Ignition device for internal combustion engine

BACKGROUND OF THE INVENTION

This invention relates to an ignition device for use with an internal combustion engine equipped on a motor 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 for converting 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 from the rectifier and a switch connected in a discharge circuit for the capacitor and operative in its closed position to discharge the charge on the capacitor into the associated ignition coil to produce an ignition voltage across the latter.

It has been commonly practiced that a source of electrical power for the ignition device referred to, that is, the source of direct current as above described is additionally used as a source of electrical power for an electric device for starting an 25 internal combustion engine which is ignited by the ignition device. In most of motor vehicles the source of direct current is composed of a storage battery having 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 30 required to flow in operation. This flow of high load current through the motor causes a great decrease in voltage across the source of 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 35 the associated engine or after it has been started and it may decrease down to a minimum possible magnitude of approximately 67 percent of the rating voltage particularly when an electric device for starting the associated engine has a very high current flowing therethrough as in starting the engine in a cold district. Although the voltage across 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 realized in view 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 under voltage decrease state.

An ignition device for an internal combustion engine meeting such requirements is described and claimed in U.S. Pat. No. 3,352,295 issued Nov. 14, 1967 to Takas Miki and assigned 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 combustion engines 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 voltage, usually of from 300 to 600 volts from the capacitor. As a result, an electric arc is formed thereacross upon the opening thereof leading to a disadvantage that the contacts . __________________________________ are brought into unusable state within a short period of time. the thyristor, the diodes being so poled that a voltage of either

In order to eliminate that disadvantage, it is considered to 65 P^0,arity is prevented from causing a short-circuiting current to dispose a thyristor in the discharge circuit for the capacitor. flow through that portion disposed between the intermediate Because of no electric arc appearing in thyristors the use of a and end terminals of the primary transformer winding, thyristor sufficiently high in dielectric strength makes it possible to form an ignition device longer in useful life than the mechanical contacts as above described. If a set of mechanical 70 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 . 2 ' 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 transformer provided on its input or primary winding with an intermediate terminal separated from its end terminals 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 through the intermediate terminal upon starting the engine and through one of the end terminals after the engine has been ¹ started.

On the other hand, the circuit for gating the thyristor is required to have an electrical energy supplied by the associated 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 wastefully consuming 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 a terminal 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 OF 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 to an intermediate terminal and an end terminal of an input 60 ^tran^f^ormer winding in the inverter respectively, and a pair of semiconductor diodes connected to both the conductors respectively to cause an electrical energy to be selectively supplied from the conductors therethrough to a circuit for gating

- · . **. · *----- —Γ νιι^ιιιν as above described with the result that the occurrence of an 75 of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawing in which a single FIG. is a schematic circuit diagram of an ignition device for an internal combustion engine constructed in accordance with the principles fifths inuontinn

3,563,221

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 j 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 16 and 18 connected in series circuit relationship, a single secondary or output winding 20 and a pair of ter- j q tiary 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 c and the other end terminal b common to the 15 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 20 one terminal of the tertiary winding 22 and an emitter electrode connected directly to the ground such a vehicle’s 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 25 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. 30 Another resistor 36 is connected across the collector and base electrodes of the transistor 28 for the purpose of first flowing a forward base cunent through the transistor 28 upon starting the inverter 12.

A pair of conductors 38 and 40 are connected at one end to ^5 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 10 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. 45

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 jq 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 terminals connected to both ends of the winding 20. The full wave rectifier 44 has 55 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 ¢0 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. 65 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 70

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 75 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 cunent 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.

3,563 · ·. ⁵

As previously described, the voltage across the source 10 is different in magnitude in the normal operation of the engine from the operation of starting engine resulting in a difference between ignition voltages available in both the operations. The invention contemplates to compensate for this difference 5 between ignition voltages.

According to the principles of the invention, the movable arm M of the transfer switch 42 is in engagement with the contact A thereof during the normal operation of the engine. Then the source 10 is connected to the common terminal b of 10 the primary transformer windings 16 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 ofthe switch 42, 15 the conductor 38 and the diode 68.

Under these circumstances, an output voltage V„ from the secondary or output winding 20 of the transformer 14 is expressed by (1) where:

N₂ = number of turns of secondary winding 20;

^Nai> = number of turns between terminals a and b of primary 25 winding 16, assuming that N_ab equals the number of turns Ni* between terminals b and c of primary winding 18; and

V_B — voltage across source 10.

Upon starting the engine the movable arm M is in engagement with the contact B of the switch 42 as previously 30 described. The source 10 is electrically coupled to the intermediate terminal d of the primary winding 16 of the transformer 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 35 secondary transformer winding 20 is expressed by

TZ z_ TVj tz z Fo — V“VB

A.b—n(2) or tz n Nz _Tr , ° ATbe+n ^B(2') ⁴⁵

V'„ = output voltage due to primary winding portion between terminals a and d;

V„ = output voltage due to primary winding portion between terminals d and c; and n = number of turns between terminals d and b of primary ⁵⁰winding 16. It is also assumed that the primary windings 16 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 terminals d and b of the $$ primary winding 16 can be selected so as to render both the output voltages K'_o and F_o approximately equal to each other in order to compensate for a difference between output voltages in the normal and starting operations of the engine. 60

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 ⁶⁵the 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 ofthe primary winding 16 resulting in a decrease in output voltage from the seconda- ⁷⁰ry winding 20 of the transformer 14. The purpose of the diodes 68 and 70 is to prevent this flow of short-circuiting cur,221 rent.