US 3218506 A
Description (OCR text may contain errors)
United States Patent PIEZOELECTRIC IGNITION SYSTEM HAVING A MAGNETICALLY ACTUATED VACUUM SWITCH Alfred L. W. Williams and Frank A. Novak, Cleveland, and Fred C. Kelly, Chesterland, Ohio, assignors to Clevite Corporation, a corporation of Ohio Filed July 19, 1962, Ser. No. 210,934 8 Claims. (Cl. 315-55) This invention relates to an improved piezoelectric ignition system employing a magnetically responsive switching arrangement. This invention is shown and described as applied to an internal combustion engine ignition system although its use is not necessarily limited thereto.
In the prior art it has been the practice to place a switching device electrically in series with and between a piezoelectric voltage generator and an energy load member such as a spark plug. Such a switch is normally mounted on the engine crankshaft and, as the switch rotates in unison with the crankshaft, the circuit is alternately closed and opened by causing a bridging conductor provided in the switch to become electrically juxtaposed with a lead cable from the voltage source and another lead cable from the spark plug. For further details of such a system see U.S. Patent No. 3,009,975, G. H. Hufferd et al., and co-pending application Serial No. 121,664, now U.S. Patent No. 3,094,108, C. B. Small et al., assigned to the same assignee as the instant invention.
When a rotating bridging conductor is utilized in an ignition circuit as above described, air gaps exist by necessity between the bridging conductor and the juxtaposed cables. This exposes the ignition system to ambient conditions with variations in such conditions having a detrimental effect on the performance of the system. A few examples will suflice. It is known that dissipation of energy occurs when an electric charge has to jump an air gap. Losses occur due to the ionization of the air in the gap. Also, the length of the arc fluctuates due to constantly changing characteristics of the air gap breakdown voltage, which has the effect of upsetting accurate ignition firing. The energy is dissipated in the air gap while the charge jumps the gap and is converted to light energy and electromagnetic radiation. Electromagnetic radiation, in turn, produces interferences in the radio spectrum. Variations in humidity and atmospheric pressure also change the effectiveness of the ignition system. Last, but not least, the switch must be carried by rotating members of the engine, which is not always desirable.
It is therefore the primary object of this invention to provide an improved piezoelectric ignition system which avoids the shortcomings of the prior art.
It is a more specific object of this invention to provide a piezoelectric ignition system which is not affected by variations in environmental conditions as were the ignition systems previously known.
It is a further object of the invention to provide a piezoelectric ignition system in which the air gap, as above described, is eliminated and the dissipation of energy formerly experienced thereat is prevented.
It is a still further object of this invention to provide a piezoelectric ignition system including a magnetically responsive vacuum switch in which the location for mounting the switch is very flexible and is not restricted to a crankshaft member. In this improved system the switch can be mounted anywhere on the engine in proximity to a rotating or moving member carrying a magnetic actuator, or both the switch and the magnet may 7 be stationary in which case a rotating or moving shield is placed between the magnet and the switch.
For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.
In the drawing:
FIGURE 1 shows a typical internal combustion engine with fragmentary portions of the flywheel;
FIGURE 2 is a detailed view of a part of the engine illustrated in FIGURE 1 equipped with the piezoelectric ignition system of this invention, the switch is shown sideways off normal position) for illustrative purposes only;
FIGURE 3 is a diagrammatic view illustrating a modified switching arrangement; and
FIGURE 4 is a diagrammatic illustration of a multicylinder engine piezoelectric ignition system according to the principles of this invention.
An aspect of the present invention resides in the provision of. an ignition system for an internal combustion engine of the type having stationary and moving members including a crankshaft, and a spark plug mounted on the engine, which includes a piezoelectric voltage source which is electrically in series with the plug and is operated by a moving member of the engine and is effective to generate, periodically, an electric potential in timed relation to the rotation of a crankshaft. A magnetically responsive vacuum switch arrangement is connected electrically in series between the voltage source and the spark plug. A magnet is disposed in operative proximity to the switch arrangement to actuate, periodically, the switch arrangement in timed relation with the rotation of a crankshaft of the engine to close and open the circuit between the voltage source and the spark plug.
Referring now to the drawing in which similar members are identified by the same numeral, there is shown in FIGURE 1 a typical internal combustion engine 10, and FIGURE 2 illustrates in greater detail a crankshaft 12 and a camshaft 14 mounted in the engine. The camshaft 14 carries an eccentric collar 16 press-fitted onto the camshaft and a rotatably disposed annular bushing 18 encircles the collar 16.
The piezoelectric ignition system which is the subject of this invention comprises a piezoelectric voltage source 20 suitably bolted to crankcase wall 22 of the engine 10 and facing a partly shown flywheel 23. The piezoelectric voltage source includes piezoelectric element 24 piezoelectrically responsive in compression and suitably confined in a housing 26. Preferably, the element 24 consists of one or more pieces of polycrystalline ceramic material such as barium titanate, lead zirconate or the like, suitably polarized and electroded.
The arrangement shown indicates the use of two ele ments (although not visible as such) which are mechanically in series and electrically in parallel. The outermost ends of the elements are grounded by contact with the housing 26 and in the center between the elements there is disposed a plurality of conductor discs 28 electrically coupled with hot lead cable 30.
A fulcrum provided lever 32 is interposed between one outer end of element 24 and the housing 26 to compress the elements upon angular movement of the lever. A high electric potential is generated when the lever squeezes the elements and the potential is held until discharged in a manner that will hereafter become more apparent. The release of the squeeze on the elements will generate another potential but of opposite polarity.
The angular movement of the lever 32 is established and correlated with the rate of rotation of the engine 0 by means of the bushing 18 which continuously bears against the lever. The bushing, of course, while as such is nonrotatable, follows the eccentric orbit of collar 16.
The lever thus causes to generate, periodically, an electric potential in timed relation with the rotation of the crankshaft 12.
The hot lead cable 30 is connected in series with a magnetically responsive vacuum switch 34 and a spark plug 36. The switch 34 is conventionally known as a reed-type switch generally having a longitudinally extending housing 38 from which the air has been evacuated creating, preferably, a vacuum of less than millimeter of mercury. The housing 38 is mounted to stationary crankcase wall 22. Two contact reeds 40 are cantilever supported at opposite ends in the housing 38 and extend toward each other therein and slightly overlap for suitable electrical juxtaposition when the reeds contact each other. By virtue of the high vacuum in the housing the air is not ionized to any substantial degree and the reeds can, therefore, be very closely spaced so that variations in the length of the are are avoided. The reeds 40 are normally spaced and are drawn together, periodically, in timed relation with the rotation of the crankshaft 12 by a magnet 42 mounted on the flywheel 23 and rotating in unison therewith. As the flywheel rotates, the magnetic field of the magnet 42 is exposed to the contact reeds 40 to close the circuit. The position of the switch 34 and the magnet 42 may, of course, be reversed with the switch being mounted on the flywheel. However, problems such as the effect of centrifugal force and others must then be taken into consideration.
Preferably, a two-pole magnet 42 is used and the magnet is so positioned on the flywheel that one contact reed is close to one pole and the other reed is close to the opposite pole of the magnet when the magnet is in operative juxtaposition to the switch.
Turning now to another aspect of the invention, one may assume that the piezoelectric voltage source 20 functions as a mechanically changed condenser, and switch 34 connects the charge capacity with an energy dissipating device such as the spark plug 36. If the spark plug is of a low resistance value, a very high peak current flows through the switch during the discharge, the extent of this current being determined by the series resistance of the total circuit from the voltage source 20 to the plug 36. This peak current tends to deteriorate the surface of the reeds 40, particularly the contact points thereof.
In order to reduce the flow of current, a series resistor of a magnitude higher than the load is placed into the circuit. As the current flows through the resistor the voltage drop and the peak of the current is lowered, but the duration of current flow is lengthened so that the same power flows through the switch. A resistor can be placed anywhere in the circuit because the current flow in the circuit should be equal. For convenience, a conventional resistance wire (see lead cable 30), currently in use for automobiles to limit the steep current wave form to prevent radio interference high frequencies, is particularly suitable.
In summary, the operation of the system is as follows. The initial rotation of the camshaft 14 causes an electric potential to be generated by actuation of voltage source 20, and the discharge of this potential to plug 36 occurs in precise timed relation with the rotation of the crankshaft 12 by exposing the magnetic field of magnet 42 to the switch 34 during each revolution of the flywheel at the exact time that firing is required. The potential generated by the release of the squeezing action is utilized in the same manner or, alternatively, it may be desirable to transmit one of the potentials to ground.
FIGURE 3 illustrates another way of disposing the magnet in relation to the switch. If it be deemed desirable to mount both the switch and the magnet in a stationary position, the switch is mounted in the manner as above described and the magnet is mounted in operative proximity onto the flywheel housing 23a. Interposed between the switch 34 and the magnet 42 is a movable magnetic field shield 44 with a magnetic window 46 to periodically permit the magnetic flux of the magnet 42 to operate the switch 34 when the window of the shield is juxtaposed to the switch. The shield 44 is most suitably mounted on and coaxial with crankshaft 12 so that when the crankshaft rotates, the switch 34 is magnetically actuated by the magnet 42 in timed relation with the rotation of the crankshaft. The window 46 must of course be suitably located to establish proper simultaneous juxtaposition of switch, window and magnet.
The window 46 may be a mere clear opening to permit passage of the magnetic flux through the shield which is constructed of high permeable material, or the window may be constructed of a material having low magnetic permeability.
FIGURE 4 illustrates a piezoelectric ignition system in accordance with this invention for a multicylinder ignition system. It should be noted that while only one particular mode of operation is illustrated, the system can readily be constructed with a single switch by one versed in the art.
Shown in FIGURE 4 is a voltage source 20 connected in series to a plurality of switches 34a-34d. The switches are mounted on the crankcase wall 22 equidistantly and in circular array. Magnet 42 is mounted on the flywheel and operates the switches 34a-34d in a predetermined sequence in timed relation with the rotation of the crankshaft 12.
While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.
1. An ignition system for an internal combustion en- Igine of the type having stationary and moving members including a crankshaft, and a spark plug mounted on the engine, comprising, in combination:
a piezoelectric voltage source electrically in series with said plug and operated by a moving member of the engine and effective to generate, periodically, an electric potential in timed relation to the rotation of said crankshaft;
magnetically responsive switch means comprising a sealed enclosure having a vacuum of at least 10-- mm. mercury and magnetically operable contact means therein, said switch means being connected electrically in series between said voltage source and said spark plug; and
a magnet disposed in operative proximity to said switch means to actuate, periodically, said switch means in timed relation with the rotation of the crankshaft to close and open said circuit between said voltage source and said plug.
2. An ignition system as set forth in claim 1, wherein said switch means is mounted to a stationary member of the engine, and said magnet is mounted to a moving member of the engine and moves in unison therewith.
3. An ignition system as set forth in claim 1, wherein said switch means and said magnet are both mounted to a stationary member of the engine; and
a magnetic field shield having a magnetic window, said shield being movably interposed between said' switch means and said magnet to periodically permit the magnetic flux of the magnet to operate said switch when the window of the shield is juxtaposed to said switch means.
4. An ignition system as set forth in claim 1, wherein said switch means is a reed-type switch having magnetically responsive contact reeds arranged, at least partly, in normally spaced overlapping relationship.
5. An ignition system as set forth in claim 4, and a resistor disposed electrically in series with said switch, said spark plug and said voltage source.
6. An electric circuit to produce a spark, comprising:
a voltage source;
a magnetically responsive reed-type switch means comprising a sealed enclosure having a vacuum of at least mm. mercury and magnetically operable contacts therein, said switch 'means being connected electrically in series with said voltage source;
a magnet operably juxtaposed in respect to said switch;
a spark member in series with said voltage source and said switch; and
a shield of high permeable magnetic material movably interposed between said switch and said magnet, said shield having a magnetic window of a very low permeability to permit passage of the magnetic flux to operate said switch when said window is in juxtaposition with said switch.
7. An electric circuit as set forth in claim 6, wherein said reed-type switch means has magnetically responsive contact reeds arranged, at least partly, in normally spaced overlapping relationship, one contact reed being positioned close to one pole of said magnet and another reed being positioned close to the opposite pole of said magnet when said window is in operative juxtaposition with said switch means.
8. An ignition system for a multicylinder internal combustion engine of the type having stationary and moving members including a crankshaft, and a spark plug for each cylinder mounted on the engine, comprising, in combination:
a piezoelectric voltage source electrically in series with each spark plug and operated by a moving member of the engine and efiective to generate, periodically, an electric potential in timed relation to the rotation of said crankshaft;
plurality of magnetically responsive switch means connected electrically in series between said voltage source and said spark plugs, each of said switch means comprising a sealed enclosure having a vacuum of at least 10- mm. mercury and magnetically operable contacts therein, the number of switch means in the circuit corresponding to the number of cylinders in the engine; and
magnet disposed in operative proximity to all of said switch means to actuate, periodically, in sequence, all of said switch means in timed relation with the movement of said crankshaft.
References Cited by the Examiner UNITED STATES PATENTS 2,544,477 3/1951 West 315209 2,999,914 9/1961 Stanaway 20019 3,009,975 11/1961 Huflferd et al. 315- X 3,013,137 12/1961 Vanden Broeck 20019 3,087,030 4/1963 Shebanow 20019 DAVID J. GALVIN, Primary Examiner.
JAMES D. KALLAM, Examiner.