Steering device

Abstract

A steering device includes: a first steering mechanism coupled to a steering wheel; and a second steering mechanism formed separately from the first steering mechanism, and arranged separately from the steering wheel. The first steering mechanism includes: a first steering shaft; a torque sensor for sensing a steering torque applied to the first steering shaft; and a first transmission mechanism for steering a first steerable road wheel. The second steering mechanism includes: a second steering shaft; a first electric motor for applying a rotational force to the second steering shaft; a control device for controlling the first electric motor based on a sensed value of the steering torque acquired by the torque sensor; and a second transmission mechanism for steering a second steerable road wheel. The first and second transmission mechanisms are linked to each other via a link mechanism for cooperation therebetween.

Description

DESCRIPTIONTITLE: STEERING DEVICEField

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

[0002] JP 2019-156082 A (henceforth referred to as patent document 1) discloses an integral type steering device mounted to a large vehicle or the like. This steering device includes an electric motor for applying a steering assist force to a steering shaft, and a speed reducer for slowing down a rotational force from the electric motor. The electric motor and the speed reducer are arranged on a side closer to the ground.

[0003] On the other hand, JP 2005-306317 A (henceforth referred to as patent document 2) discloses a steering device, in which an electric motor for applying a steering assist force to a steering shaft, and a speed reducer for slowing down a rotational force from the electric motor are arranged on a side closer to a driver's seat.Summary

[0004] In such a steering device as disclosed in patent document 1, arrangement of an electric motor and a speed reducer on the ground side may cause the electric motor or the speed reducer to interfere with vehicle peripheral devices, and thereby adversely affect mountability of components associated with the steering device.

[0005] In such a steering device as disclosed in patent document 2, arrangement of an electric motor and a speed reducer on the driver's seat side may prevent the electricmotor and the speed reducer from interfering with vehicle peripheral devices. However, the electric motor and the speed reducer are required to be arranged so as not to interfere with sensors and others provided for a steering shaft. This makes the steering device to have a complicated internal structure, and tends to make the steering device to have a long axial dimension. For example, this may cause a housing for the electric motor and others to interfere with a floor panel.

[0006] In view of the foregoing, it is desirable to provide a steering device where a first steering mechanism coupled to a steering wheel can be made to have a short axial dimension.

[0007] According to an embodiment, a steering device includes: a first steering mechanism coupled to a steering wheel; and a second steering mechanism formed separately from the first steering mechanism, and arranged separately from the steering wheel; wherein the first steering mechanism includes: a first steering shaft structured to receive input of rotation from the steering wheel; a torque sensor provided to the first steering shaft, and structured to sense a steering torque applied to the first steering shaft; a first speed reduction mechanism provided to the first steering shaft, and structured to slow down rotation from the first steering shaft; and a first transmission mechanism structured to steer a first steerable road wheel in accordance with an output from the first speed reduction mechanism; wherein the second steering mechanism includes: a second steering shaft; a first electric motor structured to apply a rotational force to the second steering shaft; a first speed reducer provided to the second steering shaft, and structured to slowdown the rotational force from the first electric motor; a control device configured to control the first electric motor based on a sensed value of the steering torque acquired by the torque sensor; a second speed reduction mechanism provided to the second steering shaft, and structured to slow down rotation from the second steering shaft; and a second transmission mechanism structured to steer a second steerable road wheel in accordance with an output from the second speed reduction mechanism; and wherein the first transmission mechanism and the second transmission mechanism are linked to each other via a link mechanism for cooperation between the first transmission mechanism and the second transmission mechanism.Brief Description of Drawings

[0008] FIG. 1 is a diagram showing a configuration of a steering device according to a first embodiment.

[0009] FIG. 2 is a longitudinal sectional view of a first steering mechanism according to the first embodiment.

[0010] FIG. 3 is a longitudinal sectional view of a second steering mechanism according to the first embodiment.

[0011] FIG. 4 is a longitudinal sectional view of a first steering mechanism according to a second embodiment.

[0012] FIG. 5 is a longitudinal sectional view of a first steering mechanism according to a third embodiment.

[0013] FIG. 6 is a longitudinal sectional view of a first steering mechanism according to a fourth embodiment.

[0014] FIG. 7 is a longitudinal sectional view of a first steering mechanism according to a fifth embodiment.

[0015] FIG. 8 is a longitudinal sectional view of a second steering mechanism according to a sixth embodiment.

[0016] FIG. 9 is a longitudinal sectional view of a second steering mechanism according to a seventh embodiment.

[0017] FIG. 10 is a longitudinal sectional view of a second steering mechanism according to an eighth embodiment.

[0018] FIG. 11 is a longitudinal sectional view of a second steering mechanism according to a ninth embodiment.

[0019] FIG. 12 is a longitudinal sectional view of a second steering mechanism according to a tenth embodiment.Description of Embodiments

[0020] In each embodiment described below, a steering device is configured as an integral type steering device mounted to a large vehicle or the like. Each steering device is configured to include a first steering mechanism coupled to a steering wheel, wherein the first steering mechanism can be made to have a short axial dimension.

[0021] [First Embodiment] FIG. 1 shows a configuration of a steering device according to a first embodiment.

[0022] The steering device is mounted to a large vehicle which has a right front road wheel as a first steerable road wheel 1R, and a left front road wheel as a second steerable road wheel IL. The first steerable road wheel 1R and the second steerable road wheel IL are connected to each other by a tie rod 2, a first tie rod arm 3R, and a second tie rod arm 3L, wherein the first tie rod arm 3R and the second tie rod arm 3L are connected to respective ends of the tie rod 2. Accordingly, the first steerable road wheel 1R and the second steerable road wheel IL can be steered in conjunction with each other.

[0023] The first steerable road wheel 1R is connected to a first steering mechanism 7R via a first steering arm 4R, a first drag link 5R, and a first pitman arm 6R. Similarly, thesecond steerable road wheel IL is connected to a second steering mechanism 7L via a second steering arm 4L, a second drag link 5L, and a second pitman arm 6L. The tie rod 2, the arms, and the links constitute a link mechanism that connects a first transmission mechanism 46 of the first steering mechanism 7R to a second transmission mechanism 78 of the second steering mechanism 7L so as to allow cooperation between the first transmission mechanism 46 and the second transmission mechanism 78.

[0024] The steering device includes the first steering mechanism 7R and the second steering mechanism 7L. The first steering mechanism 7R is coupled to a steering wheel 9 via a steering shaft 8. The second steering mechanism 7L is configured as a unit separated from the first steering mechanism 7R. The second steering mechanism 7L is not coupled to the steering wheel 9. Namely, the second steering mechanism 7L is mechanically separated from the first steering mechanism 7R and the steering wheel 9, except for connection via the tie rod 2. The first steering mechanism 7R is structured to steer the first steerable road wheel 1R by actuating the first pitman arm 6R in response to driver's operation of the steering wheel 9. The second steering mechanism 7L includes a first electric motor 11. The second steering mechanism 7L is structured to steer the second steerable road wheel IL by driving the first electric motor 11 rotationally, and thereby actuating the second pitman arm 6L. The driving of the first electric motor 11 is controlled based on a sensed value of the steering torque acquired by a torque sensor 10 (see FIG. 2) provided in the first steering mechanism 7R.

[0025] FIG. 2 shows a longitudinal section of the first steering mechanism 7R. according to the first embodiment. In FIG. 2, illustration of internal structures of a sensing section 27 and a signal processing section 28 of the torque sensor 10 is omitted for ease of understanding.

[0026] The first steering mechanism 7R. includes a first steering shaft 12, the torque sensor 10, a first ball screw mechanism 13, and a first sector gear 14 as main components. The first steering shaft 12 is coupled to the steering wheel 9. The torque sensor 10 is arranged around the first steering shaft 12, and structured to sense a steering torque applied to the first steering shaft 12. The first ball screw mechanism 13 is a speed reduction mechanism that slows down rotation from the first steering shaft 12. The first sector gear 14 is connected to the first steering shaft 12 via the first ball screw mechanism 13, and is employed to actuate the first pitman arm 6R.

[0027] In FIG. 2, for convenience of description, a first end 12a of the first steering shaft 12 is defined as an axial end of the first steering shaft 12 on a side connected to the steering wheel 9 (the upper side in FIG. 2) in a direction of a rotation axis Z1 of the first steering shaft 12, and a second end 12b of the first steering shaft 12 is defined as an axial end on a side to which a first four-point contact ball bearing 25 is attached (the lower side in FIG. 2) in the direction of the rotation axis Zl.

[0028] The first steering mechanism 7R. includes a first housing 15, a first connection member 16, and a second housing 17. The first housing 15 has a generally cylindrical tubular shape. The first connection member 16 has a generally cylindrical tubular shape and is adjacent to the firsthousing 15. The second housing 17 has a generally cylindrical tubular shape and is arranged opposite to the first housing 15 with respect to the first connection member 16. The first steering shaft 12 extends through the first housing 15 and the first connection member 16 into the second housing 17. The first steering shaft 12 includes an input shaft 18, a torsion bar 19, and an output shaft 20. The input shaft 18 is structured to receive input of a rotational force transmitted from the steering wheel 9. The output shaft 20 is connected to the input shaft 18 via the torsion bar 19.

[0029] The input shaft 18 includes a first end side shaft section 18a, an intermediate shaft section 18b, and a second end side shaft section 18c. The first end side shaft section 18a is located at the first end 12a. The intermediate shaft section 18b is formed integrally with the first end side shaft section 18a and has a larger diameter than the first end side shaft section 18a. The second end side shaft section 18c is formed integrally with the intermediate shaft section 18b and has a smaller diameter than the intermediate shaft section 18b. A dust seal 21 is arranged on an outer periphery of the intermediate shaft section 18b at a position closer to the first end side shaft section 18a. The dust seal 21 has an annular shape and is structured to prevent dust and dirt from entering the inside of the first housing 15 from the outside. A magnet part 22 is crimped and fixed to the outer periphery of the intermediate shaft section 18b at a position adjacent to the second end side shaft section 18c in the axial direction. The magnet part 22 has a cylindrical tubular shape. Change in magnetism of the magnet part 22 is sensed by the torque sensor 10.

[0030] The output shaft 20 includes a first shaft section 20a, a second shaft section 20b, a third shaft section 20c, and a fourth shaft section 20d. The first shaft section 20a has a cylindrical tubular shape and is located closer to the first end 12a. The second shaft section 20b has a cylindrical tubular shape, is formed integrally with the first shaft section 20a, and has a larger diameter than the first shaft section 20a. The third shaft section 20c is formed integrally with the second shaft section 20b and has a larger diameter than the second shaft section 20b. The fourth shaft section 20d is formed integrally with the third shaft section 20c and has a smaller diameter than the third shaft section 20c. A reduced diameter portion 27b of the sensing section 27 of the torque sensor 10 is press-fitted and fixed to an outer periphery of the first shaft section 20a. A first deep groove ball bearing 23 is arranged on an outer periphery of the second shaft section 20b, and is structured to support the second shaft section 20b rotatably. A first nut 24 is arranged around the third shaft section 20c. The first nut 24 constitutes a part of the first ball screw mechanism 13. A first four-point contact ball bearing 25 is arranged on an outer periphery of the fourth shaft section 20d. The first four-point contact ball bearing 25 supports the fourth shaft section 20d rotatably. A first fixing member 26 is arranged on an outer periphery of the fourth shaft section 20d at a position closer to the second end 12b than the first four-point contact ball bearing 25. The first fixing member 26 fixes the first four-point contact ball bearing 25 to the third shaft section 20c.

[0031] The first housing 15 is formed in a generally cylindrical tubular shape and houses the torque sensor 10arranged around the input shaft 18. The first housing 15 has an annular flange portion 15a facing the second end 12b.

[0032] The first connection member 16 is made of a metal material and has a generally cylindrical tubular shape. The first connection member 16 connects an abutment surface 15b on the second end 12b side of the flange portion 15a of the first housing 15 to an end face 17a on the first end 12a side of the second housing 17, and holds the first deep groove ball bearing 23 between the first connection member 16 and the outer periphery of the second shaft section 20b of the output shaft 20, wherein the first deep groove ball bearing 23 is provided with a shield or rubber seal.

[0033] The second housing 17 is made of a metal material and has a generally cylindrical tubular shape. The second housing 17 has a first nut housing section 17b and a first sector gear housing section 17c. The first nut housing section 17b accommodates the first nut 24 arranged around the output shaft 20. The first sector gear housing section 17c communicates with the first nut housing section 17b and accommodates the first sector gear 14.

[0034] The torque sensor 10 is a known magnetic torque sensor, and uses the magnet part 22 crimped and fixed to the outer periphery of the input shaft 18. The torque sensor 10 includes the sensing section 27 and the signal processing section 28. The sensing section 27 acquires a signal corresponding to a change in magnetism of the magnet part 22 that rotates together with the input shaft 18. The signal processing section 28 is arranged around the sensing section 27 and processes a magnetic flux sensed by the sensing section 27 to calculate the steering torque. The signal processing section 28 may be configured to calculate asteering angle instead of or in addition to the calculation of the steering torque.

[0035] The sensing section 27 (the housing of the sensing section) is formed of a synthetic resin material and a metal material to have an annular shape, and is arranged around the magnet unit 22. The axial end face of the sensing section 27 on the first end 12a side is formed with a first annular protruding portion 27a at a position adjacent to the inner periphery of the sensing section 27. The first annular protruding portion 27a protrudes toward the first end 12a in the direction of the rotation axis Z1 of the first steering shaft 12. The axial end face of the sensing section 27 on the second end 12b side is formed with a first reduced diameter portion 27b having an annular shape at a position adjacent to the inner periphery of the sensing section 27. The first reduced diameter portion 27b has a stepwise reduced diameter shape and protrudes toward the second end 12b side. The first reduced diameter portion 27b is press-fitted and fixed to the outer periphery of the first shaft section 20a of the output shaft 20, and rotates together with the output shaft 20.

[0036] The signal processing section 28 (the housing of the signal processing unit) is made of a synthetic resin material to have an annular shape, and is arranged around the sensing section 27. The axial end face of the signal processing section 28 on the second end 12b side is formed with two first rotation restricting parts 28a at positions adjacent to the outer periphery of the signal processing section 28. Each first rotation restricting part 28a has a cylindrical shape and serves to prevent the signal processing section 28 from being rotated by rotation of the sensingsection 27. As shown in FIG. 2, the two first rotation restricting parts 28a are arranged so as to be symmetrical radially of the first steering shaft 12 with respect to the output shaft 20. Each first rotation restricting part 28a has a first extension portion 28b and a first rotation restricting cylindrical portion 28c. The first extension portion 28b has a columnar shape that protrudes with a certain diameter toward the second end 12b in the direction of the rotation axis Z1 of the first steering shaft 12, and then contracts in a conical shape. The first rotation restricting cylindrical portion 28c has a cylindrical shape that protrudes from the tip of the first expansion portion 28b toward the second end 12b in the direction of the rotation axis Z1 of the first steering shaft 12. The first rotation restricting cylindrical portion 28c is inserted in a first circular recess 16b of the first connection member 16. The first circular recess 16b is formed in a surface 16a of the first connection member 16 that faces the torque sensor 10 in the axial direction of the first steering shaft 12. In this manner, the first rotation restricting cylindrical portion 28c engages with the first circular recess 16b in the axial direction of the first steering shaft 12. By this engagement, the signal processing section 28 is held by the first connection member 16. The bottom of the first circular recess 16b has a first conical portion 16c. The first conical portion 16c is tapered conically to have a diameter decreasing toward the second end 12b.

[0037] The first deep groove ball bearing 23 is arranged on the first steering shaft 12 between the second shaft section 20b of the output shaft 20 and the first connection member 16 at a position adjacent to the torque sensor 10. The first deep groove ball bearing 23 receives a radial forceacting on the output shaft 20. The first deep groove ball bearing 23 is arranged opposite to the first four-point contact ball bearing 25 with respect to the first ball screw mechanism 13 in the axial direction of the first steering shaft 12.

[0038] The outer periphery of the second shaft section 20b is formed with an annular groove at a position closer to the third shaft section 20c. A first O-ring 29, which is an annular seal member, is fitted into this annular groove. The first O-ring 29 is made of rubber in this example. The first O-ring 29 seals hermetically between the outer periphery of the second shaft section 20b and the inner periphery of the first deep groove ball bearing 23.

[0039] The first connection member 16 includes an annular portion 16d, a first annular protruding portion 16e, a second annular protruding portion 16g, and a first connection member lateral protruding portion 16h. The first annular protruding portion 16e protrudes toward the first end 12a from a portion of the upper side of the annular portion 16d adjacent to the outer periphery of the annular portion 16d. The second annular protruding portion 16g protrudes toward the second end 12b from a surface 16f on the second end 12b side of the annular portion 16d at a position closer to the inner periphery of the annular portion 16d. The first connection member lateral protruding portion 16h protrudes from the outer periphery of the annular portion 16d radially outwardly of the first steering shaft 12.

[0040] A first bolt hole 30 is formed in the first annular protruding portion 16e and the annular portion 16d to extend in the axial direction of the first steering shaft 12. A first bolt 31 as a fixing member is screwed into the first bolt hole30 through a first bolt insertion hole 15c formed in the flange portion 15a of the first housing 15.

[0041] The first connection member lateral protruding portion 16h is formed with a second bolt insertion hole 32 that extends through the first connection member lateral protruding portion 16h in the axial direction of the first steering shaft 12. The second bolt 33 as a fixing member is made to pass through the second bolt insertion hole 32 of the first connection member protruding portion 16h, and is screwed into a second bolt hole 34 formed in a housing lateral protruding portion 17d protruding from the outer periphery of the second housing 17.

[0042] The outer periphery of the second annular protruding portion 16g is formed with an annular groove. A second O-ring 35 is an annular sealing member, and is fitted into the annular groove of the second annular protruding portion 16g. The second O-ring 35 is made of rubber in this example. The second O-ring 35 seals hermetically between the outer periphery of the second annular protruding portion 16g and the inner periphery of the second housing 17. The inner periphery of the second annular protruding portion 16g extends beyond the surface 16f toward the first end 12a in the axial direction of the first steering shaft 12, and holds the outer periphery of an outer race 23a of the first deep groove ball bearing 23.

[0043] The first ball screw mechanism 13 includes a first steering shaft side ball screw groove 36, a first nut side ball screw groove 24a, and balls 37 arranged between the ball screw grooves 36 and 24a. The first steering shaft side ball screw groove 36 is a helical groove formed in the outer periphery of the third shaft section 20c of the output shaft20. The first nut side ball screw groove 24a is a helical groove formed in the inner periphery of the first nut 24. The balls 37 are arranged between the first steering shaft side ball screw groove 36 and the first nut side ball screw groove 24a. The balls 37 support the first nut 24 rotatably with respect to the third shaft section 20c of the output shaft 20.

[0044] The outer periphery of the first nut 24 is formed with first rack teeth 24b on the side facing the first sector gear housing section 17c. The first rack teeth 24b mesh with a first tooth portion 14a of the first sector gear 14.

[0045] The first four-point contact ball bearing 25 is arranged around the fourth shaft section 20d of the output shaft 20 of the first steering shaft 12. The fourth shaft section 20d of the output shaft 20 is located opposite to the torque sensor 10 with respect to the first ball screw mechanism 13 in the first steering shaft 12. The first four- point contact ball bearing 25 receives both a thrust force acting in the axial direction of the first steering shaft 12, i.e., in the direction of the rotation axis Zl, and a radial force acting in the radial direction of the first steering shaft 12. Specifically, the following discusses a force acting on one of four contact points of the first four-point contact ball bearing 25. As shown in FIG. 2, a force F acts on a contact point P on the second end 12b side of the outer race 38 of the first four-point contact ball bearing 25. This force F is decomposed into a thrust force Fl and a radial force F2, wherein the thrust force Fl acts in the direction of the rotation axis Zl of the first steering shaft 12, and wherein the radial force F2 acts radially outwardly of the first steering shaft 12. Accordingly, the first four-point contact ball bearing 25 receives the thrust force Fl acting through thecontact point P, and the radial force F2 acting also through the contact point P, wherein the radial force F2 is smaller than the thrust force Fl. In this example, the thrust force Fl is about 1.5 to 2 times the radial force F2. In this viewpoint, the first four-point contact ball bearing 25 is configured to contribute much more significantly to receipt of the thrust force Fl than to receipt of the radial force F2. In the large vehicle provided with the first sector gear 14 according to the present embodiment, the thrust force acting on the first steering shaft 12 is very large as compared to vehicles of general size. In order to receive the large thrust force and the radial force simultaneously, it is advantageous to employ the first four-point contact ball bearing 25.

[0046] The first four-point contact ball bearing 25 includes an inner race 39, the outer race 38, and balls 40. The inner race 39 is arranged on the outer periphery of the fourth shaft section 20d of the output shaft 20. The outer race 38 is disposed radially outside the inner race 39. The balls 40 are disposed between the inner race 39 and the outer race 38. The first four-point contact ball bearing 25 is press-fitted onto the inner periphery of the second housing 17. The inner periphery of the inner race 39 has a corner portion 39a on the first end 12a side, and a corner portion 39b on the second end 12b side, wherein the corner portion 39a abuts on a step 41 of the output shaft 20. The step 41 of the output shaft 20 is formed between the third shaft section 20c and the fourth shaft section 20d of the output shaft 20. On the other hand, the outer periphery of the outer race 38 has a corner portion 38a on the first end 12a side, and a corner portion 38b on the second end 12b side, wherein the cornerportion 38a abuts on a step 42 formed in the inner periphery of the second housing 17.

[0047] The first fixing member 26 is a nut member having an inner periphery where a first fixing member side internal thread 26a is formed . This first fixing member side internal thread 26a is screwed onto a fi rst steering shaft side external thread 43 formed in the outer periphery of the fou rth shaft section 20d of the output shaft 20. This screwing presses the corner portion 39b of the inner race 39, and then presses the corner portion 39a of the inner race 39 against the step 41 of the output shaft 20, thereby fixing the inner race 39 to the output shaft 20.

[0048] A first blocking member 44 has a d isk shape, a nd is a rranged on the second end 12b side of the first fou r-poi nt contact ball bearing 25 in the d irection of the rotation axis Z 1 of the first steering shaft 12. The first blocking member 44 blocks an opening of the second housing 17 on the first fou r- point contact ball bearing 25 side, and fixes the outer race 38 of the fi rst fou r-point contact ba ll bearing 25 to the second housing 17. The first blocking member 44 is made of metal or synthetic resin . The first blocking member 44 has a bottom wall 44a having a circu lar plate shape, and a cylind rical peripheral wa ll 44b extend ing from the outer periphery of the bottom wa ll 44a toward the first end 12a .

[0049] The outer periphery of the periphera l wall 44b of the first blocki ng member 44 is formed with an annu la r seal g roove at a position close to an axial end face 44c of the peripheral wall 44b. A third O-ring 45 as a n annu lar seal member is fitted into the annu lar sea l g roove. The third 0- ring 45 is made of ru bber in this example. The third O- ring 45 seals hermetica lly between the inner periphery of thesecond housing 17 a nd the outer periphery of the peripheral wa ll 44b of the first blocking member 44.

[0050] The outer periphery of the periphera l wall 44b of the first blocking member 44 is formed with a first blocking member side external thread 44d on the second end 12b side of the third O- ring 45. This first blocking member side external thread 44d is screwed onto a first housing side internal thread 17e formed in the inner periphery of an end portion of the second housing 17 on the second end 12b side. This screwing presses a n axial end face 38c of the outer race 38, and then presses the corner portion 38a of the outer race 38 against the step 42 of the second housing 17, thereby fixing the outer race 38 to the second housing 17.

[0051] The first sector gear 14 is a rranged in a swingable manner within the first sector gea r housing section 17c of the second housing 17. The first sector gea r 14 has a first axial end side linked to the first rack teeth 24b of the first nut 24 via the first tooth portion 14a, a nd a second axial end side linked to the first steera ble road wheel 1 R via the first pitman arm 6R (see FIG . 1) . The first tooth portion 14a of the first sector gear 14 and the first rack teeth 24b of the first nut 24 constitute the first transmission mechanism 46 that steers the first steera ble road wheel 1 R in accordance with an output from the first ball screw mechanism 13.

[0052] The steering device config u red as described above behaves as follows. When the steering wheel 9 is rotated by a d river, the rotation of the steering wheel 9 causes the input shaft 18 to rotate, the rotation of the input shaft 18 causes the torsion bar 19 to be twisted , and the twist of the torsion ba r 19 causes an elastic force to rotate the output shaft 20. The rotation of the output shaft 20 causes the first nut 24 totravel in the direction of the rotation axis Z1 of the first steering shaft 12, and the travel of the first nut 24 causes the first sector gear 14 to rotate. The rotation or swing of the first sector gear 14 causes the first pitman arm 6R. to be pulled in a vehicle lateral direction, and thereby causes a change in orientation of the first steerable road wheel 1R.

[0053] FIG. 3 shows a longitudinal section of the second steering mechanism 7L according to the first embodiment.

[0054] The second steering mechanism 7L includes a second steering shaft 47, the first electric motor 11, a first speed reducer 48, and a second ball screw mechanism 49 as main components. The first electric motor 11 applies a rotational force to the second steering shaft 47. The first speed reducer 48 slows down the rotational force from the first electric motor 11. The second ball screw mechanism 49 is a speed reduction mechanism that is arranged on the second steering shaft 47 and slows down rotation from the second steering shaft 47.

[0055] In FIG. 3, for convenience of description, a first end 47a of the second steering shaft 47 is defined as an axial end of the second steering shaft 47 on a side where a second deep groove ball bearing 53 is attached (the upper side in FIG. 3) in a direction of a rotation axis Z2 of the second steering shaft 47, and a second end 47b of the second steering shaft 47 is defined as an axial end of the second steering shaft 47 on a side where a second four-point contact ball bearing 55 is attached (the lower side in FIG. 3) in the direction of the rotation axis Z2.

[0056] The second steering shaft 47 is accommodated in a space surrounded by a third housing 50, a second connection member 51, and a fourth housing 52. The third housing 50has a cylindrical tubular shape. The third housing 50 has an annular flange portion 50b on the second end 47b side. The second connection member 51 has a cylindrical tubular shape and is arranged adjacent to the third housing 50. The fourth housing 52 is arranged adjacent to the second connection member 51.

[0057] The second steering shaft 47 has a first medium diameter shaft section 47c, a larger diameter shaft section 47d, a second medium diameter shaft section 47e, a first smaller diameter shaft section 47f, and a second smaller diameter shaft section 47g. The first medium diameter shaft section 47c is located at the first end 47a. The larger diameter shaft section 47d is formed integrally with the first medium diameter shaft section 47c and has a larger diameter than the first medium diameter shaft section 47c. The second medium diameter shaft section 47e is formed integrally with the larger diameter shaft section 47d and has a smaller diameter than the larger diameter shaft section 47d. The first smaller diameter shaft section 47f is formed integrally with the second medium diameter shaft section 47e and has a smaller diameter than the second medium diameter shaft section 47e. The second smaller diameter shaft section 47g is formed integrally with the first smaller diameter shaft section 47f and has a smaller diameter than the first smaller diameter shaft section 47f.

[0058] A first core 62 of a first worm wheel 60 of the first speed reducer 48 is press-fitted and fixed to the outer periphery of the first medium diameter shaft section 47c. The second deep groove ball bearing 53 is arranged on the outer periphery of the larger diameter shaft section 47d, and supports the larger diameter shaft section 47d rotatably. Asecond nut 54 is arranged around the second medium diameter shaft section 47e, and constitutes a part of the second ball screw mechanism 49. The second four-point contact ball bearing 55 is arranged on the outer periphery of the first smaller diameter shaft section 47f, and supports the first smaller diameter shaft section 47f rotatably. A second fixing member 56 is arranged around the second smaller diameter shaft section 47g, and fixes the second four-point contact ball bearing 55 to the second steering shaft 47.

[0059] The third housing 50 is formed of a metal material to have a bottomed cylindrical tubular shape. The third housing 50 accommodates the first speed reducer 48, which is arranged around the first medium diameter shaft section 47c, and the second deep groove ball bearing 53, which is arranged around the larger diameter shaft section 47d.

[0060] The second connection member 51 is made of a metal material to have a generally cylindrical tubular shape. The second connection member 51 connects an end face 50a of the third housing 50 on the second end 47b side to an end face 52a of the fourth housing 52 on the first end 47a side, and holds the second deep groove ball bearing 53 between the second connection member 51 and the outer periphery of the larger diameter shaft section 47d of the second steering shaft 47, wherein the second deep groove ball bearing 53 is provided with a shield or rubber seal.

[0061] The fourth housing 52 is made of a metal material and has a generally cylindrical tubular shape. The fourth housing 52 includes a second nut housing section 52b and a second sector gear housing section 52c. The second nut housing section 52b accommodates the second nut 54 arranged around the second steering shaft 47. The secondsector gear housing section 52c communicates with the second nut housing section 52b and accommodates a second sector gear 57.

[0062] The first electric motor 11 is drive-controlled based on a sensed value of the steering torque acquired by the torque sensor 10 placed in the first steering mechanism 7R, thereby applying a rotational force to the second steering shaft 47 via the first speed reducer 48. The first electric motor 11 is arranged opposite to the second sector gear 57 with respect to the second steering shaft 47 such that a first worm shaft 58 connected to a motor shaft not shown of the first electric motor 11 overlaps with the first medium diameter shaft section 47c of the second steering shaft 47 in the radial direction of the second steering shaft 47. The first electric motor 11 is housed in a first motor housing 11a having a bottomed cylindrical tubular shape. As shown in FIG. 3, the first motor housing 11a extends outwardly beyond the third housing 50 both in the direction of the rotation axis Z2 of the second steering shaft 47 and in the radial direction of the second steering shaft 47.

[0063] The first electric motor 11 is drive-controlled by a first control device 59 (see FIG. 1). Specifically, the first electric motor 11 is drive-controlled based on a sensed value of the steering torque that is acquired by the torque sensor 10 of the first steering mechanism 7R and then transmitted to the first control device 59.

[0064] The first speed reducer 48 includes a first worm shaft 58, and a first worm wheel 60 that meshes with the first worm shaft 58. The first worm wheel 60 is formed by insert molding to form a first gear forming part 61 around a first core 62, wherein the first core 62 is made of metal tohave a cylindrical tubular shape, and wherein the first gear forming part 61 is made of synthetic resin. The first core 62 is press-fitted to the outer periphery of the first medium diameter shaft section 47c of the second steering shaft 47, and is made to abut on the axial end face on the first end 47a side of the larger diameter shaft section 47d.

[0065] The second deep groove ball bearing 53 is disposed between the larger diameter shaft section 47d and the second connection member 51 of the second steering shaft 47. The second deep groove ball bearing 53 receives a radial force acting on the second steering shaft 47. The second deep groove ball bearing 53 is disposed opposite to the second four-point contact ball bearing 55 with respect to the second ball screw mechanism 49 in the axial direction of the second steering shaft 47.

[0066] The outer periphery of the larger diameter shaft section 47d of the second steering shaft 47 is formed with an annular groove at a central position of the larger diameter shaft section 47d in the axial direction. A fourth O-ring 63 as an annular seal member is fitted into this annular groove. The fourth O-ring 63 is formed of rubber in this example. The fourth O-ring 63 seals hermetically between the outer periphery of the larger diameter shaft section 47d and the inner periphery of the second deep groove ball bearing 53. This allows a lubricant to be stored near the first speed reducer 48 in the third housing 50, and thereby improves lubrication for meshing contact between the first worm shaft 58 and the first worm wheel 60.

[0067] The second connection member 51 includes a cylindrical main body 51a, an annular protruding portion 51b, an annular protruding portion 51c, an extension portion 51d,and a ceiling wall portion 51e. The cylindrical main body 51a has a cylindrical tubular shape. The annular protruding portion 51b protrudes radially outwardly from a central portion in the axial direction of the outer periphery of the cylindrical main body 51a. The annular protruding portion 51c protrudes radially inwardly from an axial end portion on the first end 47a side of the inner periphery of the cylindrical main body 51a. The extension portion 51d has an annular shape that extends from an axial end on the first end 47a side of the annular protruding portion 51c toward the first end 47a in the direction of the rotation axis Z2 of the second steering shaft 47. The ceiling wall portion 51e has an annular shape that extends radially inwardly from an axial end portion on the first end 47a side of the inner periphery of the extension portion 51d.

[0068] The annular protruding portion 51b of the second connection member 51 includes a portion 5 If that faces the second sector gear 57 via the fourth housing 52 in the direction of the rotation axis Z2 of the second steering shaft 47 and is extended radially outwardly as compared to the remaining portion of the annular protruding portion 51b. The portion 51f is formed with a third bolt insertion hole 64 extending through the portion 51f in the direction of the rotation axis Z2 of the second steering shaft 47. The third housing 50 and the second connection member 51 are fastened together to the fourth housing 52 by inserting a third bolt 67 as a fixing member through the third bolt insertion hole 64 of portion 5 If and a fourth bolt insertion hole 65 formed in the flange portion 50b of the third housing 50, and screwing the third bolt 67 into a third bolt hole 66 formed in the fourth housing 52.

[0069] The inner periphery of the annular protruding portion 51c and the extension portion 51d of the second connection member 51 and the outer periphery of the larger diameter shaft section 47d of the second steering shaft 47 hold the second deep groove ball bearing 53 therebetween.

[0070] The ceiling wall portion 51e of the second connection member 51 has a radial length sufficient to cover the first end 47a side of the second deep groove ball bearing 53.

[0071] The second ball screw mechanism 49 is composed of a second steering shaft side ball screw groove 68, a second nut side ball screw groove 54a, and balls 69. The second steering shaft side ball screw groove 68 is a helical groove formed in the outer periphery of the second medium diameter shaft section 47e of the second steering shaft 47. The second nut side ball screw groove 54a is a helical groove formed in the inner periphery of the second nut 54. The balls 69 are disposed between the second steering shaft ball screw groove 68 and the second nut ball screw groove 54a. The balls 69 support the second nut 54 rotatably with respect to the second medium diameter shaft section 47e.

[0072] The outer periphery of the second nut 54 is formed with second rack teeth 54b facing the second sector gear housing section 52c. The second rack teeth 54b mesh with a second tooth portion 57a formed in the second sector gear 57.

[0073] The second four-point contact ball bearing 55 receives both a thrust force acting in the axial direction of the second steering shaft 47, i.e., in the direction of the rotation axis Z2, and a radial force acting in the radial direction of the second steering shaft 47. The thrust forceand radial force received by the second four-point contact ball bearing 55 are similar to those in the relationship among the forces F, Fl, and F2 in the first four-point contact ball bearing 25 of the first steering mechanism 7R.

[0074] The second four-point contact ball bearing 55 has an inner race 70, an outer race 71, and balls 72. The inner race 70 is arranged on the outer periphery of the first smaller diameter shaft section 47f of the second steering shaft 47. The outer race 71 disposed radially outside the inner race 70. The balls 72 are disposed between the inner race 70 and the outer race 71. The second four-point contact ball bearing 55 is press-fitted onto the inner periphery of the fourth housing 52. The inner periphery of the inner race 70 has a corner portion 70a on the first end 47a side, and a corner portion 70b on the second end 47b side, wherein the corner portion 70a abuts on a step 73 formed between the second medium diameter shaft section 47e and the first smaller diameter shaft section 47f of the second steering shaft 47. On the other hand, the outer periphery of the outer race 71 has a corner portion 71a on the first end 47a side, and a corner portion 71b on the second end 47b side, wherein the corner portion 71a abuts on a step 74 formed in the inner periphery of the fourth housing 52.

[0075] The second fixing member 56 fixes the inner race 70 of the second four-point contact ball bearing 55 to the second steering shaft 47. The second fixing member 56 is a nut member having an inner periphery where a second fixing member side internal thread 56a is formed. The second fixed member side internal thread 56a is screwed onto a second steering shaft side external thread 75 formed in the outer periphery of the second smaller diameter shaft section 47g ofthe second steering shaft 47. This screwing presses the corner portion 70b of the inner race 70, and then presses the corner portion 70a of the inner race 70 against the step 73 of the second steering shaft 47, thereby fixing the inner race 70 to the second steering shaft 47.

[0076] A second blocking member 76 has a disk shape, and is arranged on the second end 47b side of the second four-point contact ball bearing 55 in the direction of the rotation axis Z2 of the second steering shaft 47. The second blocking member 76 blocks an opening of the fourth housing 52 on the second four-point contact ball bearing 55 side, and fixes the outer race 71 of the second four-point contact ball bearing 55 to the fourth housing 52. The second blocking member 76 is made of metal or synthetic resin. The second blocking member 76 has a bottom wall portion 76a, an inner peripheral wall portion 76b, an annular protruding portion 76c, and an outer peripheral wall portion 76d. The bottom wall portion 76a has a circular plate shape. The inner peripheral wall portion 76b has a cylindrical tubular shape extending from the outer periphery of the bottom wall portion 76a toward the first end 47a. The annular protruding portion 76c protrudes radially outwardly from an axial end on the first end 47a side of the inner peripheral wall portion 76b.The outer peripheral wall portion 76d has a cylindrical tubular shape extending from the outer periphery of the annular protruding portion 76c toward the second end 47b.

[0077] In the direction of the rotation axis Z2 of the second steering shaft 47, the outer peripheral wall portion 76d is longer than the inner peripheral wall portion 76b. The outer peripheral wall portion 76d has an axial end face 74e on the first end 47a side, wherein the axial end face 74e islocated closer to the first end 47a than an axial end face 74f on the first end 47a side of the annular protruding portion 76c. Accordingly, the axial end face 74e of the outer peripheral wall portion 76d abuts on the axial end face 71c on the second end 47b side of the outer race 71 of the second four-point contact ball bearing 55, whereas the axial end face 74f of the annular protruding portion 76c is separated apart from an axial end face 70c on the second end 47b side of the inner race 70 of the second four-point contact ball bearing 55.

[0078] The outer periphery of the outer peripheral wall portion 76d is formed with an annular seal groove at a position closer to the axial end face 74e. A fifth O-ring 77 as an annular seal member is fitted into this annular seal groove. The fifth O-ring 77 is made of rubber in this example. The fifth O-ring 77 seals hermetically between the inner periphery of the fourth housing 52 and the outer periphery of the outer peripheral wall portion 76d.

[0079] The outer periphery of the outer peripheral wall portion 76d is formed with a second blocking member side external thread 74g on the second end 47b side of the fifth O-ring 77. The second blocking member side external thread 74g is screwed onto a second housing side internal thread 52d formed in the inner periphery of an end portion of the fourth housing 52 on the second end 47b side. This screwing presses an axial end face 71c of the outer race 71, and then presses the corner portion 71a of the outer race 71 against the step 74 of the fourth housing 52, thereby fixing the outer race 71 to the fourth housing 52.

[0080] The second sector gear 57 is arranged in a swingable manner within the second sector gear housingsection 52c of the fou rth housing 52. The second sector gear 57 has a first axia l end side linked to the second rack teeth 54b of the second nut 54 via the second tooth portion 57a, and a second axia l end side linked to the second steerable road wheel I L via the second pitma n arm 6L (see FIG . 1) . The second tooth portion 57a of the second sector gear 57 and the second rack teeth 54b of the second nut 54 constitute the second transmission mechanism 78 that steers the second steera ble road wheel I L in accordance with an output from the second ball screw mecha nism 49.

[0081] The steering device config u red as described above behaves as follows. When the steering wheel 9 is rotated by a d river, the first electric motor 11 applies a rotational force to the second steeri ng shaft 47 via the first speed red ucer 48 in accordance with a sensed value of the steering torque acqu ired by the torque sensor 10 of the first steering mecha nism 7R. This causes the second steering shaft 47 to rotate, a nd thereby causes the second nut 54 to travel in the d irection of the rotation axis Z2 of the second steering shaft47, and the travel of the second nut 54 causes the second sector gear 57 to rotate. The rotation or swing of the second sector gear 57 causes the second pitma n arm 6L to be pu lled in the vehicle latera l d irection, a nd thereby causes a cha nge in orientation of the second steera ble road wheel I L.

[0082] [Advantageous Effects of First Embod iment] As described above, in the first embod iment, the first steering mechanism 7R. includes the torq ue sensor 10 a nd the first ball screw mechanism 13 which are mounted to the first steering shaft 12. On the other ha nd, the second steering mecha nism 7L includes the first electric motor 11 , the first speed reducer48, and the second ball screw mechanism 49 which aremounted to the second steering shaft 47. In general, a vehicle model is designed to be capable of being applied to both a right-side steering wheel and a left-side steering wheel. Accordingly, a space for accommodating a steering device including a steering wheel is ensured on each side of a center of the vehicle in a vehicle lateral direction. This results in that the side where the steering wheel 9 is not placed, i.e., the second steering shaft 47 side, has a relatively large remaining space where components associated with the steering device can be mounted. In view of the foregoing, the steering device according to the present embodiment is configured to include multiple steering shafts, namely, the first steering shaft 12 linked to the steering wheel 9 and the second steering shaft 47 arranged on the side where the steering wheel 9 is not provided, wherein the torque sensor 10 and the first ball screw mechanism 13 are mounted to the first steering shaft 12, and wherein the first electric motor 11 and the first speed reducer 48, which constitute a first steering assist mechanism, and the second ball screw mechanism 49 are mounted to the second steering shaft 47, since the first steering assist mechanism is not required to be mounted to the first steering shaft 12 side. This allows the axial dimension of the first steering mechanism 7R. arranged on the driver's seat side to be shortened, as compared to that in a comparative steering device where the first electric motor 11 and the first speed reducer 48 are arranged on the steering wheel 9 side. This makes it possible to prevent interference between the first housing 15 and the floor panel of the vehicle.

[0083] [Second Embodiment] FIG. 4 shows a longitudinal section of a first steering mechanism 7R. according to a second embodiment.

[0084] Among other things, the first steering mechanism 7R. according to the second embodiment is configured based on the first embodiment by replacing the first deep groove ball bearing 23 and the first four-point contact ball bearing 25 of the first steering mechanism 7R. according to the first embodiment with a first angular ball bearing 79 and a second angular ball bearing 80, respectively. This replacement is accompanied by provision of a fifth shaft section 20e of the output shaft 20 of the first steering shaft 12 in the second embodiment instead of the first shaft section 20a and the second shaft section 20b of the output shaft 20 of the first steering shaft 12 according to the first embodiment. Furthermore, in the second embodiment, the fourth shaft section 20d of the output shaft 20 according to the first embodiment is replaced with a sixth shaft section 20f whose axial dimension is shorter than that of the fourth shaft section 20d.

[0085] The first angular ball bearing 79 has a contact angle between an inner race 81 and balls 83 and a contact angle between an outer race 82 and the balls 83. Accordingly, the first angular ball bearing 79 receives both a thrust force acting in the axial direction of the first steering shaft 12, i.e., in the direction of the rotation axis Zl, and a radial force acting in the radial direction of the first steering shaft 12. The first angular ball bearing 79 is arranged on the outer periphery of the fifth shaft section 20e arranged on the first end 12a side of the output shaft 20, at a position adjacent to the third shaft section 20c. The inner race 81 ofthe first angular ball bearing 79 is disposed adjacent to the reduced diameter portion 27b of the sensing section 27 of the torque sensor 10 via a cylindrical spacer member 84 in the direction of the rotation axis Z1 of the first steering shaft 12. The inner race 81 has an end face 81a on the first end 12a side which abuts on an axial end face 84a on the second end 12b side of the spacer member 84. On the other hand, the inner race 81 has an end face 81b on the second end 12b side which abuts on a step 85 formed between the fifth shaft section 20e and the third shaft section 20c. The outer periphery of the outer race 82 of the first angular ball bearing 79, except for an end portion on the second end 12b side, is held by the inner periphery of the second annular protruding portion 16g of the first connection member 16.

[0086] The second angular ball bearing 80 is similar in size and configuration to the first angular ball bearing 79, and receives both thrust and radial forces acting on the output shaft 20. The second angular ball bearing 80 is arranged on the outer periphery of the sixth shaft section 20f of the output shaft 20, wherein the sixth shaft section 20f is located opposite to the torque sensor 10 with respect to the first ball screw mechanism 13. As shown in FIG. 4, the second angular ball bearing 80 is arranged to have an orientation symmetrical to the orientation of the first angular ball bearing 79 with respect to the first nut 24 in the direction of the rotation axis Z1 of the first steering shaft 12. The inner race 86 of the second angular ball bearing 80 has a corner portion 86a on the first end 12a side which abuts on a step 87 formed between the third shaft section 20c and the sixth shaft section 20f of the output shaft 20. The inner race 86 of the second angular ball bearing 80 has an end face 86bon the second end 12b side which is located closer to a third blocking member 90 described below than the second end 12b of the first steering shaft 12. The outer race 88 of the second angular ball bearing 80 is press-fitted onto a cylindrical peripheral wall portion 90b of the third blocking member 90.

[0087] The steering device according to the second embodiment includes a preload adjustment mechanism 89 for adjusting the preload of the first angular ball bearing 79 and the preload of the second angular ball bearing 80. The preload adjustment mechanism 89 has the third blocking member 90 and a fixing ring 91.

[0088] The third blocking member 90 has a bottom wall base portion 90a and a cylindrical peripheral wall portion 90b. The bottom wall base portion 90a has a circular plate shape. The cylindrical peripheral wall portion 90b has a cylindrical tubular shape extending from the outer periphery of the bottom wall base portion 90a toward the first end 12a.

[0089] The bottom wall base portion 90a has a bottom face 90c facing the first steering shaft 12. The bottom face 90c has a central portion including a recess 90d that extends from the bottom face 90c away from the first steering shaft 12. Accordingly, the bottom face 90c has a continuous annular shape adjacent to the cylindrical peripheral wall portion 90b. The bottom face 90c abuts on an end face 88a of the outer race 88 of the second angular ball bearing 80 that faces the bottom face 90c. The bottom wall base portion 90a has an outer face 90e opposite to the bottom face 90c, wherein the outer face 90e has a pair of rotation locking holes 90f each of which receives a counterpart portion of apreload device not shown, and serves for rotation of the third blocking member 90.

[0090] The outer periphery of the cylindrical peripheral wall portion 90b is formed with a third blocking member side external thread 90g on the bottom wall base portion 90a side. This third blocking member side external thread 90g is screwed onto a third housing side internal thread 17f formed in the inner periphery of an end portion of the second housing 17 on the second end 12b side. This screwing presses the output shaft 20 toward the first end 12a via the second angular ball bearing 80, and thereby presses the inner race 81 of the first angular ball bearing 79, and thereby presses the outer race 82 via the balls 83. In this way, the preload of the first angular ball bearing 79 is adjusted. Simultaneously, the screwing presses the corner portion 86a of the inner race 86 of the second angular ball bearing 80 against the step 87 via the outer race 88 and balls 92 of the second angular ball bearing 80. In this way, the preload of the second angular ball bearing 80 is adjusted.

[0091] After adjustment of the preload of the first angular ball bearing 79 and the preload of the second angular ball bearing 80, the third blocking member 90 is fixed to the second housing 17 by screwing a ring side internal thread 91a, which is formed in the inner periphery of the fixing ring 91, onto the third blocking member side external thread 90g of the third blocking member 90.

[0092] The inner periphery of the second housing 17 is formed with an annular seal groove forming protruding portion 17g at a position adjacent to the third housing side internal thread 17f, wherein the seal groove forming protruding portion 17g protrudes radially inwardly from theinner periphery of the second housing 17. The seal groove forming protruding portion 17g has an inner tip end face including an annular seal groove. A sixth O-ring 93 as an annular seal member is fitted into this seal groove. The sixth O-ring 93 is formed of rubber in this example. The sixth 0- ring 93 seals hermetically between the outer periphery of the cylindrical peripheral wall portion 90b of the third blocking member 90 and the inner periphery of the seal groove forming protruding portion 17g of the second housing 17.

[0093] [Advantageous Effects of Second Embodiment] As described above, in the second embodiment, the first steering mechanism 7R. includes the first angular ball bearing 79 arranged on the first end 12a side of the output shaft 20, and the second angular ball bearing 80 arranged on the output shaft 20 opposite to the torque sensor 10 with respect to the first ball screw mechanism 13. The first angular ball bearing 79 and the second angular ball bearing 80 can be adjusted in preload by the preload adjustment mechanism 89, so that bearing of the first steering shaft 12 can be efficiently performed in accordance with an individual difference and an usage condition of the steering device.

[0094] [Third Embodiment] FIG. 5 shows a longitudinal section of a first steering mechanism 7R. according to a third embodiment.

[0095] The first steering mechanism 7R. according to the third embodiment is configured based on the first embodiment by replacing the first ball screw mechanism 13 and the first sector gear 14 of the first steering mechanism 7R. according to the first embodiment with a first worm gear mechanism 94. This replacement is accompanied by replacement of the third shaft section 20c of the output shaft20 according to the first embodiment with a seventh shaft section 20g having a larger diameter than the third shaft section 20c and an eighth shaft section 20h having a shorter axial dimension than the third shaft section 20c in the third embodiment. Furthermore, instead of the first nut housing section 17b and the first sector gear housing section 17c according to the first embodiment, the second housing 17 according to the third embodiment has a worm housing section 17h and a worm wheel housing section 17i. The worm housing section 17h accommodates the seventh shaft section 20g and a speed reduction mechanism worm 95 formed in the outer periphery of the seventh shaft section 20g. The worm wheel housing section 17i accommodates a speed reduction mechanism worm wheel 96 that meshes with the speed reduction mechanism worm 95.

[0096] The first worm gear mechanism 94 is composed to the speed reduction mechanism worm 95 and the speed reduction mechanism worm wheel 96. The speed reduction mechanism worm 95 is formed in the outer periphery of the seventh shaft section 20g of the output shaft 20. The speed reduction mechanism worm wheel 96 meshes with the speed reduction mechanism worm 95.

[0097] The speed reduction mechanism worm 95 is formed to extend over a major part of the outer periphery of the seventh shaft section 20g, except for relatively small axial end portions on the first end 12a side and the second end 12b side.

[0098] The speed reduction mechanism worm wheel 96 is formed by insert molding to form a speed reduction mechanism gear forming part 97 around a speed reduction mechanism core 98, wherein the speed reduction mechanismgear forming part 97 is made of synthetic resin, and wherein the speed reduction mechanism core 98 is made of metal to have a cylindrical tubular shape. The inner periphery of the speed reduction mechanism core 98 is formed with a groove 98a into which a key 99 is fitted. The speed reduction mechanism core 98 is connected via this key 99 to a gear output shaft part 100 having a cylindrical shape. This gear output shaft part 100 is connected to the first pitman arm 6R. (see FIG. 1). The speed reduction mechanism worm wheel 96 may be made entirely of metal with no synthetic resin.

[0099] [Advantageous Effects of Third Embodiment] As described above, in the third embodiment, the first worm gear mechanism 94 is composed of the speed reduction mechanism worm 95 formed in the outer periphery of the seventh shaft section 20g and the speed reduction mechanism worm wheel 96 meshing with the speed reduction mechanism worm 95. In the first embodiment, rotation from the output shaft 20 is slowed down via the first ball screw mechanism 13, and then the slowed-down rotation is further slowed down via the meshing between the first rack teeth 24b of the first nut 24 and the first tooth portion 14a of the first sector gear 14. Namely, rotation from the output shaft 20 is slowed down in two stages. In contrast, in the third embodiment, rotation from the output shaft 20 is slowed down in a single stage via the meshing between the speed reduction mechanism worm 95 and the speed reduction mechanism worm wheel 96. This simplification of the configuration of the speed reduction mechanism serves to reduce the manufacturing cost of the steering device.

[0100] The first worm gear mechanism 94 according to the third embodiment has no component that travels in thedirection of the rotation axis Z1 of the first steering shaft 12, like the first nut 24 of the first ball screw mechanism 13 according to the first embodiment. This allows the axial dimensions of the first steering shaft 12 and the steering device to be shorter than those of the first embodiment.

[0101] [Fourth Embodiment] FIG. 6 shows a longitudinal section of a first steering mechanism 7R. according to a fourth embodiment.

[0102] The first steering mechanism 7R. according to the fourth embodiment is configured based on the second embodiment by replacing the first ball screw mechanism 13 and the first sector gear 14 of the first steering mechanism 7R. according to the second embodiment with the first worm gear mechanism 94 according to the third embodiment.

[0103] [Advantageous Effects of Fourth Embodiment] According to the fourth embodiment, it is possible to achieve a reduction in the manufacturing cost of the steering device and a reduction in the axial dimension of the steering device as in the third embodiment, and efficiently perform bearing of the first steering shaft 12 in accordance with an individual difference and an usage condition of the steering device.

[0104] [Fifth Embodiment] FIG. 7 shows a longitudinal section of a first steering mechanism 7R. according to a fifth embodiment.

[0105] The first steering mechanism 7R. according to the fifth embodiment is configured based on the third embodiment by replacing the first worm gear mechanism 94 according to the third embodiment with a second worm gear mechanism 101 that is a known double lead worm gear. This replacement is accompanied by replacement of the first blocking member 44 according to the third embodiment witha fourth blocking member 103 and a backlash mechanism 102.

[0106] The second worm gear mechanism 101 is composed of the speed reduction mechanism worm wheel 96 and a double lead worm 104. The double lead worm 104 is formed in the outer periphery of the seventh shaft section 20g of the output shaft 20. The speed reduction mechanism worm wheel 96 meshes with the double lead worm 104. The double lead worm 104 is configured to have upper and lower (in FIG. 7) tooth flanks having different leads. Travel of the double lead worm 104 in the direction of the rotation axis Z1 of the first steering shaft 12 causes a variation in tooth thickness of a portion 105 of the double lead worm 104 that meshes with the speed reduction mechanism gear forming part 97 of the speed reduction mechanism worm wheel 96. With this operation, backlash in the second worm gear mechanism 101 can be adjusted.

[0107] The backlash mechanism 102 includes an adjustment plug 106 and a lock ring 107. The adjustment plug 106 has a cylindrical tubular shape, and has an inner periphery including a step 106a where the inner periphery decreases in diameter in a stepwise manner from the first end 12a side toward the second end 12b side. The step 106a abuts on the corner portion 38b on the second end 12b side of the outer race 38 of the first four-point contact ball bearing 25. The inner periphery of the adjustment plug 106 is formed with a plug-side internal thread 106b at a position adjacent to a first axial end 106c on the first end 12a side of the adjustment plug 106. The plug-side internal thread 106b is screwed onto a nut-side external thread 108a formed in the outer periphery of a retaining ring 108. This screwingpresses the end face 38c of the outer race 38 against the step 106a, thereby fixing the outer race 38 to the adjustment plug 106.

[0108] The outer periphery of the adjustment plug 106 is formed with an annular seal groove near the first axial end 106c. A seventh O-ring 109 as an annular seal member is fitted into this annular seal groove. The seventh O-ring 109 is made of rubber in this example. The seventh O-ring 109 seals hermetically between the inner periphery of the second housing 17 and the outer periphery of the adjustment plug 106.

[0109] The outer periphery of the adjustment plug 106 is formed with a plug-side external thread 106d on the second end 12b side of the seventh O-ring 109. The plug-side external thread 106d is screwed onto the first housing-side internal thread 17e formed in the inner periphery of the end portion of the second housing 17 on the second end 12b side. For this screwing, the adjustment plug 106 is rotated by a backlash adjustment device not shown. This rotation of the adjustment plug 106 presses the output shaft 20 via the adjustment plug 106 and the first four-point contact ball bearing 25, and thereby causes the output shaft 20 to travel in the axial direction. With this operation, backlash is adjusted to a predetermined level. With the backlash maintained at the predetermined level, the adjustment plug 106 is fixed to the second housing 17 by screwing a ring side internal thread 107a of the lock ring 107 onto the plug side external thread 106d of the adjustment plug 106.

[0110] As shown in FIG. 7, an end face 106e on the second end 12b side of the adjustment plug 106 is formed with a pair of fourth bolt holes 106f extending in the directionof the rotation axis Z1 of the first steering shaft 2. The pair of fourth bolt holes 106f are formed in the end face 106e of the adjustment plug 106 so as to be symmetrical about the rotation axis Z1 of the first steering shaft 12. A fourth bolt 110 as a fixing member is screwed into each of the fourth bolt holes 106f.

[0111] The fourth blocking member 103 is formed in a disk shape. The fourth blocking member 103 has a disk portion 103a, and an annular standing portion 103b extending from the outer periphery of the disk portion 103a toward the first end 12a. The inner periphery of the standing portion 103b is formed with an annular protruding inner wall portion 103c protruding from the standing portion 103b toward the first end 12a. The standing portion 103b has a pair of fifth bolt insertion holes 103d through each of which the fourth bolt 110 is inserted. The pair of fifth bolt insertion holes 103d are formed at positions facing the pair of fourth bolt holes 106f of the adjustment plug 106 in the direction of the rotation axis Z1 of the first steering shaft 12. The fourth blocking member 103 is fixed to the adjustment plug 106 by screwing the fourth bolts 110 into the fourth bolt holes 106f through the fifth bolt insertion holes 103d.

[0112] [Advantageous Effects of Fifth Embodiment] In the fifth embodiment, the first steering mechanism 7R. includes the second worm gear mechanism 101 that is a double lead worm gear. With this configuration, backlash can be adjusted by moving the double lead worm 104 in the direction of the rotation axis Z1 of the first steering shaft 12, and thereby causing a variation in tooth thickness of the portion 105 of the double lead worm 104 that meshes with the speed reduction mechanism gear forming part 97 of thespeed reduction mechanism worm wheel 96. This makes it possible to suppress rattle noise from occurring at the meshing portion 105. With large backlash, an additional force is applied to the meshing portion 105 from the steering wheel 9 via the first steering shaft 12 while the vehicle is traveling on a rough road. This may cause a rattle noise at the meshing portion 105. This rattle noise can be suppressed in the steering device according to the fifth embodiment as described above. In this way, according to the fifth embodiment, with the provision of the second worm gear mechanism 101 that is a double lead worm gear, it is possible to adjust backlash suitably, and thereby suppress rattle noise.

[0113] [Sixth Embodiment] FIG. 8 shows a longitudinal section of a second steering mechanism 7L according to a sixth embodiment.

[0114] The second steering mechanism 7L according to the sixth embodiment is configured based on the first embodiment by adding a second electric motor 111 and a second speed reducer 112 to the second steering mechanism 7L according to the first embodiment.

[0115] The second electric motor 111 is similar in size and configuration to the first electric motor 11. The second electric motor 111 is drive-controlled by a second control device not shown that is mechanically and electrically integrated with the second electric motor 111. The second electric motor 111 is drive-controlled by the second control device based on a sensed value of the steering torque acquired by the torque sensor 10 arranged in the first steering mechanism 7R, and thereby applies a rotational force to the second steering shaft 47 via the second speedreducer 112. The second electric motor 111 is located on the first end 47a side of the second sector gear 57 in the axial direction of the second steering shaft 47, i.e., in the direction of the rotation axis Z2. The second electric motor 111 has a motor shaft not shown connected to a second worm shaft 113. The second worm shaft 113 is arranged to overlap with the first medium diameter shaft section 47c of the second steering shaft 47 in the radial direction of the second steering shaft 47.

[0116] The second speed reducer 112 is composed of the first worm wheel 60 and a second worm shaft 113. The first worm wheel 60 has the first gear forming part 61, which meshes with a worm formed in the outer periphery of the second worm shaft 113. Through this meshing, the second speed reducer 112 slows down rotation from the second electric motor 111.

[0117] The second electric motor 111 is housed in a second motor housing Illa that has a bottomed cylindrical tubular shape and is similar in size to the first motor housing 11a. As shown in FIG. 8, the second motor housing Illa extends outwardly beyond the third housing 50 both in the direction of the rotation axis Z2 of the second steering shaft 47 and in the radial direction of the second steering shaft 47.

[0118] [Advantageous Effects of Sixth Embodiment] As described above, in the sixth embodiment, the first electric motor 11, the first speed reducer 48, the second electric motor 111, and the second speed reducer 112 are arranged on the first end 47a side in the axial direction of the second steering shaft 47. As described above, the side where the steering wheel 9 is not placed, i.e., the second steering shaft 47 side, has a relatively large remaining space wherecomponents associated with the steering device can be mounted. In the sixth embodiment, the arrangement of the first electric motor 11 and the second electric motor 111, which are relatively large components, in the relatively large space accommodating the second steering shaft 47, serves to improve the mountability of components associated with the steering device.

[0119] Furthermore, the side of the vehicle where the steering wheel 9 is arranged is subject to a requirement that a steering mechanism is arranged almost vertically, especially in a cab-over type vehicle in which a driver's seat is located above an engine. However, on the side of the vehicle where the steering wheel 9 is not provided (i.e. the passenger seat side), a steering mechanism may be arranged in an arbitrary direction, for example, in a direction inclined with respect to the vertical direction, as long as a position of a first end Pl (see FIG. 1) of the first pitman arm 6R. is determined. Therefore, on the second steering shaft 47 side, the mountability of components associated with the steering device can be further improved by adjusting the orientation of the second steering mechanism 7L, namely, by adjusting the posture of the second steering mechanism 7L when mounted.

[0120] [Seventh Embodiment] FIG. 9 shows a longitudinal section of a second steering mechanism 7L according to a seventh embodiment.

[0121] The second steering mechanism 7L according to the seventh embodiment is configured based on the first embodiment by removing the second blocking member 76 from the second steering mechanism 7L according to the first embodiment, and adding a first fixing ring member 114, athird electric motor 115, a third speed reducer 116, and a fifth blocking member 117. Furthermore, the second steering mechanism 7L according to this embodiment includes a third smaller diameter shaft section 47h instead of the first smaller diameter shaft section 47f of the second steering shaft 47 according to the first embodiment, wherein the third smaller diameter shaft section 47h has an axial dimension longer than that of the first smaller diameter shaft section 47f. Around the third smaller diameter shaft section 47h, the second four-point contact ball bearing 55 and a second core 121 of a second worm wheel 119 of the third speed reducer 116 are arranged. The second core 121 is located on the second end 47b side of the second four-point contact ball bearing 55.

[0122] The first fixing ring member 114 is an annular member that fixes the outer race 71 of the second four-point contact ball bearing 55 to the fourth housing 52. The outer periphery of the first fixing ring member 114 is formed with a ring member side external thread 114a. The ring member side external thread 114a is screwed onto a second housing side internal thread 52e formed in the inner periphery of the fourth housing 52. This screwing presses the corner portion 71a on the first end 47a side of the outer race 71 against the step formed in the inner peripheral portion of the fourth housing 52, thereby fixing the outer race 71 to the fourth housing 52.

[0123] The third electric motor 115 is similar in size and configuration to the first electric motor 11. The third electric motor 115 is drive-controlled by a third control device not shown. The third electric motor 115 is drive-controlled by the third control device based on a sensed value of thesteering torque acquired by the torque sensor 10 arranged in the first steering mechanism 7R, and thereby applies a rotational force to the second steering shaft 47 via the third speed reducer 116. The third electric motor 115 has a motor shaft not shown connected to a third worm shaft 118. The third worm shaft 118 is arranged to overlap with the second smaller diameter shaft section 47g of the second steering shaft 47 in the radial direction of the second steering shaft 47.

[0124] The third electric motor 115 is housed in a third motor housing 115a having a bottomed cylindrical shape. As shown in FIG. 9, the third motor housing 115a extends outwardly beyond the third blocking member 117 both in the direction of the rotation axis Z2 of the second steering shaft 47 and in the radial direction of the second steering shaft 47.

[0125] The third speed reducer 116 is composed of the third worm shaft 118, and the second worm wheel 119 meshing with the third worm shaft 118. The second worm wheel 119 is formed by insert molding to form a second gear forming part 120 around a second core 121, wherein the second core 121 is made of metal to have a cylindrical tubular shape, and wherein the second gear forming part 120 is made of synthetic resin. The second core 121 has a first cylindrical base portion 121a, a first axial projecting portion 121c, a first radial outward extension portion 121d, and a first support portion 121e. The first cylindrical base portion 121a has a cylindrical tubular shape. The first axial projecting portion 121c has a cylindrical tubular shape that projects from the outer periphery of a face 121b on the second end part 47b side of the first cylindrical base portion 121a toward the second end part 47b side. The first radialoutward extension portion 121d has an annular shape that extends radially outwardly from the outer periphery of the first axial projecting portion 121c. The first support portion 121e has a cylindrical tubular shape that projects from the outer periphery of the first protruding portion 121d toward the third blocking member 117. The first cylindrical base portion 121a has a face 121f on the first end 47a side, wherein the face 121f is formed with a second recess 121g that has an annular shape and is located at a position adjacent to the outer periphery of the first cylindrical base portion 121a. The face 121f of the first cylindrical base portion 121a abuts on the axial end face 70c on the second end 47b side of the inner race 70 of the second four-point contact ball bearing 55.

[0126] Screwing between the second fixed member side internal thread 56a of the second fixing member 56 and the second steering shaft side external thread 75 of the second steering shaft 47g of the second smaller diameter shaft section 47g of the second steering shaft 47 presses the face 121b of the first cylindrical base portion 121a, and presses the corner portion 70a on the first end 47a side of the inner race 70 against the step 73 of the second steering shaft 47 via the first cylindrical base portion 121a, thereby fixing the inner race 70 and the second core 121 to the second steering shaft 47.

[0127] The fifth blocking member 117 has a bottomed cylindrical tubular shape, blocks the opening of the fourth housing 52 on the second end 47b side, and houses a part of the third speed reducer 116, the second fixing member 56, etc. The fifth blocking member 117 has an axial end portion on the first end 47a side, wherein the axial end portion has aportion 117a overlapping with the second sector gea r 57 as viewed in the d irection of the rotation axis Z2 of the second steering shaft 47, and wherein the portion 117a is formed with a blocking member fla nge 117b projecting rad ia lly outward ly from the portion 117a . The blocking member flange 117b has a centra l portion in the rad ial d irection, wherein the central portion is formed with a sixth bolt insertion hole 117c extend ing therethroug h in the d irection of the rotation axis Z2 of the second steering shaft 47, wherein a fifth bolt 122 is inserted throug h the insertion hole 117c.

[0128] Fu rthermore, the outer periphery of the fourth housing 52 is formed with a screw hole forming portion 52f extend ing rad ia lly outward ly from the outer periphery. This screw hole forming portion 52f is adjacent to the blocking member fla nge 117b. The screw hole formi ng portion 52f is formed with a fifth bolt hole 52g into which the fifth bolt 122 is screwed . By inserting the fifth bolt 122 throug h the sixth bolt insertion hole 117c and screwing the fifth bolt 122 into the fifth bolt hole 52g of the screw hole forming portion 52f, the fifth blocking member 117 is fixed to the fou rth housing 52.

[0129] [Adva ntageous Effects of Seventh Embod iment] As described above, in the seventh embod iment, the first electric motor 11 and the first speed red ucer 48 are arranged on the first end 47a side in the axia l d irection of the second steering shaft 47, a nd the third electric motor 115 a nd the third speed red ucer 116 are arranged on the second end 47b side in the axial d irection of the second steering shaft 47. Also in the seventh embod iment, the second steering shaft 47 side has a relatively large remaining space where components associated with the steering device can be mou nted . In theseventh embodiment, the arrangement of the first electric motor 11 and the third electric motor 115, which are relatively large components, in the relatively large space accommodating the second steering shaft 47, serves to improve the mountability of components associated with the steering device.

[0130] Furthermore, as in the sixth embodiment, on the side of the vehicle where the steering wheel 9 is not provided, a steering mechanism may be arranged in an arbitrary direction. Therefore, on the second steering shaft 47 side, the mountability of components associated with the steering device can be further improved by adjusting the orientation of the second steering mechanism 7L, namely, by adjusting the posture of the second steering mechanism 7L when mounted.

[0131] [Eighth Embodiment] FIG. 10 shows a longitudinal section of a second steering mechanism 7L according to an eighth embodiment.

[0132] The second steering mechanism 7L according to the eighth embodiment is configured based on the sixth embodiment by adding a part of the configuration of the second steering mechanism 7L according to the seventh embodiment, namely, the third electric motor 115 and the third speed reducer 116, to the second steering mechanism 7L according to the sixth embodiment, and further adding a fourth electric motor 123 and a fourth speed reducer 124. The addition of the fourth electric motor 123 is accompanied by removal of the second blocking member 76 employed in the sixth embodiment, and addition of a sixth blocking member 125.

[0133] The fourth electric motor 123 is similar in size and configuration to the first electric motor 11, the second electric motor 111, and the third electric motor 115. The fourth electric motor 123 is drive-controlled by a fourth control device not shown. The fourth electric motor 123 is drive-controlled by the fourth control device based on a sensed value of the steering torque acquired by the torque sensor 10 arranged in the first steering mechanism 7R, and thereby applies a rotational force to the second steering shaft 47 via the fourth speed reducer 124.

[0134] The fourth speed reducer 124 is composed of the second worm wheel 119 and a fourth worm shaft 126. The second worm wheel 119 has the second gear forming part 120, and the second gear forming part 120 meshes with a worm formed in the outer periphery of the fourth worm shaft 126. Through this meshing, the fourth speed reducer 124 slows down rotation from the fourth electric motor 123.

[0135] The sixth blocking member 125 has a bottomed cylindrical tubular shape, blocks the opening of the fourth housing 52 on the second end 47b side, and houses the third speed reducer 116, a part of the fourth speed reducer 124, the second fixed member 56, etc. The sixth blocking member 125 has an open end portion 125a, which is fixed to the outer periphery of the fourth housing 52.

[0136] [Advantageous Effects of Eighth Embodiment] As described above, in the eighth embodiment, the first electric motor 11, the first speed reducer 48, the second electric motor 111, and the second speed reducer 112 are arranged on the first end 47a side in the axial direction of the second steering shaft 47, and the third electric motor 115, the third speed reducer 116, the fourth electric motor 123, and thefourth speed reducer 124 are arranged on the second end 47b side in the axial direction of the second steering shaft 47. Also in the eighth embodiment, the second steering shaft 47 side has a relatively large remaining space where components associated with the steering device can be mounted. In the eighth embodiment, the arrangement of the first electric motor 11, the second electric motor 111, the third electric motor 115, and the fourth electric motor 123, which are relatively large components, in the relatively large space accommodating the second steering shaft 47, serves to improve the mountability of components associated with the steering device.

[0137] Furthermore, as in the sixth and seventh embodiments, on the side of the vehicle where the steering wheel 9 is not provided, a steering mechanism may be arranged in an arbitrary direction. Therefore, on the second steering shaft 47 side, the mountability of components associated with the steering device can be further improved by adjusting the orientation of the second steering mechanism 7L, namely, by adjusting the posture of the second steering mechanism 7L when mounted.

[0138] [Ninth Embodiment] FIG. 11 shows a longitudinal section of a second steering mechanism 7L according to a ninth embodiment. In FIG. 11, illustration of internal structures of a body section 128 and a sensing section 129 of a rotation angle sensor 127 is omitted for ease of understanding.

[0139] The second steering mechanism 7L according to the ninth embodiment is configured based on the first embodiment by adding a rotation angle sensor 127 to the second steering mechanism 7L according to the firstembodiment. With the addition of the rotation angle sensor 127, the third housing 50 is partially modified in shape to have a sensor housing section 50c. Furthermore, the second steering shaft 47 according to the ninth embodiment includes a fourth smaller diameter shaft section 47i formed integrally with the first medium diameter shaft section 47c.

[0140] The rotation angle sensor 127 senses a rotation angle of the second steering shaft 47 when the torque sensor 10 of the first steering mechanism 7R. fails. In this example, the rotation angle sensor 127 is a known magnetic rotation angle sensor including a main gear and a sensing gear, wherein the main gear rotates integrally with the second steering shaft 47 and transmits rotation to the sensing gear, and wherein the rotation angle of a magnet carried by the sensing gear is sensed by a magnetic sensor. Alternatively, the rotation angle sensor 127 may be configured to sense the rotation angle of the second steering shaft 47 by other means, for example, by counting slits using an encoder, wherein the slits are formed in a part that rotates integrally with the second steering shaft 47. Specifically, the rotation angle sensor 127 has a body section 128 having a main gear that rotates integrally with the second steering shaft 47, and a sensing section 129 that senses the rotation of the body section 128. The rotation angle of the second steering shaft 47 sensed by the rotation angle sensor 127 is inputted to the first control device 59 (see FIG. 1) associated with the first electric motor 11. When the torque sensor 10 of the first steering mechanism 7R. fails, the first control device 59 applies a steering assist force to the second steering shaft 47 by drive-controlling the first electric motor 11 based on the rotation angle of the second steering shaft 47. When thetorque sensor 10 of the first steering mechanism 7R. fails, the rotational force from the first steering mechanism 7R. is transmitted to the second steering mechanism 7L side via the link mechanism (see FIG. 1) between the first pitman arm 6R. and the second pitman arm 6L.

[0141] The body section 128 (the housing of the body) of the rotation angle sensor 127 is formed of a synthetic resin material and a metal material to have an annular shape, and is fixed to the outer periphery of the second steering shaft 47. The body section 128 has an axial end face on the second end 47b side, wherein the axial end face is formed with a second annular protruding portion 128a at a position adjacent to the inner periphery of the body section 128. The second annular protruding portion 128a protrudes toward the second end 47b in the direction of the rotation axis Z2 of the second steering shaft 47. The axial end face on the first end 47a side of the body section 128 is formed with a second reduced diameter portion 128b having an annular shape at a position adjacent to the inner periphery of the body section 128. The second reduced diameter portion 128b has a stepped reduced diameter shape and protrudes toward the first end 47a. The second reduced diameter portion 128b is press-fitted and fixed to the outer periphery of the fourth smaller diameter shaft section 47i of the output shaft 20, and rotates together with the output shaft 20.

[0142] The sensing section 129 (the housing of the sensing section) of the rotation angle sensor 127 is made of a synthetic resin material, is formed in an annular shape, and is arranged around the body section 128. The axial end face of the sensing section 129 on the first end 47a side is formed with two second rotation restricting parts 129a at positionsadjacent to the outer periphery of the sensing section 129. Each second rotation restricting parts 129a has a cylindrical shape and serves to prevent the sensing section 129 from being rotated by rotation of the body section 128. As shown in FIG. 11, the two second rotation restriction sections 129a are arranged so as to be symmetrical radially of the second steering shaft 47 with respect to the output shaft 20. Each second rotation restriction section 129a has a second extension portion 129b and a second rotation restriction cylindrical portion 129c. The second extension portion 129b has a cylindrical shape that protrudes with a certain diameter toward the first end 47a in the direction of the rotation axis Z2 of the second steering shaft 47, and then contracts in a conical shape. The second rotation restriction cylindrical portion 129c has a cylindrical shape that protrudes from the tip of the second extension portion 129b toward the first end 47a in the direction of the rotation axis Z2 of the second steering shaft 47. Each second rotation restriction cylindrical portion 129c engages with a second circular recess 50d of the third housing 50 in the radial direction of the second steering shaft 47. With this engagement, the sensing section 129 is held by the third housing 50. The bottom of the second circular recess 50d has a second conical portion 50e. The second conical portion 50e is tapered conically have a diameter decreasing toward the outside of the third housing 50.

[0143] [Advantageous Effects of Ninth Embodiment] As described above, in the ninth embodiment, the second steering mechanism 7L includes the rotation angle sensor 127 that senses the rotation angle of the second steering shaft 47 when the torque sensor 10 of the first steering mechanism 7R.fails. Therefore, even when the torque sensor 10 of the first steering mechanism 7R. fails, the steering assist force can be continued to be applied to the second steering shaft 47 based on a sensed value of the rotation angle acquired by the rotation angle sensor 127. This makes the steering device redundant and failsafe.

[0144] [Tenth Embodiment] FIG. 12 shows a longitudinal section of a second steering mechanism 7L according to a tenth embodiment.

[0145] The second steering mechanism 7L according to the tenth embodiment is configured based on the first embodiment by replacing the second deep groove ball bearing 53 of the second steering mechanism 7L according to the first embodiment with a third four-point contact ball bearing 130. This replacement is accompanied by removal of the first connection member 16 employed in the first embodiment, and addition of a second fixing ring 131 and a third fixing member 132. Furthermore, in this embodiment, the first medium diameter shaft section 47c and the larger diameter shaft section 47d of the second steering shaft 47 employed in the first embodiment are removed, and a fifth smaller diameter shaft section 47j formed integrally with the second medium diameter shaft section 47e, and a sixth smaller diameter shaft section 47k formed integrally with the fifth smaller diameter shaft section 47j are added. Furthermore, in this embodiment, the first core 62 of the first speed reducer 48 employed in the first embodiment is replaced with a third core 133 similar in shape to the second core 121 of the third speed reducer 116.

[0146] The third four-point contact ball bearing 130 is similar in configuration to the second four-point contact ballbearing 55, and supports the fifth smaller diameter shaft section 47j of the second steering shaft 47 rotatably. The third four-point contact ball bearing 130 is arranged on the outer periphery of the fifth smaller diameter shaft section 47j at a position adjacent to the second medium diameter shaft section 47e in the direction of the rotation axis Z2 of the second steering shaft 47. The third four-point contact ball bearing 130 has an inner race 134 having a corner portion 134a on the second end 47b side which abuts on a step 135 formed between the second medium diameter shaft section 47e and the fifth smaller diameter shaft section 47j. The third four-point contact ball bearing 130 has an outer race 136 having a corner portion 136a on the second end 47b side which abuts on a step 137 formed in the inner periphery of the fourth housing 52.

[0147] The second fixing ring 131 is an annular member that fixes the third four-point contact ball bearing 130 to the fourth housing 52. The outer periphery of the second fixing ring 131 is formed with a second ring side external thread 131a. This second ring side external thread 131a is screwed onto a fourth housing side internal thread 17j formed in the inner periphery of the axial end portion on the first end 47a side of the fourth housing 52. This screwing presses an end face 136b on the first end 47a side of the outer race 136, and presses the corner portion 136a of the outer race 136 against the step 137 of the fourth housing 52, thereby fixing the outer race 136 to the fourth housing 52.

[0148] The third core 133 has a third cylindrical base portion 133a, a third axial projecting portion 133c, a second radial outward extension portion 133d, and a second support portion 133e. The third cylindrical base portion 133a has acylindrical tubular shape. The third axial projecting portion 133c has a cylindrical tubular shape that projects from the outer periphery of a face 133b on the first end 47a side of the third cylindrical base portion 133a toward the first end 47a side. The second radial outward extension portion 133d has an annular shape that extends radially outwardly from the outer periphery of the third axial projecting portion 133c. The second support portion 133e has a cylindrical tubular shape that projects from the outer periphery of the second radial outward extension portion 133d toward the third housing 50. The third cylindrical base portion 133a has a face 133f on the second end 47b side, wherein the face 133f is formed with a second recess 133g that has an annular shape and is located at a position adjacent to the outer periphery of the third cylindrical base portion 133a. The face 133f of the third cylindrical base portion 133a abuts on an axial end face 134b on the first end 47a side of the inner race 134 of the third four-point contact ball bearing 130.

[0149] The third fixing member 132 fixes the third four- point contact ball bearing 130 and the third core 133 of the first speed reducer 48 to the second steering shaft 47. The third fixing member 132 is a nut member having an inner periphery where a third fixing member side internal thread 132a is formed. This third fixing member side internal thread 132a is screwed onto a third steering shaft side external thread 138 formed in the outer periphery of the sixth smaller diameter shaft section 47k of the second steering shaft 47. This screwing presses the corner portion 134b of the inner race 134, and then presses the corner portion 134a of the inner race 134 against the step 135 of the second steering shaft 47, thereby fixing the third four-point contact ballbearing 130 and the third core 133 of the first speed reducer 48 to the second steering shaft 47.

[0150] [Advantageous Effects of Tenth Embodiment] As described above, in the tenth embodiment, with replacement of the second deep groove ball bearing 53 of the second steering mechanism 7L according to the first embodiment with the third four-point contact ball bearing 130, the second steering mechanism 7L includes the second four-point contact ball bearing 55 arranged on the second end 47b side of the second steering shaft 47, and the third four-point contact ball bearing 130 arranged on the first end 47a side of the second steering shaft 47. Namely, the second steering mechanism 7L has two four-point contact ball bearings. This allows the second steering mechanism 7L according to the tenth embodiment to receive a thrust force twice as large as that of the first embodiment having the second four-point contact ball bearing 55 as a single four-point contact ball bearing.

Claims

CLAIMSClaim 1. A steering device comprising: a first steering mechanism coupled to a steering wheel; and a second steering mechanism formed separately from the first steering mechanism, and arranged separately from the steering wheel; wherein the first steering mechanism includes: a first steering shaft structured to receive input of rotation from the steering wheel; a torque sensor provided to the first steering shaft, and structured to sense a steering torque applied to the first steering shaft; a first speed reduction mechanism provided to the first steering shaft, and structured to slow down rotation from the first steering shaft; and a first transmission mechanism structured to steer a first steerable road wheel in accordance with an output from the first speed reduction mechanism; wherein the second steering mechanism includes: a second steering shaft; a first electric motor structured to apply a rotational force to the second steering shaft; a first speed reducer provided to the second steering shaft, and structured to slow down the rotational force from the first electric motor; a control device configured to control the first electric motor based on a sensed value of the steering torque acquired by the torque sensor;a second speed reduction mechanism provided to the second steering shaft, and structured to slow down rotation from the second steering shaft; and a second transmission mechanism structured to steer a second steerable road wheel in accordance with an output from the second speed reduction mechanism; and wherein the first transmission mechanism and the second transmission mechanism are linked to each other via a link mechanism for cooperation between the first transmission mechanism and the second transmission mechanism.Claim 2. The steering device according to claim 1, further comprising : a deep groove ball bearing located at a portion of the first steering shaft adjacent to the torque sensor, and structured to support the first steering shaft rotatably; and a first four-point contact ball bearing located at a portion of the first steering shaft opposite to the torque sensor with respect to the first speed reduction mechanism, and structured to support the first steering shaft rotatably.Claim 3. The steering device according to claim 1, further comprising : a first angular ball bearing located at a portion of the first steering shaft adjacent to the torque sensor, and structured to support the first steering shaft rotatably; and a second angular ball bearing located at a portion of the first steering shaft opposite to the torque sensor with respect to the first speed reduction mechanism, and structured to support the first steering shaft rotatably.Claim 4. The steering device according to claim 1, wherein the first speed reduction mechanism is a worm gear mechanism including: a worm provided to the first steering shaft; and a worm wheel meshing with the worm.Claim 5. The steering device according to claim 4, wherein the worm gear mechanism is a double lead worm gear mechanism.Claim 6. The steering device according to claim 1, wherein: the first electric motor and the first speed reducer are located at a first axial end side of the second steering shaft; and the second steering mechanism further includes: a second electric motor located at the first axial end side of the second steering shaft, and structured to apply a rotational force to the second steering shaft; and a second speed reducer structured to slow down the rotational force from the second electric motor.Claim 7. The steering device according to claim 1, wherein: the first electric motor and the first speed reducer are located at a first axial end side of the second steering shaft; and the second steering mechanism further includes: a third electric motor located at a second axial end side of the second steering shaft, and structured to apply a rotational force to the second steering shaft; anda third speed reducer structured to slow down the rotational force from the third electric motor.Claim 8. The steering device according to claim 1, wherein: the first electric motor and the first speed reducer are located at a first axial end side of the second steering shaft; and the second steering mechanism further includes: a second electric motor located at the first axial end side of the second steering shaft, and structured to apply a rotational force to the second steering shaft; a second speed reducer structured to slow down the rotational force from the second electric motor; a third electric motor located at a second axial end side of the second steering shaft, and structured to apply a rotational force to the second steering shaft; a third speed reducer structured to slow down the rotational force from the third electric motor; a fourth electric motor located at the second axial end side of the second steering shaft, and structured to apply a rotational force to the second steering shaft; and a fourth speed reducer structured to slow down the rotational force from the fourth electric motor.Claim 9. The steering device according to claim 1, wherein the second steering mechanism further includes a rotation angle sensor provided to the second steering shaft and structured to sense a rotation angle of the second steering shaft.Claim 10. The steering device according to claim 1, further comprising : a second four-point contact ball bearing located at a second axial end side of the second steering shaft, and structured to support the second steering shaft rotatably; and a third four-point contact ball bearing located at a first axial end side of the second steering shaft, and structured to support the second steering shaft rotatably.

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