GB2587661A

GB2587661A - Ignition coil for an engine

Info

Publication number: GB2587661A
Application number: GB1914355.1A
Authority: GB
Inventors: Wolf Eric; J Schoeber Erik
Original assignee: Delphi Automotive Systems Luxembourg SA
Current assignee: BorgWarner Luxembourg Automotive Systems SA
Priority date: 2019-10-04
Filing date: 2019-10-04
Publication date: 2021-04-07
Also published as: GB201914355D0

Abstract

An ignition coil 1 comprises: a noise suppressing resistor 16 at least partially disposed within a tubular tower housing 10 cavity and a spacer element 18 radially interposed between the noise suppressing resistor 16 and the wall of the tower housing 10, where the spacer element 18 is at least partially made of electrically insulating material. The ignition coil 1 further includes: a casing 2, a transformer assembly 5, a boot 14 and a spring connector 17. The spacer 18 may be a thin cone shaped element with a narrow inner portion 18.1 which receives a portion of the resistor 16 and an outer portion 18.3 which is in contact with the inner wall of the tower housing 10. The spacer 18 may be arranged such that the inner portion 18.1 is at the distal end of the resistor 16 and the outer portion 18.3 extends axially to surround the end region of the spring 17, and is also radially spaced from the spring, where the spring 17 connects to the resistor 16 when the coil is operational. The spacer 18 may be partially or completely formed of an insulating material, such as plastic. The transformer assembly 5 may have a pair of transformers. The coil may provide reliable operation.

Description

IGNITION COIL FOR AN ENGINE

Technical Field

[0001] The invention relates to an ignition coil for an internal combustion engine.

Background Art

[0002] Spark ignition engines, which are used inter alia in automotive vehicles, employ ignition coils which generate high voltage to the spark plug for the respective cylinder(s) of the engine. The basic element of the ignition coil is a transformer with a primary winding and a secondary winding. Under normal circumstances, this voltage is applied to a spark plug connected to the ignition coil. Since the ignition coil is fixed to the engine and linked to ground potential, there is a general risk of electrical arcs, i.e. currents flowing directly to ground, thereby bypassing the spark plug. In addition to preventing a successful ignition, such electrical arcs can seriously damage the ignition coil. Electric arcs formed through the ignition coil case, and hence damaging the case, are referred as 'high voltage punch through'.

[0003] According to a common design, the ignition coil has a plastic case that contains the transformer(s) along with other electric components necessary for the operation of the ignition coil. The inside of the case is mostly filled with an insulating material like epoxy resin which provides electrical isolation and also mechanical stability and protection for the components inside. The case commonly has a tubular outlet section or case tower, which in turn is surrounded by a tubular boot made of rubber. During assembly on the engine, the free end of the boot is engaged over a spark plug. The electrical contact with the high voltage generated by the transformer is usually established through a noise suppressor, which is mostly disposed inside of the case tower, and a coil spring that rests against the spark plug. The noise suppressor is connected to the high voltage of the secondary winding, typically via a high-voltage connector inside the case. The electrical connection between the noise suppressor and the spring is established through a metal cup placed over one end of the noise suppressor. The outer dimensions of the metal cup correspond to the inner dimensions of the outer wall of the case tower, so that the noise suppressor is also centered and aligned within the case tower. In some cases, a punch-through through the case has been observed at the end of the case tower.. This is caused by high voltage taking the least resistance way to ground.

Technical Problem [0004] It is thus an object of the present invention to improve the reliability of an ignition coil.

[0005] This problem is solved by an ignition coil according to claim 1.

General Description of the Invention

[0006] The invention provides an ignition coil for an engine, more specifically for a spark-ignition internal combustion engine. The present ignition coil has been particularly designed for application in automotive vehicles. However, the design of the present ignition coil, of interest for high voltage applications, is also suitable for operation according to other conventional ignition modes, and to spark-ignition engines in non-automotive applications, e.g. agricultural appliances, construction appliances (cranes), saws, power groups, etc. [0007] The ignition coil comprises a housing, hereinafter referred to as case', having a case cavity for a transformer assembly. The case is normally at least partially made of plastic material, and may commonly have a portion made of metal (e.g. aluminum) that serves as a heat sink, with usually a plurality of cooling ribs on its outer surface. The case cavity, i.e. the inside of the case, contains various electrical components which are herein collectively referred to as a transformer assembly. This transformer assembly comprises at least one transformer with a primary winding and a secondary winding In case of a multi-spark mode, two transformers are needed. Furthermore, the transformer assembly may comprise a printed circuit board with various components for controlling the operation of at least one transformer and charging of the transformer(s) and generating of the spark. Commonly, at least a major part of the case cavity is filled with an insulating material like epoxy resin, to mechanically protect the components inside and to provide electric insulation.

[0008] The ignition coil further comprises a tubular case tower extending from the case in an axial direction. The case tower, which could also be referred to as a high-voltage tower or an outlet section (of the case), is commonly made of non-conducting material, e.g. plastic material. It is tubular and has a case-tower wall surrounding a tower cavity. The case tower may be formed as a single piece with a part of the case and may also be considered as a part of the case. It extends in a direction which is hereinafter referred to as the axial direction, whereby a radial direction and a tangential direction are also implicitly defined. The case tower may be symmetrical about the axial direction. It can be roughly cylindrical with a circular cross-section. Normally, a length of the case tower in the axial direction is considerably larger (e.g. at least two times or three times) than a dimension perpendicular to the axial direction (e.g. a diameter), so that the case tower can be referred to as "elongate". The tower cavity communicates with the case cavity, i.e. it is connected to the case cavity, so that these could also be considered as portions of a single cavity. At one end, which can be referred to as the proximal end since it is closer to the case, the tower cavity is connected to the case cavity. At the other end, i.e. the distal end, the tower cavity is open in the axial direction, corresponding to the tubular shape of the case tower.

[0009] Furthermore, the ignition coil comprises a boot made from electrically insulating material and having an axially extending boot cavity, wherein the case tower is disposed in a proximal portion of the boot cavity. The boot can normally also be characterized as tubular, with the boot cavity extending continuously through the boot. The boot is made from elastomeric material, normally rubber. The case tower is disposed in a proximal portion of the boot cavity, i.e. the boot (or rather a portion of the boot) surrounds the case tower. The proximal portion is the portion that is closest to the case. The total length of the boot in the axial direction may be at least two times or three times the length of the case tower. The boot may be in contact with the case and may also cover a portion of the case, but it could also be spaced therefrom. The internal dimensions of the boot cavity in the proximal portion may be a little smaller than the outer dimensions of the case tower, so that the boot is held on the case tower by way of tight fitting.

[0010] A noise suppressor is at least partially disposed inside the tower cavity radially spaced from the case-tower wall. The function of noise suppressor is to suppress electromagnetic noise at the output of the High Voltage side, i.e. to suppress certain frequencies that could interfere with electronic devices in the vehicle or outside the vehicle. Such (electromagnetic) noise suppressors are known in the art and the inner structure of the noise suppressor is not limited within the scope of the invention. This may be a resistor or a combination of resistors inside a case. The shape of the noise suppressor is not limited, but it usually has an elongate shape and may e.g. be cylindrical with a circular cross-section. It is normally aligned with the axial direction. The noise suppressor is at least partially disposed inside the tower cavity, i.e. it is at least partially surrounded by the case-tower wall. A proximal portion of the noise suppressor may extend into the case cavity. It is possible, although not preferred, that a distal portion of the noise suppressor extends beyond the distal end of the case tower. The noise suppressor is radially spaced from the case-tower wall, i.e. there is a spacing between the noise suppressor the case-tower wall along the radial direction. The noise suppressor is connected to a high-voltage terminal inside the case (itself connected to the outlet side of the secondary coil(s)). The high voltage terminal applies a high-voltage pulse going through the noise suppressor. One function of the above-mentioned radial spacing is to avoid direct electrical contact between the noise suppressor and the case-tower wall, thereby keeping the high voltage from the case-tower wall.

[0011] The ignition coil further comprises a conductive spring disposed inside the boot cavity, a proximal end of the spring being at least indirectly connected to the noise suppressor and a distal end of the spring arranged for electrical connection to a spark plug. If the boot cavity comprises the above-mentioned proximal portion, a middle portion and a distal portion, the spring is at least for the major part disposed in the middle portion. Commonly, the length of the spring is chosen so that it does not extend into the distal portion, which is adapted to receive an end of the spark plug. The spark plug can be inserted into the distal portion of the boot cavity, where it can be held due to tight fitting of the boot. The function of the spring is to establish an electrical connection between the noise suppressor and the spark plug. The proximal end of the spring is at least indirectly connected (i.e. electrically connected) to the noise suppressor. Thus, when the above-mentioned high voltage is applied to the noise suppressor, it is also applied to the spring. The distal end is adapted for electrical connection to the spark plug. Preferably, the distal end is adapted to directly contact the spark plug, although it would be conceivable that the electrical connection is applied via an additional, intermediate element. Most commonly, the spring is axially aligned in the boot cavity. In fully assembled state, the spring is slightly compressed due to the ends of the spring bearing against the noise suppressor and the spark plug, respectively. Commonly, at least a major part of the spring is disposed outside the tower cavity, but at least the proximal end of the spring may extend into the tower cavity.

[0012] According to the invention, a spacer element is radially interposed between the noise suppressor and the case-tower wall, having an inner portion adjacent the noise suppressor and an outer portion adjacent the case-tower wall, which spacer element is at least partially made of an electrically insulating material so that the outer portion is insulated from the noise suppressor. The spacer element is radially interposed between the noise suppressor and the case-tower wall, so that the noise suppressor cannot be moved radially into contact with the case-tower wall. An inner portion of the spacer element is disposed adjacent the noise suppressor, i.e. one could also say that it faces the noise suppressor. This inner portion is adapted for contact with the noise suppressor. An outer portion is disposed adjacent the case-tower wall, i.e. it faces the case-tower wall and is adapted for contact with the case-tower wall. The spacer element is at least partially made an electrical insulator so that the outer portion is electrically insulated from the noise suppressor. In other words, even when the inner portion is in contact with the noise suppressor, any high voltage is prevented reaching the outer portion. Therefore, even when the outer portion is in contact with the case-tower wall, no high voltage is applied to the case-tower wall. This greatly reduces or even eliminates the risk of any punch through the case tower. One could say that the spacer element electrically insulates the noise suppressor from the case-tower wall. Another function of the spacer element is to align the noise suppressor within the case tower. Insofar, the spacer element could also be referred to as an insulation element or an alignment element.

[0013] The dimensions of the spacer element may be selected so that there is a (small) radial clearance between the inner portion and the noise suppressor or between the outer portion and the case-tower wall. Alternatively, the spacer element is designed such that the outer portion is in contact with the case-tower wall and the inner portion is in contact with the noise suppressor. In other words, the noise suppressor is held in the case tower free of (radial) play. However, depending on the material(s) of the spacer element, it could be elastically deformable so that a limited radial movement of the noise suppressor is possible.

[0014] To provide for the above-mentioned electrical insulation, it would be sufficient that only a part of the spacer element is electrically insulating. For instance, a central portion of the spacer element could be made of metal and this central portion could be interposed between the noise suppressor and the spring, thereby establishing an electrical connection. If the outer part of the spacer element is electrically insulating, this configuration still would effectively keep the high voltage away from the case-tower wall. It is preferred, though, that the spacer element is entirely made of an electrical insulator. On the one hand, this usually provides for the best electrical insulation of the case-tower wall against the high voltage present in the noise suppressor. On the other hand, this enables a simple and low-cost production of the spacer element.

[0015] The electrically insulating material for the spacer element can be any appropriate electrical insulator, including ceramic materials and plastic materials. During operation of the ignition coil, the spacer element could be subjected to elevated temperatures, wherefore electrical insulators with some heat resisting ability is advantageous (e.g. of up to 120-160°C). As an example, possible materials are PET or PBT.

[0016] To enhance the mechanical stability, it is preferred that spacer element has a tangentially continuous, annular shape. In other words, the spacer element circumferentially surrounds the noise suppressor. Along the tangential direction, the spacer element is continuous, i.e. uninterrupted.

[0017] When the spacer element is entirely made of an electrical insulator, it is preferred that the spacer element has a passage axially extending through the inner portion. This passage, which can also be referred to as a central passage or through-hole, traverses the spacer element along the axial direction. The cross-section of the passage can be adapted to the cross-section of the noise suppressor, so that the noise suppressor is inserted into the passage or passed through the passage. Preferably, the passage is circumferentially (i.e. tangentially) surrounded by the inner portion.

[0018] In the above-mentioned embodiment, it is preferred that the noise suppressor extends through the passage and is in direct electrical contact with the proximal end of the spring. In other words, the proximal end of the spring abuts the noise suppressor (normally under pretension), whereby the electrical contact is established. This configuration is mostly beneficial for its simplicity because it eliminates the need for any intermediate element interposed between the noise suppressor and the spring, while simultaneously allowing for an accurate alignment of the noise suppressor inside the case tower.

[0019] In embodiments, the outer portion of the spacer element is distally offset from the inner portion along the axial direction. In other words, the region where the spacer element is in contact with the case-tower wall, namely the outer portion, is moved further away from the case. This permits a lower electrical field strength.

[0020] In this context, the spacer element may comprise an intermediate portion between the inner portion and the outer portion, which intermediate portion tapers towards the inner portion. In other words, the radial dimension (e.g. the diameter) of the intermediate portion decreases either continuously or non-continuously from the outer portion towards the inner portion. The overall shape of the intermediate portion may be conical. The same time, the inner portion and/or the outer portion may be cylindrical.

[0021] In embodiments, the outer portion is disposed at a distal end of the case tower, or even at a distal edge of the case tower. The distal end is of course the part of the case tower that is farthest away from the case. If this is combined with the above-mentioned embodiment, the inner portion is proximally offset with respect to the outer portion and the noise suppressor does not need to extend to the distal end of the case tower along the axial direction.

[0022] In embodiments, the outer portion is distally offset from the noise suppressor and is disposed around the proximal end of the spring. In other words, while the inner portion may be in contact with the noise suppressor, the outer portion is distally offset (i.e. farther away from the case along the axial direction) from the noise suppressor. Accordingly, when the spring is in direct contact with the noise suppressor, the outer portion may be disposed around the proximal end of the spring.

[0023] Since the spring will also be subjected to high voltage during operation of the ignition coil, it is preferred that the outer portion is radially spaced from the spring. Otherwise, there would be a risk of a punch through originating from the spring and proceeding through the outer portion and the case tower. This radial spacing can be maximized as long as a sufficient mechanical stability of the spacer element is maintained.

[0024] The spacer element can be designed in a material-saving manner with a relatively thin wall. According to such an embodiment the spacer element has a spacer-element wall having a thickness equal to less than 50% of a radial dimension of the tower cavity. The thickness is measured perpendicular to the surface of the spacer-element wall, which may also be referred to as a spacer-element shell or the like. For instance, in case of a cylindrical outer portion as mentioned above, the wall thickness is measured along the radial direction. The radial dimension of the tower cavity may be the radius in case of a circular cross-section. The thickness of the spacer-element wall may preferably be less than 40% or even less than 30% of the radial d imension. Apart from saving material, the thin-walled design may also help to better insulate the case-tower wall from the noise suppressor.

Brief Description of the Drawings

[0025] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of an inventive ignition coil with a spark plug; and Fig. 2 is detail view of fig. 1

Description of Preferred Embodiments

[0026] Figs.1 and 2 show an embodiment of an inventive ignition coil 1 for a spark ignition internal combustion engine of an automotive vehicle like a passenger car. A case 2 of the ignition coil 1 is mainly made of electrically insulating plastic material, but comprises a metal heat sink plate 3, i.e. a metal plate adapted to radiate heat from the inside of the case 2 to the outside. The case 2 has a case cavity 4 in which a transformer assembly 5 is disposed. Each transformer 6 comprises a primary winding and a secondary winding, the latter of which is connected to a high voltage connector/terminal 8 inside the case 2. The case cavity 4 is mainly or entirely filled with epoxy resin for mechanical protection and electrical insulation of the inside components. The case further includes a mounting feature (not shown) for fixing the ignition coil 1 to the engine.

[0027] A tubular case tower 10 projects from the case 2 in an axial direction A. The case tower 10 is made of a single piece with the plastic parts of the case 2. It has a cylindrical case-tower wall 10.1 surrounding a tower cavity 11 that communicates with the case cavity 4. The case tower 10 itself is disposed inside a boot cavity 15 of a rubber boot 14. The boot 14, which is also tubular, extends along the axial direction A. Its boot cavity 15 has a proximal portion 15.1, in which the case tower 10 is disposed. A distal portion 15.3 of the boot cavity 15 receives a spark plug 30. The electrical connection between the high voltage terminal 8 and the spark plug 30 is established through a noise suppressor 16 and a conductive spring 17. The spring 17 may e.g. be a helical type spring made from steel. The noise suppressor 16 is mostly disposed inside the tower cavity 11, but extends into the case cavity 4, where a proximal end 16.1 of the noise suppressor is in electrical contact with the high voltage terminal 8. A proximal end 17.1 of the spring 17 rests against a distal and 16.2 of the noise suppressor 16, thereby establishing an electrical contact. The spring 17, which is disposed in an intermediate portion 15.2 of the boot cavity 15, extends to a distal end 17.2, which is held under pretension in contact with the spark plug 30 when the latter is inserted into the distal portion 15.3 of the boot cavity 15.

[0028] The noise suppressor 16 has a roughly cylindrical housing with a radius that is significantly smaller than the radius of the tower cavity 11, i.e. the noise suppressor 16 is radially spaced apart from the case tower wall 10.1. The noise suppressor is conventionally designed as a resistor element which eliminates/filters the noise at the high voltage output side of the secondary coils.

[0029] It shall be appreciated that the radial position of the noise suppressor is secured by a spacer element 18 made of plastic material. The spacer element 18 is radially interposed between the noise suppressor 16 and the case tower wall 10.1. It circumferentially surrounds the distal end 16.2 of the noise suppressor 16 and has a continuous, annular shape along the tangential direction. The spacer element 18 comprises a relatively thin spacer-element wall 18.5 with a thickness to approximately 20% of the radius of the tower cavity 11. An inner portion 18.1 of the spacer element 18 is in contact with the noise suppressor 16 while an outer portion 18.3 is in contact with the case-tower wall 10.1. The inner portion 18.1 surrounds a passage 18.4 of the spacer element 18 through which the noise suppressor 16 extends. The inner portion 18.1 and the outer portion 18.3 are both roughly cylindrical and are connected to each other by a roughly conical intermediate portion 18.2, which tapers towards the inner portion 18.1. The outer portion 18.3 is distantly offset from the inner portion 18.1 so that it is disposed at a distal end 10.2 of the case tower 10, although the distal end 16.2 of the noise suppressor 16 is proximally offset (i.e. closer to the terminal 2) from the distal end 10.2 of the case tower 10.

[0030] Apart from aligning the noise suppressor 16 within the case tower 10, an important function of the spacer element 18 is to provide electrical insulation. By the plastic material, the outer portion 18.3 is electrically insulated from the inner portion 18.1 and the noise suppressor 16. Therefore, when the noise suppressor 16 is under high voltage during the ignition process, this high voltage is kept away from the case tower 10. Preliminary tests have shown that the use of such plastic spacer element can efficiently reduce creation of electric arcs, as compared to a metal cup. Using the spacer element 18 reduces the electric field in the high voltage area. This reduces/eliminates the risk of punch troughs.

[0031] It is understood that although the spacer element 18 is made of plastic material in the embodiment shown, other electrically insulating material could be used, e.g. ceramics.

List of Reference Signs: 1 ignition coil 2 case 3 heat sink plate 4 case cavity transformer assembly 6 transformer 7 PCB 8 high-voltage terminal case tower 10.1 case-tower wall 10.2 distal end 11 tower cavity 14 Boot boot cavity 15.1 proximal portion 15.2 middle portion 15.3 distal portion 16 noise suppressor 16.1 proximal end 16.2 distal end 17 Spring 17.1 proximal end 17.2 distal end 18 spacer element 18.1 inner portion 18.2 intermediate portion 18.3 outer portion 18.4 passage 18.5 spacer-element wall spark plug A axial direction

Claims

Claims: 1 An ignition coil (1) for an engine, comprising: a case (2) having a case cavity (4); a transformer assembly (5) arranged in the case cavity (4); a tubular case tower (10) extending from the case (2) in an axial direction (A) and having a case-tower wall (10.1) surrounding a tower cavity (11) that communicates with the case cavity (4); a boot (14) made from electrically insulating material and having an axially extending boot cavity (15), wherein the case tower (10) is disposed in a proximal portion (15.1) of the boot cavity (15); a noise suppressor (16) at least partially disposed inside the tower cavity (15) radially spaced from the case-tower wall (11) and being connected to a high-voltage terminal (8) inside the case (2); a spring (17) disposed inside the boot cavity (15), a proximal end (17.1) of the spring being at least indirectly connected to the noise suppressor (16) and a distal end (17.2) of the spring (17) arranged for electrical connection to a spark plug (30); and a spacer element (18) radially interposed between the noise suppressor (16) and the case-tower wall (11), having an inner portion (18.1) adjacent the noise suppressor (16) and an outer portion (18.3) adjacent the case-tower wall (10.1), which spacer element (18) is at least partially made of an electrical insulator so that the outer portion (18.3) is insulated from the noise suppressor (16).
2 The ignition coil according to claim 1, wherein the outer portion (18.3) is in contact with the case-tower wall (10.1) and the inner portion (18.1) is in contact with the noise suppressor (16).
3. The ignition coil according to any of the preceding claims, wherein the spacer element (18) is entirely made of an electrical insulator.
4. The ignition coil according to any of the preceding claims, wherein the electrical insulator is a plastic material.
5. The ignition coil according to any of the preceding claims, wherein the spacer element (18) has a tangentially continuous, annular shape.
6. The ignition coil according to any of the preceding claims, wherein the spacer element (18) has a passage (18.4) axially extending through the inner portion.
7. The ignition coil according to any of the preceding claims, wherein the noise suppressor (16) extends through the passage (18.4) and is in direct electrical contact with the proximal end (17.1) of the spring (17).
8. The ignition coil according to any of the preceding claims, wherein the outer portion (18.3) is distally offset from the inner portion (18.1) along the axial direction.
9. The ignition coil according to claim 8, wherein the spacer element (18) comprises an intermediate portion (18.2) between the inner portion (18.1) and the outer portion (18.3), which intermediate portion (18.2) tapers towards the inner portion (18.1).
10. The ignition coil according to any of the preceding claims, wherein the outer portion (18.3) is disposed at a distal end (10.2) of the case tower (10).
11 The ignition coil according to any of the preceding claims, wherein the outer portion (18.3) is distally offset from the noise suppressor (16) and is disposed around the proximal end (17.1) of the spring (17).
12. The ignition coil according to claim 11, wherein the outer portion (18.3) is radially spaced from the spring (17).
13. The ignition coil according to any of the preceding claims, wherein the spacer element (18) has a spacer-element wall (18.5) having a thickness equal to less than 50% of a radial dimension of the tower cavity (11).
14. The ignition coil according to any of the preceding claims, wherein the transformer assembly comprises a pair of transformers, each with a primary and secondary winding, the secondary windings being connected to the high-voltage terminal.