Hand operated electric tool, especially a jigsaw

Abstract: A hand-operated electric tool, especially a jigsaw, has a motor unit provided in the tool housing (1), which motor unit contains in a motor housing (20) the stator and the rotor, wherein the rotor shaft (21) projecting with one end from the motor housing (20) is mounted in two bearings fixed in the motor housing (20). A countershaft (30) that forms an extension of the rotor shaft (21) and carries a toothed arrangement is coupled to the rotor shaft and is rotatably mounted in a bearing (31). Rotor shaft (21) and countershaft (30) engage axially with radial play and are coupled non-rotatably by co-operating radial projections (23,24) and recesses (42,43) receiving the projections. In the region of the overlapping portions of rotor shaft (21) and countershaft (30), on one of the shafts there is provided an annular portion (25,26) extending at least over a part of the circumference, which annular portion is substantially in line contact with the adjacent circumferential surface of the other shaft.

Description: The invention relates to a hand-operated electric tool, especially a jigsaw, having a motor unit provided in the tool housing, which motor unit contains in a motor housing the stator and the rotor, wherein the rotor shaft projecting with one end from the motor housing is mounted in two bearings fixed in the motor housing, having a gear arrangement which is arranged to be driven by the rotor shaft, which gear arrangement is coupled to the rotor shaft by way of a countershaft that forms an extension of the rotor shaft and is rotatably mounted in a bearing, and having a tool chuck which is arranged to be driven by means of the gear arrangement. Electric tools, especially jigsaws, in which a pre-assembled motor unit is provided for the drive, are well known. The use of the pre-assembled motor unit, which is manufactured in large piece numbers and therefore economically, has the advantage that the very compact construction of the motor unit enables it to be mounted by fixing the motor housing in the housing of the electric tool, without the rotor and stator having to mounted in separate steps and without any need for the bearings of the rotor shaft to be set in specially constructed locating regions of the housing of the electric tool. With these motor units, however, for many applications, inter alia jigsaws, it is a disadvantage that the portion of the rotor shaft projecting from the motor housing is comparatively short, so that it cannot be coupled directly to the gear arrangement arranged at distance from the motor housing in the housing of the electric tool. On the contrary, a countershaft has to be provided, which acts as an extension of the rotor shaft and has a toothed arrangement, preferably a pinion, which meshes with the input gearwheel of the gear arrangement. This countershaft has to be rotatably mounted in an additional bearing, and it is normally rigidly connected to the rotor shaft. This produces, however, a three-point bearing of the unit comprising rotor shaft and countershaft, namely, on the one hand in the two bearings of the rotor shaft and on the other hand in the additional bearing of the countershaft. The bearings of such a three-point bearing cannot be coaxially aligned with absolute accuracy, however, so that in operation cannot be coaxially aligned with absolute accuracy, however, so that in operation the rotating unit comprising rotor shaft and countershaft is subject to bending stresses. These present no problems provided that the unit comprising rotor shaft and countershaft is of comparatively stable construction and the stresses acting on this unit in the region in which it engages with the gear arrangement are not too great. As the stresses in the engagement region with the gear arrangement increase, however, for instance in a relatively high-performance jigsaw, in which additional impact stress is transferred, via the gear, from the reciprocating saw blade engaged with the workpiece to the unit comprising rotor shaft and countershaft, it has been found that there is a risk that the three-point mounted unit will fracture. US Patent No. 5765652 discloses a hand operated electric tool comprising an electric motor with a rotor shaft coupled to a co-axial countershaft via a universal joint. The invention is based on the problem of eliminating the risk of fracture arising in the known construction. To solve that problem, an electric tool of the kind mentioned in the introduction is constructed in accordance with the invention so that rotor shaft and countershaft overlap one another axially with radial play therebetween and are coupled non-rotatably to one another by radial projections on the one shaft and complementary recesses receiving the projections on the other shaft, and so that, in the region of the overlapping portions of rotor shaft and countershaft, on one of the shafts there is provided an annular portion extending at least over a part of the circumference of the one shaft and lying in a plane perpendicular to the longitudinal axis of the one shaft, which annular portion is substantially in line contact with the adjacent circumferential surface of the other shaft. With the construction in accordance with the invention, the rotor shaft mounted in the two bearings provided in the motor housing and the countershaft mounted in an additional bearing are uncoupled from one another as a consequence of the engagement with radial play, so that the inevitable misalignment of the bearings does not lead to the disadvantageous bending stresses of a three-point bearing, on the contrary, corresponding to an inevitable misalignment of their bearing arrangements, rotor shaft and countershaft are likewise not aligned exactly coaxially with respect to one another. Locking of the rotor shaft and countershaft to prevent rotation, and hence the transfer of the rotary movement from the rotor shaft to the countershaft and from there to the gear, is gear, is achieved by the interlocking engagement of rotor shaft and countershaft by virtue of the radial projections and the recesses receiving them. Since it has proved, however, that this coupling of rotor shaft and countershaft with radial play can lead to the generation of considerable noise at high speed of the rotor shaft, the radial play of the coupling is restricted in accordance with the invention by the fact that on one of the shafts there is provided an annular portion, which is substantially in line contact with the adjacent circumferential surface of the other shaft. By virtue of the line contact, engagement between annular portion and circumferential surface does not hinder possible tilting of rotor shaft and countershaft relative to one another as a consequence of misalignments of their bearing arrangements, but ensures a certain contact of rotor shaft and countershaft in the overlap region of the two shafts. This has unexpectedly led to a considerable reduction in noise during joint rotation of rotor shaft and countershaft at high speed. In a preferred practical form of the invention, two projections lying diagonally opposite one another are present, and the annular portion extends on both sides between the projections, that is, forms two diagonally opposite component portions. The rotor shaft can extend with a bushing affixed thereto into a coaxial opening in the countershaft, and the projections and the annular portion can then be formed on the bushing. A further source of noise in the coupling of rotor shaft and countershaft provided is located in the region between the lateral surfaces of the projections and the lateral surfaces faces or axially running walls for the recesses receiving the projections. Depending on the direction of rotation a lateral wall of a projection comes into torque-transferring engagement with a lateral wall of the associated recess, this engagement varying in operation in dependence on the loading occurring. These variations in engagement can lead to noise. To reduce this noise generation, the recesses can have resiliently deformable supporting portions abutting the projections on both sides. Although the variation in loading in the coupling region between rotor shaft and countershaft is not reduced thereby, the resilient construction of the supporting portions "damps" these variations, so that an effective noise reduction is achieved. In an advantageous development of the invention, a fan wheel of plastics material, in the hub of which the recesses extend, sits on the countershaft, and the supporting portions are formed integral with the fan wheel and from the plastics material thereof. The invention is explained in detail in the following with reference to the Figures showing an exemplary embodiment. Figure 1 is a diagrammatic side view of a battery-powered jigsaw. Figure 2 is a fragmentary view, partly in section, of the jigsaw from Figure 1, the section in the plane of projection according to Figure 1 running through the middle of the jigsaw. Figure 3 is a view corresponding to Figure 2, in which the section runs perpendicular to the plane of projection in Figure 1 and through the middle of the rotor shaft of the drive motor of the jigsaw. Figure 4 shows the jigsaw according to Figures 1 to 3, partly as a fragmentary view and partly in section along the line IV-IV from Figure 2. Figure 5 is a perspective view of the part of the jigsaw shown in Figure 4. Note that the construction of the jigsaw corresponds substantially to the conventional construction of an electric tool of that kind, so that details that are not essential to the invention are not explained more specifically. The customary gear for such jigsaws is not, incidentally, shown in the Figures, and the part of this gear at the front in the saw housing is indicated in Figure 3 merely as a hatched area. Furthermore, note that parts of the jigsaw housing 1 that is shown in Figure 1 are not shown in the remaining Figures, which show, at least partially, inner housing parts 13 and 14. In the absence of parts of the jigsaw housing 1, the mounting for the motor housing 20 is also not shown. The jigsaw illustrated has, as already mentioned, a jigsaw housing 1, the upper middle portion of which forms a grip region 2, beneath which there is provided a grip opening 3 into which the operating element 4 for the ON/OFF switch extends in the customary manner. A battery 15 is releasably secured to the rear end of the jigsaw housing 1. At the front upper part of the jigsaw housing 1 there is a change lever 11; this change lever is connected by way of a connection 48 to the combination of ram 10, moving back and forth in operation, and saw blade clamp 9 secured thereto, and is used in known manner to bring the saw blade clamp 9 into an opened state and a clamped state, in which a jigsaw blade 12 is retained in the clamp. The jigsaw blade 12 extends through the window, open towards the front, of a customary shoe 6, which is secured to the lower part of the jigsaw housing 1 by means of an arched portion 7. By means of an operating element, the clamped fastening of the shoe 6 can be released and by turning the shoe 6 the bearing surface thereof can be brought into an inclined position with respect to the jigsaw blade 12 and the shoe 6 can be clamped in that position again in order thus, as is common in jigsaws, to obtain an inclined cutting edge setting. The jigsaw illustrated contains a motor unit, which contains in a motor housing 20 the stator, not illustrated, and the rotor, the rotor shaft 21 of which projects at one end from the motor housing 20. In the motor unit there are two bearings, not illustrated, for rotatable mounting of the rotor shaft 21. Such motor units are commercially available and are increasingly being used in electric tools because of their favourable price. The motor unit is secured by means of screws, not illustrated in detail, to a location plate 14 in the form of a housing part which is screwed to a housing section 13. Two bearings 31 lying directly adjacent to one another and in which a countershaft 30 is rotatably mounted, are fixed In the housing section 13, which forms part of the wall of the gear housing. The countershaft 30 is aligned coaxial with the rotor shaft 21 and at its end remote from the motor unit forms a pinion 34, which, in a manner not illustrated, meshes with an input gearwheel of the enlarged cross-section 32 and forms there a recess or opening 33 open to the motor unit. In this region, the outside of the countershaft 30 is in the form of a splined shaft (Figures 4 and 5), and the hub 41 of a plastics material fan wheel 40 is placed thereon. This fan wheel extends in a space formed between retaining plate 14 and the rear wall of housing part 13 facing the motor unit. The region 32 of the countershaft 30 has diagonally opposite indentations open towards the motor unit which continue radially outwards as openings 42, 43 (Figure 5) of the hub 41 of the fan wheel 40. On both sides of each of the openings 42, 43 there are supporting portions 44, 45 and 46, 47 formed from the plastics material of the fan wheel and of integral construction therewith, which are resiliently deformable in the circumferential direction. A bushing 22 is secured non-rotatably on the free end of the rotor shaft 21, and on the bushing there are formed projections 23, 24 lying diagonally opposite one another which in the mounted state engage in the openings 42, 43 in the fan wheel. The supporting portions 44, 45, and 46. 47 then abut the sides of the projections 23, 24. Component regions 25, 26 of an annular portion (Figure 3) formed integral with the bushing 22 extend between the projections 23, 24 on both sides to form the outer surface of the bushing 22, the annular portion lying in a plane perpendicular to the longitudinal axis of the rotor shaft 21 and the longitudinal axis of the countershaft 30 arranged coaxial therewith. In the mounted state, the annular portion is in line contact with the inner circumferential surface of the opening 33 of the countershaft 30, whilst otherwise there is radial clearance between the outer surface of the bushing 22 and the inner circumferential surface of the opening 33. As is readily apparent, the engagement of the projections 23 and 24 of the bushing mounted non-rotatably on the rotor shaft 21 with the openings 42, 43 in the fan wheel 40 mounted non-rotatably on the countershaft 30 produces a coupling for transfer of the rotary movement of the rotor shaft 21 to the countershaft 30. Here, rotations of the countershaft 30 and rotor shaft 21 relative to one another, for instance as a consequence of sudden loading on the countershaft 30 resulting from impact stress occurring at the jigsaw blade 12, damped by the resiliently deformable supporting portions 44, 45 and 46, 47 abutting the projections 23, 24 laterally, so that generation of noise that is otherwise possible is considerably reduced. As already mentioned, the rotor shaft 21 is rotatably mounted in two bearings in the motor housing 20, whilst the countershaft 30 is mounted in the bearings 31 located in the housing part 13. This three-point bearing makes it practically impossible to align rotor shaft 21 and countershaft 30 exactly coaxially with one another. Because the bushing 22 is located with radial play in the opening 33 of the countershaft 30 and because there is only line contact, via the annular portion 25, 26, between inner surface of the opening 33 and outer surface of the bushing 22, rotor shaft 21 and countershaft 30 are able to engage one another with a slight misalignment, this misalignment being accommodated by a corresponding displacement of the annular portion 25, 26 within the opening 33. Despite that, the line contact between annular portion 25, 26 and inner surface of the opening 33 is maintained, and it has unexpectedly been shown that this engagement dramatically reduces the considerable generation of noise that would otherwise occur in this coupling region.

Claims: Hand-operated electric tool, especially a jigsaw, having a motor unit provided in the tool housing (1), which motor unit contains in a motor housing (20) the stator and the rotor, wherein the rotor shaft (21) projecting with one end from the motor housing (20) is mounted in two bearings fixed in the motor housing (20), having a gear arrangement that is arranged to be driven by the rotor shaft (21), which gear arrangement is coupled to the rotor shaft (21) by way of a countershaft (30) that forms an extension of the rotor shaft (21) and is rotatably mounted in a bearing (31), and having a tool chuck (9) that is arranged to be driven by means of the gear arrangement, characterised in that rotor shaft (21) and countershaft (30) overlap one another axially with radial play therebetween and are coupled non-rotatably to one another by radial projections (23, 24) on the one shaft (21) and complementary recesses (42, 43) receiving the projections (23, 24) on the other shaft (30), and in that , in the region of the overlapping portions of rotor shaft (21) and countershaft (30), on one of the shafts (21; 30) there is provided an annular portion (25, 26) extending at least over a part of the circumference of the one shaft (21;30) and lying in a plane perpendicular to the longitudinal axis of the one shaft (21;30), which annular portion is substantially in line contact with the adjacent circumferential surface of the other shaft (21;30). Electric tool as claimed in claim 1, wherein the annular portion (25,26) is substantially frustro-conical with a longitudinal axis co-axial with the longitudinal axis of the one shaft (21;30). Electric tool as claimed in either one of claims 1 or 2, characterised in that two diagonally opposite projections (23, 24) are provided and the annular portion (25, 26) extends on both sides between these projections (23, 24). Electric tool as claimed in any one of the previous claims, characterised in that the rotor shaft (21) extends with a bushing (22) affixed thereto into a coaxial opening (33) in the countershaft (30), and the projections (23, 24) and the annular portion (25, 26) are formed on the bushing (22). Electric tool as claimed in claim 4, wherein the annular portion (25,26) is in line contact with the inner circumferential surface of the co-axial opening (33) in the countershaft (30) whilst otherwise there is radial play between the outer surface of the bushing (22) and the inner circumferential surface of the co-axial opening (33). Electric tool as claimed in any one of the previous claims, characterised in that the recesses (42, 43) have resiliently deformable supporting portions (44, 45; 46, 47) which abut the projections (23, 24) on both sides. Electric tool as claimed in claim 6, characterised in that a fan wheel (40) of plastics material, in the hub (41) of which the recesses (42, 43) extend, sits on the countershaft (30), and the supporting portions (44, 45; 46, 47) are formed integral with the fan wheel (40) and from the plastics material thereof.

Inventors: BECHT REIMUND, BLICKHAN STEFAN, HERTING RAINER, STAAS ERNST, SUTTON DAVID L, BECHT, REIMUND, BLICKHAN, STEFAN, HERTING, RAINER, STAAS, ERNST, SUTTON, DAVID L
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1999
Main classification: B25F5
IPC codes: B23D51, B23D49, B25F5