JP4951389B2 - Worm gear - Google Patents

Description

  The present invention relates to a worm gear and an electric power steering apparatus to which the worm gear is applied.

Conventionally, Patent Document 1 discloses an electric power steering device to which a worm gear is applied. Generally, an involute curve is used for the tooth surface profile of the worm gear, and although it is not described in detail in Patent Document 1, it is considered that this involute curve is used.
JP 2006-142400 A

  In recent years, in order to apply an electric power steering device to a large vehicle, there is a demand for a worm gear that achieves a reduction in size while having strength capable of withstanding high output and high torque. However, in the worm gear using the involute gear, it is necessary to increase the size of the worm gear itself in order to increase the strength, and accordingly, there is a problem that the electric power steering device is also increased in size.

  The present invention has been made paying attention to the above problems, and an object thereof is to provide a worm gear that achieves both high strength and downsizing.

  To achieve the above object, according to the present invention, a worm shaft having a concave arc shape in tooth cross-section, meshing with the worm shaft, a tooth tip surface, a tooth root surface, and a tooth tip surface and a tooth root surface. The normal line in the tooth surface, which is composed of the tooth surfaces formed therebetween and intersects the pitch circle, has a worm wheel that passes through the center side of the root surface.

  Therefore, it is possible to provide a worm gear that achieves both high strength and downsizing.

Hereinafter, the best mode for implementing the worm tooth wheel of the present invention will be described with reference to embodiments shown in the drawings.

  FIG. 1 is a system configuration diagram of an electric power steering device to which the present worm gear is applied. The electric power steering device includes a motor control device 1, a steering wheel SW, a steering shaft SS, a torque sensor TS, an input shaft IN, a rack and pinion (steering mechanism: rack R and pinion P), and steered wheels FL and FR. A motor M is provided in the motor control device 1 and is driven by a power supply BATT.

  When the steering wheel SW is steered by the driver, the steering torque is detected by the torque sensor TS via the steering shaft SS and the input shaft IN. Based on the detected steering torque, the control board 300 (see FIG. 2) in the motor control device 1 outputs a drive signal to the motor M, and the motor M in the motor control device 1 is driven to rotate the pinion P. The steering assist is performed by moving the rack R in the axial direction.

[Axial sectional view]
2 is an axial sectional view of the motor control device 1, and FIG. 3 is a radial sectional view. The motor control device 1 includes a torque sensor TS, a motor housing 6, a worm housing 7, and a motor M. The axial direction of the input shaft IN is the y-axis, and the direction opposite to the pinion P is positive. Further, the input axis IN side from the motor M is set as the positive x-axis direction.

  In this application, in order to reduce the pressure applied to the teeth of the worm wheel 100, the worm wheel 100 and the worm shaft 200 are not a general involute tooth profile but a Neiman tooth profile having a curved tooth surface. That is, the tooth surface of the worm shaft 200 is a concave curved surface, and the tooth surface of the worm wheel 100 is a curved surface that is convex outward from the involute tooth surface.

  For this reason, the pressure angle in meshing of the worm wheel 100 and the worm shaft 200 changes at the meshing position, and the bending stress applied to the teeth of the worm wheel 100 is reduced.

  An input shaft IN is provided in the torque sensor housing 5, and a pinion P is provided in the worm housing 7. A brushless type motor M is accommodated in the motor housing 6 and assembled to the input shaft IN and the pinion P from the radial direction. The motor M need not be a brushless type.

  The input shaft IN and the pinion P are integrated by the torsion bar 3, and the worm wheel 100 is assembled to the pinion P and stored in the worm housing 7 from the positive y-axis direction. A motor housing 6 is assembled to the worm housing 7.

  The worm shaft 200 is connected to the output shaft of the motor M by the joint 9 and meshes with the worm wheel 100. The input shaft IN is supported by the torque sensor housing 5 and supported by the end of the pinion P so as to be relatively rotatable.

  A torque sensor TS is housed in the inner periphery of the torque sensor housing 5, and is configured to output a torque sensor signal when the torsion bar 3 is twisted by the driver's steering and the input shaft IN and the pinion P rotate relative to each other.

  The pinion P is supported by the worm housing 7, and a worm wheel 100 is provided on the outer periphery thereof to mesh with a worm shaft 200 connected to the motor M.

  The control board 300 has a microcomputer and is a circuit board in which various vehicle signals, a torque sensor TS, and a control circuit for the motor M are integrated, and controls the motor M. The control board 300 is provided with a rotational position sensor 130 that detects the rotation of the motor M.

[Details of worm shaft]
4 is a front view in the radial direction of the worm shaft 200, FIG. 5 is a cross-sectional view taken along the line C-C of the tooth portion 210 of the worm shaft 200 (cross-sectional view perpendicular to the tooth portion 210), and FIG. It is a cross-sectional view in the direction perpendicular to the tooth portion 210 ′ of the shaft.

  As described above, the worm shaft 200 of the present application is a Neiman worm, and the tooth surface shape of the tooth portion 210 in the cross section in the perpendicular direction is a concave arc shape having a radius R. On the other hand, the conventional example has a trapezoidal tooth profile, and the tooth portion 210 'has a linear shape. Therefore, if the pitch is the same, the tooth width 210 of the tooth portion 210 of the present application is larger and the tooth tip width Sa is smaller than the conventional example.

[Details of worm wheel]
(Front view and sectional view)
FIG. 7 is a partial radial sectional view of the worm wheel 100, and FIG. 8 is an axial sectional view of the worm wheel 100. The worm wheel 100 is a gear in which a core metal 101 that is a metal gear is provided with a coating portion 102 made of resin, and the coating portion 102 is covered over the entire circumference of the tooth portion of the core metal 101.

  By providing the cored bar 101, the strength of the worm wheel 100 as a whole and smooth meshing are realized. The cored bar 101 may be formed by cutting or may be formed by sintering.

  The tooth portion 110 of the worm wheel 100 has a convex arc shape corresponding to the concave arc shape of the worm shaft tooth portion 210 having a Neiman shape. Thereby, the worm wheel 100 and the worm shaft 200 form a Neiman worm. Moreover, the coating | coated part 102 is formed with the resin material which does not contain reinforcement fibers, such as glass fiber.

  When the worm wheel 100 is coated with a resin material, the worm wheel 100 is elastically deformed at the time of meshing and is thermally expanded to reduce backlash. Moreover, since the tooth thickness of the tooth part 110 becomes large by setting it as a convex circular arc shape, the intensity | strength of the worm wheel 100 increases. Therefore, sufficient strength can be secured without mixing reinforcing fibers into the covering portion 102.

  The cored bar 101 has a toothed core part 101 a that extends in the tooth tip direction from the tooth bottom of the toothed part 110. By extending the tooth core portion 101a formed of a metal material excellent in heat transfer performance to the inside of the tooth portion 110, sufficient strength can be ensured even if the covering portion 102 is a resin material that does not include reinforcing fibers. At the same time, the heat generated around the tooth portion 110 is efficiently radiated.

[Warm curvature radius]
FIG. 9 is an enlarged sectional view in the axial direction of the worm shaft during meshing. The worm shaft 200 is formed by cutting. When the radius of curvature of the cutting range forming the tooth shape of the worm wheel 100 is R and the outer radius of curvature of the tooth portion 210 of the worm shaft 200 is r, The radius of curvature of the meshing region D with the worm shaft 200 is the outer radius of curvature radius r of the worm shaft 200.

  Here, the worm wheel 100 and the worm shaft 200 of the present application have a relationship of R> r. Therefore, it is not necessary to require high machining accuracy for the worm wheel 100 having a large curvature radius. Thereby, even if the worm wheel 100 is formed with low processing accuracy, the meshing performance is satisfied.

  Further, the worm shaft 200 is surface-finished by plastic working. By smoothing the surface of the worm shaft 200 by plastic working, the worm wheel 100 side is not damaged.

  In addition, the worm shaft 200 and the worm wheel 100 do not interfere with each other except the meshing surfaces that mesh with each other in a state where the steering assist is not performed by the motor M. In a state where no assist is applied, a high load is applied to the worm wheel 100, and the steering load on the driver also increases. In this state, the driver's steering load at the time of non-assist is reduced by not interfering with other than the meshing surface.

[Comparison of tooth surface metastases]
10-12 is a figure which shows the tooth surface cross-sectional shape of a worm gear (worm wheel and worm shaft). 10 shows worm gears 100 and 200 formed with the Neiman tooth profile of the present application, FIG. 11 shows worm gears 100 ′ and 200 ′ of a general involute tooth profile of a conventional example, and FIG. 12 shows a design value different from that of the present application as a comparative example. Niemann tooth profile worm gears 100 ", 200" are shown. 10 to 12 have the same scale, and numerical values (units are omitted) correspond to each other.

  The worm wheel 100 of the present application has a Neiman tooth shape, and the tooth surface 111 has a convex shape. In addition, the tooth portion 110 of the worm wheel 100 of the present application has a positive dislocation (about +0.5 on the scale in the figure), and the tooth height C is shorter and the tooth width compared to the conventional example and the comparative example (zero dislocation amount). Is formed large. By using the positive dislocation, the tooth height is shorter and the tooth width is larger than in the conventional example and the comparative example, so that a high-strength worm wheel 100 can be obtained.

[Details of tooth surface shape]
FIG. 13 is a creation view of the tooth portion 110 in the worm wheel 100. FIG. 14 is a diagram showing a change in the meshing surface between the worm wheel 100 and the worm shaft 200. FIG. 15 is a creation view of a general involute tooth worm wheel 100 ′ in a conventional example, and FIG. 16 is a creation view of a Neiman tooth shape worm wheel 100 ″ of a comparative example.

  The curvature of the tooth surface 111 in the worm wheel 100 of the present application is such that the normal line N1 on the tooth surface 111 closer to the tooth tip surface 112 than the pitch circle Rp of the worm wheel 100 is closer to the central axis side of the worm wheel 100 than the tooth root surface 113. It is provided to pass through.

  Since it is mainly on the tooth tip side that deflection occurs due to torque transmission from the worm shaft 200, in the worm wheel 100 of the present application, the normal line N <b> 1 on the tooth tip side with respect to the pitch circle Rp is higher than the tooth base surface 113. The worm wheel 100 is designed so as to pass through the central axis side.

  Thereby, the pressure applied to the tooth tip side of the worm wheel tooth portion 110 acts on the center axis side of the tooth base surface 113 on the meshing surface of the worm wheel 100 and the worm shaft 200 tooth portions 110 and 210. Therefore, the stress applied to the tooth root surface 113 is relieved, and the deflection of the tooth portion 110 is reduced to obtain the high-strength worm wheel 100.

  Similarly, the normal line N2 on the tooth root side with respect to the pitch circle Rp and the normal line N3 on the tooth surface 111 intersecting with the pitch circle Rp are also designed to pass through the center axis side with respect to the tooth root surface 113, thereby further increasing the strength. Plan.

Further, the tooth tip width of the meshing surface 111a of the tooth surface 111 of the worm wheel 100 is A, the tooth root width of the meshing surface 111a is B, the tooth height is C, and the module is m, and is expressed by the following equation (a). The worm wheel 100 of the present application is designed so that the relationship is established.
0.825 ≦ (A / B) × (m / C) (a)
By determining each numerical value in this way, the normal lines N1, N2 and N3 at the intersections of the tooth surface 111 with the tooth tip side, the tooth root side and the pitch circle Rp are all of the worm wheel 100 than the tooth root surface 113. It will pass through the central axis. This makes it possible to design a worm wheel 100 in which the normal lines N1, N2, and N3 reliably pass through the center axis side of the tooth root surface 113.

  In the involute tooth profile of the conventional example, the normal line N1 on the tooth tip side of the tooth surface 111 ′ passes through the outer diameter side of the tooth base surface 113, so that the force applied to the tooth tip side acts on the tooth root surface 113 ′ and the tooth portion 110. The deflection of 'will occur and the strength of the worm wheel 100' decreases.

  On the other hand, as in the comparative example (see FIG. 12 and FIG. 16), a Neiman tooth profile that does not satisfy the above formula (a) ((A / B) × (m / C) = 0.75) is legal. Since one of the lines N1, N2 and N3 (N1 in FIG. 16) passes through the outer diameter side of the tooth root surface 113 ″, the force applied to the tooth tip side of the tooth surface 111 ″ is the tooth root surface 113 ″. The tooth portion 110 ″ is deflected by acting on the worm wheel, and the strength of the worm wheel is lowered.

Therefore, in order to secure the strength and improve the steering feeling, it is not sufficient to simply use the Neiman gear, and a design that satisfies the above equation (a) is required.
In Example 1, the meshing surface tooth width A = 2.8.
Mating surface root width B = 1.2
Tooth length C = 3.55
Module m = 2.13
However, there is no particular limitation as long as the numerical value satisfies the above formula (a).

  Further, in the comparative example, since the dislocation amount is 0, both sides of the tooth base surface 113 ″ are undercut when the tooth surface is created to form an undercut portion 115 ″. A high surface pressure portion 114 '' having a convex shape in the circumferential direction is formed between the uncut portion and the undercut portion 115 '' as a discontinuous curved surface.

  Since this high surface pressure portion 114 '' has a convex shape in the circumferential direction on the tooth surface 111 '' as compared with other portions, when the tooth portion 110 '' meshes with the worm shaft tooth portion 210 '', the teeth Compared with other parts on the surface 111 '', the surface pressure becomes higher, and each time it engages with this high surface pressure part 114 '', the surface pressure during engagement increases, the surface pressure fluctuation increases, and the engagement is unstable. It becomes. On the other hand, in the present application, since the tooth portion 110 is displaced, the undercut is suppressed to be lower than that of the comparative example, the variation in the surface pressure at the time of meshing is reduced, and the meshing is stabilized (see FIGS. 20 and 22).

  Further, the meshing rate between the worm shaft 200 and the worm wheel 100 is set to be larger than 1 and 1.5 or less. If the meshing rate is 2 or more, higher strength can be obtained, but the worm wheel 100 is increased in diameter accordingly. Therefore, by setting the meshing rate to be greater than 1 and 1.5 or less, the necessary and sufficient strength is obtained while avoiding an increase in the diameter of the worm wheel 100.

[Comparison of tooth root stress and tooth deflection fluctuation]
FIGS. 17-19 is a figure which shows the fluctuation | variation of the tooth root stress and tooth root deflection accompanying rotation of a worm gear. FIG. 17 shows a Neiman gear of the present application, FIG. 18 shows an involute gear of a conventional example, and FIG. 19 shows a Neiman gear of a comparative example. The scales in FIGS. 17 to 19 are the same unit. In addition, # 1 and # 2 indicate the nth and n + 1th tooth surfaces (n: natural number), respectively.

  In the comparative example in which the Neiman tooth profile is simply used, the fluctuation of the root stress and the deflection of the tooth root is not significantly different from that of the involute tooth profile of the conventional example. The original stress and the tooth root deflection are generally kept lower than those of the conventional example and the comparative example, and the maximum values are also reduced.

[Comparison of tooth surface pressure fluctuation]
20-22 is a figure which shows the fluctuation | variation of the tooth surface pressure accompanying rotation of a worm gear. 20 shows a Neiman gear of the present application, FIG. 21 shows an involute gear of a conventional example, and FIG. 22 shows a Neiman gear of a comparative example. Similar to the tooth root stress, the scales in FIGS. 20 to 22 are the same unit, and # 1 and # 2 indicate the nth and n + 1th tooth surfaces (n: natural number), respectively.

  Similar to the tooth root stress and the tooth root deflection, the present application is also kept low in the tooth surface pressure variation compared to the conventional example and the comparative example, and the surface pressure variation at the time of meshing is reduced, and the amount of deflection of the tooth portion 110 is reduced. This stabilizes the meshing and ensures a steering feeling.

  Further, in the comparative example, the tooth surface 111 '' becomes a discontinuous curved surface due to the undercut at the time of tooth surface generation, and a high surface pressure portion 114 '' having a convex shape in the circumferential direction is formed. Therefore, the worm shaft tooth portion 210 ' Each time 'engages with the high surface pressure portion 114' ', the surface pressure at the time of engagement increases, and the maximum value of the tooth surface pressure protrudes and becomes larger than in the present application and the conventional example. That is, as shown in the comparative example, simply changing to the Neiman tooth profile may not only suppress the fluctuation of the tooth surface pressure, but may increase the tooth surface pressure. Is important.

[Effect of Example 1]
(1) The worm shaft 200 having a concave arc shape in the cross-sectional shape of the teeth, meshed with the worm shaft 200, and formed between the tooth tip surface 112, the tooth root surface 113, and the tooth tip surface 112 and the tooth root surface 113. The normal line N3 in the tooth surface 111 that is composed of the tooth surface 111 that intersects the pitch circle has the worm wheel 100 that passes through the center side of the tooth root surface 113.

  A region of the tooth surface 111 that intersects the pitch circle Rp is a portion that meshes with the worm shaft 200, and torque from the worm shaft 200 is transmitted to the worm wheel 100 from here. Therefore, by designing the normal line N3 in the region intersecting with the pitch circle Rp so as to pass through the central axis side of the worm wheel 100 with respect to the tooth root surface 113, both the strength and the size of the worm wheel 100 can be reduced. be able to.

  (2) The tooth surface 111 is convex outward from the involute curve, and the value obtained by dividing the product of the width A of the tooth tip surface 112 and the module m by the width B of the tooth base surface 113 and the tooth height C is 0. It was decided that it was 825 or more. Thereby, compared with the comparative example only using the conventional involute gear and the Niemann gear, high rigidity can be obtained.

  (3) an electric motor M that applies a steering assist force to the rack P and pinion P (steering mechanism) linked to the steered wheels FL and FR, a control board 300 (electric motor control means) that drives and controls the electric motor M, A worm shaft 200 provided on the output shaft of the electric motor M and having a concave cross-sectional shape of teeth, a rack P and a pinion P, and meshing with the worm shaft 200, the steering assist force of the electric motor M is obtained. The tooth surface 111 is transmitted to the rack P and the pinion P, and includes a tooth surface 112, a tooth surface 113, and a tooth surface 111 formed between the tooth surface 112 and the tooth surface 113. And a worm wheel 100 that is convex outward from the involute curve.

  When a worm wheel coated with resin is used to smooth the steering feeling of the electric power steering apparatus, the worm wheel is deflected. If this amount of deflection increases, the meshing performance of the worm may be lowered. Therefore, the rigidity of the worm wheel 100 can be improved as described above, and an appropriate meshing performance of the worm gear can be obtained. . Therefore, the steering feeling of the electric power steering device can be improved.

  (4) The normal line N1 on the tooth surface on the tooth tip surface 112 side of the pitch circle Rp of the worm wheel 100 passes through the center side of the tooth base surface 113.

  Since the deflection caused by the torque transmission from the worm shaft 200 mainly occurs on the tooth tip side, the worm so that the normal line N1 on the tooth tip surface 112 side of the pitch circle Rp passes the center side of the tooth base surface 113. By designing the wheel 100, the worm wheel 100 with higher strength can be obtained.

  (5) The normal line N2 on the tooth root surface 113 of the worm wheel 100 passes through the center side of the tooth root surface 113.

  By designing the worm wheel 100 so that the normal line N2 on the tooth root surface 113 side also passes the center side of the tooth root surface 113 in addition to the tooth tip surface 112 side of the pitch circle Rp, the worm wheel 100 having higher strength can be obtained. Can be obtained.

  (6) (13) The meshing rate between the worm shaft 200 and the worm wheel 100 is greater than 1 and 1.5 or less.

  If the meshing rate is 2 or more, higher strength can be obtained, but the worm wheel 100 is increased in diameter accordingly. Therefore, by setting the meshing rate to be greater than 1 and 1.5 or less, it is possible to obtain a necessary and sufficient strength while avoiding an increase in the diameter of the worm wheel 100.

  (7) (14) The worm wheel 100 has a tooth profile shape that is positively displaced. By using the positive dislocation, the tooth height C is shortened and the tooth width is increased, so that a high-strength worm wheel 100 can be obtained.

  (8) (15) The tooth surface of the worm wheel 100 is made of synthetic resin.

  Smooth engagement with the worm shaft 200 can be obtained. Moreover, since moderate deflection of the worm wheel 100 occurs, the meshing rate increases, and as a result, the allowable load of the worm wheel 100 can be increased.

  (9) (16) The worm wheel 100 is provided inside the tooth surface and has a tooth core portion 101a formed of a metal material. The strength and smooth engagement of the worm wheel 100 as a whole can be realized.

  (10) (17) The synthetic resin constituting the tooth surface of the worm wheel 100 does not contain reinforcing fibers. By setting the tooth profile of the worm wheel 100 to the above-described shape, sufficient strength can be ensured even with a resin material that does not include reinforcing fibers.

  (11) (18) (20) The worm wheel 100 is formed by cutting, and the radius of curvature R in this cutting range is larger than the radius of curvature r of the meshing region with the worm shaft 200.

  By making the curvature radius R of the cutting area of the worm wheel 100 larger than the curvature radius r of the engagement area between the worm shaft 200 and the worm wheel 100, a gear satisfying the engagement performance even with low machining accuracy is obtained. Obtainable.

  (12) The worm shaft 200 is subjected to a surface finish by plastic working. By smoothing the surface of the worm shaft 200, the worm wheel 100 side is not damaged.

  (19) The worm shaft 200 and the worm wheel 100 do not interfere with each other except the meshing surfaces that mesh with each other in a state where the steering assist is not performed by the electric motor.

  In a state where the assist of the electric motor is not applied, a high load is applied to the worm wheel 100, and the steering load of the driver also increases. By not interfering with anything other than the meshing surface in this state, the driver's steering load during non-assist can be reduced.

(Other examples)
The best mode for carrying out the present invention has been described based on the embodiments. However, the specific configuration of the present invention is not limited to the embodiments, and the design does not depart from the gist of the invention. Any changes and the like are included in the present invention.

  For example, as shown in FIGS. 23 and 24, other numerical values may be used for A, B, C, and m as long as the above equation (a) is satisfied.

It is a system configuration diagram of an electric power steering device to which the present worm gear is applied. 2 is an axial sectional view of the motor control device 1. FIG. 2 is a radial cross-sectional view of the motor control device 1. FIG. 3 is a front view of the worm shaft 200 in the radial direction. FIG. CC sectional drawing (right-angle direction sectional drawing) in the worm shaft tooth | gear part 210. FIG. It is CC sectional drawing (perpendicular direction sectional drawing) in the worm shaft tooth | gear part 210 'of a prior art example (trapezoid tooth profile). FIG. 2 is a radial partial cross-sectional view of a worm wheel 100. 2 is an axial sectional view of the worm wheel 100. FIG. It is DD sectional drawing of a tooth | gear part. It is a figure which shows the tooth surface cross-sectional shape of the worm shaft 200 and worm wheel 100 of a Neiman tooth profile of this application. It is a figure which shows the tooth surface cross-sectional shape of the worm shaft 200 and the worm wheel 100 of the general involute tooth profile of a prior art example. It is a figure which shows the tooth surface cross-sectional shape of the Niemann tooth profile of a comparative example (design value different from this application). 3 is an enlarged cross-sectional view of a tooth portion 110 in a worm wheel 100. FIG. It is a figure which shows the change of the meshing surface of the worm wheel 100 and the worm shaft 200. FIG. It is an expanded sectional view of the general involute tooth profile in a prior art example. It is an expanded sectional view of a Neiman tooth profile of a comparative example (design value different from this application). It is a figure which shows the fluctuation | variation of the root stress and tooth root deflection accompanying rotation of a worm gear (this Neiman gear). It is a figure which shows the fluctuation | variation of the tooth root stress and tooth root deflection accompanying rotation of a worm gear (involute gear of a prior art example). It is a figure which shows the fluctuation | variation of tooth root stress and tooth root deflection accompanying rotation of a worm gear (Niemann gear of a comparative example). It is a figure which shows the fluctuation | variation of the tooth surface pressure accompanying rotation of a worm gear (this-application Neiman gear). It is a figure which shows the fluctuation | variation of the tooth surface pressure accompanying rotation of a worm gear (involute gear of a prior art example). It is a figure which shows the fluctuation | variation of the tooth surface pressure accompanying rotation of a worm gear (Niemann gear of a comparative example). It is a figure which shows another Example. It is a figure which shows another Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor control apparatus 3 Torsion bar 5 Torque sensor housing 6 Motor housing 7 Worm housing 100 Worm wheel 101 Core metal 101a Tooth core part 102 Cover part 110 Tooth part 111 Tooth surface 111a Engagement surface 112 Tooth tip surface 113 Tooth base surface 114 High Surface pressure part 115 Undercut part 200 Worm shaft 210 Worm shaft tooth part 300 Control board A Engagement surface tooth width B Engagement surface tooth width C Tooth length FL, FR Steering wheel IN Input shaft M Motor m Modules N1, N2 , N3 Normal P Pinion R Rack Rp Pitch circle

Claims (17)

A worm shaft in which the cross-sectional shape of the tooth has a concave arc shape;
The tooth surface is engaged with the worm shaft, the tooth tip surface, the tooth root surface, and the tooth surface formed between the tooth tip surface and the tooth root surface, and the normal line on the tooth surface intersecting the pitch circle is the tooth surface. And a worm wheel passing through the center side of the base surface. A worm shaft in which the cross-sectional shape of the tooth has a concave arc shape;
The worm shaft is meshed with a tooth tip surface, a tooth root surface, and a tooth surface formed between the tooth tip surface and the tooth root surface, and the tooth surface is convex outward from the involute curve. A value obtained by dividing the product of the width of the tooth tip surface and the module by the width of the tooth base surface and the tooth height is 0.825 or more. The worm gear according to claim 1,
The worm gear , wherein a normal line on the tooth surface on the tooth tip surface side of the worm wheel passes through the center side of the tooth root surface . The worm gear according to claim 1,
Worm gear the normal prior Kihamen of the worm wheel, characterized in that through the center side of the flank. The worm gear according to claim 1,
A mesh ratio between the worm shaft and the worm wheel is greater than 1 and 1.5 or less . The worm gear according to claim 1,
The worm wheel has a tooth profile shape that is positively displaced . The worm gear according to claim 1,
The worm gear has a tooth surface formed of a synthetic resin . The worm gear according to claim 7 ,
The worm wheel is provided inside the tooth surface and has a tooth core portion made of a metal material . The worm gear according to claim 7 ,
A synthetic resin that constitutes the tooth surface of the worm wheel does not contain reinforcing fibers . The worm gear according to claim 1 ,
The worm wheel is formed by cutting, and a radius of curvature in a range of the cutting is larger than a radius of curvature of a meshing region with the worm shaft . The worm gear according to claim 1,
The worm gear is characterized in that a surface finish is applied by plastic working . The worm gear according to claim 2 ,
A mesh ratio between the worm shaft and the worm wheel is greater than 1 and 1.5 or less . The worm gear according to claim 2,
The worm wheel has a tooth profile shape that is positively displaced . The worm gear according to claim 2,
The worm gear has a tooth surface formed of a synthetic resin . The worm gear according to claim 14 ,
The worm wheel is provided inside the tooth surface and has a tooth core portion made of a metal material . The worm gear according to claim 14 ,
A synthetic resin that constitutes the tooth surface of the worm wheel does not contain reinforcing fibers . The worm gear according to claim 2 ,
The worm wheel is formed by cutting, and a radius of curvature in a range of the cutting is larger than a radius of curvature of a meshing region with the worm shaft .

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