IGNITION CAPACITIVE DISCHARGE SYSTEM FOR INTERNAL COMBUSTION ENGINES

Abstract: An ignition capacitive discharge system for internal combustion engines particularly of small sizes, two-stroke cycle "OTTO", associable with one rotary generator of electric energy to produce an ignition signal for spark plug means (Ca), supplied directly from the supply bobbin of the discharge capacitor (C1), utilizing as discharge means of said discharge capacitor (C1) a Thyristor (SCR = Silicon Controlled Rectifier), characterized in that the pilotage of said thyristor (SCR) is operated on its cathode by a high impedance branch with the gate (G) of said Thyristor (SCR) electrically connected to mass (Fig. 4, 5, 6).

Description: Ignition capacitive discharge system for intern al com bustion en gi n e s The present invention concerns an ignition capacitive discharge system for internal combustion engines. In the field of the cycle-drivers internal combustion engines or in stationary combustion engines four pole generators that present a configuration of the type of fig. l or fig.2 commonly defined "V"-type or parallel-type are used. The statoric part is normally composed with: 1 ) supply bobbin of the spark plug capacitive discharge ignition that gives the charge of the condenser of the ignition, (EP) is normally a bobbin of very thin wire spires; 2) low-tension bobbin for signalling (visual signalling and lightening) and recharge of the battery. This bobbin is normally composed of few spires of larger diameter wire; 3) a phase captor commonly called pick-up (ignition pilot coil) that supplies the command to the ignition system to determine the sparking point. Being a 4 poles generator, there are two command impulses for each revolution, namely two sparks, dephased of 180° between them, in the case of a single-cylinder motor one of the two sparks is used for the ignition while the other is lost and however does not influence the operation of the I.C. (Internal Combustion) engine in the bicylinder motor case with cylinders at 180° the sparks are both useful. This is also valid for a six pole generator where obviously we have three sparks per revolution dephased of 120° between them. For this we understand that any coil has one end to mass and the other one is brought to the external, so from each generator three wires exit. A schema of an ignition system of this type is visible in fig.3. We do not describe the operation of this schema because it is well known, we remember that this type of solution gives good efficiency because the supply bobbin supplies current solely during the charge phase of the capacitor and the excursion of the spark phase is contained inside few grades by the same presence of the phase captor (pick-up ignition pilot coil). The drawback of this solution is the cost determined for the presence of the separate captor and in that by the generator has three exit wires. To obviate at this drawback the possible solution is to use the supply bobbin also as phase command eliminating so the phase captor and the relative conductor. This type of solution is already made. The circuits known, exploit an electric half-period for the charge of the condenser and a half-period for the command of the ignition. Such command, is given exploiting the fallen of potential on an electric resistance that normally is of lower value to limit the power dissipation. Such electric resistance of lower resistive value allows obviously a high current passage during the command phase for the ignition (in practical in this half-period the supply bobbin works in short circuit) this causes a forceful limitation of the charge quantity accumulated on the capacity (capacitor) of the ignition and a path of the ignition advance with important excursion and unlikely manageable varying the circuital parameters. So the ideal would be to have a solution in which the supply bobbin besides to the charge of the capacitor allows the same command of the ignition presenting but during the electric command half-period a high impedance having so the maximum charge yield of the capacitor besides with one path of the comparable spark advance to that obtainable with a . captor (pick-up) or a path of the spark advance manageable to the varying of the circuital parameters, all with a single conductor that connects the generator to the ignition system being the current return across the mass of the loom and of the stator of the generator. This results are obtained with the following circuital solutions. Scope of the present invention is to obviate to said drawbacks. This and other scopes are reached with the present invention as claimed, by means of an ignition capacitive discharge system for internal combustion engines particularly of small sizes, two-stroke cycle "OTTO", associable with one rotary generator of electric energy to produce an ignition signal for spark plug means, supplied directly from the supply bobbin of the discharge capacitor, utilizing as discharge means of said discharge capacitor a Thyristor (SCR = Silicon Controlled Rectifier), characterized in that the pilotage of said thyristor (SCR) is operated on its cathode by a high impedance branch with the gate of said Thyristor (SCR) connected electrically to mass. Advantageously the pilotage of the thyristor (SCR) is operated on its cathode by a high impedance branch in which a peak detector (Rl- 1 R2-C2-D3) is inserted that allows the management of the phase while 2 the gate (G) of the thyristor (SCR) is connected electrically to mass 3 In the best solution the ignition system has a circuit in which the 4 closure of the spark current across a connection mass diode is 5 foreseen. 6 With this solution we obtain the advantages of an important 7 simplification and reduction of the costs. 8 9 The invention can be better understood with the help of the I 0 following exemplificative description and drawings, in which: I I - in Figs. 1 and 2 are represented two schematic arrangement of the 1 2 device; 1 3 - in Fig. 3 is represented a schema according to prior art; 1 4 - in Fig. 4 is represented a first solution as per this invention; 1 5 - in Fig. 5 is shown the circuital solution in which we use a 1 6 inductance-capacitor bobbin with impedance controlled according to 1 7 (WO89/05055 - PCT/IT00039) and IT83365A/88 (WO89/10622 -PCT- 1 8 IT89/00024); 1 9 - in Fig. 6 is represented another simplified solution to allow the 20 excursion phase be maximized. 2 1 22 All of the following description is valid independently of the use or 2 3 not of said referenced inductance-capacitor bobbin with impedance 24 controlled. 25 During the positive half- wave of the tension of the supply bobbin 2 6 the diode D3 is polarized inversely while the diodes Dl, D2, D4 are 2 7 polarized directly so the electric current flows from the supply 2 8 bobbin across Dl, Cl, D4, D2 loading Cl with a certain potential. When the potential of the supply bobbin reverses its own polarity sign the diodes D1,D2,D4 are polarized inversely while D3 is polarized directly and the current flows across R3, C2, Rl , D3 and in small part also across R2, provided that the potential of the supply bobbin overcomes the potential of C2 that we have previously loaded. We remember that the solution is particularly efficient from an energetic point of view for the charge of Cl because the electric circuit part composed by Rl, R2, R3, C2, D2, D3 realizes a branch at high impedance and consequently strongly limits the current circulation during this phase, in practical the supply bobbin during the command phase of the SCR free rotates without working. The particular circuital configuration of the SCR piloted by the cathode with the gate directly to mass allows its priming (starting) when the current of the supply bobbin flows on R3 entering from mass and causes a fallen of potential greater than the threshold priming tension of the SCR. At this point the priming of the SCR allows the discharge of the capacity Cl on the primary coil Lp with the consequent transferring of energy to the secondary coil Ls where induces a high potential such to prime a spark on the ignition plug Ca which current can close across the diode D2 while the current of the primary coil Lp closes on the diode D4 or D4, D5 in the case where we utilizes said inductance-capacitor bobbin with controlled impedance. The circuital configuration composed by R2, C2, Rl, D3 is to realize a peak detector and this particular solution allows to manage the path of the ignition phase intervening on the resistive values Rl , R2 or on the value of the capacity C2. C2 can be eliminated for having the maximum excursion of the phase. The circuital solution being in this case particularly simple and cheap as disclosed in Fig.6.

Claims: Claims 1. An ignition capacitive discharge system for internal combustion engines particularly of small sizes, two-stroke cycle "OTTO", associable with one rotary generator of electric energy to produce an ignition signal for spark plug means (Ca), supplied directly from the supply bobbin of the discharge capacitor (Cl), utilizing as discharge means of said discharge capacitor (Cl) a Thyristor (SCR = Silicon Controlled Rectifier), characterized in that the pilotage of said thyristor (SCR) is operated on its cathode by a high impedance branch with the gate (G) of said Thyristor (SCR) electrically connected to mass (Figg.4, 5, 6). 2. An ignition system according to claim 1 , characterized in that the pilotage of the thyristor (SCR) is operated on its cathode by a high impedance branch in which a peak detector (R1-R2-C2-D3) is inserted that allows the management of the phase while the gate (G) of the thyristor (SCR) is connected electrically to mass (fιgg.4, 5, 6). 3. An ignition System according to claim 1 , characterized in that the priming threshold of the Thyristor (SCR) is determined ' by fallen of potential on resistance downwards of the supply bobbin (R3) due to the circulating current in corresponding resistance {R3, (R2, C2) Rl D3}. 4. An ignition system according to claim 1, characterized in that it comprises a diode (D2) that has the triple function of: - consent the charge of said discharge capacitor (Cl) when it is directly polarized; - consent the current passage only on resistance downwards of the supply bobbin (R3) when if is inversely polarized; - consent the . closure of the spark current successively to the discharge of the discharge capacitor (Cl). 5. An ignition system according to claim 1 , characterized in that it is provided with a circuital solution in which is foreseen the closure of the spark current across a diode (D2) to simplify the connection to the high tension bobbin.

Inventors: REGAZZI GIANNI, REGAZZI, GIANNI
Applicants: DUCATI ENERGIA SPA, DUCATI ENERGIA S.P.A.
Application year: 1991
Main classification: F02P1
IPC codes: F02P1