Wireless vehicle seat sensor unit adapted for removable vehicle seats

A vehicle seat sensor unit includes a seat occupancy sensor configured for wirelessly communicating with a control unit, at least one first seat detection sensor member and at least one second seat detection sensor member. The first seat detection sensor member is arrangeable in one out of a lower vehicle seat portion of a vehicle seat that is mountable in a vehicle in a removable manner, and a vehicle cabin floor, and the second seat detection sensor member is attachable to the other one of the lower vehicle seat portion and the vehicle cabin floor. The first seat detection sensor member and the second seat detection sensor member are configured to physically interact if mutually arranged within a specific distance. The physical interaction results in a detectable change of a status of at least one out of the first seat detection sensor member and the second seat detection sensor member.

TECHNICAL FIELD

The invention relates to a vehicle seat sensor unit, a vehicle seat sensor system including such vehicle seat sensor units, and a method for providing seat belt reminder function for vehicle seats that are mountable in a vehicle in a removable manner.

BACKGROUND OF THE INVENTION

Today's automotive safety standards require automotive vehicles to be equipped with seat belt reminder (SBR) systems for reminding a vehicle passenger to fasten the seat belt associated to the occupied vehicle seat. While until now, those seat belt reminder systems were mainly associated with front seats of the vehicle, future standards will require also rear seat to be equipped with such seat belt reminder systems.

Seat belt reminder systems typically comprise a seat occupancy sensor associated with a vehicle seat for detecting a presence of an occupant on the respective seat and for generating a signal indicative of such presence, and a seat belt fastening detector for determining a seat belt usage condition and for generating a signal indicative thereof. A control unit then uses the signals of the seat occupancy sensor and the seat belt fastening detector in order to determine whether the actual seat occupancy would require a non-fastened seat belt to be fastened and, if this is the case, to issue a corresponding warning signal.

The seat occupancy sensors usually comprise pressure-sensing devices integrated in the respective passenger seat for detecting a pressure induced by the presence of a passenger into the seat. The pressure-sensing devices, as e.g. disclosed in DE 42 37 072 C1, comprise a plurality of individual force sensors, which are connected in a suitable manner to a control unit designed for measuring a pressure-depending electrical property of said individual pressure sensors. These occupancy sensors have proven to be very reliable and well adapted to the detection of seat occupancy.

The seat belt fastening detectors typically comprise mechanical or magnetic buckle switches for detecting whether a latch of the seat belt is inserted into the seat belt buckle. One such buckle switch is e.g. disclosed in U.S. Pat. No. 5,871,063 A. As an alternative to the buckle switches, seat belt fastening detectors have been proposed which generate a buckled/unbuckled signal based on the tension in the seat belt.

One drawback of the known seat belt reminder systems lies in the fact that the seat occupancy sensor and the seat belt fastening detector usually have to be physically connected to the control unit by means of connection wires in order to be functional. This need for physically connecting the sensing device to the control unit however causes problems especially in modern cars equipped with a flexible seating system with removable and/or displaceable back seats.

In order to overcome this drawback, seat occupancy sensor systems have been proposed in which a signal representing the occupancy status is wirelessly transmitted from the seat to a control unit which is mounted in the vehicle. Such systems have e.g. been disclosed in documents U.S. Pat. No. 7,536,920 B2 or U.S. Pat. No. 7,639,125 B2. These systems solve the problem of the physical connection of the seat occupancy sensor or the seat belt fastening detector to the control unit. However, these systems suffer from the problem that the control unit, which receives a signal from a wireless seat sensor system, does not necessarily know in which location this seat is mounted in the vehicle, or whether it is correctly mounted at all. The system could, for instance, receive a signal from a seat stored in the trunk of the vehicle. Likewise, the absence of a signal from the seat sensor may be caused by a failure of the seat sensor system, or simply by the seat not being mounted in the vehicle.

SUMMARY

It is therefore an object of the invention to provide a seat occupancy sensor system which solves at least one of the above problems.

In one aspect of the present invention, this object is achieved by a vehicle seat sensor unit that comprises at least one seat occupancy sensor that is arrangeable at a surface of a vehicle seat, wherein the seat occupancy sensor is configured for wirelessly communicating with a control unit to be mounted in a vehicle. It should be noted that the expression “arrangeable at a surface of a vehicle seat”, as used in this application, shall in particular be understood as meaning that the seat occupancy sensor may be arranged at any suitable surface of the vehicle seat, such as the A-surface of the seat cushion or at the B-surface of the seat cushion or the backrest.

The vehicle seat sensor unit further includes at least one first seat detection sensor member and at least one second seat detection sensor member. The at least one first seat detection sensor member is arrangeable in one out of a lower vehicle seat portion and a vehicle cabin floor, and the at least one second seat detection sensor member is fixedly attachable to the other one out of the lower vehicle seat portion and the vehicle cabin floor to which the vehicle seat is fixedly mountable in a removable manner

The at least one first seat detection sensor member and the at least one second seat detection sensor member are configured to physically interact if mutually arranged within a specific distance. The physical interaction results in a detectable change of a status of at least one out of the at least one first seat detection sensor member and the at least one second seat detection sensor member.

The phrase “being configured to”, as used in this application, shall in particular be understood as being specifically programmed, laid out, furnished or arranged.

The term “vehicle”, as used in this application, shall particularly be understood to encompass passenger cars, trucks and buses.

It is further noted herewith that the terms “first”, “second”, etc. are used in this application for distinction purposes only, and are not meant to indicate or anticipate a sequence or a priority in any way.

The phrase “specific distance”, as used in this application, shall particularly be understood as a distance that is specific to the sensor members and the nature of their physical interaction.

The vehicle seat sensor unit can advantageously provide information on a seat occupancy and, further, information indicating a presence of a removable seat in the vehicle, even in case that the removable seat is not correctly mounted the vehicle. In a suitable embodiment, a detected absence of the physical interaction may indicate that the removable seat is not integrated in the vehicle and may, for instance, be stored nearby the vehicle or in a trunk of the vehicle. Particularly, in this way false seat belt reminder warnings can be avoided if a piece of luggage is put on the seat occupancy sensor of a removable vehicle seat that is kept in the vehicle trunk.

Preferably, the vehicle seat sensor unit comprises a number of at least n first seat detection sensor members, with n being a natural number larger than one, wherein the at least n first seat detection sensor members are arrangeable in one out of the lower vehicle seat portion and the vehicle cabin floor at mutually different mounting locations. Moreover, the vehicle seat sensor unit includes a number of m second seat detection sensor members, with m being a natural number larger than one and equal to or smaller than n.

The m second seat detection sensor members are attachable to the other one out of the lower vehicle seat portion and the vehicle cabin floor at mutually different mounting locations, such that at least two of the m second seat detection sensor members are arrangeable within a specific distance to two different first seat detection sensor members of the at least n first seat detection sensor members. By that, it can beneficially be detected if the removable vehicle seat is correctly mounted the vehicle.

In a preferred embodiment, the m second seat detection sensor members are attachable to the other one out of the lower vehicle seat portion and the vehicle cabin floor at mutually different mounting locations, such that each one of the m second seat detection sensor members is arrangeable within the specific distance to a different one of the first seat detection sensor members of the at least n first seat detection sensor members. In this way, an improved reliability with regard to assessing a correct mounting of the removable vehicle seat of the vehicle can be accomplished.

The even larger advantage of such a vehicle seat sensor system can readily be understood as follows. Defining a physical interaction of a first seat detection sensor member and a second seat detection sensor member within the specific distance as a logical value of TRUE or “1”, and defining an absence of a physical interaction of a first seat detection sensor member and a second seat detection sensor member as a logical value of FALSE or “0”, and choosing n=3 as a non-limiting example, the following status patterns can be detected for a correctly mounted removable vehicle seat:(101), (110), (111)

Herein, the first logical value indicates the presence or absence of the seat. The second logical value and the third logical value indicate if the other two first seat detection sensor members physically interact with a second seat detection sensor member or not. Where there is a logical value of “0” in the status patterns of a correctly mounted vehicle seat above, a second seat detection sensor member is obviously not required. Thus, for n=3 first seat detection sensor members, three mutually different status patterns can be detected for a correctly mounted removable vehicle seat, or, in other words, mutually different status patterns of three correctly mounted removable vehicle seats are distinguishable by installing first and second seat detection sensor members to the three removable vehicle seats according to the status patterns above. By that, the removable vehicle seats can be digitally coded by employing the disclosed embodiment of the vehicle seat sensor unit. The number m of second seat detection sensor members to be used in each one of the three removable vehicle seats is obtainable from the number of “1”s in the status patterns shown above.

In general, it can easily be obtained from the analogy of the status patterns to binary numbers that by employing a number of n first seat detection sensor members, with n being a natural number larger than one, 2(n−1)−1 mutually different status patterns can be generated, wherein the term of n−1 results from allocating one of the first seat detection sensor members to indicating the presence of the removable vehicle seat.

Furthermore, the three status patterns shown above are the status patterns that confirm a correct mounting of one of the three removable vehicle seats. Any differing detected status pattern is an indication of a removable vehicle seat being not correctly mounted.

In an information-related approach, the status pattern shown above can be understood as data sets comprising three bits of information. The first bit is used to indicate whether the removable vehicle seat is present or not. The second and third bit can take three mutually different, non-zero values: 01, 10, and 11. Thus, three bits of information facilitate 2(n−1)−1=3 different mounting possibilities.# of Bits Information on1→bit seat presence2→bits seat presence+seat not correctly mounted3→bits seat presence+3 mounting possibilities+seat not correctly mounted4→bits seat presence+7 mounting possibilities+seat not correctly mounted5→bits seat presence+15 mounting possibilities+seat not correctly mounted

Preferably, the physical interaction is of at least one out of magnetic, electromagnetic and optical nature. A variety of such first and second seat detection sensor members are well known to those skilled in the art. Examples of first and second seat detection sensor members include but are not limited to optical fibers and photodetectors, short-range radio frequency identification (RFID) tags and corresponding RFID readers, and magnets and magnetic fields-sensitive switches.

In some preferred embodiments, the at least one first seat detection sensor member or at least one of the n first seat detection sensor members comprises at least one reed switch. The at least one of the second seat detection sensor member or at least one of the second seat detection sensor members is configured to generate a magnetic field at least within a distance equal to the specific distance.

The at least one reed switch has a first switching status in the absence of a magnetic field. If the second seat detection sensor member generates a magnetic field within the specific distance, the at least one reed switch is transferred to a second switching status. Changes between the first switching status and the second switching status of the at least one reed switch can readily be detected.

The second seat detection sensor member may be designed as an electromagnet or may be formed by a permanent magnet. In this way, reliable and cost-effective first and second seat detection sensor members can be provided.

Reed switches provide the advantage of being small, robust and cost-efficient. The combination of a reed switch and an electromagnet or a permanent magnet further has the benefit of large mounting tolerances, facilitating an easy installation. The small size of a reed switch and an electromagnet or a permanent magnet enables removing or mounting the removable vehicle seat without any further installation effort regarding the first and second seat detection sensor member.

Preferably, the vehicle seat sensor unit further includes a decoder unit for detecting and evaluating the detectable changes of statuses of the first seat detection sensor members and the second seat detection sensor members. Due to the aforementioned analogy to binary numbers, the decoder unit may be a logic decoder unit processing status patterns as binary numbers, which reduces a hardware effort. The decoder unit may be configured for wirelessly communicating with the control unit.

In some preferred embodiments, the vehicle seat sensor unit further includes a seat belt fastening detector for detecting a seat belt usage condition and for generating a signal indicative thereof, the seat belt fastening detector being configured for providing the signal to the control unit. By employing the signals from the vehicle seat sensor unit, false seat belt reminder warnings can be avoided if, for instance a piece of luggage is put on the seat occupancy sensor of a removable vehicle seat that is kept in the vehicle trunk.

From the above those skilled in the art will readily appreciate that due to a symmetry between the first and second seat detection sensor members, either the first or the second seat detection sensor member is or either the first or the second seat detection sensor members are arrangeable in the vehicle seat, and the other one out of the first and second seat detection sensor member is or the other one out of the first and second seat detection sensor members are fixedly attachable at the vehicle cabin floor. The choice of which type of seat detection sensor member to arrange in the vehicle seat and which type of seat detection sensor member to attach at the vehicle cabin floor may be taken from constraints stemming from an operating principle that the seat detection sensor members are based on.

In another aspect of the invention, a vehicle seat sensor system is provided that comprises a number of k vehicle seat sensor units as disclosed herein, wherein k is a natural number and is equal to or smaller than 2(n−1)−1 and n is a natural number larger than one. The seat occupancy sensor, if applicable the seat belt fastening detector, and either the at least n first seat detection sensor members or the m second seat detection sensor members of each one of the k vehicle seat sensor units are arrangeable at a different vehicle seat of a vehicle. In this way, the removable vehicle seats of a vehicle can be digitally coded as described before, and the advantages of the vehicle seat sensor units are fully usable.

In yet another aspect of the invention, a seat belt reminder system is provided that includes an embodiment of the aforementioned vehicle seat sensor system, and further comprises a control unit configured for wireless communication with the seat occupancy sensors, the seat belt fastening detectors and the decoder units

By that, a vehicle user can be informedif a specific removable seat is mounted in the vehicle,if a removable seat is correctly mounted in the vehicle, andwhere in the vehicle a removable seat is mounted.

In yet another aspect of the invention, a vehicle seat is provided that is mountable in a vehicle in a removable manner. The vehicle seat includes embodiment of the disclosed vehicle seat sensor unit. Further, the seat occupancy sensor is arranged at a surface of the vehicle seat, and either the first or the second seat detection sensor member is or either the first or the second seat detection sensor members are arranged in the vehicle seat. The decoder unit is arranged in the vehicle seat, and the seat belt fastening detector is installed in the vehicle seat.

In yet another aspect of the present invention, the object is achieved by a method for providing seat belt reminder function for vehicle seats that are mountable in a vehicle in a removable manner, using an embodiment of the seat belt reminder system, which includes a decoder unit and a seat belt fastening detector.

The method comprises steps offor each vehicle seat, detecting the status of each one of the first seat detection sensor members or the second seat detection sensor members, whichever shows the detectable status change,for each vehicle seat, comparing the detected status with a set of predetermined codes, andin case of the detected status matching a specific code of the set of predetermined codes, communicating at least the specific code to the control unit.

By applying this method, a vehicle user can be informed if a specific removable seat is mounted in the vehicle, if a removable seat is correctly mounted in the vehicle, and where in the vehicle a removable seat is mounted.

In another preferred embodiment, the method further comprises steps ofrepetitively detecting, for each vehicle seat, the status of each one of the first seat detection sensor members or the second seat detection sensor members,recording the detected statuses,checking if at least one detected sensor member status has changed in comparison to a preceding recorded status of the sensor member,conducting at least the last two steps of the above-described method, if at least one changed sensor member status has been detected.

In this way, when one of the removable vehicle seats is installed or removed, the changed status of the seat detection sensor members will initiate the step of conducting at least the last two steps of the above-described method. Specific codes will be communicated to the control unit. In this way, the information if and where removable vehicle seats are installed is available at least at the control unit. As a further option, this information can be communicated to or retrieved by another vehicle control unit.

In a further embodiment, the method further comprises steps offor each vehicle seat, retrieving a contents of a communication with the seat occupancy sensor of a specific vehicle seat and a signal provided by the seat belt fastening detector of the specific vehicle seat,for each vehicle seat, generating a seat belt fastening warning signal based on a combination ofthe contents of the communication with the seat occupancy sensor of the specific vehicle seat,the signal provided by the seat belt fastening detector of the specific vehicle seat, andthe communicated code representing a status of the seat detection sensor members arranged at the specific vehicle seatmatching at least one predetermined condition.

In this way, false positive warnings can be prevented that may occur, for instance in a situation in which a removable vehicle seat has been removed and is being stored in a trunk of the vehicle, and a luggage piece that is heavy enough to trigger the seat occupancy sensor is put on the vehicle seat.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1schematically illustrates a vehicle formed by a passenger car with five vehicle seats30,44, three of which are fixedly mounted to a vehicle cabin floor42(FIG. 2) in a removable manner, and a seat belt reminder system10in accordance with an embodiment of the invention, in a side view. The five vehicle seats30,44inFIG. 1are arranged in two rows: three juxtaposed removable vehicle seats30being arranged as a middle row38, and a back row40comprising two juxtaposed, fixedly mounted vehicle seats44. The front seats are omitted inFIG. 1for clarity reasons. Although the front seats and the back row vehicle seats44are equipped with components that form part of the seat belt reminder system10, such as a seat occupancy sensor and a seat belt fastening detector, they will be left out of this description as they are not designed as removable vehicle seats.

Referring now toFIG. 2, each removable vehicle seat30is erected on the vehicle cabin floor42of the vehicle by a seat structure (not shown), which is designed to enable to remove or mount the vehicle seat30by hand, without or with only minor use of tools. Each vehicle seat30includes a seat cushion34for providing comfort to a seat occupant. The seat cushion34is designed for supporting the bottom of the seat occupant. A backrest36of each vehicle seat30is provided for supporting a back of the seat occupant.

The seat belt reminder system10includes a vehicle seat sensor system12and a control unit16, comprising a processor unit and a digital data memory unit, which is arranged in the vehicle but remote from the vehicle seats30,44. The control unit16is configured for wireless communication with other components of the vehicle seat sensor system12, as will be described in the following.

FIG. 2schematically shows the middle row38comprising the three juxtaposed removable vehicle seats30of the vehicle pursuant toFIG. 1and details of the seat belt reminder system10. The three removable vehicle seats30are shown as correctly mounted in the vehicle.

The vehicle seat sensor system12comprises three vehicle seat sensor units14, wherein each one of the three vehicle seats30is furnished with one of the three vehicle seat sensor units14.

Except for a left-right asymmetry and variations in the number of components that will be discussed in the following, the vehicle seat sensor units14are identically designed. Thus, for better understandability, one vehicle seat sensor unit14will be described in a representative manner, and variations among the vehicle seat sensor units14will be presented in detail.

The vehicle seat sensor unit14includes a seat occupancy sensor18that is arranged at the seat cushion34, e.g. at an A-surface of the seat cushion (i.e. the upper surface of the cushion) or at the B-surface (i.e. at the lower surface of the seat cushion) or at the backrest of the seat. The seat occupancy sensor18is connected to a common wireless communication means (not shown) of the vehicle seat sensor unit14and is configured for wirelessly communicating with the control unit16via the common wireless communication means. The vehicle seat sensor unit14further comprises a seat belt fastening detector20that is configured for detecting a usage condition of a seat belt that forms part of the vehicle seat30, and for generating a signal indicative thereof. The seat belt fastening detector20is connected to the common wireless communication means for wirelessly providing the signal to the control unit16.

Further, the vehicle seat sensor unit14comprises a number of n=3 first seat detection sensor members24and a number of m second seat detection sensor members26. Two of the three first seat detection sensor members24are visible inFIG. 2. The third first seat detection sensor member24of the vehicle seat is e.g. arranged at a left back corner of the vehicle seat30, as shown inFIG. 3, for all three removable vehicle seats30. The first seat detection sensor members24are arranged in a lower vehicle seat portion32. The second seat detection sensor members26are fixedly arranged at the vehicle cabin floor42. The number m of second seat detection sensor members26is larger than one and equal to or smaller than n and varies in this specific embodiment among the vehicle seats30between two and three.

Each of the first seat detection sensor members24comprises for instance a reed switch. Each of the second seat detection sensor members26is then preferably formed as a permanent magnet designed to generate a magnetic field having at least a specified field strength in a specific distance28. If mutually arranged within the specific distance28, the first24and the second seat detection sensor members26physically interact. As the specified magnetic field strength is sufficiently large within the specific distance28, the physical interaction results in a detectable change of a switching status of the first seat detection sensor member24. By suitably selecting the magnetic field strength, the arrangement can be made robust with regard to mounting tolerances, facilitating an easy installation.

The number n of first seat detection sensor members24are arranged at mutually different mounting locations in the lower vehicle seat portion32: left rear corner, left front corner and right front corner. The m second seat detection sensor members26are fixedly arranged at the vehicle cabin floor42at mutually different mounting locations such that each one of the m second seat detection sensor members26is arranged within the specific distance28to a different one of the n first seat detection sensor members24if the vehicle seat30is correctly mounted in the vehicle. For all three correctly mounted removable vehicle seats30, one of the m second seat detection sensor members26is fixedly mounted to the vehicle cabin floor42at a location that lies within the specific distance28to the first seat detection sensor member24arranged at the left rear corner of the vehicle seat30.

For the vehicle seat30shown on the left hand side ofFIG. 2, besides the second seat detection sensor member26arranged within the specific distance28to the first seat detection sensor member24arranged at the left back corner, another second seat detection sensor member26is arranged within the specific distance28of the first seat detection sensor member24arranged at the right front corner.

For the vehicle seat30shown in the middle ofFIG. 2, besides the second seat detection sensor member26arranged within the specific distance28to the first seat detection sensor member24arranged at the left back corner, another second seat detection sensor member26is arranged within the specific distance28to the first seat detection sensor member24arranged at the left front corner.

For the vehicle seat30shown on the right hand side ofFIG. 2, besides the second seat detection sensor member26arranged within the specific distance28to the first seat detection sensor member24arranged at the left back corner, second seat detection sensor members26are arranged within the specific distance28to the first seat detection sensor members26arranged at the left front corner and the right front corner, respectively.

The vehicle seat sensor unit14further includes a decoder unit22for detecting and evaluating the detectable changes of statuses of the first seat detection members24of the vehicle seat30. To this end, the decoder unit22is electrically connected to the reed switches of the vehicle seat30. In particular, the decoder unit22is designed as a logic decoder unit, wherein a switching status of a reed switch arranged within the specific distance28to a permanent magnet is assigned the logical value “1”, and a switching status of a reed switch arranged outside the specific distance28to a permanent magnet is assigned the logical value “0”.

From the left vehicle seat30to the right vehicle seat30shown inFIG. 2, the decoder units22can detect the following status patterns, consisting of the logical values of the switching statuses of the reed switches if the vehicle seat30is correctly mounted in the vehicle:(101), (110), (111)

It is worth noting that the status patterns for a correctly mounted vehicle seat30stays with the position within the middle row38of vehicle seats30. So, irrespective of which one of the three removable vehicle seats30is correctly mounted at a specific position within the middle row38, the detectable status pattern remains the same, and a status pattern detected by the decoder unit22of the vehicle seat30is indicative of the specific position of the correctly mounted vehicle seat30.

The decoder unit22is connected to the common wireless communication means of the vehicle seat sensor unit14and is configured for wirelessly transmitting a detected status pattern to the control unit16via the common wireless communication means.

FIG. 3schematically illustrates one of the vehicle seats30of the middle seat row38pursuant toFIG. 2in two different mounting conditions. In this specific embodiment, the mounting of the vehicle seat30is carried out by firstly aligning a rear lower edge to a guiding bracket of the seat structure (not shown), and by subsequently pivoting the vehicle seat30about an axis that runs in parallel with the rear lower edge.

In the left-hand side part ofFIG. 3, the vehicle seat30is aligned for mounting, but is not pivoted correctly in its end position for being correctly mounted as shown in the right-hand side part ofFIG. 3. The first seat detection sensor member24arranged at the left rear corner is arranged within the specific distance28to the second seat detection sensor member26that is fixedly mounted to the vehicle cabin floor42. The first seat detection sensor member24arranged at the left front corner and the first seat detection sensor member24arranged at the right front corner of the vehicle seat30are arranged outside the specific distance28to the second seat detection sensor members26.

Thus, instead of detecting status pattern (111) for the correctly mounted vehicle seat30, the decoder unit22will detect status pattern (100).

In the following, an embodiment of a method for providing seat belt reminder function, using the seat belt reminder system10pursuant toFIG. 2, will be described. A flowchart of the method is provided inFIG. 4. In preparation of using the seat belt reminder system10, it shall be understood that all involved systems, units and devices are in an operational state and configured as illustrated inFIGS. 1 and 2.

As a first step46of the method, for each removable vehicle seat30the status of each one of the first seat detection sensor members24is periodically detected, for example at a rate of 5 min−1, by the decoder unit22. After each conducted step46of detecting, the statuses are recorded in a digital data memory unit of the decoder unit22in another step48. In a further step50, it is checked if at least one detected sensor member status has changed in comparison to a preceding recorded status.

If so, in another step52of the method, for each removable vehicle seat30, the status of each one of the first seat detection sensor members24is detected by the decoder unit22of each vehicle seat sensor unit14. In an alternative step54, the last recorded statuses may be retrieved from the digital data memory unit of the decoder unit22. The detected statuses are then arranged as a status pattern by the decoder unit22and are compared with a set of predetermined codes that reside in the digital data memory unit of the decoder unit22in the next step56. In a further step58, in case of a detected status pattern matching a specific code of the set of predetermined codes, the specific code and an information code are communicated to the control unit16via the common wireless communication means.

It is worth noting that in an alternative embodiment, in which the second seat detection sensor members26are designed as electromagnets, switching one of the electromagnets on or off will initiate the previously described step52of detecting the status of each one of the first seat detection sensor members24to be carried out.

An example of the set of predetermined codes may comprise the following status patterns, which are associated to coded information:(101), (110), (111) vehicle seat30correctly mounted at position x(100) vehicle seat30present but not correctly mounted(000) vehicle seat30nearby vehicle or stored within vehicle trunk

In the next step60, for each removable vehicle seat30the control unit16retrieves a contents of a communication with the seat occupancy sensor18of the respective vehicle seat30and a signal provided by the seat belt fastening detector20of the respective vehicle seat30.

In a further step62, the control unit16generates a seat belt fastening-related warning signal if a combination of the communication contents of the seat occupancy sensor18, the signal provided by the seat belt fastening detector20and the communicated code representing a status of the seat detection sensor members24of the respective removable vehicle seat30matches at least one predetermined condition.

One example for one of the predetermined conditions may be(VEHICLE SEAT CORRECTLY MOUNTED=TRUE) AND (SEAT OCCUPIED=TRUE) AND (SEAT BELT FASTENED=FALSE),
by which positive false warnings can be prevented in a situation in which a removable vehicle seat30has been removed and is being stored in a trunk of the vehicle, and a luggage piece that is heavy enough to trigger the seat occupancy sensor18is put on the vehicle seat30.

Another example for one of the predetermined conditions may be(VEHICLE SEAT CORRECTLY MOUNTED=FALSE) AND (SEAT OCCUPIED=TRUE) AND (SEAT BELT FASTENED=(TRUE OR FALSE)),
by which a warning is given out to inform a seat occupant about the vehicle seat30not being correctly mounted.