US 20060034708 A1
A linear pump has a housing containing a cylinder and piston arrangement and a motor with a slotted stator containing a wire coil driving an armature connected to the piston to reciprocate the piston within the cylinder along a piston axis. The housing defines a pair of straight air intake vent tubes in communication with ambient air and extending to proximate the motor. The vent tubes serve to provide both the primary breathing passages of the pump as well as cooling passages for the motor.
11. A pump comprising a housing containing a motor and having an air intake opening and a vent tube extending from the intake opening to proximate the motor.
12. The pump of
13. The pump of
14. The pump of
15. The pump of
16. The pump of
17. The pump of
18. The pump of
19. A linear pump comprising a housing containing a cylinder and a piston disposed along a piston axis and a motor having a slotted stator containing a wire coil driving an armature connected to the piston to reciprocate the piston within the cylinder along the piston axis, wherein the housing defines an air intake vent tube in communication with ambient air and extending to proximate the motor.
20. The pump of
21. The pump of
The present invention relates to pumps and in particular to compact linear piston pumps.
Pumps for certain duties, such as oxygen concentration and sewage aeration, generally need to be compact and operate discreetly. It is thus important to properly muffle the working air as well as reduce vibration during operation of the pump without relying on a large, thick-walled housing to attenuate the sound and vibration. Discreet operation of the pump can be obtained by insulating the housing, however, this adds bulk and can cause cooling problems. Mufflers can be added at the output, however, this adds hardware and cost.
Such compact linear pumps/compressors are often single cylinder devices with a small piston that reciprocates rapidly within a small cylinder to pressurize the air. The rapid movement of the single piston generates considerable vibration. These vibrations are often transferred directly to the pump housing, via a direct rigid mounting connection.
To facilitate reciprocation of the piston with less vibration, it is known to suspend the drive member, such as the armature of an electromagnetic motor, by springs or like flexible members. Stacks of thin metal leaf springs are well-suited for this. However, when multiple springs are used, it can be difficult to achieve the prescribed spring rate to which the piston drive components of the pump have been tuned. Changes in the angular (about the piston axis) and/or axial (along the piston axis) orientation of the springs relative to one another can effect the spring rate. To ensure that the pump operates efficiently, it is thus important to achieve the intended spring rate and thus ensure the consistent orientation of the suspension springs, which can make pump assembly difficult.
Another problem is that the intake and exhaust valves of the valve head must open and close rapidly for each stroke of the piston. Typically, thin metal flapper valves are used for this purpose because of their ability to seat and unseat very rapidly. Since the exhaust port opens under the force of the compressed air, a valve stop is used to support the valve and prevent it from being hyper-extended beyond its elastic range. The rapid contact between the intake valve and the valve head or the exhaust valve and the valve stop can generate tapping or clicking sounds. Another problem is that the rapid opening and closing of the intake valve can cause pressure fluctuations or pulsations in the air flow upstream from the valve head. These air pulsations can generate a low-frequency, rumbling noise.
Another problem confronting the design of compact linear piston pumps is eliminating pulsations in the output air stream. Pulsations in the air downstream from the outlet has been found to alter the resonant frequency of pump when different lengths and/or diameters of output lines are attached to the pump. Changing the operational frequency of the pump causes inefficiencies that can ultimately render the pump unusable for particular applications. It can also exacerbate noise and vibration issues.
Yet another persistent problem in compact linear pump design is cooling. To decrease noise, or perhaps to make immersible or suitable for outdoor use, the working components of these pumps are often enclosed in a pump housing. With operation of the pump, friction and the current in the electromagnet coil generate heat. As is well understood, heat adversely affects the pump efficiency and life. Many times the need to keep the pump operating efficiently requires the housing to be vented or to have other measures taken which destroy, or at least significantly reduce, the noise retarding features of the housing or other components.
Accordingly, an improved linear pump is needed that addresses the aforementioned problems.
The present invention provides an improved linear pump compressor using intake air to cool the winding of an electromagnetic motor.
In particular, the invention is a linear pump having a cylinder and piston disposed along a piston axis and a motor having a stator containing a wire coil driving an armature to reciprocate the piston within the cylinder along the piston axis. The pump housing defines an air intake opening and a vent tube extends from the intake to proximate the motor.
In a preferred form, the vent tube is an integral part of the pump housing extending inwardly from the air intake opening. More preferably, the housing has a pair of intake openings and a pair of vent tubes. Since they are part of the housing, the vent tubes are rigid, and preferably extend in parallel straight toward the motor.
In other preferred forms, the vent tube(s) direct the intake air at the motor essentially perpendicular to the piston axis. And, the stator is slotted to allow intake air to pass by the wire coil. There are a plurality of axial slots spaced apart about the piston axis in the stator allowing intake air exiting the vent tube to pass directly through the motor.
The present invention thus provides a linear pump with an improved motor cooling arrangement in which intake air necessary for pump operation is routed past and through the motor during operation of the pump. Slots in the motor stator allow venting of the electromagnetic coil for even better cooling. The dual purpose vent tubes provide both the primary breathing passage for the pump as well as the motor cooling passage such that multiple routing components are not needed. Moreover, since the vent tube(s) are formed as part of the housing, no separate tubing is needed, thereby reducing assembly costs as well as junctions in the air pathway that could be potential leak points.
These and other advantages of the invention will be apparent from the detailed description and drawings.
The present invention provides an axial or linear piston pump. The term pump used herein includes a device for providing either positive or negative pressure, and thus either acting as a vacuum pump or a compressor. The pump has a compact form factor, with a preferred operating range of 2-30 psi depending upon the application (however, the pump could be designed to operate at other pressures) with low external vibration and noise and less sensitivity to pump attachments (lines, hoses, tubing, etc.) downstream from the outlet.
Referring to FIGS. 3, 5-7 and 12, the pump 20 breathes through an air intake assembly generally designated 40. The air intake 40 is configured to reduce the low, rumbling noise associated with pulsations in the intake air caused by rapid movement of the intake valve. In particular, the air intake 40 includes an inner cavity 42 defined in part by a recess in the top of the shroud 26, a seal partition 44, a filter tray 46, a filter 48 and the cover 28, which provides the upper boundary for an outer cavity 50.
As mentioned, the recessed top of the shroud 26 defines the inner cavity 42, in the floor of which are two spaced apart orifices 52 near one end (the right end in the drawings). The inner cavity 42 is bounded at the top by the partition 44 which seals against a peripheral wall 54 of the inner cavity 42. The partition 44 has a pair of spaced apart orifices 56 located at a (left) end of the inner cavity 42 opposite the orifices 52. To facilitate assembly the partition 44 includes another set of orifices 56′ at the opposite end, however, these are not used when the partition 42 is oriented as shown in the drawings. In any event, intake air flows through only the one set orifices 56 (or 56′), which is located opposite the orifices 52 in the floor of the inner cavity 42. Resting on the partition 44 is the filter tray 46 which holds the filter 48 in the outer cavity 50. The filter tray 46 has a bottom wall with a pair of openings 58 which align with orifices 56 in the partition 44. A small alignment feature 59 extends down from the underside of the filter tray 46 and fits into an opening 61 in the shroud 26 to ensure that the filter tray 46 is assembled in the proper orientation. The filter 48 is held spaced off of the bottom of the filter tray 46 by a number of small spaced apart risers 60, and is retained by a short peripheral wall 62 ringing the filter tray 46. The wall 62 has a cut-out 64 at one end (opposite the openings 58) allowing intake air to flow laterally into the filter 48. The cover 28 fits onto the shroud 26 over the filter 48 to define the outer cavity 50. Ribs 66 on the inside of the cover 28 contact the wall 62 of the filter tray 46 to keep the bottom edge of the peripheral wall 68 of the cover 28 spaced slightly from the shroud 26, and also to funnel the intake air into the outer cavity 50 through the cut-out 64. The space between the top cover 28 and the shroud 28 defines the intake air passage 36, which extends around the periphery of the cover 28. Aligned center openings in the cover 28, filter 48, filter tray 46 and partition 44 allow a bolt 69 to screw into a threaded opening 70 in the shroud 26 to secure the assembly.
Referring now to
As shown in
Referring now to
With primary reference to
The other side of the retainer collar 138 clamps one or more leaf springs 142 with a recessed groove (having alignment features as discussed below) in a spacer ring 144. The opposite side of the spacer ring 144 receives a stator 146 of the electromagnet motor 106. The stator 146 is a slotted annular member having a circular base and concentric inner 148 and outer 150 cylindrical walls (with axial slots 169 in outer wall 150), which define an annular channel 152 therebetween. A wire coil 154 is disposed in a bobbin 156 within the channel 152. The bobbin 156 has three posts that extend through openings in the base of the stator 146 and are engaged by retainers 153 to retain the bobbin 156 and coil 154. A diode (not shown) may be electrically coupled to the coil 154 to rectify the alternating current input signal so that it drives an armature (or shuttle) 158 in only one direction, preferably toward the stator 146. Conductive tabs 160 for coupling the coil 154 to the power are also included.
The armature 158 has a series of axial bores therethrough and slides in and out of a side (right in the drawing) of the stator 146 when the coil 154 is energized. The armature 158 has a short hub with an axial bore 162 that receives a bottom end of a connecting rod 164. The connecting rod 164 is suspended along the piston axis 108 by the leaf springs 142 and passes through the center bore in the stator 146. The connecting rod 164 is secured to the armature 158 and the piston 104 by a long bolt 166 threaded into the piston 104 and mounting a mass disk 168 under its head.
The stator 146 is clamped between the spacer ring 144 and another spacer ring 172. That spacer ring 172 clamps one or more additional leaf springs 142 against a second retainer collar 174. Four tie rods 173 extending through ears in the first retainer collar 138 are threaded into openings in ears of the second retainer collar 174 to unite the components of the motor 106. The retainer collars 138 and 174 also have threaded openings receiving bolts 109 to connect the motor mount 110 and thereby mount the entire drive assembly to the base plate 82 via the resilient mounts 112, as described above.
As shown in
This is important to ensure that the motor 106 has the spring rate for which it was designed. Specifically, during development the pump is tuned to operate at a frequency at or near its natural resonant frequency. In particular, the pump is operated with a load applied and using a calculated spring-mass system (i.e., the combination of spring rate of the springs 142 and mass of the moving components, namely the piston 104, armature 158, connecting rod 164 and any mass disk 168). The frequency of the input signal to the motor 106 is varied as various parameters are measured. For example, because power consumption goes up as the input frequency strays from the resonant frequency of the spring-mass system, power consumption measurements can be used to adjust the spring-mass system so that its natural frequency will be at or near that of a typical input signal, for example 60 Hz. Operating the pump at the resonant frequency improves efficiency, and reduces vibration, and thereby noise. The spring-mass system can also be adjusted to operate efficiently at different pressures. For example, by increasing mass or spring rate the spring-mass system can be made to operate at or near resonant frequency while the pump is providing increased pressure output. It should be noted that the mass disk 168 is used as a cost effective alternative to increasing or decreasing the mass of the piston, armature and/or connecting rod.
As is well understood, the piston 104 is driven by movement of the armature 158, when energy is supplied to the wire coil 154, to reciprocate within the cylinder 102. The piston 104 has an enlarged head with a peripheral groove holding a split piston ring 170 that seals against the cylinder 102 when pressure is developed. The stroke length is approximately 8 mm (4 mm in each direction) and is positioned approximately 1 mm from the top of the cylinder when at top dead center.
Given the single cylinder arrangement of the pump 20, the reciprocating piston 104, armature 158 and connecting rod 164 can cause the drive assembly inside the housing to vibrate. The leaf springs 142 absorb much of the energy from these moving components. The number, size and thickness of the leaf springs 142 are selected to achieve a spring rate determined primarily according to the mass of the piston 104 and the input frequency. The leaf springs 142 are selected so that in combination (between the two stacks) they result in a resonant frequency of the piston 104 and springs 142 (i.e., the spring-mass system) approximately equal to the input frequency, which is typically 50 or 60 Hertz. For example, in one preferred embodiment there is a stack of two springs in the second retainer collar 174 and a stack of two springs in the spacer ring 144 near the piston 104. If the stroke length were to be increased, for example if the pump to be used in an application requiring more air flow, the springs 142 could be of a thinner gauge, in which case the number of springs may be increased to three in each stack to achieve the same spring rate.
With reference to
Since the pump has only a single cylinder, the pressurized air is pulsed at the rate of the input frequency, for example 60 Hz. The inventors have determined that pulsations in the output air can adversely effect the operation of the pump. In particular, the output lines act as resonant chambers, having their own natural frequency. If the pulsations in the output air are at a different frequency, the air will effectively encounter increased resistance going through the output lines. This creates excessive back pressure on the pump so that the spring-mass system can be made to operate at a different (non-resonant) frequency, thereby decreasing the efficiency of the pump. This makes the pump more sensitive to variations in input frequency which can further decrease efficiency. By reducing the amplitude of the pulsations in the air before leaving the pump, this problem can be avoided.
To that end, as shown in
An illustrative embodiment of the present invention has been described above in detail. However, the invention should not be limited to the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced.