COMPOUND PLANETARY GEAR ASSEMBLY

Abstract: An improved compound planetary gear assembly has multiple ring gears (26, 30, 32) driven by a set of planet gears (12) and coupled to multiple loads (A, B). Two of the ring gears (30, 32) are coupled to a common load (B) via mechanical reaction paths of substantially different lengths to permit the entire assembly to fit within an envelope of reduced overall size. The shorter mechanical reaction path incorporates a compliant gear member (46) which decreases the stiffness or spring rate of the shorter path to correspond substantially with the stiffness or spring rate of the longer path, thereby insuring symmetric loading of the planet gears for smooth operation.

Description: - - COMPOUND PLANETARY GEAR ASSEMBLY This invention relates generally to epicyclic or planetary gear trains designed to drive one or more output loads at a selected speed relative to a rotary drive input. More particularly, this invention relates to an improved compound planetary gear assembly designed to drive multiple loads while fitting the gear train components within a compact, substantially minimum profile envelope. Planetary or epicyclic gear trains in general are relatively well known in the art to include one or more so- called planet gears meshed between input and output gears, wherein the planet gears are designed to rotate about their own axes and to orbit or precess about another axis in the gear train. Such planetary gear trains are commonly used to achieve a substantial speed reduction between a rotational input and output. As one example, in a typical simple planetary gear train having planet gears rotatable about a fixed axis a central sun gear is rotatably driven about a fixed central axis in meshed relation with normally three or more planet gears which are meshed in turn with an outer ring gear. The sun gear causes the planet gears to rotate about their individual axes and to orbit the sun gear while driving the outer ring with a significant speed reduction relative to the sun gear. In some planetary gear trains, the planet gears are meshed with and drive multiple output ring gears which are coupled to different structural members,, resulting in a gear train referred to normally as a compound planetary gear train. For example, in an aircraft flap actuator system, compound planetary gear trains are known wherein a primary output ring gear is mechanically coupled to a wing flap and a secondary output ring gear is mechanically coupled to a wing spar, with the primary output ring gear driving the flap through the differential action of the compound gearing. In this type of system, the secondary ring gear normally constitutes a pair of ring gears meshed at axially opposed ends of the planet gears to achieve symmetrical loading of the planet gears, with both secondary ring gears linked to the common structural load such as a wing spar or the like. Importantly, however, to achieve symmetric loading of the planet gears, the construction is such that the mechanical reaction paths between the two secondary ring gears and their common load exhibit identical stiffnesses or spring rates. This construction insures planet gear orbiting about an axis parallel to the sun and ring gears to avoid locking or binding of the planet gears during operation. In a flap actuator system of the type described above, symmetric loading of the planet gears is most commonly achieved by radial coupling of the output ring gears to their respective loads such as the wing flap and wing spar. In some compound planetary gear drive applications, radial drive coupling of the output ring gears is either not desirable or not possible. Instead, it is necessary to provide a driven output at one axial end of the gear train. In such applications, the multiple secondary output ring gears are not radially coupled to an external structural member but are coupled to an axially positioned structural member along internal mechanical paths. However, to achieve symmetric gear loading, it is still required for the mechanical paths to exhibit identical stiffnesses or spring rates, wherein this requirement has resulted in gear train configurations which suffer from inefficient use of volumetric space. There exists, therefore, a significant need for an improved compound planetary gear train designed to provide a driven output at one end of the gear train, wherein the compound gear train is designed for symmetric gear loading in a compact and space^efficient arrangement. The present invention fulfills these needs and provides further advantages., In accordance with the invention, an improved compound planetary gear assembly is provided with primary and secondary output ring gears connected mechanically to different loads. The output ring gears are coupled to their respective loads in a manner permitting the assembly to have a compact size and shape while assuring substantially symmetric loading of driving planet gears for smooth operation at all times. The improved compound planetary gear assembly includes a central sun gear meshed with a plurality of planet gears for rotatably driving the planet gears about their own axes and orbitally about the axis of the sun gear. The planet gears are meshed in turn at generally axially centered positions with the primary output ring gear which is coupled to a first load. A pair of the secondary output ring gears are meshed with the planet gears on axially opposite sides of the primary ring gear, and both of said secondary ring gears are mechanically coupled to a second load. Both the first and second loads may be movably driven, or, in the alternative, one of the loads may be stationary on a temporary or permanent basis. In accordance with a major aspect of the invention, the two secondary ring gears are mechanically coupled, to the second load by mechanical reaction paths of substantially different lengths, thereby permitting the overall assembly to fit within an envelope of relatively small diametric size. A compliant gear member is included along the shorter mechanical path to provide sufficient reduction in the stiffness or spring rate of the longer mechanical path. The relative stiffness of the two mechanical reaction paths are thus essentially equal thereby insuring substantially symmetric loading of the planet gears. in the preferred form, the compliant gear member comprises an auxiliary ring gear coupled mechanically between one of the secondary ring gears and the second load. The auxiliary ring gear includes elongated gear teeth formed with a contoured profile selected for substantially uniform stress loading along the lengths thereof. The outboard tips of these gear teeth are radiused to define rounded contours sized to fit into mating radiused sets in a spline member forming another portion of the shorter mechanical path. The gear teeth of the auxiliary gear have sufficient compliance to permit positional shifting between the gear teeth and the spline member, as permitted by the engaged radiused surfaces, to " match the compliance of the longer mechanical path associated with the other secondary ring gear. Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. In such drawings? FIGURE 1 is a somewhat schematic vertical sectional view illustrating an improved compound planetary gear assembly embodying the novel features of t * he invention? FIGURE 2 is a vertical sectional view taken generally on the line 2-2 of FIG. 1? FIGURE 3 is a vertical sectional view taken generally on the line 3-3_ of FIG. 1; FIGURE 4 is a fragmented vertical sectional view taken generally on the line 4-4 of FIG. I f FIGURE 5 is a fragmented vertical sectional view taken generally on the line 5-5 of FIG. 1? FIGURE 6 is a fragmented vertical sectional view taken generally on the line 6-β of FIG. I f and FIGURE 7 is an enlarged fragmented vertical sectional view taken generally on the line 7-7 of FIG. 1. As shown in the exemplary drawings, an improved compound planetary gear assembly referred to generally by the reference numeral (10) is designed for connection to multiple output loads, such as the loads A and B depicted in FIGURE 1. The improved gear assembly (10) is constructed to have a relatively compac size for use in specialized applications while insuring substantially symmetric loading of orbiting planet gears (12) for smooth operation particularly at high loads and/or high speed operation. The compound planetary gear assembly (10) of the present invention comprises a gearbox housing (14) having an appropriate size and shape to encase the various gearbox components. Such gearbox components traditionally include an inner sun gear (16) (FIGS. 1 and 3) supported by the housing for rotation about a central axis (18) in response to operation of a suitable drive motor (20) or the like, as will be described in more detail. The sun gear (16) includes an external encircling array of gear teeth (22) meshed with mating centrally located primary teeth (24) of a plurality of the planet gears (12) with seven planet gears being shown in the illustrative embodiment of the invention (FIG. 3) . In general terms, this set of planet gears (12) is disposed in a circular array between the sun gear (16) and a primary output ring gear (26) having an inner set of gear teeth (28) also engaged with the central .primary teeth (24) of the planet gears (12) . In operation, rotational driving of the sun gear (16) about its central axis. (18) correspondingly rotates the planet gears (12) about their individual axes and further causes those planet gears to orbit slowly about the central axis (18) . These orbital and rotational movements of the planet gears (12) result in rotational driving of the primary output ring gear (26) with substnatial speed reduction relative to the sun gear (16) , to rotatiόnally drive the load A, as depicted schematically in FIG. 1. The planet gearse (12) are also meshed with a pair of secondary output ring gears (30) and (32) which provide the compound nature of the planetary gear assembly (10) by virtue of their driving connection with the load B, as will be described in more detail. Bearings (33) conveniently support the primary ring gear (26) for rotation independently of the secondary ring gears (30) and (32) . These bearings (33) are depicted in the accompanying drawings in the form of ball bearings within tracks separating the secondary ring gear (32) and a portion of the housing coupled to the load B from the primary ring gear (26). More particularly, as viewed in FIGS. 1, 4 and 5, the planet gears (12) include sets of secondary teeth (34) and (36) respectively at the axially opposite ends thereof for meshed engagement with internal sets of teeth (38) and (40) on the two secondary ring gears (30 and (32) . The relative numbers of the teeth associated with the primary ring gear (26) such that the primary and secondary ring gears are driven at different rotational speeds, with the secondary ring gears (30) and (32) being coupled mechanically to drive the load B. This secondary output drive is conventionally obtained by means of the two secondary output ring gears (30) and (32) engaged with each planet gear (12) in a symmetric manner designed to balance forces applied to the planet gears (12) and thereby achieve smooth gearbox operation. Annular bearing rings (42) and (.44) or the like are conveniently disposed about the sun gear (16) in positions axially between the central or primary planet teeth (24) and the sets -of secondary teeth (34) and (36) to assist in retaining the planet gears in position. In accordance with a primary aspect of the invention, the two secondary output ring gears (30) and (32) are linked to the common load B by a respective pair of mechanical reaction paths leading to one axial side of the gearbox housing (14) . That is, the secondary ring gear (30) is coupled to the load B via a mechanical path of relatively short length leading directly from the gearbox components to the load B. The other secondary output ring gear (32) at the opposite axial end of the gearbox is linked to the load B via a significantly longer mechanical path extending axially through the hollow cylindrical sun gear 16 to the load B. While this arrangement results in mechanical reaction paths of significantly different lengths between the load B and the ring gears (30) and (32) , it permits the overall diametric size of the gearbox to be substantially reduced. Differences in stiffness or compliance of the two mechanical reaction paths are compensated by means of a compliant gear member (46) forming a portion of the shorter mechanical path associated with the secondary ring gear (30) to insure matching of the reaction path stiffness. As a result, notwithstanding the significant differences in reaction path length, the secondary ring gears (30) and (32) present uniform loads to the planet gears (12) for symmetric loading of the planet gears (12) at all times. As shown best in FIGS. 1 and 6, the mechanical reaction path associated with the secondary output ring gear (32) is defined by an annular drive plate (48) having outer teeth (50) meshed with the output ring gear teeth (40) . Accordingly, the drive plate (48) is locked for rotation with the outpμt ring gear (32) . The inner diameter of this drive plate (48) is engaged by means of a splined connection (52) with an inner sleeve member (54) extending coaxially within the sun gear (16) to the opposite side of the gearbox, whereat the sleeve member (54) includes a radially expanded flange (56) (FIG. 1) connected by another splined connection (58) to the load B. In contrast, the shorter mechanical reaction path associated with the other secondary output ring gear (30) is illustrated in FIGS. 1, 2 and 7. This shorter reaction path is defined by a short radially inset wall (60) joined to the axially outboard end of the output ring gear (30) , wherein the inset wall (60) is joined in turn to a short cyindrical sleeve (62) . The outer diameter surface of this short sleeve (62) is serrated or otherwise appropriately shaped in cooperation with an inner diameter surface of the compliant gear member (46) to define a splined connection (64) therebetween, as shown in FIG. 7. Elongated teeth (66) of specialized configuraton are engaged in turn with a sleeve portion (72) of the housing (14) coupled to the load B to complete the shorter mechanical path associated with the ring gear (30) . The compliant gear member (46) is formed from a selected material and with a selected configuration to introduce limited variable compliance into the shorter path associated with the output ring gear (30) , thereby matching the stiffness of the longer path associated with the related output ring gear (32) . In the preferred form, the compliant gear member (46) is formed from a hardened steel or the like as an auxiliary ring gear to include a narrow annular base ring (68) with an inner diameter shaped for splined interlock with the sleeve (62) . The elongated teeth (66) project radially outwardly from the base ring (68) on precision centers, with each tooth y (66) having flat axially opposed surfaces and a tooth profile designed for uniform stress loading along the lengths thereof, such as a parabolic tooth profile. The outermost tips of the teeth (66) terminate in a smoothly rounded or radiused shape for mating engagement into shallow smoothly rounded seats (70) on an inner diameter surface of the sleeve portion (72) joined to the load B β In operation, in response to mechanical loading of the reaction path between the load B and the output ring gear (30), the spring characteristics of the elongated teeth {66) of the compliant gear member (46) permit slight rotational misalignment or shifting between the base ring (68) and the load sleeve (72) . This shifting is accommodated without interruption in smooth gearbox operation by the rounded tips of the teeth 66 shifting or rotating within their respective rounded seats (70) , without disengagement therefrom. In practice, a shifting capability on the order of about (0.005 inch) 0.127 mm is sufficient to match the stiffness of the longer mechanical path associated with the other secondary output ring gear (32). Moreover, in a typical application of the invention, spring rate chareteristics for the compliant teeth (66) on the order of a couple hundred thousand Newton-meters (a few million inch- pounds) per radian will provide the desired compliance level. In one preferred application of the improved compound planetary gear assembly (10) , the primary and secondary output ring gears are utilized for displacing the rotor blades (not shown) of a helicopter between deployed and stored configurations, with the blades extending generally along the aircraft fuselage in a low profile manner when stored. The primary output ringgear (26) is mechanicallylinked to a latch (load A) for locking and unlocking the blades, whereas the secondary output ring gears (30) and (32) are coupled mechanically to the rotor blades (load B) to displace the blades. For example, with the blades locked in the deployed position for flight operation, the gear assembly (10) can be operated to displace the primary output ring gear (26) in a manner withdrawing the latch (load A) to unlock the blades while the secondary output ring gears (30) and (32) remain fixed. Upon cessation of latch movement, such as upon impact with a suitable stop (not shown), the primary output ting gear (26) becomes fixed and the now-mobile secondary output ring gears (30) and (32) begin to displace the blades (load B) to the stored position. Gearbox operation can be halted by appropriate switch, means (not shown) when the stored position is reached. Reverse operation of the gear assembly (10) is effective to redeploy and then relock the blades in the deployed state. Importantly, the compliant gear member (46) insures symmetric planet gear loading at all times throughout such operation which can occur with high speed reductions at 10,000:1 or higher. Moreover, the compliant gear member (46) presents sufficient compliance into the system to dissipate kinetic energy when a stop is impacted thereby avoiding the need to utilize additional system components for that function. FIGS. 1 and 2 depict one convenient apparatus for reversibly driving the sun gear (16) to achieve the reversible gearbox operation described above with respect to helicopter rotor blade deployment, together with a high overall speed reduction as required in such applications. In particular, the drive motor (20) reversibly rotates a drive shaft (74) mounted for rotation within the sleeve member (54) by suitable bearings (76) . This drive shaft (74) is meshed with radially arranged pairs of star gears (78) and (80) (FIG. 2) carried by the flange (56) on the sleeve member (54) , with three star gear sets being shown by way of example. The outer star gear (80) of each set is meshed with an outer drive ring (82) which is meshed with and transmits rotary motion to the sun gear (16) . Alternative gear assembly configurations may, of course, utilize alternative means for rotary driving of the sun gear (16) in a unidireαfe-ional or reversible manner. The primary and secondary output ring gears may be adapted for simultaneous displacement upon gearbox operation, or either may be fixed temporarily or permanently. In any case, the gear assembly can be constructed with a small profile configuration with matched stiffness in the mechanical reaction paths associated with the two secondary output ring gears. Importantly, this stiffness matching insures smooth gearbox operation without gear component binding throughout operation, including high speed and high load operation.

Claims: -11- CLAIMS 1. A compund planetary gear assembly, comprising : a sun gear (16) ; a set of planet gears (12) meshed with said sun gear (16) for rotational movement about their respective axes and for orbital movement about said sun gear upon rotational driving of said sun gear; a primary output ring gear (26) meshed in generally axially centered relation with said planet gears (12); 0 a pair of secondary output ring gears (30, 32) 11 meshed generally at opposite axial ends, respectively, with 12 said planet gears (12) ; 13 first coupling means for coupling said primary 14 output ring gear (26) to a first load (A) ; and 15. second coupling means for coupling said pair of 16 secondary output ring gears (30, 32) to a second load (B) , 17 characterized in that said second coupling means define a 18 pair of mechanical reaction paths of substantially different 19 lengths extending respectively between said second load (B) 20 and said secondary output ring gears (30, 32) said second 21 coupling means further including a compliant coupling member 22 (46) along the shorter of the two mechanical reaction paths 23 to insure substantial matching in stiffness between the two 24 mechanical reaction paths. 2. A gear assembly according to claim 1 2 characterized in that said compliant coupling member (46) 3 comprises an auxiliary ring gear (68) having elongated teeth 4 {66) each having a smoothly rounded tip, said second 5 coupling means further including a sleeve member (72) having 6 smoothly rounded seats for meshed engagement of said tips of 7 said teeth therein. 3. A gear assembly according to claim 2 2 characterized in that said second coupling means includes 3. spline means (64) for interconnecting said auxiliary ring 4 gear (68) for rotation with one of said secondary ring gears 5 (30) , said sleeve member (72) being coupled to said second 041 ' ' -12- load (B) . 3. A gear assembly according to claim 2 characterized in that said second coupling means includes spline means (64) for interconnecting said auxiliary ring gear (68) for rotation with one of said secondary ring gears (30) , said sleeve member (72) being coupled to said second load (B) . 4. A gear assembly according to any one of claims 1 to 3 characterized in that said sun gear (16) comprises a hollow cylindrical sun gear, said compliant coupling member {46) being coupled between one of said secondary ring gears (30) and said second load (B) at one axial end of said planet gear (12) , said second means further including means (48-56) extending axially through the interior of said sun gear (16) for coupling the other of said secondary ring gears (32) to said second load (B) at said one;axial end of said planet gears. 5. A compound planetary gear assembly, comprisings a sun gear (16) ; a set of planet gears (12) meshed with said sun gear (16) for rotational movement about their respective axes and for orbital movement about said sun gear upon rotational driving of said sun gear; ' at least two output ring gears (30, 32) meshed with said planet gears; and coupling means for coupling said secondary output ring gears (30, 32) to a load along respective mechanical reaction paths of substantially different lengths, characterized in that said coupling means include a compliant coupling member (46) along a shorter one of the mechanical ' reaction paths to insure substantial matching in stiffness between the mechanical reaction paths. 6. A gear assembly according to claim 5 characterized in that said compliant coupling member (46) comprises an auxiliary ring gear (68) having elongated teeth { 66) each having a smoothly rounded tip, said coupling means further including a sleeve member (72) having smoothly rounded seats for meshed engagement of said tips of said teeth therein. 7. A gear assembly according to claim 6 characterized in that said coupling means includes spline means (64) for interconnecting said auxiliary ring gear (68) for rotation with one of said output ring gears (30) , said sleeve member (72) being coupled to said load (B) . 8. A gear assembly according to any one of claims 5 to 7, characterized in that said sun gear (16) comprises a hollow cylindrical sun gear, said compliant coupling member (46) being coupled between one of said output ring gears (30) and said load (B) at one axial end of said planet gears (12), said coupling means further including means (48-56) extending axially through the interior of said sun gear (16) for coupling another of said output ring gears. (32) to said load (b) at said one axial end of said planet gears.

Inventors: MARTIN WILLIAM B, MARTIN, WILLIAM, B.
Applicants: ALLIED SIGNAL INC, ALLIED-SIGNAL INC.
Application year: 1988
Main classification: F16H1
IPC codes: B64C13, F16H1, F16H37, F16H57