Torque sensor

Abstract: A torque sensor according to this invention is so con­ structed that a plurality of magnetic cylinders mounted re­ spectively to two shafts coupled via a torsion bar are able to be electromagnetically coupled variably to each other in accordance with the relative rotation of the two shafts, and the electromagnetic coupling state of a plurality of cyl­ inders mounted to these two shafts is detected by the elec­ tromagnetic coupling detection coils wound around the cyl­ indrical members. Since the elastic members are provided on a plurality of cylinders mounted to one of the shafts and/or at least at one side in the axial direction of the two cyl­ indrical members with the cylinders and/or cylindrical members being urged in the axial direction, so that the elastic members absorb the rattling of the cylinders and/or cylindrical members in the axial direction.

Description: The present invention generally relates to a torque sensor adapted to detect torque acting to a shaft, and more particularly, to a torque sensor suitable for application to an electric motor-driven power steering arrangement of an automobile. A power steering arrangement of an electric motor-driven system has been developed in recent years so as to help to drive a steering wheel of an automobile. The power steering arrangement referred to above is of such construction that an electric motor mounted to a steering system is rotated in accordance with the detected torque applied to the steering wheel. Meanwhile, for detecting the torque applied to the steering wheel, torque sensors, for example, shown in Figs. 1 and 2, have been proposed by the inventors of the present invention or others (Japanese Utility Model Application No. 63-54841) (54841/1988). Fig. 1 is a half cross section showing the construction of the prior art torque sensor wherein an upper shaft 11A provided with the steering wheel is coaxially coupled to a lower shaft 11C provided with the steering system, via a torsion bar 11B. The upper shaft 11A is rotatably supported by a cylindrical casing 25 secured to an automobile body (not shown) via a bearing 26. A first sleeve 15b made of a non-magnetic material is securely fitted in the outer periphery of the upper end (right side in the drawing) of the lower shaft 11C, with a first cylinder 18 made of a magnetic material being securely fixed to the outer periphery thereof. One end face at the side of the lower shaft 11C of the first cylinder 18 is a flat surface perpendicular to the center of the lower shaft 11C, while the other end face at the side of the upper shaft 11A of the first cylinder 18 has many rectangular toothed parts 18a, 18a,··· spaced with an equal pitch in a peripheral direction of the cylinder. Each front end of these toothed parts 18a, 18a,··· is perpendicular to the center of the lower shaft 11C. Similarly, a second sleeve 15a made of a non-magnetic material is securely fitted in the outer periphery of the lower end (left side in the drawing) of the upper shaft 11A, and second and third cylinders 17 and 14 made of a magnetic material is fixed in the outer periphery thereof. Further, a gap forming member 20 which is ring-shaped of narrow width and made of non-magnetic material such as brass, alminum, austenite stainless steel or the like is intervened between the second and third cylinders 17 and 14, and exteriorly fitted in the outer periphery of the second sleeve 15a. The third cylinder 14 has the same configuration as that of the first cylinder 18, and is mounted to the upside down direction of the first cylinder 18. The opposite end faces of the second cylinder 17 have toothed parts 17a, 17a··· and 17b, 17b··· formed in the same configuration and with the same pitch as the aforementioned toothed parts 18a, 18a,···. Each of the toothed parts 17a, 17b is met on the same line parallel to the center of the cylinder 17. Moreover, the cylinders 18 and 17 are so positioned in the rotational direction thereof that the toothed parts 18a and 17b confront each other at the position half the tooth width when no torque acts on the torsion bar 11B. The toothed parts 17b, 17b··· of the second cylinder 17 are spaced at an appropriate distance from the toothed parts 18a, 18a··· of the first cylinder 18. The cylinders 17 and 14 are so positioned that the toothed parts 17a and 14a confront each other at the position half the tooth width thereof, in the similar manner as the toothed parts 17b and 18a, when no torque acts on the torsion bar 11B. There is a stopper 50 in the form of the narrow strip projecting parallel to the center of the upper shaft 11A in the outer peripheral surface at the lower end of the shaft 11A. On the other hand, at the upper end of the lower shaft 11C, a stopper guide groove 51 is notched with an appropriate length in the peripheral direction of the inner peripheral surface of an opening formed concentrically with the center of the lower shaft 11C. The above stopper 50 is engaged into the stopper guide groove 51. The arc length of the stopper guide groove 51 is set so that the upper and lower shafts 11A and 11C are able to rotate relatively, for example, by approximately half the tooth width of the toothed part 17b. Inside the casing 25 are securely fitted cylindrical members 19A and 19B made of magnetic material which respectively form peripheral grooves. The cylindrical member 19A is so provided as to face the confronting part of the second and third cylinders 17 and 14, and the cylindrical member 19B is so provided as to face to the confronting part of the first and second cylinders 18 and 17. A first electromagnetic coupling detection coil 32 and a second electromagnetic coupling detection coil 31 are wound around in the peripheral grooves of the cylindrical members 19B and 19A, respectively, so that the cylinders 18 and 17 are electromagnetically coupled to each other by the first electromagnetic coupling detection coil 32, while the cylinders 17 and 14 are electromagnetically coupled to each other by the second electromagnetic coupling detection coil 31. In the meantime, in the prior art torque sensor mentioned above, since the first, second and third cylinders 18, 17 and 14 as well as the cylindrical members 19A and 19B are fixed respectively as described hereinabove, the positioning accuracy of these cylinders in the axial direction depends on the accuracy of the size of each component thereof. Therefore, if the sizing accuracy is poor, the cylinders 18, 17 and 14 are obliged to be burdened with an increase in the pressing-in load in the radial direction thereof, resulting in the increase of the stress. Moreover, in such a case as above, the cylindrical members 19A and 19B come to rattle in the axial direction, bringing about such a problem that an abnormal output may occur because of the increase in the stress subsequent to the temperature change or the vibrations caused by the rattling. Moreover, although the toothed parts 17a, 17b are provided at the opposite end faces of the second cylinder 17, it is considerably difficult to position the toothed parts at one end face relative to those at the other end face, without generating positional deviations therebetween. It is a problem to be solved from the manufacturing viewpoint. The first, second and third cylinders 18, 17 and 14 are fixed by being pressed into the lower and upper shafts 11C and 11A via the non-magnetic sleeves 15b and 15a. According to this method, however, positioning of the cylinders 18, 17 and 14 in the axial direction cannot be achieved. Further, in the prior art torque sensor having the above-described construction, the third cylinder 14 can be positioned in the axial direction by the gap forming member 20 interposed between the second and third cylinders 17 and 14. However, so as to bring the third and second cylinders 14 and 17 into the electromagnetically-coupled state equal to the state of the second and first cylinders 17 and 18, such a troublesome adjusting work is disadvantageously required that the third cylinder 14 is secured to the second sleeve 15a simultaneously when the cylinder 14 is pressed against the cylinder 17 via the gap forming member 20 while the cylinder 14 is being rotated for adjustment. It is the object of the invention to provide a torque sensor wherein each cylinder and/or cylindrical member can be fixed without being influenced by the manufacturing accuracy thereof. This problem is solved, according to the invention, with the features of claim 1. According to the invention, each cylinder and/or cylindrical member is urged in the axial direction thereof by an elastic member which absorbs the rattlings of the cylinder and/or cylindrical member in the axial direction, said torque sensor being capable of generating a stable sensor output at all times without influences of the thermal expansion of each component due to the temperature change. According to a preferred embodiment of the invention, the torque sensor comprises four cylinders each of which has toothed parts formed at one end face thereof, so that the four cylinders can be easily manufactured in the same configuration with the other end face thereof being flat. According to the torque sensor of this invention, two independent magnetic circuits are constituted respectively by the two cylinders adjacent to each other among four cylinders. The magnetic circuits are stable in efficiency since the circuits are independent of each other without giving any magnetic influences. Moreover, a sleeve provided with a restricting part for restricting the axial movement of the cylinders is intervened between the central second and third cylinders among four cylinders and one shaft, which is caulked and secured to the one shaft, and accordingly the cylinders can be easily positioned in the axial direction with good securing strength. The torque sensor comprises a washer, having engaging portions which are respectively to be engaged into the gaps between the toothed parts of the cylinders, and being provided between the second cylinder fixed to one of the two shafts coupled by a torsion bar, and the third cylinder adjacent to the second cylinder, so that the second or third cylinder can be positioned in the rotational direction thereof with much ease. According to the invention, the torque sensor is comprised of a plurality of cylinders made of magnetic material and mounted to two shafts coupled via a torsion bar, and two cylindrical members made of magnetic material and provided between the outer peripheral side of the cylinders and a cylindrical casing, with electromagnetic coupling detection coils for electromagnetically coupling the cylinders being wound in the inner peripheries of the cylindrical members. The torque sensor includes an elastic member provided at least at one side in the axial direction of the plurality Of cylinders mounted to one of the shafts and/or two cylindrical members so as to fix the cylinders and/or cylindrical members in the axial direction. As mentioned above, since the cylinders and/or two cylindrical members are fixed in the urged state in the axial direction by the elastic members, these cylinders and/or cylindrical members can be prevented from rattling in the axial direction, and the thermal expansion thereof due to the temperature change is also absorbed by the elastic members. According to a preferred embodiment of the invention, the torque sensor is provided with four magnetic cylinders each having toothed parts formed at one end face at the side of one of the shafts. The second, third and fourth cylinders are mounted to one of the two shafts coupled through a torsion bar so that the toothed parts of the first and second cylinders, and those of the third and fourth cylinders respectively confront each other, while the first cylinder is mounted to the other of the two shafts. The torque sensor is further provided with two electromagnetic coupling detection coils for electromagnetically coupling the first and second cylinders to each other, and the third and fourth cylinders to each other. Moreover, a non-magnetic sleeve with a restricting part is interposed between the inner peripheral surface of the second and third cylinders and, the outer peripheral surface of the one shaft, thereby to regulate the axial movement of the second and third cylinders. The sleeve is secured to the outer periphery of the one shaft by caulking. In the above-described construction of the torque sensor, the fourth cylinder is fixedly inserted in the one shaft with the toothed parts thereof being directed towards the other shaft, and then the third cylinder is inserted in the one shaft with the toothed parts thereof being opposed to the toothed parts of the fourth cylinder. Further, the second cylinder is inserted into the one shaft with the toothed parts thereof being directed to the other shaft. To the other shaft, the first cylinder is secured in a manner that the toothed parts thereof are directed to the one shaft, confronting to the toothed parts of the second cylinder. The two electromagnetic coupling detection coils are so placed as to surround the first and second cylinders, and the third and fourth cylinders, respectively. Thus, the first and second cylinders constitute a magnetic circuit, and the third and fourth cylinders constitute another magnetic circuit. The torque sensor is comprised of a third cylinder provided in one of the two shafts coupled through a torsion bar, a first cylinder mounted to the other shaft, and one or two second cylinders interposed between the first and third cylinders and mounted to the one shaft. Toothed parts are formed at the axial end faces at the confronting side of the first and second cylinders, and also at the axial end faces at the confronting side of the third and second cylinders. The torque sensor includes electromagnetic coupling detection coils, one electromagnetically coupling the first and second cylinders and the other coupling the third and second cylinders. Moreover, the torque sensor has a washer between the second and third cylinders which has engaging portions to be inserted into the gaps of the toothed parts of the cylinders. Accordingly, in the torque sensor having the above-described construction, the second or the third cylinder can be positioned in the rotational direction by the washer between the second and third cylinders, with the engaging portions thereof being inserted into the gaps of the toothed parts of these cylinders respectively. The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. Fig. 1 is a half cross sectional view of a prior art torque sensor; Fig. 2 is a schematic perspective view of the prior art torque sensor; Fig. 3 is a longitudinal cross sectional view of a torque sensor according to one preferred embodiment of this invention; Fig. 4 is a longitudinal cross sectional view of the essential part of the torque sensor of Fig. 3; Fig. 5 is a perspective view of an elastic member made of a corrugated spring; Fig. 6 is a front view of the elastic member of Fig. 5; Fig. 7 is a view explanatory of the state where a second cylinder is fixed to an upper shaft by being urged by the elastic member in an axial direction; Fig. 8 is a perspective view of the elastic member of Fig. 7; Fig. 9 is a cross sectional view explanatory of the state where a first cylinder is securely caulked to a lower shaft; Fig. 10 is an enlarged cross sectional view of an upper part of the lower shaft of Fig. 9; Fig. 11 is an enlarged perspective view of toothed parts of the first cylinder, partially removed; Fig. 12 is a perspective view schematically showing the state where a washer is mounted to the torque sensor; Fig. 13 is a front view of a first washer employed in the torque sensor of Fig. 12; Fig. 14 is a cross section taken along the line XIV-XIV of Fig. 13; Fig. 15 is a perspective view of the first washer of Fig. 13; Fig. 16 is a perspective view of a second washer; Fig. 17 is an enlarged cross sectional view of a cylindrical member; Fig. 18 is an enlarged cross sectional view of a modified example of the cylindrical member; Fig. 19 is a graph showing the relation between the temperature change and the sensor output of the torque sensor of this invention employing cylindrical members placed opposite shown in Fig. 21; Fig. 20 is a graph showing the relation between the temperature change and the sensor output of the torque sensor of this invention employing the cylindrical member of Fig. 17; Fig. 21 is a longitudinal cross sectional view of the construction of a torque sensor according to another embodiment of this invention; Fig. 22 is a schematic perspective view of the essential part of a torque sensor according to a further embodiment of this invention; and Fig. 23 is a longitudinal cross sectional view of the torque sensor of Fig. 22. A torque sensor of this invention will be described hereinafter according to the preferred embodiments thereof with reference to the accompanying drawings. The whole construction of the torque sensor of this invention is shown in a longitudinal cross section of Fig. 3, with the essential part thereof being indicated in Fig. 4. In the torque sensor of this invention, an upper shaft 11A provided with a steering wheel (not shown) is coaxially coupled to a lower shaft 11C provided with a steering system (not shown), via a torsion bar 11B. The upper shaft 11A is rotatably supported by a cylindrical casing 25 fixed to a body of an automobile (not shown) via a bearing 26. The upper shaft 11A has an insertion hole 11a opening towards the axial direction in the center of the radial direction thereof. The torsion bar 11B is inserted through the insertion hole 11a. The outer periphery of the upper shaft 11A has a wider diameter part 11c in the upper part thereof (right side in the drawing), and a narrower diameter part 11d in the lower part thereof (left side in the drawing) through a stepped part 11b. A fourth cylinder 14 made of a magnetic material is fitted outside in the stepped part 11b of the upper shaft 11A in such a manner that the upper end thereof is pressed in contact with the stepped wall surface of the wider diameter part 11c. The fourth cylinder 14 is in contact with the stepped wall surface to such a degree that the rotation of the upper shaft 11A is able to be transmitted to the fourth cylinder 14. Further, the fourth cylinder 14 is fixed in the rotational direction thereof since the cylinder is engaged at the inner radial portion thereof with a pin 11h mounted to the upper shaft 11A. A sleeve 15 made of a non-magnetic material is exteriorly fitted in the narrower diameter part 11d in the lower part of the fourth cylinder 14 (left side in the drawing). In the outer periphery of the sleeve 15 are fitted third and second cylinders 16 and 17 made of a magnetic material having the same configuration as the fourth cylinder 14 except the size of the inner diameter. More specifically, the third and second cylinders 16 and 17 are fitted in contact with the sleeve 15 to such a degree that the rotation of the sleeve 15 subsequent to the rotation of the upper shaft 11A can be transmitted to the cylinders 16 and 17. A first and a second washers 30 and 40 of a ring shape with the narrow width are interposed between the fourth and third cylinders 14 and 16 and, between the third and second cylinders 16 and 17, as shown in Fig. 12. The washers 30 and 40 are made of non-magnetic material, each having tongue pieces to be engaged with the toothed parts of each cylinder. In consequence of this, it is prevented that the cylinders 14, 16 and 17 rotate relatively in the circumferential direction. The first washer 30 intervened between the fourth and third cylinders 14 and 16 has many tongue pieces 30a, 30a,··· to be respectively engaged into the gaps of toothed parts 14a and 16a (described later) of the cylinders 14 and 16, which is secured to the outer periphery of the sleeve 15. More specifically, as shown in Figs. 13 through 15, the first washer 30 is generally a ring-shape, and the outer periphery thereof is notched and divided into equal 12 parts in accordance with the number of gaps (8) between the toothed parts 14a or 16a of the fourth or third cylinders 14, 16. The notched parts are classified into three types. Namely, one is bent and projected to one side, constituting engaging portions 30a having approximately the same width as that of the gap between the toothed parts 14a and 14a, with a shorter length than the depth of the gap between the toothed parts 14a and 14a. The adjacent second one is bent and projected to the other side, constituting engaging portions 30a having approximately the same width as that of the gap between the toothed parts 16a and 16a, with a shorter length than the depth of the gap between the toothed parts 16a and 16a. And the third one adjacent to the second one opposite to the first one in the peripheral direction is not provided with engaging portions, but cut off the portion of the engaging portion. Accordingly, the first washer 30 is provided with the notched parts having the engaging portions 30a, and another engaging portions 30a, and without the engaging portions, sequentially in this order in the outer periphery thereof. The engaging portions 30a projecting to the one side are engaged into respective gaps of the toothed parts 14a, 14a,··· of the fourth cylinder 14, while the engaging portions 30a projecting to the other side are engaged into the gaps of the toothed parts 16a, 16a,··· of the third cylinder 16. The toothed part 14a of the fourth cylinder 14 is displaced by 30° in the peripheral direction from the toothed part 16a of the third cylinder 16. As described above, because of the first washer 30 provided between the fourth and third cylinders 14 and 16 and having the engaging portions 30a, 30a,··· inserted into the respective gaps of the toothed parts 14a and 16a of the cylinders 14 and 16, the fourth and third cylinders 14 and 16 are positioned both in the axial direction and in the rotational direction. Furthermore, as indicated in Fig. 12, the third and second cylinders 16 and 17 have key grooves 16c, 16c and 17d, 17d formed respectively at the confronting end surfaces at the confronting positions in the radial direction. On the other hand, the above-referred second washer 40 is formed with engaging portions 40a and 40a projecting to one side from the inner peripheral edge at two confronting points of the equally-divided four parts in the radial direction, and with engaging portions 40b and 40b projecting to the opposite side from the inner periphery edge at the remaining two points. Each of these engaging portions 40a, 40a, 40b and 40b has a recess notched from the outer peripheral edge towards the depth thereof at the center in the widthwise direction. According to the above-described structure, the cylinders 16 and 14 can be easily electromagnetically coupled to each other in the similar manner as the cylinders 18 and 17. Therefore, the three cylinders 14, 16 and 17 can be positioned in the rotational direction in a reduced time without annoying operations required for positioning. It is to be noted here that the first and second washers 30 and 40 are made of non-magnetic material, and accordingly never affect the magnetic coupling of the cylinders 14 and 16. The end face at the side of the upper shaft of the fourth cylinder 14 is made flat perpendicular to the center of the upper shaft 11A. On the other hand, the other end face at the lower shaft side of the fourth cylinder 14 has many, 8 according to this embodiment, rectangular toothed parts 14a, 14a,··· formed with an equal pitch in the peripheral direction of the cylinder. The front end of each toothed part 14a is rendered flat perpendicular to the center of the upper shaft 11A. Likewise, the end face at the upper shaft side of the third cylinder 16 and the end face at the lower shaft side of the second cylinder 17 are respectively formed with toothed parts 16a, 16a,··· and 17a, 17a,···. The end face at the lower shaft side of the third cylinder 16 and the end face at the upper shaft side of the second cylinder 17 are made flat perpendicular to the center of the upper shaft 11A. Therefore, the toothed parts 14a, 14a,··· of the fourth cylinder 14 confront to the toothed parts 16a, 16a, ··· of the third cylinder 16. At the upper end of the lower shaft 11C is outer-fitted a first cylinder 18 made of a magnetic material. This first cylinder 18 is of the same configuration as the fourth, third and second cylinders 14, 16 and 17 except the size of the inner diameter, with toothed parts 18a, 18a,··· thereof being spaced at a suitable distance to confront to the toothed parts 17a, 17a,··· of the second cylinder 17. There are cylindrical members 19A and 19B made of magnetic material which are fitted inside the casing 25, and a peripheral groove is formed in each of the cylindrical members 19A and 19B. The cylindrical member 19A is so provided as to face the confronting portion of the fourth and third cylinders 14 and 16, while the cylindrical member 19B is so positioned as to face the confronting portion of the second and first cylinders 17 and 18. Moreover, a first electromagnetic coupling detection coil 32 and a second electromagnetic coupling detection coil 31 are wound around in the peripheral grooves in the cylindrical members 19B and 19A, respectively, so that the first and second cylinders 18 and 17 are electromagnetically coupled to each other by the first electromagnetic coupling detection coil 32, and the third and fourth cylinders 16 and 14 are electromagnetically coupled to each other by the second electromagnetic coupling detection coil 31. The electromagnetic coupling detection coils 31 and 32 are arranged to induce a voltage corresponding to the state of the electromagnetic coupling. The positions of the cylinders 14, 16 and 17, 18 are determined by obtaining the electromagnetic coupling state thereof so that the induced voltages in the first and second electromagnetic coupling detection coils 31 and 32 are equal to each other when no torque acts on the torsion bar 11B. Accordingly, the induced voltage due to the change in the ambient temperature can be canceled or negated if the difference of the induced voltages in the coils 31 and 32 is obtained, and the state of the electromagnetic coupling corresponding to the relative rotating amount of the cylinders 17 and 18 is detected, thereby to detect the torque applied to the torsion bar 11B. As indicated in Figs. 3 and 17, the cylindrical members 19A and 19B (only the right cylindrical member 19A in Fig. 3 is shown in Fig. 17) are respectively comprised of an outer wall part 19d and an L-shaped main body 19e which are separately formed from each other, and press-in surfaces 19f and 19g between the outer wall part 19d and the main body 19e. The press-in surfaces 19f and 19g are formed into a stepped part 19h from the peripheral grooves 19a and 19b to the position slightly aside to the outer peripheral side, extending from the outer peripheral end of the stepped part 19h to the outside in the same direction as the axial direction of the cylindrical members 19A and 19B and in the opposite direction to the radial direction of the cylindrical members 19A and 19B. In the state where the main body 19e is separated from the outer wall part 19d, bobbins 41 and 42 wound around with the electromagnetic coupling detection coils 31 and 32 are placed in the peripheral grooves 19a and 19b. Thereafter, the outer wall part 19d is pressed into the main body 19e in a manner as to render the press-in surfaces 19f and 19g confront each other, whereby the cylindrical members 19A and 19B are respectively formed into one unit. A modification of the cylindrical members 19A and 19B according to the invention is shown in Fig. 18, in which the cylindrical members 19A and 19B are divided respectively into one lateral part 19ℓ and the other lateral part 19m. Specifically, a stepped dividing part is formed in the axial center of a wall part 19i in the outer periphery of each cylinder 19A, 19B, and the surfaces parallel to the axial direction of the dividing part and opposite to the radial direction thereof are made press-in surfaces 19j and 19k. When the one lateral part 19ℓ and the other lateral part 19m are separated, the bobbins 41 and 42 wound around with the electromagnetic coupling detection coils 31 and 32 are put in the peripheral grooves 19a and 19b of the one lateral part 19ℓ and then, the other lateral part 19m is pressed into the one lateral part 19ℓ in a manner that the press-in surfaces 19j and 19k thereof are faced each other. Thus, the cylindrical members 19A and 19B are formed into one unit, respectively. As is seen from the foregoing embodiment, according to this invention, each of the cylindrical members 19A and 19B is constructed by two parts which are integrally formed into one unit by inserting the press-in surfaces 19f, 19g or 19j, 19k so as to confront each other. Therefore, there is no possibility that a gap is generated in the dividing part of the cylindrical member 19A or 19B resulting from the thermal deformation or thermal expansion of the components such as the bobbins 41 and 42, etc., due to the change in the ambient temperature. Referring to Figs. 19 and 20, the graphs show the relation between the temperature change and the sensor output of a torque sensor in which the cylindrical members 19A and 19B are butted into contact and, that of the above-described torque sensor, respectively. In the graphs of Figs. 19 and 20, the temperature is indicated in the horizontal axis, the sensor output in the vertical axis. As the temperature rises, the sensor output of the torque sensor increases in Figs. 19. On the contrary, the sensor output of the torque sensor shown in Fig. 20 hardly changes in spite of the temperature change. Accordingly, it is clear that the above-described torque sensor in which the cylindrical members are integrally formed into one unit through above mentioned pressing-in can produce a stable sensor output without being influenced by the change of the ambient temperature. In the torque sensor of the above described construction, when the cylindrical members 19A and 19B are to be mounted, a spacer 37 is interposed between the upper magnetic cylindrical member 19A and the bearing 26 which has one end thereof pressed in contact with the upper end inside the casing 25 to secure the outer ring thereof, in a manner that the outer ring of the bearing 26 is in contact with the one end of the spacer 37. Then, a spacer 38 is placed between the upper cylindrical member 19A and the lower cylindrical member 19B and, a snap ring 33 is fitted in a peripheral groove 25a formed in the inner surface of the casing 25 below the lower cylindrical member 19B. Further, an elastic member 34 made of a corrugated spring which is in a wavelike form in the peripheral direction thereof and looped form in a plane view, as shown in Figs. 5 and 6, is interposed between the snap ring 33 and the lower cylindrical member 19B. As a result, the two cylindrical members 19A and 19B are fixed in the axial direction. An elastic member 35 which is a ring-shaped snap ring and provided with hooks 35a, 35a,··· projecting to one side in the axial direction from the inner periphery thereof as shown in Fig. 8 is fitted in the lower end face of the second cylinder 17 among the fourth, third and second cylinders 14, 16 and 17 mounted to the upper shaft 11A through the sleeve 15, so that the hooks 35a, 35a,··· are engaged with the stepped end face of the lower stepped portion 11f of concave shape recessed in the upper shaft 11A. Accordingly, by means of the elastic member 35, the fourth, third and second cylinders 14, 16 and 17 are fixed in the axial direction. As is seen from an enlarged view of Fig. 7, after the elastic member 35 is fitted into the upper shaft 11A, the ring-shaped portion of the elastic member 35 is brought into contact with the end face of the second cylinder 17, with the hooks 35a being pressed against the outer peripheral surface of the upper shaft 11A by the elasticity of the member 35, so that the end of each hook 35a is engaged to the stepped end face of the stepped portion 11f of the upper shaft 11A. As is understood from Fig. 10 on an enlarged scale, a small protrusion 11g is formed at the upper lateral end of the lower shaft 11C, which is caulked into a gap 18f between the toothed parts 18a and 18a of the first cylinder 18 shown in Fig. 11. Accordingly, as shown in Fig. 9, the protrusion 11g is in pressed contact with the upward end face of the gap 18f between the toothed parts 18a and 18a thereby to secure the first cylinder 18 in the axial direction. It may be possible that many protrusions 11g are formed to be caulked to every gap 18f between the toothed parts 18a and 18a of the first cylinder 18, or to a part of the gaps 18f of the toothed parts 18a. Since the first cylinder 18 is fitted at the inner diameter portion thereof with a pin 11i fastened to the lower shaft 11C, it is fixed in the rotational direction. In the above-described construction of the torque sensor of this invention, the fourth, third and second cylinders 14, 16 and 17 and the two cylindrical members 19A and 19B are securely fixed respectively by the elastic members 35 and 34 in the axial direction. As a result of this, the fourth, third and second cylinders 14, 16 and 17 and, the cylindrical members 19A and 19B can be prevented from rattling in the axial direction since the elastic members 35 and 34 absorb the rattlings of these components. Moreover, the thermal expansion of each component resulting from the change in the ambient temperature can be also absorbed by the elastic members 35 and 34. Additionally, since the fourth, third and second cylinders 14, 16 and 17 and the cylindrical members 19A and 19B are not fixed to the upper shaft 11A and the casing 25 by the pressing-in method, such stress as would be caused by the pressing-in operation is never given rise to. Consequently, from the above-described reasons, the torque sensor of this invention can generate a stable sensor output at all times. According to the embodiments of this invention, the protrusion 11g formed at the upper lateral end of the lower shaft 11C is caulked and fitted in the gap 18f of the toothed parts 18a and 18a of the first cylinder 18 to be pressed in contact with the upward end face of the cylinder 18, in other words, the first cylinder 18 can be positively and securely positioned in a simple manner by utilizing the gap 18f of the toothed parts 18a and 18a, resulting in no change in the sensor output due to the heat or the like. Moreover, the fourth, third and second cylinders 14, 16 and 17 are secured in the axial direction by the elastic member, namely, the ring-shaped snap ring having a plurality of hooks 35a, 35a··· projecting to one side in the axial direction. Therefore, it becomes advantageously easy to secure the cylinders since it is enough to press the snap ring in contact with the lower end face of the second cylinder 17, while pressing the hooks 35a against the upper shaft 11A to engage the end of each hook to the stepped end face of the stepped portion 11f of the upper shaft 11A. The ring-shaped snap ring which has many hooks 35a, 35a,··· projecting to the one side in the axial direction of the cylinder is employed for the elastic member 35 so as to secure the fourth, third and second cylinders 14, 16 and 17, as described hereinabove in the present invention. However, the elastic member 35 is not limited to this kind of a snap ring, but may be a corrugated spring which is to be intervened between a snap ring mounted to the upper shaft 11A and the second cylinder 17 so as to secure the fourth, third and second cylinders 14, 16 and 17, or other shapes of elastic members 34 and 35 may be employed. Further, it is to be noted that although all of the fourth, third and second cylinders 14, 16 and 17 and, the two cylindrical members 19A and 19B are secured to the upper shaft 11A and the casing 25 in the axial direction by the elastic members 35 and 34, respectively, in the foregoing embodiments, the present invention is not limited to this, but only the fourth, third and second cylinders 14, 16 and 17 or, only the two cylindrical members 19A and 19B may be secured in the axial direction by the elastic member 35 or 34. It may be also possible that the fourth, third and second cylinders 14, 16 and 17 and, the two cylindrical members 19A and 19B be secured at the opposite sides thereof in the axial direction by the elastic members 35 and 34, respectively. As has been fully described hereinabove, according to this invention, a plurality of cylinders and/or two cylindrical members are secured in the axial direction by the elastic members. Therefore, the plurality of the cylinders and/or two cylindrical members can be prevented from rattling in the axial direction because the elastic members absorb the rattlings. Moreover, since the elastic members absorb also the thermal expansion in each component resulting from the change in the temperature, a stable sensor output can be obtained at all times by the torque sensor of this invention. Further, the plurality of the cylinders and the two cylindrical members are not secured to one of the shafts and the casing by the pressing-in method, and accordingly no stress is generated in the shafts or the casing of the torque sensor. In the meantime, another embodiment of this invention will be described hereinafter. Fig. 21 is a longitudinal cross sectional view showing the construction of a torque sensor according to another embodiment. In the torque sensor of Fig. 21, the upper shaft 11A is provided with the insertion hole 11a through which the torsion bar is inserted. The insertion hole 11a is opening to the axial direction at the center of the radial direction of the upper shaft 11A. The outer periphery of the insertion hole 11a is formed into the wider diameter part 11c in the upper side thereof (right side in the drawing) and the narrower diameter part 11d in the lower side thereof (left side in the drawing) through the stepped part 11b. To this stepped part 11b of the upper shaft 11A, the fourth cylinder 14 made of a magnetic material is pressed and exteriorly fitted in the state that the upper end (right end in the drawing) thereof is in contact with the stepped wall surface of the wider diameter part 11c. Further, the sleeve 15 is exteriorly fitted in the narrower diameter part 11d in the lower part (left side in the drawing) of the insertion hole 11a. The non-magnetic sleeve 15 is caulked at the lower end thereof to a small diameter part 11e of tapered shape provided in the narrower diameter part 11d, and is provided at the one end thereof with a restricting part 15a for resisting movement which is projected outwards. The magnetic third and second cylinders 16 and 17 which have the same configuration as the fourth cylinder 14 except the size of the inner diameter are fitted outside in the outer periphery of the sleeve 15. It is to be noted here that the inner diameter of each of the cylinders 16 and 17 may possibly be the same as that of the fourth cylinder 14, and in such a case, all of the cylinders 14, 16 and 17 have the same configuration. Ring-shaped gap forming members 21 and 22 of a narrow width are placed between the fourth and third cylinders 14 and 16, and the third and second cylinders 16 and 17, respectively. The gap forming members 21 and 22 are non-magnetic. The end face at the side of the upper shaft of the fourth cylinder 14 is formed flat perpendicular to the center of the upper shaft 11A, whereas, the end face at the side of the lower shaft thereof is provided with many rectangular toothed parts 14a, 14a, ··· which are spaced an equal pitch each other in the peripheral direction of the cylinder. Each front end face of these toothed parts 14a, 14a, ··· is perpendicular to the center of the upper shaft 11A. Similarly, the end face at the side of the upper shaft of the third cylinder 16 and the end face at the side of the lower shaft of the second cylinder 17 are respectively formed with toothed parts 16a, 16a, ··· and, 17a, 17a,···. The end face at the lower shaft side of the third cylinder 16 and the end face at the upper shaft side of the second cylinder 17 are respectively perpendicular to the center of the upper shaft 11A. Therefore, the toothed parts 14a, 14a,··· of the fourth cylinder 14 confront the toothed parts 16a, 16a,··· of the third cylinder 16. The magnetic first cylinder 18 is fixedly fitted outside in the upper end of the lower shaft 11C. The cylinder 18 has the same configuration as the above fourth, third and second cylinders 14, 16 and 17 except the size of the inner diameter, with toothed parts 18a, 18a thereof being spaced at a suitable distance from the toothed parts 17a, 17a,··· of the second cylinder 17. Inside the casing 25 are fitted magnetic cylindrical members 19A and 19B, each of which is provided with a peripheral groove. The cylindrical member 19A is so provided as to face to the confronting position of the fourth and third cylinders 14 and 16 at the upper side, and the other cylindrical member 19B is so provided as to face the confronting position of the second and first cylinders 17 and 18 at the lower side. Moreover, in the peripheral grooves of the cylindrical members 19B and 19A, a first electromagnetic coupling detection coil 32 and a second electromagnetic coupling detection coil 31 are wound around, respectively, so that the first and second cylinders 18 and 17 are electromagnetically coupled to each other by the first electromagnetic coupling detection coil 32, with the third and fourth cylinders 16 and 14 being electromagnetically coupled to each other by the second electromagnetic coupling detection coil 31. At this time, since the third and second cylinders 16 and 17 are separated from each other, the two magnetic circuits work completely independently, thereby to avoid the magnetic influences therebetween. Hereinbelow, how to construct the torque sensor having the above described structure will be described. In the first place, the toothed parts 14a of the fourth cylinder 14 are inserted towards the lower shaft 11C to be secured to the stepped part 11b of the upper shaft 11A. Then, after the gap forming member 21 is inserted in the upper shaft 11A, the sleeve 15, in the outer periphery of which the third and second cylinders 16 and 17, and the gap forming member 22 interposed between these cylinders 16 and 17 are fitted, is fitted outside of the narrower diameter part 11d of the upper shaft 11A. The lower end of the sleeve 15 is caulked and engaged to the small diameter part 11e of tapered shape. Thus, the sleeve 15 is securely fitted outside of the upper shaft 11A. At this time, the axial movement of the third and second cylinders 16 and 17 is regulated by the projecting restricting part 15a provided with the sleeve 15. The first cylinder 18 is fixed to the upper end of the lower shaft 11C. In the above construction, it is so arranged that the toothed parts 14a and 16a of the fourth and third cylinders 14 and 16 confront each other, and the toothed parts 17a and 18a of the second and first cylinders 17 and 18 confront each other. Meanwhile, when mounting the cylindrical members 19A and 19B, the spacer 37 is intervened between the magnetic cylindrical member 19A at the upper side and the bearing 26 one end of which is in contact with the upper end inside the casing 25 to secure the outer ring thereof. The one end of the spacer 37 is in contact with the outer ring of the bearing 26. Moreover, the spacer 38 is interposed between the upper and lower cylindrical members 19A and 19B. The snap ring 33 is fitted in the peripheral groove 25a formed in the inner surface of the casing 25 below the lower cylindrical member 19B. Since the elastic member 34 made of a corrugated spring which is corrugated in the peripheral direction and is the looped form in a plane view as shown in Figs. 5 and 6 is intervened between the snap ring 33 and the lower cylindrical member 19B, the two cylindrical members 19A and 19B are fixedly secured in the urged state in the axial direction. A still further embodiment of this invention will be explained hereinbelow. Figs. 23 and 22 are respectively a longitudinal cross sectional view showing the construction of a torque sensor of the further embodiment and a schematic perspective view of the essential part thereof. Although the torque sensor in each of the foregoing two embodiments has four cylinders, the second and third cylinders 17 and 16 are integrally formed into one cylinder according to this further embodiment. In other words, the torque sensor of this embodiment has three cylinders. Moreover, a sleeve 15a is positioned in the axial direction by the elastic member 35. Further, positioning of the second and third cylinders 17 and 14 in the axial and rotational directions is achieved by the washer 30. Since the other structure is almost same as that of the foregoing embodiments, the detailed description thereof will be omitted here. As this invention may be embodied in several forms, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the meets and bounds of the claims, or equivalence of such meets and bounds thereof are therefore intended to be embraced by the claims.

Claims: A torque sensor comprising: a plurality of cylinders (14,16,17,18) made of a magnetic substance which are mounted to a first (11C) and a second shaft (11A) coupled to each other via a torsion bar, at least one cylindrical member (19A,19B) made of a magnetic substance which is provided in the outer periphery of said cylinders (14,16,17,18), with an electromagnetic coupling detection coil (31,32) being wound in the inner periphery of said cylindrical member, that the magnetic circuit for the flux produced by the detection coil comprises said cylindrical member and said plurality of cylinders, characterized in that elastic members (34,35) are provided at least at one side in the axial direction of said cylindrical member (19A,19B) and/or said plurality of cylinders (14,16,17,18) mounted to one of said shafts (11A,11C), so that said cylindrical member (19A,19B) and/or said plurality of cylinders are pressed in the axial direction against a part of the torque sensor. A torque sensor as set forth in claim 1, wherein each of said plurality of cylinders (14,16,17,18) has rectangular wave-form toothed parts (14a,16a,17a,18a) formed at one end face thereof in a manner that said toothed parts are opposed to those of the adjacent cylinder, one (18) of said plurality of cylinders (14,16,17,18) is mounted to said first shaft (11C), and the other (14,16,17) of said plurality of cylinders (14,16,17,18) are mounted to said second shaft (11A). A torque sensor as set forth in claim 1, wherein the number of said plurality of cylinders (14,16,17,18) is four, each having rectangular wave-form toothed parts (14a,16a,17a,18a) formed at one end face thereof so that the toothed parts of the first and second cylinders (18,17), and those of the third and fourth cylinders (16,14) confront each other respectively, said second, third and fourth cylinders (17,16,14) are mounted to said second shaft (11A), and said first cylinder (18) is mounted to said first shaft (11C), and the number of said cylindrical members (19A,19B) is two and the number of said detection coils (32,31) is two, which are so provided that the first magnetic circuit for the flux produced by the first detection coil (32) comprises said first and second cylinders (18,17) and said cylindrical member (19B), and the second magnetic circuit for the flux produced by the second detection coil (31) comprises said third and fourth cylinders (16,14) and said cylindrical member (19A). A torque sensor as set forth in claim 2, further comprising a sleeve (15) made of a non-magnetic substance which has a restricting part for restricting the movement in the axial direction of said plurality of cylinders (14,16,17) mounted to said second shaft (11A), and which is interposed between the inner peripheral surface of said plurality of cylinders (14,16,17) and the outer peripheral surface of said second shaft (11A). A torque sensor as set forth in claim 4, wherein said sleeve (15) is fixedly engaged to the outer periphery of said second shaft (11A) by caulking. A torque sensor as set forth in claim 1, wherein the number of said plurality of cylinders (14,17,18) is three, each of the first and third cylinders (18,14) having rectangular wave-form toothed parts (18a,14a) formed at one end face thereof and the second cylinder (17) having rectangular wave-form toothed parts (17a,17b) formed at the opposite end faces thereof so that the toothed parts (18a) of the first cylinder (18) and those (17b) at the one end face of the second cylinder (17), those (17a) at the other end face of the second cylinder and those (14a) of the third cylinder (14) confront each other, said second and third cylinders (17,14) are mounted to said second shaft (11A) and said first cylinder (18) is mounted to said first shaft (11C), and the number of said cylindrical members (19A,19B) is two and the number of said detection coils (32,31) is two, which are so provided that the first magnetic circuit for the flux produced by the first detection coil (32) comprises said first cylinder (18), the one side of said second cylinder (17) and said cylindrical member (19B), and the second magnetic circuit for the flux produced by the second detection coil (31) comprises the other side of said second cylinder (17), said third cylinder (14) and said cylindrical member (19A). A torque sensor as set forth in claim 3, further comprising a washer (30) provided between said third and fourth cylinders (16,14) and having engaging portions (30a) to be engaged into each gap of toothed parts (16a,14a) of the cylinders (16,14). A torque sensor as set forth in claim 6, further comprising a washer (30) provided between said second and third cylinders (17,14) and having engaging portions (30a) to be engaged into each gap of toothed parts (17a,14a) of the cylinders (17,14). A torque sensor as set forth in claim 1, wherein said cylindrical member (19A,19B) is formed by divided two parts (19d,19e), each with a press-in surface (19f,19g) confronting each other in the radial direction.

Inventors: NAGANO HIDENOBU, TANIGUCHI MANABU, WATANABE MASAYUKI, NAGANO, HIDENOBU, TANIGUCHI, MANABU, WATANABE, MASAYUKI
Applicants: KOYO SEIKO CO, KOYO SEIKO CO., LTD.
Application year: 1989
Main classification: G01L3
IPC codes: G01L3