EP0495434A1

EP0495434A1 - Electronic ignition control system for a vehicle internal combustion engine

Info

Publication number: EP0495434A1
Application number: EP19920100454
Authority: EP
Inventors: Daniele Rossi; Gabriele Serra
Original assignee: Weber SRL
Current assignee: Weber SRL
Priority date: 1991-01-15
Filing date: 1992-01-13
Publication date: 1992-07-22
Also published as: ITTO910021A1; IT1244997B; ITTO910021A0

Abstract

A system (1) comprising:
a first block (7) for producing an inductive discharge between the electrodes of a spark plug (6) of an engine (3);
a second block (8) for producing a capacitive discharge between the electrodes of the spark plug (6);
an electronic control system (2) to which are supplied signals relative to operating parameters and conditions of the engine (3), and which provides for selecting an inductive, capacitive, or combined inductive and capacitive discharge, and for phasing the two discharges in the case of a combined discharge;
a third block (5) enabled by the electronic control system (2), for controlling the first and second blocks (7, 8).

Description

The present invention relates to an electronic ignition control system for a vehicle internal combustion engine. For initiating combustion of a controlled ignition engine, a spark is produced between the electrodes of a spark plug on the cylinder head. Current electronic ignition systems may be inductive or capacitive discharge types, each of which features a primary and a secondary circuit. The primary circuit of inductive discharge systems comprises a current generator; a primary winding about a magnetic core; and a switch connected between one terminal of the primary winding and a reference ground, and usually consisting of an electronically controlled Darlington transistor. The secondary circuit comprises a secondary winding about the same magnetic core; a spark plug for supplying the spark inside the combustion chamber; and, possibly also, a distributor for distributing the high voltage current to the cylinders according to the ignition sequence. Appropriate control of the transistor causes a sharp variation in current in the primary circuit, which produces an extra voltage in the secondary circuit for generating the spark between the electrodes of the plugs.
Capacitive discharge systems comprise a secondary circuit as described above, and a primary circuit comprising a current generator; a voltage step-up converter; a primary winding; an electronically controlled switch parallel to the winding; and a condenser between the primary winding and switch. When the switch is open, the condenser is charged by the step-up converter. when the switch is closed, the condenser is discharged along the primary winding.
Inductive discharge systems present numerous drawbacks. Foremost of these is that, depending on the power of the engine, they require considerable electrical power, so that the circuits, particularly the magnetic core and the section of the primary winding wire, are necessarily oversized, thus increasing the size of the circuit. Moreover, electricity consumption is high, most of which is dissipated in the form of heat along the primary circuit, and the secondary circuit is less efficient than those of capacitive discharge systems, due to the available voltage being lower. As such, inductive discharge systems often fail to provide for full combustion of the fuel, especially in certain critical conditions of the engine, i.e. extremely cold startup, in which case fuel supply is considerable as compared with the air supply; maximum torque condition of supercharged engines; and when the throttle valve on the air manifold is almost entirely closed at high engine speed. The poor efficiency of the secondary circuit also results in fouling of the plugs, which thus require a higher voltage and current for producing the spark. A relatively long pre-arc time, i.e. the lapse between control of the transistor and sparking, is also produced, and, if long enough, may result in dielectric losses in the insulation of the primary winding by electrically charging the dielectric material. The pre-arc time depends on the size of the primary winding, which provides for a voltage increasing according to a given load curve. In inductive discharge systems, preignition may occur, due to the positive inverted voltage present in the secondary winding while the primary is being charged. Finally, the efficiency of inductive discharge systems depends on the power of the generator. That is, in the event of a less than nominal supply voltage, the system may fail to provide the extra voltage required by the secondary for sparking.
The drawbacks posed by capacitive discharge systems are the brief duration of the spark between the electrodes of the plug, and the complex design (and, hence, high production cost) of the primary circuit for installing the step-up converter. The extent to which combustion is assured obviously depends on the duration of the spark; while the extremely strong current in the secondary results in severe wear of the plugs.
It is an object of the present invention to provide an electronic ignition control system for a vehicle internal combustion engine, designed to overcome the aforementioned drawbacks.
According to the present invention, there is provided an electronic ignition control system for a vehicle internal combustion engine, characterised by the fact that it comprises:
a first electronic block for producing an inductive discharge between the electrodes of at least one spark plug on said engine;
a second electronic block for producing a capacitive discharge between the electrodes of said plug;
an electronic control system to which are supplied a number of signals relative to operating parameters and conditions of said engine, and which provides for processing said signals for selecting an inductive, capacitive, or combined inductive and capacitive discharge, and, in the event of the latter, for phasing said two discharges; and
a third electronic block enabled by said control system, for controlling said first and second blocks. A number of preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Fig.1 shows a block diagram of a system in accordance with the present invention;
Fig.2 shows a flow chart of the operations performed by the electronic control system in Fig.1;
Fig.3 shows one embodiment of a block in Fig.1;
Fig.s 4, 5 and 6 show three embodiments of the electric circuit for producing the spark between the electrodes of the plug;
Fig.7 shows a further embodiment of the sparking circuit.

Number 1 in Fig.1 indicates an electronic ignition control system for a vehicle internal combustion engine, designed to select between a purely inductive discharge, a purely capacitive discharge, or a timed combination discharge between the electrodes of a spark plug. System 1 comprises an electronic control system, shown schematically by block 2, to which are supplied a number of signals relative to operating parameters and conditions of the engine shown schematically by block 3. In particular, the electronic control system is supplied with signals relative to engine speed; cylinder charge; and intake air and cooling fluid temperatures. A sensor 4 also supplies a cylinder stroke signal, i.e. indicating the top dead center position of each cylinder. The term "cylinder charge" is intended to mean intake air pressure and volume; the angular position of the throttle valve on the air manifold; or any combination of these parameters.
Block 2 enables a block 5 for controlling the spark between the electrodes of the plugs shown schematically by block 6. Block 5 provides for selecting the type of discharge to be produced, by controlling an inductive discharge block 7, a capacitive discharge block 8, or both blocks 7 and 8 one after the other. Blocks 7 and 8 are connected to a block 11 representing an ignition distributor, electronic or otherwise, and which is connected to block 6. System 1 presents two electric supply lines 12 and 13, the first generally supplying block 7 with 12 volts, and the second supplying block 8 with over 300 volts. As shown more clearly later on, blocks 7 and 8 may be supplied independently, or the supply of block 8 derived from that of block 7.
Fig.2 shows a flow chart of the operation of the electronic control system in the discharge control phase. The electronic control system presents a block 14, which is supplied with signals relative to engine speed and the cylinder charge, and which, on the basis of said signals, computes the basic spark lead angle. Block 14 goes on to block 15, which is supplied with signals relative to intake air and cooling fluid temperature, and which provides for correcting the basic spark lead angle and computing the actual lead angle. Block 15 goes on to block 16, which, by a routine not shown, is supplied with signals relative to the timing of the engine, which is computed by processing most of the above signals, in particular, the engine speed and stroke signals. Block 16 first provides for determining the engine position and, hence, the engine angle, after which it identifies the synchronism immediately preceding the required instant of ignition. Block 16 goes on to block 17, which computes the waiting time between the timing-computed instant and the required instant of ignition.
Block 17 goes on to block 18, which provides for checking the above waiting time, and then goes on to block 21. From blocks 14 and 15, block 21 receives two signals, one indicating the type of discharge selected, e.g. inductive, capacitive or a combination of the two, and the other indicating the delay between the inductive and capacitive discharge commands, in the case of a combination discharge. Block 21 produces two signals respectively controlling inductive and capacitive discharge, and thus provides for selecting and establishing the time sequence of the discharge commands.
Fig.3 shows an embodiment of block 5, for performing the operations performed above by blocks 18 and 21. Block 5 presents a block 22, which receives the waiting time signal from block 17, and the output signal from blocks 14 and 15 relative to phasing of the two inductive and capacitive discharge commands. Block 22 controls a logic network consisting of four AND and two OR circuits. Of these, two AND circuits 23a, 23b and one OR circuit 24 relate to the inductive discharge command; and two AND circuits 25a, 25b and one OR circuit 26 to the capacitive discharge command.
Block 22 processes the incoming signals for making them acceptable to control by the logic network, and presents two connecting lines 27 and 28, of which line 27 is connected to a first input of circuits 23a and 25a, and line 28 to a first input of circuits 23b and 25b. A third connecting line 29 is connected directly to a second input of circuits 25a and 25b, and via an inverter 19 to a second input of circuits 23a and 23b. Line 29 provides for transferring the selected discharge or combination discharge signal, which is made acceptable to the logic network by a block 30 similar to block 22. The outputs of circuits 23a and 23b are connected to respective inputs of circuit 24, the output of which relates to the enabling signal of block 7. The outputs of circuits 25a and 25b are connected to respective inputs of circuit 26, the output of which relates to the enabling signal of block 8.
As already stated, electric supply to block 8 may be either independent or derived from that of block 7. Fig.s 4, 5 and 6 show three embodiments of blocks 7 and 8 wherein supply to block 8 is derived from that of block 7.
Number 31 in Fig.4 indicates a circuit arrangement featuring a primary and secondary circuit. The primary circuit comprises a direct current generator 32 normally consisting of the vehicle battery; a primary winding 33 about a magnetic core 34; and a Darlington transistor 35. Winding 33 presents a first terminal connected to the positive pole of generator 32, and a second terminal connected to the collector of transistor 35, the emitter of which is connected to a reference ground, and the base of which is connected to the collector via a Zener diode 36. The base of transistor 35 is controlled by the electronic control system via the output signal of circuit 24. Parallel to winding 33 is a controlled diode (SCR) 37, and, parallel to diode 37, a one-way diode 38. The anode of diode 37 is connected to the anode of a condenser 41, the cathode of which is connected to the first terminal of winding 33. The cathode of diode 37 is connected directly to the second terminal of winding 33. The cathode and anode of diode 38 are connected respectively to the anode and cathode of diode 37. The gate of diode 37 is controlled by the electronic control system via the output signal of circuit 26. The secondary circuit comprises a secondary winding 42 about core 34, each terminal of which is connected to a respective electrode of a spark plug shown schematically by block 43.
If one of two closely positioned windings is supplied with variable current, this is known to produce an induced current in the other, due to the variation in the flow chain. The phenomenon is further enhanced in the case of windings wound about the same magnetic core, and enables low-voltage energy to be converted into high-voltage, for producing violent discharges in the form of sparks. That is, if the primary winding is supplied with direct current for magnetizing the core, and the current is cut off sharply, the voltage at the terminals of the secondary becomes so high as to produce a violent discharge between the electrodes of the plug. By controlling the base of transistor 35, i.e. using a control current, the collector-emitter circuit may be disabled for producing extra voltage in the secondary circuit. The inductive nature of winding 33 results in a spurious phenomenon, which is converted into extra voltage at the terminals of the winding, and which occurs the instant the first spark is produced. As such, the extra voltage at the terminals of winding 33 may be used for charging condenser 41 via diode 38. When necessary, the gate of diode 37 may be controlled for discharging condenser 41 on to winding 33, and so producing in the secondary, after the first inductive spark, a second capacitive spark for use at a predetermined instant. Diode 36 provides for limiting the peak voltage when the collector-emitter circuit is opened, i.e. for normalizing the charging voltage of condenser 41.
Number 51 in Fig.5 indicates a circuit arrangement similar to 31, wherein diode 37 is replaced by a switch 52 controlled by the electronic control system via the output signal of circuit 26; and transistor 35 and diode 36 are replaced by a second switch 53 controlled by the electronic control system via the output signal of circuit 24. The winding 42 of the secondary circuit presents a first terminal connected to the first terminal of winding 33, and a second terminal connected to the electrode of a spark plug shown schematically by block 43. Circuit 51 operates in the same way as 31.
Number 61 in Fig.6 indicates a circuit arrangement similar to 51, except that it provides for producing a spark between the electrodes of four plugs shown schematically by blocks 43. The second terminal of winding 42 is connected to four parallel supply lines, one for each plug, and each fitted with a controlled diode 62, the gate of which is controlled by the electronic control system. Diodes 62 together represent an electronic ignition distributor, which may be represented schematically by block 11 in Fig.1. In this case, a control signal must be supplied by block 2 to block 11 for selecting the spark plug.
Number 71 in Fig.7 indicates a circuit arrangement, which, unlike those described above, provides for independent supply for the inductive and capacitive discharges. Supply for the inductive discharge consists of generator 32, and, for the capacitive discharge, of an additional direct current generator 72. Circuit 71 is similar to 51, except that, instead of being connected parallel to switch 52, diode 38 is series connected to generator 72, which provides for independently charging condenser 41. When switch 52 is closed, condenser 41 obviously discharges on to winding 33. Generator 72 may be connected to the alternator normally installed on the vehicle.
The advantages of the present invention will be clear from the foregoing description.
In particular, for producing the spark between the electrodes of the plug, the system according to the present invention provides for selecting between an inductive, capacitive or combination discharge, and, in the latter case, for determining whether the two discharges should be simultaneous or phased in relation to each other. The system can be fitted directly on to the plugs, i.e. one for each plug, by means of an ignition distributor, or may even feature a built-in distributor as shown in Fig.7. The possibility of selecting the type of discharge is obviously the main characteristic of the system according to the present invention, which thus provides for all the advantages of both inductive and capacitive discharge systems; the functional advantages of a combined discharge; and the advantage of one system substituting for the other in the event of a breakdown. A combined discharge, in particular, prolongs the spark, thus enabling a second discharge either immediately or a given time after the first. The increase in the duration of the spark also provides for improving fuel combustion, and so reducing or totally eliminating fouling of the plugs, which, as stated, does not affect the efficiency of a capacitive discharge, due to the greater strength and rapidity as compared with an inductive discharge. The system also provides for greater protection against operating failure and possible preignition.
Moreover, the system according to the present invention provides for reducing the size of winding 33 and core 34, in that, by deriving the supply of condenser 41 from that of the primary circuit, it enables recovery of the energy which, in the primary, would be totally dispersed, particularly in diode 36. This therefore results in a reduction of both energy consumption and pre-arc time, with all the advantages this entails as regards the dielectric material. In addition to the above advantages, independent supply also provides for effecting a capacitive discharge even in the event of generator 32 being run down or in any way defective.
To those skilled in the art it will be clear that changes may be made to the system as described and illustrated herein without, however, departing from the scope of the present invention.

Claims

An electronic ignition control system for a vehicle internal combustion engine (3), characterised by the fact that it comprises:
a first electronic block (7) for producing an inductive discharge between the electrodes of at least one spark plug (6, 43) on said engine (3);
a second electronic block (8) for producing a capacitive discharge between the electrodes of said plug (6, 43);
an electronic control system (2) to which are supplied a number of signals relative to operating parameters and conditions of said engine (3), and which provides for processing said signals for selecting an inductive, capacitive, or combined inductive and capacitive discharge, and, in the event of the latter, for phasing said two discharges; and
a third electronic block (5, 21) enabled by said control system (2), for controlling said first (7) and second (8) blocks.
A system as claimed in Claim 1, characterised by the fact that said electronic control system (2) comprises:
first means (14) for receiving signals relative to the speed and the cylinder charge of said engine (3), and which, as a function of said signals, computes the basic spark lead angle;
second means (15) for receiving signals relative to intake air and cooling fluid temperature, and which provide for correcting said basic spark lead angle and so computing the actual spark lead angle;
third means (16) for receiving signals relative to the timing of said engine (3), and which provide firstly for determining the engine position and, hence, the engine angle, and then for identifying the synchronism immediately preceding the required instant of ignition;
fourth means (17) for computing the waiting time between the instant computed on the basis of said timing conditions and the required instant of ignition;
fifth means (18) for checking said waiting time; and
said third block (5, 21) which, from said first and second means (14, 15), receives two signals, one indicating the type of discharge selected, and the other the delay between the inductive and capacitive discharge commands, or vice versa, in the case of a combined discharge; and which produces two signals respectively controlling the inductive and capacitive discharge.
A system as claimed in Claim 2, characterised by the fact that said third block (5, 21) comprises:
a fourth electronic block (22) for receiving said waiting time signal from said fourth means (17), and the output signal from said first and second means (14, 15) relative to the delay between the two inductive and capacitive discharge commands; and
a logic network controlled by said fourth block (22), which receives the selection signal indicating the discharge type or combination, and supplies two signals respectively controlling inductive and capacitive discharge.
A system as claimed in Claim 3, characterised by the fact that said logic network comprises four AND circuits (23a, 23b, 25a, 25b) and two OR circuits (24, 26); a first and second AND circuit (23a, 23b) and a first OR circuit (24) relating to inductive discharge control; and a third and fourth AND circuit (25a, 25b) and a second OR circuit (26) relating to capacitive discharge control.
A system as claimed in Claim 4, characterised by the fact that said fourth block (22) provides for processing and rendering said incoming signals acceptable to control by said logic network, which it controls via two connecting lines (27, 28), a first of which (27) is connected to a first input of said first and third AND circuits (23a, 25a), and a second of which (28) is connected to a first input of said second and fourth AND circuits (23b, 25b); a third connecting line (29), for transferring said discharge type and/or combination signal, being connected directly to a second input of said third and fourth AND circuits (25a, 25b) and via an inverter (19) to a second input of said first and second AND circuits (23a, 23b); the output of said first AND circuit (23a) and the output of said second AND circuit (23b) being connected to a respective input of said first OR circuit (24), the output of which relates to the enabling signal of said first block (7) for determining an inductive discharge; the output of said third AND circuit (25a) and the output of said fourth AND circuit (25b) being connected to a respective input of said second OR circuit (26), the output of which relates to the enabling signal of said second block (8) for determining a capacitive discharge.
A system as claimed in at least one of the foregoing Claims, characterised by the fact that it comprises a first direct current generator (32) for supplying said first block (7), and a second direct current generator (72) for supplying said second block (8).
A system as claimed in at least one of the foregoing Claims from 1 to 5, characterised by the fact that it comprises a first direct current generator (32) for supplying said first block (7); the supply to said second block (8) being derived from said first block (7).
A system as claimed in Claim 6 or 7, characterised by the fact that said first and second blocks (7, 8) are integrated in the same circuit arrangement (31, 51, 61 or 71).
A system as claimed in Claim 8 dependent on Claim 7, characterised by the fact that said circuit arrangement (31, 51 or 61) comprises:
a primary circuit having said first generator (32); a first winding (33) about a magnetic core (34); and a first device (35 or 53) controlled by said electronic control system (2) via a first signal from said third block (5), for cutting off and restoring current flow along said first winding (33); said first winding (33) having a first terminal connected to the positive pole of said first generator (32), and a second terminal connected to a reference ground via said first device (35 or 53);
a secondary circuit having a second winding (42) wound about said core (34) and connected to an electrode of at least one said spark plug (6, 43);
a condenser (41) having its cathode connected to a first terminal of said first winding (33);
a second device (37 or 52) controlled by said electronic control system (2) via a second signal from said third block (5), for cutting off and restoring current flow along the same, and having a first terminal connected to the anode of said condenser (41), and a second terminal connected to a second terminal of said first winding (33); and
a one-way diode (38), the cathode and anode of which are connected respectively to a first and second terminal of said second device (37 or 52).
A system as claimed in Claim 8 dependent on Claim 6, characterised by the fact that said circuit arrangement (71) comprises:
a primary circuit having said first generator (32); a first winding (33) about a magnetic core (34); and a first device (35 or 53) controlled by said electronic control system (2) via a first signal from said third block (5), for cutting off and restoring current flow along said first winding (33); said first winding (33) having a first terminal connected to the positive pole of said first generator (32), and a second terminal connected to a reference ground via said first device (35 or 53);
a secondary circuit having a second winding (42) wound about said core (34) and connected to an electrode of at least one said spark plug (6, 43);
a condenser (41) having its cathode connected to a first terminal of said first winding (33);
a second device (37 or 52) controlled by said electronic control system (2) via a second signal from said third block (5), for cutting off and restoring current flow along the same, and having a first terminal connected to the anode of said condenser (41), and a second terminal connected to a second terminal of said first winding (33);
said second generator (72); and
a one-way diode (38), the cathode of which is connected to the cathode of said condenser (41), and the anode of which is connected to said second generator (72).
A system as claimed in Claim 9 or 10, characterised by the fact that said first device comprises a Darlington transistor (35) having its collector connected to a second terminal of said first winding (33), its emitter connected to said reference ground, and its base connected to the collector via a Zener diode (36); the base of said transistor (35) being controlled by said electronic control system (2) via said first signal from said third block (5).
A system as claimed in Claim 9 or 10, characterised by the fact that said first device comprises a first switch (53) controlled by said electronic control system (2) via said first signal from said third block (5).
A system as claimed in Claim 11 or 12, characterised by the fact that said second device comprises a controlled diode (SCR) 37 having its anode connected to the anode of said condenser (41), and its cathode connected to the second terminal of said first winding (33).
A system as claimed in Claim 11 or 12, characterised by the fact that said second device comprises a second switch (52) controlled by said electronic control system (2) via said second signal from said third block (5).
A system as claimed in any one of the foregoing Claims, characterised by the fact that it comprises an ignition distributor (11) between said first and second blocks (7, 8) and said spark plugs (6, 43).
A system as claimed in Claim 15 dependent on any one of the foregoing Claims from 9 to 14, characterised by the fact that said distributor (11) is electronic, and comprises, for each cylinder of said engine (3), a third device (62) controlled by said electronic control system (2) via a third signal from said third block (5), for cutting off and restoring current flow along the same, and having a first terminal connected to a first terminal of said second winding (42).