GB2547003A

GB2547003A - Transformer assembly

Info

Publication number: GB2547003A
Application number: GB1601981.2A
Authority: GB
Inventors: Lorenz Frank; Weyand Peter
Original assignee: Delphi Automotive Systems Luxembourg SA
Current assignee: BorgWarner Luxembourg Automotive Systems SA
Priority date: 2016-02-04
Filing date: 2016-02-04
Publication date: 2017-08-09
Also published as: GB201601981D0

Abstract

An ignition transformer for an internal combustion engine has first and second I-shaped cores 36 and 44 arranged in parallel, the cores having respective primary 32 and 40 and secondary coils 34 and 42 arranged concentrically around each core. The double transformer also has a third, H-shaped core 26 whereby the third core is interposed between the I-shaped cores so as to form two adjacent rectangles. The H-shaped core has a middle leg 66 and lateral legs 68, 70, 72 and 74 that provide a magnetic return path for the I-shaped cores. Gap spacers can be placed between the I-shaped cores and adjacent legs of the H-shaped core. The double transformer is part of an ignition system of a combustion engine and has its secondary coils coupled to the electrodes of a spark plug. A control unit is energising and de-energising the primary coils by switching on and off two corresponding switches to establish an electrical arc across the electrodes.

Description

TRANSFORMER ASSEMBLY TECHNICAL FIELD OF THE INVENTION

This disclosure relates to a transformer assembly and has particular, but not exclusive application, to a transformer for an ignition system, such as for, but not limited to, automotive applications.

BACKGROUND OF THE INVENTION

The automotive industries have developed gasoline engines that use very lean air-fuel mixtures. Common combustion principles are either homogeneous lean mixtures or stratified direct injection. To get a safe ignition it is necessary to have a high energy ignition source. Well known solution as multi-charge Ignition systems have been developed. Thanks to the use of a multi-charge ignition system, it allows a control unit to use simultaneously the energy stored in two transformers to create an ignition spark and to use alternatively the energy stored either in one transformer or in the other to maintain a continuous ignition fire while reenergizing the other transformer. Such structure gives high satisfaction in the magnetic domain as being a high efficient solution. But the usage of two transformers does not provide an attractive solution for the volume of the multi-charge Ignition systems, for the assembly time and also for a cost point of view.

It is an object of the invention to provide an improved transformer that overcomes such problems.

SUMMARY OF THE INVENTION A transformer assembly comprises a first magnetic core extending along a first longitudinal axis, a second magnetic core extending along a second longitudinal axis, a first coil surrounding the first magnetic core, a second coil surrounding the first coil, a third coil surrounding the second magnetic core and a fourth coil surrounding the third coil. The transformer assembly further comprises a H shaped magnetic return path element comprising a middle leg, a first pair of lateral legs on one side of the middle leg, another pair of lateral legs on the other side of the middle leg, the H shaped magnetic return path element providing a magnetic return path for the first and the second magnetic core. The first magnetic core is located between the first pair of lateral legs and the second magnetic core is located between the second pair of lateral legs such that the transformer assembly behaves as a double transformer.

One gap component may be located between at least one end of each magnetic core and the adjacent leg of the H shaped magnetic return path element. Each magnetic core may be associated with one single gap component and in that the two gap components may be located on the same side of the H shaped magnetic return path element. One gap component may be located between each end of each magnetic core and the adjacent leg of the H shaped magnetic return path element. The first coil and the second coil may be wound in opposite directions to the third coil and the fourth coil such that the flux inside the middle leg is compensated. The cross section of each straight section of H shaped magnetic return path and the cross section of the first and the second straight section of the magnetic cores may be identical. The end surfaces of each leg of the H shaped magnetic return path element may be sloped inwardly in order to define sloping surfaces which are complementary to the associated ends of the magnetic cores, and/or of the associated end surface of the gap component. Each pair of legs may comprise the internal end surfaces oriented face to face, each magnetic core being located respectively between the internal end surfaces.

An ignition system for a combustion engine comprises a spark plug with a pair of gapped electrodes, a control unit, and the transformer assembly wherein the second coil and the fourth coil are each coupled to the gapped electrodes of the spark plug, and wherein the control unit is enabled to simultaneously energize and deenergize the first coil and the third coil of the transformer assembly by simultaneously switching on and off two corresponding switches to establish an electrical arc across the gapped electrodes of the spark plug and to sequentially energize and deenergize the first coil and the third coil by sequentially switching on and off both corresponding switches to maintain a continuous ignition fire.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be further described by way of example and with reference to the accompanying drawings in which:

Figure 1 is an electrical schematic illustration of an ignition system according to a preferred embodiment of the present invention.

Figure 2 shows a schematic longitudinal section through the transformer assembly of an ignition coil included in the ignition system of figure 1.

Figure 3 shows a schematic perspective view of the partially assembled transformer assembly of an ignition coil included in the ignition system of figure 1.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

With reference now to Figure 1, a multi-charge ignition system 10 is illustrated for producing a continuous ignition spark over a wide area of bum voltage servicing a single set of gapped electrodes in a spark plug 11 such as might be associated with a single combustion cylinder of an internal combustion engine (not shown).

The multi-charge ignition system 10 uses fast charging ignition spool, including a first winding 32 and a second winding 34 to generate the required high AC voltage and wound on a common core K1 forming a first magnetic circuit and a third winding 40 and a fourth winding 42 wound on another common core K2 forming a second magnetic circuit. Both magnetic circuits form a unique double transformer T1 in order to get a compact ignition system. The first winding 32 and the third winding 40 are the primary windings of the double transformer Tl. The second winding 34 and the fourth winding 42 are the secondary windings of the double transformer Tl. The two coil ends of the first primary winding 32 and of the second primary winding 40 of the double transformer Tl may be alternately switched to a common ground such as a chassis ground of an automobile by electrical switches Ql, Q2. These switches Ql, Q2 are preferably Insulated Gate Bipolar Transistors. The low-voltage ends of the first secondary winding 34 and of the second secondary winding 42 of the double transformer Tl are coupled to a common ground or chassis ground of an automobile through high-voltages diodes Dl, D2. Resistor Rl, for measuring the primary current Ip that flows from the primary side, is connected between the switches Ql, Q2 and ground, while resistor R2, for measuring the secondary current Is that flows from the secondary, side is connected between the diodes Dl, D2 and ground.

The high-voltage ends of the secondary ignition windings 34, 42 are coupled to one electrode of a gapped pair of electrodes in a spark plug 11 through conventional means. The other electrode of the spark plug 11 is also coupled to a common ground, conventionally by way of threaded engagement of the spark plug to the engine block.

The primary windings 32, 40 are connected to a common energizing potential that is in the figure the positive voltage of battery 15.

The charge current can be supervised by an electronic control circuit 13 that controls the state of the switches Ql, Q2. The control circuit 13 is for example responsive to engine spark timing (EST) signals to selectively couple the primary windings 32, 40 to system ground through switches Ql and Q2 respectively controlled by signals Igbtl and Igbt2 respectively. Measured primary current Ip and secondary current Is are sent to control unit 13.

Advantageously, the common energizing potential of the battery 15 is coupled by way of an ignition switch Ml to the primary windings 32, 40 at the opposite end that the grounded one. Switch Ml is preferably a MOSFET transistor. A diode D3 is coupled to transistor Ml so as to form a step-down converter. Control unit 13 is enabled to switch off switch Ml by means of a signal FET. The diode D3 may be replaced by a MOSFET.

In operation, the control circuit 13 is operative to provide an extended continuous high-energy arc across the gapped electrodes. During a first step, switches Ml, Ql and Q2 are all switched on, so that the delivered energy of the power supply 15 is stored in the magnetic circuits of the double transformers Tl. During a second step, both primary windings 32, 40 are switched off at the same time by means of switches Ql and Q2. On the secondary side of the double transformer, a high voltage is induced and an ignition spark is created through the gapped electrodes of the spark plug 11. During a third step, switch Ql is switched on and switch Q2 is switched off (or vice versa). That means that the first and the second windings 32, 34 store energy thanks to the magnetic circuit while the third and the fourth windings 40, 42 deliver energy to spark plug 11 (or vice versa). During a fourth step, when the primary current Ip increases over a limit (Ipmax), the control unit 13 detects it and switches transistor Ml off. The stored energy in the magnetic circuit that is switched on (Ql, or Q2) impels a current over diode D3 (step-down topology), so that the magnetic circuit cannot go into the magnetic saturation, its energy being limited. During a fifth step, just after the secondary current Is falls short of a secondary current threshold level (Ismin) the switch Q1 is switched off and the switch Q2 is switched on (or vice versa). Then steps 3 to 5 will be iterated by sequentially switching on and off switches Q1 and Q2 as long as the control unit 13 switches both switches Q1 and Q2 off.

Figure 2 shows a transformer assembly 20 forming the double transformer of the multi-charge ignition system 10 described through figure 1. The transformer assembly 20 comprises two magnetic components 22, 24, a magnetic return path element 26 and two gap components 28, 30. The two magnetic components 22, 24 in combination with the magnetic return path element 26, and with the two gap components 28, 30 form a magnetic circuit having a high magnetic permeability. The gap components 28, 30 may have a relative permeability in the order of 1.

Each magnetic component 22, 24 comprises a primary winding/coil 32, 40, a secondary winding/coil 34, 42, and a magnetic core 36, 44. Each primary winding 32, 40 surrounds the magnetic core 36, 44, and each secondary winding 34, 42, surrounds the primary winding 32, 40. Each magnetic core 36, 44 extending along a longitudinal axis Al, A2 is generally cylindrical in overall shape and includes two ends 45, 47, 49, 51. Advantageously, each primary winding 32, 40 extends along a primary support 54, 56 forming a primary spool. Each primary support 54, 56 is preferably made of plastic and directly surrounds each magnetic core 36, 44. Each secondary winding 34, 42 extends along a secondary support 58, 60 forming a secondary spool. Each secondary support 56, 60 is preferably made of plastic and surrounds each primary spool. Preferably, each magnetic core 36, 44 includes a straight section 62, 64 onto which the primary winding 32, 40 is wrapped. The ends 45, 47, 49, 51 of each magnetic core 36, 44 may have a shape adapted to be fixed on the magnetic return path 26.

The magnetic return path 26 is a H shaped magnetic return path also called a I shaped magnetic return path. As a H shaped, the magnetic return path 26 comprises a middle leg 66, a first pair of lateral legs 68, 70 on one side of the middle leg 66 and another pair of lateral legs 72, 74 on the other side of the middle leg 66. Preferably, the cross section of each straight section of the H shaped magnetic return path is similar to each other. The cross section of each straight section of the magnetic return path has to be understood as a transversal cross section of the straight section of the first pair of the lateral legs 68, 70, and of the second pair of the lateral legs 72, 74, in the direction of the longitudinal axis Al, and as a transversal cross section of the straight section of the middle leg 66 in the direction perpendicular to the longitudinal axis Al. Advantageously, the ends surfaces 76, 80, 82, 84 of each leg of the H shaped magnetic return path 26 are sloped inwardly such that they define sloping surfaces.

The transformer assembly 20 comprises the first magnetic core 36 and the second magnetic core 44, the first magnetic 36 core being located between the first pair of lateral legs 68, 70 and the second magnetic core 44 being located between the second pair of lateral legs 72, 74 such that the transformer assembly 20 behaves as a double transformer. The ends surfaces 46, 48, 50, 52 of each magnetic core 36, 44 are in a shape complementary to the associated inwardly sloped end surfaces 76, 80, 82, 84 of each legs 68, 70, 72, 74 of the H shaped magnetic return path 26. The transformer assembly 20 comprises two gap components 28, 30, each one of these gap components 28, 30 being located between one end surface 46, 50 of each magnetic core 36, 44 and the adjacent leg 70, 74 of the H shaped magnetic return path element 26. The two gap components 28, 30 are located on the same side of the H shaped magnetic return path 26. The end surfaces 86, 88, 90, 92 of each gap component 28, 30 are associated between the inwardly sloped end surfaces 80, 84 of each legs of the H shaped magnetic return path 26 and the complementary shape of the associated end surface 46, 50 of each magnetic core 36, 44. As an example, gap components could be realized by a permanent magnetic material as a magnet.

Preferably, the cross section of the straight section 62, 64 of each magnetic core 36, 44 and each cross section of the straight section 66, 67, 69, 71, 73 of the H shaped magnetic return path element 26 may be similar in order to have the most compact double transformer structure. The cross section of the straight section 62, 64 of each magnetic core 36, 44 has to be understood as a transversal cross section of the straight section 62, 64 of each magnetic core 36, 44 in the direction perpendicular to the longitudinal axis Al. Preferably, to optimize the efficiency of the transformer assembly 20, the orientation of the first and the second windings 32, 34 surrounding the first magnetic core 36 have to be identical but in the opposite direction as the orientation of the third and fourth windings 40, 42 surrounding the second magnetic core 44. By winding the transformer assembly 20 in the right orientation, the flux inside the middle-leg 66 of the H shaped magnetic return path element 26 is compensated such that the middle leg 66 of the transformer assembly 20 can be reduced to the half size or even less if a structure without a gap component 28, 30 is used. A structure without a gap component may be a structure without any magnetic force used in the gap, in other words, it is a structure wherein the gap is filled with air as gap component.

Optionally, two other gap components may be added between the end surfaces 48, 52 of each magnetic core 62, 64, said end surfaces 48, 52 being not equipped with the previously mentioned gap components 28, 30. The additional two gap components allow balancing of the magnetic circuit and by this allow an increase of the total flux of the circuit. The typical width for gap component 28, 30 is 0.5 to 2 mm. Gap components 28, 30 could have different thickness.

Optionally, each secondary winding 34, 42 may surround each magnetic core 36, 44 and each primary winding 32, 40 surrounds each secondary winding 34, 42. The end surfaces 76, 80, 82, 84 of each leg 68, 70, 72, 74 may be not inwardly sloped. The ends 76, 80, 82, 84 of each leg 68, 70, 72, 74 may have a similar cross section than the straight section of their associated leg.

Figure 3 shows a perspective view of the transformer assembly 20 wherein one primary windings and its associated secondary winding is not represented in order to view details on one magnetic core 44. The magnetic core 44 has a straight section 64 extending along the longitudinal axis A2. The gap component 30 is located between the end 49 of the magnetic core which and the inwardly sloped end surface 84 of one lateral leg 74 of the H shaped magnetic return path element 26. The end 49 of the magnetic core that cooperates with the gap component 30 has a vertical cross section shaped as a rectangle, wherein the end surfaces 90, 92 of the gap component 30 is associated between the inwardly sloped end surface 84 of the leg 74 of the H shaped magnetic return path 26 and the complementary shape of the associated end surface 50 of the magnetic core 44. The size area of the end surface 84 of the leg 74 is almost similar as the size area of end surfaces 90, 92 of the gap component 30. The primary support 54 of a primary spool is fixed on one lateral leg 68 of the e H shaped magnetic return path element 26, while the secondary support 58 of the secondary winding 34 that surrounds the primary spool is fixed on the other lateral leg 70 of the pair of lateral leg 68, 70. Preferably, the primary support 54 and the secondary support 58 are fixed on the ends of the pair of the lateral legs 68, 70.

Optionally, the transformer assembly 20 may be encapsulated with a housing such that it may be potted with a liquid epoxy. The magnetic return path 26 may be over molded with plastic in order to avoid any kind of cracks of the epoxy.

Claims

1- A transformer assembly (20) comprising; - a first magnetic core (36) extending along a first longitudinal axis (Al); - a second magnetic core (44) extending along a second longitudinal axis (A2); - a first coil (32) surrounding the first magnetic core (36); - a second coil (34) surrounding the first coil (32); - a third coil (40) surrounding the second magnetic core (44); - a fourth coil (42) surrounding the third coil (42); characterized in that the transformer assembly (20) further comprises - a H shaped magnetic return path element (26) comprising a middle leg (66), a first pair of lateral legs (68, 70) on one side of the middle leg (66), another pair of lateral legs (72, 74) on the other side of the middle leg (66), said H shaped magnetic return path element (26) providing a magnetic return path for the first and the second magnetic core (36, 44); said first magnetic core (36) being located between the first pair of lateral legs (68, 70) and the second magnetic core (44) being located between the second pair of lateral legs (72, 74); such that the transformer assembly (20) behaves as a double transformer (Tl).

2- Transformer assembly (20) as claimed in the preceding claim, characterized in that one gap component (28) is located between at least one end (45) of each magnetic core (36, 44) and the adjacent leg (70) of the H shaped magnetic return path element (26).

3- Transformer assembly (20) as claimed in claim 2, characterized in that each magnetic core (36, 44) is associated with one single gap component (28, 30) and in that the two gap components (28, 30) are located on the same side of the H shaped magnetic return path element (26).

4- Transformer assembly (20) according to any one of the previous claims, characterized in that one gap component (28) is located between each end (45, 47) of each magnetic core (36, 44) and the adjacent leg (68, 70) of the H shaped magnetic return path element (26).

5- Transformer assembly (20) according to any one of the preceding claims, characterized in that the first coil (32) and the second coil (34) are wound in opposite directions to the third coil (40) and the fourth coil (42) such that the flux inside the middle leg (66) is compensated.

6- Transformer assembly (20) according to any one of the preceding claims, characterized in that the cross section of each straight section (66, 67, 69, 71, 73) of H shaped magnetic return path and the cross section of the first and the second straight section (62, 64) of the magnetic cores are identical.

7- Transformer assembly (20) according to any one of the preceding claims, characterized in that the end surfaces (76, 80, 82, 84) of each leg (68, 70, 72, 74) of the H shaped magnetic return path element (26) are sloped inwardly in order to define sloping surfaces which are complementary to the associated ends (45, 47) of the magnetic cores (36), and/or of the associated end surface (86) of the gap component (28).

8- Transformer assembly (20) according to any one of claims 1 to 6, characterized in that each pair of legs (68, 70, 72, 74) comprises the internal end surfaces (76, 80) oriented face to face, each magnetic core (36, 44) being located respectively between the internal end surfaces (76, 80).

9- An ignition system (10) for a combustion engine comprising: - a spark plug (11) with a pair of gapped electrodes; - a control unit (13); characterized in that the ignition system (10) further comprises a transformer assembly (20) as claimed in any of the preceding claims wherein the second coil (34) and the fourth coil (42) are each coupled to the gapped electrodes of the spark plug (11); and wherein the control unit (13) is enabled to simultaneously energize and deenergize the first coil (32) and the third coil (40) of the transformer assembly (20) by simultaneously switching on and off two corresponding switches (Ql, Q2) to establish an electrical arc across the gapped electrodes of the spark plug (11) and to sequentially energize and deenergize the first coil (32) and the third coil (40) by sequentially switching on and off both corresponding switches (Ql, Q2) to maintain a continuous ignition fire.