Abstract:
An apparatus for removing oil from air in an air compressor that has a piston reciprocable in a cylinder to compress the air, includes an oil removal chamber associated with the compressor. An unloader valve has an unactuated condition and an actuated condition disabling flow of compressed air out of the compressor and establishing fluid communication between the cylinder and the oil removal chamber. The apparatus may include an oil discharge port for draining oil from the oil removal chamber to a location away from the cylinder, and/or a filter element in the oil removal chamber.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to compressed air systems. In particular, the present invention relates to an air compressor that uses lubricating oil and to a method and apparatus for reducing migration of oil from the compressor to the compressed air output.  
         [0003]     2. Description of the Prior Art  
         [0004]     Air compressors using lubricating oil are commonly used in, for example, air brake systems of heavy vehicles. The compressor uses engine oil or another oil for internal lubrication. Some of this oil can undesirably migrate to the air brake system via the compressed air output of the compressor, a result sometimes referred to as oil-passing or oil carry-over. For example, in one known compressor, when the compressor is in the unloaded mode, the swept volume of the cylinder is open to a small chamber in the head of the compressor where air is compressed and expanded. Oil collects in this chamber, or drains back down into the cylinder and is carried into the air stream when the compressor loads.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention in one aspect relates to removing oil from air in an air compressor that has a piston reciprocable in a cylinder to compress the air. In one embodiment, an apparatus includes an oil removal chamber associated with the compressor, and an unloader valve having an unactuated condition and having an actuated condition disabling flow of compressed air out of the compressor and establishing fluid communication between the cylinder and the oil removal chamber. In one embodiment, an apparatus may include an oil discharge port for draining oil from the oil removal chamber to a location away from the cylinder, for example the crank case, and/or a filter element in the oil removal chamber. In another embodiment, a method of removing oil may be provided. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which:  
         [0007]      FIG. 1  is a schematic illustration of portions of a compressed air supply system for a vehicle, including a compressor and an oil recirculation system in accordance with one embodiment of the invention;  
         [0008]      FIG. 2  is a schematic illustration of the compressor and oil recirculation system of  FIG. 1 ;  
         [0009]      FIG. 3  is a schematic illustration of an oil recirculation system that is another embodiment of the invention; and  
         [0010]      FIG. 4  is a schematic illustration of an oil recirculation system that is still another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     The present invention relates to compressed air systems. In particular, the present invention relates to an air compressor that uses lubricating oil and to a method and apparatus for preventing migration of oil from the compressor to the compressed air output. The present invention is applicable to air systems of differing constructions. As representative of the invention,  FIG. 1  illustrates schematically an air system  10  that is a first embodiment of the invention.  
         [0012]     The system  10  includes a compressor  12  for compressing inlet air from an inlet line  14 . Compressed air from the compressor  12  flows through a discharge line  16  line to a reservoir  18 . The reservoir  18  is connected to various system devices as shown schematically at  20 , such as vehicle brake chambers, that use compressed air to operate. A governor  22  is operative to control operation (loading and unloading) of the compressor  12 , in response to sensed pressure in a line  26  from the reservoir  18 , via a control line  24 .  
         [0013]      FIG. 2  shows schematically the compressor  12  and an apparatus  60  for removing oil from the compressed air output of the compressor  12 , being a first embodiment of the invention.  
         [0014]     The compressor  14  includes a block  32  and a cylinder head  34 . The cylinder head  34  includes portions not shown including an inlet passage connected with an inlet port, and a discharge passage connected with a discharge port. The inlet passage and the discharge passage are connected in fluid communication with the swept volume of a cylinder  36  in the block  32 . A piston  38  is reciprocable in the cylinder  36 , upon rotation of a crankshaft  40 , to compress air flowing between the inlet port and the discharge port.  
         [0015]     The compressor  12  has an unloader valve  50  that is normally closed. When the unloader valve  50  is closed, it blocks flow of air out of the cylinder  36  through an unloader passage  52 , so that the air in the cylinder  36  can be compressed by the piston  38 . The compressor  12  has an unloader port  54  for receiving an air pressure unloader signal over the control line  24 , to open (actuate) the unloader valve  50 . When the unloader valve  50  is actuated, in conjunction with operation of a discharge valve shut-off system, air can flow out of the cylinder  36  through the unloader passage  52 , thus disabling the flow of compressed air out of the compressor to the vehicle braking system air even when the piston  38  continues to reciprocate. The unloader port  24  also communicates with a discharge port shut-off valve to shut off the discharge port when in the unloaded mode.  
         [0016]     The compressor  12 , including the piston  38  and cylinder  36 , is lubricated by a lubricant (not shown) from a source, such as engine oil from the engine lubrication system  10 . Typically a small amount of the lubricating oil flows out of the cylinder  36  (migrates) into the compressed air output of the compressor  12 .  
         [0017]     The system  10  includes an apparatus  60  for removing oil from the air in the system. In the illustrated embodiments, the apparatus  60  is shown as associated with the compressor  12 ; in other embodiments, the apparatus  60  could be located or associated elsewhere in the system  10 .  
         [0018]     The apparatus  60  includes an unloaded mode delivery chamber or oil removal chamber  62 . The chamber  62  is a volume defined by chamber walls  64 . The chamber  62  is in fluid communication with the unloader passage  52  when the unloader valve  50  is open as shown in  FIG. 2 . The chamber walls  64  may be formed as one piece with the compressor block  32 , as shown in  FIG. 2 . Alternatively, the chamber walls  64  may be formed separately from the cylinder block  32 .  
         [0019]     A drain port or passage  66  at the bottom of the chamber  62  communicates with the compressor crank case  68 . A condensed oil drain valve  70  is located between the oil removal chamber  62  and the compressor crank case  68 . The valve  70  is controlled by an air pressure unloader signal from the governor  22  over the control line  24 .  
         [0020]     In the embodiment shown in  FIG. 2 , a filter element  74  is located in the chamber  62 . The filter element  74  may be any element suitable for filtering or coalescing oil from air. A regenerative aluminum filter is one example.  
         [0021]     When the pressure in the reservoir  18  is high enough that further supply of compressed air is not needed for the devices  20 , the discharge valve of the compressor  12  is closed, and air pressure is applied at the unloader port  54 , opening (actuating) the unloader valve  50 . Air that would otherwise be compressed in the cylinder  36  and delivered out the discharge port is not so compressed. Instead, air from the cylinder  36  is, on the piston up-stroke, delivered to the oil removal chamber  62  via the unloader passage  52 , which is open because of the opening of the unloader valve  50 . The air flows into the oil removal chamber  62 .  
         [0022]     As the air expands into the oil removal chamber  62 , it cools. Some of the oil in the air condenses out and collects in the chamber  62 . The chamber  62  is preferably maintained at a lower temperature than the cylinder  36 , by being external to the cylinder. This can aid in the condensing of the oil. In addition, oil in the air can be filtered, that is, physically captured by the filter element  74 . On the piston down stroke of the piston  38 , the air in the chamber  62  expands back into the cylinder  36 . This process repeats with each cycle of the piston  38 .  
         [0023]     When the compressor  12  is thus in the unloaded mode, the pressure in the oil removal chamber  62  cycles constantly, at the frequency of the compressor operation, from one atmosphere to about 4-6 atmospheres.  
         [0024]     In this manner, at least a portion of the oil is removed from the air that is discharged from the cylinder  36  on the piston up-stroke. This can reduce or minimize the amount of oil that migrates into the air flowing into the downstream parts of the system  10 .  
         [0025]     When the compressor  12  is in the loaded mode, the unloader valve  50  is closed and compressed air is delivered out of the discharge port. During the loaded cycle, oil that was entrained in the filter  74 , as well as oil collected in the chamber  62 , can drain back into the crank case  68 . Specifically, when the compressor  12  is loaded, the unloader valve  50  is closed and the drain valve  70  is opened. Oil collected in the chamber  62  is allowed to drain from the chamber to the compressor crank case  68 .  
         [0026]      FIGS. 3 and 4  illustrate oil removal apparatus  60  that are other embodiments of the invention. Features or alternatives shown in these embodiments can be substituted for or combined with, in any suitable combination, features of the embodiment of  FIG. 2 .  
         [0027]      FIG. 3  illustrates an oil removal apparatus  60   a  associated with a compressor  12   a . Parts of the apparatus  60   a  and the compressor  12   a  that are the same as, or similar to, parts of the apparatus  60  and compressor  12 , are given the same reference numerals with the suffix “a” attached.  
         [0028]     In the embodiment of  FIG. 3 , the oil removal chamber  62   a  is defined by walls  64   a  that are formed separately from the compressor block  32   a . In addition, the chamber walls  64   a  are spaced apart from the cylinder block  32   a  to define a space or air gap  80  between them. This air gap  80  helps to cool the chamber  62   a . Further, the chamber walls  64   a  are provided with cooling fins  82  to help promote cooling of the chamber  62   a . Greater temperature differential between the chamber  62   a  and the cylinder  36   a  can help to increase oil removal.  
         [0029]     The apparatus  60   a  also includes an oil drain passage  66   a  that does not connect the chamber  62   a  with the compressor crank case  68   a . Rather, the oil drain passage  66   a  opens to a port  84  on the exterior of the compressor  12   a . An oil line (not shown) can be connected to the port  84  to deliver removed oil back to the lubrication system from which it came, for example, the engine lubrication system.  
         [0030]      FIG. 4  illustrates an oil removal apparatus  60   b  associated with a compressor  12   b . Parts of the apparatus  60   b  and the compressor  12   b  that are the same as, or similar to, parts of the apparatus  60  and compressor  12 , are given the same reference numerals with the suffix “b” attached.  
         [0031]     In the embodiment of  FIG. 4 , the oil removal chamber  62   b  is defined by walls  64   b  that are formed separately from the compressor block  32   b . In addition, the walls  64   b  are spaced apart from the cylinder block  32   b . A water jacket  86  at least partially surrounds the chamber walls  64   b . The water jacket  86  can be connected with the cooling system of the compressor  12  itself. The water jacket  86  helps to cool the chamber  62   b . The water jacket  86  is one example of a cooling system that can be used.  
         [0032]     From the above description of the invention, those skilled in the art will perceive improvements, changes, and modifications in the invention. Such improvements, changes, and modifications within the skill of the art are intended to be included within the scope of the appended claims.