US2649488A - Electric ignition system for internal-combustion engines - Google Patents

Description

J. R. HARKNESS ELECTRIC IGNITION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Aug. 18, 1953 3 Sheets-Sheet 1 Filed July 31, 1952 Jase ,0/2 Harkness 18, 1953 J. R. HA NESS 2,649,488

ELECTRIC I IT 0 SYSTEM FOR INTERNAL- BUSTION ENGINES Filed July 31, 1952 3 Sheets-Sheet 2 J. R. HARKNESS ELECTRIC IGNITION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Aug. 18, 1953 s sheets-sheet :5

Filed July 51, 1952 Jasp/z EPA/75 55 Patented Aug. 18, 1953 UNITED PATENT 'OFF'ICE ELEGTRIC' IGNITION SYSTEM FOR INTER- NAL-CO'MBUSTION ENGINES Joseph R). 1Harkness,; Milwaukee, Wis., 'assignor to Briggs 8; Stratton Corporation, Milwaukee, Wis., a-corporation of Delaware Application July31, 1952, Serial No. 301,830

27 Cla ms. l

This invention relates to electric -ignitio'n systems for internal combustionenginesandehasas its=general purpose to provide a nc'vel -a'nd improved-manner of producing the high tension E; M. F. required to fire a spark plugyandthis application is a continuation-in-part of thepending application-SerialNo. 205,382, filed January 10,- 1951, now abandoned.

- Heretofore the energy source of-electricignitionsystems has been'ei-ther a battery energized ignition coil or a magneto, and in thecase of small portable single cylinder engines-,ma'gnetos have been used almost exclusively. The efiicaey of an ignition coil is; of=course,- nobetterthan its battery which not only requires periodic recharging and often must be replaced, but is subject-to a host of other disadvantages well known to any motorist, and the ordinary magneto has a disadvantageousspeed-voltage characteristic in that at cranking speeds the voltage is low while at running speeds it is excessively high.

The present invention obviates the need for either a'battery or a magneto'and"thus-overcomes the disadvantages inherent therein.

Broadly stated the invention comprehends a' voltage generator especially well" suited foruse' in electric ignition systemsfor internal combustion engines, which utilizes'the' well known piezoelectric effect. To this end'thevoltage generator of this invention comprises a ceramic polycrystal line piezoelectric element connected in series circuitw-iththe spark plug of the engine, and novel engine driven means for periodically mechanically stressing theelement. A piezoelectric element, as those skilled in the art no doubt well know, is a bod which possesses'thephysical property of producing a changein the electrical charges on its surfaces coincident with change in mechanical stress in. the element, and a ceramic polycrystalline piezoelectric element is one in which a piezoelectric material such as a polycrystalline metallic titanate, mixed with a ceramic binder is fired or vitrified into a solid ceramic body; It differs, therefore, from such well known piezoelectric material as Rochelle salt and quartz crystals which are monocrystalline.

Theoretically, it might be possible to. employ a monocrystalline material for the purposes of this invention, but as far as known monocryst'alline piezoelectric materials are incapable of'with standing the physical stresses which must be imposed upon the element to'produce a voltage high enough for satisfactory, commercially reliable spark plug firing. One aspectof the invention thus; resides inthe discovery that poly- 2 crystalline piezoelectric elements can be used to produce the voltage necessary to fire a spark plug and are capable of withstanding-thehigh mechanical stressneeded to produce the required voltage with an element small enough to beambodied in small single cylinder gasoline engines.

The piezoelectric characteristics and polycrystalline structure of metallic titanates are now fairly well recognized, and methods or formin'g them into elements for various purposes-have been commercially developed, One such method is shown, for example, in U. S; Patent No. 2,538,554; Methods of treating and charging such piezoelectric elements are also known and-have been described, for example, in Patent No. 2,507,253 and the-July 194-7- issue of The Physical Review. In fact, the art has come-to recognize these polycrystalline piezoelectric materials as a classdistinguished from Rochelle salt-andquartz crystals which occur in nature, and several-"patents have been issued in which'the term polycrystalline piezoelectric is used to con-no'te this class of piezoelectricmaterials. The Adler'Patent No. 2,540,412 and the Ellett Patent No. 2,540,194'use this term.

The invention, of course, also involves the novel manner of mounting the piezoelectridele ment and mechanically stressingthe same at the proper inst-antto assure correct timing of the spark plug firing.

With the above andother'objects in'view, which will appear as the description proceeds'jthis in'-' vention resides-in the novel construction, combi nation andarrang'ement of parts substantially as-hereinafter described andmore particularly defined by the appended claims, it being understood that such' changes in the precise embodiment of the hereindisclosed" invention may be made as come within the scope of "the claims.

The accompanying drawings illustrate two complete examples of the physical embodiments of the invention constructedaccording to the best modes so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a vertical sectional view through an internal combustion engine equipped wit'hthis invention;

Figure 2 is a detail sectional view essentially similar to Figure 1 but on an enlarged scaleoif a portion of the impact mechanism for stressing the element;

Figure 3 is a detail sectional view taken'thro'ugh Figure 1 onthe plane of the line 3- 5;

"Figure 4 is a perspective View of the voltage generating-unit per se'sh'own detached from the engine, and with portions broken away and in section; and

Figure 5 is a view similar to Figure 1 but illustrating a slightly modified embodiment of the invention.

Referring now particularly to the accompanying drawings in which like numerals indicate like parts, the numeral 5 designates generally an internal combustion engine of the portable single cylinder type having the usual crank shaft 6 and cam shaft I which, as is customary, is driven at one-half crank shaft speed. The cylinder head 8 of the engine mounts the customary spark plug 9 and in all respects other than the ignition system, the engine follows conventional design.

The ignition system of the engine comprises a voltage generator indicated generally by the numeral I0 mounted upon one wall I I of the engine crank case over a hole I2 therein which is directly adjacent to a portion of the cam shaft I.

The voltage generator consists essentially of a polycrystalline ceramic piezoelectric element I3 mounted in a yoke-like carrier I4. This element is preferably a cylindrical body and has one end thereof electrically grounded to the carrier yoke I4 and hence to the frame of the engine by a flexible conductor I5. Its other end is electrically connected through a flexible conductor I6,

terminal post I! and spark plug lead I8 with the center electrode of the spark plug. Hence, upon the application of a mechanical load of sufiicient magnitude upon the element I3 and the resulting increment in mechanical stress in the element, change in the electrical charges on its surfaces and the E. M. F. which results therefrom affords a source of voltage to fire the plug; and to assure proper timing for the firing of the plug the element is mechanically stressed by novel impact mechanism designated generally by the numeral I9, which is actuated by the cam shaft I of the engine.

The carrier yoke I4 has inner and outer end walls and 2|, respectively, the former being provided with an enlarged rectangular flange 22 which overlies the hole I2 in the wall II of the engine crank case and is fixed thereto by cap screws 23 or the like. This inner wall 20 has a bore 24 therethrough which is smaller than the diameter of the element I3, and a counterbore 25 larger in diameter than the element and opening toward the other wall 2|. A striker pin 26 is slidably received in the bore 24 with one end projecting into the engine crank case and its other end in a cap 21 loosely received in the counterbore and seated upon a cushioning pad 28 of stiff rubber or other suitable material covering the bottom of the counterbore.

The cap 21 is preferably made of a good quality hardened steel since its bottom wall serves as a pressure plate and must withstand severe impact without danger of taking a permanent set. The conductor I5 extends into the cap through a notch in the side wall thereof and has its end portion I5 which is circular and of the same diameter as the end of the element clamped between the element and a pressure equalizing pad 29 of any suitable material seated in the bottom of the cap 21.

The opposite end of the element I3 is supported by a pressure adjusting screw 30 threaded in the outer wall 2| of the yoke-like carrier, but is electrically insulated from the screw by a centering cap 3I of insulating material through which the screw 30 coacts with the cap 21 to hold the ele- 4 ment axially aligned with the striker pin 26. The end portion I6 of the flexible conductor I6, which is circular to match the end of the element, enters the cap and is clamped between it and the element in a manner similar to the way in which the conductor portion I5 is anchored.

It is important that the conductors I5 and I6 be very thin so as to conform easily and fully to the ends of the element which they overlie and thus preclude any possibility of localizing the pressure on a portion of the element. Intimate contact between the conductors and the ends of the element is also important for obvious electrical reasons.

As will be readily apparent the screw 30 affords means for applying a predetermined initial endwise compressive force upon the element I3, and to hold the screw in adjusted position a lock nut 32 is provided.

The striker pin 26 which projects through the inner wall 20 of the yoke-like carrier and into the engine crank case is in position to be struck by a hammer 33, and when so struck transmits the impact to the element I3. This hammer and a cam follower 34 are fixed on the medial portion of a tubular rocker shaft 35 which has its opposite ends journalled in bearings 36 and 31 on the inner face of the wall 20. The hammer and follower may be an integral part of the shaft, as shown, and are restrained by the bearings 36 and 31 against endwise displacement from a position at which the hammer 33 aligns with the pin 26.

The end of the pin struck by the hammer is preferably headed to provide increased area and has a flat impact surface to be engaged by the flat impact surface of the hammer; and to evenly distribute the force of the impact over the entire area of the ends of the element l3, the pad 29 and the centering cap 3I are formed of material capable of conforming to the irregularities of the end surfaces of the element as manifested through the thin conductors, and at the same time successfully resist deformation after full conformation to these surface irregularities.

A torsion spring 38 biases the cam follower and hammer in a counter-clockwise direction. This spring is an elongated rod having integral enlarged square heads 39 and 40. The head 39 is snugly received in a correspondingly shaped socket M in the end portion of the tubular rocker shaft which is journalled in the bearing 36 and the spring projects axially through and out of the other end of the rocker shaft to have its head 40 non-rotatably received in a socket 42 in a lug 43 on the back of the wall 20. This arrangement achieves compactness and at the same time enables the use of a relatively long torsion spring.

The cam follower 34 rides the periphery of a cam 44 mounted on the cam shaft 1, and which, for a purpose to be hereinafter described, has a unidirectional driving connection with the cam shaft. This unidirectional driving connection is supplied by the engagement of a spring pressed pawl 45 carried by the cam with an abrupt driving shoulder 46 on the cam shaft. As the cam rotates in a counter-clockwise direction it acts against the cam follower 34 to rock the shaft clockwise and thereby retract the hammer from the striker pin and load the torsion spring. The spring is loaded progressively during approximately three-fourths of one revolution of the cam shaft and is suddenly released as an abrupt step 41 on the cam is brought opposite .thepiezoelectric element. .ous change in mechanicalload. upon the element .the .end .of. .the cam follower. :With this. sudden .release of'thespringforce, the. hammeris driven .againstthe .striker pin 26 to effect a-sudden momentary. change inlthemechanicalrload .upon

It is .this instantaneand the resulting incrementv in mechanical stress therein .which produces .the r-desired. sparking voltage.

' The release of the stress and the,.consequent frecoil of the. element is cushioned by the. pad 28.

The manner in which the element. 13 is sup- Dor-ted against the endwise. compressive force applied thereto by the impactoflthe hammer onwthe striker. pinisimportant. The outer end wall]! of the yokeelike carrier, together with the adjusting .screw. 30, in efiect provides, an

anvil supporting then element and since this ".anvil. is rigidlytied to the supporting structure of thehammer, and thus is unyielding with respect to the hammer, substantially all of the force expended upon release of the spring is utilized to mechanically stress the element.

When the cam follower drops off the high part of thecam (asabout to take pIaceimFigure 2). and thev torsion spring has reacted, it is still .slightly.=tens ionedand holds the hammer against versible and. thus 'mustv bev protected. against reverse rotation of the. engine such as occasionally occurs just as theengine is being stopped. If

such protection were not afforded the abrupt step. on the cam would strike against the end of the cam follower with the possibility of breaking the follower, the cam shaft or .the timing gears. To protect against this. possibility the socket in which the spring pressed. pawl 45 is mounted is. designed to allow .the pawl to be cammed out of the notch which provides the driving shoulder 46 whenever there is sufficient reverse rotation of the engine to cause the step 4.1 of the cam to strike the end oithe cam follower. Obviously when the engine. is again rotated in the proper direction thespring pressed pawl assumes its driving position engaging the shoulder.

The operation. of the mechanism will be readily apparent from the foregoing description but to assure that those skilled in this art will be fully capable of practicing this invention, it should be pointed out that although the piezos electric effect or phenomena has been wellknown to the art for quite some time, monocrystalline piezoelectric materials, though they possess the piezoelectric quality, are not. .suitablefor the fulfillment of this invention, since. as noted hereinbefore, they are incapable of withstanding the mechanical stress needed to produce the voltages. required to. fire commercially available sparkplugs, and moreover theydo not possess a high enough specific energy output.

vPolycrystalline piezoelectric ceramic compositions, on the other hand, do possess the combination of mechanical and electrical characteristics necessary to enable a relatively small element to provide the voltage required tofire an ordinary spark plug and by actual test remain stable and fully operative for periods in excess of the "normal life of the engine.

suitable ceramic binder.

the cam rollowerand hammer.

; Thepolycrystalline. piezoelectric materials :which mayv be used for the .purposesof this invention are. generally classified as metallic titanates and in the form used .are .solid' polycrystalline ceramic bodies. In general such :titanateslare derived from metals of .grouplIA of the periodic system. Typical examples are .barium titanate, strontium titanate, calcium titanate, .magnesiun' titanate, aluminum titanate, manganesetitanate, the rare earth metal titanates, and mixtures of any two or more thereof.

. .In theaform in. which these metallic titanates are used inv this invention the structure ofthe titanates, and. hence the entire ceramic .body,

.ofany of the listed metallic titanates (or their functional equivalents) or of a mixture of'two or more thereof bondedlinto a solid body by a Those skilled in the art of compounding ceramic polycrystalline piezoelectric elements will have no difficulty producing an, element suitable for the purposes of this. invention.

With the element I3 inthe. form of a polycrystalline ceramic body. consisting essentially of barium titanate, which hasone of .thehighest specific energy outputs of the titanates listed in the foregoing group, and with the element having-adiameter of approximately .5. and a length of 7 approximately 1.3", and withthe torsion spring .143" in diamete1vand:2..0625 long (between its heads) peak voltages ofz'LOOO voltsare obtained with the structure illustrated and described hereinbefore. While this voltage is somewhat lower than the voltage generally used, it is entirelyv adequate, since the gap of the spark plug is far less subject. to being increased as a result of electrode erosion when compared to an ignition system of the conventional type involving the use of an. electroemagnetic circuit.

.In comparison with such conventional ignition systems-the. present invention has arelatively small electrical capacitance, stores less energy and, therefore, dissipates less energy across the gap of the spark plug. Hence, there is less spark plug electrode erosion per unit of time as com.- pared to the conventional ignition systems, with the result that less ignition voltage is required to accommodate any possible increase in spark pl g pthe invention. The mechanical energy is first stored in the torsion spring due to the action of the cam in twisting the spring. As the cam releases the cam follower the energy of the spring is converted into kinetic energy of rotation of The inertia of the cam follower and hammer is'very small and the inertia of the spring is made negligibly small in order to reduce the time required for the conversion of potential into kinetic energy. The reason for this is that there is a time delay approximately equal to. the conversion time, between the instant the cam releases the cam follower and the occurrence of the spark in thecombustion chamber of the engine. Since an internal combustion engine will not .operate properly with much variation-from the optimum time of ignition and as the aforementioned conversion time is a constant and does not change with speed, the conversion time must be kept as small as possible.

With the structural embodiment of the invention illustrated and described the inertia of the cam follower is on the order of 3 l0 pounds inches seconds squared per radian and with the relatively large torsional spring constant of the torsion spring, which is approximately 240 pound inches per radian, the time delay between release of the cam follower and the instant the hammer strikes the striker pin is quite short, being approximately only 550 microseconds.

The eifect of this 550 microsecond delay is negligible at cranking speed but at the higher operating speeds it becomes an extremely important factor since it amounts to, for example, degrees of crank shaft revolution at 3,000 R. P. M. Obviously this delay, therefore, reduces the spark advance angle as speed increases which is directly opposite to the engine requirements for optimum performance. Since this delay cannot be eliminated its reduction to as short a time as possible is of great importance and in any design of the mechanical impact mechanism these factors are controlling.

An important characteristic of the invention lies in the instantaneous change in the mechanical stress upon the element since by virtue of it the resulting sparking voltage is correspondingly instantaneous. This attribute of the invention thus adapts it especially well to use in electric ignition systems for internal combustion engines where a steep voltage wave front is one of the primar requisites;

In the embodiment of the invention thus far described, the conventional type of spark plug is employed and, accordingly, part of the circuit connecting the piezoelectric element across the spark gap of the plug is formed by the engine itself. Because of the large size of the conductor provided by the metal of the engine to which one electrode of both the piezoelectric element and the spark plug are grounded, there is considerable distributed external capacitance between the two terminals of the piezoelectric element and this external capacitance load presented to the piezoelectric element of necessity reduces the effective voltage across the spark gap. By having neither terminal of the spark plug grounded this external capacitance load is reduced to a minimum, and in Figure 5 one manner of obviating the grounding of either terminal of the spark plug is illustrated. As here shown the spark plug is of special construction with both its terminals and 5! insulated from ground and directly connected by conductors 52 and 53 to the opposite ends or electrodes of the piezoelectric element. Both ends of the element are, of course, electrically insulated from the carrier in which the element is mounted.

The manner in which the element is stressed in the construction shown in Figure 5 is also somewhat different from that described. Thus instead of the torsion spring a suitably strong coil spring 54 is employed. This spring is confined between the bottom of a well 55 in the carrier yoke l4 and a pin-like spring seat 56 received in a pocket 51 in part of the hammer 33'. The manner in which the spring is loaded and released is the same as described in connection with the previously described embodiment of the invention.

From the foregoing description taken in connection with the accompanying drawings it will be readily apparent to those skilled in this art that this invention provides an ignition system for internal combustion engines ossessing many advantages over those heretofore in common use and that while the invention is especially well adapted to this purpose the voltage generator which constitutes the heart of the invention no doubt has many other uses than that here described and would be useful wherever very high voltages at low amperage are to be produced solely by mechanical force.

What I claim as my invention is:

1. In an internal combustion engine of the reciprocating type wherein the reciprocation of a piston turns a crank shaft, said engine having a spark plug, means for firing the plug, comprising: a polycrystalline piezoelectric element; circuit means connecting the polycrystalline piezoelectric element and the spark gap of the spark plug in series circuit; and means driven from the crank shaft of the engine for momentarily mechanically stressing the polycrystalline piezoelectric element in timed relation with the reciprocation of the piston.

2. In an internal combustion engine of the reciprocating type wherein the reciprocation of a piston turns a crank shaft, said engine having a spark plug, means for firing the plug, comprising: a polycrystalline piezoelectric element having opposite electrodes; a conductor directly connecting each electrode of the polycrystalline piezo electric element with one of the two terminals of the spark plug; and means driven from the crank shaft of the engine for momentarily mechanically stressing the polycrystalline piezoelectric element in timed relation with the reciprocation of the piston.

3. In an internal combustion engine of the reciprocating type wherein the reciprocation of a piston turns a crank shaft, said engine having a spark plug one terminal of which is grounded to the engine, means for firing the plug, comprising: a polycrystalline piezoelectric element; means grounding one end of the element to the engine; a conductor directly connecting the other end of the polycrystalline piezoelectric element to the ungrounded terminal of the spark plug; and means driven from the crank shaft of the engine for momentarily mechanically stressing the polycrystalline piezoelectric element in timed relation with the reciprocation of the piston.

4. In an internal combustion engine of the reciprocating type having a crank shaft and a spark plug, means for utilizing a solid piezoelectric element as the sole source of voltage with which to fire the spark plug, comprising: a carrier for the element including means for holding the element under a predetermined degree of mechanical stress; and means for suddenly changing the mechanical stress in the piezoelectric element in timed relation with the rotation of the crank shaft, said means comprising a hammer movably mounted to have an impact stroke and a retraction stroke, means through which the impact stroke of the hammer acts to produce said change in mechanical stress, a spring acting on the hammer to produce its impact stroke, and means including a rotatable cam indirectly driven from the crank shaft of the engine for cyclically gradually retracting the hammer and thereby loading the spring and then abruptly releasing the hammer for production of its spring produced impact stroke.

5. The spark plug firing means of claim 4 wherein the driving connection between the crank shaft and the rotatable cam for cyclically retracting the hammer and abruptly releasing it is unidirectional and unipositional to accommodate possible retrograde rotation of the crank shaft.

6. In an internal combustion engine having a crank case with a cam shaft mounted therein and a spark plug, means for firing the spark plug, comprising: a polycrystalline piezoelectric element; a mounting bracket for the element having a wall secured to the crank case ,ove a hole therein adjacent to a portion of the cam shaft, said wall of the mounting bracket having a hole therethrough opening to the interior of the crank case; means mounting the polycrystalline piezoelectric element in line with the hole in said wall; a striker pin slidable in said hole with one end in position to apply end thrust onto the element; a hammer mounted on said wall of the bracket to swing about a fixed axis toward and from the other end of the striker pin; a spring biasing the hammer toward the striker pin; a cam follower rigidly connected with the hammer and projecting into the crank case toward the cam shaft; a cam on the cam shaft engaging said cam follower to periodically gradually retract the hammer and load the spring and then suddenly release the same so that the hammer strikes the pin to drive the same toward the polycrystalline piezoelectric element and thereby momentarily mechanically stress the same; means electrically grounding one end of the polycrystalline piezoelectric element to the engine; and a conductor directly connecting the other end of the polycrystalline piezoelectric element with the ungrounded terminal of the spark plug.

'7. In an internal combustion engine, the combination set forth in claim 6 further characterized by the provision of a unidirectional driving connection between the cam and the cam shaft to accommodate possible retrograde rotation of the cam shaft.

8. An ignition system for internal combustion engines of the reciprocatory type which operate over a wide speed range and have a spark plug, one terminal of which is grounded to the engine, comprising: a polycrystalline piezoelectric element; a conductor leading from one end of the polycrystalline piezoelectric element for directly electrically connecting the same with the ungrounded terminal of the spark plug; circuit means for electrically grounding the other end of the piezoelectric element to the engine; and means for periodically efiecting an instantaneous change in mechanical stress in the element in timed relation with the operation of the engine regardless of its speed, including a hammer positioned to apply an impact force upon the element as the hammer strikes, a spring biasing the hammer in the direction to effect its impact stroke, and means actuatable by a cyclically moving part of the engine for periodically gradually loading and abruptly releasing the spring.

9. An ignition system for a combustion engine having a spark plug, and comprising: a polycrystalline piezoelectric element; a rigid carrier for the element; impact mechanism mounted on the carrier and operable to eiTect a sudden increment in mechanical stress in the element, said mechanism including a cam timed with the engine cycle to release the impact upon the element atv a predetermined time in the engine cycle; means electrically grounding one end of the polycrystalline piezoelectric element to the engine; and a conductor leading from the other end of the element for directly electrically connecting theelement to the spark plug.

10. An ignition system for a combustion engine having a spark plug, comprising: a polycrystalline piezoelectric element; a rigid carrier for the element; a spring; a striker interposed between the element and the spring and through which the spring acts to apply an impact force upon the element; means electrically grounding one end of the polycrystalline piezoelectric element to to engine; a conductor leading from the other end of the element for directly electrically connecting the same to the ungrounded terminal of the spark plug; means operable by the engine to load the spring in timed relation with the engine cycle; and a spring trip released by the engine at a predetermined point in its cycle.

11. An ignition system for a variable speed combustion engine having a spark plug and comprising: a polycrystalline piezoelectric element; a rigid carrier for the element; potential mechanical energy storing means in which potential mechanical energy may be stored for any length of time; means actuated by the engine for stressing said energy storing means to store potential mechanical energy therein and for abruptly releasing said energy at a frequency determined by the speed of the engine; means for impressing the abruptly released mechanical energy upon the piezoelectric element; means electrically grounding one end of the polycrystalline piezoelectric element to the engine; and a conductor leading from the other end of the element for directly electrically connecting the same to the spark plug.

12. An ignition system for a combustion engine having a spark plug, and comprising: a polycrystalline piezoelectric element; a carrier for rigidly mounting the element in a position with one end thereof presented to the engine cam shaft; a contact part adapted to be pressed against said end of the element; a spring; a cam on the engine cam shaft; a cam follower riding the cam and operable to load the spring, the cam follower being snapped ofi the cam tip by the spring to strike the contact part; means electrically grounding one end of the polycrystalline piezoelectric element to the engine; and a conductor leading from the other end of the element for directly electrically connecting the same to the spark plug.

13. An ignition system for a combustion engine having a shaft rotatable cyclically with engine operation and a spark plug, and comprising: a polycrystalline piezoelectric element; means for mechanically stressing the element including a pressure exerting mechanism to accumulate energy under control of the engine; mechanical means under control of said cyclically rotatable shaft to discharge the accumulated energy at a predetermined time in the engine cycle; means electrically grounding one end of the element to the engine; and a conductor leading from the other end of the element for directly electrically connecting the same to the spark plug.

14. Means for producing high voltage electric impulses, comprising: an elongated solid polycrystalline piezoelectric element; a rigid carrier for the element; means engaging the polycrystalline piezoelectric element at its ends and mounting the same in the carrier under a predetermined degree of endwise compression; movable means to store potential energy; a releasing device con nected to the storing means to release the stored energy at a predetermined point in the motion of the storing means; and means connected between said energy storing means and the mounting means for the polycrystalline piezoelectric element and through which said energy when released acts to abruptly change the pressure on the element.

15. Means for producing electric impulses at a variable frequency, comprising: a solid ceramic polycrystalline piezoelectric element; a potential energy storing means in which potential mechanical energy may be stored for any length of time; a recurrently operating force exerting mechanism for stressing said energy storing means to store potential mechanical energy therein and for abruptly releasing said mechanical energy at whatever frequency said recurrently operating mechanism operates; and means for impressing the abruptly released mechanical energy upon the solid ceramic polycrystalline piezoelectric element.

16. Means for producing high voltage comprising: a solid ceramic polycrystalline piezoelectric element; a rigid carrier for the element; impact mechanism mounted on the carrier and operatively connected to the element to effect a sudden change in mechanical stress in the element; and an actuator for the impact mechanism including a spring acting on the impact mechanism and means through which an external force may act to alternately load the spring and abruptly release the same.

17. The structure set forth in claim 16 but wherein the impact mechanism comprises a hammer movably mounted upon the carrier to have an impact stroke and a retraction stroke; and wherein the spring acts on the hammer and biases it in the direction of its impact stroke.

18. The structure set forth in claim 17 but wherein the hammer is mounted on a tubular shaft journalled in bearings carried by said wall of the carrier; and wherein the spring is a torsion spring disposed within the hollow shaft with one end non-rotatably connected thereto and its other end protruding from the hollow shaft and anchored to a part of said wall of the carrier; and an arm projecting laterally from the hollow shaft and through which an external force may act to rock the shaft to retract the hammer against the force of the spring.

19. Means for producing high voltage, comprising: a solid ceramic polycrystalline piezoelectric element; a carrier for the element having rigidly connected spaced apart walls between which the element is mounted under a predetermined degree of pressure; terminal conductors clamped to the opposite ends of the element for connecting the same in an electric circuit; and impact mechanism mounted on one of said walls and operable to apply a sudden impact upon the adjacent end of the element to thereby effect an instantaneous change in mechanical stress in the element.

20. The structure set forth in claim 19 but wherein the impact mechanism comprises a hammer mounted upon said wall of the carrier for movement toward and from the adjacent end of the element; a spring having one end anchored to said wall of the carrier and its other end connected with the hammer to bias it toward the element; and means for retracting the hammer and loading the spring.

21. The structure set forth in claim 19 but wherein the impact mechanism comprises a hammer mounted upon said wall of the carrier for movement toward and from the adjacent end of the element; a torsion spring having one end anchored to a part of said wall of the carrier and its other end connected with the hammer to bias the hammer toward the element; and an actuator connected with the hammer through which an external force may act to gradually retract the hammer and load the spring and suddenly release the same.

22. Means for producing high voltage, comprising: a polycrystalline piezoelectric element; spaced apart rigidly connected walls between which the element is confined; a pressure screw for applying pressure on the element, said screw being threaded in one of said walls with its end facing the element; an electrically insulating cap between the end of the screw and the adjacent end of the element; a pressure plate supported on the other wall and bearing against the other end of the element; terminal conductors electrically connected to said opposite ends of the element for connecting the same in an electric circuit; said last named wall having a hole therethrough coaxial with the element; a striker pin slidable in said hole; and impact mechanism mounted on said wall and including a hammer positioned to strike the striker pin and drive it against the pressure plate to thereby subject the polycrystalline piezoelectric element to sudden mechanical impact forces.

23. The structure set forth in claim 22 but wherein said impact mechanism includes a spring having one end anchored to a portion of said wall and its other end connected to the hammer, said spring being biased to urge the hammer toward the striker pin; and an arm fixedly connected with the hammer and projecting therefrom to be engaged by an external actuator by which the hammer may be gradually retracted and the spring loaded and suddenly released.

24. The structure set forth in claim 22 but wherein said impact mechanism further comprises a shaft journalled in hearings on said wall and disposed crosswise to the axis of the striker pin, the hammer being fixed upon said shaft; 9. spring biasing the shaft in a direction to swing the hammer toward the element; and an arm extending from the shaft and through which an external force may act to rock the shaft to retract the hammer and load the spring.

25. In combination: a combustion engine having a cam shaft and a spark plug; a polycrystalline piezoelectric element; a rigid carrier for the element; means mounting the element in the carrier; a pressure exerting mechanism arranged to press upon the element; means to store potential mechanical energy derived from an explosion stroke of the engine; means for applying the stored mechanical energy when released to the pressure exerting mechanism; a timing and releasing device including a cam on the cam shaft of the engine to abruptly release the energy storing means and effect application of the stored energy upon the pressure exerting mechanism at the time of a succeeding explosion of the engine; and means directly connecting the polycrystalline piezoelectric element and the spark plug in series circuit so that the spark plug is fired directly by the electrical impulse produced by the polycrystalline piezoelectric element.

26. In an internal combustion engine of the reciprocating type wherein the reciprocation of a. piston turns a crank shaft, said engine having a spark plug neither terminal of which is grounded, means for firing the spark plug, comprising: a polycrystalline piezoelectric element; means mounting the polycrystalline piezoelectric element upon the engine but with both electrodes thereof electrically insulated from the engine; a conductor wire directly connecting each terminal of the spark plug with one of the two terminals of the polycrystalline piezoelectric element; and means driven by the crank shaft of the engine for momentarily mechanically stressing the polycrystalline piezoelectric element in timed relation with the reciprocation of the piston.

27. In an internal combustion engine of the reciprocating type having a crank shaft and a spark plug, means for utilizing a solid piezoelectric element as the sole source of voltage with which to fire the spark plug, comprising: a carrier for the element including means for holding the element under a predetermined degree of mechanical stress; and means for suddenly changing the mechanical stress in the piezoelectric element in timed relation with the rotation of the crank shaft, said means comprising a hammer pivoted upon part of the carrier for the element to have an impact stroke and a retraction stroke,

14 means through which the impact stroke acts to produce said change in mechanical stress, a coil spring confined between a part of the hammer remote from its pivot axis and a part of the carrier for the element to produce the impact stroke of the hammer, and means including a rotatable cam indirectly driven from the crank shaft of the engine for cyclically gradually retracting the hammer and thereby loading the spring and then abruptly releasing the hammer for production of its spring produced impact stroke.

JOSEPH R. HARKNESS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,919,480 Rieber July 25, 1933 2,248,574 Knight July 8, 1941 2,466,002 Bushcott et al Apr. 5, 1949 2,522,389 Mason Sept. 12, 1950

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