JP2015085701A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device with an angle sensor unit, free from an adverse effect of lubricant such as grease.SOLUTION: A face gear 11b is formed on an axial end face of a worm wheel 11a constituting a worm reduction gear 11. An angle sensor unit 30 includes: an intermediate gear 31 engaged with the face gear 11b; detection gears 32 and 33 engaged with the intermediate gear 31; an angle detection substrate 34; and a sensor housing (an angle sensor housing 38 and an angle sensor cover 39). The angle sensor housing 38 rotatably supports the detection gears 32 and 33, and isolates a storage space of the detection gears 32 and 33 from that of the angle detection substrate 34.

Description

  The present invention relates to an electric power steering apparatus having a steering angle sensor for detecting a steering shaft rotation angle.

In the conventional electric power steering device, auxiliary steering torque is generated from the electric motor in accordance with the steering torque applied to the steering wheel, and this is decelerated by the power transmission mechanism (worm reducer) and transmitted to the output shaft of the steering mechanism. doing. Here, the configuration of the electric power steering apparatus will be described with reference to FIG. The electric power steering apparatus 1 includes a steering angle sensor 11 that acquires a rotation angle of a steering shaft 2 that rotates around a predetermined axis. The steering shaft 2 is connected to a tie rod 7 through a reduction gear mechanism 4, universal joints 5A and 5B, and a rack and pinion mechanism 6. The steering shaft 2 is provided with a torque sensor 8 that detects a steering torque T applied to the steering wheel 3. When the torsion bar 8 a is twisted by the steering torque T, the torque sensor 8 corresponds to the steering torque T. Outputs electrical signals. An electric motor 9 that assists the steering torque T is connected to the steering shaft 2 via a reduction gear mechanism 4. Each signal output from the steering angle sensor 11 and the torque sensor 8 is transmitted to the control unit 20, and the control unit 20 controls the electric motor 9 based on each signal.
As a rudder angle sensor 11 mounted on such an electric power steering apparatus, for example, a technique described in Patent Document 1 is known. In this technology, an annular drive gear that rotates integrally with a steering shaft meshes with a driven gear to which a magnet is fixed, and a magnetic change detecting element (sensor) detects the magnetic flux direction of the magnet fixed to the driven gear, thereby steering. The rotation angle of the shaft 2 is detected. At this time, the driven gear is housed in the driven gear receiving hole of the unit housing, and the substrate on which the magnetic change detecting element is mounted is disposed close to the driven gear.

JP 2003-294409 A

Here, the steering angle information of the steering shaft is ideally sensed downstream of the steering system (on the side closer to the tire). For example, in FIG. 1, the reduction gear mechanism 4 that is not affected by the torsion of the torsion bar 8a. It is desirable to arrange the rudder angle sensor 11 on the downstream side. Furthermore, in recent years, there has been a demand for downsizing of the electric power steering apparatus. In order to reduce the number of components and wiring, the steering angle sensor 11 and the torque sensor 8, the electric motor 9, the reduction gear mechanism 4, and the control unit 20 Need to be placed close to each other. In particular, it is conceivable to bring the rudder angle sensor 11 close to the gear on the steering shaft side of the reduction gear mechanism 4.
However, a lubricant such as grease is sealed in the housing for housing the reduction gear mechanism 4 for lubrication, and a steering angle sensor made of the technique described in Patent Document 1 is arranged in the housing of the reduction gear mechanism 4. In this case, there is a possibility that the lubricant or the oil separated from the lubricant scatters and contacts the magnetic change detection element of the rudder angle sensor to induce a malfunction of the magnetic change detection element.

  Therefore, the present invention provides an electric power steering apparatus including a sensor element close to a gear that transmits a rotation angle of a steering shaft and a rudder angle sensor that prevents lubricant such as grease and oil from the lubricant from scattering on a substrate. The issue is to provide.

In order to solve the above-described problem, an aspect of the electric power steering apparatus according to the present invention includes a torque detection unit that detects a steering torque transmitted from a steering wheel, and steering in accordance with the steering torque detected by the torque detection unit. An electric motor that generates auxiliary torque, a worm reducer that decelerates and transmits the steering auxiliary torque generated by the electric motor to the output shaft of the steering mechanism of the vehicle, and a gear box housing that houses the worm reducer A steering angle detector configured to detect a rotation angle of the steering shaft, and a face gear is formed on an axial end surface of the worm wheel that constitutes the worm speed reducer. The first gear for detecting rotation, in which an intermediate gear meshing with the face gear and a magnet magnetized in the radial direction are fixed and meshed with the intermediate gear A vehicle, at least one second rotation detection gear meshed with one of the intermediate gear and the first rotation detection gear, the magnet magnetized in the radial direction being fixed, the intermediate gear and the plurality of gears A gear support for rotatably supporting the rotation detection gear, an angle detection substrate having a magnetic detection element disposed at a position facing each magnet of the rotation detection gear, at least the intermediate gear, and the rotation A sensor housing that houses the detection gear and the gear support, and has an opening through which a part of the intermediate gear is exposed in a state in which they are housed.
The sensor housing spatially separates a space for accommodating the rotation detecting gear and a space for accommodating the angle detecting substrate.
In the electric power steering according to the present invention, it is preferable that the sensor housing is made of resin.
In the electric power steering apparatus, it is preferable that the tooth gears of the face gear, the intermediate gear, and the rotation detecting gear are grease-lubricated.
In the electric power steering apparatus, the grease is preferably the same as the grease used for the worm reducer.

  Thus, by providing a partition wall between the rotation detection gear support portion of the sensor housing and the angle detection substrate housing portion, a lubricant such as grease applied to the rotation detection gear and the like, and the lubricant Even if the oil component released from the oil is scattered, it can be prevented from adhering to the magnetic detection element and the angle detection substrate.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a figure which shows the principal part around a steering assistance mechanism. It is a figure which shows the related components of an angle sensor. It is a perspective view which shows the specific structure of an angle sensor. It is sectional drawing which shows the specific structure of an angle sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus (EPS) in the present embodiment.
In the figure, symbol SM is a steering mechanism. The steering mechanism SM includes a steering wheel 1, and a steering force applied to the steering wheel 1 from a driver is transmitted to the steering shaft 2. The steering shaft 2 is rotatably mounted on the steering column 3. The steering shaft 2 has an input shaft 2a and an output shaft 2b. One end of the input shaft 2a is connected to the steering wheel 1, and the other end of the input shaft 2a is connected to one end of the output shaft 2b via a torsion bar (not shown).

The steering force transmitted to the output shaft 2b is transmitted to the intermediate shaft 5 via the universal joint 4 composed of the two yokes 4a and 4b and the cross connecting portion 4c for connecting them, It is transmitted to the pinion shaft 7 through a universal joint 6 composed of yokes 6a and 6b and a cross connecting portion 6c for connecting them.
The steering force transmitted to the pinion shaft 7 is transmitted to the left and right tie rods 9 via the steering gear 8, and the steered wheels WR and WL are steered by these tie rods 9. Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8b coupled to the pinion shaft 7 and a rack shaft 8c meshing with the pinion 8b in the housing 8a. That is, the steering gear 8 converts the rotational motion transmitted to the pinion 8b into a straight motion by the rack shaft 8c.

  A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a worm speed reducer 11 connected to the output shaft 2 b and an electric motor 12 connected to the worm speed reducer 11. Here, the electric motor 12 is an electric motor that generates a steering assist force, and is configured by, for example, a brushless motor.

A torque sensor unit 14 is disposed in the gear box housing 13 that houses the worm reduction gear 11. The torque sensor unit 14 detects the steering torque that is applied to the steering wheel 1 and transmitted to the input shaft 2a.
Further, an angle sensor unit 30 is disposed in the gear box housing 13 that houses the worm reduction gear 11. The angle sensor unit 30 detects the rotation angle of the steering shaft when the driver steers the steering wheel 1. A specific configuration of the angle sensor unit 30 will be described later.

In the above description, the torque sensor unit 14 corresponds to the torque detection unit, and the angle sensor unit 30 corresponds to the steering angle detection unit.
FIG. 2 is a diagram illustrating a main part around the steering assist mechanism 10.
The worm speed reducer 11 includes a worm and a worm wheel, which are accommodated in a gear box housing 13. The gear box housing 13 is filled with grease (not shown) for lubricating the worm and the worm wheel. The torque sensor unit 14 and the angle sensor unit 30 are attached to the side surface (gear box cover 13a) of the gear box housing 13. The angle sensor unit 30 is arranged so as to cover the torque sensor unit 14 attached to the gear box housing 13.
The torque sensor unit 14 and the angle sensor unit 30 are respectively connected to an EPS control unit (ECU) 15 with a harness (not shown).

  In addition to the steering torque detected by the torque sensor unit 14 and the steering angle detected by the angle sensor unit 30, the ECU 15 receives the vehicle speed detected by a vehicle speed sensor or the like. Then, steering assist control (steering assist) is performed to apply a steering assist force corresponding to these to the steering system. Specifically, a steering assist command value (steering assist torque command value) for generating the steering assist force by the electric motor 12 is calculated by a known procedure, and the electric motor 12 is operated based on the calculated steering assist command value. Calculate the current command value. The drive current supplied to the electric motor 12 is feedback-controlled based on the calculated current command value and the detected motor current value.

FIG. 3 is a view showing the worm wheel and the related parts of the angle sensor unit 30.
As shown in FIG. 3, the worm wheel 11a has a face gear 11b formed on its side surface. The worm wheel 11a has a configuration in which a resin portion is insert-molded on the outer periphery of a steel core metal, and a face gear 11b is formed in the resin portion. Thereby, weight reduction and favorable workability of the worm wheel 11a can be realized. Note that the face gear 11b may be formed on a cored bar, and is preferably formed on the cored bar in terms of a change in the distance between the cores due to thermal expansion or water absorption expansion.

The mounting position of the angle sensor unit 30 can be arbitrarily set as long as it is on the pitch circumference of the face gear 11b provided on the worm wheel 11a. However, it is desirable to lay out in consideration of the relationship with peripheral parts, wiring arrangement, and the like.
As shown in FIG. 3, the angle sensor unit 30 includes an intermediate gear 31, a first detection gear (first rotation detection gear) 32, a second detection gear (second rotation detection gear) 33, and At least an angle detection substrate 34 is provided. The intermediate gear 31 is a rotation transmission gear that does not have an angle detection function, and meshes with the face gear 11b. The intermediate gear 31 is engaged with a first detection gear 32 and a second detection gear 33. Thereby, the rotation of the steering shaft (output shaft 2 b) is transmitted to the detection gears 32 and 33 through the intermediate gear 31.
Grease is applied to the tooth surfaces of the intermediate gear 31, the first detection gear 32, and the second detection gear of the angle sensor unit 30 and lubricated. The intermediate gear 31 is directly meshed with the face gear 11b, and the grease used on the worm reducer 11 is the same as the grease used on the worm reducer 11 because the grease on the worm reducer side scatters and flows on the angle sensor unit 30 side. It is preferable to use one.

Magnets magnetized in the radial direction are embedded in the detection gears 32 and 33, such as a Hall IC or a magnetoresistive element on the angle detection substrate 34 disposed to face the detection gears 32 and 33. The rotation angle of each of the detection gears 32 and 33 can be detected by using a magnetic detection element (angle detection element).
Here, each of the detection gears 32 and 33 is a spur gear, and the number of teeth of the first detection gear 32 and the number of teeth of the second detection gear 33 are set to different numbers. Then, from the relationship between the two detection angles detected by the two detection gears 32 and 33, a rotation angle of 360 degrees or more (the absolute angle of the steering shaft) of the worm wheel 11a (steering shaft) can be calculated. It is like that.

In addition, the EPS angle sensor is required to be able to detect an absolute angle within a range of ± 720 degrees (4 rotations in total) with the neutral position of the steering wheel being 0 degrees. Accordingly, the number of teeth is set so that there is no overlap in the combination of phases of the two detection gears 32 and 33 within the range of four rotations.
Next, a specific configuration of the angle sensor unit 30 will be described in detail.

FIG. 4 is an exploded perspective view showing a specific configuration of the angle sensor unit 30.
The angle sensor unit 30 includes an intermediate gear 31, a first detection gear 32, a second detection gear 33, an angle detection substrate 34, an angle sensor housing 38, and an angle sensor cover 39.
A gear support portion 38a and a signal connector 38b are integrally formed in the angle sensor housing 38, and an intermediate gear 31 and detection gears 32 and 33 are incorporated therein. An angle detection substrate 34 is incorporated on the back side of the angle sensor housing 38 (the side opposite to the surface on which the gear support portion 38a is molded). At this time, the intermediate gear 31 and the detection gears 32 and 33 are supported by the gear support portion 38a, and the angle detection board 34 is connected to the signal connector 38b. The angle sensor unit 30 is configured by attaching the angle sensor cover 26 to the angle sensor housing 38 from the side where the intermediate gear 31 and the detection gears 32 and 33 are disposed.

  The engaging portions of the detection gears 32 and 33 and the gear support portions 38a and 38a are configured as shown in FIG. In the engaging portions of the detection gears 32 and 33 with the gear support portions 38a and 38a, annular projections 32b and 33b are provided so as to surround the magnets 32a and 33a embedded in the detection gears 32 and 33, respectively. Is provided. The detection gears 32 and 33 are engaged with the gear support portions 38a and 38a by the projections 32b and 33b, and are supported rotatably with respect to the angle sensor housing 38.

  The inner sides of the gear support portions 38a and 38a are separated by partition walls 38c and 38c so that the detection gears 32 and 33, the magnets 32a and 33a, and the angle detection substrate 34 and the magnetic detection element can be closely spaced at a predetermined interval. ing. In addition, the angle sensor housing 38 is structured to be spatially isolated without forming a through hole between the detection gears 32 and 33 and the angle detection substrate 34.

  As a material of the angle sensor housing 38 of the angle sensor unit 30, a nonmagnetic material such as resin or aluminum die casting can be appropriately selected, but a nonmagnetic and nonconductive resin is preferable. Further, grease lubrication is preferable for lubricating the tooth surfaces of the intermediate gear 31 and the detection gears 32 and 33 of the angle sensor unit 30. In particular, it is more preferable to use the same grease as that used for the worm reducer 11.

  With the above-described configuration, the detection gears 32 and 33 and the angle detection substrate 34 are separated from each other. Therefore, a lubricant such as grease that scatters from the space in which the detection gears 32 and 33 are accommodated, and The oil separated from the lubricant does not enter the space in which the angle detection substrate 34 is accommodated, and the oil detection causes the angle detection substrate 34 and the magnetic detection element on the angle detection substrate 34 to malfunction. It is possible to prevent adverse effects such as failure.

SM ... steering mechanism 1 ... steering wheel 2 ... steering shaft 3 ... steering column 4, 6 ... universal joint 5 ... intermediate shaft 8 ... steering gear 10 ... steering assist mechanism 11 ... worm speed reducer 11a ... worm wheel 11b ... face gear 12 ... Electric motor 13 ... gear box housing 13a ... gear box covers 13b and 13c ... fitting hole 14 ... torque sensor unit 15 ... EPS control unit (ECU)
30 ... Angle sensor unit 31 ... Intermediate gear 32 ... First detection gear (first rotation detection gear)
32a ... magnet 32b ... projection 33 ... second detection gear (second rotation detection gear)
33a ... Magnet 33b ... Projection 34 ... Angle detection substrate 35 ... Gear support member 38 ... Angle sensor housing 38a ... Detection gear support 38c ... Bulkhead 39 ... Angle sensor cover

Claims (4)

A torque detector that detects steering torque transmitted from the steering wheel; an electric motor that generates steering assist torque according to the steering torque detected by the torque detector; and the steering assist torque generated by the electric motor is decelerated. A worm reducer that transmits to the output shaft of the steering mechanism of the vehicle, and a rudder angle detector that is configured to be assembled to a gear box housing that houses the worm reducer and detects the rotation angle of the steering shaft. A face gear is formed on an axial end surface of the worm wheel constituting the worm speed reducer, and the rudder angle detection unit has an intermediate gear meshing with the face gear and a magnet magnetized in the radial direction fixed thereto. A first rotation detecting gear meshing with the intermediate gear and a magnet magnetized in the radial direction are fixed, and the intermediate gear and the first rotation detecting gear are fixed. At least one second rotation detection gear that meshes with any one of the gears for rotation, a gear support that rotatably supports the intermediate gear and the plurality of rotation detection gears, and each magnet of the rotation detection gear And at least the intermediate gear, the rotation detection gear, and the gear support, and a part of the intermediate gear in a state in which they are accommodated. A sensor housing having an opening through which is exposed,
The electric power steering apparatus according to claim 1, wherein the sensor housing separates a space for accommodating the rotation detecting gear and a space for accommodating the angle detecting substrate.   2. The electric power steering apparatus according to claim 1, wherein the sensor housing is made of resin.   3. The electric power steering apparatus according to claim 1, wherein tooth faces of the face gear, the intermediate gear, and the rotation detection gear are grease-lubricated. 4.   4. The electric power steering apparatus according to claim 3, wherein the grease is the same as the grease used for the worm reducer.

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