JP2009057009A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of poor lubrication in a reduction gear of an electric power steering system. <P>SOLUTION: The electric power steering system 1 is composed of a reduction gear 24 for transmitting the rotation of an electric motor 23 to a steering mechanism 11, a housing 26 for accommodating the reduction gear 24 and a lubricant supply device 28 for supplying a lubricant 27 formed of grease to the reduction gear 24. The lubricant supply device 28 includes a cylinder 46, a piston 47 capable of advancing and retracting in the cylinder 46 and a spring member 49 functioning as an urging member for urging the piston 47. The piston 47 partitions the inside of the cylinder 46 into a lubricant housing chamber 44 and a biasing member housing chamber 55. The piston 47 and the spring member 49 taken as a pressurization-mechanism 48 pressurize the lubricant 27 in the lubricant housing chamber 44. The pressurized lubricant 27 is supplied to a meshing part 40 between a pair of gears 31, 32 meshing with each other in the housing 26 through a supply path 45 of the lubricant housing chamber 44. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

The electric power steering apparatus includes an electric motor for obtaining a steering assist force and a speed reducer that transmits the rotation of the electric motor to a steering mechanism. The speed reducer has a plurality of gears. Grease is applied to the tooth surfaces of these gears when the speed reducer is assembled (see, for example, Patent Document 1).
JP-A-2005-132159

However, poor lubrication may occur within a short period after assembly. Specifically, in order to cope with the high output of the electric power steering device, it is considered to use a worm wheel having a metal tooth portion. During the initial running-in operation (familiar operation) of this worm wheel, poor lubrication occurred. As a result, the amount of wear on the tooth surface was excessive.
Therefore, an object of the present invention is to provide an electric power steering device that can suppress the occurrence of poor lubrication.

  The electric power steering device (1) of the present invention includes a transmission (24) for transmitting the rotation of the electric motor (23) to the steering mechanism (11), a housing (26) for housing the transmission, and a transmission. And a lubricant supply device (28) for supplying a lubricant (27) to the device, the lubricant supply device containing a lubricant in communication with the inside of the housing (39) via a supply passage (45). It includes a chamber (44) and a pressurizing mechanism (48) capable of pressurizing the lubricant in the lubricant accommodating chamber. According to the present invention, the lubricant in the lubricant accommodating chamber pressurized by the pressurizing mechanism is supplied to the transmission device in the housing through the supply path. Therefore, occurrence of poor lubrication is suppressed.

Further, in the present invention, the pressurizing mechanism includes a piston (47) capable of partitioning the inside of the cylinder (46) into the lubricant containing chamber and the biasing member containing chamber (55) and advancing and retracting the inside of the cylinder, and the biasing device. And an urging member (49) that is accommodated in the member accommodating chamber and urges the piston. In this case, the supply of the lubricant can be realized by a practical configuration.
Further, in the present invention, a cylindrical protrusion (60) for defining the supply path is formed in the end wall (51) of the cylinder, and the cylindrical protrusion is formed in the fixing hole (61) provided in the housing. There are cases where it is inserted and fixed. In this case, the lubricant supply device and the housing can be easily connected with a simple structure.

In the present invention, the transmission device may include a pair of gears (31, 32) meshing with each other, and the outlet (62) of the supply path may face the meshing portion (40) of the pair of gears. is there. In this case, the lubricant is reliably supplied to the meshing portion of the pair of gears of the transmission.
In addition, although the alphanumeric characters in the parentheses indicate reference signs of corresponding components in the embodiments described later, the scope of the claims is not limited by these reference signs.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention.
Referring to FIG. 1, an electric power steering system (EPS) 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, and a first universal joint 4 on the steering shaft 3. An intermediate shaft 5 connected to the intermediate shaft 5, a pinion shaft 7 connected to the intermediate shaft 5 via a second universal joint 6, and rack teeth 9 that mesh with pinion teeth 8 provided near the end of the pinion shaft 7. And a rack bar 10 as a turning shaft extending in the left-right direction of the automobile.

  The pinion shaft 7 and the rack bar 10 constitute a steering mechanism 11 composed of a rack and pinion mechanism. The rack bar 10 is supported in a rack housing 13 fixed to the vehicle body 12 so as to be linearly reciprocable via a plurality of bearings (not shown). A pair of tie rods 14 are coupled to the rack bar 10. Each tie rod 14 is connected to a corresponding steered wheel 16 via a corresponding knuckle arm 15.

When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted by the pinion teeth 8 and the rack teeth 9 into a linear motion of the rack bar 10 along the left-right direction of the automobile. Thereby, the turning of the steered wheels 16 is achieved.
With reference to FIG. 1, the steering shaft 3 is divided into an input shaft 17 connected to the steering member 2 and an output shaft 18 connected to the pinion shaft 7. The input shaft 17 and the output shaft 18 are connected to each other on the same axis via a torsion bar 19. When steering torque is input to the input shaft 17, the torsion bar 19 is elastically torsionally deformed, whereby the input shaft 17 and the output shaft 18 are rotated relative to each other.

  A torque sensor 20 that detects a steering torque based on the amount of relative rotational displacement between the input shaft 17 and the output shaft 18 via the torsion bar 19 is provided. A vehicle speed sensor 21 for detecting the vehicle speed is also provided. An ECU (Electronic Control Unit) 22 is provided as a control device. An electric motor 23 for generating a steering assist force and a speed reducer 24 for reducing the output rotation of the electric motor 23 are provided. The speed reducer 24 functions as a transmission device that transmits the output rotation of the electric motor 23 to the steering mechanism 11.

  Detection signals from the torque sensor 20 and the vehicle speed sensor 21 are input to the ECU 22. The ECU 22 controls the steering assisting electric motor 23 based on the torque detection result, the vehicle speed detection result, and the like. The output rotation of the electric motor 23 is decelerated via the speed reducer 24 and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 10 to assist steering.

Referring to FIG. 1, the electric power steering apparatus 1 has a steering column 25 that rotatably supports the steering shaft 3. The steering column 25 has a housing 26 that constitutes a part of the steering column 25. A torque sensor 20, an electric motor 23, and a speed reducer 24 are disposed in the housing 26.
In the present embodiment, the electric power steering device 1 includes a lubricant supply device 28 for supplying the lubricant 27 to the reduction gear 24. The lubricant supply device 28 is disposed outside the housing 26.

The housing 26 is made of a metal, for example, an aluminum alloy. Specifically, the housing 26 includes a plurality of members and has a container shape. A cavity 29 is defined inside the housing 26. A bearing (not shown) that supports the input shaft 17 and the output shaft 18 is held in the cavity 29, and the speed reducer 24 is accommodated.
The speed reducer 24 includes a worm shaft 31 as a drive gear and a worm wheel 32 as a driven gear that meshes with the worm shaft 31. The worm wheel 32 is fixed to the output shaft 18. The output shaft 18 is rotatably supported by the housing 26 via bearings (not shown) on both sides of the worm wheel 32.

FIG. 2 is a cross-sectional view of the electric power steering apparatus of FIG. 1, and mainly illustrates the speed reducer 24, the lubricant supply device 28, and the peripheral portion thereof. 3 is a cross-sectional view taken along the line III-III in FIG.
Referring to FIGS. 2 and 3, the worm wheel 32 rotates together with the intermediate portion of the output shaft 18 of the steering shaft 3 and is connected so as not to move in the axial direction. The worm wheel 32 includes a tooth portion 33 provided on the outer periphery of the worm wheel 32 and a boss portion 34 provided at a central portion in the radial direction of the worm wheel 32. The worm wheel 32 is formed of a metal member, for example, steel. The tooth portion 33 and the boss portion 34 are coupled so as to rotate together, and specifically, are integrally formed by a single member. The boss portion 34 is coupled to the output shaft 18 of the steering shaft 3 so as to rotate together.

  The worm shaft 31 has first and second end portions 35 and 36 that are separated from each other in the axial length direction, and has a tooth portion 38 at an intermediate portion 37 between the first and second end portions 35 and 36. The first end 35 of the worm shaft 31 and the output shaft of the electric motor 23 are connected coaxially via a cylindrical joint so that power can be transmitted. The first and second end portions 35 and 36 of the worm shaft 31 are rotatably supported by the housing 26 via corresponding bearings.

The worm shaft 31 is accommodated in an accommodation hole 39 formed in the housing 26. The accommodation hole 39 is a part of the cavity 29 described above. A region 41 in the accommodation hole 39 is provided with a tooth meshing portion 40 of the worm shaft 31 and the worm wheel 32 and filled with a lubricant 27 (not shown in FIG. 2).
Referring to FIG. 3, the lubricant supply device 28 includes a lubricant storage chamber 44 that stores the lubricant 27, and a supply path 45 that supplies the lubricant 27 from the lubricant storage chamber 44 to the inside of the housing 26. is doing. The lubricant supply device 28 includes a cylinder 46 and a piston 47 for partitioning the lubricant storage chamber 44. The inside of the lubricant storage chamber 44 communicates with the inside of the housing 26 via the supply path 45. The lubricant 27 is stored in the lubricant storage chamber 44.

  The lubricant supply device 28 has a pressurizing mechanism 48 that pressurizes the lubricant 27 in the lubricant accommodating chamber 44. The pressurizing mechanism 48 includes a piston 47 and a spring member 49 described later. The lubricant 27 pressurized by the pressurizing mechanism 48 moves from the lubricant accommodation chamber 44 to the inside of the housing 26, that is, the accommodation hole 39 of the cavity 29 through the supply path 45. Thereby, the lubricant 27 is supplied to the speed reducer 24.

  Specifically, the cylinder 46 includes a cylindrical cylinder tube 50 and first and second end walls 51 and 52. The first end wall 51 is formed integrally with one end portion of the cylinder tube 50 with respect to the direction S (also referred to as the axial direction S) in which the central axis of the cylinder 46 extends, thereby being fixed to the one end portion. Has been. The second end wall 52 is formed separately from the other end portion of the cylinder tube 50 in the axial direction S of the cylinder 46 and is fixed to the other end portion.

  The piston 47 has a cylindrical shape. The outer periphery of the piston 47 is fitted into the inner periphery of the cylinder tube 50 in a sealed state. Although not shown, for example, an O-ring as a sealing member may be accommodated in an accommodation groove formed on the outer periphery of the piston 47. The piston 47 is held so as to be movable along the axial direction S of the cylinder 46. The piston 47 moves from a first position with respect to the axial direction S of the cylinder 46 to a second position.

  The first position is a position where the piston 47 is relatively distant from the first end wall 51, for example, a position in the axial center of the cylinder tube 50. FIG. 3 shows the piston 47 in the first position. The second position is a position where the piston 47 is relatively close to the first end wall 51, for example, a position where the piston 47 and the first end wall 51 abut. Immediately after the electric power steering apparatus 1 is assembled, the piston 47 is positioned at the first position. In the following description, when not specifically described, the description will be made based on the case where the piston 47 is located at the first position.

Referring to FIG. 3, the piston 47 partitions the inside of the cylinder 46 into a lubricant storage chamber 44 and an urging member storage chamber 55.
The lubricant storage chamber 44 stores the lubricant 27. The lubricant 27 is preferably a grease having fluidity. When the piston 47 is in the first position, the lubricant storage chamber 44 can store a predetermined amount of the lubricant 27 that can prevent the occurrence of poor lubrication during the initial running-in operation. Further, the lubricant accommodating chamber 44 has a supply port 59 that communicates with the supply path 45. In the cross section orthogonal to the axial direction S, the cross sectional area of the supply port 59 is made smaller than the cross sectional area of the piston 47.

  The cylinder 46 and the housing 26 are connected to each other by a cylindrical protrusion 60. The cylindrical protrusion 60 extends from the first end wall 51 in the axial direction S, and is formed on the first end wall 51. A cylindrical protrusion 60 is inserted into a fixing hole 61 formed in the housing 26. The outer periphery of the cylindrical protrusion 60 is fitted in a sealed state to the inner periphery of the fixing hole 61 of the housing 26, and the cylindrical protrusion 60 is fixed to the housing 26 in this state. The cylindrical protrusion 60 defines a supply path 45 that communicates the inside of the lubricant accommodating chamber 44 with the inside of the housing 26. The supply path 45 is configured to pass the lubricant 27. The supply port 59 is provided at one end of the supply path 45. An outlet 62 is provided at the other end of the supply path 45. The outlet 62 of the supply passage 45 faces the meshing portion 40 of the worm shaft 31 and the worm wheel 32 inside the housing 26.

Referring to FIG. 3, the pressurizing mechanism 48 serves as the above-described piston 47 that can advance and retreat in the cylinder 46, and a biasing member that biases the piston 47 in the axial direction S (left side in FIG. 3) of the cylinder 46. And a spring member 49.
The spring member 49 is composed of a compression coil spring. The spring member 49 is accommodated in the biasing member accommodating chamber 55 in the cylinder 46 so that the axis of the compression coil spring coincides with the axial direction S of the cylinder 46. Regardless of where the piston 47 is positioned with respect to the axial direction S of the cylinder 46, the spring member 49 is compressed and elastically deformed in the axial direction S of the cylinder 46, so that it is not between the piston 47 and the second end wall 52. It is sandwiched between.

The spring member 49 always presses the piston 47 toward the first end wall 51 along the axial direction S of the cylinder 46. Along with this, the piston 47 presses the lubricant 27 in the lubricant accommodating chamber 44. As a result, the lubricant 27 is pressurized in the lubricant accommodating chamber 44, further pressurized in the supply path 45, and reliably supplied into the housing 26.
Referring to FIG. 3, immediately after the reduction gear 24 of the electric power steering apparatus 1 of this embodiment is assembled, the piston 47 of the lubricant supply device 28 is in the first position, and the lubricant storage chamber 44 is The lubricant 27 is filled inside, and the lubricant containing chamber 44 is filled with the lubricant 27. At the same time, a lubricant 27 is applied to the tooth surfaces of the worm shaft 31 and the worm wheel 32 of the speed reducer 24. The lubricant 27 is also filled in the region 41 around the meshing portion 40 of the worm shaft 31 and the worm wheel 32 in the housing 26 and in the vicinity of the outlet 62 of the supply path 45 of the lubricant supply device 28. . In this state, the lubricant 27 in the lubricant storage chamber 44 of the lubricant supply device 28 does not move into the housing 26 even if it is pressurized.

  FIG. 4 is a cross-sectional view of the same cross section as FIG. 3 and shows a state during initial break-in operation. FIG. 3 shows a state immediately after assembly. 3 and 4, in a state immediately after assembly, the tooth surfaces of worm shaft 31 and worm wheel 32 are usually in contact with each other at minute contact portions (for example, minute protrusions). In this state, the contact area between the tooth surfaces is small.

Therefore, before the speed reducer 24 is used by the user, an initial running-in operation of the speed reducer 24 is performed. In the initial running-in operation, the speed reducer 24 is operated under a predetermined condition. Thereby, the above-mentioned minute projections on the tooth surfaces of the worm shaft 31 and the worm wheel 32 are removed, and as a result, the contact area between the tooth surfaces is increased.
During the initial running-in operation, the surface pressure may increase excessively at the minute contact portion between the tooth surfaces. In such a case, the lubricant is pushed out from the tooth meshing portion 40, and accordingly, the lubricant 27 in the vicinity of the outlet 62 of the supply path 45 also moves. Along with this, the pressurized lubricant 27 in the lubricant accommodating chamber 44 moves to the inside of the housing 26 through the outlet 62 of the supply path 45. As a result, the lubricant 27 is supplied to the tooth meshing portion 40. Since the movement of the lubricant 27 is performed at small times as needed, the lubricant 27 is always supplied to the meshing portion 40. As a result, during the initial running-in operation, even if the surface pressure at the minute contact portion on the tooth surface increases, the occurrence of poor lubrication is prevented.

During the initial running-in operation, the piston 47 gradually moves from the first position toward the second position, and the lubricant 27 in the lubricant accommodating chamber 44 gradually decreases. When the piston 47 contacts the first end wall 51, the supply of the lubricant 27 by the lubricant supply device 28 is finished.
Further, when the initial running-in operation is completed, the contact area between the tooth surfaces is increased, so there is no possibility that the surface pressure at the contact portion of the tooth surfaces becomes excessive. As a result, there is no possibility that the oil film of the tooth surface will be cut off, so there is no problem even if the lubricant supply device 28 does not supply the lubricant 27.

  As described above with reference to FIG. 1, the electric power steering apparatus 1 of the present embodiment includes a reduction gear 24 as a transmission device for transmitting the rotation of the electric motor 23 to the steering mechanism 11, and the reduction gear. A housing 26 that accommodates 24 and a lubricant supply device 28 for supplying a lubricant 27 to the speed reducer 24 are provided. The lubricant supply device 28 includes a lubricant storage chamber 44 that communicates with the housing 26 via a supply path 45, and a pressurizing mechanism 48 that can pressurize the lubricant 27 in the lubricant storage chamber 44. It is characterized by.

  According to the present embodiment, the lubricant 27 in the lubricant storage chamber 44 pressurized by the pressurizing mechanism 48 is supplied to the speed reducer 24 in the housing 26 through the supply path 45. Therefore, occurrence of poor lubrication is suppressed. Therefore, for example, even if the lubricant is insufficient in the speed reducer 24 during the initial running-in operation, it is possible to prevent the occurrence of poor lubrication. As a result, the occurrence of tooth surface wear due to poor lubrication is suppressed. In addition, since the occurrence of tooth surface wear is suppressed, the friction is reduced in the normal operation of the speed reducer 24 of the electric power steering apparatus 1, so that the steering feeling is improved and the generation of abnormal noise is suppressed. Is done.

Further, in the present embodiment, the pressurizing mechanism 48 is configured such that the cylinder 46 is divided into the lubricant accommodating chamber 44 and the urging member accommodating chamber 55, and the piston 47 capable of moving forward and backward in the cylinder 46, and the urging member accommodating chamber. 55, and a spring member 49 as a biasing member that biases the piston 47. In this case, the supply of the lubricant 27 can be realized by a practical configuration.
With reference to FIG. 3, in the present embodiment, a cylindrical projection 60 is formed on the first end wall 51 of the cylinder 46 to partition the supply path 45 therein. This cylindrical protrusion 60 is inserted and fixed in a fixing hole 61 provided in the housing 26. In this case, the lubricant supply device 28 and the housing 26 can be easily connected with a simple structure. That is, the supply path 45 is realized by a simple structure of the cylindrical protrusion 60 formed on the first end wall 51 of the cylinder 46. Further, the cylinder 46 and the cylindrical protrusion 60 can be configured as an integral unit. In addition, the cylinder 46 is easily fixed to the housing 26 by inserting and fixing the cylindrical protrusion 60 into the fixing hole 61.

In the present embodiment, the speed reducer 24 as a transmission device includes a worm shaft 31 and a worm wheel 32 as a pair of gears that mesh with each other. The outlet 62 of the supply path 45 faces the meshing portion 40 of the pair of gears. In this case, the lubricant is reliably supplied to the meshing portion 40 of the pair of gears of the speed reducer 24.
With reference to FIG. 3, the speed reducer 24 of the present embodiment includes a worm shaft 31 and a worm wheel 32 as gears having metal teeth. Since the gear having the metal tooth portion is used to increase the output of the electric power steering apparatus 1, the surface pressure of the tooth surface tends to increase. When the surface pressure of the tooth surface increases, the lubricant is easily pushed out from the meshing portion 40 of the pair of gears. However, in this embodiment, the occurrence of poor lubrication is prevented by the lubricant supply device 28.

  Further, the speed reducer 24 of the present embodiment includes a worm shaft 31 and a worm wheel 32. Since the tooth surfaces of the worm shaft 31 and the worm wheel 32 slide with each other, the lubricant is easily pushed out from the meshing portion 40 of the worm shaft 31 and the worm wheel 32. As a result, poor lubrication is likely to occur. However, in this embodiment, the occurrence of poor lubrication is prevented by the lubricant supply device 28.

Further, the lubricant supply device 28 of the present embodiment supplies the lubricant 27 to the speed reducer 24 during the initial running-in operation. In the speed reducer 24 during the initial running-in operation, since the contact portion of the tooth surface is minute, lubrication failure tends to occur. However, in this embodiment, the occurrence of poor lubrication is prevented by the lubricant supply device 28.
Moreover, the following modifications can be considered about this embodiment. In the following description, the points different from the above-described embodiment will be mainly described.

  For example, although not shown, a spring member such as a coil spring or a disc spring may be used as the biasing member. Further, an elastic body may be used as the urging member. Examples of the elastic body include a rubber member that can be elastically deformed in addition to the above-described spring member. Further, a solenoid as an actuator may be used as the urging member. This solenoid has an iron core as a movable part and a coil for moving the iron core forward and backward. The iron core is connected to the piston. By energizing the coil, the iron core and the piston can be energized.

Further, at least a part of the container that partitions the lubricant storage chamber may be formed of an elastic film member such as a membrane that can pressurize the lubricant by its own elasticity. Thereby, the structure can be simplified.
In addition, although not shown, the lubricant supply device 28 of the above-described embodiment meshes with each other, a speed reducer having a worm shaft and a helical gear as a pair of gears meshed with each other, a speed reducer having a pair of spur gears meshed with each other, and the like. It can also be applied to a speed reducer having a pair of inclined gears. In addition, various changes can be made within the scope of the matters described in the claims.

It is a mimetic diagram of a schematic structure of an electric power steering device of one embodiment of the present invention. FIG. 2 is a cross-sectional view of the electric power steering device of FIG. 1, mainly illustrating a reduction gear, a lubricant supply device, and a peripheral portion thereof. It is sectional drawing of the III-III cross section of FIG. 2, and has shown the state immediately after an assembly. FIG. 4 illustrates a state during a break-in operation in the same cross section as FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 11 ... Steering mechanism, 23 ... Electric motor, 24 ... Reduction gear (transmission device), 26 ... Housing, 27 ... Lubricant, 28 ... Lubricant supply device, 31 ... Worm shaft (gear), 32 ... Worm wheel (gear), 39 ... Accommodating hole (inside housing), 40 ... Engagement part, 44 ... Lubricant accommodation chamber, 45 ... Supply path, 46 ... Cylinder, 47 ... Piston, 48 ... Pressure mechanism, 49 ... Spring member (biasing member), 51 ... first end wall (end wall), 55 ... biasing member accommodating chamber, 60 ... cylindrical protrusion, 61 ... fixing hole, 62 ... exit.

Claims (4)

A transmission device for transmitting the rotation of the electric motor to the steering mechanism;
A housing that houses the transmission,
A lubricant supply device for supplying a lubricant to the transmission device;
The lubricant supply device includes a lubricant storage chamber communicating with the housing through a supply path, and a pressurizing mechanism capable of pressurizing the lubricant in the lubricant storage chamber. apparatus.   2. The pressure mechanism according to claim 1, wherein the pressurizing mechanism partitions the inside of the cylinder into the lubricant accommodating chamber and the biasing member accommodating chamber, and a piston capable of advancing and retreating inside the cylinder, and energizing the piston accommodated in the biasing member accommodating chamber. And an urging member.   In Claim 2, The cylindrical projection which partitions the said supply path inside is formed in the end wall of the said cylinder, This cylindrical projection is inserted and fixed to the fixing hole provided in the housing. An electric power steering device.   4. The electric power according to claim 1, wherein the transmission includes a pair of gears that mesh with each other, and an outlet of the supply path faces a meshing portion of the pair of gears. Steering device.

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