Pin and pawl style bi-directional overrunning clutch

An overrunning clutch is provided having inner and outer members disposed about a rotational axis with the outer member radially outward of the inner member. The clutch further includes a plurality of pins projecting from one of a radially inner surface of the outer member and a radially outer surface of the inner member. The clutch further includes one or more pawls coupled to one of the inner and outer members. Each of the pawls is movable between an engagement position wherein the pawl is engaged with one of the pins to transmit torque between the inner and outer members and a disengagement position wherein the pawl is disengaged from the pin to permit relative rotation of the inner and outer members. In one embodiment, different pawls assume their respective engagement position depending on the rotational direction of the one member.

BACKGROUND OF THE INVENTION

a. Field of the Invention

This invention relates to an overrunning clutch. In particular, the instant invention relates to a clutch having a structure that enables improved control of clutch engagement, and smaller, more evenly distributed loads on clutch engagement surfaces.

b. Background Art

Clutches are used in many applications to selectively engage and disengage a driving device such as a motor with a driven device (e.g. a conveyor or a reel for a hose or cable) in order to transfer torque from the driving device to the driven device. In many clutches, engagement and/or disengagement occurs through electro-magnetic or fluid actuation or even manually by the user. These actuation methods increase the operating complexity and cost of the clutch. To address this drawback, in other clutches engagement and/or disengagement occurs mechanically through, for example, the use of springs and/or in response to external forces operating on the clutch such as centrifugal force.

One conventional type of clutch that relies on mechanical actuation is a centrifugal clutch. In a centrifugal clutch, a radially inner member of the clutch is coupled to the driving device. When the rotational speed of the driving device reaches a pre-determined level, shoes attached to the inner member of the clutch move radially outward against the bias of springs and engage a radially outer member of the clutch coupled to the driven member. Centrifugal clutches have several disadvantages, however. First, as the shoes engage the surface of the radially outer member, the shoes slide until the centrifugal force reaches a sufficient level to transmit torque. This sliding motion results in friction that increases temperatures within the clutch and wear on the surfaces of the clutch. The wear generates metal particles that abrade the surfaces of the clutch and cause even greater wear. Second, to achieve sufficient centrifugal force, the angular speed and mass of the shoes must be relatively high. As a result, the clutch is relatively large.

Another conventional type of clutch that relies on mechanical actuation is a ratchet and pawl clutch. In this type of clutch, pawls are brought into engagement with grooves formed in the surface of one of the clutch members either by spring loading or by centrifugal force. This type of clutch, however, also has several disadvantages. Formation of the grooves requires specialized manufacturing and heat treatment to increase material hardness thereby increasing manufacturing costs and complexity. The grooves also have sharp corners and edges that act as stress risers and reduce the clutch's strength and durability. Further, the relatively flat surfaces of the groove make it difficult to control the exact position of engagement by the pawls and, when multiple pawls are involved, it is common for one or more pawls to engage before others causing uneven load sharing. Further still, disengagement of the pawls from the grooves requires reverse relative motion between the clutch members to provide sufficient clearance. In ratchet and pawl clutches where clutch engagement results from centrifugal force, there are still further disadvantages. In particular, as rotational speed increases and the pawls move outward, it is difficult to prevent unwanted contact between the sharp edges of the pawls and the grooves and the resulting damage to both. Further, the pawls engage the surfaces of the grooves at relatively high speeds thereby generating high impact loads. To counteract these loads, the clutches tend to be relatively large and made from high strength materials thereby increasing costs.

The inventor herein has recognized a need for an overrunning clutch that will minimize and/or eliminate one or more of the above-identified deficiencies.

BRIEF SUMMARY OF THE INVENTION

An improved clutch is provided. In particular, an overrunning clutch is provided that enables improved control of clutch engagement and disengagement, and smaller, more evenly distributed loads on clutch engagement surfaces.

An overrunning clutch in accordance with one embodiment of the present invention includes an inner member disposed about a rotational axis and an outer member disposed about the rotational axis radially outward of the inner member. The clutch further includes a plurality of pins projecting from one of a radially inner surface of the outer member and a radially outer surface of the inner member. Finally, the clutch includes a pawl coupled to one of the inner and outer members. The pawl is movable between an engagement position wherein the pawl is engaged with a pin of the plurality of pins to transmit torque between the inner and outer members and a disengagement position wherein the pawl is disengaged from the pin to permit relative rotation of the inner and outer members. In one embodiment, the clutch further includes an actuator disposed between the inner and outer members and configured to engage the pawl upon rotation of the one member and urge the pawl towards the engagement position.

An overrunning clutch in accordance with another embodiment of the present invention includes an inner member disposed about a rotational axis and an outer member disposed about the rotational axis radially outward of the inner member. The clutch further includes a plurality of pins projecting from one of a radially inner surface of the outer member and a radially outer surface of the inner member. The clutch further includes a first pawl coupled to one of the inner and outer members. The first pawl is movable in response to rotation of the one member in a first rotational direction from a first disengagement position wherein the first pawl is disengaged from the plurality of pins to permit relative rotation of the inner and outer members to a first engagement position wherein the first pawl is engaged with a first pin of the plurality of pins to cause rotation of another member of the inner and outer members in the first rotational direction. The clutch further includes a second pawl coupled to the one member. The second pawl is movable in response to rotation of the one member in a second rotational direction opposite the first rotational direction from a second disengagement position wherein the second pawl is disengaged from the plurality of pins to permit relative rotation of the inner and outer members to a second engagement position wherein the second pawl is engaged with one of the first pin and a second pin of the plurality of pins to cause rotation of the another member in the second rotational direction. In accordance with one embodiment, the clutch may again further include an actuator disposed between the inner and outer members and configured to engage the first pawl upon rotation of the one member in the first rotational direction and urge the first pawl towards the first engagement position and configured to engage the second pawl upon rotation of the one member in the second rotational direction and urge the second pawl towards the second engagement position.

An overrunning clutch in accordance with the present invention is advantageous relative to conventional electrical, fluid or manually actuated clutches because the clutch is less complex and less costly. The clutch is also advantageous relative to conventional mechanically actuated clutches. As compared to conventional centrifugal clutches, no sliding friction is created thereby reducing heat and wear on the clutch. Further, because the inventive clutch is not dependent on the speed of the driving device, the clutch is smaller than conventional centrifugal clutches while transmitting the same torque. As compared to conventional ratchet and pawl clutches, the inventive clutch does not require sharp grooves in the surface of one of the clutch members nor relative motion between the clutch members to allow the pawls to clear the grooves. As a result, the clutch is easier and less costly to manufacture and suffers less stress upon engagement. Further, the pawls engage the pins at a relatively precise location thereby insuring relatively equal load sharing.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,FIG. 1illustrates a power generation and transmission system10. System10includes a driving device12for generating power used to drive a driven device14. The driving device12may comprise a conventional motor including, for example, an electric motor, hydraulic motor or pneumatic motor. Device12may further include a conventional gear box or speed reducer (which may be combined with the motor to form a conventional gear motor) to control the output speed and torque delivered to driven device14. Device12may output rotational torque through an output member16such as a shaft or another rotating body such as a gear, pulley or sprocket. Driven device14may comprise, for example, a conveyor or a reel on which is mounted a hose, an electric cable or a steel cable. It should be understood, that the form of device14will depend on the application and that device14may comprise any of a wide variety of devices configured to receive an input torque. Device14may input rotational torque through an input member18such as a shaft or another rotating body such as a gear, pulley or sprocket. System10may further include a clutch20in accordance with the present invention. Clutch20selectively couples devices12,14to provide torque output by device12to device14. In particular, clutch20receives torque from output member16of device12and selectively transfers torque to input member18of device14. It should be understood that output member16may be formed in device12or clutch20and, similarly, that input member18may be formed in device14or clutch20.

Referring now toFIGS. 2-4, one embodiment of a clutch20in accordance with the present invention is illustrated. Clutch20comprises an overrunning clutch and, in particular, a bi-directional overrunning clutch. An overrunning clutch is a type of mechanical clutch that is designed to drive in one direction while freewheeling or overrunning in the opposition direction. In the driving direction, the clutch also freewheels if the rotational speed of the driven device exceeds the rotational speed of the driving device. Bi-directional overrunning clutches are capable of driving and overrunning in both directions. One of the benefits of an overrunning clutch is that it allows for the overrunning of large inertia loads upon stopping and prevents any back-driving damage that may occur to the driving device12. Clutch20may include an inner member22, an outer member24, a plurality of spring engagement pins26, a plurality of mounting pins28, a plurality of springs30, a plurality of clutch engagement pins32, and a plurality of pawls34.

Inner member22is configured to receive an input torque from output member16of driving device12which may be selectively transferred to outer member24of clutch20as described in greater detail hereinbelow. Member22is annular in construction and configured to receive a shaft (not shown) extending from or to device12(e.g., the shaft may comprise input member16or may be coupled to input member16). Member22may define a keyway36or key configured to engage a matching key or keyway, respectively, in the shaft in order to couple member22to the shaft for rotation about a rotational axis38. The diameter of the radially outer surface of member22varies such that member22defines a radially outwardly extending flange40disposed at one axial or longitudinal end of member22and another radially outwardly extending flange42disposed intermediate the axial or longitudinal ends of member22. Flange42may define one or more radially extending, circumferentially spaced passageways44configured to receive set screws (not shown) used to retain clutch10on a shaft. Referring toFIG. 4, flanges40,42, define axially aligned bores46,48and50,52configured to receive opposite longitudinal ends of pins26,28, respectively. Referring again toFIG. 3, a reduced diameter portion54of member22between flanges40,42, defines a recess56through which pins26,28, extend and which is configured to receive springs30and pawls34disposed on pins26and28, respectively. Another reduced diameter portion58of member22is disposed at the opposite axial end of member22and configured to support a portion of outer member24thereon.

Outer member24is configured to transfer torque to driven device14. Member24is annular in construction and disposed about axis38radially outwardly of inner member22. Member24defines a reduced diameter portion60at one axial or longitudinal end of member24configured to be received on portion58of inner member22. A thin film of lubricant may be disposed between portion60of member24and portion58of member22. Alternatively, a bearing (e.g. sleeve bearing or roller bearing) may be disposed between members58,60. The diameter of the radially outer surface of portion60may vary to define a shoulder62against which a gear or sprocket64may be mounted for connection to input member18of driven device14either directly or, for example, through a belt. Member24also defines an enlarged diameter portion66at an opposite axial or longitudinal end of member24. The inner diameter of portion66is sized to receive flanges40,42of inner member22while allowing space for pins32which are disposed radially outwardly of flanges40,42. Portion66defines a pair of radially extending walls68,70at opposite longitudinal ends of portion66. Walls68,70, define a plurality of axially aligned, circumferentially spaced bores72,74, respectively, configured to receive opposite longitudinal ends of pins32such that a portion of each pin32intermediate the longitudinal ends of the pin32and facing pawls34is exposed.

Spring engagement pins26provide a means for retaining one end of each spring30such that springs30may be expanded and returned to an unstressed state. The longitudinal ends of pins26may be received within bores46,48, respectively, in flanges40,42of inner member22. In the illustrated embodiment, there are half as many spring engagement pins26as there are mounting pins28and the pins26,28are arranged such that a single spring engagement pin26is disposed circumferentially between two mounting pins28. Each spring engagement pin26may be configured to retain an end of two springs30(i.e. the end of a spring supported on each of the adjacent mounting pins28).

Mounting pins28provide a means for mounting springs30and pawls34on inner member22. The longitudinal ends of pins26,28may be received within bores48,52, respectively, in flanges40,42of inner member22. Each mounting pin28is configured to support a single spring30and a single pawl34and defines an axis76about which the pawl34may pivot as discussed in greater detail hereinbelow.

Springs30are provided to bias pawls34to a disengagement position (seeFIG. 5A). Springs30may comprise conventional coil springs. A spring30may be disposed about each mounting pin28. Referring toFIG. 4, springs30may be disposed on either side of a corresponding pawl34with the side determined by the orientation of the pawl34. Each spring30may have a first end coupled to spring engagement pin26and a second end coupled to pawl34. Alternative, the end coupled to spring engagement pin26may be coupled to a surface of member22.

Clutch engagement pins32provide a means for pawls34to selectively engage outer member24in order to couple inner and outer member22,24for rotation. Pins32may comprise dowel pins. Opposite longitudinal ends of each pin32are received within bores72,74in walls68,70, respectively, of member24such that a rounded surface of each pin32intermediate the longitudinal ends of the pin32may be engaged by pawls34. The use of pins32with rounded surfaces as opposed to conventional grooves formed in the surface of outer member24represents a significant improvement relative to conventional clutches. The use of pins32makes manufacturing of outer member24less complex and eliminates the need for heat treatment of the surface of member24. The elimination of the sharp corners and edges found in typical grooves reduces stress on the clutch, thereby increasing the clutch's strength and durability and makes it easier to prevent undesirable contact between the pawls34and outer member24and any resulting damage. Further, the rounded surfaces of pins32make it easier to control the position of engagement by pawls34thereby promoting more even load sharing and a reduction in impact loads thereby reducing the size and manufacturing cost of the clutch. Further still, the use of pins32rather than conventional grooves reduces the clearance required to disengage the pawls34and therefore eliminates the need for relative motion between the inner and outer members of the clutch to disengage the clutch.

Pawls34are provided to engage pins32in order to transfer torque from inner member22to outer member24. Each pawl34is supported on a mounting pin28and pivots about the rotational axis76extending through pin28. Referring toFIG. 5A, each pawl34may, in cross-section, define radially inner and outer surfaces78,80that are substantially straight and extend substantially parallel to one another. Surfaces78,80extend circumferentially relative to axis38or axis76when pawl34is in a disengagement position as shown inFIG. 5Aand the radially outer surface80may be longer than the radially inner surface78. Pawl34may further define a surface82extending in a generally radial direction relative to axis38or axis76between surfaces78,80, that is substantially straight, but curves at either end to meet surfaces78,80. Pawl34may further define a curved, concave surface84having one end extending from an end of surface78opposite the end at which surface78meets surface82. Finally, pawl34may define engagement surface86extending between the opposite end of concave surface84and surface80. The engagement surface86may be curved and defines an arcuate segment of a circle that is concentric with the bore in pawl34through which mounting pin28extends (i.e. is centered about axis76) thereby permitting disengagement of the clutch without relative motion between members22,24. Alternatively, the engagement surface86need not be concentric with the bore (with a resulting increase in torque density) if relative motion is acceptable for disengagement of the clutch. Although a particular configuration for pawl34has been described herein, it should be understood that pawl34could be configured in a variety of ways. Pawls34may be configured or shaped such that a center of gravity (illustrated by dot88inFIG. 5A) is offset from axis76and, in particular, such that a radial distance from rotational axis38to the center of gravity88is greater than a radial distance from axis38to the axis76about which pawl34pivots. As the rotational speed of driving device12increases—and therefore the rotational speed of inner member22of clutch16increases—the angular acceleration (i.e. the rate at which the speed is increasing) is transferred through mounting pins28to pawls34creating a force vector90having an origin at axis76. A corresponding reaction force vector92is created in the opposite direction with an origin at the center of gravity88of the pawl34. Because the origins are offset, the combination of the force vectors combine to cause rotation of the pawl34until the engagement surface86of pawl34is brought into engagement with one of pins32at an engagement position as shown inFIG. 5B. Once engaged, friction between the pawl34and pin32maintains engagement until the driving torque is removed. Because pawls34are actuated by angular acceleration rather than speed as in a centrifugal clutch or a conventional ratchet and pawl clutch, the pawls34engage more quickly and before the driving device12reaches its normally operating speed. As a result, impact loads are reduced relative to those found in conventional centrifugal and ratchet and pawl clutches and the overall size of the clutch can be reduced.

Pawls34are arranged two groups to provide bi-directional engagement. In particular, pairs of pawls34A,34B are located circumferentially adjacent to one another on mounting pins28that are disposed on either side of a spring engagement pin26. The pawls34A,34B are arranged in opposite orientations. Rotation of member22in one rotational direction (counterclockwise in the illustrated embodiment) causes pawl34A to move (by clockwise rotation about axis76) from a disengagement position shown inFIG. 5Awherein pawl34A is disengaged from pins32to permit relative rotation of the inner and outer members22,24to an engagement position shown inFIG. 5Bwherein pawl34A is engaged with one of the pins32to cause rotation of member24in the same (counterclockwise) rotational direction. Because of the opposite orientation of pawl34B, the clockwise rotation of pawl34B imparted by force vectors90,92keeps pawl34B from moving into an engagement position. Rotation of member22in the opposite rotational direction (clockwise in the illustrated embodiment) causes pawl34B to move (by counterclockwise rotation about axis76) from a disengagement position shown inFIG. 5Awherein pawl34B is disengaged from pins32to permit relative rotation of the inner and outer members22,24to an engagement position wherein pawl34B is engaged with one of the pins32to cause rotation of member24in the same (clockwise) rotational direction. Again, because of the opposite orientation of pawl34A, the counterclockwise rotation of pawl34A imparted by force vectors90,92keeps pawl34A from moving into an engagement position.

It should be understood that the orientation and operation of clutch20could be modified in several ways. For example, in the illustrated embodiment, springs30bias pawls34to a disengagement position and angular acceleration resulting from rotation of inner member22causes pawls34to move to an engagement position with pins32. In an alternative embodiment configured for use as a backstopping clutch, springs30may bias pawls34to an engagement position while angular acceleration resulting from rotation of inner member22causes pawls34to move to a disengagement position. In this embodiment, pawls34are configured such that a center of gravity is offset from axis76and, in particular, such that a radial distance from rotational axis38to the center of gravity88is less than a radial distance from axis38to the axis76about which pawl34pivots. As a result, the combination of force vectors90,92urges pawls34to a disengaged position. In one variation of this configuration, pawls34may all have the same orientation (as opposed to the opposite orientations of pawls34A,34B in the illustrated embodiment) such that the clutch may function as a backstopping clutch rather than a bi-directional overrunning clutch. The clutch would have several advantages relative to conventional sprag or ramp-roller backstopping clutch because the clutch would provide a higher torque density yet be simpler in constructions and less costly. In another alternative embodiment, pins32may be disposed on a radially outer surface of inner member22while pawls34are mounted on outer member24. Pawls34may again be configured such that the center of gravity causes a desired rotation of pawls34to engage or disengage pins32(depending again on whether the pawls are biased to a disengagement position or engagement position, respectively).

Referring now toFIGS. 6-8, a clutch94in accordance with another embodiment of the present invention is illustrated. Clutch94may include an inner member96, an outer member98, an actuator100, a plurality of spring engagement pins102, a plurality of mounting pins104, a plurality of springs106, a plurality of clutch engagement pins108, and a plurality of pawls110. Clutch94is intended for use in lower speed applications as compared to clutch20wherein assistance may be required to move pawls110from a disengagement position to an engagement position.

Inner member96is configured to transfer torque to input member18of driven device14. Member96is annular in construction and configured to receive a shaft (not shown) extending from or to device14(e.g., the shaft may comprise output member18or may be coupled to input member18). Member96may define a plurality of splines112(seeFIG. 6) configured to engage a matching set of splines in the shaft in order to couple member96to the shaft for rotation about a rotational axis114. The diameter of the radially outer surface of member96varies such that member96defines radially outwardly extending flanges116,118disposed at opposite axial or longitudinal ends of member96. Flanges116,118, define a plurality of axially aligned, circumferentially spaced bores120,122respectively, configured to receive opposite longitudinal ends of pins108such that a portion of each pin108intermediate the longitudinal ends of the pin108and facing pawls110is exposed.

Outer member98is configured to receive an input torque from output member16of driving device12which may be selectively transferred to inner member96of clutch94as described in greater detail hereinbelow. Member98is annular in construction and configured to receive inner member96and a portion of actuator100therein. Member98is disposed about axis114radially outwardly of inner member96. Member98defines a bore124configured to receive a shaft (not shown) extending from or to device12(e.g., the shaft may comprise input member16or may be coupled to input member16). It should be understood, however, that member98may alternatively include a driven gear or pulley attached to outer member98. Member98is further configured to receive spring engagement pins102and mounting pins104. In particular, a radially extending wall126defines bores128,130configured to receive one longitudinal end of pins102,104, respectively. The radially inner surface of member98further defines a plurality of longitudinally or axially extending recesses132configured to receive pins104.

Actuator100is provided to force pawls110into engagement with pins108upon rotation of outer member98in response to a driving torque provided by driving device12or in response to an external force acting on actuator100. Actuator100is annular in construction and disposed about axis114. A plurality of magnets134may extend from one side of actuator100for use in creating relative rotation between actuator100and outer member98(e.g. by application of an external force). A plurality of tangs136extend from the opposite side of actuator100and are received within outer member98. In particular, and with reference toFIGS. 9A-B, tangs136are disposed circumferentially between two pawls110such that, upon relative rotation between outer member98and actuator100, tangs136engage pawls110and urge pawls110into engagement with pins108. Although tangs136appear substantially rectilinear in cross-section in the illustrated embodiment, it should be understood that the shape of tangs136may be varied and may, for example, comprise rounded pins. Actuator100may be placed in frictional engagement with a stationary member in driving or driven devices12,14or another stationary object such that rotation of outer member98results in a period of relative rotation wherein pawls110are brought into engagement with tangs136by virtue of rotation of outer member98. Upon engagement of pawls110with tangs136, actuator100rotates with outer member98. Actuator100may be placed in frictional engagement with the stationary member by electromagnetic force or magnetic force, fluid force or spring force. Actuator100may be returned to this position when driving torque is no longer provided by the actions of springs106which force pawls110, and therefore tangs136back to a disengaged position. Alternatively, a separate spring (not shown) or reverse rotation of member98can be used to return actuator100to a position where tangs136are disengaged from pawls110.

Spring engagement pins102provide a means for retaining springs106such that springs106may be expanded and returned to an unstressed state. The longitudinal ends of pins102may be received within bores128in wall126of outer member98. In the illustrated embodiment, there are half as many spring engagement pins102as there are mounting pins104and the pins102,104are arranged such that a single spring engagement pin102is disposed circumferentially between two mounting pins104.

Mounting pins104provide a means for mounting pawls110on outer member98. The longitudinal ends of pins104may be received within bores130in wall126of outer member98and may be press fit within bores130. Each mounting pin104is configured to support a single pawl110and defines an axis about which the pawl110may pivot as discussed in greater detail hereinbelow.

Springs106are provided to bias pawls110to a disengagement position (seeFIG. 9A). Referring toFIGS. 10-11, springs106may comprise a leaf spring having a radially inner side configured to receive pin102and a radially outer side configured to engage pawls110on either side of pin102to retain pawls110and bias pawls110to a disengagement position. Engagement of a pawl110by a tang136of actuator100urges the pawl110to an engagement position (seeFIG. 9B) against the force of spring106. It should be understood that springs106may assume a variety of forms. For example, springs106may comprise coil springs disposed about mounting pins104and coupled at one end to a corresponding pawl110and at another end to a spring engagement pin as in clutch20or to a surface of member98.

Clutch engagement pins108provide a means for pawls110to selectively engage inner member96in order to couple inner and outer member96,98for rotation. Pins108may comprise dowel pins. Opposite longitudinal ends of each pin108are received within bores120,122in flanges116,118, respectively, of member96such that a rounded surface of each pin108intermediate the longitudinal ends of the pin108may be engaged by pawls110. Again, the use of pins108with rounded surfaces as opposed to conventional grooves formed in the surface of inner member96represents a significant improvement relative to conventional clutches. The use of pins108makes manufacturing of inner member96less complex and eliminates the need for heat treatment of the surface of member96. The elimination of the sharp corners and edges found in typical grooves reduces stress on the clutch, thereby increasing the clutch's strength and durability and makes it easier to prevent undesirable contact between the pawls110and inner member96and any resulting damage. Further, the rounded surfaces of pins108make it easier to control the position of engagement by pawls110thereby promoting more even load sharing and a reduction in impact loads thereby reducing the size and manufacturing cost of the clutch. Further still, the use of pins108rather than conventional grooves reduces the clearance required to disengage the pawls110and therefore eliminates the need for relative motion between the inner and outer members of the clutch to disengage the clutch.

Pawls110are provided to engage pins108in order to transfer torque from outer member98to inner member96. Each pawl110is supported on a mounting pin104and pivots about the rotational axis extending through pin104. Referring toFIG. 9A, each pawl110may, in cross-section, define radially inner and outer surfaces138,140that are substantially straight and extend substantially parallel to one another. Surfaces138,140extend circumferentially relative to axis114and the rotational axis of mounting pin104when pawl110is in a disengagement position as shown inFIG. 9A. The radially outer surface140is shorter than the radially inner surface138and is located intermediate the circumferential ends of the pawl110. Pawl110further defines a concave surface142configured to receive mounting pin104and that is disposed on one circumferential side of outer surface140. Pawl110further defines a curved or arcuate surface144configured to engage a tang136on actuator100that is disposed on the opposite circumferential side of outer surface140. Pawl110further defines an engagement surface146extending between curved surface144and outer surface140. The engagement surface146may be curved and defines an arcuate segment of a circle that is concentric with a circle defined by surface142centered about the axis extending through pin104thereby permitting disengagement of the clutch without relative motion between members96,98. Alternatively, the engagement surface146need not be concentric with surface142(with a resulting increase in torque density) if relative motion is acceptable for disengagement of the clutch. Although a particular configuration for pawl110has been described herein, it should again be understood that pawls110could be configured in a variety of ways. As referenced hereinabove, upon rotation of outer member98in response to a driving torque, relative motion is created between outer member98and actuator100. As shown inFIG. 9B, surface144engages a corresponding tang136forcing pawl110to pivot about a rotational axis of mounting pin104. This action forces engagement surface146into engagement with pin108to transfer torque to inner member96and driven device14. Once engaged, friction between the pawl110and pin108maintains engagement until the driving torque is removed or an overrunning condition occurs. Springs106then urge pawls110back to a disengagement position as shown inFIG. 9A.

Pawls110are again arranged in two groups to provide bi-directional engagement. In particular, pairs of pawls110A,110B are located circumferentially adjacent to one another on mounting pins104that are disposed on either side of a spring engagement pin102. The pawls110A,110B are arranged in opposite orientations. Rotation of member98in one rotational direction (clockwise in the illustrated embodiment) causes pawl110A to move (by clockwise rotation about the axis of pin104) from a disengagement position shown inFIG. 9Awherein pawl110A is disengaged from pins108to permit relative rotation of the inner and outer members96,98to an engagement position shown inFIG. 9Bwherein pawl110A is engaged with one of the pins108to cause rotation of member96in the same (clockwise) rotational direction. Rotation of member98in the opposite rotational direction (counterclockwise in the illustrated embodiment) causes pawl110B to move (by counterclockwise rotation about the axis of pin104) from a disengagement position shown inFIG. 9Awherein pawl110B is disengaged from pins108to permit relative rotation of the inner and outer members96,98to an engagement position wherein pawl110B is engaged with one of the pins108to cause rotation of member96in the same (counterclockwise) rotational direction.

An overrunning clutch20or94in accordance with the present invention is advantageous relative to conventional electrical, fluid or manually actuated clutches because the clutch20or94is less complex and less costly. The clutch20or94is also advantageous relative to conventional mechanically actuated clutches. As compared to conventional centrifugal clutches, no sliding friction is created thereby reducing heat and wear on the clutch. Further, because the inventive clutch20or94is not dependent on the speed of the driving device, the clutch is smaller than conventional centrifugal clutches while transmitting the same torque. As compared to conventional ratchet and pawl clutches, the inventive clutch does not require sharp grooves in the surface of one of the clutch members nor relative motion between the clutch members to allow the pawls to clear the grooves. As a result, the clutch20or94is easier and less costly to manufacture and suffers less stress upon engagement. Further, the pawls34of110engage the pins32or108at a relatively precise location thereby insuring relatively equal load sharing.

While the invention has been shown and described with reference to one or more particular embodiments thereof, it will be understood by those of skill in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.