JP5822090B2 - Worm reducer - Google Patents

Description

  The present invention relates to a worm reducer.

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. Usually, the contact area of the worm with respect to the worm wheel is set at the center position in the tooth width direction of the worm wheel on the tooth surface of the worm wheel.
In this case, when the load of the worm reducer increases, the worm causes various positional shifts with respect to the worm wheel. Therefore, on the tooth surface of the worm wheel, the portion on the side where the worm teeth enter the tooth groove of the worm wheel (tooth The tooth contact tends to be strong at the entrance of the groove. 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.

In addition, when mass production of worm speed reducers, there is an individual that causes strong tooth contact at the entrance portion of the tooth space of the worm wheel due to the influence of variations in component accuracy.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a worm speed reducer that can always ensure the wedge effect of lubricating oil even when a load is applied.

To achieve the object, the invention of claim 1 comprises a worm (30) and a worm wheel (40) having a tooth space (50) meshing with the worm, and the tooth surface (41, 41) of the worm wheel. 42) includes an envelope (L1) 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 equal to or greater than the maximum load during use. The first shape portion (61, 71) includes a first shape portion of the tooth surface of the worm wheel when the load is less than the maximum load during use. 621, 622; 721, 722), non-contact areas (A1, A2; B1, B2) with respect to the tooth surface of the worm are formed, and when the load is equal to or greater than the maximum load during use, the war Providing worm reducer (20) in which the entire surface of the first shape of the tooth surface of the wheel and the worm tooth surfaces are in contact.

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 .

Also, as in claim 2, positional displacement of the worm, the a first deviation which the direction (X1) parallel to the center axis of the worm wheel (C2) the worm is offset, the worm wheel The worm is offset in a direction (Y1) in which the distance (D1) between the central axis (C1) of the worm and the central axis of the worm wheel is increased or decreased within a plane (P2) orthogonal to the central axis of the second worm. 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 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.
According to a third aspect of the present invention, the tooth surface of the worm wheel is a portion of the tooth surface excluding the first shape portion, and is adjacent to at least the groove bottom side of the first shape portion, and is in contact with the worm. The 2nd shape part (62, 72) which avoided the contact may be included.

  According to the invention of claim 1, when the worm is displaced due to a high load within a range of a normal load (a load less than the maximum load in use), for example, the central portion of the first tooth surface shape portion is While the worm tooth surface is contacted only in the region including the gap, a gap is formed between the pair of end portions in the tooth width direction of the first tooth surface shape portion and the tooth surface of the worm. Lubricating oil easily enters between the tooth faces through this gap (especially the gap provided on the entrance side where the worm teeth enter the tooth space of the worm wheel), so that the wedge effect of the lubricating oil is always secured and the tooth face The lubrication state between them can always be kept good.

Further, when the normal load (maximum load less than load during use), and a pair of end portions and the worm tooth flank in the tooth width direction of the first shape portion a gap is provided between the two without contacting. Lubricating oil easily enters between the tooth faces through this gap (especially the gap provided on the entrance side where the worm teeth enter the tooth space of the worm wheel), so that the wedge effect of the lubricating oil is always secured and the tooth face The lubrication state between them can always be kept good.

Additionally, event, for example, as the maximum load equal to or better of load during use state is instantaneously occur, that the entire surface of said worm tooth face of the first shape portion are in contact, the local Durability can be improved by suppressing typical tooth contact.
According to the invention of claim 2 , considering the movable range in which the tooth surface of the worm moves due to various displacements of the worm with respect to the worm wheel, including the envelope of the movable range, the shape of the worm wheel tooth surface Since the portion is configured, the lubricating state between the tooth surfaces can be reliably improved in actual use.

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 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 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, in the case of a high load within a normal range. It is a perspective view of the principal part of a worm wheel, and shows the contact area and non-contact area of the right tooth surface, for example, in the case of a high load within a normal range.

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 is the first shape portion 61 and the second portion that is the remaining portion of the tooth surface 41 (the portion excluding the first shape portion 61). And a shape portion 62. The first shape portion 61 has an envelope L1 of a movable range in which the tooth surface 31 of the worm 30 can move due to the displacement of the worm 30 with respect to the worm wheel 40 when the load is equal to or greater than the maximum load during use. (Refer to FIG. 4). A load exceeding the maximum load during use (overload) is a load that cannot occur during actual use. The second shape portion 62 is adjacent to at least the groove bottom 51 side of the first shape portion 61 and avoids contact with the tooth surface 31 of the worm 30.

  As shown in FIG. 3B, the tooth surface 42 (for example, the right tooth surface) of the worm wheel 40 is a first shape portion 71 and a second portion (a portion excluding the first shape portion 71) of the tooth surface 42. And a shape portion 72. The first shape portion 71 is an envelope L1 of a movable range in which the tooth surface 32 of the worm 30 can move due to the positional shift of the worm 30 with respect to the worm wheel 40 when the load is equal to or greater than the maximum load during use. (Refer to FIG. 4). A load exceeding the maximum load during use (overload) is a load that cannot occur during actual use. The second shape portion 72 is adjacent to at least the groove bottom 51 side of the first shape portion 71 and avoids contact with the tooth surface 32 of the worm 30.

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 is larger than the area of the first shape portion 61 of the tooth surface 41 that is the left tooth surface.
The second shape portion 62 of the tooth surface 41 and the second shape portion 72 of the tooth surface 42 may be formed so as not to come into contact with the worm 30, and the shape is not particularly limited. For example, the tooth groove 50 is formed by forging. Suitable for you.

The positional deviation of the worm 30 when the load is equal to or greater than or equal to the maximum load during use described above includes the first positional deviation shown in FIG. 5, the second positional deviation shown in FIG. 6, and the first positional deviation shown in FIG. 3 misalignment and the fourth misalignment shown in FIG. 8 are included.
The first positional deviation shown in FIG. 5 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 misalignment is the center axis of the worm 30 in a plane P1 (corresponding to the paper surface in FIG. 5) 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 positional shift shown in FIG. 6 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. 6) including the center axis X1 of the worm 30 and perpendicular 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. 7 is that the central axis C1 of the worm 30 is inclined in a plane P1 (corresponding to the paper surface in FIG. 7) 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. 8 is that the central axis C1 of the worm 30 is within a plane P2 (corresponding to the paper surface in FIG. 8) 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, the tooth surfaces 41 and 42 of the worm wheel 40 are displaced by the position of the worm 30 with respect to the worm wheel 40 when the load is equal to or greater than the maximum load during use. 1st shape parts 61 and 71 comprised including the envelope L1 of the movable range which the tooth surfaces 31 and 32 move are included.
Therefore, when the worm 30 is displaced with respect to the worm wheel 40 in a normal load state (a load less than the maximum load during use) (corresponding to an actual use state), as shown in FIG. The tooth surface 41 (for example, the left tooth surface) contacts the tooth surface 31 of the worm 30 only in the region A0 including, for example, the central portion of the first tooth surface shape portion 61. The area of the region A0 increases as the load increases within the range of the normal load (the load less than the maximum load during use). On the other hand, non-contact areas A1 and A2 that do not contact the tooth surface 31 of the worm 30 are formed on the pair of end portions 611 and 612 of the first tooth surface shape portion 61 in the tooth width direction W1, for example.

  Accordingly, a gap (not shown) is formed between the non-contact areas A1, A2 of the pair of end portions 611, 612 in the tooth width direction W1 of the tooth surface 41 of the worm wheel 40 and the tooth surface 31 of the worm 30. Is done. Through this gap (particularly, the gap between the non-contact region provided on the entrance side where the teeth of the worm 30 enter the tooth groove 50 of the worm wheel 40 and the tooth surface 31 of the worm 30), the lubrication is performed between the tooth surfaces 41, 31. Since the oil easily enters, the wedge effect of the lubricating oil can always be ensured, and the lubrication state between the tooth surfaces 41 and 31 can always be maintained satisfactorily.

  Further, when the worm 30 is displaced with respect to the worm wheel 40 in a normal load (load less than the maximum load during use) (corresponding to an actual use state), as shown in FIG. The tooth surface 42 (for example, the right tooth surface) contacts the tooth surface 32 of the worm 30 only in the region B0 including, for example, the central portion of the first tooth surface shape portion 71. As the load increases within the normal load range, the area of the region B0 increases. On the other hand, non-contact areas B1 and B2 that do not contact the tooth surface 32 of the worm 30 are formed at the pair of end portions 711 and 712 of the first tooth surface shape portion 71 in the tooth width direction W1, for example.

  Thereby, a gap (not shown) is formed between the non-contact areas B1, B2 of the pair of end portions 711, 712 of the tooth surface 42 of the worm wheel 40 in the tooth width direction W1 and the tooth surface 32 of the worm 30. Is done. Through this gap (particularly, the gap between the non-contact area provided on the entrance side where the teeth of the worm 30 enter the tooth groove 50 of the worm wheel 40 and the tooth surface 32 of the worm 30), the lubricating oil is provided between the tooth surfaces 42, 32. Therefore, the wedge effect of the lubricating oil can be ensured at all times, and the lubrication state between the tooth surfaces 42 and 32 can always be maintained satisfactorily.

Furthermore, even if, for example, a state of load equal to or greater than the maximum load during use occurs instantaneously, the entire surface of each first tooth surface shape portion 61, 71 and the corresponding tooth surface 31 of the worm 30 are used. , 32 are in contact with each other, so that local tooth contact can be suppressed and durability can be improved.
Further, the movable range in which the tooth surfaces 31 and 32 of the worm 30 are movable due to various displacements of the worm 30 with respect to the worm wheel 40 (first to fourth displacements shown in FIGS. 5 to 8) is taken into consideration. Since the first tooth surface shape portions 61 and 72 of the worm wheel 40 are configured including the envelope L1 of the movable range, the tooth surfaces 31 and 41 of the worm 30 and the worm wheel 40 are surely used in actual use. The lubrication state between 32 and 42 can be improved.

  In addition, this invention is not limited to the said embodiment, A various change can be given within the range of a claim.

  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, 51 ... groove bottom, 61 ... first shape portion, 62 ... second shape portion, 71 ... first shape portion, 72 ... second shape portion, A0 ... region including central portion, A1, A2 ... non-contact region , B0 ... region including the central portion ... B0, B1, B2 ... non-contact region, C1 ... center axis of (worm), C2 ... center axis of worm wheel, D1 ... center distance (center axis of worm and worm) Distance from the wheel center axis), L1... Envelope, P1... Plane including the worm center axis and parallel to the worm wheel center axis, P2... Including worm center axis and perpendicular to the worm wheel center axis Surface, W1 ... tooth width direction, X1 ... center axis direction parallel to the worm wheel, (a direction to increase or decrease the distance between the center axis of the worm wheel and the worm of the central axis) direction to increase or decrease between Y1 ... center distance

Claims (3)

A worm, and a worm wheel having a tooth groove engaged with the worm,
The tooth surface of the worm wheel includes an envelope of a movable range in which the tooth surface of the worm can move due to a displacement of the worm relative to the worm wheel when the load is equal to or greater than the maximum load during use. Including a first shape portion composed of
When the load is less than the maximum load during use, the first shape portion of the tooth surface of the worm wheel forms a non-contact region with respect to the tooth surface of the worm at a pair of ends in the tooth width direction,
A worm reducer in which the entire surface of the first shape portion of the tooth surface of the worm wheel contacts the tooth surface of the worm when the load is equal to or greater than or equal to the maximum load during use . Oite to claim 1, positional displacement of the worm, the a first misalignment the worm in a direction parallel to the central axis of the worm wheel is offset, in a plane perpendicular to the 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; and the central axis of the worm wheel that includes the central axis of the worm and is parallel to the central axis of the worm wheel A third misalignment in which the central axis of the worm inclines in a plane, and a fourth misalignment in which the central axis of the worm inclines in a plane including the central axis of the worm and perpendicular to the central axis of the worm wheel. A worm reducer including misalignment. 3. The tooth surface of the worm wheel according to claim 1, wherein a tooth surface of the worm wheel is a portion excluding the first shape portion of the tooth surface, and is adjacent to at least a groove bottom side of the first shape portion and makes contact with the worm. A worm reduction gear including the avoided second shape portion.

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