DE10304081B4 - Access system for a motor vehicle - Google Patents

Abstract

Access system for a motor vehicle, preferably for locking or unlocking vehicle doors and / or a boot, consisting of:
An FSK radio transmitter (2) with two different carrier frequencies (f1, f2) within the ISM band and a modulated digital control signal (Data) of a code generator,
A radio receiver (3) for receiving the frequencies (f1, f2) transmitted by the radio transmitter (2) and the control signal (Data), the radio receiver being designed as an ASK receiver (3) which can be operated in two-channel operation, wherein each channel (ch1, ch2) is assigned one of the carrier frequencies (f1 or f2), so that each channel (ch1, ch2) has a different frequency (f1, f2),
And means for detecting and correcting a system interference caused by an interfering signal in the frequency vicinity of one of the two frequencies (f1, f2), the carrier frequencies (f1, f2) being widely spaced from each other with respect to the bandwidth of the ISM band in such a way that an interference signal (SF) at most only one of the two frequencies (f1 ...

Description

The The present invention relates to a system, in particular access system for a Motor vehicle, according to the preamble of patent claim 1.

Such a system is off DE 196 11 576 A1 previously known. In the prior art system, the receiver is formed by a two-channel ASK direct receiver having a wideband pre-stage and two separate receivers designed for frequencies f1 and f2, respectively. The transmitter is operated in the ASK method, in a state, for example 1, the frequencies f1 and f2 are repeatedly transmitted, while in the second state, eg 0, no signal is transmitted.

These Systems, so-called RKE systems (Remote Keyless Entry), serve in particular Keyless by radio e.g. Vehicle doors, To unlock or lock flaps and the like. they have themselves largely enforced in the automotive industry.

Yet Show them a big one Disadvantage on. If you are in the ISM band (Industrial, Scientific, Medical) (433.05- to 434.07 MHz), there is a risk that another transmitter interferes with the system and thus it blocks what an opening or To lock the vehicle doors prevented. Namely, the ISM band will extensively used. Most stations have a short range of about 50 to 500 meters up, but there are many of them the probability relatively high that such a transmitter that RKE system blocked. Such transmitters can be used in cordless headphone systems, Walky talkies and the like may be included.

on the other hand can sources of interference be very powerful in the ISM band. Also not negligible sources of interference are therefore medical devices, Radio amateurs and repeater stations. They dive less often but because their transmit power is relatively high, the probability is This is also relatively high, causing a disruption of the RKE system is coming.

The Bandwidth of such a jammer in the ISM band is usually about 100 kHz.

From the GB 2 310 300 A For example, a security system of the above type is known that comprises two frequencies for intercepting interference. In case one frequency is disturbed, the other undisturbed frequency can be used to generate an intact control signal. The radio receiver has an audio frequency bandpass filter of 20 kHz. This only passes control signals of an amplitude-modulated frequency of 20 kHz. The radio transmitter includes a code generator which provides each H signal with a 20 kHz audio frequency modulated at a single carrier frequency of 433.92 MHz. Interruptions of the audio frequency of 20 kHz correspond to the code. The modulated audio signal of 20 kHz generates the control signal in the receiver. In order to operate the receiver without interference, the audio frequency is changed digitally from 20 kHz (F1), that is to say to approximately 10 kHz = F2. Since a period of the frequency F2 is about twice as long, F2 is also only half as large as F1. Due to the two audio frequencies of 10 kHz and 20 kHz, a redundancy arises, whereby when an audio frequency is disturbed, the other can still be used for code signal generation in the receiver or for the recognition of the code, which prevents a blockage of the system.

It concerns with the GB 2 310 300 A in principle, the transmission of two acoustic signals of 10 kHz and 20 kHz in the audible frequency range or in the high-pitch range, which are amplitude modulated by a single carrier frequency of 433.92 MHz. That is, if z. B. the 10 kHz signal is disturbed, the 20 kHz signal is still present. The radio transmitter is therefore designed as an amplitude-modulated transmitter and the radio receiver accordingly as an amplitude-modulated receiver. Furthermore, the shows GB 2 310 300 A two parallel-connected band-pass filters in the receiver, wherein one filter is designed for 20 kHz and the other filter for 10 kHz.

If a single jammer fortuitously the same carrier frequency as the RKE system has, then the system is blocked because already the presence of this single Störträgerfrequenz this already sufficient.

The EP 0 660 901 B1 describes a RKE system, which, however, only provides protection against unauthorized access, but not against interference in the ISM band. A far end transmitter has an oscillator circuit that generates a signal at a fixed frequency of 434.09 MHz to a frequency modulated signal that varies at a rate of 15 kHz between 434.03 and 434.09 MHz. Furthermore, the system has a device for detecting the presence of the frequency-modulated signal, wherein the device contains a detector for frequency-modulated signals. The two carrier frequencies of 434.03 MHz and 434.09 MHz are relatively close together, so that there is no effective protection against interference in the ISM band. Furthermore, the document describes the use of SAW filters, a microprocessor and an RF receiver with a loss of 10 dB.

From the EP 0 393 470 A1 is a system with a transmitter and a receiver is known in which two modulation frequencies from 30 to 50 kHz and 400 to 500 kHz are alternately or successively sent, so that a high interference immunity of a digital signal to be transmitted should result. The receiver has two separate evaluation circuits, each with a receiving sensor, each evaluation circuit is assigned to one of the frequencies of 30 to 50 kHz and 400 to 500 kHz. Both evaluation circuits are ANDed, so that a received signal is accepted only when both modulation frequencies are transmitted. Infrared signals are used for transmission. However, blocking of a RKE system would not be prevented by this system.

Of the Invention is based on the object, the system of the generic type to improve that the noise immunity is increased and also the system cost-effective is.

These Task is solved by a device having the features of claim 1.

By the two carrier frequencies, which are widely spaced, in particular 0.5 MHz to 1.7 MHz, it is extremely unlikely that the radio transmitter according to the invention is disturbed, the disturbances are thus in the range of a carrier frequency very far from the other carrier frequency away. It would have to fortuitously two interfering signals or two devices at the same time and in the vicinity occur randomly the same carrier frequencies like that of the system according to the invention exhibit. This can be ruled out in practice, thereby the system very trouble-free is.

The System needed only one transmitter and only one relatively inexpensive receiver, the also a commercial Block can be, since it is designed as an ASK receiver. The use of a ASK receiver in connection with the invention FSK transmitter is possible because the frequency spectrum of a signal in one of the two channels absolute identical to that of an amplitude modulated signal. Also consumed the system requires little power as only one transmitter and only one receiver is required is. This protects the batteries, like the battery of the transmitter or the car battery.

Especially It is advantageous if the frequency difference between the two carrier frequencies is about 1 MHz. Thereby can commercial Filters and receiver modules can be used in circuit technically simple manner. Commercially available filter modules namely, have a bandwidth of about 0.7 MHz. Maximum is a filter bandwidth of 1 MHz possible, when the distance between the two carrier frequencies is 1 MHz. The Frequency characteristics can even at 1 MHz filter bandwidth do not overlap, what a clean two-channel operation and parallel connection of filters allows. The minimum distance of the carrier frequencies always matches the filter bandwidth, if any carrier frequency is arranged in the middle of a filter bandpass area.

In a further advantageous embodiment of the invention is in each Ka nal arranged a SAW filter, each a carrier frequency is assigned, which is particularly advantageous if the radio receiver as Superhet receiver with an intermediate frequency filter is formed. This is a high damping and a good filter characteristic possible. This improves additionally the interference immunity.

Further Advantages are in the subclaims contain.

Based The following description of the figures, the invention and more advantages of the same explained. Show it:

1 : a simplified schematic representation of the system according to the invention,

2 FIG. 2 is a block diagram of a variant of a transmitter according to the invention, FIG.

3 : a further variant of a transmitter according to the invention,

4 : a block diagram of the receiver according to the invention,

5 a pulse diagram with control signals,

6 : simplified frequency response curves of SAW filters,

7 FIG. 2: a simplified frequency response curve of an intermediate frequency filter of a superheterodyne receiver, FIG.

8th a frequency response curve of the total receiver filter system, and

9 : a simplified representation of frequency spectra of signals.

in the Below, the same parts are always given the same reference numerals characterized.

1 shows a simplified block diagram of the system according to the invention 1 , The system consists of a radio transmitter 2 and a radio receiver 3 and serves as an access system for a motor vehicle, in particular for locking or unlocking vehicle doors and / or a trunk. But it is also possible to activate or deactivate vation of an alarm system.

Also an application in a tire pressure monitoring system is possible. These Systems also work in the ISM band. Depending on your needs, the Operating frequency of the TPMS be tuned to the 2-channel system or for the case that the tire pressure sensor exactly at 433.92 MHz or 315 MHz works, the lower frequency can be shifted from 433.42 to 433.92 MHz become. The filter bandwidths need then be adjusted accordingly.

The radio transmitter 2 has two resonators or transmitting circuit parts, which will be explained later. The first circuit part generates a first carrier frequency f1 of 433.42 MHz, while the second transmission circuit part generates a carrier frequency of 434.42 MHz. Both circuit parts are simplified by the specification 433 MHz (f1) or 434 MHz (f2) in 1 indicated.

Both carrier frequencies f1 and f2 are alternately successively by means of a transmitting antenna 6 Posted.

At the transmitting antenna 6 So is always alternately only one of the two carrier frequencies f1 or f2, which symbolically by a switch 7 is illustrated. This switching is achieved by inverting a control signal "Data", as explained later.

This fictional switch 7 is actuated by a data stream "Data" of a code generator.When this control signal "Data" is logic "H", the first carrier frequency f1 is applied to the antenna 12. If the control signal "Data" is logic "L", it is upside down 1 MHz higher second carrier frequency f2 at the transmitting antenna 6 at. Thus, the switching frequency or switching pattern forms the code for locking or opening the vehicle doors. The data must be encoded in Manchester format. Each bit cell thus contains an equally long "low" and "high" phase. The information 1 is transmitted as a "high-low", the information "0" is transmitted as a "low-high transition".

The example arranged in a motor vehicle radio receiver is equipped with a receiving antenna 8th which receives the switching pattern of the carrier frequencies f1, f2.

In 1 is symbolically a second switch 9 pictured with the receiving antenna 8th also connected only symbolically. The second switch 9 Switches the received signal to one of two channels ch1, ch2. Therefore, from a two-channel operation of the radio receiver 3 to be spoken. This allows only a single radio receiver 3 which is a commercially available ASK receiver (ASK = Amplitude Shift Keying or digital, linear modulation form).

The transmitted radio signal corresponds to an FSK signal (FSK = Frequency Shift Keying or digital, discrete frequency modulation). It deals So it is a frequency modulated data signal, the frequency value the carrier frequency digitally changed is and not the amplitude of the carrier frequency.

Everyone Channel ch1, ch2 is equipped with a SAW filter (Surface Acoustic Wawe Fil ter) provided, which is adapted to the respective frequency f1 or f2 and generates a clean signal.

Both signals of channels ch1 and ch2 are fed to a single ASK radio receiver, which is a commercial superheterodyne receiver 11 is. The superhet receiver 11 is a high-frequency receiver in which the receiver reception frequencies f1 and f2 are converted to a low intermediate frequency of 10.7 MHz by superposition with a mixed oscillation. The superhet receiver 11 is provided with an intermediate frequency filter, which will be explained later. At the exit of the superhet receiver 11 the received code of the code generator is output at a data rate of 1 to 4 kbyte / s, this data rate of the data rate of the radio transmitter 2 equivalent.

The microprocessor or microcontroller 12 who is after the superhet receiver 11 is switched on, decrypts the code and generates control commands for unlocking or locking the doors. In a preferred variant, the microcontroller takes over 12 a selection of the two channels ch1, ch2 and switches the selected channel ch1 or ch2 either unchanged or by means of interference suppression, freed of glitches on the output of the superhet receiver 11 ,

As continues in 1 is shown controls the microcontroller 12 the switch or controls the choice of channels ch1 or ch2 with an oscillator circuit 13 which has two frequencies 13.2100 MHz and 13.2412 MHz. If other reception _{frequencies are} used, these reference _frequencies change accordingly (f _ref = f _rec - 10.7 MHz) / 32).

The oscillator circuit 13 stands with a mixer of the superhet receiver 11 in connection.

These different frequencies of 13.2100 MHz and 13.2412 MHz are required to produce a uniform intermediate frequency of 10.7 MHz with the respective input frequencies f1, f2. Here, the difference of the reception frequency of 433.42 or 434.42 MHz and a Mixer frequency (L0 = Local Oscillator frequency) in a known manner, the intermediate frequency of equal to 10.7 MHz in the case. Later explained filters are used to suppress so-called mirror frequencies and other strong sources of interference.

2 and 3 show variants of the radio transmitter.

The radio transmitter 2 according to 2 is with a transmitter microcontroller 14 which generates the code and outputs the digital control signal "Data." At the same time, the transmitter microcontroller outputs 14 an inverted control signal "Data '" off.

The radio transmitter according to 2 has a first and a second resonator 16 . 15 on. The non-negated control signal "Data" controls the second resonator 15 which generates an oscillation frequency f1 of 433.42 MHz. The negated control signal "Data '" is for controlling the first resonator 16 which oscillates at a second oscillation frequency f2 of 434.42 MHz. The two resonators 15 . 16 so alternately stabilize a designed as a transistor stage oscillator 18 , At the oscillator 18 is the transmitting antenna 6 switched so that it acts as a resonant circuit element.

Since either only one of the control inputs "Data" or "Data '" can be logic "H", this corresponds to 2 shown circuit of a switching according to 1 ,

In 2 is the frequency modulation by the oscillator 18 and frequency-determining components 15 . 16 realized, with the Oscillator 18 through the transmitter microcontroller 14 is activated, which is illustrated by the enable line.

In the 3 illustrated variant of a radio transmitter 2 ' consists of a parallel connection of transmission circuit parts 15 ' . 16 ' each with a resonant circuit. The first transmission circuit part 15 ' in this case generates the one carrier frequency f1 and can be activated by the control signal "Data." The other transmitting circuit part 16 ' generates the other carrier frequency f2 and can be activated by an inverted control signal "Data '", so that a sequential switching of the carrier frequency f1, f2 and thus also a discrete frequency modulation (FSK) corresponding to the control signal Data takes place.

4 shows another block diagram in which the receiver 3 is shown. The radio receiver 3 is with a channel switch 20 each channel ch1, ch2 is a SAW filter 21 . 22 is assigned as a bandpass filter, with a ch1, ch2 corresponding frequency f1, f2.

The superhet receiver 11 consists of a high frequency part 23 for the frequencies 433.42 MHz and 434.42 MHz, comprising an amplifier and a mixer. Furthermore, there is the superheterodyne receiver 11 from an intermediate frequency part 24 with an intermediate frequency of 10.7 MHz, an intermediate frequency filter, a demodulation stage and other functions of commercial receivers. The demodulated data (Data and Data ') are used to decode the microcontroller 12 fed. In this case, an error correction program is executed, which automatically uses the intact control signal (Data or Data ') in the absence of one of the control signals (Data or Data') as a result of a jammer and thus corrects the error.

In an advantageous embodiment, it is provided that the microcontroller 12 At the beginning of the data transmission, it evaluates the "quality" of the channel (s) ch1 and / or ch2 After this evaluation, it selects one of the two transmission channels ch1 or ch2 for the entire further transmission, which is particularly advantageous since at the beginning of a data transmission Typically, a fixed and known sequence of "L" and "H" or "0" and "1" values are transmitted so that channel estimation can be simpler and more accurate Recognizing and correcting a blockage of the system that would otherwise result from an interfering signal is used.

Instead of this channel monitoring, For "error correction", a circuit arrangement, e.g. with logical links. and / or monitoring programs be used. It is important that a redundancy is achieved and blocking the system is prevented. From both carrier frequencies f1, f2 or both channels, ch1, ch2 must not be disturbed Frequency (or channel) selected become.

5 illustrates the digital control signals "Data" and "Data".

6 shows the filter behavior of the SAW filters 21 . 22 , The bandwidth of each bandpass filter 21 . 22 is about 0.7 MHz. Because both frequencies f1, f2 are spaced apart by 1 MHz, the illustrated attenuation curves can not overlap. There is still a distance of 0.3 MHz between the two curves ch1, ch2. The attenuation is 10 dB due to the parallel connection. All attenuation values are exemplary minimum values in the region of interest of the ISM band.

Through the series connection of the SAW filters 21 . 22 with the intermediate frequency filter, its filter behavior and attenuation of 20 dB in 7 Darge is set, a high total attenuation of 30 to 35 dB is achieved ( 8th ). The bandpass width of the intermediate frequency filter is 0.4 MHz, which is smaller than that of the SAW filter 21 . 22 so that the overall bandpass width is reduced.

9 shows, in simplified terms, the frequency spectrum of the frequencies present in the channels ch1, ch2. The frequency spectrum of a channel is identical to the spectrum of an ASK-modulated transmit signal with a single carrier frequency. Therefore, it is possible to use an ASK-type receiver.

As continues in 9 is illustrated, the frequencies f1, f2 and its frequency spectra are far from each other, wherein the distance .DELTA.f is preferably 1 MHz. An approximately 100 kHz wide interference signal SF, which includes the first modulation frequency f1 and disturbs them, is far from the second frequency f2. Since a correct signal or a correct frequency f1 or f2 is sufficient, the system is particularly insensitive to interference.

Further shows 9 the width of the ISM band. With respect to this band, which is about 1.7 MHz wide, the distance between f1 and f2 of 1 MHz is relatively large. A large distance is also present at a frequency difference between f1 and f2 of, for example, about 0.5 MHz. A frequency difference of z. B. 0.1 MHz would not be enough. With a frequency difference of 0.5 MHz, the pre-filters described would have to be adjusted accordingly so that an overlap of the filter characteristics is avoided.

For example is the system according to the invention also for a use with systems for one Tire pressure monitoring, in particular with so-called TPMS (Tire preasure monitoring system) systems, suitable. These can be from the system according to the invention are received when the lower frequency of 433.42 MHz to 433.92 MHz is shifted, or if the TPMS tuned to the receiver is, i. either working on one of the two frequencies or also has a 2-channel system.

In Analog to the 434 MHz technology, the 2-channel receiver, of course, too on the usual in the US and Japan Frequency of 315 MHz work when the frequency-determining components changed accordingly become.

Claims (14)

Access system for a motor vehicle, preferably for locking or unlocking vehicle doors and / or a luggage compartment, comprising: - an FSK radio transmitter ( 2 ) with two different carrier frequencies (f1, f2) within the ISM band and a modulated digital control signal (Data) of a code generator, - a radio receiver ( 3 ) for receiving from the radio transmitter ( 2 ) transmitted frequencies (f1, f2) and the control signal (Data), wherein the radio receiver as an ASK receiver ( 3 ) operable in two-channel operation, each channel (ch1, ch2) being assigned one of the carrier frequencies (f1 or f2), so that each channel (ch1, ch2) has a different frequency (f1, f2), And means for detecting and correcting a system interference caused by an interfering signal in the frequency vicinity of one of the two frequencies (f1, f2), the carrier frequencies (f1, f2) being widely spaced from each other with respect to the bandwidth of the ISM band such that an interference signal (SF) can block at most only one of the two frequencies (f1 or f2), characterized in that in the radio receiver ( 3 ) a switch ( 9 . 20 ) provided by the antenna ( 8th ) is switched to one of the two channels (ch1, ch2), whereby the undisturbed channel is selected from both channels (ch1, ch2). System according to claim 1, characterized in that the frequency difference between the two carrier frequencies (f1, f2) is approximately 1 MHz. System according to claim 1, characterized in that in each channel (ch1, ch2) a SAW filter ( 21 . 22 ) is arranged. System according to one of the preceding claims, characterized in that the radio receiver ( 3 ) as a superheterodyne receiver ( 11 ) is formed with an intermediate frequency filter. System according to claim 4, characterized in that both SAW filters ( 21 . 22 ) are connected together at their outputs, and that the SAW filters ( 21 . 22 ) are connected in series with the intermediate frequency filter. System according to claim 5, characterized in that outside the passband the attenuation of each SAW filter ( 21 . 22 ) is at least about 10 dB and the attenuation of the intermediate frequency filter is at least about 20 dB, so that the total attenuation is at least about 30-35 dB. System according to claim 5 or 6, characterized in that the bandwidth of the passband of the intermediate frequency filter is smaller than the bandwidth of each SAW filter ( 21 . 22 ), in particular about 0.4 MHz. System according to one of claims 5 to 7, characterized in that the bandwidth of the passband of each SAW filter ( 21 . 22 ) is at most the frequency difference (delta f) of both carrier frequencies (f1, f2), preferably at most 1 MHz, in particular approximately 0.7 MHz. System according to one of claims 4 to 8, characterized that the intermediate frequency of the receiver is 10.7 MHz. System according to one of the preceding claims, characterized in that the radio transmitter ( 2 ' ) from two parallel-connected transmission circuit parts ( 15 ' . 16 ' ) each having a resonant circuit, wherein the one transmission circuit part ( 15 ' ) which generates a carrier frequency (f1) and can be activated by the control signal (Data) and the other transmitting circuit part ( 16 ) generates the other carrier frequency (f2) and by an inverted control signal (Data ') can be activated, so that the control signal (Data) corresponding sequential switching of the carrier frequency (f1, f2) and thus discrete frequency modulation (FSK) takes place. System according to one of claims 1 to 9, characterized in that the radio transmitter ( 2 ) two resonators each associated with one of the carrier frequencies (f1, f2) ( 15 . 16 ) with an oscillator ( 18 ), wherein a transmitting antenna ( 6 ) with the oscillator ( 18 ) is switched to act as a vibrating element. System according to one of the preceding claims, characterized in that the radio receiver ( 3 ) with a microcontroller ( 12 ) by which the means for detecting and correcting the interference signal is executed by a data processing program. System according to one of the preceding claims, characterized in that the radio receiver ( 3 ) with a microcontroller ( 12 ) connected to an oscillator ( 13 ), which has at least one sampling frequency (f _abt ) for the channel switch ( 9 . 20 ) of the two-channel ASK receiver ( 3 ) generated. System according to claim 1, characterized that the frequency difference between the two carrier frequencies (f1, f2) is about 0.5 MHz to about 1.7 MHz.