Linear actuator, and pump device and compressor device using the same

A linear actuator includes an inner yoke, an outer yoke and a coil for generating a magnetic field between the outer yoke and the inner yoke. The outer yoke includes a first facing portion facing the inner yoke and a second facing portion which faces the inner yoke. An insulating coil bobbin around which the coil is wound includes an engaging part which engages with both the first facing portion and the second facing portion of the outer yoke. A magnet is disposed between the inner yoke and the outer yoke and a movable body is integrally connected with the magnet. An alternating magnetic field is generated by the coil such that the movable body along with the magnet is reciprocally moved in the axial direction in conjunction with the alternating magnetic field.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Application No. 2003-073342, filed Mar. 18, 2003, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear actuator, and a pump device and a compressor device using the linear actuator.

2. Description of Related Art

A linear actuator, which is used in a pump device or a compressor device with a piston linearly moving within a cylinder, commonly uses a motor outputting a rotational movement. Therefore, a crankshaft is used between the output shaft of the motor and the piston to convert the rotational movement into a linear movement by using the crankshaft. Accordingly, the transmission efficiency of force is low.

Alternatively, as shown inFIG. 5, a linear actuator has been known which includes an inner yoke103, an outer yoke104, a coil108and a movable body106. The outer yoke104is disposed so as to face the inner yoke103with a predetermined gap space in a direction perpendicular to an axial direction which is the moving direction of the movable body106. A first gap space109A and a second gap space109B are formed between the inner yoke103and the outer yoke104. The coil108is used to generate the alternating magnetic field whose magnetic path is formed by the outer yoke104, the first gap space109A, the inner yoke103and the second gap space109B. The movable body106disposed between the inner yoke103and the outer yoke104is alternately driven in the axial direction by the alternating magnetic field.

However, in the linear actuator constituted as shown inFIG. 5, the facing portions of the outer yoke104to the inner yoke103may be displaced by the attraction force of the movable body, i.e., a magnet106to cause to be brought into contact with the magnet106. In addition, whenever the magnet106moves in the axial direction, the portion of the facing portions of the outer yoke104which is attracted by the magnet106is counterchanged alternately. Therefore, when the magnet106is driven and moved alternately in the axial direction at a high speed as in the case used in a pump device or a compressor device, the magnetic vibration may occur.

SUMMARY OF THE INVENTION

In view of the problems described above, it is advantage of the present invention to provide a linear actuator capable of preventing the facing portion of an outer yoke to an inner yoke from being displaced by the attraction force of a magnet, and also provide a pump device and a compressor device using the above-mentioned linear actuator.

In order to achieve the above advantage, according to an embodiment of the present invention, there is provided a linear actuator including an inner yoke, an outer yoke which is arranged so as to form a prescribed gap space to an outer peripheral face of the inner yoke, a coil for generating a magnetic field between the outer yoke and the inner yoke, an insulating coil bobbin around which the coil is wound, a magnet which is disposed in the prescribed gap space between the inner yoke and the outer yoke, and a movable body integrally connected with the magnet capable of moving in an axial direction. The outer yoke is provided with a first facing portion and a second facing portion which respectively face the inner yoke. The second facing portion is formed to be separated from the first facing portion in the axial direction and the coil bobbin is provided with an engaging part which engages with both the first facing portion and the second facing portion of the outer yoke.

In the linear actuator in accordance with an embodiment of the present invention, for example, when an alternating current is applied to the coil, an alternating magnetic field is generated between the outer yoke and the inner yoke and thus the movable body is moved back and forth in the axial direction corresponding to the alternating magnetic field. Therefore, the movable body can be reciprocally and linearly moved. Further, the coil bobbin around which the coil is wound is provided with the engaging part which engages with both the first facing portion and the second facing portion of the outer yoke and thus the first facing portion and the second facing portion are not displaced by the attraction force of the magnet. Accordingly, even when the portion of two facing portions which is attracted by the magnet is alternately replaced, the magnetic vibration does not generate.

In the linear actuator in accordance with an embodiment of the present invention, the outer yoke is arranged around the inner yoke so as to form a first gap space and a second gap space with respect to an outer peripheral face of the inner yoke and the coil is energized so as to generate an alternating magnetic field at the first gap space and the second gap space. In this case, the outer yoke, the first gap space, the inner yoke, the second gap space and the above-mentioned outer yoke are constituted to form the magnetic path. The outer yoke is formed so as to extend from a portion located on the outer peripheral side of the coil to the first facing portion for forming the first gap space and to the second facing portion for forming the second gap space on the inner peripheral side of the coil over the upper or lower ends of the coil. The coil is wound around the insulating coil bobbin which is used for the insulation between the first and the second facing portions of the outer yoke and the coil. The coil bobbin includes an engaging part which engages with both the first and the second facing portions of the outer yoke for preventing the facing portions from being displaced by the attraction force of the magnet.

In the linear actuator in accordance with an embodiment of the present invention, when an alternating current is applied to the coil, an alternating magnetic field is generated in the magnetic path which is formed of the outer yoke, the first gap space, the inner yoke, the second gap space and the above-mentioned outer yoke. Therefore, the movable body is moved back and forth in the axial direction corresponding to the alternating magnetic field.

In accordance with an embodiment of the present invention, the engaging part includes an engaging protrusion part protruding toward the inner yoke side from the coil bobbin and a front end portion of the first facing portion and a front end portion of the second facing portion of the outer yoke respectively engage with the engaging protrusion part from both sides in the axial direction.

In accordance with an embodiment of the present invention, the outer yoke includes a first outer yoke member and a second outer yoke member which are respectively formed in a U-shaped cross-section so as to cover the coil from both sides in the axial direction. The first outer yoke member and the second outer yoke member are constituted in such a manner that both end portions abut with each other at a portion located on the outer peripheral side of the coil while the front end portion of the first facing portion and the front end portion of the second facing portion located on the inner peripheral side of the coil respectively engage with the engaging protrusion part from both sides in the axial direction. In this case, prescribed clearances in the axial direction are preferably formed between the respective front end portions of the first and the second facing portions and the engaging protrusion part. According to the embodiment constituted above, both the end portions of the first outer yoke member and the second outer yoke member surely abut with each other at the portion located on the outer peripheral side of the coil and thus, even when the outer yoke is constituted by using two yoke members, the magnetic path in the outer yoke is surely formed.

In accordance with an embodiment of the present invention, the front end portion of the first facing portion and the front end portion of the second facing portion of the outer yoke are respectively formed with engaging recessed parts, each of which engages with the engaging protrusion part provided in the coil bobbin. The engaging protrusion part is preferably provided with a small projecting part protruding toward the inner yoke side from the position of the engaging recessed parts provided in the front end portions of the first and the second facing portions. According to the embodiment constituted above, for example, even when the first and the second facing portions vibrate in the axial direction due to the external vibration, their separated state is maintained.

Further, in accordance with an embodiment of the present invention, prescribed clearances in the axial direction are preferably provided between the front end portions of the first and the second facing portions and the engaging protrusion part. According to the embodiment constituted above, the first outer yoke member and the second outer yoke member surely abut with each other at end portions located on the outer peripheral side of the coil and thus the magnetic path is surely formed even when the outer yoke is constituted of two yoke members.

The linear actuator in accordance with the present invention is preferably used as a pump device or a compressor device for supplying various kinds of fluids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A linear actuator in accordance with an embodiment of the present invention will be described below with reference to the accompanying drawings.

Entire Constitution

FIG. 1(A)is a transverse cross-sectional view of a linear actuator in accordance with an embodiment of the present invention.FIG. 1(B)is a side view of the linear actuator inFIG. 1(A)with the right half side of the linear actuator being shown in cross section.

InFIGS. 1(A) and 1(B), the linear actuator1in the embodiment of the present invention is used for a pump device or a compressor device for supplying various types of fluids. The linear actuator1includes a frame2for holding a stator and a movable body5capable of reciprocating with respect to the frame2along the axial line “L”.

In the embodiment of the present invention, on the frame2are mounted an inner yoke3, an outer yoke4disposed on an outer side of the inner yoke3, and a coil8disposed inside of the outer yoke4. The movable body5is integrally formed with a magnet9; which is disposed between the inner yoke3and the outer yoke4. A bottom part51(upper part in the drawing) of the movable body5is constituted to be a fixing part for connecting with an actuating shaft (not shown) formed in a round bar shape or a cylindrical shape.

In the embodiment of the present invention, the inner yoke3is constituted so as to be divided into eight pieces and disposed at respective positions corresponding to eight sides of a regular octagon when viewed in the axial direction as shown inFIG. 1(A). The eight pieces of the inner yoke3are arranged at equal angles in the peripheral direction. Each piece of the inner yoke3is formed into a flat board shape made of laminated magnetic plates. The outer face of each piece of the inner yoke3opposing to the outer yoke4and its rear face (inner face) are formed in a flat face.

The outer yoke4is also constituted so as to be divided into eight pieces and disposed at respective positions corresponding to eight sides of a regular octagon when viewed in the axial direction. The eight pieces of the outer yoke4are arranged at equal angles in the peripheral direction.

Each piece of the outer yoke4is constituted of a first outer yoke member41and a second outer yoke member42. Each of the first and the second outer yoke members41and42is formed in a U-shaped cross section and they are vertically superposed to each other. In the embodiment of the present invention, each of the first and the second outer yoke members41and42is formed of a laminated body made of magnetic plates.

The first and the second outer yoke members41and42are respectively formed so as to extend from a portion located on the outer peripheral side of the coil8to a portion opposing to the outer peripheral face of the inner yoke3through an upper or lower intermediate connecting portion over the coil8. The portions opposing to the outer peripheral face of the inner yoke3are respectively formed as a first facing portion410and a second facing portion420. A first gap space6is formed so as to separate the outer peripheral face of the inner yoke3from the first facing portion410and a second gap space7is formed so as to separate the outer peripheral face of the inner yoke3from the second facing portion420in the axial direction. The end parts419and429of the first and the second outer yoke members41and42abut with each other on the outer peripheral side of the coil8.

The outer yoke4constituted as described above is held and fixed by holders21and22.

The magnet9integrally connected to the movable body5is made of a rare-earth magnet such as Nd—Fe—B system or a resin magnet. The magnet9is also constituted so as to be divided into eight pieces and disposed at respective positions corresponding to eight sides of a regular octagon when viewed in the axial direction as shown inFIG. 1(A). The eight pieces of the magnet9are arranged at equal angles in the peripheral direction. The movable body5is arranged in such a manner that the respective pieces of the magnet9are located so as to position over the area of both the first gap space6and the second gap space7formed between the inner yoke3and the outer yoke4. The front and rear faces of the respective pieces of the magnet9are respectively magnetized to be opposite magnetic poles.

Each piece of the magnet9is formed in a planar shape and held by a magnet holding part52made of resin as shown inFIG. 1(A), which is formed in the movable body5. In other words, each piece of the magnet9is held such that each side end portion of the magnet9is inserted into a groove520formed in the magnet holding part52. The magnet holding part52is formed in a roughly triangular shape when viewed in the axial direction. The portion corresponding to an apex of the triangle is positioned in a wedge-shaped manner between adjacent pieces of the inner yoke3. The portion corresponding to the base side of the triangle is positioned between adjacent pieces of the outer yoke4.

A coil bobbin80made of a resin molded product is disposed in a space constituted between the first and the second outer yoke members41and42of the outer yoke4. A coil8is wound around a trunk part81of the coil bobbin80. The outer portion of the coil8wound around the coil bobbin80is protected by a cover89made of resin.

Engaging Structure of Coil Bobbin and Outer Yoke

FIG. 2(A)is a perspective view of the coil bobbin used in the linear actuator to which the present invention is applied.FIG. 2(B)is a perspective view of a coil device in which a pair of pieces of the outer yoke is mounted on the coil bobbin.FIG. 2(C)is an explanatory perspective view which shows the important portion of the coil bobbin and the end portions of the pair of pieces of the outer yoke.

In the linear actuator1of the embodiment of the present invention, the trunk part81of the coil bobbin80ensures insulation between the coil8and the first facing portion410or the second facing portion420of the outer yoke4.

Also, as shown inFIGS. 2(A) and 2(B), engaging protrusion parts82protruding toward the inner yoke3are formed on the inner peripheral surface of the trunk part81so as to correspond to eight pieces of the outer yoke4. The engaging protrusion part82engages with both the first facing portion410and the second facing portion420and serves as an engaging part for preventing the first and second facing portions410and420from being attracted to the magnet9and displaced.

The engaging protrusion part82includes upper and lower protrusion parts823and824which are formed so as to protrude in the axial direction to form recessed parts821and822opening in the axial direction between the inner peripheral face of the trunk part81and the respective upper and lower protrusion parts823and824. In addition, the engaging protrusion part82includes a small projecting part825which is formed to be projected toward the inner yoke3side from the upper and lower protrusion parts823and824so as to be positioned between the lower end face of the first facing portion410and the upper end face of the second facing portion420on the inner yoke3side.

On the other hand, the inner peripheral side projecting part411and the outer peripheral side projecting part412are respectively formed at the lower end part of the first facing portion410. The inner peripheral side projecting part421and the outer peripheral side projecting part422are respectively formed at the upper end part of the second facing portion420. Thus, a recessed part413opening in the axial direction is formed between the projecting parts411and412and a recessed part423opening in the axial direction is formed between the projecting parts421and422.

Therefore, after the coil8is wound around the coil bobbin80, when the first and the second outer yoke members41and42are respectively attached on the coil bobbin8from both sides in the axial direction so as to surround the coil bobbin80from the upper and lower sides, the outer peripheral side projecting part412formed at the lower end part of the first opposing portion410of the first outer yoke member41and the outer peripheral side projecting part422formed at the upper end part of the second opposing portion420of the second outer yoke member42are respectively fitted into the recessed parts821and822of the engaging protrusion part82. Also, the protrusion parts823and824of the engaging protrusion part82are respectively fitted in the axial direction to the engaging recessed parts413and423which are respectively formed at the end part of the first opposing portion410and the end part of the second opposing portion420. Further, the small projecting part825of the engaging protrusion part82is positioned between the inner peripheral side projecting part411which is formed at the lower end face of the first facing portion410of the first outer yoke member41and the inner peripheral side projecting part412which are formed at the upper end face of the second facing portion420of the second outer yoke member42.

The coil bobbin80is arranged so as to surround all over the inner yoke3. Accordingly, the first facing portion410and the second facing portion420of the first and the second outer yoke members41and42do not displace radially even though they are attracted by the magnet9. This is because the first facing portion410and the second facing portion420are held by the upper and lower protrusion parts823and824of the coil bobbin80. In addition, magnetic vibration does not occur when the portion of two facing portions410and420which is attracted by the magnet9is replaced with each other. Therefore, a specific countermeasure is not required to prevent the magnetic vibration.

Further, prescribed clearances are provided between the first and the second outer yoke members41and42and the engaging protrusion part82in the axial direction as shown inFIG. 2(C). In other words, a prescribed clearance is provided in the axial direction between the bottom face of the recessed part821and the lower face of the outer peripheral side projecting part412, and a prescribed clearance is provided between the upper face of the recessed part822and the upper face of the outer peripheral side projecting part422. Also, a prescribed clearance is provided in the axial direction between the upper face of the recessed part413and the upper face of the protrusion part823, and a prescribed clearance is provided between the bottom face of the recessed part423and the lower face of the protrusion part824. Further, a prescribed clearance is also provided in the axial direction between the lower face of the inner peripheral side projecting part411and the upper face of the small projecting part825, and a prescribed clearance is also provided between the upper face of the inner peripheral side projecting part421and the lower face of the small projecting part825.

The size (width) of the recessed part413in the radial direction is set to be equal to that of the upper protrusion part823and the size (width) of the recessed part423in the radial direction is set to be equal to that of the lower protrusion part824. Therefore, the first facing portion410and the second facing portion420of the first and the second outer yoke members41and42do not displace in the radial direction even though the attractive force of the magnet9is applied. Accordingly, even though the portion of two facing portions410and420which is attracted by the magnet9is replaced alternately, the magnetic vibration does not occur.

The first and the second outer yoke members41and42are disposed so as to interpose the coil bobbin80between the first and the second outer yoke members41and42as shown inFIG. 2(B). When the first and the second outer yoke members41and42are overlaid on the coil bobbin80from both sides in the axial direction, the lower end face part419of the first outer yoke member41firstly abuts with the upper end face part429of the second outer yoke member42on the outer peripheral side of the coil8. The abutting of the lower end face part419and the upper end face part429determines the positions of the first and the second outer yoke members41and42, and in this state, the end portions of the first facing portion410and the second facing portion420of the first and the second outer yoke members41and42engage with the engaging protrusion part82. Consequently, even when the outer yoke4is constituted of the first and the second outer yoke members41and42, the magnetic path in the outer yoke4is assuredly formed.

In addition, the small projecting part825of the engaging protrusion part82is positioned between the lower end face of the first facing portion410and the upper end face of the second facing portion420of the first and the second outer yoke members41and42. Therefore, even when the first opposing portion410and the second opposing portion420vibrate in the axial direction by external vibrations, the first facing portion410and the second facing portion420can be surely maintained in a separated condition.

Operation

FIGS. 3(A) and 3(B)are explanatory sectional views showing different operated states of the linear actuator.

In the linear actuator1according to the embodiment of the present invention, when the inner face of the magnet9is magnetized in “S” pole and its outer face is magnetizing in “N” pole, the magnetic field is formed as shown by the arrowed solid lines B1and B2inFIGS. 3(A) and 3(B). In this state, when an alternating current is applied to the coil8, in a period which the current flows from the far side to the near side in the drawing as shown inFIG. 3(A), the magnetic field shown by the arrow B3in the dotted line is generated. Therefore, the direction of the magnetic field from the magnet9is the same as that of the magnetic lines of force from the coil8in the first gap space6which is formed between the outer peripheral face of the inner yoke3and the first facing portion410of the first outer yoke member41. On the other hand, the direction of the magnetic field from the magnet9is opposite to that of the magnetic lines of force from the coil8in the second gap space7which is formed between the outer peripheral face of the inner yoke3and the second facing portion420of the second outer yoke member42. As a result, a downward force (on the second gap space7side) in the axial direction is exerted on the magnet9.

However, in a period which the alternating current flows from the near side to the far side in the drawing as shown inFIG. 3(B), the magnetic field shown by the arrow B4in the dotted line is generated. Therefore, the direction of the magnetic field from the magnet9is opposite to that of the magnetic lines of force from the coil8in the first gap space6but the direction of the magnetic field from the magnet9is the same as that of the magnetic lines of force from the coil8in the second gap space7. As a result, an upward force (on the first gap space6side) in the axial direction is exerted on the magnet9.

As described above, the direction of the force in the axial direction which is applied to the magnet9is alternately changed corresponding to the direction of the alternating magnetic field generated by the coil8. Therefore, the movable body5integrally formed with the magnet9reciprocally moves in the axial direction and reciprocal linear motion can be outputted from a piston connected with the movable body5. Further, the outer yoke4, the inner yoke3and the magnet9are respectively constituted in an annular shape when viewed from the axial direction and thus a thrust force for the movable body5can be obtained over the entire circumferential direction.

Moreover, during the reciprocal operation of the magnet9moving back and forth or up and down, even though the portion of the facing portions410and420attracted by the magnet9is replaced alternately, the magnetic vibration can be prevented from occurrence. Therefore, a specific countermeasure is not required to prevent the magnetic vibration.

Example of Pump Device and Compressor Device

The linear actuator1in accordance with the embodiment of the present invention can be applied to a pump device or a compressor device as described with reference toFIGS. 4(A),4(B) and4(C).

FIG. 4(A)is a plan view of an air pump device to which the present invention is applied.FIG. 4(B)is a cross-sectional view of the air pump device inFIG. 4(A)andFIG. 4(C)is a bottom view of the air pump device. InFIG. 4(B), a portion corresponding to the linear actuator1is enclosed by the thick line.

In the air pump device100according to the embodiment of the present invention shown inFIGS. 4(A),4(B) and4(C), the base end of an actuating shaft110is connected to the movable body5of the linear actuator1by using a nut153through washers151and152. The actuating shaft110penetrates through a hole16of the frame2which holds the inner yoke3. The base end side of the actuating shaft110is supported by a bearing154fitted to the frame2and two springs161and162are mounted around the actuating shaft110. The both ends of the spring161provided on the base end side of the actuating shaft110are supported by a step part17formed on the inner face of the hole16of the frame2and an “E”-shaped snap ring163mounted on the actuating shaft110. The both ends of the spring162provided on the front end side of the actuating shaft110are supported by the “E”-shaped snap ring163and a spring engaging member164fixed on the bottom part of the frame2.

A case170provided with an air inlet port171and an air outlet port172is fixed on the bottom part of the frame2with bolts173and a filter174is mounted to the air inlet port171. A cylinder case120is arranged inside of the case170and a valve141is fixed by a valve pressing member143on a portion facing the air inlet port171in the bottom part of the cylinder case120. A valve142is fixed by a valve pressing member144on a portion facing the air outlet port172.

A piston130is disposed inside the cylinder case120so as to form a cylinder chamber122between the bottom portion of the cylinder case120and the spring engaging member164fixed on the bottom part of the frame2. A pressure ring135is mounted on the side face of the piston130to ensure airtightness with the inner peripheral face of the cylinder case120.

The piston130is fixed at the front end part of the actuating shaft110with a nut139through washers137and138and an O-ring136and reciprocally moved in the axial direction by the actuating shaft110. Therefore, when the actuating shaft110moves on the base end side in the axial direction (upward in the drawing) by the linear actuator1, air is taken into the cylinder chamber122through the air inlet port171. When the actuating shaft110moves on the front end side in the axial direction (downward in the drawing) by the linear actuator1, the air in the cylinder chamber122is discharged through the air outlet port172. Therefore, the device operates as an air pump device.

Further, the springs161and162vibrate sympathetically with the vibration of the actuating shaft110and thus a superior pump characteristic can be attained even when an air pump device100is equipped with the small-sized linear actuator1as described above.

The constitution of the air pump device can be easily modified to a compressor device. In other words, the linear actuator1in accordance with the embodiment of the present invention can be similarly applied to a compressor device.

As described above, in the linear actuator in accordance with the embodiment of the present invention, the alternating magnetic field is generated by applying the alternating current to the coil and the movable body is reciprocally driven in the axial direction in conjunction with the alternating magnetic field. Therefore, a reciprocal linear motion can be outputted from the movable body.

Further, the coil bobbin around which the coil is wound is provided with the engaging part which engages with both the first facing portion and the second facing portion of the outer yoke and thus the first facing portion and the second facing portion are not displaced even when the attractive force of the magnet is applied thereto. In addition, the magnetic vibration does not occur when the portion of two facing portions which is attracted by the magnet is alternately replaced.