Clutch having elements capable of independent operation

A freewheeling clutch includes torque transmitting elements disposed between an inner race and an outer race. The elements include active surfaces that may be defined by an angularly variable radius of curvature that varies with respect to roll angle at an increasing rate, such as an equiangular spiral, to form a constant strut angle as the elements move between a freewheeling and an engaged position.

BACKGROUND

The present invention relates to clutches, and more particularly to overrunning or one-way clutches having elements that are capable of independent operation.

Several types of clutches that transmit torque in one direction are well known. Such clutches typically have torque-transmitting elements—rollers, pawls, or sprags—disposed between an inner race and an outer race. For example,FIG. 1(Prior Art) shows a roller clutch with pockets, which includes a cam surface, formed in the outer race to contain the rollers.FIG. 2(Prior Art) shows a roller clutch similar to that shown inFIG. 1, but with a cage that retains the springs and rollers. The springs in the roller clutches shown inFIGS. 1 and 2bias the rollers toward the narrow end (that is, the portion having the smallest radial spacing) of the pockets. The cam surface of a roller clutch may also be formed on the inner race (although such a configuration is not shown in the figures).

Whether the rollers are unphased (that is, operate independently of one another) as shown inFIGS. 1 and 2, or phased (that is, urged in unison by a cage into and out of a torque transmitting position), the rollers lodge between the inner and outer races at a narrow portion of the cam surface to transmit torque in only one relative rotational direction. When the inner and outer races are rotated in the relative opposite direction, the rollers disengage as the races rotate such that no torque, or a negligible amount of torque, is transmitted. As oriented inFIGS. 1 and 2, the outer race will transmit torque to the inner race while the outer race is driven counterclockwise, and will not transmit torque while the outer race is driven clockwise.

The terms “relative rotational direction,” “rotational direction,” and “torque transmitting direction” as employed in the specification and claims refer to relative rotation between the races without regard to whether the inner race or outer race is driven. Even in the unphased examples, the rollers engage substantially simultaneously. Such simultaneous engagement prevents undue stress in the rollers and localized portions of the races, and enables the clutch to transmit torque even if one or even a few of the rollers do not engage.

FIG. 3(Prior Art) shows a schematic of a ratchet or pawl type clutch, in which a pawl pivots clear of a stop formed on the opposing race during rotation in one direction (that is, in the free-wheeling direction), but catches on the stop to transmit torque in the opposite direction (that is, the torque transmitting direction).

In addition to rollers and pawls, sprags are often employed to transmit torque between the inner and outer races of an overrunning clutch. Sprags are struts that have precisely machined cams at opposing ends that wedge between the races to transmit torque in one relative rotational direction, and that enable the races to freewheel while one race overruns the other or while the races turn in the opposite rotational direction.FIG. 4(Prior Art) illustrates a single cage sprag clutch, andFIG. 5(Prior Art) illustrates a double caged sprag clutch.

For a sprag clutch to function properly, the sprags typically must operate in phase, and therefore cages are typically required. Thus, referring toFIG. 5to illustrate a phased configuration, a conventional sprag clutch100includes an inner race102, an outer race104, several sprags106disposed between the inner race102and outer race104, and a spring108that urges the sprags106toward an engaged position such that the inner and outer contact surfaces of the sprag maintain contact with the inner and outer races, respectively. Clutch100also includes an inner cage110aand an outer cage110b, as well as an inner drag clip112aand an outer drag clip112b. The cages shown inFIG. 5hold the sprags in position relative to the races and assure equal spacing and circumferential alignment of the sprags, as well as phased operation. Forms (not shown) placed on the side of the sprags may also be employed to phase their operation without the use of cages.

The paper entitled “Automotive Sprag Clutches—Design and Application,” Society of Automotive Engineers No. 208A (E. A. Ferris) describes the importance of phased operation of sprags, and describes the high failure rate of non-phased clutches subjected to shock loads. In this regard, non-phased clutches are prone to failure at loads well below their static torque capacity. Roll over, which is associated with catastrophic clutch failure, occurs, for example, if a first sprag begins to engage prior to other sprags.

For both phased and unphased configurations, the strut angle is crucial to the design and operation of clutches, especially sprag clutches. The strut angle is formed between a line connecting the contact points of the sprag (or other torque transmitting element, such as a roller) at the cam and/or race and a radial line from the cam and/or race center to either contact point.FIG. 6(Prior Art) illustrates the strut angle, and identifies the inner strut angle, which is formed at the sprag inner contact point, and the outer strut angle, which is formed at the sprag outer contact point. The strut angle determines the normal and tangential forces experienced by the clutch components while under load. The strut angle is also important for assuring appropriate clutch engagement, especially under adverse conditions such as cold weather, under shock loads, and the like.

In addition to more traditional manufacturing techniques for forming the above clutch components, powder metallurgy today is employed to form some components. Employing powder metallurgy for forming such components generally reduces cost, enhances design flexibility, and enhances ease of manufacturing. Powder metallurgy (“PM”) techniques for forming clutch components typically include atomizing prealloyed steel or ferrous raw materials, blending the powder with components such as graphite, copper, nickel, or ferrophosphorus, injecting the mixture into a die, compacting and shaping the mixture by the application of pressure to form a compact, and ejecting the compact from the die.

The compact is then sintered wherein metallurgical bonds are developed under the influence of heat. The alloying and admixed elements enhance strength and other mechanical properties in the sintered part. According to the particular characteristics desired, secondary operations, such as sizing, coining, repressing, impregnation, infiltration, forging, machining, joining, etc., may be employed on the PM part. The term “net shape” or “net forging” will be employed to refer to a part to which no additional machining or related process are required to meet the desired tolerances common to the particular part. A term employed in the powder metallurgy field is near net PM forging, which indicates that only a relatively small amount of machining is typically required.

Each of the above clutch types, whether formed by a powder metallurgy process or other process, has drawbacks that limit its appeal. Roller clutches often are manufactured from wrought material or fully dense powder—that is, at an approximate minimum density of 7.8 g/cc. Hoop and contact stresses in a roller or sprag clutch typically require powder having a 7.80 g/cc density, which makes them more expensive than a lower density option. Moreover, for high torque ratings, roller clutches often require high alloy steels with fine surface finishes to withstand the sliding and rolling contact fatigue inherent in roller clutch design. Further, the number of rollers is constrained because a small roller diameter relative to the cam radius tends to promote cam fatigue.

Ratchet clutches in automotive applications often are manufactured using relatively high density single or double press powder metal processes, typically at approximately densities of 7.0 to 7.3 g/cc. This lower density often results in savings compared with fully dense roller and sprag clutch races. However, tight tolerances and large race diameters are sometimes required for high torque ratings, and such factors diminish or eliminate the cost savings over competing clutches. Further, because of the impact stress inherent in the ratchet design, the races manufactured out of 7.3 g/cc density pm are prone to fracture, and ratchet clutch's poorly distributed load bearing capability results in excessive wear on mating bearing surfaces.

Sprag clutch components often require tight tolerances to operate adequately. Sprags are often formed form cold-drawn wire and are machined or surface finished after hardening to achieve the precise dimensions necessary for sprags to operate acceptably and in unison. Thus, the machining and other processes that are required to produce parts within the particular tolerances often make sprag clutches more expensive than roller and pawl clutches.

It is generally a goal of the present invention to provide improved clutch and clutch components.

SUMMARY OF THE INVENTION

A clutch is provided that includes torque-transmitting elements disposed between an inner race and an outer race. Each one of the elements includes an inner active surface and an outer active surface capable of contacting the inner race and outer race, respectively, while the elements are in a torque transmitting orientation or position. The inner active surface is defined by an angularly variable radius that varies with respect to roll angle at a first rate. Similarly, the outer active surface is defined by another angularly variable radius that varies with respect to roll angle at a second rate.

The rate of change of the radius of the inner active surface (that is, the general shape of the curve) is not required to be the same as that for the outer active surface. Thus, the inner active surface may have a shape, in transverse cross section of the element, that is the mirror image of the shape of the outer active surface, or the inner active surface and outer active surface may have different shapes. The curves preferable have the same origin.

Preferably, equiangular spirals define the curves of the inner active surface and the outer active surface of the elements. Therefore, the equiangular spirals for the inner and outer active surfaces may have the constants of the same magnitude such that the shape of the curves are the same (or mirror images), or may have constants of dissimilar magnitudes. Further, the origins of the equiangular spirals of the inner and outer active surfaces may be the same or different.

The equiangular spirals or the angularly variable radii of curvature of the elements are capable of creating constant strut angles. In this regard, each one of the inner strut angle and the outer strut angle remains constant while the element moves between a disengaged position or freewheeling position to an engaged position. The inner strut angle may be the same or different than the outer strut angle. The present invention also encompasses only one of the inner active surface and the outer active surface having an angularly variable radius of curvature and/or forming an equiangular spiral.

For embodiments in which each element is disposed in a pocket, an intermediate surface of the element may be in contact with a rear wall of the pocket. A spring may be disposed between an opposing front wall of the pocket and the element to urge the element toward an engaged position. Preferably, each element includes a forwardly protruding extension to prevent the element from rotating out of spring engagement, or otherwise rotating out of position.

Embodiments of the present invention employ possible attributes of each of the three one way clutches described and combine them into one design. A roller clutch, for example, does not require phasing the way a sprag clutch does since it functions with a constant strut angle. Also, a pawl or ratchet clutch does not require phasing. An embodiment of a clutch according to an aspect of the present invention can function without means for phasing, which can serve to reduce costs associated with bearings, cages, or expensive machining operations that generally drive the cost of sprag clutches higher.

On the other hand, roller clutches cannot handle high relative velocities between the races since centrifugal forces lift the rollers off the inner race, causing the clutch to slip if engagement is attempted. Roller clutches once engaged experience sliding or skidding as the rollers attempt to take up race deflection. This sliding results in reduced contact fatigue endurance over a design using pure rolling. Ratchet clutch torque capacity using powder metal manufacturing methods is limited due to the reduced impact resistance of the manufacturing processes employed. Ratchet designs also introduce non-uniform loading on the race components causing increased wear.

Embodiments of the present invention may use full density PM for manufacturing processes, to produce relatively uniform loading of components under pure rolling conditions, while allowing non-phasing of the locking elements and high differential speeds between the races. In addition, equiangular spirals typically provide greater cam rise over a similarly sized sprag type element, allowing for more tolerance variation on the clutch components. Allowing more tolerance on race dimensions provides for less expensive manufacturing technologies to produce the clutch. The present invention is not limited to employing full density PM, nor to non-phasing elements or high differential speeds, as described more fully below.

DESCRIPTION OF PREFERRED EMBODIMENTS

According to an aspect of the present invention, a clutch10includes an inner race12, an outer race14, and plural elements16disposed between inner race12and outer race14.FIGS. 7A,7B, and7C show views of assembled clutch10. Outer race14, as best shown inFIGS. 8A and 8B, includes inwardly extending legs22that form pockets20therebetween. Thus, each pocket is formed by a main outer race surface52, a pocket rear wall54, and a pocket front wall56. Legs22may have machined surfaces facing inner race12to promote concentricity of races12and14.

An element16, as shown for example inFIGS. 9A,9B, and9C, and a spring18, shown inFIG. 10, are disposed in each, or substantially each, pocket16. Each element16includes an inner active surface30and an outer active surface32, which are defined as the portions of elements16that contact the inner race12and outer race14, respectively, during normal pivoting of the elements between the freewheeling position and the engaged position.

FIG. 12, which is an enlarged schematic view of a portion of clutch10, shows elements16from the opposite view as shown inFIG. 7B, as indicated by lines12—12in FIG.7C. As shown inFIG. 12, an inner contact point34and an outer contact point36are disposed on inner active surface30and on outer active surface32, respectively. Contact points34and36are in contact with a main or contact surface50of inner race12and main outer race surface52, respectively, at least while elements16are in a torque transmitting position as described more fully below. Because points34and36are actual points of contact, such points34and36may be defined on different portions of element16during operation.

An element rear surface40is disposed between inner active surface30and outer active surface32. A rear contact point38, disposed on element rear surface40, is capable of contacting pocket rear wall54. An element front portion or surface42is formed substantially opposite element rear surface40, and preferably includes an inner projection58aand an outer projection58b. Inner and outer projections58aand58bmay terminate in inner and outer apexes59aand59b, respectively. Projections58aand58b, which may be portions that deviate from the curves defining inner and outer active surfaces30and32, respectively, or may merely be extensions thereof, inhibit or prevent the elements from rotating out of spring engagement.

Spring18is disposed between pocket front wall56and element front portion42, and preferably urges against element outer apex59bto urge element16counterclockwise (as orientedFIG. 12) toward its engaged or torque transmitting position. Spring18preferably includes a substantially flat front end72disposed against pocket front wall56, a substantially flat rear end74disposed against element outer projection58a, and one or more leaves76therebetween.

A retainer60, which is shown inFIGS. 11A,11B, and11C, may be disposed on outer race14as shown inFIGS. 7A,7B, and7C. Retainer60preferably includes a substantially flat ring64from which plural fingers66protrude. Fingers64protrude into pockets20to position or retain springs18therein. A snap ring68preferably is employed to retain retainer60in a snap ring groove69that is disposed proximate retainer groove62. Retainer60and snap ring68may be employed on either or both sides of outer race14. As in conventional overrunning clutches, preferably, each side of pockets20includes some feature to limit the longitudinal movement of elements16.

Springs18may be secured within pockets20by any suitable means. For example, springs18may be held in place by a cage78, as shown inFIGS. 13A,13B, and13C. Cage78includes plural windows80that are formed by opposing circular rims84and ribs82disposed between opposing rims84. Windows80enable legs22to be disposed therein, and ribs82retain springs18, as described above with respect to fingers66. Further, springs18may be disposed in a small spring pockets21, which are extensions of, and in communication with, main pocket20, as shown schematically in FIG.15. In such an embodiment, first end72of each of the springs18may be disposed in spring pocket21such that the spring (that is, second end74) protrudes into main pocket20and into contact with element16.

Spring18urges against a position of element16so as to position element16such that three points of element16are in contact with races12and14and such that element16is pivoted until it spans the race height between inner and outer races12and14. Spring18urges element16toward its engaged position such that inner active surface contact point34contacts main inner contact surface50, outer active surface contact point36contacts main outer race surface52, and rear contact point38contacts pocket rear wall54. Thus, element16is in position to readily engage to its torque-transmitting position.

Even though it is an advantage that the elements described herein are capable of unphased operation, the present invention is not limited to such a configuration. Rather, it may be beneficial to provide a cage or ribbon to interconnect springs18or elements16for a variety of reasons, and the present invention encompasses such structure.

Elements16are configured to enable outer race14to freewheel with respect to inner race12while outer race14turns in a clockwise direction, which is indicated by the relative directional arrow FW in FIG.12. Alternatively, while outer race14moves in a counterclockwise direction relative to inner race12, which is indicated by the relative directional arrow TT inFIG. 12, element16is encouraged by frictional contact with inner race surface50and/or outer race surface52and by the force of spring18to move to a torque transmitting position in which element16is wedged between inner and outer race contact surfaces50and52. It is understood that such movement refers to relative movement of the races, regardless of which (or both) race are physically rotating relative to a fixed point outside the clutch.

In the embodiment shown inFIG. 12, and as explained more fully below, element inner contact surface30is defined by a first radius of curvature having an angularly variable magnitude. Likewise, element outer contact surface32is defined by a second radius of curvature having an angularly variable magnitude. In fact, preferably the magnitude or length of the radius of curvature of inner active surface30varies with respect to roll angle at an increasing rate. Likewise, the magnitude or length of the radius of curvature of the outer active surface32varies—that is, increases, with respect to the roll angle, and may increase at an increasing rate. The rate of change of the radius of curvature is not required to be constant. A vector drawn perpendicular to a tangent at any point on curve of inner or outer active surface30or32may define the radius of curvature r-c. In a preferred embodiment, the magnitude of the angle between the radial vector and the radius of curvature remains constant. The term “roll angle” as used herein is the magnitude of pivoting of a surface of element16about the origin of the radial vectors as element16moves between its at-rest, disengaged position and its fully-engaged, torque transmitting position. Thus, as explained more fully below, the roll angle for an inner and/or outer active surface that is formed by an equiangular spiral is measured about the origin of the spiral. For other embodiments, the roll angle will be clear to persons familiar with over-running clutch configurations in view of the present disclosure.

The shape of the active surfaces30and32may be defined by equiangular spirals, an example of which is shown in FIG.16.FIG. 17Ashows a pair of equiangular spirals, which are indicated by reference numerals E1and E2, superimposed over the shape of an element16. An equiangular spiral is a shape in which, in polar coordinates, the radial vector r-v is a (increasing) function of the angle theta, which is the angle between the x-axis and the radial vector. The magnitude of radial vector r-v is measured from the origin. The equiangular spirals have the characteristic that for the angle formed between a radial vector r-v (that, is a line drawn from the origin O to any point P on the spiral curve) and the tangent T for any point P is constant.

where b=tan (φ) and where r-v is the magnitude of the radial vector from the origin O to point P on the curve; θ is the angle from the x-axis (and part of the definition of r-v), a is a constant; and φ is the angle formed between the radial vector r-v and the radius of curvature r-c. Angles θ and φ may have a different value on the inside of element16than on the outside of element16.

Curve E1may have components a and b that are the same as those for curve E2, or at are different from those of E2. Further, curves E1and E2may have the same orgin, or each curve E1and E2may have its own origin that is spaced apart for the other (the latter is not shown in the Figures). Preferably, curves E1and E2have the same positive direction for angle theta (that is, clockwise as oriented in FIG.17A). Preferably all of actives surfaces30and32are formed by equiangular spirals, and the present invention encompasses elements in which only portions of the inner and outer active surfaces are formed by equiangular spirals, as well as embodiments in which active surfaces30and32are not formed by equiangular spirals but the elements provide the same function with respect to strut angle, as discribed herein. The subscripts i and o are employed herein to indicate that the variable refers to the inside and outside curves or surfaces of element16, respectively.

Referring toFIG. 18to illustrate the calculation of the strut angles, a pair of equiangular spirals E3and E4share the same origin between inner and outer races of defined diameters. To determine the strut angles, an imaginary element's position may be mathematically rotated about the center of the clutch10, and a locking distance between the races z-races is calculated for each rotational position. The element itself may be mathematically rotated about its center, and the locking distance of the element z-element may be calculated for each rotational position. Locking will occur when z-races and z-element are equal. Z-races and z-element may be calculated from the following equations, which follow from the law of cosines:
Zraces=(Or2+ir2−2Orircos ξ)1/2
Zelement=(Ro2+Ri2−2RoRicos(180−φo+φi−ξ))1/2

where ε is the phase angle between the inner and outer spirals; Oris the magnitude of the vector from the center of the clutch10to the outer contact point36; iris the magnitude of the vector from the center of the clutch10to the inner contact point36; ξ is the angle formed between Orand ir. Theta

Once z-races is equal to z-element, the strut angles α and β may be readily determined from the known geometry:
α=invcos((Z2+Or2−ir2)/(2ZOr))
β=α+ξ

where Z is the distance between inner contact point34and outer contact point36.

For any diameter of inner race contact surface50and outer race main surface52(that is, for any radial space defined between the races), an angularly variable radius of curvature may be chosen for element inner and outer active surfaces30and32such that the inner and outer strut angles remain constant regardless of roll angle. In this regard, the inner strut angle and the outer strut angle remain constant while element16moves between its freewheeling (or at-rest), disengaged position and its fully-engaged, torque transmitting position.

Thus, the strut angles are constant over a given range of motion of elements16, and the strut angles may be determined from the defined spiral and race geometries. For example, if the outer race size is increased while the inner race diameter is held constant, elements may be configured employing the principles described herein and the strut angles recalculated.FIG. 20illustrates the substantially constant strut angle of elements16by comparing such strut angles for an increasing outer race diameter with strut angles of a roller clutch and a conventional sprag clutch while holding the inner race diameter constant.

The present invention does not require that the magnitude of the inner strut angle be equal to that of the outer strut angle. In fact, in practice the magnitudes will typically differ The actual magnitude of the strut angles may be chosen according to conventional clutch design parameters in light of the present disclosure, as will be understood by persons familiar with clutch design and technology. Maintaining such constant strut angles provides benefits including enhancing uniformity of element engagement for unphased elements, especially under adverse conditions such as cold weather, under shock loads, and the like, as well as minimizing hoop stresses and localized contact stresses, and other benefits, as will be understood by persons familiar with clutch design and technology in light of the present discussion.

Obtaining such benefits does not require the strut angles to be exactly uniform under all roll angles, and thus the term “constant strut angle” encompasses strut angles that vary to some degree. Further, maintaining a constant strut angle or a strut angle within a particular range is not essential to the present invention. The present invention also contemplates that the inner strut angles among the plural elements16may vary somewhat, and that the outer strut angles among the plural elements16will vary somewhat.

In this regard, each element16may maintain an inner strut angle that changes no more than about four degrees while the element moves between its freewheeling position and its engaged position. Each element16may also maintain an outer strut angle that changes no more than about four degrees while the element moves between its freewheeling and its engaged position. More preferably, strut angles that change no more than about two degrees, and even more preferably that change no more than about one degree may be employed. In an embodiment in which the races are formed of powder metallurgy within a tolerance of approximately +/−0.006 inches and the elements are formed of cold or hot extrusion, the inner strut angles have been shown to vary among the elements (that is, the strut angle varies from one element to another) by approximately 0.1 degrees, and the outer strut angles have been shown to vary among the elements by approximately 0.1 degrees. The present invention is not limited to any particular variation of strut angles among elements16, unless expressly set forth in the claim.

Although the strut angles provided above may illustrate design guidelines, to the extent that such ranges are not recited in a particular claim, the present invention is not limited to the particular ranges disclosed, nor are the advantages referred to herein limited to such ranges. Further, the strut angle ranges may take into account component tolerances and deflection or deformation of the components under design and shock loads. For example, the claims that recite a particular range to which the strut angles are limited may be satisfied even if some of the strut angles of some of the elements fall outside of the claimed range because of dimensional variation of the parts, local load-induced component deflection, and like variables. The present invention does not require that all elements maintain a constant inner and outer strut angle.

Further, the present invention encompasses elements that employ an aspect of the present invention on only one of the inner active surface and the outer active surface. Thus, referring toFIG. 17B, an element16′ includes an active surface31that may form either the inner active surface or outer active surface. Active surface31is formed from an angularly variable radius if curvature r-c, and preferably forms a constant strut angle, as defined herein, with its corresponding race. An opposing active surface33preferably is not formed of an angularly variable radius of curvature, but rather preferably is formed having a true radius to form a segment of a circle. Thus, the race surface corresponding to active surface33may either have features to cause the strut angle to be constant (such as, for example, a cam surface—not shown in FIG.17B—which will be understood by persons familiar with clutch design and technology in light of the present disclosure) with respect to roll angle or the strut angle may be variable.

FIG. 17Cillustrates that an element16″ may be formed of a single equiangular spiral E5, which is shown in dashed lines superimposed over element16″. Thus, an inner active surface35aand outer active surface35bare formed on opposing sides of spiral E5.

The present invention encompasses structure other than elements16,16′ and16″ that maintains constant strut angles during engagement. For example,FIG. 19illustrates an alternative element116that is disposed between an inner race112and a pocket120in an outer race114. Element116has an inner active surface that is as described above with respect to reference numeral30. Inner race150is concentric, such that the inner active surface of element116forms a constant strut angle with respect to inner roll angle, as generally described above. An element outer active surface132contacts an outer race main surface or contact surface152, which is not concentric with inner race112, but rather has a cam shape. Also, element outer active surface132is cammed or non-circular (as oriented in the cross sectional view shown in FIG.19), and surfaces152and132cooperate such that element116maintains a constant outer strut angle as element pivots or moves between a fully engaged and a fully disengaged position.

The cam-on-cam configuration of the outer surface may also be formed on the inner surface. Thus, an alternative inner race main surface or contact surface150′ is shown in dashed lines to indicate that it may be formed into such a cam surface. In order to maintain a substantially constant, inner strut angle for a pivoting element, the inner active surface of element116may cammed or non-circular similar to that described above with respect to outer active surface132. The geometric configuration of surfaces132and152(and/or150′) will depend upon sizes of the components and design considerations of the particular application, and the geometric configuration for the particular application may be chosen by persons familiar with clutch technology and design in view of the present disclosure.

For the embodiment of clutch10, inner race contact surface50and main outer race surface52(that is, the surfaces on which elements16wedge to transmit torque) define substantially concentric circles, such as, for example, as shown in FIG.12. Thus, the curves defining the inner and outer elements active surfaces30and32may be defined by curves of increasing radii of curvature, such as the equiangular spiral, to form constant strut angles.

In addition to the enhanced uniformity of movement of the elements inherent in the present invention and other advantages described or inherent in the present invention and its embodiments, persons skilled in the air will recognize numerous additional benefits to the disclosed and other embodiments of present invention, such as, for example, the ability to employ powder metallurgy processes to form many of the clutch components. In this regard, conventional powder metallurgy tolerances for net shape forgings are often approximately +/−0.006 inches, which for many clutch components and applications is sufficient such that net shape forgings or near net shape forgings may be employed.

In fact, some or all of the components, including the elements16and races12and14may be net shape forgings within such tolerances while maintaining many of the advantages described herein. The choice of metal powder mix and related processing may vary according to the desired properties of the components, as will be understood by persons familiar with powder metallurgy technology and practice.

For some applications, for example, components may be formed by gas carburizing of a briquetted powder metal preform prior to hot forging to form a dense, carburized powdered metal part, which is commonly referred to as a SINTA-CARB™ process. Such technology is described in U.S. Pat. No. 3,992,763, entitled “Method Of Making Powdered Metal Parts,” which is incorporated by reference herein in its entirety. The present invention also encompasses forming the components of other materials, such as, for example, forming the elements by cold or hot extrusion (which is preferred for some applications) or machining the inner and outer races by wrought steel.

Further, it has been found that the components may fall within tolerance ranges that are a function of the component size. In this regard, it is helpful to provide dimensional tolerance limits on the components in terms of inches per inch diameter of the relevant part. The dimensional tolerance for the surface52of the outer race preferably is no more that approximately 0.003 inches per inch of race diameter. The dimensional tolerance for the surface50of the inner race preferably is no more that approximately 0.00075 inches per inch of race diameter. The dimensional tolerance of elements14may be less than or equal to approximately 0.0005 inch per inch diameter of the largest circle that may be inscribed around the outside of the element.

Embodiments of the present invention have been described to illustrate various aspects of the present invention. The present invention, however, is not limited to the particular embodiments described herein, but rather encompasses all embodiments or aspects within the broad scope of the claims. For merely a few examples, pockets are described as being formed on the outer races even though the present invention encompasses pockets being formed on the inner races or races having no pockets; the present invention encompasses caged or phased elements as well as un-caged or unphased elements; the present invention encompasses employing structural or functional features from any one of the elements or embodiments in combination with structural or functional features from any other of the elements or embodiments; and other variations too numerous to mention but flowing naturally from the present disclosure.