FLEXIBLE SHAFT COUPLING

Abstract: A flexible coupling device (10) comprises an inner hub (34), an outer hub (36) and a rubber core (38) bonded between the inner hub (34) and the outer hub (36). The axial length (L1) of the rubber core (38) at its inner radius (R1) is greater than the axial length (L2) of the rubber core (38) at its outer radius (R2). The outer radius to inner radius preferably has a ratio of about 3:1. The inner and outer hubs are connectable between a pulley (14) and a driven accessory (12). The shaft flexible coupling (10) acts as an angular damper and as a universal joint.

Description: FLEXIBLE SHAFT COUPLING Field of Invention This invention relates to a shaft decoupling device for use in a belt drive having relatively high angular vibrations and where installation space is at a premium. In particular, this invention relates to a torsionally soft coupling which acts both as an angular decoupling spring and universal joint, used singularly or in pairs with or without an associated propeller shaft, by which an accessory can be remotely mounted from the belt plane and simultaneously decoupled. Background of Invention In modern automobile engines, belt drives are used to drive various accessories. The elastic belt must transmit sharply varying torque impulses from the drive pulley to a driven pulley which drives an accessory having a high rotational inertia. The sharply varying torque causes the driven inertia to accelerate then decelerate which induces angular vibration of the driven inertia. When this forced vibration coincides with the angular resonant frequency of the driver/belt/driven inertia system, the angular vibration is greatly amplified. The amplified angular vibration causes very large and continuous oscillation in the tensions in each of the belt spans resulting in associated noise and vibration. Further, space to mount the driven accessory in a plane with the driver pulley and belt has become less and less available forcing designers to mount the accessories away from the plane of the driver. Devices, known as "decouplers", are commonly used in industry to increase the overall elasticity of the belt driven system by adding a low angular rate decoupler in series with the system. The decoupler may be inserted between the crankshaft hub and the drive pulley or between the driven pulley and the accessory that it drives. The effects of the decoupler is twofold. First, the lower overall angular rate serves to lower the angular resonant frequency of the entire system. Secondly, the decoupler cushions the drive from the sharp momentary accelerations of the crankshaft. Ideally, the reduction of the system angular rate is such that the new natural frequency is much lower than the frequency of any rotating load being forced upon it such as the engine firing frequency or the air-conditioning pumping frequency. This avoids resonant amplification during all operating speeds of forces and tensions within the system that might cause disagreeable noise or vibration. There are problems in the practical application of current decoupling devices. Decoupling devices that are mounted within the crankshaft pulley must transmit the entire accessory load making them quite large and expensive and vulnerable to failure if reduced in size. The decoupling devices located in the alternator pulley must be quite small because of the small pulley size necessary (about Va of crankshaft pulley diameter) and the limited space available in the region. This has historically led to fatigue failure because the small size forced high working stresses. Moreover, both types require a separate bearing to support the radial loads while allowing limited angular oscillation of the pulley rim relative to the hub. This bearing has historically been a source of failure because the inner and outer race rotate together while oscillating relative to one another and loaded by the belt tension. The result is a "brineUing" type bearing wear and "pounding" effect due to bearing clearance and the belt hub load. Accessories are usually driven from the crankshaft pulley, and therefore must be located in the same plane as the crankshaft pulley at the front of the engine. However, because of increasing alternator size and reduced sheet metal clearance, there is often insufficient room to mount all of the accessories at the front of the engine. Even when room is available, the permitted layouts may be so restricted and unsatisfactory that an acceptable drive is not possible. In an attempt to relieve this problem, the industry has sometimes driven accessories from the back end of the overhead camshaft. Although this may permit space, it has a number of disadvantages. First, the engine must use overhead camshaft and some do not. Secondly, the camshaft turns at one half the crankshaft speed which is too slow so a separate step-up drive is required. This results in an extra pulley and belt and sometimes an extra belt tensioner, raising cost and weight. Thirdly, the accessory imposes added load on the belt or chain which drive the camshaft. Fourthly, an additional seal is required raising the cost and possibility of oil leaks. Summary of the Invention The disadvantages of the prior art may be overcome by taking the driving force directly from the belt via a pulley but then transmitting the resulting torque via a propeller shaft through the decoupling and misalignment compensating joint or joints to the driven accessory located to the rear of the belt plane where adequate room exists. It is desirable to provide a pulley which is supported conventionally with a bearing having one raceway fixed to avoid "brinelling". It is desirable to provide a decoupling joint which is sufficiently large to avoid failures found in prior art devices. It is desirable to provide a decoupling joint which is sufficiently large to achieve a softer angular rate, improving performance. It is desirable to provide a drive shaft having a drive shaft of sufficient length allowing power to be taken from the back end of a first accessory and then mounting a second accessory in tandem to the first. According to one aspect of the invention, there is provided a shaft decoupler device which comprises an inner hub, an outer hub and a rubber core bonded between the inner hub and the outer hub. The axial length of the rubber core at its inner radius is greater than the axial length of the rubber core at its outer radius. The outer radius to inner has a ratio of about 3:1. The inner hub and outer hub are connectable between a pulley and a driven accessory. The shaft decoupler joint acts as an angular decoupling spring and as a universal joint. According to another aspect of the invention, there is provided a shaft decoupler joint having a first radius R t and a first axial length Lj and a second radius R 2 and a second axial length L, have a relationship as follows: According to another aspect of the invention, there is provided a decoupler having a tensioner for providing a tensioning force to a belt in driving engagement with the pulley. According to another aspect of the invention, there is provided a decoupler joint wherein the rubber core is molded to an inner hub and an outer hub. According to another aspect of the invention, there is provided a decoupler joint wherein both ends a relatively long shaft transmits rotational forces and is journal mounted. According to another aspect of the invention, there is provided decoupler joint having a relatively short shaft wherein the decoupler joint is mounted between a driving pulley and a driven device. Description of the Drawings In drawings which illustrate embodiments of the invention, Figure 1 is a plan view of a shaft decoupling device for remotely mounting an automobile accessory of the present invention; Figure 2 is a partial sectional view of decoupling device of Figure 1; Figure 3 is a partial sectional view of a second embodiment of a decoupling device of the present invention; Figure 4 is a graph illustrating tension fluctuation of an engine system without a decoupler of the present invention; Figure 5 is a graph illustrating tension fluctuation of an engine system incorporating the decoupler of the present invention; Figure 6 is a third embodiment of a short shaft decoupler of the present invention; Figure 7 is a fourth embodiment of a short shaft decoupler of the present invention; Figure 8 is a fifth embodiment of a short shaft decoupler of the present invention; and Figure 9 is a sixth embodiment of a short shaft decoupler of the present invention. Detailed Description of the Invention Referring to Figure 1, the shaft decoupler joint 10 of the present invention is illustrated. The shaft decoupler joint 10 is intermediate to a remotely mounted driven device 12, such as an alternator, and a pulley 14. Driven device 12 is in driving engagement with the pulley 14. Shaft decoupler joint 10 and pulley 14 and are mounted on first and second ends of a shaft 16, respectively. The second or pulley end of shaft 16 has a rotatable or journal mount. Shaft 16 engages an inner race of ball bearing assembly 18, while an outer race is mounted within base assembly 20. Base assembly 20 is mounted on a fixed location such as the engine block. Base assembly 20 provides radial support but permits some "tilting" of the inner race relative to the outer race to accommodate misalignment of the pulley and shaft. In the embodiment of Figure 1, a tensioner 22 is pivotally mounted about the base assembly 20. A spring assembly 24 is mounted between the pivoting arm 26 of tensioner 22 and the base assembly 20. A cylindrical cap 28 extends about the spring 24. Tensioner 22 is designed according to principles well known in the art. The driven device 12 has a rotating shaft 30 on which a connecting bracket is attached for rotating with shaft 30. Referring to Figure 2, the shaft decoupler joint 10 is illustrated in greater detail. The shaft decoupler joint 10 is mounted at the first end of shaft 16 and comprises an inner hub 34 having a length L, and a radius R. and an outer hub 36 having a length L, and a radius R 2 . Bonded between inner hub 34 and outer hub 36 is a flexible rubber core 38. In the preferred embodiment, inner hub 34 is integral with shaft 16. The pulley 14, shaft 16 and tensioner 22 are mounted on brackets (base assembly 20) allowing the decoupler joint 10 to be adjustable and flexible in the axial direction of the shaft 16. The rubber core 38 is flexible and acts as a universal joint permitting misalignment of the shaft 30 of the driven device 12 and the shaft 16. The use of a universal joint is not a new practice and various types of universal joints have been used to accommodate the inherent misalignment of the shafts of such an arrangement. However, there has not been available the combinati. -π of both a universal joint capable of axial, radial and angular misalignment correction together with the very low angular rate necessary for decoupling, since the angular stiffness of conventional universal joints is too high for significant decoupling. This is particularly useful and applicable to the rearward mounting of an air-conditioning compressor as these compressors are increasingly incorporating a decoupling rubber spring within the clutch of the compressor. An additional and unusual application advantage of the decoupler of the present invention is that the decoupling device 10 may be intentionally offset from or angularly misaligned to the pulley centerline in order to mount the accessory in a more convenient location. Another advantage of the decoupler joint of the present invention is that the shaft driven accessory may also have a pulley mounted on it (at the shaft end or back end) by which to transfer power to a second accessory remotely located. If this is done, then the drive shaft is also serving as a jack-shaft and additional ratios may be realized that are not practical on a single belt. In practice, the maximum practical ratio in automotive accessory drives is about 3 to 1. By jack- shafting, this ratio might be as high as 9 to 1 for light loads requiring high rotational speeds. Flange 40 extends outwardly from outer hub 36. Flange 40 is integral with the outer hub 36. Flange 40 is connected to connecting bracket 32 for transmitting rotation from shaft 16 from driven device 12. Any suitable method may be used to connect the outer hub 36 to the driven device 12. In Figure 1, a series of bolts 42 and rivets 44 circumferentially spaced about flange 40 is used to connect the outer hub 36 to connecting bracket 32. Preferably, the outer hub is positioned midway along the axial length Lj whereupon molding, the rubber core 38 will have arcuate faces 46. The sizing and selection of the rubber core 38 is made according to the following relations: 0 . 0485a K = l°9ιo-^ f - 0 . 159 T ' cons tan t) where K - Torsional spring rate [in.lb per degree] T - Torque [in.lb] S - Shear Modulus of rubber [p.s.i.] / - shear stress in torsional shear [p.s.i.] R - radius of rubber [in] L - is length of rubber, parallel to axis [in] The ratio between the radius of the outer hub to the radius of the inner hub, R 2 : R„ must be sufficiently large to reduce the resonant frequency of the system below the operating frequency and to minimize fatigue failure. In the present embodiment, the ratio R 2 : Rj must exceed 2:1, and is preferably about 3:1. Since the product LR 2 must be a constant, the length of the inner hub greatly exceeds the length of the outer hub. Referring now to Figure 3, another embodiment of the present invention is illustrated. Where components are the same as the embodiment of Figure 1, the same reference numeral is being used. The end of tubing 16 having the decoupler joint 10, has a molded nylon pilot bushing 48 which is inserted in the end of tubing 16. The pilot bushing has a central cavity for receiving a pilot bearing 50. Optionally, a pilot nut 52 engages driver device shaft 30 for supporting the pilot bushing 48. The pilot bearing 50 provides support for the end of shaft 16 as the shaft rotates, but does not allow the transmission of rotational forces from the shaft 16 to the driven device shaft 30. The pilot bearing 50 is required to provide additional rotational stability to the shaft as it rotates. The pilot bearing is contour to allow a certain small degree of misalignment between the rotation of shaft 16 and the rotation of driven device shaft 30. At the second or opposite end of shaft 16, pulley 14 is mounted for rotation. Shaft 16 has a screw stud 54 press fitted into the end of the tube 16. Screw stud 54 has a central passageway for receiving bolt 56, which has the hex head internally of the tubing 16 and a threaded end. Lock nut 58 is threadingly engaged with the bolt 56 for securing pulley 14 onto bearing assembly 18. Referring now to Figures 4 and 5, the improvements of the present decoupler of the present invention are illustrated. Figure 4 illustrates an engine system wherein the decoupler is locked with the engine idling at 750 RPM with maximum accessory load. The strain of the arm of the tensioner for tensioning the accessory belt is dramatic. Figure 5 illustrates the arm strain of the same engine operating at the same speed and load. The arm strain is dramatically reduced to acceptable levels. Referring now to Figure 6, a short shaft decoupler of the present invention is illustrated. In this embodiment, the inner hub 34 of the decoupler joint 10 is integral with the shaft 30 of the driven device 12. Outer hub 36 is integral with a cylindrical collar 60 which is connected to a rim of pulley 14 by bolts 62. Pulley 14 has an axially extending bearing surface 72. The end of shaft 30 has a threaded bore 64 for receiving bolt 66. Bolt 66 retains a bearing collar 68. Bearing cap 70 extends over bearing collar 68 presenting a bearing surface about which pulley 14 can rotate. Bearing cap 70 is made of a suitable bearing material such as NYLON modified with high molecular weight polyethylene (HDPET). In this embodiment, the driving force is transmitted to pulley 14 from collar 60, by rubber core 38 driven by shaft 30. Referring to Figure 7, another short shaft decoupler of the present invention is illustrated. In this embodiment, shaft 16 extends axially of the mounting base assembly 20. The decoupler joint 10 is mounted at the first end with inner hub 34 connected to the shaft 16. Pulley 14 has an integral disc 74 which is integral with outer hub 36. Pulley 14 is rotatably mounted on bearing assembly 18. The inner race of bearing assembly 18 is mounted on base assembly 20 which is firmly mounted on the engine block. Shaft 16 is in driving engagement with shaft 30 of the driven device 12. A spline, key and keyway arrangement or threaded engagement may used. As in the embodiment of Figure 6, the driving force is transmitted from pulley 14 to disc 74, through rubber core 38 to shaft 30. Referring to Figure 8, another short shaft decoupler of the present invention is illustrated. In this embodiment, shaft 16 is assembled to pulley 14 and can be sold as a unit. Shaft 16 is rotatably mounted on the inner race of bearing assembly 18 while the outer race is mounted within the base assembly 20 which mounted on the engine block. Inner hub 34 is sized to accommodate shaft 30 of the driven device 12 and the connection of bracket 32 and shaft 30. Connecting bracket 32 is bolted to outer hub 36. Base assembly 20 has suitable openings to permit bolting of outer hub 36 to connecting bracket 32. Base assembly 20 may also be extended as illustrated in broken lines to be capable of mounting the driven device 12. In this manner, the driven device 12 could be assembled with the decoupler for quicker installation on an assembly line. The driven device 12 with decoupler could be properly assembled and aligned away from the assembly line and thus allowing single piece installation. As in the embodiments of Figures 6 and 7, the driving force is transmitted from pulley 14 to shaft 16, through rubber core 38 to connecting bracket 32 to shaft 30. Referring to Figure 9, another short shaft decoupler of the present invention is illustrated. In this embodiment, bearing assembly 18 is mounted on a mounting bracket 76 which has an axle 78. Axle 78 has an axially extending passageway 80 to allow access for a hex key to operably engage hex extension 82 which retains the shaft decoupler to the driven device. Mounting bracket 76 is mounted on the engine block. Pulley 14 is mounted on the outer race of the bearing assembly 18. Pulley 14 has an integral disc 74 which is integral with outer hub 36. Inner hub 34 is in driving engagement with shaft 30 of driven device 12. outer hub 36 has a flange 84 for complementarily fitting with the integral disc 74 for connection thereto. A spline or key and keyway arrangement may used. As in the embodiments of Figures 6, 7 and 8, the driving force is transmitted from pulley 14 to disc 74, through rubber core 38 to shaft 30. Although the disclosure describes and illustrates the preferred embodiments of the invention, it is understood that the invention is not limited to these particular embodiments. Many variations and modifications will now occur to those skilled in the art. For definition of the invention, reference is made to the appended claims.

Claims: We claim: 1. A decoupler joint (10) comprising an inner hub (34) having a first radius Rj and a first axial length L,, an outer hub (36) having a second radius R 2 and a second axial length Lj, and a rubber core (38) bonded between said inner hub (34) and said outer hub (36) and extending within said first axial length L, and said second axial length 1^, said first axial length . being greater than said second axial length L^. 2. A decoupler joint (10) as claimed in claim 1 wherein said second radius R 2 to said first radius R 2 has a ratio greater than 2:1. 3. A decoupler joint (10) as claimed in claim 1 wherein said second radius R 2 to said first radius R 2 has a ratio of about 3:1. 4. A decoupler joint (10) as claimed in claimed 3 wherein said first radius Ri and said first axial length . and said second radius R 2 and said second axial length . have a relationship as follows: 5. A decoupler joint (10) as claimed in claim 4 wherein said inner hub (34) is axially relatively positioned midway along said second axial length. 6. A decoupler joint (10) as claimed in claim 5 wherein said rubber core (38) has concave end faces (46) which extend from the inner hub (34) to the outer hub (36). 7. A decoupler joint (10) as claimed in claim 1 wherein said outer hub (36) is connectable to a rotatably driven device (12). 8. A decoupler joint (10) as claimed in claim 1 wherein said outer hub (36) has a flange (40) for connecting with a rotatably driven device (12). 9. A decoupler comprising a decoupler joint having an inner hub (34) having a first radius Rj and a first axial length L„ an outer hub (36) having a second radius R 2 and a second axial length m, and a rubber core (38) bonded between said inner hub (34) and said outer hub (36) and extending within said first axial length L. and said second axial length - , said first axial length L, being greater than said second axial length ■ a shaft (16) integral with said inner hub (34), wherein said shaft acts a torsion spring element in combination with said rubber core (38). 10. A decoupler as claimed in claim 9 wherein said shaft (16) has a first end which is journal mounted for rotation. 11. A decoupler as claimed in claim 10 wherein said first end has a pulley (14) mounted thereon for receiving a driving force for rotating said shaft (16). 12. A decoupler as claimed in claim 11 wherein said first end has a tensioner (22) for providing a tensioning force to a belt in driving engagement with said pulley (14). 13. A decoupler as claimed in claim 11 wherein said shaft (16) has a second end opposite said first end, said second end has a bearing surface (50) for journal mounting said second end. 14. A decoupler as claimed in claim 13 wherein said first axial length , is proximate said second end. 15. A decoupler as claimed in claimed 14 wherein said first radius R,and said first axial length L, and said second radius R 2 and said second axial length Lj have a relationship as follows: 16. A decoupler as claimed in claim 15 wherein said inner hub (34) is relatively positioned midway along said second axial length Lj. 17. A decoupler as claimed in claim 16 wherein said second radius R 2 to said first radius R 2 has a ratio greater than 2:1. 18. A decoupler as claimed in claim 16 wherein said second radius R 2 to said first radius R 2 has a ratio of about 3:1. 19. A decoupler as claimed in claim 18 wherein said rubber core (38) is molded to said inner hub (34) and said outer hub (38). 20. A decoupler as claimed in claim 1 wherein said inner hub (34) is relatively positioned midway along said second axial length L-,. 21. A decoupler as claimed in claim 20 wherein said rubber core (38) has end faces (46) which extends arcuatery from the inner hub (34) to the outer hub (36). 22. A decoupler as claimed in claim 21 wherein said end faces (46) are concave. 23. A decoupler joint (10) as claimed in claim 1 wherein one of said inner hub (34) and said outer hub (36) is in driving engagement with a driving pulley (14) and the other of said inner hub (34) and said outer hub (36) is in driving engagement with a driven device (12), wherein rotational forces are transmitted from the driving pulley (14) through said rubber core (38) to said driven device (12). 24. A decoupler joint (10) as claimed in claim 23, wherein said driving pulley (14) has a rotatable mount (18). 25. A decoupler joint (10) as claimed in claim 24 wherein said rotatable mount (18) is a rolling bearing assembly having an inner race and an outer race and one of said inner race and said outer race is fixed to base assembly (20) mountable on a support surface and the other of said inner race and said outer race engages said pulley (14). 26. A decoupler comprising an inner hub (34) having a first radius and a first axial length, an outer hub (36) having a second radius and a second axial length, a rubber core (38) bonded between said inner hub (34) and said outer hub (36) and extending within said first axial length and said second axial length, said first axial length being greater than said second axial length, a pulley (14) for receiving a driving rotational force, a mounting bracket (20,76) having a bearing assembly (18) for rotatably mounting said pulley (14), wherein one of said inner hub (34) and outer hub (36) is in driving engagement with said pulley (14) and the other of said inner hub (34) and outer hub (36) is drivingly engagable to a driven device (12). 27. A decoupler as claimed in claim 26 wherein said bearing assembly (18) has an inner race and an outer race and one of said inner race and said outer race is connected to mounting bracket (20,76) and the other of said inner race and said outer race engages said pulley (14). 28. A decoupler as claimed in claim 27 wherein said inner hub is integral with a shaft and said pulley (14) is mounted at one end of the shaft (16). 29. A decoupler as claimed in claim 28 wherein said shaft (16) is journal mounted for rotation. 30. A decoupler as claimed in claim 29 wherein said shaft (16) extends through said driven device 12 capable of drivingly engaging a second driven device in tandem. 31. A decoupler as claimed in claim 26 wherein said bracket is capable of mounting said driven device (12).

Inventors: KOMOROWSKI JACEK S, LIPOWSKI ZBIGNIEW F, MEVISSEN PIERRE A, THOMEY HENRY W, KOMOROWSKI, JACEK, S., LIPOWSKI, ZBIGNIEW, F., MEVISSEN, PIERRE, A., THOMEY, HENRY, W.
Applicants: KOMOROWSKI JACEK S, LIPOWSKI ZBIGNIEW F, MEVISSEN PIERRE A, ONTARIO INC 730143, ONTARIO INC 730144, TESMA INT INC, THOMEY HENRY W, 730143 ONTARIO INC., 730144 ONTARIO INC., KOMOROWSKI, JACEK, S., LIPOWSKI, ZBIGNIEW, F., MEVISSEN, PIERRE, A., TESMA INTERNATIONAL INC., THOMEY, HENRY, W.
Application year: 1995
Main classification: F16D3
IPC codes: F02B63, F16D3, F16H7