Steering

Abstract

The steering device (10) of the present invention comprises: a steering shaft (11), which has a first ball screw groove (11a2) as one of a left thread and a right thread and a second ball screw groove (11b2) as the other of the left thread and the right thread, and steers the steering wheel by moving along the axial direction; a first electric motor (15), which generates a first driving force; a second electric motor (16), which operates independently of the first electric motor (15) and generates a second driving force; a first ball screw nut (17), which transmits the first driving force generated by the first electric motor (15) to the first ball screw groove (11a2); a second ball screw nut (18), which transmits the second driving force generated by the second electric motor (16) to the second ball screw groove (11b2); and a rotation limiting portion (19), which limits the relative rotation of the steering shaft (11) around the axis relative to the housing (14).

Description

Technical Field

[0001] The present invention relates to a steering device. Background Art

[0002] In the past, for example, there is a known steering device disclosed in Japanese Patent Gazette No. 2010-214978. This existing steering device has a split steering shaft that is connected to a steering wheel and used to steer the steering wheel and is divided into two, and is applied to a steer-by-wire steering control device in which the mechanical connection with the steering wheel operated by the driver is released. The existing steering device has a sliding screw mechanism composed of a threaded shaft portion and a sliding screw nut that form a left and right thread relationship on each split steering shaft. In addition, motors that transmit driving force via output transmission mechanisms are provided in the sliding screw mechanism. By having such a sliding screw mechanism, the existing steering device can steer even when the motor on one side fails.

[0003] However, the steering device generally enables the steering wheel supported by the suspension to move in the up-down direction, so the steering shaft (split steering shaft) and the steering wheel are connected via a ball joint. In this case, in the above-mentioned existing steering device, when the motor moves the split steering shaft axially via the sliding screw mechanism, if the driving force (torque) applied to the split steering shaft from the sliding screw nut exceeds the friction force of the ball joint, the sliding screw mechanism and the split steering shaft may rotate around the axis together due to the driving force. As a result, even if the sliding screw nut rotates, the split steering shaft will not move axially, and it may be impossible to steer the steering wheel.

[0004] Therefore, in order to prevent the split steering shaft from rotating, a rotation-stopping mechanism such as a gear rack is required for each split steering shaft. In this case, when the output of the motor increases to steer the steering wheel to the maximum, a large load is imposed on the rotation-stopping mechanism. Therefore, in order to ensure strength, the rotation-stopping mechanism needs to be enlarged and the material needs to be changed, and as a result, the steering control device of the steer-by-wire type may become larger and more expensive. Summary of the invention

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a steering device that can be reduced in cost and size.

[0006] The steering device involved in the present invention comprises: a hollow housing; a steering shaft, which is accommodated in the interior of the housing, has a first external thread groove formed by a winding method of one of a left thread and a right thread, and has a second external thread groove formed by a winding method of the other of the left thread and the right thread, and steers the left and right steering wheels by moving in the axial direction; a first nut, which is threadedly engaged with the first external thread groove and rotatably supported in the interior of the housing; a second nut, which is threadedly engaged with the second external thread groove and rotatably supported in the interior of the housing; a first drive source, which generates a first drive force; a second drive source, which operates independently of the first drive source to generate a second drive force; a first power transmission part, which transmits the first drive force generated by the first drive source to the first nut, rotates the first nut and applies an axial force to the steering shaft; and a second power transmission part, which transmits the second drive force generated by the second drive source to the second nut, rotates the second nut and applies an axial force to the steering shaft.

[0007] Accordingly, the first power transmission unit can transmit the first driving force from the first driving source to the first external thread groove via the first nut, and the second power transmission unit can transmit the second driving force from the second driving source to the second external thread groove via the second nut. The first external thread groove is one of the left and right threads, and the second external thread groove is the other of the left and right threads. Therefore, when the steering shaft is moved axially, torques acting in directions that cancel each other out can be generated in the first external thread groove and the second external thread groove through the transmitted first and second driving forces. Thus, the anti-rotation mechanism that prevents the steering shaft, the first nut, and the second nut from rotating around the axis together can be omitted to allow the steering shaft to move axially, even if the steering wheel is turned. Therefore, the steering device can be made cheap and miniaturized. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is an overall view showing the structure of the steering device.

[0009] Figure 2 It is a cross-sectional view showing the structure of the steering device in detail.

[0010] Figure 3 It is a diagram for explaining the first torque and the second torque.

[0011] Figure 4 yes Figure 2 This is a cross-sectional view of the rotation restricting portion as viewed along the line IV-IV.

[0012] Figure 5 is Figure 4 0014 is a perspective view of the rotation limiting portion as viewed from the Q direction.

[0013] Figure 6It is an overall view showing the structure of a steering device to which the steering device is applied.

[0014] Figure 7 It is a cross-sectional view showing in detail the structure of the steering device according to the first modified example.

[0015] Figure 8 It is a cross-sectional view showing in detail the structure of a steering device according to a second modified example.

[0016] Fig. 9 It is a cross-sectional view showing in detail the structure of a steering device according to a third modified example.

[0017] Fig.10 The rotation restriction portion of the fourth modification example is Figure 4 The corresponding figure.

[0018] Fig.11 The rotation restriction portion of the fifth modification example is Figure 4 The corresponding figure.

[0019] Fig.12 The rotation restriction portion of the sixth modification example is Figure 4 The corresponding figure.

[0020] Fig.13 The rotation restricting portion according to the seventh modification example is Figure 4 The corresponding figure.

[0021] Fig.14 is Fig.13 A perspective view of the rotation limiting portion as viewed from the R direction.

[0022] Fig.15 is a diagram of a deformation state of the rotation restricting portion corresponding to the fifth modification example, Fig.11 The corresponding figure.

[0023] Description of Reference Numerals

[0024] 1…steering device; 2…steering wheel; 3…steering input shaft; 4…steering angle sensor; 5…steering torque sensor; 6…reaction force actuator; 7…steering control unit; 10…steering device; 11, 111, 211, 311, 411…steering shaft; 11a…first ball screw unit; 11a1…ball (spherical rolling element); 11a2…first ball screw groove (first external thread groove); 11a3…rolling path; 11b…second ball screw unit; 11b1…ball (spherical rolling element); 11b2…second ball screw groove (second external thread groove); 11b3…rolling path; 12, 13…ball joint; 14, 114, 214, 314, 414…housing; 15… 1. An electric motor (first driving source); 15a…pulley (first power transmission part); 15b…belt (first power transmission part (endless component)); 15c…rotation angle sensor; 15d…pulley (first power transmission part); 16…second electric motor (second driving source); 16a…pulley (second power transmission part); 16b…belt (second power transmission part (endless component)); 16c…rotation angle sensor; 16d…pulley (second power transmission part); 17…first ball screw nut (first nut); 18…second ball screw nut (second nut); 19, 119, 219, 319, 419…rotation limiting part; 21, 121…protrusion (steering shaft side engaging part); 22…annular component; 22a… Outer peripheral surface of annular component; 23, 123…groove (housing side engaging portion); 221, 321, 421…steering shaft side engaging portion; 223, 323, 423…housing side engaging portion; 215…guide component; 217, 317, 417…contact portion; 315…roller; 415…pinion; 25…first electric motor (first power source); 25a…rotor; 26…second electric motor (second power source); 26a…rotor; 31a…first roller screw portion; 31a1…roller (roller-shaped rolling element); 31a2…first roller screw groove (first external thread groove); 31a3…rolling path; 31b…second roller screw portion; 31b1…roller (roller-shaped rolling element); 31b2…second roller screw groove (second external thread groove); 31b3… rolling path; 37… first roller screw nut (first nut); 38… second roller screw nut (second nut); 41a… first sliding screw portion; 41a2… trapezoidal thread groove (first external thread groove); 41b… second sliding screw portion; 41b2… trapezoidal thread groove (second external thread groove); 47… first sliding screw nut (first nut); 48… second sliding screw nut (second nut); FW1, FW2… left and right front wheels (steering wheels); G1… first reduction ratio; G2… second reduction ratio; I1… driving current; I2… driving current; S1, S2… steering control device; T1… first torque; T2… second torque; δ… electrical signal; θ1… rotation angle;θ2…rotation angle; TL1…tooth line; TL2…tooth line. ; DETAILED DESCRIPTION

[0025] (1. Structure of Steering Device 10)

[0026] The structure of the steering device 10 as one embodiment of the present invention will be described. Figure 1 As shown, the vehicle is provided with a steering shaft 11 connected to the left and right front wheels FW1 and FW2 as left and right steering wheels and used to steer the left and right front wheels FW1 and FW2. Figure 1 and Figure 2 As shown, both ends of the steering shaft 11 are connected to ball joints 12 and 13. Furthermore, the steering shaft 11 is connected to the left and right front wheels FW1 and FW2 via a link mechanism (for example, a tie rod) connected to the ball joints 12 and 13.

[0027] In addition, the steering shaft 11 is accommodated in the interior of the hollow housing 14 in a manner that allows axial displacement. The steering shaft 11 has a first ball screw groove 11a2, which is a first external thread groove formed by a winding method of one of the left thread and the right thread, in a first axial region. In addition, the steering shaft 11 has a second ball screw groove 11b2, which is a second external thread groove formed by a winding method of the other of the left thread and the right thread, in a second region different from the first region. In addition, in the present embodiment, the first region and the second region correspond to the two ends of the steering shaft 11 in the axial direction. The steering shaft 11 steers the left and right front wheels FW1, FW2 (steering wheels) by moving relative to the housing 14 in the axial direction.

[0028] Moreover, the first ball screw nut 17, which is the first nut rotatably supported inside the housing 14, is threadedly engaged with the first ball screw groove 11a2. In addition, the second ball screw nut 18, which is the second nut rotatably supported inside the housing 14, is threadedly engaged with the second ball screw groove 11b2. As a result, the first ball screw portion 11a is formed by the first ball screw groove 11a2 and the first ball screw nut 17 in the first region of the two ends of the steering shaft 11. In addition, the second ball screw portion 11b is formed by the second ball screw groove 11b2 and the second ball screw nut 18 in the second region of the steering shaft 11.

[0029] like Figure 2As shown, the first ball screw part 11a has a rolling path 11a3 for rolling balls 11a1 as spherical rolling bodies. The second ball screw part 11b has a rolling path 11b3 for rolling balls 11b1 as spherical rolling bodies. Moreover, the rolling paths 11a3 and 11b3 are in a left-right threaded relationship (mutually reversed threads). In addition, in the rolling paths 11a3 and 11b3, a plurality of balls 11a1 and 11b1 respectively circulate and roll.

[0030] In addition, if Figure 1 and Figure 2 As shown, the steering device 10 includes a first electric motor 15 as a first driving source and a second electric motor 16 as a second driving source. The first electric motor 15 and the second electric motor 16 are independently controlled by the steering control devices S1 and S2, respectively. Thus, the first electric motor 15 generates a first driving force, and the second electric motor 16 generates a second driving force independently of the first electric motor 15. Here, the first electric motor 15 and the second electric motor 16 are as shown in FIG. Figure 2 As shown, the output shafts (more specifically, a pulley 15a and a pulley 16a described later) are fixed to the housing 14 so as to face each other.

[0031] In addition, the steering device 10 includes the above-mentioned first ball screw nut 17 included in the first power transmission part and serving as a first threaded engagement member constituting the first power transmission part, and the above-mentioned second ball screw nut 18 included in the second power transmission part and serving as a second threaded engagement member constituting the second power transmission part. The first ball screw nut 17 is coaxially arranged with a first ball screw groove 11a2 of a first ball screw portion 11a provided on the steering shaft 11. The second ball screw nut is coaxially arranged with a second ball screw groove 11b2 of a second ball screw portion 11b provided on the steering shaft 11.

[0032] For the first ball screw nut 17, if Figure 2 As shown, the first driving force is transmitted from the first electric motor 15 via the pulley 15a and the pulley 15d constituting the first power transmission part, and the belt 15b as an endless member constituting the first power transmission part. The first ball screw nut 17 is accommodated and fixed in the bottomed cylindrical pulley 15d. If the first driving force is transmitted from the first electric motor 15 via the pulley 15a, the belt 15b and the pulley 15d, the first ball screw nut 17 rotates relative to the first ball screw groove 11a2.

[0033] Thus, the balls 11a1 disposed between the first ball screw groove 11a2 of the first ball screw part 11a and the first ball screw nut 17 roll along the rolling path 11a3, and the first driving force of the first electric motor 15 is converted into a force (axial force) for moving the steering shaft 11 in the axial direction, that is, a steering force for steering the left and right front wheels FW1 and FW2. In this case, the first ball screw nut 17 decelerates the rotation speed of the first driving force transmitted from the first electric motor 15 and transmits it to the first ball screw groove 11a2 of the first ball screw part 11a, that is, the steering shaft 11, so that the first torque T1 acts on the steering shaft 11 in the first ball screw part 11a.

[0034] For the second ball screw nut 18, if Figure 2 As shown, the second driving force is transmitted from the second electric motor 16 via the pulley 16a and the pulley 16d constituting the second power transmission part, and the belt 16b as an endless member constituting the second power transmission part. The second ball screw nut 18 is accommodated and fixed in the bottomed cylindrical pulley 16d. If the second driving force is transmitted from the second electric motor 16 via the pulley 16a, the belt 16b and the pulley 16d, the second ball screw nut 18 rotates relative to the second ball screw groove 11b2.

[0035] As a result, the balls 11b1 disposed between the second ball screw groove 11b2 of the second ball screw part 11b and the second ball screw nut 18 roll along the rolling path 11b3, and the second driving force of the second electric motor 16 is converted into a steering force for axially moving the steering shaft 11. In this case, the second ball screw nut 18 decelerates the rotation speed of the second driving force transmitted from the second electric motor 16 and transmits it to the second ball screw groove 11b2 of the second ball screw part 11b, that is, the steering shaft 11, so that the second torque T2 acts on the steering shaft 11 in the second ball screw part 11b.

[0036] Here, the first ball screw groove 11a2 of the first ball screw portion 11a is one of the left-hand thread and the right-hand thread as described above. In addition, the second ball screw groove 11b2 of the second ball screw portion 11b is the other of the left-hand thread and the right-hand thread. That is, the first ball screw groove 11a2 and the second ball screw groove 11b2 are arranged on the steering shaft 11 in a manner having a relationship between left and right threads (reverse threads). In addition, the first electric motor 15 and the second electric motor 16 are fixed to the housing 14 in a manner opposite to each other.

[0037] Here, in Figure 2In the embodiment, when viewed from the axial direction of the steering shaft 11 from the ball joint 12 side toward the ball joint 13 side, the first electric motor 15 and the second electric motor 16 transmit the first driving force and the second driving force in opposite rotation directions to the first ball screw nut 17 and the second ball screw nut 18. Figure 3 As shown, the first torque T1 and the second torque T2 acting on the steering shaft 11 are opposite to each other. In addition, if the rotation directions of the first electric motor 15 and the second electric motor 16 are observed based on the first electric motor 15 and the second electric motor 16 themselves, the first driving force and the second driving force have the same rotation direction.

[0038] However, when the first electric motor 15 and the second electric motor 16 transmit the first driving force and the second driving force to the first ball screw nut 17 and the second ball screw nut 18, the absolute values ​​of the first torque T1 and the second torque T2 can be equal. Thus, by completely canceling out the first torque T1 and the second torque T2, the steering shaft 11 can be moved axially without rotating, thereby steering the left and right front wheels FW1 and FW2.

[0039] Specifically, the reduction ratio at which the first ball screw nut 17 decelerates the rotation speed to the first ball screw groove 11a2 and converts it into a linear motion and transmits it is the first reduction ratio G1, and the reduction ratio at which the second ball screw nut 18 decelerates the rotation speed to the second ball screw groove 11b2 and converts it into a linear motion and transmits it is the second reduction ratio G2. In addition, the reduction ratio between the pulley 15a, the belt 15b, the pulley 15d and the first ball screw nut 17 is the same as the reduction ratio between the pulley 16a, the belt 16b, the pulley 16d and the second ball screw nut 18.

[0040] The first driving force and the second driving force generated by the first electric motor 15 and the second electric motor 16 are transmitted to the first ball screw groove 11a2 and the second ball screw groove 11b2 via the first ball screw nut 17 and the second ball screw nut 18. As a result, the first ball screw part 11a applies the first torque T1 to the steering shaft 11, and the second ball screw part 11b applies the second torque T2 to the steering shaft. In this case, when the first reduction ratio G1 and the second reduction ratio G2 are equal, by making the first driving force and the second driving force equal, the absolute values ​​of the first torque T1 and the second torque T2 acting on the steering shaft 11 are equal and the directions of action are opposite, thereby canceling each other out. Therefore, when the steering shaft 11 is moved axially, or when the steering shaft 11 is stopped at any position in the axial direction, the steering shaft 11 is prevented from rotating.

[0041] On the other hand, when the first reduction ratio G1 and the second reduction ratio G2 are different, the first electric motor 15 and the second electric motor 16 generate the first driving force and the second driving force so that the absolute values ​​of the first torque T1 and the second torque T2 that can be calculated in advance based on the first reduction ratio G1 and the second reduction ratio G2 are equal. Thus, when the steering shaft 11 is moved in the axial direction or when the steering shaft 11 is stopped at any position in the axial direction, the steering shaft 11 is prevented from rotating.

[0042] Here, for example, when the guide wire of the rolling path 11a3 in the first ball screw portion 11a and the guide wire of the rolling path 11b3 in the second ball screw portion 11b are the same, the first reduction ratio G1 and the second reduction ratio G2 can be set to the same reduction ratio.

[0043] (1-1. Rotation Restriction Section 19)

[0044] The steering device 10 includes a rotation restricting portion 19 in the central portion of the steering shaft 11, that is, between the first ball screw portion 11a and the second ball screw portion 11b provided at both ends of the steering shaft 11 (see Figure 2 The rotation restricting portion 19 is a rotation-stopping mechanism that mechanically restricts the relative rotation of the steering shaft 11 with respect to the housing 14 .

[0045] In other words, the rotation limiting unit 19 is mainly provided so that, for example, even if one of the first electric motor 15 and the second electric motor 16 fails and cannot operate, and a state is generated in which one of the first torque T1 and the second torque T2 is not generated, the steering shaft 11 will not rotate relative to the housing 14. However, the present invention is not limited to the above-mentioned form, and even if the absolute values ​​of the first torque T1 and the second torque T2 are not completely equal due to deviation, and a state is generated in which they are output slightly differently, the rotation limiting unit 19 can limit the relative rotation of the steering shaft 11 relative to the housing 14.

[0046] The rotation restricting portion 19 includes a protrusion 21 (steering shaft side engaging portion, and equivalent to one side) provided on the steering shaft 11, and a groove 23 (housing side engaging portion, and equivalent to the other side) provided on the housing 14 and engaging with a part of the protrusion 21. At this time, when the protrusion 21 engages with the groove 23, the side surface of the protrusion 21 abuts and engages with the side surface in the groove 23. In this way, the groove 23 engages with the protrusion 21, allowing the steering shaft 11 to move relative to the housing 14 in the axial direction, and restricting the relative rotation of the steering shaft 11 around the axis relative to the housing 14.

[0047] Specifically, the protrusion 21 is provided on the inner peripheral surface so as to be fitted into the outer peripheral surface 11c of the steering shaft 11 (see Figure 4) and fixed to the annular member outer peripheral surface 22a of the annular member 22 of the steering shaft 11. In other words, the protrusion 21 is provided to protrude from the outer peripheral surface 22a of the annular member 22 toward the radial outer side of the steering shaft 11. Moreover, the inner peripheral surface of the annular member 22 is fitted into the outer peripheral surface of the steering shaft 11 and fixed to the steering shaft 11.

[0048] At this time, the outer diameter of the outer peripheral surface 11c of the steering shaft 11 into which the annular member 22 is fitted is formed to be larger than the outer peripheral surface 11d of the steering shaft 11 other than the outer peripheral surface 11c into which the annular member 22 is fitted (see Figure 5 ) is slightly larger in outer diameter. As a result, the inner peripheral surface of the annular member 22 can be easily pressed into (fitted into) the outer peripheral surface 11c of the steering shaft 11, and the annular member 22 can be fixed integrally with the steering shaft 11. In addition, when the protrusion 21 is formed, since a fixing method is adopted in which the annular member 22 having the protrusion 21 is fit into a fitting portion of the steering shaft outer peripheral surface 11c having an outer diameter larger than the outer diameter of the steering shaft outer peripheral surface outside the fitting portion, a reduction in the bending strength of the steering shaft 11 can be prevented compared to a fixing method in which a hole is formed in the steering shaft 11 and a separately formed protrusion is fit into the hole.

[0049] Furthermore, in the present embodiment, the protrusion 21 is provided at one position protrudingly at an arbitrary position in the circumferential direction of the annular member outer peripheral surface 22a of the annular member 22. Figure 5 As shown, the projection 21 is formed by extending a predetermined length in the axial direction of the steering shaft 11. The length can be set to meet the function of stopping the steering shaft 11, the strength, and the durability, and to meet the conditions that the steering shaft 11 does not interfere with the undesirable places in the steering device 10 even if the steering shaft 11 moves throughout the stroke.

[0050] Next, the groove 23 will be described. The groove 23 (equivalent to the housing side engaging portion) is provided on the inner peripheral surface 14a of the housing 14 so as to extend axially. At this time, the depth of the groove 23 from the inner peripheral surface 14a can be set so that there is a gap between the front end of the protrusion 21 and the bottom surface of the groove 23, or the bottom surface of the groove 23 abuts with a relatively low surface pressure. With such a structure, the groove 23 engages with the protrusion 21, allowing the housing 14 and the steering shaft 11 to move relative to each other in the axial direction. In addition, the groove 23 engages with the protrusion 21 to limit the relative rotation of the steering shaft 11 around the axis relative to the housing 14. This will be described in detail later.

[0051] like Figure 5As shown, the groove 23 is formed by axially penetrating (communicating) the two ends of the central portion 14b having the smallest inner diameter in the inner peripheral surface of the housing 14. In addition, the groove 23 may be formed by axially penetrating only one end of the two ends of the central portion 14b without being limited to the above-mentioned form. Thus, when the steering shaft 11 is assembled into the housing 14, the protrusion 21 is inserted from one end of the two ends of the central portion 14b that axially penetrates the groove 23, so that the steering shaft 11 can also be assembled into the housing 14.

[0052] In this way, Figure 4 , Figure 5 As shown, the rotation restricting portion 19 is provided across the housing 14 and the steering shaft 11. In other words, one of the components of the rotation restricting portion 19 is provided on the housing 14, and the other component of the rotation restricting portion 19 is provided on the steering shaft 11, and the combination of the two components brings about the function of the rotation restricting portion 19. Thus, the rotation restricting portion 19 allows the steering shaft 11 to move relative to the housing 14 in the axial direction, and restricts the relative rotation of the steering shaft 11 relative to the housing 14 around the axis.

[0053] In the present embodiment, as an example, the surface of the protrusion 21 is coated with a fluororesin coating FC having lubricity (see Figure 4 In other words, a fluororesin coating FC is provided as a lubricating portion between the protrusion 21 and the groove 23. Thus, when the steering shaft 11 moves in the axial direction relative to the housing 14, the friction between the protrusion 21 and the groove 23 can be reduced, thereby enabling smooth movement.

[0054] In addition, in the above description, the fluororesin coating FC is formed on the surface of the protrusion 21, but the present invention is not limited to this form. The fluororesin coating FC may be formed on the surface of the groove 23 facing the protrusion 21 to be engaged. Furthermore, the fluororesin coating FC may be formed on the surface of both the protrusion 21 and the groove 23 facing the protrusion 21. According to these, the same effect as the above embodiment can be expected.

[0055] In addition, in the above-mentioned form, the lubricating portion provided between the protrusion 21 and the groove 23 is a fluororesin coating FC, but the present invention is not limited to this form. Any coating may be used as long as it is a resin coating having lubricity. In addition, a solid lubricant such as molybdenum disulfide or graphite (not shown) may be interposed between the protrusion 21 and the groove 23 as a lubricating portion. In addition, a liquid lubricant such as grease with high viscosity (not shown) may be interposed between the protrusion 21 and the groove 23 as a lubricating portion.

[0056] Furthermore, a bearing component made by impregnating a porous material such as sintered metal, grown cast iron, or synthetic resin with lubricating oil may be placed between the protrusion 21 and the groove 23 as a lubricating portion. At this time, the impregnated lubricating oil expands due to the temperature rise during driving. As a result, the lubricating oil seeps out and is supplied to the gap between the protrusion 21 and the groove 23, thereby playing a lubricating role. When the temperature drops, the lubricating oil returns to the inside of the bearing component again, so it can be used for a long time. Based on this, the same effect as the above-mentioned embodiment can be expected. In addition, without being limited to the above-mentioned form, the protrusion 21 can also be set on the side of the housing 14 and extended radially inward, and the groove 23 can be set on the side of the steering shaft 11. The same effect can be expected accordingly.

[0057] Furthermore, the rotation restricting portion 19 is configured not to restrict the rotation of the steering shaft 11 and not to hinder the movement of the steering shaft 11 in the axial direction during driving controlled so that the first torque T1 and the second torque T2 cancel each other out.

[0058] Therefore, the rotation restricting portion 19 does not need to have high strength, and only needs to be inexpensive and have a simple structure. Thus, the rotation restricting portion 19 can be composed of, for example, an abutting member (protrusion 21) fixed to the central portion of the steering shaft 11 and an abutted member (groove 23) provided in the housing 14. In other words, the rotation restricting portion 19 can well cope with low costs with a simple and inexpensive structure.

[0059] The steering device 10 is controlled by the steering control devices S1 and S2. The steering control devices S1 and S2 are microcomputers with CPU, ROM, RAM, etc. as main components. Figure 1 As shown, an electric signal δ indicating a target steering amount for steering the left and right front wheels FW1 and FW2 is input. In addition, the steering control device S1 inputs a rotation angle θ1 of the first electric motor 15 from a rotation angle sensor 15c such as a resolver provided in the first electric motor 15. In addition, the steering control device S2 inputs a rotation angle θ2 of the second electric motor 16 from a rotation angle sensor 16c such as a resolver provided in the second electric motor 16. Here, the rotation angle θ1 and the rotation angle θ2 correspond to the axial position of the steering shaft 11, that is, the steering amount.

[0060] The steering control devices S1 and S2 feedback control the rotation angle θ1 and the rotation angle θ2, i.e., the position of the steering shaft 11. Moreover, the steering control devices S1 and S2 perform PID control on the drive circuit (not shown), for example, to supply the drive current I1 to the first electric motor 15 and the drive current I2 to the second electric motor 16 so that the steering amount of the steering shaft 11 becomes the target steering amount (target steering shaft position) represented by the electrical signal δ. Thus, the left and right front wheels FW1 and FW2 can steer to a steering amount consistent with the target steering amount represented by the electrical signal δ. In addition, or in addition to this, the steering control devices S1 and S2 can also feedback control the drive current I1 and the drive current I2 instead of feedback controlling the rotation angle θ1 and the rotation angle θ2.

[0061] (1-2. Operation of Steering Device 10)

[0062] When the steering control devices S1 and S2 input the electric signal δ, the driving current I1 and the driving current I2 are respectively supplied to the first electric motor 15 and the second electric motor 16. When the driving current I1 is supplied to the first electric motor 15, the first driving force is transmitted to the first ball screw nut 17 via the pulley 15a, the belt 15b, and the pulley 15d. In addition, when the driving current I2 is supplied to the second electric motor 16, the second driving force acting in the same direction as the first driving force is transmitted to the second ball screw nut 18 via the pulley 16a, the belt 16b, and the pulley 16d.

[0063] When the first ball screw nut 17 transmits the first driving force from the first electric motor 15 to the first ball screw groove 11a2 of the steering shaft 11, the first torque T1 is converted into the axial force of the steering shaft 11 in the first ball screw portion 11a. In addition, when the second ball screw nut 18 transmits the second driving force from the second electric motor 16 to the second ball screw groove 11b2 of the steering shaft 11, the second torque T2 is converted into the axial force of the steering shaft 11 in the second ball screw portion 11b.

[0064] However, the first electric motor 15 and the second electric motor 16 are arranged in an opposing manner. Therefore, when the first electric motor 15 and the second electric motor 16 generate the first driving force and the second driving force in the same direction when viewed with respect to themselves, the first ball screw nut 17 and the second ball screw nut 18 rotate in opposite directions relative to the steering shaft 11. Here, the rolling path 11a3 of the first ball screw part 11a and the rolling path 11b3 of the second ball screw part 11b have a left and right thread (reverse thread) relationship. Therefore, by rotating the first ball screw nut 17 and the second ball screw nut 18 in opposite directions, an axial force, i.e., a steering force, in the same axial direction is generated on the steering shaft 11. As a result, the steering shaft 11 moves axially to steer the left and right front wheels FW1 and FW2.

[0065] In this case, the steering control device S1 performs feedback control on the rotation angle θ1 output from the rotation angle sensor 15c of the first electric motor 15, that is, the axial position of the steering shaft 11, until the target steering amount represented by the electric signal δ is reached, and performs PID control on the drive current I1 to drive the first electric motor 15. In addition, the steering control device S2 performs feedback control on the rotation angle θ2 output from the rotation angle sensor 16c of the second electric motor 16, that is, the axial position of the steering shaft 11, until the target steering amount represented by the electric signal δ is reached, and performs PID control on the drive current I2 to drive the second electric motor 16.

[0066] However, when the steering shaft 11 is moved in the axial direction, for example, the steering control devices S1 and S2 control the driving current I1 and the driving current I2 so that the absolute values ​​of the first torque T1 generated by the steering shaft 11 and the second torque T2 generated in the opposite direction to the first torque T1 are equal. Thus, the first torque T1 and the second torque T2 are offset, thereby preventing the steering shaft 11 from rotating relative to the housing 14.

[0067] However, when either the first electric motor 15 or the second electric motor 16 fails, the balance between the first torque T1 and the second torque T2 is broken. Therefore, the steering shaft 11 is subjected to a force that causes it to rotate relative to the housing 14 around its axis according to the torque T (the first torque T1 or the second torque T2) of the motor (the first electric motor 15 or the second electric motor 16) that has not failed.

[0068] However, in this embodiment, the rotation limiting portion 19 is provided. Therefore, when the steering shaft 11 is subjected to a rotational force around the axis, the side surface of one side of the protrusion 21 abuts against the side surface of one side in the groove 23 engaged via the fluororesin coating FC (lubricating portion), thereby limiting the relative rotation of the steering shaft 11 around the axis with respect to the housing 14. Thus, the rotation of the steering shaft 11 based on the torque T (first torque T1 or second torque T2) of the motor (first electric motor 15 or second electric motor 16) that has not failed is limited, and the torque T is converted into an axial force by the first ball screw portion 11a or the second ball screw portion 11b and applied to the steering shaft 11, so that the steering shaft 11 can move axially relative to the housing 14.

[0069] In this way, even if either the first electric motor 15 or the second electric motor 16 fails, the vehicle can be steered and moved to a safe place only by the torque T (first torque T1 or second torque T2) of the motor (first electric motor 15 or second electric motor 16) that has not failed, thereby improving reliability. In addition, in the rotation limiting portion 19, a lubrication portion (fluororesin coating FC) is provided between the protrusion 21 and the groove 23. Thus, when the protrusion 21 moves (slides) axially in the groove 23, it can slide smoothly with reduced resistance.

[0070] (2. Steering device using the steering device 10)

[0071] like Figure 4 As shown, the above-mentioned steering device 10 can be applied to a steer-by-wire type steering device 1. The steering device 1 includes a steering wheel 2 that is operated and turned by a driver. The steering wheel 2 is fixed to the upper end of a steering input shaft 3. The steering input shaft 3 is connected to a steering angle sensor 4, a steering torque sensor 5, and a reaction force actuator 6.

[0072] The steering angle sensor 4 detects the amount of operation of the steering wheel 2, that is, the rotation angle of the steering input shaft 3 as the steering angle, and outputs it to the steering control unit 7. The steering torque sensor 5 detects the amount of operation of the steering wheel 2, that is, the torque input to the steering input shaft 3 as the steering torque, and outputs it to the steering control unit 7. The reaction force actuator 6 includes an electric motor and a speed reduction mechanism, and applies a predetermined reaction force to the rotation operation of the steering wheel 2 by the driver.

[0073] The steering control unit 7 includes a microcomputer and a motor drive circuit with CPU, ROM, RAM, etc. as main components, and inputs the steering angle and steering torque detected by the steering angle sensor 4 and the steering torque sensor 5 to control the operation of the reaction force actuator 6. That is, the steering control unit 7 controls the operation of the reaction force actuator 6 to generate a reaction force corresponding to the steering angle and the steering torque. In addition, the control of the reaction force actuator 6 by the steering control unit 7 is not directly related to the present invention, so the description thereof is omitted.

[0074] In addition, the steering control unit 7 calculates the target steering amount of the left and right front wheels FW1 and FW2 based on at least one of the input steering angle and steering torque. Moreover, the steering control unit 7 outputs the electrical signal δ indicating the calculated target steering amount to the steering control devices S1 and S2 of the steering device 10. Thus, the steering control devices S1 and S2 drive the first electric motor 15 as the first drive source and the second electric motor 16 as the second drive source as described above based on the electrical signal δ input from the steering control unit 7. Therefore, the steering device 10 can be applied to a steering device 1 of a steer-by-wire type.

[0075] In addition, the steering device 10 can also be applied to a vehicle with an automatic driving function, for example, a vehicle that does not have a steering wheel operated by a driver, or a vehicle that normally stores a steering wheel. In a vehicle with an automatic driving function, for example, a passenger sets a destination, and a route to the destination is searched using map data mounted on the vehicle or map data stored in a map database of an external center.

[0076] Moreover, in a vehicle with an automatic driving function, for example, the vehicle is driven to a destination based on path data indicating a searched path and current position data indicating the current position of the vehicle. In this case, in the steering device 10, for example, when driving at a curve existing in front of the traveling direction, an electrical signal δ indicating the target steering amount of the left and right front wheels FW1 and FW2 that can be calculated from the path data and the current position data is input from a host control device that oversees the automatic driving. Thus, the steering control devices S1 and S2 drive the first electric motor 15 as the first drive source and the second electric motor 16 as the second drive source as described above based on the electrical signal δ input from the host control device. Therefore, the steering device 10 can be applied to a vehicle with an automatic driving function.

[0077] As can be understood from the above description, the steering device 10 of the above embodiment comprises: a hollow housing 14; a steering shaft 11 which is accommodated in the housing 14 and has a first ball screw groove 11a2 as a first external thread groove formed by a winding method of one of the left and right threads and a second ball screw groove 11b2 as a second external thread groove formed by a winding method of the other of the left and right threads, and which is axially moved to steer the left and right front wheels FW1 and FW2 as left and right steering wheels; a first ball screw nut 17 as a first nut which is threadedly engaged with the first ball screw groove 11a2 and rotatably supported in the housing 14; a first ball screw nut 17 which is threadedly engaged with the second ball screw groove 11b2 and rotatably supported in the housing 14. a second ball screw nut 18 as a second nut inside; a first electric motor 15 as a first driving source that generates a first driving force; a second electric motor 16 as a second driving source that operates independently of the first electric motor 15 to generate a second driving force; a first power transmission unit that transmits the first driving force generated by the first electric motor 15 to the first ball screw nut 17, so that the first ball screw nut 17 rotates and applies an axial force to the steering shaft 11 having a first ball screw groove 11a2; and a second power transmission unit that transmits the second driving force generated by the second electric motor 16 to the second ball screw nut 18, so that the second ball screw nut 18 rotates and applies an axial force to the steering shaft 11 having a second ball screw groove 11b2.

[0078] Accordingly, the first ball screw nut 17 can transmit the first driving force from the first electric motor 15 to the steering shaft 11 (first ball screw part 11a) having the first ball screw groove 11a2, and the second ball screw nut 18 can transmit the second driving force from the second electric motor 16 to the steering shaft 11 (second ball screw part 11b) having the second ball screw groove 11b2. The first ball screw groove 11a2 is one of the left-hand thread and the right-hand thread, and the second ball screw groove 11b2 is the other of the left-hand thread and the right-hand thread. The first ball screw groove 11a2 and the second ball screw groove 11b2 are in a left-hand thread (reverse thread) relationship.

[0079] Therefore, when the steering shaft 11 is moved axially, the first torque T1 and the second torque T2 that cancel each other out can be generated in the first ball screw part 11a and the second ball screw part 11b according to the first driving force and the second driving force transmitted. Therefore, it is possible to prevent the steering shaft 11 and the first ball screw nut 17 and the second ball screw nut 18 from rotating around the axis together and moving the steering shaft 11 axially, that is, steering the left and right front wheels FW1 and FW2. As a result, the steering device 10 can be made cheap and miniaturized.

[0080] The first electric motor 15 and the second electric motor 16 cooperate with each other to move the steering shaft 11 in the axial direction, and transmit the first and second driving forces in the same direction to the steering shaft 11 via the first ball screw nut 17 and the second ball screw nut 18 .

[0081] According to this, the first torque T1 and the second torque T2 that cancel each other out in the first ball screw part 11a and the second ball screw part 11b can be reliably generated, so that the steering shaft 11 moves axially, that is, the left and right front wheels FW1 and FW2 are steered. Therefore, it is possible to prevent the steering shaft 11 and the first ball screw nut 17 and the second ball screw nut 18 from rotating around the axis together, so that the steering shaft 11 can be reliably moved axially, thereby steering the left and right front wheels FW1 and FW2.

[0082] The steering shaft 11 is accommodated in the hollow housing 14 , and has a first ball screw portion 11 a and a second ball screw portion 11 b at both ends. The steering shaft 11 may be provided with a rotation restricting portion 19 that restricts relative rotation of the steering shaft 11 with respect to the housing 14 .

[0083] Accordingly, the rotation limiting portion 19 can be configured so as not to limit any rotation of the steering shaft 11 when the first torque T1 and the second torque T2 are normally generated. Thus, the rotation limiting portion 19 can be set to a simple structure. Even if the rotation limiting portion 19 is a simple structure, for example, when one of the first electric motor 15 and the second electric motor 16 becomes inoperable, the relative rotation of the steering shaft 11 with respect to the housing 14 can be temporarily limited. Therefore, the steering device 10 can be made inexpensive, and in addition to generating the above-mentioned first torque T1 and second torque T2, it can also have a structure that mechanically prevents the relative rotation of the steering shaft 11 with respect to the housing 14 in a lengthy manner.

[0084] In the steering device 10, the absolute values ​​of the first torque T1 applied to the steering shaft 11 in the first ball screw part 11a according to the first driving force transmitted to the first ball screw nut 17 and the second torque T2 applied to the steering shaft 11 in the second ball screw part 11b according to the second driving force transmitted to the second ball screw nut 18 are equal. Moreover, in the steering device 10, the first electric motor 15 and the second electric motor 16 generate the first driving force and the second driving force so that when the steering shaft 11 is moved in the axial direction, the absolute values ​​of the first torque T1 and the second torque T2 are equal. Furthermore, in the steering device 10, the absolute values ​​of the first driving force and the second driving force are equal, and the first reduction ratio G1 of the first ball screw nut 17 to reduce the rotation speed to the first ball screw groove 11a2 and convert it into a linear motion for transmission and the second reduction ratio G2 of the second ball screw nut 18 to reduce the rotation speed to the second ball screw groove 11b2 and convert it into a linear motion for transmission are equal.

[0085] According to these, the first torque T1 and the second torque T2 that cancel each other out in the first ball screw part 11a and the second ball screw part 11b can be generated more reliably, and the steering shaft 11 can be reliably moved in the axial direction, that is, the left and right front wheels FW1 and FW2 can be reliably steered. Therefore, it is possible to well prevent the steering shaft 11 and the first ball screw nut 17 and the second ball screw nut 18 from rotating around the axis together and make the steering shaft 11 more reliably move in the axial direction to steer the left and right front wheels FW1 and FW2.

[0086] In these cases, the first ball screw nut 17 is a first threaded engagement component (first nut) threadedly engaged with the first ball screw groove 11a2, and the second ball screw nut 18 is a second threaded engagement component (second nut) threadedly engaged with the second ball screw groove 11b2.

[0087] In addition, the first and second ball screw nuts 17 and 18 having simple structures and relatively low prices can be used as the first and second threaded members, thereby reducing the manufacturing cost of the steering device 10 and providing the steering device 10 at low prices.

[0088] In addition, the steering device 10 includes a rotation limiting portion 19, which suppresses the outer dimensions of the portion of the housing 14 that accommodates the rotation limiting portion 19 to be much smaller and cheaper than the pinion shaft storage portion of the housing of the existing EPS gear. As a result, the steering device 10 can be manufactured inexpensively and can contribute to the miniaturization of the steering device 10. In addition, in the steering device 10, even if the motor (drive source) of either the first electric motor 15 or the second electric motor 16 fails, the steering shaft 11 can be moved axially in the rotation limiting portion 19 in a state in which the relative rotation of the steering shaft 11 relative to the housing 14 is well limited. Therefore, the steering can be well controlled and the reliability is improved. In other words, even if the drive source of one side fails, the vehicle can be accurately moved to a safe place.

[0089] In addition, the rotation limiting portion 19 can be configured so as not to limit the rotation of any steering shaft 11 when the first torque T1 and the second torque T2 are normally generated. Thus, the rotation limiting portion 19 can be set to a simple structure. Moreover, even if the rotation limiting portion 19 is a simple structure, for example, when one of the first electric motor 15 and the second electric motor 16 becomes unable to operate, the relative rotation of the steering shaft 11 with respect to the housing 14 can be temporarily limited. Therefore, the steering device 10 can be made inexpensive, and in addition to generating the above-mentioned first torque T1 and second torque T2, it can also have a structure that mechanically prevents the relative rotation of the steering shaft 11 with respect to the housing 14 in a lengthy manner.

[0090] In addition, according to the above-mentioned embodiment, the first electric motor 15 and the second electric motor 16 are configured to cooperate with each other and move the steering shaft 11 in the axial direction, and the first driving force and the second driving force in the same direction based on themselves are transmitted to the steering shaft 11 via the first ball screw nut 17 and the second ball screw nut 18. In this way, in normal times, the movement of the steering shaft 11 in the axial direction is controlled in a state where the relative rotation with respect to the housing 14 can be well restricted even without using the rotation restricting portion 19.

[0091] (3. Modifications)

[0092] (3-1. First Modification)

[0093] In the above embodiment, the first electric motor 15 as the first power source and the first ball screw nut 17 as the first threaded joint member are connected via the pulley 15a, the belt 15b and the pulley 15d in a manner that can transmit power. In addition, the second electric motor 16 as the second power source and the second ball screw nut 18 as the second threaded joint member are connected via the pulley 16a, the belt 16b and the pulley 16d in a manner that can transmit power. That is, in the above embodiment, the output shaft of the first electric motor 15 and the output shaft of the second electric motor 16 are configured to be parallel to the steering shaft 11.

[0094] Instead of this, Figure 7 As shown, the first electric motor 25 and the second electric motor 26, which are configured similarly to the first electric motor 15 and the second electric motor 16, can be coaxially arranged with the steering shaft 11. Moreover, it is possible to configure the first driving force and the second driving force to be directly transmitted to the first ball screw nut 17 and the second ball screw nut 18. That is, in this case, the rotor 25a of the first electric motor 25 and the first ball screw nut 17 are integrally connected, and the rotor 26a of the second electric motor 26 and the second ball screw nut 18 are integrally connected.

[0095] In this way, even when the first electric motor 25 and the second electric motor 26 are coaxially arranged with the steering shaft 11, the steering device 10 operates in the same manner as in the above-mentioned embodiment. Therefore, the same effects as in the above-mentioned embodiment can be obtained, and in this first modified example, in particular, further miniaturization of the steering device 10 in the radial direction of the steering shaft 11 can be achieved.

[0096] (3-2. Second Modification)

[0097] In the above-mentioned embodiment and the above-mentioned first modified example, the first ball screw groove 11a2 as the first external thread groove and the second ball screw groove 11b2 as the second external thread groove are provided. In addition, in the above-mentioned embodiment and the above-mentioned first modified example, the first ball screw nut 17 is provided as the first nut and the second ball screw nut 18 is provided as the second nut. Moreover, in the above-mentioned embodiment and the above-mentioned first modified example, the balls 11a1 and 11b1 as spherical rolling bodies roll on the rolling paths 11a3 and 11b3 of the ball screw.

[0098] Instead of this, Figure 8 As shown in the example of the above embodiment, the first roller screw groove 31a2 can be set as the first external thread groove and the second roller screw groove 31b2 can be set as the second external thread groove. In this case, the first roller screw nut 37 can be set as the first nut (first threaded engagement component) and the second roller screw nut 38 can be set as the second nut (second threaded engagement component). Moreover, in the second variant, the roller 31a1 and the roller 31b1 as roller-shaped rolling bodies roll on the rolling path 31a3 and the rolling path 31b3 of the roller screw. Therefore, even in this second variant, the same effect as the above embodiment and the above first variant can be obtained.

[0099] (3-3. Third Modification)

[0100] In the above-mentioned embodiment and the above-mentioned first modified example, the first ball screw groove 11a2 as the first external thread groove and the second ball screw groove 11b2 as the second external thread groove are provided. In addition, in the above-mentioned embodiment and the above-mentioned first modified example, the first ball screw nut 17 is provided as the first nut (first threaded engagement component) and the second ball screw nut 18 is provided as the second nut (second threaded engagement component). Moreover, in the above-mentioned embodiment and the above-mentioned first modified example, the balls 11a1 and 11b1 as spherical rolling bodies roll on the rolling paths 11a3 and 11b3 of the ball screw.

[0101] In addition, in the above-mentioned second modification, the first roller screw groove 31a2 is provided as the first external thread groove and the second roller screw groove 31b2 is provided as the second external thread groove. In addition, in the above-mentioned second modification, the first roller screw nut 37 is provided as the first nut (first threaded engagement component) and the second roller screw nut 38 is provided as the second nut (second threaded engagement component). Moreover, in the second modification, the roller 31a1 and the roller 31b1 as roller-shaped rolling bodies are configured to roll on the rolling paths 31a3 and the rolling paths 31b3 of the roller screw.

[0102] Instead of this, Fig. 9As shown in the example of the above embodiment, a first sliding screw portion 41a having a trapezoidal thread groove 41a2 can be provided as a first external thread groove and a second sliding screw portion 41b having a trapezoidal thread groove 41b2 can be provided as a second external thread groove. In this case, a first sliding screw nut 47 can be provided as a first nut (first threaded engagement component) and a second sliding screw nut 48 can be provided as a second nut (second threaded engagement component). Moreover, in the third modified example, the first sliding screw nut 47 and the second sliding screw nut 48 slide and move relative to each other as they rotate in the trapezoidal thread groove 41a2 of the first sliding screw portion 41a and the trapezoidal thread groove 41b2 of the second sliding screw portion 41b. Therefore, even in this third modified example, the same effect as the above embodiment and each of the above modified examples can be obtained.

[0103] (3-4. Fourth Modification)

[0104] In the above-mentioned embodiment and each of the above-mentioned modifications, the rotation restricting portion 19 is described as being provided with only one protrusion 21 and a groove 23 at any position in the circumferential direction of the outer peripheral surface of the steering shaft 11. However, the present invention is not limited to this form. Fig.10 As shown in the fourth modification, the rotation restricting portion 119 may also be provided with a plurality of (e.g., 8) protrusions 121 and grooves 123 at equal angle intervals (e.g., 45 degree intervals) around the axis of the steering shaft 111. In addition, the 45 degree interval and 8 protrusions 121 and grooves 123 are merely examples and may be set arbitrarily.

[0105] In this way, by arranging a plurality of protrusions 121 and grooves 123 at equal angular intervals around the axis of the steering shaft 111, the same effect as in the above-described embodiment can be obtained, and the steering shaft 111 can be stably arranged at the axial center position in the housing 114. In addition, since a plurality of protrusions 121 and grooves 123 are provided, when the relative rotation of the steering shaft 111 around the axis with respect to the housing 114 is restricted, each protrusion 121 abuts against the side surface in the groove 123, thereby reducing the shared load borne, and improving durability.

[0106] (3-5. Fifth Modification)

[0107] As a fifth variation of the above embodiment, Fig.11 As shown, the rotation restricting portion 219 may include a steering shaft side engaging portion 221 provided on the steering shaft 211 and a housing side engaging portion 223 provided on the housing 214 side instead of the protrusions 21 , 121 and the grooves 23 , 123 .

[0108] like Fig.11As shown, the steering shaft side engaging portion 221 is formed on the outer peripheral surface of the steering shaft 211 with a curvature different from the cylindrical outer peripheral surface 211a formed with a predetermined curvature. In other words, the cross-sectional shape of the steering shaft 211 perpendicular to the axis is formed into a D shape, and the surface formed in the straight line portion of the D shape is formed as the steering shaft side engaging portion 221. In addition, the housing side engaging portion 223 is formed to be provided on the steering shaft opposing surface that faces the steering shaft side engaging portion 221 and abuts against the steering shaft side engaging portion 221. At this time, the engaging portion of the steering shaft side engaging portion 221 and the housing side engaging portion 223 that abut against each other on the surface is referred to as the abutting portion 217.

[0109] Furthermore, it is preferred that any lubricant (fluororesin coating FC, solid lubricant (molybdenum disulfide, graphite), or liquid lubricant, not shown) among the lubricating parts described above is provided between the housing side engaging part 223 of the abutting part 217 and the steering shaft side engaging part 221. Thus, when the steering shaft 211 and the housing 214 move relative to each other in the axial direction, the housing side engaging part 223 in the abutting part 217 can slide well on the steering shaft side engaging part 221.

[0110] Furthermore, an example of the structure of the fifth modification will be described. Fig.11 As shown, the housing side engaging portion 223 of the contact portion 217 may also be formed on a predetermined surface of a guide member 215 which is formed separately from the housing 214 and is provided on the housing 14 in a manner that is relatively movable relative to the housing 214. In this case, the guide member 215 is formed, for example, in a cylindrical or cylindrical shape, and is provided on a steering shaft opposing surface ( Fig.11 The housing side engaging portion 223 may be formed on the right end surface of the middle portion. In this case, the guide member 215 may be formed as Fig.11 As shown, the housing 214 is configured, and the back side of the housing-side engaging portion 223 is supported by a plug 216 screwed onto the housing 214 .

[0111] At this time, the plug 216 is screwed to the thread formed on the housing 214. The end surface of the plug 216 biases the back surface of the housing side engaging portion 223 of the guide member 215 toward the steering shaft 211 to fix the guide member 215. According to such a structure, the same effect as the above embodiment can be expected.

[0112] In addition, if Fig.11 As shown, a force applying member 218 such as a coil spring may be interposed between the plunger 216 and the guide member 215. That is, the magnitude of the force applied to the guide member 215 toward the steering shaft 211 can be controlled to a predetermined magnitude by the force applying member 218. Thus, the sliding resistance during the relative movement between the steering shaft 211 and the housing 214 in the axial direction can be controlled with high precision, thereby enabling accurate relative movement.

[0113] In the fifth modification, the housing side engaging portion 223 is provided on the guide member 215 formed separately from the housing 214. However, the present invention is not limited to this form, and the housing side engaging portion 223 may be formed on an integrally formed portion (not shown) integrally formed with the housing 214.

[0114] (3-6. Sixth Modification)

[0115] As a third variation of the above embodiment, the rotation limiting portion 319 may also include: Fig.12 As shown, the steering shaft side engagement portion 321 provided on the steering shaft 311 and the housing side engagement portion 323 provided on the housing 314. At this time, the steering shaft side engagement portion 321 has the same shape as the steering shaft side engagement portion 221 in the fifth modified example.

[0116] like Fig.12 As shown in FIG. 1 , the housing side engaging portion 323 is formed on the outer peripheral surface of the cylindrical roller 315. The rotation axis of the roller 315 itself is supported by the housing 314 via ball bearings 316 disposed at both ends of the rotation axis so as to be rotatable around the axis. With such a configuration, the housing side engaging portion 323 as the outer peripheral surface of the roller 315 abuts against the steering shaft side engaging portion 321 at the abutting portion 317. At this time, the abutting portions 317 contact each other in a straight line.

[0117] Furthermore, when the steering shaft 311 moves relative to the housing 314 in the axial direction, the roller 315 rolls on the steering shaft side engaging portion 321 and can move relative to it. In addition, the relative rotation of the steering shaft 311 around the axis relative to the housing 314 is accurately limited by the abutment portion 317 abutting in a linear shape. Thus, the same effect as the above-mentioned embodiment can be expected.

[0118] In addition, it is preferred that any lubricant (fluororesin coating (not shown), solid lubricant (molybdenum disulfide, graphite, not shown), or liquid lubricant (not shown)) of the lubricating portion described above is provided between the outer peripheral surface (housing side engaging portion 323) of the roller 315 of the abutment portion 317 and the steering shaft side engaging portion 321. Thus, when the steering shaft 311 and the housing 314 move relative to each other in the axial direction, the abutment portion 317 can effectively suppress the wear of the housing side engaging portion 323 and the steering shaft side engaging portion 321 due to friction.

[0119] (3-7. Seventh Modification)

[0120] As a fourth variation of the above embodiment, Fig.13 , Fig.14As shown, for the rotation limiting portion 419, the steering shaft side engaging portion may also be formed by the rack teeth 421, and the housing side engaging portion may also be formed by the pinion teeth 423 of the pinion 415 meshing with the rack teeth 421. Fig.13 , Fig.14 The rotating shaft is formed into an axis shape, and the rotating shaft is supported on the inner peripheral surface of the housing 414 via ball bearings 416, 416 arranged at both ends so as to be rotatable around its own axis. Each ball bearing 416 is supported and fixed from the axial outside of the rotating shaft C2 by each plug 418. In addition, such a support method based on ball bearings is well known and is not the main part of the invention, so it will not be described in further detail.

[0121] In the seventh variation, if Fig.14 As shown, the pinion 415 of the rotation limiting portion 419 is formed so that the tooth line TL2 of the pinion tooth 423 (housing side engagement portion) is parallel to the rotation axis C2 (axis center) of the pinion 415. In addition, the pinion 415 is configured so that the rotation axis C2 is orthogonal to the axial direction of the central axis C1 of the steering shaft 11. Fig.14 As shown, the rack teeth 421 (steering shaft side engagement portion) of the rotation limiting portion 419 is formed so that the tooth line TL1 is orthogonal to the axial direction of the central axis C1 of the steering shaft 411. In addition, the tooth line TL1 of the rack teeth 421 is formed to be parallel to the tooth line TL2 of the pinion teeth 423 (housing side engagement portion) of the pinion 415. Moreover, the rack teeth 421 and the pinion teeth 423 abut and engage with each other on the tooth surface. At this time, the engagement portion of the rack teeth 421 and the pinion teeth 423 abutting against each other on the tooth surface is called the abutment portion 417.

[0122] Furthermore, it is preferred that any lubricant (fluororesin coating FC (not shown), solid lubricant (molybdenum disulfide, graphite, not shown), or liquid lubricant (not shown)) described in the lubrication section is provided between the pinion teeth 423 and the rack teeth 421 of the abutment portion 417. Thus, when the steering shaft 411 and the housing 414 move relative to each other in the axial direction, wear of the pinion teeth 423 and the rack teeth 421 due to friction can be effectively suppressed in the abutment portion 417.

[0123] In addition, as described above, a large force is usually not applied to the abutment portion 417. In addition, even in an emergency, it is sufficient to be able to operate for a short time for evacuation. Therefore, the pinion teeth 423 and the rack teeth 421 do not need to have a large strength. In addition, in order to improve the strength of the meshing portion and reduce noise, it is not necessary to make each tooth of the pinion teeth 423 and the rack teeth 421 be a helical tooth. Therefore, since no axial force is applied to each gear, the structure of the gear device can be simplified and low cost can be achieved.

[0124] In addition, the tooth line TL2 of the pinion gear 415 may be formed parallel to the rotation axis C2 of the pinion gear 415, and the rotation axis C2 of the pinion gear 415 may be made oblique to the axial direction of the center axis C1 of the steering shaft 11, and the tooth line TL1 of the rack teeth 421 may be made oblique to the axial direction of the center axis C1 of the steering shaft 11. Even with this structure, the pinion gear 415 can be easily manufactured by extrusion molding or the like, thereby achieving low cost of the steering device 10.

[0125] According to such a structure, the steering device 10 can expect the same effect as the above-mentioned embodiment. In other words, even when the motor (drive source) of either the first electric motor 15 or the second electric motor 16 fails, the steering shaft 411 can be smoothly moved in the axial direction in a state where the relative rotation of the steering shaft 411 with respect to the housing 414 is well restricted in the rotation restricting portion 419. Therefore, even when one of the drive sources fails, the vehicle can be accurately moved to a safe place.

[0126] Furthermore, in the fifth modification, the rotation restricting portion 219 includes a steering shaft side engaging portion 221 provided on the steering shaft 211, and a housing side engaging portion 223 provided on the housing 214. The steering shaft side engaging portion 221 and the housing side engaging portion 223 abut against each other at their surfaces, and relative movement of the steering shaft 211 and the housing 214 in the axial direction is allowed, while relative rotation of the steering shaft 211 with respect to the housing 214 is restricted.

[0127] However, it is not limited to this form. Fig.15 As shown, the rotation limiting portion 219 may also be formed with respective engaging surfaces so that when the steering shaft side engaging portion 221 abuts against the housing side engaging portion 223, they abut and engage at least at one point. Fig.15 , the state in which the housing side engaging portion 223 and the steering shaft side engaging portion 221 are in contact at one point is shown. In this case, the steering shaft side engaging portion 221 is formed in the same shape as the fifth modification, and the housing side engaging portion 223 is formed by a surface having a concave and convex surface. Moreover, the apex TP of the concave and convex surface of the housing side engaging portion 223 and the steering shaft side engaging portion 221 are in contact at one point, forming a contact portion 517.

[0128] At this time, the contact position in the case where the apex TP of the concavoconvex part 223 of the housing side engaging part 223 is brought into contact with the steering shaft side engaging part 221 at only one point can be the intersection position of the normal line L of the steering shaft side engaging part 221 and the steering shaft side engaging part 221 which passes through the axis line CL of the steering shaft 211 and is orthogonal to the axis line CL. As a result, the relative rotation of the steering shaft 211 around the axis with respect to the housing 214 can be well restricted. Based on this, the effect corresponding to the above-mentioned embodiment can also be expected. In addition, without being limited to the above-mentioned form, in order to stably obtain the same effect as the above-mentioned embodiment, it is preferred that the steering shaft side engaging part 221 and the housing side engaging part 223 are brought into contact at two or more points (not shown in the figure).

[0129] When implementing the present invention, the present invention is not limited to the above-described embodiment and each of the above-described modifications, and various modifications can be made without departing from the purpose of the present invention.

[0130] For example, in the above-mentioned embodiment and each of the above-mentioned modifications, the first electric motor 15 and the second electric motor 16 (the first electric motor 25 and the second electric motor 26) are fixed to the housing 14 in a manner that the output shafts are opposed to each other. Instead of this, the first electric motor 15 and the second electric motor 16 (the first electric motor 25 and the second electric motor 26) can be arranged in a manner that the output shafts are in the same direction in the left-right direction of the steering shaft 11. In addition, the first electric motor 15 and the second electric motor 16 (the first electric motor 25 and the second electric motor 26) can be arranged so that at least one of the circumferential direction and the radial direction of the housing 14 is offset. In this way, it is possible to configure the first electric motor 15 and the second electric motor 16 (the first electric motor 25 and the second electric motor 26) to be fixed to the housing 14 and generate the first driving force and the second driving force.

[0131] In this case, the first feed screw part and the second feed screw part such as the first ball screw part 11a and the second ball screw part 11b provided on the steering shaft 11 are left-right threads (reverse threads). Therefore, when the steering shaft 11 is moved axially, for example, the second electric motor 16 generates a second driving force opposite to the first driving force generated by the first electric motor 15.

[0132] Thus, for example, the absolute values ​​of the first torque T1 generated in the first ball screw portion 11a and the second torque T2 generated in the second ball screw portion 11b are equal and opposite, and as a result, the rotation of the steering shaft 11 can be prevented. Therefore, in this case, the same effects as those of the above-mentioned embodiment and the above-mentioned modifications can be obtained, and, for example, the degree of freedom in mounting when the steering device 10 is assembled to a vehicle can be ensured.

Claims

1. A steering device, characterized in that: have: A hollow shell; A steering shaft, which is accommodated in the housing, has a first external thread groove formed by a winding method of one of a left thread and a right thread, and has a second external thread groove formed by a winding method of the other of the left thread and the right thread, and steers the left and right steering wheels by moving in the axial direction; a first nut threadably engaged with the first external thread groove and rotatably supported inside the housing; a second nut threadably engaged with the second external thread groove and rotatably supported inside the housing; a first driving source generating a first driving force; a second driving source that operates independently of the first driving source and generates a second driving force; a first power transmission part, which transmits the first driving force generated by the first driving source to the first nut, so that the first nut rotates to apply an axial force to the steering shaft; a second power transmission part that transmits the second driving force generated by the second driving source to the second nut, so that the second nut rotates to apply an axial force to the steering shaft, and a rotation limiting portion, which is arranged across the housing and the steering shaft, and allows the steering shaft to move relative to the housing in the axial direction, and limits the relative rotation of the steering shaft around the axis relative to the housing, The rotation limiting portion comprises: a steering shaft side engaging portion provided on the steering shaft; and a shell side engaging portion provided on the shell, wherein the shell side engaging portion engages with the steering shaft side engaging portion to allow relative movement of the shell and the steering shaft in the axial direction and to limit relative rotation of the steering shaft relative to the shell about the axis. The rotation limiting portion comprises: a protrusion, which is one of the steering shaft side engaging portion and the housing side engaging portion, extending radially outward of the steering shaft or radially inward of the housing; and a groove, which is the other of the steering shaft side engaging portion and the housing side engaging portion, extending in the axial direction of the steering shaft. The protrusion and the groove are provided at only one position in any circumferential direction of the outer peripheral surface of the steering shaft. The protrusion is protrudingly arranged on the outer peripheral surface of the annular component, the inner peripheral surface of the annular component is engaged with the outer peripheral surface of the steering shaft and is fixed to the steering shaft, and the outer diameter of the outer peripheral surface of the engaging portion of the steering shaft for the annular component to engage is larger than the outer diameter of the outer peripheral surface of the steering shaft outside the engaging portion.

2. The steering device according to claim 1, wherein: The first drive source and the second drive source are configured to transmit the first drive force and the second drive force to the steering shaft via the first power transmission portion and the second power transmission portion in cooperation with each other to move the steering shaft in the axial direction.

3. The steering device according to claim 1, wherein: An absolute value of a first torque acting on the steering shaft from the first nut by the first driving force transmitted to the first power transmission unit and an absolute value of a second torque acting on the steering shaft from the second nut by the second driving force transmitted to the second power transmission unit are equal.

4. The steering device according to claim 2, wherein: An absolute value of a first torque acting on the steering shaft from the first nut by the first driving force transmitted to the first power transmission unit and an absolute value of a second torque acting on the steering shaft from the second nut by the second driving force transmitted to the second power transmission unit are equal.

5. The steering device according to claim 3, wherein: The first drive source and the second drive source generate the first drive force and the second drive force such that an absolute value of the first torque and an absolute value of the second torque become equal when the steering shaft is moved in the axial direction.

6. The steering device according to claim 4, wherein: The first drive source and the second drive source generate the first drive force and the second drive force such that an absolute value of the first torque and an absolute value of the second torque become equal when the steering shaft is moved in the axial direction.

7. The steering device according to any one of claims 1 to 6, wherein: The absolute value of the first driving force is equal to the absolute value of the second driving force, and the first reduction ratio at which the first power transmission unit reduces the rotational speed to the first nut is equal to the second reduction ratio at which the second power transmission unit reduces the rotational speed to the second nut.

8. The steering device according to any one of claims 1 to 6, wherein: The first external thread groove and the second external thread groove are external thread grooves of any one of a ball screw having a rolling path for a spherical rolling element to roll, a roller screw having a rolling path for a roller-shaped rolling element to roll, and a slide screw. The first nut and the second nut are respectively corresponding to the first external thread groove and the second external thread groove, and are any one of a ball screw nut that accommodates the spherical rolling element, a roller screw nut that accommodates the roller-shaped rolling element, and a sliding screw nut that is threadedly engaged with the sliding screw.

9. The steering device according to claim 7, wherein: The first external thread groove and the second external thread groove are external thread grooves of any one of a ball screw having a rolling path for a spherical rolling element to roll, a roller screw having a rolling path for a roller-shaped rolling element to roll, and a slide screw. The first nut and the second nut are respectively corresponding to the first external thread groove and the second external thread groove, and are any one of a ball screw nut that accommodates the spherical rolling element, a roller screw nut that accommodates the roller-shaped rolling element, and a sliding screw nut that is threadedly engaged with the sliding screw.

10. The steering device according to claim 8, wherein: The first drive source and the second drive source are configured coaxially with the steering shaft and directly transmit the first drive force and the second drive force to the first nut and the second nut, or are configured parallel to the steering shaft and transmit the first drive force and the second drive force to the first nut and the second nut via an endless component.

11. The steering device according to claim 9, wherein: The first drive source and the second drive source are configured coaxially with the steering shaft and directly transmit the first drive force and the second drive force to the first nut and the second nut, or are configured parallel to the steering shaft and transmit the first drive force and the second drive force to the first nut and the second nut via an endless component.

Images