Transmission Device for a Motor Vehicle for Transmitting a Radio Signal, Wireless Key System, and Motor Vehicle

Abstract

A transmission device for a motor vehicle for transmitting a radio signal is provided. A coil antenna is provided for emitting the radio signal, and an electric driver circuit is designed to generate an electric alternating current with a specified transmission frequency in the coil antenna. The coil antenna is arranged on at least one support element, and a parasitic parallel capacitance acting parallel to an intrinsic inductance of the coil antenna is produced by virtue of the geometry and/or the material of the at least one support element and/or by virtue of the shape of the coil antenna, the parasitic parallel capacitance together with the intrinsic inductance functioning as a parallel resonant circuit with a specified intrinsic resonant frequency with respect to the driver circuit.

Claims

1.-8. (canceled)

9. A transmission device for transmitting a radio signal from a motor vehicle, the transmission device comprising: a coil antenna to emit the radio signal; and an electrical driver circuit configured to generate an electric AC current with a predetermined transmission frequency in order to produce the radio signal in the coil antenna, wherein: the coil antenna is arranged on at least one support element and, on account of a geometry and/or a support material of the at least one support element and/or on account of a geometry of a coil shape of the coil antenna, a parasitic parallel capacitance is obtained which acts in parallel with a self-inductance of the coil antenna and, together with the self-inductance, acts as a parallel resonant circuit with a predetermined natural resonant frequency with respect to the driver circuit, and a value of the natural resonant frequency is set to an integer multiple of the transmission frequency by virtue of the geometry of the respective support element, a material type of the support material, and/or the geometry of the coil shape, or a band-stop range of the parallel resonant circuit covers the integer multiple.

10. The transmission device according to claim 9, wherein the integer multiple corresponds to the fourth, fifth, sixth, or seventh harmonic of the transmission frequency, or the transmission frequency is covered by the band-stop range.

11. The transmission device according to claim 9, wherein an amplifier element of the driver circuit is interconnected with the coil antenna by way of a circuit part that is free of resonant frequency, or at least one resonant frequency of the circuit part is different from the natural resonant frequency of the parallel resonant circuit.

12. The transmission device according to claim 9, wherein the transmission frequency is set to a value in a value range from 70 kHz to 250 kHz in the driver circuit.

13. The transmission device according to claim 9, wherein the driver circuit is configured to transmit a challenge signal for a radio key.

14. A radio key system for a motor vehicle, the radio key system comprising: a control circuit for generating a transmission signal, wherein: the control circuit is coupled to the transmission device according to claim 9, the control circuit is configured to actuate the transmission device by way of the transmission signal, and the control circuit is additionally coupled to a receiver circuit for a response signal of a radio key.

15. A motor vehicle comprising the radio key system according to claim 14.

16. The motor vehicle according to claim 15, the motor vehicle further comprising a radio receiver with a predetermined reception frequency range, wherein the natural resonant frequency of the parallel resonant circuit of the transmission device of the radio key system has a value that is in the reception frequency range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows a schematic illustration of an embodiment of the motor vehicle according to an embodiment of the invention.

[0025] FIG. 2 shows a schematic equivalent circuit diagram for a coil antenna with parasitic parallel capacitance.

[0026] FIG. 3 shows a schematic equivalent circuit diagram of the coil antenna as a parallel resonant circuit.

[0027] FIG. 4 shows a graph with schematic profiles of amplitude responses against the frequency.

DETAILED DESCRIPTION OF THE DRAWINGS

[0028] In the figures, elements that have the same function have the same reference signs in each case.

[0029] FIG. 1 shows a motor vehicle 10 that for example can be a car or a truck. A transmission device 11 that can be a part of a radio key system 12, for example, can be provided in the motor vehicle 10. In this case, the transmission device 11 can be actuated by a control circuit 13 of the radio key system 12 using a transmission signal 14.

[0030] In general, a radio signal 15 can be generated by way of the transmission device 11 on the basis of the transmission signal 14 and emitted by the motor vehicle 10. To this end, the transmission device can have a coil antenna 16 and a driver circuit 17 for driving or actuating the coil antenna 16. The driver circuit 17 can take the transmission signal 14 as a basis for generating an AC current 18, for example by way of an amplifier element 19, for example an operational amplifier or a transistor circuit. The amplifier element 19 of the driver circuit 17 can be coupled to the coil antenna 16 by way of a circuit part 19′ that does not have a relevant filter property for the AC current 18, i.e. is free of resonance, for example. This can be a coaxial cable, for example.

[0031] The AC current 18 can flow in an electrical conducting element 20 of the coil antenna 16 and thereby generate an electromagnetic alternating field or a magnetic alternating field in the vicinity of the coil antenna 16, which propagates as the radio signal 15. The coil antenna 16 can be realized by a helix shape or coil shape of the conducting element 20.

[0032] In this case, the conducting element 20 can be mechanically supported by, for example, a support element 21 in the interior of the coil shape, around which the conducting element 20 can be wound, and/or by a support element 22 that can be placed around the coil antenna 16.

[0033] By virtue of the shape of the coil antenna 16 and/or the geometry and/or the support material of the respective support element 21, 22, a parasitic parallel capacitance 23 can be obtained along a course of the conducting element 20, as is represented symbolically in an equivalent circuit diagram in FIG. 2. The pitch of the coil shape is shown with an exaggerated size in FIG. 2 for the sake of better illustration, the turns of the conducting element 20 can also be touching (with an electrical insulation therebetween) or the conducting element 20 can also be in the form of a flat coil. It is shown that a differential component or a small component or a part of the parallel capacitance 23 can act on each section of the conducting element 20. By way of example, the parallel capacitance 23 can act with reference to a ground potential 24 and/or as a coupling capacitance from conductor section to conductor section.

[0034] Overall, from the perspective of a connection point 25 from which the driver circuit 17 sees the electrical effect of the coil antenna 16, an equivalent circuit diagram is obtained, as shown in FIG. 3. FIG. 3 shows the way in which a parallel resonant circuit 26—comprising the ensemble of the parallel capacitance 23 and a self-inductance 27 of the coil antenna 16 itself—is obtained overall for the connection point 25.

[0035] FIG. 4 illustrates the way in which amplitudes A of electrical signals and/or magnetic radio signals can behave over frequency f as a result. In this case it is assumed that the driver circuit 17 generates the AC current 18 at a transmission frequency S to provide a transmission frequency band 28. Harmonics or harmonic waves 29 can additionally be produced, however, the amplitude A of which is also shown here without the effect of the parallel resonant circuit 26. From the perspective of the driver circuit 17, it is possible for the parallel resonant circuit 26 to act beyond the connection point 25, the frequency response 30 of said parallel resonant circuit, with a band-stop range 31, being able to have a damping effect on the harmonic waves 29, in particular in a range of a natural frequency Fbs in the band-stop range 31. The harmonics or harmonic waves 29 in the band-stop range 31 are damped as a result, which means that, in the radio signal 15 (FIG. 1), an amplitude characteristic 32 is obtained in which there is no loss of transmission power, or only an insignificant loss of transmission power, at the transmission frequency S, whereas, in the band-stop range 31, the harmonics or harmonic waves 29 are damped compared to the case in which the band-stop range 31 is not present. The band-stop range 31 can be defined as that frequency range in which damping caused by the parallel resonant circuit 26 is greater than 3 dB, in particular greater than 6 dB, preferably greater than 10 dB. At least one harmonic or harmonic wave 29 is selectively damped in the transmission device 11 as a result. In particular, this can be a harmonic or harmonic wave 29 that can be in a reception frequency range 33 of a radio receiver of the motor vehicle 10.

[0036] This results in the deliberate use of the natural resonance of an antenna in a series resonant circuit as an emission filter (damping of harmonic waves).

LIST OF REFERENCE SIGNS

[0037] 10 Motor vehicle [0038] 11 Transmission device [0039] 12 Radio key system [0040] 13 Control circuit [0041] 14 Transmission signal [0042] 15 Radio signal [0043] 16 Coil antenna [0044] 17 Driver circuit [0045] 18 AC current [0046] 19 Amplifier element [0047] 19′ Circuit part [0048] 20 Conducting element [0049] 21 Support element [0050] 22 Support element [0051] 23 Parallel capacitance [0052] 24 Ground potential [0053] 25 Connection point [0054] 26 Parallel resonant circuit [0055] 27 Self-inductance [0056] 28 Transmission frequency band [0057] 29 Harmonic waves [0058] 30 Frequency response [0059] 31 Band-stop range [0060] 32 Amplitude characteristic [0061] 33 Reception frequency range