JP5707312B2 - Gear, worm gear mechanism having the same gear, and electric power steering apparatus having the worm gear mechanism - Google Patents

Description

  The present invention relates to an improvement technique for various gears.

  For example, an electric power steering device for a vehicle adds torque generated by an electric motor to steering torque via a worm gear mechanism. The worm gear mechanism includes a worm and a worm wheel that meshes with the worm (see, for example, Patent Document 1 (FIG. 5)).

  The worm wheel shown in Patent Document 1 includes a cored bar (hub) fitted to a shaft part and a resin gear part integrally formed on the outer periphery of the cored bar. A plurality of round holes are penetrated so that a metal core part may surround a fitting hole with a shaft part. By forming the round hole, the core bar can be reduced in weight. By reducing the weight of the cored bar, the entire worm wheel can be reduced in weight.

  In order to manufacture such a worm wheel, the cored bar part is set in an injection molding (injection molding) mold, and molten resin is supplied to the outer peripheral edge of the cored bar part. Wait for the supplied resin to solidify, and finally polish the solidified resin to adjust the shape of the gear part. The reason why the shape of the gear part is adjusted will be described in the next figure.

  As shown in FIG. 12, when the resin 202 supplied to the outer peripheral edge of the cored bar part 201 is solidified, the heat shrinking force of the resin 202 as indicated by the white arrow is applied to the cored bar part 201. . The cored bar 201 is deformed by this contraction force. In particular, the amount of deformation increases at a portion in the vicinity of the round hole 203 whose rigidity has been reduced by opening the round hole 203. As the core bar 201 is deformed, the outer periphery of the resin 202 has a shape in which a circle is distorted. In order to suppress the distortion within a predetermined amount and correct it into a circular shape, a step of molding the resin 202 is required.

  Here, when the round hole 203 is made small, the rigidity in the vicinity of the round hole 203 can be secured, and the deformation amount can be suppressed to a predetermined amount or less. If the amount of deformation can be suppressed to a predetermined amount or less, the step of molding the resin becomes unnecessary. However, when the round hole 203 is made small, the core bar portion cannot be reduced in weight.

Japanese Patent No. 3948078

  An object of the present invention is to provide a technique capable of reducing the weight of the gear while suppressing deformation of the cored bar during molding of the gear.

The invention according to claim 1 is a gear having a cored bar part attached to the shaft part and a resin gear part integrally formed on the outer periphery of the cored bar part , and the cored bar part is the cored bar. Has an opening that can be seen in a state where the gear portion is integrally formed on the outer periphery, and this opening has a core when the cored bar is viewed from the direction of the centerline. It is a long hole that gradually narrows from the center of the metal part toward the outer periphery.

  In the invention which concerns on Claim 2, the gear part is shape | molded only by injection molding, It is characterized by the above-mentioned.

  The invention according to claim 3 is characterized in that the opening is formed line-symmetrically with respect to a line-symmetric axis passing through the center of the cored bar.

  The invention according to claim 4 is characterized in that the gear according to any one of claims 1 to 3 is a worm wheel of a worm gear mechanism.

  According to a fifth aspect of the present invention, there is provided an electric power steering apparatus according to the fourth aspect of the present invention, the worm gear mechanism according to the fourth aspect, a steering system from the steering handle of the vehicle to the steering wheel, and torque generated and transmitted to the steering system via the worm gear mechanism. And an electric motor.

  In the invention according to claim 1, the opening is a long hole that gradually narrows from the center of the cored bar toward the outer periphery when the cored bar is viewed from the direction of the center line. By gradually narrowing the opening toward the outer periphery, the area of the opening in the vicinity of the outer periphery of the cored bar was reduced. When the resin supplied to the outer periphery of the cored bar is solidified, it is considered that the influence of the shrinkage force of the resin is particularly large in the vicinity of the outer periphery of the cored bar. By reducing the area of the opening in the region where the influence of the resin shrinkage force is large, the deformation amount of the cored bar due to the resin shrinkage force can be suppressed to be smaller than a predetermined value. On the other hand, by increasing the area of the opening in the inner periphery of the cored bar part, it is possible to reduce the weight of the cored bar part. By reducing the weight of the cored bar, the weight of the gear can be reduced. That is, the weight of the gear can be reduced while suppressing deformation of the cored bar during molding of the gear.

  In the invention which concerns on Claim 2, the gear part is shape | molded only by injection molding. That is, after the injection molding, polishing for correcting the shape is not performed. It can be molded with fewer steps and is beneficial.

  In the invention which concerns on Claim 3, an opening part is formed in line symmetry, and the axis of line symmetry of an opening part passes the center of a metal core part. When the gear is used, a shaft member is usually fitted in the center of the cored bar. The shaft member that supports the cored bar is a highly rigid component. The line symmetry axis of the opening passes through the center of the cored bar. That is, when the gear is used, the line-symmetric axis of the opening passes through the center of the shaft member. High rigidity can be obtained with respect to the external force applied from the outer periphery of the gear toward the center of the cored bar.

  In the invention which concerns on Claim 4, the gear concerning this invention is used for the worm wheel of a worm gear mechanism. The gear according to the present invention has high strength against external force applied from the outer periphery toward the center of the cored bar. It is desirable from the viewpoint of strength to use the gear according to the present invention for the worm gear mechanism used under various circumstances.

  In the invention according to claim 5, the worm gear mechanism according to claim 4 is mounted on the electric power steering apparatus. An electric power steering device is a device that requires precise control. The gear according to the present invention in which deformation due to heat shrinkage is sufficiently suppressed is desirably mounted on a power steering apparatus that requires precise control.

1 is a schematic diagram of an electric power steering apparatus according to 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. It is the front view and enlarged view of an opening part of the worm wheel which concern on Example 1 shown by FIG. It is a figure explaining the method of the 1st experiment conducted about the present invention. It is a figure explaining the result of the 1st experiment explained in Drawing 5. It is a figure explaining the reason of the result shown by FIG. It is a figure explaining the result of the 2nd experiment performed based on the reason demonstrated in FIG. It is a figure explaining the result of 3rd experiment performed based on the reason demonstrated in FIG. 6 is an enlarged view of an opening of a worm wheel according to Embodiment 2. FIG. 6 is an enlarged view of an opening of a worm wheel according to Embodiment 3. FIG. It is a figure explaining the problem of the prior art.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  An electric power steering apparatus according to a first embodiment will be described with reference to FIGS.

  As shown in FIG. 1, the electric power steering apparatus 10 includes a steering system 20 that extends 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 that applies an auxiliary torque to the steering system 20. Mechanism 40.

  In the steering system 20, a pinion shaft 24 (shaft portion 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 portion 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). Further, the electric motor 43 is attached and a rack guide 60 is provided.

  The rack guide 60 is rack 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.

  The electric motor 43 is attached to the outer surface of the housing 51. The motor shaft of the electric motor 43 extends into the housing 51 and is coupled to the worm shaft 46 by a coupling.

  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 (gear) 80 that meshes with the worm 70. The worm wheel 80 is hereinafter abbreviated as “wheel 80”. The center line CL of the wheel 80 is disposed substantially perpendicular to the center line WL of the worm 70. The center line CL of the wheel 80 is also the center line CL of the pinion shaft 24.

  The worm 70 is a metal product integrally formed with the worm shaft 46, for example, a steel product such as a carbon steel material for machine structure (JIS-G-4051).

  The wheel 80 includes a cored bar part 81 that is a metal product fitted to the pinion shaft 24 and a resin gear part 82 that is integrally formed with the cored bar part 81. For the gear portion 82, for example, nylon resin can be used.

Since the resin product wheel 80 is meshed with the metal product worm 70, meshing can be made relatively smooth and noise can be reduced.
The details of the wheel 80 will be described in the next figure.

  As shown in FIG. 4A, a central hole 83 supported by a pinion shaft (FIG. 3, reference numeral 24) is formed in the center of the cored bar 81. The center of the center hole 83 coincides with the center CL of the pinion axis. Six openings 85 are formed so as to surround the center hole 83. The openings 85 have the same shape and are formed at equal intervals.

  The gear portion 82 is formed so as to partially overlap the outer peripheral edge 81 a of the core metal portion 81. The gear part 82 is molded only by injection molding. Here, only injection molding means that polishing or the like for adjusting the shape of the gear portion is not performed after injection molding.

  As shown in FIG. 4B, the opening 85 includes a semicircular portion 85a having a radius r and a rectangular portion 85b having a rectangular shape formed integrally with the semicircular portion 85a. The opening 85 composed of the semicircular portion 85a and the rectangular portion 85b is formed symmetrically with respect to the line symmetry axis 86. In the rectangular portion 85b, the length of the side along the line extending from the center of the cored bar portion 81 toward the outer periphery is h, and the length of the side extending in the direction perpendicular to the side, that is, the width direction is b. ing. This length b is formed to have the same length as the diameter of the semicircular portion 81a. That is, b = 2 × r.

  Further, it is desirable that the relationship between the two sides of the rectangular portion 85b be h> b. This is because an opening 85 having a larger area can be formed by setting h> b. It is desirable that at least r + h> b. Since b = 2 × r, it is desirable that h> (1/2) × b.

  Furthermore, the length r + h in the longitudinal direction of the opening 85 is preferably at least half of the length L from the center hole 83 to the outer peripheral edge 81a of the cored bar 81 shown in FIG. . That is, r + h> (1/2) × L. By setting r + h> (1/2) × L, a large opening 85 can be secured.

  Returning to FIG. 4A, the line symmetry axis 86 of the opening 85 passes through the center CL of the cored bar 81. The line symmetry axis 86 coincides with the line symmetry axis 86 of the opening 85 formed through the center CL and facing the center CL.

The above can be summarized as follows.
The cored bar 81 is formed with an opening 85 penetrating along the center CL of the cored bar 81. The opening 85 is formed when the cored bar 81 is viewed from the direction of the center CL. This is a long hole that gradually narrows from the center CL of the portion 81 toward the outer periphery.
An experiment was conducted on such a wheel 80. Details will be described in the following figures.

As shown in FIG. 5A, a wheel 210 according to a comparative example includes a cored bar part 211, a gear part 212 formed by injection molding on the cored bar part 211, a center hole 213 having a diameter D, It consists of a circular opening 214. A plurality of wheels 210 were created while changing the radius of the opening 214. That is, the area S = (r ² × π) of the opening 214 was changed for each wheel 210 to create a plurality of wheels 210 and perform measurement.

  It was measured how much the gear portion 212 of the molded product was compressed with respect to the mold with respect to the radius R0 of the injection mold. The radius R1 of the gear portion 212 was measured at a portion passing through the center of the opening 214 having the largest compression amount. After measuring the radius R1 of the gear part 212, the deformation amount δ with respect to R0 was calculated. That is, R0−R1 = δ.

  As shown in FIG. 5B, the wheel 90 according to the embodiment includes a cored bar 91, a gear part 92 formed on the cored bar 91 by injection molding, a center hole 93 having a diameter D, And an opening 94.

  As shown in FIG. 5C, the shape of the opening 94 is such that a semicircular portion 94a having a radius r and a square portion 94b having a length in the longitudinal direction h and a length in the width direction b are integrated. It is the shape formed automatically.

A plurality of wheels 90 were created while changing the length h of the side in the longitudinal direction of the square portion 94b. In other words, the area S = (r ² × π) / 2 + b × h of the opening 94 was changed for each wheel 90, and a plurality of wheels 90 were created and measured. The measurement method is the same as in the comparative example.
The results of the experiment described with reference to FIGS. 5A to 5C will be described with reference to the next figure.

FIG. 6 shows a graph for explaining the experimental results. The horizontal axis represents the area Smm ² of the opening, and the vertical axis represents the radial deformation of δmm of the worm wheel. P1 to P3 are experimental results according to the comparative example. P4 to P8 are experimental results according to the example.

In the wheel 210 according to the comparative example, the area Smm ² of the opening was changed by changing the radius of the circular opening 214. In such a wheel 210, as indicated by a line 215, the amount of deformation δ in the radial direction of the wheel 210 increases as the area of the opening 214 increases.

In the wheel 90 according to the embodiment, by changing the length of the longitudinal sides of the opening portion 94, was varied area Smm ² of the opening. In such a wheel 90, as indicated by the line 95, the amount of change δ in the radial direction of the worm wheel did not change much. That is, the area Smm ² of the opening 94 is also changed, the radial variation δ of the worm wheel, did not change much.
The reason for this result will be described with reference to the next figure.

  As shown in FIG. 7A, when the resin is solidified, a contraction force F as indicated by a white arrow is generated. This contraction force F is considered to have a great influence on the vicinity of the outer peripheral edge 211a of the cored bar 211 in particular.

  In the wheel 210 according to the comparative example, the area of the opening 214 was increased by increasing the radius of the circular opening 214. Increasing the area of the opening 214 increases the area of the opening 214 at a portion that is easily affected by the contraction force F (see the shaded area). The opening 214 is less rigid than other parts. For this reason, the amount of deformation of the resin increases by increasing the area of the part that is easily affected by the contraction force F. As a result, it is considered that the amount of deformation increases as the area of the opening 214 increases.

  On the other hand, as shown in FIG. 7B, the opening 94 according to the embodiment is obtained by changing the length of the side in the longitudinal direction of the square portion 94b without changing the size of the semicircular portion 94a. The area of the opening 94 was changed.

  Since the size of the semicircular portion 94a was not changed, the area of the portion susceptible to the contraction force F was constant. It is considered that the deformation amount of the wheel according to the example in which the area of the part that is easily affected by the contraction force F is constant did not change even when the area of the opening 94 was increased. Compared with the opening 114 of the wheel 110 according to the comparative example, the opening 94 of the wheel 90 according to the embodiment can reduce the area of the opening 94 at a portion that is easily affected by the contraction force F (hatched line). Section). On the other hand, by expanding the opening 94 toward the center side of the wheel 90, an area equivalent to the opening 114 of the wheel 110 according to the comparative example can be ensured without changing the deformation amount much.

The above can be summarized as follows.
Returning to FIG. 4, the opening 85 is a long hole that gradually narrows from the center line CL of the core metal part 81 toward the outer periphery when the core metal part 81 is viewed from the direction of the center line CL. By gradually narrowing the opening 85 toward the outer periphery, the area of the opening 85 in the vicinity of the outer peripheral edge 81a of the cored bar 81 was reduced.

  When the resin (gear part 82) supplied to the outer periphery of the cored bar part 81 is solidified, it is considered that the influence of the contraction force of the resin is particularly large in the vicinity of the outer peripheral edge 81a of the cored bar part 81. By reducing the area of the opening 85 in the region where the influence of the resin contraction force is large, the deformation amount of the cored bar 81 due to the resin contraction force can be suppressed to be smaller than a predetermined value. On the other hand, by increasing the area of the opening 85 on the inner periphery of the cored bar 81, the cored bar 81 can be reduced in weight. By reducing the weight of the cored bar 81, the weight of the wheel 80 can be reduced. That is, a lightweight wheel 80 (gear) can be provided while suppressing deformation during molding.

  Further, since the deformation amount at the time of molding is small, it is not necessary to adjust the shape of the gear portion 82 by polishing or the like after the gear portion 82 is injection molded. It can be molded with fewer steps and is beneficial.

  Further, the opening 85 is formed in line symmetry, and the line symmetry axis 86 of the opening 85 passes through the central axis CL of the cored bar 81. When the wheel 80 is used, a shaft member (see the pinion shaft 24 in FIG. 3) is usually fitted to the central axis CL of the cored bar portion 81. The shaft member that supports the cored bar 81 is a highly rigid component. The line symmetry axis 86 of the opening 85 passes through the central axis CL of the cored bar 81. That is, when the wheel 80 is used, the line symmetry axis 86 of the opening 85 passes through the center CL of the shaft member. High rigidity can be obtained with respect to an external force applied from the outer periphery of the wheel 80 toward the central axis CL of the cored bar portion 81.

Based on the above findings, the present inventors conducted further experiments.
Returning to FIG. The present inventors have conceived to further reduce the area of the opening 94 in the vicinity of the outer peripheral edge 91a of the cored bar part 91, that is, the part susceptible to the shrinkage force of the resin. This is because by further reducing the area of the opening 94 in the vicinity of the outer peripheral edge 91a, it can be expected that the influence of contraction force is further weakened.

As shown in FIG. 5 (c), a plurality of test pieces in which the radius r of the semicircular portion 94a was changed were created and measured. In all the test pieces, the height h was changed in accordance with the change of the radius r so that the area S of the opening was the same. That is, in this experiment, the opening 94 has a shape in which a trapezoid is integrally formed in a semicircular shape. (R ² × π) / 2 + (b + 2r) × h / 2 = S = constant. As shown in FIG. 5B, the deformation amount δ was measured.

Similarly, a similar experiment was performed on the wheel 90 having a shape in which the opening 94 is formed by dividing an ellipse into two. That is, a plurality of test pieces having different heights h were prepared and experiments were performed while changing the radius r in the vicinity of the outer peripheral edge 91a and making the area S constant.
The result of an experiment in which an opening having a shape in which a trapezoid is integrally formed in a semicircular shape will be described with reference to FIG.

  FIG. 8 is a graph for explaining the result of an experiment in which an opening having a shape in which a trapezoid is integrally formed in a semicircular shape is formed. The horizontal axis indicates the radius rmm of the tip of the opening, and the vertical axis indicates the radial deformation amount δmm of the worm wheel. P4 and P9 to P12 are experimental results. P4 shows the result of the opening opened under the same conditions as P4 shown in FIG.

As indicated by a line 96, the radial variation δ of the worm wheel decreased as the radius r of the tip of the opening decreased. In particular, in P11 and P12 in which the radius r was small and the shape of the opening 94 was substantially triangular, good results could be obtained.
The result of the experiment in which the half-elliptical opening was formed will be described in the next figure.

  FIG. 9 is a graph for explaining the results of an experiment performed by forming a half-elliptical opening. The horizontal axis indicates the radius rmm of the tip of the opening, and the vertical axis indicates the radial deformation amount δmm of the worm wheel. P4 and P13 to P16 are experimental results. P4 shows the result of the opening opened under the same conditions as P4 shown in FIG.

As indicated by a line 97, the radial change amount δ of the worm wheel is smaller as the radius r of the tip of the opening is smaller.
Another embodiment will be described in the following figures.

Next, a second embodiment of the present invention will be described with reference to the drawings.
FIG. 10 shows the opening of the wheel according to the second embodiment, corresponding to FIG. 4 (b).
As shown in FIG. 10, in the wheel 100, the tip of the opening 105 has a small semicircular shape, and the entire opening 105 is formed in a substantially triangular shape.

  By forming the opening 105 in a substantially triangular shape, the area of the part that is greatly affected by the contraction force can be particularly reduced. By reducing the area of the part that is greatly affected by the shrinkage force, the lightweight wheel 100 can be manufactured while suppressing the amount of deformation during molding.

Next, Embodiment 3 of the present invention will be described with reference to the drawings.
FIG. 11 shows the opening of the wheel of the second embodiment, corresponding to FIG. 4 (b).
As shown in FIG. 11, the opening 110 of the wheel 110 is formed in a half-oval shape.

  By forming the opening 115 in a half-elliptical ellipse shape, the area of the part that is greatly affected by the contractile force can be particularly reduced. By reducing the area of the part that is greatly affected by the shrinkage force, the lightweight wheel 110 can be manufactured while suppressing the amount of deformation during molding.

  Although the gear according to the present invention has been described by taking the worm wheel of the electric power steering device as an example, the use of the gear according to the present invention is not limited to this embodiment.

  The gear of the present invention is suitable for a worm wheel of an electric power steering apparatus.

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 20 ... Steering system, 24 ... Pinion shaft (shaft part), 43 ... Electric motor, 44 ... Worm gear mechanism, 80, 100, 110 ... Wheel, 81 ... Core metal part, 82 ... Gear part, 85, 105, 115 ... opening, 86 ... line symmetry axis, CL ... center line.

Claims (5)

A gear comprising a metal core part attached to the shaft part, and a resin gear part integrally formed on the outer periphery of the metal core part,
The metal core portion, the core metal portion penetrating along the center line of a possible opening visible in a state in which the gear unit is integrally molded on the outer circumference,
The opening is a long hole that gradually narrows from the center of the cored bar toward the outer periphery when the cored bar is viewed from the direction of the center line.   The gear according to claim 1, wherein the gear portion is formed only by injection molding.   The gear according to claim 1, wherein the opening is formed in line symmetry with respect to a line symmetry axis passing through the center of the cored bar.   The worm gear mechanism according to any one of claims 1 to 3, wherein the gear is a worm wheel of a worm gear mechanism.   A worm gear mechanism according to claim 4, a steering system from a steering handle of a vehicle to a steering wheel, and an electric motor that generates torque and transmits the torque to the steering system via the worm gear mechanism. An electric power steering device.

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