A secondary voltage waveform detecting device for internal combustion engine

Abstract: In a second voltage waveform detecting device for internal combustion engine, an electrical conductor is provided in an ignition circuit in proximity of a lead wire of a secondary circuit which supplies high voltage to a spark plug in an internal combustion engine by way of the lead wire. The lead wire is provided through an insulator. A condensor is connected between the electrical conductor and the ground. A secondary voltage detector circuit which devides a secondary voltage in accordance with a static capacity of the condensor and a static capacity between the electrical conductor and the lead wire.

Description: The invention relates to a secondary voltage waveform detecting device as described in the first part of claim 1 for detecting secondary voltages induced in a secondary voltage circuit of an ignition circuit, using spark plug cables when a high voltage is induced by an ignition coil in a spark plug in an internal combustion engine. With the demands for purifying emission gases and enhancing fuel efficiency of internal combustion engines, it has become necessary to detect the firing condition in each cylinder of an internal combustion engine. In order to detect the firing condition in each of the cylinders, optical sensors have been installed within each cylinder. Alternatively, a piezoelectrical sensor has been attached to the seat pad of each spark plug. In both cases, it is troublesome and time-consuming to install a sensor for each of the cylinders, thus increasing the installation cost and taking much time in checks and maintenance. Further, it is known, for instance from documents EP-A-0,277,468 (on which the first part of claim 1 is based), DE-A-2,356,440 and JP-A-52/118,135, to use an electrode plate in the form of a ring around a high-voltage cable leading to the distributor, to detect firing pulses to the spark plugs to provide indications of mis-sparking. It is an object of the invention to provide a secondary voltage waveform detecting device which is capable of precisely detecting the waveform of a secondary voltage arising in the spark plugs installed in each cylinder of an internal combustion engine, with a relatively simple structure. According to the present invention, there is provided a secondary voltage waveform detecting device for detecting a waveform of secondary voltages applied to spark plugs installed in cylinders of an internal combustion engine, comprising: a shunt detector circuit including an electrode plate provided in an ignition circuit in proximity of a secondary circuit so as to define a predetermined capacitance therebetween, and a condenser electrically connected to the electrode plate, the secondary circuit being adapted to supply a high voltage to said spark plugs by way of plug cables surrounded by insulators; a secondary voltage detector circuit for detecting a secondary voltage waveform divided by the shunt detector circuit; and a distinction circuit electrically connected to said electrode plate and arranged to analyze the secondary voltage waveform; characterised in that said electrode plate is a corrugated metal plate embedded in an insulator, the insulator comprising a base portion having grooves corresponding to the corrugations of said electrode plate, in use, said insulated plug cables being placed within said grooves; and in that said distinction circuit is operable to feed back a signal to control means of the internal combustion engine. In order to define a capacitance between the plug cables and the electrode plate, the cables are placed in the grooves. The secondary voltage detector circuit enables the waveform of the secondary voltage which is applied across each spark plug to be detected precisely. Analyzing the waveform makes it possible to distinguish correct ignition from misfire and mis-sparking of the spark plug. Feeding the analyzed information back to a combustion control means gives a warning of worsened emission gases and a deteriorated catalyst. The secondary circuit, which supplies the secondary voltage to the spark plug, allows the definition of a substantially uniform capacitance between the lead wires and the electrode plate, thus making it possible precisely to detect the secondary voltage waveform with a single sensor device. A cavity may further be provided on a lower surface of the insulator base to install the condensor, the secondary voltage detector circuit and the distinction circuit. With such a cavity provided on the lower surface of the insulator base, the condensor, the voltage detector circuit and the distinction circuit are integrally located in the cavity for the convenience of matching, adjustment and maintenance of those circuits. The invention will further be understood from the following description, when taken together with the attached drawings, which are given by way of example only and in which: Fig. 1 is a schematic view of an ignition circuit having a secondary voltage detector circuit for internal combustion engine; Fig. 2 shows a waveform for the purpose of explaining how the secondary voltage detector circuit works; Fig.3 is a modified form of the electrical conductor; Fig. 4 is a perspective view showing how a secondary voltage detector is installed in a cavity of an insulator base according to a second embodiment of the invention; Fig. 5 is an exploded view of an electrode plate and a circuit base; Fig. 6 is a perspective view of the secondary voltage detector; Fig. 7 is a perspective view with the secondary voltage detector mounted on internal combustion engine; Fig. 8 is a schematic view of an ignition circuit having a secondary voltage detector circuit for the internal combustion engine; Fig. 9 is a view similar to Fig. 4 according to a third embodiment of the invention; Fig. 10 is a view similar to Fig. 6; and Fig. 11 is a view similar to Fig. 7. Referring to Fig. 1, there is provided an ignition circuit 100 for an internal combustion engine. Fig. 1 also shows a detecting device for detecting secondary voltages. This device shown in Fig. 1 is not in accordance with the present invention but is useful for understanding at least a first embodiment. The circuit 100 includes an ignition coil 1 having a primary coil la and a secondary coil 1b. A high tension cord 11, which means a lead wire provided through an insulator hereinafter, has one end electrically connected to the secondary coil 1b, the other end connected to a rotor 2a of a distributor 2 which integrally incorporates a contact breaker (not shown) and has, for instance, four stationery segments (Ra). To each of the stationery segments (Ra), a free end of the rotor 2a approaches to make a series gap (for instance, 0.30 mm in width) with the corresponding segments (Ra) during the rotary movement of the rotor 2a. To each of the four stationary segments (Ra), a centre electrode 3a of one of the spark plugs 3, which are installed in the four cylinders of the internal combustion engine, is electrically connected. In this instance, a secondary circuit 20a is formed by providing an electrical path from the distributor 2 to the spark plug 3. The spark plug 3 has an outer electrode 3b electrically connected to the ground so that the secondary coil 1b energizes each of the spark plugs 3 by way of the high tension cord 11, the rotor 2a and each of the stationary segments (Ra) of the distributor 2. Around the high tension cord 11 which is provided to electrically connect the secondary coil 1b to the distributor 2, is an electrical conductor 41 placed to form a secondary voltage detector 4 which includes a shunt condensor 42 and a shunt detector circuit 5. The shunt condensor 42 has one end connected to the electrical conductor 41, and having the other end connected to the ground to provide a sensor circuit portion (sensor portion) 40. In parallel with the shunt condensor 42, is an electrical resistor 43 (e.g. 500 kΩ) connected to form a discharge circuit for the shunt condensor 42. The shunt detector circuit 5 is connected between the electrical conductor 41 and the shunt condensor 42. The electrical conductor 41 is in the shape of a metallic tube 63 (e.g. 2 cm in length) surrounding the high tension cord 11 to provide a static space therebetween. The metallic tube 63 is air-tightly embedded in a rubber sleeve 62 as described in Fig. 3 hereinafter. The shunt condensor 42 has a capacity of 10000 pF, while the static space between the metallic tube and the high tension cord 11 allows a capacity of 5 pF. The sensor circuit portion 40 divides secondary voltage across the high tension cord 11 by the order of 1/2000 in which high voltage of about 20000 volt is reduced to the level of 10 volt since the secondary voltage is picked up in accordance with a ratio of static capacity of the electrical conductor 41 to that of the shunt condensor 42. An electric frequency of the high voltage is within the range of 10 KHz so that the impedance of the sensor circuit portion 40 comes to about 1.6 kΩ which substantially removes the effect of the resistor 43 on the value of the divided voltage. In the shunt detector circuit 5, the circuit 5 has a processor circuit including a microcomputer or a pulse-width distinction circuit (although not shown). A voltage waveform picked up from an intermediate point (A) between the electrical conductor 41 and the shunt condensor 42 has a capacity discharge component followed by an inductive discharge component as shown at (a) in Fig. 2 which is a voltage waveform equivalent to that of the secondary circuit directly divided in accordance with a ratio of static capacity of the electrical conductor 41 to that of the shunt condensor 42. The inductive discharge component, changes the secondary voltage waveform since an electrical resistance of a spark gap between the electrodes 3a, 3b varies from the case in which spark occurs between the electrodes 3a, 3b, and ignites air-fuel mixture gas in the cylinder to the case in which spark occurs between the electrodes 3a, 3b, but fails to ignite the air-fuel mixture gas. When the spark normally ignites the air-fuel mixture gas to generate combustion gas which is ionized at or around the spark gap to decrease the electrical resistance between the electrodes 3a, 3b. The decreased electrical resistance causes a capacity discharge in an order of 100 ampere for about 1 nano seconds followed by the inductive discharge in an order of 50 milliampere at low voltage (V1) for about 1 milliseconds until all the electrical energy of the ignition coil 1 is released. Completion of the inductive discharge is followed by a minimum voltage (P1) as shown at (a1) in Fig. 2. When the spark fails to ignite the air-fuel mixture gas, the electrical resistance between the electrodes 3a, 3b remains greater. The greater electrical resistance terminates the inductive discharge for a short period of time to remain a greater amount of electrical energy reserved in the ignition coil 1. The greatly reserved energy in the ignition coil 1 completes the capacity discharge followed by the inductive discharge at low voltage (V2) and succeeding a rapidly increased peak voltage (P2) as shown at (a2) in Fig. 2. When the spark ignites the air-fuel mixture gas, but strong swirls make the spark errant to lengthen a sustaining time period of the spark. The errant spark interrupts the discharge between the electrodes 3a, 3b and destroys the insulation of the spark gap between the electrodes 3a, 3b. In this situation, the completion of the capacity discharge followed by the inductive discharge at progressively increasing voltage (V3) and succeeding the capacity discharge again to represent an intermediate peak voltage (P3) after completing the discharge as shown at (a3) in Fig. 2. When the spark normally ignites the air-fuel mixture gas, it is adapted to generate a single short pulse. When the spark fails to ignite the air-fuel mixture gas, it is adapted to simultaneously produce a short pulse and a wider pulse. When the spark ignites the air-fuel mixture gas, but strong swirls make the spark errant to lengthen a sustaining time period of the spark. The errant spark either increases the inductive discharge level or induces the capacity discharge again, and thus adapted to produce pulses different from the above two cases. Fig. 3 shows a modified form of the electrical conductor 41 for use in a first embodiment of the invention. In Fig. 3, a plastic or rubber clamper 9 is provided which is secured to the internal combustion engine. The clamper 9 has grooves 91 (92) in which the plug cables 60 are located. Along the grooves 91 (92) of the clamper 9, is a metallic corrugation 93 embedded in the clamper 9 to serve as an electrical conductor. Fig. 4 shows a second embodiment of the invention in which a secondary voltage detector 100a is depicted. Numeral 101 designates an insulator base which is made in the shape of parallelepiped from synthetic resin. An upper surface 111 of the insulator base 101 has U-shaped grooves 112 in parallel relationship each other, the number of which corresponds to the number of the cylinders of the internal combustion engine. A lower surface 113 of the insulator base 101 has a rectangular cavity 114 to provide an accommodation space 115 while one sidewall of the insulator base 101 provides an outlet 116 for both an output and a power source. Along the grooves 112 of the insulator base 101, is a corrugated metal 120 embedded in the insulator base 101 to form a secondary voltage sensor 102 in a manner that each recess 121 of the corrugated metal 120 corresponds to each of the grooves 112. The corrugated metal 120, which acts as an electrode plate as shown in Fig. 5, is simultaneously embedded at the time of forming the insulator base 101 by means of injection moulding. A lead wire 122 electrically connects the corrugated metal 120 to a shunt condensor, a shunt detector circuit and a distinction circuit each packaged in a package substrate 103. The package substrate 103 is fixedly placed within the accommodation space 115 by means of a resin filler 104. It is noted that the recess 121 of the corrugated metal 120 may be polygonal or elliptic. It is also noted that the corrugated metal 120 may be fixedly placed within the accommodation space 115, or may be deposited layer on a lower side of the package substrate 103 in a form of conductive layer by means of printing. It is also appreciated that the corrugated metal 120 may be embedded in a lid plate 117. In each of the grooves 112 of the insulator base 101, is a high tension cord 105 which electrically connects a distributor (D) to a spark plug (P) of an internal combustion engine (E) so as to form a secondary circuit in an ignition circuit. On the upper surface 111 of the insulator base 101, is the lid plate 117 fixedly placed to secure the high tension cord 105 against removal as shown in Fig. 6. The secondary voltage detector 100a is mounted on the internal combustion engine (E) while a plug 118 is connected to the outlet 116 to introduce a lead wire to the power source and a control device of the internal combustion engine (E) as shown in Fig. 7. Fig. 8 shows the ignition circuit into which the secondary voltage detector 100a is incorporated. The ignition circuit has an ignition coil (T) comprising a primary circuit (L1) and a secondary circuit (L2) with a vehicle battery cell (V) as a power source. The primary circuit (L1) has a primary coil (La) electrically connected in series with a signal generator (SG), while the secondary circuit (L2) has a secondary coil (Lb) connected to a rotor (Da) of the distributor (D). The distributor (D) has stationary segments (Ra), the number of which corresponds to that of the cylinders of the internal combustion engine. To each of the stationary segments (Ra), a free end of the rotor 2a approaches to make a series gap with each of the segments (Ra). Each of the segments (Ra) is electrically connected to corresponding spark plugs (P) by way of the high tension cord 105. Each of the spark plugs (P) has a center electrode (Pa) and an outer electrode (Pb) to form a spark gap between the two electrodes (Pa), (Pb) across which spark occurs when energized. Meanwhile, the corrugated metal 120 is electrically connected to the ground by way of a shunt condensor (C1) to form a shunt detector 106 of the secondary voltage. To a common point between the corrugated metal 120 and the shunt condensor (C), is a secondary voltage waveform detector circuit 107 connected to which a distinction circuit (microcomputer) 108 is electrically connected. In the secondary voltage sensor 102, there is provided static space between the high tension cord 105 and the corrugated metal 120 to define static capacity of e.g. 1 pF. The shunt condensor (C) has static capacity of e.g. 3000 pF and having an electrical resistor R (e.g. 3MQ) connected in parallel therewith so as to form a discharge path for the shunt condensor (C). The shunt detector 106 allows to divide the secondary voltage induced from the secondary circuit (L2) by the order of 1/3000, which makes it possible to determine the time constant of RC-path to be approximately 9 milliseconds to render the change of the secondary voltage relatively slow. The secondary voltage waveform detector circuit 107 analyzes a voltage waveform outputted from the shunt detector 106 which is compared with a characteristic voltage waveform which previously determined by calculation or experiment. The voltage waveform divided in accordance with the secondary voltage sensor 102 and the shunt condensor (C), directly represents one which is applied to each of the spark plugs (P). The voltage waveform changes depending on the cases when the spark ignites air-fuel mixture gas in the cylinder, and on the cases when the spark occurs but fails to ignite the air-fuel mixture gas, and further depending on the cases when the spark fails due to exhausted battery cell, carbon fouling or deterioration of the spark plugs. By analyzing the difference of the changing voltage waveform, it is possible to distinguish normal ignition from misignition and misfire in each cylinder of the internal combustion engine. The distinction circuit 108 receives the output from the secondary voltage waveform detector circuit 107, and compares with the characteristic voltage waveform which previously determined by calculation or experiment so as to produce an output which is fed into a main computer or a control means which adjusts injection timing or an amount of fuel injection. Fig. 9 shows a third embodiment of the invention in which a secondary voltage detector 200 is depicted in which an insulator base 201 has no cavity equivalent of the accommodation space 114 of the second embodiment. Instead of the outlet 116 of the second embodiment, is an anchor lug 214 is attached to the insulator base 201 so as to fasten the base 201 to the internal combustion engine (E). In the insulator base 201, is a corrugated metal 220 embedded along grooves 212 which are provided with an upper surface 211 of the base 201 in the same manner as described in the second embodiment of the invention. The corrugated metal 220 has recesses 221 corresponding to grooves 212 to serve as an electrode plate. On the upper surface 211 of the base 201, is a lid plate 213 placed to fix a tension cord 203 as shown in Fig. 10. The secondary voltage detector 200 thus assembled is fasten to the internal combustion engine (E) as shown in Fig. 11. It is appreciated that both the insulator base 201 and the lid plate 213 are preferably made of heat-resistant plastic material so as to sufficiently resist against heat generated from the internal combustion engine. It is also appreciated that both the insulator base 201 and the lid plate 213 are made of light-weight ceramic material to contribute to reducing an entire weight of the vehicle. Further, it is noted that an array of grooves may be provided with the lid plate 213 in correspondence to the grooves 212 in a manner that the array of grooves is less deep than the grooves 212. While the invention has been described with reference to the specific embodiments, it is understood that this description is not to be construed in a limiting sense in as much as various modifications and additions to the specific embodiments may be made by skilled artisan without departing from the scope of the claims.

Claims: A secondary voltage waveform detecting device (100a) for detecting a waveform of secondary voltages applied to spark plugs (P) installed in cylinders of an internal combustion engine (E), comprising: a shunt detector circuit (106) including an electrode plate (93;120;220) provided in an ignition circuit in proximity of a secondary circuit (L2) so as to define a predetermined capacitance therebetween, and a condenser (C1) electrically connected to the electrode plate (93;120;220), the secondary circuit (L2) being adapted to supply a high voltage to said spark plugs (P) by way of plug cables (60;105) surrounded by insulators; a secondary voltage detector circuit (107) for detecting a secondary voltage waveform divided by the shunt detector circuit (106); and a distinction circuit (108) electrically connected to said electrode plate (93;120;220) and arranged to analyze the secondary voltage waveform; characterised in that said electrode plate (93;120;220) is a corrugated metal plate embedded in an insulator (9;101;201), the insulator comprising a base portion having grooves (92;112;212) corresponding to the corrugations of said electrode plate (93;120;220), in use, said insulated plug cables (60;105) being placed within said grooves (92;112;212); and in that said distinction circuit (108) is operable to feed back a signal to control means of the internal combustion engine (E). A secondary voltage waveform detecting device according to claim 1, wherein a cavity (115) is provided in one surface of the insulator base (101), the cavity being adapted to receive the condenser (C1), the secondary voltage detector circuit (107) and the distinction circuit (108). A secondary voltage waveform detecting device according to claim 1 or 2, wherein said insulator further comprises a lid portion (117), said electrode plate being provided in said lid portion. A secondary voltage waveform detecting device according to claim 1, wherein said insulator further comprises a lid portion (213) having lid grooves corresponding to but shallower than said grooves (92;112;212) in said base portion. An internal combustion engine having a secondary voltage waveform detecting device according to any one of the preceding claims.

Inventors: ITO YASUO, MATSUBARA YOSHIHIRO, MIYATA SHIGERU, SUZUKI TAKASHI, YOSHIDA HIDEJI, ITO, YASUO, MATSUBARA, YOSHIHIRO, MIYATA, SHIGERU, SUZUKI, TAKASHI, YOSHIDA, HIDEJI, Ito, Yasuo, c/o NGK SPARK PLUG CO., LTD., MATSUBARA, YOSHIHIRO, C/O NGK SPARK PLUG CO., LTD., MIYATA, SHIGERU, C/O NGK SPARK PLUG CO., LTD., Suzuki, Takashi, c/o NGK SPARK PLUG CO., LTD., Yoshida, Hideji, c/o NGK SPARK PLUG CO., LTD.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD
Application year: 1992
Main classification: F02P17
IPC codes: F02P17, F02P11