Power transmission mechanism and steering column device

Abstract

This power transmission mechanism (30) comprises: a screw shaft (33) rotatably provided to an outer column (5); and a drive member (35) which is provided to an inner column (7) and which is threadably engaged by the screw shaft (33). The power transmission mechanism is configured such that rotation of the screw shaft (33) causes the screw shaft (33) and the drive member (35) to move relative to each other and causes the outer column (5) and the inner column (7) to move relative to each other. The screw shaft (33) and the drive member (35) each have a multi-start thread. In the multi-start thread provided to the drive member (35), the threading start position of a second internal thread part (N2) is shifted in the circumferential direction by an angle (α) from an angle (An) obtained by dividing 360 degrees by the number of starts of the multi-start thread, with respect to the threading start position of a first internal thread part (N1) adjacent in the circumferential direction.

Description

Power Transmission Mechanism and Steering Column Device

[0001] The present invention relates to a power transmission mechanism and a steering column device.

[0002] A steering column device is known that includes a tilt mechanism that supports a steering shaft such that a jacket portion is rotatable and swings the jacket portion in the vertical direction (Patent Document 1). The tilt mechanism rotates a male screw shaft member by an electric motor, and a female screw member screwed onto the male screw shaft member moves axially together with a movable side casing. Thereby, the jacket portion swings in the vertical direction.

[0003] Japanese Patent Application Laid-Open No. 2012-25321

[0004] A clearance (backlash) for sliding is required at the screwing portion between the male screw shaft member and the female screw member, and this clearance causes play in the steering shaft. For this reason, in the conventional steering column device described above, in order to suppress play, two nuts screwed onto the male screw shaft member, a wedge member that presses the two nuts in the axial direction of the male screw shaft member, a screw member and a double nut for preventing the wedge member from coming off the movable side casing are provided. For this reason, the conventional steering column device tends to have a large number of parts, a complicated structure, and a high manufacturing cost.

[0005] The present invention has been made in view of the problems of such conventional technologies. And an object of the present invention is to provide a power transmission mechanism and a steering column device that can suppress play at the screwing portion between the male screw shaft member and the female screw member with a simpler configuration.

[0006] A power transmission mechanism according to an aspect of the present invention comprises a male screw shaft member rotatably mounted on either a support portion or a movable portion and having a male thread formed along its axial direction, and a female screw member mounted on the other of the support portion or the movable portion and into which the male screw shaft member is screwed. The rotation of the male screw shaft member causes the female screw member and the male screw shaft member to move relative to each other, and the movable portion to move relative to the support portion. The male screw shaft member and the female screw member each have a multi-start thread. In the multi-start thread of either the male screw shaft member or the female screw member, the threading start position of at least one thread is displaced circumferentially by a predetermined angle from an angle obtained by dividing 360 degrees by the number of threads in the multi-start thread with respect to the threading start position of other threads adjacent in the circumferential direction.

[0007] A steering column device according to an aspect of the present invention includes a power transmission mechanism. The power transmission mechanism includes a male screw shaft member rotatably mounted on either a support portion or a movable portion and having a male thread formed along the axial direction, and a female screw member mounted on the other of the support portion or the movable portion and into which the male screw shaft member is screwed. The rotation of the male screw shaft member causes the female screw member and the male screw shaft member to move relative to each other, and the movable portion to move relative to the support portion. The male screw shaft member and the female screw member each have a multi-start thread. In the multi-start thread of either the male screw shaft member or the female screw member, the threading start position of at least one thread is displaced circumferentially by a predetermined angle from an angle obtained by dividing 360 degrees by the number of threads in the multi-start thread with respect to the threading start position of other threads adjacent in the circumferential direction.

[0008] According to the present invention, it is possible to provide a power transmission mechanism and a steering column device that can suppress play in the threaded portion between the male screw shaft member and the female screw member with a simpler configuration.

[0009] Figure 1 is a perspective view showing an example of a steering device according to this embodiment. Figure 2 is a perspective view showing a power transmission mechanism according to this embodiment. Figure 3 is a cross-sectional view showing a screw shaft screwed into a drive member. Figure 4 is an enlarged cross-sectional view of part A in Figure 3. Figure 5 is a schematic view of the drive member alone along the line B-B in Figure 3. Figure 6 is a schematic cross-sectional view of the screw shaft alone along the line B-B in Figure 3. Figure 7 is a schematic view of the drive member alone according to a modified example corresponding to the line B-B in Figure 3. Figure 8 is a schematic cross-sectional view of the screw shaft alone according to a modified example corresponding to the line B-B in Figure 3.

[0010] The power transmission mechanism and steering column device according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] Figure 1 shows the steering column device 1 according to this embodiment. When the steering column device 1 is attached to the vehicle body, the direction indicated by the arrow FR in Figure 1 is the front of the vehicle. Hereinafter, "front" refers to the front of the vehicle, "rear" refers to the rear of the vehicle, and "left / right direction" refers to the left / right direction when viewed from the rear of the vehicle towards the front.

[0012] The steering column device 1 includes a vehicle mounting bracket 3 attached to the vehicle body (not shown), an outer column 5 supported so as to be able to swing vertically relative to the vehicle mounting bracket 3, and an inner column 7 that is movable in the front-rear direction relative to the outer column 5. The vehicle mounting bracket 3 has mounting parts 3a at multiple locations and is attached to the vehicle body by the mounting parts 3a.

[0013] The outer column 5 swings vertically relative to the vehicle mounting bracket 3 via a tilt drive motor 21, a power transmission mechanism 40 and a link mechanism 23 operated by the tilt drive motor 21, etc. These tilt drive motor 21, power transmission mechanism 40 and link mechanism 23 etc. are provided on the right side of the steering column device 1. The power transmission mechanism 40 has a screw shaft 43 as a male screw shaft member and a drive member 45 as a female screw member. When the outer column 5 swings vertically, the inner column 7 and the steering shaft 9, which is rotatably inserted into the inner column 7, also swing together. A steering wheel (not shown) is attached to the rear end of the steering shaft 9.

[0014] Therefore, the steering column device 1 is equipped with a tilt mechanism 20 that allows the steering wheel to swing freely in the vertical direction. The steering column device 1 is further equipped with a telescopic mechanism 10 that allows the steering wheel to move freely in the front-rear direction.

[0015] The telescopic mechanism 10 includes a telescopic drive motor 11, which serves as an electric actuator and is mounted on the left side of the outer column 5. The telescopic drive motor 11 is mounted on the outer column 5 together with the reduction gear mechanism 12. A screw shaft 33, which is rotationally driven by the telescopic drive motor 11, extends along the axial direction of the cylindrical inner column 7.

[0016] Furthermore, the telescopic mechanism 10 has a power transmission mechanism 30, also known as a lead screw mechanism.

[0017] The power transmission mechanisms 30 and 40 according to this embodiment will be described below.

[0018] Figures 2, 3, and 4 show the power transmission mechanism 30 provided in the telescopic mechanism 10. Figure 5 shows the drive member 35 alone, and Figure 6 shows the screw shaft 33 alone. Note that the power transmission mechanism 40 provided in the tilt mechanism 20 is configured in the same way as the power transmission mechanism 30 provided in the telescopic mechanism 10, so a detailed explanation of the power transmission mechanism 40 on the tilt mechanism 20 side will be omitted.

[0019] The power transmission mechanism 30 includes a screw shaft 33 as a male screw shaft member and a drive member 35 as a female screw member.

[0020] The screw shaft 33, which serves as the male screw shaft member, comprises a screw shaft portion 33a into which the drive member 35 is screwed, and a front screw shaft portion (not shown) located in front of the screw shaft portion 33a. The screw shaft 33 also comprises a shaft portion (not shown) located between the screw shaft portion 33a and the front screw shaft portion. The shaft portion of the screw shaft 33 is supported by the reduction mechanism 12.

[0021] The shaft portion of the screw shaft 33 is rotatable relative to the reduction mechanism 12, while its axial movement is restricted relative to the reduction mechanism 12. Depending on the mounting position or shape of the telescopic drive motor 11, or the mounting position or shape of the reduction mechanism 12, the screw shaft 33 can also be connected to the reduction mechanism 12 using a flexible shaft (not shown).

[0022] The drive member 35, which functions as a female threaded component, is equipped with a nut portion 35a. The drive member 35 is attached to a bracket 13 (see Figure 1), which in turn is attached to the inner column 7 via an opening (not shown) provided in the outer column 5. Therefore, by driving the telescopic drive motor 11 and rotating the screw shaft 33, the drive member 35 moves in the front-rear direction along the screw shaft 33. Consequently, the inner column 7, which functions as a movable part, moves in the front-rear direction relative to the outer column 5, which functions as a support part, together with the steering shaft 9.

[0023] In this embodiment, the screw shaft 33 (screw shaft portion 33a) and the drive member 35 (nut portion 35a) are each formed by a multi-start thread. In the multi-start thread of either the screw shaft portion 33a or the nut portion 35a, the starting point of at least one thread (starting position of thread cutting) is shifted by several degrees in the circumferential direction relative to the starting point of another thread adjacent in the circumferential direction. By doing so, the phase of the multi-start thread with the shifted starting point changes, and by shifting its phase relative to the other multi-start thread, play in the threaded portion between the screw shaft 33 and the drive member 35 can be suppressed.

[0024] In the embodiment shown in Figures 2 to 6, the screw shaft 33 (screw shaft portion 33a) and the drive member 35 (nut portion 35a) are each formed by a double-start thread. In this case, the screw shaft portion 33a is configured to have a first male thread portion S1 and a second male thread portion S2. These first male thread portion S1 and second male thread portion S2 are arranged at the same pitch Ps (see Figure 4). Also, when the screw shaft 33 is viewed from the axial direction, the first male thread portion S1 and the second male thread portion S2 are arranged at an angle As (180°) obtained by dividing the circumference of 360 degrees by the number of threads in the multi-start thread (see Figure 6). On the other hand, the nut portion 35a is configured to have a first female thread portion N1 and a second female thread portion N2. In this embodiment, the starting point of the thread in the second female thread portion N2 is shifted circumferentially by a few degrees (3 degrees in this embodiment) from the angle An (180°) obtained by dividing the circumference of 360 degrees by the number of threads in the multi-start thread, relative to the starting point of the thread in the first female thread portion N1 (see Figure 5). The angle α shifted circumferentially is preferably in the range of 1 to 5 degrees, taking into account the sliding resistance during driving. In Figure 4, for the sake of explanation, the second female thread portion N2 with its shifted starting point is shown with dot hatching in addition to the normal hatching.

[0025] As described above, in a multi-start screw, the starting point of the second female thread N2 is shifted circumferentially by a few degrees (angle α) from angle An relative to the starting point of the first female thread N1. By doing this, the phase of the second female thread N2, whose starting point has been shifted, changes, and its phase is shifted relative to the first female thread N1. As a result, as shown in Figure 4, the pitch between the first female thread N1 and the second female thread N2 is changed from equal pitch Pn to pitch β, forming two different pitches: a narrow pitch Pns and a wide pitch Pnl.

[0026] Therefore, when the screw shaft 33 is screwed onto the drive member 35, the threads of the two female threads N1 and N2 contact the threads of the second male thread S2 in Figure 4, sandwiching them between them. That is, the threads of the first female thread N1 contact the threads of the second male thread S2 from the left in Figure 4. Conversely, the threads of the second female thread N2 contact the threads of the second male thread S2 from the right in Figure 4. As a result, the relative axial movement between the screw shaft portion 33a of the screw shaft 33 and the nut portion 35a of the drive member 35 is restricted, and the looseness of the screw threads between them is suppressed, thereby suppressing the looseness of the steering shaft 9.

[0027] Furthermore, as shown in the modified examples in Figures 7 and 8, the screw shaft 33 (screw shaft portion 33a) and the drive member 35 (nut portion 35a) can each be formed with a three-start thread. In this case, the screw shaft portion 33a is composed of a first-start male thread portion S1, a second-start male thread portion S2, and a third-start male thread portion S3. Although not shown in the figures, these first-start male thread portions S1, S2, and S3 are arranged at the same pitch. Also, when the screw shaft 33 is viewed from the axial direction, the first-start male thread portion S1, S2, and S3 are arranged at an angle As (120°) obtained by dividing the circumference of 360 degrees by the number of threads in the multi-start thread (see Figure 8). On the other hand, the nut portion 35a is composed of a first female thread portion N1, a second female thread portion N2, and a third female thread portion N3. In Figure 7, the starting point of the thread in the third female thread portion N3 is shifted circumferentially by a few degrees (angle α) from the angle An (120°) obtained by dividing the circumference of 360 degrees by the number of threads in the multi-start screw, relative to the starting point of the thread in the second female thread portion N2. By doing this, in a multi-start screw, by shifting the starting point of at least one thread by a few degrees (angle α) in the circumferential direction, the phase of the thread is changed, and the phase relative to the other part can be shifted. As a result, the relative axial movement between the screw shaft portion 33a of the screw shaft 33 and the nut portion 35a of the drive member 35 is restricted, and the looseness of the screw threaded portion between them is suppressed, thereby suppressing the looseness of the steering shaft 9.

[0028] The effects and advantages of this embodiment will be explained below.

[0029] (1) The power transmission mechanism 30 comprises a male screw shaft member (screw shaft 33) rotatably mounted on either the support part or the movable part, with male screws (male screw parts S1, S2) formed along the axial direction, and a female screw member (drive member 35) mounted on either the support part or the movable part, with the male screw shaft member (screw shaft 33) screwed into it. The rotation of the male screw shaft member (screw shaft 33) causes the female screw member (drive member 35) and the male screw shaft member (screw shaft 33) to move relative to each other, and the movable part moves relative to the support part. The male screw shaft member (screw shaft 33) and the female screw member (drive member 35) each have multi-start threads. In a multi-start screw of either the male screw shaft member (screw shaft 33) or the female screw member (drive member 35), the threading start position of at least one screw (the second female thread portion N2) is displaced circumferentially by a predetermined angle α from an angle An obtained by dividing 360 degrees by the number of threads in the multi-start screw, relative to the threading start position of another screw (the first female thread portion N1) adjacent in the circumferential direction.

[0030] In a multi-start screw, by shifting the starting point of at least one screw by a few degrees (angle α) in the circumferential direction, the phase of the screw can be changed, thereby shifting its phase relative to the other component. As a result, play between the screw shaft portion 33a of the screw shaft 33 and the nut portion 35a of the drive member 35 can be suppressed, and since there is no need to provide a separate part to suppress the play, the number of parts can be reduced.

[0031] As described above, according to this embodiment, a power transmission mechanism 30 can be provided that can suppress play in the threaded portion between the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) with a simpler configuration.

[0032] (2) The predetermined angle α mentioned above is within the range of 1 to 5 degrees.

[0033] A suitable angle for shifting the starting point of at least one screw thread by several degrees in the circumferential direction is within the range of 1 to 5 degrees. If this range is exceeded, sliding resistance will occur during operation, and there is a risk that the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) will not be able to slide against each other. On the other hand, within this range, it is possible to suppress play in the threaded portion between the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) without affecting sliding resistance.

[0034] (3) The steering column device 1 includes a power transmission mechanism 30. The power transmission mechanism 30 includes a male screw shaft member (screw shaft 33) which is rotatably mounted on either the support part or the movable part and has male screws (male screw parts S1, S2) formed along the axial direction, and a female screw member (drive member 35) which is mounted on either the support part or the movable part and into which the male screw shaft member (screw shaft 33) is screwed. The rotation of the male screw shaft member (screw shaft 33) causes the female screw member (drive member 35) and the male screw shaft member (screw shaft 33) to move relative to each other, and the movable part moves relative to the support part. The male screw shaft member (screw shaft 33) and the female screw member (drive member 35) each have multi-start threads. In a multi-start screw of either the male screw shaft member (screw shaft 33) or the female screw member (drive member 35), the threading start position of at least one screw (the second female thread portion N2) is displaced circumferentially by a predetermined angle α from an angle An obtained by dividing 360 degrees by the number of threads in the multi-start screw, relative to the threading start position of another screw (the first female thread portion N1) adjacent in the circumferential direction.

[0035] In a multi-start screw, by shifting the starting point of at least one screw by several degrees in the circumferential direction, the phase of the screw can be changed, thereby shifting its phase relative to the other component. As a result, play between the screw shaft portion 33a of the screw shaft 33 and the nut portion 35a of the drive member 35 can be suppressed, and since there is no need to provide a separate part to suppress the play, the number of parts can be reduced.

[0036] As described above, according to this embodiment, a steering column device 1 can be provided that can suppress play in the threaded portion between the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) with a simpler configuration.

[0037] (4) The predetermined angle α is within the range of 1 to 5 degrees.

[0038] A suitable angle for shifting the starting point of at least one screw thread by several degrees in the circumferential direction is within the range of 1 to 5 degrees. If this range is exceeded, sliding resistance will occur during operation, and there is a risk that the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) will not be able to slide against each other. On the other hand, within this range, it is possible to suppress play in the threaded portion between the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) without affecting sliding resistance.

[0039] (5) The steering column device 1 is equipped with a tilt mechanism 20 that swings the steering wheel up and down, and this tilt mechanism 20 has a power transmission mechanism 40.

[0040] In a power transmission mechanism 40 using a female threaded member (drive member 45) and a male threaded shaft member (screw shaft 43), the male threaded shaft member (screw shaft 43) and the female threaded member (drive member 45) are each formed with multi-start threads. By shifting the starting point of at least one thread in the multi-start thread of either the male threaded shaft member (screw shaft 43) or the female threaded member (drive member 45) by several degrees in the circumferential direction, the phase of the thread is changed, and the phase with respect to the other component can be shifted. As a result, play in the threaded portion between the screw shaft 43 and the drive member 45 can be suppressed, and since there is no need to provide a separate part to suppress play, the number of parts can be reduced.

[0041] (6) The steering column device 1 is equipped with a telescopic mechanism 10 that moves the steering wheel in the front-rear direction, and this telescopic mechanism 10 has a power transmission mechanism 30.

[0042] In a power transmission mechanism 30 using a female screw member (drive member 35) and a male screw shaft member (screw shaft 33), the male screw shaft member (screw shaft 33) and the female screw member (drive member 35) are each formed with multi-start threads. By shifting the starting point of at least one thread in the multi-start thread of either the male screw shaft member (screw shaft 33) or the female screw member (drive member 35) by several degrees in the circumferential direction, the phase of the thread is changed, and the phase relative to the other component can be shifted. As a result, play in the threaded portion between the screw shaft 33 and the drive member 35 can be suppressed, and since there is no need to provide a separate part to suppress play, the number of parts can be reduced.

[0043] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment.

[0044] 1 Steering column device 5 Outer column (support part) 7 Inner column (movable part) 10 Telescopic mechanism 20 Tilt mechanism 30 Power transmission mechanism 33 Screw shaft (male screw shaft member) 33a Screw shaft part 35 Drive member (female screw member) 35a Nut part 40 Power transmission mechanism 43 Screw shaft (male screw shaft member) 45 Drive member (female screw member) N1 Female screw part N2 Female screw part N3 Female screw part S1 Male screw part S2 Male screw part S3 Male screw part

Claims

1. A power transmission mechanism comprising: a male screw shaft member rotatably mounted on either a support portion or a movable portion, having a male screw formed along the axial direction; and a female screw member mounted on the other of the support portion or the movable portion, into which the male screw shaft member is screwed; wherein the rotation of the male screw shaft member causes the female screw member and the male screw shaft member to move relative to each other, and the movable portion to move relative to the support portion; the male screw shaft member and the female screw member each have a multi-start thread; and in the multi-start thread of either the male screw shaft member or the female screw member, the threading start position of at least one thread is displaced circumferentially by a predetermined angle from an angle obtained by dividing 360 degrees by the number of threads in the multi-start thread with respect to the threading start position of other threads adjacent in the circumferential direction.

2. The power transmission mechanism according to claim 1, wherein the predetermined angle is within the range of 1 to 5 degrees.

3. A steering column device comprising a power transmission mechanism, the power transmission mechanism comprising: a male screw shaft member rotatably mounted on either a support portion or a movable portion and having a male screw formed along the axial direction; and a female screw member mounted on the other of the support portion or the movable portion and into which the male screw shaft member is screwed, wherein the rotation of the male screw shaft member causes the female screw member and the male screw shaft member to move relative to each other, and the movable portion to move relative to the support portion, the male screw shaft member and the female screw member each having a multi-start thread, and in the multi-start thread of either the male screw shaft member or the female screw member, the threading start position of at least one thread is displaced circumferentially by a predetermined angle from an angle obtained by dividing 360 degrees by the number of threads in the multi-start thread with respect to the threading start position of other threads adjacent in the circumferential direction.

4. The steering column device according to claim 3, wherein the predetermined angle is within the range of 1 to 5 degrees.

5. A steering column device according to claim 3 or 4, comprising a tilt mechanism for swinging the steering wheel up and down, wherein the tilt mechanism has the power transmission mechanism.

6. The steering column device according to claim 3 or 4, comprising a telescopic mechanism for moving the steering wheel in the front-rear direction, wherein the telescopic mechanism has the power transmission mechanism.

Images