CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of South African Provisional Patent

Application Serial No. 2018/04722 filed on July 16, 2018 under 35 U.S.C. § 119(e). South African Provisional Patent Application Serial No. 2018/04722 is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Compressed gas engines can be used as an alternative to internal combustion engines to supply rotational mechanical energy to various machines. However, compressed gas engines typically require highly compressed gas to match the energy content per unit mass that is contained in a combustible fuel, such as gasoline. Further, the operation of typical compressed gas engines can result in the rapid decompression of the compressed gas, leading to a significant reduction in the temperature of the air and possible freezing of the compressed gas engine.

SUMMARY

[0003] Certain embodiments of the disclosed invention may include a compressed gas engine. The compressed gas engine may include a first crankshaft, a first set of piston assemblies, a second set of piston assemblies, and a first valve assembly. The first set of piston assemblies may be coupled to the first crankshaft and comprise a first piston assembly having a first diameter and a second piston assembly having a second diameter. The second set of piston assemblies may be operatively coupled to the first crankshaft and comprise a third piston assembly having the first diameter and a fourth piston assembly having the second diameter. The second set of piston assemblies may be positioned on the crankshaft opposite the first set of piston assemblies such that the piston assemblies of the first set of piston assemblies and the piston assemblies of the second set of piston assemblies having the same diameter are aligned. An open-side cavity of the first piston assembly may be fluidly coupled to and receive compressed air from a compressed air source. A rod-side cavity of the second piston assembly may be fluidly coupled to and receive partially expanded compressed air from a rod-side cavity of the first piston assembly.

[0004] Certain embodiments of the disclosed invention may include of operating a compressed gas engine. The method may include flowing compressed gas from a compressed gas source into a rod-side cavity of a first piston assembly of a first set of piston assemblies operatively coupled to a crankshaft, the first piston assembly having a first diameter. The method may further include flowing compressed gas from the compressed gas source into an open-side cavity of a second piston assembly of a second set of piston assemblies operatively coupled to the crankshaft and opposite the first set of piston assemblies, the second piston assembly having the first diameter and being aligned with the first piston assembly. The method may also include forcing partially expanded compressed gas to flow from an open-side cavity of the first piston assembly into an open-side cavity of a third piston assembly of the first set of piston assemblies, the third piston assembly having a second diameter. The method may further include forcing partially expanded compressed gas to flow from a rod-side cavity of the second piston assembly into a rod-side cavity of a fourth piston assembly of the second set of piston assemblies, the fourth piston assembly having the second diameter and being aligned with the third piston assembly.

[0005] Other aspects of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0006] Embodiments of the compressed gas engine are described with reference to the following figures. The same numbers are used throughout the figures to reference like features and components. The features depicted in the figures are not necessarily shown to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form, and some details of elements may not be shown in the interest of clarity and conciseness. [0007] FIG. 1 is a schematic view of a compressed gas engine system according to one or more embodiments.

[0008] FIG. 2A is a schematic diagram of an engine module of FIG. 1 according to one or more embodiments.

[0009] FIG. 2B is a cross-sectional view of the engine module of FIG. 2A along line

B-B.

[0010] FIGS. 3A-3E are schematic diagrams illustrating the flow of compressed gas through the engine module of FIG. 2 A according to one or more embodiments.

[0011] FIG. 4 is a schematic diagram of an engine module according to one or more embodiments.

[0012] FIG. 5A is a schematic diagram of the compressed gas engine of FIG. 1 according to one or more embodiments.

[0013] FIG. 5B is a cross-sectional view of the compressed gas engine of FIG. 5A along line B-B.

[0014] FIGS. 6A-6J are schematic diagrams illustrating the flow of compressed gas through an engine module according to one or more embodiments.

DETAILED DESCRIPTION

[0015] Specific embodiments of the invention will now be described in detail with reference to the accompanying figures. In the following detailed description of the embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0016] In the following description of FIGS. 1-6J, any component described with regard to a figure, in various embodiments of the invention, may be equivalent to one or more like-named components described with regard to any other figure. For brevity, descriptions of these components will not be repeated with regard to each figure. Thus, each and every embodiment of the components of each figure is incorporated by reference and assumed to be optionally present within every other figure having one or more like-named components. Additionally, in accordance with various embodiments of the invention, any description of the components of a figure is to be interpreted as an optional embodiment, which may be implemented in addition to, in conjunction with, or in place of the embodiments described with regard to a corresponding like-named component in any other figure.

[0017] Throughout the application, ordinal numbers ( e.g ., first, second, third, etc.) may be used as an adjective for an element ( i.e ., any noun in the application). The use of ordinal numbers is not to necessarily imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as by the use of the terms“before”,“after”,“single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements. Additionally, as used herein, the term“about,” when used in conjunction with a target value, means within a value 10% of the target value.

[0018] The present disclosure provides a compressed gas engine system. The compressed gas engine system supplies rotational energy to rotating components, e.g., a generator, a gearbox, or a pump. The compressed gas engine system may also be used to supply rotational energy to other types of rotating components, e.g., boat propellers, electrical generators, and drive shafts for vehicles. However, the rotating components are not limited by the aforementioned examples.

[0019] FIG. 1 is a schematic diagram of a compressed gas engine system (100), according to one or more embodiments. Turning to FIG. 1, the compressed gas engine system (100) includes a compressed gas engine (102) fluidly coupled to a compressed gas source (104) and a decompressed gas container (106), and operatively coupled to one or more rotating components (108). [0020] The compressed gas engine system (100) also includes an engine management system (110) that controls the operation of the compressed gas engine (102). The engine management system (110) controls a valve assembly (not shown) used to control the flow of compressed gas through the compressed gas engine (102). As discussed in more detail below, the valve assembly may include spool valves or solenoid valves. However, the invention is not thereby limited. In other embodiments, the valve assembly may include other types of valves, e.g., ball valves, rotary valves, or other types of flow control valves. However, the valves are not limited by the aforementioned examples.

[0021] The compressed gas engine (102) decompresses the compressed gas received from the compressed gas source (104) in two or more stages, as discussed in more detail below, to provide the rotating component(s) (108) with rotational energy through a driveshaft (112) or similar structure. The decompression takes place in one or more engine modules (114, 116) that are operatively coupled together to provide a single output to the rotating component(s) (108). Although two engine modules (114, 116) are shown, this disclosure is not thereby limited. In other embodiments, the compressed gas engine (102) may include one, three, or more engine modules (114, 116).

[0022] After passing through the compressed gas engine (102), the decompressed gas typically remains at a pressure that is above ambient air pressure and is exhausted to the decompressed gas container (106) for storage. The gas stored in the decompressed gas container (106) can then be recompressed using less input energy than would otherwise be required to compress the gas that powers the compressed gas engine system (100). Alternatively, the decompressed gas can be exhausted to the atmosphere.

[0023] The compressed gas engine (102) may decompress compressed air, compressed nitrogen, or any other compressed gas to provide the rotational energy to the rotating component(s) (108). Additionally, the compressed gas engine (100) may utilize a liquefied gas, e.g., liquid nitrogen. However, in such cases, the compressed gas engine system (100) includes an expansion device (not shown) that heats the vaporizing liquefied gas to ensure the resulting compressed gas is at an appropriate temperature for use in the compressed gas engine (100).

[0024] Turning now to FIG. 2A is an engine module 114 of FIG. 1 according to one or more embodiments. The engine module 114 includes multiple piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) that each include a rod assembly (206) that divides the internal cavity (208) of the piston assembly (200A, 200B, 202A, 202B, 204 A, 204B) into an open-side cavity (210) and a rod-side cavity (212). The rod assembly (206) includes a rod (214) that is coupled to a piston (215) through a pivot (not shown) and that extends through the rod-side cavity (212) of the piston assembly (200A, 200B, 202A, 202B, 204A, 204B). The piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) also include an open-side port (216) in fluid communication with the open-side cavity (210) and a rod-side port (218) in fluid communication with the rod-side cavity (212).

[0025] As shown in FIG. 2A, the diameter of piston assemblies 204A and 204B is greater than the diameter of piston assemblies 202A and 202B, which, in turn, is greater than the diameter of piston assemblies 200 A and 200B. In at least one embodiment, the diameter of piston assemblies 202A and 202B is within a range of 1.5 to 1.6 times the diameter of piston assemblies 200A and 200B, and the diameter of piston assemblies 204A and 204B is within a range of 1.5 to 1.6 times the diameter of piston assemblies 202A and 202B. In other embodiments, the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) may have diameters of different sizes and/or diameter ratios.

[0026] The rod assemblies (206) are coupled to a crankshaft (220) through bearing assemblies (222) that allow the crankshaft (220) to rotate within the bearing assembly (222). The piston assemblies are arranged in sets, i.e., piston assemblies 200A, 202A, and 204A, or piston assemblies 200B, 202B, and 204B, which are positioned on either side of the crankshaft (220) and aligned such that the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) having the same diameter connect to the same portion of the crankshaft (220). This configuration allows the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) to rotate the crankshaft (220) as the rod assemblies (206) extend and retract.

[0027] Additionally, as seen in FIG. 2B, the piston assemblies (200A, 200B, 202A,

202B, 204A, 204B), are arranged along the same plane, e.g., the horizontal plane shown in FIG. 2B. In other embodiments, the plane may be vertical or any other orientation. The connection between the crankshaft (220) and the bearing assemblies 220 of the respective adjacent piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the same piston assembly set, i.e., piston assemblies 200A, 202A, and 204A, or piston assemblies 200B, 202B, and 204B, are radially offset by 180 degrees.

[0028] Referring back to FIG. 2A, the piston assemblies (200A, 200B, 202A, 202B,

204A, 204B) and crankshaft (220) are supported by an engine frame (224) that maintains the relative positions of the piston assemblies (200A, 200B, 202A, 202B, 204 A, 204B) and the crankshaft 220. The engine frame (224) includes multiple bearings (226), which support the crankshaft (220) while allowing the crankshaft (220) to rotate within the engine frame (224). The engine module (114) also includes two spool valves (228A, 228B) that control the flow of air through the engine module (114), as described in more detail with reference to FIGS. 3 A-3E and 6A-6J.

[0029] Turning now to FIGS. 3A-3E, FIGS. 3A-3E are schematic diagrams illustrating the flow of compressed gas through the engine module (114) of FIG. 2A according to one or more embodiments. As shown in FIG. 3A, the spool valves (228A, 228B) are actuated to a first position to allow compressed gas to flow from the compressed gas source (104) to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B, respectively. This allows compressed gas to enter the rod-side cavity (212) of piston assembly 200 A and the open-side cavity (210) of piston assembly 200B, partially expanding the compressed gas, retracting the rod assembly (206) of piston assembly 200A, and extending the rod assembly (206) of piston assembly 200B. The movement of the respective rod assemblies (206) rotates the crankshaft (220) to the position shown in FIG. 3A, while the pivot connections with the piston (215) and bearing assemblies (222) allow the rod assemblies (206) to pivot as the rod assemblies (206) extend and retract.

[0030] The spool valves (228A, 228B) are then actuated to a second position to allow compressed gas to flow from the compressed gas source (104) to the open-side port (216) of piston assembly 200A and the rod-side port (218) of piston assembly 200B, as shown in FIG. 3B. This allows compressed gas to enter the open-side cavity (210) of piston assembly 200A and the rod-side cavity (212) of piston assembly 200B, extending the rod assembly (206) of piston assembly 200A and retracting the rod assembly (206) of piston assembly 200B.

[0031] The movement of the respective rod assemblies (206) also forces the partially expanded compressed gas within the rod-side cavity (212) of piston 200A to pass through spool valve 228A and enter the rod-side cavity (212) of piston 202A through the rod-side port (218), and the partially expanded compressed gas within the open-side cavity (210) of piston 200B to pass through spool valve 228B and enter the open-side cavity (210) of piston 202B through the open-side port (216). The shifting of piston assemblies 200A, 200B, 202A, 202B to the positions shown in FIG. 3B rotates the crankshaft (220) 180 degrees from the previous position shown in FIG. 3 A.

[0032] The spool valves (228A, 228B) are then actuated back to the first position, as shown in FIG. 3C, allowing compressed gas to again enter the rod-side cavity (212) of piston assembly 200A and the open-side cavity (210) of piston assembly 200B.

[0033] The compressed gas entering piston assembly 200A retracts the rod assembly

(206) and forces the partially compressed gas within the open-side cavity (210) of piston assembly 200A to pass through spool valve 228A and enter the open-side cavity (210) of piston 202A through the open-side port (216), extending the rod assembly (206) of piston assembly 202A. The movement of the rod assembly (206) of piston assembly 202A, in turn, forces the further expanded compressed gas within the rod-side cavity (212) of piston 202A to pass through spool valve 228A and enter the rod-side cavity (212) of piston 204A through the rod-side port (218), retracting the rod assembly (206) of piston assembly 204A. [0034] As this occurs, the compressed gas entering piston assembly 200B extends the rod assembly (206) and forces the partially compressed gas within the rod-side cavity (212) of piston assembly 200B to pass through spool valve 228B and enter the rod-side cavity (212) of piston 202A through the rod-side port (218), retracting the rod assembly (206) of piston assembly 202B. The retraction of the rod assembly (206) of piston assembly 202B forces the further expanded compressed gas within the open-side cavity (210) of piston 202B to pass through spool valve 228B and enter the open-side cavity (210) of piston 204B through the open-side port (216), extending the rod assembly (206) of piston assembly 204B. The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) to the positions shown in FIG. 3C rotates the crankshaft (220) 180 degrees from the previous position shown in FIG. 3B.

[0035] The spool valves (228A, 228B) are then actuated to the second position, as shown in FIG. 3D, allowing compressed gas to again enter the open-side cavity (210) of piston assembly 200A and the rod-side cavity (212) of piston assembly 200B.

[0036] The compressed gas entering piston assembly 200A extends the rod assembly

(206) and forces the partially compressed gas within the rod-side cavity (212) of piston assembly 200A to pass through spool valve 228A and enter the rod-side cavity (212) of piston 202A through the rod-side port (218), retracting the rod assembly (206) of piston assembly 202A. In turn, the movement of the rod assembly (206) of piston assembly 202 A forces the further expanded compressed gas within the open-side cavity (210) of piston 202A to pass through spool valve 228 A and enter the open-side cavity (210) of piston 204A through the open-side port (216), extending the rod assembly (206) of piston assembly 204 A. The movement of the rod assembly (206) of piston assembly 204A exhausts the decompressed gas within the rod-side cavity (212) of piston assembly 204A into the decompressed gas container (106).

[0037] As this occurs, the compressed gas entering piston assembly 200B retracts the rod assembly (206) and forces the partially compressed gas within the open-side cavity (210) of piston assembly 200B to pass through spool valve 228B and enter the open-side cavity (210) of piston 202B through the open-side port (216), extending the rod assembly (206) of piston assembly 202B. In turn, the movement of the rod assembly (206) of piston assembly 202B forces the further expanded compressed gas within the rod-side cavity (212) of piston 202B to pass through spool valve 228B and enter the rod-side cavity (212) of piston 204B through the rod- side port (218), retracting the rod assembly (206) of piston assembly 204B. The movement of the rod assembly (206) of piston assembly 204B exhausts the decompressed gas within the open-side cavity (210) of piston assembly 204B into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) to the positions shown in FIG. 3D rotates the crankshaft (220) 180 degrees from the previous position shown in FIG. 3C.

[0038] As previously noted, the decompressed gas entering the decompressed gas container (106) may still be at a pressure that is above ambient pressure, e.g., the gas may initially be at 200 psi, be decompressed to 100 psi in piston assemblies 200A and 200B, be further decompressed to 50 psi in piston assemblies 202A and 202B, and finally be decompressed to 25 psi in piston assemblies 204A and 204B. In other embodiments, the compressed gas supply (104) may be at a pressure other than 200 psi, or the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) may decompress the compressed gas to different pressures.

[0039] The spool valves (228A, 228B) are then actuated to the first position, as shown in FIG. 3E, allowing compressed gas to again enter the rod-side cavity (212) of piston assembly 200A and the open-side cavity (210) of piston assembly 200B.

[0040] The compressed gas entering piston assembly 200A retracts the rod assembly

(206) and forces the partially compressed gas within the open-side cavity (210) of piston assembly 200A to pass through spool valve 228A and enter the open-side cavity (210) of piston 202A through the open-side port (216), extending the rod assembly (206) of piston assembly 202A. In turn, the movement of the rod assembly (206) of piston assembly 202A forces the further expanded compressed gas within the rod-side cavity (210) of piston 202 A to pass through spool valve 228 A and enter the rod-side cavity (212) of piston 204A through the rod-side port (218), retracting the rod assembly (206) of piston assembly 204A. The movement of the rod assembly (206) of piston assembly 204A exhausts the decompressed gas within the open-side cavity (210) of piston assembly 204 A into the decompressed gas container (106).

[0041] As this occurs, the compressed gas entering piston assembly 200B extends the rod assembly (206) and forces the partially compressed gas within the rod-side cavity (212) of piston assembly 200B to pass through spool valve 228B and enter the rod-side cavity (212) of piston 202B through the rod-side port (218), retracting the rod assembly (206) of piston assembly 202B. In turn, the movement of the rod assembly (206) of piston assembly 202B forces the further expanded compressed gas within the open-side cavity (210) of piston 202B to pass through spool valve 228B and enter the open-side cavity (210) of piston 204B through the open-side port (216), extending the rod assembly (206) of piston assembly 204B. The movement of the rod assembly (206) of piston assembly 204B exhausts the decompressed gas within the rod-side cavity (212) of piston assembly 204B into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) to the positions shown in FIG. 3E rotates the crankshaft (220) 180 degrees from the previous position shown in FIG. 3D.

[0042] Once the compressed gas engine (102) has reached the stage shown in FIG.

3E, the spool valves (228A, 228B) alternate between the first and the second positions as shown in FIGS. 3D and 3E. The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) continues to rotate the crankshaft (220) as the compressed gas from the compressed gas source is decompressed in the compressed gas engine.

[0043] The use of multiple piston assemblies (200A, 200B, 202A, 202B, 204A,

204B) allows the compressed gas to be gradually decompressed as it travels through the compressed gas engine 114. This prevents a sudden drop in temperature of the gas that can lead to freezing of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B). Additionally, the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) are sized such that the force applied to the crankshaft (220) by the extension and retraction of the rod assemblies (206) is about equal for each piston within the set of pistons. This allows additional energy to be extracted from the compressed gas as it is decompressed and increases the torque that can be supplied by the crankshaft (220) to rotating components (108).

[0044] Turning now to FIG. 4, FIG. 4 is a schematic diagram of an engine module

400 according to one or more embodiments. The engine module 400 functions similarly to the engine module 114 described above with reference to FIGS. 3A-3E. However the spool valves (228A, 228B) have been replaced by solenoid valves (402, 404, 406, 408, 410, 410, 414, 416, 418, 420, 422, 424). Specifically, each piston assembly (200A, 200B, 202A, 202B, 204A, 204B) includes an open-side inlet solenoid valve (402, 404, 406), an open-side outlet solenoid valve (408, 410, 410), a rod-side inlet solenoid valve (414, 416, 418) and a rod-side outlet solenoid valve (420, 422, 424).

[0045] As shown in FIG. 4, the piston assemblies (200A, 200B, 202A, 202B, 204A,

204B) are directly connected to each other through inlet solenoid valves (404, 406, 416, 418) and outlet solenoid valves (408, 410, 420, 422). Additionally piston assemblies 200A and 200B are directly connected to the compressed gas source (104) through inlet solenoid valves 402 and piston assemblies 204A and 204B are directly connected to the decompressed gas container (106) through outlet solenoid valves 424. The solenoid valves are actuated by an engine management system (110) to allow compressed gas into the respective cavities (210), (212) to allow the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) to rotate the crankshaft (220) as described above.

[0046] In one or more embodiments, inlet solenoid valves 404, 406, 416, 418 may be fluidly connected to a junction having one side fluidly connected to the respective outlet solenoid valve 408, 410, 420, 422 and the other side fluidly connected to a second solenoid valve (426) that is fluidly connected to the compressed gas source (104). This configuration allows the engine management system (110) to boost the output torque of the compressed gas engine (102) by supplementing the partially decompressed gas flowing into piston assemblies 202A, 202B, 204A, 204B with compressed gas from the compressed gas source (104).

[0047] Turning now to FIG. 5A, FIG. 5A is a schematic diagram of the compressed gas engine (102) of FIG. 1 according to one or more embodiments. The individual engine modules (114, 116) of compressed gas engine (102) are similar to those described above with reference to FIGS. 2A-3E. However, crankshafts 220 A and 220B of engine modules 114 and 116, respectively, are operatively coupled together to allow the crankshafts (220A, 220B) to rotate as a single unit. In some embodiments, the adjacent ends of the crankshafts (220 A, 220B) are castellated to allow the crankshafts (220A, 220B) to rotate as one. In other embodiments, the crankshafts (220A, 220B) utilize mechanical fasters or other similar means to function as a single unit. In at least one embodiment, a single crankshaft (not shown) extends through both engine modules (114, 116).

[0048] The connection between the adjacent piston assemblies (200 A, 200B, 202 A,

202B, 204A, 204B) of the same piston assembly set, i.e., piston assemblies 200A, 202A, and 204A, or piston assemblies 200B, 202B, and 204B, and the respective crankshaft (220A, 220B) are radially offset by 180 degrees, as described above. However, as shown in FIG. 5B, the connection between the crankshafts (220A, 220B) is such that the connection between the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) and the crankshaft (220A) of engine module 114 are radially offset 90 degrees from the connections between piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) and the crankshaft (220B) of engine module 116.

[0049] The 90 degree offset between the crankshafts (220A, 220B) causes the rod assemblies (206) of one engine module (114, 116) to be extended and retracted, while the rod assemblies (206) of the other engine module (114, 116) are in a center position, as shown in FIG. 5A. This arrangement helps to prevent hydraulic lock-up of the compressed gas engine (102).

[0050] Turning now to FIGS. 6A-6J, FIGS. 6A-6J are schematic diagrams illustrating the flow of compressed gas through the compressed gas engine module (102) of

FIG. 6A according to one or more embodiments. As shown in FIG. 6A, the spool valves (600A, 600B) are actuated to a first position to allow compressed gas to flow from the compressed gas source (104) to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 114. This retracts the rod assembly (206A) of piston assembly 200A and extends the rod assembly (206 A) of piston assembly 200B. The movement of the respective rod assemblies (206A) rotates the crankshafts (220A, 220B) to the position shown in FIG. 6A.

[0051] The spool valves (600A, 600B) are then actuated to the second position, as shown in FIG. 6B, allowing compressed gas to enter the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 116. As this occurs, compressed gas flows from the compressed gas source (104) to the open-side port (216) of piston assembly 200 A and the rod-side port (218) of piston assembly 200B of engine module 114. This extends the rod assembly (206A) of piston assembly 200A and retracts the rod assembly (206) of piston assembly 200B of engine module 114.

[0052] The flow of compressed gas into piston assemblies 200A and 200B of engine module 114 also forces the partially expanded compressed gas within the rod-side cavity (212) of piston 200 A to enter the rod-side port (218), and the partially expanded compressed gas within the open-side cavity (210) of piston 200B to enter the open-side cavity of piston 202B through the open-side port (216) of engine module 114, shifting the rod assemblies (206A) to a central position. The shifting of the piston assemblies 200A, 200B, 202A, 202B of engine module 114 and piston assemblies 200 A and 200B of engine module 116 to the positions shown in FIG. 6B rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 6A.

[0053] The spool valves (600A, 600B) are then actuated to the third position, as shown in FIG. 6C, continuing the flow of compressed gas to the open-side port (216) of piston assembly 200A and the rod-side port (218) of piston assembly 200B of engine module 114. As this occurs, compressed gas also flows from the compressed gas source (104) to the open-side port (216) of piston assembly 200A and the rod-side port (218) of piston assembly 200B of engine module 116.

[0054] The flow of compressed gas into piston assemblies 200A and 200B of engine module 116 also forces the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200A to enter the rod-side port (218) of piston assembly 202A, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200B of engine module 116 to enter the open-side port (210) of piston assembly 202B of engine module 114, shifting the rod assemblies (206B) to a central position. The shifting of piston assemblies 200A, 200B, 202A, 202B of engine module 114 and piston assemblies 200A and 200B of engine module 116 to the positions shown in FIG. 6C rotates the crankshafts (220 A, 220B) 90 degrees from the previous position shown in FIG. 6B.

[0055] The spool valves (600A, 600B) are then actuated to the fourth position, as shown in FIG. 6D, continuing the flow of compressed gas to the open-side port (216) of piston assembly 200A and the rod-side port (218) of piston assembly 200B of engine module 116. As this occurs, compressed gas also flows from the compressed gas source (104) to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 114.

[0056] The flow of compressed gas into piston assemblies 200A and 200B of engine module 114 also forces the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200A of engine module 114 to enter the open-side port (216) of piston assembly 202A, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202A of engine module 114 to enter the rod-side port (218) of piston assembly 204A of engine module 114.

[0057] At the same time, the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200B of engine module 114 is forced to enter the rod-side port (212) of piston assembly 202B of engine module 114, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly

202B of engine module 114 is forced to enter the open-side port (216) of piston assembly 204B. The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of engine module 114 and piston assemblies 200A, 200B, 202A, and 202B of engine module 116 to the positions shown in FIG. 6D rotates the crankshafts (220 A, 220B) 90 degrees from the previous position shown in FIG. 6C.

[0058] The spool valves (600A, 600B) are then actuated to back to the first position, as shown in FIG. 6E, continuing the flow of compressed gas to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 114. As this occurs, compressed gas also flows from the compressed gas source (104) to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 116.

[0059] The flow of compressed gas into piston assemblies 200A and 200B of engine module 116 also forces the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200A to enter the open-side port (216) of piston assembly 202A, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202A of engine module 116 to enter the rod-side port (212) of piston assembly 204A of engine module 116.

[0060] At the same time, the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200B of engine module 116 is forced to enter the rod-side port (212) of piston assembly 202B, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 202B of engine module 116 is forced to enter the open-side port (216) of piston assembly 204B. The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the engine modules (114, 116) to the positions shown in FIG. 6E rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 6D.

[0061] The spool valves (600A, 600B) are then actuated to second position, as shown in FIG. 6F, continuing the flow of compressed gas to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 116. As this occurs, compressed gas also flows from the compressed gas source (104) to the open-side port (216) of piston assembly 200A and the rod- side port (218) of piston assembly 200B of engine module 114. [0062] This movement also forces the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200A of engine module 114 is forced to enter the rod-side port (218) of piston assembly 202A, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 202 A of engine module 114 to enter the open-side port (216) of piston assembly 204A of engine module 114. The decompressed gas within the rod-side cavity (212) of piston assembly 204A of engine module 114 is then exhausted into the decompressed gas container (106).

[0063] At the same time, the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200B of engine module 114 is forced to enter the open-side port (216) of piston assembly 202B, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202B of engine module 114 is forced to enter the rod-side port (218) of piston assembly 204B. The decompressed gas within the open-side cavity (210) of piston assembly 204B of engine module 114 is then exhausted into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the engine modules (114, 116) to the positions shown in FIG. 6F rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 6E.

[0064] The spool valves (600 A, 600B) are then actuated to third position, as shown in

FIG. 6G, continuing the flow of compressed gas to the open-side port (218) of piston assembly 200 A and the rod-side port (218) of piston assembly 200B of engine module 114. As this occurs, compressed gas also flows from the compressed gas source (104) to the open-side port (216) of piston assembly 200 A and the rod-side port (218) of piston assembly 200B of engine module 116.

[0065] This movement also forces the partially expanded compressed gas within the rod-side cavity (218) of piston assembly 200A of engine module 116 to enter the rod-side port (218) of piston assembly 202 A, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 202A of engine module 116 to enter the open-side port (210) of piston assembly 204 A. The decompressed gas within the rod-side cavity (212) of piston assembly 204A of engine module 116 is then exhausted into the decompressed gas container (106).

[0066] At the same time, the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200B of engine module 116 is forced to enter the open-side port (216) of piston assembly 202B of engine module 116, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202B of engine module 116 is forced to enter the rod-side port (218) of piston assembly 204B. The decompressed gas within the open-side cavity (210) of piston assembly 204B of engine module 116 is then exhausted into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the engine modules (114, 116) to the positions shown in FIG. 6G rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 6F.

[0067] The spool valves (600A, 600B) are then actuated to fourth position, as shown in FIG. 6H, continuing the flow of compressed gas to the open-side port (216) of piston assembly 200A and the rod-side port (218) of piston assembly 200B of engine module 116. As this occurs, compressed gas also flows from the compressed gas source (104) to the rod-side port (218) of piston assembly 200 A and the open- side port (216) of piston assembly 200B of engine module 114.

[0068] This movement also forces the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200A of engine module 114 to enter the open-side port (216) of piston assembly 202A, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202A of engine module 114 to enter the rod-side port (218) of piston assembly 204A. The decompressed gas within the open-side cavity (210) of piston assembly 204A of engine module 114 is then exhausted into the decompressed gas container (106).

[0069] At the same time, the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200B of engine module 114 is forced to enter the rod-side port (218) of piston assembly 202B, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 202B of engine module 114 is forced to enter the open-side port (216) of piston assembly 204B. The decompressed gas within the rod-side cavity (212) of piston assembly 204B of engine module 114 is then exhausted into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the engine modules (114, 116) to the positions shown in FIG. 6H rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 6G.

[0070] The spool valves (600A, 600B) are then actuated to fourth position, as shown in FIG. 61, continuing the flow of compressed gas to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 114. As this occurs, compressed gas also flows from the compressed gas source (104) to the rod-side port (218) of piston assembly 200 A and the open- side port (216) of piston assembly 200B of engine module 116.

[0071] This movement also forces the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200A of engine module 116 to enter the open-side port (216) of piston assembly 202A, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202A of engine module 116 to enter the rod-side port (218) of piston assembly 204A. The decompressed gas within the open-side cavity (210) of piston assembly 204A of engine module 116 is then exhausted into the decompressed gas container (106).

[0072] At the same time, the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200B of engine module 116 is forced to enter the rod-side port (218) of piston assembly 202B of engine module 116, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 202B of engine module 116 is forced to enter the open-side port (216) of piston assembly 204B. The decompressed gas within the rod-side cavity (212) of piston assembly 204B of engine module 116 is then exhausted into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the engine modules (114, 116) to the positions shown in FIG. 61 rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 6H. [0073] The spool valves (600A, 600B) are then actuated to fourth position, as shown in FIG. 6J, continuing the flow of compressed gas to the rod-side port (218) of piston assembly 200A and the open-side port (216) of piston assembly 200B of engine module 116. As this occurs, compressed gas also flows from the compressed gas source (104) to the open-side port (216) of piston assembly 200A and the rod- side port (218) of piston assembly 200B of engine module 114.

[0074] This movement also forces the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 200A of engine module 114 to enter the rod-side port (218) of piston assembly 202 A, and the partially expanded compressed gas within the open-side cavity (210) of piston assembly 202A of engine module 114 to enter the open-side port (216) of piston assembly 204A of engine module 114. The decompressed gas within the rod-side cavity (212) of piston assembly 204A of engine module 114 is then exhausted into the decompressed gas container (106).

[0075] At the same time, the partially expanded compressed gas within the open-side cavity (210) of piston assembly 200B of engine module 114 is forced to enter the open-side port (216) of piston assembly 202B of engine module 114, and the partially expanded compressed gas within the rod-side cavity (212) of piston assembly 202B of engine module 114 is forced to enter the rod-side port (218) of piston assembly 204B. The decompressed gas within the open-side cavity (210) of piston assembly 204B of engine module 114 is then exhausted into the decompressed gas container (106). The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) of the engine modules (114, 116) to the positions shown in FIG. 6J rotates the crankshafts (220A, 220B) 90 degrees from the previous position shown in FIG. 61.

[0076] Once the compressed gas engine (102) has reached the stage shown in FIG. 6J, the spool valves (600 A, 600B) alternate between the first, second, third, and fourth positions as shown in FIGS. 6G through 6J. The shifting of the piston assemblies (200A, 200B, 202A, 202B, 204A, 204B) continues to rotate the crankshafts (220A, 220B) as the compressed gas from the compressed gas source is decompressed in the compressed gas engine.

[0077] One or more specific embodiments of compressed gas engine system have been described. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0078] While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.