Abstract:
An air supply system on a vehicle for inflating and deflating a tire. The system includes a compressor connected to a drier having drying material to extract water from the air and a deflation line connectable between the tire and the dryer. The air dryer is operable in a first mode in which air passing through the dryer in a first direction is dried by the dryer and a second regeneration mode in which air passes through the dryer in a direction opposite to the first to remove water collected by the dryer, characterized in that the air used for the regeneration is air deflated from the tire.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of Invention 
         [0002]    The invention relates to an air supply system on a vehicle, comprising a Tire Pressure Control System (TPCS) and an air dryer. More specifically, the invention concerns a means for drying air used within a TPCS on a tractor. 
         [0003]    Description of Related Art 
         [0004]    Vehicle air supply systems require air dryers to discharge humidity from the air before supplying it to consumers on a vehicle. Damp air can cause corrosion in pipes and other components on the vehicle, so before supplying air to consumers, or air reservoirs (for example, for the vehicle&#39;s brake system) the air is usually guided through a dryer. When the air is passing through the dryer to dry the air, this mode of operation is known as a drying mode. 
         [0005]    Due to the restricted load capacity of dryers, a second operation mode, known as a regeneration mode is required which involves passing air through the reservoir in an opposite direction and discharging it to the atmosphere. A regeneration mode thus removes water deposited in, or on the drying material of the dryer. 
         [0006]    It is known to use double chamber dryers which comprise two separate dryer reservoirs, so that if one chamber is drying the air from the compressor in a drying mode, the other chamber is in a regeneration mode. The shift between the two modes of each drying chamber is time-controlled, so that the dryer may continually be used to dry air. 
         [0007]    Furthermore, Electrically Operated Air Dryers (EOD) are also known. These dryers only require one dryer portion and the shift between the two modes of operation, that is the switch between the regeneration mode and the drying mode is not time controlled by a control unit. The two modes are controlled by measuring the volume of air passing through the dryer by measuring the compressor time or measuring the pressure rise in the reservoirs (and knowing that a certain pressure rise requires a predetermined air volume). A percentage of the volume of air in the air supply system is then guided back for the regeneration. 
         [0008]    Even if the usage of EODs reduces regeneration time, a percentage of the volume of air (approximately 12%) is still required for regeneration and is not available for the general air supply to components. For example, after drying 1000 liters of air within an air supply system, 12% of the volume, that is 120 liters must be used for regeneration. The efficiency of the system is therefore reduced. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    One aspect of the invention is directed to an air supply system on a vehicle for inflating and deflating a tire. The system includes a compressor connected to a drier provided with drying material to extract water from the air and a deflation line connectable between the tire and the dryer, said air dryer operable in a first mode in which air passing through the dryer in a first direction is dried by the dryer and a second regeneration mode in which air passes through the dryer in a direction opposite to the first to remove water collected by the dryer. The air used for the regeneration is air deflated from the tire. In this way, the efficiency of the air supply system is increased, since air for supplying consumers on the vehicles is not used for regeneration of the dryer. 
         [0010]    Preferably the system calculates a first value representing a volume of air deflated from the tire and a second value representing a volume of air needed for regeneration and compares said first and second values to calculate if there is sufficient deflated air for regeneration. 
         [0011]    If the second value is greater than the first value, the regeneration is preferably conducted using air deflated from the tire and using air from a reservoir of the dryer, or of a consumer. 
         [0012]    This way regeneration of the dryer can be ensured without impacting on the supply of air to consumers on the tractor. 
         [0013]    The compressor is preferably deactivated to enable deflated air from the tire to be fed to the dryer. 
         [0014]    More preferably, the system postpones deflation of the tire if the compressor is not deactivated. This way efficiency of the system is maintained. 
         [0015]    The air supply system preferably comprises a tire pressure control system (TPCS) circuit and a dryer circuit, wherein the compressor and dryer are located in a dryer circuit having a flow return valve arranged so that air supplied by the compressor to the tire is dried and said dryer circuit further comprising a port connectable to the TPCS circuit so that air deflated from the tire through the TPCS circuit passes through the dryer for regeneration, or is supplied directly to a consumer on the vehicle. 
         [0016]    Dry air deflated from the tire thus does not have to be dried again and can be supplied directly to consumers. 
         [0017]    Advantageously, the air supply system further comprises detection means to detect when the tire is inflated by an external air supply and where this is the case the system uses air from a reservoir of a consumer for regeneration. 
         [0018]    This way air which has not been dried prior to reaching the tire is not used for regeneration. 
         [0019]    The detection means preferably measures the tire pressure and where there is an increase in tire pressure, but the compressor has not been used to inflate the tire the system detects the use of an external air supply. 
         [0020]    Preferably, the air taken from the TPCS is provided by a reservoir located within the tire. 
         [0021]    In the case of a wheel comprising both an inner tire and an outer tire and comprising two reservoirs located on the wheel, air taken from one of these reservoirs may be used for regeneration of the dryer without affecting the pressure of the other reservoir. 
         [0022]    The air used for the regeneration from the tire may pass through a filtration means. 
         [0023]    In this way any particles from inside the tires which end up in the air used for regeneration are filtered out. Undesired particles/debris found in the tires may have resulted from wear of the tires, or may have been introduced into the tires from an external air supply. 
         [0024]    A Tire Pressure Control System (TPCS) used on agricultural tractors is able to determine the air flow (and therefore any increase or decrease in air volume over a time interval) as described in GB 1315426.5. 
         [0025]    The system can store a characteristic map of the relationship between a change in tire pressure and a change in air volume as the tire is inflated or deflated. For example, for a desired tire pressure, the system will calculate the volume of air which must be added or subtracted to reach the desired pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will now be described, by way of example only, with reference to the following drawings in which: 
           [0027]      FIG. 1  is circuit diagram of a Tractor Pressure Control System and an Electrically Operated Air Dryer embodying the invention; 
           [0028]      FIGS. 2 a -2 d    are circuit diagrams of known modes of operation of an Electrically Operated Air Dryer; 
           [0029]      FIGS. 3 and 4  are circuit diagrams of the Electrically Operated Air Dryer showing different modes of operation in accordance with the invention; 
           [0030]    and 
           [0031]      FIG. 5  is a circuit diagram of an alternative Tractor Pressure Control System with an Electrically Operated Air Dryer embodying the invention. 
       
    
    
       [0032]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
       DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0033]    The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what we presently believe is the best mode of carrying out the invention. Additionally, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
         [0034]      FIG. 1  shows a circuit diagram of a Tractor Pressure Control System (TPCS)  90  and an Electrically Operated Air Dryer (EOD)  100  on a tractor  1  having one wheel  2   a  fitted with a tire. Further tires (not shown) are connectable to the TPCS as indicated by arrow  2   b.  The tractor  1  is provided with a wheel  2   a  connected to the TPCS for inflation and deflation of its tire. For the avoidance of doubt, the term deflation means that air is let out of the tire. The term deflated air thus means the air which has been let out from the tire. A compressor  10  supplies air to components on a vehicle via the EOD. The EOD is connected to various consumers  30 ,  40 ,  50 ,  60  and the TPCS  90  via a consumer branch  20  and protection valve means  21 . Reservoirs  31 ,  41  are assigned to consumers  30 ,  40  and are equipped with pressure sensors  32 ,  42  to measure their pressure. Consumers  50  or  60  may also be equipped with respective reservoirs or sensors. Generally the reservoirs are kept at a defined pressure level, for example 8.5 bar to ensure that they can deliver the required air pressure when required, for example during braking. 
         [0035]    Protection valve means  21  balances the pressure required to be supplied to the primary set of consumers  30 ,  40  and the secondary consumers  50 ,  60  and will cut the supply to any consumer should a consumer develop a leak. In this way, the integrity of the remaining (primary) consumers is maintained. Furthermore, protection valve means  21  ensures that supply to primary consumers is prioritised over the supply to secondary consumers, such as the TPCS. In tractors or trucks, primary consumers  30  and  40  may be parallel brake circuits for a dual-circuit service brake. Secondary consumers  50 ,  60  may be a parking brake, an air suspension of the cab and wheels, or the TPCS. 
         [0036]    The components of the TPCS  90  are explained in detail: 
         [0037]    Generally, the TPCS comprises two separate circuits which represent two functions of the system. 
         [0038]    One circuit is the supply circuit  220  which is branched off the main TPCS line L 0  at connection  210  for connecting supply line L 1  to wheel  2   a  to supply air to the respective tire. This circuit must be capable of high air flow rates at high pressures to ensure fast inflation of a tire. 
         [0039]    A second circuit, control circuit  230  is also branched off the main TPCS line L 0  at connection  210  to connect with pilot control line L 2 . The control circuit  230  activates the deflation and inflation process by components of the supply circuit  220 . 
         [0040]    Control circuit  230  mainly contains pilot valves which for clarity are omitted in  FIG. 1 . Various pilot valve configurations may be used, as for example, those shown in PCT/EP2014/065935. In  FIG. 1  the pilot control valves  232  and  234  are provided for pneumatically controlling main control valve  221  and second stop valve  223  of the supply circuit  220 . All components of the control circuit are specified for low air flows as the pilot function requires only low air flows. The lower pressures and air flow in control circuit  230  enables the use of smaller and cheaper components, especially valves, which improves procurement, costs and installation space. Furthermore, the use of low pressures enables greater accuracy when sensors are installed, as the accuracy is decreased by a greater range of operation. 
         [0041]    To maintain the different pressure levels in both circuits  220 ,  230  excess flow valves  211 ,  212  are provided. If the pressure level exceeds the set level in the TPCS circuit, the connection is blocked to protect the components of the TPCS. For example, excess flow valve  211 , assigned to supply circuit  220  may be set to a maximum pressure between 7.1 to 7.5 bar, hereinafter referred to as the supply pressure. Excess flow valve  212 , assigned to pilot control circuit  230 , may be set to a maximum pressure between 4.5 to 5 bar, hereinafter referred to as the pilot control pressure. 
         [0042]    The supply circuit  220  is provided with a main control valve  221  to regulate the pressure in the tire  2   a.  The main control valve  221  is controlled by pilot valve  232 . Port  221   a  is connected to pilot control valve  232  which has two operating conditions for providing pilot control. Pilot control valve  232  is biased into a closed position  232   a  by a spring means  232   b  and can be moved to an open position  232   c  to allow air flow. In the closed position  232   a,  port  221   a  is connected to the atmosphere. The valve  232  may be moved into the open position  232   c  against the force of the spring  232   b  by energising solenoid  232   d  which is electrically connected to control unit  70 . For clarity reasons, the electric connections to the control unit  70  are only indicated by a double arrow. 
         [0043]    Main control valve  221  has two operating conditions: 
         [0044]    In a first condition, the tire of wheel  2   a  is connected to the air supply via main TPCS line L 0  and supply line L 1  for inflation of the tire. In a second condition (shown in  FIG. 1 ) the tire of wheel  2   a  is connected to the atmosphere via port  221   b  for deflation. With respect to the inflation operation, main control valve  221  is provided with a feedback via line  221   c  which ensures that the pressure level in the supply circuit after the main control valve  221  does not exceed 4.5-5 bar as the pressure in line  221   c  counteracts against the pressure coming from the control circuit  230  via the valve  232  which is set to a maximum of 4.5-5 bar. This balancing ensures that the tires are not charged with more than 5 bar representing an acceptable level. On the other hand, the higher pressure (adjusted to a maximum of 7.5 bar by excess flow valve  211 ) in the supply circuit  220  prior to main control valve  221  increases the performance of the TPCS. For clarity reasons, the electric connections to the control unit  70  are only indicated by a double arrow. 
         [0045]    A first stop valve  222  is positioned between the main stop valve  221  and the wheel  2   a  to allow inflation and deflation of the tire. First stop valve is biased into closed position  222   a  by a spring means  222   b  and can be moved to an open position  222   c  to allow air flow. The valve  222  may be moved into the open position  222   c  against the force of the spring  222   b  by energising solenoid  222   d  electrically connected to control unit  70 . For clarity reasons, the electric connections to the control unit  70  are only indicated by a double arrow. Between valve  222  and a rotatable passage  240  located in the trumpet housing of the wheel, the supply line L 1  branches off to another tire or tires on the tractor, as represented by the arrow  2   b.    
         [0046]    Each wheel has a respective rotatable passage  240  which connects the supply line L 1  in circuit  220  to the wheel  2   a.  Supply line L 1  is static relative to a second stop valve  223  located on the wheel. Second stop valve  223  is controlled pneumatically and can be moved into two positions, open position  223   a  and closed position  223   b  biased by spring means  223   c.  Valve  223  is operated by charging port  223   d  via the control circuit  230 . By charging port  223   d,  valve  223  can be moved against the spring  223   c  into an open position  223   a  to connect the interior of the tire to the supply line L 1 . Port  223   d  is connected to pilot control valve  234  which has two operating conditions for providing pilot control. Pilot control valve  234  is biased into closed position  234   a  by a spring means  234   b  and can be moved to an open position  234   c  to allow air flow. In the closed position  234   a,  port  223   d  is connected to the atmosphere. The valve  234  may be moved into the open position  234   c  against the force of the spring  234   b  by energising solenoid  234   d  which is electrically connected to control unit  70 . For clarity reasons, the electric connections to the control unit  70  are only indicated by a double arrow. 
         [0047]    By charging port  223   d  via pilot control valve  234 , valve  223  can be moved against the spring  223   c  into an open position  223   a  to connect the interior of the tire to the supply line 
         [0048]    During operation of the tractor and when the TPCS is in a stand-by mode, second stop valve  223  is in a closed position to close the tire volume. 
         [0049]    The term operation of the vehicle or machine is defined herein as meaning that the vehicle or machine is in a condition that its system or systems are sufficiently powered to for operation, for example, with the engine running. The term shut down of the vehicle is defined herein as meaning that the tractor is in a condition that its system, or systems are not sufficiently powered for operation, for example when the ignition key is removed and the driver leaves the tractor. 
         [0050]    Referring to TPCS the term stand-by mode is defined herein as meaning that the TPCS is in a condition wherein no change in tire pressure is done by the driver or an automatic control system but measurements or monitoring functions may still function. The TPCS Active mode is characterised by any change in tire pressure. 
         [0051]    If the vehicle is not in operation (shut down), TPCS is also out of operation as supply of any electric or pneumatic energy supply is cut. Consequently, in this condition the TPCS is in neither stand-by, nor in Active mode. 
         [0052]    If the tire pressure is adjusted (by manual input by the driver or an automatic control system), first and second stop valve  222 ,  223  are moved to their open positions  222   a  and  223   a.    
         [0053]    If the tires are inflated (tire pressure is increased), main control valve  221  is adjusted so that the tire is connected to the main TPCS line L 0  and the tire is charged with air. Depending on the design, the pressure adjustment may be done in two ways. Main control valve  221  is fully opened until the tire pressure, monitored by first pressure sensor  38  reaches the demanded value. Alternatively, main control valve  221  is opened to a position corresponding to the required pressure and closes when the value is reached. 
         [0054]    In case of deflation, main control valve  221  may be moved into a position in which the valve  221  is connected with the atmosphere at port  221   b  and air is discharged until the demanded pressure value, monitored by first pressure sensor  38 , is reached. 
         [0055]    At the end of any inflation or deflation process, second stop valve  223  is moved to a closed position. 
         [0056]    To measure the current tire pressure P c  of tire  2   a,  the second stop valve  223  is opened so that air from tire  2   a  flows from the tire along supply line L 1  to first stop valve  222 . If the opening and closing of the second stop valve  223  is controlled by a tractor control unit  70 , the second stop valve  223  can be opened automatically for a defined period of time before closing to achieve a static pressure in the respective supply line. The pressure in the supply line between the tire and the first stop control valve  222  can be measured by pressure sensor  38  which represents the pressure in the tire. 
         [0057]    The restriction  225  is used to determine the pressure differential. The pressure sensor  38  thereby provides the pressure in the supply line between the restriction  225  and main control valve  221  while a second pressure sensor  39  measures the pressure of the other side of the restriction  225 . Both sensors are used to calculate the pressure differential Δp across the restriction  225 . In this case, sensors  38 ,  39  measure the dynamic pressure within the arrangement. 
         [0058]    Main control valve  221  and stop valve  222  are fully opened during inflation and pressure measurements taken by sensors  38 ,  39  are not influenced as the pneumatic resistance is known and is approximately constant. Using a separate restriction  225  has the major advantage that the pressure differential is increased which increases the accuracy of the measurement. 
         [0059]    By calculating the pressure differential Δp, the air flow rate Q of the air being supplied to the tire can be calculated. By air flow rate Q, it is meant the volume of air passing a given point per unit time. The relation of pressure differential, Δp and air flow rate, Q across a restriction depends on various parameters including fluid viscosity, fluid compressibility and the geometry of the restriction. The theoretical basis of the relationship between pressure differential, Δp and air flow rate, Q are described in various publications and considered to be general engineering knowledge so that further detailed explanation is not necessary. 
         [0060]    For the embodiment described herein, the parameters can be summarised in a constant, C since the geometry of the restriction is known and remains constant and the fluid parameters mentioned above do not vary significantly within the operational range of the TPCS. This results in a simplified equation: 
         [0000]    
       
      
       Q=C×√{square root over (Δp)} 
      
     
         [0061]    If C cannot be considered to be constant, the relation between air flow rate, Q and pressure differential Δp could also be taken from tire characteristic maps stored in the tractor control unit or TPCS control unit. 
         [0062]    The tire pressure difference, Δp T  which the tire has to be increased by to achieve the desired pressure, P d  is calculated by subtraction of the desired tire pressure, P d  from the current tire pressure, P c  For a tire with known dimensions, a relationship between the tire pressure difference Δp T  and the necessary increase in tire air volume ΔV can be derived in order calculate the volume of air needed to be supplied to achieve the desired tire pressure, P d . This relationship is considered to be general engineering knowledge that the skilled person would know so that further detailed explanation is not necessary. 
         [0063]    A characteristic map is stored in the tractor control unit or TPCS control unit which provides the relationship between the tire pressure difference, Δp T  and tire air volume increase, ΔV across the operational range of the TPCS. Knowing the relationship between tire pressure difference Δp T  and tire air volume increase ΔV for tire inflation, the same can be applied when the tire is deflated. So a characteristic map can be stored for both tire inflation and deflation. 
         [0064]    Details of the air supply, especially the function of compressor  10 , EOD  100  and the consumer branch  20  are now explained. 
         [0065]    Compressor  10  is equipped with idler means  11  to provide an idle mode in which the air flow is reduced to a rate of 15% of the maximum air delivery of 1000 liters per minute. Alternatively, this efficiency function may be provided by an OFF/ON clutch cutting mechanical drive of compressor  10 . Furthermore, the compressor  10  may be electrically driven and the electric supply may be switched off by idler means  11 . 
         [0066]    The ECAD  100  comprises a dryer  101  comprising a cartridge filled with drying granules, a discharge valve  102 , a regeneration valve  103 , a compressor idler valve  104  and a check valve  105 . For clarity reasons, the electric connections of valves  102 ,  103  and  104  to the control unit  70  are only indicated by a double arrow. The granule cartridge extracts water from the air passing through it. 
         [0067]    With reference to  FIGS. 2 a    to  2   d,  the standard operating modes of the EOD are now explained: 
       Loading Mode (FIG.  2   a ) 
       [0068]    When a consumer requires air, air from compressor  10  flows to the consumer branch  20  via dryer  101  and check valve  105  as shown by the dotted path LP. During loading, discharge valve  102  is in its closed position  102   a  biased by spring  102   b,  as shown in  FIG. 2   a.  The dryer regeneration control valve  103  and idler valve  104  are also in their closed position  103   a/   104   a  biased by springs  103   b/   104   b.  Air flow in an opposite direction, that is from the consumer branch  20  to compressor  10  is prohibited by check valve  105 . 
       Idle Mode (FIG.  2   b ) 
       [0069]    If the consumer branch  20  is provided with sufficient air flow, the pressure is about 8.5 bar (this pressure is measured by sensors in reservoirs  31 ,  41 ). If this pressure is exceeded because compressor  10  is still working, the control unit  70  switches the compressor idler valve  104  from the closed position  104   a  (biased by spring  104   b ) to the open position  104   c  by energizing solenoid  104   d  to guide the air along path IP 1  from the consumer branch  20  to the compressor idler  11 . After compressor idler valve  104 , the air flow is branched-off via port  102   d  to move discharge valve  102  to open position  102   c  for connection of the compressor  10  to the atmosphere. The compressor idler  11  keeps the compressor  10  in this energy saving mode as long as pressure is applied. For normal operation, the compressor idler  11  must be connected to the atmosphere and this is done by valve  104  when in closed position  104   a.    
         [0070]    Thereby the remaining air flow (approximately 15% of the volume of air in the system) is discharged to the atmosphere with minimum resistance via discharge valve  102  along path IP 2 . 
       Overpressure Protection (FIG.  2   c ) 
       [0071]    If the pressure in the EOD circuit rises to a level above a permitted operating pressure, discharge valve  102  is opened via path OP 1  so that the connection of the compressor  10  to the atmosphere is opened (indicated by path OP 2 ). This function is a safety function when the electronic control fails or a blockage occurs which would also result in an incorrect pressure detection at pressure sensors  32 ,  42 . 
       Regeneration (FIG.  2   d ) 
       [0072]    Regeneration through the cartridge of dryer  101  may be achieved by using air from consumer reservoirs  31 ,  41  or any other reservoir connectable in a similar manner. For example, the EOD  100  may be provided with its own regeneration reservoir. Compressor idler valve  104  is opened to position  104   c  first so that the compressor  10  is brought into the idle mode (as explained above for the IDLE MODE) and air flows along path IP 1 . 
         [0073]    In addition, regeneration valve  103  is moved from its closed position  103   a  (biased by spring  103   b ) to the open position  103   c  by energizing solenoid  103   d  so that air from reservoir  31 ,  41  can by-pass the check valve  105  and enter the cartridge of dryer  101  along path RP 1 . As discharge valve  102  is already opened to position  102   c  via path IP 1  and port  102   d,  the air regenerating the dryer cartridge  101  and the air coming from the compressor  10  in the idle mode is discharged to the atmosphere. 
         [0074]    As already discussed above, the regeneration process requires a defined air flow which is taken from consumer reservoirs  31 ,  41  or reservoirs integrated in the dryer (not shown in the embodiment above). This reduces efficiency as this air flow is then not available for supplying consumers. 
         [0075]    In accordance with the invention and as shown in  FIG. 1 , port  221   b  of valve  221  through which deflated air from the tire flows is connected with the EOD  100  to use the air (which is normally discharged to the atmosphere during deflation) for the regeneration of the dryer. Therefore, port  221   b  is connected to the EOD  100  via line  80  and port  110 . As a consequence, all the air deflated from the TPCS would be guided through the dryer  101 . Alternatively, a valve may be provided in line  80  which could selectively connect the line  80  to the atmosphere. In that case, air deflated from the TPCS could be discharged to the atmosphere without passing dryer  101  if applicable. This would also have the main advantage that the rotatable passage  240  could be connected to the atmosphere so that the seals on the rotatable passage  240  (not shown) do not contact a non rotating surface. 
         [0076]    Furthermore line  80  may be equipped with a filtration means (not shown) so that the air from the tire is cleaned before it is used for the regeneration of the dryer  101 . This may be necessary as due to wear of the rubber tires, debris may be found inside the tires due to the tire becoming porous and tire particles are shed, or debris may be introduced into the tires from an external air source. 
         [0077]    Inside the EOD  100 , port  110  is connected to the dryer  101  at connection  82  which is positioned between dryer cartridge  101  and check valve  105  as shown in  FIG. 3 . 
         [0078]    As shown in  FIG. 3 , for regeneration of dryer  101  air from the TPCS flows along line  80  (indicated with path RP 2 ) while compressor  1  is switched to an idle mode. In the idle mode air flows along path IP 1  and opens valve  104  to position  104   c  so that the compressor  10  does not block regeneration with its higher air flow/pressure level. 
         [0079]    Simultaneously, discharge valve  102  is opened to position  102   c  for connection to the atmosphere so that moisture is discharged to the atmosphere. Valve  103  must be closed (position  103   a ) as shown in  FIG. 3  to avoid short circuit with reservoirs  31 ,  41 . Check valve  81  is needed to block air flow in the modes independent of TPCS as described in  FIGS. 2 a    to  2   d.    
         [0080]    Alternatively, if reservoirs  31 ,  41  of the consumer branch  20  are empty (so that the pressure level in path RP 2  is higher than the pressure in the consumer branch  20 ) air from path RP 2  could be used to provide air for path IP 1 . At connection  82  air could flow to check valve  105  and enter path IP 1  at connection  83 . This would enable the regeneration of the dryer  101  even if the compressor  10  is off or the consumer branch is empty (presuming that tires can provide sufficient air). 
         [0081]    Further functions are provided using air deflated from the tires as flow regeneration for the dryer  101 . 
       Air Volume Monitoring 
       [0082]    The air needed for regeneration is a default setting. The TPCS system can determine the amount of air released during inflation and deflation as explained above. It can therefore compare the volume of air deflated from the tire with the volume required for regeneration and calculate if sufficient air has been deflated from the tire or not. 
         [0083]    For example, if 120 liters of air is required for the regeneration of the dryer and the TPCS deflation process deflates the tire from, for example, 1.8 bar to 1.7 bar, the TPCS will only be able to deliver 100 liters for regeneration. In such a case, the system can also use some of the air in the reservoirs  31 ,  41  to complete the regeneration. 
       Compressor Deactivation Before TPCS 
       [0084]    As with regeneration using air from the reservoirs  31 ,  41 , regeneration via the TPCS requires that the compressor  10  is not fully delivering, so the compressor  10  must be brought into an idle mode, or switched off. 
         [0085]    Alternatively, the control unit may postpone deflation, for example, if the reservoirs  31 ,  41  need immediate refilling. 
       Filling the Reservoir After Shut Down 
       [0086]    Most air supply systems suffer from the fact that air is lost during longer periods of shut down of the vehicle, such as overnight. After starting the vehicle again, some initial time is required to fill the consumer reservoirs  31 ,  41  to be ready for operation. 
         [0087]    In accordance with the invention, the tire is used as an air reservoir for long periods of shut down of the tractor, such as overnight. The system can decide the conditions of the reservoir before shut down. If the reservoirs  31 ,  41  show a high pressure, the tires may be inflated to a pressure level which is higher than the level in operation. The system is then shut down. 
         [0088]    After restarting the tractor, the tire is deflated to a desired tire pressure and the deflated air is used to fill the reservoirs to the desired pressure without using the compressor  10 . 
         [0089]    For filling the reservoirs  31 ,  41  with air from the tire  2   a,  the pressure level of the reservoir must be lower than that in the tire  2   a,  but sufficient to open valve  223  on tire  2   a.  As shown in  FIG. 4  the air will flow along the path FP 1  to reservoir  30  or  40  and towards valve  104 . 
         [0090]    If compressor  10  is already running, that is the tractor engine is on, then the compressor  10  must be switched to the IDLE MODE by moving valve  104  to open position  104   c  so that air flows along path IP 1 . 
         [0091]    If the compressor  10  is not running, the pressure in reservoirs  31 ,  41  must be sufficient to open valve  223  at tire  2   a.  If valve  223  is electrically operated, no initial pressure in the reservoirs is required as pressure from the tire may be sufficient for operating valve  104 . The other valves  103  and  102  will move into the correct positions due to spring biasing when shut down. 
       Monitoring External Filing 
       [0092]    If the tires are inflated by an external source, for example, from a garage compressor, it is possible that humid air is introduced into tires  2   a.  Using the humid air for regeneration in such a case would further worsen the condition of the dryer. 
         [0093]    The system can detect external filing since the tire pressure will increase without activation of the TPCS. The TPCS or control unit  70  stores the desired pressure in the tires after each TPCS operation, even if the vehicle is shut down. Leakage would result in a tire pressure decrease but if the tire pressure has increased, external filling has been provided so that the air may be more humid than required for flow return. 
         [0094]    If the TPCS is then deflated and guides the moist air through the dryer  101 , no regeneration drying effect is provided since more moisture is brought into the system. As a consequence, the system can decided to conduct regeneration by using air from the TPCS and the reservoirs  31 , 41 , or using air solely from the reservoirs  31 ,  41 , or by conducting an extended regeneration using air from the reservoirs to discharge the additional air brought into the tires as a consequence of external filling as shown in  FIG. 4 . 
         [0000]    EOD Dryer Provided with Port for Inserting TPCS 
         [0095]    The EOD  100  must be provided with an additional TPCS input port  110  (shown in  FIG. 3 ) and check valve  81 . The port must be connected to the dryer  101  such that the regeneration valve  103  and check valve  105  can be by-passed as shown in  FIGS. 1 and 3 . 
         [0096]    The invention as described above is described with reference to one embodiment of a TPCS. The invention can also be used with alternative embodiments of TPCS, such as the one shown in  FIG. 5 . In  FIG. 5 , the EOD circuit and components of  FIGS. 1 to 4  are shown connected to an alternative TPCS  300  which is described in detail in the applicant&#39;s granted patent EP2196336. The wheel  301  of  FIG. 5  is provided with an inner tire  330  and an outer tire  320 . 
         [0097]    A first tire reservoir  310  is enclosed between the outer tire  320  and the inner tire  330  and is mainly used to adjust the pressure of the wheel. A second tire reservoir  340  is enclosed between inner tire  330  and the tire rim  350  and is mainly used to store compressed air at a relatively high pressure (around 6-8 bar) which is supplied by the compressor  10  or protection valve means  21 . A first sensor  360  is assigned to first tire reservoir  310  and a second sensor  370  is assigned to second tire reservoir  340 . 
         [0098]    TPCS  300  provides a second tire air reservoir  340  at a higher pressure level compared to the pressure in a first tire air reservoir  310  wherein both reservoirs are fluidly connectable. In accordance with the present invention, air from the first or second reservoir  310 ,  340  is used for regeneration and for refilling the reservoirs  31 ,  41  assigned to consumers  30 ,  40  after shut down. 
         [0099]    For controlling the functions of the TPCS  300 , valves  400 ,  410 ,  420  and  430  are provided. Pressure sensors  360  or  370  and valves  400 ,  410 ,  420  and  430  can communicate with control unit  70  via wireless communication, or by an electrical rotatable passage (not shown). 
         [0100]    A rotatable passage  440  pneumatically connects the rotatable wheel  301  and the components mounted on the wheel  420 ,  410 ,  400  to valve  430  which is mounted on the tractor chassis. 
         [0101]    The operating conditions of the TPCS of  FIG. 5  are: 
       Direct Tire Inflation 
       [0102]    For inflation of first reservoir  310  directly via compressor  10 , consumer branch  20  and line L 0 , valve  410  is closed (as shown in  FIG. 5 ) and valves  400 ,  420  are opened to allow air to flow to reservoir  310 . Valve  430  is brought to position  430   a  so that line  80  is closed and the line to the tire is open. Pressure sensor  360  is used to monitor the tire pressure and to stop the inflation process when the desired pressure is reached. Alternatively, characteristic maps may be used to calculate the volume of air required to attain a desired tire pressure (or, if the air flow rate is known, the inflation time can be calculated). 
       Tire Inflation Via Second Tire Reservoir  340   
       [0103]    In this mode, valve  420  is closed and valve  430  is moved to a closed position  430   b.  If valves  400  and  410  are then opened, air can flow from the second reservoir  340  to the first reservoir  310 . 
       Filling the Second Tire Reservoir  340   
       [0104]    For filling the second reservoir  340  via compressor  10 , consumer branch  20  and line L 0 , valve  400  is closed (as shown) and valves  410 ,  420  are open. Valve  430  is moved to open position  430   a.    
       Tire Deflation (Reducing Pressure in First Tire Reservoir  310 ) 
       [0105]    In this mode, valves  400 ,  420  are open, valve  410  is closed and valve  430  is moved to position  430   a.  In accordance with the invention, port  430   c  is connected to port  110  of EOD  100  to guide air back to the EOD  100  or to the reservoirs  31 ,  41 . 
         [0106]    With reference to the invention, an air supply system comprising TPCS  300  offers the same functions of regeneration, air volume monitoring, compressor deactivation before TPCS and filling the reservoir after shut down as those previously described for an air supply system comprising TPCS  90 . 
         [0107]    More specifically: 
       Regeneration 
       [0108]    For regeneration using air deflated from the wheel  301 , valve  410  is closed, valves  400  and  420  are opened and valve  430  is brought into position  430   b  so that air flows from the first reservoir  310  in the tire to dryer  101 . 
         [0109]    Advantageously, regeneration without using air deflated from the tire can be performed without affecting the pressure of the tire, that is without affecting the pressure of the first reservoir  310 . This performed by deflating air from the second reservoir  340 . This is achieved by closing valve  400 , opening valves  410 ,  420  and bringing valve  430  into position  430   b  so that air can pass from the second reservoir  340  in the tire to the dryer. 
       Filling the Reservoir After Shut Down 
       [0110]    TPCS  300  has the advantage that the reservoir  340  holds air at high pressures so that the consumer reservoirs  31 ,  41  are filled more easily and more quickly than using the air from reservoir  310 . This is because the pressure of air in the reservoir  310  is lower than the pressures of consumer reservoirs  31 ,  41 . This is especially advantageous for refilling after shut down. 
         [0111]    The invention as described in both embodiments permits regeneration of a dryer using air from the consumer reservoirs  31 ,  41 , or using air from the tire during deflation, or using air from both the tire and the consumer reservoirs. 
         [0112]    The invention is not restricted to the types of TPCS described herein but may be used when air deflated from the tire is used for the regeneration of a dryer. 
         [0113]    The foregoing has broadly outlined some of the more pertinent aspects and features of the present invention. These should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Other beneficial results can be obtained by applying the disclosed information in a different manner or by modifying the disclosed embodiments. Accordingly, other aspects and a more comprehensive understanding of the invention may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings.