JP2010071375A - Gear speed reducer and electric power steering device including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gear speed reducer and an electric power steering device including the same, capable of restraining a backlash of mutual gears caused by an increase in an inter-core distance of a gear shaft. <P>SOLUTION: This gear speed reducer 11 is stored in a housing 20 made of an aluminum alloy, and includes at least a driving gear 31 and a driven gear 32. The driving gear is provided with a driving gear body 31a made of an aluminum alloy and a steel driving tooth part 31b fixed to the outer periphery of the driving gear body by shrinkage fit or expansion fit. The driven gear is provided with a driven gear body 32a made of an aluminum alloy and a steel driven tooth part 32b fixed to the outer periphery of the driven gear body by shrinkage fit or expansion fit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gear reduction device and an electric power steering device including the gear reduction device.

  In the electric power steering device, for example, as described in Patent Document 1, an electric motor is arranged in parallel with a rotatable ball nut that is screwed through a ball to a ball screw shaft formed on a rack shaft, A motor parallel type electric power steering system having a gear reduction device in which a driving gear is connected to a motor shaft of an electric motor, a driven gear is provided on a ball nut, and the driving gear and the driven gear are engaged via an intermediate gear. There is a device.

In this type of electric power steering device, the housing that houses the gear reduction device is generally made of an aluminum alloy, and the drive gear, driven gear, and intermediate gear that make up the gear reduction device have wear resistance. It is made of steel to improve it.
JP-A-2005-280555

  For this reason, when the electric power steering device is thermally expanded, the distance between the center of the drive gear and the intermediate gear and the distance between the center of the intermediate gear and the driven gear are caused by the difference in the linear expansion coefficient between the housing and each gear of the gear reduction device. The distance increases. As the distance between the centers increases, the backlash between the drive gear and the intermediate gear and the backlash between the intermediate gear and the driven gear increase, generating rattling noise, changing the steering feeling, etc. There is a fear.

  The present invention has been made to solve the above-described conventional problems, and provides a gear reduction device capable of suppressing backlash between gears accompanying an increase in the distance between the centers of gear shafts and an electric power steering device including the gear reduction device. It is intended to provide.

  In order to solve the above-mentioned problems, a feature of the gear reduction device according to claim 1 is a gear reduction device that is housed in an aluminum alloy housing and includes at least a drive gear and a driven gear, and the drive gear. Comprises a drive gear body made of aluminum alloy and a steel drive tooth portion fixed to the outer periphery of the drive gear body by shrink fitting or cold fitting, and the driven gear is driven by aluminum alloy. A gear main body and a driven tooth portion made of steel which is fixed to the outer periphery of the driven gear main body by shrink fitting or cold fitting.

  A gear reduction device according to a second aspect of the invention is a gear reduction device that is housed in an aluminum alloy housing and includes at least a drive gear and a driven gear, and the drive gear is hardened on the outer periphery. And a driven gear body made of an aluminum alloy having a tooth portion hardened on the outer periphery thereof.

  According to a third aspect of the present invention, in the gear reduction device according to the first or second aspect, at least one of the driving gear and the driven gear has a steel inner boss that is press-fitted into the gear shaft. The gear body is fixed between the inner boss and the tooth portion by shrink fitting or cold fitting.

  According to a fourth aspect of the present invention, the gear reduction device according to the second aspect is characterized in that, in the second aspect, the curing process comprises an alumite process.

  A feature of the electric power steering device according to claim 5 is that the gear reduction device according to any one of claims 1 to 4 is provided.

  According to the invention of the gear reduction device according to claim 1, the drive gear and the driven gear of the gear reduction device housed in the aluminum alloy housing are baked on the outer circumference of the aluminum alloy gear main body and the drive gear main body. Steel teeth fixed by a fit or a cold fit, so even if the distance between the gears increases due to thermal expansion of the housing, the drive gear and the driven gear are It expands in the same way. Thereby, the backlash of gears accompanying the increase in the distance between gears can be suppressed. And since the tooth | gear part was comprised with steel, the abrasion of a tooth | gear part can be suppressed and durability of a gear reduction gear can be improved.

  According to the invention of the gear reduction device according to claim 2, the drive gear and the driven gear of the gear reduction device housed in the aluminum alloy housing have gear teeth made of a hardened outer periphery. Since each of the main bodies is provided, the backlash between the gears can be suppressed even if the distance between the gears is increased due to the thermal expansion of the housing. In addition, since the teeth are hardened, wear of the teeth can be suppressed and the durability of the gear reduction device can be improved.

  According to the invention of the gear reduction device according to the third aspect, at least one of the drive gear and the driven gear has the steel inner boss that is press-fitted into the gear shaft on the inner side. And can be press-fitted and fixed to the gear shaft reliably and easily.

  According to the invention of the gear reduction device according to claim 4, since the hardening process is an alumite process, each tooth part of the drive gear main body and the driven gear main body made of aluminum alloy can be easily hardened. .

  According to the invention of the electric power steering device according to claim 5, since the gear reduction device having the above-described configuration is provided, the backlash between the gears of the gear reduction device can be prevented regardless of the thermal expansion of the aluminum alloy housing. An electric power steering device that can be accurately suppressed can be realized, and the steering feeling can be improved.

  A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an electric power steering apparatus 10 according to the present embodiment, and FIG. 2 is a cross-sectional view of a gear reduction device 11 part built in the electric power steering apparatus 10.

  In FIG. 1, an electric power steering apparatus 10 steers a steered wheel 12 by a steering shaft 14 that transmits a steering torque applied to a steering wheel 13 to steer the steered wheel 12, and the steering torque from the steering shaft 14. For example, a steering mechanism 15 composed of a rack and pinion mechanism, and an intermediate shaft 16 as a shaft coupling connecting the steering shaft 14 and the steering mechanism 15 are provided.

  The steering mechanism 15 includes a pinion shaft 17 serving as an input shaft, a rack shaft 18 serving as a steered shaft extending in a lateral direction of the automobile (a direction orthogonal to the straight traveling direction), and a housing 20 that supports the pinion shaft 17 and the rack shaft 18. And have. The pinion shaft 17 is rotatably supported by the housing 20, and the rack shaft 18 is supported by the housing 20 so as to be linearly reciprocable. The pinion teeth 17 a of the pinion shaft 17 are meshed with the rack teeth 18 a of the rack shaft 18. Both ends of the rack shaft 18 are coupled to the steered wheels 12 via tie rods and knuckle arms.

  Thereby, when the steering wheel 13 is steered, the steering torque is transmitted to the steering mechanism 15 via the steering shaft 14 and the like, and the pinion shaft 17 is rotated. The rotation of the pinion shaft 17 is converted into linear movement of the rack shaft 18 by the pinion teeth 17a and the rack teeth 18a, whereby the steered wheels 12 are steered.

  As shown in FIG. 2, a ball screw shaft 21 is integrally formed on the rack shaft 18, and a ball nut 23 screwed to the ball screw shaft 21 via a ball 22 is concentric with the rack shaft 18. The housing 20 is supported by a bearing 24 so as to be rotatable only.

  Further, the electric power steering apparatus 10 includes a torque sensor 25 (see FIG. 1) that detects steering torque, an electric motor 26 that is controlled based on the output of the torque sensor 25 and assists the steering torque, and an electric motor 26. A gear reduction device 11 for reducing the rotation is provided. The gear reduction device 11 meshes with a driving gear 31 driven by an electric motor 26, a driven gear 32 provided on the ball nut 23, and the driving gear 31 and the driven gear 32, and the rotation of the driving gear 31 is driven by the driven gear 31. And an intermediate gear 33 that transmits to 32. The ball nut 23 constitutes a driven gear shaft.

  As shown in detail in FIG. 2, the housing 20 includes a first housing 20 a that houses the main part of the rack shaft 18 and the pinion shaft 17 constituting the steering mechanism 15, a second housing 20 b that houses the gear reduction device 11, and The housing cover 20c closes the opening of the second housing 20b. The first housing 20a, the second housing 20b, and the housing cover 20c are made of an aluminum alloy and are integrally coupled to each other by a bolt 20d or the like. A steel driven gear shaft (ball nut) 23 is supported on the second housing 20b via a bearing 24 so as to be rotatable concentrically with the ball screw shaft 21 (rack shaft 18). A driven gear 32 having a configuration to be described later is fixed to the outer periphery of the driven gear shaft 23 by press fitting.

  An electric motor 26 is installed in the second housing 20 b in parallel with the rack shaft 18. A motor shaft of the electric motor 26 is rotationally connected to one end of a drive gear shaft 36 to which a drive gear 31 having a configuration described later is attached. The drive gear shaft 36 is supported at one end (right end) in the axial direction by a bearing 37a attached to the second housing 20a, and supported at the other end (left end) in the axial direction by a bearing 37b attached to the housing cover 20c. These bearings 37a and 37b are rotatably supported around an axis parallel to the rack shaft 18.

  Further, in the second housing 20 b, an intermediate gear shaft 38 is disposed in parallel with the drive gear shaft 36 between the driven gear shaft 23 and the drive gear shaft 36. The intermediate gear shaft 38 is rotatably supported at one end (right end) in the axial direction by a bearing 39a mounted on the second housing 20b, and has the other end (left end) in the axial direction supported by a bearing 39b mounted on the housing cover 20c. It is rotatably supported. On the intermediate gear shaft 38, an intermediate gear 33 having a configuration to be described later is integrally attached between bearings 39a and 39b, and the intermediate gear 33 is engaged with the drive gear 31 and the driven gear 32, respectively. .

  The drive gear 31, the intermediate gear 33, and the driven gear 32 described above constitute the gear reduction device 11 that reduces and transmits the rotation of the electric motor 26 to the driven gear shaft 23.

  As shown in FIG. 3, the driven gear 32 described above is made of a cylindrical driven gear main body 32a made of an aluminum alloy of the same material as the housing 20, and made of steel integrally attached to the outer periphery of the driven gear main body 32a. It is comprised by the ring-shaped driven-tooth part 32b and the ring-shaped inner side boss | hub 32c made from steel attached integrally to the inner periphery of the driven gear main body 32a. The inner periphery of the driven tooth portion 32b is fitted and fixed to the outer periphery of the driven gear main body 32a by shrink fitting, and the outer periphery of the inner boss 32c is fixed to the inner periphery of the driven gear main body 32a by shrink fitting. In the driven gear 32 configured in this manner, the inner boss 32c is press-fitted into the outer periphery of the driven gear shaft (ball nut) 23 made of the same material (steel) (see FIG. 2), so that the driven gear shaft 23 Fixed to.

  As shown in FIG. 4, the drive gear 31 includes a cylindrical drive gear main body 31a made of an aluminum alloy, and a ring-shaped drive tooth portion made of steel that is integrally attached to the outer periphery of the drive gear main body 31a. 31b. The inner periphery of the drive tooth portion 31b is fitted and fixed to the outer periphery of the drive gear body 31a by shrink fitting. The drive gear 31 configured in this way is configured such that the inner circumference of the drive gear main body 31a is fitted and fixed to the outer circumference mounting portion 36a of the steel drive gear shaft 36 by shrink fitting.

  Similarly, as shown in FIG. 5, the intermediate gear 33 includes a cylindrical intermediate gear body 33a made of an aluminum alloy and a ring-shaped intermediate tooth made of steel that is integrally attached to the outer periphery of the intermediate gear body 33a. It is comprised by the part 33b. The inner periphery of the intermediate tooth portion 33b is fitted and fixed to the outer periphery of the intermediate gear body 33a by shrink fitting. The intermediate gear 33 configured in this manner is configured such that the inner periphery of the intermediate gear main body 33a is fitted and fixed to the outer peripheral mounting portion 38a of the steel intermediate gear shaft 38 by shrink fitting.

  According to the electric power steering apparatus 10 including the gear reduction device 11 having the above-described configuration, when the steering wheel 13 is steered, the steering torque is input to the pinion shaft 17, and the steering mechanism 15 including the pinion shaft 17 and the rack shaft 18 is operated. The rack shaft 18 is moved in the axial direction.

  The steering torque input to the pinion shaft 17 is detected by the torque sensor 25, and the electric motor 26 is rotationally controlled based on the detected steering torque to generate auxiliary torque. The auxiliary torque by the electric motor 26 is a driven gear shaft (ball nut) in which the driven gear 32 is press-fitted and fixed via a drive gear 31 attached on the drive gear shaft 36 and an intermediate gear 33 attached on the intermediate gear shaft 38. 23. The rack shaft 18 is moved in the axial direction by the rotation of the driven gear shaft 23, and the steering force of the steering wheel 13 by the driver is reduced.

  By the way, when the housing 20 of the electric power steering apparatus 10 is thermally expanded, the center distance D1 between the drive gear shaft 36 and the intermediate gear shaft 38 and the center distance D2 between the intermediate gear shaft 38 and the driven gear shaft 23 (see FIG. 2). ) Increase, but the drive gear body 31a of the drive gear 31 and the intermediate gear body 33a of the intermediate gear 33 and the driven gear 32 driven on the drive gear shaft 36, the intermediate gear shaft 38, and the driven gear shaft 23, respectively. Since the gear body 32 a is made of an aluminum alloy made of the same material as the housing 20, the drive gear 31, the intermediate gear 33, and the driven gear 32 are also thermally expanded in the same manner as the housing 20. As a result, backlash between the drive gear 31 and the intermediate gear 33 and backlash between the intermediate gear 33 and the driven gear 32 can be suppressed as the distance between the centers D1 and D2 increases.

  Moreover, since the tooth portions 31b, 33b, and 32b of the drive gear 31, the intermediate gear 33, and the driven gear 32 are made of steel, the strength (hardness) of the tooth portions 31b, 33b, and 32b can be secured, and wear resistance is ensured. And the durability of the gear reduction device 11 can be improved. Further, since the inner boss 32c made of steel is fixed to the inner periphery of the driven gear 32, the driven gear 32 can be easily assembled to the driven gear shaft 23 by press-fitting and fixing as in the prior art.

  According to the electric power steering apparatus 10 including the gear reduction device 11 having such a configuration, a rattling sound is generated by suppressing backlash between the drive gear 31 and the intermediate gear 33 and backlash between the intermediate gear 33 and the driven gear 32. While being able to suppress, a steering feeling can be improved.

  6 and 7 show a second embodiment of the present invention. The difference from the first embodiment is that the tooth portions 31b and 32b of the drive gear 31, the driven gear 32, and the intermediate gear 33 are as follows. , 33b are made of an aluminum alloy integrally with each gear body 31a, 32a, 33a, and each tooth portion 31b, 32b, 33b is alumite treated to ensure the hardness of the tooth portions 31b, 32b, 33b. This is to improve the wear resistance.

  That is, as shown in FIG. 6, in the driven gear 32, a driven gear main body 32a made of an aluminum alloy is integrally formed up to an outer peripheral tooth portion 32b, and at least the outer peripheral tooth portion 32b is hardened by an alumite treatment. Similarly, as shown in FIG. 7, in the drive gear 31, a drive gear body 31a made of an aluminum alloy is integrally formed up to the outer peripheral tooth portion 31b, and at least the outer peripheral tooth portion 31b is hardened by an alumite treatment. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and the intermediate gear 33 has the same configuration as that of the drive gear 31, and is not shown.

  Also in the second embodiment, as described in the first embodiment, when the housing 20 of the electric power steering apparatus 10 is thermally expanded, the center distance D1 between the drive gear 31 and the intermediate gear 33 is set. The inter-center distance D <b> 2 between the intermediate gear 33 and the driven gear 32 increases, but the drive gear 31, the intermediate gear 33, and the driven gear 32 can also be thermally expanded in the same manner as the housing 20. As a result, backlash between the drive gear 31 and the intermediate gear 33 and backlash between the intermediate gear 33 and the driven gear 32 can be suppressed, and each tooth portion 31b, 32b, 33b made of an aluminum alloy is anodized. As a result, the hardness of the tooth portions 31b, 32b, 33b can be secured, and the wear resistance can be improved.

  In the second embodiment, the hardening treatment of the tooth portions 31b, 32b, and 33b made of an aluminum alloy is not necessarily limited to the alumite treatment, and the tooth portions 31b, 32b, and 33b are made by other hardening treatments. The hardness may be ensured.

  In the above-described embodiment, the example in which the gear reduction device 11 is applied to the electric power steering device 10 has been described. However, the present invention can also be applied to other gear reduction devices housed in an aluminum alloy housing 20. Further, the gear reduction device 11 is not necessarily constituted by the drive gear 31, the driven gear 32, and the intermediate gear 33, and the intermediate gear 33 is omitted and the drive gear 31 and the driven gear 32 are directly meshed with each other. Conversely, the driving gear 31 and the driven gear 32 may be rotationally connected via a plurality of intermediate gears.

  Further, depending on the configuration of the gear reduction device 11, the inner boss 32c provided on the inner periphery of the driven gear 32 can be eliminated, and the driven gear main body 32a can be directly attached to the outer periphery of the driven gear shaft 23 by shrink fitting or driving. A steel inner boss may be attached to the inner periphery of the drive gear main body 31a of the gear 31 by shrink fitting and fixed to the outer periphery of the drive gear shaft 36 by press fitting.

  In the first embodiment described above, the tooth portions 31b, 32b, 33b are fitted into the gear bodies 31a, 32a, 33a of the drive gear 31, the driven gear 32, and the intermediate gear 33 by shrink fitting. In addition to fixing, each gear body 31a, 32a, 33a is fixed to the drive gear shaft 36, the inner boss 32c, and the intermediate gear shaft 38 by shrink fitting. It is also possible to fix by fitting with a cold fit.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the configurations described in the embodiments, and does not depart from the gist of the present invention described in the claims. It can take various forms.

It is the schematic which shows the electric power steering apparatus provided with the gear reduction device which concerns on embodiment of this invention. 1 is a cross-sectional view of a gear reduction device according to a first embodiment of the present invention. It is sectional drawing which shows the structure of a driven gear. It is sectional drawing which shows the structure of a drive gearwheel. It is sectional drawing which shows the structure of an intermediate gear. It is sectional drawing which shows the structure of the driven gear which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the drive gear which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 11 ... Gear speed reducer, 20 ... Housing, 23 ... Driven gear shaft (ball nut), 26 ... Electric motor, 31 ... Drive gear, 31a ... Drive gear main body, 31b ... Tooth part, 32 ... Driven gear, 32a ... driven gear main body, 32b ... toothed portion, 32c ... inner boss, 33 ... intermediate gear, 33a ... intermediate gear main body, 33b ... toothed portion, 36 ... drive gear shaft, 38 ... intermediate gear shaft.

Claims (5)

A gear reduction device housed in an aluminum alloy housing and having at least a drive gear and a driven gear,
The drive gear includes a drive gear body made of aluminum alloy, and a steel drive tooth portion fixed to the outer periphery of the drive gear body by shrink fitting or cold fitting,
The driven gear includes a driven gear main body made of an aluminum alloy, and a steel driven tooth portion fixed to the outer periphery of the driven gear main body by shrink fitting or cold fitting. Reducer. A gear reduction device that is housed in an aluminum alloy housing and includes at least a drive gear and a driven gear,
The drive gear includes a drive gear body made of aluminum alloy having teeth that are hardened on the outer periphery,
The driven gear includes a driven gear main body made of an aluminum alloy having teeth hardened on the outer periphery.   3. The drive gear and the driven gear according to claim 1, wherein at least one of the drive gear and the driven gear has a steel inner boss that is press-fitted into the gear shaft on the inner side, and the inner boss and the tooth portion are arranged between A gear reduction device characterized in that the gear body is fixed by shrink fitting or cold fitting.   3. The gear reduction device according to claim 2, wherein the curing process is an alumite process. An electric power steering apparatus comprising the gear reduction device according to any one of claims 1 to 4.

Images