US2981242A - Free piston gas generator - Google Patents

Description

April 25, 1961 J. G. MACDONALD FREE PISTON GAS GENERATOR Filed March 2, 1959 INV ENT E] R JOHN G MAC/J ONAL D ice Patented Apr. 25,1961

2,931,242 FREE PISTON GAS GENERATOR John G. Macdonaid, P1). Box 476, Bayfieid Road, Goderich, Ontario, {Janada Filed Mar. 2, 19 59, Ser. No. 796,535

2 Claims. c1. 123-46) This invention concerns improvements in free-piston machines used to produce hot gas under pressure which may be used to drive a turbine from which useful work is obtained.

This invention provides a free-piston gas generator which is positive and easy to start, stable, efficient and reliable in operation, simple to maintain and relatively inexpensive to manufacture. Certain features of-this invention, including the piston construction, synchronizing and mechanism and power take-off to operate a fuel injection pump are not shown in this specification as they form the subject of my US. Patent No. 2,865,349, Lubricating and Sychronizing Means for Free-Piston Engines, which may be readily applied to the present invention.

As will be understood, the present engine operates on the two stroke diesel cycle and comprises a power cylinder containing a pair of opposed pistons which form a part of compressor pistons operating in compressor cylinders at opposite ends of the power cylinder. The outer portion of each of the compressor cylinders form bounce chambers which act as air cushions to return the pistons on the inward stroke. The inner portion of the compressor cylinders. serve as air compressors to provide air for scavenging the power cylinder.

According to the invention, the engine is characterized by the fact that all the air from the compressors is directed through the power cylinder where it mixes with the exhaust gases to form hot gas under relatively high pressure.

Further,-according to the invention, the engine starting mechanism includes means for suddenly releasing a given quantity of compressed air into each of the bounce chambers and novel means are provided to insure that the air is released into both bounce chambers simultaneously to avoid stress on the synchronizing mechanism. Novel means are also provided to seal oif the bounce chambers from the starting mechanism as soon as the air has been released into said chambers and again novel means are provided to cushion the action of the starting mechanism to avoid damage from shock.

Another feature of this invention resides in providing means by which the excess air introduced for starting is released from the bounce chambers during a part of the first inward piston stroke into the scavenging airbox, the said air release means also forming a part of a bounce chamber control which automatically relates the quantity of air in the bounce chambers to the prevailing air pressure in the airbox so that as the air pressure inthe airbox is increased at higher power levels, a greater quantity of air is transferred to the bounce chambers, and as the pressure in the airbox falls, at lower power levels, the quantity of air in the bounce chambers is reduced by returning excess air to the airbox. Thus, the minimum pressure in t a part of the compressor cylinders and is controlled by the motion of the compressor pistons thus requiring a minimum number of parts. The construction also provides that the pressure of air in the airbox is in communication with the bounce chambers during a substantial portion of the piston stroke so that there will always be adequate cushioning air in the bounce chambers at all power levels.

Another important feature is the novel construction of the engine casing and attendent parts thereof which is constructed to provide perfect alignment of the opposed pistons in their respective cylinders.

Another important feature resides in the construction of the engine casing which provides means by which a skirt on the compressor pistons passes between the compressor inlet and outlet valves thus partially filling the otherwise wasted space between the valves, at the inner end of the piston stroke thus reducing the volume of the head clearance space, permitting the use of smaller compressors thus resulting in a more compact engine. This arrangement provides that the cooler outside air entering the compressor through the inlet valves impinges directly on the compressor outlet valves when entering the compressor cylinder thus providing some cooling of the outlet valves and also provides for easy servicing of the engine by ensuring proper alignment of the various parts when the engine is re-assembled. Again this arrangement provides that a maximum number of valves can be contained on a minimum amount of space, thus increasing the efficiency of the engine.

These and other objects and features will become apparent from the following detailed description taken in conjunction with the accompaning drawings in which:

Fig. 1 is a part longitudinal mid vertical sectional, part elevational view of a free piston gas generator embodying the invention and,

Fig. 2 is a fragmented, part exploded perspective view and part sectional View taken along the line 2-2 of Fig. 1.

The pistons are shown in their inward position. Arrows indicate the direction of the flow of air and gas through the valves, ducts etc. The engine is cylindrical in form and comprises a power cylinder 1, containing a pair of opposed power pistons 2, a fuel injector 3, inlet ports 4 and exhaust ports 5 which are opened and closed by the power piston. Compressor pistons 6 form an integralpart of the power pistons and operate in compressor cylinders 7. The pistons are interconnected by a suitable synchronizing mechanism (not shown) to maintain the pistons in phased relation. The outer portion of the compressor cylinders form bounce chambers 8 which provide cushions of air to store energy and return the pistons on the inward compression stroke. The inner part of the compressor cylinders form' -air compressor chambers 9 having inlet valves'lt) and outlet valves 11, through which air is delivered to the airbox 12 which surrounds the power cylinder.

tons to their outward stroke position (opposite to the position shown in the idrawirigyQA'mass of compressed air is suddenly released into the bounce chambers which pushes the pistons inward, thus compressing air in the power cylinder. At a suitable portion of the stroke,.fuel is injected which ignites spontaneously driving the pise tons outward. As thepistons move outward, the right hand piston first opens the exhaust ports 5 releasing the gas from the power cylinderto the exhaust line 13 which may be connected to a suitable A i (not illustrated). The left hand piston then uncovers the inlet ports allowing a charge of air to sweep through the power cylinder and mix with the exhaust gas. On the outward movementoffthe pistons air is compressed power producing turbine in the bounce chambers which serves to return the pistons on the next inward stroke. During the outward stroke air is inducted into the compressor chambers through the inlet valves 10. On the next inward stroke, the air is compressed and delivered through the outlet valve 11 into the airbox 12 where it is stored until the inlet ports 4 are opened by the power piston. The preceding engine operating principle is well known. The novelty of this engine resides in the following features.

To start the engine, the pistons are first moved to their outward stroke position. A spool type valve 14 is connected to a source of high pressure air to port 15. In one position of the valve as shown, the high pressure air is directed through the valve into pipes 16. When the valve spool is shifted either manually or mechanically to the alternative opposite position, the port 15 is closed off and the pipes 16 are opened to the atmosphere through port 17. The pipes 16 are connected to the starting valves 18 at points 19 and 2%. A ball type check valve 21 is shown at point 20. This valve is held closed by the compression spring 22 which exerts sufficient force to require say 10 pounds air pressure to open this valve. At point 19, the high pressure air enters the starting valve and exerts a pressure against the piston valve 23 moving it in a direction to seat the valve face 24 against the valve seat 55 against the compression of the spring 25 which requires say pounds air pressure to overcome the action of this spring. Air also enters the small cushion chamber 26 through the port 27.

When the piston valve closes, the air pressure now lifts the ball type check valve 21 and enters the air storage reservoir 28. Air also passes through the ports 29 into the reverse side or the piston valve 30. Since the area is smaller on this side of the valve 23, the valve will remain seated and'air will be held in the reservoir 28. A poppet type valve 31 is attached to the end of the piston valve as shown. As long as air pressure is maintained in the starting valve, this poppet valve 31 is held open.

When the spool valve 14 is quickly shifted, thus connecting the pipes 16 to the atmosphere, there is a sudden drop in air pressure in the pipes 1-6. The ball check valve 21 will then close, trapping the full air pressure in the reservoir28. Since the pressure in the pipes 16 has been released, full pressure in the reservoir 28 is now exerted against the piston valve 23 at 30 causing the valve to unseat and release the air from the reservoir 28 through the passage 32 into the bounce chamber 8. The very sudden relea'se'of the high pressure air into the bounce chamber tends to hammer the poppet valve 31 against its seat at 33. To overcome this difiiculty, as thepiston valve 23 moves away from its seat 55, it closes the port 27 thus trapping some air in the cushionchamber 2 6 which absorbs the shock yet allows free passage of air from the reservoir 25 into the bounce chamber. I

When the air is fully released from the reservoir, the spring 25-closes'the poppet valve thus sealing the starting valve from the bounce chamber so that the volume of the bounce chamber is maintained at normal.

valve 39 also connects to the airbox through ducts 37. It will be seen that when the compressor pistons move inward an increasing pressure of air in the airbox will cause the valve 39 to open and allow more air to enter the bounce chambers. Also, if the air pressure in the airbox decreases, when the compressor pistons uncover the ports 34, the excess air will flow out of the bounce chambers through ports 34 and valves 35 into the air-box. Thus it will be seen that the amount of air trapped in the bounce chambers is maintained in direct proportion to the pressure prevailing in the airbox at various power levels, the mini-mum air pressure in the bounce chambers being approximately equal to the prevailing pressure in the airbox. This arrangement provides automatic control of the outward stroke of the pistons at various power levels.

Referring in particular to Fig. 2 in conjunction with Fig. 1, the engine casing comprises a central tubular section 4-1 which surrounds the power cylinder. Valve mounting rings 42 and 43 are bolted to the centre section 41 by screws 56. From Fig. 2, it will be seen that the inner surfaces of the valve mounting rings 42 and 43 have milled slots 44- which are spaced circumferentially around the inner surface of each of the valve mounting rings 42, and 43. Rectangular openings 45 are provided through the wall of each ring in each slot 44.

The valve illustrated in Fig. 2 comprises a valve seat a valve reed er of thin flexible steel and a valve guard 48 having an arched inner face against which the valve reed flexes when the valve is open. The valve seat and the valve guard may be faced with plastic material such as sold under the trademark Teflon to reduce friction at the ends of the valve reed. The valves are assembled in the position shown and located in the milledslots 44 in both valve mounting rings. The compressor head 49 is clamped to the outlet valve mounting ring 43 by screws 5% which seat on the clamp ring 51 which bears against the outlet valve mounting ring 43. The compressor cylinder is bolted to the inlet valve mounting ring '42 by screws 52.

In the assembled position, it will be seen that the inlet and outlet valves associated with the valve mounting rings 42 and 43 respectively are radially disposed opposite to each other with a gap between the inlet and outlet valves at 53. A tapered skirt 54 0n the compressor piston 6 enters the gap 53 on the inner pistonstroke and reduces the volume of this annular gap to a minimum yet permits a passage adjacent the inner face of the skirt so that air can pass out of the compressor chamber through the outlet valves. I The power cylinder 1 is accurately supported in the compressor cylinder heads 49. The composite bolted construction of the cylinder head 49 and the outlet valve mounting ring 43 permits some expansion of the power cylinder without any undue distortion of the engine casing When the starting air rushes into both bounce chamhers 8 simultaneously, the pistons are driven inward and the compressor pistons 6 uncover a series of radially disposed holes or ports 34 through the wallsof the compress'or cylinders. These holes are located at a position in the stroke where the pistons have attained sufiicient inward momentum to continue in their travel'to'cause igni tion of the fuel in the power cylinders. The excess starting air passes out of the compressor cylinder through the Gil ports 34 which communicate directly with air. check valves H 35 surrounding the cylinder permitting the air to pass out but preventing the passage of air in the opposite direce tion; A collector ring 36 directs theexces's air through ducts 37-intothe airbox at 3'8. Another air check valve 39 located in the end wall 49' of the compressor cylinder permits air to flow into the bouncechaniber 8-but prevents the escape of air in the opposite direction. This due to heat. It will also be seen that this construction permits easy fabrication and assembly of the engine casing.

While the compressor valves illustrated are of the well known feather valve type, it will be understood that the efiicient venturi type inlet valves which form the invention of my co-pending US. patent application No. 690,935 may be used instead.

,While I have described the preferred form of my invention, it will beunderstood to those skilled in the art that various modifications and alterations may be made without departing from the spirit of my invention or the scope of the appended claims.

N ha'tql claim as my invention is:

1. In a free piston gasgenerator having a power cylinder containingopposed power pistons, compressor pistons operating in compressor cylinders at opposite ends of said. power cylinder, the outer portion of said compressor cylinders defining bounce chambers in which air is adapted to be compressed on the outward piston stroke to store energy to return the pistons'on the inf ward stroke, the inner end of said compressor cylinders defining air compressors adapted to deliver air into an airbox for scavenging the power cylinder, a piston stroke control comprising openings through the side wall of each of said compressor cylinders, one-way check valves opposite said openings to permit escape of air out of the respective bounce chamber into the airbox only when the respective compressor piston has moved past said openings on the inward stroke, said respective compressor piston being adapted to close said openings on the outward stroke to trap air in said respective bounce chamber, another opening within said respective bounce chamber having one-way check valves opening into said respective bounce chamber to permit air from the airbox to flow into said bounce chamber so that the minimum pressure of air in the bounce chambers is maintained approximately the same as the prevailing pressure in the airbox.

2. In a free piston gas generator, a power cylinder, a compressor cylinder at each end of said power cylinder, a pair of opposing pistons each having a portion disposed to operate in said power cylinder and a compressor piston portion disposed to operate in said compressor cylinder, the inner portion of said compressor cylinders forming air compressors having inlet and delivery valves, said delivery valves opening into a scavenging air receiver surrounding said power cylinder, the outer portion of said compressors forming bounce chambers in which air is compressed on the outward stroke of the compressor pistons storing energy to return the pistons on the inward stroke, control means to adjust the amount of air compressed in said bounce chambers in accordance with the power output, said control means comprising, in combination, a duct from said scavenging air receiver opening into each of said bounce chambers at a point beyond the stroke of said compressor pistons, at least one valve in said duct permitting the outward flow of air from said scavenging air receiver into said bounce chambers through said duct, at least one port through the side wall of at least one of said compressor cylinders, said port being located within the stroke of said compressor piston, a second valve associated with said port so that when said piston uncovers said port on the inward stroke, and places air in said bounce chamber in communication with said second valve, any excess air in said bounce chamber will open said second valve releasing said excess air into said scavenging air receiver, the air in said bounce chambers being trapped in said chambers during that portion of the outward stroke of the compressor pistons when said port is closed to said bounce chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,795,927 Huber June 18, 1957 2,815,641 Ramsey Dec. 10, 1957 2,839,035 Ramsey et al June 17, 1958 2,849,995 Lewis Sept. 2, 1958 2,897,803 Kolthofi Aug. 4, 1959

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