Thermo-sensitive actuator

Abstract: A thermo-sensitive actuator capable of operating without the need of providing a temperature detector as a separate member. The actuator includes a stator made of a magnetic material to form a yoke. A rotor is rotatably provided in an opening provided in the stator. The actuator further includes pole pieces for magnetically connecting the stator and the rotor. A magnetic source is provided in any of the magnetic paths formed by the constituent elements. A thermo-sensitive magnetic material, which shows a change in magnetic characteristics, e.g. permeability, saturated magnetic flux density, or residual magnetic flux density, according to temperature, is provided in a part of the magnetic paths.

Description: The present invention relates to a thermo-sensitive actuator which generates driving force upon detecting a temperature change in an environment or a specific apparatus. As explained below such actuators may be used to regulate an idle speed controller (hereinafter referred to as "ISC"). In some controlled systems, response conditions for control are desired to change in accordance with a temperature change in an environment or an apparatus. An example is an ISC mounted on an automobile. In this case, when the automobile is in an idling state, the intake air quantity is affected by the engine temperature. Accordingly, temperature sensors are attached to necessary positions, and detected signals from the temperature sensors are collected to obtain control conditions. As specific temperature sensors, various types of sensor have already been proposed, such as those which employ wax, and those which employ a bimetal. A specific example of changing response conditions of an apparatus in accordance with a temperature change will be explained below with regard to an automobile which is in an idling state. In the case of an automotive internal combustion engine, when the engine temperature is high, the bypass air quantity must be reduced, whereas, when the engine temperature is low, the bypass air quantity must be increased. In the case of a heater or similar device, when the temperature is low, it is necessary to increase the opening of the fuel valve to thereby increase the heat generation rate. In other words, a valve body for an ISC is required to move in such a manner that, when the temperature is low, the valve body moves with a large stroke, whereas, when the temperature is high, the valve body moves with a small stroke near the position for closing the valve to prevent runaway. Fig. 1 is a graph showing characteristics required for a rotary actuator for controlling the valve body of an ISC, in which temperature T [ o C] is plotted along the abscissa axis, and stroke [deg] is plotted along the ordinate axis. Accordingly, this type of control requires a plurality of temperature sensors or temperature-sensing actuators and also needs to constitute a control circuit taking into account temperature conditions. Consequently, the structure of the controller becomes complicated, and the reliability degrades. Further, as the number of constituent elements increases, the production cost rises. With regard to control conditions, some valves as objects to be driven need to be closed (fully closed) irrespective of the temperature when the apparatus is not energized. A fuel valve used in a heater, for example, comes under this category. In this case, when the apparatus is in an inoperative state, the fuel valve must be fully closed to prevent fuel from flowing out. U.S. Patent 1 742 138 of Faus describes a temperature responsive device in which a permanent magnet is provided with an air gap between its poles and an armature member is rotatably mounted in this air gap. The armature member has a shaft and a pair of oblong magnetic members having different temperature coefficients of permeability secured to the shaft at their centre with their longitudinal axis at an acute angle to each other. Thus, the armature member takes different rotative positions of least reluctance at different temperatures. Seki et al in IEEE Transactions on Magnetics, Vol. Mag-16, No. 5, September 1980 describe thermometers having a temperature sensitive magnetic core. A coil or iron piece is placed in an air gap of a magnetic circuit. The magnetic circuit is provided by a yoke formed in two pieces with a permanent magnet and a temperature sensitive magnetic material joining the two pieces of the yoke. We explain below how to provide a thermo-sensitive actuator in which a thermo-sensitive magnetic material whose magnetic characteristics change according to temperature is provided in a part of a magnetic path, thereby making it unnecessary to provide a temperature detector as a separate member. According to a first aspect of the invention, there is provided a thermo-sensitive actuator having a stator made of a magnetic material to form a yoke, a rotor which is a permanent magnet rotatably provided in an opening provided in said stator, and pole pieces for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a thermo-sensitive magnetic material which is provided in a part of each of rotor-side end surfaces of at least one pair of pole pieces which face each other across said rotor. The invention provides, in a second and alternative aspect thereof a thermo-sensitive actuator having stator members made of a magnetic material to constitute a stator, which forms a yoke divided into three, a rotor which is a permanent magnet rotatably provided in an opening provided in said stator, and pole pieces for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a thermo-sensitive magnetic material provided between said stator members; and an air gap provided between said stator members. In a third alternative aspect, the invention provides, a thermo-sensitive actuator having stator members made of a magnetic material to constitute a stator, which forms a yoke divided into two, a rotor which is a permanent magnet rotatably provided in an opening provided in said stator, and pole pieces for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a magnetic path formed by connecting said stator members with a space therebetween; and a thermo-sensitive magnetic material interposed in said magnetic path; and said pole pieces being formed so that the ratio of the area of surfaces of two pole pieces which face said rotor, and being associated with each yoke, to the area of surfaces of further pole pieces which face said rotor and being associated with each yoke is a predetermined value. There is provided, in a fourth and alternative aspect of this invention, a thermo-sensitive actuator having stator members made of magnetic material which together constitute a stator in the form of a yoke divided into three, a rotor which is a permanent magnet rotatably providing in an opening provided in said stator, and pole pieces for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a first thermo-sensitive magnetic material positioned between a first and a second of said stator members; a second thermo-sensitive magnetic material positioned between said second and a third of said stator members; and said first stator member being integrally connected with a pair of said pole pieces. We provide, in a fifth alternative aspect of this invention, a thermo-sensitive actuator comprising: two pole pieces which face each other across at least one subsidiary air gap to form a main air gap; a magnetic path for magnetically connecting said two pole pieces; at least one thermo-sensitive magnetic material which shows a change in magnetic characteristics according to temperature, said thermo-sensitive magnetic material, together with at least one magnetic source, being provided in said magnetic path; and a rotor which is a permanent magnet movable together with a driving shaft as one unit, said rotor being disposed in said main air gap. According to a further alternative aspect of this invention, there is provided a thermo-sensitive actuator comprising: two pole pieces which face each other across one subsidiary air gap; a thermo-sensitive magnetic material interposed between the other ends of said pole pieces, thereby forming a rectangularly bent magnetic path; a moving member which is a permanent magnet disposed in a linear space surrounded by said bent magnetic path; and at least one magnetic source provided in said magnetic path. We also explain below how our actuators can be adapted so that when used to regulate a value but not energized, they are in a characteristic (normally closed) state where the valve is closed at all times irrespective of the temperature. In the drawings: Fig. 1 is a graph showing the characteristics of a rotary actuator for controlling a valve body of an ISC. Fig. 2 is a graph showing the relationship between the permeability of thermo-sensitive magnetic materials and temperature. Fig. 3 shows the arrangement of an embodiment of thermo-sensitive actuator according to the present invention. Fig. 4 shows the arrangement of a further embodiment of thermo-sensitive actuator according to the present invention. Fig. 5 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 6 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 7 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 8 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 9 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 10 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 11 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 12 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 13 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 14 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 15 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 16 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 17 shows a model for an analysis by the finite element method. Fig. 18 shows the arrangement of Fig. 17 in a state in which the rotator is apt to rotate as a result of an analysis. Fig. 19 shows a stable (stationary) state of the rotor of Fig. 17 obtained as a result of an analysis. Fig. 20 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Fig. 21 illustrates reaction force acting in operation of the embodiment shown in Fig. 20. Fig. 22 illustrates a stable state in operation of the embodiment shown in Fig. 20. Figs. 23 and 24 are side elevational and front views of an arrangement illustrating how embodiments of our actuators may be used in practice. Fig. 25 is a sectional view illustrating application of an embodiment of actuator in accordance with the invention in an ISC. Embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 2 is a graph showing the characteristics of thermo-sensitive magnetic materials, in which permeability µ is plotted along the ordinate axis, and temperature T is plotted along the abscissa axis. As shown in the graph, there are two different types of thermo-sensitive magnetic material: one in which the permeability increases as the temperature rises (positive characteristics); and another in which the permeability decreases as the temperature rises (negative characteristics). Fig. 3 shows the arrangement of an embodiment of thermo-sensitive actuator according to one aspect of the present invention. In this embodiment, a thermo-sensitive magnetic material 35 having negative characteristics is provided in a part of the end surface of each of a pair of opposing pole pieces 11-1 and 11-4. Next, the operation will be explained. In this embodiment, since a thermo-sensitive magnetic material having negative characteristics is used, when the temperature is low, the permeability is relatively high. Accordingly, a pair of pole pieces 11-1 and 11-4 and another pair of pole pieces 11-2 and 11-3 pass magnetic flux equally with each other. Therefore, magnetic flux coming out of the permanent magnet constituting the rotor 13 forms two symmetric loops: one loop in which magnetic flux from the permanent magnet passes through the pole piece 11-2 and the stator 10 and returns to the permanent magnet through the pole piece 11-4; and another loop in which magnetic flux from the permanent magnet passes through the pole piece 11-1 and the stator 10 and returns to the permanent magnet through the pole piece 11-3. Accordingly, the rotor 13 lies in the center. When the temperature rises, the permeability of the thermo-sensitive magnetic material decreases. Consequently, the magnetic flux passing through the pole pieces 11-1 and 11-4 decreases, whereas the magnetic flux passing through the pole pieces 11-2 and 11-3 increases. Accordingly, the rotor (permanent magnet) 13 is attracted to the pole pieces 11-2 and 11-3, and thus a torque is induced in the rotor 13, causing the rotor 13 to rotate in the direction of the solid-line arrow. It should be noted that, when the temperature reaches the Curie point of the thermo-sensitive magnetic material, the thermo-sensitive magnetic material becomes paramagnetic; therefore, the rotor 13 will not rotate any longer even if the temperature rises above the Curie point. Since the amount of rotation at that time is determined by the area which the thermo-sensitive magnetic material occupies in each piece, it can be readily set. Fig. 4 shows the arrangement of a still further embodiment of the thermo-sensitive actuator according to the present invention. In Fig. 4, portions which are identical or equivalent to those in Fig. 3 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, the stator 10 is cut at a portion thereof which lies between the pole pieces 11-3 and 11-4 to provide an air gap 36. In addition, the stator 10 is provided with a magnetic source 37. The arrangement of the rest of this embodiment is the same as that shown in Fig. 3 . Next, the operation will be explained. In this case, magnetic flux produced by the coil of the magnetic source 37 generates a loop that passes through the pole pieces 11-2 and 11-3 (acting on the rotor 13 in the valve-closing direction), and another loop that passes through the pole pieces 11-1 and 11-4 (acting on the rotor 13 in the valve-opening direction). According, when the saturated magnetic flux density in the thermo-sensitive magnetic material lowers at high temperature, the magnetic flux passing through the pole pieces 11-1 and 11-4 decreases, resulting in reduction of the action of the coil in the valve-opening direction. Thus, the specifications required for the ISC are satisfied. It should be noted that, since the amount of rotation of the rotor 13 corresponding to the temperature change can be determined by varying the installation area (occupied area) of the thermo-sensitive magnetic material, the design for obtaining the required characteristics is facilitated. Fig. 5 shows the arrangement of a further embodiment of thermo-sensitive actuator according to the present invention. In Fig .5 , portions which are identical or equivalent to those in Figs. 3 and 4 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, a stator 10 comprises three stator members 10a, 10b and 10c. A thermo-sensitive magnetic material 38 is provided between the stator members 10a and 10b, and an air gap 39 is provided between the stator members 10b and 10c. In this case, the relationship between the width ℓ 1 of the thermo-sensitive magnetic material 38 and the air gap ℓ 2 is set so as to satisfy the condition of ℓ 1 >ℓ 2 , thereby making it possible to change the characteristics. Next, the operation will be explained. When the temperature is low, the thermo-sensitive magnetic material 38 passes magnetic flux equally with the stator 10. Therefore, regarding magnetic flux from the permanent magnet 13 constituting the rotor, a magnetic flux loop that passes through the pole piece 11-1, the stator member 10a, the thermo-sensitive magnetic material 38, the stator member 10b and the pole piece 11-4 is stronger than a magnetic flux loop that extends from the pole piece 11-2 to the pole piece 11-3 because the latter loop passes through the air gap 39. Consequently, the rotor 13 rotates in the valve-opening direction from the center line (the line lying between the pole pieces 11-1 and 11-2). As the temperature rises, the saturated magnetic flux density in the thermo-sensitive magnetic material lowers, and when the temperature reaches the Curie point of the thermo-sensitive magnetic material, the thermo-sensitive magnetic material becomes paramagnetic. Consequently, the thermo-sensitive magnetic material portion 38 becomes equivalent to air in terms of permeability. If the condition of ℓ 1 >ℓ 2 is set, the magnetic reluctance of the air gap 39 becomes smaller than that of the thermo-sensitive magnetic material portion 38. Accordingly, the magnetic flux passing through the pole pieces 11-1 and 11-4 decreases, whereas the magnetic flux passing through the pole pieces 11-2 and 11-3 increases. As a result, the rotor 13 is attracted to the pole pieces 11-2 and 11-3, and thus a torque is induced in the rotor 13, causing the rotor 13 to rotate in the valve-closing direction from the center line. Fig. 6 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 6, portions which are identical or equivalent to those in Fig. 5 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, a magnetic source 37 is provided. The arrangement of the rest of this embodiment is the same as that shown in Fig. 5 . First, magnetic flux produced by the coil of the magnetic source 37 generates a loop that passes through the pole pieces 11-2 and 11-3 (acting on the rotor 13 in the valve-closing direction), and another loop that passes through the pole pieces 11-1 and 11-4 (acting on the rotor 13 in the valve-opening direction). When the saturated magnetic flux density in the thermo-sensitive magnetic material lowers at high temperature, the magnetic flux passing through the pole pieces 11-1 and 11-4 decreases. In this case, the action of the coil in the valve-opening direction reduces, and thus the specifications required for the ISC are satisfied. Fig. 7 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 7 , portions which are identical or equivalent to those in Fig. 5 are denoted by the same reference numerals, and description thereof is omitted. This embodiment differs from the embodiment shown in Fig. 5 in that the thermo-sensitive magnetic material 38 is installed at a position between the pole pieces 11-4 and 11-3 (in Fig. 5 , the thermo-sensitive magnetic material 38 is installed at a position between the pole pieces 11-1 and 11-3). The operation will be explained below. When the temperature is low, the thermo-sensitive magnetic material 38 passes magnetic flux equally with the stator 10. Therefore, regarding magnetic flux from the rotor 13, a magnetic flux loop that passes through the pole piece 11-1, the stator member 10a, the thermo-sensitive magnetic material 38, the stator member 10b and the pole portion 11-4 is stronger than a magnetic flux loop that passes through the pole piece 11-2 and the stator member 10c, because the latter loop passes through the air gap 39. Consequently, the rotor 13 rotates in the valve-opening direction from the center line. On the other hand, when the temperature rises, the saturated magnetic flux density in the thermo-sensitive magnetic material 38 lowers. When the temperature reaches the Curie point of the thermo-sensitive magnetic material, the thermo-sensitive magnetic material becomes paramagnetic. In other words, the thermo-sensitive magnetic material portion 38 becomes equivalent to air in terms of permeability. Thus, the thermo-sensitive magnetic material portion 38 forms a large magnetic reluctance. In this case, the relationship between the width ℓ 2 of the air gap 39 and the width ℓ 1 of the thermo-sensitive magnetic material 38 is given by ℓ 1 >ℓ 2 . Accordingly, the magnetic flux passing through the pole pieces 11-1 and 11-4 decreases, and the balanced position moves toward the center line. However, since there is the air gap 39, the magnetic flux loop passing through the pole pieces 11-1 and 11-4 is stronger than the magnetic flux loop passing through the pole pieces 11-2 and 11-3. Therefore, the balanced position will not move beyond the center line in the valve-closing direction. Fig. 8 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 8 , portions which are identical or equivalent to those in Fig. 7 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, a magnetic source 37 is provided. The arrangement of the rest of this embodiment is the same as that shown in Fig. 7 . First, magnetic flux produced by the coil of the magnetic source 37 generates a loop that passes through the pole pieces 11-2 and 11-3 (acting on the rotor 13 in the valve-closing direction), and another loop that passes through the pole pieces 11-1 and 11-4 (acting on the rotor 13 in the valve-opening direction). However, when the temperature rises, the saturated magnetic flux density in the thermo-sensitive magnetic material 38 lowers, resulting in reduction of the magnetic flux produced by the coil. Consequently, the stroke of the rotor 13 induced by turning on/off the coil reduces, thus enabling the ISC to exhibit the required characteristics satisfactorily. Fig. 9 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 9 , a thermo-sensitive actuator body 1 has a pair of stator members 10a and 10b which are united to each other with a thermo-sensitive magnetic material 38 held therebetween. Further, the thermosensitive actuator body 1 is provided with a T-shaped space 40 in order to define the thermo-sensitive magnetic material portion 38 as a part of a magnetic path. A pair of pole pieces 11-10 and 11-40 have relatively wide opposing end surfaces. Another pair of pole pieces 11-20 and 11-30 have relatively narrow opposing end surfaces. A rotor 13 has a circular cross-sectional configuration, and rotates about a shaft 12 as a supporting point. As will be understood from the figure, the position of the rotor 13 is determined by the ratio of the area of the surfaces of the pole pieces 11-10 and 11-40 which face the rotor 13 to the area of the surfaces of the pole pieces 11-20 and 11-30 which face the rotor 13. In Fig. 9, the solid lines show magnetic paths formed when the temperature is low, and the dotted lines show magnetic paths formed when the temperature is high. Next, the operation will be explained. When the temperature is low, the thermo-sensitive magnetic material 38 passes magnetic flux equally with the stator 10. Accordingly, regarding the magnetic flux from the rotor 13, the magnetic flux loop that passes through the pole piece 11-10, the stator member 10a, the thermo-sensitive magnetic material 38, the stator member 10b and the pole piece 11-40 is stronger than the other loop. Accordingly, the magnetic flux passing through the pole pieces 11-10 and 11-40 balances with the magnetic flux passing through the pole pieces 11-20 and 11-30 at a position where the center line of the rotor 13 coincides with the mutual center line d of the pole pieces 11-10 and 11-40. When the temperature rises, the saturated magnetic flux density in the thermo-sensitive magnetic material lowers. When the temperature reaches the Curie point of the thermo-sensitive magnetic material, the thermo-sensitive magnetic material becomes paramagnetic. Consequently, the thermo-sensitive magnetic material portion 38 becomes equivalent to air in terms of permeability and hence reluctant to pass magnetic flux. At this time, the magnetic flux passing through the pole pieces 11-10 and 11-30 and the magnetic flux passing through the pole pieces 11-20 and 11-40 form symmetric loops and balance with each other (see the dotted lines in Fig. 9 ). Accordingly, the center line of the rotor 13 lies in the position c (i.e. the rotor 13 slightly rotates leftward). Fig. 10 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. Referring to Fig. 10, the thermo-sensitive actuator is provided with a magnetic source 37, and a thermo-sensitive magnetic material 38 is provided between a pair of stator members 10a and 10b. Reference numeral 40 denotes a space. The stator members 10a and 10b are connected together below the space 40 through connecting members 41 and 42. An opening 16 is provided between the stator members 10a and 10b. A rotor 13 which is attached to a shaft 12 is rotatably provided in the opening 16. A pair of relatively wide openings 16-1 are provided at both sides (left- and right-hand sides) of the rotor 13 so as to diagonally face each other across the rotor 13. Further, a pair of relatively narrow gaps 36 are provided at both sides of the rotor 13 so as to diagonally face each other across the rotor 13 at an angle to the mutual center line of the openings 16-1. Consequently, pole pieces 11-11 and 11-41 having a relatively wide area are defined at the gaps 36, and pole pieces 11-21 and 11-31 having a relatively narrow area are defined at the openings 16-1, as shown in the figure. Accordingly, magnetic flux produced by the coil of the magnetic source 37 generates a magnetic flux loop that passes through the pole pieces 11-21 and 11-31 (acting on the rotor 13 in the valve-closing direction), and a magnetic flux loop that passes through the pole pieces 11-11 and 11-41 (acting on the rotor 13 in the valve-opening direction). When the saturated magnetic flux density in the thermo-sensitive magnetic material 38 lowers at high temperature, both the magnetic flux passing through the pole pieces 11-21 and 11-31 and the magnetic flux passing through the pole pieces 11-11 and 11-41 decrease. Consequently, the stroke of the rotor 13 induced when the coil is excited reduces. Thus, the specifications required for the ISC are satisfied. The members 41 and 42 connecting the stator members 10a and 10b are necessary for fabrication and assembly purposes. It should be noted that the connecting members 41 and 42 have no effect on the magnetic circuit because the cross-sectional areas of the connecting members 41 and 42 are set at a sufficiently small value. Fig. 11 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 11, portions which are identical or equivalent to those shown in Fig. 9 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, a thermo-sensitive magnetic material 38a is disposed between stator members 10a and 10c constituting a stator 10, and another thermo-sensitive magnetic material 38b is disposed between stator members 10b and 10c constituting the stator 10. The position of the rotor 13 is determined by the ratio of the area of the surfaces of the pole pieces 11-10 and 11-40 which face the rotor 13 to the area of the surfaces of the pole pieces 11-20 and 11-30 which face the rotor 13. In operation, when the temperature is low, the thermo-sensitive magnetic materials 38a and 38b pass magnetic flux equally with the stator 10. Therefore, regarding magnetic flux from the rotor 13, the magnetic flux loop that passes through the pole piece 11-10, the stator member 10a, the thermo-sensitive magnetic material 38a, the stator member 10c, the thermo-sensitive magnetic material 38b, the stator member 10b and the pole piece 11-40 is stronger than the other loop. Accordingly, the magnetic flux passing through the pole pieces 11-10 and 11-40 balances with the magnetic flux passing through the pole pieces 11-20 and 11-30 at a position where the center line of the rotor 13 coincides with the mutual center line d of the pole pieces 11-10 and 11-40. When the temperature rises, the saturated magnetic flux density in the thermo-sensitive magnetic material lowers. When the temperature reaches the Curie point of the thermo-sensitive magnetic material, the thermo-sensitive magnetic material becomes paramagnetic. Consequently, the thermo-sensitive magnetic material portions 38a and 38b become equivalent to air in terms of permeability and hence reluctant to pass magnetic flux. Therefore, the magnetic flux passing through the pole pieces 11-10 and 11-30 and the magnetic flux passing through the pole pieces 11-20 and 11-40 form symmetric loops and balance with each other. Accordingly, the center line of the rotor 13 lies in the position c. The rotational characteristics of the rotor 13 can be precisely obtained by properly selecting the Curie temperature, thickness and cross-sectional area of each thermo-sensitive magnetic material. The rotor 13 can be controlled by the magnetic source 37. Fig. 12 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 27, a stator member 10a has a pair of pole pieces 11-1 and 11-4. In the center of the stator member 10a, a gap 36a is provided between the stator member 10a and a stator member 10c, and another gap 36b is provided between the stator member 10a and a stator member 10b. That is, the stator comprises three stator members 10a, 10b and 10c. A thermo-sensitive magnetic material 38a is held between the stator members 10a and 10b, thereby being integrated with the stator. Similarly, a thermo-sensitive magnetic material 38b is held between the stator members 10a and 10c, thereby being integrated with the stator. A magnetic source 37 is connected to an upper magnetic path provided at a position which faces the rotor portion across a space 40. In the thermo-sensitive actuator of this embodiment, when the temperature is low, the thermo-sensitive magnetic materials 38a and 38b have a relatively high permeability and hence pass magnetic flux easily. Accordingly, the magnetic flux passing through the pole pieces 11-1 and 11-3 and the magnetic flux passing through the pole pieces 11-2 and 11-4 are equal to each other. However, when the temperature rises, the permeability of the thermo-sensitive magnetic materials 38a and 38b decreases. Accordingly, the rotor 13 rotates rightward to move in the valve-closing direction. It should be noted that the addition of the magnetic source 37 makes the operation even more reliable. Fig. 13 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 13 , portions which are identical or equivalent to those shown in Fig. 12 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, the thermo-sensitive actuator is arranged so that the rotor 13 lies in the center at all times. More specifically, there is a magnetic reluctance at the joint between each thermo-sensitive magnetic material and a stator member because of a junction gap produced at the joint. Accordingly, when the temperature is low, the rotor 13 is likely to rotate in the valve-opening direction slightly beyond the center position. To compensate for the excess of rotation in the valve-opening position, a magnetic reluctance portion (referred to as "compensating portion") 42 is provided so as to cancel the magnetic reluctance of the junction gap. In this embodiment, a circular hole is provided in the magnetic path so that a desired amount of compensation is obtained by adjusting the diameter of the hole. Fig. 14 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig.14 , portions which are identical or equivalent to those shown in Fig. 13 are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, an air gap 39 is provided in the magnetic path as a compensating portion. In this embodiment, a desired amount of compensation is obtained by adjusting the gap length. Fig. 15 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig.15 , portions which are identical or equivalent to those shown in Fig. 14 are denoted by the same reference numerals, and description thereof is omitted. Since the junction gap is very small, the air gap 39 for compensating for the junction gap must also be small. It is difficult to form such a small air gap 39 by machining, and size variations also occur. Accordingly, predetermined gaps 43-1 and 43-2 are previously provided at respective positions of the stator members 10a-1 and 10c which face the thermo-sensitive magnetic materials 38a and 38b, thereby facilitating machining of gaps for compensation, and thus minimizing the effect of the junction gap. Fig. 16 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 16, a thermo-sensitive actuator body 1 comprises a magnetic path 10, pole pieces 44-1 and 44-2, a thermo-sensitive magnetic material 45-1 interposed between the pole piece 44-1 and the magnetic path 10, and another thermo-sensitive magnetic material 45-2 interposed between the pole piece 44-2 and the magnetic path 10. In addition, a main air gap 5 is provided between the pole pieces 44-1 and 44-2, and a rotor 13 which is formed from a permanent magnet is disposed in the main air gap 5. The rotor 13 is rotatable through a shaft 12. Subsidiary air gaps 36a and 36b are provided at both sides of the main air gap 5. Reference numeral 46 denotes an electromagnetic coil (magnetic source). It should be noted that the thermo-sensitive magnetic materials 45-1 and 45-2 show changes in permeability according to temperature. In this case, a thermo ferrite which passes magnetic flux easily when the temperature is low, and which becomes paramagnetic when the temperature rises to the Curie point of the material, or magnetic shunt material of Japanese Patent Publication No.49-19560 is used as the thermo-sensitive magnetic materials 45-1 and 45-2. Although in this embodiment two thermo-sensitive magnetic materials 45-1 and 45-2 are provided, it should be noted that either of them may be omitted. Next, the operation of this embodiment will be explained. First, when the electromagnetic coil 46 is not energized, the rotor 13 remains stationary at the illustrated position. The reason for this is as follows: Magnetic flux from the north pole of the rotor 13 returns to the south pole through the main air gap 5 and the pole pieces 44-1 and 44-2. At this time, there is no magnetic flux in the subsidiary air gaps 36a and 36b. That is, this state is the most stable in terms of magnetism. Next, when the electromagnetic coil 46 is energized, magnetic flux from the magnetic source passes through a path comprising the magnetic path 10, the thermo-sensitive magnetic material 45-1, the pole piece 44-1, the subsidiary air gap 36a or 36b, the pole piece 44-2, the thermo-sensitive magnetic material 45-2 and the magnetic path 10. Accordingly, the rotor 13 rotates in a direction in which the magnetic energy in the subsidiary air gaps 36a and 36b is canceled, and comes to rest at a position where the magnetic energy in the subsidiary air gaps 36a and 36b is zero, that is, where magnetic flux passing through the subsidiary air gaps 36a and 36b is zero. Accordingly, if this actuator is placed in an engine room of an automobile, when the temperature rises in accordance with the warming-up condition of the engine, the thermo-sensitive magnetic materials 45-1 and 45-2 become reluctant to pass magnetic flux. In a heater, the magnetic reluctance changes according to the environmental temperature. This means that the effect of the electromagnetic force produced by the electromagnetic coil 46 on the permanent magnet constituting the rotor 13 reduces. Accordingly, even if the value of current flowing through the electromagnetic coil 46 is kept constant, as the temperature rises, the rotor 13 moves toward the position assumed by the rotor 13 when the coil 46 is not energized. The amount of movement of the rotor 13 is determined by the thickness t and cross-sectional area ℓ of each of the thermo-sensitive magnetic materials 45-1 and 45-2. According to this embodiment, when the electromagnetic coil 46 is not energized, the rotor 13 remains stationary at a position where it is in the most stable state, that is, the rotor 13 is at rest in a position where the north and south poles of the rotor 13 faces toward the subsidiary air gaps 36b and 36a, as shown in Fig. 16, irrespective of the temperature. Even when the temperature rises, the rotor 13 is allowed to come to rest in the above-described stable position by the action of the thermo-sensitive magnetic materials 45-1 and 45-2. This means that the rotor 13 is placed in a normally closed state. As will be understood from the foregoing description, the stable state of the rotor 13 is a state where no magnetic flux flows through either of the subsidiary air gaps 36a and 36b. In designing of this type of magnetic circuit, generally, the flow of magnetism is calculated by a finite element analysis program running on a computer, and a torque induced in the rotor is further calculated. In addition, a state where the induced torque is zero is arithmetically obtained, thereby grasping the characteristics of the actuator. In this regard, calculation of a torque would require a high-performance computer. However, the above-described embodiment enables the characteristics of the actuator to be grasped on the basis only of calculation of the flow of magnetism in the stable position of the rotor. A relatively accurate result can be obtained for the calculation of the flow of magnetism even with a small-scale computer. Consequently, it is possible to shorten development time and improve design quality. Fig. 17 shows the configuration of a model for analyzing the magnetic field in a motor by the finite element method. It should be noted that the configuration shown in Fig. 17 is chosen because the analytic model uses polar coordinates. In Fig.17, portions which correspond to the constituent elements shown in Fig.16 are denoted by the same reference numerals. Fig. 18 shows the result of an analysis made by using the model shown in Fig.17. In this case, the electromagnetic coil 46 is in an energized state. As shown in Fig. 18, flows of magnetic flux from the pole piece 44-2 to the pole piece 44-1 through the subsidiary air gaps 36a and 36b are observed, and it will be understood that a torque is induced in the rotor 13, causing the rotor 13 to rotate in the direction of the arrows. Fig. 19 shows the state where the rotor 13 is at rest in the most stable position. When the rotor 13 rotates from the position shown in Fig. 18, the magnetic flux passing through the subsidiary air gaps 36a and 36b becomes zero when a predetermined position is reached. At this position, torque induced in the rotor 13 is zero, and this is the position where the rotor 13 comes to rest. Fig. 19 verifies that the rotor 13 is in a stationary position. Thus, it will be understood that a stationary position of the rotor 13 can be obtained simply by observing magnetic flux in the subsidiary air gaps 36a and 36b without the need of calculating torque induced in the rotor 13. It should be noted that Fig. 18 shows the flow of magnetic flux in a state where the rotor 13 is apt to rotate, and Fig. 19 shows the flow of magnetic flux in a stable (stationary) state of the rotor 13. Fig. 20 shows the arrangement of a still further embodiment of thermo-sensitive actuator according to the present invention. In Fig. 20 , portions which have the same functions as those shown in Fig. 16 are denoted by the same reference numerals. In this embodiment, the actuator is arranged in a direct acting form as a whole. Accordingly, a subsidiary air gap 36 is provided between pole pieces 44-1 and 44-2, and a thermo-sensitive magnetic material 45 is interposed between a magnetic path 10-1, which is provided with an electromagnetic coil 46, and the pole piece 44-1. Reference numeral 47 denotes a moving member. Next, the operation will be explained. First, when no electric current is flowing through the electromagnetic coil 46, a magnetic path is formed from the north pole of the moving member 47 to the south pole thereof through the pole piece 44-1. At this time, no magnetic flux flows through the subsidiary air gap 36. Thus, the actuator is in a stable state in the same way as in the case of Fig. 16. Accordingly, the moving member 47 is at rest in the illustrated position. To cause the moving member 47 to move in the direction of the arrow, an electric current is passed through the electromagnetic coil 46. Consequently, the moving member 47 moves and comes to rest at a predetermined position. The movement of the moving member 47 will be explained below with reference to Fig. 21. Let us consider a case where the moving member 47 has been moved to the illustrated position by external force with no current passed through the electromagnetic coil 46. In this state, magnetic flux passes through the pole piece 44-2 and via the subsidiary air gap 36 and the thermo-sensitive magnetic material 45, as illustrated in the figure. At this time, energy stored in the subsidiary air gap 36 acts as reaction force in a direction in which the energy is reduced, that is, as force that causes the moving member 47 to return to the left. When a predetermined current is passed through the electromagnetic coil 46, as shown in Fig. 22, all the magnetic flux passing through the subsidiary air gap 36 flows through the thermo-sensitive magnetic material 45. As a result, magnetic energy in the subsidiary air gap 36 becomes zero, and thus a stable state is established. In the foregoing, how reaction force is produced and then made zero to stop the moving member 47 by energizing the coil 46 has been described with reference to Figs. 20 , 21 and 22 . It should, however, be noted that the electromagnetic coil 46 must be energized to move the moving member 47, as a matter of course. Further, as the temperature rises, the thermo-sensitive magnetic material 45 becomes reluctant to pass magnetic flux, as has already been described. When the temperature reaches a predetermined Curie point, the effect of the electromagnetic coil 46 reduces, and the amount of movement decreases. When the electromagnetic coil 46 is not energized, the fully-closed position of the valve is held in a stable state. As has been described above, this embodiment not only enables the rotor to assume a position for closing the valve irrespective of the temperature when the coil is not energized, but also makes it possible to analyze the characteristics of the actuator simply by calculating the flow of magnetism. Accordingly, it is possible to shorten the development time and facilitate the design of the actuator. We shall now explain with reference to Figures 23 to 25 how actuators in accordance with the present invention as described in foregoing embodiments may be used in practical devices. Figs. 23 and 24 show one way in which an embodiment of thermo-sensitive actuator of the present invention may be actually used. In this case, the thermo-sensitive actuator is used as a drive source for a choke valve. In the side elevational view of Fig. 23, a choke valve 28 is driven by a thermo-sensitive actuator 29. More specifically, the thermo-sensitive actuator 29 drives a rack 30 so as to rotate the choke valve 28 through a pinion 31, as shown in the front view of Fig. 24. Since the thermo-sensitive actuator 29 rotates as far as the position where the torque balances with a torque generated owing to the eccentricity of the valve 28, the pinion 31 and the valve 28 can be directly connected to each other. If the thermo-sensitive actuator 29 is arranged so that it can be electromagnetically driven, positive air-fuel ratio control can be effected. Fig. 25 shows how an embodiment of thermo-sensitive actuator in accordance in the present invention may be applied to an idle speed controller (ISC) of an automobile. Shaft 12 on which the rotor of the thermo-sensitive actuator is mounted has a control valve 33 secured thereto so as to rotate together with the shaft 12. Fig. 25 is a sectional view showing the inside of the body of the ISC. Air taken in flows through a bypass passage, which is separate from the main air passage. The control valve 33 controls the quantity of air flowing through the bypass passage. Since the idle speed controller arrangement per se is known, description thereof is omitted. The control valve is rotated by using a thermo-sensitive actuator according to the present invention. Therefore, it is possible to realize idle speed control according to temperature without the need for a separate temperature detector.

Claims: A thermo-sensitive actuator having a stator (10) made of a magnetic material to form a yoke, a rotor (13) which is a permanent magnet rotatably provided in an opening provided in said stator, and pole pieces (11-1, 11-2, 11-3, 11-4) for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a thermo-sensitive magnetic material which is provided in a part of each of rotor-side end surfaces of at least one pair of pole pieces (11-1, 11-4) which face each other across said rotor. A thermo-sensitive actuator according to Claim 1, further comprising: a gap provided by cutting a magnetic path of said stator; and a magnetic source provided in said magnetic path. A thermo-sensitive actuator having stator members (10a, 10b and 10c) made of a magnetic material to constitute a stator, which forms a yoke divided into three, a rotor (13) which is a permanent magnet rotatably provided in an opening provided in said stator, and pole pieces (11-1, 11-2, 11-3, 11-4) for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a thermo-sensitive magnetic material provided between said stator members (10a and 10b); and an air gap (39) provided between said stator members (10b and 10c). A thermo-sensitive actuator according to Claim 3, further comprising: a magnetic source provided in a magnetic path. A thermo-sensitive actuator according to Claim 3, wherein said thermo-sensitive magnetic material is provided between two of the pole pieces (11-4 and 11-3). A thermo-sensitive actuator according to claim 5, further comprising: a magnetic source provided in a magnetic path between said pole pieces (11-4 and 11-3). A thermo-sensitive actuator having stator members (10a and 10b) made of a magnetic material to constitute a stator, which forms a yoke divided into two, a rotor (13) which is a permanent magnet rotatably provided in an opening provided in said stator, and pole pieces (11-10, 11-20, 11-30, 11-40) for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a magnetic path formed by connecting said stator members (10a and 10b) with a space therebetween; and a thermo-sensitive magnetic material (38) interposed in said magnetic path; and said pole pieces being formed so that the ratio of the area of surfaces of two pole pieces (11-10 and 11-40) which face said rotor, and being associated with each yoke, to the area of surfaces of further pole pieces (11-20 and 11-30) which face said rotor and being associated with each yoke is a predetermined value. A thermo-sensitive actuator according to Claim 7, further comprising a magnetic source, preferably an electromagnetic coil provided on the stator. A thermo-sensitive actuator having stator members (10a, 10b and 10c) made of magnetic material which together constitute a stator in the form of a yoke divided into three, a rotor (13) which is a permanent magnet rotatably providing in an opening provided in said stator, and pole pieces (11-1, 11-2, 11-4 and 11-3) for magnetically connecting said stator and rotor, said thermo-sensitive actuator comprising: a first thermo-sensitive magnetic material (38a) positioned between a first and a second of said stator members (10a and 10b); a second thermo-sensitive magnetic material (38b) positioned between said second and a third of said stator members (10a and 10c) ; and said first stator member (10a) being integrally connected with a pair of said pole pieces (11-1 and 11-4). A thermo-sensitive actuator according to Claim 9, further comprising a magnetic source provided in a magnetic path of said first stator member (10a). A thermo-sensitive actuator according Claim 9, further comprising a compensating portion for obtaining magnetic balance, said compensating portion being provided in a magnetic path of said first stator member (10a). A thermo-sensitive actuator according to Claim 11, wherein said compensating portion is an air gap. A thermo-sensitive actuator according to Claim 11 or 12, further comprising a predetermined air gap provided between each of said thermo-sensitive magnetic materials and one of the two stator members between which said thermo-sensitive magnetic material is positioned. A thermo-sensitive actuator comprising: two pole pieces (44-1 and 44-2) which face each other across at least one subsidiary air gap (36a or 36b) to form a main air gap (5); a magnetic path (10) for magnetically connecting said two pole pieces; at least one thermo-sensitive magnetic material (45-1 or (45-2) which shows a change in magnetic characteristics according to temperature, said thermo-sensitive magnetic material, together with at least one magnetic source (46), being provided in said magnetic path; and a rotor (13) which is a permanent magnet movable together with a driving shaft (12) as one unit, said rotor being disposed in said main air gap. A thermo-sensitive actuator comprising: two pole pieces (44-1 and 44-2) which face each other across one subsidiary air gap (36); a thermo-sensitive magnetic material (45) interposed between the other ends of said pole pieces, thereby forming a rectangularly bent magnetic path (10-1); a moving member (47) which is a permanent magnet disposed in a linear space surrounded by said bent magnetic path; and at least one magnetic source (46) provided in said magnetic path. A thermo-sensitive actuator according to Claims 14 or 15, wherein said magnetic source is an electromagnet.

Inventors: MURAJI TETSUO, MURAJI, TETSUO, Muraji, Tetsuo, c/o Mikuni Corporation
Applicants: MIKUNI KOGYO KK, MIKUNI CORPORATION
Application year: 1995
Main classification: H02K26
IPC codes: H02N10, H02K26, H02K41, F02M3, H01F7