Fastener mounting arrangement

Information

  • Patent Grant
  • 6688859
  • Patent Number
    6,688,859
  • Date Filed
    Monday, January 6, 2003
    21 years ago
  • Date Issued
    Tuesday, February 10, 2004
    20 years ago
Abstract
An air compressor includes a valve plate with cooling fins and a piston also having cooling fins. The valve plate includes an integral and angled valve plate outlet. The angling of the valve plate outlet reduces turbulence and improves compressed air flow. The pump frame of the gas compressor includes a lipless bearing bore, decreasing the distance between the portion of the frame supporting the bearing and the piston. The pump frame is flat such that a portion of the cylinder is over a portion of the motor. The flatness of this arrangement increases the strength of the pump frame. The piston bearing bore includes two clamping structures having screw holes. Each screw hole is formed from a series half-cylinder or barrel portions, which individually do not form the complete circumference of a hole. Such a screw hole does not require a core pull on casting, lowering manufacturing costs. The piston includes a piston seal which is angled with respect to the piston. The piston head is machined at an angle to lower the amount of dead space near the top of the cylinder. The compressor includes a fan which operates efficiently at different speed settings. The fan is a radial fan including two sets of fan blades, a set of inner flat fan blades which operate most efficiently at a first range of speeds and a set of outer curved fan blades which operate most efficiently at a second range of speeds. The fan blows air through the compressor in a novel air cooling pattern, propelling air axially upward along the outside of the cylinder, increasing cooling efficiency.
Description




FIELD OF THE INVENTION




The present invention relates to air compressors, in particular, oilless air compressors.




BACKGROUND INFORMATION




Generally, an oilless air compressor (also termed an air pump) provides a supply of compressed air. One configuration of an oilless air compressor includes an electric motor rotating an eccentric which, in turn, causes a piston to reciprocate up and down within a cylinder. The eccentric translates the rotary motion of the motor into a reciprocating motion for the piston. On a piston down-stroke air is pulled into the cylinder and on a piston up-stroke air is pushed out of the cylinder.




In such a design, a valve plate closes the end of the cylinder above the piston. The valve plate includes one or more inlet valves that allow air at atmospheric pressure to be pulled into the cylinder on the piston's down-stroke, but do not allow compressed air to escape to the atmosphere on the piston's up-stroke. The valve plate also includes one or more exhaust valves that allow compressed air to be pushed out of the cylinder on the piston's up-stroke but do not allow the compressed air to be pulled into the cylinder on the piston's down-stroke.




A valve plate in such an arrangement may include an outlet port leading to, for example, a pressurized air tank. On a piston up-stroke, air flows out of the outlet valves, into a chamber above the valve plate, and out of the outlet port. The arrangement of the outlet valves and the outlet port may be such that the output air flow effectively makes a 180 degree turn in the chamber, rising straight up out of the cylinder, being redirected, and exiting the outlet port in the opposite direction. This change in airflow creates turbulence and back pressure, lowering the efficiency of the compressor.




The outlet port in such a valve plate may be formed from both a threaded portion and a compression fitting made, for example, of brass. The compression fitting includes two threaded portions: one connecting with the threaded portion of the valve plate and another connecting with an outlet tube, which may be made of metal such as copper or aluminum. The tube attaches to the fitting via a compression nut and sleeve. The fitting is a discrete component which results in an increased parts count, a potential leak point, a more complex manufacturing process and greater costs.




One eccentric as used in such a compressor design includes a bearing boss, which lies outside of the axis of the motor. As the motor turns the eccentric boss moves in a circle. The boss is rotatably attached to the bottom of the piston by rotatably connecting to a piston bearing bore, a circular hole at the bottom of the piston. As the motor turns the eccentric, the piston is moved up and down. The eccentric boss is surrounded by a bearing; the bore at the bottom of the piston clamps around the bearing. The bearing reduces friction between the eccentric boss and the piston. The piston bearing bore may not be a complete circle in that a slit or small gap exists at the bottom of the piston. This slit or gap allows the bore to expand and contract slightly and allows the tension of the piston bearing bore against the bearing to be adjusted. Two clamping structures extend from the bottom of the piston, one on either side of the slit or gap, and include screw holes. A screw and bolt may be inserted into the clamping structures to alter the tension of the bore against the bearing.




The piston may be die-cast as one component. As the die-cast tool closes, molten metal is injected into the tool, and then the tool separates. The screw hole through the clamping structures extends in the direction that the tool parts separate; to create the hole a core pull is added to the die-cast tool. The use of the core pull adds to the cost of creating the piston.




Such a compressor configuration typically includes a pump frame which is attached to the motor assembly and also to the cylinder. The pump frame supports the cylinder and, since the axle of the motor extends through a bore in the pump frame to attach to the eccentric, the pump frame also helps to support the piston. A bore in the frame holds a bearing which supports the motor axle. The frame bore may include a lip on its outside edge which provides a stop for the bearing when it is pressed into the bore during manufacturing. Such a lip increases the distance between the portion of the frame supporting the axle (through the bearing) and the piston, thereby increasing the moment of force and thus increasing the stress in the frame bearing and the frame.




The spacing of the cylinder outwardly from the motor also adds to the moment and the stress on the bearing. Further, a compressor may include a pump frame with a face which is bowed outward, away from the motor. This also increases the distance between the portion of the pump frame supporting the axle and the piston.




In certain compressor designs, as the piston is forced up and down by the eccentric, the piston also wobbles, or rocks within the cylinder. Such designs may include a flexible seal, formed of a material not requiring oil lubrication, which extends around the perimeter of the piston to ensure the space above the piston is sealed as the piston rocks.




One factor reducing the life of such a piston seal is the angle of the piston during the compression stroke. When the piston is at its top dead center, the head of the piston is flat with respect to the cylinder and the surface of the cylinder head is perpendicular to the axis of the cylinder. Due to piston wobble, however, the piston head is slanted against the cylinder during both the up-stroke and the down-stroke. During the up-stroke, in which air is compressed, the piston seal is pressed unevenly against the cylinder, causing excessive wear of the piston seal.




As air is compressed by the piston, it is heated. The heated air heats components of the air compressor, causing faster wear and reducing operating efficiency. An important factor contributing to piston seal wear is its operating temperature; as the operating temperature increases the life of the seal decreases. To reduce the temperature of such pumps a cooling fan may be included. Due to the location of the fan and the arrangement of the components of certain compressors, such a cooling fan may blow air in a direction more or less perpendicular to the axis of the cylinder. Such an air flow arrangement, however, cools the cylinder inefficiently. The fan is typically connected directly to the eccentric boss and thus rotates at the same speed as the motor. While the compressor and motor may operate at different speeds, the fan may be most efficient at only one speed.




One technique for reducing heat in air compressors is described in U.S. Pat. No. 5,937,736 to Charpie. Charpie describes a piston cap having cooling fins. The piston cap is secured to the piston head, and the cooling fins extend through holes on the piston head. Such a solution is imperfect, as heat is effectively removed only from the piston head. While the cap is secured to the head, heat does not transfer effectively across gaps in metal, and thus the piston head and the piston rod (which is integral with the piston head) are not cooled by the heat sink action of the fins. The size, shape and number of the holes in the piston head limit the size, shape and number of the cooling fins. Further, a piston head with holes for cooling fins may be harder or more costly to manufacture. It is desirable to have a more efficient means for cooling a piston that also allows for easier and less costly construction.




As discussed, when the piston is at its top dead center, the head of the piston is flat with respect to the cylinder, and the surface of the cylinder head is perpendicular to the axis of the cylinder. As the piston tilts away from top dead center, one edge of the piston head rises higher than the center of the piston head. Thus a clearance volume must be provided between the top of the piston and the valve plate. This clearance volume results in a dead space above the piston, reducing the efficiency of the compressor and increasing the heat levels in the compressor.




It is desirable to have an air compressor which overcomes at least some or all of the aforementioned shortcomings of known air compressors.




SUMMARY OF THE INVENTION




The present invention provides an air compressor which overcomes the above-described problems of known air compressor designs. An air compressor in accordance with the present invention is more efficient in operation; comprises a piston which experiences less wear, has a more efficient means of cooling and is less expensive to manufacture; allows for reduced stress on the frame and bearings in operation; comprises a more efficient and effective cooling system; and is easier and less costly to construct.




An air compressor according to a preferred embodiment of the present invention includes a valve plate with cooling fins and a piston also having cooling fins. The valve plate includes an integral and angled valve plate outlet suitable for direct connection to a tube. Making the valve plate outlet integral with the valve plate allows for a simpler valve plate with a reduced number of parts, and thus a lesser cost. Angling the valve plate outlet relative to the valve plate reduces turbulence in the space above the cylinder as air is expelled from the compressor, as the exiting air is redirected at an angle of less than 180 degrees. This helps to lower flow resistance which decreases back pressure and increases efficiency.




In an exemplary embodiment, the bearing bore of the pump frame is lipless, decreasing the distance between the portion of the frame supporting the axle and the piston, decreasing the moment of force along the axle and the piston, and thus decreasing the stress on the frame and the frame bearing. Because the pump frame is flat and a portion of the cylinder is over a portion of the motor, the distance between the piston and the portion of the frame supporting the axle is decreased.




In a preferred embodiment, the piston of the compressor includes a novel design allowing for a less expensive casting process. The tension of the piston bearing bore may be adjusted by applying tension to two clamping structures. Tension is provided by a screw passing through clamping screw holes on each of the clamping structures. Each screw hole is formed from a series of structures, such as arcs, arches or barrel portions, which individually do not form the complete circumference of a hole, but when taken together form one or more holes. Such a screw hole does not require a core pull on casting, lowering manufacturing costs.




To improve the longevity of the piston seal, an exemplary embodiment of a piston in accordance with the present invention includes a piston seal which is angled with respect to the major axis of the piston. By thus angling the piston seal, the angle of the piston seal with respect to the axis of the cylinder is closer to perpendicular during a longer portion of the up-stroke than is achievable if the piston seal were not angled with respect to the major axis of the piston.




In a further exemplary embodiment, the piston head has a beveled face formed by two substantially planar portions which meet along a ridge which is substantially perpendicular to the plane in which the piston rocks. As the piston approaches and leaves top dead center, the beveled face of the piston allows the piston to approach the valve plate more closely, thereby reducing efficiency-robbing dead space between the piston and the valve plate.




In a preferred embodiment, the piston also includes cooling fins arranged on the back of the piston head and on the connecting rod. In addition to cooling the piston head directly, the cooling fins also cool the connecting rod which provides a large cooling area, substantially larger than the area of the piston head. The connecting rod is cooled by the ambient air through convection. The connecting rod, in turn, cools the piston head by conduction. This arrangement provides superior cooling of the piston over known arrangements.




In a preferred embodiment, the compressor includes a fan which operates efficiently at different speed settings. The fan is a radial fan including two sets of fan blades, a set of inner flat fan blades which operate most efficiently at a first range of fan speeds and a set of outer curved fan blades which operate most efficiently at a second range of speeds. The fan blows air through the compressor in a novel air cooling pattern, propelling air axially upward along the outside of the cylinder, increasing cooling efficiency.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

illustrates a cross section of an embodiment of an air compressor in accordance with the present invention.





FIG. 2

is a perspective view of the pump frame of the embodiment of the air compressor of FIG.


1


.





FIG. 3

is a side view of an exemplary embodiment of an air compressor piston in accordance with the present invention.





FIG. 4

is a partial cutaway view of the clamping features of an exemplary embodiment of an air compressor piston in accordance with the present invention.





FIG. 5

is a further partial cutaway view of the clamping features of an exemplary embodiment of an air compressor piston in accordance with the present invention.





FIG. 6

is a perspective view of the piston of FIG.


3


.





FIG. 7

is a further perspective view of the piston of FIG.


3


.





FIG. 8

is a perspective view of an exemplary embodiment of a valve plate of an air compressor in accordance with the present invention.





FIG. 9

is a plan view of the valve plate of FIG.


8


.





FIG. 10

illustrates an exemplary embodiment of a cooling fan of an air compressor in accordance with the present invention.











DETAILED DESCRIPTION OF THE INVENTION




In the following description, various aspects of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced using alternate configurations and arrangements. Furthermore, some well known features may be omitted or simplified in order not to obscure the present invention.





FIG. 1

illustrates a cross section of an embodiment of an air compressor in accordance with the present invention. Air compressor


1


includes a motor


4


, contained within a housing


6


, and having a rotor shaft


8


. Capacitors


10


may be coupled to the motor


4


to increase torque on startup and during operation. The rotor shaft


8


connects to an eccentric


20


, which in turn pivotally connects to a piston


100


at an eccentric boss


22


. A piston connecting rod


102


connects the two ends of the piston


100


. A fan


400


is also connected to the eccentric boss


22


. The piston


100


moves up and down inside a cylinder


30


, which is capped by a valve plate


200


. A front face or shroud


40


covers the fan


400


, piston


100


and eccentric


20


, and includes vents allowing a cooling air flow to enter the compressor


1


. A cylinder shroud


50


surrounds the cylinder


30


, defines an air space


52


surrounding the cylinder


30


, and includes vents


54


leading from the air space


52


to the ambient air. In

FIG. 1

, only one vent


54


is depicted, but multiple vents


54


may be included.




A cylinder head


32


sits above the valve plate


200


and in conjunction with the valve plate defines one or more chambers


34


,


35


. The cylinder head


32


includes an air compressor intake muffler


36


, and the valve plate


200


includes a valve plate outlet


202


, which is an angled, integral outlet port.




In operation, during a piston down-stroke, air enters the air compressor


1


via the intake muffler


36


and flows to an intake chamber


35


, through the valve plate


200


and into the cylinder


30


. During a piston up-stroke, the piston


100


pushes air out of the cylinder


30


, through the valve plate


200


into an exhaust chamber


34


and out of the valve plate outlet


202


.




The air compressor


1


includes a pump frame


500


attached to one end of the housing


6


and supporting one portion of the rotor shaft


8


. The pump frame


500


includes a pump frame bearing bore


510


through which the rotor shaft


8


extends. The pump frame


500


has a face


514


on the side of the pump frame


500


opposite the motor


4


and a face


515


facing the motor


4


. A pump frame bearing


512


sits inside the pump frame bearing bore


510


and supports the rotor shaft


8


through the pump frame


500


. The piston


100


includes a piston bearing bore


110


through which the eccentric boss


22


extends. A piston bearing


112


is seated in the piston bearing bore


110


, and reduces friction between the eccentric boss


22


and the piston bearing bore


110


.





FIG. 2

is a perspective view of the pump frame


500


of the embodiment of the air compressor of FIG.


1


. As can be seen in

FIG. 2

, the pump frame bearing bore


510


lacks a lip, and the pump frame bearing


512


is held inside the bearing bore


510


with a friction fit. In one embodiment the bearing bore


510


is a substantially smooth, unobstructed cylinder. Preferably, the pump frame bearing


512


is installed to be flush with the face


514


of the pump frame


500


which faces the cylinder


30


.




Because the bearing bore


510


lacks a lip, the pump frame bearing


512


is allowed to extend in the pump frame bore


510


up to the pump frame face


514


, thereby allowing the pump frame bearing


512


to be closer to the axis of the piston


100


, thus decreasing the moment of force on the eccentric


20


and piston


100


and thus decreasing the stress on the pump frame bearing


512


and the pump frame


500


. This arrangement increases the life of the bearing


512


. Eliminating the pump frame lip also reduces the stress on the bearing on the back end of the motor


4


. Further, smaller and thus less expensive bearings may be used. Moreover, because the pump frame bearing bore


510


lacks a lip, a machining step may be eliminated, reducing the cost of the air compressor


1


.




In an exemplary embodiment of the present invention, the face


514


of the pump frame


500


is substantially flattened, as opposed to being bowed or curved out. Because the pump frame


500


is substantially flattened, the cylinder


30


is allowed to be closer to the motor than in current designs, further decreasing the moment of force on the frame


500


and the bearing


512


. In a preferred embodiment of the present invention, at least a portion of the cylinder


30


is located at least partially over a portion of the motor


4


.




During manufacturing, an automatic tooling machine can be used to insert the pump frame bearing


512


into the pump frame bearing bore


510


. The pump frame bearing


512


is friction fitted into the pump frame bearing bore


510


. Automatically inserting the pump frame bearing


512


into a lipless bore is more difficult if the pump frame


500


is bowed out, as with conventional designs, as a stop (such as a flat surface or tool) is needed to ensure that the pump frame bearing


512


is not pushed all the way through the bore. Thus the flat pump frame


500


according to an embodiment of the present invention also allows for the easier manufacture of a lipless pump frame bore.





FIG. 3

is a side view of the piston of the embodiment of the air compressor of FIG.


1


. Generally, the piston


100


includes a piston bearing bore


110


at one end and a piston head


150


at the opposite end. A piston connecting rod


102


joins the two ends of the piston


100


. The piston head


150


includes a piston face


158


, for compressing air, and a back side


159


, which faces the connecting rod


102


. The piston


100


preferably includes a set of piston cooling fins


170


, preferably extending from the back side


159


of the piston head


150


and possibly from the connecting rod


102


. The piston


100


and its various features can be formed as a unitary component, such as by casting.




A piston bearing


112


is seated in the piston bearing bore


110


. The eccentric boss


22


(

FIG. 1

) extends through the piston bearing


112


. The end of the bearing bore


110


furthest from the piston head


150


includes a slit


114


, allowing the bearing bore


110


to expand slightly. Two clamping structures


120


and


130


extend from the piston


100


on either side of the slit


114


. Each clamping structure


120


and


130


includes a screw hole, depicted further in

FIGS. 5-8

. A screw


116


fits through the two screw holes and may be used to clamp the clamping structures


120


and


130


and thus adjust the tension of the piston bearing bore


110


. The screw


116


may be loosened to allow the piston bearing


112


to be removed and replaced. The screw


116


is secured by a nut


118


.




The piston head


150


includes a slanted or angled piston seal rim


156


, which holds a flexible piston seal


152


. A piston seal retainer


154


holds the piston seal


152


on the piston seal rim


156


. The piston seal


152


extends beyond the width of the piston head


150


and acts to stop air from leaking around the piston


100


inside the cylinder


30


. A line connecting any two points along the edge of the piston face


158


, at the end of the piston head


150


, is generally perpendicular to the axis of the piston


100


. When viewed from certain directions, the piston seal rim


156


deviates a certain angle from such a line, and thus the piston seal rim


156


is not at a right angle to the axis of the piston


100


. In a preferred embodiment, when viewed in the plane of the piston bearing bore


110


, the piston seal rim


156


is not at a right angle to the axis of the piston


100


. When viewed in an axis perpendicular to the plane in which the piston bearing bore


110


lies, the piston seal rim


156


is at substantially a right angle to the axis of the piston. Thus, if the piston face


158


is considered to be flat (in a preferred embodiment the piston face


158


includes angled planes), the piston seal rim


156


lies at an angle to the piston face


158


. In a preferred embodiment, the axis of the piston


100


and the plane of the piston seal rim


156


form a 88.5 degree angle when measured in the plane of the piston bearing bore


110


. The optimal angle will depend on the length of the piston and the size of the stroke.




The piston seal


152


lies substantially in the same plane as the angled piston seal rim


156


. Therefore, when the piston


100


is at a certain point in its up-stroke and is at a certain angle with respect to the axis of the cylinder


30


, the piston seal


152


is closer to being perpendicular with the cylinder axis than with current designs. In an exemplary embodiment, the piston seal


152


is angled two degrees (i.e., angle S in

FIG. 3

) relative to a plane perpendicular to the major axis of the piston


100


. As such, at top and bottom dead center, the piston seal


152


will be tilted two degrees relative to a plane perpendicular to the axis of the piston. Furthermore, given a typical connecting rod length and stroke, the maximum tilt of the seal


152


through the down-stroke will be nine degrees, but only five degrees through the up-stroke. For a similarly dimensioned, conventional piston with a flat piston seal, the maximum tilt will be seven degrees through both the up-and down-strokes. As mentioned, the lower degree of tilt in the more critical up-stroke afforded by the piston


100


of the present invention applies less wear on the piston seal


152


.




In one embodiment, the compressor


1


may be generally manufactured from aluminum, except for parts such as electrical parts, seals and other parts requiring different materials. The cylinder


30


may be anodized and Teflonâ„¢ impregnated. The valves may be constructed of stainless steel. The seals such as the piston seal


152


may be constructed of Teflonâ„¢ and other materials. The rotor shaft


8


may be steel. Other suitable materials may also be used.




In a further aspect of the present invention, the face of the piston head


150


is beveled to accommodate the pivoting motion of the piston


100


. In a compressor with a conventional, flat piston head, a space is required between the piston at top dead center and the valve plate so as to prevent the piston from striking the valve plate as the piston approaches and leaves top dead center. The piston


100


according to an embodiment of the present invention is designed so as to reduce the amount of this dead space by beveling the piston face


158


, allowing the piston


100


to come closer to the valve plate


200


at top dead center.




As shown in

FIG. 3

, when viewed in a direction perpendicular to the plane of the pivoting motion (i.e., the plane of the piston bearing bore


110


), the face


158


of the piston head


150


comprises two substantially planar surfaces


160


and


162


which slope upwards from the edge of the piston face


158


and meet along an edge


164


, substantially in the center of the piston face


158


. The edge


164


extends parallel to the axis of the piston bearing bore


110


. In a preferred embodiment, the surfaces


160


and


162


meet at an angle of approximately


177


degrees. The optimal angle will depend on the bore stroke and connecting rod length. When viewed from a transverse direction, the piston head


158


appears substantially flat. This aspect of the piston head


158


can also be seen clearly in FIG.


6


.




In a preferred embodiment, a fastener mounting arrangement on each of the clamping structures


120


and


130


, for holding a clamping screw, is formed from a series of structures, such as arcs, arches or cylinder portions, which individually do not form the complete circumference of a hole, but when taken together form one or more holes. Preferably the arcs or cylinder portions share the same axis, through which a screw or other connecting member may be inserted.




In alternate embodiments the screw hole may support other types of fasteners and may be used on other structures requiring fasteners. For example, a fastener mounting arrangement in accordance with the present invention may use arched or half-cylinder surfaces to hold a fastener or screw in any application requiring a fastener where easy, inexpensive manufacturing is desired.





FIG. 4

is a partial cutaway view of the clamping structures of the piston of the embodiment of the air compressor of FIG.


1


.

FIG. 5

is an opposing partial cutaway view of the clamping structures of the piston of the embodiment of the air compressor of FIG.


1


.

FIGS. 4 and 5

each show portions of the clamping structures


120


and


130


; the clamping structures


120


and


130


, and the piston


100


are shown whole in

FIGS. 3

,


6


and


7


. The portion of the clamping structures


120


and


130


shown in

FIG. 4

corresponds to the portion of the clamping structures


120


and


130


shown in FIG.


5


.




Referring to

FIGS. 4 and 5

, a bore is formed through each of the clamping structures


120


and


130


from a pair of arcuate members


122


,


124


and


132


,


134


, respectively, each of which is generally a half-cylinder. Two half-cylinders are arranged on each clamping structure


120


and


130


: the clamping structure


120


includes half-cylinders


122


and


124


, and the clamping structure


130


includes half-cylinders


132


and


134


. The two bores thus formed are aligned with a common axis so as to allow a fastener, such as a bolt or screw, to extend therethrough. The clamping structure


120


is separated from the clamping structure


130


by the slit


114


. The half-cylinder


122


does not overlap the half-cylinder


124


, and the half-cylinder


132


does not overlap the half-cylinder


134


. The bores formed by the half-cylinders


122


,


124


,


132


and


134


to not form a complete cylinder yet may still entrain a fastener placed therethrough. In each clamping structure


120


and


130


, half of the respective bore is formed by each disjoint half-cylinder. This disjoint half-cylinder structure according to an embodiment of the present invention allows the piston


100


to be cast without a pull in the die-cast tool. The disjoint half-cylinder structure may be contrasted with a bore formed as a complete cylinder, which may require a die-cast process including a pull.




To tighten the piston bearing bore


110


, a threaded bolt


116


or the like is inserted in the aforementioned bores through the clamping structures


120


and


130


. (See

FIG. 3.

) A complementary nut


118


or the like abuts against either of the clamping structures to capture the bolt


116


. In an alternate exemplary embodiment, one or more of the half-cylinder portions


122


,


124


,


132


,


134


can be formed with threads to engage the threads of the bolt


116


.





FIG. 6

is a perspective view of the piston of the air compressor of FIG.


1


. The clamping structure


120


includes half-cylinders


122


and


124


, and the clamping structure


130


includes half-cylinders


132


and


134


. The clamping structure


120


is separated from the clamping structure


130


by the slit


114


. The half-cylinder


122


does not overlap the half-cylinder


124


, and the half-cylinder


132


does not overlap the half-cylinder


134


. Therefore, the screw hole formed by the half-cylinders


122


,


124


,


132


and


134


is not a complete cylinder.




In an alternate embodiment, the fastening bore portions may be other than half-cylinders. For example, each portion may be less than one half-cylinder; e.g., an arc portion forming less than one half the circumference of a circle. Moreover, the fastening bore portions need not be circular; for example, one or more portions may have a polygonal cross-section.





FIG. 7

is a further perspective view of the piston of FIG.


6


. The piston


100


includes a piston bearing bore


110


, a piston head


150


, and a piston seal rim


156


. A piston bearing


112


may be seated in the piston bearing bore


110


. The eccentric boss


22


extends through the center of the piston bearing


112


. The piston bearing bore


110


is divided by the slit


114


.




As shown in

FIG. 7

, the piston


100


preferably includes a plurality of piston cooling fins or features


170


. In the exemplary embodiment shown, the piston cooling fins


170


are generally planar metal extensions which act to cool the entire piston


100


by increasing the surface area of the piston and thereby transferring heat from the piston


100


to air in the space behind the piston head


150


. The air behind the piston head


150


is not compressed by the piston head and as such is relatively cool and may be exchanged or replenished by the action of the fan


400


or by the action of the piston


100


itself. Moreover, the space behind the piston head


150


is in fluid communication with the ambient air. As the piston


100


reciprocates, a movement of air may be set up which aids in the transfer of heat from the piston


100


.




In an exemplary embodiment, the piston


100


is cast from a unitary piece of metal. With the cooling fins


170


thus cast as integral features of the piston


100


, the cooling fins


170


help to reduce the heat of the entire piston


100


. The cooling fins


170


on the piston


100


also help reduce the temperature of the piston seal


152


. With the piston and seal cooler, the entire air compressor


1


runs cooler. This increases the life of wear parts such as the piston seal


152


and increases the efficiency of the air compressor


1


. A wide variety of sizes, shapes and numbers of cooling fins


170


may be included. Alternately, the piston cooling fins


170


may be integral with only a portion of the piston


100


, such as the piston head portion.




In an alternate embodiment, the piston need not be constructed as one integral member. In further embodiments, cooling fins may be located on other parts of the piston, such as on the piston rod.





FIG. 8

is a perspective view of the valve plate


200


of the air compressor embodiment shown in FIG.


1


. In

FIG. 8

the valve plate


200


is seen from the side which mates with the cylinder


30


. The valve plate


200


includes an angled integral valve plate outlet


202


, which is an outlet port allowing air to exit one of the air spaces


34


(

FIG. 1

) defined by the cylinder head


32


. A valve plate outlet opening


214


extends through the valve plate outlet


202


. The valve plate


200


includes a set of exhaust holes


204


and a set of intake holes


206


. A valve (not shown) covers each of the exhaust holes


204


and intake holes


206


. During a piston up-stroke, the valves over the exhaust holes


204


open, allowing air to flow out of the cylinder


30


through the exhaust holes


204


and exit the compressor


1


via the valve plate outlet


202


. During a piston down-stroke, the valves covering the intake holes


206


open, allowing air to flow into the cylinder


30


through the intake holes


206


.




In a preferred embodiment, the valve plate


200


includes a set of cooling fins


210


. The valve plate cooling fins


210


are preferably located on the side of the valve plate


200


which mates with the piston


100


but can also be located on the opposite side of the valve plate. The valve plate cooling fins


210


are preferably planar metal extensions which act to cool the valve plate


200


. The valve plate cooling fins


210


are preferably located in a radial pattern to reduce turbulence as air flows over and around the fins. When the cylinder


30


mates with the valve plate


200


, the cooling fins


210


surround the cylinder


30


. Air provided by the cooling fan


400


flows axially along the cylinder


30


and flows over the valve plate cooling fins


210


. Heat from the cylinder


30


and the valve plate


200


is transferred to the air flowing over the cylinder


30


and the cooling fins


210


. This reduces the heat of the overall compressor


1


, and thus increases the efficiency of the compressor


1


and the life of certain wear parts.





FIG. 9

is a plan view of the valve plate of the embodiment of the air compressor of FIG.


1


. In

FIG. 9

the valve plate


200


is seen from the side which mates with the cylinder head


32


. The valve plate


200


includes an angled integral valve plate outlet


202


having a valve plate outlet opening


214


therethrough. In an exemplary embodiment, the angle between the valve plate outlet


202


and the valve plate


200


is approximately 60 degrees. Alternately, other angles may be used. The valve plate


200


includes a set of exhaust holes


204


and a set of intake holes


206


.




In operation, during a piston up-stroke, the piston


100


pushes air out of the cylinder


30


, through the valve plate


200


, into the air space


34


, and out of the valve plate outlet


202


via the valve plate outlet opening


214


. Air flows upward through the air space


34


and is redirected to flow downward out of the valve plate outlet


202


. This redirection contributes to turbulence and flow resistance which, if not reduced, may lower the efficiency of the compressor


1


. Angling the valve plate outlet


202


as shown reduces the angle at which the air must be redirected, thus reducing turbulence and flow resistance, and increasing the efficiency of the pump.




In a preferred embodiment, the valve plate outlet


202


is integral with the valve plate


200


. Making the valve plate outlet


202


integral with the valve plate


200


reduces manufacturing costs. The valve plate outlet


202


is cast and machined as part of the casting and machining of the valve plate


200


. Current designs include a valve plate outlet which includes an extra component which screws into a valve plate, increasing manufacturing costs. Furthermore, the outlet


202


can advantageously be formed to comprise a compression fitting.




A preferred embodiment of the present invention includes a fan which is efficient at multiple rotational speeds. Preferably, the fan is a centrifugal fan including two sets of fan blades: one set designed to operate most efficiently in a first range of rotational speeds, and a second set designed to operate most efficiently in a second range of rotational speeds. The fan of the present invention can thus produce greater airflow over two speed ranges.





FIG. 10

illustrates an exemplary embodiment of a fan


400


for use in an air compressor of the present invention. The fan


400


includes a set of inner fan blades


410


for propelling air at a first set of speeds, and a set of outer fan blades


420


for propelling air at a second set of speeds. Preferably, the inner fan blades


410


are substantially straight, radial, flat paddle wheel blades, and are most efficient at a range of rotational speeds centered around approximately 1,725 r.p.m. (e.g., 1,500-2,000 r.p.m.) Preferably the outer fan blades


420


are curved blower wheel blades, and are most efficient at a range of rotational speeds centered around approximately 3,450 r.p.m. (e.g., 3,000-4,000 r.p.m.) Each blade of the inner fan blades


410


may have a cutout portion, such as cutout portion


412


. The back


440


of the fan


400


may include vents or a cutout portion


442


, which allows air to flow in from the back


440


as well as from the front. Alternately, the body of the fan


400


may be solid.




In operation, the eccentric boss


22


turns the fan


400


in the direction of the forward curve of the set of fan blades


420


(counter-clockwise, as shown in FIG.


11


). A vacuum is formed in the center region of the fan


400


, and air enters the fan


400


in this center region. The spinning of the fan blades


410


and


420


causes air to be propelled radially from the center of the fan


400


to and out of the periphery of the fan


400


, flowing between the outer fan blades


420


. The fan


400


draws air in through the shroud


40


and blows the air upwards, axially around the cylinder


30


, across the valve plate cooling fins


210


, and out of the vents


54


, thereby cooling the motor


4


, valve plate


200


, cylinder


30


, and other parts of the air compressor


1


.




The speed of the motor


4


, and thus the speed of the fan


400


, may vary. If the fan


400


is rotating at a range of speeds of approximately 1,500-2,000 r.p.m., the outer fan blades


420


propel air through the fan


400


, but the inner fan blades


410


propel air through the fan


400


more efficiently. If the fan


400


is rotating at a range of speeds of approximately 3,000-4,000 r.p.m., the inner fan blades


410


propel air through the fan


400


, but the outer fan blades


420


propel air through the fan


400


more efficiently. At speeds between these ranges the fan


400


may operate with varying levels of efficiency; however, at all operational speeds the fan


400


operates more efficiently than a fan having only one set of fan blades. In one embodiment of the compressor of the present invention, a fan is tailored to correspond to certain discrete compressor speed settings.




In one embodiment, the fan


400


is molded from plastic, but may be manufactured of other materials. In alternate embodiments other types of fan blades may be used, and other numbers of sets of fan blades may be used. For example, curved fan blades need not be used. In further embodiments, the sets of fan blades may be constructed to be most efficient at other speeds. In an alternate embodiment, the variable speed fan of the present invention may be used in other applications, such as a drying or air moving apparatus.




In a preferred embodiment of the present invention, cooling air flows through the compressor


1


in a novel and efficient manner. The fan


400


draws outside air in through the shroud


40


and propels the air axially along the outside of the cylinder


30


. The cylinder shroud


50


, surrounding the cylinder


30


, defines an air space


52


. Air flows upward through the air space


52


between the cylinder


30


and the cylinder shroud


59


, past the cooling fins


210


of the valve plate


200


, and exits the compressor at the vents


54


. Such an air flow makes more efficient use of the work being done to propel cooling air by allowing the cooling air to be in greater contact with the cylinder


30


. Existing designs in which air is propelled in other directions, for example in a direction perpendicular to the cylinder, do not provide as efficient a cooling process.




While the compressor and compressor components of the present invention are described with respect to specific embodiments, it should be noted that the present invention may be implemented in different manners and used with different applications. For example, not all of the features described herein need be included in a compressor according to an embodiment of the present invention. Such a compressor may, for example, include a piston with an angled head, but omit a cooling fan which operates at multiple speeds or a pump frame with a flat face.



Claims
  • 1. A fastener mounting arrangement comprising:a first mounting member, the first mounting member including: a first arched surface having a first rim to the right of the surface and a second rim to the left of the surface, a second arched surface having a first rim to the right of the surface and a second rim to the left of the surface, wherein the first and second arched surfaces face substantially opposite directions and have a common axis and the first rims of the first and second arched surfaces are substantially adjacent to each other; and a second mounting member, the second mounting member including: a third arched surface having a first rim to the right of the surface and a second rim to the left of the surface, a fourth arched surface having a first rim to the right of the surface and a second rim to the left of the surface, wherein the third and fourth arched surfaces face substantially opposite directions and have an axis substantially common with common axis and the first rims of the third and fourth arched surfaces are substantially adjacent to each other, wherein the first and second mounting members are substantially adjacent to one another and wherein a fastener joining the first and second mounting members can be placed substantially coaxial with the common axis.
  • 2. The fastener mounting arrangement of claim 1, wherein:the fastener mounting arrangement is mounted on a piston; the first arched surface and the second arched surface are located on a first extension extending from the piston; the third arched surface and the fourth arched surface are located on a second extension extending from the piston; and the fastener mounting arrangement is cast as an integral feature of the piston.
  • 3. The fastener mounting arrangement of claim 1, wherein each of the first arched surface, second arched surface, third arched surface and fourth arched surface forms a portion of a hole.
  • 4. A fastener mounting arrangement on a cast piston having a bore hole, the fastener mounting arrangement comprising:a first extension including at least a first barrel portion and a second barrel portion; a second extension including at least a third barrel portion and fourth barrel portion; and a slit dividing the bore hole and separating the first extension from the second extension, wherein a bolt may be extended through the fastener mounting arrangement.
  • 5. The fastener mounting arrangement of claim 4 wherein a bolt may be extended through the first barrel portion, second barrel portion, third barrel portion and fourth barrel portion.
  • 6. The fastener mounting arrangement of claim 4 wherein the first barrel portion, second barrel portion, third barrel portion and fourth barrel portion share the same axis.
  • 7. The fastener mounting arrangement of claim 4 wherein each of the first barrel portion, second barrel portion, third barrel portion and fourth barrel portion forms a portion of a hole.
Parent Case Info

This application is a divisional application of U.S. patent application Ser. No. 09/637,560, filed Aug. 11, 2000, now U.S. Pat. No. 6,530,760 and incorporated herein by reference.

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