Abstract:
A super magnetostrictive actuator includes: a magnetic field generating unit, at least first and second super magnetostrictive members extensible in a longitudinal direction thereof due to action of magnetic field generated by the magnetic field generating unit, and a coupling member having a cylindrical shape and disposed coaxially between the first and second super magnetostrictive members. The second super mangetostrictive member has a cylindrical shape and is coaxially disposed to surround the outside of the first super magnetostrictive member in a radial direction thereof. Both end portions of the coupling member are coupled to one end portion of the first super magnetostrictive member and one end portion of the second super magnetostrictive member, respectively.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a super magnetostrictive actuator formed by combining at least two super magnetostrictive materials which extend and shrink in the longitudinal direction thereof due to the action of the magnetic field generated by a magnetic field generation means. 
     2. Description of the Related Art 
     Of the magnetostrictive materials which generate distortion in the magnetic field, rare earth metal monocrystal such as Tb (terbium), Dy (dysprosium) or the like known as super magnetostrictive material generates enormous magnetostriction which is about several hundred times as that generated by general magnetostrictive material such as Ni, Co or the like. Since TbFe 2  or DyFe 2 which is a binary alloy of Tb and Fe or Dy and Fe is able to generate enormous magnetostriction in the room temperature, such a binary alloy is used as a source for driving an actuator. However, enormous magnetostriction generated by such super magnetostrictive materials only exceeds the displacement of about 0.1% at most. Thus, in order to secure a required output displacement while avoiding the enlargement of the size of the actuator, it is required to combine a plurality of super magnetostrictive materials so as to accumulate slight extension and shrinkage amounts of the respective super magnetostrictive materials thereby to output the accumulated displacement. 
     Such a super magnetostrictive actuator for securing a required output displacement by combining a plurality of super magnetostrictive materials in this manner is known as disclosed in Japanese Patent Unexamined Publication NO. Hei.4-168984. 
     However, the aforesaid conventional super magnetostrictive a actuator is arranged in a manner that a plurality of super magnetostrictive materials formed in a column shape are disposed along the inner periphery of a coil formed in a cylindrical shape, and the end portions of the adjacent super magnetostrictive materials are coupled to each other by a link which is supported at its center portion by a fulcrum. According to the actuator thus arranged, an amount of extension and shrinkage of each of the super magnetostrictive materials is transmitted to the adjacent super magnetostrictive material through the link mechanism thereby to generate a required output displacement between the super magnetostrictive materials positioned at both ends. 
     However, in the conventional actuator, since the plurality of super magnetostrictive materials are coupled by the link mechanism, the number of the parts such as the link member and the fulcrum thereof etc. increases and the number of assembling processes thereof also increases. As a result, the cost of the actuator increases, and further the actuator may be prevented from moving smoothly since the magnitude of friction and the degree of wobble at a movable portion and a sliding portion increase. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the aforesaid conventional circumstances, and an object of the present invention is to provide a super magnetostrictive actuator which can obtain sufficient output displacement and operate smoothly with a simple and small-sized configuration having small number of parts. 
     In order to attain the aforesaid object, according to the present invention, there is provided a super magnetostrictive actuator formed by combining at least first and second super magnetostrictive materials which expand and shrink in a longitudinal direction thereof due to action of magnetic field generated by magnetic field generating means. The second magnetostrictive material of tubular shape is disposed coaxially so as to surround outer side of the first magnetostrictive material along radial direction thereof, and a coupling member of tubular shape disposed coaxially between the first and second super magnetostrictive materials is coupled at its both end portions to one end portion of the first magnetostrictive material and one end portion of the second magnetostrictive material, respectively. 
     According to the aforesaid configuration, when the magnetic field generating means generates magnetic field, both the first and second super magnetostrictive materials extend and shrink in the axial direction and so the deviation at the one end portion of the first magnetostrictive material is transmitted to the one end portion of the second magnetostrictive material through the coupling member. Thus, the deviation corresponding to the sum of amounts of extension/shrinkage of the first and second super magnetostrictive materials can be generated between the other end portion of the first magnetostrictive material and the other end portion of the second magnetostrictive material. Further, since the coupling member of tubular shape is disposed coaxially so as to surround the outer side of the first magnetostrictive material along the radial direction thereof and the second magnetostrictive material of tubular shape is disposed coaxially so as to surround the outer side of the coupling member along the radial direction thereof, not only can the super magnetostrictive actuator be configured in a small size but also the extension/shrinkage of the first and second super magnetostrictive materials can be effectively transmitted without causing offset load of the first and second super magnetostrictive materials. Furthermore, since the coupling member does not have a fulcrum nor a sliding portion and is merely coupled at its both end portions to the first and second super magnetostrictive materials, respectively, the number of the parts can be reduced thereby to realize a simple configuration and so the actuator is advantageous in economical efficiency, endurance and assembling efficiency. 
     Further, the magnetic field generating means may be formed by a coil disposed coaxially so as to surround the outer periphery of the second magnetostrictive material. 
     According to the aforesaid configuration, the output deviation of the super magnetostrictive actuator can be easily controlled by merely changing the pulse width or the magnitude of the current supplied to the coil. Further, since all the first and second super magnetostrictive materials, the coupling member and the coil are disposed coaxially, the super magnetostrictive actuator can be further configured in a smaller size. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a fuel injection valve; 
     FIG. 2 is an enlarged diagram of the main portion of FIG.  1 . 
     FIG. 3 is a sectional diagram taken along a line III—III in FIG. 2; 
     FIG. 4 is a fragmental perspective view of the main portion of a super magnetostrictive actuator; and 
     FIG. 5 is a diagram showing the second embodiment of the present invention which corresponds to FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be explained with reference to FIGS. 1 to  4 . 
     As shown in FIG. 1, a fuel injection valve I used in a direct injection engine for natural gas includes a housing  11  of substantially cylindrical shape. A nozzle  12  and a cap  13  are fixed to the front end portion and the rear end portion of the housing  11 , respectively. The super magnetostrictive actuator A received in the rear portion of the housing  11  includes, so as to drive the fuel injection valve I, a coil  14  serving as a magnetic field generating means, a first magnetostrictive material  15 , a second magnetostrictive material  16  and a coupling member  17 . The front end of the coil  14  which is formed in a cylindrical shape and fits in the inner peripheral surface of the housing  11  engages with the step portion  11   1  of the housing  11  through a front guide member  18  having a guide hole  18   1 . The rear end of the coil  14  is engaged with the front surface of the cap  13  through a rear guide member  19  having a guide hole  19   1  and a stopper surface  19   2 . 
     As clear also with reference to FIG. 4, the first magnetostrictive material  15  is configured by a super magnetostrictive material main body  15   1  formed in a column shape, and a front end member  15   2  and a rear end member  15   3  fixed to the front end and the rear end of the super magnetostrictive material main body  15   1 , respectively. A step portion  15   4  is formed at the outer peripheral surface of the rear end member  15   3 . The second magnetostrictive material  16  is configured by a super magnetostrictive material main body  16   1  formed in a cylindrical shape, and a front end member  16   2  and a rear end member  16   3  fixed to the front end and the rear end of the super magnetostrictive material main body  16   1 , respectively. A step portion  16   4  is formed at the inner peripheral surface of the front end member  16   2 . The coupling member  17  made of non-magnetic material and formed in substantially cylindrical shape has a step portion  17   1  at the outer peripheral surface of the front end side thereof and a step portion  17   2  at the inner peripheral surface of the rear end side thereof. 
     The second magnetostrictive material  16  is disposed at the inner side of the coil  14  which is fitted into and supported by the housing  11 . The coupling member  17  is disposed at the inner side of the second super magnetostrictive material  16 . The first magnetostrictive material  15  is disposed at the inner side of the coupling member  17 . In this state, the housing  11 , the coil  14 , the second magnetostrictive material  16 , the coupling member  17  and the first magnetostrictive material  15  are aligned concentrically with respect to the axial line L of the fuel injection valve I. 
     The rear end member  16   3  of the second magnetostrictive material  16  abuts against the stopper surface  19   2  of the rear guide member  19  and positioned thereat. The front end member  16   2  slidably fits into the inner peripheral surface of the guide hole  18   1  of the front guide member  18 . The step portion  16   4  of the front end member  16   2  of the second magnetostrictive material  16  engages with the step portion  17   1  of the front side of the coupling member  17 . The step portion  17   2  of the rear side of the coupling member  17  engages with the step portion  15   4  of the rear end member  15   3  of the first magnetostrictive material  15 . In this case, the rear end member  15   3  of the first magnetostrictive material  15  slidably fits into the guide hole  19   1  of the rear guide member  19 . 
     The super magnetostrictive material main body  15   1  of the first magnetostrictive material  15  and the super magnetostrictive material main body  16   1  of the second magnetostrictive material  16  are formed by Terfenol-D (trade name), for example. The Terfenol-D is an alloy formed by combining TbFe 2  and DyFe 2 . The alloy comprises from 27% to 30% of TbFe 2 , and 70% to 73% of DyFe 2 , and the content of Fe in the alloy is from 19% to 20%. The Terfenol-D has such a property of the positive magnetostriction (extend with respect to the direction of the magnetic field) and the magnetic anisotropic constant is approximately 0. 
     As clear also with reference to FIGS. 2 and 3, a piston  20  serving as an output member is slidably fitted into a cylinder  11   2  formed at the inner periphery of the front portion of the housing  11 . A piston rod  20   1  extending backward from the piston  20  abuts against the front end member  15   2  of the first magnetostrictive material  15 . The front end of a preload spring  21  received within the cylinder  11   2  engages with the rear end of the nozzle  12  through a collar  22  and a washer  23  and the rear end of the preload spring  21  retains with the front surface of the piston  20 . Thus, the piston  20  is biased backward due to the elastic force of the preload spring  21  applied thereto. 
     A valve seat  24  and a valve element support member  25  are received within the nozzle  12  having a nozzle hole  12   1  at the tip end thereof. A nut  26  having screws formed at the outer peripheral surface thereof is screwed around the inner peripheral surface of the nozzle  12 , so as to fix the valve seat  24  and the valve element support member  25 . The valve element support member  25  has a guide hole  25   1  which penetrates at the center portion thereof along the axial direction therethrough and four ribs  25   2  which are formed with an angular interval of 90 degrees and extend radially to the radial direction. The outer ends of the ribs  25   2  are abutted against the inner peripheral surface of the nozzle  12 , so that the valve element support member  25  is positioned to the radial direction. A valve element  27  has a head portion  27   1  and a shaft portion  27   2 . The head portion  27   1  is capable of being seated on the front surface of the valve seat  24  and the shaft portion  27   2  is slidably supported by the guide hole  25   1  of the valve element support member  25 . A spring seat  28  is provided at the rear end of the shaft portion  27   2  of the valve element  27 . A valve spring  29  is supported between the front surface of the spring seat  28  and the valve element support member  25  in a compressed state. The head portion  27   1  of the valve element  27  is biased backward by the valve spring  29  and then seated on the valve seat  24 . 
     A shim  30  is attached between the rear end of the valve spring  29  and the spring seat  28 . An amount of the preload of the valve spring  29  can be adjusted by changing the thickness of the shim  30 . 
     A fuel supply hole  11   3  is formed at the front portion of the housing  11 . The highly-pressurized fuel supplied into the cylinder  11   2  from the fuel supply hole  11   3  passes among the four ribs  25   2  and further passes a clearance between the valve seat  24  and the head portion  27   1  of the valve element  27  and then injected into the cylinder of the engine from the nozzle hole  12   1 . 
     The action of the fuel injection valve I thus configured will be explained. 
     When the piston  20  is biased backward by the elastic force of the preload spring  21  received within the cylinder  11   2  in the compressed state, the compressed preload to the axial direction acts on the first magnetostrictive material  15  whose front end member l 5   2  is pressed by the piston rod  20   1 . The compressed preload acting on the first magnetostrictive material  15  is transmitted from the step portion  15   4  of the rear end member  15   3  to the step portion  17   2  of the rear side of the coupling member  17  thereby to bias the coupling member  17  backward. The biasing force for biasing the coupling member  17  backward is transmitted from the step portion  17   1  of the front side of the coupling member  17  to the step portion  16   4  of the front end member  16   2  of the second magnetostrictive material  16 . As a result, the compressed preload in the axial direction acts on the second magnetostrictive material  16  whose rear end member  16   3  is retained by the rear guide member  19 . Each of the first magnetostrictive material  15  and the second magnetostrictive material  16  is applied with the compressed preload in the axial direction and shrinks in the axial direction in accordance with the magnitude of the compressed preload. 
     When the coil  14  is not supplied with current, the valve element  27  is biased backward by the valve spring  29  and hence the head portion  27   1  of the valve element  27  is seated on the valve seat  24 . In this case, a clearances α (see FIG. 2) with a preset size is formed between the front surface of the piston  20  and the rear end of the shaft portion  27   2  of the valve element  27  so that the head portion  27   1  of the valve element  27  is not interfered from being seated on the valve seat  24 . 
     When the coil  14  of the super magnetostrictive actuator A is supplied with current in accordance with an instruction from a fuel injection amount control apparatus so as to supply fuel to the engine, the first magnetostrictive material  15  and the second magnetostrictive material  16  extend against the compressed preload in accordance with the magnitude of the magnetic field generated by the coil  14 . As for the second magnetostrictive material  16  whose rear end member  16   3  is retained by the rear guide member  19 , the front end member  16   2  moves forward by the extension of the super magnetostrictive material main body  16   1  thereby to move forward the coupling member  17  whose step portion  17   1  of the front side of the coupling member  17  is retained by the step portion  16   4  of the front end member  16   2 . The displacement force for moving the coupling member  17  forward is transmitted from the step portion  17   2  of the rear side of the coupling member  17  to the step portion  15   4  of the rear end member  15   3  of the first magnetostrictive material  15 . As a result, the rear end member  15   3  of the first magnetostrictive material  15  moves forward by the length corresponding to the extended length of the second magnetostrictive material  16 . Further, since the super magnetostrictive material main body  15   1  of the first magnetostrictive material  15  extends against the compressed preload in accordance with the magnitude of the magnetic field generated by the coil  14 , the front end member  15   2  of the first magnetostrictive material  15  moves forward with respect to the rear end member  15   3 . 
     In this manner, the piston  20  moves forward by the length corresponding to the sum of the extended length of the first magnetostrictive material  15  and that of the second magnetostrictive material  16 . When the piston  20  moves forward, the clearances α between the front surface of the piston  20  and the rear end of the shaft portion  27   2  of the valve element  27  becomes shorter, and so the valve element  27  pushed by the piston  20  moves forward against the elastic force of the valve spring  29 , whereby the head portion  27   1  of the valve element  27  separates from the valve seat  24 . As a consequence, the highly-pressurized fuel having been supplied into the cylinder  11   2  from the fuel supply hole  11   3  passes the clearance between the valve seat  24  and the head portion  27   1  of the valve element  27  and then is injected from the nozzle hole  12   1 . Thus, an amount of fuel injection can be controlled in such a manner that the current supplied to the coil  14  is subjected to the pulse width control thereby to change the opened/closed periods of the clearance between the valve seat  24  and the head portion  27   1  of the valve element  27 , or in such a manner that the magnitude of the current supplied to the coil  14  is controlled thereby to change the size of the clearance between the valve seat  24  and the head portion  27   1  of the valve element  27 . 
     As described above, since the first magnetostrictive material  15 , the coupling member  17 , the second magnetostrictive material  16  and the coil  14  are coaxially disposed around the axial line L so as to be sequentially overlapped in this order from the inside to the outside along the radial direction, the super magnetostrictive actuator A can be formed in a compact size. Further, since all the weight of the first magnetostrictive material  15 , the coupling member  17  and the second magnetostrictive material  16  acts on the axial line L, asymmetrical deformation around the axial line L of the first magnetostrictive material  15 , the coupling member  17  and the second magnetostrictive material  16  can be prevented and the weight is efficiently transmitted, so that the smoothing operation of the super magnetostrictive actuator A can be secured. Furthermore, since the coupling member  17  does not have a fulcrum nor a sliding portion, the configuration thereof is quite simple. Accordingly, it becomes possible to reduce the number of the parts and the number of the assembling processes, and further the durability of the actuator can be improved and the rate of failure thereof can be reduced. Furthermore, since the coil  14  is employed as the magnetic field generating means, the output displacement of the super magnetostrictive actuator A can be easily and accurately controlled by merely changing the pulse width or the magnitude of the current supplied thereto. 
     When the coil  14  is supplied with current and the super magnetostrictive actuator A is operated, since the elastic force of the valve spring  29  in addition to the elastic force of the preload spring  21  simultaneously acts the first magnetostrictive material  15  and the second magnetostrictive material  16 , the sum of the elastic force of both the preload spring  21  and the valve spring  29  influences the dynamic characteristic of the super magnetostrictive actuator A. As a method of adjusting the sum of the elastic force, there are considered a first method of adjusting both the elastic force of the preload spring  21  and the elastic force of the valve spring  29 , a second method of adjusting only the elastic force of the preload spring  21 , and a third method of adjusting only the elastic force of the valve spring  29 . 
     However, when the elastic force of the preload spring  21  is changed, since the amount of shrinkage of the first magnetostrictive material  15  and the second magnetostrictive material  16  due to the preload changes, the clearances α between the front surface of the piston  20  and the rear end of the shaft portion  27   2  of the valve element  27  changes, so that new adjustment such as the replacement of the valve element  27  is required. Accordingly, the first and second methods including the changing of the elastic force of the preload spring  21  are not preferable. In contrast, according to the third method of adjusting only the elastic force of the valve spring  29 , since the elastic force of the valve spring  29  is not transmitted to the first magnetostrictive material  15  nor the second magnetostrictive material  16  at the time where the super magnetostrictive actuator A is not operated, there arises no problem that the size of the clearance α changes. 
     That is, when the elastic force of the preload spring  21  is preset at a value capable of obtaining the desired clearances α and the elastic force of the valve spring  29  is adjusted by changing the thickness of the shim  30  in this state, the sum of the elastic force of the preload spring  21  and the valve spring  29  can be adjusted to a magnitude capable of obtaining a target dynamic characteristic. Further, in this case, the size of the clearance α does not change irrespective of the adjustment of the elastic force of the valve spring  29 . In this manner, the dynamic characteristic of the super magnetostrictive actuator A can be adjusted easily without changing the size of the clearance α by such a simple procedure of merely changing the thickness of the shim  30  supporting the one end of the valve spring  29 . 
     Although in the first embodiment, the shim  30  is disposed between the rear end of the valve spring  29  and the front surface of the piston  20 , the shim  30  may be disposed between the front end of the valve spring  29  and the rear surface of the valve element support member  25  like the second embodiment shown in FIG.  5 . In such a modification, the same function and effects as in the first embodiment can be obtained. 
     Although the detailed explanation has been made as to the embodiments of the present invention, the present invention may be subjected to various changes of the design in a range of so as not to deviate from the gist of the present invention. 
     For example, although the explanation is made as to the example where the present invention is applied to the super magnetostrictive actuator A for the fuel injection valve I, the present invention may be applied to a super magnetostrictive actuator for other arbitrary usage.