US3737691A

US3737691A - Piezoelectric distributor

Info

Publication number: US3737691A
Application number: US00194590A
Authority: US
Inventors: L Hoover
Original assignee: Individual
Current assignee: PAPAS C
Priority date: 1969-07-07
Filing date: 1971-11-01
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05

Abstract

A piezoelectric generator and distributor unit for a spark ignition internal combustion engine in which a piezoelectric element is mounted in a body carried by a rotor shaft for rotation therewith. Two lever arms are pivoted on the body and engage opposed ends of the element. A plate with a cam track is fixed with respect to the rotor and engages the lower ends of the levers so that rotation of the rotor and body causes the levers alternately to compress and release the element which develops a charge at a high potential in response to being stressed by the levers. A central rotor terminal and terminals in a distributor cap provide a conductive path for transmitting charges from the unit. These terminals are surrounded by heat and electrically insulating tubes which extend beyond the ends of the terminals to provide a shield which eliminates the corona and premature arcing problems of high voltage switching in this type of distributor.

Description

United States Patent [1'91 Hoover [4 1 June 5, 1973 [54] PIEZOELECTRIC DISTRIBUTOR [75] Inventor: Lawrence E. Hoover, Detroit, Mich. Pmfmry 'f M'ner Assistant Exammer-Mark O. Budd Asslgneesr Anthony Tramlstozzl, Detnot; Attorney-Barnes, Kisselle, Raisch & Choate stantine Papas, Southfield, Mich. part interest to each [57] ABSTRACT [22] Filed: 1971 A piezoelectric generator and distributor unit for a 1 App] 19 590 spark ignition internal combustion engine in which a piezoelectric element is mounted in a body carried by Rellted use Application Data p a rotor shaft for rotation therewith. Two lever arms [62] Division of Ser. No. 839,445, July 7, 1969, Pat. No. are Pi"oted the and gage ends 3,622,717. the element. A plate with a cam track is fixed with respect to the rotor and engages the lower ends of the 52 [1,5, (3 310 33, 317 1 1 23 143 BA levers so that rotation of the rotor and body causes the [51] Int. Cl. ..-H04r 17/00 levers at y t c p ss and rel ase the element [58] lfieldoi Search ..3l0/8.3, 8.7, 9.1, hi d ve ps a charg at a high potential in 3l0/8.l; 3l7/DlG. 11,79, 81; 123/148 BA response to being stressed by the levers. A central rotor terminal and terminals in a distributor cap pro- [56] References Cited vide a conductive path for transmitting charges from the unit. These terminals are surrounded by heat and UNITED STATES PATENTS electrically insulating tubes which extend beyond the 2,856,564 10/1958 Derwin ..3l0/8.7. ux ends of the terminals 10 Provide a Shield which 3,082,333 3/1963 Hufferd et a]. ..3l0/8.7 X eliminates, the corona and premature arcing problems 3,101,420 8/1963 Hufferd et al. ..3l0/8.7 of high voltage switching in this type of distributor. 3,208,443 9/1965 Hurwitz ..3l0/8.7 X 3,397,683 8/1968 Phillips ..3l0/8.7 X 10 Claims, 8 Drawing Figures L 1 L L.-. 2 2 $6 PIEZOELECTRIC DISTRIBUTOR This is a division of application Ser. No. 839,445, filed July 7, 1969, now U.S. Pat. No. 3,622,717.

This invention relates to ignition systems and more particularly to a piezoelectric generator and distributor unit.

In a piezoelectric ignition system the high potential required for firing the spark plugs of an internal combustion engine is derived from a piezoelectric crystal or element which is stressed in timed relation with the rotationlof the engine crankshaft to provide a pulsed electrical output with sufficient electromotive force to fire the spark plugs.

An object of this invention is to provide a means of readily converting a conventional automotive ignition distributor into a piezoelectric generator and distributor unit.

Another object of this invention is to reduce the transverse loading of the driving shaft of a piezoelectric generator and distributor unit, thereby reducing the wear on the driving shaft and its journal.

Another object of this invention is to provide a means of preventing corona discharge and premature arcing between the rotor and terminal electrodes of the piezoelectric ignition distributor unit.

These and other objects, features and advantages of the invention are described in this specification and i1- lustrated in the drawings in which the manner and process of making the invention in the best mode contemplated by the inventor is disclosed by way of example only, for, since the underlying principles may be incorporated in other constructions, it is not intended to be limited to those shown, except as such limitations are clearly imposed by the appended claims.

In the drawings:

FIG. 1 is a vertical sectional view of a piezoelectric generator and distributor unit of this invention.

FIG. 2 is a sectional view on line 2-2 of FIG. 1 illustrating the high tension spark plug and ground terminals.

FIG. 3 is a plan view of the cam plate only of FIG. 1.

FIG. 4 is a sectional view on line 4-4 of FIG. 1 illustrating a pivot screw-mounting of one of the lever arms.

FIG. 5 is an end view of the left hand end (as viewed in FIG. 1) of the carrier body for the piezoelectric elements illustrating the adjustment screws for varying the pressure applied to the piezoelectric element.

FIG. 6 is a view of an alternate construction of a lever arm cam track follower.

FIG. 7 is an elevational view in section of a second embodiment of the cam plate of FIG. 1.

Referring to the drawings:

The present invention is an improvement upon the piezoelectric generator and distributor unit disclosed and claimed in my U. S. Pat. No. 3,332,409 issued on July 25, 1967, to which reference may be had for a detailed description of some of the structure and general mode of operation of my improved unit disclosed herein.

FIG. 1 illustrates a piezoelectric ignition distributor unit 20 constructed in accordance with the improved features of my present invention. Unit 20 comprises an annular housing 22, driving shaft 24, a support plate 26 connected to housing 22, a rotor shaft 27, a piezoelectric element 28, a center electrode 30, and a distributor cap 32 removably mounted on housing 22. Cap 32 has a plurality of high tension leads 33 each terminating at rotor shaft 27 may be and preferably are existing standard components already available as part of the usual distributor of an automobile engine normally adapted for use with a conventional ignition system with a battery, breaker, condenser, and coil. A suitable piezoelectric element 28 for this generator and distributor unit may be a piezoelectric ceramic tube or solid cylinder obtainable from the Clevite Electronic Components Division of Clevite Corporation of Cleveland, Ohio, as set forth in their Bulletin No. 9244-1 dated March, 1961 and other publications.

Generator-distributor unit 20 develops a current with a high electrical potential difference for firing a spark plug by applying a mechanical compressive force to piezoelectric element 28. This compressive force is developed by mounting piezoelectric ceramic element 28 in a carrier body 42 between two second-

class levers

43 and 44.

Levers

43 and 44 bear on piezoelectric element 28 and engage a die cast cam plate 46 so that rotary movement of carrier body 42 caused by rotation of shaft 27 with respect to cam plate 46 causes the levers to pivot in unison and apply a compressive force of varying magnitude along the longitudinal center line of piezoelectric element 28. The magnitude of the compressive force is varied or adjusted by moving the pivot point of lever arm 43. Lever arm 44 is pivotally mounted on a pin 48 extending through body 42, and body 42 is connected to rotor shaft 27 for rotation therewith by a pin 50. As shown in FIG. 4, lever arm 43 is pivotally mounted between a pair of

blocks

52 and 53 by pivot screws 54 and 54' respectively mounted in

blocks

52 and 53 and which engage in two opposed recesses 55 in lever arm43. As shown in FIG. 5, a pair of screws 56 with locknuts 58 threadingly engage with and protrude through the end of body 42 to bear on

blocks

52 and 53 respectively.

Blocks

52 and 53 are slidably captured within body 42 so that they can be moved longitudinally to urge pivot arm 43 into engagement with piezoelectric element 28. Since the pivot point of arm 44 is fixed in body 42,-adjustment of screws 56 varies the total force developed by

lever arms

43 and 44 when they are urged toward each other by cam plate 46.

Cam plate 46 which controls the movement of

levers

43 and 44 is connected by screws 60 and 60 (FIG. 1) to a conventional breaker and condenser mounting plate 26. As shown in FIG. 3, cam plate 46 is a flat annular plate with a central aperture 61, an annular radially sinuous cam track 62 coaxial with aperture 60, and two diametrically opposed arcuate slots 64 and 64' extending through the plate coaxial with aperture 60. Slots 64 and 64' allow cam plate 46 to be rotated with respect to fixed support plate 26 and terminals 34 to adjust the point with respect to terminals 34 at which cam plate 46 causes

lever arms

43 and 44 to exert the maximum compressive force on element 28. Cam track 62 is formed with four pairs of diametrically opposed circularly spaced cam lobes 63 so that piezoelectric element 28 will be squeezed and released eight times in 360 of rotation of body 42 with respect to cam plate 46. This provides the correct number of pulses or changes in the electrical potential or output of piezoelectric element 28 for the firing of an eight-cylinder engine, as will be explained in detail hereafter.

A second embodiment of a cam plate similar to plate 46 is shown in FIG. 7 in which the modified cam plate 66 is a sheet metal stamping with a cam track 68 in the form of a generally U-shaped channel, a pierced central aperture 70 and circumferential slots 72.

As shown in FIGS. 1 and 4, a semi-spherical tip 74 of a wear resistant material with a low coefficient of friction, such as the fluorocarbon plastic material sold under the trademark Teflon, is mounted on the lower extremity of each

lever arm

43 and 44 to provide a low friction cam follower for each lever arm. Alternatively, as shown in FIG. 6, a roller 76 can be journalled on a cylindrical end tip of each lever arm and secured by staking or peening the tip to provide a suitable cam follower.

The

lever arms

43 and 44 and the

cam plate

46 or 66 provide a structure for applying a compressive force to piezoelectric element 28 in which the reaction to the compressive force is balanced in the cam plate and carrier body 42 so that an unbalanced force or side thrust is not transmitted to rotor shaft 27 and its journal. Hence, this structure reduces the transverse loading and resultant wear on the rotor and drive shaft of the unit 20. The shape of the cam track is such that it captures or positively limits the travel in both directions of the lever arms so that they will not bounce or be subjected to extraneous movements due to their inertia when the generator and distributor unit is operating at relatively high speeds. By slidably mounting piezoelectric element 28 in body 42 so that it is restrained from shifting slightly longitudinally only by engagement with

arms

43 and 44, it will compensate for manufacturing tolerances, wear and errors in producing and assembling the components of the unit so that the reaction forces due to the compression of piezoelectric element 28 will always have substantially the same magnitude on each side of shaft 27 and hence will be properly balanced.

When center electrode 30 is aligned with a terminal electrode 34, it provides a conductive path for the high potential developed by piezoelectric element 28 when it is compressed. Center electrode 30 is made of an electrically conductive metal, such as copper, formed in the shape of an L with its short leg 31 mounted centrally on element 28 and electrically connected to one of its output terminals at 78. The long leg 31 of electrode 30 extends radially above carrier 42 and is sheathed in a tube 80 of electrical and heat insulating material, such as the heat and electrically insulating glass sold under the trademark Pyrex. The radially outer end portion of tube 80 extends or projects axially of electrode 30 slightly beyond the free end thereof. Terminal electrodes 34 are each formed from an electrically conductive metal, such as copper, and are mounted in a circumferentially spaced radially extending array in the outer wall of cap 32. A glass insulating tube 82, made of the same material as tube 80, sheaths the radially inner end of each electrode 34 and projects inwardly slightly beyond the inner end of the electrode. Preferably, there is a space of approximately 0.0l50.020 inches between adjacent faces of central electrode 30 and a terminal electrode 34 when they are axially aligned with each other, and tubes 80 and 82 each preferably extend approximately 0.005 inches beyond the outer edge of their associated terminal. The

recessing of the end faces of electrodes 30 and 34, provided by the extension of tubes and 82 beyond their respective terminals provides a refractory quality heat and electrical insulating shield which reduces or eliminates corona discharge and premature arcing problems encountered with the use of this type of distributor when it is used in high rpm. applications and to supply ignition currents of high potential. An electrically conductive pad 84 of a metal such as copper is positioned coaxially of the rotational axis of carrier 42 so as to underlie grounding electrode 38 and is electrically and mechanically connected to electrode 30 so that it can be physically contacted by electrode 38 when solenoid 40 is de-energized.

In operation, when a set of diametrically opposed lobes 63 of

cam plate

46 or 66 urge levers 43 and 44 toward each other due to the rotation of carrier 42 by shaft 27, an axial compressive force is applied to piezoelectric element 28 which causes it to develop a charge at a high potential which is then conducted through central electrode 30 to a terminal electrode 34 via the air gap therebetween when they become axially aligned. Preferably, lobes 63 are oriented relative to electrodes 30 and 34 so that peak voltage is developed when such alignment occurs. Thereafter as shaft 27 and carrier body 42 continue to rotate, lever

arms

43 and 44 are urged away from each other by the diametrically opposed inner lobes 63' of track 62, which releases or decreases the compressive force acting on piezoelectric element 28. This decrease in the compressive force acting on element 28 after it has been discharged causes it to become charged again at a high potential with a polarity opposite to the polarity of the charge caused by compression of element 28. This charge of opposite polarity can be conducted through another terminal and either used to tire a spark plug or may be bled to a common ground, thereby again discharging element 28.

If it is desired to use only charges having the same polarity to fire the spark plugs, a plurality of ground electrodes 36, and associated ground connector strips 36 leading to housing 22, (as shown in FIG. 2) are provided one between each adjacent pair of electrodes 34 -in circumferentially alternating relationship therewith through the ground circuit, and in alternating sequence therewith the charges of the opposite polarity are transmitted from the distributor through the ignition circuit distribution electrodes 34. This arrangement allows all of the spark plugs connected to terminals 34 to be fired by a sparking potential of like polarity, which may be that selected to best match the characteristics of the type of spark plugs being fired. However, it should be noted that use of a current having only one polarity merely represents an optimum condition for certain applications, and in other applications that highly satisfactory results can be obtained if both the positive and negative current pulses produced by element 28 are utilized. In the latter situation, it is only necessary to provide a cam plate with four squeezing lobes and four release lobes, and grounding terminals 36 may be eliminated from cap 32 if it is desired to use both the positive and negative current pulses of element 28 for an eight pulse output.

As set forth in my aforementioned U.S. Pat. No. 3,332,409, to provide a convenient means of deenergizing a piezoelectric ignition system so that a spark ignition engine on which the system is used can be shut down, the yieldably biased shorting terminal 38 is connected to the ground sideof element 28 so that when solenoid 40 is de-energized terminal 38 contacts disc 84 whereby the ignition leads 33 are shunted and both the positive and negative current pulses of element 28 are dissipated in the ground circuit. When solenoid 40 is energized, as by turning the ignition switch to on position, terminal 38 is disengaged from disc 84; thereby removing the shunt path and causing current flow via central terminal 30 and ignition circuit terminals 34.

From the foregoing description, it will now be apparent that piezoelectric generator and distributor unit is adapted to utilize many of the components of ordinary distributors found on most automotive and commercial spark ignition engines. The dual lever arm and cam plate structure provides a means of equalizing or balancing the opposed reactionary forces created by compressing the piezoelectric element so that a transverse load is not transmitted to the rotor and driving shafts, thereby reducing the wear and stress on these shafts and their associated journals. The stamped sheet metal cam plate 66 provides a unit which can be economically manufactured. The channel-shaped track 68 of the cam plate entraps the lower end of each lever arm so that the inertia of their pivoting mass does not cause them to bounce and thereby impede the efficiency of the piezoelectric unit when it is operated at relatively high speeds. The glass shields extending beyond the ends of the rotating center and stationary exit terminals provide an inexpensive heat resistant electrical insulator which eliminates the corona discharge and premature arcing which otherwise would adversely effect performance and efficiency. This is particularly advantageous when this type of distributor unit is used on an internal combustion engine operated at relatively high speeds because even a slightly premature ignition of the fuel in an internal combustion engine can have a substantial adverse effect on its high speed performance.

I claim:

1. In a piezoelectric generator and distributor unit having a stationary housing including a cup-like base with an end wall, a removable cap closing the mouth of the base, a distributor shaft extending through said end wall of said base, a rotor support structure in said housing connected to said distributor shaft to be rotated thereby, a plurality of circumferentially spaced terminals leading through said cap and having an end portion therein, and a rotor terminal carried by the rotor support structure having a portion sequentially juxtaposed in arc gap relation with said cap terminals in response to rotation of said rotor support structure, the improvement which comprises:

a. a body connected to the rotor support structure for rotation therewith,

b. a piezoelectric element carried by said body and having two axially opposite ends disposed on opposite sides of said shaft,

c. two lever arms pivotally carried on said body, said arms being pivotally engageable one with each of the opposite ends of said element and extending generally axially of the rotor support structure,

d. cam means having at least two diametrically opposed cam lobes lying in a plane generally transverse to the axis of rotation of the rotor support structure, said cam means being carried in said base in fixed relationship thereto and being engageable with said levers to urge said levers into engagement with said ends of said element in response to rotary movement of the rotor support structure, and

. means electrically connecting an output terminal of said element to said rotor terminal to thereby connect said element sequentially in circuit with said cap terminals.

2. The unit as defined in-claim 1 in which said cam means is a plate having a cam track therein defining said two lobes with said levers each having a follower end engaging said track.

3. The unit as defined in claim 2 in which said track comprises a groove in said plate having opposite side walls engaging each of said follower ends of said levers.

4. The unit as defined in claim 2 in which said plate is a sheet metal stamping having a channel with a generally U-shaped cross section forming said cam track.

5. The unit as defined in claim 1 in which said body slidably carries a block on which one of said lever arms is pivoted, and adjustable means for moving said block and its associated lever arm toward the associated end of said element.

6. The unit as defined in claim 1 in which each of said levers has a follower at one end thereof engageable by said lobes, each said lever being pivotally carried by said body adjacent an end thereof opposite said one end thereof, each said lever engaging the associated end of said element between said ends of said lever whereby each of said levers operates as a second-class lever.

7. The unit as defined in claim 1 in which said element is movable along its longitudinal axis between said levers whereby said element is self-centering relative to said levers in response to said levers bearing on said element.

8. The unit as defined in claim 1 wherein said means of subparagraph (e) comprises:

a. a central terminal of an electrically conductive material electrically connected to an output terminal of said piezoelectric element and carried by said body for rotation therewith, an end of said central terminal being positioned to pass sequentially in proximity to said ends of said plurality of cap terminals when said body is rotated,

b. a shield of an electrically insulative material circumscribing at least a portion of said central terminal and extending beyond said end of said central terminal, and

c. shields of an electrically insulative material, one circumscribing at least a portion of each of said cap terminals and extending beyond the end portion thereof.

9. The unit as defined in claim 8 in which each of said shields projects at least about 0.005 inches beyond the end of its associated terminal.

10. The unit as defined in claim 8 in which said insulative material is made of heat resistant and electrically insulating glass.

Claims

1. In a piezoelectric generator and distributor unit having a stationary housing including a cup-like base with an end wall, a removable cap closing the mouth of the base, a distributor shaft extending through said end wall of said base, a rotor support structure in said housing connected to said distributor shaft to be rotated thereby, a plurality of circumferentially spaced terminals leading through said cap and having an end portion therein, and a rotor terminal carried by the rotor support structure having a portion sequentially juxtaposed in arc gap relation with said cap terminals in response to rotation of said rotor support structure, the improvement which comprises: a. a body connected to the rotor support structure for rotation therewith, b. a piezoelectric element carried by said body and having two axially opposite ends disposed on opposite sides of said shaft, c. two lever arms pivotally carried on said body, said arms being pivotally engageable one with each of the opposite ends of said element and extending generally axially of the rotor support structure, d. cam means having at least two diametrically opposed cam lobes lying in a plane generally transverse to the axis of rotation of the rotor support structure, said cam means being carried in said base in fixed relationship thereto and being engageable with said levers to urge said levers into engagement with said ends of said element in response to rotary movement of the rotor support structure, and e. means electrically connecting an output terminal of said element to said rotor terminal to thereby connect said element sequentially in circuit with said cap terminals.

2. The unit as defined in claim 1 in which said cam means is a plate having a cam track therein defining said two lobes with said levers each having a follower end engaging said track.

8. The unit as defined in claim 1 wherein said means of subparagraph (e) comprises: a. a central terminal of an electrically conductive material electrically connected to an output terminal of said piezoelectric element and carried by said body for rotation therewith, an end of said central terminal being positioned to pass sequentially in proximity to said ends of said plurality of cap terminals when said body is rotated, b. a shield of an electrically insulative material circumscribing at least a portion of said central terminal and extending beyond said end of said central terminal, and c. shields of an electrically insulative material, one circumscribing at least a portion of each of said cap terminals and extending beyond the end portion thereof.