EP1540676A1

EP1540676A1 - Ignition coil having an improved power transmission

Info

Publication number: EP1540676A1
Application number: EP03750558A
Authority: EP
Inventors: Horst Hendel
Original assignee: Tyco Electronics AMP GmbH
Current assignee: TE Connectivity Germany GmbH
Priority date: 2002-09-16
Filing date: 2003-09-16
Publication date: 2005-06-15
Also published as: KR20050057344A; DE10242879A1; AU2003270209A1; WO2004027794A1; US7280023B2; US20060192644A1; JP2005539388A

Abstract

The invention relates to an ignition coil for ignition systems, particularly a rod ignition coil for internal combustion engines, comprising at least one primary winding (4) and at least one secondary winding (5), whereby a high voltage is induced in the secondary winding when there is a flow of current in the primary winding. A ferromagnetic core (2) is partially surrounded by the primary winding and by the secondary winding and, in addition, one of the two windings is at least partially surrounded by the other. The aim of the invention is to provide an improved ignition coil that guarantees an increased operational reliability and energy efficiency as well as a reduced risk of overheating during operation. To this end, at least one of the windings comprises at least one section having a winding thickness that is greater than the remaining winding thickness, whereby the diameter of the innermost windings in the at least one section is less than the diameter of the innermost windings in the remaining winding sections.

Description

Ignition coil with improved energy transfer

The present invention relates to an ignition coil for ignition systems, in particular a pencil ignition coil for internal combustion engines, with at least one primary winding and at least one secondary winding, a high voltage being induced in the secondary winding when current flows in the primary winding. A ferromagnetic core is partially enclosed by the primary winding and the secondary winding, and in addition one of the two windings is at least partially surrounded by the other.

Ignition coils of this type are usually designed to be extremely volume and weight minimized and are predominantly used in internal combustion engines in which each internal combustion cylinder is equipped with its own ignition coil and sits directly on the spark plug without complex holding elements. Such ignition coils are also referred to as single-spark ignition coils or pencil-type ignition coils and must be particularly vibration-proof and temperature-resistant, since they have direct contact with the engine block which generates and heats up.

In addition to the primary and secondary induction coils, such a single spark ignition coil has a special magnetic circuit and can also contain an electronic switching element, for example an output stage, which is connected to the induction coils to form a unit. Two plug connectors, one for connecting the high-voltage connection to the spark plug and a generally four-pin plug connector for the power supply from the vehicle electrical system and the control line, complete such an ignition coil. The ignition systems are controlled by the engine electronics, which determine the ignition timing from a large number of dynamic engine characteristics.

Single spark ignition systems of this type have the advantage over an ignition system that is fed from a single ignition coil and works according to the distributor principle that all high-voltage lines, including the mechanical drive and distributor structure, are disadvantageous in operation and wear and tear. cleanliness is subject to influence, which affect the ignition timing or impair the ignition performance.

The physical principles of energy transmission explained below apply to such ignition coils. It is assumed that an externally energized primary coil and the associated build-up of a magnetic field, which leads to inductive transmission to the secondary winding when the primary current is interrupted.

The secondary current build-up in the high-voltage section takes place solely on the basis of the induction principle from the magnetic flux reduction, which is caused by switching off the primary current and the associated change in magnetic flux. However, this current build-up and the onset of discharge do not run continuously, but in four phases, depending on the dominating physical factors. Due to the capacity of the secondary winding, the current build-up begins before the actual discharge via the spark plug electrodes immediately after the primary current reduction has started.

The first phase of the secondary current build-up starts without delay when the primary current reduction starts. This results in a charge shift corresponding to the capacity of the secondary winding, with the associated formation of corresponding electrical fields at the spark plug electrodes, which then cause the actual current breakdown. For the formation of the electrical fields required for the secondary current breakdown, a substantial primary current reduction is necessary, starting from the maximum value of the primary current. It is approx. 30% with a duration of action of 2 to 5 μsec and is determined by the ignition coil concept and the electronic switch, which influences the switch-off speed of the primary current.

When viewed losslessly and for an open circuit, the relationship applies to induction and self-induction processes

ΔΦ Uindu = N ^• - or At

The second phase of the secondary current curve is a sudden increase in the ohmic character associated with the current breakdown. It has essentially no inductive cause; rather, it results from the capacitive discharge of the charge of the secondary winding that has accumulated in the first phase.

In the third phase of the secondary current increase, pure induction processes dominate, whereby by further lowering the primary current and the consequent increase in the secondary current, the change in magnetic flux acts as the difference between the associated ampere windings (primary side decreases, secondary side increases) and accordingly the increase in the secondary current is flatter, although the lowering of the primary current is still constant at this time. Only at the end of the primary current reduction does the course flatten out and the increase in the secondary current reaches its maximum value in a soft outlet. The physical principle of the secondary current increase is expressed by the fact that in each phase of the increase only as much secondary ampere windings can occur as have been induced on the primary side of ampere windings because the magnetic field (originally generated by of the primary winding) occurs and cannot increase itself according to the energy conservation rate, not even with the quickest reduction in primary current.

For the phase of the secondary current increase, the following relationship applies to the primary current reduction when viewed without loss:

"^ secondary X θl _se kundar - pπmar X dprimar

This physical principle is largely independent of the speed of the primary switching processes, provided sufficient voltage is induced to overcome the ohmic resistances. These processes also occur regardless of the presence of an iron circle. The fourth phase of the secondary current curve represents the magnetic freewheeling of the iron circuit, in particular of the magnetic coil core, the mutual induction of the secondary coil decisively determining the effective duration of the magnetic freewheeling. The primary winding is already de-energized in this phase and an influence on the secondary side would only be possible via capacitance, insofar as it is small due to its small size.

All of the previously known small-volume ignition coils, as described, for example, in DE 199 62 279 A1, DE 199 27 820 C1, WO 99/36693, DE 199 50 566 A1, EP 1 111 630 A2 or EP 0 959 481 A2 are exposed to the risk of overheating during operation. This results from self-heating primarily due to the considerable current load (15 amperes) in the primary winding, but also due to the power loss of the secondary winding. In addition, there is the thermal load due to the relatively high ambient temperature of the engine block (up to 125 ° C). The lower calorific value on small-volume ignition coils further complicates achieving an acceptable tempered state of equilibrium (maximum 160 ° C), especially in continuous operation with the maximum ignition frequency.

From the European patent application EP 0 959 481 A2 an embodiment of a small-volume pencil ignition coil is known, in which the risk of overheating, in particular of the electronic output stage, is to be reduced, as a result of which operational safety is to be achieved even under high thermal loads. Overheating is prevented passively by trying to decouple the individual heat sources by means of a separation gap. However, this solution has the disadvantage that the actual generation of the undesired heat is not counteracted.

The object of the present invention is therefore to provide an improved ignition coil for ignition systems, in particular a pencil ignition coil for internal combustion engines, which ensures increased operational safety and energy efficiency and a reduced risk of overheating during operation.

This object is achieved by an ignition coil for ignition system, in particular a pencil ignition coil for internal combustion engines with the features of patent claim 1. The present invention is based on the finding that the high thermal load on an ignition coil can be actively reduced by considering the individual heat sources and reducing the electrical and magnetic power losses at the induction coils. This increase in energy transfer efficiency according to the invention is achieved by constricting the magnetic field in at least one section with a higher winding density than the remaining winding density, in which the diameter of the innermost turns is smaller than in the other winding sections.

A comparatively low current supply to the primary winding also relieves the thermal and electrical stress on the electronic output stage, thereby increasing operational reliability. In addition, the design of the ignition coil according to the invention has the advantage of reducing the construction volume by approximately 15% compared to the currently known and comparable ignition coil concepts. For example, a conventional pot ignition coil has a construction volume of more than 300 cm ³ (diameter 5.9 cm, length 11.5 cm). The pencil ignition coil in the embodiment according to the invention manages, including the high-voltage connection, with a volume of approximately 30 cm ³ (diameter approximately 2.2 cm, length 8.2 cm).

Finally, the solution according to the invention offers the advantage that the ignition power is subject to only relatively slight fluctuations in the entire range of the working temperature (-40 ° C. to a maximum of + 180 ° C.).

Advantageous developments of the invention are described in the subclaims.

According to an advantageous development, the secondary winding is arranged with respect to the primary winding in such a way that a section with increased winding density on one winding corresponds in the axial direction to a section with other winding density on the other winding. This penetration of the volume of the two windings can significantly improve the energy transfer. According to a further advantageous embodiment, the primary winding and secondary winding are arranged such that the primary winding encloses the secondary winding and that the section with increased winding density is a start and / or end section of the primary winding. The secondary winding is arranged in the remaining winding section of the primary winding. This offers the advantage that the high-resistance secondary winding is arranged near the core and the low-resistance primary winding, which does not require any special insulation, is arranged on the outside. A particularly small overall diameter of the ignition coil can thereby be achieved. In principle, the provision of only one section with increased winding density and reduced diameter of the innermost windings can achieve an effect which increases the efficiency. In this case, this area is expediently provided on the end outlet of the primary winding facing away from the high voltage due to the insulation advantages. On the other hand, if one provides such a region with increased winding density and reduced diameter of the innermost turns both in the beginning and in the end section of the primary winding, this has the advantage that the secondary winding is magnetically enclosed on three sides.

If a preliminary winding and / or a final winding, which is enclosed by the start and / or end section of the primary winding, is further provided on the secondary winding, the available volume can be used in a particularly effective manner.

If, instead of the usual round wire winding, a flat wire winding is used for at least one of the windings, the current density can be increased and the constriction effect on the magnetic field can be further increased. The use of flat wire has the advantage over a round wire that a larger winding density can be achieved and the necessary number of turns of the primary winding can thus be produced with less resistance without requiring more winding volume. The large area of the individual turns of flat wire also allows a far better heat flow to the outside than is the case with a round wire with a line or point contact of the turns with each other. In order to optimally guide the magnetic field, the ignition coil can furthermore have a soft magnetic sleeve which encloses the windings and the core.

A segmentation of the secondary winding can be provided to improve the dielectric strength.

To ensure the insulation strength to the primary winding while at the same time maintaining the lowest volume occupancy, the winding heights of these secondary segment windings can be made cascade-decreasing in the winding height. In accordance with the increasing high voltage from segment to segment, the wall thicknesses of the insulation towards the primary winding are increased.

Furthermore, if the end outlets of the secondary winding are led out in an axial course to the end faces of the induction coils, the at least one section with increased winding density of the primary winding can be arranged eccentrically with respect to the core and the other winding region of the primary winding.

If the start and end areas of the primary winding are designed as sections with increased winding density, it is advantageous for the magnetic field constricting effect to choose a radially offset arrangement of the eccentricity.

The invention is explained in more detail below on the basis of the advantageous embodiments shown in the accompanying drawings. Similar or corresponding details of the subject matter of the invention are provided with the same reference numerals. Show it:

Figure 1 is a sectional view of an ignition coil according to the invention according to a first embodiment.

2 shows the current curves over time of the primary side and secondary side of an ignition coil according to the invention in comparison with a conventional ignition system; 3 shows a schematic sectional illustration of a flat wire winding in comparison to a round wire winding;

4 shows a sectional illustration of an ignition coil according to the invention in accordance with a second embodiment;

Fig. 5 shows a section through the ignition coil of Fig. 4 along the section line A-A.

1 shows a longitudinal section through an ignition coil 10 according to the invention in accordance with a first embodiment. As can be seen from this schematic representation, the ignition coil 10 consists of approximately 45% highly effective insulating material 1, which is usually made of plastic with a dielectric strength of approximately 30 kV / mm and, above all, the high-voltage secondary winding 5 is electrically insulated from the other components.

The iron circuit, which has a soft magnetic core 2 with high saturation induction and a soft magnetic sleeve 3 forming the outer shell, both of which are approximately the full length of the ignition coil 10, takes up approximately 25% of the construction volume. The low-resistance primary winding 4 occupies a volume of approx. 20% and is therefore usually twice as large in volume as the high-resistance secondary winding 5 with approx. 10% share of the total volume.

Because in order to achieve this relatively small construction volume, all components of the ignition coil 10 must be severely limited in size, it does not fail to appear that the soft magnetic core 1 is actually undersized, which can only be partially compensated for by the fact that the iron circle is magnetic at the end faces is open. The result of this is that when a conventional cylindrical primary coil is energized with its constant and, due to the necessary insulation, relatively large diameter of its innermost windings, considerable magnetic stray fluxes occur which are not only lost to the useful flow, but also further weaken it, since the Stray flux partially counteracts the useful flow during primary current reduction. The entire interior of the primary coil carries the magnetic flux, since the iron core is completely must be driven to ensure the necessary induction in the secondary winding. In order to increase the magnetic flux conversion, 4 permanent magnets can be arranged on the end faces of the soft magnetic core opposite to the magnetic field of the primary winding. A higher ignition power can thus be achieved, but this can only be achieved with a corresponding increase in the primary current, as a result of which an increased thermal load occurs. The magnetic leakage flux cannot be reduced with this method; on the contrary, it can be assumed that the magnetic leakage flux increases as a percentage especially at the end outlets of the primary winding 4 due to the opposite polarity of the permanent magnets to the primary magnetic field.

Therefore, according to the invention, the magnetic leakage flux, especially at the primary winding and in particular at its end outlets, is reduced in that the end outlets of the primary winding 4 are each reduced to at least half the inner diameter in the remaining area over a length of approx. 20% of the total length of the primary coil at the same time in these start and end sections 6a, 6b the magnetic field strength is increased to approximately twice by a higher number of turns in comparison to the central region of the primary coil 4. As a result, the specific magnetic flux in these sections 6a, 6b can be approximately doubled.

According to the invention, the secondary winding 5 is arranged in the cavity-forming central region of the primary winding 4, and its connection ends 5c, 5d are securely embedded in the insulating material 1 and are led out to the outside below the constricting turns.

An efficiency-increasing effect can already be achieved by forming an area with a smaller diameter and increased winding density on one side only, in which case the end outlet 6b of the primary winding 4 facing away from the high voltage is to be preferred because of the insulation advantages.

The magnetic field emanating from the primary winding 4 is divided into a course in the soft magnetic core 2, which forms the main part, and a parallel course, the volume of which is limited on the one hand by the innermost turns of the primary winding 4 and on the other hand by the surface of the soft magnetic core 2. The cross The cut of this parallel volume is not least due to the thick insulation walls larger than the cross section of the core 2 and accordingly a considerable increase in performance is possible due to the almost full use of this magnetic field for the energy transfer to the secondary winding 5. Due to the magnetic field constricting effect and the increase in the magnetic field strength resulting from the higher number of turns, on the one hand the magnetic resistance at the magnetically open ends of the iron circuit can be compensated for and it can be achieved that the primary magnetic field increases the secondary winding 5 to a much greater extent can penetrate to effectively use this magnetic field component in energy transmission.

In the embodiment shown (as in the second embodiment of FIGS. 4 and 5), the secondary winding 5 is divided into individual segments, which is usually necessary for reasons of dielectric strength. This segmentation has a reducing effect on the mutual induction in the secondary current discharge. The result is a shortened duration of action (burning time) of the current discharge, which can become critical for a reliable ignition of the flammable gas molecules, especially if there is an inhomogeneous gas mixture or a non-ideal mixture ratio, such as in the engine start phase or in an alternating phase of the engine power tion may be the case.

Therefore, as shown in FIG. 1, the secondary winding 5 is designed with a comparatively small number of segments (here five by way of example) and for this purpose it is designed with the largest possible winding height. The insulation strength within a segment can be maintained by a smaller winding width. To ensure the insulation strength to the primary winding while maintaining the lowest volume occupancy, the winding heights of the secondary segment windings are made cascading in decreasing winding height. In accordance with the increasing high voltage from segment to segment, the wall thicknesses of the insulation towards the primary winding 4 are increased. A larger winding height of the secondary winding segments also increases the positive effect of the principle of a constricted primary winding according to the invention in that the execution of a primary winding with larger diameter differences between the central region and the constricted region is possible and the secondary winding is enclosed more intensely on three sides by the primary winding 4.

2 shows the electrical characteristic data of an ignition coil designed with the inventive features in comparison to known ignition systems of the same category as a current diagram. Curves 11 and 13 mean the primary-side and secondary-side current profile on a conventional ignition coil and curves 12 and 14 the primary-side and secondary-side current profile on an ignition coil designed according to the present invention. As can be seen from the diagram, the primary current profile corresponds to the secondary current profile with the difference that the primary current has an increasing profile, the secondary current, on the other hand, has a declining profile and the associated current strengths behave according to the product of current strength and number of turns. Otherwise, the characteristics of the current profiles are exactly mirror images, which results from the common magnetic circuit.

A further increase in the magnetic field constricting effect of the sections 6 with increased winding density and reduced diameter is obtained while maintaining the required insulation wall thicknesses by designing the primary coil 4 as a flat wire winding instead of a conventional round wire winding. As shown schematically in FIG. 3, the effect of the flat wire winding constricting the magnetic flux is considerable, in particular in comparison to a round wire diameter of approximately 0.7 mm which is usually used in primary windings. If, for example, a flat wire with a diameter of approx. 0.3 mm and the same cross-sectional area as the round wire is used instead of a round wire with a diameter of 0.7 mm, the magnetic field can be constricted by about 15% and the efficiency of energy transmission can be increased by a similar order of magnitude , This is primarily due to the increased current density in this arrangement. As can also be seen from FIG. 3, the individual flat wire turns also touch in a substantially larger surface area and thereby ensure better heat dissipation to the outside. The magnitude of the effect constricting the magnetic field can, as shown in FIG. 4, be expanded in that the end outlets of the secondary windings 5c and 5d are led out in the shortest possible way in an axial course to the end faces of the ignition coil 10. The relatively strong insulation changes around the core are therefore no longer necessary, but only partial insulation in the area of the bushings of the secondary connection ends 5c and 5d is necessary. So there is no massive all-round formation of the insulation 3 on the core 2 in a wide range. In this embodiment, the constricting sections 6a, 6b are no longer arranged concentrically to the central axis of the soft magnetic core 2 and the remaining central region of the primary winding 4. However, a significant proportion of the primary windings are brought closer to the iron core than in the embodiment in FIG. 1, and a corresponding increase in the magnetic constriction effect can thus be achieved. The arrangement of the eccentricity of the constricting sections 6a, 6b of the primary winding, which is shown in FIG. 4 and the associated sectional view of FIG. 5, is advantageous for the constricting effect, and is arranged radially offset by 180.degree.

Although only cylindrical ignition coils have been shown above, the present invention is of course applicable to any other cross section, for example a rectangular cross section. Furthermore, the present invention can also be used advantageously in other transmitters, in particular in those with a reduced volume of the iron circuit.

Claims

claims

1. Ignition coil for ignition systems, in particular pencil ignition coil for internal combustion engines, with at least one primary winding (4) and at least one secondary winding

(5), a high voltage being induced in the secondary winding (5) when current flows in the primary winding (4), and with a ferromagnetic core (2) which is at least partially enclosed by the primary winding (4) and the secondary winding (5) wherein, in addition, one of the windings (4, 5) is at least partially enclosed by the other, characterized in that at least one of the windings (4, 5) has at least one section (6) with a winding density that is increased compared to the other winding density, where - The diameter of the innermost turns in the at least one section is less than the diameter of the innermost turns in the other winding sections (9).

2. Ignition coil according to claim 1, characterized in that the secondary winding (5) with respect to the primary winding (4) is arranged such that a section with increased winding density on the one winding with one

Section of remaining winding density on the other winding corresponds in the axial direction.

3. Ignition coil according to claim 1 or 2, characterized in that the primary winding (4) encloses the secondary winding (5), and the at least one section with increased winding density, a start and / or end section (6a,

6b) is the primary winding (4) and the secondary winding (5) is arranged in the remaining winding section (9) of the primary winding (4).

4. Ignition coil according to claim 3, characterized in that the secondary winding (4) further a pre-winding (5a) and / or end winding (5b) with re reduced winding density, which is enclosed by the start and / or end section (6a, 6b) of the primary winding (4).

5. Ignition coil according to one of claims 1 to 4, characterized in that at least one of the windings (4, 5) is a flat wire winding.

6. Ignition coil according to one of claims 1 to 5, characterized in that a soft magnetic sleeve (3) encloses the windings (4, 5) and the core (2).

7. Ignition coil according to one of claims 3 to 6, characterized in that the secondary winding (5) is divided into a plurality of individual segments.

8. Ignition coil according to claim 7, characterized in that the winding heights of the individual segments are designed to decrease in cascade.

9. Ignition coil according to one of claims 3 to 8, characterized in that the at least one section with increased winding density is arranged eccentrically with respect to the central axis of the ignition coil (10).

10. Ignition coil according to claim 9, characterized in that the start section (6a) and the end section (6b) of the primary coil (4) are arranged offset by 180 ° substantially eccentrically with respect to the central axis of the ignition coil (10).