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(11) | EP 1 811 169 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A system for the start-up of a low-power internal combustion engine |
| (57) A system for facilitating the ignition of an internal combustion engine provided
with an ignition coil of inductive type comprising a primary winding, connected to
the engine switching off circuit, and a secondary winding connected to the engine
ignition plug; said system comprises an electronic board, inserted at the ends of
the primary winding of the coil and adapted for connecting an energy source to said
coil at least when the engine has to be started, said electronic board comprising
at least: a control circuit connected to means for detecting the engine piston position
and a driving circuit controlled by said control circuit for supplying energy to the
engine ignition coil when the piston is in the proximity of the top dead centre.
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[0001] The present finding relates to a system for facilitating the start-up of low-power endothermic reciprocating engines and in particular, of engines provided with an inductive-type ignition.
[0002] It is known that small internal combustion engines are provided with an ignition system consisting of a flywheel and an ignition plug. The flywheel is provided with at least one magnet and is magnetically coupled with the magnetic rolled iron core of the coil, supplying the energy and the electrical phase references for generating the spark that triggers the fuel combustion into the cylinder.
[0003] In particular, the ignition plug comprises a primary winding connected to a switching off circuit and a secondary winding connected to the engine plug.
[0004] A problem of small internal combustion engines is that for the ignition to occur, the engine flywheel must rotate at a speed of about 300-400 RPM. To this end, the ignition of these engines generally occurs with a pull system, which comprises a pulley mechanically connected to an output of the drive shaft, about which there is wound a start-up cable. A problem correlated to this type of device is that the revolution speed to which the engine flywheel is brought is a function of the strength with which the cable is pulled. It therefore occurs that if the cable is not pulled with a sufficient strength, the flywheel does not rotate fast enough to allow the engine start-up.
[0005] Therefore, in order to start the engine, the user generally has to make a considerable effort. Moreover, it should be noted that if the start-up system is actuated a few times without due strength and the engine does not start, there is the risk of flooding the engine, with all the related problems. The object of the present finding is to overcome the problems of the prior art with a simple, rational and especially inexpensive solution. The finding achieves this and other objects thanks to a start-up system for endothermic engines provided with inductive electronic ignition in accordance with the technical features described in the independent claim 1. The dependent claims define special and advantageous embodiments of the finding. In particular, according to the finding, the start-up system comprises an electronic board, inserted at the ends of the primary winding of the coil, and adapted for connecting an energy source to said coil at least upon the engine ignition. The electronic board comprises at least one control circuit, connected to means for detecting the engine piston position and a driving circuit, controlled by said control circuit, for supplying energy to the engine ignition coil.
[0006] In a preferred embodiment, the energy source used in the finding is a 12V battery. Other embodiments of the finding provide for different types of energy sources based on the specific applications the engine they must be connected to is intended for.
[0007] The control circuit comprises means for detecting the piston position, in particular the piston passage by the top dead centre. Said means are obtained by an external position sensor, such as a Hall sensor, a microswitch, an optical sensor, an inductive or capacitive or proximity sensor, or it is integrated in the control circuit which detects the flow variation induced by the rotating magnets directly from the ignition plug. The control circuit further comprises a delaying circuit that is intended for regulating the spark advance. Such circuit can alternatively be obtained using a simple timer, such as model NE555, a device manufactured by the major manufacturers of semiconductors, or by a microprocessor connected to said position sensor.
[0008] The driving circuit comprises an electronic switch, which for example can be a MOS-FET transistor or a BJT transistor or still any other electronic switch suitable for the purpose, such as a SCR diode, a GTO diode, a TRIAC diode or an IGBT transistor.
[0009] The features and advantages of the finding will appear more clearly from the following detailed description made with reference to the figures of the annexed drawing tables which illustrate, by way of a non-limiting example, two specific and preferred embodiments thereof.
[0012] From Figure 1 it is possible to see coil 1 which comprises a primary winding 2 and a secondary winding 3. The secondary winding 3 is connected to the ignition plug 4 while the primary winding 2 is connected to the ignition system 5 according to the finding by connectors J1 and J2.
[0013] The ignition system 5 comprises an electronic board 6 and an energy source 7, adapted for supplying current to the primary winding 2 at least when the engine on which coil 1 is installed is started. In the embodiment shown in the present example, the energy source 7 comprises a usual 12V battery 70.
[0014] The electronic board 6 comprises a supply circuit 8, a control circuit 9, a driving circuit 10 and an engine switching off circuit 11. The supply circuit 8 is connected to the energy source 7 and is intended for supplying energy to both the primary winding 2 of the coil and to the control circuit 9.
[0015] The supply circuit 8 comprises a diode D1 exhibiting two terminals indicated with references VBT and VPW. Terminal VBT is connected to terminal J1 of the primary winding 2 whereas terminal VPW is connected to a relay 12 that is intended for alternatively connecting terminal J2 of the primary winding 2 to the driving circuit 10 or to the switching off circuit 11.
[0016] Diode D1 is connected to the control circuit 9 by a stage for limiting and stabilising the supply voltage supplied by battery 70. Said stage comprises a ZENER diode DZ1 arranged parallel to battery 70 and serving for protection and for limiting the voltage with a resistance R1 in series that limits the current thereof. Parallel to DZ1 there is arranged condenser CE1 which has the function of levelling the supply voltage. Moreover, between the energy source 7, that is, battery 70 in the embodiment shown, and diode Dl, there is inserted a switch 13 whose closure is controlled by the user when starting up the engine.
[0017] The control circuit 9 comprises a timer 14, of the NE 555 type, provided with a delay circuit 15 consisting of resistors R2 and RV1 and of condenser C1. On the other hand, condenser C2 is a stabiliser condenser whose use is suggested in the manual of timer NE 555. Moreover, the control circuit also comprises a filter 16 consisting of resistor R3 and of condenser C3. It is noted that said delay circuit 15 and filter 16 illustrated in the present embodiment of the finding, are connected according to the instructions given in the installation manual of timer NE555. Such components may also be different based on the model of timer used.
[0018] Timer 14 is also connected to means 17 adapted for detecting the piston position, which in the illustrated embodiment, comprises a Hall effect sensor 18, connected to an input pin, indicated with reference TRG (TRIGGER), of timer 14. On the other hand, an output pin of timer 14, indicated with reference OUT, is connected to the driving circuit 10.
[0019] The driving circuit 10 comprises a controlled switch, in particular a MOS-FET transistor 19, whose gate is connected to the OUT pin of timer 14 by a resistor R8 and a condenser CE2.
[0020] Resistor R8 has the function of limiting the charge current of the gate capacity of MOS-FET transistor 19, whereas condenser CE3 has the function of eliminating the continuous component of the control signal of the timer by triggering MOS-FET 19.
[0021] The common terminal 20 of condenser CE2 and of resistor R8 is connected to earth by a diode D4, parallel to which there is inserted a resistor R9. Diode D4 carries out a function of quick recharge of condenser CE2 during the switching, and resistor R9 has the function of stand by reference of the MOS1 gate.
[0022] The DRAIN and SOURCE terminals of the MOS-FET transistor 19, on the other hand, are connected to each other and to earth by a ZENER diode TZ1, which has the function of limiting the voltage peak on the MOS-FET transistor 19.
[0023] The switching off circuit 11 comprises a switch 21 inserted between terminals J1 and J2 of the primary winding 2. Closing switch 21 prevents the spark generation since it short-circuits the primary winding 2 of the coil. The switching off circuit 11 also comprises the switching relay 12 that has the function of selectively connecting terminal J2 of the primary winding 2 with the switching off circuit 11 or with the driving circuit 10.
[0024] In detail, relay 12 consists of a switch 22 and a coil 1 for controlling the position of switch 22. As can be seen in Fig. 1, one of the two terminals of coil 1 is connected to the supply circuit by terminal VPW, whereas the other terminal is connected to earth. Anti-parallel to the coil there is inserted a safety diode D2.
[0025] In the operation of the finding, upon the engine ignition the user closes switch 13 so as to connect battery 70 to the primary winding 2 of the coil and supply the electronic board 6 of the finding, and makes sure that switch 21 is open. If switch 21 is a monostable button, which at rest is normally open, no check by the operator is required.
[0026] Closing switch 20 also causes the switching of relay 12 and therefore connects the driving circuit 10 to the primary winding 2.
[0027] After that, the user starts the engine by the usual pull system which causes the rotation of the drive shaft. When the Hall sensor detects that the piston is close to the top dead centre, it sends a signal to pin TRG (trigger) of TIMER 12, which after a certain time interval commands the conduction of the MOS-FET transistor so as to supply current to the primary winding 2 of the coil. Such current is added to that induced on the secondary winding 3 by the passage of the coil magnets. In this way, the energy supplied by the spark is given by the sum of that generated by the passage of the coil magnets and of that supplied by the battery, so as to facilitate the engine start up. Once the engine has started, the user opens switch 13 so as to disconnect the ignition system 5.
[0028] It is noted that system 5 can continue to supply energy also after the start up, that is, while the engine is running. In this case, the spark will have grater energy with consequent improvement of the energy efficiency.
[0030] In the description of the second embodiment of the finding, components equal to those already described in the first embodiment of the finding are indicated with the same reference numerals.
[0031] From Figure 2 it is possible to see coil 1 which comprises the primary winding 2 and the secondary winding 3.
[0032] The secondary winding 3 is connected to the ignition plug 4 while the primary winding 2 is connected to the ignition system 30 according to the finding by connectors J1 and J2. The ignition system 30 comprises an electronic board 31 and an energy source 7, described hereinbefore, adapted for supplying current to the primary winding 2 at least when the engine on which coil 1 is installed is started.
[0033] The electronic board 31 comprises a supply circuit 32, a control circuit 33, a driving circuit 34 and an engine switching off circuit 35. The supply circuit 32 is connected to the energy source 7 and comprises a diode D1 which exhibits two terminals indicated with references VBT and VPW. Terminal VBT is connected to terminal J1 of the primary winding 2 whereas terminal VPW is connected to relay 12 that is intended for alternatively connecting terminal J2 of the primary winding 2 to the driving circuit 34 or to the switching off circuit 35.
[0034] Diode D1 is connected to the control circuit 33 through a stage for limiting and stabilising the supply voltage supplied by battery 70. Said stage comprises a ZENER diode DZ1 arranged parallel to battery 70 and having a resistor R1 in series, which limits the current on the ZENER diode DZ1, and a condenser CE1 in parallel, which has the function of levelling the supply voltage to a level of 12V, which is the voltage value supplied by battery 70. Parallel to condenser CE1 there is inserted a voltage regulator 36 connected to a stabilising stage comprising condenser CE2 and resistor R14. The voltage regulator regulates the value of the voltage supplied to the control circuit 33 to a value of 5V.
[0035] The control circuit 33 comprises a microprocessor 38 that manages the operation of the entire ignition system 30.
[0036] In the example shown, microprocessor 38 is model ATTiny13 manufactured by the company Atmel, which provides the connecting terminals required for the system control.
[0037] It should be noted that in the present description, the term "microprocessor" refers to any programmable device. Moreover, it is noted that the microprocessor is associated to a memory unit, in se known, which can be internal or external to the microprocessor itself, of volatile type for the management of variable data and non-volatile for storing the program code and the data to retain also in the event of supply failure.
[0038] Terminal VDD is the processor supply terminal which is connected downstream of the voltage regulator 36, as can be seen in Fig. 2.
[0039] Terminal IGN of microprocessor 38 is connected to the driving circuit 34, which comprises the MOS-FET transistor 19. In particular, the gate of the MOS-FET transistor 19 is connected to terminal IGN of the microprocessor by a resistor R8 which has the function of limiting the gate current. The GATE is connected to the earth terminal GND of the microprocessor through a resistor R11 which has the function of creating a reference voltage for the gate itself. The DRAIN and SOURCE terminals of the MOS-FET transistor 19 are connected to each other through the ZENER diode TZ1, which has the function of limiting the voltage peak on the MOS-FET transistor 19. In the illustrated example, the means for detecting the piston position, that is, the passage of the engine piston by the top dead centre, are integrated into the same microprocessor, which through terminal SNS detects the voltage variations on terminal 39 of the DRAIN of the MOS-FET. In order to limit the voltage value detected by the processor between terminal SNS and terminal 39, there is inserted a safety resistor R110.
[0040] The switching off circuit 35 comprises a switch 21 inserted between terminals J1 and J2 of the primary winding 2. The switching off circuit 35 also comprises the switching relay 12 which has the function of selectively connecting terminal J2 of the primary winding 2 to the switching off circuit 35 or to the driving circuit 34. In particular, relay 12 comprises a switch 22 and a coil 23 for controlling the position of switch 22. Anti-parallel to coil 23 there is inserted a safety diode D2.
[0041] As can be seen in Fiq. 2, one of the two terminals of coil 23 is connected to the supply circuit by terminal VPW while the other terminal is connected to the microprocessor by a transistor QN1; in detail, said terminal is connected to the collector of transistor QN1, as can be seen in Fig. 2. The base of transistor QN1 is connected to terminal RLE of microprocessor 38 with the interposition of a resistor R10 while the emitter is connected to earth and to the GATE by a resistor R12. The function of transistor QN1 is to control the excitation state of coil 23 so as to control the position of switch 22.
[0042] Terminal STR of microprocessor 38 is connected to a switch 40, actuable by the user, which controls the actuation of the ignition system 30 according to the finding. As can be seen from Fig. 2, a terminal of switch 40 is connected to terminal STR trough a safety resistor R13 while the other terminal is connected to earth. Parallel to switch 40 there is also inserted a condenser C4 whose function is of anti-recoil.
[0043] The operation of the second embodiment of the finding is substantially similar to that described for the first embodiment with the only differences that the position of switch 22 is controlled by microprocessor 38 through transistor Q1, whose lock or conduction state determines the state of coil 23 and that the detection of the piston position occurs by monitoring the voltage variations at terminal 39 of the collector of the MOS-FET transistor 19.
1. A system for facilitating the ignition of an internal combustion engine provided
with an ignition coil (1) of inductive type comprising a primary winding (2), connected
to the engine switching off circuit (11, 35), and a secondary winding (3) connected
to the engine ignition plug (4) characterised in that it comprises an electronic board (6, 31), inserted at the ends of the primary winding
(2) of the coil (1) and adapted for connecting an energy source (7, 70) to said coil
(1) at least when the engine has to be started, said electronic board (6, 31) comprising
at least: a control circuit (9, 33) connected to means (17) for detecting the engine
piston position and a driving circuit (10, 34) controlled by said control circuit
(9, 33) for supplying energy to the engine ignition coil when the piston is in the
proximity of the top dead centre.
2. A system according to claim 1, characterised in that said control circuit (9, 33) comprises a delay circuit.
3. A system according to claim 2, characterised in that said delay circuit comprises a timer (14).
4. A system according to claim 2, characterised in that said delay circuit comprises a microprocessor (38).
5. A system according to claim 1, characterised in that the means for detecting the piston position comprises a position sensor.
6. A system according to claim 5, characterised in that the means (17) for detecting the piston position comprise an inductive or capacitive
or proximity sensor.
7. A system according to claim 5, characterised in that the means (17) for detecting the piston position comprise a Hall sensor (18).
8. A system according to claim 5, characterised in that said position sensor comprises an optical sensor.
9. A system according to claims 1 and 4, characterised in that the means for detecting the piston position are integrated in said microprocessor.
10. A system according to claim 9, characterised in that the means integrated in said microprocessor detect the flow variation induced by
the magnets rotating into the ignition coil.
10. A system according to claim 1, characterised in that said driving circuit (10, 34) comprises an electronic switch and at least one electromechanical
device.
12. A system according to claim 10, characterised in that said electronic switch is a MOS-FET switch (19).
13. A system according to claim 10, characterised in that said electronic switch comprises an SCR diode.
14. A system according to claim 10, characterised in that said electronic switch comprises a BJT transistor or a GTO diode or a TRIAC diode
or an IGBT transistor.
15. A system according to claim 1, characterised in that said energy source is a battery.