US 3563221 A
Description (OCR text may contain errors)
United States Patent Inventor Yasuo Tada Himeji, Japan Appl. No. 799,260 Filed Feb. 14, 1969 Patented Feb. 16, 1971 Assignee Mitsubishi Denki Kabushiki Kaisha, Tokyo, Japan Priority Feb. 19, 1968 Japan 43/ l 2053 IGNITION DEVICE FOR INTERNAL COMBUSTION ENGINE 4 Claims, 1 Drawing Fig.
11.8. CI 123/148 Int. Cl. F02p 3/06 Field of Search 123/148 (E), 179 (B); 315/209, 209 (CD), 214
 References Cited UNITED STATES PATENTS 3,131,327 4/1964 Quinn 315/214X 3,251,351 5/1966 Bowers... 123/148 3,352,295 11/1967 Miki 123/179B 3,448,732 6/1969 Weiss 123/148E Primary Examiner- Laurence M. Goodridge Attorneys-Robert E. Burns and Emmanuel J. Lobato ABSTRACT: A low DC voltage boosted by an inverter and a rectifier charges a capacitor a charge on which is, in turn, discharged into an ignition coil under control of a thyristor. Upon starting the engine, the DC voltage is applied to an intermediate terminal of a primary transformer winding in the inverter. Diodes are connected in a circuit for gating the thyristor to prevent the circuit from partly short-circuiting the primary winding through the intermediate terminal.
PATENIED FEB 1 6 I97! HHHHHHHI IGNITION DEVICE FOR INTERNAL COMBUSTION ENGINE BACKGROUND or THE INVENTION This invention relates to'an ignition device" for use with an internal combustion engine equippedon a notor vehicle or the like and more particularly to improvements in such a. device of capacitor discharge type.
The capacitor discharge type of ignition devices for use with internal combustion engines comprises generally a source of direct current, an inverter forcohverting a power of direct current provided by the source to a power of alternating current and increasing the voltage of the converted power, a rectifier for rectifying the power of alternating current from the inverter to provide a power of direct current, a capacitor charged with the power of direct current fromthe rectifier and a switch connected in a discharge circuit for the capacitor and operative in itsclosed position to discharge the charge on the capacitor into the associatedignition 'coil to produce an ignition voltage across the latter.
It has been commonly practiced that a source of electrical power for the ignitiondevice referred to, that is, the source of direct current as above described is additionally used as a source of electricalpower for an electric device for starting an internal combustion engine which ignited by the ignition device. In most of motor vehiclesfthe source of direct current electric arc across the contacts is scarcely called in question while insuring a long useful life of the resulting ignition device.
What is now called in question in the relationship between a circuit configuration for compensating for a decrease in direct current voltage applied to the associated inverter upon starting the engine and a circuit for gating the thyristor. According to Miki patent as above cited, an, inverter includes a trans former provided on its input or primary winding with an intermediate terminal separated from its end .tenninals to present a higher turn ratio associated with the intermediate terminal to the output winding of the transformer. Then the primary winding have selectively supplied thereto an electrical energy is composed of a storage batteryhaving a rating voltage of either 12 or 24 volts and the starting electric device is a starting electric motor through which a .high load current is required to flow in operation. This flow of high load current through the motor causes a great decrease in voltage across the'sourceof direct current.-For'example, with a storage battery having a rating voltage of 12 volts, the voltage thereacross will range from approximately 8 to 12 volts prior to starting the associated engine or after ithas been started and it may I decrease down to a minimum possible magnitude of approxi mately 67 percentof the rating voltage particularly when an electric device forstarting theassociated engine has a very high currentflowing therethrough as injstarting the engine in a cold districtQAlthough the voltagelacross the source for the ignition device is ideally maintained always constant this leads to the necessity of providing separate sources of electrical power for the ignition and starting devices. However this measure is difficult to be realizedinvi'ew-of the standpoint of economy. Therefore it is highly desirable to provide an ignition device including means; for compensating for any decrease in voltage applied thereto, upon starting the associated engine whereby the engine is. ignited with a sufficient ignition energy even undervoltage' decrease state.
An ignition device for an internal combustion engine rneeting such requirements is described'and claimed in U.S. Pat. No. 3,352,295 issued Nov. 14,1967 to Takas Miki and as signed to the same assignee as the present application. Like the present invention the cited patent discloses in FIGS. 1 and 2 ignition devices for internal combustionengines including a capacitor. The capacitor has its discharge circuit adapted to be open. and closed directly by a set of mechanical contacts.
; The contacts have then directly applied thereacross a high through the intermediate terminal upon starting the engine and through one of the end terminals'after the engine has been started.
On the other hand, the circuit for gating the thyristor is required to have an electrical energy supplied by the as sociated source of direct current during and after the operation of starting the engine while such: supply of the electrical energy to the gating circuit must be terminated during the suspension of operation of the engine for the purpose of preventing the source from wastefullyconsuming the electrical energy. To this end, one conductor can be connected to the source of direct current through a switch adapted to be closed upon starting the engine thereby to supply an electrical energy to. the input winding of the said transformer through the intermediate terminal while the other conductor can be connected to the source through another switch adapted to be closed after the completion of the operation of starting the engine thereby to supply an electrical energy to the input transformer winding through the one'end terminal with both the conductors connected to aterminal on the source side of the gating circuit. In this case it is to be noted that means for connecting both the conductors to the said terminal of the gating circuit be prevented from short-circuiting that portion disposed between the intermediate and end terminal of the input transformer winding. This is because if such short-circuiting occurs then the magnetic core of the transformer is impeded from changing in magnetic flux resulting in a zero output from the transformer and therefore from the inverter.
SUMMARY-0F THE-INVENTION Accordingly it is an object of the invention to provide a new and improved ignition device for use with an internal combustion engine having a long useful life and including means for compensating-for a decrease in voltage applied to the device upon starting the engine and free from any short-circuiting fault while ensuring that'the engine is ignited during the operation thereof without any waste of electrical energy during the suspension of operation of the engine.
With this object in view, the invention resides in an ignition device of capacitor discharge type for use with an internal combustion engine including an ignition capacitor charged with a rectified output from an inverter, and a thyristor connected in a circuit for discharging the capacitor and a pair of conductors for supplying electrical energies of direct current i to an intermediate terminal and an end terminal of an input transformer winding in the inverter respectively, and a pair of the thyristor, the diodes being so poled that a voltage of either dispose a thyristor in the discharge circuit for the capacitor.
Because of no electric arc appearing'in thyristors the use of a thyristor sufficiently high in dielectric'strength makes it possipolarity is prevented from causinga short-circuiting current to flow through that portion disposed between the intermediate v and end terminals of the primary transformer winding.
ble to form an ignition device longer in useful life than the mechanical contacts as above described. If a set of mechanical contacts such as above described is connected in a circuit for gating the particular thyristor, the contacts have only applied thereacross a voltage decreased by a-factor of several. tens as compared with the voltage directly provided by .the capacitor as above describedwith the result that the occurrence of an BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, it is seen that an arrangement disclosed herein comprises a source of direct current 10 such as a 12 v. storage battery equipped on a motor vehicle and an inverter generally designated by the reference numeral 12. The inverter 12 comprises transformer generally designated by the reference numeral 14 including a pair of primary or input windings l6 and 18 connected in series circuit relationship, a single secondary or output winding 20 and a pair of tertiary windings 22 and 24 with all the windings inductively disposed on a saturable magnetic core 26. The primary winding 16 includes a pair of end terminals a and b and an intermediate terminal d while the primary winding 18 includes one end terminal and the other end terminal b common to the primary winding 16. The conventional dot is used to indicate the polarity of each of the primary and tertiary windings.
A transistor 28 shown as being of the NPN type includes a collector electrode connected directly to the end terminal a of the primary winding 16, a base electrode connected directly to one terminal of the tertiary winding 22 and an emitter electrode connected directly to the ground such a vehicles chassis (not shown). Another transistor 30 shown as being also of NPN type includes similarly a collector electrode connected directly to the end terminal c of the primary winding 18, a base electrode connected directly to one terminal of the tertiary winding 24 and an emitter electrode connected directly to the ground. The emitter electrodes of both the transistors 28 and 30 are connected to the other terminals of the tertiary windings 22 and 24 through resistors 32 and 34 respectively. v
Another resistor 36 is connected across the collector and base electrodes of the transistor 28 for the purpose of first flowing a forward base current through the transistor 28 upon starting the inverter 12. I
A pair of conductors 38 and 40 are connected at one end to the end and intermediate terminals b and d of the primary winding 16 and at the other ends to a pair of stationary contacts A and B of a transfer switch 42 including a movable arm M connected to one terminal, in this case, the positive terminal of the source having the negative terminal connected to the ground. Thus it will be appreciated that the inverter 12 is operative to convert a direct current voltage supplied by the source 10 to an alternating current voltage and increase the latter voltage.
While the inverter 12 is shown as including the primary windings, the tertiary windings and the transistors in pairs to form a push-pull configuration it is to be understood that the inverter may be not necessarily of the push-pull type, if desired. In the latter case, the primary winding 18, the tertiary winding 24 and the transistor 30 are omitted.
The secondary or output winding 20 of the transformer 12 has connected thereacross a single phase full wave rectifier 44 having a pair of alternating current input tenninals connected to both ends of the winding 20. The full wave rectifier 44 has one direct current output terminal connected to the ground and the other direct current output terminal connected to the ground through an ignition capacitor 46.
An ignition coil of auto transformer type generally designated by the reference numeral 48 includes a primary winding 50 and a secondary winding 52 with the junction of both the windings connected to the junction of the rectifier 44 and the capacitor 46. The secondary winding 52 has the other end connected to an ignition plug (not shown) and the primary winding 50 has the other end connected to a thyristor 54. The thyristor 54 includes an anode electrode connected to the other end of the primary ignition winding 50, a cathode electrode connected to the ground and a gate electrode 54. The thyristor 54 along with the primary ignition winding 50 serially connected thereto forms a discharge circuit for the capacitor 46.
In order to gate the thyristor 54, a gating circuit enclosed with a dashed block 56 is operatively associated with the thyristor. The gating circuit 56 includes a resistor 58 connecting the gate electrode of the thyristor 54 to ground, a gating capacitor 60 connected to the junction of that cathode electrode 'and the resistor 58, a resistor 62 connected to the capacitor 60 and a contact breaker 64 connected between the junction of the capacitor and resistor 60 and 62 respectively and the ground. The contact breaker 64 is arranged to be open and closed by a cam rotating in synchronization with the rotation of the associated engine in the well-known manner. The cam, and engine are well known in the art and therefore they are not illustrated. The breaker 64 is put in its open position at each ignition time of the engine.
The resistor 62 is connected to an input terminal 56A to the gating circuit 56 which is, in turn, connected to the conductors 38 and 40 through the respective semiconductor diodes 68 and 70 each poled so as to permit a current to flow from the associated conductor 38 or 40 to the gating circuit 56 therethrough.
The transfer switch 42 as previously described has its movable arm M adapted to engage the contact B upon starting the engine and to engage the contact A after the completion of the starting operation and when the engine is put in operation. However it is noted that when the engine is out of operation the movable arm M assumes its neutral position as illustrated in the drawing. This is, none of the contacts A and B are in contact with the movable arm M.
In order to start the engine, a starting electric motor is connected to the source 10 through an on-off switch adapted to be closed when the movable arm M engages the contact B, although the motor and the on-off switch are not illustrated.
The arrangement thus far described is operated as follows:
The inverter 12 is a Royer circuit well known in the art and its operation will be briefly described. Upon applying a DC voltage from the source 10 to the inverter 12 through either one of the contacts A and B of the switch 42 as the case may be, the transistor 28 is first fired to permit a base current to flow therethrough. Then the transistor 28 is increasingly conducting through the feedback action of the tertiary winding 22 until the magnetic core 26 of the transformer 14 is driven to saturation. When the saturation of the magnetic core 26 has reached a point of contraflexure, the primary winding 18 has a low voltage induced in the reverse direction thereacross whereupon the transistor 30 is now fired, while the transistor 28 becomes nonconducting. Thereafter the process as above described is repeated with the conducting transistor 30. In this way the transistors 28 and 30 are alternately conducting to produce across the secondary or output winding 20 an output of square waveform having a pulse recurrence frequency corresponding to the voltage across the source 10 and increased in magnitude or voltage by the particular turn ratio between the energized portion of the primary winding and the secondary winding. The output from the transformer 14 and therefore the inverter 12 is rectified by the full wave rectifier 44 and charges the ignition capacitor 46.
Each time the thyristor 54 is conducting as will be described hereinafter, the charge on the capacitor 44 is discharged through the discharge circuit comprising the primary ignition winding 50 and the now conducting thyristor 54 whereupon a high voltage is induced across the secondary ignition winding 52 to ignite the engine in the well-known manner.
Under these circumstances, the thyristor 54 is controlled by the gating circuit 56. More specifically, with the contact breaker 64 closed; a voltage across the gate and cathode electrodes of the thyristor 54 is of zero magnitude maintaining it nonconducting. Then if the contact breaker 64 is open, a charging current flows from the source 10 into the capacitor 60 through the switch 42 and the conductor 38 or 40 as the case may be. This charging current also flows through the resistor 58 to provide a voltage drop thereacross sufficient to gate the thyristor 54 whereupon the charge on the capacitor 44 is discharged as above described, when discharged the capacitor 46 cooperates with the primary ignition winding 50 to generate an oscillatory voltage at the instant this oscillatory voltage is reversely applied to the anode and cathode electrodes of the thyristor 54 the latter is brought into its open state ready for the succeeding ignition operation.
Then the source is connected to the common terminal b of 10 the primary transformer windings l6 and 18 through the movable arm and contact M and A respectively of the switch 42 and the conductor 38 while at the same time, it is connected to the input terminal 56A to the gating circuit 56 through the movable arm M and contact A of the switch 42, the conductor 38 and the diode 68.
Under these circumstances, an output voltage V, from the secondary or output winding of the transformer 14 is expressed by Nab ' former 14 through the conductor 40 and also to the input terminal 56A to the gating circuit 56 through the diode 70.
Under these circumstances, an output voltage from the secondary transformer winding 20 is expressed by N; I I Na-n (2) N. II I ari-" (2') V',, output voltage due to primary winding portion between terminals 0 and d;
V output voltage due to primary winding portion between terminals d and c; and V n number of turns between terminals d and b of primary winding 16. it is also assumed that the primary windings l6 and 18 are equal in the number of turns to each other.
From the above equations (2) and (2') it is seen that V,
is higher than V However it will be appreciated that the number of turns n between the terminalsd and b of the primary winding 16 can be selected so as to render both the output voltages V, and V", approximately equal to each other in order to compensate for a difference between output voltages in the normal and starting operations of the engine.
In order to discuss the effect of the diodes 68 and 70, it is now assumed that the conductors 38 and 40 have been connected directly to the input terminal 56A to the gating circuit 56 with the diodes 68 and 70 omitted. Under the assumed conditions, that portion disposed between the terminals b and d of 5 the primary transformer winding 16 is short-circuited by the conductors 38 and 40. Thus in the operation of the inverter 12, a short-circuiting current flows through that portion disposed between the terminals b and d of the primary winding 16 resulting in a decrease in output voltage from the secondary winding 20 of the transformer 14. The purpose of the diodes 68 and 70 is to prevent this flow of short-circuiting current.
1. An ignition device for use with an internal combustion engine, comprising, in combination:
1. a source of direct current;
2. inverter means including a transformer comprising a saturable magnetic core, an input winding, an output winding and a feedback winding, all said windings being inductively disposed around said magnetic core and a transistor connected to both said input winding and said feedback winding;
3. said primary winding having an end terminal and an intermediate terminal presenting to said output winding a turn ratio higher than does said end terminal;
4. a first conductor connected to said end terminal of said primary transformer winding and capable of being energized by said source;
. a second conductor connected to said intermediate terminal of said primary transformer winding and capable of being energized by said source;
6. a transfer switch connected between said source and said first and second conductors such that, the same connects said source to said second conductor upon starting the engine and to said first conductor after the engine has been started and when it is in operation;
7. a rectifier for rectifying the output of the output winding of said transformer and an ignition capacitor charged with the rectified output of the output winding of said transfonner of said inverter means;
. an ignition coil including a primary winding and a secondary winding inductively coupled to each other, said pri mary winding having one end connected to said ignition capacitor;
9. a thyristor for controlling said ignition capacitor and operative in its closed state to permit said ignition capacitor to be discharged into said primary ignition coil winding to produce an ignition voltage across said secondary coil ignition winding, said thyristor having a control terminal;
.40 10. a gating circuit controlling said thyristor and having an input terminal, means operable in synchronism with the rotation of the engine to produce a gating signal and an output terminal connected with the control terminal of said thyristor; and
l l. a pair of semiconductor diodes having input and output tenninals, means connecting the output terminals of both of said diodes to the input terminal of said gating circuit, means connecting the input tenninal of one of said diodes with said first conductor, and means connecting the input terminal of the other of said diodes with said second conductor.
2. An ignition device as claimed in claim 1, wherein said transfonner of said inverter means: includes additionally another of said inverter means includes additionally another input winding and a separate feedback winding inductively disposed around said magnetic core, and wherein another transistor is connected to both said another input winding and said separate feedback winding, said transistors being alternately turned on and off.
3. An ignition device as claimed in claim 1, wherein said primary ignition winding is serially connected to said thyristor, the series arrangement of said primary ignition winding and thyristor being connected in parallel circuit relationship to said ignition capacitor.
4. An ignition device as claimed in claim 1, wherein said gating circuit includes a set of contacts: capable of being open and closed in synchronization with the rotation of the engine, a gating capacitor charged by said source upon the opening of said set of contacts, and a resistor connected to said gating capacitor to be traversed by a charging current for the latter to produce a voltage'applied as a gating signal to said thyristor.