Abstract:
An air dryer for a locomotive air supply system that includes a controller programmed to initiate a sleep mode that inhibits the air dryer and de-energizes all valves. The controller determines when it is appropriate to enter into sleep mode based on various conditions of the locomotive air supply system. More specifically, the controller is programmed to calculate whether the air dryer should be placed into sleep mode based on operational characteristics of the locomotive air supply system that are indicative that the system has been idled. The initiation of an air dryer sleep mode by the controller prevents undesirable venting of air from the air supply system and unnecessary usage of locomotive battery power.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to railway air system air dryers and, more particularly, to an air dryer control system having a sleep mode to prevent the depletion of air and power during idling times. 
         [0003]    2. Description of the Related Art 
         [0004]    A typical “twin-tower” desiccant-type air dryer includes two drying circuits that are controlled by valves. Wet inlet air flows through one circuit to remove water vapor, while dry product air counter flows through the other circuit to remove the accumulated water and regenerate the desiccant. Inlet and outlet valves for each pneumatic circuit are responsive to controlling electronics to switch the air flow between the two circuits so that one circuit is always drying while the other is regenerating. The air dryer may include a pre-filtration stage with a water separator and/or coalescer positioned upstream of the drying circuits. The pre-filtration stage removes liquid phase and aerosol water and oil that can accumulate in air supply system as a result of the compression of ambient air by the locomotive air compressors. A pre-filtration stage includes a drain valve that is used to periodically purge any accumulated liquid. For example, a typical pre-filtration drain valve actuation cycle might command a purge (open) for two seconds every two minutes. 
         [0005]    When a locomotive is parked, the driver will usually open the main circuit breaker and shut down the auxiliary electrically powered equipment, which includes the air dryer. Under certain circumstances, however, the locomotive may be parked or idled for an extended period with the electrical power left on. If the diesel engine or air compressor is turned off, the pre-filtration drain valve and desiccant regeneration valves will continue to cycle and will eventually deplete the main air reservoir and/or the locomotive battery. Some air supply systems address the problem of electrical power depletion by only operating the air dryer valves when the air compressor is running This solution, however, does not fully address the problem, as it can result in inefficient drying of the air when it is operating. For example, air can still flow through an air dryer when the compressor is off. In addition, there are many instances when the compressor is turned on but no air is actually flowing through the air dryer such that operation of the valves is wasteful. Finally, in a multiple locomotive consist where all of the locomotives are coupled together by a main reservoir trainline, the other locomotives in the consist can be supplying compressed air to the locomotive whose compressor is off. Accordingly, there is a need in the art for an air dryer control system prevents the air dryer from unnecessarily venting compressed air or wasting electricity when the locomotive air supply system is intended to be idle. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention comprises an air dryer for a locomotive air supply system having a set of valves for controlling the flow of air from an inlet through one of two dessicant towers to an outlet and a controller for piloting the set of valves. More specifically, the controller is programmed to inhibit operation of the valves in response to a determination that the locomotive air supply system is not in use. The locomotive air supply system is determined to not be in use if the air compressor supplying air to the air dryer is not in operation for a predetermined period of time, if the electrical state of a diesel locomotive coupled to the air dryer indicates a lack of usage, if there is a lack of air flow through the air dryer over a predetermined period of time, if first main reservoir lacks sufficient pressure for a predetermined period of time, if the second main reservoir has a sufficient amount of pressure in the second main reservoir relative to the first main reservoir, or if the humidity in the air exiting the air dryer over a predetermined period of time indicates a lack of use of the air supply system. Accordingly, the air dryer may include a humidity sensor coupled to the controller, and the controller may be interconnected to the air compressor, the locomotive electrical system, pressure sensors in the first and second main reservoirs. The controller may also be interconnected to a check valve positioned between the first and second main reservoirs and, optionally, a flow meter positioned to measure air flow volume in the inlet to the air dryer. 
         [0007]    The method of the present invention comprises a sleep mode control for an air dryer having a series of valves for controlling the flow of air from an inlet through at least one dessicant tower to an outlet and a controller for piloting the set of valves. The controller of the air dryer determines whether the locomotive air supply system is not in use and, if not, inhibits the series of valves during the time period the locomotive air supply system is not in use. The controller may restore normal operations periodically, or after detecting an indication that the locomotive air supply system is back in use. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0008]    The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a schematic of a locomotive air supply system having an air dryer with sleep mode according to the present invention; 
           [0010]      FIG. 2  is a schematic of an air dryer with a sleep mode according to the present invention; 
           [0011]      FIG. 3  is a schematic of an air dryer with a sleep mode according to the present invention interconnected to various elements of a locomotive air supply system; and 
           [0012]      FIG. 4  is a flowchart of a sleep mode implementation process for an air dryer according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in  FIG. 1  a locomotive air system  10  having an air compressor  12 , aftercooler  14 , first and second main reservoirs MR 1  and MR 2 , and a two-tower dessicant air dryer  16  having a sleep mode according to the present invention, as more fully described below. Second main reservoir MR 2  is coupled to the braking system  18  and a check valve  20  is positioned between the first and second main reservoirs MR 1  and MR 2 . A pre-filtration stage  22  is associated with air dryer  16  and includes a drain valve  24  that is operated according to a drain valve purge cycle time. Optionally, a flow meter  26  may be positioned in the inlet air to the air dryer. 
         [0014]    Referring to  FIG. 2 , a two-tower dessicant air dryer  16  comprises an inlet  28  for receiving air from first main reservoir MR 1 . Inlet  28  is in communication with an integral pre-filtration stage  30 , shown as including a water separator  32 , a coarse coalescer  34 , and a fine coalescer  36 . Any accumulated liquids in water separator  32 , coarse coalescer  34 , and fine coalescer  36  are expelled through drain valve  24 . A pair of inlet valves  42  and  44  are positioned downstream of pre-filtration stage  30  for diverting incoming air between one of two pathways, each of which is associated with one of two dessicant towers  46  and  48 . A temperature sensor  50  is positioned upstream of inlet valves  42  and  44  and downstream of pre-filtration stage  30 . The first pathway downstream of first inlet valve  42  leads to an exhaust valve  52  and first dessicant tower  46 . The second pathway downstream of second inlet valve  44  leads to a second exhaust valve  54  and second dessicant tower  48 . The first pathway further includes a first check valve  58  and first bypass orifice  62  downstream of first dessicant tower  46 , and the second pathway further includes a second check valve  60  and bypass orifice  64  downstream of second dessicant tower  48 . A single outlet  66  is coupled to the end of the first and second pathways, and a humidity sensor  68  is positioned upstream of outlet  66 . Inlet valves  42  and  44  and outlet valves  52  and  54  are piloted by controller  40 . Controller  40  operates inlet valves  42  and  44  and outlet valves  52  and  54  so that compressed air provided at inlet  28  is directed through one of dessicant towers  46  or  48  for drying. The other dessicant towers  46  or  28  may be regenerated by allowing dried air to reflow through bypass orifice  62  or  64  by opening the corresponding exhaust valve  52  or  54  for a given period of time. Controller  40  is also in communication with temperature sensor  50  and humidity sensor  68 . A heating element  70  may also be coupled to controller  40  and positioned in air dryer  16  to warm inlet valves  42  and  44  and outlet valves  52  and  54  is the temperature is below freezing. 
         [0015]    In addition to executing the normal operation of inlet valves  42  and  44  and outlet valves  52  and  54 , controller  40  is programmed to determine whether the operation of air dryer  16  should be inhibited, such as when the locomotive is idle of if there is no demand for drying because air is not flowing through air dryer  16 . When controller  40  determines the locomotive air system  10  is not in use, controller  40  is programmed to activate a sleep mode where actuation of drain valve  38  and/or inlet valves  42  and  44  and outlet valves  52  and  54  are suspended until controller  40  receives a signal indicating that air system  10  is in use again. When controller  40  determines that air system  10  is again in use, controller  40  may resume normal actuation of the valves. Once sleep mode is initiated, controller can de-energize the normally closed drain valve  24 , the normally open inlet valves  42  and  44  and the normally closed outlet valves  52  and  54  to avoid undesirable leakage of air from air supply system  10 . 
         [0016]    Referring to  FIG. 3 , controller  40  may be interconnected to compressor  12  to receive an input reflecting when compressor  12  is being operated. For example, controller  40  may receive a signal reflecting the status of the compressor motor driver current, the unloader, or the motor control contactors. Similarly, controller  40  may be interconnected to the locomotive electrical system  72  to determine the status of the locomotive. For example, controller  40  may be interconnected to the output of the auxiliary generator  74  to determine whether the diesel locomotive is off. Controller  40  may also be interconnected to the locomotive battery  76  to determine whether the battery voltage has dropped below a predetermined threshold, thereby indicating that the diesel engine of the locomotive is not running and battery  76  is not being recharged. Any or all of these detected events may be used as a trigger for controller  40  to initiate sleep mode. Controller  40  may implement sleep mode for a predetermined period of time, or until controller  40  detects an event indicative of the resumption of use of the locomotive air supply system  10 . 
         [0017]    Instead of, or in addition to, detecting locomotive status events, controller  40  may also be programmed to determine whether there is any air flow through air dryer  16 , or even the quality and amount of air flow through air dryer  16 , as a trigger for entering sleep mode. For example, a binary reading may be taken from check valve  20  to provide an indication whether check valve  20  is open or closed, thereby allowing controller  40  to determine whether air is flowing from MR 1  to MR 2 . Similarly, a proportional reading may be taken from check valve  20  to determine how far check valve  20  has opened. The size of the opening of check valve  20  is proportional to the pressure difference across check valve  20  and the spring rate and preload of the bias spring in check valve  20  are known. As a result, the amount of displacement of check valve  20  can be used to calculate the instantaneous flow rate across check valve  20 . The total air flow volume can then be calculated by a simple integration of the instantaneous air flow rate over a given period of time. Lastly, the system may include flow meter  26  to directly measure the flow rate. Controller  40  may then be programmed to enter into sleep mode to inhibit valve actuation if there is zero air flow or if the air flow is below a predetermined threshold over a particular time period, such as twenty-four hours. 
         [0018]    Controller  40  may also be interconnected to MR 1  or MR 2  to determine the pressure in either or both of those reservoirs. Controller  40  may then initiate sleep mode if the pressure in MR 1  is less than the low pressure governor set point used to trigger air compressor  12  to recharge system  10  as this would indicate that the locomotive is not in a state where air compressor  12  needs to replenish MR 1 . Similarly, controller  40  may be programmed to initiate sleep mode if the pressure in MR 2  is greater than the pressure in MR 1  for a predetermined number of hours, thereby indicating that MR 1  is not being recharged. The pressure in MR 1  or MR 2  may be determined by a pressure transducer or pressure switch that is interconnected to controller  40 . 
         [0019]    Controller  40  may also be programmed to measure the output of air dryer  16  to determine whether the sleep mode should be initiated. For example, a lack of change in humidity at the output of air dryer  16  may be used to infer that air supply system  10  is not in active use. For example, if the humidity remains sufficiently dry within a predetermined tolerance while the air dryer purge cycle time is at a maximum duration setting and temperature at inlet  28  is warm enough that the humidity should otherwise be increasing if there was air flow through the air dryer, controller  40  may initiate sleep mode. 
         [0020]    Controller  40  may also be programmed to determine whether the outlet humidity reflects the expected saturation level for air flowing through air dryer  16  and, if not, initiate sleep mode. If the compressed air in MR 1  is assumed to be saturated due to the compression pressure, the current air temperature and corresponding water vapor saturation level may be used to calculate the volume of air that, over time, would saturate one of desiccant towers  46  or  48  in air dryer  16 . For example, at the measured temperature, controller  40  might calculate that 500 cubic feet of air from MR 1  would saturate the desiccant of air dryer  16 . At a flow rate of 90 standard cubic feet per minute (SCFM) saturation should occur in as little as 5.5 minutes. If the humidity of outlet  66  does not reflect saturation after the expected time to saturation has passed, controller can initiate sleep mode. 
         [0021]    Instead of measuring the expected saturation time, controller  40  may instead by programmed to initiate sleep mode if the default regeneration cycle time has been reached a predetermined number of times without an increase in humidity. For any air dryer  16  having a variable regeneration cycle, controller  40  may be programmed to initiate sleep mode if the variable regeneration cycle has been extended a predetermined number of times without any resulting increase in humidity in the air passing through air dryer  16 . A subesequent increase in humidity at outlet  66  may be used to trigger controller  40  to return to normal valve control. 
         [0022]    Once controller  40  has initiated sleep mode, a change in the various triggering conditions identified above may be used by controller  40  to terminate sleep mode and to return to normal valve operation. For example, the turning on of air compressor  12 , the detection of air flow through air dryer  16 , an increase in MR 1  pressure above a predetermined threshold, power at the auxiliary generator, a recharge of the locomotive battery above a predetermined number of volts, and/or a change in the humidity at the air dryer outlet  66  may trigger a return to normal operations. Alternatively, or in addition thereto, controller  40  may be programmed to return to normal valve operations periodically, such as once every twenty-four hours, and then reenter valve control sleep mode if the conditions of air supply system  10  for initiating sleep mode are still present. 
         [0023]    Referring to  FIG. 4 , controller  40  may thus implement a sleep mode process  80  that begins with air dryer  16  in normal valve operation  82 . Controller  40  then performs a check  82  to determine whether locomotive air supply system  10  is intended to be at idle using one or more of the approaches discussed above. For example, controller  40  can check locomotive electrical system  72 , air compressor  12 , first main reservoir MR 1 , check valve  20 , air dryer  16 , or second main reservoir MR 2  for relevant status data and then perform any necessary calculations as described above to determine if system  10  is idle such that air dryer  16  should be placed into sleep mode and all valves de-energized. If a check  84  indicates that the locomotive air supply system is not in use, such as by being idle for a predetermined period of time, controller  40  inhibits air dryer valves  86 , thus putting air dryer  16  into sleep mode. Controller  40 , according to a predetermined schedule, performs a subsequent check  88  of the relevant aspects of system  10  to determine whether locomotive air supply system  10  is back in use. If so, controller  40  restores normal valve operation  90 .