The invention concerns a Sensor for determining the occupancy of a seat in a railway vehicle.

For different reasons, including health hazard, fire safety, business information, customer support reasons, it is important to know how many seats, and which specific seats, are available or occupied within a train.

Up to now no systems are known to support information which specific seats are available or occupied within a train. In the field of automobile technology it is typically required to find out the weight and size of person on each of the 4-5 seats inside a car. This information is required by an air bag system, as adjustments have to be done dependent on the type of passenger. To achieve this task inside a car, sensors such as cameras, weight sensors, infrared cameras, inductive sensors, etc. are used.

In the case of a train, using the same array of sensors would be prohibitively expensive which is not at least due to an average number of 150 persons per train wagon. Even if the costs of such sensors, e.g. infrared cameras, were not an issue, a communication network and supporting computing resources required to calculate all parameters delivered by such sensors in real time would impose an extremely compli - cated task.

A simpler solution in the field of automobile technology is to implement a pressure plate under a seat. This pressure plate generates an analog or digital (yes/no) signal indicat- ing the presence of weight. While this solution was once suitable for the specific scenario of a car, extrapolating this solution to a train (with thousands of seats) bears a lot of problems, some of which are mentioned below: A major problem is that using a pressure plate does not allow to distinguish between a person and a piece of luggage.

A further major drawback of using a solution including a pressure plate requires each seat to be supplied with a connection to a data bus and an electrical power supply. The effort required to cable 150 seats per wagon is quite high. The additional weight of all the cables is also an issue. Accordingly it is an object of the present invention to provide detection means to determine seat occupancy within a train without the drawbacks of known means.

It is proposed that the sensor comprises:

- a switch,

- a piezoelectric element being part of the switch or being attached to the switch and

- a wireless transmitter which is designed for data transmission by using an electrical energy produced by the piezoelec- trie element.

This proposed solution is very easy to install, since no cabling and no maintenance of batteries are necessary. In a particular embodiment of the invention, the switch is formed as a rocker switch. For this embodiment, current available switches being well adapted for the usage in the proposed occupancy sensor can be used. Furthermore the switch can be formed as a biased switch, which is advantageously well adapted for the proposed use, in particular if the sensor is placed under the seating surface of an associated seat. The actuator of a biased switch can return automatically in a neutral position, when a force act- ing on it is removed. For example the switch can comprise a spring- loaded actuator. A particularly simple construction can be achieved, if the switch is designed to be operated as momentary push button.

The number of false detections of a person can be reduced, if the sensor comprises a unit which cooperates with the switch for providing a weight threshold. In this way a better distinction between a person and an object like a piece of luggage is possible. Thereby, a simple construction can be achieved if the unit is formed as a mechanical unit including a clamp.

Furthermore, a high flexibility in the use of the sensor can be reached if an adjusting unit for adjusting the weight threshold is provided.

It is further proposed a sensor network comprising a set of sensors as defined above and at least a central unit for receiving the data transmitted by the wireless transmitter of the sensors. Advantageously the sensor network can be provided easily since no cabling and no maintenance of batteries are necessary.

The influence of external forces acting on the railway vehi- cle, in which the sensor network is arranged, on the rate of false detections can be reduced if the central unit is designed for correlating the data provided by the sensors with each other. Alternatively or in addition, at least an acceleration sensor placed in a car of the railway vehicle is provided, wherein the central unit is designed for correlating the data of the sensors with data of the acceleration sensor. This permits a particularly effective reduction of false detections due to external influences.

The movements of a person occupying an associated seat and/or manipulations with a piece of luggage placed on an associated seat can be taken into account, if the central unit is designed for recording the data transmitted by a sensor in order to provide a history of movements of a weight detected by said sensor.

The invention concerns furthermore a seat being equipped with a sensor as defined above. This seat can be provided by upgrading a conventional seat at low cost. It is also an object of the invention to provide a method for determining the occupancy of a seat in a railway vehicle. It is proposed that the method comprises the steps of:

- providing a sensor coupled to the seat, the sensor comprising a switch and a piezoelectric element being part of the switch or being attached to the switch,

- applying a force on the switch, the force provided inducing the piezoelectric element to provide energy,

- using the energy for a wireless data transmission by a wireless transmitter to a central unit, the data including an identification and/or position of the switch.

This method is very easy to implement, since no cabling and no maintenance of batteries are necessary. An actual status of the occupancy of a set of seats in a railway vehicle can be furthermore easily provided of the method further comprises the steps of

- detecting the data by the central unit,

- decoding the data and marking the seat corresponding to the switch as "occupied" by the central unit.

Exemplary embodiments of the invention are described below on the basis of the figures.

Figure 1: a rocker switch in a neutral position,

Figure 2 : the rocker switch in a on-position,

Figure 3 : the rocker switch in an alternative on-position, Figure 4: the rocker switch with a piezoelectric element,

Figure 5: a seat equipped with a sensor comprising the rocker switch and a wireless data transmitter,

Figure 6: the rocker switch with a solid object placed on it,

Figure 7: the rocker switch in an on-position, when a force is applied on the seating surface of the seat of Figure 5,

Figure 8 : the rocker switch of Figure 6 with a unit provid- ing a weight threshold,

Figure 9: the rocker switch of Figure 8 in an on-position, when a force is applied on the seating surface of the seat of Figure 5,

Figure 10: a railway vehicle with an arrangement of seats in a top view,

Figure 11: a network built by sensors coupled to the seats shown in Figure 10.

A usage of a wireless sensor is proposed, the sensors receiving energy by a piezoelectric element . Figures 1 to 3 show a switch 10 used according to an embodiment of the invention. A rocker switch is used, which is characterized as follows: Whenever there is no force applied on the switch 10, the switch 10 returns to the neutral, central position shown in Figure 1. This rocker switch is operated as momentary push button or spring- loaded switch. By activating the switch 10, i.e. applying a force so that the switch 10 is moved to at least one on-position shown in Figure 2 or Figure 3, a piezo- electric element 12 being part of the switch 10 (see Figure

4) or being attached to the switch 10 is producing electrical energy. This electrical energy is used for a wireless transmission of data related by a built-in wireless transmitter 14 (see Figure 5) , the data including an identification and/or position of the switch 10.

Figure 4 shows the switch 10 in the on-position of Figure 2. The switch 10 comprises a base unit 16 and an actuator 20 be- ing coupled to the base unit 16 such that is movable relative to the base unit 16. In the embodiment shown in the Figures the actuator 20 is formed as a rocker. Figure 5 shows a seat 22 comprising a seat part 24 and a backrest 26. The seat part 24 builds a seating surface 28 being substantially parallel to a floor 30 to which the seat 22 is fixed. The floor 30 is the floor of a train car 42 shown in Figure 10. A sensor 32 is fixed to the seat 22 and placed under the seating surface 28. The sensor 32 comprises the switch 10 as shown in Figure 6 and a wireless transmitter 14. The switch 10 is fixed to the seat 22 such that the base unit 16 is fixed relative to the seat part 24. Figure 6 shows a construction which uses the piezo- electrically powered wireless switch 10 to detect the presence of a person on a seat, in particular the seat 22 to which the sensor 32 is attached. The construction is placed under the seat 22. Thereby its position is such that the sen- sor 32 is placed under the seating surface 28. In Figure 6, the top rectangular filled block represents a simple solid object 34 attached to the switch 10.

Figure 7 shows the result of applying a horizontal weight, in particular on the seating surface 28. It can be easily noticed that the left side of the rocker switch 10 has been pressed down. The force provided will induce the piezoelectric element 12 to provide energy to the built-in wireless transmitter 14, which will send a signal which includes the sending address. This wireless signal will be detected by a central unit 36 (see Figure 10) which will decode its contents and will then mark the corresponding seat as Occupied' . If the force is removed, a new signal will be generated indicating that the rocker switch 10 has returned to the neutral position, as presented on Figure 6. The information contained in this signal will be mapped by the wireless receiver locat- ed in the central unit 36, which will then mark the corresponding seat as 'available' .

This embodiment of the invention is very easy to install, since no cabling and no maintenance of batteries are necessary. However, it will not be able to distinguish between a piece of luggage and a person. In a typical German high-speed train, between 15% and 20% of all seats are occupied by a piece of luggage.

According to a further embodiment of the invention this percentage of 'false positives' can be reduced. Thereby, a predefined weight threshold is added which will trigger the sensor 32.

Figure 8 depicts an advantageous embodiment of the system shown in Figure 6. According to this embodiment, a unit 38, particularly a mechanical unit including a clamp 40 forces the sensor 32, i.e. the switch 10, to one side, here, to the right side. The specific dimensions and/or material of the mechanical unit 38 can be selected as to define the required weight threshold.

The functionality of the system when weight is applied is shown in Figure 9, which has some commonalities to the behaviour of the system presented in Figure 7.

Using a weight threshold of, for example, 20 kg, the amount of 'false positives' will have an important reduction. On a typical German high speed train, less than 3% of the seats are occupied by luggage with a weight exceeding 20 kg. As a side effect, however, small children, particularly children with an age of 6 years and below will not be detected by the system, leaving an additional 'false negative' of around 5%.

Even though these numbers are certainly more manageable, it would be useful to reduce them even further. This reduction is achieved by using a further embodiment of the invention described below.

According to this embodiment of the invention, a dynamic (or adjustable) weight threshold is provided. Alternatively or additionally, the weight imposed on the sensor 32 is determined. This embodiment of the invention allows to detect changes in the weight on the seat 22. When a person is sitting, the person will most probably move often, causing a change in the weight applied on the seat 22. This weight could be measured directly by a sensor. Alternatively the weight threshold is adjusted to the value of the average weight applied on the seat 22; changes above or below this average will cause the threshold to be reached at random in- tervals. Even a sleeping person will slightly move while sleeping .

Figure 10 shows a train car 42 in a top view. An arrangement 44 of seats is shown, wherein each seat is formed by the seat 22 shown in Figure 5. In particular a sensor 32 with a switch 10 and a wireless transmitter 14 is attached to each seat 22 in the manner described above. A central unit 36 is also placed in the train car 42 in the vicinity of the seat arrangement 44 such that a wireless data communication can be established between the central unit 36 and each transmitter 14. The sensors 32 and the central unit 36 build a sensor network 46 shown in Figure 11.

A further embodiment of the invention described below is mo- tivated by the fact that during the first few minutes when a train leaves a station, the train will change tracks several times. This changing of tracks is jolting all train cars 42 including passengers and luggage. As a side effect this jolting also undesirably triggers the system described above. Other similar causes for movement are when a wind front meets the train for example while traversing a high bridge or while passing a train going in the opposite direction. Such movement originating from external causes will cause the luggage move, triggering the dynamic weight threshold or the weight sensor, which will lead to a false identification of a seat 22 being occupied by a person, which is a false positive event in the sense used above. According to this embodiment of the invention this specific problem will be a solved by using a method implying correlation between the values of the sensors 32, as explained next.

All sensors 32 (weight sensors or the triggering of the weight threshold) will be affected very similarly when such an external event has caused the movement. All persons and pieces of luggage in the same train car 42 will experience similar acceleration in the same direction. The implementation of a correlation algorithm according to this embodiment enables to eliminate such external effects and to leave only movements imposed by persons.

According to an alternative embodiment, information from other train cars 42 is used, which received the same external force a few seconds before and whereby this delay is taken into account. According to an alternative embodiment, information of a sensor 32 is correlated with acceleration sensors 48 within the train car 42. An additional case that should be taken into account is when a person opens a piece of luggage to grab some belongings, shifting the weight around. Such movement would cause a system according to the embodiments suggested up to now, to be detected as a moving person. For this case, a history of movements of the detected weight are stored according to a further embodiment of the invention.

Pieces of luggage will keep static most of the time. In the cases in which weight on a seat 22 was identified as being a piece of luggage, a time delay is advantageously added before changing this identification to being a person. This will give time for a user to grab some belongings during a couple of minutes before changing the profile of the identified weight. This principle may advantageously be used, too, when changing the profile of identified weight from a person to luggage. This principle advantageously avoids that a person falling asleep is detected as a piece of luggage. The histor- ical data may advantageously be deleted after the weight has been removed of the seat 22 for a few seconds. It may also be stored to be used later, as for the case where someone goes to the bathroom for a short while. The above mentioned correlating of the data of several sensors, correlating with acceleration sensors and/or the storing of the history of movements is performed in the central unit 36 which is equipped with at least a processing unit 50 and a memory unit 52, in which the corresponding programs are stored. The memory unit 52 can also be used to store the data of the sensors 32 and/or the result of an analysis of the sensor data.

The typical network topology for integrating the wireless components is a star topology. This means that several sensors 32 will be able to communicate with a single gateway. This gateway can act as central unit 36. More than one gateway may be required to cover all the sensors 32 in a train car 42. The intelligence mentioned before might be contained solely inside this gateway, as a gateway will have enough information available to it (information from several sensors 32) . It is also possible for the intelligence to be contained further down the network, for example concentrating information from several gateways.