US 3898534 A
A piezoelectric igniter with an impact mechanism particularly suitable for lighters. The igniter includes a piezoelectric transducer including a hammer movable toward the transducer. The hammer cooperates with an energy storage spring which is compressible by an actuation member and which is retained in a rest position by one or more magnets.
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v U United States Patent 1 1 1111 3,898,534 Mohr 1 Aug. 5, 1975 [541 PIEZOELECTRIC LIGHTER WITH IMPACT 3,366,808 l/1968 Steward 310/83 MECHANISM 3,389,275 6/1968 Brothers 310/83 I 3,449,637 6/1969 Suzuki 317/81 Inventor: alter Mohr. Frankfurt am Mam, 3,457,461 7/1969 Steinke et 211.... 317/31 Germany 3,509,388 4/1970 Mifune et a1. 310/87 3,540,823 11 1970 1313' t '1 1 1 i. 431 255  Ass1gnee: Braun Aktrengesellschaft, Frankfurt 3 541 360 $1970 a ifij v v 31/4/87 am Main. Germany 3,586,888 6/1971 Dorfman 310 33 3,729,639 4/1973 l-leinouchi et 211.. 310/83  1973 3,758,262 9/1973 Harris 431/130  Appl. No.: 387,380
Primary E.\'aminerV010dymyr Y. Mayewsky  Foreign Application Priority Data Attorney, Agent, or F irmErnest F. Marmorek Sept. 6. 1972 Germany 2243727 Jan. 19, 1973 Germany 2302638 [5 ABSTRACT 1 1 317/81; 310/8-7; 1 1; A piezoelectric igniter with an impact mechanism par- 431/255 ticularly suitable for lighters. The igniter includes a pi-  Int. C1. F23q 3/00 l tri tra d cer including a hammer movable 1 1 Field of Search 3 0/8-3, 8- 317/81, 96, toward the transducer. The hammer cooperates with 3 l7/D /67 F; 1/132, 255 an energy storage spring which is Compressible by an actuation member and which is retained in a rest posi-  Refer n s Cited tion by one or more magnets.
UNITED STATES PATENTS 0 3,364,451 1 /l968 Paul et 61. 338/47 5 Clams 6 Draw'ng F'gures PATENTEU AUG 5 I975 PIEZOELECTRIC LIGHTER WITH IMPACT MECHANISM BACKGROUND OF THE INVENTION This invention relates generally to an igniter particularly for lighters and specifically relates to such an igniter including a piezoelectric transducer and an impact mechanism therefor.
Such piezo electric igniters are generally known. They include a fixed permanent magnet to which adheres a hammer consisting of a ferromagnetic material in the rest position of the mechanism. Such a piezoelectric igniter has the drawback that a relatively large magnet must be used in order to generate the necessary holding forces. Furthermore, there is a disadvantage that the hammer after it has been removed from the magnet remains very long in the region of its attraction so that a large portion of the energy stored in the energy storage spring cannot be used for accelerating the hammer but must be used to overcome the attractive force between magnet and hammer.
Piezoelectric igniters for lighters are mass produced articles which cannot be too expensive in manufacture. Permanent magnets, which are presently available in the trade which can be used for this purpose, considering their price, do not generate the necessary holding force.
It is accordingly an object of the invention to provide a piezoelectric igniter of the type discussed herein which does not have the disadvantages of the prior art, which requires a relatively low actuation force and which may be made in a compact form.
SUMMARY OF THE INVENTION This aim of the invention is solved in that the hammer and the magnet form part of a magnetic circuit closed in the rest position. In this manner it is achieved that a holding force is generated which is high compared to the size of the magnet.
Preferably, a magnetically-conductive member is disposed at both poles of each magnet.
According to a special embodiment, the hammer forms a pot-shaped magnetically-conductive member in which is disposed a magnet. During the rest position of the hammer a fixed magnetically-conductive yoke or frame is disposed adjacent to the open side of the potshaped magnetically-conductive member. This construction has the advantage that there is no need to provide an additional heavy metal part for the hammer so that the weight of the piezoelectric igniter is reduced. The pole surface of the magnet adjacent to the magnetically-conductive yoke may carry a magnetically-conductive plate.
The pot-shaped magnetically-conductive member may be guided in a housing which is magnetically nonconductive.
According to a further expansion of the invention means are provided by means of which the fixed magnetically conductive yoke is secured to a bushing. In this manner a simple construction of the piezoelectric igniter is achieved,
In a further extension of the embodiments of the invention the magnet consists of two individual members shaped like a parallelepiped, two sides of which are provided with magnetically conductive plates, the plates being longer than the parallelepiped blocks of the magnet. This unit is secured to a housing. At the lower side of the plates there is provided a disk-shaped hammer, the lower side of which is convex while its upper side carries a guide pivot which may slide in the free space between the magnets.
According to another embodiment the magnetic circuit includes a permanent magnet, a magneticallyconductive member adjacent to the magnet and a magnetically-conductive yoke, the yoke being relatively movable with respect to the other two parts of the magnetic circuit.
The magnetically-conductive member and the permanent magnet may form the hammer.
According to a further embodiment of the invention the magnetically-conductive member and the permanent magnet may be fixed so that the yoke forms the hammer. In this case, however, the yoke must have a sufficiently large mass, but this construction may be relatively easily achieved.
Such an embodiment consists preferably in that the yoke is tiltably arranged with respect to a unit consisting of the magnetically-conductive member and the permanent magnet. Additionally, an energy storage spring may be secured to the yoke.
Preferably, the energy storage spring is arranged as a leaf spring, one end of which is secured to the yoke while the other end operates as an actuation element.
It is advantageous to arrange the elements of the magnetic circuit axially symmetrically with respect to the axis of motion because this avoids the occurrence of forces acting at an angle and preventing canting of the hammer.
A further preferred embodiment includes a permanent magnet and a magnetically-conductive element having an axial opening in which is disposed the energy storage spring and a ram serving as the actuating element.
According to a further extension of the invention, the magnetic circuit includes a shunt circuit including at least one air gap, the magnetic resistance of which is at least three times as large as the magnetic resistance of the closed magnetic circuit.
The shunt circuit may also be formed by an air gap between the magnet and the magnetically-conductive member.
A special embodiment consists in that the hammer is formed by a magnetically-conductive member having a T-shaped cross section. At the side faces of the member there is provided at least one axially polarized magnet.
The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is a side elevational view in perspective of a preferred embodiment of the piezoelectric igniter of the invention;
FIG. 5 is a longitudinal sectional view through another piezoelectric igniter embodying the invention; and
FIG. 6 is a longitudinal sectional view through a modified construction of a piezoelectric igniter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The piezoelectric igniter illustrated in FIG. 1 includes a cylindrical housing which consists of a material which is magnetically non conductive. In the lower portion of the housing there is provided a piezoelectric transducer 2 hereinafter referred to as a transducer. The transducer includes two piezoelectric crystals 3 between which is disposed a high voltage electrode 4. Within the transducer there is also disposed an impact plate.
The surface of the transducer is surrounded by an insulating layer 5. Its lower surface is disposed adjacent to the bottom 6 of the housing 1. Above the plate 7 there is disposed a pot-shaped magnetically-conductive member 8 in the interior of which is secured a permanent magnet 9 spacedfrom the side walls of the magnetically-conductive member 8. The pot-shaped magnetically conductive member 8 and the permanent magnet 9 form the hammer of the piezoelectric igniter.
Above the hammer there is disposed a yoke 10 which is magnetically conductive and which is formed as a plate adjacent the hammer and which extends into a pin-shaped extension. The yoke 10 consists of a ferromagnetic material. The lower plate-like region of the yoke 10 covers the upwardly open surface of the potshaped magnetically-conductive member 8 and in the rest position rests on the member 8 so that the magnetic circuit is closed consisting of the magneticallyconductive member 8, the permanent magnet 9 and the yoke 10. This means that there is essentially no air gap in the magnetic circuit.
The shaft of the yoke 10 is fixedly connected with a pot-shaped body preferably of a synthetic material or resin 11. The body 11 is provided with a transverse bore 12 in its upper region through which extends a holding pin 13 which in turn extends through openings 14 in the housing 1 and which fixes the yoke 10 and the synthetic resin body 11 with respect to the housing.
Above the yoke there is provided an actuation cap 15 which is provided with at least two diametrically opposite longitudinal apertures 16 which are traversed by the holding pin 13 and which limit the movement of the actuation cap. The lower edge 17 of the actuation cap 15 serves as a support for an energy storage spring 18, the other end of which rests against the pot-shaped magnetically'conductive member 8.
The piezoelectric igniter further includes a return spring 19 which is disposed between the plate 7 and a shoulder-like recess in the bottom of the pot-shaped magnetically-conductive member 8.
Such a piezoelectric igniter operates as follows: When the actuation cap 15 is depressed the energy storage spring is compressed and tensioned so that a force is exerted on the pot-shaped magnetically conductive member 8. As soon as the reactive force generated in the energy storage spring by means of the actuation cap exceeds the holding force of the hammer consisting of the magnetically-conductive piece 8 and the permanent magnet 9 by the yoke, the hammer suddenly moves away from the yoke and is accelerated by the liberation of the energy stored in the energy storage spring 18 in the direction toward the pivot of the transducer 2. The hammer only has to overcome the, attractive force which rapidly decreases with distance from the yoke as well as the force necessary for compressing the return spring 19.
When the head 20 of the magnetically-conductive member 8 impacts the plate of the transducer 2 a short duration pressure is exerted on the transducer whereby a high voltage impulse is generated at the high voltage electrode 4.
This high voltage impulse may, for example, be utilized for generating a spark in a spark gap. The spark in turn may be used for igniting the fuel of an igniter.
When the actuation cap 15 is released the energy storage spring 18 expands into its neutral position. Thereafter, the hammer 8 and 9, the energy storage spring 18 as well as the actuation cap 15, are lifted by the return spring 19 into the rest position where the hammer 8 and 9 is again held by magnetic force against the yoke 10.
FIG. 2 shows a longitudinal sectional view of the piezoelectric igniter of FIG. 1 in a plane rotated through and illustrates a slightly modified embodiment. As shown the return spring 31 is not disposed between the hammer and the transducer but is disposed in the interior space of the actuation cap 15. The actuation cap 15 consists of a ferromagnetic material so that a magnetic shunt circuit is formed by the pot-shaped magnetically-conductive member 8 through the energy storage spring 18 and the actuation cap 15 which is sufficient to lift the hammer 8 and 9 again into its rest position. The energy storage spring 18 is fixedly connected with the magnetically-conductive member 8, for example, by means of one or several pins disposed in a circular recess of the magnetically-conductive member 8. Furthermore, the energy storage spring 18 is fixedly connected at its upper end with the actuation cap 15 in the same or similar manner. Otherwise, the construction corresponds to that illustrated in FIG. 1.
FIG. 3 illustrates the upper part of a further embodiment of a piezoelectric igniter according to the inven tion. The magnet consists of two individual blocks shaped like a parallelepiped 39 which is surrounded on two sides by plates 42 of magnetically-conductive material, the plates being longer than the parallelepiped blocks 39 of the magnet. The thus formed unit is secured to the housing 41, for example, by pressing. A disk-shaped hammer 21 rests against the lower surface of the plates. The lower surface of the hammer is convex as shown while its upper portion carries a guide pivot 22 which can slide in the free space between the magnets. Y It is feasible to provide a disk, not illustrated, having a lower convex surface and disposed between the guide pin 22 and the energy storage spring 38. This disk ensures that the force of the energy storage spring 38 acts against the guide pin 22 along the axis of movement.
At the lower surface of the disk shaped hammer 21 which forms the hammer and which at the same time forms the yoke of the magnetic circuit, there rests a return spring 19.
In the central space between the two blocks 39 of the magnet there is disposed the energy storage spring 38, the lower end of which rests against the disk 21 while its upper end bears against an actuation stem 23 which is prevented from falling out of the housing by a radially inwardly directed flange 24 of the housing 41.
When the actuating stem 23 is depressed the energy storage spring 38 is tensioned. Since the reactive force of the spring is greater than the holding force of the disk-shaped hammer 21, the hammer moves easily from the magnetically-conductive plates 42 and is accelerated in the direction of the transducer whereby the return spring 19 is compressed. When the actuation stamp 23 is released, the energy storage spring 38 returns into its neutral position. Thereafter the disk 21, the energy storage spring 38 and the actuation stem 23 are returned to their rest position by the force of the re turn spring 19. Because the parts of the magnetic circuit are formed axially symmetrically with respect to the axis of motion of the movable plates, in this case the disk 21, there are no forces acting on the hammer at an angle so that the hammer is not substantially twisted from its axially symmetrical orientation during its accelerated motion.
FIG. 4 illustrates a simple embodiment of a piezoelectric igniter according to the invention. The magnetic circuit includes an L-shaped magneticallyconductive member 25. At one leg of the member 25 a permanent magnet 26 shaped like a parallelepiped is secured in such a manner that the two elements form a U. At the free ends of the magnetically-conductive member 25 and the permanent magnet 26 there are disposed a yoke 27 of a ferromagnetic material which also serves as the hammer. At the end of the yoke 27 adjacent the permanent magnet 26 there is disposed a leaf spring 29 at an inclined surface 28 of the yoke.
At the free leg of the L-shaped magneticallyconductive member 25 there is secured a U-shaped holding sheet 30 consisting of a magneticallynonconductive material. In the base region 31 of the holding sheet 30 there are arranged the piezoelectric transducer 2 in such a manner that its impact plate 32 is opposite the hammer 27. The piezoelectric igniter of FIG. 4 operates in the following manner. In order to actuate the igniter the leaf spring 29 is pressed in the direction indicated by the arrow so that the spring is bent. As soon as the bending moment of the leaf spring exceeds the holding moment of the hammer 27 of the magnetic circuit consisting of the magneticallyconductive member 25 and the permanent magnet 26, the hammer 27 lifts off the free leg of the magneticallyconductive member 25 and is accelerated by the force of the leaf spring 29 in the direction toward the impact plate 32 of the transducer 2. When the hammer 27 impacts the plate of the transducer a pressure wave is generated in the transducer 2 which generates a high voltage impulse at the high voltage electrode 4.
When the leaf spring 29 is released the hammer 27 is returned into its rest position illustrated in FIG. 4 by the leakage field lines of the magnetic circuit. In order not to impede this return motion the leaf spring 29 should consist of a material which is magneticallynonconductive or should be sufficiently far removed from the permanent magnet 26 in its actuated position.
The piezoelectric igniter illustrated in FIG. 5 includes a cylindrical housing 51 consisting of a material which is magnetically nonconductive. In the lower portion of the housing there is disposed a piezoelectric transducer 52 containing two piezoelectric crystals 53 between which is disposed a high voltage electrode 54. At the upper surface of the transducer there is disposed a semispherical impact plate 57. Above the impact plate 57 there is disposed a pot-like magnetically-conductive member 58 in the interior of which is secured a permanent magnet 59 spaced from the side wall of the magnetically-conductive member. The potshaped magnetically-conductive member 58 and the permanent magnet 59 form the hammer of the piezoelectric igniter.
Above the hammer is disposed a magnetically conductive yoke plate 60 which is secured by pins 61 to the wall of the housing 51. The yoke plate 60 is provided with a central bore 62 through which extends the shaft of a mushroom-shaped pressure transfer member 63, the head 64 of which can slide within the housing 51 with a certain play.
Between the lower surface of the head 64 and the yoke plate 60 there is anchored a return spring 65. At the upper surface of the head 64 is disposed the energy storage spring 66 disposed in the actuation cap 67.
In accordance with the invention the permanent magnet 59 is provided at the pole surface adjacent the yoke plate 60 with a magnetically-conductive plate 68 into which is secured the end of the shaft 62 of the mushroom-shaped pressure transfer member 63. The thickness of the permanent magnet 59 and of the magnetically-conductive plate 68 are so selected that the free upper surface of these elements is disposed in the plane of the edge of the potshaped magneticallyconductive member 58 adjacent the yoke plate 60.
In the rest position this edge and the magneticallyconductive plate 68 adhere to the yoke plate 60 so that the magnetic circuit does not have an air gap. In that case the permanent magnet 59 develops its maximum holding force.
When the actuation cap 67 is depressed the energy storage spring 66 is tensioned so that the force exerted on the pressure transfer member 63 increases. As soon as the force exerted by the energy storage spring 66 becomes larger than the holding force of the permanent magnet 59, the unit consisting of the members 58, 59, 68 and 63 are removed from the yoke plate 60 and moved with acceleration against the pressure plate 57. As soon as the pot-shaped magnetically-conductive member 58 impacts the plate 57, a pressure wave is created in the piezoelectric transducer 52 which results in a high voltage impulse at the high voltage electrode 54.
In the actuated state, that is when the pot-shaped magnetically conductive member 58 is in contact with the plate 57, the magnetic resistance of the magnetic surface is increased because the circuit now contains an air gap between the magnetically-conductive plates 68 and the magnetically-conductive member 58. The magnitude of this air gap, however, may be so selected that only a small leakage flux extends outwardly beyond the housing 51. In the rest state and shortly after the magnetically-conductive plate 68 is separated from the yoke plate 60, the latter causes a rapid deflection of the field lines to the edge of the pot-shaped magnetically-conductive member 58 compared to other proposed constructions.
The embodiment illustrated in FIG. 6 utilizes instead of a pot-shaped, a mushroom-shaped magneticallyconductive member 70, the shaft 71 of which is surrounded by an annular magnet 72 in such a manner that an air gap 84 remains between the two parts. This air gap may be filled with a nonconductive material.
Disposed on the surface of the pole of the permanent magnet not connected with the mushroom-shaped magnetically-conductive member 70 there is disposed a magnetically-conductive conductive annular member 73, the face of which is flush with the face of the shaft 71.
In the rest position the magnetically-conductive annular member or ring 73 and the shaft 71 adhere to the magnetically-conductive yoke 74 so that the field lines emanating from the annular magnet do not have to bridge an air gap. The holding force of the magnet is therefore at a maximum.
The yoke 74 is secured in its upper region by a pin 75 to the housing 51. The yoke 74 is so formed that an annular space is provided between it and the housing 51. In this annular space there is provided an energy storage spring 76, one end of which rests against the magneticallyconductive ring 73 and the other end against the face of an actuating cap 77. The actuating cap fits into the annular space and is provided at diametrically opposite points with longitudinal apertures 78 through which the pins 75 extend. The actuating cap 77 can accordingly be moved only to a limited extent which is defined by the length of these apertures.
Between the piezoelectric transducer 52 and the mushroomed-shaped magnetically-conductive member 70 there is further provided a return spring 79. When the actuating cap 77 is depressed the energy storage spring 76 is tensioned. Accordingly, it exerts an increasing force on the magnetically-conductive ring 73 and the parts connected thereto. As soon as the force developed by the energy storage spring 76 is greater than the holding force of the magnet and the force of the return spring 79, the unit consisting of parts 70, 72 and 73, that is the socalled hammer, moves away from the yoke 74 and impacts the impact plate 80 of the transducer 52.
In this actuated state only a small linkage flux exists from the hammer because the magnetically-conductive ring 73 collects the field lines emanating from the adjacent pore face of the ring magnet 72 and concentrates them in the air gap between the magneticallyconductive ring 73 and the shaft 71.
The described piezoelectric igniters have the advantage that they develop a relatively large holding force. On the other hand, the attractive force rapidly reduces even at a small distance of the hammer from the yoke 74 so that the energy stored in the energy storage spring 76 can be transformed to a major portion into kinetic energy of the hammer.
What is claimed is:
l. A piezoelectric igniter of the type normally used in a lighter comprising a magnetically non-conductive housing;
magneticallya piezoelectric transducer and an impact mechanism disposed in said housing and including a hammer movable between a normal rest position and an impact position away from said rest position and whereat said hammer has an impact with said transducer;
an electric circuit including electrical leads and electrodes connected to the piezoelectric transducer for ignition purposes;
spring means being operable to exert a force against said hammer in a direction toward said transducer when the potential energy of the spring means is increased;
resilient retraction means for said hammer of smaller force than said spring;
an actuating member operable to increase the potential energy of said spring means; and
a magnetic circuit comprising a fixed part, a movable part, one of said parts including a magnet having pole faces and both said parts being magneticallyconductive, said parts being sufficiently closely adjacent each other in the rest position of the hammer for closing the magnetic circuit substantially free from any air gap, said movable part being connected to the hammer and being movable therewith and being operable due to the magnetic force exerted between said parts to hold said hammer in said rest position against the force of said spring means throughout that portion of the increase in potential energy of said spring means which is at least inferior to said magnetic force;
said hammer including a pot-shaped magneticallyconductive member disposed in said hammer and having an open side, said movable part being a magnet disposed in said member, said fixed part comprising a magnetically-conductive yoke, the open side of said magnetically-conductive member being disposed next to said yoke in the rest position of said hammer.
2. Piezoelectric igniter as claimed in claim 1 wherein a magnetically-conductive member is disposed adja cent each of the poles of said magnet during said predetermined rest position but not at other times.
3. Piezoelectric igniter as claimed in claim 1 wherein the magnetically-conductive yoke is secured to said housing.
4. Piezoelectric igniter as claimed in claim 1 wherein said hammer is formed by said magnetically-conductive member and said permanent magnet.
5. a Piezoelectric lighter as claimed in claim 1 said movable part including said magnet and an additional magnetically-conductive member in contact with said magnet at all times and movable therewith together with said hammer, said magnet being a permanent magnet.
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