One-way spray clutch

Abstract: An improved cage and spring structure (10) for a sprag one-way clutch and insertable between a pair of opposed substantially concentric races (12,14) includes a series of tiltable sprags (16) supported on cam members (50) spaced around the periphery of a cage ring (22) and a plurality of independent energizing elements (26) mounted on the cam members (50) for engaging and individually biasing the sprags (16) by spring force into wedging engagement with the races (12,14).

Description: This invention relates to one-way sprag clutches having tiltable sprags disposed between concentric races for controlling torque delivery in a torque flow path between a driving member and a driven member. Conventional sprag type clutches, referred to as double cage clutches, contain two concentric metal or plastic rings, each called cages, which function to provide positioning and simultaneous actuation of each sprag. This is accomplished by designing circumferential, radial, and axial features in both cages. While the double cage clutch is an excellent performing one way clutch system, it is inherently a complex assembly. The sprags of the double cage clutch require extensive design considerations and manufacturing control to meet the application performance requirements. Double cage clutches, such as those disclosed in JP-U-63-48035; JP-A-63-180731; and JP-A-1-120440, use two cage members to space inner and outer sections of each sprag between the clutch races. A resilient ring member is located between the two cage members. The resilient ring member also includes tabs and functions to urge the sprags into a specific angle of engagement with the races. The tabs of the resilient sprag retainer or member have an inherent interdependency that can adversely affect the function of the clutch. Nonuniformity of the resilient member about its periphery can result in an uneven loading against the independent sprags and inefficiency in the clutch operation. Furthermore, such clutch assemblies often require hand assembly, which is inefficient in high volume manufacturing operations. Other one-way sprag-type clutches, such as the clutch disclosed in US-A-2 824 635, include a series of tiltable sprags disposed between a pair of concentric clutch races. A cage or retainer for spacing the sprags usually is formed as one continuous resilient ring. Such a sprag retainer functions to space the sprags and to urge the sprags into engagement with the races. A series of radial openings or windows is blanked into the ring and a tang or tab usually is formed on one side of each window. These tangs or tabs provide a circumferential spring force that acts on the sprags. This design fails to provide adequate sprag position control. Other clutches, such as those disclosed in JP-U-63-112631, include rotationally loaded sprags. Such structures are complicated, costly, and not easily machine assembled. A further example of the prior art is featured in DE-A-2027763 which discloses the features of the preamble of claim 1, and which generally discloses a one-way sprag clutch comprising concentric inner and outer races and a sprag cage structure located between the races; the sprag cage structure comprising an annular cage having axially extending circumferentially spaced cam members which define therebetween circumferentially spaced windows, tiltable sprags located one in each window, each sprag having a radially inner clutch surface and a radially outer clutch surface engageable respectively with the inner and outer races, the sprags each having a circumferential width at a location intermediate the inner and outer clutch surfaces thereof less than its circumferential width at locations adjacent the clutch surfaces, cam surfaces on the cam members on opposed sides of each of the sprags, the sprags being engageable with the cam surfaces at the sprag locations adjacent the inner and outer clutch surfaces when the sprags are tilted to a limiting angular position, and an energizing spring for each of the sprags secured to a respective cam member and adapted to engage an adjacent sprag at its intermediate location thereby to impart a continuous moment on the sprag to maintain the clutch surfaces thereof in contact with the races. More particularly, in that one-way sprag clutch, the cam surfaces on the cam members on opposite sides of each of the sprags define therebetween the circumferential windows, and the oppositely facing cam surfaces have portions converging in a radially outwardly direction from the radially inward region of the respective window and then extending generally parallel with one another in the same radially outward direction to the radially outward region of that window, by which the window is of asymmetrical funnel shape in radial planes normal to the axis of the clutch with its radially inward region wider in a circumferential direction than its radially outward region. By that design, the cam members at their radially outer ends have a wide circumferential width and the window has a relatively narrow circumferential width at its radially outward region. The described configuration of the windows of the one-way sprag clutch of DE-A-2027763 has the disadvantage that the cam surfaces only operate on the sprags when the sprags are at their extreme angular positions, giving rise to the problem that the midsections of the various sprags can splay about in any direction and the individual sprags are not uniformly operated. In accordance with the present invention as claimed, the aforesaid generally disclosed one-way sprag clutch is characterized in that each window has a generally hour-glass shape in the radial direction of the cage with the radially outward region of the window and the radially inward region of the window both being wider in a circumferential direction than the radially intermediate region of the window, adjacent cam members being engageable, at the radially intermediate region of the window defined therebetween, with the intermediate relatively narrow location of the sprag located in that window, adjacent cam members each including a pair of said cam surfaces, one such cam surface of one cam member lying circumferentially opposite one such cam surface of the adjacent cam member, those circumferentially opposed cam surfaces continuously converging in a radially outward direction from the radially inward region of the window to the radially intermediate region thereof, the other such cam surface of said one cam member lying circumferentially opposite the other such cam surface of said adjacent cam member, those circumferentially opposed cam surfaces continuously diverging in a radially outward region of the window, the cam surfaces of each cam member intersecting with one another at said intermediate region of the window. The one-way sprag clutch of the invention has the advantage that circumferential translation of the sprag is prevented as it tilts about its intermediate location, the cam surfaces fully support the sprags during all phases of clutch operation so that the sprags are uniformly operated, and the hour-glass window configuration permits maximum sprag rotation giving a wider range of operation. In a preferred embodiment each spring element has a mounting portion and a tang portion. The mounting portion is received in an opening of the cage. The springs bias the individual sprags by spring force into wedging engagement with the clutch races. The mounting portion attaches the spring element to the cage and the tang portion extends generally circumferentially. Each cam member can be made of resilient or metallic materials. In order that the invention may be well understood, there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which:- Figure 1 is a perspective view of an improved cage and sprag structure constructed in accordance with the present invention; Figures 2-5 are sectional perspective views of the cage and a sprag structure illustrating various independent energizing elements mounted on the cage for independently urging adjacent sprags; Figure 6 is a perspective view of an alternative embodiment of the improved cage and sprag structure illustrating elastomeric energizing elements; Figure 7 is a partial sectional view of a prior art single cage and sprag structure; Figure 8 is a partial sectional view of a prior art double cage and sprag structure illustrated in a freewheel position of the cage and sprags; Figure 9 is a partial sectional view of the prior art double cage and sprag structure illustrated in an engaged position of the sprags; Figure 10 is a partial sectional view of a combined cage of the present invention including cam members and illustrating sprags in a freewheel position; Figure 11 is a partial sectional view of the combined cage illustrating the sprags in an engaged position; Figure 12 is a partial sectional view of the combined cage illustrating the arrangement of adjacent cam surfaces; Figure 13 is a perspective view of the combined cage and sprag structure of the present invention; Figure 14 is an enlarged partial sectional perspective view of a cam member and sprag in the combined cage embodiment illustrating an energizing element of a C-clip type spring configuration mounted on the cam member for biasing the sprag; Figure 15 is an enlarged partial sectional perspective view like that of Figure 14 illustrating an energizing element of an elastomeric construction mounted on the cam member for biasing the sprag; Figure 16 is an enlarged partial sectional perspective view like that of Figure 14 illustrating an energizing element of a Z-spring construction mounted on the cam member for biasing the sprag; Figure 17 is an exploded perspective view of a two piece cage construction that facilitates cage, sprag and energizing spring element assembly; and Figure 18 is an enlarged sectional view of the two piece cage of Figure 17 illustrating snap or weld together assembly of the two cage pieces. Referring to Figure 1 of the drawings, an improved cage and sprag structure for a one-way clutch constructed in accordance with the present invention is generally indicated by reference numeral 10. It is used to rapidly transmit torque between rotating members. As hereinafter more fully described, the cage and sprag structure provides improved performance. Such an improved cage and sprag structure 10 also lends itself to higher levels of automated assembly. As shown in Figures 1 and 6, the improved cage and sprag structure 10 is placed between an outer race 12 and an inner race 14, shown in phantom. The races are substantially cylindrical and concentrically mounted. Each race is adapted to be respectively connected with an associated rotatable member (not shown). A plurality of torque engagement members or sprags 16 is disposed between the races 12,14, each sprag being provided with a pair of eccentric wedging surfaces 18,20 for wedging against the inner and outer races 12,14, respectively, as it is tilted into engagement with the races. A cage 22, illustrated in Figures 1-6, is adapted to be installed between the races 12,14. Cage 22 retains and spaces the sprags 16 peripherally between the races. Cage 22 has a ring shape and has a series of openings or windows 24 spaced around its periphery for receiving the tiltable sprags 16. Cage 22 also includes independent energizing elements 26, best seen in Figures 2-5, that are retained in the openings 24. These energizing elements 26 are formed from metal or composite materials as individual components. Each energizing element 26 includes a mounting portion 28 and a tang portion 30. The mounting portion 28 attaches the element 26 to the cage and the tang portion 30 circumferentially extends within an opening 24. Each element 26 thereby acts independently upon an individual sprag 16 received in an opening 24. Precise forming of each individual energizing element 26 contributes to the overall performance in the assembly of the one-way clutch. Such elements 26 provide and maintain a more uniform individual loading against the sprags 16 than the loading that would result from energizing springs on a resilient spring or band-type spring of conventional design. Although the objects of the improved cage and sprag structure can be accomplished with metallic assemblies using such materials as steel, aluminum or bronze, it is preferable for the cage 22 to be comprised of high temperature, engineered plastics such as polyetherimides or nylons or PES polyethersulfones. Such engineered plastics can be reinforced with reinforcing materials such as carbon fibers or glass or clay or mica to increase the overall mechanical characteristics of the plastics. Figures 2-6 illustrate various embodiments of the improved cage and sprag structure 10. Figure 2 illustrates the use of a metallic energizing element 26 having a mounting portion 28 and tang portion 30 circumferentially extending within the opening 24 of the cage 22. As illustrated, the cage 22 has a rectangular cross-section, which lends greater support to the sprags 16. Figures 3, 4 and 6 illustrate energizing elements 26 comprised of high temperature elastomers such as nitryl rubber or silicone or fluoroelastomers or polyacrylate or neoprene or polyurethane. These elements 26 are mounted by the respective attachment portions 28 in the cage 22. Their tang portions 30 circumferentially extend within respective openings 24. As illustrated in Figures 1-5 and 6, cage 22 has a wide radial cross-sectional shape. This shape gives more support to the sprags 16 and eliminates the need to provide a cage having two concentric ring members as in the case of the prior art designs disclosed in the Japanese patent documents identified above. This shape also facilitates the mounting of metal or elastomeric energizing elements 26. Figures 10-18 illustrate yet another embodiment of the cage 22'' wherein a cam member 50 extends into the openings 24 of the cage to provide support for the sprags 16 in their positions of engagement as well as in their free wheel/overrunning positions and all positions therebetween. As a comparison, Figures 7-9 illustrate prior art cage and sprag structures. In Figure 7, a single cage design is illustrated. It can be seen that sprag control or support is minimal because the cage only contacts the sprags at one point, which is in the center of the sprag. In Figures 8 and 9 a typical double cage design is illustrated. In such an arrangement the two rings are relatively moveable and unable to support the sprags in their nonengaged positions. In Figure 10 the sprags 16 are shown supported by cam members 50 in the freewheel or overrunning position. In Figure 11 sprags 16 are shown supported by cam members 50 in the engaged position. It becomes apparent then that the cam member 50 allows a combined cage to possess at least all the sprag control found in the double cage design. As shown in Figures 12 and 13, each pair of cam members includes engaged cam surface portions 52 and free wheel cam surface portions 54 that provide sprag 16 support along the body of the sprag. When such a cage 22 is inserted between a pair of clutch-races, the resultant clutch has been found to meet or exceed the performance of a conventional double cage clutch. It can be appreciated that while cam members 50 limit extreme angular positioning of the sprags 16, once the cam members position the sprags into engagement with respective inner and outer clutch races, that the cam members do not inhibit sprag/race cooperation. As illustrated in Figure 13, cam members 50 extend axially and provide a sufficient surface to support sprags 16. Cam members 50 also eliminate latching, or pop out of the sprags 16 through the windows. Cam members 50 can also provide a mount for the independent energizing spring elements 26. The combination of improved cage design and use of individual energizing elements serve to angle the sprags 16 in the engagement direction during the free wheel/overrunning mode of operation. The attachment of the spring elements 26 to the cam members 50 increases the total effectiveness of a one way clutch. The independent energizing elements 26, while providing forces to the sprags equivalent to the forces exerted by a band spring in a double cage clutch design, provide more opportunity for higher levels of automated assembly. Figure 14 illustrates the use of a C-clip type spring independent energizing element 26. Figure 15 illustrates the use of an elastomeric-type independent energizing element 26 as hereinabove described. Figure 16 illustrates the use of a Z-spring type independent energizing element 26. In Figure 17, cage 22'' is illustrated as a two piece construction. Each piece defines half of the cage and has a flange section 42' and an axially extending cam member portion 50'. At the distal ends of the cam member portions 50', there are provided mating connecting members 56, 58 which allow the two pieces to be connected together as shown in Figure 17. As illustrated, connected cam member portions 50' include a portion for mounting the energizing spring members 26 therein. This mounting portion 60 is configured for the type of energizing spring element 26 used. The two piece construction facilitates automated assembly and allows the sprags 16 and energizing spring elements 26 to be mounted on one half of the cage 22" before the other half of the cage is connected to the first half. This type of assembly is preferred to a one piece construction for the benefit of assembling access for sprags and springs. Preferably the two piece plastic cage 22" is of plastic construction. Each piece can be molded separately with axially drawn dies but they may be made also by other manufacturing techniques. Alternatively cage 22" can be of metal construction or of a combination of metal and plastic. The metal construction may include formed or powdered metal technology.

Claims: A one-way sprag clutch comprising concentric inner (14) and outer (12) races and a sprag cage structure (10) located between the races (12, 14); the sprag cage structure (10) comprising an annular cage (22; 22") having axially extending circumferentially spaced cam members (50) which define therebetween circumferentially spaced windows (24), tiltable sprags (16) located one in each window (24), each sprag (16) having a radially inner clutch surface (20) and a radially outer clutch surface (18) engageable respectively with the inner (14) and outer (12) races, the sprags (16) each having a circumferential width at a location intermediate the inner (20) and outer (18) clutch surfaces thereof less than its circumferential width at locations adjacent the clutch surfaces (18, 20), cam surfaces (52, 54) on the cam members (50) on opposed sides of each of the sprags (16), the sprags (16) being engageable with the cam surfaces (52, 54) at the sprag locations adjacent the inner (20) and outer (18) clutch surfaces when the sprags (16) are tilted to a limiting angular position, and an energizing spring (26) for each of the sprags (16) secured to a respective cam member (50) and adapted to engage an adjacent sprag (16) at its intermediate location thereby to impart a continuous moment on the sprag (16) to maintain the clutch surfaces (18, 20) thereof in contact with the races (12, 14), characterized in that each window (24) has a generally hour-glass shape substantially constant shape in the radial direction of the cage (22; 22") with the radially outward region of the window (24) and the radially inward region of the window (24) both being wider in a circumferential direction than the radially intermediate region of the window (24), adjacent cam members (50) being engageable, at the radially intermediate region of the window (24) defined therebetween, with the intermediate relatively narrow location of the sprag (16) located in that window (24), adjacent cam members (50) each including a pair of said cam surfaces (52, 54), one such cam surface (50) of one cam member (50) lying circumferentially opposite one such cam surface (54) of the adjacent cam member (50), those circumferentially opposed cam surfaces (52, 54) continuously converging in a radially outward direction from the radially inward region of the window (24) to the radially intermediate region thereof, the other such cam surface (54) of said one cam member (50) lying circumferentially opposite the other such cam surface (52) of said adjacent cam member (50), those circumferentially opposed cam surfaces (54, 52) continuously diverging in a radially outward region of the window (24), the cam surfaces (52, 54) of each cam member intersecting with one another at said intermediate region of the window (24). A one-way sprag clutch as claimed in claim 1, wherein said one cam surface (52) of said one cam member (50) lies diagonally opposite said other cam surface (52) of said adjacen cam member (50), and said one cam surface (54) of said one cam member (50) lies diagonally opposite said other cam surface (54) of said adjacent cam member (50), the pair of diagonally opposed cam surfaces (52) limiting tilting motion of the sprag (16) in the window (24) in a clutch engaging direction, and the pair of diagonally opposed cam surfaces (54) limiting opposite tilting motion of the sprag (16) in a clutch diengaging direction. A one-way sprag clutch as claimed in claim 1 or 2, wherein the cam members (50) extend substantially radially between the inner (14) and outer (12) races, and the cam surfaces (52, 54) are substantially flat surfaces positioned at an angle to the radial axis of the cam members (50). A one-way sprag clutch as claimed in any of the preceding claims, wherein the sprags (16) are each of generally hour-glass shape in the radial direction of the sprag (16). A one-way sprag clutch as claimed in any of the preceding claims, wherein the cam members (50) are each formed on one circumferential side thereof with a spring pocket, one end of each spring (26) being positioned in the respective spring pocket. A one-way sprag clutch as claimed in any of the preceding claims, wherein the cam members (50) eliminate latching, or "pop out" of the sprags (16) through the windows (24). A one-way sprag clutch as claimed in any of the preceding claims, wherein the cage (22") includes two connectable cage pieces, each cage piece including a flange section (42') and an axially extending cam member portion (50') and means (56, 58) for mating the cage pieces together to form a one piece cage (22"). A one-way sprag clutch as claimed in any of the preceding claims, wherein the cage (22; 22") is comprised of high temperature engineered plastics such as polyetherimide, nylon or PES polyethersulfone. A one-way sprag clutch as claimed in claim 8, wherein said high temperature engineered plastics are reinforced with carbon fibres or glass or clay or mica. A one-way sprag clutch as claimed in any of claims 1 to 7, wherein the cage (22; 22") is comprised of metal material such as steel, aluminium or bronze. A one-way sprag clutch as claimed in any of claims 1 to 7, wherein the cage (22; 22") is comprised of a combination of metal and plastic material. A one-way sprag clutch as claimed in any of the preceding claims, wherein the energizing springs (26) comprise high temperature elastomers such as nitrile rubber or silicone of fluoroelastomers or polyacrylate or neoprene or polyurethane. A one-way sprag clutch as claimed in any of the preceding claims, wherein the cage (22) has a cross section of a generally rectangular shape defined by spaced flanges (42) connected by the cam members (50).

Inventors: MALECHA GREGORY J, RUTKE RUSSELL J, MALECHA, GREGORY J., RUTKE, RUSSELL J.
Applicants: BORG WARNER AUTOMOTIVE MORSE T, BORG-WARNER AUTOMOTIVE MORSE TEC CORPORATION
Application year: 1993
Main classification: F16D41
IPC codes: F16D41