track chain assembly. EP-A-0006250 discloses a tooth structure for a drive sprocket, comprising a resilient pad. FR-A-948981 discloses a drive sprocket assembly comprising a housing having a mounting portion, a circular hub portion, and first and second circular flanges, the first flange being spaced from and substantially parallel to the second flange, the first and second flanges defining a space therebetween, the first flange having first and second arrays of equally spaced through holes, the second flange having third and fourth arrays of equally spaced through holes, each one of the first array of holes being in substantial axial alignment with a respective one of the third array of holes, and each one of the second array of holes being in substantial axial alignment with a respective one of the fourth array of holes; a plurality of individually replaceable drive members, each having first and second retaining portions and first and second driving portions, the drive members being teeth, positioned within the space between the first and second flanges and equally spaced around the hub portion; and a plurality of retaining pins, each being arranged to penetrate a respective one of the holes in the first flange and a corresponding aligned hole in the second flange to thereby secure the drive members to the flanges and hub portion. According to the present invention, such an assembly is characterised by a plurality of resilient pads, each being arranged to fit against a respective one of the first and second retaining portions; and a plurality of retaining members, each being arranged to fit against a respective one of the resilient pads; whereby the drive members are secured to the flanges via the retaining members. In self track-laying vehicles utilizing endless track assemblies, the driving power from the vehicle is transferred to the endless track assembly by toothed sprocket members. As the sprocket members contact the endless track, noise is generated, and this noise can reach objectionable levels. Additionally, the noise is often transferred into the track assemblies and other machine components, where it is amplified. The subject invention provides a reduced noise level sprocket assembly for driving the endless track by utilizing a plurality of individual drive teeth of low mass which are resiliently isolated from other components of the drive sprocket assembly. Additionally, the undercarriage components and power train of the vehicle will experience lower stress since the resiliency of the subject sprocket assembly will limit shock loads. In the accompanying drawings:- Fig. 1 is a diagrammatic side elevational view of a vehicle incorporating a sprocket assembly of the present invention; Fig. 2 is an enlarged diagrammatic side elevational view, partly in section, of the sprocket assembly; Fig. 3 is a diagrammatic sectional view taken generally along the line III-III in Fig. 2; Fig. 4 is a diagrammatic sectional view taken generally along the line IV-IV in Fig. 3; and, Fig. 5 is a diagrammatic exploded view of the tooth structure of the sprocket assembly. Referring to the drawings, a vehicle 10, such as a track-laying tractor 10, has a powered drive system 12, a resilient drive sprocket assembly 14, first and second idler wheels 16,18, and an endless track chain assembly 20 which encircles the sprocket assembly 14 and the idler wheels 16,18. The sprocket assembly 14 is adapted to transfer power from the vehicle 10 to the track assembly 20. It is to be understood that many of the vehicle components, including the sprocket assembly 14, the idler wheels 16,18, and the track chain assembly 20 are duplicated on the side of the vehicle 10 which is not illustrated. Since these duplicate components operate in the same manner as those shown, the description and operation of the components illustrated applies to both sides of the vehicle. The sprocket assembly 14 includes a housing 22 having a mounting portion 24, a circular hub portion 26, and first and second radially extending spaced apart circular flanges 28,30. The first flange 28 is spaced from and is substantially parallel to the second flange 30. The two flanges 28,30 define a space 32 therebetween. The first flange 28 has first and second pluralities, or arrays, of equally spaced through holes 34,36, and the second flange 30 has third and fourth pluralities, or arrays, of equally spaced through holes 38,40. The first and third arrays of holes 34,38 are arranged in a circle having a first radius "r", and the second and fourth arrays of holes 36,40 are arranged in a circle having a second radius "R", with the second radius "R" being greater than the first radius "r". Each hole 34 in the first array is in substantially axial alignment with one of the holes 38 in the third array, and each hole 36 in the second array is in substantially axial alignment with one of the holes 40 in the fourth array. A plurality of individually replaceable resilient drive tooth structures 42 are positioned within the space 32 between the first and second flanges 28,30. The tooth structures 42 are equally spaced around the hub portion 26 and are retained within the space 32 by a plurality of retaining pins 44. Each one of the pins 44 is adapted to penetrate one of the holes 34,36 in the first flange 28 and a corresponding aligned hole 38,40 in the second flange 30. Each tooth structure 42 includes a metallic drive member, or tooth 46, first and second non-metallic resilient pads 48,50, and first and second metallic retaining members 52,54. Each of the drive members 46 has first and second driving portions 56,58, first and second concave side retaining portions 60,62, and a base portion 64. Each of the retaining members 52,54 has first and second accurately shaped concave pockets 66,68. The pockets 66,68 are substantially similar in size and shape and are adapted to mate with the circumferential surfaces of the retaining pins 44. One of the first and second resilient pads 48,50 is adapted to fit against the respective first and second retaining portions 60,62 of each drive tooth 46, and one of the first and second retaining members 52,54 is adapted to fit against the respective first and second resilient pads 48, 50. Preferably, the resilient pads 48,50 are bonded to the tooth retaining portions 60,62 and the retaining members 52,54 are bonded to the resilient pads 48,50. It is also preferable that the resilient pads 48,50 be formed of an elastomeric material. With particular reference to Figures 3 and 4, a resilient cushion band 70 of elastomeric material encircles the hub portion 26 and is positioned between the hub portion 26 and the drive members 46. Preferably, the drive members 46 and the retaining members 52,54 are formed of a powdered metal material. In order for the pins 44 to hold the tooth structures 42 securely in place, the diameter of each of the holes 34,36,38,40 in the flanges 28,30 is slightly smaller than the diameter of the pins 44. With particular reference to Figures 2 and 3, the centres of one hole of the first and third arrays 34,38 lie in a common plane with the centres of one hole of the second and fourth arrays 36,40. The centres of the other holes of the first, second, third, and fourth arrays 34,36,38,40 lie on similar but different planes. The subject sprocket assembly 14 is particularly useful with earthmoving equipment and more specifically, self track-laying vehicles, such as the vehicle 10. Power from the engine of the vehicle 10 is transmitted to the drive system 12, which then rotates the sprocket assembly 14. As the sprocket assembly 14 rotates, the teeth 46 contact portions of the track chain assembly 20, rotate it, and thereby propel the vehicle 10. As the metal teeth 46 contact the metal track chain assembly 20, considerable noise is generated. Because the teeth 46 are isolated from the metal hub portion 26 of the housing 22, the noise is not transferred into the housing 22 and the drive system 12 where it could be amplified. Also, because of the resilient mounting and isolation of the tooth structures 42, each tooth 46 is a relatively small member which produces very little noise as it contacts the track chain assembly 20. Any amplification of such noise by the track chain assembly 20 is therefore of small magnitude. Isolation and resilient mounting of the teeth 46 are provided by the various components of the tooth structures 42. To begin the build-up of the sprocket assembly 14, the resilient cushion band 70 is initially secured to the hub portion 26 of the housing 22. The plurality of tooth structures 42 are then inserted between the first and second flanges 28,30 until the base portion 64 of each tooth 46 contacts the cushion band 70. Each of the tooth structures 42 has been previously pre-assembled. This includes bonding of the first and second non-metallic pads 48,50 to the first and second side retaining portions 60,62 respectively, and the subsequent bonding of the first and second retaining members 52,54 to the first and second non-metallic pads 48,50 respectively. Once the pre-assembled tooth structures 42 are in place between the first and second flanges 28,30, the first circle of retaining pins 44 are driven through the first and third arrays of aligned holes 34 and 38 in the first and second flanges 28,30. This first group of retaining pins 44, arranged on the first circle having the radius "r", produces little or no compression of the first and second non-metallic pads 48,50 and the resilient band 70. The second circle of retaining pins 44 are then driven through the second and fourth arrays of aligned holes 36 and 40 in the first and second flanges 28,30. As the retaining pins 44 are driven into place, they contact the concave pockets 66,68 of the retaining members 52,54. As the pins 44, arranged on the second circle having the larger radius "R", are driven into place, they produce a relatively large compression of the non-metallic pads 48,50 and the resilient band 70. In order to produce the maximum preload on the non-metallic pads 48,50, some permanent deformation of these pads 48,50 may occur. When all of the pins 44 have been driven into place, the sprocket assembly is complete and each tooth structure 42 is resiliently isolated from the hub 26 and from adjoining tooth structures 42. Replacement of individually worn or damaged teeth 46 is easily provided by the subject sprocket assembly 14. Once the worn tooth 46 has been identified, the two pins 44 on each side of the tooth 46 are removed and the tooth 46 is then easily extracted from between the flanges 28,30. A new tooth structure 46 is then inserted and the four retaining pins 44 are driven back into place to secure the new tooth structure 46 and once again make a complete sprocket assembly 14.

Claims: 1. A resilient drive sprocket assembly (14) comprising a housing (22) having a mounting portion (24), a circular hub portion (26), and first and second circular flanges (28,30), the first flange (28) being spaced from and substantially parallel to the second flange (30), the first and second flanges (28,30) defining a space (32) therebetween, the first flange (28) having first and second arrays of equally spaced through holes (34,36), the second flange (30) having third and fourth arrays of equally spaced through holes (38,40), each one of the first array of holes (34) being in substantial axial alignment with a respective one of the third array of holes (38), and each one of the second array of holes (36) being in substantial axial alignment with a respective one of the fourth array of holes (40); a plurality of individually replaceable drive members (46), each having first and second retaining portions (60,62) and first and second driving portions (56,58), the drive members (46) being teeth, positioned within the space (32) between the first and second flanges (28,30) and equally spaced around the hub portion (26); and a plurality of retaining pins (44), each being arranged to penetrate a respective one of the holes (34,36) in the first flange (28) and a corresponding aligned hole (38,40) in the second flange (30) to thereby secure the drive members (46) to the flanges (28,30) and hub portion (26); characterised by a plurality of resilient pads (48,50), each being arranged to fit against a respective one of the first and second retaining portions (60,62); and a plurality of retaining members (52,54), each being arranged to fit against a respective one of the resilient pads (48,50); whereby the drive members (46) are secured to the flanges (28, 30) via the retaining members (52, 54). 2. An assembly according to claim 1, including a resilient cushion band (70) encircling the hub portion (26) and positioned between the hub portion (26) and the drive members (46). 3. An assembly according to claim 2, wherein the cushion band (70) is formed of an elastomeric material. 4. An assembly (14), according to any one of the preceding claims, wherein the resilient pads (48,50) are formed of an elastomeric material. 5. An assembly according to any one of the preceding claims, wherein the drive members (46) are formed of a powdered metal material. 6. An assembly according to any one of the preceding claims, wherein the retaining members (52,54) are formed of a powdered metal material. 7. An assembly according to any one of the preceding claims, wherein the diameters of the holes (34,36,38,40) in the first and second flanges (28,30) are smaller than the diameters of the corresponding pins (44). 8. An assembly according to any one of the preceding claims, wherein each of the retaining members (52,54) has first and second arcuately shaped pockets (66,68), each arranged to mate with the circumferential surface of a respective one of the retaining pins (44). 9. An assembly (14) according to any one of the preceding claims, wherein the axis of each pair of aligned holes of the first and third arrays of holes (34,38) lies in a common axial plane of the hub portion (26) with the axis of one pair of aligned holes of the second and fourth arrays (36,40) of holes, the axes of the other holes lying on different axial planes. 10. An assembly according to any one of the preceding claims, wherein the resilient pads (48,50) are bonded to the drive members (46). 11. An assembly according to any one of the preceding claims, wherein the retaining members (52,54) are bonded to the resilient pads (48,50). 12. An assembly according to any one of the preceding claims, wherein the first and third arrays of holes (34,38) are arranged on a first circle on the first and second flanges (28,30). 13. An assembly according to claim 12, wherein the second and fourth arrays of holes (36,40) are arranged on a second circle on the first and second flanges (28,30) having a radius (R) greater than a radius "r" of the first circle.

Inventors: OERTLEY, THOMAS EARL
Applicants: CATERPILLAR INC.
Application year: 1990
Main classification: B62D55
IPC codes: F16H55, B62D55