Patent Publication Number: US-2016245268-A1

Title: Pump with quick discharge function

Description:
RELATED APPLICATION 
     This application claims priority to FR 15 51595, filed Feb. 25, 2015. 
     TECHNICAL FIELD 
     The present invention relates to a pump, designed to increase the pressure in an enclosed space, in particular to act on a pressure-sensitive element, for example a pneumatic actuator. 
     BACKGROUND 
     Already known in the state of the art is a pump including a hollow body and a piston, housed in the hollow body movably in a longitudinal direction, the piston defining, with the hollow body, a compression chamber with a variable volume based on a position of the piston in the longitudinal direction. The hollow body typically includes: an intake opening, designed to communicate with a fluid source and able to communicate with the compression chamber; a first non-return arranged between the intake opening and the compression chamber, which allows the passage of fluid from the intake opening to the compression chamber and prohibits the passage of fluid from the compression chamber to the intake chamber; an expulsion opening, which emerges in the compression chamber and communicates with an expulsion duct; and a second non-return arranged between the compression chamber and the expulsion duct, which allows the passage of fluid from compression chamber to the expulsion duct and prohibits the passage of fluid from the expulsion duct to the compression chamber. 
     When the piston moves in a first direction, the volume of the compression chamber increases and fluid fills the compression chamber by passing through the intake opening. 
     When the piston moves in a second direction opposite the first, the volume of the compression chamber decreases and the fluid is expelled through the expulsion opening. The first and second non-returns allow the fluid to flow only in one direction. 
     By applying oscillating movements to the piston in the first direction, then the second direction along the longitudinal direction, this piston expels a desired quantity of fluid in the expulsion duct. When this expulsion duct is connected to an enclosed space, the pressure in the enclosed space then increases. The invention also aims to improve such a pump, in particular for applications where a quick return to the initial position may be desired. 
     SUMMARY 
     To that end, the invention in particular relates to a pump including a hollow body and a piston, housed in the hollow body movably in a longitudinal direction, defining, with the hollow body, a compression chamber with a variable volume depending on the position of the piston in the longitudinal direction, the hollow body including: an intake opening designed to communicate with a fluid source and able to communicate with the compression chamber, 
     a first non-return member arranged between the intake opening and the compression chamber to allow the passage of fluid from the intake opening to the compression chamber, and to prohibit the passage of fluid from the compression chamber to the intake chamber, 
     an expulsion opening emerging in the compression chamber and communicating with an expulsion duct, 
     a second non-return member arranged between the compression chamber and the expulsion duct to allow the passage of fluid from compression chamber to the expulsion duct, and to prohibit the passage of fluid from the expulsion duct to the compression chamber 
     and wherein 
     the hollow body includes a discharge opening communicating with the expulsion duct and able to communicate with the intake opening, and a third non-return member movable between an open position, in which the expulsion duct communicates with the intake opening, and a closed position prohibiting the passage of fluid between the expulsion duct and the intake opening, and 
     the pump includes a movable element or member to move for the third non-return member. 
     By moving the third non-return member into the open position, the expulsion duct communicates with the intake opening, such that the high-pressure fluid contained in the expulsion duct is discharged through the intake opening, until the pressure in the expulsion duct is reduced to the pressure of the fluid source, for example the atmospheric pressure. 
     It is thus possible to discharge the pump quickly, making its use possible for applications where such a quick discharge is desirable. 
     A pump according to the invention can further comprise one or more of the following features, considered alone or in any technically possible combinations. 
     The displacement member includes: a ferromagnetic element movable between a first position, in which the third non-return member is in the open position, and a second position, in which the third non-return means are in the closed position, an elastic member biasing the ferromagnetic element toward its first position, and an electric coil surrounding the ferromagnetic element and electrically connected to a power supply able to apply an adjustable current. The position of the ferromagnetic element depends on the voltage of the current. 
     The third non-return member includes a non-return gate biased in the closed position by an elastic member, and the displacement member includes an actuating element secured to the piston and designed to cooperate with the non-return gate to move the non-return gate into the open position by pushing the non-return gate against the biasing of the elastic member, when the piston is in a predetermined discharge position, and said ferromagnetic element is formed by a rod secured to the piston. 
     The piston is movable, in the longitudinal direction, between: a first extreme position, in which the actuating element cooperates with the non-return gate, and in which the volume of the compression chamber is maximal, a second extreme position, in which the volume of the compression chamber is minimal, and at least one intermediate position, in which the actuating element is kept at a distance from the non-return gate. 
     The third non-return member includes a non-return gate, the ferromagnetic element being formed by this non-return gate. 
     The piston includes a rod made from a ferromagnetic material, in particular soft iron, extending in the longitudinal direction, the pump including an electric coil surrounding the rod and electrically connected to a power supply able to apply a variable electric current, the position of the piston depending on the voltage of the electric current. 
     The intake opening includes a filter. 
     The pump includes a variable volume fluid reservoir forming the fluid source. 
     The fluid is gas, in particular air. 
     The invention also relates to an assembly of a pump and a pressure-sensitive controllable element controlled by the pump, wherein the pump is as previously defined, the controllable element being connected to the expulsion duct of the pump. 
     For example, the controllable element includes a movable membrane of an expansion vessel equipping a Rankine system, the Rankine system comprising: 
     an evaporator, 
     a steam machine arranged downstream from the evaporator, 
     a condenser arranged downstream from the steam machine, 
     a pumping device arranged downstream from the condenser, and 
     the expansion vessel arranged between the condenser and the pumping device, the expansion vessel including: 
     an enclosure, 
     the movable membrane, mounted movably in the enclosure and separating the enclosure into a first part communicating with the condenser and the pumping device, and a second part communicating with the expulsion duct of the pump. 
     According to another example, the controllable element is a valve actuator, in particular for a motor vehicle exhaust device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood using the following description, provided solely as an example and done in reference to the appended figures, in which: 
         FIG. 1  is a diagrammatic sectional view of an assembly of a pump according to one example embodiment and a controllable element controlled by the pump, the pump including a piston shown in an intermediate position; 
         FIG. 2  is a view similar to  FIG. 1  of the pump in which the piston is shown in a first extreme position; 
         FIG. 3  is a view similar to  FIG. 2  of the pump in which the piston is shown in a second extreme position; 
         FIG. 4  diagrammatically shows an assembly of a pump according to a second example embodiment and an element controlled by the pump; 
         FIG. 5  is a view similar to  FIG. 4  of the pump according to  FIG. 4  in a discharge situation; 
         FIG. 6  diagrammatically shows a pump according to a third example embodiment of the invention; and 
         FIG. 7  shows an assembly of a pump according to the invention and an element controllable by the pump, equipping a Rankine system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an assembly  8  including a pump  10  and a pressure-sensitive controllable element  12  that is controlled by the pump  10 . 
     In this example, the controllable element  12  is a pneumatic actuator designed to control an exhaust valve of an exhaust device of the motor vehicle. This controllable element  12  traditionally includes a body  14  defining a chamber  16  in which a tight membrane  18  is housed separating the chamber  16  into first  16 A and second  16 B compartments. The membrane  18  is movable in the chamber  16 , such that the volume of the compartments  16 A and  16 B depends on the position of this membrane  18 . 
     The membrane  18  is connected to a rod  20 , such that the movement of the membrane  18  causes the movement of the rod  20 . 
     The actuator  12  lastly includes an elastic member  22 , in particular a spring, applying an elastic biasing force, biasing the membrane  18  toward a first position, shown in  FIG. 1 , in which the volume of the first compartment  16 A is minimal or null, and the volume of the second compartment  16 B is maximal. The membrane  18  is movable to a second position, in which the volume of the first compartment  16 A is maximal and the volume of the second compartment  16 B is minimal or null. 
     The rod  20  is connected to the exhaust valve. The exhaust valve is movable between a closed position and an open position. More particularly, the exhaust valve is in the closed position when the membrane  18  is in the first position, and in the open position when the membrane  18  is in the second position. 
     It will be noted that the membrane  18  can assume various intermediate positions between the first and second positions, each of these intermediate positions corresponding to an intermediate position of the valve between the closed position and the open position. 
     In order to move the membrane  18 , the pressure is varied in the first compartment  16 A. Thus, by increasing this pressure, a pressure force is opposed against the elastic biasing force of the elastic member  22 , which makes it possible to move the membrane  18  when the pressure force is greater than the elastic force. 
     Conversely, when the pressure decreases, the pressure force becomes lower than the elastic force, such that the membrane  18  is returned toward its first position by the elastic member  22 . 
     The pressure in the first compartment  16 A is controlled by the pump  10 . 
     The pump  10  includes a hollow body  24  and a piston  26  housed in the hollow body  24  and movably in the longitudinal direction X. The hollow body  24 , for example, has a generally cylindrical shape extending in the longitudinal direction X. 
     The piston  26  defines, with the hollow body  24 , a compression chamber  28  with a variable volume based on a position of the piston  26  in the longitudinal direction X. 
     The piston  26  is movable in the longitudinal direction X between a first extreme position, shown in  FIG. 2 , in which the volume of the compression chamber  28  is maximal, and a second extreme position, shown in  FIG. 3 , in which the volume of the compression chamber  28  is minimal. The piston  26  can assume any intermediate position between the first and second extreme positions, and in particular a so-called idle position, shown in  FIG. 1 , which will be described later in more detail. 
     The hollow body  24  includes an intake opening  30 , designed to communicate with a fluid source, and able to communicate with the compression chamber  28 . 
     The fluid source is, for example, the atmosphere surrounding the pump  10 , in which case the fluid is air. In this case, the intake opening  30  is advantageously equipped with an air filter in order to avoid any contamination of the hollow body  24  by unwanted particles and/or liquids. 
     Alternatively, the fluid source is formed by a reservoir connected to the intake opening  30 . Such a reservoir has a variable volume, such that the pressure remains constant in this reservoir when fluid is suctioned by the pump  10 . In this case, the fluid can also be air, or alternatively oil or any other possible fluid. 
     In the described example, the intake opening  30  communicates with the compression chamber  28  through orifices  32  arranged in the piston  26 . A first non-return member  34 , arranged between the intake opening  30  and the compression chamber  28 , allows the passage of fluid from the intake opening  30  toward the compression chamber  28 , and prohibits the passage of fluid from the compression chamber  28  toward the intake opening  30 . In the described example, the first non-return member  34  is formed by a non-return membrane able to unstick from the piston  26  when fluid passes through from the intake opening  30  toward the compression chamber  28 , and to press against the piston  26  so as to close off the orifices  32  to prohibit the passage of fluid from the compression chamber  28  toward the intake opening  30 . 
     The hollow body  24  further includes an expulsion opening  36 , emerging in the compression chamber  28 , and communicating with the expulsion duct  38 . A second non-return member  40 , in particular a non-return gate of the traditional type, is arranged between the expulsion opening  36  and the expulsion duct  38  to allow the passage of fluid from the compression chamber  28  toward the expulsion duct  38 , and to prohibit the passage of fluid from the expulsion duct  38  toward the compression chamber  28 . 
     When the piston  26  moves from its idle position, shown in  FIG. 1 , toward its second extreme position, shown in  FIG. 3 , the fluid contained in the compression chamber  28  is expelled through the expulsion opening  36 , this expulsion being authorized by the second non-return member  40 . During this movement, the non-return membrane of the first non-return member  34  is pressed against the passage orifices  32  of the piston  26 , such that the fluid does not escape through these passage orifices  32 . 
     When the piston  26  moves from its second extreme position shown in  FIG. 3  toward its idle position shown in  FIG. 1 , the volume of the compression chamber  28  increases, and its pressure decreases such that fluid is suctioned in this compression chamber  28 . Due to the second non-return member  40 , the fluid is not suctioned from the expulsion duct  38 . However, the first non-return member  34  allows the passage of fluid through the passage orifices  32 , such that the fluid is suctioned from the fluid source through the intake opening  30  and the passage orifices  32 . 
     By reiterating the movements of the piston  26  described above, fluid is gradually introduced into the expulsion duct  38 . 
     As shown in  FIG. 1 , the expulsion duct  38  communicates with the first compartment  16 A of the actuator  12 , which is an enclosed space, such that the gradual introduction of fluid in the expulsion duct  38  increases the pressure in this expulsion duct  38  and in the first compartment  16 A up to a desired pressure. This pressure increase causes the movement of the membrane  18 , as previously indicated. 
     The piston  26  includes a rod  42  made from a ferromagnetic material, in particular soft iron, extending in the longitudinal direction X in the hollow body  24 . 
     The pump  10  then includes an electric coil  44 , surrounding the rod  42 , and electrically connected to a power supply able to apply a variable current to the electric coil  44 . Thus, the position of the piston  26  depends on the voltage of this electric current. More particularly, an increase in the electric current tends to drive the piston  26  toward its second extreme position. 
     The pump  10  further includes an elastic member  46 , applying an elastic force biasing the piston  26  toward its first extreme position. Thus, the magnetic force induced by the electric current flowing in the coil  44  opposes the elastic force applied by the elastic member  46  on the piston  26 . The stronger the electric current is, the greater the magnetic force is, the piston  26  moving toward its second extreme position when the magnetic force is greater than the elastic force of the elastic member. Conversely, by decreasing the electric current, the magnetic force decreases, and the piston  26  moves toward its first extreme position when this magnetic force is below the elastic force applied by the elastic member  46 . 
     The piston  26  stays in its idle position, shown in  FIG. 1 , when a relatively low holding current, for example 5 volts, is applied to the coil  44 , in order to generate an opposite magnetic force with a value equal to the elastic force. 
     The hollow body  24  of the pump  10  according to the invention includes a discharge opening  48 , communicating with the expulsion duct  38  and able to communicate with the intake opening  30 . For example, this discharge opening  48  communicates with the expulsion duct  38  via a bypass duct  50 . 
     A third non-return member  52  is arranged between this discharge opening  48  and this bypass duct  50 . This third non-return member  52  is movable between an open position, shown in  FIG. 2 , in which the expulsion duct  38  communicates with the intake opening  30 , and a closed position prohibiting the passage of fluid between the expulsion duct  38  and the intake opening  30 . 
     The pump  10  includes a movable element or member  54  to move the third non-return member  52 . 
     In the first described example, the third non-return member  52  includes a non-return gate  52 A biased in the closed position by an elastic member  52 B. The movable member  54  includes an actuating element  56 , in particular formed by a striker, secured to the piston  26 , and for example, supported by the rod  42 . This actuating element  56  is designed to cooperate with the non-return gate  52 A to move it into the open position, by pushing it against the biasing of the elastic member  52 B, when the piston  26  is in the first extreme position. This first extreme position therefore forms a discharge position. 
     It will be noted that the piston  26  enters its first extreme position when the electric current flowing in the coil  44  is null, in which case no magnetic force opposes the elastic force applied by the elastic member  46  on the piston  26 . The discharge can therefore be done simply and quickly, by interrupting the electric current flowing in the coil  44 . 
       FIG. 4  shows a pump  10  according to a second example embodiment of the invention. In this  FIG. 4 , the elements similar to those of the preceding figures are designated by identical references. 
     In this example, the pump  10  is an oil pump. In this case, the actuator  12  is a jack, including a piston  58  movable in a body  60 , and separating this body  60  into a first compartment  62  communicating with the evacuation duct  38  of the pump  10 , and a second compartment  64 . 
     The jack  12  also includes an elastic member  66  biasing the piston  58  toward a first position in which the first compartment  62  has a minimal or null volume. The rod  20  is secured to the piston  58  on the one hand, and to a valve element  68  on the other hand, such that this valve element  68  is movable based on the position of the piston  58  via the rod  20 . 
     According to this second embodiment, the intake opening  30  is connected to a reservoir  70  filled with oil, and including a flexible pouch  72  with a variable volume based on the quantity of oil in that pouch  72 . The pump  10  includes an intake duct  74  that extends between the intake opening  30  and the compression chamber  28 . 
     The first non-return member  34  then includes a non-return gate authorizing the passage of fluid from the intake duct  74  toward the compression chamber  28  and prohibiting the passage of fluid from the compression chamber  28  toward the intake duct  74 . 
     In this embodiment, the piston  26  does not include a passage opening. However, as before, the volume of the compression chamber  28  depends on the position of the piston  26 . 
     As before, the compression chamber  28  includes an expulsion opening  36 , emerging in the compression chamber  28 , and communicating with the expulsion duct  38 . The second non-return member  40  is arranged at this expulsion opening  36 , between the compression chamber  28  and the expulsion duct  38 , in order to allow the passage of oil from the compression chamber  28  toward the expulsion duct  38 , and to prohibit the passage of fluid from the expulsion duct  38  toward the compression chamber  28 . 
     The operation of this pump is identical to that of the pump according to the first embodiment. 
     According to this second embodiment, the discharge opening  48  is arranged in a discharge duct  76  extending between the expulsion duct  38  and the intake duct  74 . The third non-return member  52  is housed in this discharge duct  76 . 
     The movable member  54  then includes a ferromagnetic element  78  movable between a first position, in which the third non-return member  52  is in the open position, and a second position, in which the third non-return member  52  is in a closed position. The movable member  54  also includes an elastic member  80  biasing the ferromagnetic element  78  toward its first position, as well as a coil  82  surrounding the ferromagnetic element  78 , and electrically connected to a power supply able to apply an adjustable current, the position of the ferromagnetic element depending on the voltage of the current. More particularly, the third non-return member  52  includes a non-return gate, with the ferromagnetic element  78  being formed by this non-return gate. 
     As shown in  FIG. 5 , when the current is interrupted in the coil  82 , no magnetic force is applied on the non-return gate  78 , such that it is only subject to the elastic force of the elastic member  80 , which drives it toward its first position. In this position, the expulsion duct  38  communicates with the intake duct  74 , such that the high-pressure oil contained in the expulsion duct  38  is evacuated toward the reservoir  70 . Thus, the pump can be discharged very simply by interrupting the current flowing in the electric coil  82 . 
     However, during normal operation of the pump, a holding current flows continuously in the coil  82  to keep the gate  78  in its closed position. The magnetic force thus applied to the gate  78 , added to the pressure force from the oil contained in the expulsion duct  38 , keeps the gate in the closed position against the elastic force applied by the elastic member  80 . 
       FIG. 6  shows a pump  10  according to a third example embodiment of the invention. In this  FIG. 6 , the elements similar to those of the preceding figures are designated by identical references. 
     According to this third embodiment, the pump  10  is an air pump. 
     For example, the intake opening  30  is connected to a reservoir  70 , including a pouch  72  with a variable volume, forming an air source. The air flows from the intake opening  30  to the compression chamber  28  via at least one intake duct  74  and by passing through the first non-return member  34 . When the volume of the compression chamber  28  decreases, the air is expelled up to an expulsion duct  38 , through an expulsion opening  36  including the second non-return member  40 . 
     As in the second embodiment, the discharge opening  48  is arranged between the expulsion duct  38  and the intake duct  74 , and includes a gate  78  made from a ferromagnetic material that is surrounded by an electric coil  82 . 
     The operation of this pump  10  according to the third embodiment is similar to the operation of the pump  10  according to the second embodiment previously described. 
       FIG. 7  shows a Rankine system  100  using a pump  10  according to the invention, for example according to any one of the embodiments previously described. More particularly, the pump  10  is advantageously an air pump. 
     The Rankine system  100  traditionally includes an evaporator  102 , a steam machine  104  arranged downstream from the evaporator  102 , a condenser  106  arranged downstream from the steam machine  104 , and a pumping device  108  arranged downstream from the condenser  106 , as well as an expansion vessel  110  arranged between the condenser and the pumping device  108 . 
     The Rankine system  100  is designed to recover the exhaust gas heat emitted by a gasoline or diesel internal combustion engine, by evaporating the working fluid, for example ethanol water, R134, R245 or any other fluid having the requisite characteristics, in the evaporator  102  generally arranged downstream from a pollution control system. 
     The working fluid is next expanded in the steam machine  104 , of the piston engine type, the turbine type, or any other type making it possible to convert a pressurized gas at a certain temperature into mechanical work. The steam machine  104  therefore provides mechanical work, which can, for example, next be converted into electricity. 
     Once expanded, the fluid is condensed in the condenser  106 , which is formed by a heat exchanger with a cold source, for example the cooling water of the motor vehicle or the ambient air. 
     Once the fluid has returned to liquid state, it is pumped by the pumping device  108  to be reintroduced into the evaporator  102 . The pressure obtained in this evaporator  102  is imposed by the steam machine  104 . 
     Such a Rankine system operates in a closed loop, without loss of working fluid. 
     For the proper operation of the Rankine system, it is necessary to minimize the external leaks and prohibit air from entering. Certain fluids, such as ethanol water, are completely liquid at the pressures and temperatures encountered when the vehicle is stopped (atmospheric pressures and temperatures). Air must absolutely be banished in an enclosed system, since it is compressible. Thus, if an air bubble was suctioned by the pumping device  108 , the flow rate would be unpredictable. Consequently, when the vehicle is stopped and cooled, all of the fluid is in liquid form if the internal pressure of the system is at the atmospheric pressure. 
     Conversely, if the volume dedicated to the working fluid is constant, the internal cold pressure would decrease until reaching a pressure of approximately 0.1 bars, corresponding to the saturating steam pressure around 20 to 40° C. In other words, part of the working fluid would remain in steam form at a very low pressure and ambient temperature. 
     A vehicle such as a car is stopped for the majority of its lifetime. Yet under these conditions, the pressure prevailing inside is so low relative to the atmospheric pressure that the risk of introducing a little bit of air during these long exposures is high. To eliminate any leakage risk, it is necessary for the system to be at atmospheric pressure during stops of the vehicle. If the system is at atmospheric pressure when stopped without air inside, then the entire fluid circuit is in liquid form. 
     When the engine is turned on, the exhaust gases heat the working fluid to convert it into steam. This steam has a lower density than the corresponding liquid. The additional volume necessary for steam formation can be procured by an additional element, which is the expansion vessel  110 . 
     The expansion vessel  110  includes an enclosure  112  and a membrane  114 , mounted movably in the enclosure  112 , separating the enclosure  112  into a first part  116  communicating with the condenser  106  and the pumping device  108 , and a second part  118  communicating with the expulsion duct  38  of the pump  10 . Thus, the pump  10  can manage the pressure in this second part  118  of the enclosure  112 . This second part  118  is, for example, equipped with a pressure sensor, making it possible to determine the pressure in this second part  118 . 
     Advantageously, the membrane  114  is made from metal to have satisfactory sealing and to prevent the migration of gas particles through this membrane during the lifetime of the vehicle. 
     It should be noted that the system is generally not completely tight. It is therefore preferable to store, in the expansion vessel  110 , a buffer volume of working fluid that will decrease as part of the fluid from the system is lost. Such a buffer volume is sufficient to cover the leakage of the system, which is approximately 200 cm 3  for the lifetime of the vehicle, which is generally 15 years and 5000 hours of use. 
     In such a Rankine system, once the working fluid is expanded (at the outlet of the steam machine  104 ), it is condensed in the condenser  106 . The condenser is supplied with a low-temperature fluid (for example, engine cooling water, or ambient air). The condensation pressure depends on the temperature of this low-temperature fluid. 
     For certain working fluids (water, water ethanol mixture, acetone, toluene, etc., for example), the expansion vessel  110  makes it possible to account for the increased volume of the working fluid due to its passage from the liquid state to the steam state in part of the evaporator  102 , in the steam machine  104  and in part of the condenser  106 . 
     The aim of the association of the expansion vessel  110  with the condenser  106  is to ensure the lowest possible pressure at the outlet of the steam machine  104  while ensuring that the working fluid is completely liquid at the outlet of the condenser  106 , and above all at the inlet of the high-pressure pump  108 , in order to ensure that the latter is always pumping liquid. 
     It is therefore necessary to manage the pressure of the working liquid between the condenser  106  and the pump  108 . To that end, the temperature of the cold source (engine water generally known in the injection computer, or ambient air, which is also measured at the engine intake) is known, as well as the flow rate of this cold source (water flow rate depends on the engine rating, and the air flow rate depends on the speed of the vehicle and/or the speed of the fan). This temperature and this flow rate make it possible to calculate the thermal flow. 
     It is therefore possible to know the temperature of the working fluid either by calculation or by measuring it directly. The geometric definition of the expansion vessel  110  makes it possible to know, at any point in the operation of the cycle, the resultant pressure of the working fluid. Yet in some cases, this pressure must be corrected to be sure of the working fluid state. 
     To adapt the pressure to the temperature of the cold source, a pressure is applied in the part  116  that is managed using the pump  10 . 
     Advantageously, the pressure in the first part  116  is measured by the pressure sensor, which makes it possible to apply the necessary pressure to ensure that the fluid is liquid at the outlet of the condenser  106 , irrespective of the temperature of the cold source. 
     It will be noted that the invention is not limited to the described embodiment, but could assume various alternatives. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.