US3271624A - Apparatus for producing electric impulses - Google Patents

Description

Sept. 6, 1966 C, s, 1 KlNGMA ETAL 3,271,624

APPARATUS FOR PRODUCING ELECTRIC IMPULsEs 2 Sheets-Sheet 1 Filed May '7, 1964 INVENTOR. CORNELIS S.J. KINGMA PIETER SMID ATTUR/VEY FIB. 2

Sept' 5, 1966 c. s. J. KINGMA ETAL 3,271,624

APPARATUS FOR PBODUCING ELECTRIC IMPULSES Filed May '7, 1964 2 Sheets-Sheet 2 FIE'. 3c PIE. 3d

INVENTOR.

CORNELIS S.J.KlNGM/ BY PIETER SMID vwp A 7' TOR/VE Y United States Patent O 3,271,624 APPARATUS FOR PRODUCING ELECTRIC IMPULSES Cornelis Sacharias Johnnes Kingma, Baambrugge, and

Pieter Smid, Haarlem, Netherlands, assignors to Honeywell G.m.b.H., Frankfurt am Main, Germany, a corporation of Germany Filed May 7, 1964, Ser. No. 365,705 Claims priority, application Germany, May 24, 1963, H 49,251 3 Claims. (Cl. 317-81) It is well known to use electrical ignition for gas burners. The main advantage of the so-called magneto type electrical ignition is that electrical connections to a voltage supply are not required. It is furthermore well known to create electrical ignition pulses for internal combustion engines by impact-like mechanical stressing of piezo-electric crystals. The electrodes of such piezoelectric crystals are connected to the ignition plug of the internal combustion engine. A hammer, driven by the engine cam shaft, periodically strikes the piezo-electric crystal so that electrical charges are created on the electrodes of the crystal, the char-ges being used for producing an ignition spark in an electrical circuit. Also, with such a piezo-electric ignitor no voltage supply is needed.

The present invention deals with an apparatus for producing electrical impulses by means of a hammer which applies a sudden impact to a piezo-electric body having electrodes on opposite surfaces. It is an object of the invention to provide a simple and compact ignitor which preferably may be operated manually and in particular is to be used to generate a spark to ignite gas burner-s. Another object of the invention is to control the mechanical stress of the piezo-electric body in such a manner that is no destruction of the piezo-electric crystal. Another object is to provide a long life and a reliable operation of the ignitor.

According to the invention this is accomplished by providing a self-aligning supporting means for that surface of the crystal which is opposite the surface beaten by the hammer. Because of this self-alignment, no transver-se forces are supplied to the crystal. The supporting means preferably is used as an electrode for the high voltage impulses.

The invention can be realized by various constructions. According to a preferred embodiment of the invention the supporting means is provided with a hole shaped like a spherical cap on the side opposite the crystal. This supporting member is in touch with a ball or a part of a ball and can be turned and pivoted with respect t-o this ball. Instead of a ball-like surface another rotation symmetrical body for instance an ellipsoid can be used. In order to have as little friction as possible between the ball-like surface and the spherical cap it is preferable that these two parts `have a different radius of curvature. The spherical cap might be replaced by a conical shape. As shown in FIGURE 1, the configuration of this supporting means may be such that a ball or a body with ball-like surfaces is located between two supporting members with holes of b-all-like or conical shape.

The ball and the spherical cap can also change their places. As shown in FIGURE 2 the plate supporting the piezo-electric crystal is ball-like shaped on the side opposite the crystal and projects into the hole of the supporting member.

Although the provisions las described are concerned with that side of the piezo-electric crystal opposite to the hammer, it is of course also desired that no transverse forces are supplied to the side of the crystal which is adjacent to the hammer. In order to meet this requirement the impact -of the hammer is transferred to the crystal by means of a ball which is guided in a hole on the front of the hammer and is guided by the housing. In order to have an almost equal impact pressure over the whole surface of the crystal a rigid metal plate lies on the crystal and transfers the impact to the crystal. The crystal may be made of barium titanate or lead-zinc titanate, as examples.

As mentioned above, the hand i-gnitor should be simple and compact. For meeting this object in accordance with the invention, a helical spring for loading the hammer cc-axially surrounds the crystal `and the supporting means as shown in FIGURE 2. This helical spring has one end supported by a flange of a cup like housing which is xed to the hammer and which covers and surrounds the crystal as well as the supporting means. The other end of the helical spring abuts against the cover of a second housing which surrounds the first housing and the helical spring. With a flange of this second housing the ignitor can be mounted to a supporting plate of frame.

It is self-evident that the ignition voltage produced by the ignitor should be the same with each operation of the ignitor. In order to obtain such a constant ignition voltage in accordance with the invention the electrodes of the crystal are discharged automatically before and/or after every ignition impulse. This provision, which also contributes to the reliability of the ignitor, can be realized in that a shorting switch is provided which short circuits the electrodes when the hammer is moved to load the helical spring. The contact lever of this shorting switch preferably is spring loaded and is automatically closed when the hammer is moved to load its spring. The shorting switch can be operated by the cuplike first housing surrounding the hammer.

A further method for producing an almost constant ignition voltage consists in compelling the same spring load of the hammer for every operation. This is achieved in accordance with the invention when the hammer is mechanical fixed to a tilting lever which is suddenly pivoted by means of a spring force. The principle of such a tilting lever arrangement corresponds to the principle of the well-known snap acting switches. According to a preferred embodiment of the invention the one end of Va tension spring is fixed to the free end of the tilting lever whilst the other end of the spring is pivotal fixed to an actuator lever. The pivot of the actuator is chosen in such a manner that during loading the spring the vector of the spring force passes an unstable position and therefore effects =a sudden tilting of the tilting lever. The unstable position depends upon the pivot of the tilting lever and upon the working point of the spring. The hammer, which is to strike the crystal, can be located on the line between the piv-ot of the tilting lever and the working point of the spring, or on the prolongation of this line, or out of this line. An embodiment in accordance with the last mentioned example is shown in FIGURES 3ft-3d. In these drawings the impact mechanism of the hammer is shown diagrammatically only.

In order to explain the invention and according features more in detail, reference is made to embodiments of the invention as shown by example in the drawings.

In the arrangement as shown in FIGURE l a housing 2 covering the piezo-electric crystal 13 and its supporting means is fixed to the sleeve 1 by means of an inner thread. On the other side of the sleeve a second housing 3 is fixed to the sleeve and covers the hammer and the helical spring for actuating the impact. The plunger 4 carries on its front end a funnel-like endplate 5 which supports one end of the helical spring 6. The ball 7 projects into the funnel-like hollow of the plate 5. The ball 7, after compression of the spring 6 and release of the handle 8,

ignitor.

3 lWill strike the steel plate 9 by means of the force off spring 6. The ball 7 is guided within the housing 3. The end of the spring 6 opposite the ball 7 is supported against the endplate 11 which covers the opening of the cylindrical housing 3.

In the other housing 2 the. piezo-electric crystal 13 and its supporting means are located. In referring to the piezo-electric body as a crysta it should be mentioned that not only monocrystalline but also polycrystalline bodies can be used. The front side of `crystal 13 opposite the impact plate 9 lies at upon a supporting part 14 which .is provided with a spherical hollow 15. Between this supporting part 14 .and a symmetrically formed supporting part 16, a ball 17 is positioned so that the supporting part 14, and p-articularly its surface adjacent to the crystal is maintained parallel to the front surface of the crystal. Connected to the supporting part 16 by means of a pin 19 is the high voltage electrode 20 of the A cylindrical insulating sleeve 21 is provided for electrical insulation between crystal 13, its supporting means, and the pin 19 on the one side, and the housing 2 on the other side. An insulating ring 22 holds the crystal in its radial position. As the parts 14, 17, 16, 19 and 20 are of metal they represent the electrical connection between the high voltage electrode and the one layer or electrode of the crystal. The impact plate 9, or a corresponding electrode on the adjacent front surface of the crystal, serves as a connection with the housing 2 which usually is grounded. For fastening the ignitor to the carrier plate or chassis, the sleeve 1 or one of the housings 2 or 3 can be provided with suitable flanges or other mounting means or can be iixed by means of brackets. When threading the housing 2 into the sleeve 1, the end plate 23 and the insulating bushing 21 press the crystal and its supporting means against the impact plate 9 and the spring plate 10. Therefore, the crystal and its supporting means are held under a prestress in their position relatively to another. It can be seen that the part of the ball adjacent to the supporting part 14 could also be part of the supporting part 16. In such a case, the supporting part 16 would have -a bal1-like projection instead of a spherical or conical hollow. The radii of curvature of the ball and of the hollow are different. In the structure as shown in FIGURE l the hollow :has a shape -of -a yconical frustum.

The ball 7 can be rigidly xed to the plunger 4. Then the plate only serves as a bearing for the spring 6.

FIGURE 2 shows an embodiment of the invention which is characterized by an especially compact construction. This is achieved by having the helical spring 36 coaxially surround the crystal 43 and its supporting means. After loading the spring by means of the handle 3S, and then releasing this handle, the spring force will accelerate the plunger 34 in direction to strike the impact plate 39. The plunger 34 is rigidly iixed to a housing 33 which covers the plunger 34, the crystal 43, and its supporting means. A cylindrical space is provided between the plunger housing 33 and the outer housing 31 which covers the whole arrangement. The helical plunger spring 36 is positioned in this cylindrical space. The spring has one end engaging the ange 35 of the cuplike inner housing 33 and with its other end engaging the cover plate of the outer housing 31. The spring 36 is loaded by drawing the plunger 34 and the lhousing 33 up by means of the handle 38. When the handle 38 is released, the plunger 34, with the ball 37 in its front hollow 32, suddenly moves down and strikes the rigid metallic impact plate 39. This impact plate transfers the pressure force to the crystal 43. Both end surfaces of the cryst-al 43 are ycovered by a brass disc 44. The axial position of the impact plate 39 and of the crystal 43 with its supporting means inside the insulating bushing 51 is fixed by means of a spring ring 45 and a spring disc 46. The crystal abutting surface of the supporting member 47 lies iiatly upon the brass disc 44. The side of snap acting switches.

of this supporting member 47 opposite to the crystal is ball-like curved `and projects into a spherical or conical hole of the supporting member 4S. Hereby the supporting member 47 is turnable and pivotal with respect to the supporting member 48 and will place itself automatically into parallel position to the end surface of the crystal 43. By means of a spring disc 46 which abuts against the spring ring 45 the crystal 43 together with its supporting means is brought under such a pre-stress so that no looseness can arise between these parts. Such a looseness would decrease the impact force to which the crystal was subjected and thereby red-uce the voltage created at the electrodes of the crystal. The complete ignitor is mounted to the wall 40 by means of a ange 30 onthe outery housing 31. The front part of the cylindrical insulating body 51 which surrounds the conductor pin 49 and bears the high voltage terminal 50 projects through a hole in the wall 40. It is secured in this position by means of a spring ring 52.

A compulsory discharge of the -crystal 43 before starting a new operation of the ignitor is effected by means of la shorting switch. The contact lever 61 of this switch short circuits the electrodes of the crystal when the spring 36 is loaded. In the position as shown in FIGURE 2, the spring 36 is not loaded. The flange 35 of the cuplike housing 33 engages a plunger 62 and pivots the contact lever 61 out of contact with the high voltage terminal 50. When loading the spring 36, by drawing the plunger 35 to the right, the contact lever 61 will come into contact with the terminal 50 under the iniluence of spring 63. Thereby the termin-al 50 is connected electrically to the housing and the crystal electrodes are discharged. The contact lever 61 is rightangled and the plunger 62 engages the lever 61 in the corner of the lever. The plunger 62 projects through an opening in the wall 40. Preferably the Contact lever 61 is part of the spring 63 and is pivotal about an axle 65 carried by the bracket 64. The spring 63 and the lever 61 can be separate parts. The radial position of the crystal is secured by means of an insulating spacing ring 42.

The voltage created by the crystal depends on the mechanical pressure supplied to the crystal. It therefore is desired to have the same impact force with every ignition operation. Such a constant ignition voltage is guaranteed with the aforementioned examples of the invention if the plunger is drawn back to a stop e.g.^to a position Where the spring is completely loaded. If then the plunger is suddenly released, the same high voltage will be created with every operation. If, however, the plunger is not completely drawn back, or is slowly released, the impact force supplied to the crystal will be smaller and therefore the ignition voltage will also be smaller. In order to avoid this, the invention provides a loading and releasing mechanism for the plunger as explained in the following with respect to FIGURES 3a to 3d. This mechanism is based on the well `known principle When loading the spring, not only the amount of the vector of the spring force is varied, but also its direction is varied so that this vector passes through an unstable position. After passing through the unstable position, the spring is suddenly released and thereby the striking action is initiated.

As shown in FIGURES 3a to 3d, the plunger or hammer 71 is rigidly fixed to the tilting lever 72. The tilting lever 72 is pivoted about the xed axle 73. At the end of the tilting lever 72 opposite the pivot 73 a tension spring 74 is xed to the free end of a lever 75. This lever, by means of a handle 76, can be pivoted about the axle 77. It is an object of this arrangement that the hammer 71 strike the -crystal 78 suddenly. FIGURE 3a shows the normal position of this arrangement. The spring force of spring 74 presses the tilting lever 72 to the left against the stop 79. If now, by pressing the handle 76 downwards, the lever 75 is pivoted in clockwise direction, the lever 75 goes to the intermediate position as shown in FIGURE 3b. By doing this the vector of the spring force has increased (the spring has been loaded) and the vector additionally has changed its direction. Depending upon the weight and the distance of the hammer from the tilting lever 72, a definite direction of the vector of the spring force exists in which the position of the tilting lever is unstable. It is assumed that this position has just been reached in FIGURE 3b. If now the handle is furthermore moved in clockwise direction, the tilting lever 72 suddenly accelerates t-he hammer 71 in the direction of the crystal 78 because of the force of the loaded spring 74. As this action arises at a given angular position of the lever 75, and as the spring has reached a given load, the hammer 71 strikes the crystal 78 with a given pressure with every operation of the handle 76. It is of no importance how far the handle 76 is moved in clockwise direction after passing the unstable position. The impact force is determined only by the spring force when passing the unstable position. Also, in the end position of the hammer as shown in FIGURE 3c, a residual spring load is present in order to avoid vibrations and fluttering of the hammer with respect to the crystal.

If now the operator releases the handle 76, the force of spring 74 returns the lever in a counterclockwise direction as shown by the arrows in FIGURE 3d. After passing the unstable position, the spring 74 moves the hammer in counterclockwise direction until it engages the stop 79. During this movement, after passing the unstable position, the hammer 71 disengages the crystal. During the movement, before passing the unstable position, the hammer 71 engages the crystal 78 so that up to this moment only the lever 75 with the handle 76 and the spring 74 are changing position. It is obvious that the hammer 71 could also be positioned on the tilting lever 72, or in the prolongation of the tilting lever 72. The handle need not be rigidly xed to the lever 75. Instead of this a plunger could be used which is pressed from the left side against the lever 75 and thereby pivots the lever in clockwise direction. The operation of the impact mechanism would remain the same.

Other modifications of our invention will be apparent to those skilled in the art and we intend that our invention be limited to structures as defined in the following claims.

We claim as our invention:

1. A piezoelectric spark ignitor, comprising:

a piezoelectric crystal having an axis along which a force is to be applied to generate a high voltage, said crystal having a pair of end faces at spaced ends along said axis,

a metallic impact plate mounted to engage one of said end faces and having a surface generally normal to said axis,

self aligning support members having mating curved sufaces and having a surface to engage the other of said end faces,

means prestressing said crystal between said plate and said support members,

a hammer having a ball-like member spring biased against said plate and engaging the same at a point,

and switch means actuated by movement of said hammer away from said plate to short circuit said crystal prior to striking of said plate by said hammer.

2. A concentrically arranged piezoelectric spark ignitor for manually generating a spark for use in igniting a gas llame or the like, comprising:

an insulating support member having an open cupshaped recess with metallic contact means mounted in the bottom thereof, said metallic contact means having a divergent walled recess formed therein with walls diverging toward the opening in said support member,

a metallic crystal support having a ball-like curved surface positioned within said divergent walled recess and having a flat surface opposite said curved surface,

a piezoelectric crystal, having generally parallel end faces, mounted within said support member with one end face engaging the at surface of said crystal support,

a metallic impact plate engaging said other end face of said crystal,

means engaging said impact plate to force said crystal toward the bottom of said support member to prestress said crystal,

a manually movable hammer including a handle and a ball-like surface which engages said impact plate at a point,

a spring concentric with said support member and arranged to bias said hammer against said impact plate such that movement of said handle away from said plate stores energy in said spring, and release of said handle cause an abrupt impact on said impact plate,

and means adapted to connect said contact means and said impact plate to spark electrodes.

3. A piezoelectric spark ignitor, comprising:

a piezoelectric crystal having generally parallel end faces,

means prestressing said crystal by applying a force to the end faces thereof, said means comprising a gen erally flat impact plate engaging one end face, a self aligning support engaging the other end face, and means compressing said crystal between said impact plate and said support,

pivotally mounted hammer means including a ball-like portion to strike said impact plate at a point contact,

a pivoted actuating lever for said hammer including an end portion and a spring -connecting said end portion to said hammer, said end portion normally being positioned to one side of the pivot of said hammer means to normally bias said hammer away from said impact plate, said actuating lever being effective upon movement of said end thereof to load said spring and to move said end portion to the other side of the pivot of said hammer means to thus cause said hammer means to strike said impact plate,

and metallic means adapted to electrically connect said crystal end faces to ignition electrode means.

References Cited bythe Examiner UNITED STATES PATENTS 2,717,916 9/1955 Harkness 123-148 3,200,295 8/ 1965 Owens et al 317-84 3,201,984 8/1965 Hinnah et al. 73-141 3,211,949 10/1965 Slaymaker et al 315-55 FOREIGN PATENTS 606,498 10/ 1960 Canada.

966,552 8/1957 Germany. 1,164,141 2/ 1964 Germany.

RICHARD M. WOOD, Primary Examiner. V. Y. MAYEWSKY, Assistant Examiner.

Claims (1)

1. A PIEZOELECTRIC SPARK IGNITOR, COMPRISING: A PIEZOELECTRIC CRYSTAL HAVING AN AXIS ALONG WHICH A FORCE IS TO BE APPLIED TO GENERATE A HIGH VOLTAGE, SAID CRYSTAL HAVING A PAIR OF END FACES AT SPACED ENDS ALONG SAID AXIS, A METALLIC IMPACT PLATE MOUNTED TO ENGAGE ONE OF SAID END FACES AND HAVING A SURFACE GENERALLY NORMAL TO SAID AXIS, SELF ALIGNING SUPPORT MEMBERS HAVING MATING CURVED SUFACES AND HAVING A SURFACE TO ENGAGE THE OTHER OF SAID END FACES, MEANS PRESTRESSING SAID CRYSTAL BETWEEN SAID PLATE AND SAID SUPPORT MEMBERS,

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