Overrunning clutch having a cage design for directing lube flow

Abstract: An overrunning clutch comprises opposed inner (12) and outer (14) races defining an annular space (16) therebetween, unidirectional drive means such as sprags (18), and a cage (22), the cage (22) being disposed in the annular space (16) and cooperating with the sprags (18). The cage (22) includes a plurality of interconnecting elements (24,41), each of which has an inner side (28) facing the inner race (12), the inner side of each interconnecting element (24,41) being contoured to redirect at least a portion of the lubrication supplied through oil holes (20) back toward the inner race (12).

Description: One-way or overrunning clutches transmit torque in one direction only and are generally used to disengage a drive connection automatically when torque is applied in the reverse direction. Overrunning clutch elements generally are contained within the annular space between two opposed, concentric races. The inner race is keyed or otherwise fixed to an input shaft, and the outer race is fixed to a hub, or sleeve, from which the drive is ultimately taken. Alternatively, the outer race may form the torque input member and the inner race may form the torque output member. In a sprag-type overrunning clutch, a series of rocking tumblers or sprags is held together within a cage. The cage typically includes two rings and a crimped ribbon spring in the annular space between the rings. All three components of the cage are pierced to accommodate the sprags. The ribbon spring biases the sprags upright between the inner and outer races of the drive coupling. Because the radial clearance between the races is not enough for the sprags to rock all the way to their top dead centre positions, the sprags jam between the races. As long as the drive is in the direction tending to keep the sprags thus jammed, torque is transmitted from the input shaft, through the inner race, and finally to the outer race. Whenever the drive is reversed, the sprags tend to lay down against the influence of the ribbon spring, and no torque is transmitted. A second type of overrunning clutch uses rollers instead of sprags. These rollers are housed in inclined recesses formed in the annular space between the inner and outer races. When the shaft is rotated in one direction, the rollers run up the inclines and jam between the inner and outer races. If the shaft is thereafter rotated in the other direction, the rollers run down the inclines and are freed in the space between the two races, which is wider than the diameter of the rollers. To obviate backlash in the system, the rollers may be spring-loaded up the inclines. Because the two races rotate at high relative speeds, heat and friction can quickly wear down the components of the overrunning clutch, particularly the contact surface between the inner race and the sprags or rollers. Adequate lubrication of the components of an overrunning clutch is, therefore, very important. Various designs have been proposed for supplying lubrication to the overrunning clutch components. These include US-A-4875564 to Leitz et al., which discloses a sprag clutch having bores provided through lateral discs flanking the cage and the sprags. This allows oil to flow through the bores and into the space between the inner and outer races. US-A-4874069 to Lederman discloses a roller clutch provided with an internal oil passage in the cage that is open to one side. Oil which is normally supplied from oil passages in the inner race can then be supplied to the internal oil passage in the cage. Therefore, pressurized oil can be distributed all the way through to the centre of the cage. US-A-4756395 to Zloteck discloses a sprag-type overrunning clutch having an actuating ring in the form of a sleeve bushing. Recesses formed in the inner radial surface of the bushing trap lubricant and create a fluid drag as the surface of the inner race rotates relative to the bushing at high relative RPM. This drag tends to displace the bushing relative to the sprag retainer so as to lift the sprags from the inner race surface in the overrunning mode, thereby reducing sprag wear. A problem with these designs is that lubrication is not readily retained close to the inner race. The centrifugal force of the rapidly spinning races tends to fling the lubrication radially outwardly, away from the inner race. Because the inner race is the primary wear surface, an overabundance of oil must constantly be supplied to adequately lubricate the inner race contact surface. Another design having the same problem is featured in US-A-4714803 to Lederman which generally discloses an overrunning clutch comprising an inner race having a central axis of rotation, an outer race disposed around the inner race, the inner and outer races defining an annular space therebetween, unidirectional drive means for fixing the outer race against rotation relative to the inner race, means for supplying lubrication from the inner race to the annular space between the inner and outer races, and a cage disposed in the annular space between the inner and outer races and retaining the unidirectional drive means, the cage including a plurality of interconnecting elements each having an inner side facing the inner race and an outer side facing the outer race. It is an object of the present invention to minimize the aforementioned problem of retaining lubrication close to the inner race. This object is accomplished, in accordance with the present invention as claimed, in that the aforementioned generally disclosed overrunning clutch is characterized by either the inner side of at least one of the interconnecting elements being, or each interconnecting element being provided with a lube slot which is, contoured for redirecting at least a portion of the lubrication supplied from the inner race back towards the inner race. Attention is also drawn to US-A-2292988 and US-A-4913271 both relating to overrunning clutches. In order that the present invention may be well understood there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawing, in which: Figure 1 is a cross-sectional view of a sprag-type overrunning clutch embodying the present invention; Figure 2 is a cross-sectional view of a roller-type overrunning clutch embodying the present invention; and Figure 3 is a cross-sectional view of an alternative interconnecting element for the embodiment of the present invention shown in Figure 2. Referring first to Figure 1, there is shown an overrunning clutch 10 including a hardened steel inner race 12 and a hardened steel outer race 14. The inner race 12 is keyed or otherwise fixed to a drive shaft (not shown) having a central axis of rotation. The outer race 14, which is fixed to a hub or sleeve (not shown) from which the drive is ultimately taken, is disposed around and generally coaxial with the inner race 12. The inner and outer races define a radially extending annular space 16 between their opposed faces. A plurality of sprags 18 is disposed in the annular space 16. They function as unidirectional drive means for selectively fixing the outer race 14 against rotation in one direction relative to the inner race 12. Thus, when the inner race 12 is rotated in the clockwise direction as shown in Figure 1, the sprags 18 jam short of their fully upright position, and torque is transmitted to the outer race 14. When the inner race is rotated in the opposite direction, however, the sprags 18 lay down so that no torque is transmitted. Oil holes 20 are in fluid communication with a source of lubricant, and supply lubrication from the inner race 12 to the annular space 16 between the inner and outer races. Preferably, the lubrication is oil that is provided under pressure by a pump (not shown). A cage 22, preferably made of moulded aluminum or a composite material, is also disposed in the annular space 16. It encompasses and retains the sprags 18. The cage 22 includes a plurality of interconnecting elements 24, each of which generally has an outer side 26 and an inner side 28. The outer side 26 faces the outer race 14, while the inner side 28 faces the inner race 12. Spring means (not shown) may also be provided in the cage 22 to normally bias the sprags 18 toward their top dead centre position. The inner side 28 of the interconnecting elements 24 is specially contoured to redirect at least a portion of the lubrication supplied through the oil holes 20 in the inner race 12 back toward the inner race 12. To accomplish this, the surface of the inner side 28 of the interconnecting elements 24 is concave. Preferably, the deepest indentation of the concave surface is situated closer to the point at which the oil contacts the inner side 28, with the concave surface tapering more gradually along the path of the oil flow as it is expelled from the inner side 28. When oil is supplied through the lube holes 20, it thus follows the path shown generally by the arrows. It should be understood, however, that the optimum inner cage profile to produce the desired hydrodynamic action is a function of design parameters such as the quantity, spacing and angle of the oil holes 20 in a particular application. Figure 2 shows an alternative embodiment of the present invention in cooperation with a roller-type overrunning clutch 10'. In this embodiment, the annular space 16' between the races includes a series of spaced apart inclines 38 formed in the outer race 14'. As one skilled in the art can appreciate, these inclines could alternatively be formed in the inner race 12, as shown in the aforementioned US-A-4714803 to Lederman. A series of rollers 40 is provided in the annular space 16'. The rollers 40 are biased toward the narrow end of each incline 38 and against interconnecting elements 41 by lightly loaded springs 42. When the inner race 12' rotates in the clockwise direction as shown in Figure 2, the rollers are jammed between the races, and torque is transmitted. When the inner race 12' rotates in the opposite direction, the rollers 40 are freed, and no torque is transmitted to the outer race 14'. The oil holes 20' again supply lubrication from the inner race 12'. The oil flows out of the oil holes 20' and along the contoured surface of inner side 28' of the interconnecting elements 41. In this embodiment, the concave inner surface 28' is more uniformly parabolic than the surface of inner side 28 of the embodiment shown in Figure 1. The function is the same, however, as the oil is directed back along the inner side 28' and toward the inner race 12'. The arrows again indicates the general flow of the oil against the rotation of the inner race 12'. Figure 3 illustrates an alternative design for the interconnecting elements as shown at 41''. The inner side 28'' of the interconnecting element 41'' is slightly curved along its length so as to conform at all paints to the curvature of the inner race 12'', but alternatively the inner side 28'' might be generally planar with sufficient clearance from the inner race 12'' to avoid interference with race 12'' during operation. An arcuate lube slot 50 is formed through the interconnecting element 41'', extending from an entry point on the inner side 28'' to an exit point on the side wall 52 of the interconnecting element 41''. The lube slot 50 is preferably formed in the shape of a venturi or nozzle, such that the oil flows through the wider portion of lube slot 50 and accelerates through the narrower throat of the slot 50 before it is discharged through the side wall 52, and back against the inner race 12''. The particular shape of the slot 50 is dictated to provide optimum lubrication flow through the range of speeds to which the inner race 12'' and outer race 14'' operate.

Claims: An overrunning clutch comprising an inner race (12; 12'; 12'') having a central axis of rotation, an outer race (14; 14'; 14'') disposed around the inner race (12; 12''; 12''), the inner (12; 12'; 12'') and outer (14; 14'; 14'') races defining an annular space (16; 16') therebetween, unidirectional drive means (18; 40) for fixing the outer race (14; 14'; 14'') against rotation relative to the inner race (12; 12'; 12''), means (20; 20') for supplying lubrication from the inner race (12' 12'; 12'') to the annular space (16; 16') between the inner (12; 12'; 12'') and outer (14; 14'; 14'') races, and a cage (22) disposed in the annular space (16; 16') between the inner (12; 12'; 12'') and outer (14; 14'; 14'') races and retaining the unidirectional drive means (18; 40), the cage (22) including a plurality of interconnecting elements (24; 41; 41'') each having an inner side (28; 28'; 28'') facing the inner race (12; 12'; 12'') and an outer side (26) facing the outer race (14; 14'; 14''); characterized in that either the inner side (28; 28') of at least one of the interconnecting elements (24; 41) being, or each interconnecting element (41'') being provided with a lube slot (50) which is, contoured for redirecting at least a portion of the lubrication supplied from the inner race (12; 12'; 12'') back towards the inner race (12; 12'; 12''). An overrunning clutch as claimed in claim 1, wherein the contoured inner side (28; 28') of the interconnecting elements (24; 41) is concave. An overrunning clutch as claimed in claim 1, wherein the lube slot (50) is in the form of a venturi. An overrunning clutch as claimed in claim 1 or claim 3, wherein the lube slot (50) is arcuate. An overrunning clutch as claimed in claim 1, claim 3 or claim 4, wherein the inner side (28'') of the interconnecting element (41'') is curved to conform to the curvature of the inner race (12''). An overrunning clutch as claimed in claim 1 or claim 2, wherein the unidirectional drive means (18) comprises a plurality of sprags (18) disposed in the annular space (16) between the inner (12) and the outer (14) races. An overrunning clutch as claimed in any of claims 1, 3, 4 or 5, wherein the annular space (16') between the inner (12', 12'') and outer (14'; 14'') races includes a series of spaced apart inclines (38), and the unidirectional drive means (40) comprises a plurality of rollers (40) disposed in the annular space (16'). An overrunning clutch as claimed in any of the preceding claims, wherein the means (20; 20') for supplying lubrication from the inner race (12; 12'; 12'') comprises a plurality of oil holes (20; 20') formed in the inner race (12; 12'; 12'') and in fluid communication with a source of lubricant. An overrunning clutch as claimed in any of the preceding claims, wherein the outer race (14; 14'; 14'') is generally coaxial with the inner race (12; 12'; 12'').

Inventors: MALECHA GREGORY J, MALECHA, GREGORY J.
Applicants: BORG WARNER AUTOMOTIVE, BORG-WARNER AUTOMOTIVE TRANSMISSION AND ENGINE COMPONENTS CORPORATION
Application year: 1992
Main classification: F16D41
IPC codes: F16D41