Worm reduction gear

Abstract

To provide a worm reduction gear capable of improving quietness.SOLUTION: A worm reducer comprises: a worm shaft; a worm wheel meshing with the worm shaft; a housing for storing the worm shaft and the worm wheel; a second bearing supporting a second end of the worm shaft; and a coil spring urging the worm shaft toward the worm wheel via the second bearing. The housing has a worm shaft storage portion 33 for storing the worm shaft. The worm shaft storage portion 33 is provided with a spring hole 81 opened to an inner peripheral surface of the worm shaft storage portion 33 and storing the coil spring 62 therein. Recesses 87 are provided on an edge of the spring hole 81 in the inner peripheral surface of the worm shaft storage portion 33, the recesses being positioned on both sides in a circumferential direction of the worm shaft with respect to the center of the spring hole 81. A part of a tip of the coil spring 62 that contacts with the second bearing 54 can enter the recess 87.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a worm reduction gear. [Background technology]

[0002] 2. Description of the Related Art Worm reduction gears having a worm shaft and a worm wheel are known in the art and are used in, for example, electric power steering devices to reduce the speed of rotation of a motor and transmit the reduced speed to a steering shaft.

[0003] In a worm reduction gear used in an electric power steering device, for example, when the steering direction is reversed, a gear rattle noise may occur due to backlash between the worm shaft and the worm wheel. In consideration of this, for example, Patent Documents 1 and 2 disclose a worm reduction gear configured such that a first end of a worm shaft is tiltably connected to a motor shaft and a second end is biased toward the worm wheel by a biasing member. In such a worm reduction gear, the backlash is reduced by bringing the worm shaft close to the worm wheel, and the generation of gear rattle noise can be suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-179237 A [Patent Document 2] JP 2012-101638 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been an increasing demand for quieter worm reduction gears, but the reality is that even with the above-mentioned configuration, it cannot be said that the required level is met. Therefore, there is a demand for the development of new technology that can achieve even quieter operation. [Means for solving the problem]

[0006] A worm reducer that solves the above problems includes a worm shaft having a first end connected to a motor and a second end opposite the first end, a worm wheel that meshes with the worm shaft, a housing that accommodates the worm shaft and the worm wheel, a bearing that supports the second end, and a coil spring that biases the worm shaft toward the worm wheel via the bearing, wherein the housing has a worm shaft accommodating portion that accommodates the worm shaft, and a worm wheel accommodating portion that accommodates the worm wheel, the worm shaft accommodating portion has a spring hole that opens to an inner circumferential surface of the worm shaft accommodating portion and accommodates the coil spring, an edge of the spring hole on the inner circumferential surface of the worm shaft accommodating portion is provided with recesses located on both circumferential sides of the worm shaft with respect to the center of the spring hole, and a part of the tip of the coil spring that comes into contact with the bearing is able to enter the recesses.

[0007] For example, when the worm shaft rotates around its axis, the tip of the coil spring may swing in the circumferential direction of the worm shaft with the base end of the coil spring as a fulcrum. As a result, the tip of the coil spring may collide with the housing, generating a hammering sound. In this regard, with the above-mentioned configuration, when the tip of the coil spring swings in the circumferential direction of the worm shaft, it enters the recess, making it less likely for the tip to collide with the housing. This makes it possible to suppress the generation of hammering sounds.

[0008] In the above worm reduction gear, the recess may be provided around the entire circumference of the spring hole. In a configuration in which the worm shaft is accommodated in the worm shaft accommodating portion so as to be displaceable in the axial direction, the tip of the coil spring may vibrate in the axial direction in association with the axial displacement of the worm shaft. With the above configuration, even in such a case, the tip of the coil spring is less likely to collide with the housing, and the generation of hitting noise can be suppressed. In addition, by providing a recess around the entire circumference of the spring hole in a configuration in which the axial displacement of the worm shaft is restricted, the housing can be used in common with a housing used in a configuration in which the axial displacement of the worm shaft is permitted.

[0009] In the above-mentioned worm reducer, a groove portion extending circumferentially of the worm shaft is provided on the inner surface of the worm shaft accommodating portion, an elastic member is arranged in the groove portion and is sandwiched between a bottom surface of the groove portion and an outer peripheral surface of the bearing, and the groove portion may overlap a portion of the spring hole in the axial direction of the worm shaft.

[0010] According to the above configuration, for example, when the bearing is displaced in a direction away from the worm wheel together with the worm shaft, the elastic member is compressed, thereby attenuating the displacement speed (momentum) of the bearing. This makes it possible to suppress the generation of abnormal noise caused by the bearing colliding with the inner peripheral surface of the worm shaft housing. Meanwhile, in the above configuration, a part of the inner peripheral surface of the spring hole is cut out by the groove, so that the tip of the coil spring is likely to vibrate. Therefore, in the above configuration, providing a recess on the edge of the spring hole is very effective.

[0011] In the above worm reduction gear, the spring hole may be formed by a part of the worm shaft receiving portion. According to the above configuration, unlike the case where the spring hole is formed by a cylindrical member attached to the worm shaft receiving portion, for example, an increase in the number of parts of the worm reduction gear can be prevented. Effect of the Invention

[0012] According to the present invention, the quietness of the worm reduction gear can be improved. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram of an electric power steering device according to an embodiment; [Diagram 2] 2 is a partial cross-sectional view taken along the axial direction of a worm shaft of a worm reduction gear provided in the electric power steering device of FIG. 1. [Diagram 3] 3 is an enlarged cross-sectional view of the vicinity of a coil spring in the worm reduction gear of FIG. 2. [Figure 4] 3 is a side view of the worm shaft receiving portion of the worm reduction gear in FIG. 2, as viewed from the axial direction with an end cover and an elastic member removed. [Diagram 5] 3 is an exploded perspective view of a part of a worm shaft housing portion, a coil spring, a cap, and an elastic member in the worm reduction gear of FIG. 2. [Figure 6] 6 is a cross-sectional view taken along line VI-VI in FIG. 3, and perpendicular to the axial direction of the worm shaft in the vicinity of an elastic member in the worm reduction gear. [Figure 7] 7 is a cross-sectional view taken along line VII-VII in FIG. 3, perpendicular to the axial direction of the worm shaft in the vicinity of a coil spring in the worm reduction gear. [Figure 8] 13 is a cross-sectional view taken perpendicular to the axial direction of the worm shaft in the vicinity of a coil spring in a worm reduction gear according to a modified example. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment in which a worm reduction gear is applied to an electric power steering device will be described with reference to the drawings. In this specification, "cylindrical" means that the whole is cylindrical, and includes a cylindrical shape formed by combining multiple parts or portions, and a C-shape having a notch or the like. The shape of the "cylindrical" includes, but is not limited to, a circle, an ellipse, and a polygon with sharp or rounded corners when viewed in the axial direction. In addition, "facing" in this specification refers to surfaces or members facing each other, and includes not only a case where the surfaces or members are completely facing each other, but also a case where the surfaces or members are partially facing each other. In addition, in this specification, "facing" includes both a case where a member other than the two parts is interposed between the two parts, and a case where nothing is interposed between the two parts.

[0015] (Overall composition) As shown in FIG. 1, the electric power steering device 1 includes a steering mechanism 4 that steers steered wheels 3 based on the operation of a steering wheel 2 by a driver, and a steering force assist device 5 that applies an assist force to the steering mechanism 4 to assist the steering operation.

[0016] The steering mechanism 4 includes a steering shaft 11 to which the steering wheel 2 is fixed, a rack shaft 12 connected to the steering shaft 11, and a rack-and-pinion mechanism 13 that converts the rotation of the steering shaft 11 into the reciprocating motion of the rack shaft 12. The steering shaft 11 is configured by connecting a column shaft 14, an intermediate shaft 15, and a pinion shaft 16 in this order from the side where the steering wheel 2 is located.

[0017] The rack-and-pinion mechanism 13 is configured by meshing rack teeth of the rack shaft 12 with pinion teeth of the pinion shaft 16. Tie rods 17 are rotatably connected to both ends of the rack shaft 12 via ball joints (not shown). The ends of the tie rods 17 are connected to a knuckle (not shown) to which the steered wheels 3 are attached. Thus, in the electric power steering device 1, the rotation of the steering shaft 11 accompanying a steering operation is converted into axial movement of the rack shaft 12 by the rack-and-pinion mechanism 13. The axial movement of the rack shaft 12 is then transmitted to the knuckle via the tie rods 17, thereby changing the steering angle of the steered wheels 3, i.e., the traveling direction of the vehicle.

[0018] The steering force assist device 5 includes a motor 21, which is a drive source, and a worm reduction gear 22. The worm reduction gear 22 includes a worm shaft 23 connected to the motor 21, and a worm wheel 24 connected to the column shaft 14. The electric power steering device 1 applies an assist force to the steering mechanism 4 by reducing the rotation of the motor 21 by the worm reduction gear 22 and transmitting the rotation to the column shaft 14.

[0019] (Worm reducer 22) 2, the worm reducer 22 includes the worm shaft 23 and the worm wheel 24, as well as a housing 31 that accommodates them. The housing 31 includes a motor attachment portion 32 for fixing the motor 21, a worm shaft accommodating portion 33 that accommodates the worm shaft 23, and a worm wheel accommodating portion 34 that accommodates the worm wheel 24.

[0020] The motor mounting portion 32 is, for example, cylindrical with an end wall at one end. The worm shaft accommodating portion 33 is, for example, long and cylindrical. The worm shaft accommodating portion 33 is provided continuously with the end wall of the motor mounting portion 32 so as to be arranged coaxially with the motor mounting portion 32. The worm shaft accommodating portion 33 is open on both sides in the axial direction, and the inside of the worm shaft accommodating portion 33 communicates with the inside of the motor mounting portion 32. In the following description, the side of the worm shaft accommodating portion 33 that is continuous with the motor mounting portion 32 (the right side in FIG. 2) is referred to as the first side, and the opposite side (the left side in FIG. 2) is referred to as the second side. That is, the first opening 35 of the worm shaft accommodating portion 33 on the first side opens to the inner bottom surface of the end wall of the motor mounting portion 32. The second opening 36 of the worm shaft accommodating portion 33 on the second side is closed by an end cover 37. The worm wheel accommodating portion 34 is, for example, cylindrical. The worm wheel accommodating portion 34 is provided so as to overlap a part of the peripheral wall of the worm shaft accommodating portion 33. As a result, the inside of the worm wheel accommodating portion 34 communicates with the inside of the worm shaft accommodating portion 33.

[0021] A part of the motor 21 is fitted into and fixed to the open end of the motor mounting portion 32. A motor shaft 41, which is a rotating shaft of the motor 21, protrudes into the motor mounting portion 32 when the motor 21 is fixed to the motor mounting portion 32.

[0022] The worm shaft 23 is accommodated in the worm shaft accommodating portion 33 so as to be rotatable around its axis. Specifically, the worm shaft 23 has a first end 51 coupled to the motor shaft 41 and a second end 52 opposite to the first end 51. The first end 51 is rotatably supported by a first bearing 53 provided in a first opening 35 of the worm shaft accommodating portion 33, and the second end 52 is rotatably supported by a second bearing 54 provided in a second opening 36 of the worm shaft accommodating portion 33. The first and second bearings 53, 54 may be, for example, ball bearings.

[0023] The worm wheel 24 meshed with the worm shaft 23 is rotatably housed in the worm wheel housing 34. The worm wheel 24 is connected to the column shaft 14 so as to be rotatable together with the column shaft 14. As a result, the rotation of the motor 21 is reduced in speed by the worm shaft 23 and the worm wheel 24 and transmitted to the column shaft 14.

[0024] Here, the worm shaft 23 has a first end 51 connected to the motor shaft 41 via a shaft coupling 61 so as to be tiltable, and a second end 52 is biased toward the worm wheel 24 (substantially downward in FIG. 2) by a coil spring 62, which is a biasing member. In this embodiment, the coil spring 62 biases the second bearing 54 with its seat winding portion in direct contact with the outer peripheral surface of the outer ring of the second bearing 54. In other words, the seat winding portion of the coil spring 62 corresponds to the tip portion. As a result, in the worm reduction gear 22, the axial distance between the worm shaft 23 and the worm wheel 24 is adjusted to reduce backlash. The backlash reduction structure will be described in detail below.

[0025] (Backlash reduction structure) The first bearing 53 supporting the first end 51 of the worm shaft 23 has a relatively large internal gap, allowing tilting of the worm shaft 23. The first bearing 53 is fixed to the first opening 35 of the worm shaft accommodating portion 33 by a fixing member 55. Specifically, the first bearing 53 is pressed against a step between the first opening 35 and the center of the worm shaft accommodating portion 33 by the fixing member 55, thereby being fixed to the first opening 35. As a result, in this embodiment, axial displacement of the worm shaft 23 is restricted.

[0026] The inner diameter of the second opening 36 of the worm shaft accommodating portion 33 is set to be larger than the outer diameter of the second bearing 54 supporting the second end 52 of the worm shaft 23. This allows the second bearing 54 to move radially within the second opening 36. Therefore, the worm shaft 23 is supported rotatably by the first and second bearings 53, 54 while being permitted to tilt relative to the motor shaft 41. Note that an elastic member 63 is provided between the outer peripheral surface of the outer ring of the second bearing 54 and the inner peripheral surface of the second opening 36, as described later.

[0027] The shaft coupling 61 connects the worm shaft 23 to the motor shaft 41 so as to be tiltable and transmit torque. The shaft coupling 61 of this embodiment includes a pair of joints (yokes) 73, 74 having a plurality of engaging claws 71, 72 protruding in opposing directions, and an elastic body 75 interposed between the joints 73, 74. The joint 73 is connected to the motor shaft 41 so as to rotate integrally therewith, and the joint 74 is connected to the worm shaft 23 so as to rotate integrally therewith. The shaft coupling 61 allows the worm shaft 23 to tilt relative to the motor shaft 41 by compressing the elastic body 75 between the joints 73, 74. The shaft coupling 61 transmits torque between the motor shaft 41 and the worm shaft 23 by engaging the engaging claws 71, 72 with each other via the elastic body 75.

[0028] As shown in FIG. 3, the second opening 36 of the worm shaft accommodating portion 33 is provided with a spring hole 81 that opens to the inner peripheral surface of the worm shaft accommodating portion 33 and accommodates the coil spring 62. The inner diameter of the spring hole 81 is set to be slightly larger than the outer diameter of the coil spring 62. As a result, the spring hole 81 guides the expansion and contraction of the coil spring 62 so that the coil spring 62 does not buckle when compressed. The inner diameter of the spring hole 81 is smaller than the length of the second bearing 54 along the axial direction. The center of the spring hole 81 faces radially to the center of the second bearing 54 in the axial direction. Therefore, the entire spring hole 81 faces radially to the second bearing 54. The spring hole 81 is provided in a portion of the worm shaft accommodating portion 33 opposite the worm wheel 24 with respect to the axis of the worm shaft 23. In the following description, the side where the spring hole 81 is provided with respect to the axis of the worm shaft 23 is sometimes referred to as the upper side, and the opposite side, i.e., the side where the worm wheel 24 is arranged, is sometimes referred to as the lower side.

[0029] The worm shaft accommodating portion 33 has an insertion hole 82 that is continuous with the upper side of the spring hole 81 and opens to the outside of the worm shaft accommodating portion 33. In the illustrated example, the inner diameter of the insertion hole 82 is set to be larger than the inner diameter of the spring hole 81. The insertion hole 82 is closed by, for example, inserting a cylindrical cap 83.

[0030] 3, 4 and 5, a groove portion 84 and a fitting portion 85 are provided in this order from the first side on the inner circumferential surface of the second opening 36 of the worm shaft accommodating portion 33. For ease of explanation, FIG. 5 shows a part of the worm shaft accommodating portion 33 in a half cross-sectional view, and does not show members other than the coil spring 62, the cap 83, and the elastic member 63.

[0031] The groove portion 84 extends over the entire circumference of the inner peripheral surface of the worm shaft accommodating portion 33. The groove portion 84 faces only a part of the axial range of the second bearing 54 in the radial direction, not the entire axial range of the second bearing 54. In the illustrated example, the groove portion 84 faces a range slightly narrower than the second half of the axial range of the second bearing 54. As a result, the groove portion 84 overlaps with a part of the spring hole 81 in the axial direction of the worm shaft 23. That is, in the worm shaft accommodating portion 33, the axial range in which the groove portion 84 is provided overlaps with the axial range in which the spring hole 81 is provided. Among the portion that defines the inner peripheral surface of the spring hole 81 in the worm shaft accommodating portion 33, the portion close to the second side is cut out by the groove portion 84. In addition, an engagement hole 86 is provided in an upper portion of the inner peripheral surface of the groove portion 84. The engagement hole 86 has, for example, a rectangular shape when viewed from the inner peripheral side of the worm shaft accommodating portion 33, and opens to the inner peripheral surface of the groove portion 84 and the second side.

[0032] The fitting portion 85 is provided contiguous to the second side of the groove portion 84. The fitting portion 85 extends around the entire circumference of the inner circumferential surface of the worm shaft accommodating portion 33. The inner diameter of the fitting portion 85 is set to be larger than the inner diameter of the groove portion 84. The end cover 37 is fixed to the fitting portion 85.

[0033] As shown in FIG. 3, FIG. 5, and FIG. 6, the groove 84 is provided with an elastic member 63 made of, for example, a rubber material. The elastic member 63 has a roughly semicylindrical main body 91, a connecting portion 92 that connects both circumferential ends of the main body 91 to each other on the second side of the main body 91, and a protruding portion 93 that protrudes radially outward from the circumferential center of the main body 91. A notch 94 that opens to the first side is provided in the main body 91 at a position facing the coil spring 62. The notch 94 has, for example, a semicircular shape. As shown in FIG. 6, the elastic member 63 is attached to the worm shaft housing 33 so that the main body 91 is sandwiched between the bottom surface of the groove 84 and the outer circumferential surface of the outer ring of the second bearing 54. The main body 91 of this embodiment extends over a circumferential range that is slightly larger than the upper half of the second bearing 54. The notch 94 prevents the elastic member 63 from interfering with the coil spring 62. 3, with the elastic member 63 attached, the protrusion 93 is disposed within the engagement hole 86. This restricts the elastic member 63 from rotating around the axis of the worm shaft 23.

[0034] Here, the inventors have found, as a result of intensive research, that when the worm shaft 23 rotates around its axis, the tip end of the coil spring 62 may vibrate in the circumferential direction of the worm shaft 23 with the base end of the coil spring 62 as a fulcrum. More specifically, when the worm shaft 23 rotates repeatedly and finely around its axis, for example, when traveling on a rough road, the tip end of the coil spring 62 may vibrate in the circumferential direction of the worm shaft 23. In particular, in a configuration in which a part defining the inner circumferential surface of the spring hole 81 in the worm shaft housing portion 33 is cut out as in this embodiment, the coil spring 62 is likely to vibrate. When the tip end of the coil spring 62 vibrates around the base end as a fulcrum, the displacement (acceleration) of the tip end becomes large, and when the tip end hits the housing 31, a hitting sound may be generated.

[0035] In consideration of this, as shown in Fig. 7, recesses 87 are provided on the edge of the spring hole 81 in the inner peripheral surface of the worm shaft housing 33, located on both circumferential sides of the worm shaft 23 with respect to the center of the spring hole 81. In this embodiment, the recesses 87 are provided not only on both circumferential sides of the worm shaft 23 with respect to the center of the spring hole 81, but also around the entire circumference of the spring hole 81. Since part of the spring hole 81 overlaps with the groove portion 84 as described above, the recesses 87 also overlap with the groove portion 84. No other members are provided within the recess 87, and part of the tip end of the coil spring 62 can enter the recess 87 without coming into contact with other members.

[0036] Next, the operation and effects of this embodiment will be described. (1) Recesses 87 are provided on the edge of the spring hole 81 in the inner peripheral surface of the worm shaft housing 33, located on both sides in the circumferential direction of the worm shaft 23 with respect to the center of the spring hole 81, and a part of the tip of the coil spring 62 can enter the recess 87. According to the above configuration, when the tip of the coil spring 62 swings in the circumferential direction of the worm shaft 23, it enters the recess 87, so the tip is less likely to collide with the housing 31. This makes it possible to suppress the generation of hitting sounds. Note that when the tip of the coil spring 62 swings around the base end as a fulcrum, the displacement of the center of the coil spring 62 is not large, so that hitting sounds are less likely to occur even if it comes into contact with the housing 31.

[0037] (2) The recess 87 is provided around the entire circumference of the spring hole 81. Here, as described in Patent Document 2, for example, in a configuration in which the worm shaft 23 is accommodated in the worm shaft accommodation portion 33 so as to be displaceable in the axial direction, the tip of the coil spring 62 may oscillate in the axial direction as the worm shaft 23 oscillates in the axial direction. According to the above configuration, even if the tip of the coil spring 62 oscillates in the axial direction, the tip of the coil spring 62 is less likely to collide with the housing 31, and the generation of hitting noise can be suppressed. In addition, by providing the recess 87 around the entire circumference of the spring hole 81 in a configuration in which the axial displacement of the worm shaft 23 is restricted as in the present embodiment, the housing 31 can be used in common with a housing used in a configuration in which the axial displacement of the worm shaft 23 is permitted.

[0038] (3) A groove 84 extending in the circumferential direction of the second bearing 54 is provided on the inner circumferential surface of the worm shaft accommodating portion 33, and the elastic member 63 is disposed in the groove 84 and is sandwiched between the bottom surface of the groove 84 and the outer circumferential surface of the second bearing 54. The groove 84 overlaps with a portion of the spring hole 81 in the axial direction of the worm shaft 23.

[0039] According to the above configuration, for example, when the second bearing 54 is displaced integrally with the worm shaft 23 in a direction away from the worm wheel 24, the elastic member 63 is compressed, thereby attenuating the displacement speed (momentum) of the second bearing 54. This makes it possible to suppress the generation of abnormal noise caused by the second bearing 54 colliding with the inner circumferential surface of the worm shaft accommodating portion 33. Meanwhile, in the above configuration, since part of the inner circumferential surface of the spring hole 81 is cut out by the groove portion 84, the tip portion of the coil spring 62 is likely to vibrate. Therefore, in the above configuration, providing the recess 87 on the edge portion of the spring hole 81 is very effective.

[0040] (4) The spring hole 81 is formed by a part of the worm shaft housing 33. According to the above configuration, unlike the case where the spring hole 81 is formed by, for example, a cylindrical member attached to the worm shaft housing 33, an increase in the number of parts of the worm reduction gear 22 can be prevented.

[0041] This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs. In the above embodiment, the seat winding portion of the coil spring 62 comes into contact with the outer circumferential surface of the second bearing 54 to bias the second bearing 54. However, this is not limited to the above, and a receiving member that is a separate member from the winding portion of the coil spring 62 may be fixed to the seat winding portion, and the second bearing 54 may be biased via this receiving member. In such a configuration in which the coil spring 62 includes a receiving member, the tip end of the coil spring 62 may include the receiving member.

[0042] In the above embodiment, the spring hole 81 is formed by a part of the worm shaft accommodating portion 33 (housing 31). However, this is not limited to this, and the spring hole 81 may be formed by a cylindrical member attached to the worm shaft accommodating portion 33.

[0043] For example, in the example shown in FIG. 8, the worm shaft housing 33 is provided with a large diameter hole 101 having an inner diameter sufficiently larger than the outer diameter of the coil spring 62, instead of the spring hole 81. A cylindrical collar 102 is fitted into the large diameter hole 101. The collar 102 is made of, for example, a resin material, but is not limited thereto, and may be made of a metal material, a rubber material, or the like. The collar 102 may have a slit extending over its entire axial area. The inner diameter of the collar 102 is set to be slightly larger than the outer diameter of the coil spring 62. That is, in this example, the inner circumference of the collar 102 is used as the spring hole 81a.

[0044] In the example shown in the figure, the length of the collar 102 along the axial direction is shorter than the length of the large diameter hole 101 along the axial direction. The collar 102 is fitted into the large diameter hole 101 so that one end of the collar 102 abuts against the cap 83. As a result, the other end of the collar 102 does not extend to the inner peripheral surface of the worm shaft accommodating portion 33, and a gap is formed between the other end of the collar 102 and the outer ring of the second bearing 54. In other words, the other end of the collar 102, i.e., the edge of the spring hole 81a, is recessed with respect to the inner peripheral surface of the worm shaft accommodating portion 33. A part of the tip of the coil spring 62 can enter this recessed portion, and this portion functions as the recess 87a. In this configuration, the shape of the worm shaft accommodating portion 33 can be simplified compared to the case where the spring hole 81 and the recess 87 are provided in the worm shaft accommodating portion 33.

[0045] In the above embodiment, the groove portion 84 only needs to extend over the circumferential range in which the main body portion 91 of the elastic member 63 is disposed, and does not need to extend over the entire circumference of the inner circumferential surface of the worm shaft accommodating portion 33.

[0046] In the above embodiment, the elastic member 63 only needs to have a portion that is sandwiched between the bottom surface of the groove portion 84 and the outer circumferential surface of the second bearing 54, and the shape of the elastic member 63 can be changed as appropriate. For example, the elastic member 63 does not need to have the connecting portion 92 or the protruding portion 93. In addition, the main body portion 91 does not need to be semi-cylindrical.

[0047] In the above embodiment, the worm reduction gear 22 does not have to include the elastic member 63. In this case, the worm shaft receiving portion 33 does not have to have the groove portion 84. In the above embodiment, it is sufficient that the recesses 87 are provided on both circumferential sides of the worm shaft 23 when viewed from the center of the spring hole 81. For example, it is not necessary for a recess to be provided in the axial direction of the worm shaft 23 when viewed from the center of the spring hole 81.

[0048] In the above embodiment, for example, elastic rings may be provided on both axial sides of the first bearing 53 so that the worm shaft 23 is accommodated in the worm shaft accommodating portion 33 so as to be displaceable in the axial direction.

[0049] In the above embodiment, the worm reduction gear 22 is applied to the electric power steering device 1, but the invention is not limited to this and may be applied to other devices. Next, the technical ideas that can be understood from the above embodiment and modifications will be described below together with their effects.

[0050] (Note 1) The spring hole may be formed by a cylindrical member attached to the worm shaft receiving portion. According to the above configuration, the shape of the worm shaft receiving portion can be simplified compared to a case in which a spring hole and a recess are provided in the worm shaft receiving portion. [Explanation of symbols]

[0051] 21…Motor 22...Worm reducer 23…Worm shaft 24…Worm wheel 31. Housing 33…Worm shaft housing 34…Worm wheel housing 51...First end 52…Second end 62...Coil spring 63...Elastic member 81, 81a...Spring hole 84…Groove 87, 87a…recess

Claims

1. a worm shaft having a first end coupled to a motor and a second end opposite the first end; a worm wheel meshing with the worm shaft; a housing that accommodates the worm shaft and the worm wheel; A bearing supporting the second end; a coil spring that biases the worm shaft toward the worm wheel via the bearing, The housing has a worm shaft accommodating portion that accommodates the worm shaft and a worm wheel accommodating portion that accommodates the worm wheel, The worm shaft accommodating portion has a spring hole that opens to an inner circumferential surface of the worm shaft accommodating portion and accommodates the coil spring. A recess is provided on an edge of the spring hole in an inner peripheral surface of the worm shaft accommodating portion, the recess being located on both sides in a circumferential direction of the worm shaft with respect to a center of the spring hole, A worm reducer, wherein a portion of a tip end of the coil spring that contacts the bearing is capable of entering the recess.

2. The worm reduction gear according to claim 1 , wherein the recess is provided around the entire circumference of the spring hole.

3. A groove portion extending in a circumferential direction of the worm shaft is provided on an inner peripheral surface of the worm shaft housing portion, an elastic member is disposed in the groove and is sandwiched between a bottom surface of the groove and an outer circumferential surface of the bearing; The worm reduction gear according to claim 1 or 2, wherein the groove portion overlaps with a portion of the spring hole in the axial direction of the worm shaft.

4. The worm reduction gear according to claim 1 or 2, wherein the spring hole is formed by a part of the worm shaft accommodating portion.

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