Coding method for an electronic key.

p0001The invention relates to a method for code protection in an electronic key, particularly for motor vehicles with built-in central locking, which consists of a transmitter which transmits a coded infrared signal which is received by a matched to the code receiver, the code of the signal at the transmitter and receiver is adjustable.

p0002In such electronic keys, is in which broadcast a coded IR signal from the transmitter and decoded at the receiver side, there is the danger that can be accommodated the coded signal from any IR receiver and is then stored, if in itself during the transmission process ray region of the IR transmitter is located. In this way, relatively simple leaves a copy of the electronic key manufacture, so that it is also made possible unauthorized to open, for example, an automobile.

p0003The copy option described could only be avoided if the transmitter and receiver are brought together so close that a second receiver is not in the transmitter beam area. However, this can on the one hand in motor vehicles accomplish bad because the receiver inside the vehicle is arranged so that, for example, practically not be reflections on the windows and avoid the other hand, it also contradicts the convenient handling of such electronic locks.

p0004An electronic key of the aforementioned kind is known from DE-A-29 06 665th In the known electronic key, it is possible zu'verstellen the code of the signal at the transmitter and at the receiver by means of switches. This is basically possible to change the code so that the unauthorized use of the vehicle can be difficult. However, there is a risk that, for example, the code on the transmitter and receiver is tuned differently, so that the vehicle can no longer be open. A user will not be set after each unlocking action a new code to the transmitter and receiver, so that the copy option described above, an unauthorized use of the vehicle is not excluded according to experience.

p0005Object of the invention is to provide a_'.A Method of code - to provide assurance for an electronic key of the aforementioned kind, by which an unauthorized use of Kraftfährzeugen is prevented by copying the signal transmission side in a secure manner.

p0006This object is achieved in the method mentioned solved according to the invention, that a number of code numbers 1 are stored to n in the transmitter and the receiver, and that after each transmission and reception when the transmitter and receiver, a new matching code number is adjusted automatically ,

p0007In the method according to the invention is thus sent on the first Aufschließversuch example the code 0, the receiver is also tuned to this code 0 and open the lock. In the second unlocking the code 1 is, for example, sent to the receiver is also aware and open. This process continues until after the nth opening the coding order again with the code 0 starts.

p0008The inventive method provides the advantage that copying described above is possible in principle that the copied code, however, is no longer valid in the next attempt, because the receiver is always sensitized to the next in cyclic sequence code. Paying and sequence of such a cycle can be freely selected and only one transmitter / receiver combination (key / lock combination) valid.

p0009An embodiment of the method provides that the transmitter and receiver are connected together electronically after a successful unlocking action and this is the relevant transmitter code is transmitted to the receiver. This is possible, for example, by the transmitter and receiver are connected while driving by means of a plug connection.

p0010Another Aüsführungsform is that at Urinitialisierung the transmitter transmits a reset code to the transmitter and receiver are synchronized to the same code. This ensures in any case that the transmitter and receiver are both tuned to the same code number, ie run synchronously. The Urinitialisierung is required for example in case of power failure and reseating with batteries. The transmitter begins before sending the code 0, with a reset code that lets the receiver also with Code 0 start.

p0011A development of the invention is that the receiver to the transmitter transmitted after each unlocking an acknowledgment signal for switching to the next code. Through this so-called. "Hand-shaking" method can advantageously a backup synchronization during operation can be achieved. For this purpose, however, a receiver and a transmitter on the receiver side is required on the transmitter side. If you send the code example in groups of 3 x 8 bits, so can be transmitted after the first group already an acknowledgment. If this is not received, the further transmission of the code is stopped. For additional safety time criteria are possible here.

p0012Further advantages of the inventive method are explained in connection with the following embodiments. Show the associated drawing<ul><li>Fig. 1 is a block diagram of an electronic key, and</li><li>FIG. 2 is a block diagram of an electronic key with handshaking.</li></ul>

p0013In the figure 1 is shown das.Blockschaltbild an electronic key, which consists of a transmitter 1 and a receiver second The transmitter 1 controls, for example via the amplifier 3 to a photo diode 4, which emits an infrared signal 5 is received by a phototransistor. 6 The signal at the phototransistor 6 is the receiver 2 supplied through the amplifier 7, on whose output 8 a signal 9 is displayed, by the central locking system of the motor vehicle is controlled.

p0014For example, there are transmitter 1 and receiver 2 of one CMOS microprocessor with subsequent amplifiers 3 and 7 and infra-red transmitting diode 4 and infrared phototransistor 6. Instead of the photo transistor 6 may also include a receiver diode may be connected. This arrangement provides a simple way of. large number of coding possibilities. In a so-called "m-bit telegram", this gives 2^m- Combinations with m = 24 z. B. 16 million. For example, given per vehicle n (eg 10 codes), so the number of possibilities is reduced, although to 1 / n (1.6 million), but considering the order so arise per vehicle again n! Permutations of the order of these n codes and thus 10!, Ie 3.6 million. For n = 11, about 40 million possible combinations. These combinations are selected and stored, so that it is ensured in the fabrication, that a vehicle is working with only one code set, and that therefore only one key for a vehicle exists in a suitable manner.

p0015In the figure 2, an embodiment of an electronic key is illustrated, which operates with a Acknowledgments (hand-shaking process). The transmitter 10 controls via the amplifier 12 to a photodiode 11, which transmits the encoded infrared signal 14 so that the phototransistor 15 via the amplifier 16 to the receiver 11 is fed. At the output 17 of the receiver 11, the signal 18 for controlling the central locking is on. The receiver 11 has the ability to control the photodiode 20, the signal 21 the phototransistor 22 received after the successful unlocking, which feeds the transmitter 10 via the amplifier 23, the acknowledgment signal through the amplifier 19th

p0016The inventive method allows in a simple manner to form an electronic key for motor vehicles from theft. The transmitter can be configured for example in the order of a matchbox, so that it can be easily carried.