AU638443B2 - Magneto construction - Google Patents

Description

MAGNETO CONSTRUCTION

The present invention relates to magnetos for internal combustion engines and, in particular, to a magneto construction which increases the efficiency of the coil by increas ing the high tension voltage output for the spark plug whilst at the same time reducing the amount of secondary wire used. Preferably the magneto construction is also able to be used for charging of light duty batteries, as well as lowering other manufacturing costs of the coll assembly of the magneto.

BACKGROUND ART

A substantial cost in the construction of magnetos is the cost of the ignition coil and, in particular, the cost of the wire of the secondary winding since this winding conventionally has from 8,000 to 10,000 turns compared with only approximately 140 to 180 turns in the primary winding. In addition, there is a substantial amount of time involved in actually winding the secondary winding even though the winding is wound by machine. It follows therefore that if the number of turns in the secondary winding can be reduced, and the amount of wire used is also reduced in greater proportion than the turns saved, then this leads to a considerable saving in cost in the coil assembly and thus in the overall magneto.

OBJECT OF THE INVENTION

It is an object of the invention to provide a magneto construction which substantially reduces the cost of construction.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is disclosed a magneto construction for internal combustion engines, said magneto

construction including a magnetically permeable core able to be positioned adjacent a magnet carrying rotor and energised by relative movement between said core and rotor, said core carrying a coil arrangement comprising a secondary winding wound on a spool and a primary winding co-axial to the secondary winding, wherein said primary and secondary windings are side by side and longitudinally co-axial, and wherein said primary winding is positioned closer to said rotor or, if exchanging the postions of the primary and secondary windings does not result in the primary winding being closer to the rotor in one of said positions, then the primary winding is positioned closer to that portion of said core in which the spark

triggering change of flux occurs. According to a preferred embodiment of the present invention not only are there considerable savings made in the secondary wire used, but also savings in coil construction costs and, for certain engines, considerable savings in armature steel.

According to the preferred embodiment of the present invention, because the primary winding is closer to the magnet energy source, and because the primary winding has a higher wattage output than primary windings of conventional ignition colls, then sufficient extra energy is available from the normally unused two pulses of one polarity (generally negative) for charging a light duty battery for electric start engines such as lawnmowers.

According to the present invention there is also disclosed a method of forming a coil arrangement for a magneto construction for internal combustion engines, said method comprising the steps of:

securing one end of a secondary winding wire to a first boss of a moulded plastic spool, winding said secondary winding onto said spool, and securing the other end of said secondary winding wire to a second boss of said spool.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described with reference to the drawings in which:

Fig. 1 is an exploded perspective view of a first prior art coil assembly,

Fig. 2 is an exploded perspective view of a second prior art coil assembly,

Fig. 3 is an exploded perspective view similar to Fig. 2 but illustrating the coil assembly of the preferred embodiment,

Figs. 4,5 & 6 are each schematic cross-sectional views through a prior art coil and iron core lamination assembly,

Each of Figs. 7 to 12 is a similar view to that of Fig. 4 but of a different embodiment of a lamination and coil assembly in accordance with the present invention, the rotor R not being illustrated,

Fig. 13 is a schematic cross-sectional view through a single leg lamination and coil arrangement, again the rotor R not being illustrated, Fig. 14 is a view similar to Fig. 13 but of a preferred armature, coil and rotor pole pieces having reduced dimensions, Fig. 15 is a view similar to Fig. 14 but of a preferred coil arrangement on a core as used on a three pole magnetic rotor, and

Fig. 16 is a view similar to Fig. 15 but showing an alternative coil arrangement.

BEST MODE OF CARRYING OUT THE INVENTION

Turning now to Fig. 1 a conventional coil assembly is illustrated in which a primary winding 1 is wound around an Iron core (not illustrated), and a secondary winding 2 is wound around the primary winding. In the arrangement of Fig. 1 the secondary winding 2 is provided with paper interleaving 8 for each layer of wire and this has been the conventional method of Ignition coil manufacturing for about 100 years. If it were not for this paper interleaving, the high voltage between the axially extensive layers of the secondary winding 2 would cause a breakdown of the insulation of the wire. The wire of the secondary winding 2 prior to commencement of winding, and just prior to completion of the winding, is joined by being soldered to some larger diameter wire since the fine wire of the secondary winding cannot be handled to any extent without breaking. In addition, after completion of the winding a length of adhesive tape is ecured to the paper insulation in order to maintain both the larger diameter wire and the secondary winding in their wound state.

The windings 1 and 2 are generally potted in varnish, pitch or epoxy resin or the like after the primary and secondary windings have been interconnected by soldering and inserted into a case. Additional steps prior to potting include making the connection of the secondary winding to a high tension lead and soldering the ends of the primary winding to respective terminals which are usually frictionally fitted to the case after insertion of the coils.

Fig. 2 is a more recent development of an ignition coil assembly and is illustrated having a primary winding 1 and a secondary winding 2 which is would on a spool 3 have four compartments 4. Fig. 2 illustrates the assembly in an exploded state, however, it will be appreciated by those skilled in the art that the primary winding 1 is pressed over a central hollow base 5 of a coil cup in the form of a moulded plastic case 6. Then the spool 3 carrying the secondary winding 2 is pressed into the case 6 and the entire arrangement is potted in an epoxy resin or the like (not illustrated). One end of the secondary winding 2 is connected from the compartment 4 closest to the rotor (not illustrated) to a high tension outlet 7. The other end of the secondary winding is connected to the earthed end of the primary winding 1. The free end of the primary winding is connected to an electronic ignition circuit.

The spool winding of secondary coils has a number of advantages over the older paper interleaving method of secondary winding. There is a saving of machine time in winding as paper interleaving machines are slow in speed and therefore less efficient. Spool wound coils do have a better high voltage secondary winding output for the same number of turns compared to paper interleaved coils. Two metal pins 4A and 4B are inserted in the spool for terminating each end respectively of the very small diameter wire from which the secondary winding 4 is wound. To the pin 4A is soldered the end 1A of the primary winding 1 as well as an earth/ground wire 1C to the outside of the coil for fixing to the engine block (not illustrated). To the other pin 4B a high tension wire 4C from the outside of the coil is connected. This generally takes the form of a separate layer diameter interconnecting wire 4C. The other end IB of the primary winding is generally connected to the outside of the coil, to an on/off switch wire, and sometimes also to an external electronic ignition module.

Amongst the disadvantages of the prior art four compartment spool of Fig. 2 is the high cost of the precision moulded compartment spools in both tooling cost and unit price. Thus a large throughput or manufacturing volume is necessary to make it economical. Metal pin inserts are an added expense as well as the labour cost or extra machine cost for insertion of these pins into the spool. Not only do the dividing walls and wire transfer chambers for each compartment add to the overall cost of tooling, but the axial length of the spool is increased and this therefore adds bulk to the coil size. Furthermore, this bulk limits the number of turns that can be placed on the spool especially if a coil is to be designed for a large cross section iron core. This problem is also compounded if the new coil design requires a larger primary coil, either in wire diameter or increased turns. Once the spool is designed and made the primary winding cannot be altered except to be made smaller. It will be appreciated that in both the prior art arrangements illustrated in Figs. 1 and 2, both the primary winding 1 and secondary winding 2 are co-axial; with the secondardy winding 2 surrounding the primary winding 1 and having a large diameter. There is a reason for this to be found in magnetic circuit theory since in order to achieve a good transformer action, or close coupling, between the primary and secondary windings, it is necessary for all the magnetic flux produced by the primary winding current to link all the turns of the secondary winding. It Is therefore thought that if the secondary winding surrounds the primary winding, this desirable result is easily achieved.

Turning now to Fig. 3, the preferred embodiment of the coil assembly of the present invention is illustrated therein. A primary winding 10 is wound in substantially conventional fashion but with shorter length and larger diameter and heat sealed in order to hold the turns together immediately after completion of the winding. A moulded plastic spool 11 is provided with two compartments 12 and 13 at one end, and a recess 30 at the other end to receive the primary winding 10. A secondary winding 14 is would sequentially by first securing one end of the wire by wrapping it around a notched upstand or boss 16, then winding the compartment 13 to form half the secondary winding 14, then winding the compartment 12 to complete the secondary winding 14, and then terminating the winding by wrapping the wire around an upstand 15.

Located on the front face 17 of the case 11 are two mounting lugs 18, 19. A third mounting lug (not illustrated) is provided on the underside of the case 11. These three mounting lugs mate with the three corresponding apertures 20, 21 and 22 in a carrier plate 23. The carrier plate 23 has two connectors 24, 25 retained by friction fits on the carrier plate 23 in order to provide connection points for each end of the primary winding. An electronic ignition circuit (not illustrated) can also be attached to plate 23 if desired.

Also on the front face 17 are a pair of mounting bosses 26, 27 which are moulded with the case 11. Aligned with notched upstand 16 is a further mounting boss 29.

Also illustrated in Fig. 3 is a high tension lead outlet 31 having a generally cylindrical body 32 into which is received a high tens ion cable 33. Extending from the body 32 is a flange 34 having a pair of holes 35,36 dimensioned to receive mounting bosses 26, 27 in a frictional fit. Also located on the underside of the body 32 is an opening 38. The opening 38 is dimensioned to be a frictional fit with the mounting boss 29.

The body 32 also has an L-shaped slot 39 in its upper surface into which the metallic conductor of the high tension cable 33 (after being stripped of its insulting cover) can be placed for subsequent soldering to the upstand 15.

The method of assembly of the coil assembly of Fig. 3 is as follows:- First the secondary winding 14 is wound onto the case 11 with one end of the secondary winding being wrapped around the notched upstand 16 as described above and the other end of the secondary winding being wrapped around the upstand 15 as also indicated above. As this stage the upstands 15 and 16 can be either hand or automatically soldered, or solder dipped, if so desired. Then the carrier plate 23 is located on the case 11 by interconnection of the mountings lugs 18 and 19, and the unillustrated lug, with the corresponding openings 20, 21 and 22.

Next, the primary winding 10 is pressed into the recess 30 of the case 11 and one end of the primary winding is passed over the notch of the notched upstand 16, soldered to the wrapped wires on upstand 16, and then taken down to, say, connector 25 and soldered to same. The other end of the primary winding is taken directly to the other connector 24 and soldered to same. If required an ignition module can be inserted into a moulded pocket (not illustrated) of the carrier 23 and its leads soldered to connectors 24 and 25.

Finally, the body 32 is positoned on the case 11 by inter-engagement of the mounting bosses 26, 27 with the holes 35, 36 and the mounting boss 29 with the opening 38. The stripped conductor (not illustrated) of the high tension cable 33 is then passed along the L-shaped slot 39 and soldered to upstand 15 which extends alongside the flange 34.

The advantage of using moulded plastic upstands or bosses as terminating pins is the saving of purchasing or making the conventional metal insert pins. As well there is a saving in the cost of inserting same into the plastic spool. Furthermore, the plastic upstand 15,16 can be moulded with a recess or groove 48 formed, for example, between two ridges 49 on one side as illustrated in the detailed view in Fig. 3. Since the wire is wrapped several times around grooved upstand, there is an air gap between the wire and the plastic. Therefore the wires can absorb the solder quickly and cleanly like a wick and without undue heat having to be applied thereby possibly distorting the plastic upstand. These upstands, whether moulded with a groove or not, can be soldered after being wire wrapped by either solder dipping or hand soldering.

It will be appreciated that, compared to other coil constructions, in the above described condition during the assembly, no taping is required to hold any wires, no pins are required for insertion Into the spool for terminating the two ends of the secondary winding, no separate (large diameter) wires are needed for the primary and secondary Interconnections or outside connections, no separate (large diameter) wire is needed to connect one end of secondary winding with the external high tension lead; and the complete assembly procedure for the coil, with or without ignition circuit, is carried out before placing the assembled coil Into the moulded plastic coil cup for epoxying or potting. Also prior art coil assemblies generally have connectors inserted into the edge of the moulded plastic coil cup and hence require further soldering or interconnecting after the coil assembly is placed into that coil cup. Furthermore, in the present arrangement all the solder points are easily accessible.

The above described arrangement saves a substantial amount of assembly time and labour skills to thereby provide a low cost arrangement. Also the arrangement is suitable for robotic soldering.

A further advantage with the preferred embodiment is the substantial saving of copper secondary winding wire actually used, which being of such small size (approximately .06mm diameter) is extemely expensive and the major material cost of the ignition coil. Conventionally, the secondary winding of the magneto ignition coil surrounds the primary winding and therefore has a larger diameter with a large average circumference. Since the secondary winding 14 does not wind around, or surround, the primary winding 10 but is longitudinally co-axial, then its average diameter, or in the case of a square or rectangular spool, it average "circumference", is much less than conventional prior art coils. A comparison is made in the table I at the rear of the specification.

Another advantage of the arrangement of Fig. 3 is that the overall size of the coil is reduced with the elimination of the extra dividing and wire transfer chambers. There are also considerable savings in tooling costs with the elimination of these extra chambers and wall sections. A still further advantage of the arrangement of Fig. 3 is the faster winding time compared to the four compartment spool coils. After

completion of winding of each chamber of the multi-chamber spool, the winding machine has to slow down to, or near to, zero revolutions so that the winding machine can feed the small diameter wire across the dividing wall, into the transfer chamber, then through a slot into the next winding compartment, and then increase its winding speed. With a four compartment spool this sequence occurs three times compared to just once for the preferred embodiment.

Another advantage of the arrangement of Fig. 3 is that there is flexibility in that wire turn ratios can be varied at any time. Hence the same mouldings for spool and coil can be used for different engine requirements without requiring further expensive tooling for new spools and coil cups.

Turning now to Figs. 4 to 12 inclusive, in each instance a

conventional permeable core 40 of U-shaped configuration was used, the core 40 being formed from a stack of laminations. A rotor R having a magnet 45 and pole pieces 46, 47 was also used and the direction of rotation was as illustrated. An air gap of 0.010 inch (0.25mm) was maintained in each instance between the rotor R and the ends of the legs of the core 40.

With this equipment in common, a series of comparison tests were performed using different colls the details of which are described hereafter. In each instance the ignition coil configurations were formed from a primary winding PW and a secondary winding SW. A high tension cable 43 was connected as illustrated to one end of the secondary winding SW. In all instances (except Fig. 4 which has paper interleaving) each secondary winding SW is formed into one or more compartments by being wound onto a single or a multl-compartment spool.

Fig. 4 uses the prior art arrangement of Fig. 1 used by VICTA of Sydney, Australia (Victa Part No. MA05556A). In this coil the primary winding PW and secondary winding SW are co-axial and radially spaced with the secondary winding Sw using paper insulation.

Fig. 5 uses the prior art arrangement for multi-compartment spool type as illustrated in Fig. 2, and is used by BERNARD M0TEURS of Paris, France and manufactured by PVL ELECKTRONIK of Nuremburg, West Germany. In this coil the primary winding PW and the secondary winding SW are co-axial and radially spaced, with the secondary winding SW having a large diameter and surrounding the primary winding PW. The secondary winding SW is wound onto a spool similar to the spool 2 (Fig. 2) with four separate winding compartments 4, separated by dividing walls and transfer chambers with the last wound compartment closest to the rotor R (Fig. 5).

Fig. 6 illustrates another prior art arrangement illustrated in Fig. 36 of U.S. Patent No. 4,163,437 (issued to the present applicants) in which the primary winding PW and the secondary winding SW are longitudinally co-axial and thus lie alongside each other. The secondary winding SW is located between the primary winding PW and the magnet carrying rotor. This coil arrangement was never manufactured as the secondary voltage output was very low. Therefore this prior art arrangement was unsuitable for production.

For each of the arrangements illustrated in Figs. 4 to 12 inclusive, Tables I and II list the coil characteristics and results obtained for different rotor speeds from 300RPM through to 3000RPM. The primary windings PW of each of the coil arrangements of Figs. 6 to 13 inclusive are identical. Each coil arrangement was connected to the same transistor ignition circuit of the type illustrated in Fig. 3 of the abovementioned U.S. Patent 4,163,437. In each instance the resistive potential divider of the ignition circuit was adjusted to suit a very low RPM start engine (as is required for lawnmowers), so as to cause initial triggering of the ignition circuit with each coil at a rotor speed of 300RPM. The secondary winding SW was on open circuit connected to an oscilloscope and the open circuit secondary voltage was measured for each rotor speed indicated.

From Table I it will be seen that substantial savings in secondary winding wire can be achieved together with increased secondary winding output voltage. If increased secondary winding output is not required then the arrangement of Fig. 8 can be used thereby achieving a saving in secondary winding wire of the order of 50%.

From a comparison of the results of Table II, it will be seen that although Figs. 6 and 8 have identical primary windings, exchanging the positions of the primary and secondary windings so that the primary winding PW is nearer the rotor R, substantially increases the secondary winding voltage generated at each given rotor speed. A similar comment applies in relation to Figs. 7 and 9 which again have identical primary and secondary windings save only that the primary winding PW is closer to the rotor R magnet in the arrangement of Fig. 9. Again this closer positioning of the primary winding PW produces the better electrical result.

Again a comparison of the results of Table II for the coils of Figs. 9 and 10 and Figs. 11 and 12 where the only different is the position of the connection of the high tension cable 43, indicates that the connection of the high tension cable 43 to that compartment of the multiple

compartment secondary winding furthest away from the primary winding PW provides an increase in the secondary winding voltage. This is

particularly helpful for starting when extra secondary voltage is needed.

It will be appreciated that the number of primary winding turns, specified at 270 in Table II can be increased or decreased by, said 50 turns results in a drop in the secondary winding voltage by 0.5kV. This applies for the same diameter wire. If the number of primary winding turns is reduced to 240 and the wire diameter increased from 0.475mm to 0.56mm then the secondary winding voltage is increased by 0.75 kV.

Table III at the rear of the specification provides a further comparison between the arrangements of Figs. 1 and 4, Figs. 2 and 5, and Figs. 3 and 12. Here for each coil the open circuit peak primary winding voltage (PV) of the single (positive polarity) pulse used to trigger the ignition circuit was measured at each rotor speed. Then with the primary winding short circuited, the peak primary winding current (A) for the positive pulse was measured on an oscilloscope using a current probe which clamps around the conductor carrying the current to be measured.

Although this peak voltage and peak current are not obtained under identical conditions, multiplying these two quantities togetehr provide an approximate indication for comparison purposes of the peak watts (W) generated by the three difference coils at each rotor speed. It will be appreciated that for the same identical energy input derived from the same rotor R, the coil of Figs. 3 and 12 is appreciably more efficient giving as it does a much large electrical output for the primary winding PW. This is thought to arise from its position closer to the rotor R. In addition, the close coupling of the secondary winding SW of Fig. 12 by being side by side and longitudinally co-axial, together with the increased primary winding electrical performance results in a substantial improvement in secondary winding output.

In Fig. 13 a different magnetic circuit arrangment is illustrated. Here an L-shaped portion of the iron core 40 was removed so as to leave a permeable core 50 in the form of only a straight single radial leg rather than a U-shaped configuration as is conventionally the case. The rotor R was used as before with the same air gap as before, i.e. 0.010 inches (0.25mm).

Experimental results for the magnetic core arrangement of Fig. 13 with the preferred coil arrangement of Fig. 12 are indicated on the third row of Table IV. To enable a comparison with the conventional prior art coils of Figs. 4 and 5 of Table I, the coil arrangements of Fig. 4 and 5 were then placed onto the core 50 of Fig. 13. The lesser electrical results are as indicated in the first row of Table IV. Similarly, the lesser electrical results with the prior art coil arrangement of Fig. 5 located on the core 50 of Fig. 13 are as indicated on the second row of Table IV.

The voltages given for the third row of Table IV are directly comparable with the voltages given in the row for Fig. 12 in Table II. The results for the first three rows of Table IV were arranged with the initial triggering speed for the transistor circuit set at 300 RPM.

The fourth to sixth rows of Table IV indicate the electrical results for the same arrangement as for the third row but with the triggering speed of the transistor ignition circuit adjusted for starting at 400, 500, and 600 RPM respectively which are starting speeds which are suitable for faster starting engines such as brushcutters, chainsaws, etc which have a small rotating mass.

Fig. 14 is a development of Fig. 13 and illustrates the preferred coil arrangement fitted to a core 51 which is a single radial leg designed for installation in a small engine. The core 51 is of simple construction being manufactured from strip steel with a dramatic saving in both steel costs and tooling costs over core 40, for example, since approximately 80% less steel is used and the material can be pre-slit. The coil 52 still has the same primary winding PW and secondary winding SW as in Figs. 12 and 13, but the external dimensions have been reduced hence reducing the overall bulk of the coil arrangement. This allows for streamlining and better airflow of cooling air for the engine from its fan and also for a smaller engine profile which is an advantage in the market place. Furthermore, as well as a reduction in weight of the iron core 50, there is also a reduction in weight of the magnetic pole pieces 53,54 of the rotor 55.

Whilst still retaining the same size magnet 45, the pole pieces 53, 54 can be dramatically reduced in size, not only saving cost but also saving weight, whilst not affecting the magnetic qualities of this overall arrangement. In small engines the rotor is always a part of the fan and the coll and armature are placed in the air stream. The single core 51 and smaller profile coil 52 have less air resistance and therefore allows better streamlining of engine layout as well as a smaller overall profile of engine.

Fig. 15 illustrates the coil arrangement of Fig. 12 fitted to the middle portion of a two legged permeable core 60 but with a rotor 61 having three magnetic poles 62, 63 and 64.

In this arrangement results comparable with Fig; 12 are obtained by rotating the rotor 61 clockwise as seen in Fig. 15. Turning the coll arrangement around so as to reverse the position of the primary winding PW and secondary winding SW (and still maintaining clockwise rotor rotation) produces a reduced result comparable with that of Fig. 7 relative to Fig. 10. Alternatively, a reduced result is obtained by rotating the rotor 61 anti-clockwise with the coil arrangement being as illustrated in Fig. 15. Finally, reversing both the direction of rotation and the relative position of the primary and secondary windings reproduces the original superior result. It should be understood in this connection that the connections between the primary winding and ignition module are always arranged so that the ignition module triggers on the large central induced primary winding pulse.

Fig. 16 also illustrates a coil arrangement 71 of an embodiment of the present invention fitted to a prior art permeable core arrangement 70 which is operable with a three magnetic pole rotor 61, as in Fig. 15. The permeable core 70 is that used by the Briggs 8. Stratton Corporation where the coil windings are almost totally surrounded by two arms 73, 74 of the permeable core 70. As shown in Fig. 16, a single spool 75 for the secondary winding SW is possible due to the larger diameter available for the secondary winding SW in this construction. In this embodiment, the body 32 of Fig. 3 and the spool are integrally formed. A reduced axial length, smaller diameter, multi compartment spool can also be used in lieu of the single compartment spool as illustrated. The same comments regarding rotor direction of rotation and the orientation of the primary and secondary windings as made in relation to Fig. 15 also apply to Fig. 16.

The preferred coil arrangements of Figs. 12-16 can also be used on other permeable cores such as three leg E-cores arrangements where the primary and secondary windings are located on the centre leg of the

E-shaped core. Again an increased output is obtained by placing the primary winding closer to the rotor on the centre leg of the E-shaped core.

It is thought that the improved result obtained by placing the primary winding closer to the rotor than the secondary winding on a radially extending portion of a magnetically permeable core is due to leakage flux. By radially extending portions of a core is meant the coil carrying leg of the core 40 of Figs. 4-12, the core 50 of Fig. 13, the core 51 of Fig. 14, and the centre leg of the well known E-shaped core such as that illustrated in Fig. 32 of the abovementioned U.S. Patent No. 4,163,437.

From a consideration of Fig. 6 and Fig. 14, it will be seen that any leakage magnetic flux which passes only partially along the leg of the core near to the rotor, before then passing into the air to return to the rotor, does not link the primary winding PW in Fig. 6 but only (partially) the secondary winding which is not relevant since it is the induced primary winding current which is interrupted. The reverse is true for Fig. 14, for example, and thus the improved result since the more flux which links the primary winding the greater the primary winding current and the greater the rate of change of primary winding current at the moment of triggering the ignition circuit. In this connection it is thought that better use of rotor flux more than compensates for any lessening of the close coupling between primary and secondary windings.

However, for the permeable cores 60 and 70 of Figs. 15 and 16

respectively, the primary and secondary windings both lie on what may be regarded as a "circumferentially" extending portion of the magnetically permeable core. However, the better results are obtained with the primary winding PW closer to the trailing leg. It will be apparent to those skilled in the art that the approach of the central North pole piece 63 to the trailing leg of the core 60, 70 is what brings about ignition. Again any leakage flux which extends along the trailing leg and only partially into the circumferential portion before returning to the rotor 61, 72 will link the primary winding PW only when the primary and secondary windings are as illustrated - and not when reversed (assuming the same direction of rotation).

The same considerations as for Figs. 15 and 16 also apply to an internal I-shaped core as illustrated in Fig. 34 of the abovementioned U.S. Patent.

This hypothesis will be seen to be consistent with the results for the core 40 of Figs. 4-12 since again the ignition is triggered by the change of flux brought about as the north (trailing) pole piece approaches the trailing leg of the core 40.

Another aspect of the present invention is the use of the two

(generally negative polarity) smaller pulses which are generated to either side of the main ignition triggering pulse, to charge a light duty starter battery. This can be achieved using a diode bypass arrangement to charge the battery and saves the cost of a separate charging coil, and in some cases also saves the cost of the separate internal rotor magnets used for engergizing separate internal charging colls.

The peak negative voltages, PV1 and PV2 peak "short circuit" currents Al and A2, and the wattages obtained by multiplying these two quantities together for each of the first and second of these pulses are indicated in Table V. Also indicated is the sum of the wattages (W1 + W2) which is indicative of the battery charging capability of the coil arrangements in question. It will be seen that this capability is substantially higher for the arrangement of Fig. 12 relative to the arrangements of Figs. 4 or 5.

The foregoing describes only some embodiments of the present invention and modifications obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. T A B L E I

FIG. SWT S.W. S.W. OUTPUT % LESS WIRE THAN

AVERAGE WIRE AT 300 RPM FIG 1 & 4 2 & 5 CIRCUMFERENCE LENGTH

USED

1 & 4 9350 103.7mm 970 metres 12.5KV - -

5 9800 106.8mm 1047 metres 13.0KV - -

3 & 12 7800 89.5mm 698 metres 15.75KV 28% 33%

8 5300 89.5mm 474 metres 12.5KV 51% 54%

T A B L E II

FIG. PWT SWT SW RPM & SECONDARY VOLTAGE IN KV

WIRE 300RPM 400RPM 500RPM 600RPM 1000RPM 2000RPM 3000RPM

LENGTH 4 180 9350 970 metres 12.5 12.5 12.5 12.5 13.0 13.5 13.5

5 160 9800 1047 metres 13.0 13.5 13.5 13.75 14.0 14.5 14.75

6 270 5300 474 metres 9.5 9.5 9.5 9.5 9.5 9.5 9.5

7 270 8500 750 metres 12.5 13.0 13.0 13.25 13.25 13.25 13.25

8 270 5300 474 metres 12.5 12.5 12.5 12.5 13.0 13.0 13.0

9 270 8500 750 metres 14.75 14.75 14.75 15.0 15.5 15.75 16.0

10 270 8500 750 metres 15.0 15.5 15.5 15.5 15.5 15.5 15.5

11 270 7800 698 metres 13.5 14.0 14.0 14.0 14.25 14.5 15.0

12 270 7800 698 metres 15.75 15.75 15.75 15.75 16.0 16.0 16.0

T A B L E III

FIGS. 1 & 4 FIGS. 2 & 5 FIGS. 3 & 12

RPM PV A W PV A W PV A W

300 10 1.7 17 8.5 1.85 15.7 16 1.3 10.8

400 13 2.0 26 11 2.15 23.7 22 1.55 34.1

500 16 2.1 33.6 14 2.35 32.9 26.5 1.75 46.4

600 20 2.25 45 17 2.45 41.7 32 1.85 59.21 000 32 2.5 80 28 2.8 78.4 51 2.1 107.1

T A B L E IV

RPM & SECONDARY VOLTAGE IN KV

FIG. 300RPM 400RPM 500RPM 600RPM 1000RPM 2000RPM 3000RPM

4 10.25KV 10.25KV 10.25KV 10.25KV 10.5KV 11.25KV 11.5KV

5 9.0KV 9.5KV 9.5KV 9.5KV 10.0KV 10.5KV 11.0KV

13 13.75KV 13.75KV 14.25KV 14.25KV 14.25KV 14.5KV 14.5KV

13 - 15.5KV 15.5KV 15.5KV 15.75KV 15.75KV 16.0KV

13 - - 16.0KV 16.0KV 16.25KV 16.25KV 16.5KV

13 - - - 16.75KV 17.0KV 17.0KV 17.25KV

T A B L E V

RPM PV1 A1 W1 PV2 A2 W2 W1 + W2

FIG.4 10000 20 1.7 34 16 .7 11.2 45.2

1500 29 2.0 58 21 .6 12.6 70.6

2000 38 2.2 83.6 30 .5 15.0 98.6

2500 48 2.3 110.4 38 .4 15.2 125.6

3000 56 2.4 134.4 44 .35 15.4 149.8

FIG.5 1000 14 1.6 22.4 10 .8 8 30.4

1500 22 1.95 42.9 16 .75 12 54.9

2000 29.5 2.15 63.4 21 .6 12.6 76

2500 37 2.4 88.8 26 .55 14.3 103.1

3000 43 2.6 111.8 30.5 .4 12.2 124

FIG.12 1000 30 1.25 37.5 24 .6 14.4 51.9

1500 44 1.5 66 35 .5 17.5 83.5

2000 58 1.65 95.7 46 .4 18.4 114.1

2500 72 1.75 126 58 .35 20.3 146.3

3000 81 1.9 153.9 66 .35 23.1 177

Claims (16)

1. A magneto construction for internal combustion engines, said magneto construction including a magnetically permeable core able to be positioned adjacent a magnet carrying rotor and energised by relative movement between said core and rotor, said core carrying a coll arrangement comprising a secondary winding wound on a spool and a primary winding co-axial to the secondary winding, wherein said primary and secondary windings are side by side and longitudinally co-axial, and wherein said primary winding is positioned closer to said rotor or, if exchanging the positions of the primary and secondary windings does not result in the primary winding being closer to the rotor in one of said positions, then the primary winding is positioned closer to that portion of said core in which the spark

triggering change of flux occurs.

2. A magneto construction as claimed in claim 1 wherein said spool has at least two longitudinally co-axial side-by-side compartments.

3. A magneto construction as claimed in claim 1 wherein said secondary winding spool is moulded from plastics material and includes a pair of integrally formed moulded bosses, and the secondary winding is wound with fine wire which is directly terminated on said bosses.

4. A magneto construction as claimed in claim 3 wherein at least one of said bosses has a groove over which said wire is wound, said groove acting as a wick for molten solder.

5. A magneto construction as claimed in claim 1 wherein a high tension lead is carried by a moulded plastic body which is secured to said spool by engagement of engageable components on said body and spool respectively.

6. A magneto construction as claimed in claim 1 wherein the high tension lead is insertable into a recess formed integrally with the spool.

7. A magneto construction as claimed in claim 1 wherein said primary winding is located in a recess formed in said spool, said recess being alongside said secondary winding.

8. A magneto construction as claimed in claim 1 wherein ancillary equipment is mounted on a carrier which is secured to said spool by engagement of engageable components on said carrier and spool respectively.

9. A magneto construction as claimed in claim 2 wherein a high tension lead is connected to that end of said secondary winding which is remote from said primary winding.

10. A magneto construction as claimed in claim 1 wherein said

magnetically permeable core which carries said coll has a generally

I-shaped configuration and its longitudinal axis is substantially radial to said rotor.

11. A method of forming a coil arrangement for a magneto construction for Internal combustion engines, said method comprising the steps of:

securing one end of a secondary winding wire to a first boss of a moulded plastic spool, winding said secondary winding onto said spool, and securing the other end of said secondary winding wire to a second boss of said spool.

12. A method as claimed in claim 11 wherein a carrier for ancillary equipment is secured to said spool by inter-engagement of engageable parts formed on said carrier and spool respectively.

13. A method as claimed in claim 11 wherein a primary winding is longitudinally co-axially arranged relative to said secondary winding, one end of said primary winding being electrically connected to the secondary winding at said boss which is closer to said primary winding.

14. A method as claimed in claim 13 wherein a high tension lead is connected to said boss remote from said primary winding.

15. A method as claimed in claim 14 wherein said high tension lead is carried by a body secured to said spool by inter-engagement of engageable parts formed on said body and spool respectively.

16. A method as claimed in claim 14 wherein said high tension lead is located in a recess integrally formed in said spool.