Abstract:
An electronic ignition controller operable from a Hall Effect pickup Device in a ballast-resistorless, inductive-type ignition system for an automotive vehicle internal combustion engine and featuring programmed dwell and automatic shut-down timer circuits, which control current dissipation in the ignition coil. The programmed dwell timer circuit enables energization of the ignition coil for a controlled or substantially constant period of time over substantially the entire range of engine operating speeds up to a predetermined high engine speed above which the ignition system reverts to a constant duty cycle characteristic determined by the character of the triggering input or pickup device. The automatic shut-down timer circuit operates to block the energization of the ignition coil if the controller remains in a state of conduction that maintains the ignition coil energized for a predetermined prolonged period of time that is greater than the actual dwell period or ON time of the coil at low engine or cranking speeds.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to electronic ignition controllers for internal combustion engines of automotive-type vehicles and, more particularly, to a low-cost, reliable electronic ignition controller, which is triggerable from a breakerless or velocity-insensitive Hall Effect pickup Device and is designed for use with a standard-type automotive ignition coil in a ballast-resistorless, inductive-type ignition system. 
     Prior forms of ignition controllers exhibiting some of the above characteristics are represented by U.S. Pat. Nos. 3,705,988; 3,861,370; 3,875,920 and 3,906,920, none of which, however, makes any provision for protection of the ignition coil from damage due to excessive current dissipation at low speed engine operation and/or during stalled engine or delayed starting conditions. 
     The invention seeks to avoid the above deficiencies in automotive vehicle-type ignition systems, which do not employ a ballast resistor, and seeks in other ways to provide a simple, reliable and low cost electronic ignition controller 
     SUMMARY OF THE INVENTION 
     Towards the accomplishment of the above and related objects, the invention provides an electronic ignition controller which is especially suited for use with a Hall Effect-type switching Device and features a pair of timing switching circuits using programmed unijunction transistors for providing a programmed dwell timer circuit and an automatic shut-down timer circuit. The programmed dwell timer circuit provides a delay characteristic, which delays for a fixed or variable controlled delay period, the turn-on or energization of the ignition coil from a triggering signal applied to the input of the controller. The delay period is a function of engine speed and, in the embodiment presented herein, may vary accordingly to provide a substantially constant period of coil energization sufficient to charge the coil over a wide range of engine operating speeds without impairment to the dwell period of the controller at high engine speeds. 
     The automatic shut-down timer circuit senses whether the ignition controller is in a state of conduction that permits the ignition coil to be energized from the vehicle electrical current source and operates to change the conductive state of the controller and to block the energization of the ignition coil only if the controller is in and remains in the aforesaid state of conduction for a predetermined prolonged period of time that is greater than the dwell period or ON time of the coil at the lowest of engine speeds, say at engine cranking speeds of around 50 rpm. 
     The internal design of the controller further includes protective circuits for the ignition coil connected to its output, for the Hall Effect Generator or pickup trigger Device connected to its input and for the internal semiconductor components employed therein from the otherwise damaging effects of positive and negative going transients appearing on the electrical supply conductors and from the effects of high voltages induced in the coil and appearing at the output semiconductor switching device under unloaded coil conditions. 
     The above and other objects, features and advantages of the invention, together with the manner in which they are realized, will appear more fully from consideration of the following detailed description made with reference to the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an electrical schematic circuit of the electronic ignition controller in accordance with the present invention; 
     FIG. 2 depicts timing wave form signals which appear at various designated points in the circuit of FIG. 1 in relation to the position of the shutter or trigger wheel as depicted in FIG. 2(s), and are useful in understanding the operation thereof; 
     FIG. 3 depicts several additional timing wave forms useful in understanding the operation of the programmed dwell circuit of FIG. 1; and 
     FIG. 4 depicts the delay, dwell and duty cycle versus engine speed characteristics of the programmed dwell circuit employed in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 1 illustrates in electrical schematic form a breakerless ignition system 10 for a multi-cylinder, internal combustion engine 12 having a plurality of sparking-type firing devices 14 for igniting the fuel-air mixture conducted to the individual engine cylinders for combustably powering the engine. The ignition system is of the inductive storage-type in which energy from a low-tension electrical current source 16 is inductively stored in the field of an ignition coil 20 whose primary winding 21 is periodically interrupted by a mechanical or electronic control switch unit 24 to collapse the field and induce high tension energy therein. The high tension energy extracted from the secondary winding 22 of the ignition coil is supplied from its high tension output terminal H and is sequentially distributed to the individual spark plugs 14 of the engine through distributor device 26 driven from and at one-half engine speed. 
     The primary winding 21 of the ignition coil is shown connected at its plus (+) terminal through a manually operable control switch 29 to the elevated or plus potential side of the low tension D.C. electrical current source 16, which includes a negatively-grounded storage battery 17 charged from an alternator-rectifier 18 and associated voltage regulator 19. The negative terminal (-) of the ignition coil, common to one side of the secondary and primary windings thereof, is connected to the negatively-grounded side of the source 16 through the interrupter or control unit 24, which, in the apparatus of the present invention, is of the breakerless electronic switch variety triggered from a pickup Device 30 operated in synchronism with the engine. 
     The pickup 30 is shown as contained in the distributor 26, and includes a pair of relatively movable elements such as a trigger or shutter wheel 32 driven in synchronism and at one-half engine speed past an electrical sensor device 36. In the preferred form of the invention the pickup is of the velocity insensitive variety, and the sensor 36 is a Hall Effect generator or switching device, which exhibits a bi-stable switching conductivity or impedance characteristic when the sensor is alternately exposed to and removed from the influence of a constant intensity radiation source 38, as a permanent magnet. Sensor 36 is spaced from the magnet by an air gap 37 in which is interposed a portion of the rim or periphery of the trigger or shutter wheel 32, which is of a cup-shape formation with a plurality of arcuately spaced, ferrous metal vanes 33 and arcuate slots or windows 34 formed about the periphery thereof and functions as a field gating or shunting element, successively interposing a metallic vane or field shunting portion 33 followed by an aperture, window or cutout portion 34 between the stationary magnet 38 and the Hall Device 36. 
     In the illustrated embodiment of the invention, the shutter wheel 32 has a total of six shunting elements or vanes 33, one of which is provided in each 60° sector thereof or for each cylinder or firing event in the engine 12. Each vane spans an arcuate distance of 48 mechanical degrees and each slot or window 34 spans an arcuate distance 12°, whereby the shutter wheel may be characterized as an 80% shutter wheel, providing a duty cycle of 80%. Such a duty cycle will provide in the controller a dwell period of sufficient duration, viz., 3.2 milliseconds, for adequate charging of the ignition coil at a high engine speed of 5,000 rpm for a six cylinder engine. 
     However, at low engine speeds of, say, 500 rpm for example, it will be noted that 80% duty cycle shutter will cause the coil to be charged for 32 milliseconds, which will be seen to cause excessive current dissipation therein. Such current dissipation is eliminated in accordance with the programmed dwell timer circuit feature of the present invention without the use of a ballast resistor, as will more fully appear later herein. 
     Continuing with the description of the Hall Effect Device 36, the latter has a high potential and a low potential terminal, P and G, which are adapted to be connected to the high potential side and to the low potential side respectively, of a source of d.c. operating potential, and when so connected, develops between a third or output terminal A and its reference or low potential G, a constant amplitude, essentially rectangular electrical pulse signal. The output signal from or appearing at terminal A of the Hall Effect Device is shown in FIG. 2A herein and has a pulse repetition rate, which is related to the product of one-half the engine speed and the number of engine cylinders and which is of a fixed duty cycle or ON/OFF ratio in terms of distributor angle or percentage of the ignition cycle. 
     Thus, when a metallic vane 33 is interposed in the air gap 37 between the permanent magnet 38 and the Hall sensor Device 36, the conductivity of the latter is low and the voltage at terminal A is high. Control unit 24 then conducts charging current from the source 16 for the ignition coil 20. Conversely, when the Hall Device is exposed to the magnet field, the conductivity of the sensor is high, the voltage level at terminal A is low and the ignition coil is blocked and is not drawing current from the charging source. 
     The electronic control unit 24 is a five terminal case grounded structure, three of whose terminals, labelled P+, A and G, are adapted to be connected to the corresponding terminals of the Hall Effect Device as shown, with a fourth terminal J2 of the control unit adapted to be connected to the B+ or J2 terminal on the load side of the vehicle ignition switch 28. A fifth or output terminal, labelled O, of the electronic control unit is adapted to be connected to the negative side (-) of the ignition coil 20, whose positive (+) terminal is shown connected to the run-start contact R, S of the vehicle ignition switch 28. Ignition coil 20 is a standard coil of the conventional low secondary to primary turns ratio-type, typically 100:1, as customarily employed in the ignition systems of internal combustion engines for street or passenger car automotive vehicles. 
     Internally, the electronic control unit 24 comprises an input stage 40, the programmed dwell or pulse delay timer stage 50, an automatic shut-down timer stage 60, a driver amplifier stage 70, an inverter stage 80, and a power output stage 90, all of which employ switching type semiconductor devices. Devices 42, 72, 82 and 92 are shown as NPN silicon transistors of which the device 92 is shown as a Darlington pair, while the devices 52 and 62 are programmable unijunction transistors, also called complementary SCR devices. Several additional solid state semiconductor devices in the form of silicon-diodes D1-D6 and a Zener diode DZ are employed in the circuit for circuit protection, temperature compensation, filtering and circuit isolation purposes. 
     Input transistor 42 of the input stage 40 is adapted to be connected across the B+ or supply voltage source 16 in a circuit from the J2 terminal connected through a current limiting resistor 41 to the collector electrode of transistor 42 whose emitter electrode is connected to case ground. Base current drive is supplied to transistor 42 through a voltage divider comprised of resistors 46 and 47 of which resistor 46 is connected to the J2 terminal and resistor 47 is connected to the base electrode of transistor 42 through a temperature compensation diode D2. The divider junction J is connected to the input terminal A of the electronic control unit 24 for connection to the corresponding output terminal of the Hall Effect Device 36. 
     The programmed dwell timer circuit 50 includes a timing capacitor 56, which may have a value of, say, 0.22 mfd, for example, and is connected in a charging circuit to be charged from B+ through resistor 41, diode D3 and resistor 51 when transistor 42 is non-conductive, the resistors 41 and 51 having assumed values of, say, 1000 ohms and 33,000 ohms, respectively. When transistor 42 is conductive, however, diode D3 is back-biased, and timing capacitor 56 is then connected in a discharge timing circuit through resistor 57, which may have an assumed value of, say, 82,000 ohms and is connected at its ungrounded side to the gate electrode of PUT device 52. At its anode electrode, PUT 52 is connected to the junction J of the voltage divider 46, 47 and its cathode electrode is connected through resistor 58 to case ground, so that it will latch into conduction when the voltage applied to its gate control electrode from the aforesaid capacitor discharging circuit falls one diode drop (0.6v) below the voltage at the divider junction. With assumed values of 4,700 ohms and 1,000 ohms for the resistors 46 and 47 and a 12.0 volt B+ source, the voltage level at the voltage divider junction J will be slightly above 3 volts, for example, considering the effect of the diode drop of the base emitter junction of transistor 42. 
     The automatic shut-down timer circuit 60 is similarly constituted to the programmed dwell timer circuit 60, except that the charging circuit and the discharging circuit for the timing capacitor 66 employed therein will have a much faster charging rate and a much slower discharging rate, respectively than the corresponding capacitor charging and discharging circuits of the programmed dwell timer circuit. Capacitor 66, which may have a capacitance value of 1.5 mfd for example, is connected to be rapidly charged from B+ through resistor 41 and isolation diode D4 and to discharge through resistor 67, which may have a resistance value of 1 megohm and is connected between the gate electrode of PUT device 62 and ground. PUT 62 is grounded at its cathode electrode with its anode connected to the junction J of the voltage divider 46, 47, the potential level of which thus programs the operation of the PUT 62 in relation to the potential applied to the gate electrode from the capacitor discharge timing circuit of the automatic shut-down timer 60. 
     Transistor 72 of the driver stage amplifier 70 has its base input electrode directly connected to the junction between resistor 58 and the cathode electrode of PUT 52. The collector electrode of transistor 72 is connected directly to the base input electrode of transistor 82 of the inverter stage amplifier 80 and also to the B+ supply terminal through a current limiting resistor 71, which provides base current drive to the transistor 82 when transistor 72 is non-conductive. The collector electrode of the inverter stage transistor 82 is connected through a current limiting resistor 81 to the B+ supply line and through an isolation diode D5 whose cathode electrode is connected to resistor 86 and to the base input electrode of the Darlington output switching transistor 92. The emitter electrode of transistor 92 is connected to case ground and its common collector electrode is connected to output terminal O for connection to the ignition coil 16. 
     The Darlington output transistor 92 is provided with several circuit protection networks, including a transient feedback circuit comprised of a capacitor 95 and a resistor 97, which are serially connected between its collector output and base input electrodes. This circuit suppresses leakage reactance effect of the ignition coil and eliminates the need for the large capacitor which otherwise would be connected across the output electrode to the output transistor of the breaker points as customarily employed in prior forms of ignition systems. 
     Another circuit, including resistors 100 and 102 and a Zener diode, Dz, is provided to protect the output switching transistor 92 from the damaging effects of the high induced voltages that may appear at the collector of the output transistor under no-load ignition coil conditions when the output transistor is not conducting. Resistors 100 and 102 are connected as a voltage divider in a circuit between the collector electrode of the output switching transistor 92 and to the B+ supply bus, while the Zener diode Dz is connected as shown between the divider junction and the base of transistor 92. Should the voltage at the collector of transistor 92 rise above the voltage rating of the zener diode, as it may during no-load or unconnected ignition coil secondary conditions, the Zener breaks down to conduct current into the base of transistor 92 to turn it on slightly and limit the rise of the voltage at its collector output. 
     Further protection devices are provided in the input circuit including a diode D1, which is shown connected between the J2 terminal and case ground and provides circuit protection for negative going or reverse transients appearing on the supply conductors. Protection to the Hall Device from the otherwise damaging effects of positive-going voltage transients appearing on the B+ supply line is provided by an attenuation filter 110 comprised of a resistor 112, which is internally connected between the J2 terminal and the P+ terminals of the electronic control unit, and a capacitor 114, which is connected across the P+ terminal and case ground. Capacitor 116 and diode D6, which are connected between the input terminal A and case ground of the control unit 24, provide RF suppression to protect the base of the input transistor 42. 
     The operation of the ignition controller of FIG. 1 with the programmed dwell timer circuit may be understood from FIGS. 2 and 3. Assuming that at time t1, an aperture or cut-out portion 34 of the shutter wheel 32 has rotated into the air gap 37 and is positioned between magnet 38 and the Hall Effect Device 36, the conductivity of the latter will be high and its impedance or output will be low, as shown in FIG. 2A. Input transistor 42 will be deprived of base current and rendered non-conductive. The voltage at the collector electrode of transistor 42 will be high, whereby capacitor 56 will commence to charge towards B+ through resistor 41, isolation diode D3 and resistor 51 through capacitor 56 to ground. With the assumed values of resistance and capacitance for resistors 41 and 51 and capacitor 56, the charging circuit will have a charging RC time constant of approximately 7 milliseconds. 
     As the anode of the PUT device 52 is being held at or near ground potential by the conducting Hall Device 36, the PUT 52 will be off and render the driver stage transistor 72 non-conducting. Inverter stage transistor 82 will therefore be conducting and output transistor 92 will be non-conductive to block current draw for the ignition coil. 
     At time t2, a metallic vane portion 33 of the shutter wheel 32 will have rotated into position in the air gap 37 between the magnet 38 and the Hall Device 36, which will therefor switch to its low conductivity or high impedance characteristic to permit base current to be supplied to the input transistor 42. The latter will therefore turn on, dropping the voltage at its collector to substantially ground potential. Isolation diode D3 will then become back-biased to permit timing capacitor 56 to discharge through resistor 57, which provides a discharge time constant with capacitor 56 of approximately 18 milliseconds. 
     When the voltage on the gate control electrode of the programmed uni-junction transistor device 52 has dropped or decayed to a level one diode voltage drop below the programmed voltage level, say, (3.0 volts) at its anode electrode at a time depicted as t3 in FIG. 2, the PUT latches into conduction to supply base current drive to driver amplifier transistor 72. This action turns off the transistor 82 of the inverter stage 80 and turns on the output transistor 92 to conduct current through the primary of the ignition coil 21 and commence the dwell or coil charging period, d, of the controller, as shown in FIG. 2I(c). 
     The dwell period, d, continues until time t4 when the trailing edge of a vane 33 of the shutter wheel 32 passes from between the magnet 38 and the Hall Device 36 to expose the Hall Device 36 to expose the Hall Device through a window 34 to the magnet field, thereby increasing its conductivity and again dropping the voltage level at terminal A as shown in FIG. 2A. Input transistor 42, PUT 52 and driver stage transistor 72 then switch OFF, inverter stage transistor 82 switches ON, and the output transistor 92 switches OFF. Timing capacitor 56 then starts to charge again through resistors 41 and 51 to B+. 
     It will be seen that the programmed dwell time circuit functions to delay the turn-on of the output transistor 92 and the energization of the ignition coil from the turn on of the input transistor 42 by the shutter wheel and that the delay period, Δ, which extends from time t2 to t3, is a function of engine speed. The charge level attained on the timing capacitor 56 during its charging interval from time t1 to t2 is a function of engine speed, and the higher the engine speed, the less time the capacitor will have to charge whereby the charge level will decrease with increasing engine speed. 
     It is apparent that at some engine speed the charge attained on the capacitor C56 when the shutter switches input transistor ON again, will only be 2.4 volts or one diode drop below the programmed voltage at the anode of PUT 52 so that PUT 52 will switch directly ON and OFF with the shutter at this speed. The controller switches ON and OFF with the shutter wheel, and the system reverts to a constant duty cycle system. With reference to FIGS. 3A-F, assuming that the engine speed is 5000 rpm, the delay, Δ, at that speed will be zero to provide a dwell period for the charging of the coil of 3.2 ms, as indicated in FIG. 3B. At 2,500 rpm, both the dwell and the delay will be 3.2 milliseconds as shown at 3 C &amp; D, and at 1,250 rpm, the delay, Δ will be 9.6 milliseconds as shown in FIGS. 3E and F in order to provide a substantially constant period of energization of the ignition coil of 3.2 milliseconds for the aforesaid 6 vane 48°/60° or 80% duty cycle shutter used with a six cylinder engine. 
     With reference to FIG. 4 it will be seen that the delay, Δ, varies as an inverse function of engine speed, while the duty cycle of the controller increases with engine speed up to a high engine speed of say, 5,000 rpm after which the duty cycle of the controller is determined solely by the physical geometric characteristics of the shutter wheel and reverts to a constant duty cycle or ON/OFF time period. The actual dwell time d as a percentage of the ignition cycle remains constant over the substantially entire range of engine speed until an engine speed of 5,000 rpm at which speed the actual dwell time decreases accordingly. 
     By way of comparison, it will be noted that the timing capacitor 66 of the automatic shut-down timer circuit 60 has a much faster charging period than the charging circuit for the capacitor 56 of the programmed dwell circuit 50 and becomes fully charged during the interval t1 to t2 when the window 34 of the shutter wheel 32 is positioned in the air gap between the permanent magnet 38 and the Hall Effect Device 36. Also as shown at (C2) in FIG. 2, the discharge period of the timing capacitor 66 of the automatic shut-down circuit is much slower than that of the discharge timing circuit of the programmed dwell circuit 60. In the illustrated embodiment of the circuit, the discharge time constant of the shut-down circuit is in the order of 1.5 seconds as compared to the 18 millisecond discharge time constant of the programmed dwell circuit. Consequently, the programmed uni-junction transistor or PUT device 62 of the automatic shut-down circuit 60 does not turn on during normal operation of the controller circuit while, or so long as the shutter wheel is rotating. 
     In the event the engine should stop with the shutter wheel 32 positioned with a vane 33 in the air gap 37 of the Hall Device, the input transistor 42 will be left in a conducting condition and output transistor 92 will turn ON after the delay period afforded by or the RC discharge timing circuit of the programmed dwell circuit has timed out. Because of the considerably longer discharge time period of the RC discharge timing circuit of the automatic shut-down time circuit, the capacitor 66 of the latter circuit continues to discharge until the potential at the gate control electrode of PUT 62 falls one diode voltage drop below the programmed voltage of its anode electrode. At such time, PUT 62 is actuated to drop the voltage at the divider junction J at or near ground and turn off transistor 42 as well as PUT 52 of the programmed dwell circuit. This action results in turning OFF the driver stage transistor 72, turning on the inverter stage transistor 82 and cutting off the output switching transistor 92, thereby turning OFF the energization of the ignition coil. The PUT device 52 stays on even though the shutter vane is still in the air gap 37 between the magnet and the Hall device until such time as the engine is subsequently cranked and the shutter vane is moved out of the air gap, at which point in time and space the PUT 52 is quenched and turned off, as shown and more fully discussed in related copending application U.S. Ser. No. 743,021, filed of even date and of common ownership herewith, U.S. Pat. No. 4,106,460.