US2498860A - Ignition system for internal-combustion engines - Google Patents

Description

Feb. 28, 1950 2,498,860

IGNITION SYSTEM FOR INTERNAL-couBUsTIoN ENGINES l w. LUTTMER Filed July ll, 1947 Patented Feb. 28, 1950 IGNITION SYSTEM FOR INTERNAL- i I COMBUSTION ENGINES Willem Luttmer, Bietchley, England, asslgnor to Wipac Development Limited, Bletchley, England, a, British company Application July 11, 1947, Serial No. 780,446 In Great Britain Match 4, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires March 4, 1966 3 Claims. (Cl. 171-209) The present invention relates to ignition systems for internal combustion engines and has for its principal object to provide an improved ignition system capable of generating an adequate sparking voltage at very low engine speeds.

According to the present invention an ignition device for an internal combustion engine comprises a core of magnetic material surrounded by a winding and two permanent magnets arranged to apply magneto-motive forces respectively in opposite senses to the core, the arrangement being such that by the use of a, suitable inductor, paths of relatively low reluctance separate from the core can be provided to reduce the said magnetomotive forces applied to the core alternately to a relatively low value and hence produce flux reversals in the core.

Such a device may be used as the stator in an ignition system, the rotor comprising the inductor fixed or coupled to the engine shaft.

One embodiment of the invention will be described, by way of example, with reference to the accompanying drawing, in which Figure 1 is a diagrammatic part front sectional elevation of the embodiment, and

Figure 2 is a diagrammatic side elevation on a reduced scale, showing two diametrically opposite inductors.

Throughout Figures 1 and 2 like parts are given like references.

Referring to Figure 1, two permanent magnets I and II have a common closed magnetic circuit constituted by two laminated pole pieces I2 and I3, a laminated core III and a third pole piece I5, all of which are of high permeability magnetic material. The `south poles of the magnets I0 and II are arranged to bear against the pole pieces I2 and I3 respectively and the north poles both bear against the pole piece l5. Thus the magnets are arranged in series relatively to the core Il and oppose one another, that is to say they apply magneto-motive forces in opposite senses to the :sore I4. The magnets III and II are ar-v ranged to be of substantially equal pole strengths whereby the resultant flux in the core I4 is approximately zero.

All these parts are mounted on a frame I6 which has an aperture I1 through which is passed the crankshaft I8 of an engine (not shown). The, frame I6 is splgotted on to the crankcase of the engine at a circumference I9 concentric with thej crankshaft I8, and is held in place by two bolts'. passed through two concentric slots 20 and 2|2 into the crankcase. The reason for providing the slots 20 and 2I will be given later.

Mounted around the laminated core I4 is a primary winding 22 and a secondary winding 23. One terminal of the primary winding 22 is directly earthed at 24, the other terminal being connected to earth through the contacts of a contact breaker 25 which co-operates with a cam 25 mounted on the crankshaft I8.

Fixed to the crankshaft I 8 ls a cast iron flywheel 21 which rotates about a common axis 21 with the crankshaft in the direction of the arrow 28, and cast integral with the flywheel is a cast iron inductor 29.

The laminated pole pieces I2 and I 3 have upper arms 30 and 3| respectively and the inductnr 29 when rotated with the ilywheel 21 is arranged to passvclose to the upper surfaces of the arms 3l and 3| and the pole piece I5. The length of the co-operating surface 32 of the inductor 29, in the direction of rotation, is arranged to be approximately equal to the gap between the edges 33 and 34 of the arms 30 and 3l respectively.

There will now be described the eiect upon the flux in the core I4 when the inductor 29 is rotated with the flywheel 21. When the inductor 29 is approaching the left arm 30 the flux in the core I4 is substantially zero as previously described. On reaching a position where it bridges the gap between the arm 30 and the pole piece I5, that is to say where it greatly reduces the reluctance of that gap, a path of low reluctance is set up from the north pole of the magnet Il through the pole piece I5, the inductor 29 and the arm l0 to the south pole of the magnet Il. When this occurs the majority of the nux from the magnet III is shunted through this path, resulting in a flux being set up in the core Il, in a left to right direction in the drawing. This flux is due to the magnet II. Thus an electromotive force is induced in the primary Winding 22.

0n the inductor 29 moving to a central position where it bridges both gaps between the arm 30 and the pole piece I5, and the pole piece I5 and the arm II respectively, the flux through the core I4 once more falls to approximately zero. On moving further, however, the lnductor uncovers the gap between the arm 30 andthe pole piece I5 at the same time continuing to bridge the gap between the pole piece I5 and the arm 3|.

When this occurs a flux due to the magnet Il is set up in the core I4 and in a direction from right to left in the drawing.

Thus as the Inductor 29 passes through the central position, the reluctance of the gap between the pole piece I5 and the arm 30 commences to increase at substantially the instant when the reluctance of the gap between the pole piece I and the arm 3| .becomes a minimum, a reversal of flux takes place through the core I4 and a second E. M. F. is induced in the primary winding 22.

When the inductor 29 moves to a position where the reluctance of the gap between the arm 3 I, and the pole piece |5 is once again at its relatively high value, the flux in the core Il falls to approximately zero and for a third time an E. M. F. is induced in the primary winding 22.

The contact breaker is arranged to open when the second E. M. F. due to the reversal of flux through the core Il, is substantially at its peak. The frame I6 is mounted for limite-d rotaand 2| and c an be moved to adjust this timing.

When the contact breaker 25 opens, a relatively high E. M. F. is induced in the secondary winding 23, this E. M. F. being used for engine ignition purposes. i

The contact breaker 25 may be arranged to close just after the cessation of the first E. M. F., to open at substantially the peak of the second E. M. F., and to remain open until the inductor 29, or another inductor on the -ilywheel 21, reaches a position where once again the first E. M. F. of the next cycle has just fallen to zero.

With this embodiment it is found possible to bearing to wear considerably before it prevents obtain a substantially constant amplitude of secy ondary E. M. F.s over a wide range of engine speeds.

. With a four cylinder engine two diametrically opposite inductors are provided as shown in Fig.- ure 2, at 29 and 35, whereby two ignition E. M. F.s are provided during each cycle of the crankshaft and the balance of the flywheel 21 is lnot disturbed.

In this case a suitable distributor 31 is 4provided,

one end of the secondary windingl 23 (Figure 1) being connected to the arm 3 3 of the distributor, the other end of the secondary winding 23 being earthed. Four sparking plugs 39, one for each cylinder of the four cylinder engine, have their terminals 40 connected to the four output termi- -nals 4| respectively of the distributor 31, and have their metal casings earthed at 42. Where the ,number of cylinders in the engine, and hence the number of inductors on the flywheel 21, is such that the flywheel is not balanced by diametrically opposite inductors, one or more non-magnetic protrusions may be provided for balancing purposes.

The magnets I0 and the pole pieces I2, I3 and I5, the core I4 and the windings 22 and 23 may be arranged in a hermetically sealed container vshown at 36 in Figure 2, or the container l or moulding havin the remaining parts ern-V bedded therein. e above-mentioned timing of the contact breaker 25 has been found to result in the production of satisfactory secondary E. M. F.s at low speed without producing excessive primary current at high speeds.

In some engines it is possible for the main satisfactory operation of the engine. Such wear usually takes place at the bottom of thebearing. The said magnetic circuit is therefore preferably mounted with the two permanent magnets I0 and I I disposed symmetrically with respect to the horizontal plane containing the axis 21' of the ywheel 21. The air gap between the inductor 29 andthe pole piece I5 and the arms 30 and 3| then remains nearly constant in spite of wear of the main bearing.

1. An ignition device for an internal combustion engine, comprising a core of magnetic material, a winding surrounding said core, two permanent magnets arranged to apply magneto-motive forces respectively in opposite senses to said core, a magnetic circuit extending between the poles of each magnet and consisting of a structure of magnetic material having two polar surfaces defining a gap of relativelyr high reluctance, an inductor mounted for rotation about an axis, a surface on said inductor to co-operate with said structure in the vicinity of said gaps, said surface having a length in the directlonof said rotation substantially equal to the distance between those of said polar surfaces whichy are farthest apart in said direction, for reducing greatly the reluctance of each gap alternately.

2. An internal vcombustionrengine having a flywheel of cast ferro-magnetic material and an ignition system comprising a core of magnetic material, two permanent magnets arranged to apply magneto-motive forces respectively in opposite senses to said core, an inductor cast integrally with said flywheel for providing paths of relatively low reluctance, separate from said core, between the poles of said magnets, to reduce the said magneto-motive forces applied to said core alternately to a relatively low value, and hence produce flux reversals in said core.

3. An internal combustion engine having a iiywheel rotatable about an axis and an ignition system comprising a core of magnetic material, two

permanent magnets arranged to apply magnetomotive forces respectively in opposite senses to said core, an inductor upon and rotatable with said flywheel for providing paths of relatively low reluctance, separate from said core, between the `poles of said magnets, to reduce the said magnetomotive forces applied to said core alternately to a relatively low value, and hence produce ux reversals in said core, said core and magnets being disposed in approximately the same horizontal plane as said axis.

WILLEM LUTTMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS France Jan. 9, 1912

Images