Transmission device

Abstract

To provide a transmission device including a driving shaft cantilevered, for improving the fatigue strength of the driving shaft.SOLUTION: A transmission device (1) includes a power transmission body (27) rotatable around a center axis (C1) while receiving rotation driving force from a driving source, and a rotary shaft (11) around which the power transmission body (27) is fixed, and which is rotatable around the center axis (C1) and cantilevered. Between a free end (FE) of the rotary shaft (11) and a cantilevered supported region (SE), compression stress (Sc) is loaded on the rotary shaft (11).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a transmission device for transmitting a rotational driving force. [Background technology]

[0002] In a transmission device that transmits a rotary driving force, a drive shaft that rotates due to the power from a drive source rotates while being subjected to bending stress. An example of this rotary bending is a transmission device that rotates a drive shaft that is supported at one end via an endless belt and a pulley around which the belt is wound. Since this drive shaft rotates while receiving the tension of the belt via the pulley, it is used in a rotary bending state where it receives a radial load while rotating. Due to the fatigue strength of this drive shaft, there is a risk of breakage at the threaded portion or stepped portion.

[0003] A method for preventing damage to the drive shaft and the support member due to this rotary bending is proposed in Patent Document 1. Patent Document 1 claims that seizure and wear can be prevented by preventing contact between structural members of the oil pump caused by bending deformation of the drive shaft. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-229448 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the proposal in Patent Document 1 can prevent contact between structural members of the oil pump due to bending deformation of the drive shaft, it allows bending deformation of the drive shaft itself, so it cannot reduce the bending stress generated in the drive shaft itself. Therefore, it is not possible to avoid or suppress the rotational bending state of the drive shaft, so it is not possible to reduce the risk of fatigue strength of the drive shaft. Specifically, Patent Document 1 discloses a structure in which a spline connection is used to prevent bending deformation on the drive shaft side from contacting or interfering with the pump structural members on the driven side.

[0006] Meanwhile, in the above-mentioned transmission device that rotates a drive shaft supported at one end via a belt and a pulley, the drive shaft to which the pulley is fixed (pulley fixed shaft) is supported at one end by a bearing. In this case, the pulley fixed shaft supported at one end is subjected to bending deformation while a radial force acts on it during rotation due to the initial tension of the belt and the tensile force from the belt during driving. As a result, the pulley fixed shaft is subjected to a stress from rotational bending, reducing the fatigue strength of the shaft. The reduction in fatigue strength is particularly noticeable in the stepped portion of the shaft where stress is concentrated, the threaded portion, and the fixed portion of the shaft that is the end of the cantilever support.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to improve the fatigue strength of a drive shaft in a transmission device having a drive shaft supported by a cantilever. [Means for solving the problem]

[0008] The transmission device of the present invention comprises: a power transmission body that is rotatable about a central axis when receiving a rotational driving force from a driving source; The power transmission body is fixed to the periphery of a rotating shaft, and the rotating shaft is rotatable about a central axis and cantilevered. A compressive stress is applied to the rotating shaft between the free end of the rotating shaft and the support area by the cantilever support.

[0009] The transmission preferably comprises a bearing for rotatably supporting the rotating shaft, and the rotating shaft is rotatably supported by the bearing in the support region.

[0010] In the transmission, preferably a stress-loading shaft member disposed about a central axis of the rotating shaft; The stress-loaded shaft member is A tensile stress is applied between the support region and the free end, and thus a compressive stress is applied to the rotating shaft.

[0011] The rotation axis is preferably a receiving chamber formed of a gap along a central axis for receiving a stress-loaded shaft member; The stress-loaded shaft member is a threaded portion that is screwed onto the rotating shaft in the support region; A torso portion accommodated in the accommodation chamber; and a head that is engaged with the free end.

[0012] The threaded portion preferably has It is screwed onto the rotating shaft in a region that overlaps with the support region.

[0013] In the transmission device, the power transmission body is preferably a toothed pulley around which a toothed belt of the power transmission belt is wound, or a combination of a plurality of gears.

[0014] The rotation shaft preferably constitutes a ball screw shaft of a ball screw. Effect of the Invention

[0015] According to the transmission device of the present invention, the fatigue strength of the rotating shaft can be improved by generating compressive stress between the free end and the support area in the cantilever support. [Brief description of the drawings]

[0016] [Figure 1] 1 is a partial cross-sectional view showing a schematic configuration of a transmission device according to an embodiment. [Diagram 2] 5A to 5C are diagrams illustrating a stress state in a rotating shaft of the transmission device according to the embodiment. [Diagram 3] FIG. 3 is a diagram showing a fatigue limit diagram of the rotating shaft in the stress state of FIG. 2. [Figure 4] FIG. 13 is a diagram showing another example of applying a compressive stress. [Diagram 5] 1 is a diagram showing a schematic configuration of a ball screw which is a preferred application example of a transmission device according to an embodiment; [Figure 6]1 is a diagram showing a schematic configuration of power transmission by a gear train, which is a preferred application example of a transmission device according to an embodiment. [Figure 7] 1 is a diagram showing a schematic configuration of power transmission by a belt and pulleys, which is a preferred application example of a transmission device according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a transmission device 1 according to an embodiment will be described with reference to the accompanying drawings. [Summary of Transmission Device 1] The transmission device 1 transmits the rotational driving force of an electric motor serving as a driving source (not shown) to a rotatable driving shaft 11, and further transmits the rotational driving force of the driving shaft 11 to a driven member. The transmission device 1 transmits power from the driving source to the driving shaft 11 by belt transmission, and the driving shaft 11 is loaded with an initial tension due to the belt transmission and a tensile force during driving, generating stress due to rotational bending. The transmission device 1 reduces the tensile stress by a combined stress of compressive stress and bending stress generated in a necessary area of ​​the driving shaft 11.

[0018] [Configuration of transmission device 1: See Figure 1] The transmission device 1 includes a drive shaft 11 that is rotationally driven about a central axis C1 by the rotational driving force of a drive source, bearings 13, 13 that rotatably support the drive shaft 11, and a housing 15 that accommodates and holds the bearings 13, 13. The drive shaft 11 rotates while being supported by the bearings 13, 13 that are held in the housing 15. In the transmission device 1, the front (F), rear (R), horizontal (H) and vertical (V) directions are defined as shown in Fig. 1. Note that the front (F) and rear (R) have relative meanings.

[0019] The drive shaft 11 has an internal thread 17 cut on its outer periphery forward (F) of the portion supported by the bearings 13, 13, and a nut 19 that fixes the bearings 13, 13 is screwed into this internal thread 17, whereby the bearings 13, 13 and the drive shaft 11 supported by the bearings 13, 13 are accommodated and held in the housing 15. The drive shaft 11 is formed with a smaller diameter forward (F) of the internal thread 17, so that a stepped portion 21 is formed in a continuous circumferential direction. The drive shaft 11 has an accommodation chamber 23 formed around the central axis C1 from the end at the front (F) to the rear (R). The accommodation chamber 23 is, for example, drilled to the rear end E that reaches the bearings 13, 13, and a female thread 25 for fixing a bolt is formed on the outer periphery of the chamber 23 in a predetermined range from the rear end E to the front (F). No elements such as threads are formed in the accommodation chamber 23 in front of the female thread 25 (F).

[0020] The drive shaft 11 constitutes a part of the driven member behind (R) the part housed in the housing 15. A pulley 27 is fixed to the drive shaft 11 as a power transmission body ahead (F) of the part housed in the housing 15, and the drive shaft 11 rotates in conjunction with the rotation of the pulley 27. The drive shaft 11 is cantilever-supported with the part supported by the bearings 13, 13 being the support area SE, and the front (F) side where the pulley 27 is provided being the free end FE.

[0021] One end of an endless belt 29 is wound around the pulley 27, and the other end of the belt 29 is wound around, for example, an output shaft of an electric motor (not shown). The belt 29 is wound around the pulley 27 and the output shaft (not shown) of the electric motor with a predetermined initial tension, and this initial tension is applied to the drive shaft 11 to which the pulley 27 is fixed. When the electric motor is driven to rotate the pulley 27 via the belt 29, a drive tension is applied to the drive shaft 11 via the pulley 27 in addition to the initial tension. Due to these initial tension and drive tension, a radial load perpendicular to the central axis C1 is applied to the rotating drive shaft 11. The cantilever-supported drive shaft 11 rotates while receiving a bending load Lb and a bending stress Sb due to the radial load caused by the belt transmission.

[0022] In order to suppress fatigue strength due to the bending load Lb / bending stress Sb, the transmission device 1 applies a compressive stress Sc to the drive shaft 11 between the support area SE and the free end FE. This compressive stress Sc reduces the average stress generated in the drive shaft 11. The transmission 1 uses a fastener 31 to apply a compressive stress Sc. The fastener 31 includes a head 31A, a body 31B connected to the head 31A, and a threaded portion 31C having a male thread connected to the body 31B on its outer periphery. The fastener 31 is inserted into the housing chamber 23 of the drive shaft 11 from the side of the threaded portion 31C, and the threaded portion 31C is screwed into the female thread 25 formed in the housing chamber 23. The head 31A contacts the support end 24 of the drive shaft 11 around the housing chamber 23. By screwing the threaded portion 31C deeply toward the rear (R) of the female thread 25, the head 31A can be strongly pressed against the support end 24. As a result, a tensile stress St is generated in the fastener 31 in the direction of the central axis C1, and a compressive stress Sc is generated in the drive shaft 11 in response. The compressive stress Sc occurs between the support end 24 with which the head 31A contacts and the internal thread 25 to which the threaded portion 31C is fastened. The portion where the internal thread 25 is provided overlaps with the support region SE, and the compressive stress Sc of the drive shaft 11 occurs between the free end FE and the support region SE.

[0023] [Stress state: see Figure 2] The stress state of the transmission 1 when a compressive stress Sc is applied to the drive shaft 11 will be described with reference to FIG. The upper left of Fig. 2 shows that only compressive stress Sc is applied to the drive shaft 11, and the upper right of Fig. 2 shows that only bending stress Sb is applied to the drive shaft 11. In Fig. 2, compressive stress Sc is shown by a dashed line, and tensile stress St is shown by a solid line.

[0024] As shown in FIG. 2, the compressive stress Sc has a constant value regardless of the radial position of the drive shaft 11. As shown in FIG. 2, when a bending stress Sb is applied, a tensile stress St is generated above the central axis C1, and a compressive stress Sc is generated below the central axis C1, depending on the direction of bending.

[0025] In practice, the stress state α shown in Fig. 2 is combined with the stress state β shown in Fig. 2. The stress state γ resulting from this combination is shown in the lower part of Fig. 2. By combining the stress states α and β, in the stress state γ, the tensile stress becomes small while the compressive stress Sc becomes large. The female thread 25 for the fastener 31 is formed so as to overlap with the support area SE by the bearing 13 so that a compressive stress Sc by the fastener 31 acts between the fixed portion of the pulley 27 where the bending stress Sb acts and the support area SE by the bearing 13.

[0026] [Fatigue limit diagram according to stress state γ: Figure 3] Therefore, let us consider the fatigue limit diagram in the stress state γ. The fatigue limit diagram in Fig. 3 is based on the modified Goodman diagram. In Fig. 3, the stress state γ is when an initial load M (compressive stress Sc) due to compression by the fastener 31 acts on the drive shaft 11. Therefore, the operating point Q of the drive shaft 11 is shifted to the left of the origin in the figure, where the average stress is 0 (zero). Note that when the initial load M (compressive stress Sc) is not acting, the operating point P is on the vertical axis where the average stress is 0. In other words, when the initial load M is applied, the operating point Q is displaced to the negative side.

[0027] The fatigue safety factors at operating points Q and P are calculated as follows, and the fatigue safety factor increases by applying a compressive stress as the initial load M. Therefore, the transmission device 1 according to this embodiment can improve the fatigue strength of the drive shaft 11. Note that below, σw is the fatigue limit of the metal material, σa1 is the stress amplitude at operating point P when the initial load M (compressive stress Sc) due to compression by the fastener 31 is not acting on the drive shaft 11, σMA is the fatigue limit when the initial load M (compressive stress Sc) due to compression by the fastener 31 acts on the drive shaft 11, and MA and MQ are the lengths of the line segments MA and MQ, respectively. No initial load M f1: f1=σw / σa1 With initial load M f2: f2=MA / MQ=σMA / σa1 σMA>σw , f2>f1

[0028] [Other means of applying compressive stress: see Figure 4] Although an example has been described above in which a single-threaded bolt is used as the fastener 31, it is also possible to use a double-threaded bolt 26 in which male threads 26A, 26B are formed on both axial ends, as shown in Fig. 4(a). In this case, the male thread 26A is screwed into a nut 28 in which a female thread is formed, and the male thread 26B is screwed into a female thread 25 formed on the drive shaft 11. By tightening the nut 28, a compressive stress Sc can be generated. 4(b), for example, bolt 12 is formed integrally with drive shaft 11. One end of bolt 12 has a fixed portion 12B connected to drive shaft 11, and the other end has a male thread 12A into which a nut 28 is screwed. By tightening nut 28, compressive stress Sc can be generated.

[0029] [Preferred form of belt transmission] There are several types of belt transmissions, including flat belts, V-belts, and toothed belts. Among these, toothed belts transmit a larger amount of power than flat belts and V-belts. Therefore, when a toothed belt is used, the radial load due to the drive tension (T2) is large, and in recent years, the power transmitted by toothed belts has improved, and the radial load due to the belt tension tends to increase. Therefore, the effect of improving the fatigue limit by applying a compressive stress Sc to the drive shaft 11 becomes significant.

[0030] [Preferred use: See Figure 5] A preferred application of the transmission device 1 is a ball screw. As shown in FIG. 5, the ball screw 40 includes a ball screw shaft 41 that is rotatable about a central axis C2, and a ball screw nut 45 that is screwed onto the ball screw shaft 41. The ball screw shaft 41 is rotatably supported by a movable body via a ball screw nut 45, and is rotatably supported by a fixed body whose position is fixed via a screw bearing 43. The ball screw shaft 41 is thus rotatable, but movement in the axial direction C is restricted. As shown in Fig. 5, the ball screw nut 45 is screwed onto the ball screw shaft 41, and this ball screw nut 45 is fixed to and supported by a movable body that is capable of moving in one direction.

[0031] The ball screw 40 is driven by a drive motor 50. A belt 55 is wound around a pulley 53 fixed to an output shaft 51 of the drive motor 50 and a pulley 47 fixed to the ball screw shaft 41. Therefore, when the drive motor 50 is rotated, for example, forward and reverse, the ball screw nut 45 can be moved in the front-rear direction. Examples of the movable body and the fixed body include a movable platen and a fixed platen in an injection molding machine and a die-casting machine.

[0032] In recent years, with the advancement of ball screw technology, the life of ball screws has improved, and there is a tendency to make the diameter of the ball screw shaft smaller. In addition, the radial load caused by the belt tension has also increased. If the present invention is applied to the driven end 48 of the ball screw shaft 41, it is effective as a measure to improve the fatigue strength of the cantilever support part.

[0033] [Power transmission by gear train: see Figure 6] In the above embodiment, the transmission device 1 using the belt and pulleys has been described, but the present invention can also be applied to a transmission device 2 using a gear train in which a plurality of gears mesh with each other. The transmission device 2 includes a drive source motor 50, which is a drive source, and a driven body 60 to which the driving force of the drive source motor 50 is transmitted. A main driving gear 56 is fixed to an output shaft 51 of the drive source motor 50, a driven gear 63 is fixed to a rotation shaft 61 of the driven body 60, and the main driving gear 56 and the driven gear 63 mesh with each other. As an example, the output shaft 51 rotates counterclockwise as indicated by the arrow in the figure, and the rotation shaft 61 rotates clockwise as indicated by the arrow in the figure. Although the gear train in FIG. 6 shows an example in which two gears mesh, the present invention can also be applied to a gear train in which three or more gears mesh.

[0034] In the transmission device 2, when the drive source motor 50 is driven, a driving force and a reaction force as shown in Fig. 6 are generated. That is, in a power transmission portion where the main gear 56 and the driven gear 63 mesh, a driving force DF56 is applied from the main gear 56 to the driven gear 63 in the rightward direction in the figure, and a reaction force RF63 of the driving force DF56 is applied to the main gear 56 in the leftward direction in the figure. Therefore, a reaction force RF51 is applied to the output shaft 51 in the leftward direction in the figure, and a driving force DF61 is applied to the rotating shaft 61 in the rightward direction in the figure. Both the reaction force RF51 and the driving force DF61 are radial loads on the respective shafts, and generate a bending stress Sb in the rotating shaft 61.

[0035] As described above, bending stress occurs in the rotating shaft 61 of the driven body 60, and by applying a compressive stress (Sc) to the rotating shaft 61 as described above, the fatigue strength of the rotating shaft 61 can be improved. As is clear from FIG. 6, bending stress can also occur in the output shaft 51 of the drive motor 50, and therefore the output shaft 51 can also be subjected to compressive stress (Sc).

[0036] [Power transmission by pulleys: see Figure 7] Corresponding to the driving force and reaction force shown for the gear train, the driving force and reaction force for power transmission by a pulley will be shown below.

[0037] The transmission device 3 includes a drive motor 50 and a driven body 60 to which the driving force of the drive motor 50 is transmitted. A drive pulley 53 is fixed to an output shaft 51 of the drive motor 50, a driven pulley 65 is fixed to a rotating shaft 61 of the driven body 60, and a belt 55 is wound around the drive pulley 53 and the driven pulley 65. As an example, the output shaft 51 and the rotating shaft 61 rotate counterclockwise as indicated by the arrow in the figure.

[0038] In the transmission device 3, when the drive source motor 50 is driven, the forces shown in Fig. 7 are generated. That is, a tensile force T55 acts on the belt 55 as a driving force. The tensile force T55 causes a force DU61 that pulls the driven pulley 65 substantially upward to act on the rotating shaft 61, and a reaction force RF51 in the opposite direction to the force DU61 is generated on the output shaft 51. Both the force DU61 and the reaction force RF51 are radial loads on the respective shafts.

[0039] In addition to the above, the configurations given in the above embodiments can be selected or appropriately changed to other configurations without departing from the spirit of the present invention. For example, the compressive stress applying structure of the present invention may be applied to the output shaft of a drive motor. In this case, although the output shaft is not rotatably supported by a bearing, it is nonetheless supported by a cantilever, and therefore it is preferable to apply the present invention to the output shaft. The present invention can also be applied to a friction wheel on which a load acts in the same manner as in a gear train. [Explanation of symbols]

[0040] 1,2 Transmission device 11 Drive shaft 12 Volts 12A male thread 12B Fixed part 13 Bearings 15 Housing 19 Nut 21 Stepped section 23 Containment Room 24 Support end 26 Double threaded bolt 27 Pulley 28 Nut 29 Belt 31 Fasteners 31A Head 31B Torso 31C Threaded section 40 Ball screw 41 Ball screw shaft 45 Ball screw nut 47 Pulley 50 Driving motor 51 Output shaft 53 Pulley 55 Belt C-axis direction C1,C2 center axis Sb bending stress Sc Compressive stress St Tensile stress SE support area FE free end

Claims

1. a power transmission body that is rotatable about a central axis when receiving a rotational driving force from a driving source; a rotation shaft to which the power transmission body is fixed and which is rotatable about the central axis and cantilevered, A transmission device, in which compressive stress is applied to the rotating shaft between the free end of the rotating shaft and the cantilever support area.

2. A bearing is provided to rotatably support the rotating shaft, In the support region, the rotating shaft is rotatably supported by the bearing.

2. The transmission according to claim 1.

3. a stress-loaded shaft member disposed about the central axis of the rotating shaft; The stress-applied shaft member is A tensile stress is applied between the free end and the support region, so that the compressive stress is applied to the rotating shaft.

2. The transmission according to claim 1.

4. The rotation axis is a receiving chamber formed of a gap along the central axis for receiving the stress-applied shaft member; The stress-applied shaft member is a threaded portion that is screwed onto the rotating shaft in the support region; A body portion accommodated in the accommodation chamber; a head engaged with the free end.

4. The transmission according to claim 3.

5. The screw portion is The support region is screwed onto the rotating shaft in an overlapping region with the support region.

5. The transmission according to claim 4.

6. The power transmission body is A toothed pulley around which a toothed belt of a power transmission belt is wound, or It is a combination of multiple gears.

2. The transmission according to claim 1.

7. The rotation shaft constitutes a ball screw shaft of a ball screw.

2. The transmission according to claim 1.

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