Vehicle steering device

Abstract

A vehicle steering device (10) comprises: a first housing (51) which accommodates a steering shaft (26); a second housing (52) which is connected to one end of the first housing (51); a belt transmission mechanism (60) and a ball screw (70) which transmit a driving force generated by a drive source (43) to the steering shaft (26); and a double-row four-point-contact ball bearing (80) which supports a nut (73) of the ball screw (70) in the first housing (51). A driven pulley (62) of the belt transmission mechanism (60) is connected to the nut (73). An inner ring (81) of the double-row four-point-contact ball bearing (80) is fitted to an outer circumferential portion (73a) of the nut (73). An outer ring (82) of the double-row four-point-contact ball bearing (80) is fitted to an inner circumferential portion (55a) of the first housing (51).

Description

Vehicle steering device

[0001] The present invention relates to a vehicle steering system having a belt and a ball screw.

[0002] Among vehicle steering devices, there is a power steering device of a type in which a driving force generated by a driving source such as an electric motor is transmitted to a steering shaft (e.g., a rack shaft) by a belt and a ball screw. The wheels can be steered by moving the steering shaft in the axial direction. This type of vehicle steering device is known, for example, from Patent Document 1.

[0003] The vehicle steering device known from Patent Document 1 includes a housing, a rack shaft (steered shaft), a ball screw nut, multiple balls, and a bearing. A threaded portion is formed on the outer periphery of the rack shaft, and the ball screw nut is threadedly engaged with the threaded portion via multiple balls. The bearing is installed between the inner periphery of the housing and the outer periphery of the ball screw nut, and is sandwiched by the housing from both sides in the axial direction of the rack shaft. This bearing is configured as a double-row angular contact ball bearing.

[0004] Special Publication No. 2006-509979

[0005] By using a double-row angular contact ball bearing as the bearing for the vehicle steering device known from Patent Document 1, it is possible for a single bearing to bear a fixed amount of axial load in both directions. However, there is room for improvement in order to reduce the size of the vehicle steering device.

[0006] An object of the present invention is to provide a vehicle steering device that can be made smaller.

[0007] After extensive research, the inventors discovered that by using a double-row four-point contact ball bearing instead of a double-row angular contact ball bearing, axial loads can be supported by both double-row four-point contact ball bearings, and radial loads can also be supported by both double-row four-point contact ball bearings. By taking these measures, both axial and radial loads can be supported by the double-row four-point contact ball bearing, which is thought to enable the bearing size to be reduced. The present invention was completed based on this discovery.

[0008] The present disclosure will be described below. According to one aspect of the present disclosure, a vehicle steering device includes a steerable shaft connected to an input shaft by a rack-and-pinion mechanism and movable in a vehicle width direction, a first housing accommodating the input shaft and the steerable shaft, and a second housing coupled to one end of the first housing. The vehicle steering device further includes a drive source provided in the second housing, a belt transmission mechanism and a ball screw capable of transmitting a driving force generated by the drive source to the steerable shaft. The vehicle steering device further includes a bearing supporting a nut constituting a part of the ball screw on the first housing. A driven pulley constituting a part of the belt transmission mechanism is connected to the nut and accommodated in the second housing. The bearing is configured as a double-row four-point contact ball bearing. An inner ring of the double-row four-point contact ball bearing is engaged with an outer periphery of the nut. An outer ring of the double-row four-point contact ball bearing is engaged with an inner periphery of the first housing.

[0009] According to another aspect of the present disclosure, a vehicle steering device includes a steerable shaft connected to an input shaft by a rack-and-pinion mechanism and movable in a vehicle width direction, a first housing accommodating the input shaft and the steerable shaft, and a second housing coupled to one end of the first housing. The vehicle steering device further includes a drive source provided in the second housing, a belt transmission mechanism and a ball screw capable of transmitting a driving force generated by the drive source to the steerable shaft. The vehicle steering device further includes a bearing that supports a nut constituting a part of the ball screw on the first housing via a hub of a driven pulley constituting a part of the belt transmission mechanism. The hub is connected to the nut and accommodated in the second housing. The bearing is configured as a double-row four-point contact ball bearing. The inner ring of the double-row four-point contact ball bearing is engaged with the outer periphery of the hub. The outer ring of the double-row four-point contact ball bearing is engaged with the inner periphery of the first housing.

[0010] According to the present invention, the size of the bearing can be reduced, and as a result, the first housing that fits with the bearing can also be made smaller, so it is possible to provide a vehicle steering device that can be made smaller.

[0011] 1 is a schematic diagram of a vehicle steering device according to a first embodiment. FIG. 1 is a cross-sectional view of the second transmission mechanism and its surroundings shown in FIG. 2. FIG. 4A is an enlarged view of the double-row four-point contact ball bearing and its surroundings shown in FIG. 2. FIG. 4A is a schematic diagram of the combination of the driven pulley, ball screw nut, and double-row four-point contact ball bearing shown in FIG. 2, showing a state in which the inner ring of the double-row four-point contact ball bearing is subjected to an axial load in a direction away from the driven pulley, and FIG. 4B is a diagram showing a state in which the inner ring shown in FIG. 4A is subjected to an axial load in a direction in which it contacts the driven pulley. FIG. 5A is a schematic diagram showing that the balls are positioned in the direction of application of a radial load when the double-row four-point contact ball bearing shown in FIG. 4A is viewed from the axial direction, and FIG. 5B is a schematic diagram showing that the balls are positioned in the direction of application of the radial load compared to the state shown in FIG. 5A. ...C is a diagram showing the results of an investigation into the difference in the variation value of the inner ring inclination angle due to differences in radial internal clearance. 9 is a diagram showing the results of a study on the difference in fluctuation value of the axial displacement amount due to the difference in the radial internal clearance. It is a diagram showing the results of a study on the difference in fluctuation value of the radial displacement amount due to the difference in the radial internal clearance. It is a cross-sectional view of the second transmission mechanism and its surroundings of the vehicle steering device according to Example 2. It is an enlarged view of the double-row four-point contact ball bearing and its surroundings shown in FIG.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. Note that the embodiments shown in the accompanying drawings are merely examples of the present invention, and the present invention is not limited to these embodiments.

[0013] First Embodiment A vehicle steering device 10 according to a first embodiment will be described with reference to FIGS. 1 to 8. FIG.

[0014] As shown in FIG. 1, a vehicle steering device 10 includes a steering system 20 extending from a steering wheel 21 of the vehicle to wheels 31, 31 (steerable wheels 31, 31), and an assist torque mechanism 40 that applies an assist torque to the steering system 20.

[0015] The steering system 20 includes a steering shaft 22 connected to a steering wheel 21, an input shaft 24 connected to the steering shaft 22 by a universal joint 23, and a steered shaft 26 connected to the input shaft 24 by a first transmission mechanism 25. Left and right wheels 31, 31 (on both sides in the vehicle width direction) are connected to both ends of the steered shaft 26 via ball joints 27, 27, tie rods 28, 28, and knuckles 29, 29.

[0016] The first transmission mechanism 25 is configured, for example, by a rack-and-pinion mechanism. The steering shaft 26 is movable in the axial direction (vehicle width direction). The rack-and-pinion mechanism 25 is configured by a pinion 25 a provided on the input shaft 24 and a rack 25 b provided on the steering shaft 26 so as to be able to mesh with the pinion 25 a.

[0017] According to the steering system 20, when the driver turns the steering wheel 21, the left and right wheels 31, 31 can be steered by the steering torque via the first transmission mechanism 25, the steering shaft 26, and the left and right tie rods 28, 28.

[0018] The assist torque mechanism 40 includes a steering torque sensor 41, a control unit 42, an electric motor 43 (drive source 43), and a second transmission mechanism 44. The steering torque sensor 41 detects the steering torque of the steering system 20 applied to the steering wheel 21. The control unit 42 generates a control signal based on the torque detection signal of the steering torque sensor 41. The electric motor 43 generates motor torque (assist torque), i.e., driving force, corresponding to the steering torque based on the control signal from the control unit 42. The second transmission mechanism 44 transmits the assist torque generated by the electric motor 43 to the steered shaft 26.

[0019] According to this vehicle steering device 10 , the wheels 31 , 31 can be steered by the steering shaft 26 using a combined torque obtained by adding the auxiliary torque of the electric motor 43 to the steering torque of the driver.

[0020] The first transmission mechanism 25 is accommodated in a housing 50. The steering shaft 26 is also accommodated in the housing 50 so as to be movable in the vehicle width direction St (axial direction St). Both ends of the steering shaft 26 protrude from both ends of the housing 50 in the vehicle width direction.

[0021] The housing 50 extends in the vehicle width direction St and has a through-hole 50a that penetrates in the vehicle width direction St. The housing 50 is divided into two parts in the vehicle width direction, a first housing 51 and a second housing 52, which are integrated together by fastening with bolts 53 (see FIG. 2 ). The electric motor 43 is attached to the second housing 52. An output shaft 43a (motor shaft 43a) of the electric motor 43 is positioned parallel to the steering shaft 26.

[0022] As shown in FIG. 2 , the housing 50 further has a storage chamber 54 inside the joint between the first housing 51 and the second housing 52. This storage chamber 54 includes a first storage chamber 55 and a second storage chamber 56. In other words, the housing 50 is composed of the first housing 51, which has the first storage chamber 55 at one end, and the second housing 52, which has the second storage chamber 56 at one end. The first storage chamber 55 and the second storage chamber 56 are continuous in the axial direction of the housing 50 and have a larger diameter than the through-hole 50a. The inner circumferential surface 55a of the first storage chamber 55 formed in the first housing 51 is sometimes referred to as the "inner circumferential portion 55a (inner circumferential surface 55a) of the first housing 51," and the inner circumferential surface 56a of the second storage chamber 56 is sometimes referred to as the "inner circumferential portion 56a (inner circumferential surface 56a) of the second housing 52." The second housing 52 has a cylindrical end 57 that faces one end of the first housing 51. By fitting the end 57 of the second housing 52 into the inner circumferential surface 55a of the first storage chamber 55, the first housing 51 and the second housing 52 are positioned concentrically.

[0023] The first housing 51 has an inner wall surface 51a (first inner wall surface 51a) that forms the bottom surface of the first storage chamber 55. A tip surface 57a (second inner wall surface 57a) of the end portion 57 of the second housing 52 faces the first inner wall surface 51a. The first inner wall surface 51a and the second inner wall surface 57a are flat surfaces that are perpendicular to the steering axis 26.

[0024] 2, the second transmission mechanism 44 is housed in a housing chamber 54. The second transmission mechanism 44 includes, for example, a belt transmission mechanism 60 and a ball screw 70.

[0025] The belt transmission mechanism 60 includes a drive pulley 61 provided on the output shaft 43 a of the electric motor 43, a driven pulley 62 provided on a nut 73 of the ball screw 70, and a belt 63 wound around the drive pulley 61 and the driven pulley 62. The belt 63 is, for example, a timing belt. The connection structure of the driven pulley 62 to the nut 73 will be described later.

[0026] Ball screw 70 is a type of conversion mechanism that converts rotational motion into linear motion, and transmits the driving force generated by electric motor 43, i.e., auxiliary torque, to the steered shaft 26. Ball screw 70 includes a threaded portion 71 (female thread 71) formed on steered shaft 26, a plurality of balls 72, and a nut 73 connected to threaded portion 71 via the plurality of balls 72. Nut 73 is rotatably supported on first housing 51 by bearing 80, and its relative axial movement with respect to bearing 80 is restricted.

[0027] 3, the bearing 80 is configured as a double-row four-point contact ball bearing. This bearing 80 may also be referred to as a "double-row four-point contact ball bearing 80."

[0028] This double-row four-point contact ball bearing 80 is a type of rolling bearing, and comprises an inner ring 81, an outer ring 82, two rows of multiple four-point contact balls 83 arranged between the inner ring 81 and the outer ring 82, and a retainer 84.

[0029] The inner ring 81 is formed from a single member and has two rows of raceway surfaces 81a, 81a arranged in the axial direction on its outer periphery. The outer ring 82 is formed from a single member and has two rows of raceway surfaces 82a, 82a arranged in the axial direction on its inner periphery. Each raceway surface 81a, 81a, 82a, 82a has the same cross-sectional shape. Furthermore, the cross-sectional shapes of each raceway surface 81a, 81a, 82a, 82a are bilaterally symmetrical with respect to the center of the bottom of the raceway surface, and each has the same radius of curvature. Balls 83 roll between the raceway surfaces 81a, 81a of the inner ring 81 and the raceway surfaces 82a, 82a of the outer ring 82. The balls 83 are made of, for example, steel balls. The cage 84 is a member that partially surrounds the balls 83, maintaining a constant spacing in the circumferential direction, and is made of, for example, a resin material. Each of the raceway surfaces 81a, 81a, 82a, 82a and the balls 83 arranged on each of the raceway surfaces 81a, 81a, 82a, 82a are in contact with each other at four points.

[0030] As described above, the double-row four-point contact ball bearing 80 includes an inner ring 81 made of a single member having two rows of raceway surfaces 81 a, 81 a on its outer periphery, an outer ring 82 made of a single member having two rows of raceway surfaces 82 a, 82 a on its inner periphery, and two rows of four-point contact balls 83 that roll between the raceway surfaces 81 a, 81 a of the inner ring 81 and the raceway surfaces 82 a, 82 a of the outer ring 82. This double-row four-point contact ball bearing 80 can distribute the load acting on each ball 83, thereby increasing the load capacity. As a result, a compact bearing can be provided that ensures support rigidity while reducing torque loss. This contributes to the miniaturization of the first housing 51 into which the double-row four-point contact ball bearing 80 fits.

[0031] Furthermore, the double-row four-point contact ball bearing 80 is provided with seals 85, 85 between both end portions 81b, 81b of the inner ring 81 and both end portions 82b, 82b of the outer ring 82. Therefore, the seals 85, 85 can prevent dirt from entering the double-row four-point contact ball bearing 80 and oil from leaking. This is advantageous for maintaining the radial internal clearance of the double-row four-point contact ball bearing 80.

[0032] The seal portions 85, 85 may be of either a contact type that comes into contact with the inner ring 81, or a non-contact type that does not come into contact with the inner ring 81. The contact type improves sealing performance because the inner ring 81 and the seal portions 85, 85 come into contact with each other and there are no gaps. The non-contact type reduces frictional resistance because the inner ring 81 and the seal portions 85, 85 are separated.

[0033] The inner peripheral surface 81c of the inner ring 81 of the double-row four-point contact ball bearing 80 is fitted to the outer peripheral portion 73a (outer peripheral surface 73a) of the nut 73. Furthermore, the inner ring 81 is sandwiched between a stepped surface 73b on the outer peripheral portion 73a of the nut 73 and a bearing nut 91 screwed onto the nut 73. For this reason, relative movement in the axial direction between the inner ring 81 and the nut 73 is restricted.

[0034] The outer peripheral surface 82c of the outer ring 82 of the double-row four-point contact ball bearing 80 is fitted into the inner peripheral portion 55a of the first housing 51 (first storage chamber 55). There is an extremely small gap between the inner peripheral portion 55a of the first housing 51 and the outer peripheral surface 82c of the outer ring 82. Therefore, when a load acts on the double-row four-point contact ball bearing 80 in the axial direction St, the double-row four-point contact ball bearing 80 can move in the axial direction St of the steered shaft 26 relative to the first housing 51.

[0035] In contrast, a pair of elastic annular support portions 92, 92 are located on both sides of the outer ring 82 of the double-row four-point contact ball bearing 80. The pair of support portions 92, 92 face each other in the axial direction St of the steered shaft 26, sandwiching the double-row four-point contact ball bearing 80 therebetween. In this way, the double-row four-point contact ball bearing 80 and the pair of support portions 92, 92 are located between the first inner wall surface 51a and the second inner wall surface 57a in the storage chamber 54. The side surfaces 82d, 82d of the outer ring 82 of the double-row four-point contact ball bearing 80 are elastically supported in the axial direction St of the steered shaft 26 (so-called floating support) around the entire circumference by the pair of annular support portions 92, 92. As a result, the nut 73 is elastically supported indirectly in the axial direction St of the steered shaft 26 via the double-row four-point contact ball bearing 80. The support portions 92, 92 are formed of annular elastic bodies.

[0036] The hub 62a of the driven pulley 62 is connected to a nut 73 and is housed in the second housing 52 (second storage chamber 56). More specifically, the hub 62a is fitted onto an outer circumferential portion 73a of the nut 73 and is restricted in both relative rotation and relative axial movement with respect to the nut 73. As shown in Fig. 2, the hub 62a of the driven pulley 62 and the belt 63 are located apart from the double-row four-point contact ball bearing 80 in the axial direction St of the steered shaft 26. The double-row four-point contact ball bearing 80 is housed in the first housing 51 (first storage chamber 55).

[0037] The above description of the first embodiment can be summarized as follows. As shown in Fig. 1, the vehicle steering device 10 includes a steered shaft 26 that is connected to the input shaft 24 by a rack-and-pinion mechanism 25 and is movable in the vehicle width direction St, a first housing 51 that houses the input shaft 24 and the steered shaft 26, and a second housing 52 that is connected to one end of the first housing 51. The vehicle steering device 10 also includes a drive source 43 (electric motor 43) that is provided in the second housing 52, and a belt transmission mechanism 60 and a ball screw 70 that can transmit the drive force generated by the drive source 43 to the steered shaft 26. As shown in Fig. 2, the vehicle steering device 10 also includes a bearing 80 that supports a nut 73 that forms part of the ball screw 70 on the first housing 51.

[0038] 2, the driven pulley 62, which forms part of the belt transmission mechanism 60, is connected to the nut 73 and is housed in the second housing 52. The bearing 80 is constituted by a double-row four-point contact ball bearing 80. An inner ring 81 of this double-row four-point contact ball bearing 80 is engaged with the outer periphery 73a of the nut 73. An outer ring 82 of the double-row four-point contact ball bearing 80 is engaged with the inner periphery 55a of the first housing 51.

[0039] As described above, in the first embodiment, a double-row four-point contact ball bearing is used for the bearing 80. This double-row four-point contact ball bearing 80 (bearing 80) can withstand axial loads in both axial directions. Moreover, radial loads can also be supported by both of the two rows of four-point contact balls 83 of the double-row four-point contact ball bearing 80. Because the double-row four-point contact ball bearing 80 can adequately support both axial and radial loads, the size of the bearing 80 can be reduced. As a result, the first housing 51 (housing 50) that fits into the bearing 80 can also be made smaller, making it possible to provide a vehicle steering device 10 that can be made more compact.

[0040] In addition, a moment is generated in the bearing 80 due to the belt tension acting on the driven pulley 62. In the first embodiment, the double-row four-point contact ball bearing 80, which has excellent durability against radial loads, is used as the bearing 80, thereby making it possible to provide a vehicle steering device 10 with high rigidity against large radial loads.

[0041] Incidentally, rolling bearings have radial internal clearance, including double-row four-point contact ball bearing 80. Here, "radial internal clearance" refers to the amount of radial movement that the other, unfixed, raceway ring can make when one of the two raceways 81, 82 (inner race 81 and outer race 82) of double-row four-point contact ball bearing 80 is fixed, without the application of a load.

[0042] Generally, quietness within the vehicle cabin is required to improve the comfort of the vehicle. To this end, it is also required to minimize the operating noise of the vehicle steering device 10. The inventors analyzed the effect of the radial internal clearance of the double-row four-point contact ball bearing 80 on the operating noise of the vehicle steering device 10.

[0043] First, the vibration states of the inner rings of the double-row four-point contact ball bearing 80 and a typical single-row four-point contact ball bearing (an example of related art) when an external force is applied (when an external force load is applied) were compared.

[0044] 4A is a schematic representation of an assembly model combining the driven pulley 62, nut 73 of ball screw 70, and double-row four-point contact ball bearing 80 shown in FIG. 2. The axial center distance from the double-row four-point contact ball bearing 80 to the driven pulley 62 is Ln. Of the two ball rows in the double-row four-point contact ball bearing 80, the row closer to the driven pulley 62 is referred to as the first row L1, and the row farther from it is referred to as the second row L2.

[0045] When tension is applied from the belt 63 to the driven pulley 62, a radial load Kr acts on the nut 73 and the double-row four-point contact ball bearing 80. As a result, a counterclockwise moment is generated on the double-row four-point contact ball bearing 80, tilting the inner ring of the double-row four-point contact ball bearing 80 by the tilt angle θ. In this state, an axial load Ka acts on the inner ring, causing it to displace slightly in the axial direction. The axial load Ka in the direction in which the inner ring moves away from the driven pulley 62 is indicated by a "+" sign, as a "positive axial load Ka+." Meanwhile, in FIG. 4B, the axial load Ka in the direction in which the inner ring contacts the driven pulley 62 is indicated by a "-" sign, as a "negative axial load Ka-." In the case of the vehicle steering device 10 of FIG. 1, the positive axial load Ka+ occurs when the steering wheel 21 is steered to the left. The negative axial load Ka- occurs when the steering wheel 21 is steered to the right.

[0046] Figure 5A shows the state in which ball 83 is positioned in the direction of action of radial load Kr when double-row four-point contact ball bearing 80 shown in Figure 4A is viewed from the axial direction. Figure 5B shows the state in which balls 83, 83 are positioned in the direction of action of radial load Kr, compared to the state in Figure 5A.

[0047] 5A and 5B, as the inner ring 81 rotates, the positions of the balls 83 change circumferentially relative to the direction of action of the radial load Kr. In other words, the inner ring 81 is displaced in the radial direction. The radial displacement of the inner ring 81 is Ra. The difference between the maximum and minimum values ​​of this radial displacement Ra is called the fluctuation value ΔR of the radial displacement Ra. This fluctuation value ΔR depends on the radial internal clearance.

[0048] Furthermore, as the inner ring 81 is displaced in the radial direction, it tilts as shown in Figures 4A and 4B. The inclination angle of this inner ring 81 is θ. The difference between the maximum and minimum values ​​of the inclination angle θ of the inner ring 81 is called the fluctuation value Δθ of the inclination angle θ. This fluctuation value Δθ depends on the radial internal clearance.

[0049] 4A and 4B, when an axial load Ka (i.e., Ka+, Ka-) acts on the inner ring 81 of a double-row four-point contact ball bearing 80, the inner ring 81 is displaced in the axial direction (axial direction). The amount of displacement of the inner ring 81 in the axial direction (axial displacement amount) is Sr. The difference between the maximum and minimum values ​​of this axial displacement amount Sr is called the fluctuation value ΔS of the axial displacement amount Sr. This fluctuation value ΔS depends on the radial internal clearance.

[0050] 6, 7 and 8 compare the double-row four-point contact ball bearing 80 with the single-row four-point contact ball bearing. The double-row four-point contact ball bearing 80 and the single-row four-point contact ball bearing were examined under the same conditions.

[0051] FIG. 6 shows the results of an investigation into the difference in the variation value Δθ of the inclination angle θ due to differences in the radial internal clearance Cr, with the radial internal clearance Cr (μm) of each bearing on the horizontal axis and the variation value Δθ of the inner ring inclination angle θ on the vertical axis.

[0052] The characteristic of the variation Δθ of the inclination angle θ when the single-row four-point contact ball bearing is subjected to a positive axial load Ka+ is shown by the first characteristic line Q1. According to this, regardless of differences in the radial internal clearance Cr, the variation Δθ of the inclination angle θ is constant at approximately zero. Furthermore, the characteristic of the variation Δθ of the inclination angle θ when the single-row four-point contact ball bearing is subjected to a negative axial load Ka- is shown by the second characteristic line Q2. According to this, as the radial internal clearance Cr increases, the variation Δθ of the inclination angle θ increases significantly.

[0053] In contrast, the characteristic of the fluctuation value Δθ of the inclination angle θ when the double-row four-point contact ball bearing 80 is subjected to a positive axial load Ka+ is shown by the third characteristic line Q3. According to this, regardless of differences in the radial internal clearance Cr, the fluctuation value Δθ of the inclination angle θ is constant at approximately zero. In other words, when the double-row four-point contact ball bearing 80 is subjected to a positive axial load Ka+, the characteristic is approximately the same as in the case of the single-row four-point contact ball bearing of the comparative example.

[0054] Furthermore, the characteristic of the variation Δθ of the inclination angle θ when the double-row four-point contact ball bearing 80 is subjected to a negative axial load Ka- is shown by the fourth characteristic line Q4. According to the fourth characteristic line Q4, as the radial internal clearance Cr increases, the variation Δθ of the inclination angle θ increases, but it is smaller than that of the second characteristic line Q2. In particular, when the radial internal clearance Cr is 11 μm, the variation Δθ of the inclination angle θ is less than half that of the second characteristic line Q2, demonstrating that this is more advantageous than a single-row four-point contact ball bearing.

[0055] FIG. 7 shows the results of an investigation into the difference in the fluctuation value ΔS of the axial displacement Sr due to differences in the radial internal clearance Cr, with the horizontal axis representing the radial internal clearance Cr (μm) of each bearing and the vertical axis representing the fluctuation value ΔS of the axial displacement Sr of the inner ring.

[0056] The characteristic of the fluctuation value ΔS of the axial displacement Sr when the single-row four-point contact ball bearing is subjected to a positive axial load Ka+ is shown by the first characteristic line Q11. The characteristic of the fluctuation value ΔS of the axial displacement Sr when the single-row four-point contact ball bearing is subjected to a negative axial load Ka- is shown by the second characteristic line Q12. The characteristic of the fluctuation value ΔS of the axial displacement Sr when the double-row four-point contact ball bearing 80 is subjected to a positive axial load Ka+ is shown by the third characteristic line Q13. The characteristic of the fluctuation value ΔS of the axial displacement Sr when the double-row four-point contact ball bearing 80 is subjected to a negative axial load Ka- is shown by the fourth characteristic line Q14. According to this, in any of the characteristic lines Q11, Q12, Q13, and Q14, regardless of the radial internal clearance Cr, the characteristic of the fluctuation value ΔS is constant at approximately zero.

[0057] FIG. 8 shows the results of an investigation into the difference in the fluctuation value ΔR of the radial displacement Ra due to differences in the radial internal clearance Cr, with the horizontal axis representing the radial internal clearance Cr (μm) of each bearing and the vertical axis representing the fluctuation value ΔR of the radial displacement Ra of the inner ring.

[0058] The characteristic of the fluctuation value ΔR of the radial displacement Ra when the single-row four-point contact ball bearing is subjected to a positive axial load Ka+ is shown by the first characteristic line Q21. The characteristic of the fluctuation value ΔR of the radial displacement Ra when the single-row four-point contact ball bearing is subjected to a negative axial load Ka- is shown by the second characteristic line Q22. The characteristic of the fluctuation value ΔR of the radial displacement Ra when the double-row four-point contact ball bearing 80 is subjected to a positive axial load Ka+ is shown by the third characteristic line Q23. The characteristic of the fluctuation value ΔR of the radial displacement Ra when the double-row four-point contact ball bearing 80 is subjected to a negative axial load Ka- is shown by the fourth characteristic line Q24.

[0059] This shows that the characteristic of the fluctuation value ΔR of the radial displacement Ra is similar to the characteristic of the fluctuation value Δθ of the inclination angle θ. Moreover, according to the fourth characteristic line Q24, as the radial internal clearance Cr increases, the fluctuation value ΔR of the radial displacement Ra increases, but is smaller than that of the second characteristic line Q22.

[0060] As a result of the above, it was found that, compared to a single-row four-point contact ball bearing, if the radial internal clearance is the same, the double-row four-point contact ball bearing 80 has less vibration of the inner ring when an external force is applied, and is therefore advantageous in suppressing the generation of operating noise. As a result, it has been found that employing the double-row four-point contact ball bearing 80 is extremely advantageous in suppressing the operating noise of the vehicle steering device 10.

[0061] <Embodiment 2> A vehicle steering device 100 according to embodiment 2 will be described with reference to Figures 9 and 10. Figure 9 corresponds to Figure 2, and Figure 10 corresponds to Figure 3.

[0062] The vehicle steering device 100 of the second embodiment is characterized in that the hub 62a of the driven pulley 62 of the first embodiment shown in Fig. 2 is changed to a hub 162a of a driven pulley 162 shown in Fig. 9 and Fig. 10. Specifically, the vehicle steering device 100 of the second embodiment is characterized in that the nut 73 of the ball screw 70 is supported by a double-row four-point contact ball bearing 80 via the hub 162a of the driven pulley 162.

[0063] Other configurations of the vehicle steering device 100 are common to the vehicle steering device 10 according to the above-described embodiment 1. The same reference numerals will be used for the parts common to the vehicle steering device 10 according to embodiment 1, and detailed descriptions thereof will be omitted.

[0064] More specifically, the hub 162a of the driven pulley 162 is connected to the nut 73. More specifically, the hub 162a is fitted onto the outer periphery 73a of the nut 73, and both its relative rotation and relative axial movement with respect to the nut 73 are restricted. As shown in Figure 9, the belt 63 is positioned away from the double-row four-point contact ball bearing 80 in the axial direction of the steered shaft 26. The double-row four-point contact ball bearing 80 is housed in the first housing 51 (first storage chamber 55). Of the driven pulley 162 housed in the second housing 52 (second storage chamber 56), only the hub 162a extends into the first housing 51 (first storage chamber 55).

[0065] As shown in Figure 10, the inner ring 81 of the double-row four-point contact ball bearing 80 is fitted to one outer periphery 162b (outer periphery surface 162b) of the hub 162a. Furthermore, the inner ring 81 is sandwiched between a stepped surface 162c on the outer periphery 162b of the hub 162a and a bearing nut 191 screwed onto the hub 162a. Therefore, relative movement in the axial direction between the inner ring 81 and the hub 162a is restricted. As a result, relative movement in the axial direction between the inner ring 81 and the nut 73 is restricted.

[0066] As shown in Figures 9 and 10, the outer ring 82 of the double-row four-point contact ball bearing 80 is fitted to the inner peripheral portion 55a of the first housing 51. A pair of elastic annular support portions 192, 192 are located on both sides of the outer ring 82 of the double-row four-point contact ball bearing 80. The pair of support portions 192, 192 face each other in the axial direction of the steered shaft 26, sandwiching the double-row four-point contact ball bearing 80 therebetween. These support portions 192, 192 may correspond to the support portions 92, 92 of the first embodiment shown in Figure 3 above. In this way, the double-row four-point contact ball bearing 80 and the pair of support portions 192, 192 are located between the first inner wall surface 51a and the second inner wall surface 57a in the storage chamber 54. The support portion 192 interposed between one end face of the outer ring 82 and the second inner wall surface 57a may be supported by a collar 193.

[0067] The above description of the second embodiment can be summarized as follows. As shown in FIGS. 1 and 9 , the vehicle steering device 100 of the second embodiment includes a steered shaft 26 that is connected to the input shaft 24 by a rack-and-pinion mechanism 25 and is movable in the vehicle width direction St, a first housing 51 that houses the input shaft 24 and the steered shaft 26, and a second housing 52 that is coupled to one end of the first housing 51. The vehicle steering device 100 also includes a drive source 43 (electric motor 43) provided in the second housing 52, and a belt transmission mechanism 60 and a ball screw 70 that can transmit the driving force generated by the drive source 43 to the steered shaft 26. As shown in FIG. 9 , the vehicle steering device 100 also includes a bearing 80 that supports a nut 73 that forms part of the ball screw 70 on the first housing 51 via a hub 162 a of a driven pulley 162 that forms part of the belt transmission mechanism 60.

[0068] 9, the hub 162a is connected to the nut 73 and is housed in the second housing 52. The bearing 80 is constituted by a double-row four-point contact ball bearing 80. An inner ring 81 of this double-row four-point contact ball bearing 80 is engaged with the outer periphery 162b of the hub 162a. An outer ring 82 of the double-row four-point contact ball bearing 80 is engaged with the inner periphery 55a of the first housing 51.

[0069] As described above, in the second embodiment, a double-row four-point contact ball bearing is used for the bearing 80. This double-row four-point contact ball bearing 80 (bearing 80) can withstand axial loads in both axial directions. Moreover, radial loads can also be supported by both of the two rows of four-point contact balls 83 of the double-row four-point contact ball bearing 80. Because the double-row four-point contact ball bearing 80 can adequately support both axial and radial loads, the size of the bearing 80 can be reduced. As a result, the first housing 51 (housing 50) that fits with the bearing 80 can also be made smaller, making it possible to provide a vehicle steering device 100 that can be made more compact.

[0070] Other functions and effects of the second embodiment are the same as those of the first embodiment.

[0071] The vehicle steering devices 10, 100 according to the present invention are not limited to the embodiments as long as they exhibit the functions and effects of the present invention.

[0072] The vehicle steering apparatus 10, 100 of the present invention is suitable for installation in an automobile.

[0073] 10...vehicle steering device, 24...input shaft, 25...rack and pinion mechanism, 26...steered shaft, 43...drive source (electric motor), 51...first housing, 52...second housing, 55a...inner peripheral portion (inner peripheral surface) of first housing, 60...belt transmission mechanism, 62...driven pulley, 62a...hub, 70...ball screw, 71...threaded portion formed on steering shaft, 72...ball, 73...nut, 73a...outer peripheral portion (outer peripheral surface), 80...bearing (double row four-point contact ball bearing), 81...inner ring (race ring), 81b...end portion, 81c...inner peripheral surface, 82...outer ring (race ring), 82b...end portion, 82c...outer peripheral surface, 83...ball, 85...seal portion, 100...vehicle steering device, 162...driven pulley, 162a...hub, 162b...outer periphery (outer periphery surface), 162c...step surface.

Claims

1. A vehicle steering apparatus comprising: a steering shaft connected to an input shaft by a rack and pinion mechanism and movable in the vehicle width direction; a first housing housing the input shaft and the steering shaft; a second housing coupled to one end of the first housing; a drive source provided in the second housing; a belt transmission mechanism and a ball screw capable of transmitting a driving force generated by the drive source to the steering shaft; and a bearing supporting a nut forming a part of the ball screw in the first housing, wherein a driven pulley forming a part of the belt transmission mechanism is connected to the nut and housed in the second housing, the bearing is constituted by a double row four-point contact ball bearing, an inner ring of the double row four-point contact ball bearing is fitted to an outer peripheral portion of the nut, and an outer ring of the double row four-point contact ball bearing is fitted to an inner peripheral portion of the first housing.

2. The vehicle steering apparatus according to claim 1, wherein the double row four-point contact ball bearing includes an inner ring, an outer ring, and two rows of four-point contact balls provided between the inner ring and the outer ring, the inner ring is formed of a member having two rows of raceways on an outer periphery, the outer ring is formed of a member having two rows of raceways on an inner periphery, and the balls are capable of rolling between the raceway of the inner ring and the raceway of the outer ring.

3. The vehicle steering apparatus according to claim 2, wherein the double row four-point contact ball bearing is provided with seal portions respectively between both end portions of the inner ring and both end portions of the outer ring.

4. A vehicle steering device comprising: a steerable shaft connected to an input shaft by a rack and pinion mechanism and movable in a vehicle width direction; a first housing accommodating the input shaft and the steerable shaft; a second housing coupled to one end of the first housing; a drive source provided in the second housing; a belt transmission mechanism and a ball screw capable of transmitting a driving force generated by the drive source to the steerable shaft; and a bearing supporting a nut constituting part of the ball screw on the first housing via a hub of a driven pulley constituting part of the belt transmission mechanism, the hub being connected to the nut and accommodated in the second housing, the bearing being a double row four point contact ball bearing, an inner ring of the double row four point contact ball bearing engaging with an outer periphery of the hub, and an outer ring of the double row four point contact ball bearing engaging with an inner periphery of the first housing.

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