Abstract:
To provide an efficient piston pump having a small number of parts and simple assembly steps, and consuming less current in achieving a relatively-low ultimate pressure. The piston pump comprises: a suction port ( 28 ) through which gas sucked by varying the volume of a pump chamber ( 22 ) defined by a cylinder ( 12 ) and a piston ( 14 ) fitted in the cylinder ( 12 ) passes as the piston ( 14 ) is reciprocated, an exhaust port ( 20 ) through which the gas discharged by varying the volume of the pump chamber ( 22 ) passes, a suction valve ( 26 ) installed in the suction port ( 28 ) disposed on a piston top, and an exhaust valve ( 18 ) installed in the exhaust port ( 20 ) disposed on a top of the cylinder ( 12 ).

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a piston pump for compressing gas such as air. More particularly, the present invention relates to a piston pump that is compact in size and light in weight and is used in an area of a relatively low pressure. The present invention further relates to a blood pressure monitor using this piston pump.  
       RELATED ART  
       [0002]     A blood pressure monitor generally includes a pump capable of sending compressed air to fasten an arm, or the like. An automated blood pressure monitor, in particular, has been widely put on the market in recent years and a diaphragm type pump has been used (for example, JP-A-63-289276). An example will be explained with reference to  FIG. 32 . Rotation of a rotary shaft  940  of a motor  942  is converted to reciprocating motion by a crank shaft  938  and is transmitted to a connecting rod  936  and then to a crasher  954  having a fitting portion adjusted by an iron ball  952 . The crasher  954  moves up and down a diaphragm  900 . When the diaphragm  900  is pulled down by the crasher  954 , air is sucked from external atmosphere through a suction port (a suction port of a left side chamber is not shown) and further into the diaphragm as a valve  928  opens. When the diaphragm  900  is pushed up by the crasher  954 , on the other hand, an exhaust valve  918  opens and air is discharged from a discharge port  932 .  
         [0003]     However, such a diaphragm type pump has a large number of components and needs complicated assembly processes as well as a large consumed current at a relatively low ultimate pressure. On the other hand, a piston pump in the prior art contains mechanical fastening components such as screws and springs in a similar manner as the diaphragm type pump described above, is more expensive, and does not necessarily have high efficiency at a relatively low ultimate pressure. This invention is made in view of the above needs and it is an object to provide a simple and compact piston pump having high efficiency.  
       DISCLOSURE OF THE INVENTION  
       [0004]     To satisfy such needs, a piston pump according to the present invention includes a cylindrical cylinder; a piston reciprocating inside the cylinder; a suction port through which sucked gas passes when a volume of a pump chamber defined by the cylinder and the piston is changed by reciprocating motion of the piston inserted into the cylinder; an exhaust port through which discharged gas passes when the volume of the pump chamber is changed; a suction valve arranged at the suction port disposed at a top portion of the piston; and an exhaust valve arranged at the exhaust port disposed at a top portion of the cylinder.  
         [0005]     More concretely, the present invention provides a piston pump, or the like, having the following features.  
         [0006]     (1) A piston pump comprising: a cylindrical cylinder; a piston reciprocating inside the cylinder; a suction port through which gas sucked into a pump chamber defined by the cylinder and the piston passes; and an exhaust port through which the gas discharged from the pump chamber passes; wherein the piston pump sucks the gas through the suction port and discharges the gas through the exhaust port as the volume of the pump chamber is changed by reciprocating motion of the piston; wherein the suction port is arranged at a top of the piston with a suction valve, which opens as the volume of the pump chamber is increased; and wherein the exhaust port is arranged at a top of the cylinder with an exhaust valve, which opens when the volume of the pump chamber is decreases.  
         [0007]     The piston pump according to the present invention includes the cylindrical cylinder, the piston reciprocating inside the cylinder, the suction port through which gas sucked into the pump chamber defined by the cylinder and the piston passes, and the exhaust port through which gas discharged from the pump chamber passes. The cylindrical cylinder may be in a so-called tubular shape such that an outside the cylinder has a shape of a circular cylinder and an inside thereof is hollow. The outside may have an entirely different shape. The piston is inserted into this cylinder. The piston preferably has an outside shape profiling the inside shape of the cylinder. The piston may reciprocate in an axial direction of the cylinder along the inner wall of the cylinder and the piston more preferably has a shape so that this reciprocating motion can be smoothly carried out.  
         [0008]     A pump chamber encompassed by the piston (especially, a top portion (or head)), the cylinder inner wall and the cylinder top portion (or distal end portion) is defined inside the cylinder. Therefore, the volume of the pump chamber varies depending on the position of the piston in the axial direction on the cylinder side.  
         [0009]     The gas to be sucked and discharged may be ordinary gas such as air, oxygen, nitrogen, and carbon dioxide, or may be that which is subject to phase changes depending on conditions such as vapor and freon, or a mixture thereof, or that mixed with solid substance such as a particle. Furthermore, not only the gas but also fluid such as liquid can be applied to the piston pump according to the present invention. Suction and discharge to and from the pump chamber is mainly conducted in association with the change of the volume of the pump chamber, and the suction port and the exhaust port through which the gas sucked and discharged passes are arranged in at least one element forming the pump chamber (hereinafter called “forming element”). These ports (hereinafter called “openings”) may be single or plural, or one opening may operate as the suction port and the exhaust port. A plurality of openings may operate as the suction port and the exhaust port. These openings may open to the pump chamber side at least for a predetermined time or at a certain timing in each forming element in which the opening is formed.  
         [0010]     To change the volume of the pump chamber by the reciprocating motion, to suck the gas from the suction port and to discharge the gas from the exhaust port, the piston can reciprocate while keeping predetermined air-tightness with the cylinder inner wall on which it slides. The predetermined air-tightness is air-tightness sufficient enough for the piston pump. The reciprocating motion of the piston is conducted by the driving force mainly transmitted from outside to the piston. The pressure of the pump chamber drops in comparison with the external pressure when the piston moves by the external driving force while keeping air-tightness and the volume of the pump chamber increases. Therefore, the suction valve provided to the suction port may open. The suction valve can be arranged at the top portion (or head) and/or an intermediate part or a bottom part of the piston but is preferably arranged at the top portion. For, the minimum volume of the pump chamber can be much more reduced. When the volume of the pump chamber is decreased due to the motion of the piston in the opposite direction, the exhaust valve provided to the exhaust port may open. This exhaust valve may be arranged at the top portion (or distal end or head) of the cylinder.  
         [0011]     In this way, when the suction port having the suction valve is arranged at the top of the piston and the exhaust port having the exhaust valve is arranged at the top of the cylinder, arrangement efficiency can be improved in comparison with the case where both suction port and exhaust port are arranged at the top of the piston (or at the top of the cylinder) and the diameters of the cylinder and the piston can be decreased.  
         [0012]     The flow of the gas is likely to become unidirectional and a smooth flow can be expected. When the cylinder top portion is flat and the top portion of the piston is flat, too, for example, mutual interference does not easily occur when the piston exists at the upper dead point and the minimum pump chamber volume can be kept small. Eventually, the compression ratio can be increased even at the same stroke. The suction port and the exhaust port described above may be mere holes (or ports) inclusive of circular openings formed in a flat plate. They may be formed by a section of a hose, a tube, a pipe, and so forth. Though the suction valve and the exhaust valve are not limited, a flap valve or the like is suitably used and other valves of arbitrary types can be used, too. For example, a part of the periphery of a flat, flexible sheet-like valve is fixed in a hinge form and opening/closing of the valve may be conducted. It is also possible to use a valve having an umbrella shape and opened/closed due to flexibility of the umbrella surface.  
         [0013]     (2) The piston pump according to (1), wherein the suction valve is arranged on a side of the pump chamber.  
         [0014]     The arrangement in which the suction valve is arranged on the pump chamber side may represent a valve that is arranged on the pump chamber side of the piston, whose suction port is closed when the suction valve comes into close contact with the piston and is opened when force that separates the suction valve from the piston acts. For example, it is the case where the suction valve is arranged at the top portion of the piston and is arranged on the pump chamber side of the wall forming the top portion. More specifically, when a flap type valve is arranged on the pump chamber side of the wall forming the top portion of the piston and is so disposed as to cover the suction port formed in the wall forming the top portion, the suction valve can be opened without using a high control technology, in particular, when the pump chamber is at a lower pressure than the external pressure and can be closed when the pump chamber is at a higher pressure than the external pressure. Here, the external pressure may mean the pressure or the space on the opposite side to the pump chamber side of the suction port or the atmospheric pressure or may mean the pressure or the space on the feeding side of the gas to be sucked.  
         [0015]     (3) The piston pump according to (1) or (2), wherein the exhaust valve is arranged on an opposite side to the pump chamber of the top of the cylinder.  
         [0016]     The arrangement in which the exhaust valve is arranged at the top portion of the cylinder on the opposite side to the pump chamber may mean that the exhaust valve is arranged at the top portion of the cylinder and is arranged on the wall forming the top portion on the opposite side to the pump chamber. Here, the top portion of the cylinder is preferably a portion that forms one of the ends of the cylinder in the axial direction. The axial direction is more preferably a direction extending along the direction of the reciprocating motion of the piston. The top portion of the cylinder is preferably a member that closes one of the ends of the cylinder and is more preferably a member that forms a plate or a wall.  
         [0017]     When the flap type valve is arranged on the opposite side of the wall forming the top portion of the cylinder to the pump chamber side and the valve is so installed as to cover the exhaust port, the exhaust valve can be closed without using a particularly high control technology when the pressure of the pump chamber becomes lower than external air. When the pump chamber reaches a higher pressure than external air, the exhaust valve can be opened. Here, the external air may mean the space or the pressure of the exhaust port on the opposite side to the pump chamber side and may mean the space or the pressure on the feed side of the gas to be exhausted. As described above, because the suction valve and the exhaust valve operate in the interlocking arrangement, the pump can be efficiently operated.  
         [0018]     (4) The piston pump according to any one from (1) to (3), wherein the piston has an opening communicating with the suction port on an opposite side to the pump chamber, wherein the opening is arranged so as to allow air sucked through the suction port into the pump chamber to pass and a plenum capable of storing the air to communicate with the opening; and wherein the plenum is encompassed by an enclosure having at least one plenum suction port.  
         [0019]     Here, the plenum may include a space such as the air chamber. The opening portion communicating with the suction port may be open to the plenum so as to be allowed to suck air from the plenum. This plenum is encompassed by an enclosure being composed of one or a plurality of walls, and such an enclosure may define the principal portions of the plenum. The shape of the enclosure may include a rectangle, a circle or their combination and a so-called boxed shape can encompass the plenum. The plenum suction port may be an opening formed in the plenum. For example, the plenum suction port may include an opening portion formed in the enclosure of the plenum. A valve that can be opened and closed may be disposed in this opening portion.  
         [0020]     (5) A piston pump including a cylindrical cylinder having a top portion; a piston reciprocating inside the cylinder; a suction port through which gas sucked into a pump chamber defined on a side of the top portion of the cylinder by the cylinder and the piston passes; and an exhaust port through which the gas discharged from the pump chamber passes; wherein the piston pump sucks the gas from the suction port and discharges the gas through the exhaust port as a volume of the pump chamber is changed by reciprocating motion of the piston; wherein the suction port is arranged at the top portion of the cylinder with a suction valve, which opens when the volume of the pump chamber is increased; and the exhaust port is arranged at the piston with an exhaust valve, which opens when the volume of the pump chamber is decreased.  
         [0021]     (6) The piston pump according to (5), wherein the suction valve is arranged on a side of the pump chamber.  
         [0022]     (7) The piston pump according to any one from (1) to (6), wherein the piston engages with a coupling member in such a manner that the coupling member is capable of turning in a circumferential direction thereof, and wherein the coupling member is connected to a connecting member driven such that the engaged piston is reciprocated inside the cylinder.  
         [0023]     The piston may be connected to the connecting member through the ring-like coupling member capable of rotating in the circumferential direction of the piston. Being capable of turning in the circumferential direction of piston may represent the state where the coupling member is capable of turning clockwise and/or counterclockwise. The turning may be turning of one round or partial turning. The coupling member may be a member that connects the piston and the connecting member and transmits mechanical force from the connecting member to the piston while keeping a predetermined degree of freedom with the piston. The coupling member may include a coupling member (inclusive of a coupling ring of later-appearing embodiments) disposed on the side other than the top portion (that is, end portion of piston positioned on pump chamber side), for example, the base bottom side (that is, the side corresponding to far side from pump chamber), and capable of rotating in the circumferential direction of the piston (for example, in circumferential direction when piston is a circular cylinder piston). The connecting member (which may include a connecting ring in later-appearing embodiments) connected to this coupling member may be driven by external driving force. This external driving force may include any kind and is not limited. For example, it may be driving force by a crank shaft connected to a motor shaft. The crank shaft converts the rotary motion to the reciprocating motion.  
         [0024]     (8) The piston pump according to (7), wherein the piston comprises therein a recess portion formed continuously in the circumferential direction of the piston and engaged with the coupling member, the recess portion including at least a part of a first predetermined spherical surface; wherein the coupling member has a projection portion formed continuously in the circumferential direction such that the projection portion corresponds to the recess portion, the projection portion including at least a part of a predetermined second spherical surface to engage with the recess such that the projection portion is capable of turning in the circumferential direction and in an axial direction; and wherein the piston reciprocates when the projection portion and the recess portion engage with each other so as to transmit driving force from the connecting member to the piston.  
         [0025]     The inside of piston may include the side that does not face the inner wall of the cylinder. In a piston having a circular cup-like shape one of the ends of which is closed, for example, the term may include the inside of the cup or the cylindrical hollow portion. The inside recess portion may contain a groove that is recessed to a portion corresponding to the inner wall of the cup. The recess of this recess portion more preferably has substantially the same radius of curvature as that of a spherical surface formed when a ball is inscribed with the inside of the cup. The projection portion of the coupling member more preferably has substantially the same radius of curvature as that of a spherical surface that is substantially the same, or a little smaller, so that the recess portion can be engaged. The recess portion and/or the projection portion are more preferably continuous in the circumferential direction of the piston.  
         [0026]     (9) The piston pump according to any one from (1) to (8), wherein at least a portion of the piston sliding on an inner wall of the cylinder is composed of a self-lubricating material.  
         [0027]     The construction in which at least a portion of the piston sliding on the inner wall of the cylinder is formed of a self-lubricating material may be a construction in which a member formed of such a self-lubricating material is disposed on the inner wall side of the cylinder, that is, around the outer periphery of the piston. The construction may include a construction in which the self-lubricating material is coated around the outer periphery of the piston. The self-lubricating material need not always be disposed around the entire outer periphery but may be disposed partially. To make the lubricating performance uniform in the peripheral direction, the material is preferably arranged in the entire outer periphery and may be arranged in a single or a plurality of layers such as a belt wound on the piston, whenever necessary. The self-lubricating material has by itself the self-lubricating property and may be a mixture of the self-lubricating material with a lubricant in other cases, and they can be used appropriately without limitation. It is possible, for example, to use a composite material of an organic solid lubricant such as Teflon (registered trade mark) and an inorganic solid lubricant such as molybdenum disulfide and graphite. Furthermore, a lubricant impregnated with a liquid such as oil or silicon may be suitably used. Polymer materials and synthetic resins explained in later-appearing embodiments may also be included. These materials can be used for the piston, the cylinder, the piston head, the cylinder head, the coupling member, the connecting member, the crank shaft, the housing and other components.  
         [0028]     The materials excellent in the sliding performance can be used not only for the piston but also for other members (for example, the cylinder, the coupling member, the connecting member, etc) and their counter-part members. It is preferred to use the material described above for both of them depending on the sliding condition. Not only the material but also the surface characteristics (surface coarseness, for example) of the material are sometimes important.  
         [0029]     (10) The piston pump according to any one from (1) to (9), wherein the cylinder comprises a top plenum defined by a top enclosure fixed to the top portion of the cylinder and a motor housing fixed at a position spaced apart by a predetermined distance from the top portion such that the cylinder is connected and fixed to at least a part of the motor housing; wherein the motor housing is composed of a base portion fixed to the cylinder such that the base portion holds a motor for driving the piston so as to reciprocate inside the cylinder and a cover portion disposed along the base portion such that the cover portion fastens the motor by sandwiching the motor with the base portion; and wherein the cover portion and the base portion are engaged with a connecting mechanism capable of engagement and disengagement.  
         [0030]     The top enclosure may include closure members (which may include cylinder head or head plate, for example) of the top portion of the cylinder and walls encompassing the top plenum. For example, the top enclosure may include the enclosure member described above as a base material, side walls having a predetermined height and extending substantially vertically on and over the base material and a ceiling plate expanding substantially parallel to the base material on the side walls. The top plenum may include a space such as an air chamber. The top enclosure may include an exhaust or discharge port opening to the outside of a piston pump system and communicating with the plenum. This discharge port may take a tubular shape as a discharge port. A portion spaced apart by a predetermined distance from the top portion of the cylinder may exist at a position a little spaced apart from the top portion along the cylinder. In other words, the motor housing is more preferably fixed to the cylinder but not directly to the cylinder top portion. When the cylinder is used as a structure, the weight or size of the overall piston pump can be reduced. Therefore, the motor housing is fixed to the cylinder and the motor fixed to this motor housing is fixed to the cylinder.  
         [0031]     (11) The piston pump according to any one from (1) to (10), wherein the piston pump is connected to a blood pressure monitor.  
         [0032]     (12) A piston pump in which a piston reciprocates inside a cylinder having a cylinder head for pressurization, the piston pump is characterized in that: 
        &lt;1&gt; an inner diameter of the cylinder is not exceeding approximately 20 mm;     &lt;2&gt; a throughput of the piston pump is not exceeding approximately 6.0 liters/min;     &lt;3&gt; pressurization characteristics thereof can be maintained even after approximately 10,000 reciprocating motions of the piston; and     &lt;4&gt; the cylinder and the cylinder head are non-mechanically coupled.        
 
         [0037]     The construction in which &lt;1&gt; the inner diameter of the cylinder is equal to or not greater than approximately 20 mm in the piston pump that reciprocates inside the cylinder having the cylinder head and conducts pressurization may be a construction in which the inner diameter of the cylinder used as a main component of the piston pump is equal to or not greater than approximately 20 mm. More preferably, the cylinder inner diameter of a pump for a wrist blood pressure monitor is equal to or not greater than approximately 8.5 mm and the cylinder inner diameter of an upper arm blood pressure monitor is equal to or not greater than approximately 18 mm. Here, the cylinder head may represent a member (inclusive of component) at the cylinder top portion and may include a member (inclusive of component) directly bonded to the member of the cylinder top portion. The size of the piston pump according to the present invention can be made compact due to its structure and its component structure. The construction in which &lt;2&gt; the discharge throughput of the piston pump is equal to or not greater than approximately 6.0 liters/min may represent that the discharge throughput when the pump is operated under a non-loaded condition is equal to or not greater than approximately 6.0 liters/min. More preferably, the discharge throughput of the piston pump is equal to or not greater than approximately 1.0 liter/min in the case of a wrist type pump and is equal to or not greater than approximately 5.5 liters in an upper arm type pump. The construction in which &lt;3&gt; pressurization characteristics can be maintained even by reciprocating motion of the piston of approximately 10,000 times may represent that predetermined performance of the piston pump such as a maximum ultimate pressure and/or a pressure ultimate speed can be maintained even when the piston is reciprocated approximately 10,000 times. More preferably, the pressurization characteristics can be maintained even by the reciprocating motion of the piston of at least approximately 30,000 times. The construction in which &lt;4&gt; the cylinder and the cylinder head are non-mechanically coupled may represent that the cylinder head formed by bonding the valve plate and the manifold constituting the cylinder and the end face of the top portion of the cylinder are coupled by a non-mechanical method such as bonding, welding, deposition, and the like. Bonding is particularly preferably made by welding and/or deposition. The cylinder and the cylinder head may well be bonded by welding and/or deposition without using screws or fitting using springs. According to such a construction, seal performance can be easily secured and the pump can be rendered compact. For, when mechanical bonding members such as the screws are used, it is necessary in some cases not only to bore screw holes or to secure spaces for screw threads but also to use screws capable of securing air-tightness.  
         [0038]     (13) A method of producing a piston pump including a cylindrical cylinder, a piston reciprocating inside the cylinder; a suction port through which gas sucked into a pump chamber defined by the cylinder and the piston passes and an exhaust port through which the gas discharged from the pump chamber passes; the method comprising the steps of: producing a piston pump pre-assembly comprising the cylinder and a cylinder top portion in which the exhaust port is formed; conducting a leakage inspection of the piston pump pre-assembly; and producing a piston pump by further assembling components to the piston pump pre-assembly.  
         [0039]     The piston pump pre-assembly may include the cylinder and the cylinder top portion in which the exhaust port is formed, and may be a semi-finished product of the piston pump containing those components which are necessary for conducting a leakage inspection of the piston pump. The step of forming this piston pump pre-assembly does not require assembly using screws and springs. In other words, the production of the piston pump pre-assembly may be carried out by conducting combination inclusive of butting of components and assembling and conducting non-mechanical bonding such as bonding, welding, deposition, and so forth. The leakage inspection of the piston pump pre-assembly is necessary for the piston pump but need not always be made for the finished product of the piston pump. The production of the piston pump by further assembling components to the piston pump pre-assembly may mean that those components which are once removed from the piston pump pre-assembly in the subsequent step of finishing the piston pump need not be assembled again.  
         [0040]     The piston pump to be connected to the blood pressure monitor may represent a piston pump that is exclusively used for an instrument for measuring the blood pressure. However, the piston pump does not exclude other applications and may include the application of the measurement of the blood pressure. The piston pump used for the instrument for measuring the blood pressure may include a pump for generating an air pressure necessary for pressing (fastening) the portion necessary for the blood pressure measurement such as the wrist or the arm of people.  
         [0041]     (14) A blood pressure monitor utilizing the piston pump according to any one from (1) to (12). 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]      FIG. 1  is a view showing in section a piston pump according to an embodiment of the present invention under the state where a motor housing is open.  
         [0043]      FIG. 2  is a view showing the piston pump according to the embodiment of the present invention under the state where a side surface of the piston pump is partially shown in section by removing a part of components.  
         [0044]      FIG. 3  is an expanded view of the piston pump according to the embodiment of the present invention when the piston pump is expanded into components.  
         [0045]      FIG. 4  is a sectional view of a piston as a component of the piston pump according to an embodiment of the present invention.  
         [0046]      FIG. 5  is a perspective view when the piston as a component of the piston pump according to the present invention is viewed from its top.  
         [0047]      FIG. 6  is a perspective view when the piston as a component of the piston pump according to the present invention is viewed from its base bottom side.  
         [0048]      FIG. 7  is a side view of a connecting ring as a component of the piston pump according to the embodiment of the present invention.  
         [0049]      FIG. 8  is a sectional view of the connecting ring as a component of the piston pump according to the embodiment of the present invention.  
         [0050]      FIG. 9  is an upper surface view of the connecting ring as a component of the piston pump according to the embodiment of the present invention.  
         [0051]      FIG. 10  is a perspective view of the connecting ring as a component of the piston pump according to the embodiment of the present invention.  
         [0052]      FIG. 11  is a front view of the connecting ring as a component of the piston pump according to the embodiment of the present invention.  
         [0053]      FIG. 12  is a schematic sectional view for explaining the function of the connecting ring as a component of the piston pump according to the embodiment of the present invention.  
         [0054]      FIG. 13  is an X-X′ sectional view of  FIG. 12 .  
         [0055]      FIG. 14  is a sectional view showing deformation of a recess portion of the piston when the connecting ring shown in  FIG. 13  is taken out.  
         [0056]      FIG. 15  is a schematic view when deformation of the recess portion of the piston shown in  FIG. 14  is viewed from the base bottom side of the piston.  
         [0057]      FIG. 16  shows a gas leakage inspection apparatus of the piston pump, and a method for the apparatus, according to the embodiment of the present invention.  
         [0058]      FIG. 17  is a view showing in a section a piston pump pre-assembly used for the gas leakage inspection of the piston pump according to the present invention.  
         [0059]      FIG. 18  is a graph showing the relation between an ultimate pressure reached by the piston pump according to the embodiment of the present invention and a consumed current.  
         [0060]      FIG. 19  is a flowchart showing a production method of the piston pump according to the present invention inclusive of a gas leakage inspection step.  
         [0061]      FIG. 20  shows a section of the piston pump according to the embodiment of the present invention under the state where a cover portion of the motor housing is closed.  
         [0062]      FIG. 21  shows a section of the piston pump according to the embodiment of the present invention under the state where suction/exhaust is reversed and a cover with pin of the motor housing is opened.  
         [0063]      FIG. 22  is a perspective view showing a production form of a motor housing having a cover with pin and used for the piston pump according to the embodiment of the present invention.  
         [0064]      FIG. 23  is a perspective view showing an assembly form of the motor housing having a cover with pin and used for the piston pump according to the embodiment of the present invention.  
         [0065]      FIG. 24  is a perspective view showing the assembly form when a motor engaging with a piston is inserted into a motor housing having a cover with pin and used for the piston pump according to the embodiment of the present invention.  
         [0066]      FIG. 25  is a perspective view showing an overall form of the motor shown in  FIG. 24 .  
         [0067]      FIG. 26  is a perspective view under the state where the piston pump according to the embodiment of the present invention has been assembled.  
         [0068]      FIG. 27  is an upper surface view showing a control principal portion of a blood pressure monitor to which the piston pump according to the embodiment of the present invention can be fitted.  
         [0069]      FIG. 28  is a sectional view of a substrate of the control principal portion shown in  FIG. 27 .  
         [0070]      FIG. 29  is an upper surface view of a pressurization portion when a diaphragm pump according to the prior art is fitted to the control principal portion shown in  FIG. 27 .  
         [0071]      FIG. 30  is an upper surface view of the control principal portion when the piston pump according to the present invention is fitted to the control principal portion shown in  FIG. 27 .  
         [0072]      FIG. 31  shows a section of the piston pump according to the embodiment of the present invention under the state where a crank chamber at a cylinder lower part is sealed and a motor housing equipped with a crank chamber suction port is closed.  
         [0073]      FIG. 32  is a view showing, partly in section, a diaphragm pump of a Comparative Example.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0074]     The present invention will be hereinafter explained in further detail about an embodiment thereof with reference to the drawings. The embodiment represents concrete component names, materials, numerical values, etc, as a preferred example of the present invention but the present invention is not limited to the embodiment.  
         [0075]      FIG. 1  is a sectional view of a piston pump  10  according to an embodiment of the present invention. The piston pump  10  of this embodiment mainly comprises a housing for accommodating a motor  42 , constituted by a housing substrate material  44  and a cover  47 , a piston  14  driven by the motor  42 , a cylinder  12  into which the piston  14  is inserted and a valve plate  16  forming a cylinder top portion, and a manifold  30  deposited to the valve plate  16 . The motor  42  positioned at a lower left position in the drawing is supported by the cover  47  in such a manner as to strike the lower part of the housing substrate material  44 . A degree of freedom of the motor  42  in a transverse direction in the drawing is restricted by an upward protuberance  49  formed at a substantial center of the cover  47  and the degree of its freedom in a rotating direction is restricted as the motor  42  is sandwiched between the housing substrate material  44  and the cover  47 . The cover  47  is connected by a side member  45  playing the role of a hinge in such a manner as to hang down from the housing substrate material  44 . The cover  47  closes the housing by sandwiching the motor  42  with the housing substrate material  44  as described above and fixes the motor  42  inside the housing. At this time, a protuberance  43  on the right side of a protuberance portion extending upward at the extreme right of the cover in the drawing engages with an opening  51  formed at a lower part of a side member  46  existing at a position opposing the side member  45  to prevent the cover  47  from falling down in the drawing and to keep it under the closed state. The cylinder  12  is positioned on the right side in the drawing, is coupled and fixed with the housing (particularly, the housing substrate material  44 ) and extends vertically in the drawing. The piston  14  is inserted into the cylinder  12  and reciprocates in an axial direction that is the vertical direction in the drawing. The valve plate  16  is coupled with and arranged on the cylinder  12  in the drawing by depositing a deposition portion  15  so as to keep gas-tightness and forms the top portion of the cylinder  12 . The valve plate  16  has the manifold  30  that is deposited to a deposition portion  17  at the upper part in the drawing. A space  31  defined by the manifold  30  and the valve plate  16  is a chamber for air exhausted and the deposition portion  17  is deposited in such a manner as to keep air-tightness of this chamber. In other words, the space  31  functioning as a top plenum is defined by the valve plate  16  and the manifold  30  that together function as a top enclosure. An air outlet (discharge port  32 ) of the chamber constituted by the space  31  is disposed on the left side of the manifold  30  in the drawing.  
         [0076]     The rotation of the driving shaft  40 , that extends to the right in the drawing, of the motor  42  accommodated in the housing is transmitted to the crank shaft  38  pressure-fitted into the driving shaft  40 . Because the driving shaft  40  is press-fitted to the position deviated by a predetermined distance L from the center of the crank shaft  38  having a cylindrical shape, however, the rotary motion is converted to the reciprocating motion in the vertical direction (see  FIG. 2 ). The crank shaft  38  is so fitted into the ring opening portion  36   c  (see  FIG. 8 ) of the connecting ring  36  as to be capable of rotating. The outer periphery of the crank shaft  38  slides with the inner surface of the open portion of the connecting ring  36  when the crank shaft  38  rotates. For, the connecting ring  36  is fixed in the rotating direction described above and cannot follow and rotate. The driving shaft  40  is eccentrically connected to the crank shaft  38 , the axial position of the driving shaft  40  is fixed by a bearing of the motor  42  and the motor  42  is fixed to the housing. Therefore, the connecting ring  36  changes its position relative to the housing, that is, relative to the fixed cylinder  12  but is restricted by the coupling ring  34  formed integrally with the connecting ring  36 , the piston  14  to which the coupling ring  36  is connected and the inner wall of the cylinder  12  into which the piston  14  is fitted, thereby causing the reciprocating motion of the piston. The coupling ring  34  integrally bonded with the connecting ring  36  absorbs to a certain extent the motion of the connecting ring  36  due to the crank shaft  38  in the foreground and depth sides of the drawing by freedom of the coupling ring  34  in the piston circumferential direction and by the spherical outer peripheral surface of the coupling ring received by a spherical seat  37  of the piston inner surface in the circumferential direction and transmits this motion to the piston  14  as the vertical reciprocating motion in the drawing (see  FIG. 4 ). In other words, the rotation of the motor  42  allows the piston  14  fitted into the cylinder  12  to reciprocate in the vertical direction in the drawing.  
         [0077]     When the piston  14  is pulled down in the drawing, the volume of the pump chamber  22  defined by the top portion of the piston  14 , the inner wall of the cylinder  12  and the valve plate  16  at the top of the cylinder increases and the pressure inside the pump chamber  22  drops. Consequently, an umbrella-shaped suction valve  26  inserted into a hole  29  formed at the center axis position of the piston  26  opens and air is introduced through the suction port  28  from the external atmosphere below the piston  14 . The coupling ring  34  has a ring-like shape and its center portion is hollow with the exception of the connection portion with the connecting ring  36 . Therefore, air sucked from the suction port  28  comes from the hollow portion  35  of the piston  14  (see  FIG. 4 ). This air passes through the spaces on both of the sides (or one of the sides) of the connection portion of the coupling ring  34  pressure fitted into the piston  14  and from the lower side (or the base bottom side) of the piston  14 . The crank shaft  38 , etc, is arranged and accommodated in the housing (housing substrate material  44 , side members  45  and  46  and cover  47 ) below the piston  14  but has sufficient opening because a partition plate  48  has openings. Consequently, air can be sucked substantially freely from below the piston pump  10 . Incidentally,  FIG. 1  shows the state where the piston  14  is pulled down almost to the lower dead point.  
         [0078]     The volume of the pump chamber  22  decreases while the pressure inside the pump chamber  22  increases when the piston  14  is pulled up in the drawing. Therefore, air having a high pressure inside the pump chamber opens the umbrella-shaped exhaust valve  18  fitted into the hole  24  disposed at a position of the valve plate  16  corresponding to the cylinder center axis and arranged at the top (or distal end portion) of the cylinder  12  through the exhaust port  20  opened by the valve plate  16  arranged at the top (or distal end portion) of the cylinder  12 . Air inside the pump chamber is from thence exhausted. Air so exhausted is discharged from the discharge port  32  through the space  31  inside the manifold.  
         [0079]     In the embodiment, the portions that frequently slide are a set of the crank shaft  38  and the connecting ring  36  and a set of the piston  14  and the cylinder  12 . To satisfy their sliding characteristics, an organic material such as a synthetic resin is preferably used and its surface coarseness is as small as possible and is preferably a mirror surface or approximate to the mirror surface. More concretely, the crank shaft  38 , the connecting ring  36  and the piston  14  of this embodiment use “Lubmer” (registered trade mark) of Mitsui Petrochemical Co., Ltd. This Lubmer is a specific polyolefin resin having high sliding characteristics. It is also possible to use ultra-high molecular weight polyethylene (for example, “Hizex Million”, a product of Mitsui Petrochemical Co., Ltd), polyacetal and nylon (6, 66) as the sliding member besides the specific polyolefin resin described above. In this embodiment, the cylinder  12 , the valve plate  16  and the manifold  30  that are integral with the housing are formed of a polymer material comprising “Stylac” (registered trade mark) of Asahi Kasei K. K. These components are made of the same ABS in view of their fusibility. The valve uses an ordinary NBR rubber.  
         [0080]     Each bonding member shown in the drawing is bonded by ultrasonic deposition at a respective deposition portion.  
         [0081]      FIG. 2  is a partial sectional view of the piston pump of the embodiment when a part of the components viewed from the right side of  FIG. 1  is removed. The uppermost rectangular component is the manifold  30 . The manifold  30  and the valve plate  16  below the former are bonded to each other by ultrasonic deposition capable of keeping air-tightness in the same way as bonding between the cylinder  12  integrated with the housing below the valve plate  16  and the valve plate  16 . The piston  14  inserted into the cylinder  12  has the suction port  28  and the suction valve  26  (see  FIG. 1 ). The spherical seat  37  exists in the recess portion formed in the inner peripheral surface of the piston  14  below the piston  14  (see  FIG. 4 ). The spherical seat  37  is finished into the annular spherical shape so that it mates with the convex outer circumference of the coupling ring  34  that is brought into contact with the spherical seat  37 . The coupling ring  34  is press-fitted into this recess. The convex of the coupling ring  34  and the upper and lower tilt portions of the recess in which the coupling ring  34  exists and the coupling ring  34  move up and down the piston  14  without falling off from this recess. The position of the driving shaft of the motor  42  does not change with respect to the housing in the drawing. Therefore, the connecting ring  36  moves up and down and to the right and left in the drawing with respect to the housing when the motor  42  rotates. When moving up and down, the connecting ring  36  simultaneously moves up and down the piston  14 . When the connecting ring  36  moves to the right and left, however, the connecting ring  36  undergoes deformation at the joint portion with the coupling ring  34  because the cylinder  12  restricts the movement of the connecting ring  36 . It is therefore possible to absorb this motion, or to absorb this motion with the coupling ring  34  due to the slip in the spherical seat  7 . Because the coupling ring  34  has freedom to a certain extent in its circumferential direction, it can absorb the movement of the driving shaft  40  of the motor  42 . Therefore, the piston pump can flexibly cope with unexpected movement and deformation of the piston  14  and the crank shaft  38  because freedom for absorbing the movement is secured in various directions.  
         [0082]      FIG. 3  is a view when the piston pump  10  of the embodiment is expanded into each component. The piston pump  10  serially includes, from above, the manifold  30  having the discharge port  32 , the valve  18  as the exhaust valve inserted into the hole  24  of the valve plate  16 , the valve plate  16  bonded to the manifold  30  by ultrasonic welding, the cylinder  12  having this valve plate  16  as its top (or distal end portion), the housing (housing substrate material  44 , cover  47 , side members  45  and  46 ) integrally including the cylinder  12 , the valve  26  inserted into the center hole of the piston  14  and operating as the suction valve, the piston  14  inserted into the cylinder  12 , the coupling ring  34  press-fitted into the spherical seat  37  as the recess of the lower part (or base bottom side) of the inside of the piston  14  and transmitting the driving force of the reciprocating motion to the piston  14 , the connecting ring  36  integrally coupled with the coupling ring  34 , the crank shaft  38  inserted to the inner circumference of the connecting ring  36 , the driving shaft  40  pressure fitted into the crank shaft and driven for rotation and the motor  42  for driving the driving shaft  40 . As can be seen clearly from the drawing, the components are mainly connected and assembled in the vertical direction in the drawing and assembly itself is extremely simple and easy. Therefore, this piston pump can be made compact in scale. Furthermore, mechanical fastening members (screws, rivets, bolts and nuts, nails, etc, for example) that have ordinarily been used for assembling these components are not necessary. In other words, it can be the that assembly is made by using non-mechanical fastening members. Assembly by using non-mechanical fastening members may mean bonding by bonding, deposition, welding, etc and assembly such as press-fitting, fitting, insert molding, insertion, etc (inclusive of detent of assembly component itself, latch mechanism by engagement member). The assembly step becomes short in time and production efficiency is high because assembly is made by such non-mechanical fastening members. In this embodiment, the manifold  30 , the valve plate  16  and the cylinder  12  are bonded by ultrasonic deposition, respectively. The valve  18  and the valve plate  16 , the valve  26  and the piston  14 , the piston  14  and the coupling ring  34 , the connecting ring  36  and the crank shaft  38  and the crank shaft  38  and the driving shaft  40  can be detachably assembled by fitting, respectively.  
         [0083]     FIGS.  4  to  6  are views for explaining in detail the piston  14 . The hole  29  for fitting the valve is disposed at the center of the piston  14  in such a manner as to communicate with the hollow portion  35  inside the piston and a plurality of suction ports  28  is arranged around the hole. The umbrella portion of the valve  26  (see  FIG. 3 ) of the valve  26  fitted into the hole  29  covers these suction ports. The recess is formed below (or base bottom side) the hollow portion  35  inside the piston and the spherical seat  37  is disposed in the recess.  
         [0084]     FIGS.  7  to  11  show the connecting ring  36  molded integrally with the coupling ring  34  as the coupling member when the connecting ring  36  is viewed from various angles. A projection portion  34   a  is formed around the entire outer circumference of the coupling ring  34  and the curvature of this projection portion  34   a  is so set as to be capable of rotating in, or engaging rotatably with, the spherical seat  37  (see  FIG. 4 ) existing in the recess of the piston  14 . The curvature of the projection portion  34   a  is a little smaller than the curvature of the spherical seat  37 , for example. In other words, the radius of curvature of the spherical seat  37  is a little greater than the radius of curvature of the projection portion  34   a . A hollow portion  34   b  exists on the inner circumferential side of the coupling ring  34  and operates as an air passage. The coupling ring  34  and the connecting ring  36  are coupled by a coupling portion  33  and are integrally molded.  
         [0085]     When this integral member is viewed from the upper surface, the rectangular coupling portion  33  can be seen through the hollow coupling ring  34 . Gaps  33   a  are provided above and below the coupling portion  33  and operate as passages for feeding necessary air to the suction ports  28  of the piston  14 . The connecting ring  36  has substantially flat outer and inner circumferential surfaces  36   a  and  36   b . The crank shaft  38  is fitted into the ring opening portion  36   c  as the space defined by this inner circumferential surface  36   b.    
         [0086]     FIGS.  12  to  15  schematically show the mode of engagement and disengagement between the spherical seat  37  as the recess portion of the piston  14  and the projection portion  34   a  of the coupling ring  34 . The coupling ring  34 ′ that exists inside the spherical seat  37  at a substantially horizontal position when the piston is driven can rotate not only in the circumferential direction of the piston  14  but also in the direction corresponding to the movement in the axial direction as shown in  FIG. 12 . In the drawing, the member  14 ′ representing schematically the base bottom portion of the piston  14  is shown upside down in the reverse way to  FIG. 1 . The coupling ring  34  can be pivotally rotated in this way when the connecting ring  36  protruding from the spherical seat  37  is moved back and forth and to the right and left. However, it is extremely difficult for the coupling ring  34  to fall off as such because the diameter of the opening  19  at the upper part of the member  14 ′ schematically representing the base bottom portion of the piston  14  is sufficiently smaller than the diameter of the projection portion  34   a  of the coupling ring  34 .  
         [0087]     Therefore, to remove the coupling ring  34  from the recess portion having the spherical seat  37 , the coupling ring  34  is tilted by an angle of inclination a in such a manner that at least a part of the projection portion  34   a  protrudes from the opening  19  of the member  14 ′ schematically representing the base bottom portion of the piston  14  on the base bottom side (upper side in the drawing). Next, the connecting ring  36  is pushed with the portion  19   a  that is the edge of the opening  19  and strikes the side surface of the connecting ring  36  as the support point to allow a pulling force F for pulling out the coupling ring  34  from the opening  19  to operate. At this time, the opening  19  is expanded by the outer circumferential surface of the projection portion  34   a  in P and Q directions. Because this expanding force operates on only the portion that keeps contact in practice, the original opening  19 ′ need not be expanded as a whole but may be sufficiently expanded so as to form an elliptic opening  19 . Therefore, the pulling force F need not be much great.  
         [0088]      FIG. 16  is a view for explaining a gas leakage inspection step of the piston pump according to this embodiment. The piston pump of the embodiment mainly handles a gas of a low pressure and is not considered as a pressure container. Therefore, a predetermined inspection is necessary. The greatest square in the drawing represents an inspection apparatus  50 . The inspection apparatus  50  has a round start switch  54  at an upper part of a front panel and a green lamp  56  and a red lamp  58  indicating the inspection result are arranged below the start switch  54 . The inspection apparatus  50  has therein a 100 cc-tank  60  (capacity is different when inspection standard is different). The tank  60  is connected to a pipe  62  extending outward. A sensor  52  is fitted to the tank  60  and measures the change of the pressure inside the tank. A power source is disposed at a lower right position of the inspection apparatus  50  and can be connected to the pump, etc, as the inspected body. A pump pre-assembly  11  as the inspection object is connected to the distal end of the pipe  62 . Another pipe  64  is connected in a T shape to an intermediate part of the pipe  62 . A valve  66  is arranged at an intermediate part of the pipe  64  and is connected to an external pump  68 . Here, the power source is used when the inspection object can by itself make pressurization and is not particularly necessary in this embodiment because the external pump  68  conducts pressurization.  
         [0089]      FIG. 17  shows the pump pre-assembly  11  as the inspection object shown in  FIG. 16 . The inspection object mentioned hereby includes the valve plate  16  and the exhaust valve  18  deposited to the top of the cylinder  12  and the manifold  30  deposited to the valve plate  16  in the piston pump of the embodiment described above exclusive of the piston and its accessorial components and the motor and its accessorial components. Air-tightness of the space  31  defined by the valve plate  16  and the manifold  30  or the air chamber is the inspection object in the inspection and the piston, etc, need not be inspected. To carry out the inspection, the valve  66  is first opened and the pressure inside the tank is set to approximately 300 mmHg by the external pump  68  (see  FIG. 16 ). At this time, the pump pre-assembly  11  as the inspection object may be connected so that it is not affected by the pressurization step by disposing still another valve at an intermediate part of the pipe  62 . When a predetermined pressure is reached by the external pump  68 , the valve  66  is closed, the start switch  54  is turned ON and the inspection is started. When the absence of leakage to a certain extent is confirmed after the passage of approximately 15 seconds, the green lamp  56  is lit and when the leakage is great, the red lamp  58  is lit. As described above, in the piston pump according to this embodiment, the inspection can be made under the state of the piston pump pre-assembly, and defective products can be rejected at an early stage and productivity can be improved.  
         [0090]      FIG. 18  is a graph showing an ultimate pressure and consumed power when the piston pump of this embodiment is operated at a predetermined capacity (100 cc in the drawing). The result of a diaphragm pump having a similar capacity is indicated by broken line. In this graph, a large consumed current means the necessity of large power and when comparison is made at the same pressure, lower power efficiency means greater consumed power. In the piston pump according to this embodiment, the current when a pressure of approximately 5 KPa is reached is approximately 180 mA and the current value becomes greater as the pressure rises. The current value is approximately 270 mA at a pressure of approximately 27 KPa necessary for a blood pressure monitor that can be conceived as an application example of this piston pump. In contrast, in the diaphragm pump, the current value is approximately 270 mA at approximately 5 KPa and approximately 320 mA at approximately 27 KPa. In other words, it can be understood that the piston pump according to the embodiment has the advantage that it is excellent in current efficiency in a range that is used in practice.  
         [0091]      FIG. 19  illustrates a production process of the piston pump according to this embodiment. First, a valve that is to become the exhaust valve  18  is fitted into the hole  24  of the valve plate  16  to fabricate a valve plate assembly (S- 01 ). Next, the cylinder  12 , the valve plate assembly and the manifold  30  are bonded by ultrasonic deposition to fabricate the piston pump pre-assembly (S- 02 ). The leakage inspection described above is carried out for this piston pump pre-assembly as the inspection object (S- 03 ). Those inspection objects which are approved in the inspection are sent to the next step and those rejected are repaired or discarded. The piston assembly is fabricated in parallel with the steps described above. First, the valve that is to become the suction valve  26  is fitted into the hole  29  of the piston  14  to fabricate the piston equipped with the valve (S- 11 ). Next, the coupling ring  34  having the connecting ring  36  coupled thereto is press-fitted (inserted) into the piston with the valve to fabricate the piston assembly (S- 12 ). The crank shaft  38  is press-fitted to the driving shaft  40  of the motor  42  in parallel with the production step described above and the motor equipped with the shaft is produced (S- 21 ). The crank shaft of the motor equipped with the shaft is inserted into the connecting ring of the piston assembly described above and a piston-cam-motor provisional assembly is produced (S- 13 ). The piston of the piston-cam-motor provisional assembly is inserted into the cylinder of the piston pump pre-assembly described above and at the same time, the motor is fitted to the housing (S- 04 ). The cover  47  of the housing is closed and the projection  43  is meshed with the opening  51  to complete the piston pump of this embodiment (S- 05 ). As described above, the piston pump according to this embodiment can be produced with a drastically smaller number of production steps while the gas leakage test is inserted into the production steps.  
         [0092]      FIG. 20  is a sectional view showing a piston pump  10 ′ according to another embodiment. Since the basic construction is the same as the one shown in  FIG. 1 , common portions are omitted. The cover  47  is closed and the plenum  53  is defined by the right side portion  47   a  of the cover  47 , the side member  46 , the partition plate  48   a , the shaft opening portion  48   b , the partition plate  48   c  on the cover side and the piston  14 . Because the pressure of this plenum  53  is reduced by the operation of the pump chamber  22  of the piston pump  10 ′, air is sucked through the shaft opening portion  48   b . The noise generated at the sliding portions can be prevented from going out when the components having a large number of sliding portions are encompassed in this way by the enclosure.  
         [0093]      FIG. 21  is a sectional view showing a piston pump  10 ″ according to still another embodiment. Because the basic construction is the same as the one shown in  FIG. 1 , the common portions are omitted. This piston pump  10 ″ is directed to suction or pressure reduction but not to exhaust. Therefore, handle portions of the valves  18  and  26  are inserted and fixed from the lower side in the drawing into the insertion holes  24  and  29  in the valve plate  16  and the piston  14 . In this construction, air moves in the reverse direction to the explanation of  FIG. 1 , the pressure of the space  31  is reduced and air is sucked from outside through the discharge port  32 . A wall  73  at the depth that is omitted from  FIG. 1  for simplification is expressed beyond the crank shaft  38 . Holes  78  and  78  for accommodating projections  76  and  76  disposed on the cover  47  are disposed at both ends of the wall  73  at the depth. The cover  47  can be kept under the closed state when these projections  76  and  76  are fitted (inserted) into the holes  78  and  78 , respectively. Fitting between the projection  76 ,  76  and the holes  78 ,  78  may be loose fit but is preferably close fit to a certain extent. Fitting may also be sliding fit. This is to obtain desired pull-out resistance. The shape may be a simple rod shape or a rod shape having a projection at an intermediate part. When a polymer material such as a plastic material is used, the shape is more preferably the simple rod shape. At this time, the partition plate  72  having the opening on the side of the housing substrate material  44  and the partition plate  74  on the side of the cover  47  butt against each other and form the plenum  53  shown in  FIG. 20 .  
         [0094]      FIGS. 22 and 23  illustrate a housing  70 ′ equipped with a cylinder that is produced by providing a closing mechanism of the cover  47  shown in  FIG. 21  to the housing  70  with the cylinder shown in  FIG. 3 . When the shape is such a planar shape, molding by injection molding, etc, becomes easier and more preferable. Four projections  76  constituting the closing mechanism of the cover  47  protrude upward. Each side member  45  operating as the hinge is under the return state ( FIG. 23 ) from the state where it is largely bent ( FIG. 22 ) and its form is shaped so that the closing mechanism can operate. It can be seen that the wall covering the side surface of the plenum  53  is molded integrally with the cylinder  12 . Holes  78  are bored at four corners of this rectangular wall and can fit to the projections  76 .  
         [0095]      FIG. 24  illustrates the state where the motor  42  is accommodated half inside the motor housing. The driving shaft  40  of the motor  42  is pressed into the crank shaft  38  and the crank shaft  38  is inserted into the ring opening portion  36   c  as the inside space of the connecting ring  36 . The coupling ring  34  coupling with the connecting ring  36  engages with the spherical seat  37  of the piston  14  (see  FIG. 2 ). When the cover  47  is pushed in from this state, the pump assembly can be easily fabricated. The valve plate is hereby omitted for simplification but such an assembly can be assembled after the valve plate is bonded by ultrasonic deposition in practice.  
         [0096]      FIG. 25  illustrates the motor  42  used in this embodiment. Terminals  42   a  and  42   b  protruding up and down from an insulating end face are provided on the opposite side of the driving shaft  40  of the motor  42  and supply necessary power to the motor  42 . Connection is easy because these terminals  42   a  and  42   b  are exposed from the opening portion of the side member  45 .  
         [0097]      FIG. 26  is a sketch showing the piston pump  10 ′″ under the state in which the cover  47  shown in  FIG. 24  is fitted. The valve plate  16  is deposited to the top of the cylinder  12  and the manifold  30  having the discharge port  32  is further deposited. The direction of the discharge port  32  faces right in the drawing like a beak of a duck moving forth on a water surface contrary to the case of  FIG. 1 .  
         [0098]     Referring to FIGS.  27  to  30 , a control main portion  80  of the blood pressure monitor having the pump assembled therein will be explained. A battery accommodation portion  92  is arranged to the left in an elongated form inside the rectangular control main portion  80 . A control portion  90  of a printed wiring board (PCB) is arranged on the right side of this battery accommodation portion  92 . A power source portion  90   a  is arranged in this control portion and supplies power to the pump. A pump accommodation portion  82  is defined by a transverse pump support rib  84   a  and a longitudinal pump support rib  84   b  on the further right of the control portion  90 . A solenoid valve  86  is arranged above the control portion  90  and is opened and closed in accordance with the control of the control portion  90 . An opening portion  88  at the center of the solenoid valve  86  is an air discharge port and air is sent from thence to a cuff pressing an arm or a wrist.  FIG. 28  illustrates the section of a substrate  81  for putting the components described above on a substrate surface  81   a . Both ends are obliquely lifted up to a certain extent so that a display surface  81   b  of the blood pressure monitor at the lower part in the drawing can be neatly designed.  
         [0099]      FIG. 29  illustrates the state in which a diaphragm pump  910  is stored in the pump accommodation portion  82  shown in  FIG. 27 . The pump support ribs  84   a  and  84   b  effectively support the diaphragm pump  910  and power is supplied from the power source portion  90   a  to the electrode terminals  910   a  and  910   b  through lead wires. A discharge port of the diaphragm pump  910  is connected by a flexible tube  83  in such a manner as to send discharge air to a suction port  87  of the solenoid valve  86  connected to the other end of the flexible tube  83 .  FIG. 30  illustrates the case where the diaphragm pump  910  is replaced by the piston pump  10 ′″ of the embodiment shown in  FIG. 26 . Air is sent from the discharge port  32  of the piston pump  10 ′″ to the suction port  87  of the solenoid valve  86  through the tube  83  connected in the same way as in  FIG. 29 . The rest of the constructions and operations are the same and are therefore omitted. It can be understood from these drawings that the pump has high versatility because the piston pump  10 ′″ of  FIG. 26  can be easily fitted to the control main portion  80  of the blood pressure monitor using the diaphragm pump.  
         [0100]      FIG. 31  shows in section a piston pump  10 ″″ according to still another embodiment. The explanation of overlapping portions will be omitted because the construction is basically the same as the constructions shown in  FIGS. 1, 20  and  21 . Each wall as the enclosure encompassing the plenum  53  is constituted by a partition plate  72 ′ having a smaller shaft opening portion, a partition plate  74 ′ of the cover  47 , the side member  46  and a right side portion  47   a  of the cover  47 . A rip-seal type rubber seal  77  is fitted to the partition plates  72 ′ and  74 ′ to increase air-tightness. The rubber seal  77  need not be disposed when air-tightness is not much required. The side member  46  has a suction port  79  facing right. According to this construction, a pump capable of sucking and exhausting (from the discharge port  32 ), though small in size, can be provided. Incidentally, the discharge port  32  can be directed in all directions as described so far and this can be accomplished by an extremely convenient method of changing the direction at the time of deposition of the manifold  30 .  
         [0101]     The piston pump of the present invention described above includes the suction port through which the gas sucked in accordance with the change of the volume of the pump chamber defined by the cylinder and the piston due to the reciprocating motion of the piston inserted into the cylinder passes, the exhaust port through which the gas exhausted in accordance with the change of the volume of the pump chamber passes, the suction valve disposed at the suction port arranged at the top of the piston, and the exhaust valve disposed at the exhaust port arranged at the top of the cylinder. Therefore, the piston pump has the advantages that the construction is simple, the number of components is small and the scale can be rendered compact. Consumed current is small and pump efficiency is high.