JP5790976B2 - Worm reducer and electric power steering device - Google Patents

Description

  The present invention relates to a worm reducer and an electric power steering device.

In Patent Literature 1, in a power steering gear mechanism, when a steel worm and a plastic worm wheel mesh with each other, a technique for producing an effective contour of a tooth surface so that a line contact portion is generated in the tooth height direction. Has been proposed (see, for example, Patent Document 1).
On the other hand, with the recent increase in output of electric power steering devices, the worm speed reducer used as a speed reduction mechanism has increased in size, and the layout on the vehicle has become very strict. In particular, when resin is used as the gear portion of the worm wheel, the worm wheel tends to be large in order to satisfy the strength. In addition, a resin that can withstand high strength is expensive, and the manufacturing cost increases.

JP 2004-161268 A

Therefore, it is conceivable to use a metal gear. However, when the load on the worm reducer increases and the worm position shifts with respect to the worm wheel, the tooth surface of the worm hits the edge of the tooth surface of the worm wheel, resulting in increased operating noise. To do.
Also, when the load on the worm reducer increases and the worm position shifts with respect to the worm wheel, the portion of the worm wheel tooth surface where the worm teeth enter the tooth groove of the worm wheel (tooth groove) ), The tooth contact tends to be strong. As a result, the lubrication effect due to the so-called wedge effect is reduced between the tooth surfaces, and the lubrication state is deteriorated. When the lubrication state is deteriorated, the temperature is increased, and the lubrication state is further deteriorated. Therefore, wear increases with long-term use, and durability decreases. Further, since the backlash increases due to the increase in wear, the rattling noise increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a worm reduction gear and an electric power steering device that have low operating noise and rattling noise and are excellent in durability.

  In order to achieve the object, the invention of claim 1 comprises a worm (30) and a worm wheel (40) having a tooth groove (50) meshing with the worm, and the tooth surface (41, 42) of the worm wheel. Includes a first shape portion (61, 71), a second shape portion (62, 72) surrounding the first shape portion, and a third shape portion surrounding the first shape portion and surrounded by the second shape portion ( 63, 73), and the first shape portion is configured to include an envelope surface of a movable range in which the tooth surface of the worm is movable due to a positional shift of the worm with respect to the worm wheel at a normal load. The second shape portion includes an envelope surface (L1) of a movable range in which the tooth surface of the worm is movable due to a displacement of the worm with respect to the worm wheel in an overload exceeding a maximum load during use. The second The shape portion includes an envelope surface of a movable range in which the tooth surface of the worm is movable due to a displacement of the worm relative to the worm wheel when the load is between the maximum value of the normal load and the minimum value of the overload. The speed reducer (20) comprised by this is provided.

In addition, although the alphanumeric character in a parenthesis represents the corresponding component etc. in embodiment mentioned later, this does not mean that this invention should be limited to those embodiment as a matter of course. The same applies hereinafter.
According to a second aspect of the present invention, the third shape portion may include a shape that smoothly connects the first shape portion and the second shape portion.

Further, as in a third aspect, the third shape portion may be an R shape portion.
According to a fourth aspect of the present invention, the positional deviation of the worm includes a first positional deviation in which the worm is offset in a direction (X1) parallel to the central axis (C2) of the worm wheel, and the worm wheel. A second position where the worm is offset in a direction (Y1) to increase or decrease the distance (D1) between the central axis (C1) of the worm and the central axis of the worm wheel within a plane (P2) orthogonal to the central axis. A misalignment, a third misalignment in which the central axis of the worm is inclined in a plane (P1) including the central axis of the worm and parallel to the central axis of the worm wheel, and including the central axis of the worm and the Including at least one of a fourth misalignment in which the central axis of the worm is inclined in a plane orthogonal to the central axis of the worm wheel. Good.

  Further, the invention according to claim 5 is an electric motor (19) for assisting steering, and the worm speed reducer (20) according to any one of claims 1 to 4, wherein the rotation of the electric motor is decelerated. An electric power steering device (1) is provided.

  According to the first aspect of the present invention, when the load is normal (that is, relatively low load), the first shape portion comes into contact with the tooth surface of the worm in a good tooth contact state. When near the maximum load during use, in addition to the first shape portion, the third shape portion is in contact with the tooth surface of the worm, and is mainly in surface contact with the third shape portion in a high load state (for example, the maximum during use) Load). That is, since the edge contact between the tooth surfaces can be suppressed, the operation sound can be reduced.

  In addition, a gap is formed between, for example, a pair of end portions in the tooth width direction of the second shape portion that does not come into contact with each other even in the vicinity of the maximum load and the tooth surface of the worm. That is, even if the worm becomes larger in the movable range of the worm, the lubricating oil easily enters between the tooth surfaces through the gap (particularly, a gap provided on the inlet side where the worm teeth enter the tooth groove of the worm wheel). Therefore, the wedge effect of the lubricating oil can be secured and the lubrication state between the tooth surfaces can be maintained well, so that wear can be suppressed. As a result, the increase in backlash can be suppressed over a long period of time, and the generation of rattling noise can be reduced over a long period of time.

According to the invention of claim 2, since the third shape portion smoothly connects the first shape portion and the second shape portion, even if the movable range of the worm increases, the edge between the tooth surfaces It is possible to suppress the occurrence of a hit and to suppress an increase in operating noise.
According to the invention of claim 3, since the first shape portion and the second shape portion are more smoothly connected by the R shape portion as the third shape portion, occurrence per edge is surely suppressed. Thus, an increase in operating noise can be reliably suppressed.

According to the invention of claim 4, considering the movable range in which the tooth surface of the worm moves due to various misalignment of the worm with respect to the worm wheel, including the envelope surface of the movable range, the shape portion of the worm wheel Therefore, the lubrication state between the tooth surfaces can be reliably improved in actual use.
According to the fifth aspect of the present invention, it is possible to realize an electric power steering apparatus that is small in operating noise and rattling noise and excellent in durability.

1 is a partial cross-sectional view illustrating a schematic configuration of an electric power steering apparatus including a worm reduction gear according to an embodiment of the present invention. It is a schematic perspective view of a worm gear mechanism. It is a perspective view of the principal part of a worm wheel, for example, shows one tooth surface (here, it is called a left tooth surface). It is a perspective view of the principal part of a worm wheel, for example, has shown the other tooth surface (it is called right tooth surface here). It is a schematic perspective view which shows the envelope surface of the movable range which the worm tooth surface moves due to the position shift of the worm with respect to the worm wheel at the time of overload. It is a schematic sectional drawing of the principal part of one tooth surface of a worm wheel. It is a schematic sectional drawing of the principal part of the other tooth surface of a worm wheel. It is the schematic of a worm speed reducer, and shows the 1st position shift by which a worm is offset in the direction parallel to the central axis of a worm wheel. It is the schematic of a worm reduction gear, and shows the 2nd position shift by which a worm is offset in the direction which increases the distance between the central axis of a worm and the central axis of a worm wheel in the plane orthogonal to the central axis of a worm wheel. ing. FIG. 3 is a schematic view of a worm reduction gear, and shows a third misalignment in which the central axis of the worm is inclined in a plane including the central axis of the worm and parallel to the central axis of the worm wheel. It is the schematic which shows the 4th position shift in which the central axis of a worm inclines in the plane containing the central axis of a worm and orthogonal to the central axis of a worm wheel. It is a perspective view of the principal part of a worm wheel, and shows the contact area and non-contact area of the left tooth surface, for example, at the time of regular load. It is a perspective view of the principal part of a worm wheel, and shows the contact area and non-contact area of the left tooth surface, for example, at the time of high load near the maximum load at the time of use.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic view of an electric power steering apparatus including a worm wheel according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering member 2 including a steering wheel, a steering mechanism 4 that steers a steered wheel 3 in conjunction with the rotation of the steering member 2, and a driver's steering. And a steering assist mechanism 5 for assisting. The steering member 2 and the steering mechanism 4 are mechanically connected via a steering shaft 6 and an intermediate shaft 7.

In the present embodiment, a description will be given according to an example in which the steering assist mechanism 5 applies assist force (steering assist force) to the steering shaft 6. However, the present invention can also be applied to a structure in which the steering assist mechanism 5 applies assist force to the pinion shaft described later.
The steering shaft 6 includes an input shaft 8 connected to the steering member 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable on the same axis.

  A torque sensor 11 disposed around the steering shaft 6 detects the steering torque input to the steering member 2 based on the relative rotational displacement amounts of the input shaft 8 and the output shaft 9. The torque detection result of the torque sensor 11 is input to an ECU (Electronic Control Unit) 12 as a control device. The vehicle speed detection result from the vehicle speed sensor 13 is input to the ECU 12. The intermediate shaft 7 connects the steering shaft 6 and the steering mechanism 4.

The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 14 and a rack shaft 15 as a steered shaft. A steered wheel 3 is connected to each end of the rack shaft 15 via a tie rod 16 and a knuckle arm (not shown).
The pinion shaft 14 is connected to the intermediate shaft 7. The pinion shaft 14 rotates in conjunction with the steering of the steering member 2. A pinion 17 is provided at the tip (the lower end in FIG. 1) of the pinion shaft 14.

  The rack shaft 15 extends linearly along the left-right direction of the automobile. A rack 18 that meshes with the pinion 17 is formed in the middle of the rack shaft 15 in the axial direction. By the pinion 17 and the rack 18, the rotation of the pinion shaft 14 is converted into the axial movement of the rack shaft 15. The steered wheels 3 can be steered by moving the rack shaft 15 in the axial direction.

When the steering member 2 is steered (rotated), this rotation is transmitted to the pinion shaft 14 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 14 is converted into the axial movement of the rack shaft 15 by the pinion 17 and the rack 18. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 19 for assisting steering and a worm speed reducer 20 as a transmission mechanism for transmitting the output torque of the electric motor 19 to the steering mechanism 4. The worm speed reducer 20 includes a worm 30 as a drive gear and a worm wheel 40 as a driven gear that meshes with the worm 30. The worm speed reducer 20 is accommodated in the gear housing 21. In the gear housing 21, at least a meshing region between the worm 30 and the worm wheel 40 is filled with a lubricant (not shown) such as grease containing a lubricating oil component, and the tooth surfaces of the worm 30 and the worm wheel 40. A lubricant is interposed between them.

The worm 30 is connected to a rotating shaft (not shown) of the electric motor 19 through a joint (not shown). The worm 30 is rotationally driven by the electric motor 19. The worm wheel 40 is coupled to the steering shaft 6 so as to be integrally rotatable.
When the electric motor 19 rotationally drives the worm 30, the worm wheel 40 is rotationally driven by the worm 30, and the worm wheel 40 and the steering shaft 6 rotate integrally. Then, the rotation of the steering shaft 6 is transmitted to the pinion shaft 14 via the intermediate shaft 7. The rotation of the pinion shaft 14 is converted into the axial movement of the rack shaft 15. Thereby, the steered wheel 3 is steered. In other words, the steered wheels 3 are steered by rotating the worm 30 by the electric motor 19.

  The electric motor 19 is a three-phase brushless motor, and is controlled by the ECU 12 as a control device. The ECU 12 controls the electric motor 19 based on the torque detection result from the torque sensor 11, the vehicle speed detection result from the vehicle speed sensor 13, and the like. Specifically, the ECU 12 determines a target assist amount using a map in which the relationship between the torque and the target assist amount is stored for each vehicle speed, and controls the assist force generated by the electric motor 19 to approach the target assist amount. To do.

As shown in FIG. 2, the worm 30 of the worm speed reducer 20 has a pair of tooth surfaces 31 and 32 opposed in the axial direction, and the tooth surfaces 31 and 32 are continuous in a spiral shape.
On the outer periphery of the worm wheel 40, a plurality of tooth grooves 50 are formed at equal intervals in the circumferential direction. The worm wheel 40 has a pair of tooth surfaces 41 and 42 that are opposed to each other in each tooth gap 50 and mesh with the pair of tooth surfaces 31 and 32 of the worm 30, respectively.

As shown in FIG. 3A, the tooth surface 41 (for example, the left tooth surface) of the worm wheel 40 surrounds the first shape portion 61, the second shape portion 62 surrounding the first shape portion 61, and the first shape portion 61. And a third shape portion 63 surrounded by the second shape portion 62.
The second shape portion 62 has an envelope surface L1 in a movable range in which the tooth surface 31 of the worm 30 is movable due to the positional deviation of the worm 30 with respect to the worm wheel 40 in the case of an overload exceeding the maximum load during use (FIG. 4). Reference). The envelope surface L1 is an assembly of envelopes in the movable range. The maximum load during use occurs, for example, when stationary. A load exceeding the maximum load during use (overload) is a load that cannot occur during normal use. However, there is a risk of overload in the event of an emergency such as when the steered wheel rides on a curb.

The first shape portion 61 is configured to include an envelope surface (not shown) of a movable range in which the tooth surface 31 of the worm 30 is movable due to the displacement of the worm 30 with respect to the worm wheel 40 during a normal load. Yes.
The third shape portion 63 moves the tooth surface 31 of the worm 30 due to the displacement of the worm 30 with respect to the worm wheel 40 when the load is higher than the minimum value of the overload and exceeds the maximum value of the normal load. The movable surface is configured to include an envelope surface (not shown). As shown in FIG. 5A, the third shape portion 63 may have any shape that smoothly connects between the end portion 61a of the first shape portion 61 and the end portion 62a of the second shape portion 62, for example, an R shape. Formed in an R-shaped part having

As shown in FIG. 3B, the tooth surface 42 (for example, the right tooth surface) of the worm wheel 40 surrounds the first shape portion 71, the second shape portion 72 surrounding the first shape portion 71, and the first shape portion 71. And a third shape portion 73 surrounded by the second shape portion 72.
The second shape portion 72 has an envelope surface L1 in a movable range in which the tooth surface 32 of the worm 30 is movable due to the displacement of the worm 30 with respect to the worm wheel 40 in the case of an overload exceeding the maximum load during use (FIG. 4). Reference). The maximum load during use occurs, for example, when stationary. A load exceeding the maximum load during use (overload) is a load that cannot occur during normal use. However, there is a risk of overload in the event of an emergency such as when the steered wheel rides on a curb.

The first shape portion 71 is configured to include an envelope surface (not shown) of a movable range in which the tooth surface 32 of the worm 30 is movable due to a positional shift of the worm 30 with respect to the worm wheel 40 during a normal load. Yes.
The third shape portion 73 allows the tooth surface 32 of the worm 30 to move due to the displacement of the worm 30 with respect to the worm wheel 40 when the load is less than the minimum value of the overload and exceeds the maximum value of the normal load. The movable surface is configured to include an envelope surface (not shown). As shown in FIG. 5B, the third shape portion 73 only needs to have a shape that smoothly connects the end portion 71a of the first shape portion 71 and the end portion 72a of the second shape portion 72, for example, an R shape. Formed in an R-shaped part having

When the worm 30 is configured as a right-handed spiral, the meshing load of the tooth surface 42 that is the right tooth surface of the worm wheel 40 is larger than the meshing load of the tooth surface 41 that is the left tooth surface, for example. For example, the area of the first shape portion 71 of the tooth surface 42 that is the right tooth surface may be larger than the area of the first shape portion 61 of the tooth surface 41 that is the left tooth surface.
The portion 64 surrounding the second shape portion 62 of the tooth surface 41 and the portion 74 surrounding the second shape portion 72 of the tooth surface 42 may be formed so as not to contact the worm 30, and the shape is not particularly limited. For example, it is suitable when the tooth gap 50 is formed by forging.

The positional deviation of the worm 30 in the case of an overload exceeding the maximum load during use described above includes the first positional deviation shown in FIG. 6, the second positional deviation shown in FIG. 7, and the third position shown in FIG. The deviation and the fourth positional deviation shown in FIG. 9 are included.
The first positional deviation shown in FIG. 6 is a positional deviation in which the worm 30 is offset in a direction X1 parallel to the central axis C2 of the worm wheel 40. More specifically, the first displacement is the center axis of the worm 30 in a plane P1 (corresponding to the paper surface in FIG. 6) including the center axis C1 of the worm 30 and parallel to the center axis C2 of the worm wheel 40. C1 is a positional offset offset in the direction X1 parallel to the central axis C2 of the worm wheel 40.

  The second misalignment shown in FIG. 7 is a position where the worm 30 is offset in the direction Y1 in which the distance D1 between the centers of the worm 30 and the worm wheel 40 is increased or decreased in the plane P2 orthogonal to the central axis C2 of the worm wheel 40. It is a gap. More specifically, the second misalignment is the center axis of the worm 30 in a plane P2 (corresponding to the paper surface in FIG. 7) including the center axis X1 of the worm 30 and orthogonal to the center axis C2 of the worm wheel 40. This is a displacement in which the center axis C1 of the worm 30 is offset in the direction Y1 in which the center distance D1 that is the distance between C1 and the center axis C2 of the worm wheel 40 is increased or decreased.

The third misalignment shown in FIG. 8 is that the central axis C1 of the worm 30 is inclined in a plane P1 (corresponding to the paper surface in FIG. 8) that includes the central axis C1 of the worm 30 and is parallel to the central axis C2 of the worm wheel 40. Misalignment.
The fourth misalignment shown in FIG. 9 is that the central axis C1 of the worm 30 is within a plane P2 (corresponding to the paper surface in FIG. 9) that includes the central axis C1 of the worm 30 and is orthogonal to the central axis C2 of the worm wheel 40. This is a tilted displacement.

According to the present embodiment, for example, assuming that the worm 30 rotates clockwise, when the load is normal (that is, relatively low load), the first shape portion of the tooth surface 41 of the worm wheel 40 is shown in FIG. 10A. 61 contacts the tooth surface 31 of the worm 30 in a state of good tooth contact.
When the load is near the maximum load during use, as shown in FIG. 10B, in addition to the first shape portion 61, the third shape portion 63 is in surface contact with the tooth surface 31 of the worm 30, High load (for example, maximum load during use) can be received mainly in the surface contact state by the third shape portion 63. In other words, since the edge contact between the tooth surfaces 31 and 41 can be suppressed, the operating sound can be reduced.

  Further, even when the load is close to the maximum load during use, for example, a pair of end portions 621 and 622 of the second shape portion 62 in the tooth width direction W1 and the teeth of the worm 30 that do not contact in actual use. A gap is formed between the surface 31. That is, even if the worm 30 is moved within the movable range, the lubricating oil is provided between the tooth surfaces 31 and 41 through the gap (particularly, the gap provided on the inlet side where the teeth of the worm 30 enter the tooth groove 50 of the worm wheel 40). Becomes easy to invade. Therefore, the wedge effect of the lubricating oil can be secured and the lubrication state between the tooth surfaces 31 and 41 can be maintained well, so that wear can be suppressed. As a result, the increase in backlash can be suppressed over a long period of time, and the generation of rattling noise can be reduced over a long period of time.

Thus, it is possible to realize the worm speed reducer 20 with low operating noise and excellent durability, and consequently, the electric power steering apparatus 1 with low operating noise and excellent durability.
Further, since the third shape portion 63 smoothly connects the first shape portion 61 and the second shape portion 62, even if the movable range of the worm 30 is increased, the teeth of the worm 30 are not affected by the worm wheel 40. It is possible to suppress an increase in operating noise by suppressing edge contact with the tooth surface. In particular, since the first shape portion 61 and the second shape portion 62 are more smoothly connected by the R shape portion as the third shape portion 63, the occurrence per edge is reliably suppressed, An increase in operating noise can be reliably suppressed. Further, the R-shaped portion is easy to process and is advantageous in manufacturing.

Further, considering the movable range in which the tooth surface 31 of the worm 30 is movable due to various positional shifts of the worm 30 with respect to the worm wheel 40, each shape portion of the worm wheel 40 is included including the envelope surface of the movable range. Since it comprises, in actual use, the lubrication state between the tooth surfaces 31 and 41 can be improved reliably.
Although not shown, for example, when the worm 30 rotates clockwise, the relationship between the respective shape portions 71 to 73 of the tooth surface 42 of the worm wheel 40 and the tooth surface 32 of the worm 30 is shown in FIGS. 10A and 10B. The relationship between the shape portions 61 to 63 of the tooth surface 41 of the worm wheel 40 and the tooth surface 31 of the worm 30 shown in FIG.

In the event of an emergency in which the steered wheel 3 rides on a curb or the like and the worm gear mechanism 20 receives excessive reverse input, an overload occurs and the second shapes of the tooth surfaces 41 and 42 of the worm wheel 40 are generated. Even if the teeth of the worm 30 come into contact with the portions 62 and 72, such a situation is a moment and does not affect durability such as wear.
The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the position shift of the worm 30 in the case of an overload exceeding the maximum load during use includes the first position shift illustrated in FIG. 6, the second position shift illustrated in FIG. The third positional deviation and the fourth positional deviation shown in FIG. 9 are all included, but the present invention is not limited to this. That is, the position shift of the worm 30 at the time of overload exceeding the maximum load during use includes the first position shift shown in FIG. 6, the second position shift shown in FIG. 7, and the third position shown in FIG. It is sufficient that at least one of the shift and the fourth positional shift shown in FIG. 9 is included. In addition, the present invention can be variously modified within the scope of the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 5 ... Steering assist mechanism, 19 ... Electric motor, 20 ... Worm speed reducer, 30 ... Worm, 31, 32 ... Tooth surface, 40 ... Worm wheel, 41, 42 ... Tooth surface, 50 ... Tooth Groove, 61 ... first shape portion, 62 ... second shape portion, 63 ... third shape portion, 71 ... first shape portion, 72 ... second shape portion, 73 ... third shape portion, C1 (of worm) Center axis, C2 ... center axis of (worm wheel), D1 ... center distance (distance between worm center axis and worm wheel center axis), L1 ... envelope surface, P1 ... worm center axis and worm wheel A plane parallel to the central axis of the worm wheel, P2 ... a plane including the central axis of the worm and perpendicular to the central axis of the worm wheel, W1 ... tooth width direction, X1 ... a direction parallel to the central axis of the worm wheel, Y1 ... center Direction to increase or decrease the distance (the direction to increase or decrease the distance of the worm of the central axis and the central axis of the worm wheel)

Claims (5)

A worm and a worm wheel having a tooth groove meshing with the worm,
The tooth surface of the worm wheel includes a first shape portion, a second shape portion surrounding the first shape portion, and a third shape portion surrounding the first shape portion and surrounded by the second shape portion,
The first shape portion is configured to include an envelope surface of a movable range in which the tooth surface of the worm is movable due to a position shift of the worm with respect to the worm wheel at a normal load,
The second shape part is configured to include an envelope surface of a movable range in which the tooth surface of the worm is movable due to a displacement of the worm with respect to the worm wheel when an overload exceeds a maximum load during use.
The third shape portion has a movable range in which the tooth surface of the worm is movable due to a displacement of the worm with respect to the worm wheel at a high load that is less than the minimum value of the overload and exceeds the maximum value of the normal load. Worm speed reducer configured to include the envelope surface.   The worm reducer according to claim 1, wherein the third shape portion includes a shape that smoothly connects the first shape portion and the second shape portion.   The worm reducer according to claim 2, wherein the third shape portion is an R shape portion.   4. The positional deviation of the worm according to claim 1, wherein the positional deviation of the worm includes a first positional deviation in which the worm is offset in a direction parallel to a central axis of the worm wheel, and a central axis of the worm wheel. A second misalignment in which the worm is offset in a direction to increase or decrease the distance between the central axis of the worm and the central axis of the worm wheel within an orthogonal plane; and the central axis of the worm, A third misalignment in which the central axis of the worm is inclined in a plane parallel to the central axis, and the central axis of the worm is in a plane including the central axis of the worm and perpendicular to the central axis of the worm wheel. A worm speed reducer including at least one of a tilted fourth misalignment.   An electric power steering apparatus comprising: an electric motor for assisting steering; and the worm reducer according to any one of claims 1 to 4 that decelerates rotation of the electric motor.

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