JP4658345B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an electric power steering apparatus.
[0002]
[Prior art]
In recent years, electric power steering devices have been frequently used in order to reduce the steering force of the steering wheel to give a comfortable steering feeling. This type of electric power steering device generates an auxiliary torque corresponding to the steering torque with an electric motor, and transmits this auxiliary torque to the rack shaft of the steering system. For example, Japanese Patent Laid-Open No. 7-165089 “Steering Device” (Hereinafter referred to as “conventional technology”) is known.
[0003]
As shown in FIGS. 1, 2, and 4 of the above publication, the conventional technology described above applies steering torque applied to the steering wheel 3 (the numbers are those cited in the publication; the same applies hereinafter) to the steering shaft 4. The torsion bar, the output shaft 5, and the rack and pinion mechanism are transmitted to the rack shaft 2, and the auxiliary torque generated by the motor 20 according to the steering torque is transmitted to the rack shaft 2 via the ball nut mechanism 33. A steering wheel (not shown) is steered by the rack shaft 2.
[0004]
[Problems to be solved by the invention]
In the above conventional technique, when the vehicle is driven, the steering wheel is slightly displaced in the vehicle width direction according to the road surface condition, for example, the unevenness of the road surface. This minute displacement in the vehicle width direction is converted into a minute displacement in the axial direction of the rack shaft 2. The minute displacement in the axial direction of the rack shaft 2 is transmitted to the steering wheel 3 through a path of the rack and pinion mechanism → the output shaft 5 → the steering shaft 4, and the rotor of the electric motor 20 through the path of the rack shaft 2 → the ball nut mechanism 33. It is also transmitted to 22. This is because the ball nut mechanism 33 is directly connected to the rotor 22.
[0005]
By the way, the driver can know the road surface condition (road surface information) to some extent through the steering wheel 3 by manually sensing a small change in the amount of displacement transmitted from the steering wheel to the steering wheel 3 through the rack shaft 2. Thus, it is often preferable for steering to know the road surface condition to some extent.
However, in the above conventional technique, the minute displacement in the axial direction of the rack shaft 2 is attenuated by the inertia of the rotor 22 which is a mass body. For this reason, it is difficult for a minute displacement to be transmitted from the rack shaft 2 to the steering wheel 3.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of reliably grasping a road surface condition through a steering wheel by making it easy to transmit a minute displacement from a steering wheel to the steering wheel with a simple configuration.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to a first aspect of the present invention, the steering torque applied to the steering wheel is transmitted to the rack shaft via the rack and pinion mechanism, and the auxiliary torque generated by the electric motor according to the steering torque is transmitted to the output shaft of the electric motor. In the electric power steering apparatus in which the steering wheel is steered by the rack shaft and is attached to the rack shaft via a ball screw, the output shaft of the electric motor is a tubular shape that is rotatably fitted to the rack shaft. The ball screw is composed of a threaded portion formed on the rack shaft and an outer cylindrical nut attached to the threaded portion via a ball. Between the outer peripheral surface of the output shaft and the inner peripheral surface of the nut By interposing a cylindrical elastic body and adding a torque limiter in the radially inward direction of the elastic body between the outer peripheral surface of the output shaft and the inner peripheral surface of the elastic body, auxiliary torque is transferred from the output shaft. Together configured to transmit to the threaded portion through the ball and the elastic member and the nut and Kurimitta, characterized in that the as not transmitted is above a certain torque from the output shaft to the nut.
[0008]
The elastic body allows the rack shaft to be slightly displaced in the axial direction. Therefore, most of the minute displacement transmitted from the steering wheel to the rack shaft is transmitted to the steering wheel without being attenuated by the electric motor. The driver can surely grasp the road surface condition (road surface information) through the steering wheel by feeling a slight change in the amount of displacement transmitted from the steering wheel to the steering wheel.
[0009]
Furthermore, by adding a torque limiter between the output shaft and the ball screw of the motor, since the as not transmitted is above a certain torque, it does not act excessive torque to the motor.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present invention.
The electric power steering apparatus 10 includes a steering system 20 from a vehicle steering wheel 21 to steering wheels 29, 29, and an auxiliary torque mechanism 40 that applies auxiliary torque to the steering system 20. The electric power steering device 10 is an end take-off type steering device in which steering torque is extracted from both ends of the rack shaft 26.
[0011]
The steering system 20 is connected to a steering wheel 21 via a steering shaft 22 and universal shaft joints 23, 23, and a pinion shaft 24 is connected to the pinion shaft 24 via a rack and pinion mechanism 25. The left and right steering wheels 29, 29 are connected to both ends of 26 through left and right tie rods 27, 27 and knuckle 28, 28.
The rack and pinion mechanism 25 is obtained by meshing a rack 32 formed on the rack shaft 26 with a pinion 31 formed on the pinion shaft 24.
When the driver steers the steering wheel 21, the left and right steering wheels 29, 29 can be steered by the steering torque via the rack and pinion mechanism 25 and the left and right tie rods 27, 27.
[0012]
The auxiliary torque mechanism 40 detects the steering torque of the steering system 20 applied to the steering wheel 21 by the steering torque sensor 41, generates a control signal by the control means 47 based on this detection signal, and converts the steering torque to the steering torque based on this control signal. A corresponding auxiliary torque is generated by the electric motor 50, and the auxiliary torque is transmitted to the rack shaft 26 via a ball screw 70 as a torque transmission member.
[0013]
In summary, the electric power steering apparatus 10 transmits the steering torque applied to the steering wheel 21 of the vehicle to the rack shaft 26 via the rack and pinion mechanism 25, and the electric motor 50 is generated according to the steering torque. Auxiliary torque is applied to the rack shaft 26 from the output shaft of the electric motor 50 via the ball screw 70, and the steering wheels 29 and 29 are steered by the rack shaft 26. Therefore, the steering wheels 29 and 29 can be steered by the combined torque obtained by adding the auxiliary torque of the electric motor 50 to the steering torque of the steering system 20.
[0014]
FIG. 2 is a principle diagram of a steering torque sensor according to the present invention.
The steering torque sensor 41 is a magnetostrictive torque sensor that, when a torque acts on a pinion shaft 24 having a magnetostrictive characteristic, such as a steel material, electromagnetically detects a magnetostrictive effect generated according to the torque with an electric coil. It is. Such a magnetostrictive torque sensor is a known sensor as disclosed in Japanese Patent Application Laid-Open No. 6-221940, “Magnetostrictive Torque Sensor”. Hereinafter, an outline of the steering torque sensor 41 will be described.
[0015]
The steering torque sensor 41 includes an excitation coil 42 formed in an approximately 8 shape and a detection coil 43 formed in an approximately 8 shape and substantially the same size as the excitation coil 42, substantially concentrically and substantially orthogonal to each other. These excitation / detection coils 42 and 43 are arranged as a set of magnetic heads 44 in the vicinity of the outer peripheral surface of the pinion shaft 24. That is, an approximately 8-shaped excitation coil 42 is arranged opposite to the outer peripheral surface of the pinion shaft 24, and an approximately 8-shaped detection coil 43 is overlapped on the excitation coil 42 in a state where the phase is changed by 90 °. Combined. In this case, the 8-shaped linear portion forming the exciting coil 42 is arranged so as to be substantially parallel to the outer periphery of the pinion shaft 24 or substantially parallel to the longitudinal direction of the shaft.
[0016]
If an AC voltage (excitation voltage) having a high frequency of about 20 to 100 kHz is supplied from the excitation voltage supply source 45 to the excitation coil 42, the detection coil 43 generates an excitation voltage corresponding to the magnetostriction effect of the pinion shaft 24 based on the torque. An alternating voltage (output voltage) having the same frequency can be obtained.
The output voltage is in phase with or opposite to the excitation voltage depending on the direction of the torque acting on the pinion shaft 24. The amplitude of the output voltage at this time is proportional to the magnitude of the torque. Therefore, if the output voltage is synchronously rectified based on the phase of the excitation voltage, the magnitude and direction of the torque can be detected.
The output voltage is amplified by the output voltage amplifier 46 and is output to the control means 47 as a detection signal of the steering torque sensor 41.
[0017]
FIG. 3 is an overall configuration diagram of the electric power steering apparatus according to the present invention, and shows a cross section of the main part.
The electric power steering apparatus 10 includes a rack and pinion mechanism 25 (see FIG. 1), an electric motor 50, and a ball screw 70 that are housed in a housing 101 that extends in the vehicle width direction (the left-right direction in the figure).
The housing 101 is assembled into one elongated gear box by bolting one end surfaces of the generally tubular first housing 102 and second housing 103 together. The first housing 102 includes a bracket 104 for attaching to a vehicle body (not shown). The second housing 103 also serves as an electric motor case in the electric motor 50.
[0018]
The rack shaft 26 extending in the vehicle width direction is a shaft that penetrates the housing 101 so as to slide in the vehicle width direction. Such a rack shaft 26 is connected to the rack and pinion mechanism 25 at one end on the right side of the figure, and is connected to the ball screw 70 at the substantially longitudinal center position, and is located at the other end side (position closer to the end than the ball screw 70) ) In which the electric motor 50 is arranged.
In the figure, 105 and 105 are ball joints, and 106 and 106 are dust seal boots.
[0019]
4 is a cross-sectional view taken along line 4-4 of FIG. 3, and shows a vertical cross-sectional structure of the electric power steering apparatus 10. As shown in FIG.
In the electric power steering apparatus 10, the rack and pinion mechanism 25 and the steering torque sensor 41 are accommodated in a first housing 102, and an upper opening of the first housing 102 is closed with a lid 107. The steering torque sensor 41 is attached to the first housing 102 or the lid 107.
[0020]
The first housing 102 is set in a vertical position by rotatably supporting the lower end portion and the longitudinal center portion of the pinion shaft 24 via two upper and lower bearings 108 and 109, and the rack guide 120 is mounted on the first housing 102. Prepare.
[0021]
The pinion shaft 24 is formed integrally with a pinion 31 at a lower portion, further formed with a screw portion 111 at a lower end portion, and projecting an upper end portion outward from the lid 107. By screwing the nut 112 into the screw portion 111, the movement of the pinion shaft 24 in the axial longitudinal direction (axial direction) can be restricted.
113 is a cap nut, 114 is a spacer, 115 is a retaining ring, 116 is an oil seal, and 117 is an O-ring.
[0022]
The rack guide 120 includes a guide part 121 that contacts the rack shaft 26 from the side opposite to the rack 32, and an adjustment bolt 123 that pushes the guide part 121 through a compression spring 122. According to such a rack guide 120, the guide bolt 121 is preloaded on the rack 32 by the guide portion 121 by pressing the guide portion 121 with an appropriate pressing force via the compression spring 122 with the adjusting bolt 123 screwed into the first housing 102. And the rack 32 can be pressed against the pinion 31. Reference numeral 124 denotes a contact member for sliding the back surface of the rack shaft 26, and reference numeral 125 denotes a lock nut.
[0023]
FIG. 5 is a cross-sectional view of a main part around the rack shaft, the electric motor, and the ball screw according to the present invention.
The electric motor 50 includes a cylindrical ferromagnetic yoke 51 fitted in the second housing 103, and a plurality of permanent magnet stators 52 (...) arranged in the yoke 51. The same shall apply hereinafter), and the stators 52... Aligned in the second housing 103 in an aligned state, the internal stator holder 54, and the interior of the stators 52 (ie, the internal stator holder 54. And a rotor 55 disposed inside.
[0024]
The rotor 55 includes a tubular output shaft 56 that is rotatably fitted to the rack shaft 26, a core 57 that is fitted to the outer peripheral surface of the output shaft 56, and a coil that is wound around the outer peripheral surface of the core 57. 58 and a commutator 59 connected to the coil 58. The commutator 59 is attached to the outer peripheral portion of the output shaft 56 at the side of the coil 58, and a flat surface facing the left end side (the left side in the figure) of the rack shaft 26 is a brush contact surface.
The brush 61 that contacts the brush contact surface of the commutator 59 is accommodated in the second housing 103 via the brush holder 62. Reference numeral 63 denotes a compression spring for generating a brush bullet, and reference numeral 64 denotes a brush cord.
[0025]
The output shaft 56 has the output end 56 a facing the nut 73 of the ball screw 70. The first housing 102 rotatably supports the output end 56 a side of the output shaft 56 via the nut 73 of the ball screw 70 and the first bearing 131. The second housing 103 rotatably supports the non-output end side of the output shaft 56 via the second bearing 132 and the bush 133. The first and second bearings 131 and 132 are rolling bearings.
[0026]
The ball screw 70 includes a screw portion (thread groove) 71 formed on the rack shaft 26, a large number of balls 72 (... indicates a plurality, the same applies hereinafter), and a ball 72. A ball nut mechanism comprising a nut 73 of the outer cylinder part attached via The ball screw 70 transmits the auxiliary torque of the electric motor 50 from the nut 73 to the screw portion 71 via the balls 72..., And the ball 72 that has reached the end of the thread groove of the nut 73. Is a general configuration of a so-called internal circulation type or external circulation type in which circulation is performed through a tube (not shown).
[0027]
The first bearing 131 is a bearing in which axial movement with respect to the first housing 102 is restricted by the lock screw 134 and the center of the nut 73 or a position near the nut 73 is rotatably supported.
The nut 73 includes a support portion 74 fitted to the first bearing 131 and a large-diameter portion 75 that is connected to one end of the support portion 74 and has a larger diameter than the support portion 74. The axial movement of the nut 73 relative to the first housing 102 can be restricted by sandwiching the first bearing 131 fitted to the support portion 74 between the large diameter portion 75 and the lock screw 135. As a result, the nut 73 can rotate and cannot move in the axial direction.
The bush 133 is a member interposed between the inner peripheral surface of the second housing 103 and the outer peripheral surface of the outer ring of the second bearing 132.
[0028]
This figure shows that the flange 103a at one end of the second housing 103 is coupled to the flange 102a at one end of the first housing 102 by a bolt 136.
In the figure, 137 is a spacer, and 138 is an O-ring.
[0029]
FIG. 6 is a cross-sectional view showing a connection structure between an electric motor and a ball screw according to the present invention.
In the present invention, the elastic body 83 is interposed between the output shaft 56 of the electric motor 50 and the ball screw 70 so that the elastic body 83 is elastically deformed when the rack shaft 26 is about to be slightly displaced in the axial direction. Thus, a minute displacement of the rack shaft 26 is allowed.
More specifically, in the connection structure, a cylindrical elastic connecting member 80 is rotatably fitted to the outer peripheral surface of the output end 56 a of the output shaft 56, and the large portion of the nut 73 is attached to the outer peripheral surface of the elastic connecting member 80. The inner peripheral surface of the diameter portion 75 is attached so as not to rotate.
[0030]
The elastic connecting member 80 is obtained by integrally incorporating a cylindrical elastic body 83 between a metal inner ring 81 and a metal outer ring 82. More specifically, the elastic connecting member 80 is obtained by integrating the elastic body 83 on the inner ring 81 and the outer ring 82 by performing an integration process such as a baking process or an adhesion process and fixing them together.
[0031]
The elastic body 83 is a member having a property of returning to its original shape when the external force is removed after being deformed by applying an external force, that is, a property capable of elastic deformation.
Regarding the elastic body 83, in particular, the following (1) and (2) are sufficiently taken into consideration, and the material, shape, and dimensions are determined after examining the spring constant and durability. Examples of the material of the elastic body 83 include rubber and soft resin.
(1) Auxiliary torque transmission performance by the elastic body 83.
(2) Performance allowing the rack shaft 26 to be slightly displaced in the axial direction.
By giving sufficient consideration to the above (1) and (2), the response delay when the steering wheel 21 (see FIG. 1) is started is not affected.
[0032]
Furthermore, the present invention is characterized in that a torque limiter 90 is added between the output shaft 56 of the electric motor 50 and the ball screw 70 so that a torque exceeding a certain level is not transmitted.
More specifically, a groove 56b having a constant width is formed over the entire circumference on the outer peripheral surface of the output end 56a of the output shaft 56, and the torque limiter 90 is fitted into the groove 56b, whereby the output shaft 56 of the electric motor 50 is elastically connected. A torque limiter 90 is interposed between the inner ring 81 of the member 80.
[0033]
FIGS. 7A and 7B are exploded views showing a connecting structure of the electric motor, the ball screw, and the torque limiter according to the present invention. (A) shows the state which decomposed | disassembled the output shaft 56 of the electric motor 50, the nut 73 of the ball screw 70, the elastic connection member 80, and the torque limiter 90. FIG. (B) expands and shows the b part of said (a).
The torque limiter 90 is based on an annular metal band 91 having a constant width and a very small plate thickness (for example, a plate thickness of 0.3 mm), and is cut only at one location around the band 91. The band 91 is formed by integrally forming a plurality of engaging projections 92... Elongated in the axial direction at a constant pitch (for example, a pitch of 6 to 7 mm) in the circumferential direction over the entire circumference on the outer peripheral surface. These engaging ridges 92... Are formed by, for example, pressing the band 91 so that the protruding portion (for example, height 0.7 mm, The projection tip has an arcuate cross section.
[0034]
Such a torque limiter 90 is a member that interrupts the transmission of torque above a certain level, and is generally also referred to as a tolerance ring.
The inner surface of the band 91 is fitted to the bottom surface of the groove 56b in the output shaft 56, and the inner surface of the inner ring 81 of the elastic connecting member 80 is fitted to the protrusion front surfaces of the plurality of engaging protrusions 92. Torque can be transmitted by the frictional force between these members.
Further, the plurality of engaging ridges 92... Can be elastically deformed inwardly in the diameter of the band 91 according to a certain torque or more. The frictional force between the members 56, 81, 90 is reduced by the deformation of the engaging protrusions 92.
[0035]
By the way, when a member having an uneven surface, such as the tolerance ring, is used as the torque limiter 90, it is preferable to ensure a uniform surface pressure between the elastic body 83 and the torque limiter 90. In order to ensure a uniform surface pressure, the present invention is such that an inner ring 81 (a high-rigidity metal ring) is interposed between the elastic body 83 and the torque limiter 90.
[0036]
Here, returning to FIG. 6, the operation of the output shaft 56, the nut 73, the elastic connecting member 80, and the torque limiter 90 will be described.
The auxiliary torque generated by the electric motor 50 is the path of the output shaft 56 → the torque limiter 90 → the inner ring 81 of the elastic connecting member 80 → the elastic body 83 → the outer ring 82 → the nut 73 of the ball screw 70 → the ball 72. Is transmitted to the rack shaft 26. As a result, the auxiliary torque can be converted into thrust (axial force on the rack shaft 26) and applied to the rack shaft 26.
[0037]
On the other hand, when a torque of a certain level or more is applied to the torque limiter 90, the engaging ridges 92... Are slightly elastically deformed radially inward of the band 91, so that the frictional force between the members 56, 81, 90 is descend. As a result, a torque exceeding a certain level is not transmitted between the output shaft 56 and the nut 73. Therefore, excessive torque does not act on the electric motor 50.
[0038]
Next, the operation of the electric power steering apparatus 10 having the above configuration will be described with reference to FIG.
FIGS. 8A to 8C are explanatory views of the operation of the electric power steering apparatus. (A) And (b) shows the electric power steering apparatus 10 of this invention, (c) shows the electric power steering apparatus 200 of a comparative example.
[0039]
The electric power steering apparatus 200 of the comparative example shown in (c) is obtained by directly connecting a nut 73 of a ball screw 70 to the output shaft 56 of the electric motor 50.
When the vehicle is driven, the steering wheel is slightly displaced in the vehicle width direction according to the road surface condition, for example, the unevenness of the road surface. This minute displacement in the vehicle width direction is converted into a minute displacement in the axial direction of the rack shaft 26. The minute displacement in the axial direction of the rack shaft 26 is transmitted to the ball screw 70 in addition to being transmitted to the pinion shaft 24 through the rack and pinion mechanism 25. The minute displacement transmitted to the ball screw 70 is also transmitted from the nut 73 to the output shaft 56 of the electric motor 50. As a result, the minute displacement transmitted to the rack shaft 26 can be attenuated by the electric motor 50.
[0040]
Specifically, the minute displacement transmitted to the ball screw 70 tries to rotate the rotor 55 of the electric motor 50 by rotating the nut 73. On the other hand, the rotor 22 which is a mass body always tries to keep the current state due to inertia. As a result, the electric motor 50 cancels and attenuates the minute displacement of the rack shaft 26 in the axial direction. In this way, the minute displacement transmitted to the rack shaft 26 is attenuated by the electric motor 50. Accordingly, the minute displacement transmitted to the rack shaft 26 is less likely to be transmitted to the steering wheel 21 by the amount attenuated by the electric motor 50.
[0041]
On the other hand, as shown in (a), in the electric power steering apparatus 10 of the present invention, the elastic body 83 is interposed in the auxiliary torque transmission path Li between the output shaft 56 of the electric motor 50 and the ball screw 70. Is. Therefore, (1) steering torque T1 applied from the steering wheel 21 to the rack shaft 26, and (2) auxiliary torque T2 applied from the electric motor 50 to the rack shaft 26 via the auxiliary torque transmission path Li and the elastic body 83. The steering wheel can be steered.
[0042]
Since the electric power steering device 10 is configured as described above, as shown in (b), when the rack shaft 26 is about to be slightly displaced in the axial direction, the elastic body 83 is elastically deformed, so that the rack shaft 26 is Allow minute displacement. Here, the “minute displacement” is a minute displacement within a range in which the elastic body 83 can be elastically deformed among the displacements of the rack shaft 26 in the axial direction.
Therefore, most of the minute displacement transmitted from the steering wheel to the rack shaft 26 is transmitted to the steering wheel 21 via the pinion shaft 24 without being attenuated by the electric motor 50. For this reason, the driver can always grasp the road surface condition (road surface information) through the steering wheel 21 by sensing a slight change in the amount of displacement transmitted from the steering wheel to the steering wheel 21 by hand.
[0043]
Here, the description returns to the electric power steering apparatus 10 of the present invention shown in FIG. The present invention employs a magnetostrictive torque sensor as the steering torque sensor 41. The magnetostrictive torque sensor is an electromagnetic sensor that detects the magnetostrictive effect generated according to the steering torque applied to the pinion shaft 24 having magnetostrictive characteristics, using an electric coil. Therefore, unlike the prior art, it is not necessary to divide the pinion shaft 24 in the longitudinal direction in order to detect the steering torque and to connect these divided shafts with a torsion bar.
Further, when the elastic body 83 is used, the magnetostrictive torque sensor can transmit a more accurate minute displacement to the steering wheel 21 as compared with a torsion bar type steering torque sensor.
[0044]
Even when a torsion bar type steering torque sensor is used, the relative displacement amount in the torsion bar is very small compared to the minute displacement amount due to the deformation of the elastic body 83. This can be transmitted to the steering wheel 21.
Therefore, a torsion bar type steering torque sensor can be employed as the steering torque sensor 41 of the present invention. As an electric power steering device 10 using a torsion bar type steering torque sensor, for example, there is a configuration as shown in FIG.
[0045]
FIG. 9 is a modification of the electric power steering apparatus according to the present invention, and is a cross-sectional view corresponding to FIG.
The electric power steering apparatus 10 according to the modified example divides the pinion shaft 24 into an upper shaft 24A and a lower shaft 24B in the longitudinal direction, and connects the upper and lower shafts 24A and 24B with a torsion bar 141. The relative torsion angles of the upper and lower shafts 24A and 24B are detected by the steering torque sensor 140. That is, the steering torque sensor 140 detects the steering torque according to the relative displacement amount of the upper and lower shafts 24A and 24B.
[0046]
Specifically, the torsion bar type steering torque sensor 140 includes a torsion bar 141, a slider 142, and a variable inductance sensor unit 147. More specifically, a cylindrical slider 142 is slidably fitted to the upper and lower shafts 24A and 24B, and an inclined groove 143 and a vertically long straight groove 144 provided on the slider 142 are connected to the pin 145 of the upper shaft 24A. It spans between the pins 146 of the lower shaft 24B.
[0047]
The slider 142 can slide up and down according to the relative torsional displacement of the upper and lower shafts 24A and 24B. The sliding amount of the slider 142 at this time is proportional to the torque. The variable inductance type sensor unit 147 converts the slide amount into an electric signal, and outputs it to the control means 47 (see FIG. 1) as a steering torque detection signal.
In the figure, 151 is a lid, 152 and 153 are bearings, and 154 is an oil seal.
[0048]
FIG. 10 is a modification of the electric power steering apparatus according to the present invention, and is a cross-sectional view of the main part corresponding to FIG.
In the electric power steering apparatus 10 according to the modification, the elastic connecting member 80 is directly connected to the output shaft 56 of the electric motor 50, and the torque limiter 90 is interposed between the elastic connecting member 80 and the nut 73 of the ball screw 70. It is characterized by. Other configurations and operations are the same as those shown in FIGS. 1 to 9 and are therefore given the same reference numerals, and descriptions thereof are omitted.
[0049]
In the above-described embodiment of the present invention, the structure in which the nut 73 is coupled to the output shaft 56 via the elastic body 83 is a coupling capable of transmitting torque between at least the output shaft 56, the elastic body 83, and the nut 73. Any structure can be used. Therefore, the elastic connecting member 80 may be configured only by the elastic body 83 without providing the inner ring 81 and the outer ring 82. Further, the fixing structure of the elastic body 83 is not limited to baking or adhesion, and may be serration coupling, for example.
Further, the torque limiter 90 may be a member that blocks transmission of torque above a certain level.
In the invention of claim 1, the presence or absence of the torque limiter 90 is arbitrary.
[0050]
【The invention's effect】
The present invention exhibits the following effects by the above configuration.
According to the first aspect, since the elastic body is interposed between the output shaft of the electric motor and the ball screw, the elastic body can allow the rack shaft to be slightly displaced in the axial direction. Therefore, most of the minute displacement transmitted from the steering wheel to the rack shaft is transmitted to the steering wheel without being attenuated by the electric motor. Therefore, the driver can surely grasp the road surface condition (road surface information) through the steering wheel by feeling a slight change in the amount of displacement transmitted from the steering wheel to the steering wheel.
Furthermore, since only an elastic body is interposed between the output shaft of the electric motor and the ball screw, only one elastic body is required. It is possible to allow the rack shaft to be slightly displaced in the axial direction with a small number of parts and an inexpensive and simple configuration.
[0051]
Furthermore, by adding a torque limiter between the output shaft and the ball screw of the motor, since the as not transmitted is above a certain torque, it does not act excessive torque to the motor.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an electric power steering device according to the present invention. FIG. 2 is a principle diagram of a steering torque sensor according to the present invention. FIG. 3 is an overall configuration diagram of an electric power steering device according to the present invention. 4 is a cross-sectional view taken along line 4-4 of FIG. 5. FIG. 5 is a cross-sectional view of the main parts around the rack shaft, the electric motor, and the ball screw according to the present invention. FIG. 7 is an exploded view showing a connection structure of an electric motor, a ball screw and a torque limiter according to the present invention. FIG. 8 is a diagram for explaining the operation of the electric power steering apparatus. FIG. 10 is a diagram showing a modification of the electric power steering apparatus according to the present invention.
DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 21 ... Steering wheel, 24 ... Pinion shaft, 25 ... Rack and pinion mechanism, 26 ... Rack shaft, 29 ... Steering wheel, 41 ... Steering torque sensor, 50 ... Electric motor, 56 ... Output shaft of electric motor , 70: Ball screw, 83: Elastic body, 90: Torque limiter, Li: Auxiliary torque transmission path, T1: Steering torque, T2: Auxiliary torque

Claims (1)

The steering torque applied to the steering wheel is transmitted to the rack shaft via the rack and pinion mechanism, and the auxiliary torque generated by the electric motor according to the steering torque is applied to the rack shaft via the ball screw from the output shaft of the electric motor. In the electric power steering apparatus that steers the steering wheel by the rack shaft,
The output shaft of the electric motor is a tubular shaft that is rotatably fitted to the rack shaft,
The ball screw comprises a screw portion formed on the rack shaft, and a nut of an outer cylinder portion attached to the screw portion via a ball,
A cylindrical elastic body is interposed between the outer peripheral surface of the output shaft and the inner peripheral surface of the nut,
By adding a torque limiter between the outer peripheral surface of the output shaft and the inner peripheral surface of the elastic body in the radially inward direction of the elastic body, the auxiliary torque is transmitted from the output shaft to the torque limiter and the elastic body. The electric power steering apparatus is configured to transmit to the screw portion via the nut and the ball, and to prevent a torque exceeding a certain level from being transmitted from the output shaft to the nut .

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