Abstract:
An air compressor with a cylinder head attached to a cylinder deck of a crankcase is disclosed. Openings are provided through the cylinder deck and cylinder head and elongated fasteners having a fastening complement are used to provide a compressed engagement between the deck and cylinder head. Using a fastener inserted through the openings and a fastener complement reduces the potential that the bore is distorted during assembly without adding material to the assembly that undesirably increases its weight or complicates foundry operations. Machining of the deck is also simplified by providing the opening therethrough.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This application relates to a compressor assembly, and more particularly, to an air compressor, such as one that provides and maintains air under pressure for operating air brakes and/or associated air-operated auxiliary systems associated with heavy vehicles.  
           [0002]    Conventional air compressor assemblies having a cylinder head and a crankcase are assembled with threaded fasteners or bolts that pass through openings in the cylinder head into blind end threaded openings in a cylinder deck of the crankcase to which the cylinder head is attached. The openings in the cylinder head are aligned with the threaded openings in the cylinder deck to allow the fasteners to pass through the cylinder head into the cylinder deck. Typically, there are four or six such sets of openings, spaced around the cylinder head and the cylinder deck. A typical assembly is shown in FIG. 3.  
           [0003]    As the assembly is drawn together by tightening the fasteners, the potential exists that bores within cylinders in the crankcase will become distorted by, among other causes, uneven application of tightening forces to the fasteners spaced around the assembly. Bore distortion could adversely affect the operation of the air compressor by impacting sealing arrangements of cylinders within the bores, resulting in increased leakage of oil from the compressor assembly. Such increased leakage could contaminate downstream components in a compressed air system and could cause environmental concerns.  
           [0004]    Distortion of compressor components is a known problem, as discussed in U.S. Pat. No. 4,530,323. As therein discussed, elongated threaded fasteners pass through openings in the cylinder head and are threadedly received in recesses of a cylinder block. The problem addressed therein, however, relates to distortion in the cylinder head and provision of reinforcing ribs is taught to address that problem.  
           [0005]    Similarly, U.S. Pat. No. 5,630,389 is concerned with flexing and potential cracking of the cylinder head upon tightening of fasteners used to secure the cylinder head to an engine block. The solution proposed in that patent is to situate the fasteners closer to the engine block, thereby reducing flexing of the cylinder head and associated potential cracking of the cylinder head.  
           [0006]    U.S. Pat. No. 5,873,331 is also concerned with even distribution of clamping forces from a cylinder head to an engine block. The proposed solution taught therein is to orient bolt receiving columns in a particular manner and thereby more uniformly distribute bolt forces and thus reduce assembly distortions.  
           [0007]    Still another proposed solution offered by U.S. Pat. No. 6,016,783 is to provide an induction hardened cylinder head with selected surfaces areas contacted by heads of fastener bolts.  
           [0008]    In the field of internal combustion engines, U.S. Pat. No. 5,072,697 discloses use of aligned bolt holes in the cylinder head and block, and retention of the bolts through use of fastener nuts. A similar arrangement is illustrated in a plastic composite construction for an internal combustion engine in U.S. Pat. No. 4,848,292.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides an air compressor assembly that reduces cylinder bore distortion without adding material to the cylinder deck, which would increase the weight and the rigidity of the assembly. The present invention also provides a method of reducing bore distortions in an air compressor in a simple, economical manner.  
           [0010]    The air compressor assembly of the present invention includes a crankcase having at least one cylinder formed therein that receives a piston for compressing air. A cylinder head is secured to the crankcase. The cylinder head and a portion of the crankcase, herein identified as the cylinder deck, include aligned openings that freely receive fasteners therethrough. The fasteners are threaded along one end and secured by a fastening nut.  
           [0011]    A method of reducing bore distortions in an air compressor is also disclosed that includes providing a crankcase with at least one cylinder bore, supplying a cylinder head for attachment to a crankcase, forming openings in the cylinder head and crankcase without any threads, and inserting fasteners through the openings.  
           [0012]    The present invention provides reduction of bore distortion in the crankcase, improved sealing characteristics about the piston, reduced adverse impact on the environment, simplified machining of the cylinder deck or crankcase, and does not add material or weight to the assembly.  
           [0013]    Still other features of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention may take physical form in certain parts and arrangements of parts, an embodiment of which is described in detail in this specification and illustrated in the accompanying drawings.  
         [0015]    [0015]FIG. 1 is an exploded perspective view of a cylinder head and crankcase for an air compressor.  
         [0016]    [0016]FIG. 2 is a longitudinal cross-section through a conventional compressor.  
         [0017]    [0017]FIG. 3 is an enlarged cross-sectional view of prior art attachment of the cylinder head to the crankcase.  
         [0018]    [0018]FIG. 4 is an elevational view of a compressor in accordance with the present invention, shown partly in section. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIG. 1 illustrates a conventional air compressor assembly. The compressor assembly includes a body or crankcase  10  and a cylinder head  20 . The crankcase  10  includes an upper, terminal portion having a planar surface, identified as cylinder deck  22 . First and second cylinder bores  24  are formed in the crankcase  10  and each bore  24  houses a piston  26 , as shown in FIG. 2, to pressurize air in chamber  30  located above the piston  26  for an associated compressed air system or other use (not shown). Each piston  26  has seal rings  28  along a peripheral portion thereof and is driven via connecting rod  32  that is secured to a crankshaft  34  to convert the rotary input drive (not shown) into reciprocating movement of the piston  26 . Further details of the structure and operation of the air compressor assembly are generally conventional and may be of any suitable conventional design.  
         [0020]    [0020]FIG. 1 illustrates that the cylinder head  20  sealingly engages or mates with the cylinder deck  22  along a planar interface. A gasket  40 , such as a metallic or graphite gasket, may be interposed between the cylinder head  20  and the cylinder deck  22 . The gasket  40  includes enlarged openings  42  that accommodate passage of air from the respective cylinder bores  24 . In addition, smaller openings  44  are spaced along the periphery of the gasket  40 . The smaller openings  44  are dimensioned and positioned for alignment with associated openings  50  in the cylinder deck of the crankcase.  
         [0021]    In addition, openings  52  are provided in the cylinder head  20  and are likewise dimensioned and positioned for alignment with the respective openings  44  in the gasket  40  and openings  50  formed in the cylinder deck  22 . The openings  52  have a smooth bore, without threads. Fasteners  54 , such as elongated threaded bolts, are dimensioned for receipt through the aligned openings  52 ,  44 ,  50  of the cylinder head  20 , gasket  40 , and cylinder deck  22 , respectively. Each fastener has an enlarged head portion  56  at one end and is preferably threaded at a second end  58 .  
         [0022]    [0022]FIG. 3 illustrates conventional attachment of the cylinder head  20  to the crankcase  10 , wherein like components are referenced by like numerals with a primed (′) suffix. Thus, cylinder head  20 ′ includes openings  52 ′ therethrough at predetermined locations. The crankcase  10 ′ includes a cylinder deck  22 ′ having mounting recesses  60  that are blind-end recesses and internally threaded. Stated another way, the individual fasteners  54 ′ are dimensioned for threaded engagement with the internal threads of the recess  60 . The head portion  56 ′ has a dimension larger than the opening  52 ′ in the cylinder head. In this manner, when threaded ends  58 ′ of the fastener  54 ′ engage with the threaded recess  60  in the cylinder deck  22 ′, the cylinder head  20 ′ compressingly engages the cylinder deck  22 ′ and gasket (not shown in FIG. 3). This provides a desired seal engagement between the cylinder head  20 ′ and the crankcase  10 ′ of the compressor assembly that allows the compressed air to be transferred in a pressurized state for downstream use such as air braking, etc.  
         [0023]    Cylinder bores  24 , as illustrated in FIG. 1, may be adversely affected by this mounting arrangement, because additional stresses arising during formation of the threaded recesses  60  and assembly of the cylinder head  20  and crankcase  10  can result in undesirable distortion of the cylinder bores  24 . Distortion of the bores  24  results in less than optimal sealing of the piston seal rings  28 , as shown in FIG. 2, with the cylinder wall and thereby presents the potential that oil bypasses the rings  28  and is introduced into the compressed air in chamber  30 . Eliminating distortions in the bore  24  improves the overall quality of the compressed air system, by reducing passage of oil to the chamber  30  and entrainment of oil in the compressed air system.  
         [0024]    One embodiment of the invention is illustrated in FIG. 4. Openings  50  provided in the cylinder deck  22  of the crankcase  10  illustrated in FIG. 1 are dimensioned to freely receive the elongated fasteners  54  therethrough. This is in contrast to the mounting recesses  60  used in the conventional arrangement of FIG. 3. In addition, the internal threading necessary for the mounting recesses  60  is removed, which eliminates another machining step and the potential for distortion that can arise therewith. Thus, the openings  50  are of smooth bore, without threads. The fasteners  54  are slightly elongated and the second end  58  cooperates with fastener complements  70 . Fastener complements  70  may be any device that prevents the fastener  54  from being inadvertently withdrawn, and includes nuts, cotter pins, clips, or the like.  
         [0025]    In a preferred embodiment, the cylinder deck  22  and the cylinder head  20  are substantially rectangular, in which case it is desirable that there be at least four fasteners  54  located at corners of the cylinder deck  22  that are mounted in this manner. Other shapes mounting arrangements, such as six fasteners  54  as illustrated in FIG. 1, or two fasteners  54 , or eight fasteners  54 , may be used without departing from the spirit and scope of the invention. The choice and arrangement of the fasteners  54  and associated openings  52 ,  44 ,  50  are within the discretion of the user, depending on cost, materials, and other considerations.  
         [0026]    In this manner, the cylinder head  20  still compressingly engages the cylinder deck  22  through the clamping force imparted by the fasteners  54 . Here, however the fastener head  56  and the associated fastener complement  70  place the fastener  54  in a tension state that clampingly engages the cylinder head  20  to the crankcase  10  while limiting the prospect for distortion to arise. Simplified machining of the components is achieved and bore distortions are addressed without adding material or undesirable weight or increased rigidity to the crankcase  10 .  
         [0027]    The invention has been described with reference to a preferred embodiment. Modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims of the equivalents thereof.