US3221213A

US3221213A - Position-indicating apparatus and ignition system employing same

Info

Publication number: US3221213A
Application number: US272343A
Authority: US
Inventors: John R Mckinney
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-04-11
Filing date: 1963-04-11
Publication date: 1965-11-30
Anticipated expiration: 1982-11-30

Description

Nov. 30, 1965 J, c m 3,221,213

POSITION-INDICATING APPARATUS AND IGNITION SYSTEM EMPLOYING SAME Filed April 11, 1963 I sPAhK PLUG-S L J J mm'oT-vmm? 5:535? D GENERATING CIRCUITRY ASSEMBLY PIC-3.2.

INVENTDR'. dOl/N R. M K/NNEV .er WA United States Patent 3,221,213 POSITION-INDICATENG APPARATUS AND HGNITION SYSTEM EMPLOYING SAME John R. McKinney, 111 Brittany Drive, Chalfont, Pa. Fiied Apr. 11, 1963, Ser. No. 272,343 Claims. (Cl. 315-209) This invention relates to apparatus for producing electrical indications of the position of an adjacent object, and particularly to apparatus suitable for use in an ignition system to produce electrical pulses synchronized with rotation of an object such as the cam shaft of an internal combustion engine. The invention also relates to apparatus for sensing the strength of a magnetic field.

Ignition systems for internal combustion engines are known in which pulses of high voltage are applied to ignition-producing spark plugs in timed relation to the occurrence of the combustion phase of the engine cycle in each cylinder. For this purpose there are commonly employed an electrical circuit for producing pulses of high voltage, a distributor with rotor for applying the high-voltage pulses in sequence to the various cylinders when the engine employs more than one cylinder, and breaker-switch apparatus opened and closed by a camming arrangement synchronized with rotation of the cam shaft, the breaker-switch apparatus being connected to the electrical circuit producing the high-voltage pulses so as to control the times at which such pulses are generated, in well known manner. Typically the breakerswitch apparatus is opened and closed by the pressure of camming surfaces located on a shaft driving the distributor rotor, to open and close directly a circuit through the primary of an ignition coil. More recently it has been proposed to use opening and closing of the breakerswitch apparatus to turn on and off a power transistor having its emitter-to-collector path in series with the ignition-coil primary, thereby reducing the current and voltage which the breaker points must withstand and generally obviating the necessity for use of a condenser across the breaker points.

While such ignition systems using breaker-switch apparatus have been used commercially for many years, they possess the inherent drawback that the timing, and in many cases the magnitude, of the high-voltage pulses is affected by unavoidable wear between the camming surfaces and the breaker-switch apparatus, as well as by wear and electrical deterioration and pitting of the breaker-switch points. In addition, because mechanical opening and closing of physical switch elements is employed, it is ditiicult to operate the breaker-switch apparatus with sufficiently accurate timing at the high rates associated with high engine speeds, and therefore the engine power potentially achievable at high engine speeds is not fully realized in most cases. For these and other reasons it has been recognized that it would be desirable to eliminate the breaker-switch apparatus entirely from such engines.

Proposals have been made to eliminate the breakerswitch apparatus by replacing it with a piezoelectric element having mechanical means associated therewith, cammed or geared to the engine cam shaft, for shocking or stressing the piezoelectric element to cause it to generate voltage pulses for controlling the times of occurrence of ignition pulses. However, moving physical contacts, productive of wear adversely affecting the timing and/ or magnitude of ignition pulses, are again employed.

Similar problems arise in other situations in which it is desired to produce electrical pulses synchronized with motion of a physical object, particularly where an accurately-timed electrical pulse is to be produced Whenever a rotating object attains a predetermined angular position.

Patented Nov. 30, 1965 Accordingly it is an object of my invention to provide new and improved apparatus for sensing and providing electrical indications of the position of a physical object, and particularly of its angular position.

Another object is to provide such apparatus which does not require physical contact between the object whose position is sensed and the apparatus for sensing it.

A further object is to provide new and improved apparatus for producing electrical pulses in timed synchronization with the attainment by a rotating member of predetermined angular positions.

Another object is to provide apparatus for producing an electrical pulse each time a piston or vane of an internal combustion engine reaches a position for which an ignition spark is desired, without requiring the use of breaker-switch apparatus.

It is a further object to provide apparatus of the lastmentioned type which is capable of accurate and reliable operation at high engine speeds, which exhibits a minimum of deterioration in performance upon longcontinued operation, and which is compatible with, and suitable for substitution in, existing types of ignition systems.

It is also an object to provide a new and improved device for sensing the strength of a magnetic field.

These and other objects of the invention are achieved by the provision of apparatus comprising a piezoelectric element, a body of magnetic material joined to said element, and means, at least a portion of which is of magnetic material and movable with respect to said element through positions adjacent but spaced from said body of magnetic material, for varying the magnetic field acting on said body to produce diiferent forces between said body and said element for predetermined dilferent positions of said means, thereby to change the stresses on said piezoelectric element and to cause said elementto generate electrical voltages of a magnitude dependent on the contemporaneous position of said means.

For example, in a preferred form of the invention as applied to internal combustion engines, a piezoelectric element having a magnetic material thereon is positioned so that, as the rotor of the distributor of an internal combustion engine turns through each of a plurality of predetermined, discrete, angular positions for which ignition of spark plugs is to be produced, a changing magnetic force acts on the magnetic material and changes markedly the pressure between the piezoelectric element and the magnetic body thereon, in turn causing the piezoelectric element to generate a marked voltage change, or pulse, each time one of said angular positions is reached. These voltage pulses may then be used to actuate a highvoltage generating ignition circuit, preferably a transistorized circuit, to cause the circuit to generate highvoltage ignition pulses for application to the spark plugs at the optimum times for ignition of the combustible gas in the engine cylinders.

In this system the use of contact-actuated devices such as breaker switches is eliminated, and accordingly this source of deterioration of performance due to wear is eliminated, and the accuracy and consistency of performance at high engine speeds greatly enhanced. Unlike various other piezoelectric ignition systems which have been proposed, there is no wear and no failure at high speeds due to mechanical coupling to the piezoelectric element, and the relatively gentle and reproducible forces exerted on the piezoelectric element in the system of my invention conduce to long and reliable life of the element and to the generation of a voltage pulse of reproducible waveform well suited for the purpose of ignition voltage control.

These and other objects and features of the invention will be more readily comprehended from a consideration of the following detailed description in connection with the accompanying drawings, in which:

FIGURE 1 is a representation, partly in perspective and partly schematic, showng one type of ignition system for an internal combustion engine to which the invention is applicable;

FIGURE 2 is an elevational view, partly in section and partly broken away, of a part of the system of FIGURE 1 showing in detail one form of angular-position indicating apparatus in accordance with the invention;

FIGURE 3 is a top view of a portion of the angularposition indicating apparatus of FIGURE 2; and

FIGURE 4 is an enlarged fragmentary view in perspective of a part of said angular-position indicating apparatus.

Referring now to the specific embodiment of the invention illustrated in the figures by way of example only, FIGURE 1 illustrates an ignition system for an internal combustion engine such as a four-cylinder automobile engine (not shown), comprising ignition-voltage genera ing circuitry for developing and for applying highvoltage pulses by way of cable 11 to a distributor and timing assembly 12, which contains the usual voltage-distributing arrangement for supplying the high-voltage pulses in sequence to four spark plugs 14, 16, 18 and 20 by way of

cables

22, 24, 26 and 28 respectively. The distributor and timing assembly 12 also includes means in accordance with the invention for producing relatively small-amplitude electrical control pulses and for supplying them by way of

cables

32 and 34 to the circuitry 10 to control the times at which high-voltage pulses are generated therein so that they will occur at phases of the cycle of the engine which are optimum for gas ignition in the engine cylinders. It is understood that a rotor shaft 35 is connected in conventional manner to rotate in synchronism with the engine cam shaft, and that high-voltage pulses are therefore to be generated at four predetermined, equi-spaced, angular positions of the rotor shaft 35.

The ignition-voltage generating circuitry 10 for responding to each relatively-small amplitude control pulse supplied thereto from

cables

32 and 34 to produce a corresponding high-voltage pulse at cable 11 may be of any of a large variety of forms which will readily occur to one skilled in the art. For the present purpose it is preferred and advantageous to employ a transistorized circuit, which may be of the type shown in which the secondary 36 of a voltage step-up transformer 38 has its primary 40 connected in series with a battery 42, an ignition switch 44, a current-limiting resistor and the emitter-to-collector current path of a power transistor 46. The polarity of the battery is such that when the transistor is turned on by an appropriate voltage between its base and emitter, an intense current flows through the transformer primary 40, and when the transistor is turned off the primary current ceases abruptly. In the example shown the transistor 46 is of the PNP type and its collector and the positive terminal of battery 42 are grounded, for example to the engine block, so that negative control voltages at the transistor base turn on the transistor and positive voltages turn it off. Ernitter-to-base bias is provided by the two resistors and 52 connected in series between collector and emitter, the base being connected to the interconnection of the resistors. By suitably proportioning the values of the

resistors

50 and 52 the transistor 46 may be biased normally on and turned off momentarily by a positive control pulse from cable 32, or may be biased normally off and turned on momentarily by a negative control pulse. For the present example it will be assumed that the former biasing arrangement is used. In this case, when ignition switch 44 is closed current flows through the primary 40 of ignition coil 38 until the engine turns rotor shaft 35 through a position for which a positive control pulse is applied to cable 32 at which time current through primary 4%] ceases suddenly and a high-voltage amplified many times with respect to the control pulse is produced across the secondary $6 for application to the spark plugs.

As mentioned earlier, the exact form of the ignitionvoltage generating circuitry 10 is not critical to the invention in its broader aspects, and the particular circuit shown has been chosen primarily for simplicity and clarity of exposition. It will be understood, for example, that ordinary diodes and/or zener diodes may be connected at the input to the transistor to limit the amplitude of applied control pulses or to eliminate control pulses of polarity opposite to the desired one, that a plurality of transistors or of other devices such as vacuum tubes may be used for increased gain and stability, and that any of a variety of types and connections of ignition coil may be used. In some cases it will be desirable to include a D.C.-'olocking capacitor between cable 32 and the interconnection of resistors 59 and 52. In addition it will be understood that other conventional elements, such as the generator and starter circuits (not shown) for the engine, may be appropriately connected into the circuit in known manner.

Considering now the arrangement for producing control pulses across

cables

32 and 34 in accordance with the invention, with particular reference to the view of distributor and timer assembly 12 shown in FIGURE 2, a conventional housing of insulating material having a lower portion 50 and a removable cap portion 52 is mounted with rotor shaft 35 extending concentrically therein, the arrangement being such that the rotor is free to rotate with respect to the housing. The upper end of the rotor shaft carries the usual insulating rotor arm 56 with its distributor contact 57, high-voltage pulses from cable 11 being distributed in sequence to the various spark plug cables by way of rotor contact pin 58 and distributor contact 57 as the rotor shaft turns in synchronism with the engine cam shaft.

The lower portion Stl of the housing supports a mounting plate 59 having a central aperture to clear the rotor shaft 35. A suporting block 69 of an electrically-conductive non-magnetic material such as aluminum is mounted in fixed position on plate 59, preferably electrically insulated therefrom by an insulating layer 61. Mounted rigidly to the top of block 69 in cantilever fashion, by any appropriate means such as an insulating clamp or soldering for example, is a wafer-shaped piezoelectric element 62 having the property of producing voltage differences between its top and bottom surfaces when mechanically stressed. Piezoelectric element 62 may be of conventional type, comprising for example a wafer of crystalline barium titanate 62A having separate, mutually insulated,

conductive contact layers

62B and 62C plated on its opposite major surfaces. The layer 62C is in electrical contact with block at. To the top surface of piezoelectric element 62 beyond the supporting surface of block 6% there is affixed a body 64 of magnetic material which is susceptible of attraction by a magnet, and is typically of iron. Fastening of body 64 may be accomplished by conventional means, such as cementing, soldering, or mechanical crimping. In the preferred embodiment shown, the magnetic body 64 is generally U-shaped so as to fit over the top of element 62 and down opposite sides thereof, element 62 being of a width such that the spacing between the downwardly-extending sides of body 64 is substantially the same as that between the poles of the fixed magnet presently to be described; it will be understood that short-circuiting of

electrodes

62B and 62C to each other is prevented, for example by coating of the latter elements with an insulating cement 65.

Mounted on plate 59 directly beneath magnetic body 64 is a permanent magnet of U-shaped cross section having its north and south poles spaced circumferentially around plate 59 and extending upward toward piezoelectric element 62. Preferably piezoelectric element 62 is centered above the space between the magnet poles. Since body 64 is of magnetic material it is attracted downwardly by the magnetic field from magnet 70, thus exerting a fiexure stress on piezoelectric element 62 tending to bend downwardly its free end and to produce a voltage between

conductive layers

62B and 62C. The magnitude of this force varies with the strength of the magnetic field reaching body 64, and in accordance with the invention this magnetic field is caused to vary as a function of angular position of rotor shaft 35, as follows.

Attached in a plane normal to rotor shaft 35 and so as to rotate therewith, is a generally circular field-modifying plate 80 of a magnetic material such as steel, vertically positioned on shaft 35 so as to move in rotation between magnet 70 and piezoelectric element 62 without contacting either. Plate 80 is provided with a number of peripheral apertures equal to the number of sparkplugs, in this case four, circumferentially spaced from each other at 90 angular intervals. In the form shown the apertures are similar to each other, each having a circular portion, such as 82, of FIGURES 3 and 4 which may easily be punched out from the plate 80, and a rectangular channel 84 extending from the circular portion to the periphery of plate 80. The sides of the channels are provided with downwardly-extending parallel flanges such as 86 and 88, preferably spaced from each other by the distance between the poles of magnet 70, and readily formed by cutting plate 80 adjacent each circular aperture and bending down the edges of each cut. The height of the flanges such as 86 and 88 is such as to clear the poles of magnet 70 by a small margin upon rotation of plate 80.

In operation, as rotor shaft 35 turns, the magnetic field reaching magnetic body 64 has a relatively small, reference value when the plane portion of plate 80 is interposed between it and magnet 70, due to the substantial spacing and the interposition of the continuous sheet of magnetic material of plate 80. However, when a rectangular aperture such as 84 reaches magnet 70, the magnetic field at magnetic body 64 increases, and reaches a maximum when a pair of flanges such as 86 and 88 are aligned with the magnet poles as shown in FIGURE 4. In the latter case the aligned flanges provide paths of low magnetic reluctance from magnet 70 to the edges of the rectangular aperture in plate 80, and the absence of magnetic material in the rectangular aperture and in the adjacent circular aperture permits strong fringing of magnetic field lines from magnet 70 upwards to magnetic body 64, increasing many-fold the downward force on piezoelectric element 62 and causing it to be flexurally stressed and to generate a voltage change of predetermined polarity between its opposite contact layers 62B and 62C. The operation is therefore that of a flux gate. Stresses adequate to provide several volts of voltage change are readily produced with very small angular deflections of piezoelectric element 62 of the order of a few microns so that small spacings between plate 80 and element 62 may be used without danger of physical contact between them. As plate 80 rotates farther, the magnetic field at body 64 decreases again to its small reference value, and the downward stress on piezoelectric element 62 is relieved so as to generate a voltage change of opposite polarity.

Accordingly, as each of the apertures in plate 80 passes in succession over magnet 79 a positive-going and a negative-going control voltage pulse are produced and delivered across

cables

32 and 34 to operate circuitry and produce a high-voltage pulse at cable 11. The times of occurrence of the control pulses are indicative of the attainment by rotor shaft 35 of specific predetermined angular positions. By locating the apertures in plate 80 angularly so that either the negative or positive pulse occurs at a time such as to produce a high-voltage pulse at cable 11 when ignition of a spark plug is desired, the

necessary synchronization of ignition pulses with engine operation is obtained. For the present purposes I prefer to use a positive pulse generated when piezoelectric element 62 is downwardly flexed to cut off a normally-on transistor 46. Such operation is readily provided by one skilled in the art by using well-known materials cut in known ways for the piezoelectric element.

It is noted that there is no physical contact between the control-voltagegenerating piezoelectric element 62 and the moving angular-position-indicating plate and no moving switch parts or high-current switch contacts are employed. Accordingly the system is long-lived, simple in construction, accurate even at very high engine speeds, and compatible with the usual type of ignition-system equipment commonly employed.

From the foregoing it will be apparent that the invention is in no way limited to the particular type of apparatus illustrated. Basically the invention involves modifying the magnetic force acting on a magnetic body joined to a piezoelectric element, in accordance with the relative positions of the body and an object whose position is to be indicated. For example, the magnetic material on the piezoelectric element may be magnetized, permanent-magnet material, in which case the magnet of FIGURE 2 may be, but is not necessarily, replaced by loW-retentivity magnetic material. Alternatively the plate 81) may be replaced with an element having discrete regions of strong permanent magnetization, as by locating separate magnets in the positions occupied by the apertures in plate 80, in which case magnet 70 and plate 80 are unnecessary. In other embodiments the relative motion may be provided by mounting one or more piezoelectric elements for rotation past a fixed permanent magnet. Magnetic repulsion, rather than attraction, can be used in some instances. Various geometric arrangements and types of relative motion may also be employed to produce other types of stress of the piezoelectric material, such as compressional or shear stress. Many other diverse embodiments of my invention will occur to one skilled in the art in view of the foregoing disclosure, and accordingly the scope and spirit of the invention is to be limited only by the appended claims.

I claim:

1. Apparatus for producing position-indicating electrical variations, comprising:

a piezoelectric element; a body of magnetic material on said element; magnetic means, at least a part of which is of magnetic material and movable relative tosaid body through positions adjacent but spaced from said body, for producing different magnetic forces on said body for different ones of said positions, thereby to produce stresses on said element and voltages therefrom indicative of the position of said part of said means with respect to said body; and motive means for moving said part relative to said body through said positions adjacent said body;

said magnetic means comprising an element for producing a magnetic field at said body and a member rotatable adjacent said body in response to said motive means for varying the strength of said magnetic field as a function of the angular position of said member with respect to said body.

2. Apparatus in accordance with claim 1 in which said piezoelectric element is mounted to flex in response to changes in said magnetic field.

3. Apparatus in accordance with claim 1, in which said element for producing a magnetic field comprises a permanent magnet spaced from said body and in which said rotatable member has portions of differing magnetic effect on said body, said portions being rotatable between said body and said permanent magnet.

4. Apparatus in accordance with claim 3, in which said rotatable member comprises magnetic material defining at least one aperture therein and is disposed for rotation of said aperture through the region between said body and said permanent magnet.

5. Apparatus in accordance with claim 4, in which said rotatable member is of flux-gate form to increase the magnetic field at said body when said aperture is disposed between said body and said permanent magnet.

6. In an ignition system for a combustion engine of the class employing a shaft rotating in timed angular phase relation to the phase of the engine cycle, apparatus comprising:

a piezoelectric element responsive to changes in pressure thereon to produce voltage pulses;

a magneic body connected to said piezoelectric element to exert on said element a pressure dependent upon the magnetic field strength at said body;

rotatable magnetic means having different portions of different magnetic characteristics disposed circumferentially thereof, and angularly movable relative to said magnetic body in timed relation to rotation of said shaft to produce at said body a magnetic field varying in accordance with angular position of said shaft, thereby to produce from said piezoelectric element voltage pulses in predetermined timephase relation to attainment by said shaft of predetermined angular positions; and

means for rotating said rotatable magnetic means in response to rotation of said shaft.

7. Apparatus in accordance with claim 6, comprising a permanent magnet spaced from said body and fixed with respect thereto, and in which said magnetic means comprises a magnetic member rotatable between said permanent magnet and said body.

8. In an ignition system for internal combustion engines comprising at least one spark-ignition element for producing combustion in an engine cylinder, means responsive to electrical signals for developing high-voltage pulses for application to said spark-ignition element, and a shaft rotating in fixed time-phase relation to the operat ing phase of said engine, the combination therewith of:

a piezoelectric element;

a magnetic body on said element;

a magnetic member connected to rotate adjacent said magnetic body in synchronism with said shaft to vary the magnetic force on said body and the mechanical stresses on said piezoelectric element, thereby to produce voltage pulses across said piezoelectric element in synchronism with said shaft rotation, means for rotating said magnetic member in esponse to rotation of said shaft; and

means for supplying said voltage pulws to said means for developing high-voltage pulses, to control the time of generation of said high-voltage pulses.

9. Apparatus in accordance with claim 8, comprising a high-voltage distributor supplied with said high-voltage pulses and having a rotor connector and a plurality of distributor contacts disposed to be contacted in sequence by said rotor connector upon rotation thereof, and in which said shaft is connected to rotate said rotor connector.

10. Apparatus for producing position-indicating electrical variations, comprising an elongated piezoelectric element mounted in a fixed position at one end and having a first magnetic means attached thereon at the other end, second magnetic means including means movable relative to said first magnetic means and through a series of discrete positions adjacent to but spaced from the first magnetic means, said first and second magnetic means including means for imposing a mechanical stressing force on said piezoelectric element at each of said positions for generating a voltage variation indicative of the position of said movable means, and motive means mechanically connected to said movable means for moving the same in sequence through said positions.

References Cited by the Examiner UNITED STATES PATENTS 2,683,856 7/1954 Kornei 3222 2,827,531 3/1958 OBrien 20()87.3 2,875,353 2/1959 Cavalieri et al. 3108.5 2,954,506 9/1960 Harkness 315-209 JOHN W. HUCKERT, Primary Examiner.

JAMES D. KALLAIH, DAVID J. GALVIN, Examiners.

Claims

1. APPARATUS FOR PRODUCING POSITION-INDICATING ELECTRICAL VARIATIONS, COMPRISING: A PIEZOELECTRIC ELEMENT; A BODY OF MAGNETIC MATERIAL ON SAID ELEMENT; MAGNETIC MEANS, AT LEAST A PART OF WHICH IS OF MAGNETIC MATERIAL AND MOVABLE RELATIVE TO SAID BODY THROUGH POSITIONS ADJACENT BUT SPACED FROM SAID BODY, FOR PRODUCING DIFFERENT MAGNETIC FORCES ON SAID BODY FOR DIFFERENT ONES OF SAID POSITIONS, THEREBY TO PRODUCE STRESSES ON SAID ELEMENT AND VOLTAGES THEREFROM INDICATIVE OF THE POSITION OF SAID PART OF SAID MEANS WITH RESPECT TO SAID BODY; AND MOTIVE MEANS FOR MOVING SAID PART RELATIVE TO SAID BODY THROUGH SAID POSITIONS ADJACENT SAID BODY; SAID MAGNETIC MEANS COMPRISING AN ELEMENT FOR PRODUCING A MAGNETIC FIELD AT SAID BODY AND A MEMBER ROTATABLE ADJACENT SAID BODY IN RESPONSE TO SAID MOTIVE MEANS FOR VARYING THE STRENGTH OF SAID MAGNETIC FIELD AS A FUNCTION OF THE ANGULAR POSITION OF SAID MEMBER WITH RESPECT TO SAID BODY.