Abstract:
A fluid cooler comprises a first stage fluid cooler and a downstream second stage fluid cooler. A flow line connects the first and second stages. A valve senses a condition of the fluid in the flow line, and to bypass the second stage fluid cooler if it is determined that additional cooling is not necessary. An air compressor incorporating the cooler is also claimed as is a method of operating a fluid cooler.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a two-stage oil cooler, wherein an interstage bypass directs oil around the second stage, when additional cooling is unnecessary. 
         [0002]    Compressors typically require oil, which can become hot during operation of the compressor. Thus, oil is routed from the compressor through an oil cooler, such that the oil is periodically cooled and returned to the compressor. One application for a compressor is in an air compressor. Typically, the oil coolers are sized to handle high ambient temperature conditions, at which the oil will become quite hot. When the same oil cooler is used in lower ambient temperatures, the oil is not as hot, and there may be too much cooling capacity in the oil coolers. 
         [0003]    Typical compressors may be provided with a valve that restricts the compressor intake to reduce its capacity, which can also result in the oil being cooler than the preferred operating temperature. 
         [0004]    Compressors can also be associated with the ability to vary the speed of the compressor, thus reducing its capacity, which can also result in the oil being cooler. 
         [0005]    The thermal cycles associated with an oversize oil cooler can induce stress in the core of the oil cooler, reducing its strength and its ability to withstand internal pressures. 
         [0006]    It has been proposed to include a bypass valve into multi-stage heat exchangers. However, the valve associated with this arrangement was at a downstream end of a bypass line, and only served to reduce the amount of fluid passing through the second stage heat exchanger. 
       SUMMARY OF THE INVENTION 
       [0007]    A fluid cooler comprises a first stage fluid cooler and a downstream second stage fluid cooler. A flow line connects the first and second stages. A valve senses a condition of the fluid in the flow line, and bypasses the second stage fluid cooler if it is determined that additional cooling is not necessary. An air compressor incorporating the cooler is also claimed as is a method of operating a fluid cooler. 
         [0008]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  schematically shows a system incorporating the present invention. 
           [0010]      FIG. 2  shows the  FIG. 1  system in an alternative position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0011]    System  20  includes a compressor  22  that receives air from line  21 , and compresses that air, delivering it towards a compressed air outlet  23 . An oil separator vessel  25  is positioned on the outlet of the compressor  22 , and includes a separator element  17 . The separator may be as known. Separated oil flows through line  125  towards an oil cooler  27 . Downstream of the oil cooler  27 , oil is returned through a line  19  back to compressor  22 . While the present invention is illustrated in an air compressor, an oil cooler  27  of this invention may be incorporated into use with other compressors for other applications, and for other cooling applications beyond compressor oil coolers. 
         [0012]    The oil cooler  27  has at least two stages, and incorporates a first stage  24  and a downstream second stage  32 . Oil from the compressor  22  passes into an inlet manifold  31  in first stage  24 , then passes through flow channels, shown here schematically as tubes  26 , to a discharge plenum  33 . Air circulates around the channels and cools the oil. From the discharge manifold  33 , the oil flows into a connecting flow line  28  leading to a connection  30  to an inlet manifold  34  of the second stage  32  of the oil cooler. While not illustrated, the second stage  32  will also include oil channels. It should be understood that the oil cooler stages  24  and  32 , and the flow channels, may be of any one of numerous configurations, and may include fins, etc. 
         [0013]    When inlet manifold  34  receives the oil from the line  30 , it passes through the cooler and to a discharge manifold  36 , which then leads to a line returning the oil to the compressor  22 . A bypass line  41  is connected to line  28  and includes a valve  40 . A spring  44  biases the valve to the position shown in  FIG. 1 . In the position shown in  FIG. 1 , the oil is bypassed around the second stage  32 , and goes directly to the discharge manifold  36 . 
         [0014]    When the oil does not require additional cooling in second stage  32 , the valve  40  remains in the position shown in  FIG. 1 , and the oil will bypass the second stage  32 . All cooling will be done in the first stage  24 , and the concerns mentioned above are avoided. A sensor  42  on the valve  40  monitors the temperature of the oil at line  28 . If the oil temperature is above a threshold when reaching valve  40 , then sensor  42  will drive the valve to the position shown in  FIG. 2 , at which position oil flows through the valve  40 , and to line  30  leading to the second stage oil cooler  32 . 
         [0015]    As can be appreciated from the figures, the valves are either “full on” or “full off” and when in the  FIG. 1  position, will entirely bypass the second stage oil cooler  32 . In the position of  FIG. 2 , no fluid will flow through the bypass line, and it will be entirely blocked off. In addition, since the valve is at an upstream end of the bypass line, there will not be a dead volume of the fluid. The specifically disclosed valve will transition between the full on and full off positions, and there will be a state of transition where the fluid may be partially directed to both destinations. However, this will be a temporary condition, and the valve will eventually arrive at the  FIG. 1  or the  FIG. 2  position. 
         [0016]    In one embodiment, the sensor  42  may be a wax element that expands when exposed to a predetermined temperature to drive the valve to the  FIG. 2  position. On the other hand, other temperature sensitive elements may be utilized. In addition, the valve  40  could be provided by an electronically controlled valve wherein an electronic sensor senses temperatures and drives the valve to the  FIG. 2  position when the predetermined temperature is met. 
         [0017]    While the valve  40  and its associated components including sensor  42  and spring  44  are shown schematically, a worker of ordinary skill in the art would recognize how to provide a valve that can operate to achieve the disclosed functions. Moreover, other types of valves that operate in other manners would come within the scope of this invention. As an example, a valve may be normally biased to the  FIG. 2  position, and driven to the  FIG. 1  position, and would still come within the scope of this invention. 
         [0018]    In addition, while the figures show an oil cooler, this invention can be incorporated into coolers for other fluids besides oil. 
         [0019]    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 invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.