Contactless magnet ignition system

Abstract

 A contactless magnet ignition system comprises a first core (6) of U-shaped cross-sectional configuration carrying an ignition coil (10, 11) on its central portion (7). A second core (9) carrying a control winding (23) is disposed outside of the primary winding perpendicular to the main axis of the first core (6) and spaced therefrom within the space defined between the legs (8) thereof. A permanent magnet rotor component (3 to 5) is adapted to induce respective voltages at the terminals of the primary winding (10) and the control winding (23).
A transistor (19) is controlled by the control winding (23) for interrupting the current flowing through the primary winding (10) so as to induce in the secondary winding (11) a voltage adapted to cause a spark to be generated across a spark plug (12).

Description

[0001] The present invention relates to a contactless magnetic- induction ignition system for internal combustion engines.

[0002] Magnet ignition systems are generally based on the principle of the generation of a voltage in a conductor subjected to a variable magnetic flux. More particularly, a sudden decrease of the magnetic flux in a core carrying an electric conductor is effective to induce a high voltage which may be applied to a spark plug, resulting in the generation of a spark, and thus in ignition of the combustion mixture.

[0003] Known contactless magnet ignition systems for internal combustion engines normally employ electronic circuits for interrupting the current flow in the primary winding so as to induce in the secondary winding a high voltage effective to generate a spark at the proper instant during the operating cycle of the engine.

[0004] For controlling the timing of this interruption it is known to employ an auxiliary coil adapted to control the electronic circuit.

[0005] This auxiliary coil is normally mounted together with the ignition coil proper on a single magnetic core, so that the voltage generated in the auxiliary winding is induced by a part of the magnetic flux which is thus unable to contribute to the current flow in the short-circuited primary winding.

[0006] The performance of these nagnet ignition systems are unsatisfactory, particularly due to the fact that the ignition spark is unstable and of irregular strength.

[0007] These shortcomings may be minimized by mounting the primary and auxiliary windings on separate cores, as described for example in British Patent 1,602,?29. In particular, the auxiliary winding and the respective core are disposed closely adjacent the core of the primary winding interiorly of the latter.

[0008] This solution is not either fully satisfactory because, due to the relative positioning of the various components, the short-circuiting of the primary winding is effective to induce disturbances in the auxiliary winding which alter the operation of the entire ignition system, and paticularly interfere with the synchronism of the ignition spark.

[0009] It is an object of the present invention to provide a contactless magnet ignition system capable of ensuring reliable, regular and accurate operation.

[0010] According to the invention, this object is attained in a contactless magnet ignition system comprising a first core of U-shaped cross-sectional configuration carrying a primary winding on its central portion defined between the legs of said U-shape.

[0011] A second core carries a control winding, while a rotor carrying at least one permanent magnet is adapted to generate a variable flux in said cores for inducing respective voltages at the terminals of the windings. Control means are controleld by the voltage induced in said control winding for interrupting the current flow in a closing circuit of said primary winding.

[0012] This ignition system is essentially characterized in that said second core is disposed outside of said primary winding with its axis substantially perpendicular to the main axis of said first core and spaced therefrom within the space enclosed between said legs.

[0013] The characteristics and advantages of the invention will become more clearly evident from the following description, given by way of a non-limiting example with referecne to the accompanying drawings, wherein:

fig. 1 shows a diagrammatic cross-sectional view of the main parts of an ignition system according to the invention, and

fig. 2 shows the electronic circuit of the ignition system of fig. 1 in a preferred embodiment of the invention.

[0014] With reference to fig. 1, the ignition system comprises a rotatory component having two magnetic poles and formed of a rotor 3 proper made of a ferromagnetic material (constituting one polarity) and carrying a permanent magnet 4 provided with a pole shoe member 5 mace of a ferromagnetic material (constituting the other polarity).

[0015] The rotatory component shown in fig. 1 is adapted to rotate in the clockwise direction and is driven by the shaft of an internal combustion engine.

[0016] The stationary component of the ignition system comprises a first magnetic core 6 of U-shaped cross-sectional configuration includign a central portion 7 defined between two legs 8 extending towards rotor 3..

[0017] Disposed on central portion 7 of core 6 is the ignition coil of the system comprising a primary winding 10 and a secondary winding 11 connected to the electrodes of a spark plug 12 (fig. 2).

[0018] With particular reference to fig. 2, the ignition system comprises an electronic circuit 13 for short-circuiting primary winding 10, circuit 13 being of a per se known type and essentially including two Darlington-connected transistors 14, 15, resistors 16, 17 a polarization diode 18.

[0019] Additionally connecte_'d in parallel to primary winding 10 is a transistor 19 in series with a polarization resistor 20.

[0020] The collector of transistor 19 is connected to the base of transistor 14, while its base is connected via a resistor 21 and a rectifier diode 22 to a terminal of a control winding 23. The other terminal of control wincing 23 is grounded, and the base of transistor 19 is also connected to ground through a capacitor 24. According to one aspect of the invention, capacitor 24 and resistor 21 together form a time constant circuit having a double function as will be explained.

[0021] According to another aspect of the invention, control winding 23 is disposed on a second core 9 separate from first core 6 and disposed outside of primary winding 10.

[0022] As particularly shown in fig. 1, second core 9 is disposed with its axis substantially perpendicular to the main axis of first core 6 and at a substantial distance therefrom within the space defined between legs 8. Second core 9 and the associated control winding 23 are preferably mounted on a base plate (not shown) carrying the main electronic components of the circuit shown in fig. 2.

[0023] In a per se known manner, second core 9 and control winding 23 are disposed at a slightly offset location with respect to first core 6 and ignition coil 10, 11 (taking into account the direction of rotation of rotor 3). As a result, a voltage pulse is generated in ccntrol winding 23 when the current flowing through primary winding 10 is substantially at its maximum value. The operation of the circuit shown in fig. 2 is per se known. The electronic circuit 13 is normally made conductive by the voltage generated in primary winding 10, so that the latter is practically short-circuited. As the current flowing through primary winding 10 is substantially at its maximum value, rotor 3. 4, 5 acts to induce in control winding 23 a voltage pulse which is applied through diode 22 and time constant circuit 21, 24 to transistor 19 to render the latter conductive. As a result, electronic circuit 13 is abruptly brought to the non-conducting state, causing an overvoltage to appear at the terminals of primary winding 10, such cvervoltage being transmitted to secondary winding 11 for causing an ignition spark to be generated across the electrodes of spark plug 12.

[0024] By suitably dimensioning RC circuit 21, 24 it is possible to adjust (in combination with the physical location of control winding 23) the blocking instant of electronic circuit 13 and thus the instant at which the spark is dis- charegd across spark plug 12.

[0025] In addition, RC circuit 21, 24 controls the switching speed of transistor 19 so as to limit the value of the overvoltage at the terminals of the electronoc circuit 13 as the latter is blocked. In this manner it is avoided that the overvoltage at the terminals cf electronic circuit 13 exceeds the breakdown voltage, whereby the reliability of the entire ignition system is improved.

[0026] In any case, the particular positioning of cores 6 and 9 and the respective windigns 10, 11 and 23 relative to one another minimizes the possibility of interference signals being induced in control winding 23 (particularly on short-circuiting primary winding 10). As a result, the ignition system functions in a highly accurate manner so as to attain the above stated object of the invention.

[0027] The described ignition system may of course be modified in various manners within the scope of the characteristics set forth in the appended claims.

Claims

1. A contactless magnet ignition system comprising a first core of U-shaped cross-sectional configuration carrying a primary winding on a central portion defined between the legs of said U-shape, a second core carrying a control winding, and a rotor carrying at least one permanent magnet adapted to create a variable flux in said cores for inducing respective voltages at the terminals of said windings, and control means controlled by the voltage induced in said control winding for interrupting the current flow in a closing circuit of said primary winding, characterized in that said second core (9) is disposed outside of said primary winding (10) with its axis substantially perpendicular to the main axis of said first core (6) and spaced therefrom within the space defined between said legs (8).

2. An ignition system according to claim 1, characterized in that said control means (19) are controleld by the voltage induced in said control winding (23) via a delay circuit (21, 24).

Drawing