ROTARY DRIVING DEVICE USED FOR ROTARY ACTUATOR

Abstract: A rotary driving device is constituted by a pair of stator magnetic poles having end faces opposing through gaps; a ro­ tor of magnetic material rotatably supported inside the stator magnetic pole pair, having two pole surfaces between two planes parallel with the axis of rotation; and an excitation coil of the stator magnetic pole pair. The positions of the gaps be­ tween the end faces of the stator magnetic pole pair along the circumferential direction are changed along the axial direction, thereby output and detent torques are obtained effectively and satisfactorily.

Description: The present invention relates to a rotary driving device used for a rotary actuator. The rotary driving device according to the present invention is used as an actuator for driving, e.g., a rotary valve. A conventional rotary driving device is, for example, constituted by stator magnetic poles, fixed in a housing, and a rotor of a permanent magnet rotatably supported by a shaft inside the magnetic poles. The polarity of the stator magnetic poles are reversed by an excitation coil, thereby rotating the rotor. A conventional device is disclosed in FR-A-1307883. This rotary driving device has a pair of C-shaped magnetic poles which oppose each other across gaps, a rotor mounted for rotation on a shaft inside the poles and an excitation coil for generating a magnetic force between the magnetic pole pair and the rotor. In other known devices the rotor has a cylindrical shape, and the respective stator magnetic poles are arranged on an identical circumference so that distances between inner end faces of the stator magnetic poles and a center of rotation of the rotor become the same. For this reason, lines of magnetic force from the rotor are distributed to be wider than an outer periphery thereof, and a magnetic attractive force between the stator magnetic poles and the rotor is weakened. Therefore, when external rotation or vibration is applied to the excitation coil in a nonconductive state, the rotor is easily rotated and cannot maintain a stable rest position. In particular, when a rotary driving device of this type is compactly formed, i.e., into a shallow outer shape, the outer diameter of the rotor is decreased. Therefore, when the excitation coil is rendered nonconductive, the rest torque of the rotor becomes small and a stable rest position cannot be maintained. In addition, when the excitation coil is energized, only a small output torque can be obtained from the rotor, for the same reason as described above. The present invention has been made in consideration of the above situation, and has as its object to provide a compact, improved rotary driving device which can effectively generate an output torque and a detent torque. According to the present invention, there is provided a rotary driving device comprising: a case defining an outer shape of the rotary driving device; a pair of stator magnetic poles fixed inside said case and having end portions opposing through gaps; a rotor of magnetic material rotatably supported inside said stator magnetic pole pair and having two pole surfaces forming two planes parallel with the axis of rotation; a rotary shaft for rotatably supporting said rotor; and an excitation coil for generating a magnetic force between said stator magnetic pole pair and said rotor, characterized by the circumferential positions of said gaps between the opposing end portions of said stator magnetic pole pair changing with corresponding change in position in the direction of the axis of rotation. With the above arrangement, when the excitation coil is energized and the rotor is rotated, the rotor receives an attractive or repulsive force from an end portion or inner surface of the nearest stator magnetic pole in accordance with a rotational angle. Thus, the rotor is stable at any rotational angle, and a large rotational torque can be obtained. Since the two pole surfaces of the rotor abut against the stator magnetic pole and an upper or lower portion of the rotor opposes an inner surface of the stator magnetic pole, a large detent torque can be obtained. In order that the invention may be better understood an embodiment thereof will be described by way of example with reference to the accompanying drawings in which; Figure 1A and 1B are views showing an example of a prior art rotary driving device; Figure 2 is a sectional view showing a rotary driving device according to an embodiment of the present invention; Figure 3 is a perspective view showing an important part of the device shown in Fig. 2; Fig. 4 is a perspective view showing an important part of the device shown in Fig. 3; Figs. 5 and 6 are sectional views of the device shown in Fig. 2 taken along lines V-V and VI-VI, respectively; and Figs. 7 and 8 are graphs showing characteristics of the device shown in Fig 2, respectively. Before entering into the description of the preferred embodiment, an example of a prior art rotary driving device for a rotary actuator will be described with reference to Figs. 1A and 1B. As shown in Figs. 1A and 1B, a rotary driving device is constituted by stator magnetic poles 82, 83, 84 and 85 fixed in a housing 81 and a rotor 87 as a permanent magnet rotatably supported by a shaft 86 inside the magnetic poles. The polarities of the stator magnetic poles 82 and 83 or 84 and 85 are reversed by an excitation coil, thereby rotating the rotor 87. In the device shown in Figs. 1A and 1B, the rotor 87 has a cylindrical shape, and the respective stator magnetic poles are arranged on an identical circumference so that distances between inner end faces of the stator magnetic poles 82, 83, 84, and 85 and a rotating center of the rotor 87 become the same. For this reason, lines of magnetic force from the rotor 87 are distributed to be wider than an outer periphery thereof, as shown in Fig. 1B, and a magnetic attractive force between the stator magnetic poles 82, 83, 84, and 85 and the rotor 87 is weakened. When external rotation or vibration is applied to the excitation coil in a nonconductive state, the rotor is easily rotated and cannot maintain a stable rest position. A rotary driving device according to an embodiment of the present invention is shown in Figs. 2, 3, and 4. The rotary driving device shown in Fig. 2, 3, and 4 is used as a torque motor for switching valves. Reference numeral 11 denotes a cylindrical case which comprises a nonmagnetic member and stores components of the rotary driving device to be described later in detail. The case 11 is coupled to a housing 71 of a valve portion 7, and a selector valve is housed in the housing 71. In the valve portion 7, an output shaft 72 which rotates together with a rotor 6 as a rotor is rotatably supported by a bearing 18 fixed to the housing 71. Reference numeral 19 denotes a plate which comprises a nonmagnetic member and fixes the bearing 18 to the housing 71; and 17, a thrust washer of the output shaft 72 fixed thereto. The output shaft 72 also serves as a valve needle 731, i.e., as a component of the valve portion, and a valve port 732 provided in the axial direction and a valve port 733 communicating with the valve port 732 and open to the outer periphery of the valve needle 731 are provided in the valve needle 731. The valve needle 731 is inserted in a hole 741 of the housing 71. The housing 71 is provided with input and output ports 742 and 743 for a fluid, thus forming a rotor valve which switches the fluid by rotation of the output shaft 72. When the valve needle 731 is located at a position shown in Fig. 2, the input port 742, the valve ports 732 and 733, and the output port 743 communicate with each other, and open the valve. However, when the valve needle 731 is rotated from this position, communication between the valve port 733 and the output port 743 is interrupted, thus closing the valve. Figure 3 is perspective view of the main part of the rotary driving device. Reference numeral 21 denotes an excitation coil; 3 and 4, a pair of stator magnetic poles fixed to an inner portion of the case 11 and having substantially an arc shape; and 6, a rotor comprising a permanent magnet which is magnetized in a radial direction so that one side of a magnetized end face exhibits the N pole and the other side exhibits the S pole. It should be noted that a central portion of the rotor 6 need not be flat. Inner surfaces of the stator magnetic pole 3 and 4 and an outer peripheral end face of the rotor 6 are arranged to be separated at a constant distance. A yoke 26 transmits an excitation magnetic flux of the excitation coil 21 to the stator magnetic poles 3 and 4. The stator magnetic pole 3 has a substantially arced shape constituted by an arc portion 3A with end faces 311, 312, 313, 321, 322, and 323, and a contact portion 3B with contact surfaces 331 and 341. The end faces 311, 313, 321, 323, 331, and 341 are parallel to the axis rotation of of the rotor 6. The end face 312 between the end faces 311 and 313 and the end face 322 between the end faces 321 and 323 are inclined with respect to the axis of rotation. Positions of the end faces 311, 312, 313, 321, 322, and 323 in the circumferential direction are deviated along the axial direction. A deviation amount is substantially equal to rotational range ϑ of the rotor 6. A shape of the intermediate end faces 312 and 322 can be referred to as a helical shape with respect to the axis of rotation. On the other hand, the contact end faces 331 and 341 of the stator magnetic pole 3 abut against a portion of flat surfaces 61 and 62 of the rotor 6, thereby limiting rotation of the rotor and obtaining a large detent torque. The rotor 6 abuts against the end faces 331 and 441 through nonmagnetic members 331a and 441a of, e.g., a rubber or resin, provided thereto and is stopped. The stator magnetic pole 4 also has opposing end faces 411, 412, 413, 422, and 423 and contact end faces 431 and 441 as in the magnetic pole 3, and are arranged symmetrical with the axis of rotation. The lengths (g) of gaps 51, 52, 53, 54, 55, and 56 of the opposing end faces of the stator magnetic poles 3 and 4 are set to be equal to each other. A distance between the surfaces 61 and 62 of the rotor 6, i.e., a height (h) of the rotor 6, is set to be larger than the gap length (g). The relative positional relationship between the stator magnetic poles 3 and 4 and the rotatonal position of the rotor 6 is illustrated in Figs. 5 and 6. Figures 5 and 6 are sectional views taken along lines V-V and VI-VI of Fig.2. At a counterclockwise rotation limit position of the rotor 6 (upper parts of Figs. 5 and 6), the rotor 6 abuts against the contact end faces 441 and 331 of the stator magnetic poles 3 and 4 through the nonmagnetic member 441a and 331a. At a clockwise rotation limit position of the rotor 6 (lower parts of Figs. 5 and 6), the rotor 6 abuts against the contact end faces 341 and 431 of the stator magnetic poles 3 and 4 through nonmagnetic members 341a and 431a. First, a case will be described wherein the rotor is at the clockwise rotation limit position. Referring to the upper drawing of Fig. 5, an edge portion 631 of the rotor 6 opposes a portion near the opposing end face 311 of the arc portion 3A of the stator magnetic pole 3, and an edge portion 642 opposes a portion near the opposing end face 421 of the arc portion 4A of the stator magnetic pole 4. For this reason, in the conductive state, a rotational torque can be obtained between the stator magnetic poles 3 and 4. Referring to the upper drawing of Fig. 6, the two edge portions 631 and 632 at one end of the rotor 6 and two edge portions 641 and 642 at the other end thereof oppose inner surfaces of the arc portions 3A and 4A of the stator magnetic poles 3 and 4. A case will be described wherein the rotor is at the counterclockwise rotation limit position. Referring to the lower drawing of Fig. 5, the two edge portions 631 and 632 at one end of the rotor 6 and the two edge portions 641 and 642 at the other end thereof oppose inner surfaces of the arc portions 3A and 4A of the stator magnetic poles 3 and 4. Referring to the lower drawing of Fig. 6, the edge portion 632 at one end of the rotor 6 opposes a portion near the end face 413 of the stator magnetic pole 4, and the edge portion 641 at the other end thereof opposes a portion near the end face 323 of the stator magnetic pole 3. For this reason, in the conductive state, a rotational torque can be obtained between the stator magnetic poles 3 and 4 and the rotor 6. As described above, at the positions of the upper parts of Figs. 5 and 6, the detent torque and the output torque are together generated by upper and lower portions of the rotor 6. The operation of the device shown in Figs. 2 and 3 will be described with reference to Figs. 5 and 6. A magnetic flux (Φ₁) as a part of a rest torque at the positions of the upper parts of Figs. 5 and 6 forms, due to a magnetic flux generated from the rotor comprising the permanent magnet, a closed loop as follows: the edge portion 632 of the rotor 6 → the stator magnetic pole 4 → the yoke 26 → the stator magnetic pole 3 → the edge portion 641 of the rotor 6. As shown in the lower part of Fig. 5, in the lower portion of the rotor 6, a magnetic flux (Φ₂) is present to form a closed loop as follows: the edge portions 631 and 632 of the rotor 6 → the arc portion 4A of the stator magnetic pole 4 → the yoke 26 → the arc portion 3A of the stator magnetic pole 3 → the edge portions 642 and 641 of the rotor 6. The rotor 6 can generate a large detent torque by these magnetic fluxes (Φ₁ , Φ₂). In this case, the detent torque becomes weak with only the magnetic flux (Φ₁) at the upper portion of the rotor shown in the upper part of Fig. 5, and a magnetic balance is lost due to variations in size and the like. Therefore, the rotor may be shifted from the position shown in the upper part of Fig. 5 to the position shown in the lower part thereof. However, the detent torque which can satisfactorily hold the rotor 6 can be obtained by the magnetic flux (Φ₂) at the lower portion (the upper part of Fig. 6) of the rotor 6 due to the shapes of the stator magnetic poles 3 and 4. The operation for generating a rotational force for rotating the rotor 6 from the rest position shown in the upper parts of Figs. 5 and 6 to the position of the lower parts of Figs. 5 and 6 by energizing the excitation coil 21 will be described. When the stator magnetic poles 4 and 3 are respectively magnetized to the S and N poles, a repulsive force F(1) is applied to the rotor 6 near the end faces 411, 413, 321, and 323 of the stator magnetic poles, and an attractive force F(2) is applied to the rotor 6 near the end faces 421 and 323 of the stator magnetic pole. Thus, the rotor 6 is rotated to the position of the lower parts of Figs. 5 and 6. At the same time, the rotor 6 causes the output shaft 72 to generate the output torque. The rotating force at this time obtains an activation torque by the upper portion of the rotor (the upper part of Fig. 5). This is because, at the position of the upper part of Fig. 5, the end faces 421 and 311 of the stator magnetic poles oppose the edge portions 642 and 641 of the rotor 6. In view of this, a change in magnetic energy W with respect to the rotational angle ϑ of the rotor 6 is large, and the attraction force F(2) is expressed by the following relation, thus obtaining a large activation torque: F(2) = dW/dϑ (kg) Meanwhile, since a change in magnetic energy W with respect to the rotational angle ϑ is small at the lower portion of the rotor (the upper part of Fig. 6), the lower portion of the rotor does not contribute much to generation of the output torque. Note that when the gaps between the stator magnetic poles 3 and 4 are helically arranged with respect to the axis of rotation, the output torque can be increased within the overall rotational angle ϑ of the rotor 6. The detent torque and the activation torque at the position in the lower parts of Figs. 5 and 6 are also determined by the stator magnetic poles 3 and 4 and the rotor 6 as those at the position in the upper parts of Figs. 5 and 6. At the position of the lower parts of Figs. 5 and 6, the magnetic flux from the rotor 6 is divided at the lower portion of the rotor (the lower part of Fig. 6) into a magnetic flux (Φ₃) forming the following closed loop: the edge portion 631 of the rotor 6 → the stator magnetic pole 3 → the yoke 26 → the stator magnetic pole 4 → the edge portion 642 of the rotor 6, and at the upper portion of the rotor (the lower part of Fig. 5) into a magnetic flux (Φ₄) forming the following closed loop: the edge portions 631 and 632 of the rotor 6 → the stator magnetic pole 3 → the yoke 26 → the stator magnetic pole 4 → the edge portions 642 and 641 of the rotor 6. The detent torque is generated from the rotor 6 by these magnetic fluxes (Φ₃ , Φ₄). As described above, the detent torque can be stably generated from the rotor 6 by the magnetic flux (Φ₄). When the rotor 6 is at the rest position of the lower parts of Figs. 5 and 6, the excitation coil 21 is energized in a direction opposite to the above case so as to generate the N and S poles from the stator magnetic poles 3 and 4. Then, an attractive force F(3) is applied to the rotor 6 near the end faces 413 and 323 of the stator magnetic poles, and the rotor 6 is pivoted counterclockwise from the position shown in the lower parts of Figs. 5 and 6 to the position shown in the upper parts thereof. At the same time, the rotor 6 causes the output shaft 72 to generate the output torque. At the lower portion of the rotor (the lower part of Fig. 6), the end faces 413 and 323 of the stator magnetic poles oppose the edge portions 632 and 641 of the rotor 6, thus obtaining a large activation torque. As described above, according to the present invention, the rotary driving device can be provided wherein the gap positions of the opposing end faces of the stator magnetic pole pair are provided to be inclined in a circumferential direction, whereby the upper and lower portions of the rotor effectively and satisfactorily generate the output torque and the detent torque together. Figure 7 shows characteristics of the output torque T(OUTPUT) with respect to the rotational angle ϑ of the rotor, and Fig. 8 shows characteristics of the output torque T(DETENT) with respect to the rotational angle ϑ of the rotor. Referring to Figs. 7 and 8, a chain-line curve CURVE-1 represents the conventional device shown in Figs. 1A and 1B, and a solid-line curve CURVE-2 represents the device according to this embodiment shown in Figs. 2 and 3.

Claims: A rotary driving device comprising: a case (11) defining an outer shape of the rotary driving device; a pair of stator magnetic poles (3,4) fixed inside said case (11) and having end portions (311,312,313, 321,322,323;411,412,413,421,422,423) opposing through gaps (51 - 56); a rotor (6) of magnetic material rotatably supported inside said stator magnetic pole pair (3,4) and having two pole surfaces forming two planes (61,62) parallel with the axis of rotation; a rotary shaft (72) for rotatably supporting said rotor (6); and an excitation coil (21) for generating a magnetic force between said stator magnetic pole pair (3,4) and said rotor (6), characterised by the circumferential positions of said gaps (51 - 56) between the opposing end portions (311,312,313,321, 322,323;411,412,413,421,422,423) of said stator magnetic pole pair (3,4) changing with corresponding change in position in the direction of the axis of rotation. A device according to claim 1, wherein the overall change in the circumferential positions of each gap (51 to 56) between the opposing end portions (311,312,etc) of said stator magnetic pole pair (3,4) is substantially equal to the range of rotation of said rotor (6). A device according to claim 1 or claim 2, wherein the gaps (51 to 56) between the end portions (311,312,etc) of said stator magnetic pole pair (3,4) are smaller than a distance between the two flat surfaces (61,62) of said rotor (6). A device according to any preceding claim wherein a contact end face portion (331,341,431,441) is provided on an inner surface of at least one of said pair of stator magnetic poles (3,4) for regulating the rotation of said rotor (6) within the rotational angular range between a first and a second position by the abutting of a surface of said rotor (6) against said contact end face portion (331,341,431,441) of said stator magnetic pole (3,4). A device according to claim 4, wherein a nonmagnetic member (331a,341a,431a,441a) is fixed to a contact surface of each of said contact portions (331,341,431,441) of said stator magnetic poles (3,4). A device according to claim 4 or claim 5 wherein the change in circumferential position of said gaps (51 to 56) is such that, when said rotor (6) is positioned at either said first or said second position, a predetermined part of an end portion (631,632,641,642) of said rotor (6) is opposite to the inside of an end portion (3A,4A) of a first magnetic pole of said stator magnetic pole pair (3,4), while the remainder part of said end portion (631,632,641,642) of said rotor (6) is adjacent to said end portion of said second magnetic pole (3,4) of said stator magnetic pole pair. A device according to any preceding claim, wherein said excitation coil (21) is located at a position on the extension of the axis of rotation of said rotor (6). A device according to any preceding claim, wherein a valve body (72) is able to rotate together with the axis of rotation of said rotor (6) for changing the cross-sectional area of path of fluid.

Inventors: MURATA, SYUUJI, SOGABE, ICHITA, YOKOYA, YUJI
Applicants: NIPPONDENSO CO., LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1985
Main classification: H01F7
IPC codes: H01F7, H02K33