EP0096353A2

EP0096353A2 - A radio-frequency-noise-suppressive ignition system for an automotive vehicle's engine

Info

Publication number: EP0096353A2
Application number: EP83105401A
Authority: EP
Inventors: Masazumi Sone
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1982-06-03
Filing date: 1983-05-31
Publication date: 1983-12-21
Also published as: EP0096353A3; JPS58211573A

Abstract

A radio-frequency-noise-suppressive ignition system for an automotive vehicle's engine, comprising a plurality of spark plugs (1) each installed within a corresponding engine cylinder having an elongated monolithic resistor (7) equal to or more than eight millimeter long, noise suppressive resistance-contained high-tension cables (13), one of which being connected between a secondary winding of an ignition coil (27) and distributor (24), the others of which being connected between a plurality of fixed electrodes (17) of the distributor (24) and respectuve spark plugs (1), the distributor (24) having a rotor (22) electrically connected to a center electrode (16) via a contactor (19) made of a high-resistance material which is connected to the secondary winding of the ignition coil (27), the rotor (22) including a rotor electrode (21) having a discharge gap (20) against each of the fixed electrodes (17) and a dielectric material (25) preferably made of silicone glass secured to a portion of at least one of the top and bottom surface areas of the rotor electrode (21), and a resistance material (29) provided at an intermediate part of the rotor electrode (21) between one end of the rotor electrode (21) which is connected to the contactor (19) and the portion of the rotor electrode (21) to which the dielectric material (25) is secured.

Description

BACKGROUND OF THE INENTION

Field of the Invention

The present invention relates generally to an ignition system for an internal combustion engine of an automotive vehicle, and more specifically to an ignition system of a radio-frequency-noise-suppressive type, wherein each of spark plugs installed within a corresponding engine cylinder has an elongated monolithic resistor between a central electrode and discharge electrode equal to or more than eight millimeters of resistance length. The ignition system uses noise-suppressive-type high tension cables including a resistance and distributor having a rotor wherein a resistance material is interposed at an intermediate portion of a rotor electrode and a dielectric material is secured to either the upper end or lower end surfaces of the rotor electrode.

Description of the Prior Art

An engine ignition system mounted in an automotive vehicle mainly comprises, as is well known, a distributor, spark plugs, and high-tension cables. At the time of spark discharge, a large current having a steep rise time flows through the distributor and spark plug to ignite an air-fuel mixture supplied within an engine combustion chamber. The large current generates electromagnetic wave noise which disturbs communication from a radio equipment, etc. Such noise generation has become a social problem due to the rapid increase in numbers of automotive vehicles. Some countries have passed laws which prescribe maximum allowable electromagnetic wave noise electric field strength for automotive vehicles, e.g. under the recommendation of International Special Committee on Radio Interference (CISPR).
Under such circumstances, as a measure for preventing or reducing radio-frequency wave noise, it has become common practice to install a resistor into each spark plug or to install resistive wires into each high-tension cable.
In recent years, however, regulations against noise electromagnetic wave radiation have become more strict, i.e., the maximum allowable electromagnetic wave noise electric field strength and such measures as described above cannot satisfy these -strict regulations.
To cope with such strict regulations, a distributor for distributing a high surge voltage generated at an ignition coil into each spark plug must be included in measures for suppressing electromagnetic wave generation.
There is a distributor, e.g., having a construction of a type wherein a gap between a rotor electrode and each fixed electrode is made wider than the conventional one or having a construction of a type wherein a metal oxide coating is formed at a part of rotor electrode discharge surface.
However, it is not sufficient to exhibit a remarkable noise suppressive effect in a case when using such a distributor and a higher voltage is required than the conventional ignition system since an energy loss is generated between the wide gap and countermeasure for preventing high voltage leakage becomes difficult. In this way, there arises other problems than the measure for preventing noise wave generation.
To solve the above-described problem, the' applicant has developed a radio-frequency noise suppressive ignition system wherein parts having a large noise suppressive effect, i.e., a distributor having a rotor to which a dielectric material is added, resistor-equipped spark plugs having a considerably longer resistance path than the conventional resistance path, and resistive high-tension cables are combined so that an inexpensive noise suppressive ignition system can be achieved having a large noise suppressive effect without affecting engine performance.
Such a noise suppressive ignition system has already filed in Japan (file number: Sho 55-101265 published number Sho 57-26272).
However, in a case when such a noise suppressive ignition system as described above is applied to an internal combustion engine of an automotive vehicle, the experiment shows the noise suppressive effect becomes insufficiently reduced dependently on shapes or models of the applied automotive vehicles, particularly, within a relatively low frequency band of 20 MHz through 100 MHz.

SUMMARY OF THE INVENTION

With the above-described problem in mind, it is an object of the present invention to provide a radio-frequency noise suppressive ignition system having a sufficient noise suppressive effect over all radio frequency bands regardless of the shapes or models of the applied automotive vehicles.
This can be achieved by providing a resistance material of approximately 5 through 20 kiloohms at an intermediate portion of a rotor electrode (in the vicinity of the intermediate portion) of the distributor in order to attenuate a high-frequency noise current flowing through the spark plugs via high-tension cables so as to suppress the generation of electromagnetic wave noise within the distributor, in addition to the elongated resistor-equipped spark plugs, resistive noise-suppressive high tension cables, and distributor having the rotor electrode, at either top or bottom surface of which the dielectric material is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be obtained from the following detailed description taken in conjunction with the drawings in which like reference numerals designate corresponding elements and in which:

Fig. 1 is a partially sectioned view of a conventional ignition system which has been filed in Japan (file number: Sho 55-101265);
Fig. 2 is a characteristic graph of a relative noise electromagnetic wave level against a discharge voltage;
Fig. 3 is a frequency characteristic graph against a noise electric field strength;
Figs. 4(a) and 4(b) are frequency characteristic' graphs against a noise electric field strength;
Fig. 5 is a partially sectioned view of a rotor of a distributor according to the present invention; and
Figs. 6(a) and 6(b) show frequency characteristic graphs of the noise electric field strength.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will be made to the drawings in order to facilitate understanding of the present invention.
Fig. 1 shows a noise suppressive type ignition system for which a patent application has been filed in Japan by the* Fig. 1, numeral 1 denotes a spark plug with a long resistance path provided in each cylinder of an internal combustion engine, numeral 24 denotes a distributor having a plurality of fixed electrodes 17 which correspond to each spark plug 1, one rotor electrode 21 which revolves in ^*applicant. In synchronization with the engine and located so as to approach and pass each of the fixed electrodes 17 sequencially, numeral 13 denotes noise suppressive type high tension cables each connected between the fixed electrode 17 and corresponding spark plug 1, and numeral 28 denotes noise-suppressive type high tension cables connected between a center electrode 16 of the distributor 24 and ignition coil 27.
Each of the respective components constituting the ignition system will be described hereinafter.
First, the spark plug 1 with the long resistance path t made of a monolithic resistor equal to or more than 8 mm of resistance length is installed within each engine cylinder of the internal combustion engine. It should be noted that the other spark plugs have the same construction as the spark plug shown in Fig. 1. The spark plug 1 with the long resistance path includes a plug screw portion 2 provided at a lower part thereof for screwing the spark plug 1 to the corresponding portion. in each cylinder, a discharge electrode 4 located at the lower edge of the screw portion 2, and central electrode 8.
Whereas a conventional plug has a monolithic resistor of length ¹ ranging from 5 to 6 mm, the spark plug 1 has a resistor with a length exceeding 8 mm and preferably about 15 mm. In the spark plug 1 shown in Fig. 1, numeral 3 denotes a grounded side electrode, numeral 5 denotes a seal ring, numeral 6 denotes a sealing material made of a conductive material, and numeral 9 denotes a shell.
A noise-suppressive effect of the resistor-equipped spark plug 1 may be caused by a filter formed by an electrostatic capacitance between the monolthic resistor 7 and plug screwing portion 2 and resistance of the monolithic resistor 7 itself. A parallel capacitance is inserted between both ends of the monolithic resistor 1.
If the parallel capacitance is large, a high-frequency current flows into the plug shell 9 via the parallel capacitance so that the filtering effect becomes reduced.
On condition that the resistance material is the- same, the parallel capacitance becomes reduced a^ts the length of the resistance path t becomes longer. In practice, such a filtering effect appears remarkably when the length of the resistance path is 12 through 15 mm.
The distributor 24 comprises an axle 14, rubber cap 15, central electrode 16, fixed electrodes 17, spring 18, contactor 19, rotor electrode 21 made of a conductive metal, rotor 22, cap 23, dielectric material 25, and caulking portion 26. Numeral 20 denotes a discharge gap formed between the rotor electrode 21 and fixed electrode 17 while the rotor electrode 21 approaches one of the fixed electrodes 17. The axle 14 is engaged with a camshaft of the engine through a wheel to synchronize with the engine speed. Therefore, the rotor electrode 21 rotates in synchronization with the engine, and is located to approach and pass sequencially in front of each fixed electrode 17.
In addition, a rotor wherein the dielectric material 25 is attached at either upper end or lower end of the rotor electrode 21 is called a dielectric material attached rotor. In Fig. 1, the dielectric material 25 is attached between the rotor electrode 21 and rotor 22 (i.e., at the lower end of the rotor electrode 21).
In general, there is a close relationship between the noise electromagnetic wave generated through a discharge and discharge voltage as shown in Fig. 2. If the discharge voltage is reduced, the noise generation level is' accordingly reduced.
If the above-described dielectric material attached rotor is used, the discharge voltage across the gap 20 between the rotor electrode 21 and fixed electrode 17 is reduced so that the generation of noise waves can remarkably be suppressed.
In the dielectric material attached rotor, the rotor electrode 21 is made of a stainless steel or brass and the dielectric material 25 used thereat is made of a silicone material. Particularly, a silicone glass is most preferable in terms of noise suppressive effect, heat resistance effect, workability, arc resistance effect, and corona resistance effect. The silicone glass is manufactured by impregnating or applying a silicone resin such as a silicone wanish to glass fabrics.
Experiments have indicated that in a case when a stainless steel having a thickness of 0.6 mm is used as the rotor electrode 21 and silicone glass having a thickness of 0.5 mm is used as the dielectric material 25, the discharge voltage across the gap 20 ranges from 4 to 5 kilovolts and the noise electric field strength is reduced by approximately 15 dB as compared with the normal rotor electrode made of brass.
The noise-suppressive high tension cable 13 is used to connect each fixed electrode 17 to the corresponding resistor-equipped spark plug 1. The other noise-suppressive high tension 28 is used to connect the central electrode 16 of the distributor 24 and secondary winding (not shown electrically) of the ignition coil 27.
Such noise-suppressive high tension cables comprise carbon-impregnated wires 10 covered with a braided wire 12, insulating sheath 11, and tube 13 made of silicone rubber. The carbon-impregnated wires 10 has a uniform resistance per length of 8 through 20 kiloohms per meter.
Various combinations of the spark plug, distributor, and high tension cable which have taken . measures for suppressing noise wave generation and have not taken such measures are listed in a Table in an annex and these measurement results are shown in Fig. 3.
In this graph, 0 dB represents 1 uV/m.
In this Table, the elements denoted by brackets have not taken measures for suppressing noise and symbols A through D correspond to A through D shown in Fig. 3.
The measurement results shown in Fig. 3 are results measured actually when various ignition systems in combination of the elements listed in the Table are installed within an internal combustion engine having a displacement of 1,500 cc mounted in a bonnet-type automotive vehicle. In addition, symbol E denotes a law- regulated maximum allowable noise level under a corresponding law (e.g., CISPR recommendation No. 18/2).
As appreciated from Fig. 3, if there are one of the elements (A, B, C) in which no noise suppressive effect is measured, the entire noise level can be determined at' the most significant noise component generated from the element in which no noise suppression measure is carried out, thereby the entire noise suppressive effect being reduced. A large noise suppressive effect can be obtained by 10 through 30 dB only in a case where all elements have taken noise suppression measures, as shown by D of Fig. 3.
As appreciated from Fig. 3, the line D in which all elements have taken noise suppressive measures remarkably lower than the line E. However, the line D comes near the line E in a region of 20 through 100 MHz.
Figs. 4(a) and 4(b) show the measurement results in the case of trucks, wherein Fig. 4(b) shows a cab-over engine. In these drawings, 0 dB represents 1 µV/m.
Figs. 4(a) and 4(b), in more detail show the measurement results when the ignition system comprising the elements in the combination of D is applied to a truck. Particularly, the line D in Fig. 4(a) denotes the elements in combination of D which are applied to a cab-over engine truck in which a four-cycle 2,000 cc internal combustion engine is mounted and the line D in Fig. 4(b) denotes the elements in combination of D which are applied to a two-box cab behind-engine truck in which is mounted a four-cycle 1,500 cc internal combustion engine.
As appreciated from these drawings, there are cases where the line D is higher than the line E in a frequency region from 20 to 100 MHz depending on the vehicle models.
On the other hand, the hoise-suppressive high tension cable 28 generally has a length of about 30 centimeter and one end thereof is connected to the low-resistance ignition coil 27. A lead wire (not shown in the drawings) is connected between a primary winding of the ignition coil and vehicle battery to supply a DC voltage to the primary winding thereof.
The noise current which does not attenuate through such a short noise-suppressive high tension cable 28 flows from a secondary winding of the low-resistance ignition coil 27 to the lead wire at the primary winding thereof so that the noise electromagnetic wave is radiated from the ignition coil and lead wire as an antenna. Therefore, it is necessary to further improve the noise suppressive effect.
Although it is not certain that the noise level becomes higher when the elements in combination of D are applied to such trucks, the shape of vehicle or height of their internal combustion engines with respect to the earth surface may contribute to such indications of higher noise level.
Various analyses to solve the reduction of the noise electromagnetic wave in the vicinity of 20 through 100 MHz indicate the following facts.
That is to say, a high-frequency noise current caused by a spark discharge between the rotor electrode 21 and each of the fixed electrodes 17 flows into both noise suppressive high-tension cables 13 connected betweeh each of the fixed electrodes 17 and corresponding spark plug 1 and noise-suppressive high-tension cable 28 connected between the central electrode 16 and ignition coil 27.
Consequently, a noise electromagnetic wave is radiated from both noise-suppressive high- tension cables 13 and 18 as a kind of antenna.
However, since each noise-suppressive high-tension cable 13 generally has a length of about 60 through 70 centimeters and one end of the high-tension cable 13 is finally grounded through the resistor-equipped spark plug 1, the noise current described above is greatly attenuated and thereby the generation of noise wave is remarkably reduced because of short length of an effective antenna.
The present invention is based on the above-described matter.
That is to say, the present invention is directed to provide a resistance material at an intemediate portion of the rotor electrode 21, in more detail, between a contact at which the contactor 19 comes in touch with the rotor electrode 21 and two layers in which the dielectric material 25 is placed above or below the rotor electrode 21.
Fig. 5 shows one preferred embodiment of the present invention.
In Fig. 5, numeral 29 denotes a resistance material inserted at the intermediate portion described hereinabove: The resistance material 29 is, preferably, of a wire-wound resistor type or carbon film resistor type. The resistance value of the resistance material 29 ranges from 5 to 20 kiloohms.
The ignition energy is sent from the ignition coil 27 through the contactor 19 to a discharge end of the rotor electrode 21. The discharge end is a tip of the rotor electrode 21 which faces toward one of the fixed electrodes 17 through the discharge gap 20 when the rotor 22 is revolved.
A kind of resistor-and-capacitor type filter is formed with the resistance material 29 and stray capacitance of the distributor and internal combustion engine with respect to the earth. This resistor-and-capacitor type filter serves to attenuate the high-frequency noise current, thus reducing the noise current flowing through the ignition coil 27 and lead wire connected to the primary winding of the ignition coil.
Figs. 6(a) and 6(b) show measurement results of noise wave electric field strength in the case when the ignition system according to the present invention is used. The measurement requirements are the same as those in the case of Figs. 4(a) and 4(b).
The charcteristic graphs shown in Figs. 6(a) and 6(b) are measurement results in the case when the wire-wound resistor having a resistance value of 12 kiloohms is used as the resistance material. It is preferable to use a high-resistance material, e.g., made of ceramics as the contactor 19. Consequently, the noise suppressive effect is furthermore increased.
As appreciated from Figs. 6 (a) and 6(b), the noise level is reduced in a frequency region from 20 to 100 MHz, i.e., the line of F being lower than the line of E.
As described hereinabove, the noise electromagnetic wave is radiated from each of the distributor, spark plugs, and high-tension cables constituting the ignition system. Furthermore, the maximum electric field strength of noise wave formed totally from the individual elements of the ignition system is dominated by the maximum noise electric field strength among the noise waves radiated from the individual elements. The experiment indicates that it is less effective in preventing noise wave radiation to take the noise suppressive measures for the individual elements, separately. Since the experiment ensures that it is necessary to carry out the noise suppressive measure on the entire ignition system, the present invention is directed to suppresss the noise wave radiation by taking the noise suppressive measures for all the elements constituting the ignition system. Therefore, according to the present invention, the ignition system can suppress the noise wave generation over an entire frequency range from a low- frequency region of about 20 MHz to a high-frequency region of about 250 MHz.
It will clearly be'understood by those skilled in the art that various changes and modification may be made without departing from the spirit of the present invention which is defined by the appended claims.

Claims

1. A noise-suppressive ignition system for a multicylinder internal combustion engine of an automotive vehicle, comprising a discharge energy generating means (27) which operatively generates a discharge energy intense enough to ignite an air-fuel mixture supplied within the engine; characterized by

(a) a discharge energy distributing means (27) including rotating means (22) having a rotor electrode member (21) electrically connected to said discharge energy generating means (27) via a center electrode member (16) thereof and which rotates with an engine Camshaft, the rotor electrode member (21) being made of a conductive material and a dielectric material (25) made of a silicone resin containing glass fabric being secured to at least a portion of at least one of top and bottom surface areas of said rotor electrode member (21), a plurality of fixed electrode members (17) located symmetrically about said rotating means (22) and each forming a small discharge gap (20) with said electrode member of said rotating means (22) when said rotor electrode member (21) of said rotating means approaches the end thereof, and a resistance material (29) being interposed between said center electrode member (16) and the portion of said rotor electrode member (21) to which said dielectric material (25) is secured;

(b) a plurality of spark plugs (1) each mounted in a corresponding engine cylinder and including a monolithic resistor having a sufficient length to provide a high-frequency noise filtering effect which bridges a central electrode (9) thereof to a discharge electrode (4) provided at a tip thereof and a grounded side electrode (3) which forms a spark discharge gap with said discharge electrode; and

(c) a plurality of noise-suppressive high tension cables (13), one of which electrically connects said discharge generating means (27) and rotating means (22) of said distributing means (24) via said center electrode member (16) and the others of which connect the fixed electrodes (17) of said distributing means (24) to the corresponding central electrodes (9) of said spark plugs (1).

2. A noise-suppressive ignition system as set forth in claim 1, wherein said resistance material (29) is a wire-wound type resistor.

3. A noise-suppressive ignition system as set forth in claim 1, wherein said resistance material (29) is a carbon-film resistor.

4. A noise-suppressive ignition system as set forth in either claim 2 or 3, wherein said resistance material (29) has a resistance value ranging from 5 to 20 kiloohms.

5. A noise-suppressive ignition system as set forth in claim 1, wherein said center electrode member (16) includes a contactor (19) which is brought in contact with said rotor electrode member (22), said contactor (19) being made of high resistance material.

6. A noise-suppressive ignition system as set forth in claim 5, wherein said contactor (19) is made of ceramics.