Piston mounting and balancing system
A compact 180° opposed piston pump/compressor minimizes axial spacing between its pistons on the drive shaft and has mass-balanced pistons designed to reduce the shaking couple and noise from reciprocation of the pistons. The piston assemblies can have members, such as cup retainers, that are of different masses selected to compensate for the difference in piston masses and thereby equalize the masses of the pistons. Each piston assembly can be mounted to the drive shaft at eccentrics that occupy minimal or no space between the pistons.
This application is a continuation-in-part of U.S. application Ser. No. 10/338,950, filed on Jan. 8, 2003, now allowed and issue fee paid.
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
BACKGROUND OF THE INVENTIONThe present invention relates to pumps and in particular to compact piston pumps.
Pumps for medical applications, such as used in oxygen concentrators, generally need to be compact and quiet to operate discreetly in homes and hospitals. It is thus important to properly muffle the working air as well as reduce vibration during operation of the pump.
One problem with conventional pumps is that they can create excessive noise and vibration as the piston(s) are reciprocated, especially if they are improperly balanced. One reason for this in opposed piston pumps is that the pistons may be coupled to the drive shaft by a single retainer or eccentric element between the connecting rods of the piston. Ordinarily, an eccentric element is mounted to the drive shaft and two nibs or bosses extend axially from each side of the eccentric element to mount the pistons to the drive shaft. A moment, or shaking couple, arises as the drive shaft is turn because of the axial spacing between the pistons.
Another problem with conventional pumps is sealing the crankcase and cylinder(s). Improper sealing of the cylinders to the crankcase or the valve head(s) can cause pressurized air to leak to the outside of the pump, which both reduces pumping efficiency and makes noise. Typical sealing arrangements are either prone to leakage or require costly machining operations on the valve plate. Also, many crankcases are made with open necks to allow the pistons to be slid into the crankcase easily during assembly. Typically, the openings in the neck terminate at the cylinders, which have curved exterior surfaces. This makes sealing the crankcase difficult and typically requires separate seals in addition to that sealing the end of the crankcase, thus increasing assembly complexity and creating a potential leak path between the neck seals and the end seal.
Another problem with conventional pumps is that the valve stops can create excessive noise during operation. Typically, thin flapper valves are used to control the intake and exhaust ports of the valve heads. Because of 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. Usually the stops have undersides that ramp up from the valve plate to support the tip of the valve farther from the valve plate than the neck of the valve. The valves are usually metal and the stops can be metal or plastic, however, in either case the rapid contact between the two surfaces can generate tapping or clicking sounds that are unacceptable in medical applications. Another problem here is that the thin flat flapper valve can succumb to surface attraction between the flapper and the stop and essentially “stick” to the stop and thus remain open.
Yet another problem confronting the design of low-noise pumps is properly muffling the intake and/or exhaust chambers of the valve heads. This can be done by attaching a muffler element to the valve head either direction or via suitable hoses. Another technique is to run the exhaust air into the crankcase on the non-pressure side of the piston head. In this case, if the crankcase is closed and the pistons are in phase, the crankcase will usually be vented through a muffler to avoid generating pulsations in the pump. Even using the later technique, the valve heads are usually exhausted through hoses leading to the crankcase, which is vented through a muffler directly mounted to the crankcase or at the end of a hose.
Accordingly, an improved pump is needed which addresses the aforementioned problems.
SUMMARY OF THE INVENTIONIn accordance with one aspect, the invention provides a piston and drive shaft assembly for a pump or compressor. The invention includes two piston assemblies each having a head and a connecting rod. The connecting rods have openings in which fit open center bearings that mount to the drive shaft on eccentric elements. The piston assemblies each have a mass member of a different mass than that of the other mass member. The mass difference of the mass members is essentially equal to the mass difference of the two pistons so as to essentially equalize the total mass of each piston assembly.
The invention further provides a pump or compressor having a motor with a drive shaft housed in a crankcase having a pair of cylinders. At least two mass balanced piston assemblies as described above are mounted to the drive shaft.
In preferred forms, the eccentric elements are separate disk shaped parts that having axial bores that allow them to fit onto the drive shaft. Preferably, the eccentrics each have an axial dimension no more than substantially the axial dimension of the connecting rods, and the connecting rods are mounted to the drive shaft spaced apart no more than {fraction (1/16)}″. The eccentric elements are preferably press-fit into centers of inner races of the bearings.
The mass members can be cup retainers mounted to the piston heads and weighted so that the moments effected on the drive shaft by the pistons are the about the same. For example, when one piston has a larger piston head and is thus heavier, a lighter would be mounted to the larger piston to equalize the total mass of each piston assembly. One way to accomplish this is to make the retainers of different sizes and/or materials. Different density metals or polymers could be used. For example, one retainer could be zinc and the other magnesium or aluminum, or both could be plastics of different densities or sizes or one could be a plastic and the other a metal.
The invention thus provides a compact pump or compressor with decreased shaking couple on the drive shaft and thus lower noise and improved pump efficiency. These and other advantages of the invention will be apparent from the detailed description and drawings. What follows is a description of the preferred embodiments of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiments are not intended as the only embodiments within the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to
Referring to
The plug supports 84 and 85 help maintain the seal of the neck plugs 70 and 71. However, the pointed corners of the neck plugs 70 and 71 can flex away from the crankcase and cylinders somewhat to allow a leak path to relieve transient high pressure situations. The seal is designed primarily for low pressure applications to seal off air leaks for noise reductions. The corners of the neck plugs will unseat slightly when the internal pressure reaches about 15 psi as a pressure relief. The assembly could, of course, be used in higher pressure applications by using a more rigid elastomer or modifying the backing plate to prevent the seal from unseating.
Referring to
Referring to
Importantly, the connecting rods 98 and 99 of the pistons 90 and 91 are mounted on the drive shaft 114 so that the connecting rods 98 and 99 are substantially adjacent to one another, that is within ⅛ inches (preferably less than {fraction (1/16)}″) or as close as possible. Preferably, the pistons are mounted on the drive shaft as close as possible with only air space between the connecting rods. This is to reduce the moment or shaking couple about the drive shaft 114 caused by the axial displacement of the piston assemblies 38 and 39. While some moment remains, this arrangement provides a significant improvement over the prior art in that there is no other element (eccentric or otherwise) on the shaft between the pistons so that their axial displacement is minimized.
As shown in
Air flow through the cylinders is controlled by the valving on the valve plates 44 and 45. Referring to
The intake 120 and exhaust 122 ports are controlled by respective flapper valves 130 and 132. The flapper valves 130 and 132 are identically shaped thin, metal valves. The valves 130 and 132 each have a middle section 134 defining an opening 136 and an alignment tab 139 as well as two identical paddles 140 extending from the middle section 130 in opposite directions approximately 30 degrees from vertical. The paddles 140 have narrow necks 142 and relative large flat heads 144. The heads are sized slightly larger than the intake and exhaust ports and the necks are narrow to let the valves flex more easily under the force of the pressurized air, and thus reduce power consumption. Each flapper valve 130 and 132 is mounted to the valve plate 44 by a fastener 146 inserted through the opening 136 in the middle section 134 of the valve and threaded into bores in the valve plate. The intake valve 130 is mounted at the inside of the cylinder 40 and the exhaust valve 132 is mounted in the exhaust chamber 128.
Referring to
Another feature of the pump 30 is the use of transfer tubes 158 with air passageways formed in the body of the crankcase 36 (outside of the internal chamber) to either couple an intake or exhaust chamber to the inside of the crankcase or to couple the valve heads together (in parallel between exhaust chambers and/or between intake chambers or in series with the exhaust chamber of one valve head connected to the intake chamber of the other valve head) without the need for hoses. Referring now to
As mentioned, the crankcase 36 has two sets of interior passageways 170 and 171 in the walls of the crankcase opening at the transfer openings 164 and 165. Depending on the desired operation of the pump, there can be only one of these passageways 170 and 171 or one set of these passageways in one side of the crankcase. One or both of these passageways may also open to the channels 78 and 79, which open to the interior of the crankcase. This can be done by boring through section 174 or by casting the crankcase to block off or connect passageways as needed. In the parallel pressure embodiment of the pump shown in
Since the pistons are of different sizes, they have different masses. The difference in masses will make the pistons out of balance and thus effect unequal moments on the drive shaft, which would cause vibration, noise and lower pump efficiency. Preferably, the retainers 96C and 97C are selected to have different masses, substantially equal to the difference in the masses of the other parts of the pistons (such as the connecting rods and the heads/pans). This can be accomplished by making the retainers 96C and 97C from disparate materials or of different thicknesses. Different density metals or polymers could be used. Both could be metals or plastic of different densities or sizes, or one could be a plastic and the other a metal. In one preferred form, the retainer 96C is made of a suitable zinc composition so that it has a greater mass (despite its smaller diameter) than retainer 97C, which is made of an aluminum. Thus, the heavier retainer 96C would make up the difference in mass of the smaller piston 90C. The result is equally balanced piston assemblies and improved operation of the pump when the application requires different flow volumes in the cylinders.
The pump also differs from that described above in that it has only one transfer tube 158C connecting the exhaust side of valve head 47C to passageway 171C (through a transfer opening) in the crankcase 36C. Passageway 171C intersects with channel 78C (as shown in
This embodiment of the pump is thus constructed so that air can be drawn from the load (through a hose (not shown) connected to barb 200) and into the intake chamber of valve head 47C. Surrounding air can also be brought in through barb 202 (to which preferably a muffler (not shown)) is mounted. Air from the higher pressure side valve head 46C exhaust chamber will be exhausted through barb 204 to the load (after passing through hoses and valves as needed). The exhaust chamber of the vacuum side valve head 47C will exhaust through the transfer tube 158C and the crankcase passageway 171 C to the non-pressure side of the inside of the crankcase 36C, which is vented through barb 206 and another muffler (not shown). Passing the exhaust through the crankcase prior to the muffler provides further (two-stage) sound attenuation beneficial in low-noise applications, such as when used with medical devices.
It should be appreciated that preferred embodiments of the invention have been described above. However, many modifications and variations to these preferred embodiments will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. For example, while only two-cylinder embodiments were shown, the principles of the invention could apply to a single-cylinder pump or to three or four cylinder pumps, such pumps having a double shafted motor and additional crankcases, cylinders, pistons and valve heads. For multi-cylinder pumps, the valve heads of all of the cylinders could be coupled in series or parallel through the transfer tubes and integral crankcase passageways, like those described above. Shared valve heads for multiple cylinders could also be incorporated into such a pump. The pump of the present invention could also include transfer tubes which connect directly to the valve heads/plates to join air chambers without connected to passageways in the crankcase.
Therefore, the invention should not be limited to the described embodiments. To ascertain the full scope of the invention, the following claims should be referenced.
Claims
1. A piston and drive shaft assembly for a pump, comprising at least two piston assemblies having:
- first and second pistons each having a head and a connecting rod, the connecting rods defining respective first and second openings;
- first and second bearings disposed in the first and second openings and having open centers;
- first and second eccentric elements disposed in the centers of the respective first and second bearings; and
- first and second mass members coupled to the respective first and second pistons having different masses essentially equal to a mass difference of the first and second pistons so as to essentially equalize the total mass of each piston assembly.
2. The assembly of claim 1, wherein the eccentric elements are disk shaped.
3. The assembly of claim 1, wherein the first and second bearings each have an outer race rotatable with respect an inner race defining the center opening and wherein the outer races are press-fit in the first and second openings of the connecting rods and the eccentric elements are press-fit into the openings defined by the inner races.
4. The assembly of claim 1, wherein the first and second mass members are retainers mounted to the heads of the respective first and second pistons, wherein the first piston has a greater mass than the second piston and the first retainer has a lesser mass than the second retainer.
5. The assembly of claim 4, wherein the first retainer is made of a different material than the second retainer.
6. The assembly of claim 5, wherein the first retainer is zinc and the second retainer is magnesium.
7. The assembly of claim 5, wherein the first retainer is zinc and the second retainer is aluminum.
8. The assembly of claim 1, wherein the connecting rods of the first and second pistons are mounted to the drive shaft spaced apart no more than {fraction (1/16)} inch.
9. The assembly of claim 1, wherein the first eccentric element has an axial dimension no more than substantially the axial dimension of the first piston connecting rod and the second eccentric element has an axial dimension no more than substantially the axial dimension of the second piston connecting rod.
10. The assembly of claim 1, wherein the first and second eccentric elements each have an axial through bore and extend axially to one side substantially no further than a face of the corresponding piston connecting rod.
11. The assembly of claim 1, wherein at least on of the first and second retainers is plastic.
12. A pump, comprising;
- a motor having a drive shaft;
- a crankcase housing the drive shaft and having a pair of cylinders;
- at least two piston assemblies including:
- two pistons each having a head disposed in one of the cylinders and a connecting rod extending from the head to the drive shaft;
- two bearings disposed in openings in the connecting rods axially offset along the drive shaft;
- two eccentric elements disposed in the bearings; and
- two mass members coupled to the pistons having different masses essentially equal to a mass difference of the pistons so as to essentially equalize the total mass of each piston assembly.
13. The pump of claim 12, wherein the mass members are cup retainers attached to the piston heads so that the center of gravity is at essentially the same location of each piston.
14. The pump of claim 12, wherein the eccentric members have axial through bores receiving the drive shaft.
15. A pump or compressor comprising a pair of piston assemblies, each assembly having a piston with a head and a connecting rod, which mounts a bearing that is rotatably mountable to a drive shaft by an eccentric element, and a mass member coupled to the piston, wherein the mass member of one assembly is different than that of the other assembly such that a mass difference of the mass members is essentially equal to a mass difference of the pistons.
16. The pump or compressor of claim 15, wherein each of the mass members is selected from the group of materials including metals and polymers.
Type: Application
Filed: Nov 22, 2004
Publication Date: Mar 31, 2005
Inventor: Shawn Leu (Newton, WI)
Application Number: 10/995,726