Abstract:
A tire-pressure adjusting device for a vehicle tire inflation system distributes a compressed-air supply to a plurality of pneumatic apparatuses each comprising a rotary transmitter and measures the tire pressures of vehicle tires connected to the rotary transmitters. The tire-pressure adjusting device includes a control apparatus for receiving a pressure measurement signal and for outputting control signals and a modulation valve apparatus for receiving the control signals and for pneumatically activating one of a plurality of connected rotary transmitters in order to fill and to measure the pressure of at least one vehicle tire connected to the rotary transmitter. The modulation valve apparatus includes a rotary valve, which has a control element that can be rotated into a plurality of rotational positions. The control element activates one of the plurality of pneumatic apparatuses in each of the rotational positions of the control element.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a tire pressure adjustment apparatus for a tire inflation system of a vehicle. 
     BACKGROUND OF THE INVENTION 
     EP 1 051 302 B1 describes a tire pressure adjustment apparatus of the general type under consideration. In particular, in the case of agricultural vehicles such as tractors, for example, the tire pressure can be checked and adjusted by the vehicle itself. For this purpose, in the region of the wheel connections or wheel rims, rotary transmitters allow compressed air at the tire pressure to be transmitted to the connected vehicle tires of the vehicle wheels. It is thus possible for the tire pressure to be checked and for compressed air to be replenished or discharged. The tire pressure adjustment apparatus generally has a compressed-air port for a compressed-air supply, an electronic control device, a modulator valve device actuated by way of the electronic control device, and a pressure sensor that is read out by the control device. Through corresponding actuation of the modulator valve device, a pressure transmitter can be connected, for inflation purposes, to the compressed-air supply and can be connected, for pressure measurement purposes, to the pressure sensor. 
     In the case of a relatively large number of wheels or axles, the number of valves required in the modulator valve device correspondingly greatly increases, which leads to considerable outlay in terms of apparatus, generally with multiple valve stages for the successive distribution of the compressed air. Correspondingly, the number of solenoid valves that must be supplied with electrical current by the control device increases. 
     Also, the design of the rotary transmitters for a reliable sealing-off action during tire inflation and tire pressure measurement and for reliable separation during normal operation of the vehicle generally requires a certain level of outlay in terms of circuitry. Reliable rotary transmitters are, in part, designed with a control port for the sealing-off action, that is, for pneumatic coupling, and an inflation port for inflation and pressure measurement, in order to prevent leaks and faults during inflation and pressure measurement. In the case of such a design with two ports, it is, in turn, generally possible to provide a pneumatic device—preferably in the vicinity of the axle or tire—between the modulation valve device and the rotary transmitter, and connected to the pneumatic connecting line passing from the modulation valve device. The pneumatic device initially applies a pressure shock to the control port and subsequently aerates the inflation port. Such additional pneumatic devices for the actuation of rotary transmitters are correspondingly associated with a considerable level of outlay in terms of hardware. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to provide a tire pressure adjustment apparatus for a tire inflation system of a vehicle that permits reliable tire inflation and pressure measurement with relatively little outlay. 
     According to an embodiment of the present invention, the modulation valve device, which is provided for selectively connecting the individual rotary transmitters to the inflation port and to the pressure sensor, has a rotary valve with a rotatable positioner. The rotatable positioner is adjustable into multiple rotational settings or positions in which it connects in each case the compressed-air port and/or the pressure sensor to one of the rotary transmitters. 
     According to embodiments of the present invention, instead of providing a cascade or series of electropneumatic valves, a single rotary valve is employed that permits a selective assignment or distribution by way of its multiple rotational settings. With a greater number of rotary transmitters for actuation, an increasing, possibly even exponentially increasing, number of solenoid valves must be provided. It will be appreciated that a rotary valve with multiple rotational settings for the selective connection of one of several outlet ports permits a considerable reduction in outlay in terms of valve hardware. The conventional complex modulation valve device, which is provided between the compressed-air supply and the external connecting lines leading to the rotary transmitters, can thus be replaced, for example, with one pilot control valve device with a relatively small number of pneumatic and electropneumatic valves and the rotary valve. 
     The entire tire pressure adjustment apparatus together with the rotary valve, an upstream pilot control valve device, a control device and a pressure sensor can be accommodated in a common housing, such that the electrical lines formed between the control device and the rotary valve and the pilot control valve device for the transmission of control signals and a pressure measurement signal are accommodated entirely in the housing, without external electrical lines, which, in particular in the automotive sector, are subjected to high loads. The tire pressure adjustment apparatus can thus form a compact, reliable unit or a module that can be placed between the compressed-air supply and external connecting lines that lead to the rotary transmitters or to pneumatic devices that accommodate the rotary transmitters. 
     For this purpose, the rotary valve preferably has one or two internal connecting lines that connect an inlet port to one of several outlet ports. The rotary valve advantageously has a stator relative to which the positioner is rotatable. The compressed-air ports of the rotary valve, that is, the inlet and outlet ports, can be provided on the stator, such that the rotatable positioner serves merely for the selective connection of the corresponding ports of the stator. By means of such a design, the outlay in terms of hardware for forming the rotatable parts is low; the positioner, which must be adjusted mechanically, that is, for example a revolver or rotor, may basically be equipped substantially with one or more connecting lines, without more complex structure. 
     Thus, according to embodiments of the present invention, a rotational adjustment is intentionally selected that, by contrast to conventional solenoid valves, not only has two position states that can be set by linear adjustment but requires a rotation. In this way, it is possible to dispense with the formation of switching cascades or other hierarchical structures with a multiplicity of valves. In this case, a rotary valve is selected, as this preferably permits an adjustment in only one direction, the direction of rotation, and nevertheless a resetting movement into the initial position is possible because, in the case of a preferably symmetrical division, the initial position can be reached again after the predefined number of rotational settings. Thus, by means of a single positioning process, it is possible for multiple different rotational settings, and, in turn, an initial position, in particular neutral position or rest position, to be successively assumed by actuation. It is possible, despite the possibly greater number of settings, for the outlay in terms of hardware for adjustment purposes to be kept low. 
     An electric positioning drive apparatus actuated by the control device can be utilized to adjust the rotary valve into its admissible rotational settings. The electric positioning drive apparatus may for example be in the form of an electromechanical plunger that, when energized, performs a mechanical length adjustment in order to correspondingly rotate the rotary valve onward in a predefined direction of rotation. Alternatively, the drive may be provided by way of an electric stepper motor. 
     The rotary valve may, in different embodiments, receive and distribute a single compressed-air line or two compressed-air lines. In the case of the embodiment with a single compressed-air line, the rotary transmitters are thus actuated by way of a single pneumatic connecting line, for example with suitable pneumatic signal transmission as described in EP 1 051 302 B1, or by way of, in each case, one upstream pneumatic device that actuates a control inlet and inflation inlet of the rotary transmitter. 
     In the case of the embodiment with two compressed-air lines, two pneumatic lines may be formed in the rotatable positioner, such that an external control line and an external inflation line run to each rotary transmitter. In this way, a simpler design of the pneumatic devices close to the wheels is made possible, it no longer being the case that the pneumatic devices receive the pressure signals from a single pneumatic connecting line in order, from these, to successively permit an actuation of the control port and subsequently of the inflation port. 
     The rotatable positioner may furthermore be axially adjustable relative to the stator; in this way, an embodiment is made possible in which the rotatable positioner is remote or decoupled from the stator in the intermediate settings between the admissible rotational settings, and a pneumatic connection of the inlet port to the respective outlet port is realized only in the admissible rotational settings. For this purpose, a sliding or rolling device with axial adjustment may be provided between the stator and the rotatable positioner; the sliding or rolling device may be realized for example by way of a cam track or undulating track formed on one of the two components, and a sliding device or rolling device formed on the other component, such that, in each case, an axial offset is generated in the event of a rotation. 
     Between the rotatable positioner and the stator there may be mounted suitable spring devices. In one advantageous embodiment, a first spring device is provided, which separates the rotatable positioner from the stator or pushes the rotatable positioner away from the stator, and a second, opposing spring device is provided, which serves for generating a second spring force that pushes the rotatable positioner against the stator; in this case, the second spring force changes its spring strength in a manner dependent on the rotational setting. In the case of the embodiment with undulating tracks or cam tracks, the second spring device may be formed by individual springs, which are provided on an adjustable guide wheel or adjustable sliding head. The springs are thus compressed or relaxed to a greater extent in a manner dependent on the position on the cam track—peak or trough—such that, in the more intensely compressed state, the springs impart the relatively high spring force, which overcomes the opposing first spring force and leads to connection or coupling. 
     Furthermore, an embodiment of the rotary valve with ceramic surfaces that slide on one another may also be provided in which, for example on the stator, there is formed a pattern of holes, the individual holes being connected by connecting lines of the positioner in accordance with the rotational setting. 
     In the design of the rotary valve for the connection and/or distribution both of a control line and of an inflation line, it is advantageously the case that two connecting lines are formed in the rotatable positioner (or revolver or rotor). In this case, a first inlet port may be provided, for example radially in the center, that is, for example directly in the axis of rotation, and the other inlet port may be formed by an outer radial ring, such that a first connecting line connects the central hole to an inner circular ring of connection holes, and a second connecting line connects the radially outer ring to an outer circular ring of connection holes. Thus, the distribution of two lines by way of a single rotatable positioner is also possible using only one positioning drive apparatus. 
     The design of a rotary valve advantageously permits the integration of the pressure sensor and/or of the further valves of the pilot control valve unit, that is, of solenoid valves and pneumatic valves. In this case, bores may be formed in the stator, in which or to which the pressure sensor and/or the further valves of the pilot control valve unit are connected and/or integrated, such that a compact, reliable and robust design is made possible. 
     The rotary valve may be divided into six rotational settings, that is, adjusted in 60° steps. In this case, such a division permits the use of a uniform rotary valve, and possibly also of a uniform tire pressure adjustment apparatus, in different vehicles, both in two-axle and three-axle vehicles. This can cover most types of vehicle, both heavy goods vehicles and trailer vehicles, for example also agricultural vehicles such as tractors. 
     It is thus possible for a tire pressure modulator to be formed that, in one housing, accommodates both the rotary valve and the electric pilot-control valves between the compressed-air supply and the rotary valve. Furthermore, the electronics control unit (ECU) is advantageously also accommodated in the housing, such that electrical actuation and energization is performed entirely within the housing. External electrical lines outside the modulator housing are thus no longer necessary, whereby robustness and reliability are considerably increased. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements, arrangement of parts, and the various steps and the relation of one or more of such steps with respect to each of the others, all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is discussed in greater detail below with reference to the appended drawings, in which: 
         FIG. 1  shows an electropneumatic circuit diagram of a vehicle with a tire inflation system according to an embodiment of the present invention; 
         FIG. 2  shows a tire pressure adjustment apparatus of the tire inflation system according to an embodiment of the present invention, in the main position, in a section along the axis of rotation of the rotary valve; 
         FIG. 3  is an illustration, corresponding to  FIG. 2 , in an aeration position; 
         FIG. 4  is an illustration, corresponding to  FIG. 2 , in a tire pressure measurement position; 
         FIG. 5  shows further views of the rotary valve as per the embodiment depicted in  FIG. 2 ; 
         FIG. 6  is an illustration of a select-low valve for use with twin tires in accordance with an embodiment of the present invention; 
         FIG. 7  is an electropneumatic circuit diagram of a vehicle with a tire inflation system according to a further embodiment of the present invention with distribution of control pressure and pressure; and 
         FIG. 8  shows views of the distributor surface of the rotary valve of  FIG. 7 . 
     
    
    
     LIST OF REFERENCE CHARACTERS 
     
         
         
           
               1  Vehicle 
               2  Tire inflation system 
               3  Front tire 
               4  Rear tire 
               5  Compressed-air supply 
               6  Control device 
               8  Tire pressure modulator 
               8   a  Compressed-air inlet/inlet port 
               8   b  Housing 
               10  Front pneumatic devices 
               11  Rear pneumatic devices 
               14  2/2 shut-off valve (solenoid shut-off valve) 
               15  Pressure sensor 
               16  3/2 directional valve 
               18  Rotary valve 
               18   a  Inlet port 
               18   b ,  18   c ,  18   d ,  18   e  Outlet ports 
               19  Positioning drive apparatus 
               19   a  Electromagnetic plunger 
               19   b  Center of rotation 
               19   c  Electromagnet 
               20  Internal distributor line 
               21  External connecting lines 
               22  Rotary transmitter pressure controller 
               24  Rotary transmitter 
               24   a  Control port of the rotary transmitter 
               24   b  Inflation port 
               25  Tire pressure control valve 
               26  Throttle 
               28  Select-low valve device/twin-tire control valve 
               30  Stator 
               31  Bore 
               32  Revolver, positioner, rotor 
               33  Bores 
               34  Annular spring, spring device 
               35  Bore 
               36  Cylinder chamber 
               38  Ventilation port 
               39  Drive surfaces 
               40  Guide wheels 
               42  Cam track 
               42   a  Elevations (peaks) 
               42   b  Depressions (troughs) 
               44  Guides 
               45  Springs, second spring device 
               102  Tire inflation system 
               108  Tire pressure modulator 
               116   a ,  116   b  3/2 directional valves 
               118  Rotary valve 
               118   al  Inflation inlet port 
               118   a   2  Control inlet port 
               118   b   1  Inflation line outlet ports 
               118   b   2  Control line outlet ports 
               120   a ,  120   b  Internal distributor lines 
               121   a  External control line 
               121   b  External inflation line 
               128  Flow transfer shut-off valve 
               130  Stator 
               132  Revolver, positioner, rotor 
               218  Annular groove 
             S 1 , S 2 , S 3  First, second, third control signal 
             S 2   a  Control signal 
             S 2   b  Control signal 
             S 4  Pressure measurement signal 
             A Axis of rotation 
             P Arrow, direction of rotation 
           
         
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a vehicle  1  having a tire inflation system  2 , front tires  3 , and rear tires  4 . Front tires  3  and rear tires  4  are parts of the front wheels and rear wheels and are inflated by way of the tire inflation system  2 , wherein the tire pressure of the tires is advantageously regulated. The rear tires  4  are in each case dual tires or tires of dual wheels (twin tires). 
     The tire inflation system  2  is fed from a compressed-air supply  5 , which represents a connection to a compressor or advantageously to a reservoir that is connected to a compressor. The tire inflation system  2  has a tire pressure modulator  8  (TPC modulator, tire pressure control modulator), which is outlined by dashed lines and which serves as a tire pressure adjustment device, and pneumatic devices  10  and  11 , which are connected to the tire pressure modulator  8  by way of external distributor lines  21 . The front tires  3  are connected to the two front pneumatic devices  10 , and each of the two (twin) rear tires  4  of the dual wheels are connected to the two rear pneumatic devices  11 . 
     The tire pressure modulator  8  is pneumatically connected by way of a compressed-air inlet  8   a  to the compressed-air supply  5  and has an electronic control device  6  that, internally within the tire pressure modulator  8 , outputs control signals S 1 , S 2  and S 3  and receives a pressure measurement signal S 4 , the tire pressure modulator furthermore having a 2/2 shut-off valve (solenoid shut-off valve)  14 , which is connected to the compressed-air inlet  8   a  and which is actuated by way of the first signal S 1 , and a pressure sensor  15 , which is connected to the outlet of the 2/2 shut-off valve  14  and which outputs the pressure measurement signal S 4 . Furthermore, in parallel with the pressure sensor  15 , there is connected to the outlet of the 2/2 shut-off valve  14  a 3/2 directional valve  16 , which is switched by way of the second control signal S 2  and which, in rest position, imparts a blocking action and, when it receives the second control signal S 2 , connects the inlet of the pressure sensor  15  and the outlet of the 2/2 shut-off valve  14  to an inlet port  18   a  of a rotary valve  18 . 
     The rotary valve  18  is adjusted by way of an adjustment drive apparatus  19 , which is actuated by way of a third control signal (positioning signal) S 3 . The rotary valve  18  has the inlet port  18   a  and four outlet ports  18   b ,  18   c ,  18   d ,  18   e , wherein the outlet ports  18   b  and  18   c  are provided for the first pneumatic devices  10  of the front tires  3  and the outlet ports  18   d  and  18   e  are provided for the second pneumatic devices  11  of the rear tires  4 . The rotary valve  18  has a stator  30  and a positioner, the revolver  32 , which is rotatable relative to the stator  30  and in which there is formed an internal distributor line  20 , which is connected to the inlet port  18   a  and which, in the various rotational settings of the revolver  32 , is selectively connected to one of the outlet ports  18   b ,  18   c ,  18   d ,  18   e . In addition to the four operating switching positions there may advantageously also be provided a rest switching position (or, as shown here, two rest switching positions), in which the internal distributor line  20  is not connected to any of the outlet ports  18   b  to  18   e.    
     As can be seen from the schematic circuit diagram of  FIG. 1 , the outlet ports  18   b ,  18   c ,  18   d ,  18   e  are arranged so as to be distributed in the circumferential direction with the same radial spacing to an axis of rotation A; the internal distributor line  20  runs from the axis of rotation A radially outward, and in the various switching positions is connected to, in each case, one of the outlet ports  18   b  to  18   d . The internal distributor line  20  thus constitutes a distributor finger, which is adjustable in the rotational direction about the axis of rotation A. The positioning drive apparatus  19  adjusts the revolver  32  relative to the stator  30 ; for a simpler mechanical design, the rotational adjustment is advantageously performed in each case in a uniform rotational direction, indicated by arrow P, and by a fixed angle of rotation. In the case of the sixfold division shown in  FIG. 1 , the four rotational settings for the connection of  18   b ,  18   c ,  18   d ,  18   e  and two rest positions are provided. The 60° division advantageously makes it possible for even three-axle vehicles to be equipped therewith, and thus a uniform rotary valve can be used for most heavy goods vehicles and trailers. 
     The positioning drive apparatus  19  thus adjusts the revolver  32  in each case through 360°/6=60°, wherein, when all of the rotational settings are run through cyclically, a corresponding number of positioning processes can be performed. 
     By way of the first control signal S 1 , the control device  6  actuates the 2/2 shut-off valve  14  so as to start an inflation process and, for this purpose, to connect the compressed-air supply  5  to the 3/2 directional valve  16 . By way of the second control signal S 2 , the control device correspondingly actuates the 3/2 directional valve  16  so as to switch the latter from the blocking main position into a pass-through position, such that the rotary valve  18  is connected to the compressed-air supply  5 . If the 3/2 directional valve  16  is actuated with the 2/2 shut-off valve  14  closed, only the pressure sensor  15  is connected to the rotary valve  18 , without any influence being imparted by the compressed-air supply, thus permitting a pressure measurement of the pressure at the respectively connected outlet port  18   b ,  18   c ,  18   d ,  18   c.    
     The pneumatic devices  10  and  11  each serve, when charged with compressed air by the tire pressure modulator  8  via the, in each case, one external connecting line  21 , to pneumatically couple, that is, seal off, the initially decoupled tire  3  or  4  in a first step, and to subsequently permit an inflation and/or pressure measurement of the respectively connected tire  3  or  4  via the external connecting line  21  in a second step. For this purpose, the pneumatic devices  10  and  11  each have a rotary transmitter pressure controller  22 , which may be of structurally identical form in all pneumatic devices  10  and  11 , a downstream rotary transmitter  24 , a tire pressure control valve  25 , which is advantageously in the form of a flow transfer valve, and preferably a throttle  26 . In the case of the use of twin wheels or dual rear tires  4 , as is shown, an additional valve device is advantageously provided, in this case a select-low valve device  28  (also referred to as twin-tire control valve), which is in the form of a pneumatically double-acting 3/2 directional valve, such that the connected rear tire  4  with the relatively high pressure is connected through by the twin-tire control valve  28 , in each case, such that the inlet thereof is connected to the other rear tire  4 , such that automatic regulation is performed whereby it is always the tire with the relatively low pressure that is inflated. In this case, other twin-tire control valves  28 , such as are known per sc, or more complex valve devices, are however correspondingly also possible. 
     The valves  25 ,  28  and the throttle  26  are thus already provided in the rotating region of the respective wheel; the rotary transmitter  24  constitutes a pneumatically actuated clutch. During the sealing-off process, the rotary transmitter pressure controller  22  connects pressure to a control port  24   a  of the rotary transmitter  24  in a manner known per se, whereby the sealing-off of the rotary transmitter  24  is effected, such that subsequently, the inflation can be performed via an inflation port  24   b  of the rotary transmitter  24 , wherein the compressed air introduced during the inflation process is initially connected through by the tire pressure control valve  25 , which is in the form of a flow transfer valve, and subsequently inflates the front tires  3  and/or the rear tires  4 . Even during a subsequent pressure measurement, the tire pressure control valve  25  remains open, wherein the inflation port  24   b  also remains open. 
       FIGS. 2 to 4  show, by way of example, the construction of the tire pressure modulator  8 , which in this case also accommodates the control device  6 , such that electrical lines run only within the housing  8   b  of the tire pressure modulator  8 . The control device  6  (ECU) may be mounted on the housing  8   b  or on the inner side of a housing wall. The stator  30  is mounted fixedly in the housing  8   b ; the inlet port  8   a  is formed in the stator  30 . Furthermore, the electrically actuated (solenoid)  2 / 2  shut-off valve  14  and the pressure sensor  15  are accommodated in or on the stator  30 ; a bore  31  advantageously runs along the axis of rotation A through the stator  30 , such that the 2/2 shut-off valve  14  can for example be received in the bore  31 , and the pressure sensor  15  can be connected to the bore  31 . The stator  30  accommodates the revolver  32 , which serves as positioner and in which the internal distributor line  20  is formed. Between the revolver  32  and the stator  30  there is provided a spring device in the form of an annular spring  34 , which thus generates a spring preload in an axial direction, that is, in the direction of the axis of rotation A, and which, in the ventilation position shown in  FIG. 2 , lifts the revolver  32  from the stator  30 . In the stator  30  there are furthermore formed bores  33 , which run parallel to the axis of rotation A and which connect a cylinder chamber  36 , which is formed between the stator  30  and the revolver  32 , to the respective outlet ports  18   b  to  18   e . In the ventilation position of  FIG. 2 , it is thus the case that all of the outlet ports  18   b  to  18   e  are connected via the cylinder chamber  36 , and via a bore  35  running from the cylinder chamber  36  through the stator  30 , to a ventilation port  38  of the rotary valve  18 , which serves as compressed-air distributor, and the outlet ports are thus aerated. The compressed-air supply  5  is shut off by way of the 2/2 shut-off valve  14 , which is present in its blocking rest position. 
     The positioning drive apparatus  19  may, for example, act, as shown, on drive surfaces  39  of the revolver  32 , and is mounted on the housing. 
     In this embodiment of  FIG. 2 , coupling and decoupling of the revolver  32  in an axial direction is thus realized; for this purpose, guide wheels  40  are provided on a cam track  42  with elevations (peaks)  42   a  and depressions (troughs)  42   b , as can be seen in  FIG. 5 , which shows the guide wheels  40  correspondingly in a side view. The guide wheels  40  are guided in an axial direction in guides  44  and are pushed, in each case, against the cam track  42  by second spring devices, which are in the form of springs  45 , such that, as the revolver  32  rotates about the axis of rotation A and thus the cam track  42  formed on the revolver  32  rotates, the guide wheels perform spring-compression deflection movements in the axial direction. The cam track  42  is designed, or provided with an undulation, such that a coupling or pressing of the revolver  32  against the stator  30  is realized only in the admissible adjustment positions, in which the internal distributor line  20  connects the central bore  31  of the stator  30  to, in each case, one outlet port  18   b  to  18   e.    
     Thus, the spring strength of the annular spring  34 , which pushes the revolver  32  away from the stator  30 , and thus upward in  FIG. 2 , and the spring strengths of the second spring devices  45 , which push the revolver  32  downward in  FIG. 2  and thus against the stator  30 , are advantageously coordinated with one another. When the guide wheels  40  on the cam tracks  42  pass an elevation  42   a , the spring devices  45  are compressed, such that the spring force imparted by them increases and, in sum total, the spring devices  45  overcome the annular spring  34 ; and coupling takes place. 
       FIG. 3  shows an aeration position or admissible adjustment position. As shown by a comparison with  FIG. 5 , the guide wheels  40  are, in this case, bearing against elevations  42   a , whereas in  FIG. 2 , they are bearing against depressions  42   b . In this aeration position of  FIG. 3 , therefore, one of the four admissible distribution settings has been assumed. By way of its cam track  42 , the revolver  32  is pushed downward against the stator  30 . The ventilation path via the ventilation port  38  is closed off; the 2/2 shut-off valve  14  is actuated so as to open by way of a control signal S 2  from the control device  6 , and connects the compressed-air supply  5  via the open 2/2 shut-off valve  14  and the bore  31  of the stator  30 , the internal distributor line  20  in the revolver  32 , and the bore  33 , which is relevant in this case, to the desired outlet port  18   b  to  18   e , and thus via a respective pneumatic device  10  or  11  to a front tire  3  or rear tire  4 . 
     Opening and closing are thus performed by way of the cam track  42  and the guide wheels  40 . The actuation with the positioning drive apparatus  19 , that is, of the revolver drive, by way of the control signals S 3  is coupled to the transmission of the second control signal S 2  to the 2/2 shut-off valve  14 . 
     Following inflation, in each case, one tire pressure measurement is performed in the tire pressure measurement position of  FIG. 4 , in which the revolver  32  is not adjusted relative to the inflation position of  FIG. 3 , that is, remains in its respective rotational setting; thus, no control signal S 3  is output. By contrast, by way of the second control signal S 2 , the 2/2 shut-off valve  14  is closed, such that the compressed-air supply  5  is shut off. Thus, the pressure sensor  15  remains connected via the bore  31 , the internal distributor line  20 , the respective bore  33  and an unchanged rotary transmitter pressure controller  22 , and further unchanged valves  25  and possibly  28 , to the respective front tire or rear tire  4 , such that the pressure sensor  15  can thus perform a pressure measurement and thus outputs a pressure measurement signal S 4  to the control device  6 . The ventilation path via the ventilation port  38  thus remains blocked. 
     The plan view of  FIG. 5  shows a design of the positioning drive apparatus  19 , which, in this case, is provided in the form of an electromagnetic plunger  19   a , which is mounted at a center of rotation  19   b  and which, when it receives a control signal S 3 , is attracted by an electromagnet  19   c  (for example counter to the action of a spring) such that the electromagnetic plunger is pivoted about its center of rotation  19   b  and, during adjustment, actuates, in each case, one of the drive surfaces  39 , that is, pivots the revolver  32  in the direction of rotation indicated by the arrow P. In the case of the cam track design, an adjustment from a depression  42   b  to an elevation  42   a  or slightly beyond the latter can be sufficient, such that subsequently the guide wheel  40  rolls down, under the relaxation action of its spring device  45 , into the following depression  42   b.    
     Other electrically actuated adjustment drive devices  19  are basically also possible. 
       FIG. 6  shows a select-low valve device  28 . That rear tire  4  of the twin-tire system, which is at the lower pressure, is always automatically connected. In the event of line leakage or a tire defect, the intact tire is automatically protected, as it is shut off by the select-low valve device  28  formed as flow transfer valve. By means of a defined switching hysteresis, for example of 0.1 bar, it can be ensured that, in the event that both rear tires  4  are at the same pressure, no high-frequency oscillation of the select-low valve device  28  can occur. 
       FIG. 7  shows a further embodiment of a tire inflation system  102 , in which identical or similar elements are denoted by the same or similar reference signs to those in  FIG. 1 . In this embodiment, two-stage actuation of the rotary transmitter  24  is no longer necessary; instead, by way of the tire inflation pressure modulator  108 , an external control line  121   a  and an external inflation line  121   b  are actuated separately. For this purpose, in the revolver  132 , there are provided two internal distributor lines  120   a  and  120   b , which are adjusted, in each case, in parallel or simultaneously. For this purpose, the tire pressure modulator  108  has two 3/2 directional valves  116   a  and  116   b , which are actuated by way of control signals S 2   a , S 2   b  of the control device  6 . By way of the 3/2 directional valve  116   a , the compressed-air supply  5  is connected directly to the control inlet port  118   a   2  of the rotary valve  118 , and via the internal distributor line  120   a  in the respective switching position to a control line  121   a  and to the control port  24   a  of the respective rotary transmitter  24 , whereby sealing (coupling) is thus realized; subsequently, the first control signal S 1  is output to the 2/2 shut-off valve  14 , and outputting of the control signal S 2   b  causes the further 3/2 directional valve  116   b  to be opened, such that the rotary valve  118  is supplied with compressed air by way of its inflation inlet port  118   al  and—with unchanged rotational setting or switching position—outputs compressed air via the internal distributor line  120   b  and an external inflation line  121   b  to the inflation port  24   b  of the rotary transmitter  24 . 
     The front tires  3  are, in turn, connected via a tire pressure control valve  25 , in the form of a simple flow transfer valve (2/2 flow transfer shut-off valve), and possibly a throttle  26 , to the rotary transmitter  24 . The valve configuration at the rear tires  4  may correspond. In the embodiment shown, a flow transfer valve  128  is provided by way of the tire pressure control valve  25  and the throttle  26  in parallel for each rear tire  4  of a twin tire; it is basically also possible here for some other valve configuration to be provided for the rear tires  4 . 
     In the embodiment of  FIG. 7 , therefore, the rotary transmitter pressure controller  22  of  FIG. 1  is omitted, because owing to the parallel transfer of the two external connecting lines  121   a  and  121   b , that is, of the control line  121   a  and the inflation line  121   b , correspondingly direct actuation of the ports  24   a  and  24   b  of the rotary transmitter  24  is possible. It is basically also possible in the embodiment of  FIG. 7  for coupling and decoupling to be realized by way of a cam track or some other axial adjustment. 
     Advantageously, the revolver  132  is in the form of a ceramic revolver, which bears against a ceramic surface; a design without or with axial adjustment may be provided. In  FIG. 8 , bores or ports are provided in a stellate pattern in the stator  130 ; a central port is provided as an inflation line inlet port  118   a   1  in the center of the stator  130 ; by contrast, the control inlet port  118   a   2  is provided eccentrically and is connected to an annular groove  218 . Furthermore, in the stator  130 , inflation line outlet ports  118   b   1  are provided on an inner circular path, to which inflation line outlet ports the external inflation lines  121   b  are connected, and control line outlet ports  118   b   2  are provided on an outer circular path, to which control line outlet ports, in each case, one external control line  121   a  is connected. 
     The internal distributor lines  120   a  and  120   b  are provided in the revolver  132  as per  FIG. 8 ; the internal distributor line  120   b  serves for the connection of the central inflation line inlet port  118   al  to an inflation line outlet port  118   b   1  formed on the inner circular path. Correspondingly, the internal distributor line  120   a  serves to connect, in each case, the outer control inlet port  118   a   2  to a control line outlet port  118   b   2  provided on an outer circular path. Thus, the two internal distributor lines  120   a  and  120   b  can, in each case, connect corresponding ports to one another simultaneously. 
     Thus, in the embodiment of  FIGS. 7 and 8 , the following steps of the inflation and measurement process are performed: 
     Proceeding from the rest position, inflation is performed in that, firstly, by way of the control signal S 3 , a corresponding position of the revolver  132  is set such that the respective front tire  3  or rear tire  4  is connected. Subsequently, by way of the control signal S 2   a , the 3/2 directional valve  16   a  for the control line is opened, and thus the control port  24   a  is aerated via the external control line  121   a  on the respective rotary transmitter  24 , and thus a sealing action is applied. Subsequently, the first control signal S 1  and the control signal S 2   b  are output simultaneously or successively, and thus compressed air is output via the external inflation line  121   b  and the rotary transmitter  24  and the opening tire pressure control valve  25  to the respective tire  3  or  4 . 
     For the measurement of the pressure, the control signal S 2   a  continues to be output. The first control signal S 1  is deactivated, such that the 2/2 shut-off valve  14  assumes a blocking position. By way of the external inflation line  121   b , a pressure measurement by means of the pressure sensor  15  can thus be performed. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.