INDUCTIVE DISCHARGE IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES

Abstract: An inductive discharge ignition system for internal combustion engines, comprises a permanent magnet (3, 3') rotating synchronously with the engine and passing in front of an ignition coil (1, 1') and a control coil (2) during its movement. The control coil controls a controlled discharge electronic circuit connected in series with the primary winding (7, 24) of the ignition coil, the secondary winding (8, 8') of which is connected to the electrodes of a spark plug (13). The assembly formed from the ignition coil (1, 1') and the control coil (2) is configured in such a manner as to trigger the spark with an advance compatible with that required by the engine on starting, the core (9) of the control coil (2) having at least one portion (9'') extending tangentially to the movement of the permanent magnet (3, 3') and such as to modify the control voltage curve (15) in the sense of generating a voltage peak (18) for controlling the controlled discharge circuit, to give correct advance for maximum engine speed.

Description: INDUCTIVE DISCHARGE IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES This invention relates to an inductive discharg ignition system for internal combustion engines. Inductive discharge systems for internal combustio engines are known- Essentially, they use a permanent magne connected to the crankshaft so that it rotates synchronousl with it. The rotating magnet is faced by an ignition coi wound on a magnetic core and comprising a primary winding an a secondary winding. The secondary winding is connected t the electrodes of a spark plug, and the primary winding i connected to an electronic circuit which interrupts it. Thi interruption is controlled by a small control coil generall located in proximity to the ignition coil- In practice th engine rotation, and thus the relative movement between th permanent magnet and the ignition coil, induces a electromo ive force in the primary winding of this latter, t cause circulation of a current which is suddenly interrupte by the electronic circuit when the permanent magnet passes i front of the control coil- The sudden and considerable flu variation which occurs on interruption of the primary curren i n the ignition coil induces a high secondary voltage whic triggers the spark between the spark plug electrodes- The shape of the various parts and their locations ar determined such that the primary current interruption take place when this current is at its maximum value, and in synchronism with the operating cycle of the internal combustion engine- However, in practice the petrol-air mixture requires a certain time to ignite, and it is therefore necessary for the igni ion command, ie the interrup ion in the primary circuit of the ignition coil, to take place with a certain advance relative to the predetermined moment of explosion- This is generally obtained by positioning the control coil in angular advance of that position of the permanent magnet shaft which corresponds to the top dead centre of the relative cylinder- Again, as the time required for the petrol-air mixture to burn completely is substantially constant whereas the advance ime, ie the time interval between the moment in which the permanent magnet passes in front of the control coil and the moment corresponding to said top dead centre, is related to the engine rotational speed, this adjustment system cannot be effective both at high and low engine speed- Two methods are currently used to obviate this drawback. One of this consists of inducing the interruption in the primary current by means of a microprocessor or in any event by a sophis icated electronic circuit which takes account of the engine rotational speed and adjusts the ignition advance on this basis- This methods is without doubt valid, bu involves a high construc ional cost and the need for central electronic control unit, and for these reasons canno be advantageously used in small internal combustion enginees in which its cost and overall size impose very restrictiv limits. Another known methods currently used for small interna combustion engines is to set the ignition advance t correspond to maximum rotational speed, ie to norma operating conditions, and to use a controlled discharg transistor in the electronic primary current interruptio circuit to ensure operation in proper time- The main drawback of this method is that at speeds othe than the maximum speed, and in particular on starting, ignition takes place too soon before the piston has reache its top dead centre, resulting in kick-back which is highl undesirable not only because of the stress to which th engine is subjected but also of its effect on the operator, who generally starts the engine manually. An object of the invention is to solve this problem b providing automatic advance adjustment in small internal combustion engines, both on starting and at maximum engine speeds- A further object of the invention is to solve this problem in an extremely reliable, simple and economical form and requiring lit le space- These and further objects which will be more apparent from the description given hereinafter are attained according to the invention by an inductive discharge ignition system for internal combustion engines as described in claim. The invention, deriving from a series of experimental tests conducted in order to observe the behaviour of the control coil output voltage as the shape of the core varies, is based on the surprising observation that if the shape of the core, instead of being rectilinear in a direction radial to the rotational motion of the permanent magnet, also comprises a tangen ial component, the normally existing voltage peak is displaced in the delay direction, and in its place there forms another voltage peak having an amplitude related to the rotational speed of the engine and in particular increasing with it- Some preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section through an ignition system according to the invention; Figure 2 shows a simplified electrical schematic of th invent ion; Figure 3 shows the pattern of the control coil output voltag in relation to the threshold value of the controlle discharge transistor and to the pattern of th ignition coil primary current ia traditional ignition system, under minimum engine spee (star ing) condi ions; Figures 4 to 6 show the pattern of the same quantities in a ignition system according to the invention, unde three different operating conditions; Figure 7 shows some different core shapes for the control coi 1 ; Figure 8 shows the pattern of the control voltage and primary current curves or a different shape of control coil core; and Figure 9 shows in schematic section the ignition system according to the invention applied to an alternator. As can be seen from the figures the inductive discharge ignition system of the invention comprises a fixed ignition coil indicated overall by 1 , a fixed control coil indicated overall by 2, and a permanent magnet 3 mounted on the engine flywheel 4 in position such that when the magnet rotates in the direction of the arrow 5 of Figure 1 it passes firstly in front of a pole piece of the ignition coil 1 and then in front of the control coil 2- The configuration of the ignition coil and control coil and their position relative to the flywheel are determined such that the ignition advance substantially corresponds to that required at minimum engine rotational speed, ie on start ing- The ignition coil 1 comprises an E-shaped core ό with three pole pieces facing the flywheel 4, and a primary winding 7 and secondary winding 8 arranged concentrically to each other about its central portion. The control coil 2 comprises a core 9 and a winding 10 arranged about it- The core 9 comprises a part l positioned perpendicular to the circumferential surface of the flywheel 4, ie radial to its axis of rotation, and two parts 9' ' perpendicular to the preceding. From the circuit aspect, the winding 10 is connected to the input of an SCR transistor 11 having a threshold value less than the amplitude of the voltage peak which is generated, as will be apparent hereinafter, by the flux variation through the core on passage of the magnet 3- The output of the SCR transistor 11 is connected to a Darlington circuit, indicated schematically as a transistor 12, which is connected to the primary winding 7 of t ignit ion σoi 1 1 - The secondary winding 8 of the coil 1 is connected t the electrodes of a spark plug 13- To better understand the operation of the ignitio system according to the invention and the considerabl differences compared with a traditional system, it will be advantageou firstly to examine the operation of the traditional case wit reference of Figure 3, specifically for a rotational speed o 500 r.p.m-, corresponding substantially to startin σondit ions. When the engine is s ill at rest the SCR 11 an transistor 12 do not conduct and no current passes throug the primary winding 7- On starting, the passage of the permanent magnet 3 i front of the ignition coil 1 results in a flux variatio which induces a current in its primary winding 7. The patter of this current is represented by the curve 14 in Figure 3 in which the horizontal axes represent the angular positio of the permanent magnet 3 relative to a predetermine reference position, and the vertical axes indicate th primary current intensity. It can be clearly seen from thes graphs that when the magnet 3 passes in front of the pole pieces of the core 6 of the coil 1, the primary current assumes a "bel1-shaped" pattern. When the magnet 3 passes in front of the control coil 2, it induces in its winding 10 a voltage the pattern of which is represented by the curve 15 of Figure 3- In this graph the horizontal axes again represent the angular position of the permanent magnet 3, whereas the vertical axes represent the control voltage- Figure 3 also shows at 16 the pattern (constant) of the threshold voltage of the SCR 11- Essentially, the voltage induced in the primary winding 7 on passage of the permanent magnet 3 is sufficient to polarize the transistor 12 which thus shorts the primary circuit so that a high current passes through it. When this current reaches a sufficiently high value, the voltage peak 17 induced in the winding 10 of the control coil 2 at minimum speed, and in particular on starting, trips the SCR 11, which inhibits the transistor 12 and suddenly interrupts current passage through the primary winding 7- This sudden interrup ion produces a sudden intense flux variation in the core ό, and thus a high secondary voltage, which powers the spark plug 13- In traditional system the position of the assembl comprising the ignition coil 1 and the control coil 2 i determined such that the voltage peak 17 which trips the SC 11 occurs at a moment such as to trigger the spark in th spark plug 13 with an advance corresponding to maximum spee operation- This peak is followed by a second peak 18 whic can just be seen in Figure 3, but does not influence th operation of the assembly. In contrast, according to the invention the particula shape of the core 9 of the control coil 2, and in particula the presence of the two tangential parts 9' ' , substantiall reduces the amplitude of the first peak 17, making i practically without influence at low speeds, whereas i enhances the amplitude of the second peak 18 to make it abl to trip the SCR 11 and trigger the park in the spark plug 13 This takes place with an ignition advance which makes th operation of the ignition system satisfy the condition required for starting- In addition, as the rotational spee of the engine increases the curve 15 showing the voltag induced in the winding 10 of the control coil 2 changes i the sense that the peak 17 increases progressively i ampl itude. When this amplitude reaches the threshold value of th SCR 11, which occours at full speed operation, the SCR 11 trips in advance of the position in which it was controlled by the peak 18, with the double effect of advancing the spark formation in the spark plug 13, and of nullifying the effect of said peak 18. Wore particularly Figure 4, which corresponds to the same operating conditions as Figure 3, shows the curve 15 of the voltage induced in the coil 1, which at a certain moment exceeds the threshold voltage of the SCR 11 to cause interruption of the primary current in the coil 1, when this current has the value indicated by the curve 14 at the same abscissa value. The rotational speed of the engine in the experimental situation of Figure 4 corresponds to 500 r-p-m-, with the voltage induced in the coil 2 showing inversion between the two peaks 17 and 18- Figure 5 (750 r-p-m- ) shows the increase amplitude of the first peak 17, but still insufficient to reach the threshold level 16 of the SCR 11, and this therefore continues to be tripped by the peak 18- Figure 6 (1050 r-p-m. ) shows that the amplitude of the peak 17 is such as to exceed the threshold level 16 of the SCR 11, so that this is tripped at a primary current level slightly different from the preceding, but s ill high- Th distance expressed in degrees between the two peaks 17 and 1 is about 12° and corresponds approximately to the differenc between the advance required for starting and that require for maximum engine speed- Essentially, by virtue of this very simple expedient o giving the core 9 of the control coil 2 a particular shape, correct advance is automatically obtained both at high engin speed and on starting. The wave form of the control voltage is related to th characteristics of the core 9 of the control coil 2 , and i the illustrated example corresponds to the shape of the cor shown in Figure 1 - Varying this shape varies the pattern o the control voltage, thus providing considerable facility fo adjusting the engine ignition advance- Figure 7 shows further shapes of the core 9 of the coil 2, giving different corresponding wave forms of the control voltage 15- It has also been found that the control voltage curve 15 also varies as the thickness of the laminations forming the core 9 varies- Thus by suitable choices it is possible to give the curve 15 the form of a ramp the slope of which increases as the engine r-p-m- increases- In this manner an almost continuous adjustment of the ignition advance can be obtained, from very low r-p-m- values (starting) to maximum r-p-m- values- Figure 8 schema ically illustrated this principle- In this respect it can be seen that the control voltage curve 15 is substantially linear in the portion corresponding to high primary current values, and intersects the curve 16, which represents the threshold level of the SCR 11, at a point 19 which corresponds to the ignition advance required for starting- As the engine r-p-m- increases the slope of the linear portion of the curve 15 increases, ie that portion rotates in the direction indicated by the arrow 20 in figure 8, to intersect the curve 16 at increasingly advanced points. In this manner an effective automatic adjustment can be obtained practically over the entire range of the variation of the engine rotational speed- The embodiment shown in Figure 9 relates to an alternator with a rotating magnet 3' and a salient pole stator- One of these poles 21 is provided with a winding which is connected in series with an electronic circuit 23 for interrupting the primary current and with another primary winding 24 provided on the core 6 1 of an external ignition coil 1' , which also comprises a secondary winding 8' for powering the spark plug 13- The control coil 2 is provided t the side of pole 21- The operation is substantially the same in this case, i the sense that the various parts are located such that th ignition advance is compatible with that required fo starting. The particular shape of the core of the contro coil means that its response curve can be modified in th sense of increasing this advance as the engine r-p-m. increases, so that at full speed the correct value for thi operating condition is obtained-

Claims: C L A I M S 1- An inductive discharge ignition system for internal combustion engines, comprising a permanent magnet (3, 3') rotating synchronously with the engine and passing in front of an ignition coil (1, 1') and a control coil (2) during its movement, said control coil controlling a controlled discharge electronic circuit connected in series with the primary winding (7, 24) of the ignition coil, the secondary winding (8, 8') of which is connected to the electrodes of a spark plug (13), characterised in that the assembly formed from the ignition coil (1, 1' ) and the control coil (2) is configured in such a manner as to trigger the spark with an advance compatible with that required by the engine on starting, the core (9) of the control coil (2) having at least one portion (9 1 1 ) extending tangentially to the movement of the permanent magnet (3, 3') and such as to modify the control voltage curve (15) in the sense of generating a voltage peak (18) for controlling the controlled discharge circuit, to give correct advance for maximum engine speed- 2- An ignition system as claimed in claim 1, characterised in that the core (9) of the control coil (2) comprises a portion (9' ) perpendicular to the movement of the permanent magnet (3) and at least one portion (9 1 1 ) positioned at on end of the portion (9') and perpendicular thereto- 3. An ignition system as claimed in claim 2 , characterise in that the core (9) comprises a portion (9' ) and tw portions (9 1 1 ) positioned at both ends of this latter- 4- An ignition system as claimed in claim 2, characterise in that at last one of the tangential portions (9' ' ) of th core (9) comprises at the end distant from the portion (9 1 ) short portion parallel to this latter- 5- An ignition system as claimed in claim 4, characterise in that the core (9) comprises two tangential portions (9 1 1 ) positioned at both ends of the portion (9' ). of thes tangential portions that further from the permanent magnet (3) having at its end a sort portion bent parallel to th port ion (9' ) . 6. An ignition system as claimed in claim 1 comprising an alternator with an annular permanent magnet (3' ) and a salient pole stator, characterised in that on one pole (21) there is wound a primary winding connected in series with a second primary winding (24) pertaining to the ignition coil (1' ), between the two primary windings there being interposed an electronic circuit (23) controlled by the control coil (2), which is positioned in proximity to said pole (22). 7- An ignition system as claimed in one or more of claims 1 to 6, characterised in that the core (9) of the control coil (2) is constructed of laminations of such a thickness that the control voltage curve (15) comprises a linear portion (20) at high primary current values (14), the slope of said linear portion increasing with the engine rotational speed such that the thresold value of said controlled discharge electronic circuit is reached at a time corresponding to the correct ignition advance for the particular engine speed concerned.

Inventors: IMOLI DANTE, IMOLI, DANTE
Applicants: IDM SRL, IDM S.R.L.
Application year: 1990
Main classification: F02P1
IPC codes: F02P1