Patent Application
20060104833
Not applicable.
Not applicable.
The invention relates generally to the field of pumps, such as compressors and vacuum pumps, and more particularly, to a compressor having a fan guard with a channel to direct cooling air to a piston cylinder.
Reciprocating piston or diaphragm pumps typically have a metal housing, for example, a cast aluminum alloy, in which bearings are mounted which journal the shaft which drives the pump. A metal housing is needed, particularly for larger pumps, to withstand the forces of driving the piston or diaphragm and containing the pressure exerted in the compression chamber of the pump.
A rotary electric motor is usually used to drive these pumps and the motor requires cooling. In one such pump, the motor is provided between two housings, each of which is separate from the other and houses one compression chamber. The shaft of the motor is a through shaft so that each end of the shaft mounts one of the pistons or diaphragms that work to vary the volume of the compression chamber in the housing at the corresponding end of the shaft. Further out from where the piston or diaphragm is mounted, a rotary fan blade is mounted to each end of the shaft to draw a flow of cooling air into the housing at that end and blow it onto the rotor and stator coils of the motor.
For cooling efficiency, it is desirable to make the part of the housing in which the rotary fan blade is mounted circular and just slightly larger than the diameter of the fan blade. The clearance between the tips of the fan blades and the interior housing surface should be as small as possible because, if not, the air drawn into the housing by the fan blades will simply blow back out past the tips of the blade, and not be directed over the coils of the motor. For applications in which the pump is contained inside of a separate enclosure, it may be permissible to leave open the end of the housing at which the fan blade is mounted. However, if the pump is going to be exposed or sold as a stand-alone product, the end of the housing must be closed with a cover that permits air to be drawn into the housing, but prevents the insertion of larger objects or fingers. This cover, typically called a fan guard, should not deleteriously affect the operation of the fan nor add to the lateral size or detract from the appearance of the fan.
The effectiveness of the cooling system in reducing the stator temperature of the motor affects the range of applications in which the pump may be employed. The voltage at which the motor is driven and the output pressure of the pump affect the amount of heat that is generated in the motor. More effective cooling expands the range of applications suitable for a given pump and motor.
The motor is not the only temperature-sensitive component in a pump. Wobble pistons are sometimes used in oil-less air compressors and vacuum pumps. A wobble piston includes a peripheral seal on the piston head that engages the cylinder bore. The piston head and its connecting rod are fixed to each other, and the connecting rod is mounted on an eccentric on a shaft. As the eccentric is turned by the shaft, the wobble piston is moved in and out and “wobbles” from side to side. Wobble pistons typically employ a Teflon® or other similar material disc or cup which serves both as a guide for the wobble piston and as a pneumatic seal between the piston and the wall of the cylinder in which it moves. The working surface of the cylinder has a hardened polished surface, providing a smooth surface for cooperating with the Teflon® seal of the piston. The service life of the Teflon® material depends in part on the temperature of the cylinder with which the seal interfaces. A higher temperature typically corresponds to a shorter service life due to increased friction between the cup and the cylinder wall.
The bearings used to support the motor shaft also have a service life determined at least in part by temperature. Generally, a higher bearing temperature equates to a shorter bearing service life.
Hence, cooling efficiency not only affects the range of applications for a particular pump, but also the service life of temperature-sensitive components in the pump. The present invention addresses these problems.
The present invention is directed generally to a fan guard that directs cooling air flow to a piston cylinder.
One aspect of the invention is seen in a pump including a housing, a shaft supported by the housing, a piston assembly, a fan blade, and a fan guard. The piston assembly includes a piston cylinder and is operably coupled to the shaft. The fan blade is operable to generate cooling flow. The fan guard is mounted to the housing and includes a channel configured to direct at least a first portion of the cooling flow to the piston cylinder.
Another aspect of the present invention is seen in a fan guard. The fan guard includes a front surface defining a cooling flow opening and sidewalls defining a channel having a first end proximate the cooling flow opening. A baffle is positioned proximate a second end of the channel.
Other objects, advantages and features of the present invention will become apparent from the following specification when taken in conjunction with the accompanying drawings.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
While the present invention may be embodied in any of several different forms, the present invention is described here with the understanding that the present disclosure is to be considered as setting forth an exemplification of the present invention that is not intended to limit the invention to the specific embodiment(s) illustrated. Nothing in this application is considered critical or essential to the present invention unless explicitly indicated as being “critical” or “essential.”
Referring to
The housings 14, 16 are provided with ventilation slots 39 to allow the exhausting of cooling air. The housings 14, 16 mount bearings 40 which journal the shaft 34. The housings 14, 16 also have openings (not shown) in them which provide for the axial through-flow of air so that air moved by the fan blade 36 reaches the coils of the motor 12.
The pump 10 includes a piston assembly 42 including a piston cylinder 44 and a piston head 46 operating within the piston cylinder 44 to compress the operating fluid (e.g., air) to provide the pumping action. The piston head 46 is coupled by a connecting rod 48 to an eccentric 50 fixed to the shaft 34. In operation, the shaft 34 and attached eccentric 50 rotates causing the connecting rod 48 and piston head 46 to move within the piston cylinder 44. A flapper valve (not shown) mounted to the valve plate 52 allows the air to enter the piston cylinder 44 on the downstroke of the piston cycle and seals to prevent air passage on the upstroke. The piston head 46 also includes a piston cup 54 constructed of Teflon® or other similar material that provides a sliding seal between the piston head 46 and the piston cylinder 44. The piston cup 54 has a service life that may vary based on the temperature of the piston cylinder 44, with a higher cylinder temperature resulting in a shorter service life.
Besides allowing axial cooling air flow to dissipate heat that is transferred from the motor 12 to the housings 14, 16 to the bearings 40, the fan guard 32 also directs cooling flow over the piston cylinder 44 to dissipate heat generated during the compression process. The housings 14, 16 includes openings 56 (shown in
Turning now to
The fan guard 32 includes sidewalls 70 that define a channel 72. The channel 72 terminates in a baffle 74 that changes the direction of radial cooling flow generated by the rotary fan blade 36 to impinge on the piston cylinder 44, as indicated by the arrow 76 shown in
Returning to
Redirecting cooling flow over the piston cylinder 44, as described herein, reduces the operating temperature of the piston assembly 42. The combination of the rotary fan blade 36 and fan guard 32 also reduces the temperature of the bearings 40 and the motor 12. Such temperature reductions increase the operating lives of the piston cup 54 and the bearings 40 for a given set of operating conditions. The improved heat dissipation characteristics may also be employed to extend the operating range of the pump 10 to allow operation at higher pressures, different voltages, and/or lower frequency voltage inputs.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
