Steering device

Abstract

Steering device includes a conversion mechanism (5) converting rotational movement of an input shaft (1) into linear movement in a direction along an output shaft (3) arranged orthogonal to the input shaft (1), an assist mechanism (6) applying a steering assist force to the output shaft (3) according to a steering torque and a steering direction, a pitman arm (7) arranged at a radially outer side of the input shaft (1), and a link (8) coupled to the output shaft (3) and to a point P3 of force of the pitman arm (7) and rocking the pitman arm (7) by pushing or pulling the point P3 of force of the pitman arm (7) according to application of the steering assist force to the output shaft (3). The conversion mechanism (5) includes a gear mechanism (39) having the first and second bevel gears (41, 42), and a ball screw mechanism (40).

Description

[0001] DESCRIPTION

[0002] TITLE : STEERING DEVICE

[0003] FIELD

[0004] [ 0001 . ] The present disclosure relates to a steering device .

[0005] BACKGROUND

[0006] [ 0002 . ] Japanese Patent No . 7003287 (hereinafter is referred to as JP7003287 or Patent Document 1 ) discloses an integral type steering device mounted on a large vehicle or the like . This steering device includes an input shaft , a power cylinder that is capable of generating a steering assist torque by sliding movement , in a housing, of a piston provided on an outer periphery of the input shaft , and a sector gear, as an output shaft , having a tooth portion that is engaged with a tooth portion provided on an outer peripheral surface of the piston . The outer peripheral surface of the piston and an inner peripheral surface of the housing are liquid-tightly sealed by an annular seal member . Furthermore , a pitman arm that transmits the steering assist torque to a steered wheel side is connected to the sector gear . The pitman arm is arranged at a radially outer side of the housing that accommodates therein the input shaft .

[0007] SUMMARY

[0008] [ 0003 . ] In the steering device of Patent Document 1 , due to resistance between the seal member and the housing during sliding movement of the piston, there is a risk that transmission ef ficiency of the steering assist torque in the steering device will reduce . Furthermore , the piston slides inside the housing while its outer peripheral surface is being pressed against the inner peripheral surface of the housing by component of force of the engagement between the tooth portion of the sector gear and the tooth portion of the piston . This also causes a problem of reducing the transmission ef ficiency of the steering assist torque in the steering device . In addition, the engagement in itsel f between the tooth portion of the sector gear and the tooth portion of the piston is also a factor in reducing the transmission ef ficiency of the steering assist torque in the steering device .

[0009] [ 0004 . ] Additionally, there is a design constraint to generally arrange the pitman arm at a radially outer side of the housing accommodating therein the input shaft , on various vehicles having the integral type steering device as disclosed in Patent Document 1 . Moreover, a configuration of a link from the pitman arm to a steered wheel is generally speci fied uni formly . For these reasons , i f an arrangement position of the pitman arm and / or its surrounding link configuration are to be changed, there arises a problem of requiring a signi ficant design change . [ 0005 . ] The present invention was made in view of the above problems . An obj ect of the present invention is therefore to provide a steering device that is capable of improving the transmission ef ficiency of the steering assist torque without requiring a signi ficant change of design from the pitman arm to the steered wheel side .

[0010] [ 0006 . ] According to one aspect of the present invention, a steering device comprises : an input shaft inputting a rotational force from a steering wheel ; a conversion mechanism configured to convert a rotational movement of the input shaft into a linear movement in a direction along an output shaft that is arranged so as to cross the input shaft ; a torque sensor provided at the input shaft , and detecting a steering torque and a steering direction of the input shaft ; an assist mechanism configured to apply a steering assist force to the output shaft according to the steering torque and the steering direction; a pitman arm arranged at a radially outer side of the input shaft , wherein the pitman arm has a pivot as a center of rock of the pitman arm, a point of force to which the steering assist force from the output shaft is applied, and a point of application on which a force to a steered wheel side acts , when the pitman arm rocks ; and a link coupled to the output shaft and to the point of force of the pitman arm, and configured to rock the pitman arm by pushing or pulling the point of force according to application of the steering assist force to the output shaft .

[0011] BRIEF DESCRIPTION OF DRAWINGS

[0012] [ 0007 . ] Fig. 1 is a sectional view of a steering device according to a first embodiment.

[0013] Fig. 2 is a cross section of the steering device according to the first embodiment, cut by a plane along a line A-A of Fig. 1.

[0014] Fig. 3 is an explanatory diagram schematically showing an assist mechanism for applying a steering assist force to an output shaft.

[0015] Fig. 4 is a cross section of a hydraulic pump, cut by a plane along a line B-B of Fig. 1.

[0016] Fig. 5 is an explanatory diagram showing a state of rock (or swing) of a pitman arm according to the first embodiment.

[0017] Fig. 6 is a sectional view of a steering device according to a second embodiment.

[0018] Fig. 7 is a cross section of the steering device according to the second embodiment, cut by a plane along a line C-C of Fig. 6.

[0019] Fig. 8 is an explanatory diagram showing a state of rock (or swing) of a pitman arm according to the second embodiment.

[0020] Fig. 9 is a sectional view of a steering device according to a third embodiment.

[0021] Fig. 10 is a longitudinal cross section of an input shaft and its surrounding components of the steering device according to the third embodiment.

[0022] Fig. 11 is a sectional view of a steering device according to a fourth embodiment. Fig. 12 is a longitudinal cross section of an input shaft and its surrounding components of the steering device according to the fourth embodiment. DESCRIPTION OF EMBODIMENTS [0008.] Embodiments of a steering device according to the present invention will be described below with reference to the drawings. The steering device according to the present invention is mainly used for relatively large vehicles such as trucks. Instead of employing a power cylinder or an engine- driven pump as in a conventional integral type steering device, the steering device according to the present invention employs a hydraulic pump 50 driven by an electric motor 51.

[0023] [0009.] Fig. 1 is a sectional view of a steering device according to a first embodiment. In the following description, a side (an upper side of Fig. 1) where an input shaft 1 is linked to a steering wheel (not shown) in a direction along a rotation axis Z of the input shaft 1 is referred to as "one end", and a side (a lower side of Fig. 1) where a first bevel gear 41 is formed is referred to as "the other end". Fig. 1 illustrates the sectional view of the steering device when the steering wheel is at a neutral position. Fig. 2 is a cross section of the steering device according to the first embodiment, cut by a plane along a line A-A of Fig. 1. Fig. 3 is an explanatory diagram schematically showing an assist mechanism 6 for applying a steering assist force to an output shaft 3. Fig. 4 is a cross section of a hydraulic pump 50, cut by a plane along a line B-B of Fig. 1. Fig. 5 is an explanatory diagram showing a state of rock (or swing) of a pitman arm 7 according to the first embodiment. [0010.] The steering device is configured mainly by the input shaft 1, a torque sensor 2, the output shaft 3, a housing 4, a conversion mechanism 5, the assist mechanism 6, the pitman arm 7, and a link 8. [0011.] The input shaft 1, except one end side thereof, is accommodated in after-described first housing 13, intermediate member 14 and second housing 15 that form the housing 4. The input shaft 1 has a first shaft 9, a second shaft 10, and a third shaft 11. The first shaft 9 is linked, at one end side thereof, to the steering wheel (not shown) , and inputs driver's steering torque. The other end portion of the first shaft 9 is inserted into an opening recessed portion formed at one end side of the second shaft 10. The second shaft 10 is relatively rotatably connected, at one end side thereof, to the first shaft 9 via a torsion bar 12. The second shaft 10 is rotatably supported by a bearing, e.g. a first ball bearing Bl, provided at an inner peripheral portion of the intermediate member 14. The third shaft 11 is fitted, at one end side thereof, onto an outer periphery of the other end portion of the second shaft 10 by splinefitting. One end side of the third shaft 11 is rotatably supported by a bearing, e.g. a second ball bearing B2, and the other end side of the third shaft 11 is rotatably supported by a bearing, e . g . a third ball bearing B3 .

[0024] [ 0012 . ] The first housing 13 is formed into a cylindrical tubular shape with a metal material such as aluminum alloy and cast iron . The first housing 13 is located at one end side of the input shaft 1 , and is fixed to the cylindrical tubular intermediate member 14 with a plurality of fastening members (not shown) , e . g . a plurality of screw members (not shown) .

[0025] [ 0013 . ] The second housing 15 is formed into a cylindrical tubular shape with a metal material such as aluminum alloy and cast iron . The second housing 15 has a cylindrical tubular portion 15a that mainly accommodates therein the third shaft 11 of the input shaft 1 , and a tubular protruding portion 15b that communicates with the cylindrical tubular portion 15a and that mainly accommodates therein a part of the output shaft 3 . An axial direction one end portion 15c of the cylindrical tubular portion 15a is fixed to an end portion 14a, located at the other end side , of the intermediate member 14 . Furthermore , an annular bearing retaining member 16 to retain ( or support ) the third ball bearing B3 is screwed into an inner peripheral portion of an axial direction other end portion 15d of the cylindrical tubular portion 15a . An opening of the bearing retaining member 16 is covered with a substantially disk-shaped first cover member 17 . [0014.] The tubular protruding portion 15b protrudes from an outer peripheral portion, located at the axial direction other end portion 15d side, of the cylindrical tubular portion 15a toward a radially outer side of the input shaft 1 (in a radially outward direction of the input shaft 1) . As illustrated in Fig. 1, a mounting portion 18 for mounting the steering device to a vehicle is formed integrally with a back side (at a depth side in Fig. 1) of the tubular protruding portion 15b and a back side of the cylindrical tubular portion 15a.

[0026] [0015.] The mounting portion 18 has a relatively thick rectangular plate shape. The mounting portion 18 is formed so that, when viewed from a direction orthogonal to a plane of Fig. 1, most of a short side 18a, which extends along a radial direction of the input shaft 1, of the mounting portion 18 is located at an after-described boss portion 18b side (i.e. the mounting portion 18 is formed off center toward the after-described pitman arm 7) . As seen in Fig. 1, the boss portion 18b for mounting the steering device to the vehicle is provided at a position that overlaps the end portion 14a of the intermediate member 14 in the radial direction of the input shaft 1, in a section, located at the tubular protruding portion 15b side, of the mounting portion 18. In addition, three boss portions 18c, 18d and 18e for mounting the steering device to the vehicle are provided in a section, located at an opposite side to the tubular protruding portion 15b, of the mounting portion 18 . Moreover, as can be seen in Fig . 2 , a boss portion 18 f for mounting the steering device to the vehicle is provided at the tubular protruding portion 15b of the mounting portion 18 .

[0027] [ 0016 . ] As shown in Figs . 1 and 2 , the mounting portion 18 has a cylindrical tubular shaft accommodating portion 19 formed at a substantially same position as the boss portion 18d provided at an opposite side to the tubular protruding portion 15b with respect to an axial direction of the input shaft 1 , between the tubular protruding portion 15b and the boss portion 18b . As can be seen in Fig . 2 , a closed-bottomed tubular second cover member 20 is screwed into one end portion 19a of the shaft accommodating portion 19 , thereby closing the one end portion 19a of the shaft accommodating portion 19 . The shaft accommodating portion 19 accommodates a part of an arm fixing shaft 21 that secures the pitman arm 7 .

[0028] [ 0017 . ] The arm fixing shaft 21 has a small diameter shaft portion 21a, a large diameter shaft portion 21b formed integrally with the small diameter shaft portion 21a and having a diameter that is larger than that of the small diameter shaft portion 21a, a middle diameter shaft portion 21c formed integrally with the large diameter shaft portion 21b and having a diameter that is smaller than that of the large diameter shaft portion 21b and larger than that of the small diameter shaft portion 21a, and a top end portion 21d formed integrally with the middle diameter shaft portion 21c and having a diameter that is smaller than that of the middle diameter shaft portion 21c .

[0029] [ 0018 . ] As illustrated in Fig . 2 , a bearing, e . g . a fourth ball bearing B4 , for rotatably supporting the small diameter shaft portion 21a is provided at an outer peripheral portion of the small diameter shaft portion 21a .

[0030] [ 0019 . ] Furthermore , a bearing, e . g . a sliding bearing 22 , for rotatably supporting the middle diameter shaft portion 21c is provided at a position, adj acent to the large diameter shaft portion 21b, of an outer peripheral portion of the middle diameter shaft portion 21c . At a position located at an opposite side to the large diameter shaft portion 21b with respect to the sliding bearing 22 , a pair of first seal members 23 are provided to seal an inner peripheral surface of the shaft accommodating portion 19 and an outer peripheral surface of the middle diameter shaft portion 21c . As can be seen in Fig . 2 , a portion, adj acent to the top end portion 21d, on the outer peripheral surface of the middle diameter shaft portion 21c is formed into a conical tapered shape that tapers toward the top end portion 21d . This conical tapered portion is provided with a serration 21e . Further, this tapered serration 21e is fitted to a serration 24a formed at a shaft fixing hole 24 of the pitman arm 7. The pitman arm 7 is then fixed to the arm fixing shaft 21 by tightening a nut 25. [0020.] An axis (axial center) of the arm fixing shaft 21 structured above becomes a pivot Pl of the pitman arm 7 when rocking (or swinging) .

[0031] [0021.] The torque sensor 2 is a well-known magnetic-type torque sensor using magnet portions 26 that are fixed (swaged) to an outer peripheral surface of the first shaft 9. The torque sensor 2 detects a steering torque and a steering direction of the input shaft 1. The torque sensor 2 has a detection unit 27 that detects a signal according to magnetic changes of the magnet portions 26 rotating together with the first shaft 9, and a signal processing unit 28 that is arranged around the detection unit 27 and calculates the steering torque by processing a magnetic flux detected by the detection unit 27.

[0032] [0022.] The output shaft 3 is provided at a radially outer side of the input shaft 1 on the other end side of the input shaft 1. As shown in Fig. 1, the output shaft 3 is arranged so as to cross the input shaft 1, more specifically, so as to be perpendicular to the input shaft 1. The output shaft 3 has a shaft body 29, a connecting shaft 30, and a nut member 31.

[0033] [0023.] The shaft body 29 is shaped into a long cylindrical column that extends along the radial direction of the input shaft 1. The shaft body 29 has a radial direction one end 29a at a position away from the input shaft 1 , and a radial direction other end 29b at a position close to the input shaft 1 .

[0034] [ 0024 . ] The radial direction other end 29b of the shaft body 29 is connected to one end of the connecting shaft 30 by spline-connection . The shaft body 29 is provided, at a position close to the radial direction other end 29b, with a diameterwidening portion 29c whose diameter widens in a radial direction of the output shaft 3 . A bearing, e . g . a fi fth ball bearing B5 , for rotatably supporting the shaft body 29 is provided on an outer periphery of this diameter-widening portion 29c . Furthermore , an annular first bearing detachment prevention member 32 for preventing detachment of the fi fth ball bearing B5 is provided at a position adj acent to the fi fth ball bearing B5 on the second cover member 20 side in the radial direction of the input shaft 1 . The first bearing detachment prevention member 32 and the diameter-widening portion 29c of the shaft body 29 are liquid-tightly sealed by a second seal member 33 made of e . g . rubber .

[0035] [ 0025 . ] As can be seen in Fig . 1 , most of the shaft body 29 is accommodated in a cylinder 34 that is shaped into a cylindrical tube with a metal material such as aluminum alloy and cast iron . An end portion 34a, located at the input shaft 1 side , of both end portions 34a and 34b of the cylinder 34 in its longitudinal direction is connected to an outer peripheral portion of a tip of the tubular protruding portion 15b of the second housing 15.

[0036] [0026.] As for the end portion 34b of the cylinder 34, a third cover member 35 is joined to the end portion 34b. The third cover member 35 is formed into a disk shape. The third cover member 35 is provided, at the middle thereof in a radial direction, with a center bore portion 35a which is formed along the radial direction of the input shaft 1, i.e. along an axial direction of the output shaft 3 and into which the nut member 31 is slidably inserted. A gap between the center bore portion 35a and the nut member 31 is liquid-tightly sealed by a pair of third seal members 36 made of e.g. rubber.

[0037] [0027.] On an end surface 35b, facing the inside of the cylinder 34, of both end surfaces 35b and 35c of the third cover member 35 in the axial direction of the output shaft 3, a first hole portion 35d is formed. A first shaft end 37a of a long thinner cylindrical column guide member 37 is inserted into this first hole portion 35d. A second shaft end 37b of the guide member 37 is inserted into a second hole portion 32a provided at the first bearing detachment prevention member 32. The guide member 37 extends parallel to the shaft body 29.

[0038] [0028.] The connecting shaft 30 is a shaft that connects the third shaft 11 of the input shaft 1 and the shaft body 29 of the output shaft 3. A length, along the axial direction of the output shaft 3, of the connecting shaft 30 is shorter than a length, along the axial direction of the output shaft 3 , of the shaft body 29 . A bearing, e . g . a sixth ball bearing B6 , for rotatably supporting the connecting shaft 30 is provided at an outer peripheral portion of a middle portion, in the axial direction of the output shaft 3 , of the connecting shaft 30 . Furthermore , an annular second bearing detachment prevention member 38 for preventing detachment of the sixth ball bearing B6 is provided at a position adj acent to the sixth ball bearing B6 on the first bearing detachment prevention member 32 side in the axial direction of the output shaft 3 .

[0039] [ 0029 . ] The nut member 31 will be described in detail later .

[0040] [ 0030 . ] The conversion mechanism 5 includes a gear mechanism 39 that converts a rotational movement of the input shaft 1 into a linear movement in a direction along the output shaft 3 arranged orthogonal to the input shaft 1 , and a ball screw mechanism 40 .

[0041] [ 0031 . ] The gear mechanism 39 has the first bevel gear 41 formed at an annular protruding portion 11b that protrudes radially outwards from an end portion I la on the other end side of the third shaft 11 of the input shaft 1 and further protrudes in an obliquely upward direction, and a second bevel gear 42 formed at the outer peripheral portion, located close to an end portion 30a on the input shaft 1 side , of the connecting shaft 30 . The gear mechanism 39 converts a rotational force from the input shaft 1 into a rotation of the output shaft 3 arranged orthogonal to the input shaft 1 , by engagement between the first bevel gear 41 and the second bevel gear 42 . A speed ratio of the first bevel gear 41 and the second bevel gear 42 is set to , for instance , "2 : 1" .

[0042] [ 0032 . ] The ball screw mechanism 40 is configured by a shaft-side ball screw groove 29d that is a spiral groove provided on an outer peripheral side of the shaft body 29 of the output shaft 3 , a nutside ball screw groove 43 that is a spiral groove provided on an inner peripheral side of an oil chamber dividing portion 31c formed at the nut member 31 , and a plurality of balls 44 disposed between the ball screw grooves 29d and 43 . The balls 44 rotatably support the nut member 31 relative to the shaft body 29 . An outer peripheral surface of the nut member 31 is in sliding-contact with an inner peripheral surface of the cylinder 34 . With this sliding-contact , the oil chamber dividing portion 31c of the nut member 31 can slide along the radial direction of the input shaft 1 , i . e . along the axial direction of the output shaft 3 , inside the cylinder 34 .

[0043] [ 0033 . ] The nut member 31 is formed into a closed- bottomed tubular shape with a metal material . The nut member 31 has a base portion 31a, a cylindrical tubular portion 31b extending from an outer edge of the base portion 31a toward the input shaft 1 along the axial direction of the output shaft 3 , and the cylindrical tubular oil chamber dividing portion 31c j oined to an end portion, located at an opposite side to the base portion 31a, of the cylindrical tubular portion 31b .

[0044] [ 0034 . ] The base portion 31a is fixed to a supporting member 46 through a fixing member 45 such as a screw . This supporting member 46 is movable according to a rotation of the shaft body 29 and / or a movement of the nut member 31 by oil supply into the cylinder 34 through the hydraulic pump 50 described later .

[0045] [ 0035 . ] Furthermore , a rubber boot 47 formed into bellows with e . g . a rubber material is provided between a boot attachment portion 80 provided at the supporting member 46 and the third cover member 35 . The rubber boot 47 suppresses the entry of foreign matter into the cylinder 34 through a gap between an inner peripheral surface of the third cover member 35 and the outer peripheral surface of the cylindrical tubular portion 31b of the nut member 31 .

[0046] [ 0036 . ] A length, along the axial direction of the output shaft 3 , of a space in the cylindrical tubular portion 31b and the oil chamber dividing portion 31c corresponds to a length from a tip 32b of the first bearing detachment prevention member 32 to the radial direction one end 29a of the shaft body 29 .

[0047] [ 0037 . ] The oil chamber dividing portion 31c partitions an internal space of the cylinder 34 into a first oil chamber R1 located at the input shaft 1 side and a second oil chamber R2 located at the third cover member 35 side . As shown in Fig . 1 , a through hole 31d is formed at a portion, on the pivot Pl side of the pitman arm 7 with respect to the shaft body 29 , of the oil chamber dividing portion 31c so as to penetrate the oil chamber dividing portion 31c along the axial direction of the output shaft 3 . The guide member 37 is inserted into this through hole 31d . The guide member 37 prevents rotation of the nut member 31 when the nut member 31 moves , and also guides the movement of the nut member 31 along the axial direction of the output shaft 3 .

[0048] [ 0038 . ] As can be seen in Fig . 1 , a gap between an outer peripheral surface of the guide member 37 and an inner peripheral surface of the through hole 31d is liquid-tightly sealed by an annular fourth seal member 48 made of e . g . rubber . In addition, a gap between an outer peripheral surface of the oil chamber dividing portion 31c and the inner peripheral surface of the cylinder 34 is liquid- tightly sealed by an annular fi fth seal member 49 made of e . g . rubber . At a position, located at an opposite side to the guide member 37 with respect to the shaft body 29 , of the oil chamber dividing portion 31c, a recessed portion 39e is formed so as to be recessed from the outer peripheral surface of the oil chamber dividing portion 31c toward the shaft body 29 . [0039.] The assist mechanism 6 applies a steering assist force to the nut member 31 of the output shaft 3 according to the steering torque and the steering direction detected by the torque sensor 2. The assist mechanism 6 includes the hydraulic pump 50, the electric motor 51, an ECU controller 52, and the cylinder 34.

[0049] [0040.] The hydraulic pump 50 is configured as an internal gear pump that can supply an oil pressure (a hydraulic pressure) to the cylinder 34 serving as a hydraulic cylinder and that can switch the supply of the hydraulic pressure between two directions according to a rotation direction of the electric motor 51. It is noted that the hydraulic pump 50 could be configured as an external gear pump, instead of the internal gear pump. Furthermore, the hydraulic pump 50 is not limited to the internal gear pump and the external gear pump, but may be other types of pumps capable of switching the supply of the hydraulic pressure between two directions. The hydraulic pump 50 has a tank 53, a driving gear 54, a driven gear 55, a first check valve 57, a second check valve 59, an annular member 60 for gear, and a cover member 61.

[0050] [0041.] The tank 53 mainly accommodates therein the driving gear 54, the driven gear 55, the first check valve 57, the second check valve 59, and the annular member 60.

[0051] [0042.] The driving gear 54 is fixed to an outer peripheral portion of a motor shaft 51a of the electric motor 51. As illustrated in Fig. 4, the driving gear 54 has, at an outer peripheral portion thereof, a plurality of tooth portions 54a (six tooth portions 54a in the present embodiment) formed so as to be arranged at regular intervals along a circumferential direction of the driving gear 54. [0043.] The driven gear 55 is annular in shape, and is provided at an outer circumferential side of the driving gear 54. As illustrated in Fig. 4, the driven gear 55 has, at an inner peripheral portion thereof, a plurality of tooth portions 55a (seven tooth portions 55a in the present embodiment) formed so as to be arranged at regular intervals along a circumferential direction of the driven gear 55. When the driving gear 54 rotates, the driven gear 55 rotates in the same direction as the driving gear 54 by engagement between the tooth portions 54a and the tooth portions 55a. As can be seen in Fig. 4, spaces are made between four circumferentially adjacent tooth portions 55a of the driven gear 55 and four circumferentially adjacent tooth portions 54a of the driving gear 54. Oil discharged from after-described second interconnecting portion 66 and fourth interconnecting portion 71 that are provided at the cylinder 34 is supplied into these spaces. Also, for instance, when a volume of the oil decreases at a low temperature, oil is supplied to the spaces from the tank 53 via the first check valve 57 and the second check valve 59. [ 0044 . ] The annular member 60 is annular in shape . The annular member 60 accommodates therein the driving gear 54 fixed to the motor shaft 51a of the electric motor 51 , and the driven gear 55 surrounding the driving gear 54 .

[0052] [ 0045 . ] The cover member 61 is formed into a disk shape . The cover member 61 is provided so as to cover the tank 53 while being contiguous to the driving gear 54 , the driven gear 55 and the annular member 60 . As can be seen in Fig . 1 , a first flow passage inlet 63 having an L-shaped cross section and forming a part of a first flow passage 62 is formed at a portion, facing a boundary between the driving gear 54 and the driven gear 55 on the first check valve 57 side , of the inside of the cover member 61 . The first flow passage inlet 63 communicates with a first interconnecting portion 64 having an internal passage 64a that also forms a part of the first flow passage 62 and that communicates with the first flow passage inlet 63 . The first interconnecting portion 64 communicates with a first tube 65 forming a part of the first flow passage 62 . The first tube 65 communicates with the second interconnecting portion 66 having an internal passage 66a that also forms a part of the first flow passage 62 and that communicates with the first tube 65 . The second interconnecting portion 66 communicates with the first oil chamber R1 of the cylinder 34 . [ 0046 . ] Likewise , as can be seen in Fig . 1 , a second flow passage inlet 68 having an L-shaped cross section and forming a part of a second flow passage 67 is formed at a portion, facing a boundary between the driving gear 54 and the driven gear 55 on the second check valve 59 side , of the inside of the cover member 61 . The second flow passage inlet

[0053] 68 communicates with a third interconnecting portion

[0054] 69 having an internal passage 69a that also forms a part of the second flow passage 67 and that communicates with the second flow passage inlet 68 . The third interconnecting portion 69 communicates with a second tube 70 forming a part of the second flow passage 67 . The second tube 70 communicates with the fourth interconnecting portion 71 having an internal passage 71a that also forms a part of the second flow passage 67 and that communicates with the second tube 70 . The fourth interconnecting portion 71 communicates with the second oil chamber R2 of the cylinder 34 .

[0055] [ 0047 . ] The electric motor 51 is configured as a three-phase brushless motor, and drives the hydraulic pump 50 . The electric motor 51 is controlled and driven by the ECU controller 52 . [ 0048 . ] The ECU controller 52 controls and drives the electric motor 51 according to a motor torque based on the steering torque and the steering direction, and thus a hydraulic pressure required for steering assist for the output shaft 3 by the cylinder 34 serving as the hydraulic cylinder is supplied to the first oil chamber R1 or the second oil chamber R2 of the cylinder 34.

[0056] [0049.] In the assist mechanism 6 described above, when a driver turns the steering wheel to the left, the electric motor 51 rotates in a left rotational direction (in an counterclockwise direction in Fig. 4) , and by a pumping action by the tooth portions 54a and the tooth portions 55a, a hydraulic pressure flows into the first oil chamber R1 via the first flow passage 62. Further, due to increase in the hydraulic pressure in the first oil chamber Rl, the oil chamber dividing portion 31c is pressed to the third cover member 35 side, and thus the nut member 31 moves to the third cover member 35 side.

[0057] [0050.] On the other hand, when the driver turns the steering wheel to the right, the electric motor 51 rotates in a right rotational direction (in a clockwise direction in Fig. 4) , and by a pumping action by the tooth portions 54a and the tooth portions 55a, a hydraulic pressure flows into the second oil chamber R2 via the second flow passage 67. Further, due to increase in the hydraulic pressure in the second oil chamber R2, the oil chamber dividing portion 31c is pressed to the input shaft 1 side, and thus the nut member 31 moves to the input shaft 1 side.

[0058] [0051.] As illustrated in Fig. 1, the pitman arm 7 is arranged at a radially outer side of the input shaft 1, more specifically, at a side of the cylindrical tubular portion 15a of the second housing 15 accommodating therein the input shaft 1 . As shown in Fig . 2 , the pitman arm 7 has the above- mentioned shaft fixing hole 24 to which the middle diameter shaft portion 21c of the arm fixing shaft 21 is fixed, a first securing hole 73 to which one end side shaft portion 72a forming one end portion of a drag link 72 is fixed, and a second securing hole 74 to which a link one end portion 8a forming one end portion of the link 8 is fixed .

[0059] [ 0052 . ] The shaft fixing hole 24 is formed at a position close to a longitudinal direction one end portion 7a of the pitman arm 7 .

[0060] [ 0053 . ] The first securing hole 73 is formed at a position close to a longitudinal direction other end portion 7b of the pitman arm 7 . In an attitude of the pitman arm 7 shown in Figs . 1 and 2 , the first securing hole 73 is positioned at a lower side with respect to the shaft fixing hole 24 in the axial direction of the input shaft 1 . In other words , in the attitude of the pitman arm 7 shown in Figs . 1 and 2 , the first securing hole 73 is positioned at a lower side with respect to the shaft fixing hole 24 in a vertical direction ( an up-and-down direction of the vehicle ) . A center of the first securing hole 73 becomes a point P2 of application ( or a point P2 of action) that moves the drag link 72 when the pitman arm 7 rocks ( or swings ) .

[0061] [ 0054 . ] The second securing hole 74 is formed at a substantially middle position between the shaft fixing hole 24 and the first securing hole 73 in the longitudinal direction of the pitman arm 7 . In the attitude of the pitman arm 7 shown in Figs . 1 and 2 , the second securing hole 74 is positioned at a lower side with respect to the shaft fixing hole 24 and at an upper side with respect to the first securing hole 73 in the axial direction of the input shaft 1 . In other words , in the attitude of the pitman arm 7 shown in Figs . 1 and 2 , the second securing hole 74 is positioned at a lower side with respect to the shaft fixing hole 24 and at an upper side with respect to the first securing hole 73 in the vertical direction ( the up-and-down direction of the vehicle ) . A center of the second securing hole 74 becomes a point P3 of force to which a force from the link 8 is applied when the link 8 moves according to the movement of the nut member 31 upon operation of the hydraulic pump 50 of the assist mechanism 6 . The point P3 of force is positioned at a lower side with respect to the pivot Pl and at an upper side with respect to the point P2 of application in the vertical direction .

[0062] [ 0055 . ] The link 8 is formed into a long bar shape ( or a long rod shape ) with a metal material . The link one end portion 8a of the link 8 is fixed to the second securing hole 74 of the pitman arm 7 , whereas a link other end portion 8b of the link 8 is fixed to the supporting member 46 that supports the nut member 31 of the output shaft 3 . The link 8 pushes or pulls ( draws ) the point P3 of force of the pitman arm 7 according to application of the steering assist force to the nut member 31 by the operation of the hydraulic pump 50, thereby rocking (or swinging) the pitman arm 7. For instance, when turning the steering wheel to the left, due to increase in the hydraulic pressure in the first oil chamber Rl, the nut member 31 moves to the third cover member 35 side (in a rightward direction in Fig. 5) , then the link 8 is pulled in rightwards in Fig. 5. With this, the point P3 of force of the pitman arm 7 at a neutral position shown by a solid line moves to a position of a point yl of force, and the pitman arm 7 rocks (or swings) in a counterclockwise direction in Fig. 5, then moves to a position shown by a two-dot chain line LI. On the other hand, when turning the steering wheel to the right, due to increase in the hydraulic pressure in the second oil chamber R2, the nut member 31 moves to the input shaft 1 side (in a leftward direction in Fig. 5) , then the link 8 is pushed in leftwards in Fig. 5. With this, the point P3 of force of the pitman arm 7 at the neutral position shown by the solid line moves to a position of a point y2 of force, and the pitman arm 7 rocks (or swings) in a clockwise direction in Fig. 5, then moves to a position shown by a two-dot chain line L2. [0056.] As described above, in the first embodiment, the steering device includes the conversion mechanism 5 that converts the rotational movement of the input shaft 1 into the linear movement in the direction along the output shaft 3 arranged orthogonal to the input shaft 1 , the assist mechanism 6 that applies the steering assist force to the output shaft 3 according to the steering torque and the steering direction detected by the torque sensor 2 , the pitman arm 7 arranged at the radially outer side of the input shaft 1 , and the link 8 that is coupled to the nut member 31 of the output shaft 3 and to the point P3 of force of the pitman arm 7 and that rocks ( or swings ) the pitman arm 7 by pushing or pulling ( drawing) the point P3 of force of the pitman arm 7 according to application of the steering assist force to the nut member 31 .

[0063] [ 0057 . ] The steering device of the first embodiment as described above is not provided with the piston provided on the outer periphery of the input shaft , and the sector gear having the tooth portion engaged with the tooth portion provided on the outer peripheral surface of the piston, which are provided in the related art steering device . Therefore , the problem of reducing the transmission ef ficiency of the steering assist torque , which is caused by resistance between the seal member and the housing during sliding movement of the piston, the sliding of the piston inside the housing while its outer peripheral surface is being pressed against the inner peripheral surface of the housing, and the engagement between the tooth portion of the sector gear and the tooth portion of the piston, and which is posed in the related art steering device , is not posed in the steering device of the present embodiment .

[0064] [ 0058 . ] Furthermore , in the present embodiment , steered wheels are steered by pushing and pulling the pitman arm 7 via the link 8 while maintaining the pitman arm 7 at the radially outer side of the input shaft 1 , which is a desirable position in design of the pitman arm 7 , more speci fically, at the side of the cylindrical tubular portion 15a of the second housing 15 . Therefore , a signi ficant change of design from the pitman arm 7 to the steered wheel side is not required .

[0065] [ 0059 . ] Accordingly, according to the configuration of the present embodiment , it is possible to improve the transmission ef ficiency of the steering assist torque without requiring a signi ficant change of design from the pitman arm 7 to the steered wheel side .

[0066] [ 0060 . ] Moreover, in the present embodiment , the conversion mechanism 5 includes the gear mechanism 39 having the first bevel gear 41 and the second bevel gear 42 that are engaged with each other, and the ball screw mechanism 40 having the shaft-side ball screw groove 29d, the nut-side ball screw groove 43 , and the balls 44 . Therefore , the relatively large sector gear and the piston having the tooth portion engaged with the tooth portion of the sector gear, which are provided in the related art steering device , are not required in the steering device of the present embodiment . It is thus possible to transmit a steering force efficiently from the input shaft 1 to the output shaft 3.

[0067] [0061.] Fig. 6 is a sectional view of the steering device according to a second embodiment. Fig. 7 is a cross section of the steering device according to the second embodiment, cut by a plane along a line C-C of Fig. 6. Fig. 8 is an explanatory diagram showing a state of rock (or swing) of the pitman arm 7 according to the second embodiment.

[0068] [0062.] In the second embodiment, a position of the pivot Pl of the pitman arm 7 and a position of the point P3 of force of the pitman arm 7, of the first embodiment are interchanged. That is, in the configuration of the steering device of the second embodiment, the pitman arm 7 is structured such that the point P3 of force is positioned at an upper side with respect to the pivot Pl in the vertical direction. Thanks to this structure, in the second embodiment, an axial length of the third shaft 11 of the input shaft 1, and an axial length of the cylindrical tubular portion 15a of the second housing 15 become shorter. In addition, in the present embodiment, the first bevel gear 41 is formed at an annular protruding portion 11c that protrudes radially outwards from an end portion Ila on the other end side of the third shaft 11 of the input shaft 1 and further protrudes in an obliquely downward direction. Furthermore, in the present embodiment, the first cover member 17 of the first embodiment is eliminated . Instead, the bearing retaining member 16 , a bottom wall portion 15e , and the tubular protruding portion 15b are formed integrally with the cylindrical tubular portion 15a . [ 0063 . ] As illustrated in Fig . 6 , the mounting portion 18 for mounting the steering device to a vehicle is formed integrally with the bottom wall portion 15e and the tubular protruding portion 15b . The mounting portion 18 has a relatively thick rectangular plate shape . As can be seen in Fig . 6 , most of the mounting portion 18 is located at a lower side with respect to the bottom wall portion 15e and the tubular protruding portion 15b in the vertical direction . A boss portion 18b provided at the tubular protruding portion 15b side is positioned at a lower side with respect to the output shaft 3 and at an upper side with respect to the point P2 of application of the pitman arm 7 in the vertical direction .

[0069] [ 0064 . ] As shown in Fig . 6 , when viewed from a direction of the arm fixing shaft 21 ( a direction orthogonal to a plane of Fig . 6 ) , the point P3 of force of the pitman arm 7 is provided at a position that is located at an upper side with respect to the shaft body 29 in the vertical direction and that overlaps the tubular protruding portion 15b .

[0070] [ 0065 . ] In addition, the pivot Pl of the pitman arm

[0071] 7 is provided at a position close to the boss portion 18b between the point P3 of force and the boss portion 18b in the vertical direction . [0066.] In the present embodiment, for instance, when turning the steering wheel to the left, due to increase in the hydraulic pressure in the first oil chamber Rl, the nut member 31 moves to the third cover member 35 side (in a rightward direction in Fig. 8) , then the link 8 is pulled in rightwards in Fig. 8. With this, the point P3 of force of the pitman arm 7 at a neutral position shown by a solid line moves to a position of a point y3 of force, and the pitman arm 7 rocks (or swings) in a clockwise direction in Fig. 8, then moves to a position shown by a two-dot chain line L3. On the other hand, when turning the steering wheel to the right, due to increase in the hydraulic pressure in the second oil chamber R2, the nut member 31 moves to the input shaft 1 side (in a leftward direction in Fig. 8) , then the link 8 is pushed in leftwards in Fig. 8. With this, the point P3 of force of the pitman arm 7 at the neutral position shown by the solid line moves to a position of a point y4 of force, and the pitman arm 7 rocks (or swings) in a counterclockwise direction in Fig. 8, then moves to a position shown by a two-dot chain line L4.

[0072] [0067.] As described above, in the second embodiment, the input shaft 1 extends along the vertical direction, and the point P3 of force of the pitman arm 7 is positioned at the upper side with respect to the pivot Pl in the vertical direction.

[0073] More specifically, the point P3 of force is positioned at the upper side with respect to the output shaft 3 in the vertical direction, and the pivot Pl is positioned at the lower side with respect to the output shaft 3 in the vertical direction . By a positional relationship between these point P3 of force and pivot Pl , as compared with the configuration of the first embodiment in which the point P3 of force is positioned at the lower side with respect to the pivot Pl in the vertical direction, an axial dimension of the third shaft 11 of the input shaft 1 , and an axial dimension of the second housing 15 accommodating therein the third shaft 11 can be shorter . It is therefore possible to reduce the physical si ze of the steering device , and achieve reduction in manufacturing costs of the steering device .

[0074] [ 0068 . ] Fig . 9 is a sectional view of the steering device according to a third embodiment . Fig . 10 is a longitudinal cross section of the input shaft 1 and its surrounding components of the steering device according to the third embodiment .

[0075] [ 0069 . ] In the third embodiment , the gear mechanism 39 and the ball screw mechanism 40 of the conversion mechanism 5 of the first embodiment are eliminated . Instead, the conversion mechanism 5 is configured as a rack-and-pinion mechanism having a pinion gear (pinion teeth) l id provided at the third shaft 11 of the input shaft 1 , and a rack gear ( rack teeth) 75e provided at the output shaft 3 and engaged with the pinion gear l id . With this configuration, in the third embodiment , the output shaft 3 does not have the shaft body 29 , the connecting shaft 30 , and the nut member 31 , but has a single rack shaft 75 .

[0076] [ 0070 . ] The rack shaft 75 is formed into a long cylindrical column shape with a metal material . The rack shaft 75 has a base shaft portion 75a, and a rack shaft portion 75b formed integrally with the base shaft portion 75a . An axial direction one end 75c of the base shaft portion 75a is fixed to the supporting member 46 through the fixing member 45 . An axial direction other end 75d of the base shaft portion 75a is formed integrally with the rack shaft portion 75b . A portion, located close to the axial direction other end 75d, of the base shaft portion 75a is formed so as to have a larger diameter than those of the other portions , and this portion serves as the oil chamber dividing portion 31c that partitions the internal space of the cylinder 34 into the first oil chamber R1 and the second oil chamber R2 . The rack shaft portion 75b is provided, on an outer periphery thereof , with the rack gear 75e engaged with the pinion gear l id provided at the third shaft 11 of the input shaft 1 .

[0077] [ 0071 . ] The end portion 34a, located at the input shaft 1 side , of the cylinder 34 accommodating therein a part of the rack shaft 75 is connected to an opening end portion 76a of a third housing 76 . The third housing 76 can mainly accommodate the rack shaft 75 . The third housing 76 is formed into a long narrow closed-bottomed cylindrical tubular shape with a stroke of movement of the rack shaft 75 according to the rotation of the input shaft 1 taken into account . The third housing 76 is formed integrally with the second housing 15 and the mounting portion 18 .

[0078] [ 0072 . ] As illustrated in Fig . 10 , a cylindrical tubular rack retainer accommodating wall portion 15f that protrudes from an outer peripheral portion of the cylindrical tubular portion 15a so as to be perpendicular to the rack shaft 75 is formed integrally with the cylindrical tubular portion 15a of the second housing 15 . The rack retainer accommodating wall portion 15f accommodates therein a rack retainer 77 , a spring 78 for forcing the rack shaft 75 toward the third shaft 11 , and a closed- bottomed cylindrical tubular closing lid member 81 for supporting the spring 78 . The rack shaft 75 is forced toward the third shaft 11 by the spring 78 and the rack retainer 77 , thereby suppressing a backlash between the rack gear 75e provided on the outer periphery of the rack shaft 75 and the pinion gear l id provided on the outer periphery of the third shaft 11 .

[0079] [ 0073 . ] In addition, as shown in Fig . 10 , a cylindrical tubular bearing fixing member 79 is disposed at an outer peripheral portion, located at an upper side with respect to the pinion gear l id, of the third shaft 11 . A bearing, e . g . a seventh ball bearing B7 , for rotatably supporting the third shaft 11 is fixed to a circular recessed portion 79a formed at the other end side of the bearing fixing member 79 .

[0080] [ 0074 . ] In the third embodiment , the steering device includes the conversion mechanism 5 that converts the rotational movement of the input shaft 1 into the linear movement in the direction along the output shaft 3 arranged orthogonal to the input shaft 1 , the assist mechanism 6 that applies the steering assist force to the output shaft 3 according to the steering torque and the steering direction detected by the torque sensor 2 , the pitman arm 7 arranged at the radially outer side of the input shaft 1 , and the link 8 that is coupled to the rack shaft 75 of the output shaft 3 and to the point P3 of force of the pitman arm 7 and that rocks ( or swings ) the pitman arm 7 by pushing or pulling ( drawing) the point P3 of force of the pitman arm 7 according to application of the steering assist force to the rack shaft 75 . Therefore , since the piston and the sector gear as in the related art steering device are not provided in the steering device of the present embodiment , the problem of reducing the transmission ef ficiency of the steering assist torque is not posed in the steering device of the present embodiment .

[0081] [ 0075 . ] Furthermore , in the present embodiment , steered wheels can be steered by pushing and pulling the pitman arm 7 via the link 8 while maintaining the pitman arm 7 at the radially outer side of the input shaft 1 , which is a desirable position of the pitman arm 7, more specifically, at the side of the cylindrical tubular portion 15a of the second housing 15. Therefore, a significant change of design from the pitman arm 7 to the steered wheel side is not required.

[0082] [0076.] Accordingly, according to the configuration of the third embodiment as well, it is possible to improve the transmission efficiency of the steering assist torque without requiring a significant change of design from the pitman arm 7 to the steered wheel side .

[0083] [0077.] Moreover, in the third embodiment, the conversion mechanism 5 includes the pinion gear (the pinion teeth) lid provided at the third shaft 11 of the input shaft 1, and the rack gear (the rack teeth) 75e provided at the rack shaft portion 75b of the output shaft 3 and engaged with the pinion gear lid. Such rack-and-pinion mechanism having the pinion gear lid and the rack gear 75e can also transmit a steering force efficiently from the input shaft 1 to the output shaft 3 while suppressing reduction in the transmission efficiency of the steering assist torque, without employing the relatively large sector gear and the piston having the tooth portion engaged with the tooth portion of the sector gear, which are provided in the related art steering device.

[0084] [0078.] Fig. 11 is a sectional view of the steering device according to a fourth embodiment. Fig. 12 is a longitudinal cross section of the input shaft 1 and its surrounding components of the steering device according to the fourth embodiment .

[0085] [ 0079 . ] In the fourth embodiment , a position of the pivot Pl of the pitman arm 7 and a position of the point P3 of force of the pitman arm 7 , of the third embodiment are interchanged . That is , in the configuration of the steering device of the fourth embodiment , the pitman arm 7 is structured such that the point P3 of force is positioned at an upper side with respect to the pivot Pl in the vertical direction . Thanks to this structure , in the fourth embodiment , as compared with the third embodiment , an axial length of the third shaft 11 of the input shaft 1 , an axial length of the cylindrical tubular portion 15a of the second housing 15 , and an axial length of the bearing fixing member 79 become shorter . Furthermore , unlike the third embodiment , the mounting portion 18 is formed integrally with the second housing 15 so that most of the mounting portion 18 is situated at a lower side with respect to the third housing 76 .

[0086] [ 0080 . ] As described above , in the fourth embodiment , the point P3 of force of the pitman arm 7 is positioned at the upper side with respect to the pivot Pl in the vertical direction . By a positional relationship between these point P3 of force and pivot Pl , as compared with the configuration of the third embodiment in which the point P3 of force is positioned at the lower side with respect to the pivot Pl in the vertical direction, an axial dimension of the third shaft 11 of the input shaft 1, an axial dimension of the second housing 15, and an axial dimension of the bearing fixing member 79 can be shorter. It is therefore possible to reduce the physical size of the steering device, and achieve reduction in manufacturing costs of the steering device.

[0087] DESCRIPTION OF REFERENCE SYMBOLS [0081. ]

[0088] 1 ■■■ input shaft

[0089] 2 ■■■ torque sensor

[0090] 3 ■■■ output shaft

[0091] 5 ■■■ conversion mechanism

[0092] 6 ■■■ assist mechanism

[0093] 7 ■■■ pitman arm

[0094] 8 ■■■ link lid ■■■ pinion gear 31 ■■■ nut member

[0095] 39 ■■■ gear mechanism

[0096] 40 ■■■ ball screw mechanism

[0097] 41 ■■■ first bevel gear

[0098] 42 ■■■ second bevel gear

[0099] 50 ■■■ hydraulic pump

[0100] 51 ■■■ electric motor

[0101] 52 ■■■ ECU controller

[0102] Pl ■■■ pivot

[0103] P2 ■■■ point of application P3 ■■■ point of force

[0104] 75 ■■■ rack shaft

[0105] 75e ■■■ rack gear

Claims

- 39 -CLAIMS

1. A steering device comprising : an input shaft inputting a rotational force from a steering wheel ; a conversion mechanism configured to convert a rotational movement of the input shaft into a linear movement in a direction along an output shaft that is arranged so as to cross the input shaft ; a torque sensor provided at the input shaft , and detecting a steering torque and a steering direction of the input shaft ; an assist mechanism configured to apply a steering assist force to the output shaft according to the steering torque and the steering direction; a pitman arm arranged at a radially outer side of the input shaft , wherein the pitman arm has a pivot as a center of rock of the pitman arm, a point of force to which the steering assist force from the output shaft is applied, and a point of application on which a force to a steered wheel side acts , when the pitman arm rocks ; and a link coupled to the output shaft and to the point of force of the pitman arm, and configured to rock the pitman arm by pushing or pulling the point of force according to application of the steering assist force to the output shaft .- 40 -

2. The steering device as claimed in claim 1 , wherein the conversion mechanism includes a gear mechanism, and a ball screw mechanism, the gear mechanism has a first bevel gear formed at the input shaft , and a second bevel gear formed at the output shaft and engaged with the first bevel gear, and the ball screw mechanism has a shaft-side ball screw groove provided at the output shaft , a nutside ball screw groove provided at a nut member that slides on an outer periphery of the output shaft , and a plurality of balls disposed between the shaft-side ball screw groove and the nut-side ball screw groove .

3. The steering device as claimed in claim 1 , wherein the conversion mechanism has a pinion gear provided at the input shaft , and a rack gear provided at the output shaft and engaged with the pinion gear .

4. The steering device as claimed in claim 2 , wherein the input shaft extends in a vertical direction, and the point of force is positioned at a lower side with respect to the pivot of the pitman arm in the vertical direction .- 41

5. The steering device as claimed in claim 2 , wherein the input shaft extends in a vertical direction, and the point of force is positioned at an upper side with respect to the pivot of the pitman arm in the vertical direction .

6. The steering device as claimed in claim 3 , wherein the input shaft extends in a vertical direction, and the point of force is positioned at a lower side with respect to the pivot of the pitman arm in the vertical direction .

7. The steering device as claimed in claim 3 , wherein the input shaft extends in a vertical direction, and the point of force is positioned at an upper side with respect to the pivot of the pitman arm in the vertical direction .

Images