Shafting connection

Abstract: A press fit joint shafting connection for hollow cylindrical steel shafts (1,2) has shaft end faces provided with excentrically arranged axial recesses (21,22) wider than the main shaft bores (3,4). An annular toughened steel locking insert (5) having an excentrically arranged through bore (6) is retained in the space formed by said excentrically arranged bores (21,22) when the shaft ends meet. The degree of excentricity of the bore (6) in the locking insert (5) corresponds to that of the excentrically arranged shaft recesses (21,22) while the locking insert bore diameter (6) corresponds to the diameter of the main shaft bores (3,4). The inner bores (3,4,6) with free lumen are in alignment in a mounted state. A corresponding shafting method is also described.

Description: The present invention relates to a shafting connection and, more particularly, to a shafting connection for connecting a first hollow steel shaft to a second hollow steel shaft, said shafts having identical outer diameters at least in regions extending from their abutting ends, comprising a friction coupling including an inner sleeve with an inner cylindrical surface arranged for frictional contact with the outer surface of said terminal region of the shafts, said friction coupling being arranged to be fitted on the aligned shafts to cover both shafts near their abutting ends, each of said shafts in a region extending from their abutting ends having a second concentric bore of same diameter for receiving an annular insert, said second bores being wider than the main shaft bores, the diameters of said second bores being essentially identical. Such connections are used, i.a., for shafting of controllable pitch propeller and similar shafts. Both solid and hollow marine shafts are usually connected to each other by means of press fit joints; see, e.g., published Swedish patent application No. 353 374 (application No. 8838/68). Such joints are sleeves which are fitted around the abutting cylindrical shaft ends, comprising inner and outer sleeve members with co-acting tapered surfaces. Hydraulic means are used for their assembly/disassembly. The torque transmission capacity of cylindrical shafts with or without cylindrical inner bores connected by press fit couplings solely depends on frictional force between the individual parts of the shafting assembly. Deformation of sleeve and shafts at high torque results in loss of friction and makes the shafts slip. The transmission of high torque by hollow shafts shafted in this way constitutes a particular problem since hollow shafts are more easily deformed than solid shafts. To achieve torque transmission rates for hollow shafts comparable to those of solid shafts of same width, the former have to be reinforced by sleeves of toughened steel sunk into recesses turned beneath the coupling seatings, cf. "The OK couplings from OVAKO STEEL", brochure No. K1-189, page 13, OVAKO STEEL Coupings AB, 1988. For hollow shafts with an inner diameter/outer diameter ratio exceeding 0,55, even normal torque cannot be fully transmitted. Since a torque transmission safety factor against slipping of more than 2,5 of the normal torque is required by most marine classification authorities, specifications cannot be met with the known shafting connection even for shafts with that diameter ratio falling substantially below the 0,55 value. Furthermore, for a given application, it is desirable to decrease the shaft diameter while keeping maximum torque transmission values constant. In respect of shafts as such, this can be achieved by use of high quality alloyed steel. Such improvement however, is not parallelled by an increased efficiency of the now smaller press fit joint. Also for this reason, improvement of torque transmission efficiency of press fit joints is desirable. It is thus an object of the present invention to provide a shafting connection for hollow steel shafts that has torque transmission properties superior to those known in the art. In accordance with the present invention, a shafting connection for hollow steel shafts is provided which improves torque transmission by 20 to 50 % compared with traditional shafting connections for shafts of same dimensions. According to the present invention there is provided a shafting connection for connecting a first hollow steel shaft to a second hollow steel in which the second bores in the butt faces of the shafts for receiving a cylindrical insert are arranged with equal excentricity in respect to the main shaft bores. The annular insert which is a locking insert advantageously has substantial extension in both second bores and has an excentrically arranged through bore, the degree of excentricity essentially corresponding to that of the excentrically arranged second bores in the respective shaft. It is preferred for the bore diameter of said annular locking insert to essentially correspond to the diameter of the main shaft bore. According to an advantageous aspect of the invention by which the zone of increased shaft stability is extended further along the shafts, an intermediate bore is arranged between the excentrically arranged bore extending from the end of the respective shaft and the main shaft bore and being in alignment with the latter, and which intermediate bore has a diameter larger than the diameter of the main shaft bore but smaller than the outer diameter of the excentrically arranged annular locking insert. Into the intermediate bore a symmetric annular sleeve insert is fitted having an outer diameter essentially corresponding to the diameter of said intermediate bore, an inner diameter essentially corresponding to the diameter of the main shaft bore and having an axial extension not exceeding that of said intermediate bore. It is preferred for the annular locking insert to be made of toughened steel with a yield point of at least 850N/mm 2 . It is also preferred for the symmetric annular insert to be made of toughened steel with a yield point of at least 850N/mm 2 . It is furthermore preferred for the bore of the annular locking insert to have an excentricity corresponding to 10 - 30 % of the outer diameter of said insert. According to a preferred aspect of the invention, the ratio of length to outer diameter of the annnular locking insert is 2.0:1.0 - 0.75:1.0, more preferred 1.7:1:0 - 1,1:1,0, most preferred about 1.4:1.0. A preferred embodiment of the invention in which the interface zone where the shafts meet is further strengthened comprises two pairs of matching annular locking insert halves mirroring each other and joining each other face-to-face, one each arranged in each second bore, the axial extension of each of said bores being substantially less than the axial extension of the respective annular locking insert half, said locking insert halves in their portions external of said second bores being surrounded excentrically by a cylindrical mounting element interspaced between the abutting ends of the shafts and having a bore diameter corresponding to said second shaft bore diameter and an outer diameter corresponding to the diameter of the shaft, the excentricity of the cylindrical mounting element corresponding to that of said second bore. The mounting element is preferably made of toughened steel. It is advantageous for the bore of the annular locking insert halves to have an excentricity corresponding to 10 - 30 % of the outer diameter of the insert, for the length to outer diameter ratio of the combined annular locking insert halves to be 3.0:1.0 - 0.5:1.0, and for the ratio of inner to outer diameter of the mounting element to be 0,6 - 0,85. The annular locking insert halves and the mounting element are preferably made of toughened steel. Furthermore, in accordance with the invention, there is provided an annular locking insert or insert half for a shafting connection of hollow steel shafts having an excentrically arranged through bore. According to a particularly advantageous aspect of the invention, the mounting element comprises two about half moon-shaped element halves mirroring each other in an axial plane. This arrangement allows the shafting connection to be disassembled without need for pulling the shafts apart. It is a further object of the invention to provide a method for shafting two cylindrical hollow shafts having a main centrally arranged bore. According to the present invention, the shafting method comprises the following steps: (a) providing in the butt faces of the shafts excentric cylindrical second bores extending in the direction of the shaft axis, (b) fitting a first annular locking insert having an excentrically arranged bore into one of said second bores, (c) aligning said one main shaft bore with the bore of said first annular locking insert, (d) axially displacing one of the shafts in the direction of the other shaft until abutment, followed or preceded by alignment of the inner bores of the assembly, (e) fitting a press fit joint over the the shafts ends and activating the joint. It is preferred for the shaft bores and the annular locking insert bore to be kept in alignment while fitting and activating the press fit joint. According to a preferred aspect of the method according to the invention, cylindrical intermediate bores are provided between said second bores and said main shaft bores, with which they are aligned, and cylindrical symmetric sleeve inserts are fitted into said intermediate bores prior to step (b). According to a further preferred aspect of the method according to the invention, prior to step (d) a second annular locking insert mirroring said first annular locking insert is fitted into the excentrically arranged bore of the other shaft and a cylindrical mounting element having an excentrically arranged bore is slided over one of the cylindrical inserts. According to another preferred aspect of the invention, the method further includes the steps of fitting a second annular locking insert mirroring the first annular locking insert into the excentrically arranged bore of the other shaft, and of fitting two about half moon-shaped mounting element halves around the annular locking insert, which steps are preceded by or consecutive to step (d), respectively. The invention will now be explained in more detail by reference to preferred embodiments illustrated in drawings, in which: Fig. 1 is a longitudinal section through a first preferred embodiment in a mounted state, Fig. 2 is a longitudinal section through a second preferred embodiment in a mounted state, Fig. 3 is a longitudinal section through a third preferred embodiment in a mounted state, Fig. 4 is a longitudinal section through a fourth preferred embodiment in a mounted state, Fig. 5 is a section perpendicular to the axis of the locking insert and the locking insert half of the first and second, and third and fourth embodiments, respectively, Fig. 6 is a preferred aspect of the mounting element of the third and fourth preferred embodiment, Fig. 7 is an axial end view of the object in Fig. 6. Two cylindrical propeller steel shafts 1, 2 with central bores 3, 4, (axis A) are aligned and abutting with their flat faces (Fig. 1). The end portions of the shafts 1, 2 have excentrically arranged (axis B) cylindrical recesses 21, 22. The cylindrical space thus formed is occupied by a snugly fitting locking insert 5 of thoughened steel with an excentrically arranged through bore 6 of same diameter as the main shaft bores 3, 4. The bores 3, 4, and 6 are in alignment. The shafts 1, 2 are surrounded by an activated pressure fit joint assembly indicated in the Figures by inner and outer sleeves 8, 9 tapering at their interface but otherwise cylindrical. The sleeves 8, 9 are axially centered at the interface between the shafts 1, 2. The compression exerted by the pressure fit joint assembly stabilizes the shafts 1, 2 and thus their connection. The embodiment shown in Fig. 2 differs from that in Fig. 1 in that further bores or recesses 10, 11 with a diameter larger than that of the main shaft bores 3, 4 but smaller than that of the recesses 21, 22 are arranged concentrically in respect of the main shaft bores 3, 4 and in alignment with them. The bores 10, 11 are extending axially from the inner end of recesses 21, 22. Their extension is approximately matching that of the axial extension of the press fit joint assembly 8, 9. Cylindrical sleeve inserts or sockets 12, 13 of toughened steel are fitted into bores 10, 11. The lumen 14, 15 of the inserts 12, 13 essentially corresponds to that of the main shaft bores 3, 4. The embodiment shown in Fig. 3 has an annular locking element consisting of mirroring halves 51, 52 occupying excentrically arranged shallow recesses 31, 32 in the end faces 54, 55 of the cylindrical shafts 19, 20 (axis A') and raising above faces 54, 55. The annular locking element halves 51, 52 are in abutting contact which each other while the shaft end faces 54, 55 are spaced apart. The interstice between faces 54, 55 is occupied by an annular mounting element 53 of toughened steel having an excentrically arranged bore 56 (axis B'). The outer diameter of the annular mounting element 53 thus corresponds to that of the shafts 19, 20 whereas its inner diameter corresponds to the outer diameter of the annular locking insert halves 51, 52. The embodiment shown in Fig. 4 differs from that in Fig. 3 in that bores or recesses 70, 71 with a diameter larger than that of the main shaft bores 30, 40 but smaller than that of the shallow recesses 31, 32 are arranged concentrically in respect of the main shaft bores 30, 40 and in alignment with them. The bores 70, 71 are extending axially from the inner end of recesses 31, 32. Their extension is approximately matching that of the axial extension of the press fit joint assembly 8, 9. Hollow cylindrical inserts or sockets 12, 13 of toughened steel are fitted into bores 70, 71. The lumen 14, 15 of the inserts 12, 13 essentially correspond to that of the main shaft bores 30, 40. As shown in Figs. 6 and 7, the mounting element 53 may comprise two symmetric halves 53a and 53b. This enables the connection to be partially disassembled without pulling the shafts apart. It is not required for the entire cylindrical hollow shafts to be of same outer and inner diameter; it suffices for their end portions at which they are joined to fulfil that requirement. A precision fit of the individual parts of the shafting connection assembly is a prerequisite for optimal function.

Claims: Shafting connection for connecting a first hollow cylindrical steel shaft (1;19) to a second hollow cylindrical steel shaft (2;20), each said shaft (1,2;19,20) having a main shaft bore (3,4;30,40) and said shafts (1,2;19,20) having identical outer diameters at least in regions extending from their abutting ends, comprising a friction coupling including an inner sleeve (8) with an inner cylindrical surface arranged for frictional contact with the outer surface of said terminal region of the shafts (1,2;19,20), said friction coupling being arranged to be fitted on the aligned shafts (1,2;19,20) to cover both shafts (1,2;19,20) near their abutting ends, each of said shafts (1,2;19,20) in a region extending from their abutting ends having a second bore 21,22 of same diameter for receiving an annular insert 5, said second bores 21,22 being wider than the main shaft bores (3,4;30,40), characterized in that said second bores 21,22 are arranged with equal excentricity in respect to the main shaft bores (3,4;30,40). Shafting connection according to claim 1, characterized in that said annular insert (5) is a locking insert having substantial extension in both second bores (21,22) and having an excentrically arranged through bore (6), the degree of excentricity essentially corresponding to that of the excentrically arranged bore (21,22) in the respective shaft (1,2). Shafting connection according to claim 1 or 2, characterized in that the bore (6) diameter of said annular locking insert (5) essentially corresponds to the diameter of the main shaft bores (3,4). Shafting connection according to any of claims 1 - 3, characterized in that between the excentrically arranged bore (21,22) extending from the end of the respective shaft (1,2) and the symmetrically arranged main shaft bore (3,4), an intermediate bore (10,11) is arranged having an axis coinciding with the main shaft bore (3,4) axis and having a diameter larger than the diameter of the main shaft bore (3,4) but smaller than the outer diameter of the annular locking insert (5), into which intermediate bore (10,11) a symmetric sleeve insert (12,13) is fitted having an outer diameter essentially corresponding to the diameter of the intermediate bore (10,11), an inner diameter essentially corresponding to the diameter of the main shaft bore (3,4) and an axial extension not exceeding that of said intermediate bore (10,11). Shafting connection according to any of claims 1 - 4, characterized in that the annular locking insert (5) is made of toughened steel with a yield point of at least 850N/mm 2 . Shafting connection according to claim 4 or 5, characterized in that said symmetric sleeve insert (12,13) is made of toughened steel with a yield point of at least 850N/mm 2 . Shafting connection according to any of claims 1 - 6, characterized in that the bore (6) of the annular locking insert (5) has an excentricity corresponding to 10 - 30 % of the outer diameter of the insert (5). Shafting connection according to any of claims 1 - 7, characterized in that the ratio of length to outer diameter of the annular locking insert (5) is 2.0:1.0 - 0.75:1.0. Shafting connection according to any of claims 1 - 8, characterized in that the ratio of length to outer diameter of the annular locking insert (5) is 1.7:1.0 - 1.1:1.0. Shafting connection according to any of claims 1 - 9, characterized in that the ratio of length to outer diameter of the annular locking insert (5) is about 1.4:1.0. Shafting connection according to any of claims 1 - 10, characterized in that said annular locking insert (5) comprises a pair of matching locking insert halves (51,52) mirroring each other and joining each other face-to-face, one each arranged in each second bore (31,32), the axial extension of each of said bores (31,32) being substantially less than the axial extension of the respective locking insert half (51,52), said locking insert halves (51,52) in their portions external of said second bores (31,32) being surrounded by a cylindrical mounting element (53) interspaced between the abutting ends (55,54) of said shafts (10;20) and having an inner bore (56) diameter corresponding to said second shaft bore (31,32) diameter and an outer diameter corresponding to the diameter of the shaft (19;20), the excentricity of themounting element (53) corresponding to that of said second bore (31,32). Shafting connection according to claim 11, characterized in that the bore (60) of the annular locking insert halves (51,52) has an excentricity corresponding to 10 - 30 % of the outer diameter of the insert. Shafting connection according to claims 11 and 12, characterized in that the ratio of length to outer diameter of the combined annular locking insert halves (51,52) is 3.0:1.0 - 0.5:1.0. Shafting connection according to claims 11 - 13, characterized in that the ratio of inner to outer diameter of the mounting element (53) is 0,6 - 0,85. Shafting connection according to claims 11 - 14, characterized in that the annular locking insert halves (51,52) and the mounting element are made of toughened steel. Shafting connection according to claims 11 - 15, characterized in that the mounting element (53) comprises two about half moon-shaped element halves (53a,53b) mirroring each other in an axial plane. Annular locking insert (5) or insert half (51,52) for a shafting connection according to any of claims 1 to 16, characterized in that it has an excentrically arranged through bore (6;60). Method for shafting two cylindrical hollow shafts having centrally arranged main shaft bores, characterized in that it comprises the steps of: (a) providing in the butt faces of the shafts excentric cylindrical second bores extending in the direction of the shaft axis, (b) fitting an annular locking insert having an excentrically arranged bore into one of said shaft bores, (c) aligning said one shaft bore with the bore of said annular locking insert, (d) axially displacing one of the shafts in the direction of the other shaft until abutment, followed or preceded by alignment of the inner bores of the assembly, (e) fitting a press fit joint over the shaft ends and activating the joint. Method according to claim 18, characterized in that the shaft bores and the annular locking insert bore are kept in alignment while fitting and activating the press fit joint. Method according to claim 18 or 19, characterized in that, prior to step (b) it further comprises the steps of: providing cylindrical intermediate bores between said second bores and said main shaft bores, with which they are aligned, fitting symmetric inserts into said intermediate bores. Method according to any of claims 18 to 20, characterized in that, prior to step (d), it further includes the steps of: fitting a second annular locking insert mirroring said first annular locking insert into the excentrically arranged bore of the other shaft, sliding a cylindrical mounting element having an excentrically arranged bore over one of the annular locking inserts. Method according to any of claims 18 to 20, characterized in that, prior to step (d), it further includes the step of: fitting a second annular locking insert mirroring said first annular locking insert into the excentrically arranged bore of the other shaft, and, after completion of step (d), it further includes the step of: fitting two about half moon-shaped mounting element halves around the annular locking inserts.

Inventors: NESTEROV VLADIMIR, SERGEEV VILALY, SUNDBERG STAFFAN, NESTEROV, VLADIMIR, SERGEEV, VILALY, SUNDBERG, STAFFAN
Applicants: OVAKO COUPLINGS AB
Application year: 1993
Main classification: F16D1
IPC codes: F16D1