JP2008137600A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight electric power steering device capable of achieving high output. <P>SOLUTION: A housing 25 for storing a metallic small-diameter gear 21 and a metallic large-diameter gear 22 includes a metallic main housing 28 and a synthetic resin-made or synthetic rubber-made sub-housing 29. The main housing 28 forms a skeleton of the housing 25 to cover a part of the small-diameter gear 21 and the large-diameter gear 22. The sub-housing 29 covers the entire main housing 28 including the small-diameter gear 21 and the large-diameter gear 22, and is connected to the main housing 28. The small-diameter gear 21 and the large-diameter gear 22 are rotatably supported by the main housing 28 via first and second bearings 26a, 26b, 27a, 27b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus including an electric motor for assisting steering.

Some electric power steering devices for vehicles include a reduction gear that amplifies the output of an electric motor (for example, see Patent Document 1).
In the electric power steering apparatus described in Patent Document 1, the output of the electric motor is amplified by decelerating the rotation of the rotating shaft of the electric motor by the worm shaft and the worm wheel as a speed reducer, and the amplified output is steered. The steering operation is assisted by transmitting to the mechanism.

The worm wheel includes an annular cored bar and a synthetic resin member that surrounds the cored bar and has teeth formed on the outer periphery. The worm shaft and the worm wheel are rotatably supported by the housing via bearings.
JP 2006-175891 A

However, in the reduction gear as described above, there is a problem that a large force cannot be transmitted between the worm shaft and the worm wheel due to restrictions on the strength of the synthetic resin member, that is, the reduction gear cannot be increased in output.
In order to solve this problem, it is conceivable that the entire worm wheel is made of a strong metal. In this case, however, there is a problem that the weight increases.

  The present invention has been made based on such a background, and an object thereof is to provide an electric power steering apparatus that is lightweight and can achieve high output.

  In order to achieve the above object, the present invention includes a reduction gear (23) for transmitting the output of the steering assisting electric motor (20) to the steering mechanism (2), and a storage chamber (S) for storing the reduction gear. ), And the reduction gear includes a small-diameter gear (21) supported by the housing via a first bearing (26a, 26b), and a second bearing (27a, 27b) and a large-diameter gear (22) made of a metal meshing with the small-diameter gear, and the housing includes a main housing (28) made of a metal member and a resin or a resin supported by the main housing. A sub-housing (29) containing rubber, the main housing comprising a first part (33a, 33b) for supporting the first bearing and a second part (34a) for supporting the second bearing. 34b) and a connecting portion (37a, 37b) for connecting the first portion and the second portion, and a part of the storage chamber is partitioned only by the sub-housing. Power steering device (1).

According to the present invention, since a strong metal is used as the large-diameter gear, a large assist torque can be transmitted.
Moreover, since a part of the storage chamber is partitioned only by a lightweight sub-housing such as a resin, the weight of the entire housing can be reduced regardless of an increase in the weight of the large-diameter gear. In addition, the main housing made of a metal member includes first and second portions that support bearings for the small-diameter gear and the large-diameter gear, respectively, and a connecting portion that connects the first and second portions. Since the main housing forms a strong skeleton in the entire housing, both gears can be firmly held.

  By the way, as a material constituting the main housing, it is conceivable to use a material containing aluminum which has been conventionally used for a housing and a material containing strong iron as a large-diameter gear. However, in this case, the backlash amount at the meshing portion between the large-diameter gear and the small-diameter gear varies due to changes in the ambient temperature, and there is a risk that rattling noise increases or friction increases at the meshing portion. .

  Therefore, it is preferable that the metal constituting the large-diameter gear and the metal member have the same linear expansion coefficient. Specifically, it is preferable that the metal and the metal member constituting the large-diameter gear are made of a material containing iron. In this case, it is possible to increase the output of the speed reducer and to prevent fluctuations in the backlash amount due to changes in the atmospheric temperature.

In the present invention, the speed reducer includes a parallel shaft gear mechanism, and the first portion of the main housing includes first bearing holding holes (35a, 35b) for holding a first bearing, The second portion of the main housing may include second bearing retaining holes (36a, 36b) that retain the second bearing.
In this case, the main housing supports the small-diameter gear via the first bearing held in the first bearing holding hole, and the second housing holds the second bearing held in the second bearing holding hole. Large diameter gears can be supported.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention.
Referring to FIG. 1, an electric power steering apparatus 1 according to this embodiment is a so-called column assist type electric power steering apparatus, and includes a steering mechanism 2 including a rack and pinion mechanism, and a steering assist force applied to the steering mechanism 2. And a steering assist mechanism 3 for imparting.

  The steering mechanism 2 includes a steering shaft 5 connected to a steering wheel 4 as a steering member, an intermediate shaft 7 connected to the steering shaft 5 via a universal joint 6, and an intermediate shaft 7 connected to the intermediate shaft 7 via a universal joint 8. The pinion shaft 9 has a rack 11 that meshes with a pinion 10 provided at the tip of the pinion shaft 9 and has a rack shaft 12 as a steering shaft extending in the left-right direction of the vehicle.

  Tie rods 13 are coupled to both ends of the rack shaft 12, and each tie rod 13 is coupled to a steering wheel 14 via a knuckle arm (not shown). When the steering wheel 4 is operated and the steering shaft 5 rotates, this rotation is converted into an axial movement of the rack shaft 12 along the left-right direction of the vehicle by the pinion 10 and the rack 11. Thereby, steering of the steering wheel 14 is achieved.

  The steering shaft 5 is divided into an input shaft 15 connected to the steering wheel 4 and an output shaft 16 connected to the pinion shaft 9. The input shaft 15 and the output shaft 16 are relatively rotatable via a torsion bar 17 and are connected coaxially. A torque sensor 18 disposed around the steering shaft 5 can detect the steering torque input to the steering wheel 4 from the relative rotation amounts of the input shaft 15 and the output shaft 16. The steering torque detected by the torque sensor 18 is input to an ECU 19 (Electronic Control Unit).

The steering assist mechanism 3 includes an electric motor 20 for assisting steering, and a speed reducer 23 including a small diameter gear 21 and a large diameter gear 22. The speed reducer 23 decelerates the rotation of the electric motor 20 to amplify the output of the electric motor 20, and the amplified output is transmitted to the steering mechanism 2 as a steering assist force to assist the steering operation. it can.
The electric motor 20 is controlled by the ECU 19. That is, the ECU 19 determines the steering assist force based on the steering torque input from the torque sensor 18, the vehicle speed input from a vehicle speed sensor (not shown), and the like, and the electric motor 20 is determined based on the determined steering assist force. Is controlled.

The small-diameter gear 21 and the large-diameter gear 22 are meshed with each other, and constitute a parallel shaft gear mechanism in which the respective central axes are arranged in parallel. As the small-diameter gear 21 and the large-diameter gear 22, for example, a spur gear or a helical gear can be used.
FIG. 2 is a partial cross-sectional view schematically showing a schematic configuration of the steering assist mechanism 3. FIG. 3 is a plan view of the first divided main housing 30, and FIG. 4 is a plan view of the second divided main housing 31. FIG. 5 is a plan view of the first divided sub-housing 46, and FIG. 6 is a plan view of the second divided sub-housing 47.

  With reference to FIG. 2, the small-diameter gear 21 is a cylindrical external gear, and is formed in the middle of the axial direction of the gear shaft 24 parallel to the steering shaft 5. The large-diameter gear 22 is an annular outer gear formed of a metal containing iron (iron or iron alloy), and the output shaft 16 of the steering shaft 5 is press-fitted and fitted to the inner periphery thereof, for example. Yes. The large-diameter gear 22 is integrally rotatable with the output shaft 16 and is coaxially connected.

  The small-diameter gear 21 and the large-diameter gear 22 are accommodated in a storage chamber S defined by a housing 25, and are supported by the housing 25 so as to be rotatable via a plurality of bearings. Specifically, the gear shaft 24 on which the small-diameter gear 21 is formed is rotatably supported by a pair of first bearings 26a and 26b disposed on both sides of the small-diameter gear 21, and the pair of first gears. The bearings 26 a and 26 b are supported by the housing 25. The output shaft 16 to which the large-diameter gear 22 is coupled is rotatably supported by a pair of second bearings 27a and 27b disposed on both sides of the large-diameter gear 22, and the pair of second bearings. 27 a and 27 b are supported by the housing 25. That is, the large-diameter gear 22 is rotatably supported by the housing 25 via the pair of second bearings 27 a and 27 b and the output shaft 16.

  As the first and second bearings 26a, 26b, 27a, and 27b, for example, a rolling bearing or a sliding bearing can be used. In the present embodiment, rolling ball bearings are used as the first and second bearings 26a, 26b, 27a, 27b. A region including the meshing portion of the small diameter gear 21 and the large diameter gear 22 is filled with a lubricant such as grease.

The housing 25 is composed of a main housing 28 formed of the same kind of material having the same linear expansion coefficient as that of the large gear 22 (material including iron: iron or iron alloy), synthetic resin such as ABS resin, or polybutadiene, for example. The auxiliary housing 29 is made of synthetic rubber.
The main housing 28 is formed by combining a first divided main housing 30 and a second divided main housing 31.

  Referring to FIGS. 2 and 3, the first divided main housing 30 includes a main body portion 32 having a substantially rectangular plate shape, and a first boss 33 a including a cylindrical protrusion protruding from the main body portion 32. And a second boss 34a. The first boss 33a functions as a first portion that holds the first bearing 26a. That is, the first bearing 26a is fitted and held in the first bearing holding hole 35a formed by the first boss 33a. The second boss 34a functions as a second portion that holds the second bearing 27a. That is, the second bearing 27a is fitted and held in the second bearing holding hole 36a formed by the second boss 34a.

The main body portion 32 of the first divided main housing 30 includes a plate-like connecting portion 37a for connecting the first boss 33a as the first portion and the second boss 34a as the second portion to each other, A first extending portion 38 extending from the first boss 33a in the direction opposite to the connecting portion 37a, and a second extending portion extending from the second boss 34a in the direction opposite to the connecting portion 37a. 39.
Referring to FIGS. 2 and 4, the second divided main housing 31 includes a main body portion 40 having a groove shape and a cylindrical protrusion protruding from a web 41 having a substantially rectangular plate shape. The 1st boss | hub 33b and 2nd boss | hub 34b which consist of are provided. The first boss 33b functions as a first portion that holds the first bearing 26b. That is, the first bearing 26b is fitted and held in the first bearing holding hole 35b formed by the first boss 33b. The second boss 34b functions as a second portion that holds the second bearing 27b. That is, the second bearing 27b is fitted and held in the second bearing holding hole 36b formed by the second boss 34b.

  The main body portion 40 of the second divided main housing 31 includes the web 41, a pair of flanges 42 and 43 provided at both ends of the web 41, and a first extending plate 44 extending from the tips of the flanges 42 and 43. And a second extending plate 45. The web 41 includes a plate-like connecting portion 37b that connects the first boss 33b as the first portion and the second boss 34b as the second portion to each other.

On the other hand, the sub-housing 29 is formed by combining a first divided sub-housing 46 and a second divided sub-housing 47 (see FIG. 2).
Referring to FIGS. 2 and 5, the first divided sub-housing 46 includes a main body portion 48 having a generally disc shape, and a first boss 49 a including a cylindrical protrusion protruding from the main body portion 48. And a second boss 50a. The first boss 49a and the second boss 50a correspond to the first boss 33a and the second boss 34a provided in the first divided main housing 30, respectively. The inner surfaces of the first boss 49a and the second boss 50a are fitted to the outer surfaces of the first boss 33a and the second boss 34a, respectively.

The main body 48 of the first divided sub-housing 46 includes a disk part 51 and a rectangular protruding part 52 that protrudes radially outward from the disk part 51. The disc part 51 includes a plate-like connecting part 53a that connects the first boss 49a and the second boss 50a to each other.
A part of the first divided sub-housing 46 covers at least a part of the first divided main housing 30.

  Referring to FIGS. 2 and 6, the second divided sub-housing 47 projects from a cylindrical main body portion 54 having one end opened, and a cylindrical portion 55 as an end wall at the other end of the main body portion 54. A first boss 49b and a second boss 50b made of the formed cylindrical projection are provided. The inner surfaces of the first boss 49b and the second boss 50b correspond to the first boss 33b and the second boss 34b provided in the second divided main housing 31, respectively. The inner surfaces of the first boss 49b and the second boss 50b are fitted to the outer surfaces of the first boss 33b and the second boss 34b, respectively.

The main body portion 54 of the second divided sub-housing 47 includes the disk portion 55, a cylindrical peripheral wall 56 provided along the periphery of the disk portion 55, and a radially outward direction from the tip of the peripheral wall 56. And an annular flange 57 extending in the direction. The disc portion 55 includes a plate-like connecting portion 53b that connects the first boss 49b and the second boss 50b to each other.
A part of the second divided sub-housing 47 covers at least a part of the second divided main housing 31.

  The first divided main housing 30 and the second divided main housing 31 are combined to form the main housing 28, and the first divided sub housing 46 and the second divided sub housing 47 are sandwiched between the main housing 28. The sub-housing 29 is configured by combining them, and then the housing 25 is assembled by screwing bolts 58 as attachment members into screw holes 67 as attachment holes formed in the respective housings 30, 31, 46, 47. At this time, the annular flange 57 of the second divided sub-housing 47 is brought into contact with the peripheral edge of the main body 48 of the first divided sub-housing 46, so that the storage chamber S that is a sealed space is partitioned. Thereby, it is possible to prevent the lubricant from leaking out of the housing 25. The main housing 28 forms a skeleton of the housing 25.

  Referring to FIG. 2, the outer ring of the first bearing 26a is, for example, press-fitted into the first bearing holding hole 35a, and the end of the outer ring is connected to the inner periphery of the first bearing holding hole 35a. Is engaged with an annular stepped portion 70 formed on the surface. On the other hand, the gear shaft 24 is press-fitted into the inner ring of the first bearing 26a, for example, and the end of the inner ring engages with an annular step 71 formed at the end of the small-diameter gear 21. Yes. The first bearing 26 a is restricted from moving in the axial direction by the annular step portions 70 and 71. In addition, a sealing plug 59 for sealing the first bearing holding hole 35 a is screwed into the first boss 33 a of the first divided main housing 30 from the outside of the housing 25.

  For example, the outer ring of the first bearing 26b is press-fitted into the first bearing holding hole 35b. The end of the outer ring of the first bearing 26b is fitted to the end of the first bearing 26b from the outside of the housing 25. A preload adjusting plug 61 screwed into the hole 35b is engaged. On the other hand, the gear shaft 24 is press-fitted into the inner ring of the first bearing 26b, for example, and the end of the inner ring of the first bearing 26b is an annular stepped portion 72 formed at the end of the small-diameter gear 21. Is engaged. A preload in the axial direction X1 of the gear shaft 24 is applied to the outer ring of the first bearing 26 b by a preload adjusting plug 61. Thereby, the internal gap (the gap between the inner ring and the outer ring and the rolling element) of the first bearing 26b is removed. Further, the internal clearance of the first bearing 26a is a preload from the preload adjusting plug 61 transmitted to the inner ring of the first bearing 26a via the outer ring, the rolling element, the inner ring and the small diameter gear 21 of the first bearing 26b. Has been removed by. The preload adjusting plug 61 is fixed to the housing 25 by a lock nut 62 screwed into the outer periphery thereof.

  For example, the outer ring of the second bearing 27a is press-fitted into the second bearing holding hole 36a, and the end of the outer ring of the second bearing 27a is formed on the inner periphery of the second bearing holding hole 36a. The annular stepped portion 73 is engaged. On the other hand, the output shaft 16 is press-fitted into the inner ring of the second bearing 27a, for example. A preload adjusting nut 60 screwed into the output shaft 16 is engaged with the end of the inner ring of the second bearing 27a, and the preload in the axial direction Y1a is given to the inner ring by the preload adjusting nut 60. ing. As a result, the internal gap (the gap between the inner ring and the outer ring and the rolling element) of the second bearing 27a is removed.

  For example, the outer ring of the second bearing 27b is press-fitted into the second bearing holding hole 36b, and the end of the outer ring of the second bearing 27b is formed on the inner periphery of the second bearing holding hole 36b. The annular stepped portion 74 is engaged. On the other hand, the output shaft 16 is press-fitted into the inner ring of the second bearing 27b, for example. One end of the inner ring of the second bearing 27b is engaged with an annular step 75 formed on the output shaft 16, and a fixing nut 63 screwed into the output shaft 16 is engaged with the other end. Yes. The inner ring of the second bearing 27b is clamped in the axial direction Y1 by the annular step 75 and the fixing nut 63 and is fixed to the output shaft 16. The internal clearance of the second bearing 27 b is removed by preload from the preload adjusting nut 60 transmitted to the inner ring of the second bearing 27 b via the inner ring of the second bearing 27 a and the output shaft 16. ing.

  The cylindrical motor housing 64 that constitutes a part of the electric motor 20 is fixed to a part of the housing 25 corresponding to the first boss 33 b of the second divided main housing 31. The electric motor 20 includes a cylindrical rotor 65 and an annular stator 66 that surrounds the rotor 65 at a predetermined interval. The stator 66 is fixed to the inner periphery of the motor housing 64. A part of the gear shaft 24 protruding from the housing 25 is press-fitted and fitted to the inner periphery of the rotor 65, for example, and the rotor 65 is fixed to the gear shaft 24. In other words, in the present embodiment, the gear shaft 24 functions as the rotating shaft of the electric motor 20, thereby reducing the number of parts. The lock nut 62 for fixing the preload adjusting plug 61 is disposed at a position corresponding to the first bearing 26 b and the rotor 65 inside the motor housing 64.

As described above, in the present embodiment, the reduction gear 23 can have high output by forming the large-diameter gear 22 from the metal containing iron (iron or iron alloy).
Further, the entire housing 25 can be reduced in weight by forming the sub housing 29 constituting a part of the housing 25 from the synthetic resin, the synthetic rubber or the like. Therefore, by forming the large-diameter gear 22 from the metal containing iron (iron or iron alloy), the weight of the electric power steering apparatus 1 as a whole is increased although the weight of the speed reducer 23 is increased as compared with the conventional configuration. Can be suppressed.

  Moreover, the main housing 28 made of the metal member (iron or iron alloy) supports the first bearings 26a and 26b and the second bearings 27a and 27b, respectively, and the first boss 33a and 33b and the second boss 34a. , 34b, and connecting portions 37a, 37b for connecting the first bosses 33a, 33b and the second bosses 34a, 34b, respectively, and the main housing 28 provides a strong skeleton within the entire housing 25. Since it is formed, both gears 21 and 22 can be firmly held. Furthermore, the noise and vibration from the reduction gear 23 can be reduced by forming the sub housing 29 with the synthetic resin or the synthetic rubber.

  Furthermore, the main housing 28 and the large-diameter gear 22 are formed of iron or an iron alloy as the same kind of material having the same linear expansion coefficient, so that the meshing portion of the small-diameter gear 21 and the large-diameter gear 22 due to changes in the ambient temperature. Variations in the amount of backlash can be prevented. Thereby, it is possible to prevent an increase in rattling noise and friction at the meshing portion.

FIG. 7 is a partial cross-sectional view schematically showing a schematic configuration of a steering assist mechanism 3a according to another embodiment of the present invention. In FIG. 7, the same components as those shown in FIG. 2 described above are denoted by the same reference numerals as those in FIG.
Referring to FIG. 7, the steering assist mechanism 3a shown in FIG. 7 is mainly different from the steering assist mechanism 3 shown in FIG. 2 in that a preload is applied to the pair of first bearings 26a and 26b. A preload adjusting plug 76 for removing the internal gap is screwed into the first bearing holding hole 35a on the side opposite to the electric motor 20, and a fixing plug 77 for fixing the first bearing 26b is electrically driven. That is, it is screwed into the first bearing holding hole 35b on the motor 20 side. The diameter of the tool engagement hole 78 formed in the inner periphery of the fixing plug 77 is larger than the outer diameter of the rotor 65.

  In the present embodiment, even after the motor housing 64 is fixed to the housing 25, the preload applied to the pair of first bearings 26a and 26b is adjusted by adjusting the screwing amount of the preload adjusting plug 76. be able to. Even after the rotor 65 is fixed to the gear shaft 24, the fixing plug 77 can be removed from the housing 25 and the gear shaft 24 can be detached from the housing 25. Furthermore, since the lock nut 62 is not required for the steering assist mechanism 3 shown in FIG. 2, the distance between the small-diameter gear 21 and the rotor 65 in the axial direction X1 can be shortened. Thereby, the electric motor 20 can be reduced in size.

The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims. For example, in the above-described embodiment, the case where the reduction gear 23 is a parallel shaft gear mechanism has been described. However, the reduction gear 23 may be a cross shaft gear mechanism such as a bevel gear, or a staggered difference such as a worm gear or a hypoid gear. A gear mechanism may be used.
In the above-described embodiment, the example in which the sub housing 29 is connected to the main housing 28 by the bolt 58 has been described. However, the sub housing 29 may be fixed to the main housing 28 by, for example, bonding or insert molding.

  Moreover, you may provide reinforcement parts, such as a rib, in the 1st division | segmentation main housing 30 and the 2nd division | segmentation main housing 31, for example. Thereby, the strength of the main housing 28 can be improved. Therefore, the main housing 28 can be reduced in size, and the housing 25 can be further reduced in weight.

It is a mimetic diagram showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is a fragmentary sectional view showing typically a schematic structure of a steering auxiliary mechanism. It is a top view of the 1st division | segmentation main housing. It is a top view of the 2nd division | segmentation main housing. It is a top view of the 1st division subhousing. It is a top view of the 2nd division subhousing. It is a fragmentary sectional view showing typically a schematic structure of a steering auxiliary mechanism concerning another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering mechanism, 23 ... Reduction gear, 20 ... Electric motor, 21 ... Small diameter gear, 22 ... Large diameter gear, 25 ... Housing , 26a, 26b ... first bearing, 27a, 27b ... second bearing, 28 ... main housing, 29 ... sub housing, 33a, 33b ... first boss (first ), 34a, 34b, second boss (second portion), 35a, 35b, first bearing retaining hole, 36a, 36b, second bearing retaining hole, 37a, 37b. ... Connection part, S ... Container

Claims (4)

A speed reducer for transmitting the output of the steering assist electric motor to the steering mechanism;
A housing that divides a storage chamber for storing the speed reducer,
The speed reducer includes a small-diameter gear supported by a housing via a first bearing, and a large-diameter gear supported by the housing via a second bearing and made of metal that meshes with the small-diameter gear.
The housing includes a main housing constituted by a metal member, and a sub-housing including resin or rubber supported by the main housing,
The main housing includes a first part that supports the first bearing, a second part that supports the second bearing, and a connecting part that connects the first part and the second part,
An electric power steering apparatus, wherein a part of the storage chamber is partitioned only by a sub-housing.   2. The electric power steering apparatus according to claim 1, wherein the metal constituting the large-diameter gear and the metal member have the same linear expansion coefficient.   3. The electric power steering apparatus according to claim 2, wherein the metal and the metal member constituting the large-diameter gear are made of a material containing iron. In Claims 1-3, the reduction gear includes a parallel shaft gear mechanism,
The first portion of the main housing includes a first bearing holding hole that holds a first bearing, and the second portion of the main housing includes a second bearing holding hole that holds a second bearing. An electric power steering device comprising:

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