Patent Publication Number: US-8539997-B2

Title: Filling head for filling in a fluid into a filler neck of a tank

Description:
The invention relates to a filling head for filling in a fluid into a filler neck of a tank. 
     Such a filling head is provided to connect a filling line, i.e. a hose, pipe, or the like, to a filler neck of a tank such that the filling process can be enabled. It is possible to use such filling heads in many areas and for different liquids. In the context of the present invention, those liquids are considered in particular where even minor leakages represent a problem, and therefore the proper filling process should be specially monitored. This holds true in particular for filling motor vehicle tanks with an aqueous urea solution. 
     EP 2 281 774 A1 describes a device for filling a container especially with a urea solution. A connecting hollow body with a filler neck collar is provided for being connected to a connecting support element of the tank. The filler neck collar and the filler neck of the tank are connected to each other liquid-tight. A thread or bayonet lock is provided for the connection. A filling and ventilation element is provided to supply liquid and remove the displaced air through a filling tube. At the tip of the filling tube, a valve element is provided that opens when the flow pressure of the liquid is sufficient, thereby enabling the filling process. The filling device has two sensors by means of which operation is monitored, that is, a level sensor by means of which it can be determined whether the liquid level of the liquid dispensed through the filler neck of the tank has already reached the filling and ventilation element, and a position sensor by means of which it can be determined if the filling device is correctly connected to the filler neck of the tank. The position sensor is an optical sensor that identifies the correct position of the top edge of the filler neck of the tank and reports it to electrical controls. The filling process can only start when the position sensor receives the signal that the filler neck of the tank is connected to the filling device in the correct position and sealed. 
     The object of the invention is to propose a filling head that is particularly secure against misuse. 
     This object is achieved by a filling head according to claim  1 . Dependent claims refer to advantageous embodiments of the invention. 
     According to the invention, the filling head has a connecting part for connecting to the filler neck of a tank. The connection is preferably liquid-tight to prevent liquid from leaking. To create a mechanical connection, a rotary connecting element is provided, i.e., for example a bayonet lock or screwed connection that forms a connection by rotating relative to the filler neck of the tank. The mechanical connection is preferably designed such that it cannot be released by simply pulling the filling head off of the filler neck of the tank, but is rather released by rotating in the direction opposite the direction of connection. This ensures on the one hand that the connection will not independently loosen or be unintentionally released. On the other hand, a seal can also be ensured through the rotation, for example, by means of a thread or lock. 
     In addition, the filling head has a torque limitation for the rotary connecting element, e.g. threads. Such torque limitation is useful to prevent misuse by excessively tightening the rotary connection. Torque limitation is realized by means of a torque limiting coupling device that forms a releasable coupling between a rotatable operating part, especially suitable for manual operation, and the rotary connecting element. This coupling is designed such that, at least in one direction of rotation, the rotary connecting element also rotates with the operating part rotating as long as the torque remains below a threshold torque. Once the connection between the rotary connecting element and the filler neck of the tank is completely established, that is, the rotary connecting element is fixed there, further operation, i.e., for example the exertion of manual force on the operating part, increases the torque. Above the threshold torque, the torque-limiting coupling device is released and decouples the operating part from the rotary connecting element, thus permitting further rotation of the operating part without an increased torque being transmitted to the rotary connecting element. This prevents the rotary connection between the rotary connecting element and the filler neck of the tank from being overloaded which could otherwise damage the connection or prevent its manual release. 
     According to the invention, a sensor is provided to determine the triggering of the torque-limiting coupling device and, in case such triggering took place, to send a release signal for the established connection. After the release signal is evaluated, the filling process can start. 
     The torque limitation is thus not only used as a mechanical safety function to prevent damage, it can also serve to indicate that the connection has been properly established. The release signal that is preferably output by a control device, the filling process being enabled by the control device only after the release signal is available, requires the filling head to be placed on a correct and appropriate filler neck. It also requires that the rotary connection has been engaged up to the threshold torque. This ensures that the connection is sufficiently tight and, if applicable, sufficiently sealed before the release signal enables the filling process. The release signal indicates that the connecting part is correctly positioned on the filler neck of the tank, thereby excluding the danger of improper filling. In addition, the release signal also indicates that the rotary connection has been established with sufficient tightening torque, thereby providing a seal. 
     Various mechanisms can be used for triggering. Whereas a purely mechanical design of the torque-limiting coupling device is preferred for a simple, reliable and economical solution, the actual measurement of the torque and corresponding actuation can also be electromechanical. It is particularly preferable for the torque-limiting coupling device to have at least one locking element such as a locking pawl that establishes a nonrotating coupling in a first position and does not form such a nonrotating coupling in a second, triggered position, thereby decoupling the rotatable operating part from the rotary connection element. It is also preferable for the locking element to be spring-loaded in the direction of the first position, i.e., establish the coupling in a basic position, wherein the decoupling preferably occurs by a movement (shifting, rotation, etc.) of the locking element against the spring loading. 
     Thus a latching connection is preferable as the torque limiting coupling, that has a latching stroke upon triggering. This latching stroke can be detected with a suitable sensor. 
     A plurality of locking elements are preferred so that the locking function and the arising forces are distributed over a larger area. The locking elements are preferably arranged in a circle. 
     According to a development of the invention, the locking element is movably, particularly preferably shiftably, mounted between the first position (coupling) and the second position (decoupling), preferably with only one degree of freedom. The shift can for example occur in a radial direction. As explained in the context of the following discussion of exemplary embodiments, it is however preferable for the locking element to be axially shiftable in relation to the direction of rotation of the operating part or the rotary connecting element (or particularly preferably both). A coupling device can for example be formed such that a first and second coupling part are arranged axially adjacent to each other and are coupled in the first position by one or more locking elements and decoupled from each other when the locking element(s) is/are shifted into the second position axially with reference to the common direction of rotation. 
     According to a development of the invention, the locking element and/or the operating part and/or the rotary connecting element have a contact surface that is inclined at an angle in relation to the direction of displacement of the locking element. Alternately to a straight surface with a constant angle of inclination, the contact surface can also have a curved shape (bent shape), i.e., a variable angle in relation to the direction of displacement. The locking element and either the operating part or rotary connecting element preferably have mating surfaces with the cited angle or respectively curved shape in relation to the direction of shifting. When torque is transmitted, force is applied to the inclined contact surface. Given the angled arrangement, this force can comprise a force component in the direction in which the locking element is shifted. When transmitted to a rotary element, force is automatically transmitted to the locking element to move it toward its second position (decoupling). By dividing the active force into different force components at the inclined plane formed by the inclined contact surface, the force acting in the direction of the shift can be substantially proportional to the transmitted torque (apart from friction effects, etc.). This allows the threshold for the triggering torque to be specifically set. A triggering characteristic can be specified by means of a variable angle of a curved shape. 
     As mentioned, the torque-limiting effect of the coupling device exists in at least one direction of rotation, that is, preferably in the closing direction, i.e., the direction in which the rotary connection is tightened between the rotary connecting element and the filler neck of the tank. Different couplings are possible in the opposite direction. Torque limitation can also occur in this case as well. It is however preferable that there is no limitation in the opposite direction of rotation to ensure that the rotary connection can always be released. 
     In the above-described design of the torque-limiting coupling device with a locking element having a contact surface, different behavior for the opposing directions of rotation can be achieved in that the locking element, and/or the operating part, and/or the rotary connecting element comprise a first and second contact surface having different angles in relation to the shifting direction of the locking element. Preferably, the first contact surface is active when torque is transmitted in a first direction of rotation, and the second contact surface is active when torque is transmitted in the second, opposite direction of rotation. In the first direction of rotation in which the rotary connection is established, the contact surface is preferably inclined. The second contact surface that acts in the second direction of rotation can also be inclined, but it is preferably arranged parallel to the shifting direction (angle of zero degrees) so that no torque limiting is provided in the direction of release. 
     The triggering of the torque-limiting coupling device can be detected by a sensor in various ways. It is especially preferred to detect the movement of an element on the coupling device by means of a sensor. This can for example be a locking element described above that can move between the first and second position, and the sensor detects the position of the locking element and emits it as an electric signal. 
     Various types of sensor elements can be used for sensor detection including in particular optical sensors, magnetic sensors and inductive sensors. Inductive sensors and magnetic sensors are preferable because they are immune to contamination. 
     A light barrier can for example serve as an optical sensor that can detect the shifting of an element of the coupling device. Such a shift can also be determined by means of an inductive sensor. As described below in association with preferred embodiments, it is preferable to use a magnetic sensor where an element of the coupling device has a permanent magnet or a ferromagnetic part, and the approach of an element that generates a magnetic field, or a conductive element, is detected by means of a magnetic sensor such as a GMR sensor, Hall sensor, or a reed switch which is preferable because it can be purely passive. A reed opening switch, i.e., a reed contact, is particularly preferable that is closed in a resting state and opens when a permanent magnet element approaches the coupling device, or a reed changeover contact that switches a central pole between two outputs when a magnetic field approaches. Alternately, a change in distance resulting from triggering, for example between an element of the coupling device and the remaining filling head, can be detected by means of an ultrasonic sensor. 
     The electric signaling from the sensor can be modified by means of an electric circuit. If for example the sensor signal is not generated as a constant signal but only as a transient signal, e.g. as a pulse, a logic circuit can process this transient signal and e.g. emit it as a constant electrical signal. 
     In the context of a preferred embodiment, a support element is provided that is shifted from a resting position into a triggered position when the operating part is rotated in the closing direction of the rotary connection and thereby triggers the torque-limiting coupling device. A sensor is provided to determine the position, i.e., either the triggered position or resting position of the support element, and emit it as an electrical signal. A release signal can only be generated when the sensor determines the shift of the support element into the triggered position. 
     The support element is preferably part of a locking unit that prevents the support element from shifting from the triggered position back into the resting position without first rotating the operating part in the opening direction. The locking unit causes the support element to return to the resting position with the counter-rotation necessary to release the connection. This ensures that, after the rotary connection is established by applying the necessary threshold torque, the support element detected by the sensor initially remains in the triggered position, thus allowing the release signal to be continuously emitted by the sensor. This release signal can be continuously monitored for the duration of the filling process. Under the effect of the locking unit, it continues as long as there is no active counter-rotation. 
     The support element is moved between the resting position and triggered position preferably by a coupling element. This coupling element is preferably connected to the operating part. The support element is mounted in a guide in relation to the coupling element so that it moves from the resting position into the triggered position when the rotary connecting element rotates in relation to the operating part. As long as the coupling exists between the operating part and rotary connecting element, such a relative rotation does not occur, and the support element remains in the resting position. Only after the torque-limiting coupling device is triggered does the relative rotation occur such that the guide moves the support element from the resting position into the triggered position. A type of sliding block guide is preferable as a guide where on the support element, or preferably on the coupling element, at least one guide rail or guide edge is provided, that triggers the described movement when engaged with an engaging element such as a projection, pin, etc. of the respective other element. 
     It is particularly preferable for the coupling element and support element to be designed as concentrically arranged ring elements where the guide is arranged in the area between the coupling element and support element. 
     In a preferred embodiment, the locking unit is formed by a coupling element and support element. The locking unit or guide is preferably formed by cams that engage in pockets in a mating element. The cams can preferably be formed on the coupling element whereas the pockets are provided in the support element. The reverse arrangement is equally possible. It is particularly preferable for the coupling element and a support element to be nested, preferably concentrically, and cams are formed on the inside of the coupling element. The support element can move axially in the resting position. Upon triggering, the support element moves axially, and the travel of the element can be determined by the sensor. The cams of the coupling element engage in the pockets formed in the support element, thereby locking it in the triggered position so that the coupling does not completely engage independent of further actuation in the closing direction; rather, the axial position continues to correspond to the triggered position, and the sensor can continue to transmit the release signal. The cams only slide out of the pockets when there is a counter-rotation in the direction of opening to axially release the coupling element so that it can return into the resting position. 
    
    
     
       In the following, embodiments of the invention will be described in greater detail with reference to drawings. In the figures: 
         FIG. 1  shows a partial schematic side view of a tank and a filling head arranged in front of it; 
         FIG. 2  shows a side view of the filling head and filler neck of a tank from  FIG. 1 ; 
         FIG. 3   a - 3   c  show a partial section along the line A . . . A from  FIG. 2  with a partial sketch; 
         FIG. 4  shows an exploded side view of a second embodiment of a filling head; 
         FIGS. 5 ,  6  show perspective exploded views of a coupling device of the filling head from  FIG. 4 ; 
         FIG. 7  shows a longitudinal section of the coupling device from  FIG. 5 ,  FIG. 6 ; 
         FIG. 8  shows a side view of a third embodiment of a filling head; 
         FIG. 9  shows an exploded side view of the third embodiment of a filling head according to  FIG. 8 ; 
         FIG. 10  shows a perspective exploded view of a coupling device of the filling head from  FIGS. 8 ,  9 ; 
     
    
    
       FIG. 1  schematically portrays a tank  12  with a filler neck of the tank  14  arranged thereupon and with a filling opening  16  as the terminus surrounded by an outer thread  18 . 
     In front of the filling opening  16 , a filling head  10  is arranged that is connected to a filling and ventilation pipe  20  that is connected via a hose  22  to a supply device (tank, pump, etc. that is not shown). 
     The filling head  10 , filling and ventilation pipe  20  and hose  22  in the illustrated example are equipment of a filling station for aqueous urea solution to fill the tank  12  arranged in a motor vehicle. Alternately, this solution can be also employed for other filling tasks using other liquids, especially fuel or other aggressive or hazardous liquids. 
     As shown in  FIG. 2 ,  3   a - 3   c , the filling head  10  with the projecting filling and centering pipe  24  is introduced into the filling opening  16  of the filler neck of the tank  14 . An inner threaded sleeve  26  as a threaded element on the filling head  10  is screwed onto the outer thread  18  of the filler neck of the tank  14  to ensure a mechanically secure and liquid-tight connection. This is done by rotating the operating sleeve  30 . In the addressed example as shown in  FIG. 3   a - 3   c , the screwed connection between the operating head  10  and filler neck of the tank  14  is created by rotating the operating sleeve  30  to the right until a flange on the filling head comes to rest and seals against the filler neck of the tank, and the filling process can begin. In an alternative embodiment, a left-hand thread can for example also be used. 
     To ensure that the threaded connection  18 ,  26  is not overtightened, a torque limiting coupling device  32  is provided as shown in the sketched example in  FIG. 3   b ,  3   c . This comprises a first coupling part  34  that is non-rotatably connected to the operating sleeve  30 , and a second coupling part  36  that is non-rotatably connected to the threaded element  26 . As shown in  FIG. 3   b , the coupling elements  34 ,  36  are coupled to each other in a resting state by means of locking pawls  38  that are pretensioned in the axial direction by means of spring elements  40  and extend out of guides within the first coupling element  34  into engaging seats  42  in the second coupling element  36 . 
     The locking pawls  38  establish a coupling between the first and second coupling elements  34 ,  36  so that they are initially non-rotatably coupled. 
     However, the seats  42  in the second coupling element  36  and the tips of the locking pawls  38  are arranged at an angle, that is, they contact each other at an angle of inclination that is greater than 0° and less than 90° in relation to the axial direction. The inclined plane that this formed generates force which acts within the guides on the locking pawls  38  in an axial direction, i.e., their potential shifting direction, counter to the force of the springs  40  in a rotation in the direction of closing with a corresponding application of pressure to the contact surfaces between the locking pawls  38  and seats  42 . Alternately to a flat surface under a constant angle of inclination, a curved shape with a variable angle of inclination could also be used. 
     If the force generated at the inclined contact surfaces exceeds the spring force, the locking pawls  38  are displaced out of the seats  42  of the bottom coupling part as shown in  FIG. 3   c , and thereby ensure that the bottom coupling part  36  is decoupled from the top coupling part  34 . The torque-limiting coupling device  32  is thereby triggered and, due to the decoupling, no longer transmits the torque applied to the operating sleeve  30  to the threaded element  26 . Instead, the top coupling part  34  slips with reference to the bottom coupling part  36 . 
     The torque at which the described decoupling occurs depends on the angle of inclination between the contact surfaces of the locking pawls  38  and seats  42  in the bottom coupling part  36 , on the pairing of the materials and resulting friction values, on the number of locking pawls  38  and the force of the springs  40 . A threshold torque can be set by suitably choosing these elements, wherein the coupling device  32  only transmits torque from the operating sleeve  30  to the threaded element  26  when rotating in the closing direction as long as the torque lies below the threshold. Once the screwed connection is fully established as shown in  FIG. 3   c  so that further rotation in the closing direction is impossible, applying torque to the operating sleeve above the threshold torque causes the torque-limiting coupling device  32  to be triggered. 
     The triggering of the torque-limiting coupling device  32  is detected by a sensor  41  that, depending thereupon, sends a release signal as an electrical signal via an electrical line  44 . In the illustrated embodiment, the sensor  41  detects the shift of at least one of the locking pawls  38  within the first coupling part  34 . In the home position shown in  FIG. 3   b  in which all locking pawls  38  still generate a coupling between the first coupling part  34  and the second coupling part  36 , the sensor  41  is arranged at a distance from one of the locking pawls  38 . If however this locking pawl  38  shifts axially to the rear as shown in  FIG. 3   c  as is the case when coupling device  32  is triggered, the sensor  41  detects the resulting new position of the locking pawl  38  and can emit a release signal. 
     The sensor  41  can be designed in this case as e.g. an optical sensor to determine the shift of the locking pawl  38  into the second position. The locking pawl  38  can also be designed as a ferromagnetic part, wherein the sensor  41  then can be designed as an inductive or capacitive sensor, or as a Hall sensor, to detect the locking pawl  38  in its second position. 
     The electrical line  44  is connected to a control device (not shown) for the entire filling station. The control device outputs the sensor signal and only releases the filling process when the release signal indicates that the connection has been established. 
     Consequently, at first the threaded element  26  of the filling head  10  must be completely screwed onto the filler neck of the tank  14  sufficiently and with such force before starting the filling process to have at least briefly triggered the torque-limiting coupling device  32 . In the illustrated embodiment, depending on the resulting state of the coupling element  34 ,  36 , the locking pawl  38  may return to the first coupling position under further rotation, and the sensor will not continue to emit a release signal even though the mechanical connection still exists. This can, however, be taken into account by a logic circuit that turns the transient release signal into a continuous signal, or by corresponding processing in the control device such that, as a result, a short release signal can be treated as sufficient for permanently releasing the filling process. 
     In a second embodiment of the invention according to  FIG. 4-7 , this logic function is realized mechanically, i.e., the mechanical design ensures that the release signal of a sensor is applied continuously as long as the connection exists, i.e., the release signal continues until the operating sleeve  30  is rotated in the direction of disconnection. 
       FIG. 4  shows elements of a filling head  100  according to the second embodiment of the invention. The filling head  100  according to the second embodiment and the filling head  10  according to the first embodiment have a number of commonalities. The same elements are identified by the same reference numbers. The differences primarily arise from the different design of the coupling device. 
     The individual components of the filling head  100  are shown in the exploded view in  FIG. 4 . A torque-limiting coupling device  132  is placed on the centering pipe holder  152 , wherein a helical spring  154  acts between the elements. A filling and centering pipe  24  is held on the centering pipe holder  152  in an assembled state and arranged coaxially within the coupling device  132 . A pipeline  156  connects the filling and ventilation pipe  20  to the filling and centering pipe  24  and serves to conduct the liquid, whereas the air displaced by the liquid while filling can flow back in the area around the line  156 . 
     In the assembled state, a operating sleeve  30  is placed over the outside of the elements of the filling head  100  so that the filling and centering pipe  24  extends therefrom at the front end. 
     As explained in association with the first embodiment, the operating sleeve  30  serves to operate the filling head  100  when screwing it onto a filler neck of the tank. An inner thread  26  that establishes the screwed connection to the filler neck of the tank is provided as a part of the torque-limiting coupling device  132  shown together with its elements in the enlarged views in  FIG. 5-7 . In  FIG. 5-7 , the consistently fixed elements that do not simultaneously rotate, i.e., the centering pipe holder  152  and filling and centering pipe  24 , are not shown for the sake of clarity. 
     As can be seen in the exploded view in  FIG. 5 , the coupling device  132  has a coupling ring  160  with a support ring  162  and a brake ring  164  arranged coaxially and sequentially within its interior. The brake ring  164  is mounted on the centering pipe holder  152  and is arranged in a nonrotating yet axially displaceable manner. The centering pipe holder  152  always remains fixed when the filling head is screwed onto the filler neck of the tank and therefore does not rotate with the operating sleeve  30  and the coupling ring  160  coupled thereto. In an assembled state ( FIG. 7 ), a magnetic ring  172  is arranged within the support ring  162  and has a magnetic field that can act on a reed switch element  141  depending on the axial position of the support ring  162 . In an alternative design (not shown), a more economical bar magnet is used instead of a magnetic ring  172 . 
     The coupling ring  160  in the illustrated example has four locking pawl elements that are evenly distributed over the circumference and each have an axial displaceable locking pawl  138 , a housing for guiding the locking pawl  138  in an axially displaceable manner, and a helical spring (not shown) inside to pretension the locking pawl toward the right in  FIG. 5-7 , i.e., the direction toward the rotary connecting element  26 . Fewer or more locking pawls can alternatively be provided. The tip of the locking pawls is designed asymmetrically and, in the illustrated example, has a bevel of approximately 45° to one side, whereas it terminates straight on the other side. 
     Integral with the threaded element  26  a coupling part  136  is provided with seats  42  which are, adapted to the shape of the locking pawls  138 , also designed asymmetrically, beveled on one side and straight on the other side. 
     In the assembled state, the locking pawls  138  engage in the seats  42  of the coupling part  136  and, in their home position established by the springs, therefore lock the coupling ring  160  to the second coupling part  136  and hence the threaded element  26  to initially create a nonrotating connection. As explained in the context of the first exemplary embodiment, on the one hand the shape of the locking pawls  138  and seats  42  that is beveled on one side as well as the axial displacability and spring-loading of the locking pawls  138  on the other hand form a torque-limiting coupling between the coupling ring  160 , that is nonrotatably connected to the operating sleeve  30  when the filling head  100  is in an assembled state, and the coupling element  136  and threaded element  26 , and it is triggered in the closing direction of the rotary connection between the threaded element  26  and filler neck of the tank above a threshold torque; however, in the opposite rotational direction, full coupling is generated without torque limitation due to the straight shape of the locking pawls  138  and seats  42 . 
     The purely mechanical function of the torque-limiting coupling device is hence already realized by the locking pawls  138  mounted in the coupling ring  160  and the coupling element  136 . Together with the magnetic ring  172  and reed switch  141 , the support ring  162  and brake ring  164  that have engaging teeth  168 ,  170  serve to generate an electrical release signal when the torque-limiting coupling device  132  has been triggered once while screwing the filling head  100  onto a filler neck of the tank, and serve to maintain this electrical signal until the filling head  100  is rotated in the opposite direction in the releasing direction of the rotary connection. 
     For this purpose, the coupling ring  160  has a plurality of pins  176  distributed over the circumference of its inner surface that project inward toward the support ring  162 . On its outer surface, the support ring  162  has matching guide tracks  178  in which the pins  176  are guided. 
     On the outer surface of the support ring  162 , the guides  178  run slanted at an angle of elevation relative to the longitudinal mid-axis and end on the left side in  FIG. 5-7  in a straight guide section  180  that runs parallel to the longitudinal mid-axis. 
     On its right side in  FIG. 5-7 , the support ring  162  has engaging prongs  182 . In a basic state ( FIG. 7 ), that is, without previously triggering the coupling element, the engaging prongs  182  are engaged in the seats  142 . At the same time, the teeth  170  of the support ring  162  are engaged in the teeth  168  of the brake ring  164 . Under the pressure supplied by the spring  154 , the brake ring  164  presses the support ring  162  axially to the right in  FIG. 5-7  toward the coupling element  136 . 
     If the filling head  100  is used without triggering the coupling device  132 , for example by screwing the threaded element  26  onto a filler neck of a tank without exceeding the threshold torque, the elements of the coupling device  132  shown in  FIG. 5-7  all rotate together with the exception of the brake ring  164 : The operating sleeve  30  rotates the coupling ring  160  connected nonrotatably thereto with the locking pawls  138 , and these cause the coupling element  136  to rotate along with the threaded element  26  integrally connected thereto. Since the engaging prongs  182  are engaged in the seats  42  of the threaded element  136 , the support ring  162  also rotates at the same time. The teeth  168 ,  170  slip in relation to the fixed brake ring  164 . 
     However, if the threshold torque is exceeded, thereby causing triggering of the coupling device  132  and a relative rotation between the coupling ring  160  and locking pawls  138  on the one hand and the coupling element  136  and threaded element  26  on the other hand, the support ring  162  and coupling ring  160  no longer move synchronously. Because the support ring  162  is coupled to the coupling part  136  by means of the engaging prongs  182 . This allows relative rotation between the support ring  160  and coupling ring  162 . 
     Under this relative rotation, the pins  176  guided in the guides  178  cause the support ring  162  to shift axially to the left in  FIG. 5-7 , i.e., opposite the initial tension from the brake ring  164  on which the spring  154  acts. The support ring  162  and the magnetic ring  172  firmly connected thereto hence lift in an axial direction. This causes the reed switch contact  141  to enter the magnetic field of the magnetic ring  172 . 
     The reed switch  141  is designed as an opening contact, i.e., the contact is initially closed without the influence of an external magnetic field so that an electrical short circuit is signaled via the connecting line. The effect of the magnetic field of the magnetic ring  172  that results from the described axial shift of the support ring  162  when the coupling device  132  is triggered opens the reed contact to create an electrical open circuit in the line. 
     This axially shifted position of the support ring  162  and associated constant release signal (electrical open circuit) exist until the coupling ring  160  is rotated in the opposite direction in the opening direction of the rotary connection. Then the support ring  162  shoves the pins  176  guided in the guides  178  axially back into the position on the right in  FIG. 5-7  so that the magnetic ring  172  moves away from the reed switch  174 , and the contact is closed after the effect of the magnetic field is removed. The release signal is canceled by the electrical short-circuit generated in this manner. 
       FIG. 8  shows a filling head  200  according to a third embodiment of the invention. The filling head  200  according to the third embodiment again has extensive commonalities with the previous embodiments. The same elements are identified by the same reference numbers. The differences primarily arise from the different design of the coupling device. 
     The individual components of the filling head  200  are shown in the exploded view in  FIG. 9 . As is the case with the second embodiment, a filling and centering pipe  24 , a centering pipe holder  152  and operating sleeve  30  are provided. 
     A torque-limiting coupling device  232  is formed by a threaded element  26  having an inner thread for screwing onto the filler neck of the tank and a support element  262  coupleable thereto having a magnetic ring  272  that as a whole is axially shiftable in relation to the coupling element  260 . The support element  262  has a ring of locking pawl elements  238 . Integral with the threaded element  26  a coupling part  236  is provided with seats  42  designed asymmetrically beveled on one side adapted to the shape of the locking pawls  238 . 
     In the basic position, the locking pawls  238  engage in the seats  42  of the coupling part  236 . A spring  254  acts upon the support ring  262  to ensure its engagement so that the coupling device  232  transmits torque in its basic position. 
     When the threshold torque is exceeded, the coupling device  232  is triggered as described with reference to the previous embodiments, wherein the support ring  262  shifts axially against the pressure of the spring  254  so that the locking pawls  238  slide out of the seats  42  along their angled contact surfaces. In this triggered position, the coupling device  232  is disengaged and slip occurs. 
     The axial shift of the support ring  262  and the magnetic ring  272  connected thereto is detected by a reed switch  241  acting as a sensor that emits an electrical release signal when the magnetic ring  272  approaches. 
     The support ring  262  and coupling ring  26   o  hence form a locking unit. As can be seen in particular in  FIG. 9 , especially the outer shape of the support ring  262  and the corresponding inner contour of the coupling ring  260  form a lock in the triggered position such that the support ring  262  remains in its axially shifted position, so that the magnetic ring  272  remains positioned next to the sensor  241  and continuously a release signal is emitted. 
     This lock is caused by cams  276  arranged on the inside of the support ring  260  that engage in a guide profile  278  in the support ring  262 . Pockets  279  are hence formed within the guide profile  278  on the support ring  262 . 
     In the resting position, the cams  276  lie within longitudinally extending channels of the guide profile  278 , thus rendering the support ring  262  axially shiftable. When the coupling device  232  is triggered by rotation in the closing direction, i.e. to the right in  FIG. 10 , and the support ring  262  correspondingly shifts axially against the pressure of the spring  254 , the cams  276  enter the pockets  279  formed by the guide profile  278  and axially lock the support ring  262  there in the triggered position. The cams  276  are locked in the pockets  279  by projections  281 . 
     The locked connection thus formed is only released upon counter-rotation. The cams  276  overcome the projections  281  and leave the pockets  279  to make the support ring  262  again axially moveable, and the locking pawls  278  slide back into the seats  42 . The magnetic ring  272  also moves away from the sensor  141  which causes the release signal to stop. 
     The particularly simple mechanics of the second embodiment also ensure that the coupling device  232  is reliably triggered when the threshold torque is exceeded, that this triggering is reliably detected by the travel of the support ring  262 , and that the release signal emitted by the sensor  241  continues until a counter-rotation is carried out in the opening direction. 
     Deviations from the illustrated embodiments are possible. In particular, the illustrated embodiments can be combined so that, for example, the inner design of the filling head  10  according to the first embodiment can be formed by a connecting piece, a pipeline and a centering pipe holder as shown for the second embodiment in  FIG. 4 .