WO2023062408A1

WO2023062408A1 - Integrated twin air-dryer cartridge

Info

Publication number: WO2023062408A1
Application number: PCT/IB2021/059401
Authority: WO
Inventors: Ganesan SUDHAGAR; Thalaimalai ROHINIKUMAR; Thameesdeen Sahul Hameed
Original assignee: Zf Commercial Vehicle Control Systems India Limited
Priority date: 2021-10-13
Filing date: 2021-10-13
Publication date: 2023-04-20

Abstract

The invention is directed to an air-dryer cartridge (100) with compact dimension for use in an air-drying device (150) of a commercial vehicle, the air-dryer cartridge comprising a peripheral drying unit (102) and a central drying unit (104), each comprising a respective first air-port (105, 107) and a respective second air-port (106, 108), and a respective drying chamber (109, 110) arranged between the respective first and second air-ports and comprising a respective desiccant material (111, 112); characterized in that the peripheral drying unit and the central drying unit are arranged in a common housing member (113) in a substantially concentrically manner, such that the drying chamber (109) of the peripheral drying unit (102) peripherally encloses the drying chamber (110) of the central drying unit (104).

Description

Integrated twin air-dryer cartridge

The invention is directed to an air-dryer cartridge, to an air-drying device, to a method for controlling operation of an air-drying device, to a computer program product, to a braking system, to a suspension system, and to a commercial vehicle.

A typical commercial vehicle air brake system comprises a compressor and a dryer upstream of the brakes or any other air-based system for extracting moisture from the compressed air by means of a bed of desiccant. The dried air then normally passes to one or more air reservoirs for use in operation of the service brake. Once there is sufficient compressed air in the reservoir, the compressor will normally idle, for example by opening an exhaust valve on the compressor, until there is demand for further air to be pumped to the reservoir. The provision of air-drying devices in vehicle air systems is well known. The air dryer device is typically positioned intermediate an air source, for example a compressor, and a reservoir. The air dryer includes a desiccant material, for example a moisture adsorbing material such as silica gel, which removes moisture from the air supplied by the compressor so as to prevent said moisture being deposited downstream in the vehicle air system where it may over time damage components of the air system. So as to address the build-up of moisture in the desiccant material the air dryer is periodically purged to atmosphere with dry air from the reservoir. Purging of the desiccant, in a so- called regeneration phase, is typically undertaken during periods when the compressor is idle and no significant demands for dry air are being made of the reservoir. The desiccant material is typically provided in a removable canister, hereinafter referred to as a cartridge, which is attached to the air dryer. WO 00/01466 describes an air dryer for a vehicle braking system that is regenerated by dry air, which has already passed through the air dryer. The drying media is periodically heated to improve moisture take-up during regeneration.

CA2236778A1 describes a twin air-drying system for cleaning and drying a stream of unpurified pressurized gas received from a source thereof for use of a pneumatic system. The drying system includes a manifold block provided with the plurality of ports. A separator and sump is connected to such block and to one of the ports for initially separating moisture and particulates from such stream of unpurified gas, and for directing the remainder of the stream to the one port in the block. A pair of desiccant containing canisters are thread ably mounted on a surface of the block opposite that of the separator and sump by two respective threaded shuttle valves. The canisters and shuttle valves are in addition connected in fluid communication with certain of the ports provided in the block for supplying and removing pressurized air from the canisters. A port is provided for discharging dry clean air from the block. Other ports provided in the block exhaust purged air to the atmosphere. Additionally, two ports are provided in the sump for respectively releasing liquid collected in the sump and for admitting pressurize air from a compressor. The switching of the two drying assemblies alternately between the drying and the purging modes allows the twin air-drying system to exsiccate the air more efficiently than known single airdrying systems.

Known twin air-drying systems, however, are larger than single air-drying systems. The length of a twin air-drying system in a given direction is at least twice the diameter of an individual cartridge. It would be beneficial to provide air-drying cartridges with a compact design that enables a reduction of material costs while maintaining the functionality of twin air-drying systems, which in turn depends on the desiccant volume and airflow length within the desiccant.

According to a first aspect of the present invention, an air-dryer cartridge is disclosed. The air-dryer cartridge is configured for use in an air-drying device of a commercial vehicle. The air-dryer cartridge comprises a peripheral drying unit and a central drying unit, each comprising a respective first air-port and a respective second air-port, and a respective drying chamber arranged between the respective first and second air-ports. The respective drying chamber comprises and comprising a respective desiccant material. Thus, each of the peripheral drying unit and the central drying unit comprise a respective first airport, a respective second air-port and a respective drying chamber filled with a respective desiccant material and arranged between the respective first and second air-ports.

In the air-dryer cartridge of the first aspect of the invention, the peripheral drying unit and the central drying unit are arranged in a common housing member, preferably in a substantially concentrically manner, such that the drying chamber of the peripheral drying unit peripherally encloses the drying chamber of the central drying unit.

Thus, the air-dryer cartridge is provided in a more compact design and, having a single housing member and thus reducing the material costs than known twin systems, while maintaining its functionality. The two drying units are thus integrated in a single air-dryer cartridge while enabling a maintenance of the same air travel length on the desiccant material by an appropriate choice of dimensions.

In the following, developments of the air-dryer cartridge of the first aspect of the invention will be presented.

In a preferred development, the central drying unit has a circular cross section in a direction perpendicular to a longitudinal direction and the peripheral drying unit has an annular cross section perpendicular to said longitudinal direction. Preferably, both the central and the peripheral unit share a same rotational symmetry axis that is parallel to the longitudinal direction. For further facilitating the exchange of used air-dryer cartridges, in a development, the air-dryer cartridge of the invention comprises connecting means arranged and configured for releasably connecting the air-dryer cartridge to an external air-flow control unit, as it will be discussed with more detail below. The connecting means include, but are not limited to, bayonet-type connectors, threads, twist-lock connectors or any other suitable connecting means known per se by the person skilled in the art. The air-dryer cartridge can therefore be periodically replaced so as to take into account degradation in the performance of the desiccant material over time.

In another development the air-dryer cartridge further comprises a compression unit that is arranged between a distal portion of the housing member in the longitudinal direction, i.e. a portion further away from the first and second airports, which are preferably located at a base of the air-dryer cartridge, and the central drying unit and configured to exert a compressive force on the desiccant material of the central drying unit, and preferably also on the desiccant material of the peripheral drying unit. In a preferred embodiment, the distal portion of the housing member is a dome-shaped distal portion with its concave side facing the drying units and the convex side facing outwards. Preferably, the compression unit comprises a conical spring with its narrow end close to the distal end of the housing member and the wider end close to the drying units. The conical spring is advantageously provided to retain the desiccant within the drying chamber and to provide compact constriction.

It is not unknown for the air supplied by the compressor to include a mist of very fine oil droplets and/or particulate matter such as dust. The oil droplets are generated from the lubricating oil present in the compressor by the reciprocating action of the compressor. The oil mist and/or the particulate matter typically passes through the air dryer and is subsequently deposited in the reservoir or further downstream in vehicle air system. While oil and dust deposited in this manner is much less likely to damage air system components in the same manner as moisture, its deposit may lead over time to such problems as, for example, the constriction of narrow passageways in air system components and the degradation of elastomeric seals. In a particular development, an air-dryer cartridge is provided which is configured to prevent the transmission of oil and dust there through. In this development at least one of the peripheral drying unit and the central drying unit, and preferably both the peripheral unit and the central unit, further comprises a filter unit arranged between the first air-port and the desiccant material and configured to filter out predetermined particles from an air flow entering the respective peripheral or central drying unit though the first air-port. The predetermined particles include but are not limited to dust, aerosols, oil, etc. The filter unit are preferably located downstream the first airports and upstream from the drying chamber, i.e., between the respective first air-port and the drying chamber of the given peripheral or central drying unit. The filter unit is arranged upstream of the desiccant material such that during a drying phase operation, as it will be explained below, the fluid flow entering the drying unit through the first air-port passes through the filter and then on to the drying chamber including the desiccant before reaching the second air-port. In a development further comprising a compression unit, preferably, at least some of the compression force applied by the compression unit, e.g. by the conical spring, is transmitted to the filter unit. The compression unit thus urges the desiccant material and the filter towards the base of the cartridge, i.e. the section opposite to the distal portion of the housing member in the longitudinal direction.

According to a second aspect of the present invention, an air-drying device is disclosed. The air dryer device is configured to be positioned intermediate an air source, for example a compressor, and a reservoir and to be used for removing moisture from the air supplied by the compressor so as to prevent said moisture being deposited downstream in the vehicle air system where it may over time damage components of said air system.

The air-drying device of the second aspect comprises an air-dryer cartridge according to the first aspect of the present invention for drying compressed air, and therefore, shares all of the advantages described with respect to the airdryer cartridge. In the context of the present invention, compressed air refers to the air provided by an air supply unit or compressed-air supply unit such as a compressor.

The air-drying device also comprises an air-flow control unit configured to control flow of the compressed air in at least one of a first operation-phase and a second operation-phase, preferably, in an alternate manner, in both the first and the second operation phase.

The air-flow control unit comprises an inlet port for connection to a compressed air supply unit, such as a compressor, for receiving the compressed air therefrom. It also comprises an outlet port for providing dried air and being connected to the respective second air-ports of the central and the peripheral drying units of the air-dryer cartridge.

When the air-drying device is operating in the first-operation-phase, the airdrying device is configured to perform a charging phase in the peripheral drying unit, for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port to the air system downstream of the air-drying device. Also in the first operation-phase, the airdrying device is configured to perform a regeneration phase in the central drying unit, for regenerating, i.e., purging or drying, the desiccant material in the central drying unit. This is done by using a second portion of the dried air provided by the peripheral drying unit.

When the air-drying device is operating in the second operation-phase, the airdrying device is configured to perform a charging phase in the central drying unit, for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port to the air system downstream of the air-drying device. Also in the second operation-phase, the air-drying device is configured to perform a regeneration phase in the peripheral drying unit, for regenerating, i.e., purging or drying the desiccant material in the peripheral drying unit. This is done by using a second portion of the dried air provided by the central drying unit. ln the charging phase, irrespectively of whether the air-drying device is operating in the first operation-phase or the second operation-phase, the air enters the respective drying unit (i.e., the peripheral drying unit in the first operation-phase and the central drying unit in the second operation-phase) through its first air-port and leaves the respective drying unit through its second air-port. Analogously, in the regeneration phase, the air enters the respective drying unit (i.e., the central drying unit in the first operation-phase and the peripheral drying unit in the second operation-phase) through its second air-port and leaves the respective drying unit through its first air-port.

Thus, in the first operation-phase, the compressed air provided by the compressed-air supply unit enters the air-flow control unit via the inlet port and is then directed to the first air-port of the peripheral drying unit, where the air is dried. The dried air is then provided by the peripheral drying unit via its second air-port. This is referred to as a charging phase of the peripheral drying unit. The provided dried air is divided into two separate portions. A first portion is provided to the air reservoir located downstream for storage and operation of air-based systems such as brakes or suspension. A second portion of the dried air is provided to the central drying unit for performing a regeneration phase of said central unit. In the regeneration phase, the desiccant material is regenerated, purged or dried by the second portion of the dried air provided by the peripheral unit. The second portion of the dried air enters the central drying unit via the second air-port, transverses the desiccant material taking with it some of the humidity collected by the desiccant material in a previous charging phase and exits the central drying unit via its first air-port.

Conversely, in the second operation-phase the air from the compressed-air supply unit is first directed to the central drying unit for performing a charging phase, and the resulting dried air is divided into two portions, a first one directed to the reservoir of the air system located downstream and a second one used for a regeneration phase of the peripheral drying unit. Thus, the flow path within the respective drying unit is inverted between the charging phase and the regeneration phase.

As the person skilled in the art clearly recognizes, the first and the second operation-phases are interchangeable, so that operation of the air-drying device does not necessarily have to start with the first operation-phase and may start with any one of the first or the second operation phases without any substantial impact in the performance.

Preferably, the air-drying device comprises an exhaust port for exhausting the air used for regenerating the desiccant material in the regeneration phase.

Typically, a respective valve controls the flow of compressed air through the first air-ports, so that at any given time only one of the first air-ports of the peripheral drying unit and the central drying unit is in fluid communication with the air inlet. This regulates the operation in the first or in the second operation-phase.

In a development, the air-flow control unit of the air-drying device further comprises a timing-unit configured to alternately control flow of the received compressed air in the first operation-phase and the second operation-phase, in accordance with predetermined time-operation parameters. The time-operation parameters may depend on a pressure value at the air reservoir. For example, when a predetermined pressure value is reached (exemplarily 60 psi (413 kPa)) the timing unit is configured to alternately control flow of the received compressed air in the first operation-phase and the second operation-phase every 60 seconds, i.e., the first and the second operation-phases last 60 second each, after which the operation phase is switched, i.e. from the first to the second operation-phase and from the second to the first operation-phase. The given pressure value and time are only an example and other pressure values and times can be used.

Preferably, in a development, the air-dryer cartridge comprises connecting means and the air-flow control unit further comprises co-operating connecting means arranged and configured to cooperate with the connecting means of the air-dryer cartridge for releasably connecting the air dryer-cartridge to the air-flow control unit. Suitable cooperating connection means include, but are not limited to cooperating thread structures, bayonet type connections, twist-lock- connectors, releasable snap-fit connectors, etc.

In another development, the air-flow control unit comprises a stacking of a number of layers. In particular, a first layer is adapted as a cartridge-connection layer. The cartridge-connection layer comprises respective cartridge-connecting ducts for connection with the first air-ports and the second air ports of the peripheral drying unit and the central drying unit. Further, a second layer is adapted as a flow-distribution layer and comprises the inlet-port and internal passages that are controlled by valves and are arranged and configured for connecting the inlet port to the cartridge-connecting ducts of the cartridge connection layer.

This particular development presents an adapted layered concept that facilitates production and assembly of the air-flow control unit. In existing twin air-drying devices, the air-flow control unit, also referred to as the body, is typically a PDC body that has a complicated designed, and where the assembly of the different parts is not straightforward. However, in the case of this particular development, the axial symmetry of the air-dryer cartridge facilitates a layered design of the air-flow control unit that enables easy assembly and manufacturability and avoids the complexity in the casting body.

In a preferred development, the stacking of the layers of the air-flow control unit is along a longitudinal direction and/or the cartridge-connecting ducts are oriented in the longitudinal direction.

A third aspect of the present invention is formed by an air-based system in the form of a braking system for a commercial vehicle. The braking system comprises a compressed-air supply unit, arranged and configured to provide compressed air, an air-drying device according to the second aspect of the invention that is connected via the inlet port to the compressed-air supply unit and configured to receive the compressed air, to dry the received compressed air and to provide dried air via the outlet port, an air reservoir connected to the outlet port of the air-drying device and configured to store dried air and a braking unit connected to the air reservoir and configured to apply a braking force to wheels of the vehicle upon provision of dried air from the air-reservoir.

A fourth aspect of the present invention is formed by an air-based system in the form of a suspension system for a commercial vehicle. The suspension system comprises a compressed-air supply unit, arranged and configured to provide compressed air, an air-drying device according to the second aspect of the invention that is connected via the inlet port to the compressed-air supply unit and configured to receive the compressed air, to dry the received compressed air and to provide dried air via the outlet port, an air reservoir connected to the outlet port of the air-drying device and configured to store dried air, and a suspension unit connected to the air reservoir and configured to apply damping function on the vehicle based on a provision of dried air from the air-reservoir.

In a fifth aspect of the present invention a commercial vehicle is provided with an air-drying device according to the second aspect of the present invention. The commercial vehicle comprises a compressed-air supply unit, typically an air compressor, arranged and configured to provide compressed air for an airbased system of the commercial vehicle, such as, but not limited to, a braking system or a suspension system. The commercial vehicle also comprises an airdrying device according to the second aspect of the present invention, which, as explained above, comprises an air-dryer cartridge in accordance with the first aspect of the invention. The air-drying device is connected via the inlet port to the compressed-air supply unit and is configured to receive the compressed air, to dry the received compressed air and to provide dried air via the outlet port. Further, the commercial vehicle comprises air reservoir connected to the outlet port of the air-drying device and configured to store dried air for further operation of an air-based system, such as a braking system according to the third aspect or a suspension system according to the fourth aspect of the invention.

A sixth aspect of the present invention is formed by a method for operating an air-drying device in accordance with the second aspect of the invention. The method comprises:

- receiving compressed air via an inlet port;

- controlling flow of the compressed air in at least one of a first operation-phase and a second operation-phase, wherein in the first operation-phase, the method comprises: performing a charging phase in the peripheral drying unit for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port; and performing a regeneration phase in the central drying unit for regenerating the desiccant material in the central drying unit using a second portion of the dried air provided by the peripheral drying unit; and wherein in the second operation-phase the method comprises performing a charging phase in the central drying unit for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port; and performing a regeneration phase in the peripheral drying unit for regenerating the desiccant material in the peripheral drying unit using a second portion of the dried air provided by the central drying unit; and wherein in the charging phase the method comprises: supplying compressed air to the respective drying unit through its first airport; and outputting dried air from the respective drying unit through its second airport; and wherein in the regeneration phase the method comprises supplying dried air to the respective drying unit through its second airport; and outputting exhaust air from the respective drying unit through its first airport. A seventh aspect of the invention is formed by computer program product comprising instructions to cause the air-drying device of the second aspect of the invention to execute the steps of the method of the sixth aspect.

It shall be understood that the air-dryer cartridge of claim 1 , the air-drying device of claim 7, the braking system of claim 13, the suspension system of claim 14 the commercial vehicle of claim 15, the method for operating an airdrying device of claim 16 and the computer program product of claim 17 have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims.

It shall be understood that a preferred embodiment of the present invention can also be any combination of the dependent claims or above embodiments with the respective independent claim.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

In the following drawings it is shown in:

Fig. 1 : a schematic diagram of an air-based system, in particular a braking system;

Fig. 2A and Fig. 2B: a schematic diagram of a known twin air-drying device under operation;

Fig. 3A: a schematic cross sectional view of an embodiment of an air-drying device in accordance with the invention connected to a comprised-air supply unit;

Fig. 3B: an enlarged view of the section labelled as “B” in Fig. 3A Fig. 4: a cross sectional view of the inventive air-dryer cartridge along the plane “A-A “ as shown in Fig. 3;

Fig. 5: a schematic diagram of an air-based system comprising a braking system and a suspension system according to a preferred embodiment;

Fig. 6: a schematic block diagram of a commercial vehicle according to a preferred embodiment;

Fig. 7: a flow diagram of a method for operating an air-drying device in accordance with a preferred embodiment.

Fig. 1 shows a schematic diagram of an air-based system, in particular a braking system 1 , for instance for use in a commercial vehicle. The braking system comprises a compressed air supply unit, such as a compressor 20, an air-drying device, in particular a twin air-drying device 10, and a braking unit 30. The operation of the braking system 1 will be explained in the following with further reference to Figs. 2A and 2B, which show schematic diagrams of the twin air-drying device 10 under operation.

For the following description, the following definitions apply.

An air compressor 20 is a device that is configured to pump air to an air-based system, such as braking system 1 , and thus to build air pressure in said air system.

An air-drying device 10 is a device that dries, and eventually also cools, and filters, the air delivered by the air compressor 20.

A governor 22, or air governor, is a device that controls the operation of the air compressor 20 by monitoring air pressure in the supply tank or dried air reservoir 24 of the air-based system 1. The governor 22 is configured to initiate the compressor 20 unload cycle when a predetermined cut-out pressure is reached. It is also configured to control the air-drying device 10 by sending an air signal at the beginning of the compressor unload cycle, to a control port of the air-drying device 10. This initiates the purge cycle. When the signal is stopped, the purge valve 15 closes and the drying cycle begins.

A compressor load cycle is the time during which the air compressor 20 is building air pressure in an air-based system 1 . A compressor unload cycle is the time during which the air compressor 20 is idling and is not building air pressure in the air system 1 .

The cut-in pressure is the pressure level in the air system supply tank 24 that triggers the compressor load cycle. The cut-out pressure is the pressure level in the air system supply tank 24 that triggers the compressor unload cycle.

Desiccant is typically a granular substance that has a high affinity for water. It catches and retains moisture from the air stream.

A drying cycle, also referred to as charging cycle or charging phase is the time during which the air-drying device 10 removes moisture from, and eventually also cools and filters, the air delivered by the air compressor 20.

Purge is referred to as a blast of air (decompression) from the air-drying device 10 purge valve at the beginning of the compressor unload cycle.

The purge cycle refers to the time during which the air-drying device 10 is undergoing purge and regeneration. It begins at the start of the compressor unload cycle and normally ends well before the beginning of the compressor load cycle.

Regeneration, or regeneration phase, refers to the relatively mild backflow of air through the non-loaded air dryer cartridge and out the purge valve. A small amount of air from one cartridge is used to remove moisture from the other cartridge. This readies the cartridge for the next cycle. The cycle may last a predetermined time, e.g., 50-60 seconds, and then a timer switches it to the other cartridge.

The twin air-drying device 10 comprises an air-drying unit 11 that includes two air-dryer cartridges 11 A, 11 B, each of which contains a desiccant material for drying compressed air, and an air-flow control unit 12. The air-dryer cartridges 11 A, 11 B, may also contain a filter unit for enabling additional filtering for oil and/or aerosol particles.

The governor 22 is configured to monitor the pressure in the supply tank 24, for instance via a reservoir-to-governor line 25. The process begins when a pressure in the dried air reservoir, or supply tank, 24 drops below a cut-in pressure (e.g. approximately 100 psi). When this occurs, the governor 22 is configured to turn on the compressor 20. The compressor receives air via a compressor intake line 21 and sends air to the supply port 13 of the air-drying device 10 and the air-drying cycle starts.

An air-drying cycle begins as air enters the air-drying device 10 at the supply port 13. Air flows past the air-flow control unit 12 through a piston or a diaphragm (not shown) into the first cartridge 11 A. Air flows through the cartridge 11A where it is dried. Moisture, and optionally contaminants, are filtered out through the desiccant material in the cartridge 11A and, in a particular implementation, through a filtering unit. Dried air flows to the delivery port 14 of the air-drying device 10 for delivery to the dried air reservoir 24, also referred to as the supply tank of the braking unit 30. However, some dried air is diverted to the second cartridge 11 B where it moves upward through the desiccant material. This cleans and dries (or in other words, regenerates) the desiccant material.

While the compressor 10 is running, a mild flow of air will vent to atmosphere through a purge valve 15. At a given pressure value, e.g., 60 psi (413 kPa) or greater, the air-drying device 10 is configured to switch air flow between the cartridges 11 A, 11 B at predetermined intervals, for example every 60 seconds. The switching of air is controlled, for example, by a timer/solenoid (not shown) comprised by the airdrying device 10. For example, pistons in the air-flow control unit 12 shift from right to left, reversing the airflow pattern. A mild purge, or puff of air, can be heard at the purge valve 15 at the time of shift. The air-drying cycle continues as the cartridge functions are reversed. Incoming air from the compressor 10 enters the second (left) cartridge 11 B for drying and then flows to the delivery port 14. A small amount of dried air flows into the first (right) cartridge 11 A to regenerate desiccant. Alternating air drying cycles continue, switching between the cartridges 11 A, 11 B, e.g., every 60 seconds.

When the dried air reservoir 24 reaches a predetermined cut-out pressure, the governor 22 is configured to unload the compressor 20. The compressor 24 supplies air to an unloader port 16 of the air-flow control unit 12 of the air-drying device 10 and the air-drying device purges via the purge valve 15.

The dried air reservoir is typically controllably connected to the braking system reservoir 27 via check valves 26. The braking system reservoir is then fluidly connected to the braking units

Typical dimensions of the known twin air-drying device 10 along the direction labelled as D in Fig. 2 are around 290-300 mm. The overall envelop dimension is high due to the desiccant cartridges being separate units.

Fig. 3A shows a schematic cross sectional view of an embodiment of an airdrying device 150 in accordance with the invention connected to a compressed- air supply unit 160. The air-drying device 150 comprises an air-dryer cartridge 100 and an air-flow control unit 156, releasable connected to each other. The air-dryer cartridge 100 for suitable for use in an air-drying device 150, for instance in a commercial vehicle. The air-dryer cartridge 100 comprises a peripheral drying unit 102 and a central drying unit 104. Each one of the peripheral drying unit 102 and the central drying unit 104 comprises a respective first air-port 105, 106 and a respective second air-port 107, 108. In addition, each of the peripheral and central drying units 102, 104, comprise a respective drying chamber, i.e., a peripheral drying chamber 109 and a central drying chamber 110, each arranged, in the sense of an air-flow path, between the respective first and second air-ports and comprising a respective desiccant material 111 , 112.

The peripheral drying unit 102 and the central drying unit 104 are arranged in a common housing member 113, in a substantially concentrically manner, such that the drying chamber 109 of the peripheral drying unit 102 peripherally encloses the drying chamber 110 of the central drying unit 104.

This design where the one of the drying units, namely the central drying unit 104 is peripherally surrounded by the peripheral drying unit 102 enables a reduction of the dimension along the direction D indicated in Fig. 3A when compared to the dimension in the same direction of a known twin air-drying device, such as device 10 of Fig. 2, having substantially the same desiccant volume and air flow length on the desiccant. This is achievable with a dimension of the air-drying device 150 along direction D of approximately 245-250 mm instead of approximately 300 mm as in the case of the known twin air-drying device 10 of Fig. 2. Thus, the air-drying device 150 offers a similar functionality with a compact size along the direction D. In general, for obtaining a circle of radius R with an equal area as two circles of smaller radius r, the value of R is found to be V2 - r. Thus, the length along the direction D of the two circles of radius r placed adjacent to each other is 4 times their radius, whereas the length along the direction D of the larger circle is 2 times R, i.e., 2V2 ■ r, which is approximately 71% of the length in the direction D of the two circles with smaller radius.

The air-dryer cartridge 100 comprises a compression unit 116 that is arranged between a distal portion 115 of the housing member, in the longitudinal direction, i.e. a portion further away from second air-ports, which are preferably located at a base of the air-dryer cartridge, and the central drying unit 104 and configured to exert a compressive force F on the desiccant material 1 12 of the central drying unit 104, and preferably also on the desiccant material 1 11 of the peripheral drying unit 102. In this particular embodiment of the air-dryer cartridge 100, the distal portion 1 15 of the housing member 113 is a domeshaped distal portion with its concave side facing the drying units 102, 104 and the convex side facing outwards. Preferably, the compression unit 116 comprises a conical spring 117 with its narrow end close to the distal end 115 of the housing member 1 13 and the wider end close to the drying units 102, 104. The conical spring is advantageously provided to retain the desiccant 111 , 112 within the drying chamber and to provide compact constriction. In the example shown in Fig. 3A, the compression unit 116 comprises a first conical spring that is arranged and configured to exert a compressive force on an intermediate structure that in turn is arranged and configured to exert force on both the desiccant material 11 1 of the peripheral drying unit 102 and on a second conical spring 117.1 that is arranged and configured to exert force on the desiccant material 112 of the central drying unit 104.

The air-dryer cartridge 100 may additionally comprise a filter unit. In particular at least one of the peripheral drying unit 102 and the central drying unit 104, an preferably both drying units comprise a respective filter unit 118 arranged between the first air-port 105, 107 and the desiccant material 11 1 , 112 and configured to filter out predetermined particles from an air flow entering the respective drying unit though the first air-port 105, 107.

The inventive air-drying device comprising the inventive air-dryer cartridge enables the integration of the two drying units 102, 104 into a single housing 113, while providing a serviceable air-dryer cartridge 100. Under operation, the air-drying device 150 follows the same principle as the known twin air-drying device 10 of Fig.2, wherein the peripheral drying unit 102 and the central drying unit 104 assume the roles of the first cartridge 11 A and the second cartridge 11 B (or of the second cartridge 1 1 B and the first cartridgel 1 A) respectively. The air-drying device, in particular the air-flow control unit 156 further comprises an exhaust port 157 for exhausting, typically to the exterior, the air used for regenerating the desiccant material in the regeneration phase.

Fig. 3B shows an enlarged view of the section labelled as B in Fig. 3A. The airdryer cartridge 100 optionally comprises connecting means 114 for realisably connecting the air-dryer cartridge 100 to the external air-flow control unit 156. Conversely, the air-flow control unit 156 further comprises cooperating connecting means 158 arranged and configured to cooperate with the connecting means 114 of the air-dryer cartridge 100 for realisably connecting the air dryer-cartridge 100 to the air-flow control unit 156. The connecting means 114, 158 include, but are not limited to, bayonet-type connectors, threads, twist-lock connectors or any other suitable connecting means known per se by the person skilled in the art. The air-dryer cartridge 100 can therefore be periodically replaced so as to take into account degradation in the performance of the desiccant material 111 , 112 over time.

Additionally, the inventive air-drying device 150 presents an adapted layered concept that facilitates production and assembly of the air-flow control unit. In existing twin air-drying devices, such as, for instance, twin air-drying device 10 of Figs. 2A and 2B, the air-flow control unit 12, also referred to as the body, is a PDC body that has a complicated designed, and where the assembly of the different parts is not straight forward. However, in the case of the inventive airdrying device, the axial symmetry of the air-dryer cartridge facilitates a layered design of the air-flow control unit 156 that enables easy assembly and manufacturability and avoids the complexity in the casting body 12.

In particular, the air-flow control unit 156 comprises a stacking of a number of layers, in this particular example two layers, wherein a first layer is adapted as a cartridge-connection layer 156.1 and comprises respective cartridge-connecting ducts 105.1 , 106.1 , 107.1 , 108.1 for connection with the first air-ports 105,107 and the second air ports 106,108 of the peripheral drying unit 102 and the central drying unit 104, and wherein a second layer is adapted as a flow- distribution layer 156.2 and comprises the inlet-port 152 and internal passages 162 controlled by valves 155 for connecting the inlet port 152 to the cartridgeconnecting ducts 105.1 , 106.1 , 107.1 , 108.1 of the cartridge connection layer 156.1. In this particular example, the stacking of the layers 156.1 , 156.2 of the air-flow control unit 156 is along a longitudinal direction L and/or the cartridgeconnecting ducts, in particular with a substantially cylindrical shape are oriented in the longitudinal direction.

The cartridge-connecting duct 105.1 connects the flow-distribution layer 156.1 to the first air-port 105 of the peripheral drying unit 102. The cartridgeconnecting duct 106.1 connects the flow-distribution layer 156.1 to the second air-port 106 of the peripheral drying unit 102. The cartridge-connecting duct 107.1 connects the flow-distribution layer 156.1 to the first air-port 107 of the central drying unit 104. Analogously, the cartridge-connecting duct 108.1 connects the flow-distribution layer 156.1 to the second air-port 105 of the central drying unit 102.

Fig. 4 shows a cross sectional view of the inventive air-dryer cartridge along the plane AA shown in Fig. 3. As it can be seen in Fig. 4, the air-dryer cartridge 100 has a substantially circular cross section. In particular the central drying unit 104 has a circular cross section perpendicular to a longitudinal direction L and the peripheral drying unit 102 has an annular cross section perpendicular to said longitudinal direction L. Fig. 4 shows the common housing member 113 as an outermost feature of the air-dryer cartridge 100. Adjacent to it, there first air-port 105 of the peripheral unit is shown. Said first air-port has an annular cross section and extends along the longitudinal direction from a proximal section of the air-dryer cartridge, i.e. that section that is brought into contact with the airflow control unit 158 of the air-drying device 150. The air-port ends close to the upper distal section of the housing member 113, where it is connected to the drying chamber 109 of the peripheral drying unit 102 comprising the desiccant material 1 11. The first air-port 107 of the central drying unit 104 is concentrically arranged with respect to the first air-port 105 of the peripheral unit 102, and also extends along the longitudinal direction from the proximal section of the air- dryer cartridge, i.e. that section that is brought into contact with the air-flow control unit 158 of the air-drying device 150 and ends close to the upper distal section of the housing member 113, where it is connected to the drying chamber 110 of the central drying unit 104 comprising the desiccant material 112.

Under operation, in the charging phase, the dried air enters the respective drying unit via the first air-port, travels along the longitudinal direction of the housing member 1 13, where it can be advantageously filtered by a filter unit 118, if provided, and then enters the corresponding drying chamber where it gets dried as it traverses the desiccant material from an upper section back to the proximal section of the air-cartridge, where the second air-port is located. Also under operation, but in the regeneration phase, part of the dried air provided by that drying unit operating in the charging phase is provided to the second air-port of the drying unit undergoing the regeneration phase. The dried air enters the drying chamber, and carries away with it the humidity stored in the desiccant material during a previous charging phase of said drying unit. The air, now with moisture, enters the first air-port and then travels back to the proximal section of the air-dryer cartridge where it enters the air-flow control unit 158 and then exits the device through the exhaust port.

The air-flow control unit 156 advantageously comprises suitable valves 155 that control the flow of air from the inlet port 152 to the first air-port of that drying unit currently operating in the charging phase while blocking the a fluid communication between the inlet port 152 and the first air-port of that drying unit currently operating in the regeneration phase.

Fig.5 shows a schematic diagram of an air-based system comprising a braking system 200 and, alternatively or additionally, a suspension system 300 according to the invention. A suspension system generally refers to the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two.

An air-based braking system or, more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle. Air brakes are advantageously used in large heavy vehicles, particularly those having multiple trailers, which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers.

The air-based system can be used in a commercial vehicle, as it will be explained with reference to Fig.6. The air-based system comprises a compressed-air supply unit 202, for instance a compressor such as compressor 20 of Fig. 1 , which, as explained above, is arranged and configured to provide compressed air to the air-based system. The air-based system comprises an air-drying device 250 according to the invention, which is connected via an inlet port 152 to the compressed-air supply unit 202 and configured to receive the compressed air, to dry the received compressed air and to provide dried air via an outlet port 154. The air-based system also comprises an air reservoir 204 or dried-air supply, which is connected to the outlet port 154 of the air-drying device 250 and configured to store dried air. The air-based system comprises at least one of a braking unit 206 and a suspension unit 306, preferably both. The braking unit 206 and/or the suspension unit 306 are connected to the air reservoir 204. The braking unit 206 is configured to apply a braking force to wheels of the vehicle upon provision of dried air from the air-reservoir 206. The suspension unit 306 is configured to apply damping function on the vehicle upon provision of dried air from the air-reservoir 204.

Advantageously, the air-drying device 250 of the air-based system of Fig. 5 includes an air-flow control unit that comprises a timing-unit 159 configured to alternately control flow of the received compressed air in the first phase and the second phase, in accordance with predetermined time-operation parameters. For example, depending on the pressure value of the air in the air-reservoir, the timing-unit 159 is configured to control the duration of the first and second operation-phases by opening and closing the corresponding valves that allow fluid communication between the inlet port of the air-flow control unit and the first air-ports of the corresponding drying units of the air-dryer cartridge.

Damping generally refers to the control of motion or oscillation, as seen with the use of hydraulic/pneumatic gates and valves in a vehicle's shock absorber. Damping controls the travel speed and resistance of the vehicle's suspension. An undamped car will oscillate up and down. With proper damping levels, the vehicle will settle back to a normal state in a minimal amount of time. Most damping in modern vehicles can be controlled by increasing or decreasing the resistance to fluid flow in the shock absorber.

Fig. 6 shows a schematic block diagram of a commercial vehicle according 400 to the invention. The commercial vehicle comprises a suspension system that includes a suspension unit 306 connected to the wheels 402 of the vehicle 400. As stated above, the suspension unit includes the system of tires, tire air, springs, shock absorbers and linkages that connects the vehicle 400 to its wheels 402 and allows relative motion between the two. The suspension system 300 is advantageously configured to apply damping function on the vehicle 400 based on the provision of dried air from the air-reservoir 204 to the suspension unit 306. The commercial vehicle 400 also comprises a braking system that includes a braking unit 206, wherein typically compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle 400. The commercial vehicle may comprise an electronic control unit 450, which is connected (see dotted lines in Fig. 6) to the compressed-air supply unit 202, the air-drying device 250 and optionally also to the air reservoir 204, and/or to the suspension unit 306 and/or to the braking unit 206 and configured to control operation of the compressed-air supply unit 202 and of the air-drying device 250. For instance the electronic control unit may receive status information from the air reservoir 204, for example pertaining to the pressure of the air stored therein, of from the braking and/or suspension units 206, 306, for example pertaining its current operation, and based on the received status information, operate the compressed-air supply unit 202 and the air-drying device 250 in accordance with predetermined operation parameter. The timing-unit 159 is advantageously implemented as part of the electronic control unit 450.

Fig. 7 shows a flow diagram of a method 500 for operating an air-drying device 150, 250 in accordance with the invention. The method comprises, in a step 502, receiving compressed, typically from a compressed-air supply unit 202, such as a compressor 20 air, via an inlet port 152. The method also comprises, in a step 504, controlling flow of the compressed air in at least one of a first operation-phase and a second operation-phase, wherein in the first operationphase, the method comprises, in a step 506.1 , performing a charging phase in the peripheral drying unit 102 for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port and, in a step 506.2, performing a regeneration phase in the central drying unit 104 for regenerating the desiccant material 1 12 in the central drying unit 104 using a second portion of the dried air provided by the peripheral drying unit 102. While operating in the second operation-phase, the method comprises, in a step 508.1 , performing a charging phase in the central drying unit 104 for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port and, in a step, 508.2, performing a regeneration phase in the peripheral drying unit 102 for regenerating the desiccant material 1 11 in the peripheral drying unit 102 using a second portion of the dried air provided by the central drying unit 104. While operating a given drying unit in the charging phase, the method comprises, in a step, 510.1 , supplying compressed air to the respective drying unit through its first air-port, and, in a step 510.2, outputting dried air from the respective drying unit through its second air-port. While operating a given drying unit in the regeneration phase, the method comprises, in a step 512.1 , supplying dried air to the respective drying unit through its second air-port, and, in a step 512.2, outputting exhaust air from the respective drying unit through its first air-port. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

A single unit or device may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE SIGNS (PART OF THE DESCRIPTION)

1 Braking system

10 Twin air-drying device

11 Air-drying unit

11 A First air-drying cartridge

11 B Second air-drying cartridge

12 Air-flow control unit of twin air-drying device

13 Supply port

14 Delivery port

15 Purge valve

16 Unloader port of air drying-unit

20 Compressor

21 Compressor intake line

22 Governor

23 Unloader port of compressor

24 (Dried-) air reservoir

25 Reservoir-to-governor line

26 Check valves

27 Braking system reservoir

30 Braking unit

100 Air-dryer cartridge

102 Peripheral drying unit

104 Central drying unit

105 First air-port of peripheral drying unit

105.1 Cartridge connection duct

106 Second air-port of peripheral drying unit

106.1 Cartridge connection duct

107 First air-port of central drying unit Cartridge connection duct

Second air-port of central drying unit Cartridge connection duct

Drying chamber of peripheral drying unit Drying chamber of central drying unit Desiccant material of peripheral drying unit Desiccant material of central drying unit Common housing member

Connecting means

Distal portion of the housing member Compression unit

Conical spring

Second conical spring

Filter unit

Air-drying device

Inlet port

Outlet port

Valves

Air-flow control unit

Cartridge-connection layer Flow-distribution layer Exhaust port

Cooperating connecting means

Timing-unit

Compressed-air supply unit Internal passages

Braking system

Compressed-air supply unit

Air reservoir

Braking unit

Air-drying device

Suspension system

Suspension unit 400 Commercial vehicle

402 Wheels

450 Electronic control unit

500 Method for controlling operation of air-drying device

502 Receiving compressed air

504 Controlling flow of the compressed air

506.1 Charging phase in peripheral drying unit

506.2 Regeneration phase in central drying unit

508.1 Charging phase in central drying unit

508.2 Regeneration phase in peripheral drying unit

510.1 Supply compressed air to first air-port

510.2 Output dried air through second air-port

512.1 Supply dried air to second air-port

512.2 Output exhaust air through first air-port

A-A Cutting plane

B Enlarged section

D Direction of reduced length

L Longitudinal direction

Claims

- 29 -

1 . An air-dryer cartridge (100) for use in an air-drying device (150) of a commercial vehicle, the air-dryer cartridge comprising a peripheral drying unit (102) and a central drying unit (104), each comprising a respective first air-port (105, 107) and a respective second air-port (106, 108), and a respective drying chamber (109, 110) arranged between the respective first and second air-ports and comprising a respective desiccant material (111 , 112); characterized in that the peripheral drying unit and the central drying unit are arranged in a common housing member (113) in a substantially concentrically manner, such that the drying chamber (109) of the peripheral drying unit (102) peripherally encloses the drying chamber (110) of the central drying unit (104).

2. The air-dryer cartridge (100) of claim 1 , wherein the central drying unit (104) has a circular cross section perpendicular to a longitudinal direction (L) and the peripheral drying unit (102) has an annular cross section perpendicular to said longitudinal direction (L).

3. The air-dryer cartridge (100) of claim 1 or 2, further comprising connecting means (114) for releasably connecting the air-dryer cartridge (100) to an air-flow control unit (156), in particular wherein the air-flow control unit (156) is external to the air-dryer cartridge (100).

4. The air-dryer cartridge (100) of any of the preceding claims, further comprising a compression unit (116) arranged between a distal portion (115) of the housing member (113) and the central drying unit (104) and configured to exert a compressive force (F) on the desiccant material (112) of the central drying unit. - 30 -

5. The air-dryer cartridge (100) of claim 4, wherein the compression unit (1 16) comprises at least one conical spring (117)

6. The air-dryer cartridge (100) of any of the preceding claims, wherein at least one of the peripheral drying unit (102) and the central drying unit (104) further comprises a filter unit (1 18) arranged between the first air-port (105, 107) and the desiccant material (11 1 , 1 12) and configured to filter out predetermined particles from an air flow entering the respective drying unit though the first airport (105, 107).

7. An air-drying device (150), comprising

- an air-dryer cartridge (100) according to any of the claims 1 to 6 for drying compressed air; and

- an air-flow control unit (156) configured to control flow of the compressed air in at least one of a first operation-phase and a second operation-phase, the airflow control unit (156) comprising:

- an inlet port (152) for receiving the compressed air from a compressed air supply unit (160); and

- an outlet port (154) for providing dried air and connected to the respective second air-ports (106, 108) of the central and the peripheral drying units (102, 104) of the air-dryer cartridge ; wherein, in the first-operation-phase: the air-drying device (150) is configured to perform a charging phase in the peripheral drying unit (102), for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port (154), and to perform a regeneration phase in the central drying unit (104) for regenerating the desiccant material (1 12) in the central drying unit (104) using a second portion of the dried air provided by the peripheral drying unit (102); and, wherein in the second operation-phase: the air-drying device (150) is configured to perform a charging phase in the central drying unit (104) for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port (154), and a regeneration phase in the peripheral drying unit (102) for regenerating the desiccant material (111 ) in the peripheral drying unit (102) using a second portion of the dried air provided by the central drying unit (104); wherein

- in the charging phase the air enters the respective drying unit (102, 104) through its first air-port (105, 107) and leaves the respective drying unit (102, 104) through its second air-port (106,108) and

- - in the regeneration phase the air enters the respective drying unit (102, 104) through its second air-port (106, 108) and leaves the respective drying unit (102, 104) through its first air-port (105, 107).

8. The air-drying device (150) of claim 7, wherein the air-flow control unit (156) further comprises an exhaust port (157) for exhausting, the air used for regenerating the desiccant material in the regeneration phase.

9. The air-drying device (150) of claim 7 or 8, wherein the air-flow control unit (156) further comprises a timing-unit (159) configured to alternately control flow of the received compressed air in the first phase and a the second phase, in accordance with predetermined time-operation parameters.

10. The air-drying device (150) of any of the claims 7 to 9, wherein the air-dryer cartridge (100) comprises connecting means (1 14) for releasably connecting the air-dryer cartridge (100) to an air-flow control unit (156), wherein the air-flow control unit (156) further comprises cooperating connecting means (158) arranged and configured to cooperate with the connecting means (1 14) of the air-dryer cartridge (100) for releasably connecting the air dryer-cartridge

(100) to the air-flow control unit (156).

11 . The air-drying device (150) of any of the claims 7 to 10, wherein the air-flow control unit (156) comprises a stacking of a number of layers wherein a first layer is adapted as a cartridge-connection layer (156.1 ) and comprises respective cartridge-connecting ducts (105.1 , 106.1 , 107.1 , 108.1 ) for connection with the first air-ports (105,107) and the second air ports (106,108) of the peripheral drying unit (102) and the central drying unit (104), and wherein a second layer is adapted as a flow-distribution layer (156.2) and comprises the inlet-port (152) and internal passages (162) controlled by valves (155) for connecting the inlet port (152) to the cartridge-connecting ducts (105.1 , 106.1 , 107.1 , 108.1 ) of the cartridge connection layer (156.1 ).

12. The air-drying device (150) of claim 11 , wherein the stacking of the layers (156.1 , 156.2) of the air-flow control unit is along a longitudinal direction (L) and/or the cartridge-connecting ducts are oriented in the longitudinal direction (L).

13. A braking system (200) for a commercial vehicle (500), the braking system (200) comprising:

- a compressed-air supply unit (202), arranged and configured to provide compressed air;

- an air-drying device (250) according to any of the claims 7 to 12 connected via the inlet port (152) to the compressed-air supply unit (202) and configured to receive the compressed air, to dry the received compressed air and to provide dried air via the outlet port (154);

- an air reservoir (204) connected to the outlet port (154) of the air-drying device (250) and configured to store dried air; and

- a braking unit (206) connected to the air reservoir and configured to apply a braking force to wheels of the vehicle upon provision of dried air from the airreservoir.

14. A suspension system (300) for a commercial vehicle, the suspension system (300) comprising:

- an air-drying device (250) according to any of the claims 7 to 12 connected via the inlet port (152) to the compressed-air supply unit (202) and configured to - 33 - receive the compressed air, to dry the received compressed air and to provide dried air via the outlet port (154); and

- an air reservoir (204) connected to the outlet port of the air-drying device and configured to store dried air;

- a suspension unit (306) connected to the air reservoir and configured to apply damping function on the vehicle based on a provision of dried air from the airreservoir.

15. A commercial vehicle (400) comprising:

- an air-drying device (150, 250) according to any of the claims 7 to 12 connected via the inlet port (152) to a compressed-air supply unit (202) and configured to receive the compressed air, to dry the received compressed air and to provide dried air via the outlet port (154); and

- an air reservoir(204) connected to the outlet port (154) of the air-drying device (152) and configured to store dried air for further operation of an air-based system (200, 300) of the commercial vehicle, in particular a braking system (200) according to claim 13 of the commercial vehicle or a suspension system (300) according to claim 14 of the commercial vehicle.

16. Method (500) for operating an air-drying device in accordance with any of the claims 7 to 12, the method comprising:

- receiving (502) compressed air via an inlet port;

- controlling (504) flow of the compressed air in at least one of a first operationphase and a second operation-phase, wherein in the first operation-phase, the method comprises: performing a charging phase (506.1 ) in the peripheral drying unit (102) for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port; and performing a regeneration phase (506.2) in the central drying unit (104) for regenerating the desiccant material (112) in the central drying unit (104) using a second portion of the dried air provided by the peripheral drying unit (102) and wherein in the second operation-phase the method comprises - 34 - performing a charging phase (508.1) in the central drying unit (104) for drying the received compressed air and providing dried air, wherein a first portion of the dried air is provided via the outlet port; and performing a regeneration phase (508.2) in the peripheral drying unit (102) for regenerating the desiccant material (111) in the peripheral drying unit (102) using a second portion of the dried air provided by the central drying unit (104); and wherein in the charging phase the method comprises: supplying (510.1) compressed air to the respective drying unit through its first air-port; and outputting (510.2) dried air from the respective drying unit through its second air-port; and wherein in the regeneration phase the method comprises supplying (512.1) dried air to the respective drying unit through its second air-port; and outputting (512.2) exhaust air from the respective drying unit through its first air-port.

17. A computer program product comprising instructions to cause the airdrying device of any of the claims 7 to 12 to execute the steps of the method of claim 16.