Seal Means for a Stirling Engine or the Like

The present invention relates to a seal means, and more particularly, to a seal means especially for use in a Stirling engine.

Generally, the Stirling engine requires that to ensure high efficiency a fluid having a relatively small molecular weight, such as hydrogen or helium, is adopted as working fluid and is sealed under high pressure.

To explain a prior art seal means used in the Stirling engine, reference will be made more particularly to FIG. 1:

In FIG. 1 there is provided a cylinder 1 including a piston 2 capable of moving up and down, the piston 2 having a piston rod 3. The reference numeral 4 designates a rolling seal, which is fixed to the piston rod 3 at its inner side, and to a seal support 5 at its outer side. The piston rod 3 is connected to a crosshead 7 which is guided by a crosshead guide 6. The crosshead 7 is connected to a crank shaft 12 by a connecting rod 8. The crank shaft 12 is carried on bearings 10. The reference numeral 9 designates a crankcase which contains lubricating oil 13 whereby the bearings 10, the crosshead 7 and other components are lubricated. The crank shaft 12 is sealed by means of a mechanical seal 11. The reference numerals 14 and 101 designate a buffer tank, and a cylinder chamber, respectively, the buffer tank being connected to a buffer chamber 102 located at the portion below the piston 2.

In operation, the pressure (PA) of the working fluid in the cylinder chamber 101 changes with time, which is so well known in the art that the description will be omitted for simplicity. The pressure (PB) in the buffer chamber 102, and the pressure (PC) in the crankcase 9 are virtually equalized to each other under the operation of the buffer tank 14, due to an arrangement where, though it is not shown, the buffer tank 14 and the crankcase 9 are connected to each other by means of a pressure equalizing pipe having an oil filter or the like. These equal pressures ensure that no difference in pressure occurs across the rolling seal 4, thereby protecting the seal against breakage under a differentiated pressure. In this way the pressure difference between the working fluid acting on the top and the bottom of the piston 2, respectively, is transmitted to the crosshead 7 through the piston rod 3, wherein the pressure difference is expressed by:

In this way the driving force is reciprocally transmitted to the crosshead 7, and converted into a rotating force through the connecting rod 8 and the crank shaft 12. The rotating force is finally transmitted to outside as a driving power.

The inner side portion of the rolling seal 4 moves together with the piston rod 3 because of its being fixed thereto, and thus the rolling seal 4 prevents the lubricating oil 13 from splashing the inside of the cylinder 1. The mechanical seal 11 prevents the working fluid under high pressure and the lubricating oil 13 from leaking out of the crankcase 9.

As described above, in the conventional seal means the pressures in the crankcase 9 and the buffer chamber 102 are virtually equalized. Accordingly with the use of a high pressure hydrogen or helium so as to enhance the efficiency of the engine, the weight of the crankcase 9 will be disadvantageously increased because of its anti-pressure structure. The working fluid is likely to leak out of the crankcase through the mechanical seal. In addition, the rolling seal cannot withstand a long period of use because of the limited strength of the material although the sealing function is sufficient. These negative factors have made it difficult to adopt the prior art seal means in practical use in the Stirling engine.

The present invention is directed to solve the problems pointed out with respect to the conventional seal means employed in the Stirling engine, and it is an object of the present invention to provide a seal means adapted for use in the Stirling engine, which makes it possible to use a light-weight crankcase, and ensures a long, continuous sealing efficiency.

Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

According to the present invention, there is provided a seal means for use in the Stirling engine or the like, the seal means comprising:

a cylinder including a piston reciprocating therein, and a buffer chamber located in one of the spaces produced at the both sides of the piston;

a tank for storing the working fluid in the buffer chamber when the engine is at rest, the tank being located outside the cylinder;

a means for introducing the working fluid in the tank into the buffer chamber under pressure when the engine is started;

a crank shaft driven by means of the piston through a piston rod;

a crankcase for accommodating the crank shaft;

a plurality of packings for preventing the working fluid in the buffer chamber from entering the crankcase by flowing along the outer surface of the moving piston rod, the packings being arranged in contact with the outer surface of the piston rod; and

a means for returning the working fluid leaked in the packings from the buffer chamber through the moving piston rod to the buffer chamber.

FIG. 1 is a schematic view exemplifying a prior art seal means employed in the Stirling engine;

FIG. 2 is a schematic cross-sectional view on an enlarged scale showing a seal means embodying the present invention, which is applied to the Stirling engine;

FIG. 3 is a schematic view showing the whole system of the Stirling engine to which the seal means of the invention is applied including a means for introducing the working fluid into the buffer chamber, and a means for returning leaked working fluid; and

FIGS. 4 (a) and 4 (b) are diagrams showing the pressure changes with time, and the interrelated operations of the components occurring during the operation of the Stirling engine.

The present invention will be more particularly described with reference to FIGS. 2 to 4, wherein like reference numerals designate like elements and components to those in FIG. 1:

FIG. 2 shows a rod seal arrangement provided in a lower section of a cylinder 1. The rod seal arrangement has been devised by improving the conventional sliding seal. There are provided a piston rod 3 reciprocating up and down, a seal support 5, an upper seal member 401, a lower seal member 402, a return path 15 for allowing a leaked fluid to return, and a sealing chamber 103. The upper seal member 401 includes rod packings 41a to 41f whereby the working fluid is sealed, and the lower seal member 402 includes rod packings 42a to 42d whereby the lubricating oil is sealed.

Referring to FIG. 3, the working fluid is stored in a tank 22 outside the cylinder 1, the tank 22 being connected to a buffer chamber 102 through a pipe at which a first valve (V1) 18 is provided. In addition, the tank 22 is connected to an inlet side of a second compressor (C2) 17. The outlet side of the second compressor 17 is connected to the buffer chamber 102 through a pipe at which a second valve (V2) 19 is provided. A pressure detector (P) 21 is also provided at the pipe.

The reference numeral 16 designates a first compressor (C1) designed to return the leaked fluid to the buffer chamber 102, whose inlet side is connected to the return path 15, and whose outlet side is connected to the buffer chamber 102 through a pipe.

FIG. 4 (a) and (b) show how the pressure changes with time, and how the components are operated in an interrelated manner.

An example of the operation will be described, but the description of the manner of obtaining a rotary motion from the crank shaft 12 through the action of the working fluid in the cylinder 1 will be omitted because of its being well known in the art.

When the Stirling engine is at rest, the internal pressures (PA), (PB), (PC) and (PT) in the cylinder chamber 101, the buffer chamber 102, the crankcase 9 and the tank 22 are respectively equal to one another, all of which are kept low.

When the engine is to be started, the first valve 18 is closed, the second valve 19 is opened, and the second compressor 17 is operated, thereby introducing the working fluid in the tank 22 into the buffer chamber 102 under pressure. As a result, the internal pressure (PB) therein gradually rises until it reaches the pressure required to operate the engine, which is detected by the pressure detector 21 thereby to stop the second compressor 17 and to make the second valve 19 closed.

When the internal pressure (PB) in the buffer chamber 102 rises, the working fluid is caused to leak into the sealing chamber 103 through the rod packings 41a to 41c. In order to return this leaked fluid to the buffer chamber 102 under pressure, the first compressor 16 is continuously operated while the engine is in operation. The first valve 18 is closed when the engine is started and when it is in normal operation, as well.

Another group of rod packings 42a to 42d are designed to prevent the lubricating oil 13 in the crankcase 9 from splashing the sealing chamber 103 and other components inside the cylinder 1, and furthermore heat exchangers (not shown) or the like furnished to the engine. These components are kept safe from adverse influences possibly resulting from the splashed oil.

When the engine is to be stopped, the first and second compressors 16 and 17 are stopped, and the first valve 18 is opened, thereby causing the working fluid in the buffer chamber 102 to return to the tank 22. In this way the internal pressure (PB) in the buffer chamber 102 lowers until it becomes equal to the internal pressure (PC) in the crankcase 9.

By the operation described above, the Stirling engine is operated to generate a driving power with the internal pressure in the buffer chamber 102 being kept high and with that in the crankcase 9 being kept low.

In the seal means of the invention applied to the Stirling engine, it will be appreciated that the sliding seal adopted in this seal means ensures a sealing efficiency with a pressure difference between in the buffer chamber 102 and in the crankcase 9. Accordingly, it is possible to hold the inside of the crankcase 9 at a low pressure, thereby enabling to reduce the weight of the crankcase 9. When the working fluid is leaked through the sliding seal, the leaked working fluid is returned to the buffer chamber 102 by a second compressor 16, thereby enabling to hold the constant pressure in the buffer chamber 102. Furthermore, the durability of the mechanical seal 11 of the crankcase 9 is enhanced because of the low pressure inside the crankcase 9. There is an advantage that the durability of the sliding seal 5 is longer than that of the conventional rodstock seal. The pressure in the buffer chamber 102 is enough to be high only in the normal operation because of the provision of the tank 22, thereby reducing the load applied to the sliding seal.

Besides, the seal means of the present invention is not limited in application to the Stirling engine, but is widely applicable to compressors having the same structure as that of the Stirling engine.