Flyweight actuated clutch

Abstract: A flyweight actuated clutch assembly (50), e.g. for pneumatic starter, comprises a first clutch member (80), e.g. operatively associated with a starter output shaft (60), a second clutch member (90) associated with a starter input shaft and axially displaceable relative to the first clutch member (80) from an engaged position to a disengaged position, a plurality of first flyweights (102) and a plurality of second flyweights (104). The first flyweights (102) are displaceable radially outwardly in response to the rotational speed of the output shaft (60) so as to generate a disengagement bias force which biases the second clutch member (90) out of engagement with the first clutch member (80). The second flyweights (104) are displaceable radially outwardly in response to the rotational speed of the input shaft so as to generate a proengagement bias force which opposes the disengagement bias force.

Description: Technical Field The present invention relates generally to clutches for use on unidirectional drive systems, and more specifically to a fly-ball actuated clutch particularly suitable for use in a starter for starting engines, such as aircraft turbine engines. Background Art Clutches are commonly utilized in unidirectional drive systems for transmitting drive torque from a drive shaft to a driven shaft. For example, starters of the type commonly used to start engines, in particular the turbine engines of modern gas turbine powered aircraft, often employ a pawl and ratchet type clutch which functions to transmit rotational drive torque from a drive shaft of the starter to drive the engine being started to starting speed. One type of starter often employing a pawl and ratchet clutch is the pneumatic starter, also known as an air turbine starter, such as disclosed, for example, in United States Patent Nos. 3,727,733; 4,899,534; 4,914,906; and 4,926,631. A pawl and ratchet clutch of the type commonly used in such pneumatic starters includes a toothed ratchet member mounted on a central drive shaft and a plurality of pivotal pawls supported from and rotating with a driven output shaft disposed coaxially about the drive shaft. The pawls are operatively disposed at circumferentially spaced intervals about the ratchet member in cooperative relationship therewith. Each pawl is biased to pivot radially inwardly by a leaf spring operatively associated therewith to engage a tooth of the ratchet member thereby coupling the drive shaft in driving relationship to the driven output shaft so long as the pawls remain engaged with the teeth of the ratchet member. The drive shaft is connected, either directly or through suitable reduction gearing as desired, to the shaft of the pneumatic starter turbine, which is powered by extracting energy from a flow of pressurized fluid passed through the turbine of the starter. To start the turbine engine, the output end of the driven output shaft of the starter is connected, for example by mating splines, to an engine shaft operatively connected to the main engine shaft through a gear box, and pressurized fluid, typically compressed air, is passed through the turbine of the pneumatic starter. As the starter turbine extracts energy from the compressed air passing therethrough, the drive shaft of the starter turbine is rotated to in turn rotatably drive the output shaft of the starter, and consequently the turbine engine shaft connected thereto, through the engagement of the pawls pivotally mounted to the output shaft with the ratchet member mounted to the drive shaft. Typically, the starter is designed to accelerate the engine shaft from zero to a predetermined cut-off speed, typically of about 5000 revolutions per minute, in about one minute or less. Once engine light-off has occurred and the engine shaft is rotating at the desired cut-off speed, the flow of pressurized air to the starter turbine is terminated. With the flow of pressurized air to the starter turbine shut-off, the drive shaft of the starter rapidly slows down. Consequently, the ratchet member mounted to the starter drive shaft also rapidly slows down, while the pawls supported from the starter output shaft continue to rotate with the shaft of the operating turbine engine at the relatively high cut-off speed. The pawls become disengaged from the ratchet member when the rotational speed of the output shaft exceeds a threshold speed whereat the pawls lift-off of the ratchet member, that is pivot radially outwardly out of contact with the teeth of the ratchet member, under the influence of the centrifugal forces acting thereon due to the continued rotation of the pawls at the relatively high speed of the engine shaft. The pawls remain disengaged from the ratchet member so long as the rotational speed of the engine shaft remains high enough that the centrifugal forces acting on the pawls exceed the opposing moment imposed on the pawls by the force of the bias springs. When the turbine engine is later shut-down, the operating speed of the engine shaft of the turbine engine to which the output shaft of the starter is connected decreases as the turbine engine spools down. As the starter output shaft slows down, the centrifugal force on the pawls consequently decreases and the force of each bias spring progressively pivots its associated pawl radially inwardly again toward the ratchet member until each pawl again contacts the ratchet teeth on the non-rotating ratchet member so as to ratchet in a position to allow for reengagement of the clutch. The speed at which the reengagement of the pawls with the ratchet member occurs, commonly referred to as the reengagement speed, is less than the pawl lift-off speed by an amount commonly referred to as the clutch hysteresis. On pawl and ratchet clutches, when reengagement occurs with the ratchet member rotating at too high of a rotational speed relative to the pawls, a crash reengagement occurs which often results in substantial, if not catastrophic, damage to the clutch. Crash reengagement generally takes place when following an aborted turbine start occurring after the turbine has exceeded pawl lift-off speed, the starter is reactivated in an attempt to restart the turbine engine, before the shaft of the turbine engine has spooled down to a speed below that at which pawl reengagement occurs. When air flow to the starter is reinitiated without the pawls and ratchet being engaged, there is no load on the starter and, consequently, the starter shaft and the ratchet member mounted thereto rapidly accelerate to a free running speed which is substantially above the pawl reengagement speed. As the turbine engine continues to spool down to the pawl reengagement speed, the pawls will eventually pivot inwardly, as the centrifugal force urging them outwardly deteriorates, until the pawls recontact the ratchet member. With the ratchet member rotating at a free running speed substantially greater than the speed at which the pawls are now rotating, a violent reengagement will take place. To avoid such a crash reengagement, it is customary to delay restart of the turbine engine until it is certain that the turbine engine has slow down to the point at which the pawls have already reengaged that ratchet member before the starter is reactivated by supplying air flow to the starter turbine. It would be desirable, however, to provide a clutch assembly which is not suspectable to crash reengagement, but rather facilitates reengagement without a crash reengagement. In GB-A-866 046 there is disclosed a clutch assembly as defined in the precharacterizing portion of independent claim 1 utilizing radially displaceable balls to both urge engagement and disengagement between the members of the clutch assembly on the engine and starter turbine. There is apparently an equal number of engagement balls and disengagement balls and the overall mass of the engagement and disengagement balls is apparently the same. Reengagement following an aborted turbine start is facilitated since the engagement balls force the disengagement balls out of their disengaging positions as soon as the turbine engine has decelerated to essentially the speed of the starter turbine to permit reengagement of the clutch members. Using engagement and disengagement balls of equal overall mass minimizes proengagement ratcheting, but it has been found that late reengagement can occur which can harm the teeth of the clutch members. Disclosure of Invention It is an object of the present invention to provide a clutch assembly suitable for use in transmitting rotational drive torque from a driving member to a driven member which further facilitates engagement without crash engagement in the event that reengagement occurs after the driven member has reached a speed greater than that of the driving member. To achieve this, there is provided in accordance with the invention a clutch assembly for use in transmitting rotational drive torque from a driving member to a driven member, comprising: a first clutch member operatively associated with the driven member whereby said driven member rotates with said first clutch member, said first clutch member having engagement means extending therefrom; a second clutch member operatively associated with the driving member whereby said second clutch member rotates with said driving member, said second clutch member having engagement means extending therefrom adapted to engage the engagement means of said first clutch member, said second clutch member being axially displaceable relative to said first clutch member between a first position whereat the engagement means of said second clutch member is operatively engaged with the engagement means of said first clutch member so as to transmit the rotational drive torque from the driving member to the driven member and a second position whereat the engagement means of said second clutch member is disengaged from the engagement means of said first clutch member; first counterweight means for generating a bias force axially biasing said second clutch member toward the disengaged position, said first counterweight means being displaceable radially outwardly in response to the rotational speed of said driven member, the disengagement bias force generated having a magnitude which varies with the radial position of said first counterweight means, the magnitude increasing as the first counterweight means is displaced further radially outwardly; second counterweight means for generating a proengagement bias force opposed to said disengagement bias force, said second counterweight means being displaceable outwardly in response to the rotational speed of the driving member, the proengagement bias force generated having a magnitude which varies with the radial position of said second counterweight means, the magnitude increasing as the second counterweight means is displaced further radially outwardly, characterized in that said first counterweight means has first overall mass and said second counterweight means has a second overall mass, the second overall mass being greater than the first overall mass. Advantageous features of the clutch assembly are recited in the dependent claims. Using engagement counterweight means having a greater overall mass than the disengagement counterweight means allows the ratcheting reengagement of the clutch members to be achieved at starter turbine speeds substantially less than the turbine engine speed since the engaging balls push the disengaging balls radially inward before the speeds become equal. Thus, as soon as the two clutch members rotate at the same speed the heavier engagement counterweight means can cam the two clutch members into engagement. Brief Description of the Drawings The aforementioned and other features and advantages of the present invention will become more apparent in light of the following detailed description of the invention and the embodiment thereof illustrated in the accompanying drawing, wherein: Figure 1 is a partially-sectioned side elevational view of a pneumatic starter incorporating an embodiment of the clutch assembly of the present invention; Figure 2 is a sectional side elevational view of the embodiment of the clutch assembly of the present invention shown in Figure 1 illustrating the disposition of the clutch assembly at standstill; Figure 3 is a sectional side elevational view of the embodiment of the clutch assembly of the present invention shown in Figure 1 illustrating the disposition of the clutch assembly while transmitting drive torque; Figure 4 is a sectional side elevational view of the embodiment of the clutch assembly of the present invention shown in Figure 1 illustrating the disposition of the clutch assembly at disengagement; and Figure 5 is a sectional side elevational view of the embodiment of the clutch assembly of the present invention shown in Figure 1 illustrating the disposition of the clutch assembly while free-running after disengagement. Best Mode For Carrying Out The Invention Referring now to Figure 1, there is depicted therein a pneumatic starter 10 of the general type often utilized to start gas turbine engines, such as for example aircraft turbine engines. The pneumatic starter 10, also known as an air turbine starter, includes a turbine wheel 20 which is driven by a compressed gas, most commonly compressed air from an external supply, passing therethrough so as to extract energy from the gas and convert the extracted energy to mechanical energy in a manner well known in the art. Although the present invention is described herein with reference to an air turbine starter, it is to be understood that the clutch assembly of the present invention has application to any unidirectional drive system wherein a clutch is utilized to transmit rotation from a driving shaft to a driven shaft. The pneumatic starter 10 has a gear housing 12 disposed between and mounted to an inlet housing 14 and a transmission housing 16. The inlet housing 14 defines a flow chamber 15 having an axial flow inlet 25 and an annular flow outlet 35. Disposed within the flow chamber 15 intermediate therebetween is turbine wheel 20 having a plurality of blades 22 disposed about its outer circumference and a central axially extending shaft 24. The turbine wheel 20 is mounted to its shaft 24 such that the shaft 24 is driven in rotation about its axis as the turbine wheel 20 is caused to rotate by the compressed air supplied from an external source thereof to the flow inlet 25 and passing through the turbine blades 22 to the flow outlet 35. A turbine shield 17, having a plurality of stator vanes 19 disposed circumferentially thereabout, may be disposed within the flow chamber 15 forward of the turbine wheel 20 to ensure that the incoming compressed air is properly directed through the turbine blades 22 in a desired manner. A flow deflector 21 may be disposed downstream of the turbine wheel 20 to direct the exhaust air from the turbine blades 22 to the flow outlet 35. The energy extracted from the compressed air via the turbine wheel 20 is transmitted through the turbine shaft 24 to drive one or more planetary gear assemblies 30, for example three gear assemblies disposed at equal circumferentially spaced intervals about the end 26 of the turbine shaft 24. Each planetary gear assembly 30 comprises a drive gear 32 on one end of a central support shaft 34 rotatably supported via bearing means 36, for example roller bearings, on a stationary shaft 33, and a second gear 38 also provided on the support shaft 34 on the other end thereof. Advantageously, the drive gear 32, the second gear 38 and support shaft 34 may be formed as a single integral member. The drive gear 32 of each gear assembly 30 is operatively connected via intermeshing teeth members to a sun gear 28 provided on end 26 of the turbine shaft 24 and the second gear 38 of each planetary gear assembly 30 is operatively connected via intermeshing teeth members to a ring gear 40 disposed coaxially about the axis 11 of the turbine shaft 24. Extending axially outwardly through a central opening 18 in the transmission housing section 16 of the starter 10 and coaxially along the axis 11 thereof, is an output shaft 60 which has a distal end 62 provided with means, such as for example splines 64, for engaging an engine shaft (not shown) in the gear box of the turbine engine (not shown), such as an aircraft turbine engine, on which the starter 10 is utilized to start the turbine engine. The output shaft 60 is rotatably supported on bearing means 66 disposed in the central opening 18 and carried on housing section 16. The ring gear 40 has a generally cylindrical member which extends axially about the axis 11. A first set of gear teeth 41 is disposed about the inner circumference of the inboard end of the ring gear 40, which teeth 41 operatively intermesh with the teeth 31 of the second gears 38 of each planetary gear 30. A second set of teeth 43 is disposed about the inner circumference of the outboard end of the ring gear 40, which operatively intermesh with mating teeth of a ring gear carrier 50 disposed coaxially about the axis 11 and supported for rotation about the axis 11 on bearing 29 mounted on a central strut member 39 extending inwardly from the housing 12. Referring now to Figure 2, the ring gear carrier 50 advantageously comprises a first member 52 supported for rotation on the bearing 29 and having a flange portion extending radially outwardly therefrom and a second member 54 having a radial flange portion which is mounted to the flange portion of the first member 52 so as to extend radially outwardly therefrom and a generally cylindrical body portion extending axially outwardly therefrom. The outer circumferential portion of the flange of the second member 54 is provided with teeth 53 which operatively intermesh with the teeth 43 of the ring gear 40. A second set of teeth 55 is disposed about the inner circumference of the cylindrical portion 56 of the second member 54 of the ring gear carrier 50. A clutch assembly 70 is operatively disposed between the ring gear carrier 50 and the output shaft 60. The clutch assembly includes a first clutch member 80 having engagement means 82 associated therewith, and second clutch member 90 having engagement means 92 associated therewith. The first clutch member 80 is operatively associated with the output shaft 60 whereby the output shaft 60 rotates with the first clutch member 80, while the second clutch member 90 is operatively associated with the drive shaft 24 of the starter turbine 10, whereby the second clutch member 90 is driven in rotation by the drive shaft 24. The engagement means 82 of the first clutch member 80 and the engagement means 92 of the second clutch member 90 are adapted to engage each other so as to transmit rotational drive torque when engaged from the drive shaft 24 to the output shaft 60. The first clutch member 80, which may be formed integrally with the output shaft 60 or may be a separate member mounted to the output shaft 60, is axially stationary during operation, while the second clutch member 90 is axially displaceable relative to said first clutch member 80 between a first position, as illustrated in Figure 3, whereat the engagement means 92 of the second clutch member 90 is operatively engaged with the engagement means 82 of the first clutch member 80 so as to transmit the rotational drive torque from the drive shaft 24 to the output shaft 60, and a second position, as illustrated in Figure 4, whereat the engagement means 92 of the second clutch member 90 is disengaged from the engagement means 82 of the first clutch member 80. Advantageously, the second clutch member 90 may comprise an annular disc-like member 94 having a set of teeth 95 disposed about its outer circumference and adapted to engage with the teeth 55 disposed about the inner circumference of a cylindrical flange 56 extending axially outboardly from the flange 54 of the ring gear carrier 50. The teeth 95 and 55 advantageously comprise engaging spline means which mate such that the second clutch member 90 is axially displaceable along the flange 54 and driven in rotation with the ring gear carrier 50 which is driven by the drive shaft 24. Most advantageously, each of the spline means 95 and 55 comprises a helical spline disposed at an angle to the axis 11, preferably of about 45 degrees. A resilient bias means 96 may be provided for biasing the second clutch member 90 towards the first clutch member 80 thereby ensuring that the engagement means 92 of the second clutch member 90 are in engagement with the engagement means 82 of the first clutch member 80 when the clutch assembly is at standstill as illustrated in Figure 2. Advantageously, the bias means 96 may comprise a wave spring coaxially disposed about the axis 11 and between member 52 of the ring gear carrier 50 and the back side of the second clutch member 90. Additionally, a second resilient bias means 97 may be provided for biasing the ring gear carrier 50 toward the output shaft 60 thereby assisting the first bias means 95 by positioning the ring gear carrier 50 outboardly toward the output shaft 60 when the clutch assembly is at standstill. Advantageously, the bias means 97 may comprise a wave spring coaxially disposed about the axis 11 and between the bearing means 29 and a radially inwardly directed flange member 58 of the ring gear carrier 50. The clutch assembly 70 further includes speed responsive clutch biasing means 100 for differentially biasing the second clutch member 90 out of engagement with the first clutch member 80 whenever the rotational speed of the first clutch member 80, which rotates with the output shaft 60, is sufficiently greater than the rotational speed of the second clutch member 90, which is driven by the turbine shaft 24, that the disengagement bias force overcomes the spring force. In the preferred embodiment of the invention, the speed responsive clutch biasing means also comprises means for neutralizing the bias towards disengagement as the rotational speed of the second clutch member 90 approaches the rotational speed of the first clutch member 90. Thus, in the event of a clutch reengagement following an abortive start, the speed responsive biasing means 100 is operative in response to the increasing rotational speed of the second clutch member 90 driven by the turbine shaft 24 to neutralize the differential force biasing the second clutch member 90 towards disengagement from the first clutch member 80 as the rotational speed of the accelerating second clutch member 80 approaches the rotational speed of the decelerating first clutch member 80, thereby allowing the resilient bias spring means 96 to exert sufficient force upon the second clutch member 90 to bring the engagement means 92 thereof and the engagement means 82 of the first clutch member 80 into ratcheting engagement before the speed of the decelerating first clutch member 80 slows down to the same speed as the accelerating second clutch member 90, thus avoiding a crash reengagement. Referring now to Figures 2 through 5, the speed responsive biasing means 100 advantageously comprises a first counterweight means 102 being selectively positionable in response to the rotational speed of the output shaft 60 so as to generate a disengagement bias force acting to increasingly bias the second clutch member 90 away from engagement with the first clutch member 80 as the rotational speed of the output shaft 60 increases, a second counterweight means 104 being selectively positionable in response to the rotational speed of the turbine shaft 24 so as to generate a bias force which counteracts the disengagement bias force generated by the first counterweight means 102, this engagement bias force increasing as the rotational speed of the turbine shaft 24 increases, and means for supporting the first and second counterweight means 102 and 104 in operative association with the first and second clutch members 80 and 90. The support means may comprise a first support member 110 adapted to support the first counterweight means 102 and a second support member 120 adapted to support the second counterweight means 104. The first support member 110 has a cylindrical central portion 112 by which the first support member 110 is slidably mounted to an axially extending shaft 114 mounted to or formed integrally with the output shaft 60 so as to rotate therewith and has an annular end face extending radially outwardly and disposed in facing relationship to an opposed end face 81 of the first clutch member 80. The first support member 110 may be provided with track means 116 which in operative association with the opposing end face 81 of the first clutch member 80 form a plurality of races 115, each of which provides a path along which the first counterweight means 102, which advantageously comprises a plurality of flyweight means, one per race, such as for example spherical balls or cylindrical slugs, travel in response to the speed of the output shaft 60. The end face 81 may be provided with pockets 83 formed therein as extensions of the races 115. The second member 120 is supported for rotation relative to the first member 110 on bearing 122 disposed coaxially about the cylindrical portion 112 of the first member 110, and has a radially outwardly extending annular end face 124 disposed in opposed facing relationship to the radially inwardly directed flange member 58 of the ring gear carrier 50. The opposing end face 59 of the flange member 58 of the ring gear carrier 50 may be provided with track means 126 which in operative association with the opposing face of the second member 120 form a plurality of races 125, each of which provides a path along which the second counterweight means 104, which advantageously comprises a plurality of flyweight means, one per race, such as for example spherical balls or cylindrical slugs, travel in response to the speed of the ring gear carrier 50 which is driven by the turbine shaft 24. The second member 120 may be provided with pockets 63 formed therein as extensions of the races 125. Additionally, the second member 120 has a circumferential flange portion 126 extending radially outwardly from its outer circumferential surface and adapted to abut against an outboardly facing surface of the second clutch member 90. When the clutch assembly of the present invention is at standstill, that is when both the air turbine shaft 24 and the output shaft 60 are at rest, i.e. not rotating, as illustrated in Figure 2, the first flyweight means 102 and the second flyweight means 104 are both at rest and neither are generating any bias forces. In this condition, the second clutch member 90 is biased forwardly, that is outboardly, by the first resilient spring means 96 such that the engagement means 92 thereof is engaged with the engagement means 82 of the first clutch member 80. However, a small axial gap 5 remains between the clutch assembly and the circumferential lip 57 of the ring gear carrier 50. Upon the supply of motive fluid to the air turbine, the turbine shaft 24 begins to rotate and rapidly accelerate from rest to a predetermined cut-off speed, typically in the range of 4500 to 6500 revolutions per minute. Whenever torque is applied to drive the turbine shaft 24, as illustrated in Figure 3, the axial gap 5 is eliminated and the ring gear 40 is driven in rotation in response thereto, which in turn drives the ring gear carrier 50 and thus the second clutch member 90 which is splined to the ring carrier gear 50 as hereinbefore described. With the first and second clutch members 80 and 90 already engaged at standstill, drive torque is transferred from the second clutch member 90 to the first clutch member 80 to drive the output shaft 60 in rotation from rest to the predetermined cut-off speed. When the first and second clutch members are engaged in drive relationship, the rotational speed of the first clutch member 80 and the second clutch member 90 are the same throughout the acceleration process. As the clutch members accelerate, both the first flyweight means 102 and the second flyweight means 104 move radially outwardly in their respective races under the influence of centrifugal forces as illustrated in Figure 3. By providing the second flyweight means 104 with a greater overall mass than the overall mass of the first flyweight means 102, for example by selecting more or heavier fly balls for the second flyweight means than for the first flyweight means, the proengagement bias force generated by the outward movement of the second flyweight means 104 exceeds the disengagement bias force generated by the outward movement of the first flyweight means 102. Having a greater overall mass than the first flyweight means 102, the members making up the second flyweight means 104 reach the outer extent of their respective races during the acceleration process. As torque builds up, the ring gear carrier 50 is displaced axially rearwardly, i.e. inboardly, against the second bias spring 97, while the first bias spring 96 continues to hold the second clutch member 90 in engagement with the first clutch member 80. As a result of the application of torque, a firm, positive torque transmitting relationship is maintained throughout the acceleration process until the predetermined cut-off speed is reached at which the clutch members disengage. After this speed is reached, the clutch members are free running and the flow of motive fluid to the starter turbine is terminated. Upon termination of the flow of motive fluid to the starter turbine, the turbine shaft 24 rapidly decelerates, while the output shaft 60 continues to rapidly accelerate as it is splined to the shaft of the turbine engine which is lighted-off during the acceleration process. Thus, following cut-off, the engagement means 82 of the first clutch member 80 will ratchet along the engagement means 92 of the second clutch member 90. As the second clutch member 90 is axially translatable along the ring gear carrier 50, the forces exerted upon the engagement means 92 of the second clutch member 90 by the still accelerating engagement means 82 of the first clutch member 80 will cause the second clutch member to translate rearwardly against the first bias spring 96 during ratcheting as illustrated in Figure 4. The engagement means 82 and 92 comprise mating surfaces contoured to provide for positive torque transmission when the clutch members are rotating in one direction and to facilitate disengagement when the clutch members are rotating in the opposite direction. Advantageously, the engagement means 82 and 92 may comprise helical mating surfaces. The first clutch member 80 will continue to ratchet on the second clutch member 90 until the rotational speed of the output shaft 60, which is accelerating with the engine shaft, substantially exceeds, for example by about 4000 revolutions per minute, the rotational speed of the decelerating turbine shaft 24. At that point, the second clutch member 90 is completely disengaged from the first clutch member 80 as illustrated in Figure 5, and the output shaft 60 is free running, being driven by the engine shaft to which it is connected. In the free running mode, the second clutch member 90 has translated rearwardly, i.e. inboardly away from the first clutch member 80 as the disengagement bias force generated by the first flyweight means 102, whose members are continuing to move radially outwardly until they reach the outer extent of their respective races under the influence of the centrifugal forces resulting from the rapidly increasing speed of the output shaft 60 as it accelerates to engine operating speed, typically in the range of about 16,000 rpm, now exceeds the proengagement bias force generated by the second flyweight means 104, which force is rapidly decreasing to zero as the turbine shaft 24 rapidly decelerates to zero and the members of the second flyweight means 104 return to rest position. As a result, the entire biasing means assembly 100 translates axially rearwardly under the force exerted thereon by the first flyweight means 102, bringing with it the second clutch member 90 which is engaged by the circumferential flange portion 128 extending radially outwardly from the outer circumferential surface of the second member 120 of the biasing means assembly 100. With the second clutch member so positioned, the first bias spring 96 is compressed and the gap 5 between the clutch assembly and the lip 57 of the ring gear carrier 50 is reestablished. In the event of an aborted engine start following disengagement, the clutch assembly of the present invention facilitates restart of the engine through the starter without crash reengagement of the first and second clutch members of the clutch assembly. In such a case, the output shaft 60 decelerates as the turbine shaft 24 accelerates upon restart of the turbine starter by supplying motive fluid thereto. As the turbine shaft 24 accelerates, the members forming the second flyweight means 104 again move radially outwardly in their respective races, while the members forming the first flyweight means 102 move radially inwardly in their respective races. As a result, the proengagement bias force generated by the second flyweight means 104 rapidly increases as the turbine shaft 24 accelerates, while the disengagement bias force generated by the first flyweight means 102 deteriorates as the output shaft 60 slowly decelerates with the engine shaft to which it is connected. As the rotational speed of the second clutch member 90, which is accelerating with the starter turbine shaft 24, approaches the rotational speed of the first clutch member 80, the proengagement bias force generated by the second flyweight means 104 will gradually overcome the disengagement bias force generated by the first flyweight means 102, thereby permitting the bias spring 96 to push the second clutch member 90 outboardly, first bringing the second clutch member 90 into ratcheting engagement with the first clutch member 80 and then, as the speeds of the first and second clutch members become equal, bring the second clutch member 90 into torque transmitting reengagement with the first clutch member 80, whereby the torque transmitting relationship from the starter turbine shaft 24 to the output shaft 60 is established without crash engagement and the restart of the engine to which the output shaft 60 is connected may be reinitiated.

Claims: A clutch assembly for use in transmitting rotational drive torque from a driving member (24) to a driven member (60), comprising: a first clutch member (80) operatively associated with the driven member (60) whereby said driven member (60) rotates with said first clutch member (80), said first clutch (80) member having engagement means (82) extending therefrom; a second clutch member (90) operatively associated with the driving member (24) whereby said second clutch member (90) rotates with said driving member (24), said second clutch member (90) having engagement means (92) extending therefrom adapted to engage the engagement means (82) of said first clutch member (80), said second clutch member (90) being axially displaceable relative to said first clutch member (80) between a first position whereat the engagement means (92) of said second clutch member (90) is operatively engaged with the engagement means (82) of said first clutch member (80) so as to transmit the rotational drive torque from the driving member (24) to the driven member (60) and a second position whereat the engagement means (92) of said second clutch member (90) is disengaged from the engagement means (82) of said first clutch member (80); first counterweight means (102) for generating a bias force axially biasing said second clutch member (90) toward the disengaged position, said first counterweight means (102) being displaceable radially outwardly in response to the rotational speed of said driven member (60), the disengagement bias force generated having a magnitude which varies with the radial position of said first counterweight means (102), the magnitude increasing as the first counterweight means (102) is displaced further radially outwardly; second counterweight means (104) for generating a proengagement bias force opposed to said disengagement bias force, said second counterweight means (104) being displaceable outwardly in response to the rotational speed of the driving member (24), the proengagement bias force generated having a magnitude which varies with the radial position of said second counterweight means (104), the magnitude increasing as the second counterweight means (104) is displaced further radially outwardly, characterized in that said first counterweight means (102) has first overall mass and said second counterweight means (104) has a second overall mass, the second overall mass being greater than the first overall mass. A clutch assembly as recited in claim 1 wherein said first counterweight means (102) comprises a plurality of first flyweights (102) and means for supporting said first flyweights (102) for rotation with said first clutch member (80) whereby said first flyweight means (102) are displaceable radially outwardly in response to the rotational speed of said driven member (60), and said second counterweight means (104) comprises a plurality of second flyweights (104) and means for supporting said second flyweights (104) for rotation with said second clutch member (90) whereby said second flyweight means (104) are displaceable radially outwardly in response to the rotational speed of said driving member (24). A clutch assembly as recited in claim 2 wherein said first flyweight means (102) comprises a plurality of first spherical balls (102), and said second flyweight means (104) comprises a plurality of second spherical balls (104), there being more second spherical balls (104) than first spherical balls (102) whereby said greater overall mass is realized. A clutch assembly as recited in any of claims 1 to 3, wherein the engagement means (82, 92) of the first and second clutch members (80, 90) comprise mating surfaces, preferably helical mating surfaces, contoured to provide for positive torque transmission when the clutch members (80, 90) rotate in one direction and to facilitate disengagement when the clutch members (80, 90) rotate in the opposite direction.

Inventors: QUENNEVILLE RAYMOND N, QUENNEVILLE, RAYMOND N.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1993
Main classification: F16D43
IPC codes: F16D43