HIGH-ENERGY IGNITION APPARATUS

Abstract: A high-energy ignition apparatus has an ignition coil which generates from an output of an ignition circuit a high voltage for causing an electrical discharge between elec­ trodes of an ignition plug, and a DC-DC converter which generates a voltage sufficiently high for maintaining the discharge occurring at the ignition plug. The output of the DC-DC converter is superposed on the discharge current induced by the ignition coil. Further, the ignition coil and a transformer for the DC-DC converter are integrally molded by means of a molding resin, thereby improving the electri­ cal insulating properties and allowing the apparatus to be easily mounted on a vehicle.

Description: Technical Field The present invention relates to an ignition device for internal combustion engines and, more particularly, to a high-energy ignition device in which the output from a DC-DC converter is superposed on the discharge current through a sparking plug such as to attain a long duration of the discharge in the sparking plug. Background Art An ignition device is a device for allowing a high voltage discharge between two electrodes of a sparking plug such as to ignite a mixture in the engine, thereby triggering an explosive combustion. In order to attain a higher fuel economy and higher output power, it is necesssary to effect stable and efficient combustion of the mixture. A high voltage on the order of 10 to 20 KV is required for breaking the insulation across the electrode gap in the sparking plug. However, once the insulation is broken, the discharge can be maintained with only a medium-high voltage of 1 to 2 KV. In view of this fact, a proposal has been made in which a high voltage pulse generated by an ignition coil is applied at the beginning to break the insulation in the sparking plug and, after the breakage of the insulation, a medium-high voltage generated by a DC-DC converter is superposed on the discharge current, thereby to maintain the discharge for a longer time. This ignition device, however, requires complicated wiring for connecting three constituent elements: namely an IC igniter, ignition coil and a DC-DC converter. It is quite troublesome to find sufficient room for accommodating these components and wiring in the restricted space of the engine compartment. FR-A-2 360 198 shows an ignition device including an interrupter, an ignition coil and a DC-DC-converter consisting of a transformer, an oscillator and a rectifier for producing a DC-voltage to be superposed on the pulse voltage provided by the ignition coil. But in contrast to the present invention this document does not disclose the features of embedding specific lines and circuit parts, respectively, in the forming resin within a casing for ensuring sufficiently strong insulation and for reducing the overall size of the ignition device. FR-A-2 432 096 describes an ignition device wherein a mechanical interrupter is replaced by a Hall-transducer. However, this publication does not relate to an ignition device with a supplementary DC-DC converter. From US-A 4 393 850 a high-energy ignition device for an engine is known, having a pickup, an ignition circuit, an igniter coil and a DC-DC converter. None of these elements are enclosed within a forming resin so that a sufficiently strong insulation cannot always be guaranteed. Embedding certain ones of said elements in a forming resin could further lead to a problem of overheating the device, as a good heat transport, for example away from the ignition coil, cannot be provided if it is embedded in forming resin without provision of further cooling means. It is an object of the present invention to provide a high-energy ignition device which permits simplification of the wiring and reduced size. This object is achieved by the present invention by providing a high-energy device which is characterised by the features recited in claim 1. JP-U- 55-143 677 describes an ignition device having all components of the ignition circuit embedded and integrated with a forming resin. But apart from the fact that said ignition circuit does not have a DC-DC-voltage converter, the output of which is superimposed to the high-voltage pulses provided by an ignition coil, contrary to the present invention, this document teaches to embed and to integrate with a forming resin the whole ignition device, whereas the present invention selects for embedment and integration only those components of the device which are in the middle- and high-voltage range. Brief Description of the Drawings Fig. 1 is a circuit diagram of a high-energy ignition device to which the invention is applied; Fig. 2 is a front elevational view of a high-energy ignition device in accordance with the invention; Fig. 3 is a perspective view of a high-energy ignition device in accordance with the invention; and Fig. 4 is a sectional view of the high-energy ignition device of the invention, taken along the line IV-IV of Fig. 2. Best Mode for Carrying Out the Invention Referring to Fig. 1 showing a circuit diagram which is an embodiment of the invention, a battery 10 is connected through a key switch 12 to an igniter coil 14 and an output transformer 18 of a DC-DC converter 16. The igniter coil 14 has a primary coil 20 one terminal 22 of which is connected through a line 23 to a line 24 leading to the battery 10, while the other terminal 26 is connected through a line 28 to the collector 34 of a transistor 32 in an ignition circuit 30. The emitter 36 of the transistor 32 is grounded, while the base 38 of the same receives the output signal from a pickup coil 40 which generates a signal synchronous with the engine operation. A circuit connected between the pickup coil 40 and the base of the transistor 32 (a switching device) is well known to those skilled in the art and, therefore, is not described in detail. The transistor 32 is adapted to be turned on and off by the output from the pickup coil 40 in synchronism with the engine operation, thereby interrupting the electric current in the primary coil 20 of the igniter coil 14. A secondary coil 44 which is magnetically coupled to the primary coil 20 through an iron core 42 is adapted to produce a high-voltage pulse when the current in the primary coil 20 is abruptly interrupted. The secondary coil 44 has a terminal 46 which is connected through a line 48 to the rotor 52 of a distributor 50. The rotor 52 is adapted to rotate in synchronism with the engine operation such as to successively contact the stationary contacts 54, 56, 58 and 60 of the distributor, thus generating sparks in the sparking plugs 62, 64, 66 and 68 corresponding to these stationary contacts. One of the terminals 22 of the primary coil 20 is connected through a line 70 to the primary coil 72 of the output transformer 18. The primary coil 72 has a terminal 74 which is connected through a line 76 to an output terminal 75 of an oscillator 77 adapted to oscillate at a predetermined frequency, and another terminal 78 which is connected through a line 79 to the collector 82 of a transistor 80 which is a switching element. The emitter 84 of the transistor 80 is grounded, while the base 86 is connected to the other output terminal 88 of the oscillator 77. A secondary coil 90 of the output transformer 18 has a terminal 92 which is connected through a line 94 to a diode 96 which in turn is connected through a line 98 to a terminal 100 of the secondary coil of the igniter coil. The plus side of the diode 96 is grounded through a smoothing capacitor 102 and a line 104. The secondary coil 90 is magnetically coupled to the primary coil 72 through an iron core 106, while the other end is grounded through a line 110. In the circuit arrangement described above, the transistor 32 is turned off by the output voltage of a pickup coil 40 which operates in synchronism with the engine operation, so that the current in the primary coil 20 is decreased abruptly. Consequently, a pulse of a voltage high enough to break the insulation gap in the sparking plug is generated in the secondary coil 44. The DC-DC converter 16 turns the switching transistor 80 on and off in response to the output signal from the oscillator 77, thus intermittently applying an electric current from the battery 10 to the primary coil 72 of the output transformer 18. The secondary coil 90 of the transformer 18 produces a voltage of about 2 KV which is superposed on the high voltage pulse generated in the secondary coil 44 of the igniter coil 14 through a rectifier circuit constituted by the diode 96 and the capacitor 102. The above-mentioned high-voltage pulse is applied to one of the sparking plugs 62 to 68 selected by the distributor 50, thus breaking the insulation in the sparking plug. Once the insulation is broken, the discharge is maintained by the output from the DC-DC converter 16. With this arrangement, it is possible to obtain a discharge of long duration, thus enabling efficient combustion of the mixture. Certain circuit constituents such as the igniter coil 14, output transformer 18, high-voltage diode 96, capacitor 102 and certain connecting lines as claimed in claim 1 are integrally resin-molded as shown in Figs. 2 to 4. The igniter coil is composed of the iron core which is formed by laminating L-shaped silica steel sheets, as well as the primary and secondary coils 20, 44. In order to reduce the size, this coil is constructed as a closed magnetic circuit type igniter coil. The primary coil 20 and the secondary coil 44 are impregnated with an epoxy varnish in a vacuum atmosphere after the coil winding, thus ensuring the insulation (see Fig. 4). The DC-DC converter 16 has an aluminum case 114 accommodating the oscillator 77 and the switching transistor 80 and having heat radiating fins, 112, the transformer 18, having a ferrite core 106, the diode 96 and the capacitor 102. In order to reduce the size of the DC-DC converter 16, it is necessary to design the oscillator 77 such as to oscillate at a high frequency. In order to minimize the generation of heat in the transformer 18 due to leak of high-frequency current in the primary coil 72, the described embodiment of the invention employs a ferrite having a large magnetic permeability as the iron core 106. The primary coil 72 and the secondary coil 90 are impregnated with an epoxy varnish after the coil winding for perfect insulation (see Fig. 4). The igniter coil 14 and the transformer 18 thus electrically connected are integrated as they are injected with a forming resin 116. According to the invention, a resin having a good electrical insulation properties and excellent heat resistance and mechanical strength, e.g., PBT reinforced with glass, is preferably used as the forming resin 116. The aluminum case 114 accommodating the oscillator 77 is fixed to the transformer 18 and also to the igniter coil 14, and the line 118 is connected to a terminal 122 through a connector 120 and is secured by a mounting piece 124 which serves also as a grounding path leading to the chassis. The power supply for the oscillator 77 in the aluminum case 114 is connected through the line 76 to a power supply terminal 126 on the rear of the case 114, although not shown. The ground side of the oscillator 77 and of the switching transistor 80 is connected to the mounting piece 124 through a ground path 128. A terminal 130 is connected to the transistor 32 in the ignition circuit. In the ignition device of the invention having the described construction, high electrical insulation is ensured and the number of cords leading to the outside is minimized because most of the wiring is fixed in the forming resin. The wiring does not hinder the mounting of the ignition device in the engine compartment, thus facilitating the installation in the vehicle. In addition, the overall size of the ignition device is reduced advantageously. Electric current of high voltage generated in the igniter coil flows in the lines 98 and 104, so that a cord equivalent to the line 48 has to be used for the wiring to these parts and particular care has to be taken to ensure insulation, unless the construction in accordance with the invention is employed. Namely, since the cords 98 and 104 are embedded in a forming resin in the invention, sufficiently strong insulation is ensured and the handling of the device as a whole is facilitated. Thus, the invention provides a high-energy ignition device which has a strong electrical insulation between parts and which is easy to mount on vehicles.

Claims: A high-energy ignition device for an engine, the high energy ignition device comprising: a pickup (40) for generating an output synchronous with the operations of the engine; an ignition circuit (30) including a switching device (32) adapted to be turned on and off in accordance with the output from the pickup; an igniter coil (14) including a primary coil (20) connected to the switching device, a secondary coil (44) in which a high voltage is generated in response to an abrupt turning on and off of electric current in the primary coil, and an iron core (42) between the primary and secondary coils; and a DC-DC converter (16) including a transformer (18), including a primary coil (72), a secondary coil (90) and a magnetic core (106) between the primary and secondary coils, a switching element (80) connected in series to the primary coil, and an oscillator (77) for turning the switching element on and off at a predetermined frequency, the DC-DC converter being adapted to produce, at the output side of the secondary coil, a DC voltage lower than the pulse voltage generated by the igniter coil and adapted to be superposed on the current produced by the igniter coil; wherein said igniter coil (14), said transformer (18) of said DC-DC converter (16), a first line (110) connected between one end of said secondary coil of said transformer (18) and ground, a diode (96) having a cathode connected to the other end of said secondary coil of said transformer, a smoothing capacitor (102) one end of which is connected to an anode of said diode, a second line (104) connected between the other end of said capacitor and ground, and a third line (98) connected between said anode of said diode and one end of said secondary coil of said igniter coil, are integrated with and enclosed within a forming resin (116) for facilitating a sufficiently strong electrical insulation, and wherein an aluminum case (114) accommodating said oscillator and said switching element (80) is fixed to said igniter coil and said transformer (18) outside said forming resin. A high-energy ignition device according to claim 1, wherein said aluminum case is provided with heat radiating fins.

Inventors: YOSHINARI TAKASHI, YOSHINARI, TAKASHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1984
Main classification: F02P15
IPC codes: F02P3, F23Q3