Vehicle key for passive access systems and corresponding method

Abstract

A radio key for an access system of a motor vehicle includes a receiver circuit with at least three LF receiver coils for reception of a low frequency signal. The receiver coils are oriented in different spatial directions. A central control circuit includes a microcontroller coupled to the receiver circuit. The control circuit with the microcontroller can assume an energy-reduced resting state and an active operating state. The receiver circuit is configured to awaken the control circuit from the resting state when a signal is received by the LF receiver coils. The central control circuit is configured to activate each of the LF receiver coils separately and to query a received signal strength. The central control circuit then selects the LF receiver coil with the highest signal strength for a subsequent signal reception.

Claims

1. A radio key for an access system of a motor vehicle, comprising a receiver circuit with at least three LF receiver coils for a low frequency signal reception, wherein the LF receiver coils are oriented in different spatial directions, a central control circuit comprising a microcontroller, wherein the control circuit including the microcontroller can assume various operating states, at least one of which is an energy-reduced resting state, and one of which is an active operating state, wherein the receiver circuit is coupled to the central control circuit, wherein the receiver circuit is configured to detect LF wakeup signals and to wake up the control circuit from the energy-reduced resting state when such a wakeup signal is received through the LF receiver coils by the receiver circuit, wherein the central control circuit is configured to activate each of the LF receiver coils of the receiver circuit separately after it has been woken up from the resting state, and to query a received signal strength of each of the receiver coils, wherein the control circuit selects the LF receiver coil with the highest signal strength for a subsequent signal reception.

2. The radio key according to claim 1, wherein the receiver circuit with the LF coil assembly is configured as an integrated module, and wherein the control circuit is separate from the integrated module.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention shall now be described in greater detail based on the attached drawings.

(2) FIG. 1 shows, schematically, a system composed of a vehicle-side communication unit and a mobile vehicle key;

(3) FIG. 2 shows a flow chart for a keyless entry method according to the prior art;

(4) FIG. 3 shows the sequence of a keyless entry method according to the invention.

DETAILED DESCRIPTION

(5) A schematic view of a vehicle-side communication device 1 is shown in FIG. 1.

(6) A vehicle key 2 interacts with the communication unit 1 via a wireless communication connection, in order to make a passive access system available. A central control device 3 is incorporated in the vehicle-side communication unit. Numerous transmission coils 4a, 4b, 4c for a low frequency (LF) communication are coupled to the central control device 3. The low frequency communication takes place in this example at 125 kHz. Furthermore, a communication circuit 5 is provided, which is coupled to a high frequency antenna 6. A high frequency communication can be carried out via the communication circuit 5 by activating the antenna 6.

(7) An LF communication module 10 is disposed in the vehicle key 2, which has a receiver circuit, and coils for receiving low frequency signals coupled to the receiver circuit. The coils are configured as a so-called 3D coil assembly. The individual coils face in different spatial directions thereby, to enable an improved reception of the low frequency signals when the vehicle key 2 is in any position.

(8) A control device 11 is coupled to the receiver circuit 10, which can assume an energy-reduced standby mode. The standby mode is an energy-reduced state, in which the energy consumption of the device in the vehicle key 2 is decreased, because the control device is inactive. It is possible to wakeup the control circuit 11 by an activation thereof via the receiver circuit 10, when it receives an appropriate wakeup signal.

(9) The control device 11 has a microcontroller and a memory for executable program codes. Furthermore, a communication circuit 12 is coupled to the control device 11, which in turn is connected to a transceiver antenna 13 for high frequency communication.

(10) When in operation, the communication unit of the vehicle transmits wakeup signals via the antennas 4a, 4b, 4c in short time intervals (e.g. 250 ms), for waking up a vehicle key in the proximity of the vehicle, Such a system, which repeatedly queries the surroundings, is referred to as a so-called polling system. If the key 2 is in the proximity of the vehicle, the field strength of the LF wakeup signals is sufficient for detection by the receiver device 10. The wakeup signal is received by the receiver device 10, and the control device 11 is then woken up in response to the wakeup signal, thus activating it to an operating state.

(11) It is fundamentally possible for the receiver circuit 10 to already make a pre-selection of one of the receiver coils of the receiver circuit 10 based on the received wakeup signal and the signals of the 3D coil assembly. It is provided according to the invention, however, that after the waking up of the control device 11, this control device 11 activates each of the coils in the 3D coil assembly. Depending on the signal responses, in particular an RSSI value determination, the control circuit 11 selects one of the coils in the receiver circuit 10, via which the low frequency signals are received. The signals are subsequently decoded, and based on the decoded signals, a high frequency communication via the communication circuit 12 and the antenna 13 is initiated with the corresponding vehicle-side components, the antenna 6 and the communication circuit 5.

(12) FIG. 2 shows a method for selecting the antenna according to the prior art, in order to illustrate the differences to the method according to the invention.

(13) According to the prior art, a wakeup signal is transmitted in the low frequency range by the vehicle in step 10. A vehicle key receives the wakeup signal via a 3D coil assembly. The receiver circuit that is coupled to the coils for low frequency communication selects the LF receiver antenna that is to be used based on the signal strengths of the individual antennas or their response times. The control circuit with the microcontroller in the vehicle key is subsequently woken up. The low frequency data are received via this pre-selected antenna, and the data are then decoded.

(14) In the further course of authentication of the vehicle key, an RSSI determination of the received signal strengths can later take place. This is then carried out in turn using the antenna coil pre-selected by the receiver circuit. This RSSI determination is used to determine more precisely the Position of the vehicle key in or around the vehicle, e.g. in order to validate authorization for executing a function.

(15) FIG. 3 shows a corresponding relationship according to the invention. In accordance with the invention, the sequence of the steps is changed, and the means for executing the respective steps are modified.

(16) A wakeup signal is likewise transmitted by the vehicle in step 110, which is then received via the LF coil assembly and the associated receiver circuit in step 120.

(17) The control circuit with the microcontroller is subsequently woken up, as shown in step 130. The microcontroller in the control circuit executes an RSSI query for each of the low frequency antennas in the 3D antenna assembly in step 140. Based an the determined values, the antenna with the highest RSSI value is then selected. The selection of the coil that is selected for low frequency data reception, and thus for receiving the data that are to be decoded, therefore does not take place in the receiver circuit, but takes place instead in the control circuit with the microprocessor, this being after the wakeup process. It is thus essential that, in accordance with the invention, the microcontroller in the control circuit is first woken up, and only after this is a coil in the 3D coil assembly selected for data reception and decoding. The coil selection is made thereby by a control part of the key, which is in a standby mode when the LF reception first takes place, and is only available after a wakeup process.

(18) Data reception of the low frequency signals via the selected antenna subsequently takes place, as shown in step 160, and the received data are then decoded in step 170.

(19) In the further course of the method, the determined RSSI data can be used for a further evaluation of the position of the vehicle key in relationship to the vehicle. It is not necessary to carry out a further determination of the RSSI data, because the measurements by the microcontroller in the active state can already be referenced. Nevertheless, a further RSSI query can fundamentally take place in the later course of the authentication.