JP2009248724A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of maintaining lubrication property over a long period of time without deteriorating startability by a grease in chilling time. <P>SOLUTION: The electric power steering device 1 performs turning of a vehicle by driving an electric motor M according to steering input and transmitting drive force of the electric motor M to a steering system through a worm gear 61 and a worm wheel 62. The worm gear 61 or the worm wheel 62 is coated with the grease G. On an axial lower end part of the worm wheel 62, a grease returning mechanism 7 having a meshing part 73 meshing with the worm gear 61 at an outer diameter side of the worm wheel 62 is provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus using an electric motor as a drive source.

  Conventionally, as a power steering device for reducing the steering force of a steering wheel, an electric power steering device using an electric motor as a power source has been used (see, for example, Patent Document 1). In general, an electric power steering device assists a driver's steering operation by boosting the rotational torque of an electric motor by a speed reduction mechanism composed of a worm gear and a worm wheel and applying it to a rack shaft via a rack and pinion mechanism. is there.

FIG. 11 is a schematic view showing a speed reduction mechanism in which a conventional electric power steering apparatus is installed.
As shown in FIG. 11, the reduction mechanism 200 of the conventional electric power steering apparatus 100 includes a worm reduction mechanism including a worm gear 300 installed on a rotor shaft of an electric motor (not shown) and a worm wheel 400. It is used.
In recent years, the speed reduction mechanism 200 of the electric power steering apparatus 100 has been increasingly used as a worm speed reduction mechanism that can be expected to reduce the number of parts and reduce the size from the viewpoint of cost and mountability on a vehicle.

  In addition, since the electric power steering apparatus 100 has an effect of improving the fuel efficiency, the number of applicable vehicles has been expanded, and it is necessary to cope with higher output. For this reason, the gear ratio of the speed reduction mechanism 200 tends to increase. Since the worm speed reduction mechanism is a slip transmission, it is important to reduce wear and heat generated by the lubricant.

  The lubricant includes oil and grease 500. Oil is superior to grease 500 in terms of lubrication performance and cooling performance. In the electric power steering apparatus 100, a worm reduction mechanism and a rack and pinion mechanism are arranged in the same space of the gear housing. For this reason, it is necessary to select and use oil suitable for both the worm speed reduction mechanism and the rack and pinion mechanism.

  However, in the worm reduction mechanism, a metal worm gear and a resin worm wheel are used in order to reduce rattling noise (tooth noise). In the rack and pinion mechanism, in order to withstand a high load, both the rack and the pinion are made of metal. Thus, since the gear material of the worm reduction mechanism and the rack and pinion mechanism are different from each other, it is difficult to select oil suitable for both.

  For this reason, it is also conceivable to use a suitable oil for the space in the gear housing, separating the worm speed reduction mechanism and the rack and pinion mechanism. However, in this method, in order to prevent two types of oil from being mixed, it is necessary to completely separate both installation spaces with an oil seal or the like. New issues such as deterioration will occur. Therefore, grease 500 is used for lubrication of the worm reduction mechanism.

  Since the grease 500 has high viscosity, it easily adheres to the tooth surface of the worm gear 300. However, as shown in FIG. 11, the grease 500 has poor anti-fluidity, and even if a large amount of grease 500 is applied to the tooth surface, both ends of the worm gear 300 in the axial direction are engaged due to the engagement of the worm gear 300 and the worm wheel 400. And the worm wheel 400 are pushed out to both ends of the tooth trace direction.

  For this reason, the grease 500 that contributes to the lubrication of the worm gear 300 and the worm wheel 400 is a small amount of grease 500 remaining on the tooth surface with which the gear meshes. The grease 500 pushed out from the meshing region S where the worm gear 300 and the worm wheel 400 mesh with each other remains in a state of flowing away from the meshing region S, and the tooth surface where the worm gear 300 and the worm wheel 400 mesh. It will never return again. The amount of the grease 500 remaining on the tooth surface of the meshing area S also decreases with the passage of time. When the grease 500 decreases, the lubricity deteriorates, heat generation increases, and further, the grease 500 decreases and deteriorates, and the wear of the worm wheel 400 increases rapidly.

As devices that have been invented to solve such problems, there are known electric power steering devices disclosed in Patent Documents 2 and 3.
The electric power steering device of Patent Document 2 is provided with a surrounding portion surrounding the worm wheel in the housing and gradually reduces the surrounding portion along the rotation direction of the worm wheel in order to push the grease back into the tooth groove of the worm wheel. An inclined part is provided. By forming in this way, the grease pushed out in the direction of the tooth trace of the worm wheel is again drawn into the tooth groove of the worm wheel by the inclined portion, so that the lubrication is maintained.

The electric power steering device of Patent Document 3 flows out from both ends of the worm wheel in the tooth trace direction by screwing a large-diameter disk protruding outward from the tooth tip of the worm wheel to the cylindrical end surface of the worm wheel. To reduce the grease to be.
Japanese Patent No. 3888607 JP 2005-69476 A JP 2007-303487 A

  In the electric power steering apparatus described in Patent Document 1, the surrounding portion is installed so as to be swingable by a predetermined range with respect to the gear housing. However, when the accumulated grease exceeds a predetermined range, it cannot be avoided that the grease becomes a resistance of rotation in which the worm wheel and the surrounding portion rotate relatively. The grease resistance becomes significant in a low temperature environment where the viscosity of the grease increases. For this reason, the viscosity of the grease increases in cold regions, and there is a problem that the steering becomes heavy for a while after the vehicle is started until the temperature of the meshing portion between the worm gear and the worm wheel rises. It was.

  In the electric power steering device described in Patent Document 2, since the amount of grease pushed back into the tooth space of the worm wheel due to the viscosity of the grease is small, the cylindrical end surface of the surrounding portion that faces the cylindrical end surface of the worm wheel from the inclined portion More grease accumulates between the two. For this reason, since the cylindrical end surface of the worm wheel and the cylindrical end surface of the surrounding portion rotate relatively, the accumulated grease serves as a resistance to relative rotation. As a result, there is a problem that steering at the beginning of turning of the steering wheel having a small assist torque becomes heavy.

The electric power steering device described in Patent Document 3 can maintain the lubrication for a long period of time because the grease that is prevented from flowing out from the tooth trace direction of the worm wheel is pushed out and reduced in the tooth profile direction of the worm wheel. There was a problem that it was not possible.
The large-diameter disk is screwed to the worm wheel only for the purpose of maintaining grease lubrication. For this reason, the number of parts and the number of assembly steps are large, and there is a problem that the assemblability (workability of assembling work) is deteriorated. Moreover, since the screw is used, there is a possibility that the steering is locked due to the biting caused by the screw dropping.

  Therefore, the present invention was devised to solve the above-described problems, and provides an electric power steering device that can maintain lubricity for a long period of time without deteriorating startability by grease when cold. The task is to do.

  In order to solve the above problem, the electric power steering apparatus according to claim 1 drives an electric motor in response to a steering input, and transmits the driving force of the electric motor to a steering system via a worm gear and a worm wheel. An electric power steering device that steers the vehicle by applying grease to the worm gear or the worm wheel, and having an outer diameter side from the worm wheel at a lower end portion in an axial direction of the worm wheel. And a grease return mechanism having a meshing portion meshing with the worm gear.

  According to such a configuration, the grease return mechanism can be suppressed from being pushed out toward the tooth trace of the worm wheel by being installed at the lower end portion in the axial direction of the worm wheel. Furthermore, the grease accumulated at both ends of the worm gear can be scraped to the meshing area where the worm wheel meshes with the worm wheel at the center of the worm gear. For this reason, when the worm gear meshes with the worm wheel, the grease pushed out at both ends of the worm gear can be circulated to the central portion (engagement region) of the worm gear. As a result, the grease return mechanism can maintain the lubricity over a long period of time by suppressing the decrease in grease by the meshing portion. Further, since the grease return mechanism rotates integrally with the worm wheel, it is possible to suppress an increase in the steering force due to the viscosity of the grease becoming hard at the start in a cold region.

  The invention according to claim 2 is the electric power steering apparatus according to claim 1, wherein a part of the meshing portion arranged on the inner diameter side of the worm wheel is located on the outer diameter side of the worm wheel. It is characterized in that it is set larger in the axial direction than the arranged part.

  According to this configuration, the engagement portion is configured such that a part of the worm wheel disposed on the inner diameter side of the worm wheel is set larger in the axial direction than a portion disposed on the outer diameter side of the worm wheel, so that the grease is And flow out of the speed reduction mechanism composed of the worm wheel.

  A third aspect of the present invention is the electric power steering apparatus according to the first aspect, wherein the grease return mechanism includes a grease reservoir that suppresses the grease from moving in the outer diameter direction of the worm wheel. It is characterized by having.

  According to this configuration, the grease return mechanism has the grease reservoir that suppresses the grease from moving in the outer diameter direction of the worm wheel, thereby suppressing the decrease in the grease and maintaining the lubricity for a long period of time. be able to.

  According to the electric power steering device of the present invention, the lubricity can be maintained over a long period of time without deteriorating the startability due to the hardening of the grease during cold weather.

Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram showing an electric power steering apparatus according to an embodiment of the present invention.

≪Configuration of electric power steering device≫
As shown in FIG. 1, the electric power steering apparatus 1 drives an electric motor M in accordance with a steering input, and transmits the power of the electric motor M to a steering system via a speed reduction mechanism 6, thereby turning the vehicle. It is a device that performs assist. The electric power steering apparatus 1 includes a steering shaft 3 coupled to the steering wheel 2, a steering torque sensor 4 that detects a steering torque acting on the steering shaft 3, a vehicle speed sensor 5 that detects a vehicle speed, and a speed reduction mechanism 6. An electric motor M for applying a steering assist force to the steering shaft 3, a drive control unit (ECU) 8 for controlling the driving of the electric motor M, and a rack shaft 10 connected via a rack and pinion mechanism 9. ing. Steering wheels (front wheels) 12 are connected to both ends of the rack shaft 10 (in FIG. 1, one side of the rack shaft 10 is not shown) via tie rods 11 and the like.

≪Steering shaft≫
The steering shaft 3 is a shaft that rotates together with the rotation operation of the steering wheel 2. The steering shaft 3 is integrally provided with a worm wheel 62 of the speed reduction mechanism 6 and a pinion 91 of the rack and pinion mechanism 9.

  FIG. 2 is a cross-sectional view showing a speed reduction mechanism and a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention. 3A and 3B are views showing a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention. FIG. 3A is an enlarged cross-sectional view of the main part, FIG. 3B is an enlarged perspective view of the main part, and FIG. FIG. FIG. 4 is a view showing a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, and (a) is an enlarged plan view of a main part showing a state when the worm wheel is rotated in the right direction. ) Is an enlarged cross-sectional view of a main part showing a state when the worm wheel is rotated rightward. FIG. 5 is a view showing a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, and (a) is an enlarged plan view of a main part showing a state when the worm wheel is rotated leftward. ) Is an enlarged cross-sectional view of a main part showing a state when the worm wheel is rotated leftward.

≪Electric motor configuration≫
As shown in FIG. 1, the electric motor M is composed of, for example, a brushless DC motor provided with a resolver (not shown) for detecting the rotation angle of the rotor, and houses, for example, the speed reduction mechanism 6 and the rack and pinion mechanism 9. The gear housing 13 (see FIG. 2) is housed. As shown in FIG. 2, the rotor shaft (not shown) that rotates integrally with the rotor of the electric motor M is provided with a worm gear shaft 61a via an elastic body such as rubber or a coupling (not shown) such as serration. The rotation and torque of the electric motor M are transmitted to the worm gear 61 by being connected.

≪Deceleration mechanism configuration≫
The speed reduction mechanism 6 shown in FIG. 2 has a function of boosting the rotational torque of the electric motor M and transmitting it to the steering shaft 3, and is composed of a speed reduction gear mechanism. The speed reduction mechanism 6 includes, for example, a worm gear 61 that is connected to the rotor shaft (not shown) of the electric motor M and rotates therewith and a worm wheel 62 provided on the steering shaft 3 to engage the gear speed reduction mechanism. It is composed. The deceleration mechanism 6 is provided with a grease return mechanism 7.

<Configuration of worm gear>
As shown in FIG. 2, the worm gear 61 is made of, for example, a single thread and includes a worm gear shaft 61a and a tooth profile portion 61b integrally formed with the worm gear shaft 61a. The worm gear 61 is rotatably supported by bearings (not shown) made of ball bearings or the like installed at both ends of the worm gear shaft 61a, and the same as the rotor shaft of the electric motor M when the electric motor M rotates. It is designed to rotate. Grease G (see FIGS. 4 and 5) is applied to the worm gear 61 and the worm wheel 62.

<Configuration of worm wheel>
A worm wheel 62 shown in FIG. 2 is a gear for decelerating and transmitting the rotation of the worm gear 61 to the steering shaft 3. In the case of a so-called column type electric power steering apparatus 1 as shown in FIG. 1, the worm wheel 62 is integrally provided on the steering shaft 3. The steering shaft 3 is supported by the gear housing 13 with bearings 31 formed of bearings and the like installed at a plurality of locations in the gear housing 13 interposed therebetween. A grease return mechanism 7 to be described later is provided at a lower end portion 62 a in the axial direction of the worm wheel 62.
In the case of a so-called pinion type electric power steering device, the worm wheel 62 is integrally provided on the pinion shaft.

≪Configuration of grease return mechanism≫
As shown in FIG. 3 (a), the grease return mechanism 7 has grease G applied to the tooth profile portions 61b and 62b and the tooth bottoms 61c and 62c in which the worm gear 61 and the worm wheel 62 are engaged with each other (FIG. 4 and FIG. 5) is to prevent the worm gear 61 from flowing toward both ends, and to store the grease G (see FIGS. 4 and 5) in the mesh region S where the worm gear 61 meshes with the worm wheel 62. is there. The grease return mechanism 7 is mainly configured by a grease holding plate 71 installed at the lower end 62 a of the worm wheel 62.

<Configuration of grease holding plate>
As shown in FIG. 3 (a), the grease holding plate 71 maintains the grease G (see FIGS. 4 and 5) applied to the worm gear 61 and the worm wheel 62 over a long period of time. It is a member for improving durability. The grease holding plate 71 includes a holding plate main body 72, a meshing portion 73, and a grease reservoir 74. The holding plate main body 72, the meshing portion 73, and the grease reservoir 74 are integrally formed of, for example, a synthetic resin. The grease holding plate 71 is made of a plate-shaped member having an outer diameter larger than the tooth tip of the worm wheel 62.

<Configuration of main body of holding plate>
The holding plate main body 72 is formed of a substantially annular plate member having a through hole 72a through which the steering shaft 3 is inserted at the center. The holding plate main body 72 has no gap on the lower surface of the worm wheel 62 due to the screw N (see FIG. 2), or the grease G (see FIGS. 4 and 5) cannot enter between the grease holding plate 71 and the worm wheel 62. It is fixed in a state where a gap of a certain degree is interposed. A bent portion 72 b that is bent upward is formed on the outer periphery of the holding plate main body 72. From the inner wall of the bent portion 72b toward the inner side (axial direction), the rib 73a and the meshing portion 73 are continuously provided at an interval (see FIG. 3C) that matches the pitch of the worm gear 61 and the worm wheel 62. Yes.
The holding plate main body 72 may be bonded to the lower surface of the worm wheel 62 with an adhesive, or may be integrally formed on the lower surface of the worm wheel 62.

<Configuration of meshing part>
The meshing portion 73 is a portion that meshes with the worm gear 61 on the outer diameter side (radially outer side) from the worm wheel 62. The meshing portion 73 protrudes upward from the axial lower end 62a of the tooth tip of the worm wheel 62 on the upper surface of the holding plate main body 72 and is in the vicinity of the worm gear shaft 61a (tooth bottom 61c) of the worm gear 61. It is extended to. Part of the meshing portion 73 disposed on the inner diameter side (worm wheel 62 side) of the worm wheel 62 protrudes larger in the axial direction than the reinforcing rib 73a disposed on the outer diameter side of the worm wheel 62, and It is set so as to mesh with the tooth profile portion 61 b of the worm gear 61. The number of the ribs 73a and the meshing portions 73 is the same as the number of teeth of the worm wheel 62, for example.
Note that the number of ribs 73a and meshing portions 73 may be set at intervals of multiples of the pitch as long as they are formed in accordance with the pitch between worm gear 61 and worm wheel 62.

<Configuration of grease reservoir>
As shown in FIG. 3A, the grease reservoir 74 is a part for suppressing the grease G (see FIGS. 4 and 5) from flowing out in the outer diameter direction of the worm wheel 62. The grease reservoir 74 is disposed on the holding plate main body 72 between a wall-shaped bent portion 72b formed on the periphery of the holding plate main body 72 and a tooth bottom 62c of the worm wheel 62, and between them It is provided to store G. That is, the grease reservoir 74 suppresses the grease G from flowing radially outward by the bent portion 72b, and suppresses the grease G from flowing radially inward by the tooth bottom 62c of the worm wheel 62. ing.

≪Grease composition≫
The grease G is made of a lubricant having a high viscosity so as not to flow down from the tooth surfaces of the applied worm gear 61 and worm wheel 62. The viscosity, components, and the like of the grease G are not particularly limited, and may be a commonly used grease G or a viscous fluid such as a highly viscous hydraulic oil. The grease G may be a lubricant that is not called grease.

≪Action≫
Next, the operation of the electric power steering apparatus 1 according to the embodiment of the present invention will be described with reference to FIGS.
In the electric power steering apparatus 1 shown in FIG. 1, when the driver steers the steering wheel 2, the rack shaft 10 linearly reciprocates via the rack and pinion mechanism 9 by the steering torque applied to the steering shaft 3, and the tie rod 11. The steered wheels 12 are steered through the above.

  At this time, the drive control unit (ECU) 8 sets a target current value to flow to the electric motor M based on the steering torque signal input from the steering torque sensor 4 and the vehicle speed signal input from the vehicle speed sensor 5, The electric motor M is driven by current feedback control so that the deviation between the target current value and a motor current value input from a motor current sensor (not shown) becomes zero. As a result, the electric motor M generates an appropriate steering assist force (assist force), and this steering assist force is decelerated and rotated by the worm gear 61 and the worm wheel 62 to be applied to the steering shaft 3. The steering force during the steering operation can be reduced.

Next, the operation of the grease return mechanism 7 of the electric power steering apparatus 1 according to the embodiment of the present invention will be described mainly with reference to FIGS.
FIG. 4 is a view showing a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, and (a) is an enlarged plan view of a main part showing a state when the worm wheel is rotated in the right direction. ) Is an enlarged cross-sectional view of a main part showing a state when the worm wheel is rotated rightward. FIG. 5 is a view showing a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, and (a) is an enlarged plan view of a main part showing a state when the worm wheel is rotated leftward. ) Is an enlarged cross-sectional view of a main part showing a state when the worm wheel is rotated leftward.

First, the movement when the grease G is scraped by the grease return mechanism 7 will be described with reference to FIGS. 4 and 5.
As shown in FIGS. 4A and 4B, grease G is applied to a portion where the worm gear 61 and the worm wheel 62 are engaged with each other. For example, when the electric motor M (see FIG. 2) rotates in the right direction (arrow B direction), the worm gear 61 rotates in the same direction. The worm wheel 62 rotates to the right (arrow A direction) by one pitch when the worm gear 61 makes one rotation. The grease holding plate 71, the meshing portion 73, and the grease reservoir 74 of the grease return mechanism 7 rotate together with the worm wheel 62 in the right direction (arrow A direction).

  As shown in FIG. 4B, since the meshing portion 73 extends to the vicinity of the tooth bottom 61c of the worm gear 61, when the worm gear 61 rotates, the grease adhered to the tooth bottom 61c and the tooth profile portion 61b. Abuts on G.

  For this reason, as shown in FIG. 4A, the meshing portion 73 causes the grease G between the meshing tooth portions 61 b of the meshing worm gear 61 to flow in the right direction (arrow A direction) to rotate, thereby causing the worm gear 61 to move. The tooth profile portion 61b is scraped and collected at the central portion (engagement region S). The meshing part 73 can scrape and collect the grease G that has approached the one end part side of the worm gear 61 to the meshing area S of the worm gear 61 where the worm gear 61 and the worm wheel 62 are always meshed.

  Then, the steering wheel 2 (see FIG. 1) is operated in the opposite direction, and the electric motor M (see FIG. 2) rotates to the right (arrow D direction) as shown in FIGS. 5 (a) and 5 (b). Then, the worm gear 61 rotates in the same direction. The worm wheel 62 rotates leftward (arrow C direction) by one pitch when the worm gear 61 makes one rotation. The grease holding plate 71, the meshing portion 73, and the grease reservoir 74 of the grease return mechanism 7 rotate integrally with the worm wheel 62 in the left direction (arrow C direction).

As shown in FIG. 5 (b), when the worm gear 61 rotates, the grease G attached to the tooth bottom 61c and the tooth profile portion 61b abuts against the opposite surface to the meshing portion 73.
Therefore, as shown in FIG. 5A, the meshing portion 73 causes the grease G between the tooth shape portions 61 b of the worm gear 61 to flow in the left direction (arrow C direction) to rotate, and the tooth shape portion 61 b of the worm gear 61. Scraping to the center of the whole. The meshing portion 73 can scrape and accumulate the grease G that has been approaching the other end of the worm gear 61 in the meshing region S of the worm gear 61 where the worm gear 61 and the worm wheel 62 are constantly meshed.

  As described above, the grease return mechanism 7 always uses the worm gear 61 in which the worm gear 61 and the worm wheel 62 mesh with the grease G attached to the worm gear 61 as the worm gear 61 and the worm wheel 62 rotate. Squeezed into the meshing area S at the center of the. For this reason, since the grease G is collected at an optimum location where the worm gear 61 and the worm wheel 62 mesh with each other, the lubricity can be maintained over a long period of time.

Next, with reference to FIG. 6 and FIG. 7, it will be described that the grease G circulates in the meshing region S in which the worm gear 61 and the worm wheel 62 mesh.
FIG. 6 is a view showing a grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, wherein (a) is an enlarged plan view of a main part showing a state where the fitting portion scrapes the grease. ) Is an enlarged cross-sectional view of a main part showing a state in which the fitting portion rakes the grease to the meshing region and circulates it. FIG. 7 is a view showing the grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, and is an enlarged cross-sectional view of the main part showing the state of the grease accumulated in the grease reservoir.

As shown in FIGS. 6A and 6B, as described above, the grease G is scraped together at the central portion of the worm gear 61 by the meshing portion 73, but when the worm gear 61 and the worm wheel 62 mesh, It is pushed out to the end side. When the grease holding plate 71 rotates together with the worm wheel 62, the clearance L1 between the grease reservoir 74 and the tooth surface of the worm gear 61 gradually decreases to the clearance L2. In the meshing area S of the worm gear 61 with the worm wheel 62, the clearance L2 is minimized.
However, the grease G scrapes the grease G having the meshing portion 73 attached to the tooth surface of the worm gear 61 from the both end portions of the worm gear 61 to the meshing region S in the central portion, so that the grease G is worm gear 61 and the worm wheel. During the rotation of 62, it always works to re-supply.

  The grease return mechanism 7 maintains the lubricity of the grease G over a long period of time by circulating not only the outside of the worm wheel 62 in the tooth trace direction but also the grease G accumulated at both ends of the worm gear 61 to the meshing region S. Can do. Furthermore, as shown in FIG. 7, the grease G is accumulated in the grease reservoir 74 between the meshing portions 73, and the circulation for replenishing the meshing region S is made permanent. For this reason, since the grease G is adjusted so that an appropriate amount of grease G is always supplied without being excessively supplied to the meshing region S, resistance due to the grease G can be suppressed.

  The grease reservoir 74 is not collected by the meshing portion 73, but the grease G, whose temperature has been increased due to friction due to the operation of the worm gear 61 and the worm wheel 62 and whose viscosity has decreased, is caused by the centrifugal force accompanying the rotation of the worm gear 61. Outflow to the outside of the speed reduction mechanism 6 can be suppressed. The grease G whose outflow is suppressed is collected by the tooth tip of the worm gear 61 and accumulated in the grease reservoir 74 as shown in FIG. The grease reservoir 74 has a high sliding efficiency and can be lubricated by supplying grease G to the tooth tip of the worm gear 61 that needs the most lubrication, so that the lubrication efficiency is good.

≪First modification≫
The present invention is not limited to the above-described embodiment, and various modifications and changes can be made within the scope of the technical idea. The present invention extends to these modifications and changes. Of course.

Next, a first modification of the present invention will be described with reference to FIGS.
FIG. 8 is a view showing a first modification of the grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, wherein (a) is an enlarged cross-sectional view of the main part, and (b) is an enlarged perspective view of the main part. (C) is an enlarged plan view of a main part.

For example, as shown in FIGS. 8A to 8C, the grease holding plate 71A of the grease return mechanism 7A is formed to have a thickness T1 at the base end portion of the meshing portion 73A, and the volume of the grease reservoir portion 74A is increased. It may be small.
Thus, the meshing part 73 can improve rigidity and durability by forming the tip part in a thin plate shape and forming the base end part thickly.

Further, as shown in FIGS. 8B and 8C, the base end portion of the meshing portion 73A tapers outward from the axial center side in a plan view like the tooth profile of the worm gear 61 and the worm wheel 62. You may form so that it may become a shape.
If the meshing portion 73A is formed in this way, the meshing portion 73A can mesh with the tooth surface of the worm gear 61 without rattling. Even if the meshing portion 73A is formed in this way, the function of scraping the grease G (not shown) to the meshing region S where the worm gear 61 and the worm wheel 62 mesh with each other as shown in FIG.

≪Second modification≫
Next, a second modification of the present invention will be described with reference to FIGS.
FIG. 9 is a view showing a second modification of the grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention, wherein (a) is an enlarged cross-sectional view of the main part, and (b) is an enlarged perspective view of the main part. (C) is an enlarged plan view of a main part.

  Furthermore, as shown in FIGS. 9A to 9C, the grease holding plate 71B of the grease return mechanism 7B may be formed to have a large thickness T2 at the tip end portion of the meshing portion 73B. In this case, the upper end portion of the meshing portion 73B is formed in a trapezoidal shape so as to be tapered from the axial center side toward the outer peripheral side in plan view so as to follow the tooth shapes of the worm gear 61 and the worm wheel 62. The upper end portion of the rib 73Ba is formed so as to incline from the end portion of the front end surface of the meshing portion 73B to the bent portion 73Bb on the outer peripheral edge.

  If the meshing part 73B and the rib 73Ba are formed in this way, the meshing part 73B can mesh with the tooth surface of the worm gear 61 without rattling, and the strength and rigidity can be improved.

<< Third Modification >>
Next, a third modification of the present invention will be described with reference to FIG.
FIG. 10 is a cross-sectional view showing a third modification of the grease return mechanism of the electric power steering apparatus according to the embodiment of the present invention.

In the above-described embodiment, the entire grease holding plate 71 (see FIGS. 2 and 3) is formed of resin. However, the grease holding plate 71C of the grease return mechanism 7C is made of metal as shown in FIG. An annular holding plate main body 72C and a resin grease reservoir 74C formed around the holding plate main body 72C may be integrally formed.
In this case, the grease holding plate 71C is fixed to the lower end 62a of the worm wheel 62 by screwing or the like. The meshing portion 73C is integrally formed with the grease reservoir 74C by resin.
Further, the grease holding plate 71 may be provided with a gear mechanism that absorbs backlash between the worm gear 61 and the worm wheel 61.

  The present invention also relates to a structure (steer-by-wire) in which the steering wheel 2 and the steered wheel of the steering system are mechanically separated and the electric motor M generates all of the steered force for the steered wheel. Any device using the worm gear 61 and the worm wheel 62 can be applied.

1 is a schematic configuration diagram illustrating an electric power steering apparatus according to an embodiment of the present invention. It is sectional drawing which shows the deceleration mechanism and grease return mechanism of the electric power steering apparatus which concern on embodiment of this invention. It is a figure which shows the grease return mechanism of the electric power steering device which concerns on embodiment of this invention, (a) is a principal part expanded sectional view, (b) is a principal part enlarged perspective view, (c) is a principal part enlarged plan view. It is. It is a figure which shows the grease return mechanism of the electric power steering device which concerns on embodiment of this invention, (a) is a principal part enlarged plan view which shows a state when a worm wheel rotates rightward, (b) is a worm wheel. It is a principal part expanded sectional view which shows a state when is rotated rightward. It is a figure which shows the grease return mechanism of the electric power steering apparatus which concerns on embodiment of this invention, (a) is a principal part enlarged plan view which shows a state when a worm wheel rotates to the left direction, (b) is a worm wheel. It is a principal part expanded sectional view which shows a state when is rotated to the left direction. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the grease return mechanism of the electric power steering apparatus which concerns on embodiment of this invention, (a) is a principal part enlarged plan view which shows the state in which the fitting part is scraping grease, (b) is a fitting It is a principal part expanded sectional view which shows the state which the part scrapes and circulates grease to a meshing area | region. It is a figure which shows the grease return mechanism of the electric power steering device which concerns on embodiment of this invention, and is a principal part expanded sectional view which shows the state of the grease collected in the grease storage part. It is a figure which shows the 1st modification of the grease return mechanism of the electric power steering apparatus which concerns on embodiment of this invention, (a) is a principal part expanded sectional view, (b) is a principal part expanded perspective view, (c) is a figure. It is a principal part enlarged plan view. It is a figure which shows the 2nd modification of the grease return mechanism of the electric power steering apparatus which concerns on embodiment of this invention, (a) is a principal part expanded sectional view, (b) is a principal part enlarged perspective view, (c) is a figure. It is a principal part enlarged plan view. It is sectional drawing which shows the 3rd modification of the grease return mechanism of the electric power steering apparatus which concerns on embodiment of this invention. It is the schematic which shows the deceleration mechanism in which the conventional electric power steering apparatus is installed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering wheel 3 Steering shaft 6 Deceleration mechanism 7, 7A, 7B, 7C Grease return mechanism 61 Worm gear 62 Worm wheel 62a Lower end part 71, 71A, 71B, 71C Grease holding plate 73, 73A, 73B, 73C Engagement 74, 74A, 74C Grease reservoir G Grease M Electric motor

Claims (3)

An electric power steering device for driving a vehicle by driving an electric motor in accordance with a steering input and transmitting a driving force of the electric motor to a steering system via a worm gear and a worm wheel,
Grease is applied to the worm gear or the worm wheel,
An electric power steering apparatus comprising a grease return mechanism having a meshing portion that meshes with the worm gear on an outer diameter side of the worm wheel at a lower end portion in an axial direction of the worm wheel.   The meshing portion is configured such that a part of the worm wheel disposed on the inner diameter side of the worm wheel is set to be larger in the axial direction than a portion disposed on the outer diameter side of the worm wheel. The electric power steering apparatus as described.   2. The electric power steering apparatus according to claim 1, wherein the grease return mechanism includes a grease reservoir that suppresses movement of the grease in an outer diameter direction of the worm wheel.

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