AN ARRANGEMENT IN GENERATORS FOR IGNITION SYSTEMS GENERATING VOLTAGES FOR CONTROL AND CHARGING

Abstract: The invention relates to a generator arrangement, particularly in ignition system for internal combustion engines. The arrangement is composed of a multi-leg core (9) of magnetically conducting material having its legs (10-17) radially projecting towards a cooperating magneto flywheel (1). The magneto flywheel has one section (5) of an extension corresponding to two core legs and with an unsymmetrical magnet flux (between 4 and 6), and one section having as many north poles as south poles. The legs carry windings (18-25) uniformly wound and connected into groups. One group comprises two windings (18, 25) interconnected such that they only emit an induced voltage (28, 29) when passing the borders or ends of the unsymmetrical section. The second group (19-24) emits an induced combined voltage. The voltage of said first mentioned group controls the ignition process, whereas the second group charges a condenser, component of the ignition system.

Description: AN ARRANGEMENT IN GENERATORS FOR IGNITION SYSTEMS GENERATING VOLTAGES FOR CONTROL AND CHARGING Technical field In condenser ignition systems for single-cylindrical internal com¬ bustion engines there is a need for at least two different voltage levels, that is, one for charging the condenser component of the system and one for controlling the electronic circuits triggering the sparks. Often there is also a need for voltage supply to other electronic circuits, which are not associated with the ignition system proper. It is difficult to combine in a simple and inexpensive manner a generator winding for e.g. charging said ignition condenser and providing at the same time a suitable control signal to the control electronics for the spark discharge. It is desirable in prac¬ tice that in order to solve the above problems, for example, one single iron core is used which carries the necessary windings for generating control voltage as well as charging voltage. In doing so it should of course be pur¬ sued that the control voltage part requires the smallest winding space pos- sible in order that it be possible to expand the other generator windings to the necessary extent. It is also desirable that it be possible to wind all windings in a simple manner in the same manufacturing process. Prior art The magneto core legs, which are to carry the windings, are suitably arranged in star shape for cooperation with the magneto wheel rotating thereabout. Such structures belong to prior art and in this connection reference can be made to the Swedish Patent No. 425 423 and the German Dit¬ to No. 32 23 039 and the Swedish Appln No. 8803329-5. Summary of the invention It is advisable that in an arrangement according to the present inven¬ tion the magnet poles, intended for cooperation with core legs in a magnet core, are arranged to move in a path with the core legs provided in coope¬ ration therewith. The magnet poles are spaced along the path and alternat- ingly magnetized by a different polarity. The core legs are spaced in cor- respondence to the magnet pole spacing, and each core leg carries at least one winding, the windings being interconnected such that they form, electri¬ cally, at least two groups. One group comprises two windings on separate core legs connected such that the voltages induced will cancel one another when there is a uniformly field-alternating magnet flux through the legs. The magnet pole path is such that it has at least one section magnetically unsymmetrical and one section magnetically symmetrical wherein as many north poles as south poles are provided alternatingly. The arrangement is preferab¬ ly such that said one group will produce, in passing said sections of the magnet pole path, an induced voltage. Suitably the other group of windings are interconnected such that they cooperate to form a combined voltage creat- ed by induction from the symmetrical as well as the unsymmetrical section of the magnet pole path. The voltages now mentioned could be used to advantage in an associated ignition system for a single-cylinder internal combustion engine, the voltage of said first group controlling the ignition process and the voltage of said second group preferably bringing about charging of the condenser component of the ignition system. By the present invention the advantage is attained that, from a manufacturing point of view, the generator part as well as the control voltage part can be wound in essenti¬ ally the same winding process, and that properly adjusted charging as well as controlling voltages can be generated at the same time. By the invention it is also attained that unnecessary disturbances in the magnet system are eliminated, a well defined output signal then being possible to obtain. Features characterizing the present invention will appear from the accompanying claims. Description of the figures The invention will be described in greater detail with reference to the accompanying drawings, which illustrate diagrammatically ' structures of an arrangement according to the invention. Fig. 1 shows a diagrammatical elevation of a generator arrangement in one rotational position. Fig. 2 shows the arrangement of Fig. 1 in a second rotational position. Fig. 3 illustrates a further arrangement. Fig. 4 shows a modification. Description of a first embodiment The arrangement comprises a magneto flywheel carrying six magnets 2- , 6-8 spaced along the periphery of the flywheel. The section 5 between magnet pole 4 and magnet pole 6 does not include any magnet poles. Centrally of the flywheel a generator core 9 is provided having eight core legs 10-17 radially projecting from said flywheel 1. The spacing of legs 10-17 is such that it agrees with the spacing or pitch with respect to magnet poles 2-4, 6-8 and the space corresponding to section 5, to which section two legs are attributed. Neither a shaft for support of wheel 1 nor an associated internal cumbustion engine are shown. Windings or coils 18-25 are provided on the core legs 10-17. It is assumed in this case that all coils are wound using a wire of one and the same dimension or gauge and in one and the same di- rection. The windings 19-24 are connected in series such that they coact in view of building up or increasing voltage. Points for tapping the volta¬ ges generated in the windings are designated 26 and 27. On the other hand, windings 18 and 25 are connected such that when voltages are induced therein, as the windings are traversed by symmetrically changing magnet fields, said voltages will cancel each other, that is, the windings are oppositely inter¬ connected. When, however, the unsymmetrical section of the magneto wheel is passed by the core legs concerned voltage pulses will be induced which can be tapped at the tapping points 28 and 29. It is assumed that the magneto flywheel is rotated in the direction of arrow 30. Operation of the arrangement In Fig. 1 the magneto flywheel has such a rotational position that core legs 10, 11, 12, 15, 16 and 17 are traversed by a symmetrically alter¬ nating field, whereas core legs 13 and 14 do not coact with any magnet pole. In this momentary position there is generated in the windings 19, 20, 23 and 24 voltages which create, by the series connection, a summation voltage which can be tapped at tapping points 26 and 27. As mentioned before, in this moment the core legs 13 and 14 are not exposed to any essential induc¬ tion as they are only affected by stray fields. Consequently lower voltages ma y arise in the windings 21 and 22, which voltages can be added to or sub- stracted from the other voltages generated in associated windings. During the moment just mentioned of the magneto flywheel rotation core legs 10 and 17 are traversed by a symmetrically alternating field, which means that those voltages generated in associated coils 18 and 25 cancel one another. Thus there will be no resultant voltage at tapping points 28 and 29. When the magneto flywheel has rotated into a position as shown in Fig. 2, core legs 11, 12, 13, 14, 15 and 16 are traversed by a symmetrically al¬ ternating magnet flux. Core legs 10 and 17, however, do not cooperate with any magnet pole. As stated before, when the borders or ends of section 5 pass core legs 10 and 17 an unsymmetry in the magetic field arises, which results in voltage pulses induced in windings 18 and 25, causing a resultant voltage to arise between tapping points 28 and 29. Said last mentioned vol¬ tage is considerably lower than the voltage arising across tapping points 26 and 27. Now, this fact can be utilized to advantage in such a way that the voltage across tapping points 26 and 27 is used for charging a charge condenser (about 400 volts) present in the ignition system, whereas the voltage which can be tapped across points 28 and 29 is used for controlling the ignition process. The voltage arising across the last mentioned tapping points is only a fraction of the first mentioned voltage (in practice about 5 volts ) . Consequently, by an arrangement as described above a very advantageous generator means can be obtained for driving an ignition system, for instance, for power saws. From the point of manufacture the structure is extremely favourable as all coils can be constructed uniformly, which means that those windings which are intended for controlling the ignition need not be specifically dimensioned, which is normally the case, but the whole device can be mounted in e.g. an automatic winding machine which winds, in an equi¬ valent manner, one coil after another on the respective core leg. By this construction and by the unsymmetrical, in view of magnet flux, section of the magnet pole path and by the two windings 18 and 25 being connected in opposition it is attained that one adequate voltage is obtained for charging the ignition condenser concerned and one adequate voltage is obtained for controlling the ignition process. Furthermore, it should be pointed out that a marked voltage pulse is obtained for trigging the ignition process, e.g. in the rotational position preceding that shown in Fig. 2. From the point of induction, controlling the ignition process by means of voltages induced by unsymmetry in the magnet path is no ideal procedure as, due to stray inductions, voltage wave forms of a none-desired character arise. It is therefore desirable to concentrate in general the induction area to a smaller section of the magnet path. Fig- 3 illustrates a solution in accordance to which magnets 4 and 6 have been extended so as to form poles 4' and 6'. Then the free space 5 will be considerably shorter than in Figs. 1 and 2, bringing with it that the field concentration there will be more manifest. By the arrangement shown the space 5 will here be equal to the distance between the other magnets, that is, a balanced symmetry is created. In applying such a solution the voltage wave intended for trigging will be considerably "cleaner" and more pronounced then in the case according to Figs. 1 and 2. The arrangement in accordance with Fig. 4 is equivalent, in principle, to the arrangement of Fig. 3, although no interconnected poles are used here but two separate magnets located in the section 5 according to Figs. 1 and 2 and arranged such that two north poles will be next to each other on one side of section 5 and two south poles next to each other on the other side. As a matter of course an arrangement according to the invention can be provided for controlling several ignition processes, that is, several pairs of cooperating windings, such as 18 and 25, can be provided. This means that the number of core legs could suitably be increased beyond what has been shown above, as well as the number of magnet poles.

Claims: Claims 1. An arrangement in generators, in particular for ignition systems, includ¬ ing a flywheel (1) with magnet poles (2-8) distributed therealong, which flywheel surrounds a multi-leg magnet core (9) stationary in relationship to the path of the poles and cooperating therewith, the legs (10-17) being distributed in correspondence to the pitch or spacing of the magnet poles and carrying windings (18-25) which are essentially uniformly wound and electrically forming at least two groups (19-24 and 18, 25, respectively), characterized in that one of the groups comprises two λ.indings (18, 25) on adjacent legs connected such that the voltages induced by a uniformly al- ternating magnet flux through the legs will cancel one another, and that at least a first section of the magnet path (between 4 and 6), substantial¬ ly corresponding to two core leg pitches, exhibits a magnetic unsymmetry a second section of the magnet path is magnetically symmetrical and has as many north poles as south poles provided thereon, said one group (18, 25) creating, when passing the borders of said unsymmetrical section of the magnet path, an induced voltage (28 and 29) lower than that induced by the second group (19-24), said voltages being arranged respectively to control the ignition process in an associated internal combustion engine and to charge a condenser included in the ignition system, the second group having windings (19-24) interconnected such that they cooperate to form a combined voltage (26, 27) including the effect of induction exercised by symmetrical as well as unsymmetrical sections of the magnet path. 2. An arrangement according to claim 1, characterized in that the two mag- nets (4, 6) located adjacent the first unsymmetrical section have a shape (4, 4'; 6, 6') so as to extend into said first section. 3. An arrangement according to claim 2, characterized in that said extended magnets (4, 4': 6, 6'j, each covers an aera substantially corresponding to two core leg pitches. 4. An arrangement according to claim 1, characterized in that the first un¬ symmetrical section includes two magnets of different polarity so arranged that a north pole within the first section will be located adjacent a north pole within the second section, whereas a south pole within the first section will be located adjacent a south pole within the second section.

Inventors: AAGREN ANDERS, BENGTSSON JOERGEN, AAGREN, ANDERS, BENGTSSON, JOERGEN
Applicants: SEM AB
Application year: 1990
Main classification: F02P1
IPC codes: F02P1, F02P15, H02K21