Abstract:
A gear meshing with a pinion controls the angle of rotation of a valve element which is brought into sliding contact with a valve seat, thereby controlling the opening and closing of a communicating hole of outflow pipe. During welding the valve seat plate and a housing, a hook portion of an upper portion of the gear is retained by a retaining portion to cause the valve element to be spaced apart from the valve seat. After natural cooling, the pinion is remotely operated by an electric motor to rotate the gear, thereby canceling the holding. A resilient arm causes the gear to be disengaged from the retaining portion by its urging force, brings the valve element into pressure contact with the valve seat, and allows the opening/closing operation to function smoothly.

Description:
[0001]    The present application is based on Japanese Patent Application No. 2001-248919, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a motor-operated expansion valve, and more particularly to a mechanism for avoiding welding heat applied to a valve element.  
           [0003]    Generally, a motor-operated expansion valve consists of a main body making up a valve mechanism and a housing for hermetically sealing the valve mechanism. For example, in a three-way valve in a motor-operated expansion valve  100  shown in FIG. 13 (disclosed in Japanese Patent Publication No. JP-A-2000-310348), the opening and closing of two outflow pipes  106   a  and  106   b  are controlled by a single valve element  102  provided at a distal end of a rotor  101 . Therefore, to ensure that the heat from a tungsten inert gas (TIG) welding position  104   a  for gastightly sealing a housing  104  and a main body  105  will not adversely affect a sliding contact surface  102   a  of the valve element  102 , the valve element  102  is disposed in a central portion of the main body  105  which is the farthest from the welding position  104   a  at an outer periphery of the housing. Furthermore, to make it difficult for the welding heat from welds  105   b  at the outflow pipes  106   a  and  106   b  to be transmitted to the resin-made valve element  102 , a thick machined part having a large thermal capacity is used for a metallic valve seat plate portion.  
           [0004]    In addition, communicating holes  107   a  and  107   b  communicating with the two outflow pipes  106   a  and  106   b  are formed in a valve seat  105   a  in such a manner as to be open to a valve chamber  109 , and are selectively caused to communicate with an inlet port  110  through the valve element  102  inside the valve chamber  109 . As shown in FIGS. 14A to  14 D, a rib  103  has a shape which surrounds a crescent recess  111 , and the single valve element  102  changes over the partition of the communicating holes  107   a  and  107   b  in four modes in correspondence with the angle of rotation of the rotating shaft  101  which is displaced in response to an electrical signal sent from a stator coil  112 . Namely, FIG. 14A shows a state in which the communicating hole  107   a  is closed and the communicating hole  107   b  is open; FIG. 14B shows a state in which both the communicating hole  107   a  and the communicating hole  107   b  are closed; FIG. 14C shows a state in which the communicating hole  107   a  is open and the communicating hole  107   b  is closed; and FIG. 14D shows a state in which both the communicating hole  107   a  and the communicating hole  107   b  are open.  
           [0005]    In the mechanism shown in FIG. 13, in which the opening and closing of the two outflow pipes  106   a  and  106   b  are thus controlled by the single valve element  102 , firstly, the distance between the two outflow pipes  106   a  and  106   b  is short, and the working of parts and the blazing and welding operation are difficult. Secondly, since the changeover of the four modes (open/close, close/open, open/open, and close/close) shown in FIGS. 14A through 14D is effected while the single valve element  102  is turned by one revolution, there is no leeway in the space, which makes it impossible to construct a multi-way valve of four or more ways.  
           [0006]    Thirdly, it is impossible to independently change the flowrate control pattern of the two outflow pipes  106   a  and  106   b , and the pattern becomes a simple one comprising only the changeover between open and close. Fourthly, since the resin-made valve element  102  is brought into pressure contact with the valve seat  105   a  by a spring  108 , if the temperature of the metal becomes high, irregularities occur on the resin surface, and the surface roughness of the resin becomes destroyed due to heat, resulting in the occurrence of leakage in the fully closed state. Accordingly, to avoid the welding heat, it is necessary to finish TIG welding in a short time and effect rapid cooling after welding so as to minimize the effect on the resin-made valve element. For this reason, the operation requires expert skill, and uncertainty remains in the stability of quality and in reliability.  
         SUMMARY OF THE INVENTION  
         [0007]    The object of the invention is to provide a valve drive device in which the above problem is overcome in a suitable manner.  
           [0008]    To overcome the problem, there has been conceived and embodied a three-way valve  200   a  of a motor-operated expansion valve  200  having the construction shown in FIG. 15. Valve elements  202   a  and  202   b  are separately provided for openings  207   a  and  207   b  of outflow pipes  206   a  and  206   b  which are selectively made to communicate with an inflow pipe  210  in a valve chamber  209 , and the valve elements  202   a  and  202   b  are rotated in response to inputs of electrical signals from a stator coil  212  so as to control the opening and closing of the openings  207   a  and  207   b.    
           [0009]    However, since the positions of the valve elements  202   a  and  202   b  geared with and disposed radially from a pinion  203  formed integrally with a rotor  201  with respect to the two outflow pipes  206   a  and  206   b  are close to an outer peripheral portion  204   a  which is subject to heating by TIG welding for gastightly sealing a housing  204  and a main-body base plate  205 , the resin-made valve elements  202   a  and  202   b  which are held in pressure contact with a valve seat  205   a  by leaf springs  208  are directly exposed to welding heat and become deteriorated or deformed, possibly resulting in faulty functioning.  
           [0010]    In addition, consideration must also be given to the fact that the valve elements  202   a  and  202   b  are similarly affected by welding heat from welds  205   b  for gastightly connecting the outflow pipes  206   a  and  206   b  to the main-body base plate  205 . To avoid the effect of such welding heat on the valve elements  202   a  and  202   b , it is necessary to increase the thermal capacity by enlarging the circumference of the metallic main-body base plate  205  including the valve seat or by increasing the thickness thereof. Hence, there are problems in terms of cost and miniaturization.  
           [0011]    In the present invention, to solve these problems, an air heat-insulation layer is formed by holding the valve element in an initial period of assembly and thereby providing a gap between the valve element and the valve seat.  
           [0012]    In accordance with the invention, there is provided a valve drive device having a plurality of openings for communicating with an inflow pipe and an outflow pipe, said valve drive device comprising:  
           [0013]    a valve element for opening and closing said openings;  
           [0014]    a driving member for driving said valve element;  
           [0015]    a rotation transmitting member for transmitting rotation from said driving member to said valve element;  
           [0016]    a valve seat plate in which said openings are formed and on which said valve element is slid in pressure contact therewith so as to open and close said openings; and  
           [0017]    a housing for gastightly sealing said valve seat plate and said valve element together with said driving member and said rotation transmitting member so as to form a hermetically sealed space; and  
           [0018]    a holding device provided for tentatively retaining said valve element at a spaced-apart position spaced apart from said valve seat plate;  
           [0019]    wherein said valve element is retained at the space-apart position when said valve seat plate and said housing are welded together.  
           [0020]    By the above construction, an air layer extremely excelling in heat insulation is formed between the valve element and the valve seat plate, so that the valve element can be protected from welding heat, and the deformation of a sliding contact surface is prevented. Therefore, it is possible to satisfactorily maintain the sealing characteristic of the valve element.  
           [0021]    In the invention, the holding device causes the valve element to be spaced apart from the valve seat plate in opposition to an urging device for bringing the valve element into pressure contact with the valve seat plate, the retention by the holding device is canceled after welding, and the valve element which returned to an abutment position against the valve seat plate by the urging device is spaced apart to a position in which rotating operation of the valve element for opening and closing is not interfered by the holding device. Thus, in the state in which the valve element is retained prior to effecting the starting of initial setting, the air insulating layer can be secured, and it is possible to effect the welding of the piping. In addition, the retention by the holding device is irreversible, and the valve element which has been disengaged once is disengaged completely and reliably from the holding device. The valve element upon cancellation of the retention is brought into close contact with the valve seat plate to allow the openings to sufficiently maintain gastightness, and its rotating operation for opening and closing can be effected quite freely without trouble.  
           [0022]    Furthermore, the holding operation for retaining the valve element by the holding device is effected by the rotation of the valve element, and there is provided a restricting position for preventing the rotation at a predetermined angle of rotation. Namely, by setting the restricting position for preventing the rotation by the operation of holding the valve element by its rotation, each rotation transmitting member (gear) is retained at a position (meshing position) in which the rotation transmitting member is in a state of being interlocked with the driving member (pinion), so that the driving member (pinion) is capable of being smoothly linked with the rotation transmitting member (gear) without mutually interfering therewith. Since there is no need to adjust the angles of rotation of the gears at the time of assembly, a gear assembly jig is not required, and the assembling process can be simplified.  
           [0023]    In addition, since the cancellation of the retention of the urging device and the valve element is effected by the operation of the valve element itself, after the valve drive device is gastightly sealed in the housing, the retention can be reliably canceled by electrical remote operation from the outside. Conversely, since the mechanical retention cannot be canceled unless the electrical operation is used, the sealing characteristic of the valve element does not deteriorate even if heat treatment is provided for the exterior fittings prior to wiring.  
           [0024]    Furthermore, a relative angular relationship between origins of starting of the valve elements and a preventing portion provided on the rotation transmitting member for mechanically preventing the rotation at the origins of starting are uniformly defined by the restricting position. Since the proper angular position of the gear is thus ensured automatically in the assembly of parts by virtue of the restricting position, and because the number of pulses up to an electrical origin of the rotor by the pulse driving from the stator can be set in advance, the matching of origins of mechanical starting of the valve elements can be easily attained without resorting to visual observation after the valve drive device has been gastightly sealed in the housing.  
           [0025]    Preferably, the rotation transmitting member is a gear. 
       
    
    
     BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    [0026]FIG. 1 is a sectional side view of an embodiment of a motor-operated expansion valve including a valve drive device in accordance with the invention;  
         [0027]    [0027]FIGS. 2A to  2 C are diagrams illustrating a valve seat plate in the valve drive device in accordance with the invention, in which FIG. 2A is a plan view, FIG. 2B is a sectional view taken along line b-b of FIG. 2A; and FIG. 2C is a rear view taken in the direction of arrows c-c of FIG. 2B;  
         [0028]    [0028]FIGS. 3A to  3 D are explanatory diagrams of exterior fitting members in the valve drive device in accordance with the invention, in which FIG. 3A is a rear view illustrating the joining between a pipe holding member and the valve seat plate, FIG. 3B is a rear view illustrating the joining between a stator positioning frame and the pipe holding member, FIG. 3C is a sectional view taken along line c-c in FIG. 3B, and FIG. 3D is a sectional view taken along line d-d in FIG. 3B;  
         [0029]    [0029]FIGS. 4A and 4B are part drawings of a valve-element holding device in the valve drive device in accordance with the invention, in which FIG. 4A is a plan view, and FIG. 4B is a sectional view taken along line b-b of FIG. 4B;  
         [0030]    [0030]FIG. 5 is a perspective view explaining a state in which a valve element is retained by the valve-element holding device in the valve drive device in accordance with the invention;  
         [0031]    [0031]FIG. 6 is a partial plan view explaining the meshing relationship between a pinion and a gear retained by a valve-element retaining portion of the valve-element holding device in the valve drive device in accordance with the invention;  
         [0032]    [0032]FIG. 7 is a partial assembly drawing of the valve-element holding device and the gear in the valve drive device in accordance with the invention, and is a sectional side view explaining the gear and the valve element which are in a retained position;  
         [0033]    [0033]FIG. 8 is an enlarged sectional side view of the valve drive device in accordance with the invention;  
         [0034]    [0034]FIGS. 9A and 9B are partial assembly drawings of the valve element and the gear in the valve drive device in accordance with the invention, in which FIG. 9A is a rear view, and FIG. 9B is a sectional view taken along line b-b of FIG. 9B;  
         [0035]    [0035]FIGS. 10A to  10 C are part drawings of the gear in the valve drive device in accordance with the invention, in which FIG. 10A is a rear view, FIG. 10B is a sectional view taken along line b-b of FIG. 10A; and FIG. 10C is a plan view;  
         [0036]    [0036]FIGS. 11A to  11 C are part drawings of the valve element in the valve drive device in accordance with the invention, in which FIG. 11A is a rear view, FIG. 11B is a sectional view taken along line b-b of FIG. 11A, and FIG. 11C is a plan view taken in the direction of arrows c in FIG. 11B;  
         [0037]    [0037]FIGS. 12A to  12 D are explanatory diagrams illustrating open-close modes of the valve element in the valve drive device in accordance with the invention in which FIG. 12A shows a state in which the valve A is open and the valve B is open, FIG. 12B shows a state in which the valve A is open and the valve B is closed, FIG. 12C shows a state in which the valve A is closed and the valve B is closed, and FIG. 12D shows a state in which the valve A is closed and the valve B is open;  
         [0038]    [0038]FIG. 13 is a sectional side view of portions of an example of a conventional motor-operated expansion valve;  
         [0039]    [0039]FIGS. 14A to  14 D are views taken along line XIV-XIV of FIG. 13, and are rear views explaining open-close modes of the valve; and  
         [0040]    [0040]FIG. 15 is a sectional side view of another example of the conventional motor-operated expansion valve. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]    Referring now to the accompanying drawings, a description will be given of an embodiment of a valve drive device in accordance with the invention. FIG. 1 is a vertical sectional side view of an embodiment of a motor-operated expansion valve  10  in its entirety which includes a valve drive device  11  in accordance with the invention. The valve drive device  11  is formed on a valve seat plate  13  (see FIGS. 2A to  2 C) formed by subjecting a metal plate to press forming, and is gastightly sealed by a housing  14 , and is adapted to rotatively drive a rotor  15  by a stator  16  provided circumferentially on the housing  14  in close contact with the outer side thereof. As a drive signal is inputted from a computer (not shown) to a conductor  16   b  connected to a stator coil  16   a  of the stator  16 , the valve drive device  11  controls the rotation and stop of the rotor  15  at a predetermined angle.  
         [0042]    The rotor  15  has a magnet  15   a  fixed integrally to its outer periphery and a pinion  17  formed on an end portion thereof on the valve seat plate  13  side, and is rotatably supported by a rotor supporting shaft  18  which is fixed. The diameter of the housing  14  is reduced such that an outer peripheral surface of the magnet  15   a  of the rotor  15  and an inner peripheral surface of the stator coil  16   a  are located close to each other, and the rotor  15  is provided with a recess  14   a  fitting to one end of the supporting shaft  18  of the rotor  15  on a closed end side of the housing  14  so as to stably support the one end at a central position. An open end  14   b  side of the housing  14  has an enlarged diameter and is provided with a stepped portion  14   c  for mounting the stator  16  thereon. An inner surface of the open end  14   b  having the enlarged diameter is closely fitted to an enlarged-diameter peripheral edge portion  13   a  at the stepped outer periphery of the valve seat plate  13  formed by press forming. If the open end  14   b  of the housing  14  is fitted on the enlarged-diameter peripheral edge portion  13   a  of the valve seat plate  13 , a central hole  13   b  of the valve seat plate  13  and the fixed-shaft supporting recess  14   a  of the housing  14  are aligned on the same axis.  
         [0043]    [0043]FIG. 2A is a plan view of the valve seat plate  13  as seen from a valve seat  23  side; FIG. 2B is a sectional view taken along line b-b of FIG. 2A; and FIG. 2C is a rear view taken in the direction of arrows c-c of FIG. 2B. The central hole  13   b  extends through the valve seat plate  13 , the rotor supporting shaft  18  is press fitted from a reverse surface  13   f  side located away from the valve seat  23 , is passed through the valve seat plate  13 , and is provided uprightly to a height for fitting to the recess  14   a  in the center of the housing  14  on the valve seat  23  side.  
         [0044]    Fixing holes  13   c  for supporting shafts  21 A and  21 B of two gears of the same shape (see FIGS. 9A through 10B) meshing with the rotor pinion  17  are formed in two symmetrical portions of the valve seat plate  13  on both sides of the central hole  13   b . The gears  20 A and  20 B are rotatably supported by the supporting shafts  21 A and  21 B as rotation transmitting members. In addition, the valve seat plate  13  is shallowly stamped by press forming to form a pair of circular steps  13   d  which are each concentric with the shaft fixing hole  13   c  and has an outside diameter approximately equivalent to the diameter of each of the gears  20 A and  20 B and to form a pair of smooth flat surfaces  13   e , thereby forming the two valve seats  23  (see FIGS. 2A and 2B). The depth of each recessed flat surface  13   e  is illustrated in exaggerated form. As a result, each valve seat  23  which abuts against a sliding contact surface  24   a  (−A, −B) (see FIGS. 11A and 11B) of a valve element  24  provided projectingly on the lower surface of each of the gears  20 A and  20 B with a predetermined pattern can be secured with required surface roughness in a limited portion of the valve seat plate  13 .  
         [0045]    A small-diameter communicating hole  25  (A, B) communicating with an outflow pipe  28  (A, B) is formed in each of these valve seats  23  at an appropriate position close to an edge of the valve seat plate  13 . Further, a communicating hole  27  communicating with an inflow pipe  26  is formed in a portion of the valve seat plate  13  which does not interfere with the valve seat  23 . In addition, shallow stepped holes  29  substantially concentric with the communicating holes  25 A,  25 B, and  27  and fitting to the outside diameters of the outflow pipes  28 A and  28 B and the inflow pipe  26  are respectively formed by stamping (the illustration is exaggerated). Further, positioning projections  13   g  are vertically embossed at three portions from the reverse surface  13   f  side.  
         [0046]    [0046]FIGS. 3A and 3B are illustrations of the valve seat plate as viewed from the reverse surface  13   f  side. A pipe supporting plate  30  such as the one shown in FIG. 3A is superposed on the reverse surface  13   f  of the valve seat plate  13  provided with the stepped holes  29 , such that knock holes  30   h  formed in the pipe supporting plate  30  in correspondence with the positioning projections  13   g  are fitted to the positioning projections  13   g . The pipe supporting plate  30  is then secured to the valve seat plate  13  by caulking the positioning projections  13   g . The pipe supporting plate  30  is a thin metal plate formed by press forming, and stepped portions  30   a  formed by bending, such as those shown in FIGS. 3C and 3D, are provided at positions corresponding to the stepped holes  29  for fitting the three pipes including the inflow pipe  26  and the first and second outflow pipes  28 A and  28 B, thereby forming holding brackets  30   b  spaced apart from the fixing surface with respect to the valve seat plate  13 . Further, through holes  30   c , which support side surfaces of the pipes by coming into close contact with the outside diameter portions of the inflow pipe  26  and the first and second outflow pipes  28 A and  28 B and hold the pipes in an upright state in cooperation with the stepped holes  29 , are formed in the pipe supporting plate  30  at positions aligned with the respective pipe-fitting stepped holes  29 .  
         [0047]    Side grooves  30   e  in the form of key hole extend from the through holes  30   c  to facilitate the pouring of a brazing filler metal and ensure that gastight sealing can be effected reliably. In addition, loosely inserting holes  30   d  surrounding with large leeway the outside diameter portions of the supporting shafts  18 ,  21 A, and  21 B are formed in the pipe supporting plate  30  at positions corresponding to the central hole  13   b  and the shaft fixing holes  13   c  of the valve seat plate  13 . Further, the brazing filler metal is deposited on joints between the outer peripheries of the supporting shafts  18 ,  21 A, and  21 B and the reverse surface  13   f  of the valve seat plate, thereby facilitating the ensuring of gastightness.  
         [0048]    Further, retaining pieces  30   g  are cut out in the pipe supporting plate  30 , and a stator positioning frame  40  is superposed on the pipe supporting plate  30  by allowing the retaining pieces  30   g  to be passed through its elongated rectangular holes  40   d , and the retaining pieces  30   g  are then bent to effect tab connection, as shown in FIG. 3B. As shown in FIG. 1, a positioning retainer  40   b  for resiliently engaging a recess  16   c  for specifying the mounting direction of the stator coil  16   a  is provided uprightly on the stator positioning frame  40 .  
         [0049]    As a result, as for the pipe supporting plate  30  whose positional relationship with the valve seat plate  13  is fixed by the positioning projection  13   g , its positional relationship with the stator positioning frame  40  is determined by the retaining pieces  30   g . Hence, it is possible to mechanically determine the mounting direction of the stator coil  16   a  which is set by the retainer  40   b  of the stator positioning frame  40 , as well as the relationship of layout with respect to the rotating angles of the gears  20 A and  20 B. In addition, a mounting seat  40   a  for the motor-operated expansion valve  10  is formed in the stator positioning frame  40  by bending an extended portion of its outer edge, and two mounting holes  40   c  through which fixing bolts (not shown) are inserted are formed in the mounting seat  40   a.    
         [0050]    [0050]FIGS. 3C and 3D are sectional views taken along line c-c and line d-d, respectively, of FIG. 3B, and are diagrams which are inverted with respect to the direction illustrated in FIG. 1. A total of three supporting shafts, including the rotor supporting shaft  18  and the two gear supporting shafts  21 A and  21 B, are respectively press fitted in the central hole  13   b  and the shaft fixing holes  13   c  from the direction of the reverse surface  13   f  of the valve seat plate. Further, a total of three pipes, including the inflow pipe  26  and the first and second outflow pipes  28 A and  28 B, are inserted and fitted in the corresponding through holes  30   c  in the pipe supporting plate  30 , and are set upright, and their end faces are seated in the stepped holes  29  recessed in the reverse surface  13   f  of the valve seat plate  13 . Welding or brazing is effected with respect to these six regions for exteriorly fitting the total of six members from the reverse surface  13   f  side of the valve seat plate, and gastightness is thereby ensured. Thus, since the distance between the pipes can be made long, and all the inflow pipe  26  and the outflow pipes  28 A and  28 B are arranged in the identical reverse surface  13   f , the assembly and the brazing operation from the same direction are facilitated, and the operating efficiency improves, so that the quality becomes stabilized.  
         [0051]    [0051]FIGS. 4A and 4B show a multifunctional valve-element holding device, in which FIG. 4A is a plan view, and FIG. 4B is a sectional view taken along line b-b of FIG. 4A. As for the valve-element holding device  35 , a base  35   a  has an annular shape in which a loosely inserting hole  35   b  for the pinion  17  extending from the rotor  15  is provided in its center. A pair of belt-shaped portions extending from an outer periphery of the base  35   a  at substantially symmetrical positions are bent orthogonally downward, as shown in FIG. 4B, so as to form a pair of leg portions  35   c . A pair of through holes  35   e  through which the bear supporting shafts  21 A and  21 B are inserted are formed in the base  35   a  at positions corresponding to the gear supporting shafts  21 A and  21 B.  
         [0052]    A pair of arcuate resilient arms  35   d , which respectively surround the through holes  35   e  in their distal circular land portions  35   f , are each cut out by punching out two arcuate slots  35   g , thereby forming a pair of cantilevered resilient beams. The arcuate slots  35   g  are made to communicate with the outside of the annular base  35   a  by cutting off their outer edge portions, thereby similarly forming a pair of cantilevered beams constituting a pair of valve-element retaining portions  34 . Distal ends of the valve-element retaining portions  34  are finished to a length for setting the teeth of the gears  20 A and  20 B in a specific direction so as to form a pair of restricting positions  34   a.    
         [0053]    Namely, the valve-element holding device  35  has a combination of four functions including: the function for supporting the annular base  35   a  to a specific height from the valve seat plate  13  by the leg portions  35   c ; the function for retaining the valve elements  24 A and  24 B shown in FIGS. 9A and 9B to the height of the annular base  35   a  by the valve-element retaining portions  34 ; a jig function for positioning the teeth of the gears  20 A and  20 B in a specific direction by the restricting positions  34   a  of the valve-element retaining portions  34 ; and the function of bringing the valve elements  24 A and  24 B into pressure contact with the valve seat  23  through the bears  20 A and  20 B by the resilient arms  35   d.    
         [0054]    [0054]FIG. 5 is a perspective view illustrating a form in which the gear  20 A is lifted upward against the urging force with which the resilient arm  35   d  inserted through the through hole  35   e  from above the gear  20 A inserted in the supporting shaft  21 A presses a gear boss end portion  20   a  toward the valve seat  23 , and the gear  20 A is retained by the valve-element retaining portion  34  of the valve-element holding device  35 . The gear  20 A is rotatably supported by the supporting shaft  21 A, and is slidable along the supporting shaft  21 A. Although only the gear  20 A is shown in enlarged form to simplify the illustration, the same applies to the gear  20 B as well. The gear  20 A is rotated until the valve-element retaining portion  34  is forcibly inserted onto a lower side of a pocket-like hook portion  20   b  recessed in an upper portion of the gear in opposition to its resiliency, and an innermost barrier  20   c  abuts against the restricting position  34   a  at the distal end of the valve-element retaining portion  34 . Each of the gears  20 A and  20 B is clamped by the resiliently restoring forces of the resilient arm  35   d  and the valve-element retaining portion  34 , and their relational positions are oriented with respect to their angles of mutual rotation in this state.  
         [0055]    [0055]FIG. 6 shows that the pinion  17  which has been fitted over the rotor supporting shaft  18  from above and lowered is able to smoothly mesh with both gears  20 A and  20 B, whose relative positions have been thus related, simultaneously without interfering with each other. Namely, since the gears  20 A and  20 B are oriented at the restricting positions  34   a , the meshing with the pinion  17  can be effected without needing to mutually adjust the positions of the teeth.  
         [0056]    [0056]FIG. 7 is a schematic side view, partly in section, illustrating a form in which the boss end portion  20   a  of the gear  20 A is pressed downward by the resilient arm  35   d , and the valve-element retaining portion  34  lifts up the hook portion  20   b  of the gear  20 A from below by its resiliency against the urging force of the resilient arm  35   d , with the result that the pinion  17  meshes with the gear  20 A, which is in a state of being clamped at a height spaced apart from the valve seat plate  13 , without needing to mutually adjust the relational positions of the teeth. Although only the gear  20 A is shown in enlarged form in FIG. 7 to avoid the complication of the illustration, the same applies to the gear  20 B as well.  
         [0057]    As shown in FIGS. 5 and 7, the valve element  24 A which is integral with the gear  20 A and is supported by frictional connection is held at a spaced-apart position above the valve seat plate  13 , and an air insulation layer  50  is formed therebetween. Hence, the pinion  17  serving as a driving member above the valve seat plate  13  and including the rotor  15 , the gears  20 A and  20 B which are rotation transmitting members, and the valve elements  24 A and  24 B are all covered with the housing  14 . The open end  14   a  of the housing  14  is then fitted to the peripheral edge portion  13   a  of the valve seat plate  13 , and their end faces are brought into close contact with each other.  
         [0058]    As shown in FIG. 8, a leaf spring  36  provided on an outer periphery of the supporting-shaft supporting recess  14   a  concentrically with the rotor  15  in an upper portion of the housing  14  urges the rotor in the axial direction to eliminate play in the thrust direction, and acts to absorb the thermal expansion and shrinkage of the rotor  15 . In addition, a lower end  37  of the rotor  15  is supported by a washer  38  formed of a ceramic-base heat insulating material. The valve-element holding device  35  is held stably since its annular base  35   a  is brought into pressure contact with the inner surface of the enlarged-diameter stepped portion  14   c  of the housing  14 . A joint S between the open end  14   b  of the housing  14  and the peripheral edge portion  13   a  of the valve seat plate  13  is gastightly sealed by TIG welding over its entire periphery in a state in which the valve elements  24 A and  24 B are retained by the valve-element holding device  35 , and the gap  50  is maintained between each of the valve elements  24 A and  24 B and the valve seat  23 . Since the air layer  50  between each of the valve elements  24 A and  24 B and the valve seat plate  13  demonstrates a heat insulating effect, welding can be effected by taking time to allow a gastight seal to be effected reliably, and since natural heat dissipation is subsequently possible, the welding quality can be improved.  
         [0059]    After the welding heat has been completely dissipated, the exterior fitting of the valve drive device  11  is effected (see FIG. 1). The stator  16  is fitted over the outer periphery of the housing  14 , and the mounting direction of the stator coil  16   a  is specified by the recess  16   c  with which the retainer  40   b  of the stator positioning frame  40  is engaged. Electric power and a control pulse signal are supplied to the stator coil  16   a  through the conductor  16   b  to rotate the rotor  15  by a predetermined number of steps, which in turn causes the gears  20 A and  20 B to be driven in the direction in which the hook portions  20   b  are disengaged from the valve-element retaining portions  34 . The moment the hook portions  20   b  are disengaged from the valve-element retaining portions  34 , the gears  20 A and  20 B are pushed by the resilient arms  35   d , move to sufficiently spaced-apart lower positions where the gears  20 A and  20 B are not interfered by the valve-element retaining portions  34 , bringing the respective sliding contact surfaces  24   a  of the valve elements  24 A and  24 B into pressure contact with the respective valve seats  23 . Further, the gears  20 A and  20 B which have become free each rotate up to and stops at the position located immediately before a non-gear projection  32  abuts against the pinion  17  (see FIG. 12A).  
         [0060]    This stop position determines an origin of mechanical starting. Accordingly, even if a pulse for forcibly effecting further rotation in the same direction is supplied to the stator coil  16   a , the rotation of the gear  20 A is mechanically prevented as the non-gear projection  32  abuts against the pinion  17 . Accordingly, an origin of the electrical signal pulse is set to this stop position. The mounting direction of the stator coil  16   a  and the relational position with the respect to the origin of gear starting are not destroyed insofar as the retainer  40   b  of the stator positioning frame  40  maintains its engagement with the recess  16   c  for specifying the direction of the stator coil  16   a . The gears  20 A and  20 B are capable of rotating smoothly in either direction irrespective of the valve-element holding device  35 . Since the origin of gear starting mechanically determines the origin of the angle of rotation of the rotor  15 , after the matching with the origin of the pulse signal, the valve elements  24 A and  24 B can be freely rotated to change the areas covering the openings of the communicating holes  25  (A, B) in correspondence with the angles of rotation of the valve elements  24 A and  24 B in view of patterns of the sliding contact surfaces  24   a  thereof, thereby making it possible to effect reliable flowrate control in accordance with predetermined patterns.  
         [0061]    Even if the stator  16  is drawn out by being disengaged from the retainer  40   b  due to an unexpected event, the restoration of the origin of the signal pulse is possible by restoring the engagement between the direction-specifying recess  16   c  of the stator  16  and the retainer  40   b  and by detecting the position where the non-gear projection  32  of the gear  20 A abuts against the pinion  17  and the rotation is mechanically prevented.  
         [0062]    [0062]FIG. 9A is a plan view in which the valve element  24  (A, B) and the gear  20  (A, B) , as viewed from the valve seat side, are combined, and FIG. 9B is a sectional view taken along line b-b of FIG. 9A. FIG. 10A is a plan view of the gear  20  (A, B), and FIG. 10B is a sectional view taken along line b-b of FIG. 10A. In addition, FIG. 10C is a rear view of FIG. 10A. The gear  20  (A, B) is provided with the non-gear projection  32  incapable of meshing with the pinion  17  by partially dropping the teeth. Consequently, the rotation of the gear  20  (A, B) is restricted, and it is possible to set the origin of starting.  
         [0063]    A through hole  20   d  through which the supporting shaft  21  (A, B) is loosely fitted, is formed in the center of the gear  20  (A, B), and a pair of bearing bushes B, which are rotatably brought into sliding contact with the supporting shaft  21  (A, B), are press fitted in openings at both ends of the gear  20  (A, B). In addition, the gear  20  has the drive pin  20   c  which is fitted to a hole with a bottom  24   b  of the valve element  24  (A, B) to restrict the radial direction. The gear  20  (A, B) rotates about the supporting shaft  21  (A, B) integrally with the valve element  24  (A, B) while bringing the valve element  24  (A, B) into pressure contact with the valve seat  23 .  
         [0064]    [0064]FIG. 11A is a rear view of the valve element  24  (A, B), and FIG. 11B is a sectional view taken along line b-b of FIG. 11A. In addition, FIG. 11C is a plan view taken in the direction of arrows c in FIG. 11B. A step is provided between a surface perpendicular to the axis of the valve element  24  (A, B) and the sliding contact surface  24   a  (−A, −B) shown by cross hatching, and the sliding contact surface  24   a  (−A, −B) slides in close contact with the smooth valve seat surface  13   e  recessed in the valve seat plate  13 . Accordingly, as for the communicating holes  25 A and  25 B covered completely by the sliding contact surface  24   a  (−A, −B), channels leading from a valve chamber  22  to the outflow pipes  28 A and  28 B are closed and are shut off from the inflow pipe  26 . By virtue of the stepped pattern of the sliding contact surface  24   a  (−A, −B), the communicating holes  25 A and  25 B undergo gradual transition between the fully open state and the fully closed state in correspondence with the angle of rotation of the gear  20  (A, B), thereby effecting regulation of the flowrate.  
         [0065]    A space portion G whose diameter is larger than the outside diameter of the supporting shaft  21  (A, B) is formed in the center of the valve element  24  (A, B). The space portion G makes it possible to maintain the close contact of necessary portions of the sliding contact surface  24   a  (−A, −B) irrespective of a defect in the flatness occurring at the time of press fitting of the supporting shaft  21  (A, B) and without being interfered by the oozing out of the welding filler metal at the root of the supporting shaft  21  (A, B). By separating the valve element  24  (A, B) from the driven gear  20  (A, B) in the above-described manner, the sliding contact portion can be formed with uniform shape and thickness, and required flatness and surface roughness can be secured for the sliding contact surface  24   a  (−A, −B). Moreover, the valve element  24  (A, B) can be fabricated by molding which facilitates the formation of a smooth surface, and a material for which heat resistance is not required can be selected freely. Thus, since the valve element  24  (A, B) can be molded with appropriate hardness and resiliency irrespective of the gear, the valve element  24  (A, B) can be formed of a material excelling in the contact based on the resiliency of its own.  
         [0066]    Next, a brief description will be given of the operation of the motor-operated expansion valve  10  with reference to FIGS. 12A to  12 D. FIG. 12A illustrates a form in which the valve seat plate  13  is viewed in the direction of arrows XII-XII of FIG. 1. The four modes in which the contour patterns of the sliding contact surfaces  24   a -A and  24   a -B open and close the communicating holes  25 A and  25 B are shown in FIGS. 12A to  12 D. FIG. 12A shows a state in which both the first communicating hole  25 A and the second communicating hole  25 B are open; FIG. 12B shows a state in which the first communicating hole  25 A is open and the second communicating hole  25 B is closed; FIG. 12C shows a state in which both the first communicating hole  25 A and the second communicating hole  25 B are closed; and FIG. 12D shows a state in which the first communicating hole  25 A is closed and the second communicating hole  25 B is open.  
         [0067]    Although the embodiment has been described above, the invention is not limited to the illustrated embodiment, and it is expected that, concerning its shape, arrangement, and the like, various changes concerning detailed parts and modifications of parts such as their restructuring can be made within the scope that does not depart from the constituent requirements of the invention. For example, the valve element may be provided with a roof portion or the like to directly raise the valve element by a spring, or a separate member having the shape of an L-shaped washer is placed between the gear and the valve element, and the separate member may be engaged with a spring to raise the valve element. In addition, the gist of the invention is naturally compatible with the motor-operated expansion valve cited as the conventional example.  
         [0068]    As is apparent from the foregoing description, according to the valve drive device in accordance with the invention, the valve element is capable of being spaced apart from the valve seat plate, and holding device is provided for tentatively retaining the valve element at a spaced-apart position spaced apart from the valve seat plate when the valve seat plate and the housing are welded together. For this reason, an air layer extremely excelling in heat insulation is formed between the valve element and the valve seat plate, so that the valve element can be protected from welding heat, and the deformation of a sliding contact surface is prevented. Therefore, it is possible to satisfactorily maintain the sealing characteristic of the valve element.