JP2012057660A - Worm gear mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a worm gear mechanism capable of suppressing backlash of the worm gear mechanism and quickly and reliably transmitting torque from a worm to a rotary shaft.SOLUTION: A worm wheel 80 of the worm gear mechanism 44 comprises: a rotary board 81 which is attached to the rotary shaft 24 while regulating the relative rotation with respect to the rotary shaft; a middle board 82 the one side of which faces one side of the rotary board; a wheel body 83 the one side of which faces the other side of the middle board; a plurality of first balls 84 which connect faces opposed to each other of the rotary board and the middle board, to each other; and a plurality of second balls 85 which connect faces opposed to each other of the middle board and the wheel body, to each other. The wheel body has teeth 83c to be engaged with the worm 70 on the outer circumferential surface and is energized in such a direction that the teeth are engaged with the worm by an energizing member 102.

Description

  The present invention relates to an improved technique for a worm gear mechanism.

  For example, a worm gear mechanism mounted on an electric power steering apparatus includes a worm connected to an electric motor and a worm wheel for torque transmission connected to a load. Torque generated by the electric motor is transmitted from the worm to the load via the worm wheel. In such a worm gear mechanism, a technique for reducing backlash between worm teeth and worm wheel teeth has been developed (see, for example, Patent Document 1).

  The worm gear mechanism known from Patent Document 1 uses one of the following two techniques to reduce backlash.

  In the first technique, the worm shaft having a worm is displaceable toward the worm wheel, and the backlash is reduced by urging the worm shaft toward the worm wheel by a spring. However, in the first technique, since the worm shaft tilts, it is necessary to pay attention to the connection configuration between the worm shaft and the output shaft of the electric motor.

  In the second technique, the worm wheel is displaceable toward the worm shaft, and the backlash is reduced by urging the worm wheel toward the worm shaft by the urging means. The biasing means is made of a synthetic rubber elastic ring. The worm wheel is fitted to the rotary shaft through an elastic ring so that a rotational force can be transmitted. As the center of the worm wheel is offset toward the worm shaft with respect to the rotation shaft, the elastic ring is partially compressed. As a result, the elastic ring urges the worm wheel toward the worm shaft by the elastic force.

  However, in the second technique, the elastic ring is elastically displaced not only in the radial direction but also in the rotational direction in which torque is transmitted. For this reason, the timing at which the torque is transmitted from the worm wheel to the rotating shaft may be slightly delayed, so-called time delay may occur. For example, in an electric power steering device, the followability of an elastic ring becomes a problem when the steering wheel is steered back. In order to transmit the torque from the worm wheel to the rotating shaft quickly and reliably without time delay, there is room for improvement. Furthermore, there is room for improvement in order to increase the durability of the elastic ring.

JP 2000-43739 A

  An object of the present invention is to provide a technique capable of suppressing backlash between a worm and a worm wheel and transmitting torque from the worm to the rotating shaft quickly and reliably.

  The invention according to claim 1 is a worm gear mechanism comprising a worm and a worm wheel meshing with the worm, wherein the worm wheel is mounted on a rotating disk that is mounted with its relative rotation restricted with respect to a rotating shaft, An intermediate disk that faces one side of the rotating disk, a circular wheel body that faces the other surface of the intermediate disk, and the rotating disk and the intermediate disk face each other. A plurality of first balls for connecting the surfaces, and a plurality of second balls for connecting the mutually facing surfaces of the intermediate plate and the wheel body, the rotating plate and the intermediate plate facing each other. The mating surfaces each have a first fitting groove that extends linearly in the radial direction of the rotating shaft while facing each other, and the plurality of first balls fitted in these first fitting grooves, Times The surfaces of the intermediate plate and the wheel body facing each other only in the radial direction of the shaft have second fitting grooves extending linearly in the radial direction of the rotating shaft while facing each other, The plurality of second balls fitted in the second fitting grooves are connected to each other only in the radial direction of the rotating shaft, and the second fitting grooves are orthogonal to the first fitting grooves. The wheel body has teeth on the outer peripheral surface that mesh with the worm, and is biased by a biasing member in a direction that meshes with the worm.

  The invention according to claim 2 is characterized in that the biasing member is provided between a housing for housing the worm wheel and the wheel body.

  In the invention according to claim 3, the wheel main body has a through hole penetrating the rotating shaft, and the urging member is made of an elastic body interposed between the rotating shaft and the through hole. Features.

  In the invention which concerns on Claim 1, the mechanism of an Oldham coupling is applied and the rotary disk, the intermediate disk, the wheel main body, and the 1st and 2nd ball | bowl are combined. The Oldham joint is a joint that can transmit the rotation of the first shaft as it is to the second shaft that is not on the same center line as the first shaft and is parallel to the first shaft. is there. By adopting such a configuration, the wheel body can be moved relative to the rotating shaft only in the “radial direction” of the rotating shaft, and the relative rotation is restricted and connected to the “rotating direction” of the rotating shaft. Yes. In other words, the wheel body is flexible with respect to the rotation axis in the radial direction of the rotation axis, and is firmly connected to the rotation direction of the rotation axis. For this reason, even if the rotation center of the worm wheel is different from the axis of the rotation shaft, torque can be reliably transmitted from the wheel body to the rotation shaft.

  Further, the wheel main body is urged by the urging member in a direction in which teeth on the outer peripheral surface mesh with the worm. In other words, the urging force acts on the wheel body so as to move in the radial direction of the rotation shaft. On the other hand, the wheel body is movable relative to the rotation axis in the radial direction of the rotation axis. Therefore, the teeth of the wheel body are always pressed against the teeth of the worm by the biasing force. The teeth of the worm and the teeth of the wheel body can always maintain a good meshing state without having backlash.

  On the other hand, with respect to the rotation direction of the rotation shaft, the wheel body is firmly connected to the rotation shaft, that is, relative rotation is restricted in the rotation direction of the rotation shaft. For this reason, the torque transmitted from the worm to the wheel body can be transmitted quickly and reliably from the wheel body to the rotating shaft without time delay. For example, when a control torque that changes every moment for controlling the load is transmitted from the worm to the rotating shaft, there is no time delay when the control torque is transmitted from the wheel body to the rotating shaft. Therefore, the controllability for controlling the load is enhanced.

  Thus, backlash between the worm and the worm wheel can be suppressed, and torque can be transmitted quickly and reliably from the worm to the rotating shaft.

  Further, according to the first aspect of the present invention, the wheel body is urged in a direction to engage with the worm. For this reason, consideration is given to the connection configuration between the shaft of the power source such as an electric motor for driving the worm and the worm shaft, as in the case of urging the worm and the worm shaft in the direction of meshing with the wheel body. No need to pay.

  In the invention according to claim 2, the urging member is provided between the housing for housing the worm wheel and the wheel body. For this reason, the structure of a biasing member can be simplified.

  In the invention which concerns on Claim 3, the wheel main body is urged | biased in the direction which meshes with a worm | warm by the elastic body interposed between the through-hole of the wheel main body, and the rotating shaft. For this reason, the structure of a biasing member can be simplified. In addition, the wheel body is restricted from rotating relative to the rotation axis in the rotation direction. For this reason, when the rotating shaft and the wheel body rotate, no torque acts on the elastic body. That is, the elastic body only needs to have a function of urging the wheel body in the direction of meshing with the worm, and durability can be improved. In addition, the torque transmitted from the worm to the wheel body can be transmitted quickly and reliably from the wheel body to the rotating shaft without time delay.

1 is a schematic diagram of an electric power steering apparatus including a worm gear mechanism according to a first embodiment of the present invention. It is a whole block diagram of the electric power steering apparatus shown by FIG. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2. FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. It is the figure which expanded the worm gear mechanism shown by FIG. FIG. 6 is an exploded view of a part of the worm wheel shown in FIG. 5. It is the figure which expanded the principal part of the worm wheel shown by FIG. It is the top view which fractured | ruptured the principal part of the electric power steering apparatus provided with the worm gear mechanism of Example 2 which concerns on this invention. It is the figure which expanded the principal part of the worm wheel shown by FIG.

  EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated below based on an accompanying drawing.

  An example in which the worm gear mechanism according to the first embodiment is mounted on an electric power steering apparatus will be described.

  As shown in FIG. 1, the electric power steering apparatus 10 according to the first embodiment includes a steering system 20 from a steering wheel 21 of a vehicle to steering wheels 29 and 29 (for example, front wheels) of the vehicle, and an auxiliary torque in the steering system 20. And an auxiliary torque mechanism 40 for applying.

  In the steering system 20, a pinion shaft 24 (rotary shaft 24) is connected to a steering wheel 21 via a steering shaft 22 and universal shaft joints 23, 23, and a rack shaft 26 is connected to the pinion shaft 24 via a rack and pinion mechanism 25. The left and right steering wheels 29, 29 are connected to both ends of the rack shaft 26 via left and right tie rods 27, 27 and knuckle 28, 28.

  The rack and pinion mechanism 25 includes a pinion 31 formed on the pinion shaft 24 and a rack 32 formed on the rack shaft 26.

  According to the steering system 20, when the driver steers the steering wheel 21, the left and right steering wheels 29 and 29 are steered by the steering torque via the rack and pinion mechanism 25 and the left and right tie rods 27 and 27. Can do.

  The auxiliary torque mechanism 40 detects the steering torque of the steering system 20 applied to the steering wheel 21 with the steering torque sensor 41, and generates a control signal with the control unit 42 based on the torque detection signal of the steering torque sensor 41. An auxiliary torque corresponding to the steering torque is generated by the electric motor 43 based on the signal, this auxiliary torque is transmitted to the pinion shaft 24 through the worm gear mechanism 44, and the auxiliary torque is further transmitted from the pinion shaft 24 to the rack and This is a mechanism for transmitting to the pinion mechanism 25.

  The steering torque sensor 41 detects the torque applied to the pinion shaft 24 and outputs it as a torque detection signal, and is constituted by, for example, a magnetostrictive torque sensor or a torsion bar torque sensor.

  According to the electric power steering apparatus 10, the steering wheels 29 and 29 can be steered by the rack shaft 26 by a combined torque obtained by adding the auxiliary torque of the electric motor 43 to the steering torque of the driver.

  As shown in FIG. 2, the housing 51 extends in the vehicle width direction (left-right direction in the figure), and accommodates the rack shaft 26 so as to be slidable in the axial direction. The rack shaft 26 is connected to tie rods 27, 27 via ball joints 52, 52 at both longitudinal ends protruding from the housing 51.

  As shown in FIG. 3, the electric power steering apparatus 10 houses the pinion shaft 24, the rack and pinion mechanism 25, the steering torque sensor 41, and the worm gear mechanism 44 in the housing 51, and the upper opening of the housing 51 is formed in the upper cover portion 53. It was closed with. The steering torque sensor 41 is attached to the upper cover portion 53.

  The housing 51 has an upper portion 24u, a longitudinal center portion 24m, and a lower end 24d of the pinion shaft 24 extending vertically through three bearings (a first bearing 55, a second bearing 56, and a third bearing 57 in order from top to bottom). The electric motor 43 is attached and a rack guide 60 is provided. The three bearings 55 to 57 are ball bearings. The outer ring of the third bearing 57 is fixed by being press-fitted into the fitting hole of the housing 51.

  The rack guide 60 is a pressing means that includes a guide portion 61 that contacts the rack shaft 26 from the side opposite to the rack 32, and an adjustment bolt 63 that presses the guide portion 61 via a compression spring 62.

  As shown in FIG. 4, the electric motor 43 includes a lateral motor shaft 43 a and is attached to the housing 51. The motor shaft 43 a extends into the housing 51 and is connected to the worm shaft 46 by a coupling 45. The housing 51 rotatably supports both ends of a horizontally extending worm shaft 46 via bearings 47 and 48.

  As shown in FIGS. 3 and 4, the worm gear mechanism 44 is an auxiliary torque transmission mechanism that transmits auxiliary torque generated by the electric motor 43 to the pinion shaft 24, that is, a booster mechanism. More specifically, the worm gear mechanism 44 includes a worm 70 and a worm wheel 80 that meshes with the worm 70. The worm wheel 80 is hereinafter abbreviated as “wheel 80”.

  The worm 70 is a metal product formed integrally with the worm shaft 46. The wheel 80 is attached to the pinion shaft 24 (rotating shaft 24) such that relative movement in the direction perpendicular to the axis is possible and relative rotation is restricted. By engaging the load-side wheel 80 with the drive-side worm 70, torque can be transmitted from the worm 70 to the load via the wheel 80.

  Next, a specific configuration of the wheel 80 will be described in detail. As shown in FIGS. 5 and 6, the wheel 80 includes a rotary disk 81, an intermediate disk 82, a wheel body 83, a plurality of first balls 84, a plurality of second balls 85, a first ball holder 86, and a second ball holder 86. And a ball holder 87. A set of the plurality of first balls 84 is referred to as a “first ball row 88”. A set of the plurality of second balls 85 is referred to as a “second ball row 89”.

  The turntable 81 is a disk-shaped member that is attached to the pinion shaft 24 while restricting relative rotation. For example, the rotating plate 81 is attached by press-fitting to the rotating plate attaching portion 24m1 located at the longitudinal center portion 24m of the pinion shaft 24, or the pin 101 penetrating the shaft (illustrated by an imaginary line in FIG. 5). Attached by spline, serration or key. In the case of press-fitting or attachment with the pin 101, relative movement in the axial direction of the turntable 81 with respect to the pinion shaft 24 is also restricted. As shown in FIGS. 5 to 7, the rotating plate 81 has one surface 81 a formed flat, and a cylindrical boss portion 81 c fitted to the pinion shaft 24 at the center of the other surface 81 b. It is integrally formed. The rotation center line CL of the turntable 81 matches the axis line CL (center line) of the pinion shaft 24. A first ball holder 86, an intermediate board 82, a second ball holder 87, and a wheel main body 83 are stacked on the rotating disk 81 in this order.

  As shown in FIGS. 6 and 7, the intermediate plate 82 is a disk-shaped member in which the one surface 82 a faces the one surface 81 a of the rotating plate 81 via the first ball holder 86. The center has a through hole 82c through which the pinion shaft 24 passes.

  As shown in FIGS. 6 and 7, the wheel body 83 is a member whose one surface 83 a faces the other surface 82 b of the intermediate plate 82 via the second ball cage 87, and has an outer peripheral surface. A plurality of teeth 83c are provided over the entire circumference. The plurality of teeth 83c mesh with the teeth 71 of the worm 70 shown in FIG.

  More specifically, the wheel main body 83 has a bottomed cylindrical shape (so-called generally crown-shaped, cap-shaped) having a space Sp that can be covered by covering the rotating plate 81 and the intermediate plate 82 from one side in the axial direction. The outer peripheral surface has teeth 83c, and the inner flat bottom surface 83a serves as one surface 83a of the wheel body 83.

  The wheel main body 83 has an annular wheel portion 91 having a plurality of teeth 83c on the outer peripheral surface, and a bottomed cylindrical shape integrally formed on the inner peripheral portion of the wheel portion 91 (so-called generally crowned shape). The base portion 92 is formed. The wheel portion 91 is a resin product such as nylon resin. The base 92 is a metal product fixed to the inside of the wheel portion 91 so as to be a core material of the wheel portion 91, and is generally formed in a cup shape having an open bottom. The base 92 includes a flat hollow disk-shaped bottom plate 92a (also referred to as an upper plate 92a), and a cylindrical portion that extends downward from the outer periphery of the bottom plate 92a toward the turntable 81 along the inner peripheral surface of the wheel portion 91. 92b. The bottom plate 92a has a through hole 92c through which the pinion shaft 24 passes in the center. The space Sp is formed by the bottom plate 92a and the cylindrical portion 92b. The wheel main body 83 may be formed of a single material in which the wheel portion 91 also serves as the base portion 92.

  The mutually facing surfaces 81a and 82a of the rotary plate 81 and the intermediate plate 82 are parallel to each other. These mutually facing surfaces 81a and 82a have first fitting grooves 81d and 82d that extend in a straight line in the radial direction of the pinion shaft 24 while facing each other. The rotary disk 81 and the intermediate disk 82 are connected to each other only in the radial direction (perpendicular to the axis) of the pinion shaft 24 by a plurality of first balls 84 fitted in the first fitting grooves 81d and 82d. In other words, the intermediate plate 82 is connected to the rotary plate 81 so as to be capable of relative movement in the direction perpendicular to the axis and with relative rotation restricted.

  The mutually facing surfaces 82b and 83a of the intermediate plate 82 and the wheel main body 83 are parallel to each other. These mutually facing surfaces 82b and 83a have second fitting grooves 82e and 83e that extend in a straight line in the radial direction of the pinion shaft 24 while facing each other. The second fitting grooves 82e and 83e are positioned orthogonal to the first fitting grooves 81d and 82d. That is, when the intermediate board 82 is viewed from one surface 82a, the first fitting grooves 81d and 82d and the second fitting grooves 82e and 83e are arranged in a cross shape. All of these fitting grooves 81d, 82d, 82e, and 83e are set to have the same shape and the same dimensions as each other, and the groove depth is uniform, and the rotation plate 81, the intermediate plate 82, and the wheel main body 83 are Through each center. The cross-sectional shape of each of the fitting grooves 81d, 82d, 82e, and 83e is, for example, an arc-shaped cross section (an arch-shaped cross section or a gothic arc-shaped cross section) or a tapered cross section that tapers from each surface.

  The intermediate plate 82 and the wheel main body 83 are connected to each other only in the radial direction (perpendicular to the axis) of the pinion shaft 24 by a plurality of second balls 85 fitted in the second fitting grooves 82e and 83e. That is, the wheel main body 83 is connected to the intermediate plate 82 such that the wheel main body 83 can be relatively moved in the direction perpendicular to the axis and the relative rotation is restricted.

  The first ball cage 86 is a thin disk-shaped member interposed between one surface 81a of the rotating disk 81 and one surface 82a of the intermediate disk 82, and the pinion shaft 24 is passed through the center. It has a through hole 86a. The first ball holder 86 has a plurality of holding holes 86b for holding the plurality of first balls 84 at a predetermined pitch.

  The second ball holder 87 has substantially the same configuration as the first ball holder 86. The second ball cage 87 is a thin disk-shaped member interposed between the other surface 82b of the intermediate plate 82 and the one surface 83a of the wheel body 83, and the pinion shaft 24 is passed through the center. A through hole 87a is provided. Here, the second ball holder 87 has a plurality of holding holes 87b for holding the plurality of second balls 85 at a predetermined pitch.

  The plurality of first balls 84 and the plurality of second balls 85 are all steel balls set to the same diameter. The presence or absence of the first and second ball holders 86 and 87 is arbitrary.

  As shown in FIG. 7, the size of the space Sp of the wheel body 83 is such that the rotating plate 81 (excluding the boss portion 81 c), the intermediate plate 82, the plurality of first and second balls 84 and 85, and the first and first The size is set such that the two-ball cages 86 and 87 can be accommodated. By storing these members in the space Sp, the entire wheel 80 can be reduced in size.

  The diameter of the through hole 82c of the intermediate plate 82, the diameter of the through hole 92c of the wheel body 83 (the through hole 92c of the base 92), and the diameters of the through holes 86a and 87a of the first and second ball cages 86 and 87 are both d1 (hereinafter referred to as the hole diameter d1). On the other hand, in the pinion shaft 24, the shaft fitting portion 24m2 located at the portion 24m2 where the through holes 82c, 86a, 87a, 92c are located, that is, the longitudinal center portion 24m of the pinion shaft 24, is d2. The wheel fitting portion 24m2 is adjacent to the rotating plate mounting portion 24m1. The hole diameter d1 is larger than the shaft diameter d2 (d1> d2). The size δ1 of the gap between each through hole 82c, 86a, 87a, 92c and the pinion shaft 24 is represented by “δ1 = (d1−d2) / 2”.

  The inner diameter of the cylindrical portion of the wheel main body 83 formed in a crown shape (the inner diameter of the base 92) is D1. On the other hand, the outer diameter of the turntable 81, the outer diameter of the intermediate board 82, and the outer diameters of the first and second ball cages 86 and 87 are all D2. The inner diameter D1 is larger than the outer diameter D2 (D1> D2). The size δ2 of the gap between the rotary plate 81, the intermediate plate 82, the first and second ball holders 86 and 87, and the wheel body 83 is represented by “δ2 = (D1−D2) / 2”.

  The allowable displacement amount ΔSL that allows the wheel body 83 to be displaced in the radial direction with respect to the pinion shaft 24 is the same as the smaller value of the gap size δ1 and the gap size δ2. The sizes of the gaps δ1 and δ2 are set to a sufficient size necessary for suppressing the backlash between the worm 70 and the wheel 80.

  As shown in FIGS. 3 to 5, the wheel body 83 is urged by the urging member 102 in the direction in which the teeth 83 c mesh with the teeth 71 of the worm 70. This urging member 102 is configured by a strip-like “plate spring” provided between the housing 51 for housing the wheel 80 and the wheel main body 83.

  More specifically, as shown in FIG. 4, the housing 51 has a recess 51 a formed on an arcuate inner peripheral surface. The recess 51a is located on the opposite side of the worm 70 with respect to the center line CL of the pinion shaft 24, and is formed in an arc shape with the center line CL as a reference. Further, the recess 51 a is formed symmetrically with respect to a straight line CrL that is orthogonal to the center line CL of the pinion shaft 24 and also orthogonal to the center line WL of the worm 70.

  The leaf spring 102 is hooked on the housing 51 by fitting both ends of the leaf spring 102 into the opposite ends of the arcuate recess 51a while bending the leaf spring 102 in the thickness direction. The leaf spring 102 attached to the housing 51 is bent in an arc shape around the center line CL of the pinion shaft 24, that is, in an arc shape so as to wrap around the outer peripheral surface of the wheel body 83. For this reason, the leaf spring 102 is configured such that the outer peripheral surface of the wheel main body 83 (for example, the tooth tip surface of the teeth 83c) is in the direction in which the teeth 83c of the wheel main body 83 are engaged with the teeth 71 of the worm 70, that is, the backlash between the teeth 71 and 83c. Energize in the direction of disappearing.

  As described above, the wheel 80 applies the Oldham coupling mechanism so that the wheel body 83 can move relative to the pinion shaft 24 only in the radial direction of the pinion shaft 24 and rotate the pinion shaft 24. In the direction, relative rotation is restricted and connected. Here, the Oldham joint is a joint that can transmit the rotation of the first shaft as it is to the second shaft that is not on the same center line as the first shaft and is parallel to the first shaft. It is. The combined structure of the rotary plate 81, the intermediate plate 82, the wheel body 83, the plurality of first balls 84, and the plurality of second balls 85 substantially forms an Oldham joint.

The attachment structure of the second bearing 56 and the wheel 80 to the pinion shaft 24 and the housing 51 is as follows.
As shown in FIGS. 3 and 5, the inner ring of the second bearing 56 is press-fitted into the longitudinal central portion 24 m of the pinion shaft 24. A retaining ring 105 (caulking ring 105) is fitted into the lower portion of the longitudinal central portion 24m of the pinion shaft 24. The retaining ring 105 positions the lower end surface of the inner ring of the second bearing 56 via the spacer 106. For this reason, the second bearing 56 is restricted from being displaced in the axial direction toward the lower end 24d of the pinion shaft 24.

The outer ring of the second bearing 56 is positioned in the housing 51 by being vertically sandwiched between the stepped surface 51c of the fitting hole 51b of the housing 51 and the annular lock nut 107 screwed into the fitting hole 51b of the housing. And assembled. The lock nut 107 has a thin portion at one end portion, and the looseness with respect to the housing 51 is restricted by caulking the thin portion with the notch groove of the housing 51.
The lock nut 107 is tightened by a tool that passes through the work holes 81f and 81f of the rotating plate 81 shown in FIG.

  An appropriate biasing force is applied between the first fitting grooves 81d and 82d and the plurality of first balls 84 and between the second fitting grooves 82e and 83e and the plurality of second balls 85 by the preload adjusting unit 110. That is, preload (also referred to as “preload”) is applied. By applying the preload, the operating state of the plurality of first balls 84 with respect to the first fitting grooves 81d and 82d and the operating state of the plurality of second balls 85 with respect to the second fitting grooves 82e and 83e are optimal. It becomes a state.

  The preload adjusting unit 110 includes a male screw 111, a disc spring 112, an adjusting nut 113, and a lock nut 114. The male screw 111 is formed adjacent to the wheel fitting portion 24m2 in the longitudinal central portion 24m of the pinion shaft 24. The disc spring 112 passes through the pinion shaft 24 and is applied to the other surface 83b of the wheel body 83 (the surface 83b that does not have the second fitting grooves 82e and 83e). The adjustment nut 113 is a member that adjusts the urging force (preload) that urges the other surface 83 b of the wheel body 83 via the disc spring 112 by adjusting the screwing amount with respect to the male screw 111. The lock nut 114 regulates the looseness of the adjustment nut 113 after adjustment.

  As described above, when the turntable 81 is press-fitted into the pinion shaft 24 or fixed by the pin 101, the position of the turntable 81 in the axial direction with respect to the pinion shaft 24 is naturally determined. For this reason, the position of the pinion shaft 24 with respect to the housing 51 is also determined. Further, since the intermediate plate 82, the wheel main body 83, the plurality of first balls 84, and the plurality of second balls 85 are sandwiched between the rotary plate 81 and the preload adjusting unit 110, the wheel for the pinion shaft 24 and the housing 51. The position of 80 is also determined. The wheel 80 is restricted from being displaced in the axial direction with respect to the pinion shaft 24.

  On the other hand, when the turntable 81 is attached to the pinion shaft 24 with any one of splines, serrations, and keys restricted only by relative rotation, it is provided between the inner ring of the second bearing 56 and the preload adjusting unit 110. Since the intermediate plate 82, the wheel body 83, the plurality of first balls 84, and the plurality of second balls 85 are sandwiched, the position of the wheel 80 with respect to the pinion shaft 24 and the housing 51 is determined. The wheel 80 is restricted from being displaced in the axial direction with respect to the pinion shaft 24.

Next, the operation of the worm gear mechanism 44 having the above configuration will be described.
As shown in FIG. 3, the leaf spring 102 always urges the wheel body 83 in a direction to engage the worm 70. For this reason, there is no backlash between the teeth 71 of the worm 70 and the teeth 83 c of the wheel body 83. Thereafter, the electric motor 43 begins to generate auxiliary torque, and when this auxiliary torque increases, the component force corresponding to the pressure angle of the teeth 71 of the worm 70 gradually increases. When the increased component force acts on the teeth 83 c of the wheel body 83, the wheel body 83 is displaced in a direction away from the teeth 71 of the worm 70 against the urging force of the leaf spring 102. As a result, the teeth 71 of the worm 70 and the teeth 83c of the wheel body 83 rotate in an optimal meshing state.

  Thus, the auxiliary torque generated by the electric motor 43 is transmitted from the worm 70 to the wheel body 83, and further, the second fitting groove 83e of the wheel body 83, the plurality of second balls 85, and the intermediate panel 82 shown in FIG. The second fitting groove 82e, the intermediate plate 82, the first fitting groove 82d of the intermediate plate 82, the plurality of first balls 84, the first fitting groove 81d of the rotating plate 81, and the pinion shaft 24 along the path of the rotating plate 81. Is transmitted to.

  As is apparent from the above description, in the first embodiment, the wheel 80 applies the mechanism of the Oldham coupling, and the rotating plate 81, the intermediate plate 82, the wheel body 83, the plurality of first balls 84, and the plurality of second balls. The ball 85 is combined. With this configuration, the wheel main body 83 can be moved relative to the pinion shaft 24 only in the radial direction of the pinion shaft 24, and the relative rotation is restricted in the rotation direction of the pinion shaft 24 and is connected. Yes. That is, the wheel body 83 is flexible with respect to the pinion shaft 24 in the radial direction of the pinion shaft 24 and is firmly connected to the rotation direction of the pinion shaft 24. For this reason, even when the rotation center of the wheel 80 is different from the axis CL of the pinion shaft 24, torque can be reliably transmitted from the wheel body 83 to the pinion shaft 24.

  Further, the wheel body 83 is urged by the leaf spring 102 (the urging member 102) in the direction in which the teeth 83c provided on the outer peripheral surface mesh with the worm 70. That is, the urging force acts on the wheel body 83 so as to move in the radial direction of the pinion shaft 24. On the other hand, the wheel main body 83 can move relative to the pinion shaft 24 in the radial direction of the pinion shaft 24. Accordingly, the teeth 83 c of the wheel body 83 are always pressed against the teeth 71 of the worm 70 by the urging force. The teeth 71 of the worm 70 and the teeth 83c of the wheel body 83 can always maintain a good meshing state without having backlash.

  On the other hand, with respect to the rotation direction of the pinion shaft 24, the wheel body 83 is firmly connected to the pinion shaft 24, that is, relative rotation is restricted in the rotation direction of the pinion shaft 24. For this reason, the torque transmitted from the worm 70 to the wheel body 83 can be transmitted quickly and reliably from the wheel body 83 to the pinion shaft 24 without a time delay. For example, when a control torque that changes every moment for controlling the load is transmitted from the worm to the pinion shaft 24, there is no time delay when the control torque is transmitted from the wheel body 83 to the pinion shaft 24. Therefore, the controllability for controlling the load is enhanced.

  In the electric power steering apparatus 10 shown in FIG. 1, when the steering wheel 21 is turned back, the auxiliary torque generated by the electric motor 43 is transmitted quickly and reliably from the wheel body 83 to the pinion shaft 24 without time delay. . For this reason, the auxiliary torque is quickly and reliably transmitted from the electric motor 43 to the steering system 20 without a time delay. By the combined torque obtained by adding the assist torque of the electric motor 43 to the steering torque of the driver, the steering wheels 29 and 29 can be quickly and reliably steered by the rack shaft 26.

  Thus, backlash between the worm 70 and the wheel 80 can be suppressed, and torque can be transmitted from the worm 70 to the pinion shaft 24 quickly and reliably.

  Further, in the first embodiment, the wheel body 83 is urged in a direction to mesh with the worm 70. Therefore, as in the case of urging the worm 70 and the worm shaft 46 in the prior art in the direction of meshing with the wheel body 83, the motor shaft 43a and the worm shaft 46 of the electric motor 43 for driving the worm 70, There is no need to pay attention to the consolidated structure.

  Further, in the first embodiment, the urging member 102 is provided between the housing 51 for housing the wheel 80 and the wheel main body 83. For this reason, the structure of the urging member 102 can be simplified.

  Next, the worm gear mechanism according to the second embodiment will be described with reference to FIGS. FIG. 8 shows Example 2 corresponding to FIG. FIG. 9 shows Example 2 corresponding to FIG. The worm gear mechanism 44A according to the second embodiment is characterized in that the biasing member 102 according to the first embodiment shown in FIGS. 3 to 5 is changed to the biasing member 120 shown in FIGS. Is the same as the configuration shown in FIGS.

  Specifically, the urging member 120 according to the second embodiment is formed of an elastic body interposed between the pinion shaft 24 (rotating shaft 24) and the through hole 92c of the wheel main body 83. More specifically, the urging member 120 of the second embodiment is an annular member, and is an integrally molded product including an inner ring 121, an outer ring 122, and an elastic ring 123. The inner ring 121, the outer ring 122, and the elastic ring 123 are arranged concentrically. The annular inner ring 121 and the annular outer ring 122 are made of a rigid material such as a metal material. The elastic ring 123 is an annular member interposed between the inner ring 121 and the outer ring 122, and is made of an elastic material such as rubber. For example, the elastic ring 123 is integrated with the inner ring 121 and the outer ring 122 by vulcanization adhesion. The urging member 120 is interposed between the pinion shaft 24 and the wheel body 83 by fitting the wheel fitting portion 24 m 2 of the pinion shaft 24 to the inner ring 121 and fitting the outer ring 122 to the through hole 92 c of the wheel body 83. Will intervene.

  As shown in FIG. 8, the teeth 83 c of the wheel 80 are engaged with the teeth 71 of the worm 70 so as to be in contact with each other, that is, without backlash. In this state, the center HL of the wheel main body 83 is offset from the center CL of the pinion shaft 24 by the offset amount Of outward in the radial direction of the wheel main body 83 so as to be separated from the teeth 71 of the worm 70. For this reason, the elastic ring 123 has a portion near the worm 70 compressed in the radial direction. The compressed portion of the elastic ring 123 is urged in a direction in which the teeth 71 and 83c mesh with each other by its own elastic force.

  Thus, in Example 2, in addition to exhibiting the function and effect of Example 1, the following function and effect are exhibited. That is, the wheel body 83 is urged in the direction of meshing with the worm 70 by the elastic body 120 interposed between the through hole 92 c of the wheel body 83 and the pinion shaft 24. For this reason, the structure of the urging member 120 (elastic body 120) can be simplified. Moreover, the wheel body 83 is restricted from rotating relative to the pinion shaft 24 in the rotational direction. For this reason, when the pinion shaft 24 and the wheel main body 83 rotate, no torque acts on the elastic body 120. That is, the elastic body 120 only needs to have a function of urging the wheel body 83 in the direction of meshing with the worm 70, and durability can be improved. In addition, the torque transmitted from the worm 70 to the wheel body 83 can be transmitted quickly and reliably from the wheel body 83 to the pinion shaft 24 without a time delay.

  The worm gear mechanisms 44 and 44A of the present invention detect the steering torque generated by the steering wheel 21 by the steering torque sensor 41, and the electric motor 43 generates auxiliary torque in response to the detection signal of the steering torque sensor 41. This is suitable for the vehicle electric power steering apparatus 10 that transmits the auxiliary torque to the steering system 20 via the worm gear mechanism 44.

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 20 ... Steering system, 21 ... Steering wheel, 24 ... Rotating shaft, 29 ... Steering wheel, 43 ... Electric motor, 44, 44A ... Worm gear mechanism, 51 ... Housing, 70 ... Worm, 71 ... Teeth , 80 ... Worm wheel, 81 ... Rotary disc, 81a ... One surface of the rotary disc, 81d ... First fitting groove, 82 ... Intermediate disc, 82a ... One surface of the intermediate disc, 82b ... Other surface of the intermediate disc , 82d ... first fitting groove, 82e ... second fitting groove, 83 ... wheel body, 83a ... one surface of the wheel body, 83c ... tooth, 83e ... second fitting groove, 84 ... first ball, 85 ... second ball, 102 ... biasing member, 120 ... elastic body (biasing member).

Claims (3)

A worm gear mechanism comprising a worm and a worm wheel meshing with the worm,
The worm wheel is
A turntable that is mounted with its relative rotation restricted to the rotation axis;
An intermediate board with one side facing one side of the rotating board;
A circular wheel body, one of which faces the other surface of the intermediate board,
A plurality of first balls that connect the mutually facing surfaces of the rotating disk and the intermediate disk;
A plurality of second balls connecting the mutually facing surfaces of the intermediate plate and the wheel body,
The mutually facing surfaces of the rotating disk and the intermediate disk have first fitting grooves that extend in a straight line in the radial direction of the rotating shaft while facing each other, and are fitted into these first fitting grooves. The plurality of first balls are connected to each other only in the radial direction of the rotation shaft,
The mutually facing surfaces of the intermediate plate and the wheel main body have second fitting grooves that extend in a straight line in the radial direction of the rotating shaft while facing each other, and are fitted into these second fitting grooves. The plurality of second balls are connected to each other only in the radial direction of the rotation shaft,
The second fitting groove is positioned orthogonal to the first fitting groove,
The wheel body has teeth engaging with the worm on an outer peripheral surface, and the teeth are urged by a urging member in a direction engaging with the worm.   The worm gear mechanism according to claim 1, wherein the urging member is provided between a housing for housing the worm wheel and the wheel body. The wheel body has a through-hole penetrating the rotating shaft,
2. The worm gear mechanism according to claim 1, wherein the urging member is made of an elastic body interposed between the rotating shaft and the through hole.

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