Patent Publication Number: US-2022219493-A1

Title: Sensor system for vehicle tires and vehicle tires

Description:
The present invention relates to a sensor system for a vehicle tire. It also relates to a vehicle tire, in particular a solid rubber tire, having such a sensor system. 
     WO 2018/077502 A1 discloses the practice of using sensor elements in solid rubber tires. The problem here is the connection between the individual sensor element and a control unit assigned to the sensor element, for example a microcontroller. 
     This connection is typically made via wires or metallic conductor tracks. However, these are exposed to strong deformation forces, especially in solid rubber tires, and can therefore tear under long-term stress. This is particularly critical when the sensor element is not intended to be arranged in the area of the rim and thus in the vicinity of the control unit, but rather further outside in the tire. 
     It is an object of the present invention to specify a sensor system for a vehicle tire which does not have this disadvantage, but is constructed in a particularly robust manner and is therefore also suitable for monitoring the wear and tear on solid rubber tires. 
     This object is achieved with the subject matter of patent claim  1 . The dependent claims relate to advantageous embodiments and developments. 
     One aspect of the invention specifies a sensor system for a vehicle tire having at least one sensor and at least one control unit, wherein the sensor is electrically connected to the control unit by means of at least one conductor track made of an electrically conductive elastomer. 
     Here and in the following, an electrically conductive elastomer is understood as meaning an elastomer which has an electrical resistivity of less than 1000 Ωm or even less than 100 Ωm. Such elastomers are sometimes also referred to as “conductive rubber” and can be produced, for example, by using conductive particles as fillers. 
     Thus, according to the invention, an electrically conductive elastomer takes over the electrical connection between the sensor and the control unit. This has the advantage—in particular compared to metallic conductor tracks only embedded in an elastomer—that the entire electrical connection between the sensor and the control unit is sufficiently elastic to take part in deformations of the tire. The electrical connection is therefore permanently stable. As has been found, the electrical conductivity of electrically conductive elastomer is sufficient to transmit sensor signals to the control unit. 
     In one embodiment, the at least one sensor is in the form of a temperature sensor. Such a temperature sensor can be arranged, in particular, in an intermediate layer which is located in the center of the tire and in which the energy introduced by tire deformation is converted into heat. An observation of the temperature profile in the intermediate layer allows conclusions to be drawn about the condition of the intermediate layer and its damage. 
     Any damage that has occurred or the preceding increase in temperature, which can even lead to liquefaction of the material, is generally not visible from the outside, since the outside of the tire hardly heats up due to the low thermal conductivity of the rubber. In order to be able to correctly record the tire temperature inside, an integrated temperature sensor in the middle of the intermediate layer is advantageous. 
     According to one embodiment, the at least one sensor is in the form of a wear sensor and has areas which form areas of a tread of a vehicle tire and are exposed to wear during operation. 
     For example, the wear sensor may be in the form of a resistive sensor and may have a number of current paths which are connected in parallel and can be arranged at different distances from a tread of the vehicle tire. 
     In this case, the number of current paths connected in parallel is reduced with increasing wear, with the result that the electrical resistance of the sensor changes. 
     Alternatively, the wear sensor may be in the form of a capacitive sensor and may have at least one first electrode made of an electrically conductive elastomer, at least one second electrode made of an electrically conductive elastomer, and at least one dielectric layer which is made of a further, electrically insulating elastomer and is arranged between the electrodes, wherein the electrodes and the layer can be arranged perpendicular to a tread of the vehicle tire. 
     In this embodiment, the area of the electrodes is reduced with increasing wear of the vehicle tire, with the result that the capacitance of the capacitor formed from the electrodes and the electrical layer changes. Such a wear sensor can be used to quantify the wear of a solid rubber tire in a particularly simple manner. 
     One aspect specifies a vehicle tire having the described sensor system, wherein the vehicle tire is in the form of a solid rubber tire, in particular. For example, it can be a tire for a floor conveyor or a similar work machine. 
     The “intelligent” vehicle tire equipped with the sensor system has the advantage that the sensor system allows precise monitoring of the condition of the vehicle tires, wherein electrical connections are particularly robust at the same time and the vehicle tire having the sensor system is thus particularly resilient and has a long service life. 
     The sensor of the sensor system can be arranged in a layer of the vehicle tire, depending on the type of sensor. For example, a temperature sensor can be advantageously arranged in an intermediate layer of the tire, while a wear sensor can be advantageously arranged in the area of a tread of the vehicle tire. 
     The sensor system is arranged, in particular, in a hole in the vehicle tire. 
     A further aspect of the invention specifies a wheel system having the described vehicle tire, which wheel system also comprises a rim in addition to the vehicle tire. In this case, the control unit of the sensor system is arranged on a rim of the wheel system. Alternatively, it is also conceivable to arrange the control unit in the vehicle tire. 
    
    
     
       Embodiments are explained in more detail below with reference to the schematic figures. 
         FIG. 1  shows a section through a solid rubber tire having a sensor system according to one embodiment of the invention; 
         FIG. 2  shows a sensor in the form of a temperature sensor according to one embodiment of the invention; 
         FIG. 3  shows a connector for establishing an electrical connection between the sensor and the control unit according to one embodiment of the invention; 
         FIG. 4  shows a longitudinal section view of a sensor in the form of a wear sensor according to a first embodiment of the invention; 
         FIG. 5  shows a side view of the sensor according to  FIG. 4 , and 
         FIG. 6  shows a sectional view of a sensor in the form of a wear sensor according to a second embodiment of the invention. 
     
    
    
       FIG. 1  shows a vehicle tire  1  which is in the form of a solid rubber tire and is arranged on a rim  5  of a wheel system. The vehicle tire  1  has various elastomer layers. However, use in a pneumatic tire is also conceivable. In a known manner, the elastomer layers form a bottom layer  4  with steel reinforcements  6 , an intermediate layer  3  and a running layer  2 , each of which has different properties. In particular, the intermediate layer  3  is designed to be relatively elastic in order to minimize the rolling resistance and thus to reduce the generation of heat. 
     The vehicle tire  1  has, in a hole (not illustrated), a sensor system  10  having a first sensor  11  and a second sensor  12  as well as a control unit  13  which is in the form of a microcontroller in the embodiment shown and is arranged or fastened in the area of the rim  5 , for example in a molded-in pocket. 
     The sensor  11  is arranged in the running layer  2  and is in the form of a wear sensor. An area  27  of the sensor  11  forms a small area of a tread  7  of the vehicle tire  1  and, like this, is exposed to wear during operation. The sensor  11  is connected to the control unit  13  via electrical connections  14  made of electrically conductive elastomers. 
     The second sensor  12  is arranged in the intermediate layer  3  and is in the form of a temperature sensor. It also has a connection  14  made of an electrically conductive elastomer to the control unit  13 . 
       FIG. 2  shows the sensor  12  in the form of a temperature sensor. As can be seen in this illustration, the sensor  12  has two contact connections  18 . It is also conceivable for the sensor  12  to have more contact connections  18 . In the present embodiment, however, a sensor  12  was used, the signals from which can be advantageously tapped off via its supply line, with the result that only two contact connections  18  are required. The connections  18  are electrically connected to the control unit  13  by means of the connection  14 . In the embodiment shown in  FIG. 2 , the connection  14  is made up of individual connectors  17 , wherein one connector  14  makes contact with one contact connection  18  in each case. 
       FIG. 3  shows an alternative embodiment in which the connection has only a single connector  20  which is constructed from individual conductor tracks  21  made of electrically conductive elastomer in an electrically insulating matrix  22 . For example, the matrix  22  can be produced as an extruded profile from an insulating elastomer and the grooves can be filled with electrically conductive elastomer. 
     The connection  14  does not have any metallic wires or conductor tracks, but rather is composed entirely of electrically conductive elastomer and possibly additionally (in particular as sheathing) electrically insulating elastomer. It therefore forms a conductor track made of an electrically conductive elastomer. It is therefore designed to be at least as flexible as the layers of the vehicle tire surrounding it. This prevents electrical connections from breaking. 
     The connections  14  made of electrically conductive elastomer typically have diameters of a few millimeters, for example approximately  2  mm. As has been found, the sensor signals can thus be transmitted satisfactorily. 
     The dashed line  19  in  FIGS. 2, 4, 5 and 6  indicates an encapsulation of the sensor  11 ,  12  and its contact connections  18  by means of a potting compound which can be provided for the purpose of protecting the electrical contact connections  18 , in particular. 
       FIG. 4  shows an embodiment of the first sensor  11  which is in the form of a resistive wear sensor. According to this embodiment, the sensor  11  has two different elastomers, namely an insulator  23  and an electrical conductor  24 . In this case, the insulator  23  forms a layer which is interrupted in places between two layers of the electrical conductor  24 . Contact is made with each layer of the electrical conductor  24  by means of a contact connection  18 . The two electrically conductive layers  31 ,  32  are connected to one another by means of connections  25  made of the electrically conductive elastomer. The connections  25  are in the form of openings in the layer of the insulator  23 . 
     In the side view according to  FIG. 5 , it can be seen that the connections  25  were produced by making individual holes  26  in a sandwich structure comprising a layer  31  of the conductor  24 , a layer of the insulator  23  and a layer  32  of the conductor  24  and filling them with the conductor  24 . The sandwich structure made of two different elastomers can be produced, for example, by means of a triplex extruder. 
     The connections  25  form areas of current paths which lead from one contact connection  18  to the other contact connection  18 . With increasing wear of the vehicle tire  1 , into which the sensor  11  is drawn, for example with the aid of a cord  16 , some of the connections  25  are removed. This changes the electrical resistance of the sensor. 
       FIG. 6  shows an alternative embodiment of a sensor  11  which is also in the form of a wear sensor, but is in the form of a capacitive wear sensor. In this embodiment, the sensor  11  has a layer structure comprising three electrically conductive layers and two electrically insulating layers arranged in between in each case, which can be produced, in particular, by means of an extrusion process. In this case, two outer electrically conductive layers form a first electrode  28 , while the inner electrically conductive layer forms a second electrode  29  and the insulating material arranged in between forms a dielectric layer  30 . 
     Overall, the sensor  11  thus forms a capacitor with an area which decreases with increasing wear of the vehicle tire and therefore also of the sensor  11 , wherein both the electrode area and the area of the dielectric layer  30  decrease in the embodiment shown. This also reduces the capacitance of the sensor  11 , which is proportional to the electrode area. The capacitance is evaluated by means of the control unit  13  in order to determine the mileage or the wear of the vehicle tire  1 . 
     The electrodes  28 ,  29  and the dielectric  30  are arranged in this case perpendicular to the tread  7  of the vehicle tire  1  in order to ensure that the capacitor area is reduced with increasing wear. 
     The vehicle tire  1  in  FIG. 1  has both a (resistive or capacitive) wear sensor  11  and a temperature sensor  12  as well as a control unit  13  which receives signals from both sensors  11 ,  12  and is connected to both via conductor tracks made of electrically conductive elastomer. It is also conceivable to provide only one of the two sensors  11 ,  12  or a control unit  13  for each of the sensors  11 ,  12 . 
     As has been found, the sensor  11  also reacts to deformations. This makes it possible to also infer the load, the speed and the distance covered from the sensor signal. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Vehicle tire 
           2  Running layer 
           3  Intermediate layer 
           4  Bottom layer 
           5  Rim 
           6  Steel reinforcement 
           7  Tread 
           10  Sensor system 
           11  Sensor 
           12  Sensor 
           13  Control unit 
           14  Connection 
           16  Cord 
           17  Connector 
           18  Contact connection 
           19  Dashed line 
           20  Connector 
           21  Conductor track 
           22  Matrix 
           23  Insulator 
           24  Conductor 
           25  Connection 
           26  Hole 
           27  Area 
           28  First electrode 
           29  Second electrode 
           30  Dielectric layer 
           31  Layer 
           32  Layer