Abstract:
An oil-less compressor, having polymeric seals and a crank mechanism which is vulnerable to dust arising from such seals, is provided with a dust-exclusion barrier that protects the crank mechanism from being exposed to such dust. The first stage of the compressor preferably draws its intake from the crankcase, providing a pressure differential and gas flow that sweeps seal dust away from the crank mechanism.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an oil-less compressor that delivers high-pressure gas to a storage reservoir. In particular, it relates to a home refuelling appliance for refuelling motor vehicles that operate on gaseous fuels. 
       BACKGROUND TO THE INVENTION 
       [0002]    A number of applications exist which require gas to be compressed to a high-pressure, e.g. 3000 psi, without introducing traces of lubricants into the compressed gas. Thus, natural gas fuelled motor vehicles may require an oil-less compressor to compress gas for delivery to a tank or reservoir carried by the vehicle. This is one, preferred, example of an application of the present invention. 
         [0003]    In the past, natural gas fuelled motor vehicles have generally been refueled at commercial refuelling facilities. Provision has also existed for home refuelling systems that produce compressed natural gas from the low-pressure natural gas lines available at residential sites. Particularly in the case of a home refuelling appliance, it is desirable for such units to be installed for long term, unattended operation. An oil-less compressor provided with features of the invention would be especially suited for both of these applications, but the invention has general application wherever an oil-less compressor having dry seals that produce contaminating dust is employed. 
         [0004]    In a high pressure oil-free gas compressor compression is preferably maintained through dry seals based upon the use of polymeric ring materials. A disadvantage of this system is that the polymeric ring materials generate dust which is potentially damaging to the bearings in the compressor mechanism. A need exists for a system which will reduce the wear and damage that can arise within the compressor from the formation of such dust. This invention addresses that need. 
         [0005]    The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims, which conclude this Specification. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention relates to an oil-less compressor, and particularly to a multi-stage compressor for refuelling gas-powered vehicles. Accordingly, the invention in one aspect addresses a gas compressor assembly which comprise 
         [0007]    a) a gas compressor having at least a first stage with at least one cylinder with dry seals having a piston mounted therein with a piston rod connected to the piston and extending into a crank case cavity; 
         [0008]    b) a crank mechanism which is located in the crank case cavity connected to operate the piston rod; and 
         [0009]    c) a low-pressure gas supply inlet for connection to a source of gas and delivery of gas to said first stage; and 
         [0010]    d) a high-pressure gas discharge outlet for delivery of compressed gas to an external reservoir; 
         [0011]    said compressor assembly further comprising a dust control enclosure having a sidewall through which the piston rod passes, said dust control enclosure forming a barrier between the dry seals and the crank mechanism that substantially limits dust from the dry seals accessing the crank mechanism. 
         [0012]    The dust control enclosure is preferably in the form of a sleeve which when fitted forms a cap with penetrations through its sidewalls which have dust-excluding seals through which the rod(s) pass. Such seals are preferably in the form of washer-like rings made of felt-like material. This arrangement effectively confines dust generated by deterioration of the sealing rings to remain on the piston and cylinder sides of the dust control enclosure. 
         [0013]    According to a further variant of the invention, the low pressure gas supply inlet delivers gas to the crank case cavity, and the first stage of the compressor takes its intake of gas to be compressed from the crank case cavity on the piston side of the dust control enclosure. 
         [0014]    The compressor unit of the invention in a preferred variant is a multi-stage compressor, e.g. a four stage compressor having pairs of opposed, linearly reciprocating, pistons. The pistons are preferably driven in pairs by Scotch yokes as a specific type of crank mechanism, actuated by a shaft extending from the crank case cavity to a motor. According to this system, the piston rods move in a straight line. 
         [0015]    In order to minimize the extent to which ring dust can enter the bearings of the Scotch yokes, the dust control enclosure is installed within the crank case portion of the compressor. This enclosure, preferably made of substantially rigid polymeric plastic material, may be in the form of a sleeve which, when mounted on the bearing housing flange, forms a cap or cup that surrounds the crank mechanism. This cap has sidewalls through which the piston rods pass as they extend inwardly to connect to the Scotch yokes. It is at these penetrations through the sidewalls of this enclosure that dust-excluding seals in the form of washers made of felt-like material are preferably installed. 
         [0016]    Because line gas enters the first stage of the compressor by flowing first through the crank case cavity before following a gas flow path to the piston side of the dust control enclosure, and because the first stage takes its intake of gas to be compressed from the region outside the dust control enclosure, a pressure differential exists within the compressor unit. The region around the Scotch yokes benefits from an overpressure of up to nearly the line gas pressure e.g. 0.2 to 0.5 psi with respect to the pressure outside the dust control enclosure, on the piston seals side where ring dust forms. Thus a continuous flow of dust-free incoming gas sweeps through this higher-pressure region before entering the first compression stage. This flow operates to help exclude dust from entering the region around the Scotch yokes. 
         [0017]    The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]      FIG. 1  is a pictorial representation of a gaseous fuel motor vehicle parked in a garage having a home refuelling appliance according to the invention mounted on its inner wall. 
           [0019]      FIG. 2  is a schematic depiction of the principal components of the appliance with the front shroud/cover of the housing removed, including the unitary motor/compressor assembly, its casing, control circuits, other support elements including various sensors. 
           [0020]      FIG. 3  is a cross-sectional side view of the appliance of  FIGS. 1 and 2  exposing the compressor and motor assembly and showing the location of the dust control enclosure in cross-section in relation to the first and third stage cylinders in the compressor. 
           [0021]      FIG. 4  is an enlarged view of  FIG. 3  showing the compressor in detail. 
           [0022]      FIG. 5  is perspective view depicting the dust control enclosure with holes to allow penetration by piston rods within the motor/compressor assembly of  FIG. 3 . 
           [0023]      FIG. 6  is a top view of the enclosure of  FIG. 5 . 
           [0024]      FIG. 7  is a cross-sectional side view of the enclosure of  FIG. 6 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    In  FIG. 1  the home refueling appliance  1  is shown mounted on a garage wall with the high-pressure discharge hose  2  connected to a car, the inlet hose  3  connected to a source of gas, and the electrical cord  4  plugged into a standard household receptacle. 
         [0026]    The compressor unit of the invention in a preferred variant is a multi-stage compressor  5 , e.g. a four stage compressor  5  having pairs of opposed, linearly reciprocating, pistons  50 , shown in Figures. The pistons  50  are preferably driven in pairs by Scotch yokes  51  actuated by a drive/crank shaft  52  extending from the motor  27  into the crank case cavity  14 . The compressor unit is provided with a low-pressure gas supply inlet  59  for connection to a source of gas and a high-pressure gas discharge outlet  70  for delivery of compressed gas to an external reservoir. 
         [0027]      FIG. 3  schematically depicts the unit operating in compression mode. Gas  6  which has been fed into the interior crank case volume  14  of the casing  26  is drawn into the first  28  of a series of four compression stages of compressor  5 . The gas  6 , which typically has a pressure of between about 0.2 and 0.5 psi, is drawn into the interior casing volume  14  by the suction created by the first compression stage  28 . 
         [0028]    On leaving the first stage  28 , the gas  6  passes through a desiccant bed  7  contained within an absorption chamber  29 . Upon exiting the absorption chamber  29 , the dried gas continues into the condenser  30  which is, at this stage, passive. Exiting the condenser  30 , the gas  6  proceeds to the next, second stage  32  of the compressor  5  for completion of the compression process. 
         [0029]    The compressor  5 , motor  27  and motor control circuitry  45  are all located within the casing  26 , (counting the compressor block as part of the casing). The main logic controller  46 , fed-power from a power supply, is able to activate the motor  27 , and govern its speed in the variable speed version, through motor control circuitry  45 . The wall of the casing  26  acts as heat sink for the heat produced by the motor controller circuitry  45  and as a shield against outgoing electromagnetic emissions. 
         [0030]    On start-up, low motor speeds are adopted to reduce otherwise high start-up current drains on the electrical supply system. This enables the unit to operate off of a standard household voltage, e.g. 110-120 volt, moderately fused electrical supply system. After start-up, the initial process of compression can be effected with a high motor speed. Once higher pressures have been established in the motor vehicle fuel reservoir, motor speed is reduced in order to moderate ring wear and limit power consumption. This procedure is especially suited to oil-less compressors  5  as the wear rate of the sealing rings  53  within the compressor cylinders  54  of such units increases when the compressor system is operated at high speed against a high-back pressure. 
         [0031]    Additionally, the speed of the electric motor  27  may be controlled to avoid natural resonant frequencies arising from its mechanical components that would otherwise increase the noise and vibration generated by the unit. 
         [0032]    As shown in  FIGS. 3 and 4 , the pistons  50  mounted in their respective cylinders  54  are each provided with dry seals  53 . The pistons  50  are connected each by a piston rod  57  to the Scotch yoke crank mechanism  51  located in the crank case cavity  14 . The piston rods  50  pass through the sidewall  55  of the dust control enclosure  56  which forms a barrier between the dry seals  53  on the pistons  50  and the crank mechanism  51 , excluding dust from the dry seals  53  accessing the crank mechanism  51 . 
         [0033]    The dust control enclosure  56  as shown in  FIGS. 5 ,  6 , and  7  is in the form of a sleeve fitted to the bearings support  58 , shown in  FIGS. 3 and 4 , to form a cap installed within the crank case portion  14  of the compressor  5 . This enclosure  56  is provided with penetrations  60  through its sidewalls  55  which have dust-excluding dust seals  71 . The rods  57  pass through these dust seals  71  as they extend inwardly to connect to the crank mechanism  51 . Such dust seals  71  are preferably in the form of washers made of felt-like material that are compatible with the compressor environment. The dust control enclosure  56  is preferably made of semi-rigid polymeric plastic material with similar compatibility. The dust control enclosure  56  as shown is mounted on the bearing housing flange. 
         [0034]    The low-pressure gas supply inlet  59  delivers gas  6  to the crank case cavity  14  where the Scotch yoke mechanism  51  is present. The first stage  28  of the compressor  5  takes its intake of gas  6  to be compressed from the crank case cavity  14  on the piston side of the dust control enclosure  56  through first cylinder supply valve  72  fitted within the piston  50 . Because gas  6  enters the first stage  28  of the compressor  5  by flowing first through the crank case cavity  14  within the region of the dust control enclosure and then through a partially constricted passageway  80  linking both sides of the dust control enclosure, and because the first stage  28  takes its intake of gas  6  to be compressed from the region outside the dust control enclosure  56 , a pressure differential generally exists within the compressor unit between these two regions. Thus a continuous flow of dust-free incoming gas  6  sweeps through this higher-pressure region of the crank case cavity  14  before entering the first compression stage  28 . This flow operates to help exclude piston seal dust from remaining in the crank mechanism  51 . Further gas flow to the next stage  32  and subsequent stages occurs through sealed conduits. 
         [0035]    Additionally, the cool and dust-free arriving gas flow coming from the low-pressure gas supply inlet  59  passes first around the crank mechanism  51  components in the crank case volume  14  contained by the dust enclosure to provide cooling. This is advantageous as the Scotch Yoke drives generate significant heat due to bearing friction. 
         [0036]    Similarly, for the second stage  32  and further stages, if present, the dust enclosure  56  minimizes the presence of dust in the crank case cavity by reason of the barrier that it provides and the general pressure differential that is maintained. 
         [0037]    The Scotch yoke mechanism  51  is able to serve two opposed cylinders located in a common plane. When four cylinders are employed, the second pair of cylinders is in a second plane. Accordingly, the further penetrations or openings  60 A in the dust control enclosure  56  needed to accommodate the further piston rods  50  are off-set from the first pair of openings  60 . 
         [0038]    On this basis a system is provided that protects the crank mechanism from dust arising from the dry seals. 
       CONCLUSION 
       [0039]    The foregoing has constituted a description of specific embodiments showing how the invention may be applied and put into use. These embodiments are only exemplary. The invention in its broadest, and more specific aspects, is further described and defined in the claims which now follow. 
         [0040]    These claims, and the language used therein, are to be understood in terms of the variants of the invention which have been described. They are not to be restricted to such variants, but are to be read as covering the full scope of the invention as is implicit within the invention and the disclosure that has been provided herein.