Abstract:
An energy efficient oxygen concentrator for filling high pressure portable cylinders with medical oxygen for use by ambulatory patients. Two compressors provide two pressurized air sources, one for operating an oxygen concentrator to provide a stream of oxygen enriched gas, and the other for driving a pressure intensifier for filling portable oxygen cylinders. Pressurized exhaust from the pressure intensifier is returned to the inlet side of at least one of the compressors for reducing the energy required to drive the compressor. Preferably, each compressor has a single reciprocating piston, a single motor drives both pistons and the pressurized exhaust from pressure intensifier is provided to the inlets for both compressors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicants claim priority to U.S. Provisional Patent Application Ser. No. 60/728,595 filed Oct. 19, 2005. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     TECHNICAL FIELD 
     The invention relates to a medical oxygen concentrator combined with a pressure intensifier for filling a portable oxygen cylinder for use primarily by ambulatory persons. 
     BACKGROUND OF THE INVENTION 
     Medical oxygen is normally provided to patients who require supplemental oxygen either from pressurized cylinders delivered to the patient&#39;s home or from an oxygen concentrator. An oxygen concentrator separates nitrogen from air to provide an oxygen enriched gas having a concentration of up to about 95% oxygen. The oxygen concentrator operates by using a compressor to apply pressurized air to a gas separation element, such as a molecular sieve bed, which will pass oxygen while having an affinity for nitrogen. Over a relatively short time, the gas separation element will become saturated with nitrogen and its efficiency decreases. Typically, an oxygen concentrator is provided with two or more molecular sieve beds. While at least one molecular sieve bed is operated to produce a flow of oxygen enriched gas, nitrogen is purged from at least one other molecular sieve beds by a limited back flow of the nitrogen free oxygen enriched gas from an operating sieve bed. 
     A common type of compressor used to operate an oxygen concentrator comprises a single electric motor having two reciprocating piston compressors driven from opposite ends of the motor shaft. Each compressor includes a piston which is reciprocated in a cylinder by the motor. The two cylinders are connected together to provide the air flow and pressure required to produce a desired maximum oxygen enriched gas output. An oxygen concentrator may be designed, for example, to provide a maximum continuous flow of 5 liters per minute, or more, of oxygen enriched gas having an oxygen concentration of up to about 95% at a pressure of 8.5 psig. 
     Oxygen enriched gas from an oxygen concentrator is delivered to the patient through a hose and a nasal cannula. The hose may be sufficiently long to allow the patient to walk around an area of his or her home. However, most oxygen concentrators are not sufficiently small and light weight to allow an ambulatory patient to leave the home. For trips away from the home, either a portable compressed oxygen cylinder or a portable liquid oxygen container are typically used to provide the patient&#39;s supplemental oxygen needs. Oxygen dealers deliver filled portable oxygen cylinders to the patient&#39;s home as needed by an ambulatory patient when traveling away from the home oxygen source. Regular home delivery of oxygen results on an ongoing high expense either for insurance companies or for the patient. 
     In addition to supplying oxygen enriched gas directly to a patient, some oxygen concentrators have been connected to a compressors or to a pressure intensifiers for increasing the gas pressure of the oxygen enriched gas product stream to the level needed for filling a portable cylinder which the patient may use when traveling away from the home. When the oxygen concentrator simultaneously provides the patient&#39;s requirements for supplemental oxygen and fills a cylinder, the time required to fill the cylinder is long, since the patient&#39;s needs must be met first and only oxygen enriched gas in excess of the patient&#39;s needs can be used to fill the cylinder. In some prior art cylinder filling oxygen concentrators, a separate stand alone motor driven compressor is used to increase the gas pressure to the level needed to fill the cylinder. In other cylinder filling oxygen concentrators, a portion of the above atmospheric pressure oxygen enriched gas from the oxygen concentrator has been used to drive a pressure intensifier which increases the pressure to the high level required to fill the cylinder. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention, apparatus is provided for producing oxygen enriched gas and for filling portable high pressure oxygen cylinders with the gas. Two reciprocating piston compressors are provided, one for supplying a flow of pressurized air to operate the oxygen concentrator and one for providing a flow of pressurized air for driving a pressure intensifier. The above atmospheric pressure exhaust air from the pressure intensifier is returned to the inlet of at least one of the compressors, and preferably to the inlets of both compressors, to increase the efficiency of the oxygen concentrator. Preferably, the reciprocation pistons of the two compressors are driven from opposite ends of a motor shaft. One compressor cylinder is connected to provide pressurized feed air to an oxygen concentrator. The other cylinder is connected to provide pressurized air for driving a pressure intensifier which increases the pressure of the oxygen enriched gas stream from the oxygen concentrator. Above atmospheric pressure exhaust air from the pressure intensifier is returned to the inlet to at least one of the two compressor and preferably to the inlets to both compressors to increase the efficiency of the compressors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a cylinder filling oxygen concentrator according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows apparatus  10  for filling a portable gas cylinder  11  with oxygen enriched product gas from an oxygen concentrator  12 . The apparatus  10  includes a compressor unit  13  having a single motor  14  which drives two reciprocating piston compressors  15  and  16  from opposite ends of a motor shaft in a manner well known in the art. Each compressor  15  and  16  has a piston (not shown) mounted to reciprocate in a cylinder (not shown), an inlet port and an outlet port. For a conventional compressor unit of this type, the inlet ports for the two compressors  15  and  16  may be connected together and the outlet ports for the two compressors  15  and  16  are connected together. Alternately, the outlet port from one compressor  15  or  16  may be connected to the inlet port of the other compressor  16  or  15  to provide a higher outlet pressure at a lower flow rate. According to one aspect of the invention, the outlet ports for the two compressors  15  and  16  are not connected together. An outlet port  17  from the compressor  15  provides pressurized air for operating the oxygen concentrator  12 , and an outlet port  18  from the compressor  16  provides pressurized air for driving a pressure intensifier  19 . 
     An ambient air inlet  20  is connected through a filter  21  and a check valve  22  to a line  23  which is in turn connected to an inlet port  24  to the compressor  15  and to an inlet port  25  to the compressor  16 . The oxygen concentrator  12  includes two molecular sieve beds  26  and  27 , or other filter elements which will pass oxygen molecules while preventing the passage of nitrogen molecules. The pressurized air outlet port  17  from the compressor  15  is connected through a valve  28  to inlets  29  and  30  to the molecular sieve beds  26  and  27 , respectively. The valve  28  also is connected through a muffler or noise reducer  31  to an exhaust vent  32 . An outlet  33  from the molecular sieve bed  26  is connected through a check valve  34  and a line  35  to an accumulator  36  which stores oxygen enriched product gas from the oxygen concentrator  12 . An outlet  37  from the molecular sieve bed  27  is connected through a check valve  38  to the line  36 , also for delivering oxygen enriched product gas to the accumulator  36 . The outlets  37  and  38  are also connected together through a flow restricting orifice  39 . 
     The valve  28  is of a known type used in oxygen concentrators and may be one or more solenoid operated valves or a rotary valve, for example. In a first operating mode, the valve  28  applies pressurized air from the cylinder outlet port  17  to the inlet  29  on the molecular sieve bed  26  and connects the inlet side  30  of the molecular sieve bed  27  to the exhaust vent  32 . Gas composed primarily of oxygen passes through the sieve bed  26  and the check valve  34  to the accumulator  36 . A small portion of the product gas at the outlet  33  also flows through the orifice  39  and the outlet  37  of the sieve bed  27  to purge nitrogen from the sieve bed  27 . In a second operating mode, the valve  28  applies pressurized feed air to the inlet  30  of the molecular sieve bed  27  and connects the inlet  29  to the sieve bed  27  to the exhaust vent  32 . Oxygen rich product gas flows from the outlet  37  through the check valve  38  to the accumulator  36 , and through the orifice  39  to the outlet  33  of the sieve bed  26  to purge nitrogen from the sieve bed  26 . A controller  40  periodically cycles the valve  28  so that the molecular sieve beds  26  and  27  alternately operated in filter and purge modes. It will be appreciated that the oxygen concentrator  12  may have more than two gas separating elements, and that the valve  28  may have more than two modes. For example, the sieve bed  27  may be purged for only a portion of the time the sieve bed  26  is operating in the filter mode, and the bed  26  may be purged for only a portion of the time the sieve bed  27  is operating in the filter mode. The drawing only shows an exemplary oxygen concentrator. The invention may be implemented using various known types of oxygen concentrators. 
     The pressure intensifier  19  may be of a known type which has been used in the past for increasing the pressure of product gas from an oxygen concentrator for filling a portable oxygen cylinder. The pressure intensifier is shown as including a relatively large diameter cylinder  45  in which a piston  46  reciprocates. A connecting rod  47  connects from the center of one side of the piston  46  to a much smaller diameter piston  48  which reciprocates in a cylinder  49 , and a connecting rod  50  connects from the center of an opposite side of the piston  46  to a much smaller diameter piston  51  which reciprocates in a cylinder  52 . As the piston  46  is reciprocated in the cylinder  45 , the smaller pistons  48  and  51  are simultaneously reciprocated in opposite directions in their respective cylinders  49  and  52 . Thus, when the piston  48  is driven in a compression stroke, the piston  51  is simultaneously driven in an intake stroke, and when the piston  48  is driven in an intake stroke, the piston  51  is simultaneously driven in a compression stroke. 
     The oxygen enriched gas from the accumulator  36  is applied through a filter  53  and a line  54  to an inlet port  55  for the cylinder  49 . An outlet port  56  from the cylinder  49  is connected through a check valve  57  to an inlet port  58  for the cylinder  52 . The cylinder  52  has a high pressure gas outlet port  59  which is connected through a check valve  60 , a quick connect fitting  61  on a cylinder post  62  to fill the cylinder  11  with oxygen enriched gas. A pressure switch or a pressure sensor  63  and a relief valve  64  are connected between the check valve  60  and the quick connect fitting  61 . The pressure switch or sensor  63  is connected to the controller  40  for indicating when the cylinder has reached its filled pressure. The controller  40  then stops the apparatus  10 . 
     The piston  46  divides the cylinder  45  into a first chamber  65  on the piston rod  47  side of the piston  46  and a second chamber  66  on the piston rod  50  side of the piston  46 . The chamber  65  connects to a port  67  and the chamber  66  connects to a port  68 . The outlet port  18  from the compressor  16  is connected through a solenoid operated valve  69  to the ports  67  when the valve  69  is unactuated and to the port  68  when the valve  69  is actuated. Cycling of the valve  69  is controlled by the controller  40 . In the illustrated position of the valve  69 , the outlet port  18  from the compressor  16  is connected through the valve  69  to the chamber  65  and the chamber  66  is vented to drive the pistons  46 ,  48  and  51  in an upward direction in the orientation shown in  FIG. 1 . When the valve  69  is actuated, pressurized air from the compressor  16  is delivered to the chamber  66  and the chamber  65  is vented to drive the pistons  46 ,  48  and  51  in a downward direction. According to the prior art, the pressurized air in the chambers  65  and  66  was vented through the valve  69  to atmosphere. 
     According to a feature of the invention, the valve  69 , when unactuated, connects the chamber  66  to the line  23  and thence to at least one of and preferably to both of the inlet ports  17  and  25  on the compressors  15  and  16  rather than venting the chamber  66  to the atmosphere. When the valve  69  is actuated, the chamber  65  is connected through the valve  69  to the line  23 . The check valve  22  prevents the above atmospheric pressure exhausted from the chambers  65  and  66  from flowing through the filter  21  and the inlet  20 , while allowing atmospheric air to be drawn into the inlet ports  17  and  25  when there is insufficient pressurized air vented from the pressure intensifier  19  to meet the intake needs for the compressors  15  and  16 . By applying above atmospheric pressure exhaust air from the pressure intensifier to the inlet ports  17  and  18  on the compressors  15  and  16 , the energy efficiency of the compressor  13  is significantly increased. 
     As the piston  48  is driven in an upward direction in the cylinder  48 , oxygen enriched gas from the accumulator  36  flows through the filter  53 , the line  54  and the port  55  into the cylinder  49 . When the pistons  48  and  51  are driven in a downward direction, the gas pressure increases in the cylinder  48  and flows through the port  56  and the check valve  57  and into the cylinder  52 . Since the gas volume decreases as the pressure increases and the pistons  48  and  51  have the same length stroke, the piston  51  and cylinder  52  will have a smaller diameter than the piston  48  and cylinder  49 . At the end of the downward stroke of the pistons  46 ,  48  and  51 , the position of the valve  69  changes and the pistons are driven in an upward direction. This increases the pressure of the oxygen enriched gas in the cylinder  52  and the gas flows through the check valve  60  to the cylinder  11 . When the pressure in the cylinder  11  reaches a preset maximum pressure, the pressure switch or sensor  63  causes the controller  40  to stop the motor  14  to stop operation of the oxygen concentrator  12  and the pressure intensifier  19 . 
     It will be appreciated that various modifications and changes may be made to the above described preferred embodiment of without departing from the scope of the following claims. The invention is shown with a compressor  15  supplying pressurized air to the oxygen concentrator  12  and a separate compressor  16  supplying pressurized air to drive the pressure intensifier  19 . It will be appreciated that the apparatus  10  may be provided with a single compressor connected to provide a portion of its output to operate the oxygen concentrator  12  and to provide a portion of its output to operate the pressure intensifier  19 . In this situation, the pressurized exhaust air vented from the pressure intensifier  19  is supplied to the inlet port for the single compressor. It also will be appreciated that the invention is applicable to cylinder filling apparatus having other known configurations for the oxygen concentrator and/or other known configurations for the pneumatically driven pressure intensifier.