Pumps – Three or more cylinders arranged in parallel – radial – or... – Radial cylinders
Reexamination Certificate
1998-01-27
2001-09-04
Tyler, Cheryl J. (Department: 3746)
Pumps
Three or more cylinders arranged in parallel, radial, or...
Radial cylinders
C417S415000, C417S466000, C417S467000, C417S534000, C092S072000
Reexamination Certificate
active
06283723
ABSTRACT:
This invention relates to the field of positive fluid displacement machines that have use throughout the automotive, chemical processing, power generation and refrigeration equipment industries. These industries and others will soon have fuel cell energy sources available for executing their functions. It is expected that fuel cell powering systems will be one of the major beneficiaries of the invention to be described.
BACKGROUND OF THE INVENTION
There are numerous devices which displace and/or expand fluids, both gaseous and liquid. Such devices have been implemented in both piston and rotary apparatus. They have been implemented within the same drive line and sometimes on the same shaft. However, the compression and expansion functions have not been implemented within the same device.
The present invention builds upon the technology of U.S. Pat. Nos. 4,907,950, 5,004,404 and 5,114,321, all of which are incorporated herein by reference. Those patents describe a variable positive fluid displacement device comprised of two sets of piston pairs operating in a rigidly connected configuration, each piston pair at 90 degrees to the other. The above-referenced patents have been used as a compressor and also as an expander and in either a 2 or 4 piston configuration. All pistons are operated from a common drive shaft and the pumping/compression or vacuum/expansion of each chamber port has a different peak position in time as a function of the position of the chamber valving which is also driven and controlled by shaft rotation.
The variable positive displacement device of the above-referenced patents can be used to benefit those fuel cell systems in which compressed air is used as an oxygen source. A first such device is used as a compressor with the variable displacement feature used to provide control over fuel cell power output. For vehicular use such control acts as an accelerator to provide a desired transient response. By using a second variable or fixed displacement device as an expander, the overall efficiency of the system can be improved. As an expander, it will return power to the system as a function of the amount of energy available to its intake stream and its recovery efficiency. This now has the desirable result of lowering the power consumption for the compressing function. These concepts are discussed in the publication, incorporated herein by reference, “A Variable Displacement Compressor/Expander for Vehicular Fuel Cell Air Management,” SAE International, 400 Commonwealth Drive, Warrendale, Pa. 15096-0001. U.S. Pat. No. 5,434,016 discusses the use of a rotary compressor in a fuel cell system with a variable capacity expander, both compressor and expander preset to desired values.
SUMMARY OF THE INVENTION
Briefly stated, this invention provides for the performance of more than one function in a single device with at least one set of opposed pistons constructed to operate in accordance with the basic principle of the three U.S. Patents mentioned above and incorporated herein by reference. This invention recognizes and takes advantage of the relative independence of each piston in a piston pair to set them to operate as different devices. Thus, for example, one piston operates as a compressor while a second piston operates as an expander. Since both pistons are on the same drive shaft and are rotating at the same speed, power is returned to the drive shaft by the expander thus improving the efficiency of the compressor—all done in the context of a single integrated device.
An integrated compressor/expander with two pairs of pistons is especially advantageous. One pair can be used for compression—a second pair for expansion, all within one device to save weight, space and cost while providing efficient compression and means for power output control. Additional benefits are possible with this arrangement, such as providing a device with different volumetric displacements per revolution per pair. If desired, all four pistons can have different volumetric displacements. When used with a fuel cell inserted between the compressor function and expander function, the different volumetric displacements per opposing pair results in a pressure ratio generated across the fuel cell. The maximum value of the pressure ratio is the relative displaced volumes of the compressor and expander expressed as follows:
Pressure Ratio (Pr)
=
Volume (compressor)/time
Volume (expander)/time
This can create a more stable Pr for applications where it is desired that the flow mass delivered by the system be primarily a function of the speed of the input drive shaft to the compressor. Dynamic control of the pressure ratio can be obtained for the system by taking advantage of the technology in the referenced patents to incorporate a variable displacement capability. Control range could vary from a maximum Pr of the basic design displacements to a minimum Pr=1, where the displacements are of equal value. By enabling control of the relative displacements per revolution and control of the revolutions per minute, two degrees of freedom are provided to enhance the control system of the end application. For example, the variable displacement feature can be used to control pressure ratio independently of compressor speed so that changes in compressor speed can be used to result in relatively linear changes in fuel cell power output.
The device of this invention can be used to supply more than one device. For example, in a fuel cell system, one piston, operating as a compressor, can supply compressed air to the fuel cell stack at a first pressure; a second piston, operating as a compressor, can supply compressed air to a reformer at a second pressure; a third piston, operating as an expander, can receive exhaust at a third pressure from the fuel cell stack; and a fourth piston, operating as an expander, can receive exhaust at a fourth pressure from the reformer.
A first embodiment of the integrated device is described herein with a first set of two opposing pistons operating in traveling cylinders and a second set of two opposing pistons operating in stationary bores. The second set of pistons are at right angles to the first set. A second embodiment has both a first set and a second set of opposing pistons operating in traveling cylinders. A third embodiment utilizes both sets of opposing pistons in stationary bores. In all embodiments, only one set of opposing pistons could be used, if desired. In all embodiments, the device can utilize the variable displacement capability of the three patents named above and incorporated by reference herein, or the device can be of fixed displacement.
Note that the pistons can be operated in parallel to supply a function, for example, compression, or they could be operated in series to provide a multi-stage function.
The advantages of such devices are numerous and some are mentioned above. Several other advantages are as follows:
(1) A piston compressor produces a higher Pr in a single stage than a rotary compressor. This can lower the number of compressor stages required to obtain a pressure ratio greater than two.
(2) The piston compressor does not need to rotate as fast as a rotary compressor to begin generating pressure.
(3) Good sealing systems for a piston compressor are easier to achieve and not as costly especially as the Pr increases. Piston seals have cheaper parts than the costly precision parts used in rotary compressors.
(4) Since piston compressors can operate at slower speeds than rotaries, there is less noise generated.
(5) With this invention, the length of the mechanical train between the compressor function and the expander supplemental power input to the drive shaft is considerably shorter, i.e. one less machine is in the loop. This results in a lower frictional loss to the system and less power is required for the compressing function.
(6) Being able to control the Pr with the expander function within the same device can eliminate the need for a pressure regulation valve.
REFERENCES:
patent: 2130037 (1938-09-01), Skarlund
patent: 3
Barber Jeffrey Lewis
Cronin Jeremiah J.
Milburn Ski Muir
Rohrer Charles E.
Tyler Cheryl J.
Vairex Corporation
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