Method for operating a compressed-air supply system controlled by the water load value of the granular desiccant; corresponding vehicle compressed-air supply system

Abstract

The invention relates to a method for operating a compressed-air supply system (1), which supplies compressed air to connected compressed-air consumers (16, 18; 20) via at least one compressed-air line (24), wherein the compressed-air supply system has at least one compressor (2), an air dryer (5) and a switchover valve (12), the air dryer (5) having a granular adsorption desiccant (10), the switchover valve being actuable by means of an electronic control device (14), in a first switching position (A) of the switchover valve (12) moist compressed air generated by the compressor being passed over the grains of the adsorption desiccant in a drying phase, as a result of which the adsorption desiccant absorbs atmospheric moisture from the moist compressed air, and in a second switching position (B) of the switchover valve (12) dry compressed air taken from the compressed-air supply system being passed over the grains of the adsorption desiccant in a regeneration phase, as a result of which the adsorption desiccant releases moisture to the dry compressed air, which is then subsequently discharged to the surrounding area (28). According to the invention, a water load value indicating the current water load of the adsorption desiccant is ascertained in the control device, the water load value is determined by means of at least two numerical values, and the switchover valve (12) is controlled with respect to the start and the duration of the drying phase and / or the regeneration phase depending on the water load value.

Description

[0001] Hanover, September 16, 2024 IP, Copi, Marondel / sw 303483-DE-NP EM 303483

[0002] Method for operating a compressed air supply system

[0003] The invention relates to a method for operating a compressed air supply system, for example of a vehicle, which supplies connected compressed air consumers with compressed air via at least one compressed air line, wherein the compressed air supply system comprises at least one compressor, one air dryer and one switching valve, wherein the air dryer comprises a granular desiccant, wherein the switching valve can be actuated by means of an electronic control device, wherein in a first switching position A of the switching valve, moist compressed air generated by the compressor is passed over the granules of the desiccant in a drying phase, whereby the desiccant absorbs moisture from the moist compressed air, and wherein in a second switching position B of the switching valve, dry compressed air taken from the compressed air supply system is passed over the granules of the desiccant in a regeneration phase.This causes the desiccant to release moisture into the dry compressed air, which is then subsequently released into the environment.

[0004] From DE 24 19 178 A1, it is known that when air is drawn in and compressed from the atmosphere, compressed air is produced which is supersaturated with water vapor. After condensation is removed from the compressed air, it must be further dried in a compressed air generation system to prevent corrosion or ice formation at low temperatures in the components supplied with this compressed air. In known compressed air supply systems, an air dryer is typically used for this purpose, which is subjected to the generated compressed air. Such air dryers usually have a replaceable cartridge attached to the housing, in which a granular desiccant is arranged. When moist compressed air is passed over this desiccant, it absorbs a large proportion of the moisture present in the compressed air.The result is sufficiently dry compressed air that can be supplied to a compressed air tank and / or compressed air consumers via compressed air lines of a compressed air system.

[0005] Since the desiccant's capacity to absorb moisture or water is limited, the water must be removed from the desiccant as needed, i.e., it must be regenerated. When the compressor is not running, this is typically done by drawing dry air, also known as regeneration air, from a previously filled compressed air tank and / or from the compressed air lines of the compressed air system, depressurizing it to ambient pressure, and then passing it in the opposite direction through the air dryer or over the desiccant contained in the cartridge. During this process, the desiccant releases water into the regeneration air and is thus dried. The water-enriched regeneration air is then released into the environment.

[0006] In the aforementioned DE 24 19 178 A1, the process for regenerating the desiccant is controlled depending on the moisture content of the compressed air in a compressed air tank of a compressed air generation system. For this purpose, a humidity sensor that determines the compressed air humidity and a switching valve are used. To enable the cost-effective production of a compressed air generation system, it would be advantageous if such a humidity sensor were not required.

[0007] To operate a compressed air generation system as efficiently as possible with regard to energy consumption, the described regeneration process should not be carried out too frequently, as this results in a loss of compressed air from the system or the compressed air tank located therein. Furthermore, the compressor is typically not operated during a regeneration process, meaning no additional compressed air is generated during regeneration phases. Therefore, it is crucial to know the current air-drying capacity of the desiccant in the air dryer as precisely as possible.

[0008] To determine the air-drying capacity of the desiccant, the volume of moist compressed air supplied to the air dryer is conventionally measured during an air-drying phase. Previous tests have roughly determined the maximum volume of compressed air that can adequately dry the desiccant in the air dryer under standardized ambient conditions. Once this volume of moist compressed air is reached, the compressor is switched off or not restarted, and the described regeneration process is then carried out.

[0009] The volume of dry compressed air required for regeneration, i.e., drying the desiccant, was also previously determined through experiments. Knowing the flow rate of the compressed air through the air dryer, the necessary duration of the regeneration process can then be determined, and a switching valve can be controlled accordingly.

[0010] While this described procedure does function, it is unsatisfactory because it disregards many influencing factors that affect air drying behavior and the regeneration behavior of the desiccant. For example, the control values ​​mentioned above, determined through experiments, are only valid for the specific air dryers and their desiccant cartridges under investigation, including the quantity, arrangement, and type of desiccant. Furthermore, only standardized environmental conditions are used for the aforementioned experiments.

[0011] The object of the invention is therefore to present a method for operating a compressed air supply system which can determine the optimal time for the start and duration of a regeneration process on an adsorption desiccant of an air dryer and control this regeneration process accordingly. The aim is to keep the number and / or duration of regeneration processes as low as possible.

[0012] This problem is solved by a method for operating a compressed air supply system with the features of claim 1. Advantageous further developments are defined in the dependent claims.

[0013] Accordingly, the invention relates to a method for operating a compressed air supply system which supplies connected compressed air consumers with compressed air via at least one compressed air line, wherein the compressed air supply system comprises at least one compressor, one air dryer and one switching valve, wherein the air dryer comprises a granular desiccant, wherein the switching valve can be actuated by means of an electronic control device, wherein in a first switching position A of the switching valve, moist compressed air generated by the compressor is passed over the granules of the desiccant in a drying phase, whereby the desiccant absorbs moisture from the moist compressed air, and wherein in a second switching position B of the switching valve, dry compressed air taken from the compressed air supply system is passed over the granules of the desiccant in a regeneration phase.This causes the desiccant to release moisture into the dry compressed air, which is then subsequently released into the environment.

[0014] The task at hand is solved in this method by determining a water loading value in the control device that indicates the current water loading of the adsorption desiccant, by determining the water loading value using at least two numerical values, and by controlling the switching valve with regard to the start and duration of the drying phase and / or the regeneration phase depending on the water loading value.

[0015] The term "water loading of the desiccant" refers to the amount of water stored in the desiccant of the air dryer. The water loading value is given, for example, in grams per cubic meter or per cubic centimeter.

[0016] By using at least two numerical values ​​to determine the water content of the desiccant, its remaining drying capacity can be determined much more accurately than before. This allows the number and / or duration of regeneration processes to be kept to an optimal minimum.

[0017] It is advantageous if the at least two numerical values ​​used to describe the water load of the desiccant represent constant or time-varying physical-technical quantities. Constant physical-technical quantities are those that do not change during the process, such as the diameter of the cartridge in which the desiccant is arranged, and / or the quantity of the desiccant, and / or its physical properties. Time-varying physical-technical quantities include, for example, the ambient temperature or the flow rate of the compressed air passed through the air dryer or its cartridge during a regeneration process.

[0018] With regard to the physical-technical quantities, it may be intended that at least two of the following quantities are used to determine the water loading of the adsorption desiccant:

[0019] - the volume of compressed air passed through the desiccant,

[0020] - the water absorption capacity of the adsorption desiccant,

[0021] - the water release capacity of the adsorption desiccant,

[0022] - the ambient temperature,

[0023] - the temperature of the adsorption desiccant,

[0024] - the pressure of the dry compressed air supplied to the adsorption desiccant,

[0025] - the temperature of the dry compressed air supplied to the adsorption desiccant,

[0026] - the temperature of the moist compressed air supplied to the adsorption desiccant,

[0027] - the flow rate of the dry compressed air supplied to the adsorption desiccant,

[0028] - the flow rate of the moist compressed air supplied to the adsorption desiccant,

[0029] - the mean flow path length through the adsorption desiccant,

[0030] - the geometry of the grains of the adsorption desiccant,

[0031] - the size of the adsorption desiccant grains,

[0032] - the porosity of the granules of the adsorption desiccant,

[0033] - the volume of the pores in the grains of the adsorption desiccant,

[0034] - the arrangement of the granules of the adsorption desiccant,

[0035] - the packing density of the adsorbent granules,

[0036] - the mass of the desiccant adsorbed onto the air dryer,

[0037] - the sum of all granules of the desiccant adsorbed onto the air dryer,

[0038] - the value for the total surface area of ​​the adsorption desiccant granules arranged on the air dryer,

[0039] - the specific heat capacity of the adsorption desiccant grains, - the diffusion rate of water radially into a grain of the adsorption desiccant at a given operating temperature of the adsorption desiccant,

[0040] - the diffusion rate of water radially out of the grain of the adsorption desiccant at a given operating temperature of the adsorption desiccant.

[0041] In a further embodiment of the process, it may be provided that the water absorption capacity and the water release capacity of the granules of the adsorption desiccant in its radially outer region and in its radially inner region are taken into account.

[0042] This process characteristic is based on the understanding that water penetrates the surface of each granule of the desiccant more quickly than its subsequent deeper penetration into the granule. If such a granule is conceptually divided into radially adjacent layers, the surface area of ​​each layer, and thus its absolute water absorption capacity, decreases with further radial penetration. Furthermore, penetration into the granule is energetically easier at the outer surface than further radially inward. In summary, water penetrates the granule more easily at the outer edges than at the inner edges. However, the behavior may differ when considering the opposite radial direction.For example, it may be useful to direct the moist compressed air supplied by the compressor through the air dryer or its desiccant cartridge at a different flow rate during a drying phase than the dry compressed air during a regeneration process.

[0043] Based on the above findings, it is therefore possible to control the switching valve with regard to the start and duration of the drying phase and / or the start and duration of the regeneration phase, depending on short-duration and long-duration air drying conditions at the granules of the desiccant, or more generally at the desiccant itself. A short-duration air drying condition is, for example, the easier penetration of water into the outer surface of a granule of the desiccant. A long-duration air drying condition is, for example, the poorer penetration of water in the radially inner region of a granule of the desiccant.

[0044] Furthermore, based on the aforementioned findings regarding the drying phases, it can be taken into account that the granules of the desiccant have a radially outer region and a radially inner region, each with a certain radial extent and permeated by water at different rates. Based on a previously determined average geometry, average size, and porosity of the desiccant granules, a first average diffusion rate for water within the granules is determined. This rate represents the rate at which water moves into the granules from the radial outside to the radial inside during a drying phase. This first average diffusion rate is then used to determine the optimal time to begin and / or the optimal duration of a drying phase.

[0045] Similarly, with regard to the regeneration phases, it can be provided that the granules of the adsorption desiccant have a radially outer area and a radially inner area, each of which has a certain radial extent and is penetrated by water at different speeds.

[0046] Based on a previously determined mean geometry, mean size and porosity of the adsorption desiccant grains, a second mean diffusion rate for water in the grains is determined, at which water moves from radially inside to radially outside during a regeneration phase, and this second mean diffusion rate is taken into account for determining an optimal time of initiation and / or an optimal duration of the regeneration phase.

[0047] If the granules of the adsorption desiccant have different properties with regard to radial water transport, another embodiment of the process may provide that, after a sufficient quantity of compressed air has been generated for the respective application, several regeneration phases are carried out in quick succession, with sufficient time elapsed between the respective regeneration phases so that, taking into account the two diffusion rates, a worthwhile amount of water has penetrated from the radially inner region of the granules of the adsorption desiccant into the radially outer region of these granules for a subsequent short regeneration phase.

[0048] It can also be provided that, after a sufficient quantity of compressed air has been generated for the respective application, a regeneration process is carried out as soon as a predetermined large, radially outer area of ​​the adsorption desiccant granules has been recharged with water by a previous drying process.

[0049] It can be defined that the radially outer region of the adsorption desiccant grains is determined to be large enough to comprise 30% to 60%, preferably 40%, of the average volume of the adsorption desiccant grains.

[0050] However, it can also be specified that the radially outer area of ​​the adsorption desiccant grains is determined to be so large that it comprises 30% to 60%, preferably 40%, of the moisture absorption capacity of the adsorption desiccant grains.

[0051] The control unit can also control the switching valve with regard to the start and duration of a drying phase and / or a regeneration phase depending on the determined spatial distribution of the water load of the adsorption desiccant granules within a cartridge of the air dryer.

[0052] It can be provided that the axial and / or radial spatial distribution of the water content of the adsorption desiccant granules at the air dryer is described by a two-dimensional mathematical matrix, the first dimension of which represents the flow direction of the compressed air through the adsorption desiccant, and the second dimension of which indicates the number of radial regions of the adsorption desiccant granules that are more or less saturated with water. Furthermore, it can be provided that the total amount of water present at the air dryer is determined from the information about the axial and / or radial spatial distribution of the water content of the adsorption desiccant granules, and that the switching valve is controlled with regard to the start and duration of a drying phase and / or a regeneration phase depending on the determined total amount of water in the adsorption desiccant.

[0053] Furthermore, it may be provided that the volume of compressed air and its humidity are determined in at least one compressed air line and / or in at least one compressed air reservoir of the compressed air supply system and / or in at least one device that can be operated by means of compressed air, and that the determined total volume of dry compressed air and its humidity value are used to control the start and / or duration of a regeneration phase.

[0054] The method according to the invention can also be used in a compressed air supply system that includes at least one compressor, one air dryer, one switching valve, one control unit, and additionally a humidity sensor. In this case, the method is used as a virtual, indirectly acting humidity sensor, which is used to control the switching valve as a replacement for the actual humidity sensor only when the latter malfunctions. This may seem superfluous at first glance; however, knowledge of the air dryer's drying capacity plays a crucial role, especially in the operation of a commercial vehicle, so the described redundancy represents a genuine improvement.

[0055] Finally, the invention also relates to a compressed air supply system for a vehicle, by means of which compressed air consumers can be supplied with compressed air, wherein the compressed air supply system comprises at least one compressor, one air dryer, and a switching valve controllable by a control device, as well as optionally a humidity sensor, wherein the aforementioned compressed air components are connected to one another via compressed air lines, and in which a granular desiccant is arranged in the air dryer. According to the invention, the control device for carrying out the method according to at least one of the method claims is designed and arranged in this compressed air supply system.

[0056] The invention is explained in more detail below with reference to the embodiment shown in the accompanying drawing. The drawing shows

[0057] Fig. 1 shows a simplified schematic representation of a compressed air supply system of a vehicle, on whose air dryer a regeneration process for its adsorption desiccant can be carried out, and

[0058] Fig. 2 shows the compressed air supply system according to Fig. 1, which additionally has a humidity sensor.

[0059] Figure 1 shows the compressed air supply system 1 of a vehicle, comprising a compressor 2, an air filter 4, an air dryer 5, a control unit 14, a changeover valve 12 controllable by the control unit 14, a multi-circuit protection valve 15, two compressed air consumers 16, 18, and a compressed air reservoir 20. The air dryer 5 has a housing 6 to which a cartridge 8 is replaceably attached. The cartridge 8 contains a granular desiccant 10, by means of which compressed air supplied by the compressor 2 via the air filter 4 to the air dryer 5 can be dried. For this purpose, the compressed air flows through compressed air lines shown as arrows, of which only one compressed air line 24 is labeled.

[0060] Coming from the air dryer 5, the dried compressed air passes via the switching valve 12 to the multi-circuit protection valve 15, from where the compressed air is directed as required to at least one of the compressed air consumers 16, 18 and / or to the compressed air tank 20.

[0061] The changeover valve 12 is designed as a solenoid valve with two switching positions A and B and is connected to the control unit 14 via a first control line 26. The control unit 14 is also connected to the compressor 2 via a second control line 27 and controls its operation. Furthermore, the control unit 14 is connected via at least one sensor line 21 to sensors 32 for recording physical and technical values, which provide the control unit 14 with information about the operating conditions of the compressed air supply system 1 and about the basic and current water retention capacity of the desiccant 10. This first sensor line 21 could, for example, be a CAN bus line.

[0062] As illustrated in Fig. 1, the compressed air supplied by the compressor 2 is dried in a drying phase in the air dryer 5 and then directed as required via the switching valve 12, which is switched in its first switching position A, and via the multi-circuit protection valve 15 to the compressed air consumers 16, 18 and the compressed air reservoir 20.

[0063] In Fig. 2, the changeover valve 12 is switched to its second switching position B by means of the control device 14, so that dry compressed air coming from the compressed air tank 20 is guided through the multi-circuit protection valve 15 and the changeover valve 12 in the opposite flow direction through the air dryer 5 during a regeneration phase. Here, the adsorption desiccant 10 is dried by the supplied compressed air, which is then discharged, now carrying moisture, into the environment 28.

[0064] In contrast to Fig. 1, the compressed air supply system 1 according to Fig. 2 has a humidity sensor 30, which is arranged in the pressure medium line 24 between the changeover valve 12 and the multi-circuit protection valve 15. The humidity sensor 30 is connected to the control unit 14 via a second sensor line 22, so that the control unit is always informed about the humidity of the compressed air downstream of the air dryer 5 and can control the changeover valve 12 with regard to the regeneration or drying of the adsorption desiccant 10.

[0065] If the humidity of the compressed air, as determined by the humidity sensor 30, exceeds a previously defined humidity limit, this indicates that the air-drying capacity of the desiccant 10 at the air dryer 5 will soon no longer be sufficient to dry the compressed air supplied by the compressor 2 as intended. Consequently, the compressor 2 is switched off or remains switched off, and a regeneration process is carried out after the changeover valve 12 is actuated to its second switching position B.

[0066] In the event of a failure or technical malfunction of the humidity sensor 30, the method according to the invention takes over the determination of the air-drying capacity of the adsorption desiccant 10 as described. Based on this information, the control unit 14 controls the compressor 2 and the switching valve 12 to carry out a drying phase or a regeneration phase.

[0067] Reference numeral list (part of the description)

[0068] Compressed air supply system

[0069] compressor

[0070] Air filter

[0071] Air dryer

[0072] Air dryer housing

[0073] Cartridge with desiccant for the air dryer

[0074] Adsorption drying agent

[0075] Diverter valve

[0076] Control unit

[0077] Multi-circuit protection valve

[0078] First compressed air consumer

[0079] Second compressed air consumer

[0080] Compressed air tank; (compressed air consumer)

[0081] First sensor line, CAN bus line

[0082] Second sensor line

[0083] compressed air line

[0084] First control line

[0085] Second control line

[0086] Vicinity

[0087] humidity sensor

[0088] Additional sensors

Claims

Patent claims 1. Method for operating a compressed air supply system (1) which supplies connected compressed air consumers (16, 18; 20) with compressed air via at least one compressed air line (24), wherein the compressed air supply system (1) comprises at least one compressor (2), one air dryer (5) and one changeover valve (12), wherein the air dryer (5) comprises a granular desiccant (10), wherein the changeover valve (12) is actuated by means of an electronic control device (14), wherein in a first switching position (A) of the changeover valve (12) moist compressed air generated by the compressor (2) is passed over the granules of the desiccant (10) in a drying phase, whereby the desiccant (10) absorbs moisture from the moist compressed air,and wherein, in a second switching position (B) of the changeover valve (12), dry compressed air taken from the compressed air supply system (1) is passed over the granules of the adsorption desiccant (10) in a regeneration phase, whereby the adsorption desiccant (10) releases moisture to the dry compressed air, which is then subsequently discharged into the environment (28), characterized in that a water loading value indicating the current water loading of the adsorption desiccant (10) is determined in the control device (14), that the water loading value is determined by means of at least two numerical values, and that the changeover valve (12) is controlled with regard to the start and duration of the drying phase and / or the regeneration phase depending on the water loading value.

2. Method according to claim 1, characterized in that the at least two numerical values ​​represent constant or time-changing physical-technical quantities.

3. Method according to claim 2, characterized in that at least two of the following parameters are used to determine the water loading of the adsorption desiccant (10): - the volume of compressed air passed through the adsorption desiccant (10), - the water absorption capacity of the adsorbent desiccant (10), - the water release capacity of the adsorption desiccant (10), - the ambient temperature, - the temperature of the adsorption desiccant (10), - the pressure of the dry compressed air supplied to the adsorption desiccant, - the temperature of the dry compressed air supplied to the adsorption desiccant, - the temperature of the moist compressed air supplied to the adsorption desiccant, - the flow rate of the dry compressed air supplied to the adsorption desiccant (10), - the flow rate of the moist compressed air supplied to the adsorption desiccant (10), - the mean flow path length through the adsorption desiccant (10), - the geometry of the grains of the adsorption desiccant (10), - the size of the adsorption desiccant grains (10), - the porosity of the granules of the adsorption desiccant (10), - the volume of the pores in the grains of the adsorption desiccant (10), - the arrangement of the granules of the adsorption desiccant (10), - the packing density of the adsorbent granules (10), - the mass of the adsorption desiccant (10) at the air dryer, - the sum of all granules of the adsorption desiccant (10) at the air dryer, - the value for the total surface area of ​​the granules of the adsorption desiccant (10) arranged on the air dryer (6), - the specific heat capacity of the granules of the adsorption desiccant (10), - the diffusion rate of water radially into a grain of the adsorption desiccant (10) at a predetermined operating temperature of the adsorption desiccant (10), - the diffusion rate of water radially out of the grain of the adsorption desiccant (10) at a given operating temperature of the adsorption desiccant (10).

4. Method according to one of the preceding claims, characterized in that the water absorption capacity and the water release capacity of the granules of the adsorption desiccant (10) are taken into account in a radially outer region and in a radially inner region of the adsorption desiccant (10).

5. Method according to one of the preceding claims, characterized in that the switching valve (12) is controlled with respect to the start and duration of the drying phase and / or the regeneration phase depending on short-duration air drying conditions and long-duration air drying conditions at the adsorption desiccant (10).

6. A method according to one of claims 4 to 5, characterized in that the grains of the adsorption desiccant (10) have a radially outer region and a radially inner region, each of which has a certain radial extent and is penetrated by water at different rates, that, starting from a previously determined mean geometry, mean size and porosity of the grains of the adsorption desiccant (10), a first mean diffusion rate for water in the grains is determined, at which water moves into the grains from radially outside to radially inside during a drying phase, and that this first mean diffusion rate is taken into account for determining an optimal time of commencement of a drying phase and / or for determining an optimal duration of a drying phase.

7. A method according to one of claims 4 to 5, characterized in that the grains of the adsorption desiccant (10) have a radially outer region and a radially inner region, each of which has a certain radial extent and is penetrated by water at different speeds, that, starting from a previously determined mean geometry, mean size and porosity of the grains of the adsorption desiccant (10), a second mean diffusion rate for water in the grains is determined, at which water moves from radially inside to radially outside in the grains during a regeneration phase, and that this second mean diffusion rate is taken into account for determining an optimal time of commencement and / or an optimal duration of the regeneration phase.

8. Method according to one of claims 6 and 7, characterized in that, after a sufficient quantity of compressed air has been generated for the respective application, several regeneration phases are carried out in quick succession. a sufficient amount of time passes between the respective regeneration phases so that, taking into account the two diffusion rates, a worthwhile amount of water has penetrated from the inner region of the granules of the adsorption desiccant (10) into the outer region of these granules for a subsequent short-term regeneration phase.

9. Method according to one of claims 1 to 8, characterized in that, after a sufficient quantity of compressed air has been generated for the respective application, a regeneration process is carried out when a predetermined large radial outer area of ​​the granules of the adsorption desiccant (10) is loaded with water by a prior drying process.

10. Method according to claim 9, characterized in that the radially outer region of the granules of the adsorption desiccant (10) is determined to be so large as to comprise 30% to 60%, preferably 40% of the average volume of the granules of the adsorption desiccant (10).

11. Method according to claim 9, characterized in that the radially outer region of the granules of the adsorption desiccant (10) is determined to be so large as to comprise 30% to 60%, preferably 40% of the moisture absorption capacity of the granules of the adsorption desiccant (10).

12. Method according to one of claims 1 to 11, characterized in that the switching valve (12) is controlled with regard to the start and duration of a drying phase and / or a regeneration phase depending on the determined spatial distribution of the water loading of the granules of the adsorption desiccant (10).

13. Method according to claim 12, characterized in that the axial and / or radial spatial distribution of the water loading of the granules of the adsorption desiccant (10) on the air dryer (4) is described by a two-dimensional mathematical matrix, the first matrix dimension of which represents the flow direction of the compressed air through the adsorption desiccant (10), and the second Matrix dimension indicates the number of radial regions of the granules of the adsorption desiccant (10) which are more or less loaded with water.

14. Method according to claim 13, characterized in that the total amount of water present at the air dryer (4) is determined from the information on the axial and / or radial spatial distribution of the water loading of the granules of the adsorption desiccant (10), and that the switching valve (12) is controlled with regard to the start and duration of a drying phase and / or a regeneration phase depending on the determined total amount of water in the adsorption desiccant (10).

15. Method according to one of the preceding claims, characterized in that the volume of the compressed air and its humidity are determined in at least one compressed air line (24) and / or in at least one compressed air reservoir (22) of the compressed air supply system (1) and / or in at least one device operable by means of compressed air, and that the determined total volume of the dry compressed air and its humidity value are used to control the start and / or duration of a regeneration phase.

16. Method for operating a compressed air supply system (1) of a vehicle according to one of the preceding claims, wherein the compressed air supply system (1) comprises at least a compressor (2), a humidity sensor (30), an air dryer (5), a switching valve (12) and a control device (14), characterized in that this method is operated as a virtual humidity sensor, which serves to check the correct function of the real humidity sensor (30), and which is used to control the switching valve (12) only if the real humidity sensor (30) has a technical defect.

17. Compressed air supply system (1) of a vehicle, by means of which compressed air consumers (16, 18; 20) can be supplied with compressed air, wherein the compressed air supply system (1) comprises at least one compressor (2), one air dryer (5) and a changeover valve (12) controllable by a control device (14) and optionally a humidity sensor, wherein the aforementioned compressed air components are connected via compressed air lines (24) are connected to each other, and in which a granular adsorption desiccant (10) is arranged in the air dryer (5), characterized in that the control device (14) for carrying out the method according to at least one of the method claims is designed and arranged.

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