This invention relates to ignition systems, and, more particularly, to an ignition distributor which conveys a high electric voltage to spark plugs according a particular firing order and with precise timing and reliability.
Ignition distributors for internal combustion engines conventionally include a distributor shaft connected to a drive pinion in the engine block so that the distributor shaft rotates at the same speed as does the cam shaft of the engine. The distributor shaft carries a contact-breaker cam having a plurality of lobes, the number of which correspond to the number of spark plugs to be energized. A movable breaker point or contact lever is pivotally mounted adjacent to the cam and a stationary breaker point is fixedly mounted adjacent to the cam, the contact lever being spring loaded so that it normally touches the stationary point. A distributor rotor is mounted on the upper end of the distributor shaft and has an electrode which extends outwardly toward a plurality of stationary contacts which, in turn, are electrically connected to the spark plugs.
The primary portion of the ignition circuit includes a low voltage battery (6 or 12 volts) in series with a primary winding of an ignition coil, and the movable and fixed breaker points. When the points are in contact current flows through the primary winding generating a magnetic field and when the contact-breaker cam separates the points effecting interruption of the primary circuit, the magnetic field produced by the primary winding collapses inducing a high voltage (in the tens of thousands) in a secondary winding mounted adjacent to the primary winding. The induced voltage is applied to a particular contact and, through the contact, to a spark plug resulting in the production of a spark.
Many attempts have been made to eliminate the "make and break" relationship between the movable and fixed breaker points because the breaker points contaminate and wear out. The gap between the points is critical and if the gap is too small, interruption of the primary circuit at high speeds often does not occur, resulting in failure to fire the spark plugs. If the gap is too large the engine is difficult to start. Furthermore, because the "make and break" relationship between the points depends upon the spring return of the contact lever toward the fixed point, missing often occurs at high speeds even with properly gapped points. Engine misfiring caused by faulty breaker points is one major cause of air pollution due to emission of noxious gases. It also results in inefficient combustion requiring more fuel than would otherwise be consumed, contaminating other parts such as spark plugs and amplifying the air pollution problem.
In spite of the many attempts to overcome these disadvantages, no satisfactory system presently exists. Several magnetic inductive systems have been developed to overcome the need for the breaker points. However, these systems are unsatisfactory because either a) they have been unable to produce sufficient energy at low speeds to properly fire the spark plugs or they produce too much energy at very high speeds which tend to damage or prematurely wear out the spark plugs, or b) timing of the spark plug firing is not sufficiently accurate.
Accordingly, it is an objective of this invention to provide an ignition system which operates effectively and efficiently for long periods of time without the need for frequent maintenance and part replacement and which operates equally well at high and low speeds.
It is another objective of this invention to provide an ignition system which obviates the need for the conventional "make and break" contact system thereby reducing maintenance costs and improving the operation of the engine.
A further objective of this invention is to provide an ignition system which may be manufactured easily and inexpensively and which may be utilized in the ignition system of existing engines.
Briefly described, this invention in one form comprises an ignition system having a primary circuit, a trigger for actuating the primary circuit and a secondary circuit responsive to the primary circuit. The secondary circuit is conventional and includes a secondary winding of an ignition coil and conventional circuitry associated therewith having a distributor rotor, contacts and leads to individual spark plugs. The primary circuit includes a conventional primary winding of the ignition coil. However, the conventional contact-breaker cam and movable and fixed breaker points are replaced by an electronic valve which is actuated withprecision timing by the triggering means.
A preferred form of the triggering means of this invention includes a rotary member drivingly connected to the cam shaft of an engine and having a plurality of wires equiangularly spaced thereabout. Each wire is formed to have a shell and central core, the shell having the capacity to be permanently magnetized in an axial direction and having a high coercivity. The core has a relatively low coercivity and the capacity to be magnetized in a first generally axial direction by the shell. The magnetization of the core is reversible by application of a second magnetic field having a direction reverse to that of the shell and a magnitude greater than that of the shell and, when the second magnetic field is removed, the magnetic field of the shell remagnetizes the core in the first axial direction. A sensor is mounted adjacent to the rotor and, in one form, includes a permanent magnet having a magnetic field greater in strength than that of the wire shell and reversed in direction to the field of the shell. The sensor also includes a conductive wire coil. As each wire becomes juxtaposed to the sensor, the sensor magnet effects reversal of the direction of the magnetic field of the core and as the wire passes the field of the sensor magnet, the shell magnetically captures the core significantly modifying the magnetic field to which the sensor coil is exposed. This field change induces a current in the sensor coil. The induced current is amplified and directed to the control element of the electronic valve which is connected in series with a battery and the primary winding of the ignition coil. As the rotary member turns, each time a wire becomes juxtaposed to the sensor a pulse is generated which closes the electronic valve resulting in the passage of a current through the primary winding. The current through the primary winding generates a magnetic field which induces a greatly increased voltage in the step-up secondary winding of the ignition coil. The higher voltage of the secondary winding is directed to the particular contact which corresponds to the wire on the rotor which is juxtaposed to the sensor and to a specific spark plug effecting generation of a spark to fire the combustion mixture within the cylinder in which the spark plug is mounted.
Since the pulse generated by reversal of the wire core's magnetic field in juxtaposition to the sensor is amplified to a level sufficient to trigger the electronic valve and since the current passing through the primary coil is not dependent upon the magnitude of the generated pulse but instead is provided by the battery, the voltage across the secondary of the ignition coil is approximately the same regardless of the speed of the engine. Furthermore, the elimination of the "make and break" contacts eliminates a critical part of the ignition system and one which must be constantly maintained since the distributor breaker points contaminate and wear out rapidly.
DESCRIPTION OF THE DRAWINGS
The invention together with these and other objectives and attendant advantages will be better understood from the detailed description below taken together with the accompanying drawings in which:
FIG. 1 is a schematic sectional view of a pulse generating wire and sensor used in the ignition system of this invention.
FIG. 2 is a plan view of the triggering means of the ignition system of this invention.
FIG. 3 is a sectional view taken along lines 3--3 of FIG. 2.
FIG. 4 is an end view of the sensor of FIG. 2.
FIG. 5 is a schematic circuit diagram of the ignition system of this invention.
FIG. 6 is a perspective view, partially schematic, of a preferred form of ignition distributor of this invention.
Before discussing the details of the present invention, it is important that one understands the structure and operation of the primary element of the ignition distributor of this invention. To this end reference is made to U.S. Pat. application, Ser. No. 173,070 filed Aug. 19, 1971 entitled Self-Nucleating Magnetic Wire and filed by the inventor of the present invention. The subject matter of that co-pending application is incorporated herein. For facilitating understanding of this invention a brief description, with reference to FIG. 1, of the self-nucleating magnetic wire follows. A magnetizable wire 10 is treated to form a shell 12 and central core 14, the shell having the capacity to be permanently magnetized in an axial direction and having high coercivity. The core 14 has a relatively low coercivity. Such a wire can be formed by drawing a wire of ferro-magnetic material and work-hardening the wire such as by circumferentially straining it to form a relatively "hard" magnetic wire shell 12 having relatively high magnetic retentivity and coercivity. The wire has a relatively "soft" magnetic core 14 having relatively low coercivity. Both the shell and the core are magnetically anisotropic with an easy axis of magnetization parallel to the axis of the wire 10. The wire is then magnetized by subjecting it to an external magnetic field. The relatively "hard" shell 12 has a retentivity and coercivity sufficiently greater than that of the relatively "soft" core 14 so that when the external magnetic field is removed the shell retains its charge and couples or "captures" the core by magnetizing the core in an axial direction opposite to the direction of magnetization of the shell. In this fashion the core 14 forms a magnetic return path or shunt for the shell 12 as shown by flux lines illustrated in FIG. 1 and a domain wall interface is formed between the core and shell.
When the wire 10 is subjected to an external magnetic field of greater magnitude than the field of the shell and having a polarity opposite to that of the shell, such as by bringing a permanent magnet 16 into close proximity to the wire 10, the external field to which the wire is subjected increases until a point is reached at which time the external magnet 16 "captures" the core 14 from the shell 12 by reversing the flux direction of the core through the process of nucleation of a magnetic domain. Reversal of the field direction of the core results in an abrupt change in the magnetic flux surrounding the wire 10. When the permanent magnet 16 is removed from the wire 10 the shell recaptures the core providing an additional abrupt and more pronounced change in the magnetic flux surrounding the wire. In general, the rate of propagation of the domain wall along the wire is a function of the wire composition, metallurgical structure, diameter and length and of the strength of the external magnetic field. A coil 18 placed adjacent to the wire 10 will have a current pulse induced therein by this abruptly changing magnetic field and that current pulse may then be utilized as described below.
A plurality of such wires 10 is used to form the triggering means of the ignition distributor of this invention. With reference now to FIGS. 2 and 3 there is illustrated a rotor 20 having an annular rim or flange 22, a hub 24 having a central opening 26 for receiving a distributor drive shaft 28 and an intermediate web 30 connecting the flange 22 and hub 24. A plurality of equiangularly spaced straight wires 10 are mounted in axially extending partially circular recesses 32 formed on the outer surface of the flange 22. It has been found that for an ignition distributor the wire preferably is made from an alloy of 48 percent iron and 52 percent nickel, with each wire having a diameter of approximately 0.0159 inch and a length of approximately 0.625 inch. The number of wires is an integral function of the number of spark plugs intended to be fired. For example, in a 6 cylinder engine having 6 spark plugs, 6 wires are equiangularly spaced about the periphery of the rotor 20 or, in other words, the wires are spaced apart 60°. For certain applications it may be desired to utilize fewer wires, such as 3, and to rotate the rotor 20 sufficiently fast so as to allow each wire to service 2 spark plugs, or to utilize more wires, such as 12, and reduce the speed of rotor rotation. It also is possible to utilize a single wire 10 to fire a plurality of spark plugs with a different spark plug being fired with each revolution of the rotor 20. This will be better understood from the detailed description below of the entire ignition distributor system and the relevance of the wire in the timing of the spark plug firing.
A sensor or readout head 40 is mounted in close proximity to the outer surface of the flange 22 at a position which shall be referred to throughout as the sensing station 42. The function of the readout head 40 is to acknowledge, through generation of a signal, the presence of a wire 10 at the sensing station 42. The readout head 40 comprises an inductive sensor 44 having a pickup coil 46 encircling the center bridge 48 of a generally square-A shaped soft iron laminated pickup core 50. The core 50, in addition to the center bridge 48, further includes a pair of parallel legs 52, 54 and a rear bridge 56 with the free ends of the legs 52, 54 serving as pickup poles and being located in close proximity to the outer surface of the distributor rotor flange 22.
The readout head 40 also includes a pair of opposed U-shaped permanent magnets 60, 62 which preferably are substantially identical and have substantially equal magnetic characteristics. The permanent magnets 60, 62 are mounted on opposite sides of the inductive sensor 44 and in engagement with the pickup core 50. The two permanent magnets 60, 62 are mounted in opposed magnetic relationship such that each pole of each magnet faces an opposite pole of the other magnet (see FIG. 4). The opposed permanent magnets 60, 62 are laterally offset in opposite lateral directions relative to a plane 64 extending through the pickup core 50. This is accomplished by having the like inner poles (for example-north) of the permanent magnets 60, 62 engaging the sides of the legs 52, 54 of the pickup core 50. The readout head 40 is mounted so that the plane 64 extending through the pickup core center line is inclined (approximate 12° as shown in FIG. 4) to the axis of the rotor 20. However, because the permanent magnets are laterally offset with respect to the pickup core 50, the permanent magnetic field between the opposed permanent magnets 60, 62 is substantially parallel to the axis of the rotor 20 and magnetic wires 10 at the sensing station 42. Furthermore, since the polarity of the fields on opposite sides of the pickup core 50 are equal in magnitude and opposite in polarity a zero or null magnetic field position is established midway between the permanent magnets. For controlling the magnetic fields surrounding the readout head 40, it has been found helpful to employ a thin U-shaped soft iron magnetic shield 66 around the back and partially around the sides of the inductive sensor with the sides of the shield 66 extending generally parallel to the axis of the magnetic wires 10.
Assuming that the rotor 20 rotates in a clockwise direction as viewed in FIG. 2, the magnetic wires tend to pass from left to right across the readout head 40 as viewed in FIG. 4. As each wire approaches the sensing station 42 its shell 12 is subjected to the "leading" permanent magnetic field 67 of the readout head 40 which has been set to have the opposite magnetic orientation as the wire shell 12. In the example illustrated in FIG. 4 the wire shell 12 has its south pole at its upper end and north pole at its lower end which is opposite to the orientation of the left side of the permanent magnets 60, 62. Before the wire 10 reaches the influence of the leading permanent magnetic field 67 the wire core 14 has its north pole at its upper end and south pole at its lower end due to the induction of such an orientation by the dominant shell 12. When the wire 10 is in the leading permanent magnetic field 67 the left side of the permanent magnets 60, 62 captures the core 14 from the shell 12 and reverses its magnetic orientation so that the upper end of the wire core becomes south and the lower end north. However, as the wire passes the leading magnetic field 67 it approaches the null position where the magnetic field due to the permanent magnetic field is zero. When the magnetic field of the permanent magnets 60, 62 drops below a certain level depending upon the strength of the shell 12, the shell recaptures the core 14 and reverses the core's magnetic field. The resultant nucleation causing the core reversal produces an abrupt change in the magnetic field to which the inductive sensor coil 46 is exposed inducing a strong electrical pulse in the inductive sensor 44. Because of the inclination of the readout head 40 one end of the wire 10 (in this present case upper end) sees the reduced magnetic field of the permanent magnets or the null position before the other end thereby ensuring that the direction of propagation of the domain wall always is the same and the induced pulse polarity always is the same.
When the wire passes the null position 42 it enters the "trailing" field 68 of the permanent magnets 60, 62 which has an orientation coinciding with that of the wire shell 12 and, therefore, has no effect on the core 14.
IGNITION SYSTEM (FIGS. 5 AND 6)
Turning now to FIG. 5 there is illustrated a schematic diagram showing the ignition distribution system 100 and associated circuitry. The system 100 can be divided into three basic segments, the primary circuit 101, the triggering means 102 and the secondary circuit 103. The primary circuit 101 includes a low voltage battery 104, in the order of 6 or 12 volts, connected in series with an ignition switch 105 and a primary winding 106 of an ignition coil 108, all of which are included in conventional ignition systems. The primary circuit 101 also includes a normally open electronic valve 110 such as a semiconductor controlled rectifier (SCR) connected in series with the battery 104 and primary winding 106.
The triggering means comprises the rotor 20 and readout head 40 discussed above operatively connected to the control element or base 112 of the electronic valve 110 preferably through an amplifier 114. The normally open electronic valve 110 prevents current from passing through the primary winding 106 until there is an occurrence of a predetermined event. Such an event occurs when a wire 10 mounted on the rotor 20, after reaching the sensing station 42 and having the direction of magnetization of the core 14 captured and reversed by the leading permanent magnetic field 67 of the readout head 40, approaches the null position where the shell 12 recaptures core and abruptly reverses its direction of magnetization. The reversal caused by the shell 12 abruptly changes the magnetic field to which the inductive sensor 44 of the readout head 40 is subjected inducing a strong electric current pulse in the inductive sensor 46. That pulse is amplified by the amplifier 114 to a level at least high enough to trigger the electronic valve 110 closing the valve and permitting the current to flow through the primary winding 106 of the ignition coil 108. In some instances the induced pulse can be strong enough to trigger the electronic valve directly eliminating the need for an amplifier 114.
The increase of current through the primary winding 106 produces a changing magnetic field and induces a current in the secondary circuit 103 by inducing a current in the secondary winding 118 of the ignition coil 108. Since the battery is approximately 6 or 12 volts and since tens of thousands of volts are required to fire the spark plugs 116 the ignition coil serves as a setup transformer. The secondary winding is electrically connected by a high tension lead 120 to a rotating contact arm or distributor rotor 122 rotatably mounted adjacent to a distributor disk 124. A plurality of contacts 126, such as a tungsten electrode for each spark plug 116 or cylinder of the engine, are mounted about the periphery of the disk 124 so that as the distributor rotor 126 rotates it sequentially touches the contacts 126 providing a path for the current from the secondary winding 118 to the spark plugs 116 through conductors 128.
It is mentioned above that the triggering pulse is produced by the abrupt change in magnetic flux at the sensing station caused by the wire shell 12 reversing the wire core's polarity. It is also clear that the magnetic flux will be abruptly changed when the core's polarity is reversed by the leading permanent magnetic field 67. The flux change caused by the leading magnetic field 67 is of a significantly smaller magnitude than that of the change caused by the shell. The location of the peak of the leading field 67 is established at a distance from the pickup coil 46 such that the flux change resulting from the reversal of the wire core's polarity when captured by the magnets 60, 62 produces a pulse in the pickup coil 46 of less than a predetermined magnitude so that the electronic valve 110 is not closed. However, the peak of the leading field 67 must be close enough to the coil so that the shell's recapturing of the wire core 14 as the wire passes the leading field peak takes place close enough to the pickup coil to produce the electronic valve triggering signal. Since it is essential that the spark plugs or other combustion ignition devices fire at precisely the right moment, it is important that a large current surge take place through the primary winding 106 upon the triggering of the electronic valve 110. In order to improve the response time of the primary winding 106, a capacitor 130 is placed across the primary winding 106. The capacitor is charged by the battery 104 and when the electronic valve 110 is fired the capacitor 130 discharges through the primary winding 106 making additional current available to more rapidly increase the magnetic field of the primary winding 106. The distributor rotor 122 directs the high voltage to each spark plug in the proper firing order and each contact 126 corresponds with a particular spark plug 116 and a particular wire 10 on the primary rotor 20.
If desired, and in order to further insure that combustion takes place within each cylinder at the desired time, one or more "backup" wires can be added behind each primary wire 10 so that if the spark generated by the first wire did not sufficiently ignite the gas in the cylinder, the subsequent sparks generated by the adjacent backup wires would insure total ignition.
FIG. 6 illustrates the mounting of the ignition distribution system 100 in a manner which facilitates substitution of this system for conventional ignition systems. The rotor 20 is mounted on a distributor shaft 28 which, through a conventional pinion 1 and worm gear arrangement 138, is driven by an engine cam shaft 140. The distributor rotor 122 also is mounted on the distributor shaft 28 so that it rotates in conjunction with the rotor 20. The distributor disk 124 is fixedly mounted to the distributor casing 142 and may form the cover of the casing. The contacts 126 are equiangularly spaced about the periphery of the disk 124. With this particular arrangement the ignition timing is a function of the cam shaft speed or, in other words, engine speed.
Such a system also lends itself to control of the timing of pulse generation and spark plug firing depending upon the occurrence of one or more predetermined conditions. For example, instead of directly connecting the distributor shaft 28 to the cam shaft 140, an electromagnetic clutch (not shown) can be used which is controlled by one or more signals representative of conditions such as temperature, manifold pressure, engine speed, etc. The speed and phase of rotor rotation can be varied by the clutch as a function of these conditions.
While the above described triggering means has the wires 10 mounted on a rotor, the pulses induced in the induction sensor 44 also could be obtained by providing relative reciprocating motion between the wires 10 and the inductive sensor 46 such as by mounting the wires on an oscillating member (not shown).
It will be appreciated that in place of the constantly impacting, sparking distributor points of a conventional ignition distributor, this invention provides a special non-contact system including merely a rotating member 20 with a plurality of specially fabricated wires 10 and a solid state readout head including basically a coil 46 and a pair of permanent magnets 60, 62. A sharply defined pulse of substantially constant magnitude is generated each time a wire 10 passes the sensing station 42 thereby accurately timing the firing of the spark plugs regardless of engine speed.
In addition to being low in cost, simple to manufacture, and essentially maintenance free, the ignition system of this invention improves the accuracy of timing since it does not depend upon spring constants nor is it subjected to contact arcing or pitting. The ignition system is not sensitive to the engine speed and provides exact timing regardless of engine speed.