EP1611639A1

EP1611639A1 - Antenna comprising a ferrite core for a car door closing system

Info

Publication number: EP1611639A1
Application number: EP04723950A
Authority: EP
Inventors: Elio Mariotto; Peter Kull
Original assignee: Schaffner EMV AG
Current assignee: Schaffner EMV AG
Priority date: 2003-04-10
Filing date: 2004-03-29
Publication date: 2006-01-04
Also published as: WO2004091044A1

Abstract

The invention relates to an electronic circuit containing: a carrier (2; 13); at least one antenna (3) that is fixed to said carrier and has a ferrite core (31) and a plurality of windings (32); and a frame (30) which surrounds said ferrite core (31). Said windings are wound around said frame, and said antenna (3) is fixed to said carrier (2; 13) in such a way that the ferrite core can move along the longitudinal axis thereof. In another form of embodiment, a different material is used for the films (30A, 30B) laminated on the ferrite core, for example a nonferrous metal having a thickness of approximately 0.05 mm, or a high-strength plastic material, for example fibreglass-reinforced epoxy such as that used for printed circuit boards.

Description

ANTENNA WITH A FERRITE CORE FOR A CAR DOOR LOCKING SYSTEM

The present invention relates to an antenna, in particular a mechanically reinforced antenna, for example an antenna, which can be used for a car door locking system.

In such a car door locking system, a vehicle door locking system is unlocked by means of an electronic control circuit integrated in the vehicle door handle, that is, from a state that prevents opening of the door or flap to a state that enables opening of the door or flap.

In the case of locking systems of the type mentioned above, it is already known to allow a person access to a vehicle by querying data from a contactless portable data carrier (for example in a chip card or in a key hanger). The data query is triggered by a mechanical switching element or by a proximity sensor, which triggers the forwarding of a data query to the external portable data carrier when a person approaches the handle. The data carrier (for example a transponder) is "woken up" by the received data query and answers it by sending an identification message to the locking system. The control circuit only releases the door when the identification is valid.

In order to communicate with the external contactless data carrier, known electronic control circuits for vehicle door locking systems often comprise a transmitter or a transceiver with an antenna, which consists, for example, of an induction coil. The induction coil generates an electromagnetic field that is received by the external data carrier. The desired range is typically around one and a half meters. To achieve this range at the desired frequency, an induction coil with a large inductance must be provided. Such an inductance can only be achieved if the induction coil comprises a large ferrite core. To achieve this range, the induction coil must be installed outside the car body so that the electromagnetic field is not damped. The optimal position for mounting the induction coil is inside the car door handle, very close to the data carrier of an approaching person and to the other electronic and mechanical parts of the car door locking system.

For aerodynamic and design reasons, however, many car door handles are made very thin, so that the available thickness for the induction coil is limited. In this case, the ferrite core must be very thin and long. However, thin ferrite cores can break if the car door handle is handled roughly and if the housing around the control circuit is deformed. This risk must be reduced, because otherwise the driver could no longer get into his car.

It is therefore an object of the invention to provide an antenna in which the risk of the ferrite core breaking can be significantly reduced.

Another goal is to provide an antenna in which the ferrite core does not fall apart in the event of a break.

Another goal is to provide an antenna that can also be used for purposes other than car door locking systems.

According to the invention, these objectives are achieved by an electronic control circuit according to claim 1, preferred exemplary embodiments being specified in the dependent claims.

In particular, these goals are achieved by an electronic circuit having a carrier (for example a printed circuit board or a housing) and an antenna with a ferrite core and a plurality of windings attached to the named carrier. Around the ferrite core a frame is provided around, the windings being wound around the named frame. According to the invention, the antenna is attached to the carrier in such a way that the named ferrite core can move along its longitudinal axis.

These goals are also achieved by an antenna having a ferrite core and a plurality of turns, a frame being provided around the said ferrite core, the named turns being wound around the named frame, and the frame being only two opposite long sides of the Ferrite core covers.

This has the advantage that the ferrite core is reinforced by the frame without the thickness and the height of the ferrite core being increased at the same time. These two small dimensions of the ferrite core are much more critical than the length for many applications, especially in car door handles.

These goals are still achieved by an antenna with a ferrite core and a plurality of turns, in which a metal frame is provided around the ferrite core, the turns being wound around the frame. The frame can consist of sheet metal foils, for example.

This has the advantage that the ferrite core passes through the frame

Shocks is protected. In addition, a possible point load is distributed through the frame, so that chipping or breaking out of corners is avoided.

In the event of a break, the frame also prevents the ferrite from falling apart. The ferrite parts remain gapless, so that an air gap and thus a decrease in the inductance is avoided.

In one variant, air gaps that could still arise are bridged magnetically by the metal frame. The frame can also reduce the electromagnetic radiation and sensitivity of the ferrite core.

Preferred exemplary embodiments of the invention are described in more detail below with reference to the accompanying drawings. Show it:

Fig. 1 is a perspective view of a first embodiment of the antenna with a frame made of plastic and a carrier (in this case a plastic housing) which can be installed in a car door handle.

FIG. 2 shows a detail of one end of the antenna of FIG. 1.

3 shows a detail of the other end of the antenna of FIG. 1.

Fig. 4 is a perspective view of a first embodiment of the antenna of Figure 1 with a frame made of plastic, without a carrier.

5, 6 and 8 show a detail of the first end of the antenna of FIG. 1, without a carrier.

Fig. 7 shows a detail of the other end of the antenna of Figure 1, without a carrier.

Fig. 9 is a partial perspective view of the antenna of Figure 1 with a frame made of plastic, a carrier (in this case a plastic housing) and a circuit board.

Fig. 10 is a perspective view of the antenna of Figure 1 on a circuit board

11 shows a detail of FIG. 10 Fig. 12 is a cross section of the antenna of Figure 1 in the frame and in the housing.

13 shows a perspective illustration of a second exemplary embodiment of the antenna with a frame which consists of two sheet metal foils.

Figures 1 to 12 show a first embodiment of an antenna according to the invention, which is particularly suitable for a vehicle door locking system in a car door pull handle. The control circuit 1 of the locking system can be seen in particular in FIGS. 10 and 11. It comprises a printed circuit board 2 on which all components of the control circuit 1 are mounted. The circuit board 2 preferably has a thickness of 0.3 mm or less, preferably even 0.2 mm or less, and is therefore flexible and hardly susceptible to breakage. It is housed in a synthetic insulating housing 13 which longitudinally fills most of a cavity in a car door handle.

The control circuit comprises a touch sensor, not shown, which triggers a signal as soon as the user places a finger on the outer side of the handle. A proximity sensor 5 triggers another signal when a hand or another grounded object approaches. These signals are interpreted by the control circuit in order to forward a data query to an external contactless data carrier, not shown.

The data carrier preferably consists of a transponder (which can be integrated, for example, in a chip card or in a key holder) and is "awakened" by this data query. If the data query is addressed to him, he responds with a response which includes an identification of the data carrier or which is signed with such an identification. The response is received by the electronic locking system in the vehicle in order to trigger the unlocking of the car door locking system if it contains the expected identification or if it was signed with this expected identification. The control circuit 1 comprises a contactless transmitter-receiver in order to exchange data with the external contactless data carrier. In the variant shown, the contactless transceiver comprises an antenna with an induction coil 3.

The induction coil consists, for example, of a winding of an electrically insulated wire 32 on a plate-shaped ferromagnetic ferrite core 31. In order to achieve the required inductance, the length of the ferrite core 31 is greater than 40 mm. Its thickness is preferably less than 4 mm, so that assembly in a car door handle is possible. In a preferred variant, the profile of the ferrite core 31 is X-shaped. Those skilled in the art will understand that instead of a ferrite core, another soft magnetic core (for example made of an amorphous material or a laminated core) could also be used. Accordingly, "ferrite core" is used in this description and in the claims as a general term for all soft-magnetic induction coil cores.

According to the invention, the induction coil 3 comprises a frame 30 around the ferrite core 31, the windings being wound around the frame. Since the winding is not made directly around the ferrite core 31, the mechanical stress on the ferrite core by the winding is also reduced and the insulation between the winding wire and the ferrite core is increased. In this first example shown, the frame consists of a single plastic part, which can be injection molded, for example, and which extends over the entire length of the small side of the ferrite core. The inner width of the frame 30 corresponds to the width of the ferrite core with a small tolerance, so that no lateral play remains between the ferrite core 31 and the frame 30 and the ferrite core is thus precisely laterally positioned. A plastic part can be manufactured much more precisely than the ferrite core, so that better position tolerances are achieved. The plastic frame is preferably made from a single part, so that it is stable and that there are no play tolerances due to the connection between several parts. There is a small clearance 303 (FIGS. 6 and 8) in the direction of the height and the length of the ferrite core, so that the ferrite core 31 can easily move longitudinally within the frame 30 in the event of bending stresses and / or thermal expansion. The ferrite core 31 can preferably be displaced by at least one millimeter along its longitudinal axis. The play between the ferrite core and the housing also permits easier assembly of the ferrite core.

In order that the ferrite core 31 can move longitudinally within the frame 30, the antenna is preferably not cast in. This also reduces the forces caused by the potting compound. In addition, the stray capacities are reduced and stabilized by the air insulation (compared to a solution with polyamide molding or potting).

One end of the frame 30 is fixed by two posts 130 which engage in holes 300. As a result, it is positioned exactly in the housing 13 (FIGS. 1 to 3) and assembly is only possible in the correct direction. At the other end, the frame can move freely, which further reduces stresses due to bending and thermal expansion. The frame 30 is thus fastened in a clearly unmistakably defined mounting position in the housing.

The turns 32 are wrapped around the frame 30. The winding wire ends 320 are hooked into grooves 301 of the frame 30 and fixed and positioned for further connection precisely and reproducibly, so that they can be soldered on automatically or soldered on with ultrasound. The grooves 301 and a wire guide 302 define the winding direction, so that the wires cannot be fixed if the winding direction is incorrect. The wires leave the plastic frame at the level of the circuit board so that they can be soldered or welded more easily. The wire guide also allows the wire ends 320 to be guided precisely, so that the scattering factor of the antenna is reduced and stabilized. In addition, the risk of short circuits between the windings and the ferrite edges is eliminated. The wire length can also vary with different ferrite large constant, which leads to a stable inductance value. In cold conditions, the wire stretch is reduced by the elasticity of the plastic frame 30.

Housing 13 has longitudinal walls 131 that laterally position the sides of frame 30 without holes, without restricting its longitudinal position. The walls 131 also separate the antenna 3 from the proximity electrodes 5 (FIG. 11). A transverse wall 132 also separates the antenna 3 from the connection space, so that the connection space can be sealed by means of potting, glue or overmoulding.

A V-groove 310 shown in FIG. 12 latches in the frame 30 on both longitudinal flanks of the ferrite core 31. After the winding, the ferrite core 31 and the frame 30 are thus connected to one another without play. A longitudinal movement is still possible without great forces by sliding. The frame and the V-groove also prevent the ferrite core from falling apart in the event of a break, so that a function with reduced properties is made possible.

In the exemplary embodiment shown, the antenna 3 is mounted on a printed circuit board 2 in the housing 13, a distance between the housing 13 and the printed circuit board 2 being defined by the antenna, as can be seen in particular in FIG. 9. The circuit board is positioned through the posts 130 of the housing 13 and secured by collars 3000 around the holes 300 through the frame 3. The collars 3000 can have different shapes in order to prevent the circuit board 2 from being inserted on the wrong side. The control circuit 1 mentioned is also mounted on the printed circuit board 2.

The protective frame 13 and the possibility of the ferrite core 3 moving longitudinally within the frame and the frame inside the housing has the advantage that breakage of the ferrite core is very unlikely, so that large, sudden deviations in the inductance of the antenna are prevented. It should also be noted that the ferrite core 31 can move longitudinally to the two carriers 13 and 2.

During assembly, the antenna 3 is preferably first mounted and soldered on the printed circuit board 2 and then fastened in the housing. However, it is also possible to first mount the antenna 3 into the housing 13 and then to mount the printed circuit board 2 thereon. However, this has the disadvantage that the connecting wires for connection to the printed circuit board are led out through slots and then have to be soldered.

A second embodiment of an antenna according to the

Invention is shown in Figure 13. In this variant, the frame around the ferrite core 31 consists of two foils 30A and 30B (for example sheet metal foils which are glued, glued, welded, soldered, laminated, rolled, poured or evaporated onto the ferrite core). The foils 30A, 30B are made of a material with good high-frequency properties and the highest possible strength and elasticity. For example, the thickness is approximately 0.025mm. Thicker foils give higher strengths, but lower spool qualities, while thinner foils give higher spool qualities and lower strength. As a variant, the foils consist of several laminated layers, for example each 0.025mm thick; this allows the strength to be increased without reducing the quality of the coil. Suitable foils are, for example, a transformer plate of 0.05mm, a high-silicon special core sheet (NK Super HF-Core) and one or more Finemet (protected trademark) or amorphous core foils. In one embodiment, not shown, only one side of the ferrite core is covered with a film.

In a further embodiment, a different material is used for the foils 30A, 30B laminated onto the ferrite core, for example non-ferrous metal of approximately 0.05 mm thickness or a high-strength plastic material, for example glass-fiber reinforced epoxy, as is used for printed circuit boards. The ferrite core framed in this way can be provided with surface insulation before winding. This can be done by painting, powder coating, dipping, wrapping with insulating foils, insulating tape, overmolding with hard plastic or soft plastic in the form of a bobbin. Furthermore, U-profiles or frames can be used as winding wire protection and guidance.

The foils 30A, 30B mechanically reinforce the ferrite core 31 against breakage and, in the event of breakage, prevent an appreciable air gap from being created. If an air gap were nevertheless created, it would be bridged magnetically and the inductance would decrease only insignificantly. In addition, a possible point load is distributed, so that chipping or breaking out of corners is avoided.

The sheet metal foils 30A, 30B are preferably grounded with low resistance, so that the electromagnetic radiation and sensitivity are greatly reduced. Silvering the sheets could also further improve the shielding effect.

This second embodiment can be used for car door handles as well as for other antenna applications (including radio receivers, transmitters, direction finders, navigation devices, metal detectors, etc.).

In both embodiments, the frame 30 preferably covers only two or at most four opposite sides of the ferrite core, so that only one, or two, dimensions of the ferrite core are enlarged by the frame. In particular, only one of the critical small dimensions of the ferrite core (that is to say only the height or only the thickness) is changed in both variants.

In a further embodiment, the core 31 of the antenna 3 and thus the entire antenna 3 is flexible. The flexible core 31 consists, for example, of several thin, flexible layers of a magnetic material which are held together with flexible fastening means. In In a further embodiment, the magnetic core is formed from an amorphous magnetic material (that is to say from a flexible casting compound into which small particles of a material with high permeability, such as ferrite particles, for example, are cast). In yet another embodiment, the magnetic core is in several parts. For example, it consists of several smaller parts made of a possibly hard magnetic material such as ferrite, which are preferably connected to a magnetic flexible material.

Claims

Expectations

1. Electronic circuit, comprising: a carrier (2; 13), at least one antenna (3) fastened on the named carrier with a ferrite core (31) and a plurality of windings (32), a frame (30) around the named ferrite core (31) around, said turns being wound around said frame (30), characterized in that said antenna (3) is mounted on said support (2; 13) such that said ferrite core extends along its longitudinal Axis can move relative to the named carrier (13).

2. Electronic circuit according to claim 1, in which said ferrite core (31) can move longitudinally within said frame (30), and in which said frame (30) can move longitudinally relative to said carrier (2, 13) ,

3. Antenna (3) with a ferrite core (31) and a plurality of windings (32), a frame (30) being provided around said ferrite core (31), said windings being wound around said frame, characterized that the named frame (30) only covers two opposite long sides of the ferrite core.

4. Antenna according to one of claims 1 to 3, in which only one of the small dimensions of the ferrite core (31) by the named

Frame (30) is changed.

5. Antenna according to one of claims 1 to 4, wherein said frame (30) is a plastic frame.

6. Antenna according to claim 5, wherein said plastic frame comprises wire guides (301) and / or fastening hooks (302) for the winding wire.

7. Antenna according to claim 6, wherein the named wire guides (301) and / or fastening hooks (302) are designed such that an incorrect winding sense is not possible.

8. Antenna according to one of claims 1 to 7, in which a single longitudinal end of said frame has fastening means (300) for fastening on a carrier (3, 13).

9. Antenna according to claim 8, wherein said fastening means are fastening holes (300) for posts (130).

10. Antenna according to one of claims 3 to 9, wherein said ferrite core (31) can move longitudinally within said frame (30).

11. Antenna according to one of claims 1 to 10, in which the two winding wire ends (320) leave the named frame (30) at positions precisely defined by the named frame.

12. Antenna according to one of claims 1 to 11, wherein said ferrite core (31) has a groove which latches in said frame (30).

13. An antenna according to claim 12, wherein said ferrite core (31) can slide relative to said frame (30).

14. Antenna according to one of claims 1 to 3, wherein said frame consists of sheet metal foils (30A, 30B).

15. Antenna according to claim 14, wherein the sheet metal foils are attached to the broad sides of said ferrite core (31).

16. Antenna according to one of claims 14 to 15, in which a plurality of sheet metal foils are attached to each side of said ferrite core (31).

17. Antenna according to one of claims 1 to 16, wherein surface insulation is provided between said frame (30A, 30B) and said windings (32).

18. Antenna according to claim 16, wherein said surface insulation is achieved by painting, powder coating, dipping, wrapping with insulating films and / or extrusion coating with plastic.

19. Antenna according to one of claims 14 to 18, in which said sheet metal foils (30A, 30B) are glued, glued, welded, soldered, laminated, rolled, poured or evaporated onto said ferrite core (31).

20. Antenna according to one of claims 14 to 19, in which the said sheet metal foils (30A, 30B) consist of a material that enables a magnetic bridging of air gaps that can occur in the event of breakage.

21. Antenna according to one of claims 14 to 20, in which said sheet metal foils (30A, 30B) are connected to earth.

22. An antenna according to claim 21, wherein said

Sheet metal foils (30A, 30B) are silver-plated.

23. Antenna according to one of claims 14 to 22, in which the thickness of said sheet metal foils (30A, 30B) is 0.025 mm.

24. Antenna according to one of claims 3 to 23, with a carrier (2; 13) on which said antenna (3) is fastened in such a way that said ferrite core (31) can move along its longitudinal axis.

25. Control circuit for a car door locking system with an antenna according to one of claims 1 to 14.

26. Control circuit according to claim 24, wherein said frame (30) is mounted on a circuit board (2).

27. Control circuit according to claim 25, which in a housing

(13) is mounted.

28. Control circuit according to claim 26, which is in the housing

(13) is mounted so that the named ferrite core (31) can move longitudinally.

29. Control circuit according to one of claims 26 to 27, wherein said antenna (3) separates the circuit board (2) from said housing (13).

30. Control circuit according to one of claims 26 to 27, wherein said housing (13) has transverse walls (132) for separating said antenna from a space filled with a potting compound.