Patent Publication Number: US-10781932-B2

Title: Valve drive device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-104956, filed on May 31, 2018, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     At least an embodiment of the present invention relates to a valve drive device for driving a valve that regulates a fluid flow rate. 
     BACKGROUND 
     Conventionally, there is a refrigerant valve device that supplies a refrigerant to cool the inside of a refrigerator or the like. Some of such refrigerant valve devices include a valve drive device for driving a valve to adjust the supply amount of the refrigerant that is supplied to the inside of the refrigerator (Japanese Patent No. 5615993). 
     The refrigerant valve device described in Japanese Patent No. 5615993 includes: on a base provided with a refrigerant inlet, a refrigerant outlet, and a valve seat surface, a valve element that is rotatable about a position close to either the refrigerant inlet or the refrigerant outlet; and a valve element drive mechanism for rotating the valve element. The valve element drive mechanism includes a stepping motor (hereinafter referred to as a motor), a pinion that rotates integrally with the drive shaft of the motor, and an output gear that meshes with the pinion and rotates integrally with the valve element. 
     When the motor rotates, the valve element as well as the output gear rotates through the pinion rotating integrally with the motor. Thus, the valve element can adjust the degree of the opening of either the refrigerant inlet or the refrigerant outlet, and can regulate the supply amount of the refrigerant. 
     In this valve element drive mechanism, by rotating the pinion in a forward rotation direction, the output gear and the valve element can be rotated from a first rotation-restricted position to a second rotation-restricted position that is a position obtained by rotating the motor in the forward rotation direction. 
     Here, when the motor is rotated in the reverse rotation direction to rotate the motor from the second rotation-restricted position to the first rotation-restricted position to adjust the supply amount of the refrigerant, the arm unit of the output gear abuts on the abutted unit of the pinion, and the rotation of the pinion in the reverse rotation direction is restricted. As a result, the motor tries to continue the rotation in the reverse rotation direction in a state where the rotation of the pinion in the reverse rotation direction is restricted, and thus, a step-out occurs in the motor. As a result, during the step-out of the motor, the arm unit and the abutted unit may collide with each other and thus generate noise (collision noise). 
     It is discussed that a configuration for the valve element drive mechanism is achieved to prevent the step-out of the motor and to suppress the generation of the noise, for example, by cutting off the transmission of power from the pinion to the output gear at the first rotation-restricted position. 
     Incidentally, if the valve element drive mechanism is configured to cut off the transmission of power from the pinion to the output gear at the first rotation-restricted position, it is desirable that the configuration enables power transmission with the pinion meshing with the output gear to rotate the output gear from the first rotation-restricted position to the second rotation-restricted position. That is, it is desirable to provide a power switching means in the valve element drive mechanism. For example, it is discussed that such a power switching means includes a clutch mechanism or the like, for example, so that when the pinion is rotated in the reverse rotation direction at the first rotation-restricted position, the pinion and the output gear do not mesh with each other; when the pinion is rotated in the forward rotation direction, the pinion and the output gear mesh with each other. 
     If the power switching means includes the clutch mechanism or the like, exciting the motor to switch from a power non-transmission state to a power transmission state at the first rotation-restricted position may cause a shift of the pinion from an optimal phase of meshing in which the teeth of the pinion and the output gear are fit with each other. In this case, it is necessary to rotate the pinion until the pinion reaches the optimum phase of meshing, which results in a time lag until power switching occurs in the power transmission switching means. As a result, in the valve element drive mechanism, the responsiveness at the time of power transmission switching will be reduced. 
     At least an embodiment of the present invention has been made in view of the above consideration, and an object of at least an embodiment of the present invention is to provide a valve drive device capable of improving the responsiveness of power switching at the time of power switching. 
     SUMMARY 
     According to one aspect of the present disclosure, there is provided a valve drive device comprising: a base including a fluid inlet, a fluid outlet, and a valve seat surface, at least one of the fluid inlet and the fluid outlet being opened at the valve seat surface; a cover configured to define a valve chamber such that the fluid inlet and the fluid outlet communicate with each other between the valve seat surface and the cover; a valve element provided at any one of the fluid inlet and the fluid outlet in the valve chamber, configured to open and close the any one of the fluid inlet and the fluid outlet, and having a contact surface sliding on the valve seat surface; and a valve element driver configured to drive and rotate the valve element, wherein the valve element driver includes: a motor including a stator having at least one core member with a plurality of pole teeth and a drive coil, and a rotor provided with a drive magnet; a drive gear configured to rotate together with the rotor; a driven gear configured to rotate the valve element by rotating the drive gear, in a state of meshing with the drive gear; and a power transmission switching unit configured to switch between a power transmission state where the drive gear and the driven gear mesh with each other and a power non-transmission state where a meshing state between the drive gear and the driven gear is released, the power transmission switching unit includes: a plurality of convex units formed on the drive gear and protruding toward a radial direction of the drive gear; and a rotation restriction unit provided on the driven gear and configured to engage with each of the convex units to perform switching from the power non-transmission state to the power transmission state, wherein the convex units are provided on the drive gear according to an N pole or an S pole of the drive magnet, and wherein when the stator is excited with an initial excitation pattern in the power non-transmission state, at least one magnetic pole of the drive magnet is located at a position according to the initial excitation pattern, one of the convex units is located at a position corresponding to the rotation restriction unit, and the drive gear and the driven gear do not mesh with each other. 
     In this aspect, “one of the convex units is located at a position corresponding to the rotation restriction unit” means that one of the convex units is located at a position immediately before being engaged with the rotation restriction unit. Specifically, it means a position such that when an excitation pattern of the stator is switched from the initial excitation pattern to another excitation pattern to rotate the rotor in a state where one of the convex units is located at a position according to the initial excitation pattern, one of the convex units is engaged with the rotation restriction unit to cause the drive gear and the driven gear to mesh with each other within several patterns from the initial excitation pattern and the shift to a state of transmitting the power from the drive gear to the driven gear is thus allowed. 
     According to this aspect, the power transmission switching unit includes a plurality of convex units that are formed on the drive gear and protrude toward a radial direction of the drive gear, and a rotation restriction unit that is provided on the driven gear and is engaged with each of the convex units to perform switching from the power non-transmission state to the power transmission state, and the convex units are provided on the drive gear according to the N pole or S pole of the drive magnet, and when the stator is excited with an initial excitation pattern in the power non-transmission state, a magnetic pole of the drive magnet is located at a position according to the initial excitation pattern, one of the convex units is located at a position corresponding to the rotation regulating unit, and the drive gear and the driven gear do not mesh with each other, and thus, one of the convex units can be located at the position corresponding to the rotation regulating unit when the stator of the motor is excited with the initial excitation pattern. Accordingly, when the rotor is rotated, the convex units and the rotation restriction unit can be engaged with each other, thereby making it possible to perform switching from the power non-transmission state to the power transmission state. Therefore, the responsiveness of power switching at the time of power switching in the valve element drive mechanism can be improved. 
     In the valve drive device according to at least an embodiment of the present invention, the number of the at least one magnetic pole of the drive magnet is half of the number of pole teeth provided on the at least one core member. According to this aspect, the above-described operation and effect can be obtained. 
     In the valve drive device according to at least an embodiment of the present invention, the at least one core member includes four core members, and the stator is formed by laminating the four core members, and if the number of the at least one magnetic pole of the drive magnet is eight, each core member has four pole teeth. 
     According to this aspect, the stator is formed by laminating four core members, and if the number of magnetic poles of the drive magnet is eight, each core member has four pole teeth, and thus, the number of magnetic poles of the drive magnet is twice the number of pole teeth of the core member. As a result, when a predetermined core member is excited, a magnetic pole of the drive magnet located at a position facing a pole tooth (for example, the N pole) at a position corresponding to power switching is one of the four magnetic poles (for example, the S poles) each having a pole opposite to the pole of the pole tooth. That is, for the excited core member, the drive magnet has one of four position patterns, which makes it easy to position the rotor with respect to the stator. 
     In the valve drive device according to at least an embodiment of the present invention, the driven gear includes a meshing unit in which teeth are formed along a circumferential direction of the driven gear, and a non-meshing unit in which no teeth are formed in the circumferential direction. 
     According to this aspect, the above-described operation and effect can be obtained. 
     In the valve drive device according to at least an embodiment of the present invention, the meshing unit is continuously formed along the circumferential direction, and when switching from the power transmission state to the power non-transmission state is performed, meshing of the drive gear and the driven gear is released. 
     According to this aspect, the meshing unit is continuously formed along the circumferential direction, and when switching from the power transmission state to the power non-transmission state is performed, meshing of the drive gear and the driven gear is released, and thus, the drive gear is located at the non-meshing unit in which no teeth are formed in the power non-transmission state and the drive gear does not contact the driven gear even when the drive gear as well as the motor continue to rotate. Therefore, the collision between the drive gear and the driven gear can be prevented and the generation of a collision noise can be prevented. 
     In the valve drive device according to at least an embodiment of the present invention, the rotation restriction unit is a lever member that is pivotably attached to the non-meshing unit of the driven gear with respect to the driven gear and urged outward in a radial direction of the driven gear and includes a first contact unit configured to contact each of the convex units when the drive gear is rotated in a first direction and a second contact unit configured to contact each of the convex units when the drive gear is rotated in a second direction that is an opposite direction to the first direction, wherein when a convex unit among the plurality of convex units contacts the first contact unit, the rotation restriction unit is pressed by the convex unit to rotate the driven gear, teeth of the drive gear and teeth of the driven gear mesh with each other, and the power transmission state is obtained, and wherein when a convex unit among the plurality of convex units contacts the second contact unit, the rotation restriction unit pivots inward in the radial direction against an urging force urging the rotation restriction unit, the drive gear rotates idly without the teeth of the drive gear meshing with the teeth of the driven gear to maintain the power non-transmission state. 
     According to this aspect, the rotation restriction unit configured as the lever member includes the first contact unit and the second contact unit; when each of the convex units contacts the first contact unit, the rotation restriction unit is pressed by the convex unit to rotate the driven gear, teeth of the drive gear and teeth of the driven gear mesh with each other, and the power transmission state is obtained; and when each of the convex units contacts the second contact unit, the rotation restriction unit pivots inward in the radial direction against an urging force urging the rotation restriction unit, the drive gear rotates idly without the teeth of the drive gear meshing with the teeth of the driven gear to maintain the power non-transmission state, and thus, power can be transmitted or disconnected from the motor to the driven gear solely by switching a portion to be contacted by the convex units according to a rotation direction of the drive gear. Therefore, the rotation restriction unit can be configured in a simple manner. 
     The valve drive device according to at least an embodiment of the present invention includes an urging member configured to urge the rotation restriction unit outward in the radial direction of the driven gear. According to this aspect, the above-described operation and effect can be obtained. 
     In the valve drive device according to at least an embodiment of the present invention, the urging member is a torsion spring held by a shaft of the driven gear, the driven gear is provided with a holding unit configured to hold one end of the torsion spring, and the other end of the torsion spring urges the rotation restriction unit. 
     According to this aspect, the urging member is a torsion spring held by a shaft of the driven gear, the driven gear is provided with a holding unit configured to hold one end of the torsion spring, the other end of the torsion spring urges the rotation restriction unit, and thus, the holding configuration of the urging member in the driven gear can be simplified. 
     In the valve drive device according to at least an embodiment of the present invention, the drive gear is provided with a lock avoidance tooth at a position corresponding to the convex unit in the circumferential direction, and an addendum circle diameter of the lock avoidance tooth is smaller than an addendum circle diameter of a tooth other than the lock avoidance tooth. 
     Here, for example, the drive gear and the driven gear may be a locked state where the tips of the respective teeth contact each other due to their phase relationship so that they do not mesh. According to this aspect, the drive gear is provided with lock avoidance teeth at positions corresponding to the convex units in the circumferential direction, the addendum circle diameter of the lock avoidance teeth is smaller than the addendum circle diameter of teeth other than the lock avoidance teeth, and thus, by locating the lock avoidance tooth at the position of the tooth of the drive gear in a phase that causes the locked state of the tooth of the drive gear and the tooth of the driven gear, the locked state can be suppressed from occurring, the drive gear and the driven gear can mesh smoothly with each other, and the occurrence of abnormal operation (displacement of designated step position) and operation failure can be suppressed. 
     According to at least an embodiment of the present invention, when the stator of the motor is excited with the initial excitation pattern, one of the convex units can be located at a position corresponding to the rotation restriction unit. Accordingly, when the rotor is rotated, the convex units and the rotation restriction unit can be engaged with each other, thereby making it possible to perform switching from the power non-transmission state to the power transmission state. Therefore, the responsiveness of power switching at the time of power switching in the valve element drive mechanism can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures. 
         FIG. 1  is a perspective view of a valve drive device according to the present embodiment; 
         FIG. 2  is a side sectional view of the valve drive device according to the present embodiment; 
         FIG. 3  is a perspective view of a drive coil in the valve drive device; 
         FIG. 4  is an exploded perspective view of a core member that constitutes the drive coil; 
         FIG. 5  is a perspective view of a cover defining a valve chamber in the valve drive device; 
         FIG. 6  is a perspective view of a valve element drive mechanism in the valve drive device; 
         FIG. 7  is a perspective view of the valve element drive mechanism in the valve drive device; 
         FIG. 8  is a perspective view of an output gear; 
         FIG. 9  is a plan view of an output gear; 
         FIG. 10  is an exploded perspective view of a driven portion in the valve element drive mechanism; 
         FIG. 11  is a perspective view of a driven gear; 
         FIG. 12  is a perspective view of a rotation restriction unit; 
         FIG. 13  is a perspective view of a valve element as viewed from the side opposite to a valve seat surface; 
         FIG. 14  is a perspective view of the valve element as viewed from the seat surface side; 
         FIG. 15  illustrates diagrams of opened and closed states of a first valve and a second valve in each step; 
         FIG. 16  illustrates diagrams of phase states of the output gear and the driven gear and states of the valve element; 
         FIG. 17  illustrates diagrams of phase states of the output gear and the driven gear and states of the valve element; 
         FIG. 18  illustrates diagrams of a phase state of the output gear and the driven gear and a state of the valve element; 
         FIG. 19  illustrates diagrams of excitation states of a motor and states of the valve element drive mechanism in an origin returning operation; 
         FIG. 20  illustrates diagrams of excitation states of the motor and states of the valve element drive mechanism in the origin returning operation; 
         FIG. 21  illustrates diagrams of excitation states of the motor and states of the valve element drive mechanism in the origin returning operation; 
         FIG. 22  illustrates diagrams of excitation states of the motor and states of the valve element drive mechanism at the time of driving the valve element; 
         FIG. 23  illustrates diagrams of excitation states of the motor and states of the valve element drive mechanism at the time of driving the valve element; 
         FIG. 24  illustrates a diagram of a relationship between the output gear and the driven gear at an origin position; 
         FIG. 25  is a perspective view of the driven gear; 
         FIG. 26A  and  FIG. 26B  illustrate a diagram of a state where the co-rotation of the driven gear with respect to a drive gear is restricted by a second rotation restriction unit; 
         FIG. 27  illustrates a diagram of a relationship of the center position of a pivot shaft of the rotation restriction unit with respect to the driven gear; and 
         FIG. 28  is a perspective view illustrating another embodiment of the driven gear. 
     
    
    
     DETAILED DESCRIPTION 
     At least an embodiment of the present invention will be described with reference to the drawings, below. It is noted that the same elements in each embodiment are assigned with the same reference numerals and will be described in only the first embodiment, and description of the same elements in the subsequent embodiments will be omitted. 
       FIG. 1  is a perspective view of a valve drive device according to the present embodiment;  FIG. 2  is a side sectional view of the valve drive device according to the present embodiment;  FIG. 3  is a perspective view of a drive coil in the valve drive device;  FIG. 4  is an exploded perspective view of a core member that constitutes the drive coil; and  FIG. 5  is a perspective view of a cover defining a valve chamber in the valve drive device. 
       FIG. 6  and  FIG. 7  are perspective views of a valve element drive mechanism in the valve drive device;  FIG. 8  is a perspective view of an output gear;  FIG. 9  is a plan view of the output gear;  FIG. 10  is an exploded perspective view of a driven portion in the valve element drive mechanism;  FIG. 11  is a perspective view of a driven gear; and  FIG. 12  is a perspective view of a rotation restriction unit. 
       FIG. 13  is a perspective view of a valve element as viewed from the side opposite to a valve seat surface;  FIG. 14  is a perspective view of the valve element as viewed from the valve seat surface side;  FIG. 15  illustrates diagrams of opened and closed states of a first valve and a second valve in each step; and  FIG. 16 ,  FIG. 17 , and  FIG. 18  illustrate diagrams of phase states of the output gear and the driven gear and states of the valve element. 
       FIG. 19 ,  FIG. 20  and  FIG. 21  illustrate diagrams of excitation states of a motor and states of the valve element drive mechanism in an origin returning operation;  FIG. 22  and  FIG. 23  illustrate diagrams of excitation states of the motor and states of the valve element drive mechanism at the time of driving the valve element; and  FIG. 24  illustrates a diagram of a relationship between the output gear and the driven gear at an origin position. 
       FIG. 25  is a perspective view of the driven gear;  FIG. 26A  and  FIG. 26B  illustrate a diagram of a state where the co-rotation of the driven gear with respect to a drive gear is restricted by a second rotation restriction unit;  FIG. 27  illustrates a diagram of a relationship of the central position of a pivot shaft of the rotation restriction unit with respect to the driven gear; and  FIG. 28  is a perspective view illustrating another embodiment of the driven gear. 
     Embodiment 
     Overview of Valve Drive Device 
     A valve drive device  10  according to the present embodiment will be described with reference to  FIG. 1  to  FIG. 6 . The valve drive device  10  is mounted in a refrigerator as an example, and adjusts the supply amount of a refrigerant (fluid) for cooling inside the refrigerator. The valve drive device  10  includes a valve main body  12 , an inflow pipe  14  extending from the valve main body  12 , a first outflow pipe  16  and a second outflow pipe  18  which each extend parallel to the inflow pipe  14 , and a cover member  20  which covers an upper portion of the valve main body  12 . It is noted that in the following description, for convenience, the extending direction of the inflow pipe  14 , the first outflow pipe  16 , and the second outflow pipe  18  is defined as the up-down direction, the valve main body  12  is defined as the upper side, and the inflow pipe  14 , the first outflow pipe  16  and the second outflow pipe  18  are defined as the lower side. 
     In  FIG. 2 , the valve main body  12  includes a base member  22 , a motor  24 , a sealing cover  26  as a “cover”, a base main body  28 , and a valve element drive mechanism  30 . The base main body  28  has an upper surface  28   a . The inflow pipe  14 , the first outflow pipe  16 , and the second outflow pipe  18  are attached to the base main body  28 . A sealing cover  26  ( FIG. 5 ) is attached over the base main body  28 . The base main body  28  and the sealing cover  26  define a valve chamber  32 . 
     As illustrated in  FIG. 6 , a fluid inlet  28   b  is formed on the upper surface  28   a . The fluid inlet  28   b  is in communication with the inflow pipe  14  attached to the base main body  28 . A refrigerant (fluid) is supplied from the inflow pipe  14  into the valve chamber  32 . 
     On the other hand, a valve seat constitutional member  34  (see  FIG. 2 ,  FIG. 7 ,  FIG. 10 , and  FIG. 16  to  FIG. 18 ) is attached to the base main body  28 . The first outflow pipe  16  and the second outflow pipe  18  are attached to the valve seat constitutional member  34 ; a first fluid outlet  34   a  as a “fluid outlet” in communication with the first outflow pipe  16  and a second fluid outlet  34   b  as a “fluid outlet” in communication with the second outflow pipe  18  are provided in the valve seat constitutional member  34 . The fluid supplied from the inflow pipe  14  into the valve chamber  32  flows out from the first fluid outlet  34   a  to the first outflow pipe  16 , or from the second fluid outlet  34   b  to the second outflow pipe  18 . It is noted that in the present embodiment, the base main body  28  and the valve seat constitutional member  34  constitute a “base”. 
     As illustrated in  FIG. 2 , the motor  24  includes a stator  36  and a rotor  40  to which a drive magnet  38  is attached. The stator  36  is disposed to surround the rotor  40  with the sealing cover  26  interposed therebetween. 
     In the present embodiment, the stator  36  is provided with four core members  42  as illustrated in  FIG. 4 . On each of the core members  42 , four pole teeth  42   a  are formed. Therefore, in the present embodiment, the stator  36  has sixteen pole teeth  42   a . A winding is wound as a drive coil  37  on each of the core members  42  stacked in the stator  36 . One end of the drive coil  37  (winding) wound around the stator  36  is bound and connected to one end of a motor terminal  44  ( FIG. 3 ). The motor terminal  44  is electrically connected to a connector, a board, or the like (not illustrated) to supply power to the stator  36 . 
     As illustrated in  FIG. 2  and  FIG. 6 , the rotor  40  includes the drive magnet  38 , a drive gear  46 , and a spindle  48 . The drive gear  46  and the drive magnet  38  are rotatably attached to the spindle  48 . The drive magnet  38  is attached to the drive gear  46 . The upper end of the spindle  48  is supported by a bearing unit  26   a  formed in the sealing cover  26 , and the lower end of the spindle  48  is supported by a bearing unit  28   c  formed in the base main body  28 . In the present embodiment, the rotor  40  is configured to rotate within the valve chamber  32  about the spindle  48  as the rotation center by the drive magnet  38  when the stator  36  (drive coil  37 ) is excited. 
     Overview of Valve Element Drive Mechanism 
     A configuration of the valve element drive mechanism  30  will be described with reference to  FIG. 6  to  FIG. 14 . As illustrated in  FIG. 6  and  FIG. 7 , the valve element drive mechanism  30  includes the motor  24 , the drive gear  46 , a driven gear  50 , and a power transmission switching unit  52 . The power transmission switching unit  52 , which will be described later, is configured to switch between a power transmission state of transmitting power between the drive gear  46  and the driven gear  50  and a power non-transmission state of not transmitting the power. 
     As illustrated in  FIG. 8  and  FIG. 9 , a gear unit  46   a  is formed at a lower end of the drive gear  46 . A plurality of convex units  46   b  are formed above the gear unit  46   a . The tooth of the gear unit  46   a  corresponding to the convex unit  46   b  in the circumferential direction of the drive gear  46  is configured as a lock avoidance tooth  46   c.    
     The plurality of convex units  46   b  protrude from the main body  46   d  of the drive gear  46  outward in the radial direction of the drive gear  46 . In the present embodiment, the convex unit  46   b  is formed in a flat plate shape as an example. It is noted that the shape of the convex unit  46   b  is not limited to a flat plate shape, and may have any shape as long as the convex unit  46   b  can be engaged with the rotation restriction unit  62  described later. In the present embodiment, the plurality of convex units  46   b  are each formed at positions corresponding to the N pole or the S pole of the drive magnet  38  in the circumferential direction of the drive gear  46 . 
     In the present embodiment, the number of magnetic poles of the drive magnet  38  is, for example, eight (see  FIG. 19  to  FIG. 23 ). Therefore, in the present embodiment, the convex units  46   b  are provided at four positions in the drive gear  46 . Specifically, the convex units  46   b  are provided at equal intervals in the circumferential direction of the drive gear  46  in the drive gear  46 , and in the present embodiment, the convex units  46   b , which are formed at four positions, are provided at 90 degrees to each other. In the present embodiment, the convex unit  46   b  is formed to have a thickness corresponding to the tooth thickness of the tooth of the gear unit  46   a  of the drive gear  46 . 
     Referring to  FIG. 9 , in the present embodiment, the addendum circle diameter of the lock avoidance tooth  46   c  is set to d 1 . On the other hand, in the gear unit  46   a , the addendum circle diameter of teeth other than the lock avoidance tooth is set to d 2 . In the present embodiment, the addendum circle diameter d 1  is set to be smaller than the addendum circle diameter d 2 . The circle indicated by a dot chain line in  FIG. 9  illustrates the addendum circle diameter of the lock avoidance teeth  46   c , and the circle indicated by a two-dot chain line illustrates the addendum circle diameter of the teeth other than the lock avoidance tooth  46   c.    
     Then, a configuration of the driven gear  50  side that is driven to rotate with respect to the drive gear  46  will be described. As illustrated in  FIG. 2 , a spindle  54  is inserted at the radial center of the driven gear  50 . The driven gear  50  is configured to be rotatable about the spindle  54 . Below the driven gear  50 , a valve element  56  is provided. In the present embodiment, the valve element  56  is configured to be rotatable about the spindle  54  integrally with the driven gear  50 . Below the valve element  56 , the valve seat constitutional member  34  is provided. The upper surface of the valve seat constitutional member  34  is configured as a valve seat surface  34   c.    
     Further, a through hole  34   d  is formed at the center of the valve seat constitutional member  34 , and the spindle  54  is inserted thereinto. It is noted that in  FIG. 7 , the illustration of the spindle  54  is omitted. In  FIG. 7 , the arrow with reference numeral R 1  indicates a first direction which is one rotation direction of the drive gear  46 , and the arrow with reference numeral R 2  indicates a second direction which is the other rotation direction of the drive gear  46 . 
     A holding member  58  is attached to an upper portion of the driven gear  50 . The spindle  54  is passed through the holding member  58 . Further, the holding member  58  is configured as a cylindrical member having a flange unit  58   a  formed at the upper portion, and a torsion spring  60  as a “urging member” is passed through and held by a cylindrical unit  58   b . Further, the lever-shaped rotation restriction unit  62  is attached to the upper portion of the driven gear  50 . 
     Referring to  FIG. 7 ,  FIG. 10 ,  FIG. 11 , and  FIG. 25 , the driven gear  50  is formed with a meshing unit  50   a  in which a plurality of teeth are continuously formed along the circumferential direction on the outer peripheral portion and a non-meshing unit  50   b  in which no teeth are formed. Further, in the outer peripheral portion of the driven gear  50 , a first rotation restriction unit  50   c  configured to restrict the rotation of the driven gear  50  in the first direction R 1  is provided at an end of the meshing unit  50   a  on the second direction R 2  side; the non-meshing unit  50   b  is provided at an end of the meshing unit  50   a  on the first direction R 1  side. Furthermore, a second rotation restriction unit  50   k  as a “co-rotation prevention unit” is provided at an end of the non-meshing unit  50   b  on the first direction R 1  side. It is noted that in  FIG. 11 , the arrow with reference numeral R 1  indicates the driven rotation direction of the driven gear  50  when the drive gear  46  rotates in the first direction, and the arrow with reference numeral R 2  indicates the driven rotation direction of the driven gear  50  when the drive gear  46  rotates in the second direction. It is noted that the reference numeral for the second rotation restriction unit  50   k  is omitted in  FIG. 16  to  FIG. 23 . 
     It is noted that in the present embodiment, as illustrated mainly in step S 0  of  FIG. 16 , when the reference circle diameter of the drive gear  46  and the reference circle diameter of the driven gear  50  are compared, the reference circle diameter of the driven gear  50  is formed larger. In addition, the number of teeth of the gear unit  46   a  of the drive gear  46  is smaller than the number of teeth formed on the meshing unit  50   a  of the driven gear  50 . Therefore, in the power transmission state where the gear unit  46   a  of the drive gear  46  and the meshing unit  50   a  of the driven gear  50  mesh with each other to rotate, the rotation of the motor  24  can be transmitted to the driven gear  50  at reduced speed, a large torque can thus be obtained even with a small power source, and accordingly, the valve element  56  described later can be surely driven. 
     Further, as illustrated in  FIG. 11 , a through hole  50   d  into which the spindle  54  is inserted is provided at the center of the driven gear  50 . Furthermore, a concave unit  50   e  is formed around the through hole  50   d  on the upper surface of the driven gear  50  to receive a part of the holding member  58  and engage with the holding member  58 . The holding member  58  engaged with the concave unit  50   e  constitutes a shaft portion of the driven gear  50  as well as the spindle  54  and holds the torsion spring  60 . 
     In addition, an arc-shaped holding unit  50   f  is provided to surround the concave unit  50   e  on the upper surface of the driven gear  50 . As illustrated in  FIG. 7 , the holding unit  50   f  is configured to engage with one end  60   a  of the torsion spring  60  and hold the one end  60   a . Further, on the upper surface of the driven gear  50 , a through hole  50   g  and a lever rotation restriction unit  50   h  are provided. 
     Rotation Restriction Unit 
     Referring to  FIG. 12 , the rotation restriction unit  62  includes a pivot shaft  62   a  and a lever unit  62   b . On the lever unit  62   b , a first contact unit  62   c , a second contact unit  62   d , and a spring holding unit  62   e  are provided. The spring holding unit  62   e  includes a spring contact unit  62   f  and a spring detachment prevention unit  62   g.    
     As illustrated in  FIG. 7 , the rotation restriction unit  62  is pivotably attached to an upper portion of the driven gear  50 . Specifically, the pivot shaft  62   a  of the rotation restriction unit  62  is inserted into the through hole  50   g  ( FIG. 11 ) of the driven gear  50 . The rotation restriction unit  62  is configured to pivot the pivot shaft  62   a  with respect to the driven gear  50 . 
     The other end  60   b  of the torsion spring  60  contacts the spring contact unit  62   f  of the spring holding unit  62   e  of the lever unit  62   b  of the rotation restriction unit  62 , and is pressed by the other end  60   b  of the torsion spring  60 . In the spring holding unit  62   e , the spring detachment prevention unit  62   g  is provided on the opposite side of the spring contact unit  62   f  with interposing the other end  60   b  of the torsion spring  60 . When the other end  60   b  of the torsion spring  60  in contact with the spring contact unit  62   f  is separated from the spring contact unit  62   f  due to the rotation state of the rotation restriction unit  62 , the spring detachment prevention unit  62   g  prevents the other end  60   b  of the torsion spring  60  from being detached from the spring holding unit  62   e.    
     In the present embodiment, the rotation restriction unit  62  receives an urging force of the torsion spring  60  so that the second contact unit  62   d  of the lever unit  62   b  presses the lever rotation restriction unit  50   h  in contact with the lever rotation restriction unit  50   h  of the driven gear  50 . That is, the lever unit  62   b  of the rotation restriction unit  62  is urged outward in the radial direction of the driven gear  50  by the urging force of the torsion spring  60 , and the pivoting outward in the radial direction is restricted at the position where the second contact unit  62   d  contacts the lever rotation restriction unit  50   h.    
     On the other hand, when the second contact unit  62   d  is pressed inward in the radial direction of the driven gear  50  against the urging force of the torsion spring  60 , the rotation restriction unit  62  pivots inward in the radial direction of the driven gear  50  about the pivot shaft  62   a . When the pressure inward in the radial direction against the second contact unit  62   d  is released, the lever unit  62   b  pivots back to the position where the second contact unit  62   d  contacts the lever rotation restriction unit  50   h  by the urging force of the torsion spring  60 . 
     In the present embodiment, the driven gear  50  is formed with a convex-shaped unit  50   n  protruding outward in the radial direction and upward in the thickness direction. On one side of the convex-shaped unit  50   n  in the circumferential direction of the driven gear  50 , the first rotation restriction unit  50   c  is formed; on the other side, the second rotation restriction unit  50   k  is formed. In the convex-shaped unit  50   n , the lever rotation restriction unit  50   h  is formed on the inner side of the driven gear  50  in the radial direction. In the convex-shaped unit  50   n , the lever rotation restriction unit  50   h  is formed to be concave outward in the radial direction to receive a portion of the pivot shaft  62   a  and a portion of the lever unit  62   b  of the lever-shaped rotation restriction unit  62 . 
     Valve Element 
     The valve element  56  will be described with reference to  FIG. 10 ,  FIG. 13  and  FIG. 14 . As illustrated in  FIG. 13  and  FIG. 14 , the valve element  56  is configured as a disc-like member. A through hole  56   a  is provided at a center of the valve element  56 . The spindle  54  is inserted into the through hole  56   a . The lower surface of the valve element  56  is configured as a sliding surface  56   b  sliding on the valve seat surface  34   c  of the valve seat constitutional member  34 . In the valve element  56 , a portion of the sliding surface  56   b  is cut away to form a cutout unit  56   c.    
     As illustrated in  FIG. 14 , the cutout unit  56   c  has a shape that is concave upward with respect to the sliding surface  56   b  of the valve element  56 . It is noted that two through holes  56   d  are provided in the cutout unit  56   c . In the present embodiment, as an example, bosses (not illustrated) protruding from the lower surface of the driven gear  50  are inserted into the through holes  56   d , so that the driven gear  50  and the valve element  56  are integrally rotatable. 
     Further, on the valve element  56 , an orifice  56   e  that penetrates in the up-down direction and opens at the sliding surface  56   b  is provided. In the present embodiment, the orifice  56   e  has a portion narrower than the first fluid outlet  34   a  and the second fluid outlet  34   b  in the fluid path. It is noted that more preferably, the orifice  56   e  has a narrowest portion in the fluid path. 
     The configuration described above is a main configuration of the valve drive device  10  and the valve element drive mechanism  30 , and the following will describe control of fluid of the valve element  56  by the valve element drive mechanism  30 , and the power transmission state and the power non-transmission state of the drive gear  46  and the driven gear  50  in order. 
     Fluid Control by Valve Element 
     Flow rate control of fluid from the fluid inlet  28   b  to at least one of the first fluid outlet  34   a  and the second fluid outlet  34   b  will be described with reference to  FIG. 15  to  FIG. 18 . In step S 0  of  FIG. 16 , the drive gear  46  is located at the origin position with respect to the driven gear  50 . The relationship between the teeth of the drive gear  46  and the teeth of the driven gear  50  at the origin position will be described later. 
     As illustrated in  FIG. 16 , in step S 0  (origin position), the cutout unit  56   c  of the valve element  56  is located above the first fluid outlet  34   a  and the second fluid outlet  34   b . Accordingly, since the valve element  56  does not close the first fluid outlet  34   a  and the second fluid outlet  34   b , the first fluid outlet  34   a  and the second fluid outlet  34   b  are in the opened state. Thus, the fluid supplied from the fluid inlet  28   b  into the valve chamber  32  flows out to the first outflow pipe  16  and the second outflow pipe  18  through the first fluid outlet  34   a  and the second fluid outlet  34   b  (see opening/closing mode of  FIG. 15 ). 
     Then, the motor  24  is rotationally driven to rotate the drive gear  46  as well as the rotor  40  in the first direction R 1 . At this time, the driven gear  50  meshing with the drive gear  46  is also driven to rotate (in the clockwise direction in  FIG. 16 ) and shifts to the state of step S 1  (the center diagram in  FIG. 16 ). The driven rotation of the driven gear  50  causes the valve element  56  to slide against the valve seat constitutional member  34  in the clockwise direction in  FIG. 16  with the sliding surface  56   b  in close contact with the valve seat surface  34   c . Also in step S 1 , since the cutout unit  56   c  is located above the first fluid outlet  34   a  and the second fluid outlet  34   b , the first fluid outlet  34   a  and the second fluid outlet  34   b  open, that is, are in the opening mode in  FIG. 15 . 
     As illustrated in the lower diagram of  FIG. 16 , when the drive gear  46  is further rotated in the first direction R 1 , the state of step S 1  is shifted to the state of step S 2 . In this state, the orifice  56   e  is located above the first fluid outlet  34   a , and the cutout unit  56   c  is located above the second fluid outlet  34   b . The first fluid outlet  34   a  is in a state where the flow rate of the fluid flowing out from the first fluid outlet  34   a  is restricted by the orifice  56   e.    
     That is, the flow rate of the fluid flowing out from the first fluid outlet  34   a  restricted by the orifice  56   e  is lower than the flow rate of the fluid flowing out from the first fluid outlet  34   a  in the completely opened state as in steps S 0  and S 1 . That is, this corresponds to a slightly opening mode in step S 2  of  FIG. 15 . The second fluid outlet  34   b  is in the opened state, and thus is in an opening mode. 
     Then, as illustrated in the upper diagram in  FIG. 17 , when the drive gear  46  is further rotated in the first direction R 1 , the state of step S 2  is shifted to the state of step S 3 . In this state, the orifice  56   e  is out of the position above the first fluid outlet  34   a . The first fluid outlet  34   a  is covered with and closed by the sliding surface  56   b  of the valve element  56 . Accordingly, the first fluid outlet  34   a  is in a closing mode ( FIG. 15 ), and the path of fluid from the valve chamber  32  to the first outflow pipe  16  is blocked. On the other hand, the cutout unit  56   c  is located above the second fluid outlet  34   b . Accordingly, the second fluid outlet  34   b  is open, and thus is in the opening mode ( FIG. 15 ). 
     Then, as illustrated in the center diagram of  FIG. 17 , when the drive gear  46  is further rotated in the first direction R 1 , the state of step S 3  is shifted to the state of step S 4 . In this state, the first fluid outlet  34   a  is covered with and closed by the sliding surface  56   b  of the valve element  56 . Accordingly, the first fluid outlet  34   a  maintains the state of the closing mode ( FIG. 15 ) continuing from step S 3 , and the state where the path of fluid from the valve chamber  32  to the first outflow pipe  16  is blocked is maintained. 
     Furthermore, the orifice  56   e  is located above the second fluid outlet  34   b . Accordingly, the second fluid outlet  34   b  is in a state where the flow rate of the fluid flowing out from the second fluid outlet  34   b  is restricted by the orifice  56   e , and the second fluid outlet  34   b  is in the slightly opening mode in step S 4  of  FIG. 15 . 
     Then, as illustrated in the lower diagram of  FIG. 17 , when the drive gear  46  is further rotated in the first direction R 1 , the state of step S 4  is shifted to the state of step S 5 . In the state of step S 5 , the first fluid outlet  34   a  and the second fluid outlet  34   b  are covered with the sliding surface  56   b  of the valve element  56  and are in the closed state. That is, this corresponds to the closing mode in step S 5  of  FIG. 15 . In this state, the path of fluid from the valve chamber  32  to the first outflow pipe  16  and the second outflow pipe  18  is blocked. 
     Then, as illustrated in  FIG. 18 , when the drive gear  46  is further rotated in the first direction R 1 , the state of step S 5  is shifted to the state of step S 6 . In the state of step S 6 , the cutout unit  56   c  is again located above the first fluid outlet  34   a . Accordingly, the first fluid outlet  34   a  is completely open, and is in the opening mode in  FIG. 15 . On the other hand, the second fluid outlet  34   b  maintains the closed state where it is covered with the sliding surface  56   b  of the valve element  56 , and thus, the state where the path of fluid from the valve chamber  32  to the second outflow pipe  18  is blocked is maintained. That is, this corresponds to the closing mode in step S 6  of  FIG. 15 . 
     In the present embodiment, the valve element  56  is rotated with respect to the valve seat constitutional member  34  by the motor  24  so that each of the first fluid outlet  34   a  and the second fluid outlet  34   b  can be switched to the opened state, the slightly opened state, or the closed state, and thus, the flow rate of the fluid flowing out from the valve chamber  32  to each of the first outflow pipe  16  and the second outflow pipe  18  can be adjusted. 
     Excitation Pattern of Drive Coil 
     Then, the origin position returning operation of the power transmission switching unit  52  of the valve element drive mechanism  30  will be described with reference to  FIG. 19  to  FIG. 21 . In the left side diagrams of  FIG. 19  to  FIG. 21 , the left side diagrams schematically illustrate the position of the magnetic poles of the drive magnet  38  according to the excitation pattern of the stator  36 , and the right side diagrams schematically illustrate states of the power transmission switching unit  52  corresponding to the left side diagrams. It is noted that as an example, in the stator  36  and the drive magnet  38 , areas solid-filled with black dots each indicate the S pole and areas filled with black each indicates the N pole; in the stator  36 , areas not filled each indicate a non-excited state. 
     In the present embodiment, sixteen pole teeth  42   a  of the stator  36  are provided, and the magnetic poles of the drive magnet  38  are set to eight. In the following description, the rotor  40  is rotated by exciting each of the pole teeth  42   a  of the stator  36  with eight excitation patterns. Hereinafter, in steps S 9  and S 17  in  FIG. 19  to  FIG. 21 , the excitation pattern of the stator  36  is defined as an initial excitation pattern, that is, a first excitation pattern, and the position of the magnetic poles of the drive magnet  38  in the first excitation pattern of the stator  36  is defined as the origin position. 
     The rotor  40  rotates in the second direction R 2  from step S 7  in  FIG. 19  to step S 17  in  FIG. 21 . The first excitation pattern (see step S 9 ), which is the initial excitation pattern, indicates an excited state where the S pole and the N pole are each excited at four poles and there is one non-excited pole tooth  42   a  between the pole tooth  42   a  excited to the S pole and the pole tooth  42   a  excited to the N pole. 
     Next, in a second excitation pattern (see step S 10 ), the non-excited pole tooth  42   a  located on the second direction R 2  side of the pole tooth  42   a  excited to the S pole or the N pole is excited to the S pole or the N pole. Specifically, the pole tooth  42   a  located on the second direction R 2  side of the pole tooth  42   a  excited to the S pole is excited to the S pole, and the pole tooth  42   a  located on the second direction R 2  side of the pole tooth  42   a  excited to the N pole is excited to the N pole. Then, in a third excitation pattern (see step S 11  in  FIG. 20 ), the pole teeth excited in the first excitation pattern are brought into the non-excited state. Thus, the third excitation pattern indicates a state where the polarity goes forward by one pole tooth in the second direction R 2 , which is the rotation direction of the rotor  40 , with respect to the first excitation pattern. 
     Thereafter, when the state is shifted from the third excitation pattern of step S 11  to a fourth excitation pattern of step S 12  and then a fifth excitation pattern of step S 13 , the polarity goes forward by one pole tooth in the second direction R 2 , which is the rotation direction of the rotor  40 . Likewise, when the state is shifted from the fifth excitation pattern of step S 13  to a sixth excitation pattern of step S 14  and then a seventh excitation pattern of step S 15 , the polarity goes forward by one pole tooth in the second direction R 2 , which is the rotation direction of the rotor  40 ; when the state is shifted from the seventh excitation pattern of step S 15  to an eighth excitation pattern of step S 16  and then a ninth excitation pattern of step S 17 , the polarity goes forward by one pole tooth in the second direction R 2 , which is the rotation direction of the rotor  40 . 
     In the present embodiment, when the excitation is sequentially performed from the first excitation pattern (step S 9 ) to the eighth excitation pattern (step S 16 ) in the stator  36 , the excitation pattern returns to the first excitation pattern. During the eight excitation patterns, the pole tooth  42   a  excited to the S pole or the N pole in the first excitation pattern is bought into a state where the polarity goes forward by four pole teeth on the second direction R 2  side. 
     On the other hand, the drive magnet  38  has eight poles. In the first excitation pattern (step S 9 ) of the stator  36 , in the drive magnet  38 , a portion having a polarity (N pole) opposite to the polarity (for example, S pole) of the excited pole tooth  42   a  of the stator  36  is located at a position facing the pole tooth  42   a . In step S 9 , the pole tooth  42   a  excited to the S pole of the stator  36  faces a portion with the N pole of the drive magnet  38 , and the pole tooth  42   a  excited to the N pole of the stator  36  faces a portion with the S pole of the drive magnet  38 . 
     The excited pole teeth  42   a  in the stator  36  is increased by one on the second direction R 2  side when the first excitation pattern is switched to the second excitation pattern, and thus, the drive magnet  38  also moves in the second direction R 2  by one excited pole tooth. Thus, the drive magnet  38  moves in the second direction R 2  each time the excitation pattern of the stator  36  is switched. Accordingly, by sequentially switching the excitation pattern from the first excitation pattern to the eighth excitation pattern of the stator  36 , the rotor  40  as well as the drive magnet  38  rotates in the second direction R 2 . 
     Switching from the Power Transmission State to the Power Non-Transmission State 
     In step S 7 , the drive gear  46  rotates in the second direction R 2 . In the state of step S 7 , the gear unit  46   a  of the drive gear  46  meshes with the meshing unit  50   a  of the driven gear  50 . It is noted that step S 7  indicates the middle of returning to the origin position by switching the rotation direction to the second direction after the drive gear  46  is rotated toward the first direction R 1  side to rotate the driven gear  50  to be driven. 
     When the state is shifted to step S 9  through step S 8 , the drive gear  46  returns to the origin position with respect to the driven gear  50 . Here, the origin position indicates a state where the meshing state between the gear unit  46   a  of the drive gear  46  and the meshing unit  50   a  of the driven gear  50  is released, and the gear unit  46   a  is located within the non-meshing unit  50   b  of the driven gear  50 . In this state, when the drive gear  46  rotates in the second direction, the power non-transmission state is provided where the power is not transmitted from the drive gear  46  to the driven gear  50 . 
     Specifically, referring to the right side diagrams of steps S 9 , S 11 , S 13 , S 15 , and S 17 , when the drive gear  46  rotates in the second direction R 2 , the four convex units  46   b  also rotate in the second direction R 2 . As the state is shifted from steps S 9  to S 11 , the convex unit  46   b  facing the second contact unit  62   d  of the rotation restriction unit  62  approaches the second contact unit  62   d  while rotating in the second direction R 2 , and finally contacts the second contact unit  62   d  in step S 11 . 
     When the drive gear  46  is further rotated in the second direction R 2 , the convex unit  46   b  in contact with the second contact unit  62   d  will rotate in the second direction R 2 . At this time, the convex unit  46   b  presses the second contact unit  62   d  against the urging force of the torsion spring  60  as illustrated in the right diagrams of steps S 13  and S 15 . As a result, the rotation restriction unit  62  pivots inward in the radial direction of the driven gear  50  about the pivot shaft  62   a  ( FIG. 12 ). 
     Thereafter, as illustrated in steps S 15  to S 17 , when the drive gear  46  is further rotated in the second direction R 2 , the convex unit  46   b  which has pressed the second contact unit  62   d  is separated from the second contact unit  62   d . As a result, the rotation restriction unit  62  pivots outward in the radial direction by the urging force of the torsion spring  60 , and pivots to the position where the second contact unit  62   d  contacts the lever rotation restriction unit  50   h  ( FIG. 11 ) of the driven gear  50 . 
     In the present embodiment, when the drive gear  46  is rotated in the second direction R 2  with the gear unit  46   a  of the drive gear  46  located within the non-meshing unit  50   b  of the driven gear  50 , the gear unit  46   a  continues to rotate idly in the non-meshing unit  50   b  while the convex unit  46   b  intermittently repeats contact with and separation from the second contact unit  62   d  of the rotation restriction unit  62 . Therefore, it is possible to prevent inadvertent contact between the tooth of the drive gear  46  and the tooth of the driven gear  50  in the power non-transmission state, and to prevent the generation of a collision noise when the teeth collide. 
     When the gear unit  46   a  continuously rotates idly in the non-meshing unit  50   b , the state continues where the meshing state between the gear unit  46   a  of the drive gear  46  and the meshing unit  50   a  of the driven gear  50  is released. As a result, the power non-transmission state where the power of the motor  24  is not transmitted from the drive gear  46  to the driven gear  50  is maintained. Therefore, the possibility that the motor  24  may be out of step can be reduced, and thus, noise caused by the step-out can be suppressed. 
     The second rotation restriction unit  50   k  will be described with reference to  FIG. 26A  and  FIG. 26B . The upper and lower diagrams of  FIG. 26A  and  FIG. 26B  illustrate the relationship between the drive gear  46  and the driven gear  50  in steps S 13  to S 15 . In the upper diagram of  FIG. 26A  and  FIG. 26B , when the convex unit  46   b  contacts the second contact unit  62   d  of the rotation restriction unit  62  to press the second contact unit  62   d , the convex unit  46   b  rotates in the second direction R 2 , and thus, the second contact unit  62   d  is pressed to rotate in the counterclockwise direction in  FIG. 26A  and  FIG. 26B . 
     Here, the second contact unit  62   d  pressed by the convex unit  46   b  will rotate together with the driven gear  50  in the counterclockwise direction in  FIG. 26A  and  FIG. 26B . In the present embodiment, in the driven gear  50 , the second rotation restriction unit  50   k  is provided on the first direction R 1  side of the non-meshing unit  50   b . When the driven gear  50  rotates together with the second contact unit  62   d  in the counterclockwise direction in  FIG. 26A  and  FIG. 26B , the driven gear  50  contacts the gear of the gear unit  46   a  of the drive gear  46  located in the non-meshing unit  50   b  (the upper diagram in  FIG. 26A  and  FIG. 26B ). 
     When the second rotation restriction unit  50   k  contacts the tooth of the gear unit  46   a , the counterclockwise rotation of the driven gear  50  in  FIG. 26A  and  FIG. 26B  is restricted. Furthermore, even when the drive gear  46  continues to rotate in the second direction R 2  in this state, the state where the second rotation restriction unit  50   k  contacts one of the teeth of the gear unit  46   a  (the lower diagram in  FIG. 26A  and  FIG. 26B ) is maintained, and thus, the rotation-restricted state of the driven gear  50  is also maintained. Thus, the gear unit  46   a  of the drive gear  46  can rotate idly in the non-meshing unit  50   b , and the power non-transmission state can be maintained. 
     Switching from the Power Non-Transmission State to the Power Transmission State 
     Then, switching from the power non-transmission state to the power transmission state will be described with reference to  FIG. 22  to  FIG. 24 . In the present embodiment, in a state where the gear unit  46   a  of the drive gear  46  is located within the non-meshing unit  50   b  of the driven gear  50 , that is, in the power non-transmission state, when the stator  36  is excited with the first excitation pattern being the initial excitation pattern, the drive magnet  38  moves to a magnetic pole position according to the first excitation pattern of the stator  36 . As a result, the drive gear  46  is also located at a position corresponding to the drive magnet  38 . 
     Specifically, in the present embodiment, the convex unit  46   b  is formed according to the magnetic pole of the N pole or the S pole of the drive magnet  38 . In the present embodiment, since the drive magnet  38  has eight poles, four convex units  46   b  are formed and disposed at equal intervals in the circumferential direction of the drive gear  46 . In the present embodiment, the convex unit  46   b  is provided according to the S pole of the drive magnet  38 . 
     When the stator  36  is excited with the first excitation pattern, the S pole of the drive magnet  38  is located at a position facing the pole tooth  42   a  magnetized to the N pole of the stator  36 . As a result, the convex unit  46   b  disposed at the position corresponding to the S pole of the drive magnet  38  is located at a position corresponding to the first contact unit  62   c  of the rotation restriction unit  62  (step S 18  in  FIG. 22 ). In this state, the gear unit  46   a  of the drive gear  46  and the meshing unit  50   a  of the driven gear  50  are not yet in the state of meshing. It is noted that in the present specification, the position corresponding to the first contact unit  62   c  of the rotation restriction unit  62  in the convex unit  46   b  refers to a position where the convex unit  46   b  contacts the first contact unit  62   c  to allow switching from the power non-transmission state to the power transmission state in the course of switching the excitation patter from the first excitation pattern to several excitation patterns, as described later. 
     In this state, when the excitation pattern of the stator  36  is switched from the first excitation pattern to the eighth excitation pattern, the drive gear  46  rotates in the first direction R 1 , the convex unit  46   b  located at the position corresponding to the first contact unit  62   c  of the rotation restriction unit  62  contacts the first contact unit  62   c  (the right diagram of step S 19  in  FIG. 22 ). Furthermore, switching the excitation pattern of the stator  36  from the eighth excitation pattern to the seventh excitation pattern (step S 20  in  FIG. 22 ), the sixth excitation pattern (step S 21  in  FIG. 23 ), and the fifth excitation pattern (step S 22  in  FIG. 23 ) in that order causes the drive gear  46  to rotate in the first direction R 1  and thus causes the convex unit  46   b  in contact with the first contact unit  62   c  to press the first contact unit  62   c  in the clockwise direction in  FIG. 23 . 
     Here, since the convex unit  46   b  in contact with the first contact unit  62   c  presses the first contact unit  62   c  toward the pivot shaft  62   a  in the direction intersecting the first contact unit  62   c , the rotation restriction unit  62  cannot pivot. As a result, the driven gear  50  is pressed by the convex unit  46   b  through the first contact unit  62   c  of the rotation restriction unit  62  and rotates in the clockwise direction in  FIG. 23 . Thus, the gear unit  46   a  of the drive gear  46  comes out of the non-meshing unit  50   b  of the driven gear  50  and meshes with the meshing unit  50   a . Thus, the power of the motor  24  is transmitted from the drive gear  46  to the driven gear  50 . That is, in the driven gear  50 , the power non-transmission state is switched to the power transmission state. 
     Furthermore, as illustrated in steps S 23  and S 24 , rotating the drive gear  46  in the first direction R 1  makes it possible to rotate the driven gear  50  in the clockwise direction in  FIG. 23 , and thus, the operations for the valve element  56  from steps S 1  to S 6  can be performed. 
     Then, the relationship between the drive gear  46  and the driven gear  50  at the origin position (the state of step S 18  in  FIG. 22 ) will be described with reference to  FIG. 24 . In the present embodiment, when the drive gear  46  is located at the origin position, the convex unit  46   b  is located at a position corresponding to the first contact unit  62   c  of the rotation restriction unit  62 . Here, the lock avoidance tooth  46   c  is formed at a position corresponding to the convex unit  46   b  in the circumferential direction of the drive gear  46 . 
     In  FIG. 24 , a circular arc indicated by a two-dot chain line illustrates an addendum circle of the teeth other than the lock avoidance tooth  46   c  in the gear unit  46   a  of the drive gear  46 . In  FIG. 24 , in the state where the drive gear  46  is located at the origin position, a tooth  50   j  at the boundary between the meshing unit  50   a  and the non-meshing unit  50   b  of the driven gear  50  is located at a position where it interferes with an addendum circle of the teeth other than the lock avoidance tooth  46   c.    
     In this state, when the drive gear  46  is to rotate in the first direction in the state where a tooth other than the lock avoidance tooth  46   c  is disposed at the position of the lock avoidance tooth  46   c , a contact of the tooth  50   j  of the driven gear  50  and the tooth disposed at the position of the lock avoidance tooth  46   c  and other than the lock avoidance tooth  46   c  may cause a locked state of the drive gear  46  and the driven gear  50 . 
     In the present embodiment, when the drive gear  46  is located at the origin position, the lock avoidance tooth  46   c  of the drive gear  46  is disposed close to the tooth  50   j  of the driven gear  50 . Thus, since the addendum circle of the lock avoidance teeth  46   c  is smaller than the addendum circle of the teeth other than the lock avoidance tooth  46   c , a gap  64  can be formed between the tooth  50   j  of the driven gear  50  and the lock avoidance tooth  46   c  of the drive gear  46 . The formed gap  64  makes it possible to avoid the locked state of the drive gear  46  and the driven gear  50 . As a result, in the power transmission switching unit  52 , switching from the power non-transmission state to the power transmission state between the drive gear  46  and the driven gear  50  can be smoothly performed, and thus, the occurrence of abnormal operation (displacement of the gear unit  46   a  of the drive gear  46  with respect to the excitation pattern) and operation failure can be suppressed. 
     In the present embodiment, the number of magnetic poles of the drive magnet  38  is set to half the number of pole teeth  42   a  of the core member  42 . In addition, since the convex units  46   b  are formed according to the N pole or the S pole of the drive magnet  38 , when the stator  36  is excited with the first excitation pattern, one convex unit  46   b  of the plurality of convex units  46   b  is always located at a position corresponding to the first contact unit  62   c  of the rotation restriction unit  62 . Thus, when the excitation pattern is sequentially switched in the first direction from the first excitation pattern, the tooth of the drive gear  46  and the tooth of the driven gear  50  mesh with each other within several patterns, and thus, can be brought into the power transmission state. As a result, the responsiveness of switching of the power transmission state in the power transmission switching unit  52  can be enhanced. 
     Further, in the present embodiment, the stator  36  is configured by laminating four core members  42 . When the number of magnetic poles of the drive magnet  38  is eight, each of the core members  42  has four pole teeth  42   a , and accordingly, the number of magnetic poles of the drive magnet  38  is twice the number of pole teeth  42   a  of the core member  42 . As a result, when the predetermined core member  42  is excited, the magnetic pole of the drive magnet  38  located at the position facing the pole tooth  42   a  (for example, the N pole) at the position corresponding to the power switching is any one of the four magnetic poles (for example, the S pole) which are opposite to the pole of the pole tooth  42   a . That is, with respect to the excited core member  42 , the drive magnet  38  has any one of the four position patterns (patterns in which the positions of the magnetic poles of the drive magnet  38  in step S 9  in  FIG. 19  are shifted by 90 degrees to each other). The drive magnet  38  has a magnetic pole opposite to the magnetic pole of the pole tooth  42   a  of the predetermined core member  42  regardless of any of the four position patterns. Therefore, positioning of the rotor  40  with respect to the stator  36  can be easily performed. 
     As described above, in the present embodiment, the rotation restriction unit  62  in the power transmission switching unit  52  is configured to allow the driven gear  50  to rotate when the drive gear  46  rotates in the first direction, and to restrict the rotation of the driven gear  50  when the drive gear  46  rotates in the second direction. That is, the rotation restriction unit  62  is configured as a clutch mechanism. By using the configuration of a known clutch mechanism in the rotation restriction unit  62  in the present embodiment, the design time and the costs can be reduced. 
     The rotation restriction unit  62  in the present embodiment transmits power from the drive gear  46  to the driven gear  50  when the drive gear  46  rotates in the first direction, and cuts off the power transmission from the drive gear  46  to the driven gear  50  when the drive gear  46  rotates in the second direction, thus, the power transmission state can be switched simply by switching the rotation direction of the drive gear  46 , and therefore, the configuration of the rotation restriction unit  62  can be simplified. 
     Modification of the Embodiment 
     (1) In the present embodiment, the configuration is employed where the rotation restriction unit  62  is urged by the torsion spring  60  as an example of the “urging member”. However, instead of this configuration, the urging member may be configured by a plate spring or the like.
 
(2) In the present embodiment, the configuration is employed where the power transmission switching unit  52  switches the power transmission by switching the engagement state (contact with the first contact unit  62   c  or the second contact unit  62   d ) between the convex unit  46   b  and the rotation restriction unit  62 . However, instead of this configuration, a configuration may be employed where the rotation restriction unit  62  is provided with a known ratchet mechanism to cause the drive gear  46  to rotate idly.
 
(3) In the present embodiment, the configuration is employed where the drive magnet  38  has eight magnetic poles, and the convex units  46   b  are provided at four positions corresponding to either the N pole or the S pole. However, a configuration may be employed where when the drive magnet  38  has four poles, two convex units  46   b  are provided; when the drive magnet  38  has six poles, three convex units  46   b  are provided; and when the drive magnet  38  has ten poles, five convex units  46   b  are provided.
 
(4) In the present embodiment, the configuration is employed where the second rotation restriction unit  50   k  is provided on the other side of the convex-shaped unit  50   n  in the circumferential direction of the driven gear  50 . However, instead of this configuration, as illustrated in  FIG. 28 , a configuration may be employed where at a position corresponding to a non-meshing unit  66   a  of a driven gear  66 , a second rotation restriction unit  66   c  may be provided at the tip of a protruding unit  66   b  protruding in the radial direction of the driven gear  66 . In the present embodiment, the second rotation restriction unit  66   c  is configured to be engageable with the main body  46   d  of the drive gear  46 , and as an example, is configured as a curved surface abuttable on the outer periphery of the main body  46   d . When the driven gear  66  is about to co-rotate with the drive gear  46 , the second rotation restriction unit  66   c  contacts the main body  46   d  of the drive gear  46 , restricts the rotation of the driven gear  66 , and suppresses the driven gear  66  from co-rotating.
 
     It is noted that at least an embodiment of the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention described in the claims, and such modifications are also included in the scope of at least an embodiment of the present invention.