CAPACITIVE IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES

Abstract: An ignition system for use in internal combustion engines, in which there is provided a plurality of charging means (L1, L2), at least one of the plurality of charging means being adapted to provide charge to a plurality of charge storage means (C1, C2), in a predetermined manner, the charge storage means being arranged to collectively activate a spark means (T1).

Description: CAPACITIVE IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGIN ES Field of Invention The present invention relates to a method of producing spark in an ignition system, particularly a capacitive discharge ignition system for internal combustion engines and also to an improved capacitive discharge ignition system therefor. Related Application The present invention is related to the disclosure in PCT/AU91/00524 filed by the present Applicant on 15 November, 1991. The contents of the PCT application are herein incorporated by reference. Background Art In the motor industry, there has been a trend to use electronic ignition systems to improve the efficiency and performance of internal combustion engines by producing a spark with desired characteristics to initiate combustion of an air-fuel mixture, particularly the lean mixtures encountered in stratified charge engines. Nevertheless, in the case of capacitive discharge ignition systems, where sufficient spark voltage can build up in a relatively short period, it has been found that the spark produced by the spark voltage is typically of relatively brief duration. Such relatively brief spark duration characteristics are even more pronounced in a capacitive discharge ignition system having a low-capacitance high-voltage charge storage means such as a capacitor. A high-voltage will cause a high discharging current to pass through the primary coil of an ignition system to induce the necessary spark voltage in the secondary coil of the ignition system to produce a spark at the spark gap. However, the low- capacitance limits the duration of that current and thus, the duration of the spark produced. It has been realised that the spark duration provided by such prior art ignition systems may sometimes be too brief to properly ignite the air-fuel mixture, particularly for a lean mixture. This may cause adverse pollution effects and may result in undesirable operating characteristics of the engine. A proposal to merely increase the capacitance of the charge storage means or capacitor would not significantly extend the spark duration, but rather would cause a more intense spark. Another proposal to provide a resistor in the primary circuit to reduce the rate of discharge would also reduce the amount of the discharging current and the energy available for the spark. Further, the use of transistors of the type referred to as "silicon controlled rectifiers" to initiate the discharge of energy from the charge storage means or capacitor would invariably allow the energy which has been stored in the primary coil during the discharge to dissipate within the primary circuit and also potentially prevent the use of any secondary or flyback spark if this were desired. Summary of the Invention The present invention has as its object to alleviate some of the disadvantages discussed above. It is an object of the present invention to provide a method of producing an improved and extended duration spark in an ignition system for internal combustion engines. It is a further object of the present invention to provide an improved charging method and apparatus for an ignition system for use with internal combustion engines. In accordance with one aspect of the present invention there is provided an ignition system in which there is provided a plurality of charging means, at least one of said plurality of charging means being adapted to provide a charge to a plurality of charge storage means, preferably of different storage capacity, in a predetermined manner, the charge storage means being arranged to collectively activate a spark means. In a preferred embodiment, the ignition system is used in an internal combustion engine. Preferably, the ignition system provides at least one charging means arranged to provide at least part of the charge for at least two charge storage means. Additionally, the ignition system may include at least two charging means arranged to provide the charge for at least one charge storage means. Preferably, at least one of the charging means is arranged to provide part or all of the charge for at least one charge storage means. Conveniently, at least one respective charging means is arranged to be substantially matched to the capacity of at least one of the respective charge storage means. Preferably, respective charging means may be arranged to be substantially matched to the capacity of respective charge storage means. Preferably, at least one charge storage means is of a high capacitance and at least one other charge storage means is of a low capacitance. Furthermore, preferably the ignition system is a capacitative discharge ignition system, wherein the charge storage means are conveniently connected to the primary coil of a spark means, the spark means having a secondary coil connected to a spark gap. The present invention is predicated on the need to provide a spark duration in excess of about 1.5 mS in an internal combustion engine. The present invention results from the discovery that spark duration may be extended by providing more than one charging means to provide charge to more than one charge storage means and that in delivering the charge from the plurality of charging means to the plurality of charge storage means in a predetermined manner, the charge storage means are capable of delivering energy for an extended spark. By using two charge coils instead of one, and dividing the various portions of the current waves generated thereby, the transfer of energy from the charge coils to the charge storage means is optimised, resulting in spark durations of approximately 2mS. The present invention seeks to optimise the use of each coil by closely matching the drive capability of each of the coils to one of each of the individual charge storage means. In another aspect, the present invention provides a method of providing charge from a plurality of charging means to a plurality of charge storage means in an ignition system, the method including the step of distributing the charge from at least one of the plurality of charging means to a plurality of charge storage means, preferably of different capacities, in order to charge the charge storage means. In a preferred embodiment, the method can be used for ignition of internal combustion engines. Preferably, at least one charging means provides at least part of the charge for at least two charge storage means. Additionally, at least two charging means may provide the charge for at least one charge storage means. Preferably, at least one of the charging means is arranged to provide part or all of the charge for at least one charge storage means. Preferably, at least one charging means substantially matches the capacity of at least one of said charge storage means. Respective charging means may substantially match the capacity of a respective charge storage means. Preferably, at least one charge storage means is of a high capacitance and at least one other charge storage means is of a low capacitance. The present invention is predicated on the discovery that in the process of charging two charge storage means via two charging means instead of one, rather than using one first half of the charging wave of a single charging means to charge one first charge storage means and the other second half of the charging wave to charge a second charge storage means (until a nominal voltage is attained in the second charge storage means and then applying the residual of the second half of the charging wave to further charge the first charge storage means), an unbalanced charging methodology can be utilized to charge the two charge storage means by way of two charging means. In a preferred form, one charge storage means is charged by receiving approximately three half wave portions made up of two half waves from a first charging means and one half wave from a second charging means, and the second charge storage means is charged by receiving the other one half wave portion from the second charging means. This results, inter alia, in the ability to provide (a) a lower cost isolation means in the form of a relatively low cost diode instead of a higher cost zener diode as disclosed in PCT/AU 91/00524 and (b) an extended spark duration of in excess of about 1.5 ms. Description of the Invention The present invention will now be described with reference to two embodiments thereof, and with reference to the accompanying drawings. It should be clearly understood, however, that the description of the embodiments, and the drawings, are given purely for the purpose of explanation and exemplification only, and are not intended to be limitative of the scope of the present invention in any way. Figure 1 shows a schematic diagram of one form of ignition system in accordance with the present invention; and Figure 2 shows a schematic diagram of a second form of ignition system in accordance with the present invention. A dual rate capacitive discharge ignition system, for example for use in internal combustion engines, normally uses a single charge coil to generate the charge current to be distributed to two storage means. Until recently, small engines fitted with fuel injection systems have not required spark durations in excess of 1 mS. However, recent demand for more efficient combustion management in internal combustion engines and the desire to use capacitive discharge ignition systems on small engines of larger capacity requires spark durations in excess of 1.5mS to maintain stability of combustion. By using two charge coils instead of one, and dividing various portions of the charging waves created thereby, the transfer of energy from the charge coils to a plurality of charge storage means or capacitors is optimised, resulting in spark durations of up to 2mS. Twin coil arrangements in known capacitive discharge ignition systems are normally used for the purpose of maintaining a more constant combined output drive capability over a wide speed range whereas, the invention described herein optimises the use of each coil by closely matching the drive capabilities thereof to the respective capacities of the individual charge storage means. Each of the two coils of the preferred embodiments develop a full charging wave wherein said full charging waves are to be applied for the charging of two charge storage means, each of which are connected to the primary winding of an ignition coil. In regard to the embodiment as shown in Figure 1, one charge coil (L1) is chosen to be of relatively low impedance, and is able to deliver a substantial current into a high capacitance capacitor ("storage means C1"). The rectifier arrangement of diodes D4 and D1 and D2 and D3 allows all of the current generated by this coil (L1) to be delivered into charge storage means, C1. The other charge coil (L2) has a much higher impedance but a correspondingly higher output voltage. Only one half of the charging wave generated thereby is required to sufficiently charge a lower capacitance capacitor ("storage means C2") to a higher voltage and thus the other half of that charging wave is redirected to storage means C1 (which by nature of its higher capacity limits the coil output voltage for that half wave). The rectifier arrangement of diodes D4 and D7 and D6 and D3 allows all of the current generated by this coil (L2) to be delivered into charge storage means C1 and C2. The diode D5 serves as a charge isolation means between the charge storage means C1 and C2. The low capacitance capacitor (C2) may be selected from a range of capacitances of 0.47 μF to 4.7 μF. The higher capacitance capacitor (C1) may be selected from a range of capacitances of 22 μF to 680 μF. Capacitance values outside these ranges may be used, but it has been determined that such values, if used, are unlikely to have any additional benefit in achieving extended spark duration or delivery. Furthermore, the ratio of capacitors C2:C1 has been found to be optimum in the range of 1 :20 to 1 :200. In addition, it has been found that in general the higher the capacitance value selected for C1 , the more energy that is able to be stored, and thus the longer the spark duration delivered. In the present embodiment, each of the two charge coils L1 and L2 develop a full wave in phase for at least one charge cycle per discharge cycle for delivery to capacitors C1 and C2, there being potentially more than one one charge cycle per discharge cycle in the system. The significant change in the charging is that instead of using one half wave from a single charge coil to charge storage means C1 and the other half wave for storage means C2 (until a nominal voltage of say 300V is attained and then applying this second half wave to further charge storage means C1), two charge coils are used wherein three half waves now charge storage means 01 and one half wave charges storage means 02. The storage isolation means D5 may then be a lower cost diode instead of higher cost zener diode(s). 5 The delivery of three half waves and one half wave are enabled by redirecting part of the charge from one coil (L2) to one of the capacitors (01). It has also been found that by providing to one charge storage means (i.e: 01) three half waves, that charge storage means can be provided in the form of a higher value component, and thus store more energy, resulting in an increased 10 delivery of energy/charge for providing a spark of increased duration at the spark gap S1. As a further alternative, it may also be possible to re-direct one half wave from L1 to 02 in a similar fashion to that noted above. Hence, in such an alternative, the charge coils L1 and L2 provide three half waves to charge 15 storage means 02 and a single half wave from L1 is used to charge storage means 01. However, this alternative would require a zener diode in place of diode D5 of Figure 1 and so the advantage of avoiding the use of a zener diode is diluted. Figure 2 shows a further embodiment in which the charge storage means 20 01 is charged with separate half waves from the respective charge coils (L1 and L2). The rectifier arrangement of diodes D4, D1 and D7 allows the two half waves to be delivered into charge storage means 01. Similarly, the other charge storage means 02 is also charged with separate half waves from the respective charge coils (L1 and L2). The rectifier 25 arrangement of diodes D2, D3 and D6 allows the two half waves to be delivered into charge storage means 02. Hence, in this embodiment, both the charging waves of charge coils L1 and L2 are split to charge storage means 01 and 02. Each of the two charge coils L1 and L2 develop a full wave in phase for at least one charge/discharge 30 cycle per discharge cycle for delivery to capacitors 01 and 02. Though the charging sequence is different to that described for the embodiment as shown in Figure 1, the operation and structure are in accordance with the invention. It should be noted that there is a limit to the amount of charge that can be transferred into the spark gap S1. This limit is dependent on the efficiency of the ignition coil T*ι to transfer energy from the primary winding into the secondary winding; that is, the slowest rate of change of primary current which will be transformed into the secondary winding. This occurs until the rate of change of current is so slow as to not induce a current into the secondary winding. At this point a flyback commences in the same fashion as described in the Applicant's prior patent application referred to hereinbefore. With the large capacitance capacitor C1 set to around 470 μF, it has been found that the rate of change of current delivered to the primary winding of the ignition coil T-* approaches a performance result which is sufficient to meet current engine requirements. Another side effect of the rate of change of the current is that the secondary or flyback spark is of higher energy and longer duration than was previously possible. Furthermore, as shown in Figure 1 , a significant enhancement has been attained in the embodiment as disclosed by replacing the switching device and flyback control means of Fig. 2 of PCT/AU91/00524 with a single transistor Q1. Preferably, the transistor is an insulated gate bipolar transistor (IGBT) of a suitable rating. The present invention may also be utilized in existing capacitative or non- capacitative ignition systems. It may also be possible to substitute for capacitors C1 , 02 (as disclosed in Figures 1 and 2) batteries B1 , B2 for use as charge storage means. The batteries would also require to be adapted to high and low voltage operation in a similar fashion to the embodiments shown in Figures 1 and 2. In this alternative configuration, the ignition system may be similarly wired, except for some changes necessitated due to the use of batteries rather than capacitors, as would be known by an artisan. The same or a similar charging methodology can be implemented in such an alternative ignition system. The invention is equally applicable in a system including any desired number of charge coils, charge storage means and charge storage isolation means. Therefore, the embodiments described are indicative only and other variations may be developed by the skilled artisan which still fall within the scope of the present invention.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An ignition system, in which there is provided a plurality of charging means, at least one of said plurality of charging means being adapted to provide charge to a plurality of charge storage means in a predetermined manner, the charge storage means being arranged to collectively activate a spark means. 2. The ignition system as claimed in claim 1, characterised in that said plurality of charge storage means includes charge storage means of differing storage capacity. 3. The ignition system as claimed in claim 1 or 2, characterised in that at least one charging means is arranged to provide at least part of the charge for at least two charge storage means. 4. The ignition system as claimed in claims 1 to 3, characterised in that at least two charging means are arranged to provide at least part of the charge for at least one charge storage means. 5. The ignition system as claimed in any one of claims 1 to 4, characterised in that at least one of said charging means is arranged to provide at least part of the charge for at least one charge storage means. 6. The ignition system as claimed in any one of claims 1 to 5, characterised in that at least one of said charging means is arranged to provide all of the charge for at least one charge storage means. 7. The ignition system as claimed in any one of claims 1 to 6, characterised in that at least one charging means is arranged to be substantially matched to the capacity of at least one charge storage means. 8. The ignition system as claimed in any one of claims 1 to 7, characterised in that at least one charge storage means has high storage capacity and at least one other charge storage means has low storage capacity. 9. The ignition system as claimed in any one of claims 1 to 8, characterised in that said system is a capacitive discharge ignition system. 10. The ignition system as claimed in any one of claims 1 to 9, characterised in that said spark means includes a primary coil and a secondary coil connected to a spark gap wherein said plurality of charge storage means are connected to said primary coil of said spark means. 11. The ignition system as claimed in any one of claims 1 to 10, characterised in that two charge storage means are included and the ratio of capacitance between both charge storage means is between 1 :20 and 1 :200. 12. A method of providing charge from a plurality of charging means to a plurality of charge storage means in an ignition system, the method including the step of distributing the charge from at least one of the plurality of charging means to a plurality of charge storage means in order to charge the charge storage means. 13. The method as claimed in claim 12, characterised in that said plurality of charge storage means includes charge storage means of differing storage capacity. 14. The method as claimed in claim 12 or 13, characterised in that at least one charging means provides at least part of the charge for at least two charge storage means. 15. The method as claimed in claims 12 to 14, characterised in that at least two charging means provide at least part of the charge for at least one charge storage means. 16. The method as claimed in any one of claims 12 to 15, characterised in that at least one of said charging means is arranged to provide at least part of the charge for at least one charge storage means. 17. The method as claimed in any one of claims 12 to 15, characterised in that at least one of said charging means is arranged to provide all of the charge for at least one charge storage means. 18. The method as claimed in any one of claims 12 to 17, characterised in that at least one charge storage means has high storage capacity and at least one other charge storage means has low storage capacity. 19. The method as claimed in any one of claims 12 to 18, characterised in that charge is provided to charge the storage means in an unbalanced manner such that at least one charge storage means receives more charge than another charge storage means. 20. The method as claimed in any one of claims 12 to 18, characterised in that at least one charging means substantially matches the capacity of at least one of said charge storage means. 21. Ignition systems as claimed in any one of claims 1 to 11 to be used in an internal combustion engine. 22. The method as claimed in any one of claims 12 to 20 wherein said ignition system is used for ignition of an internal combustion engine.

Inventors: BASSO STEVEN MICHAEL, CEBIS MARTIN JOHN PETER, BASSO, STEVEN, MICHAEL, CEBIS, MARTIN, JOHN, PETER
Applicants: BASSO STEVEN MICHAEL, CEBIS MARTIN JOHN PETER, ORBITAL ENG PTY, BASSO, STEVEN, MICHAEL, CEBIS, MARTIN, JOHN, PETER, ORBITAL ENGINE COMPANY (AUSTRALIA) PTY. LIMITED
Application year: 1993
Main classification: F02P3
IPC codes: F02P1, F02P3, F02P9