The present application discloses a natural gas compressor, a natural gas compressor assembly, a system for compressing natural gas, and a method of compressing natural gas. In certain embodiments, the natural gas compressor comprises a housing, a plurality of cylinder piston assemblies disposed within the housing, and a drive system for moving the pistons of the cylinder piston assemblies to compress natural gas within the cylinders of the assemblies. Each cylinder piston assembly comprises a piston for compressing natural gas within a cylinder of the assembly. The plurality of cylinder piston assemblies are fluidly connected in sequence such that each assembly forms a compression stage of the compressor.

BACKGROUND

Natural gas compressors for refueling vehicles are often too large to be installed within an automobile and may introduce lubricants such as oil or grease into the compressed gas which may harm the vehicle. Such compressors also often require significant service and maintenance, sometimes as often as every 8 hours. Further, the product life cycles of these compressors are often short as major service is required to overhaul complicated cranks, yokes, and sliders within the compressor that wear or fail.

SUMMARY

The present application discloses a natural gas compressor, a natural gas compressor assembly, a system for compressing natural gas, and a method of compressing natural gas.

In certain embodiments, the natural gas compressor comprises a housing, a plurality of cylinder piston assemblies disposed within the housing, and a drive system for moving the pistons of the cylinder piston assemblies to compress natural gas within the cylinders of the assemblies. Each assembly comprises a non-lubricated piston for compressing natural gas within a cylinder of the assembly. The plurality of cylinder piston assemblies are fluidly connected in sequence such that each assembly forms a compression stage of the compressor. The pressure of compressed natural gas exiting the last cylinder piston assembly of the compressor is between about 2000 and 5000 psi when a drive shaft of the drive system is rotating between about 50 and 500 RPM.

In certain embodiments, the natural gas compressor assembly comprises a motor, a torque multiplier connected to the motor, a natural gas compressor having a drive shaft connected to the torque multiplier, and an intercooler that cools the natural gas between the compression stages of the compressor. The natural gas compressor comprises a housing, a plurality of cylinder piston assemblies disposed within the housing, a water jacket having at least one conduit that cools the cylinder piston assemblies, and a drive system for moving the pistons of the cylinder piston assemblies to compress natural gas within the cylinders of the assemblies. Each cylinder piston assembly comprises a movable and non-lubricated piston for compressing natural gas within a cylinder of the assembly. The plurality of cylinder piston assemblies are fluidly connected in sequence such that each assembly forms a compression stage of the compressor. The intercooler comprises a tank and a plurality of conduits in fluid communication with the cylinder piston assemblies. In certain embodiments, a natural gas compression system comprises a natural gas compressor assembly and a compressed natural gas storage tank fluidly connected to the natural gas compressor of the assembly.

These and additional embodiments will become apparent in the course of the following detailed description.

DESCRIPTION OF EMBODIMENTS

The natural gas compression system of the present application is suitable for in-vehicle or home use and requires minimal service. The natural gas compressor of the system has an increased efficiency and service interval relative to conventional natural gas compressors. For example, in certain embodiments, the compressor has an oil free design, runs at a slower speed than conventional compressors, and has a planar water-cooled head. The oil free compression zone of the compressor limits the need for expensive, complicated filters and dryers which require constant service, maintenance, and replacement. Further, the capability of the compressor to operate at slower speeds permits the use of organic seals such as, for example, seals made of polyamide, polyimide, polyfluroethylene (PTFE), poly[terafluoroethylene-co-perfluoro (alkyl vinyl ether)], polyetherketone (PEEK), polyphenylene sulfide (PPS), and/or blends, mixtures, or combinations thereof. These organic seals are often less expensive, easier to produce, and more readily available than other seals.

The efficiency of the natural gas compressor is further enhanced by a water cooling system. By compacting the design and introducing a water jacket, the cooling is brought closer to the source of the heat which increases heat transfer, reduces cylinder temperatures, prolongs the life of the compressor components, and accomplishes densification of the gas. These features also permit the use of a simple mechanical drivetrain having a straight crankshaft connected to eccentrics, which are connected to piston push rods with a driving member or walking beam. The components of the compressor are robust, compact, and permit guide bushings in multiple locations to eliminate side loading of piston seals, further prolonging life and increasing efficiency of the compressor.

In certain embodiments, the natural gas compressor comprises a water-cooled, 3 to 5 cylinder design with separation of oil and gas pathways running at low rpm's. The natural gas compressor is activated by an electric motor which is attached to a torque multiplier. The torque multiplier or gear reducer reduces the rpm's of the motor to that of the crankshaft rpm's desired to operate the compressor. The compressor has a gas flow path which takes the home source of natural gas at a pressure of about ½ to 3 psi and compresses the gas up to at least 3600 psi. The water-cooled compressor has a water pathway that takes the circulating water through the compressor with intimate contact on each cylinder wall to a common water-cooling bath containing inter-stage plumbing, also called an intercooler. The water circulation is driven by a water pump and may use the radiator coolant located onboard the vehicle. The output of the compressor delivers the natural gas to the compressed natural gas (CNG) tank located onboard the vehicle. In certain embodiments, the natural gas compressor comprises a water-cooled, 5 cylinder design arranged with a common linear head.

FIG. 1schematically illustrates a natural gas compression system100according to an embodiment of the present application. As shown, the system100includes a compressor assembly170comprising a motor160, a torque multiplier or gear reducer102, a natural gas compressor104, and an intercooler106. The system100further comprises a water pump108, a radiator110, and a compressed natural gas (CNG) storage tank112. The motor160drives the compressor104which compresses the natural gas150and delivers the compressed natural gas152to be stored in the CNG storage tank112. The motor160may be a variety of different types of motors such as an electric motor, hydraulic motor, an engine (e.g., an engine of the vehicle), or the like. In certain embodiments, the motor is an AC induction motor having 2-3 HP, running between 1700 and 3600 RPM, and operating on 110V or 220V; however, the motor may also be a DC motor as well.

The natural gas compression system100comprises a water circulation system for cooling the natural gas and compressor components as the gas is compressed by the compressor104. It should be understood that other coolants may be used in lieu of or in addition to the water of the circulation system. Thus, the water cooling systems and components described herein may be configured for use with other liquid coolants. For example, the water cooling system of the present application may comprise water and ethylene glycol. As illustrated inFIG. 1, the circulation system comprises the intercooler106, the pump108, and the radiator110. The circulation system may be configured to cool the natural gas as it is compressed within a cylinder of the compressor104and/or as the compressed natural gas is transferred from one stage to the next in the compressor.

For example, as illustrated inFIG. 1, the compressed natural gas exits the compressor104and passes through the intercooler106between the various stages of compression to cool the gas. In certain embodiments, the natural gas travels through the intercooler106in conduits (e.g., stainless steel tubing) which facilitates the transfer of heat from the compressed gas to the intercooler water bath. The heated water180of the intercooler106exits the intercooler and is circulated by the pump108through the radiator110for cooling. The cooled water182exits the radiator110and returns to the intercooler106. In certain embodiments, the radiator110may be a water-air radiator onboard the vehicle. The onboard radiator may be the original radiator of the vehicle for engine cooling or another radiator in addition to the original radiator. Further, the pump108may be the water pump onboard the vehicle, whether the original pump or another pump in addition to the original pump.

The compressor104the system100may be a variety of compressors capable of compressing natural gas to between about 3000 and 5000 psi. The compressor104generally has multiple piston cylinder assemblies fluidly connected in sequence to form multiple compression stages, e.g., 2, 3, 4, 5 or more stages of compression.

In certain embodiments, the compressor104comprises a housing, a plurality of cylinder piston assemblies disposed within the housing, a water jacket having at least one conduit that cools the cylinder piston assemblies, at least one cylinder head secured to the housing and comprising a plurality of cylinder head conduits that fluidly connect the cylinder piston assemblies, an intercooler that cools the natural gas between the compression stages of the compressor, and a drive system for moving the pistons of the cylinder piston assemblies to compress natural gas within the cylinders of the assemblies. Each cylinder piston assembly comprises a non-lubricated piston for compressing natural gas within a cylinder of the assembly. Thus, each cylinder piston assembly comprises a piston, cylinder, and seal and is non-lubricated in that no additional lubricants are used during compression of the gas within the cylinder. The plurality of cylinder piston assemblies are fluidly connected in sequence such that each assembly forms a compression stage of the compressor. In one embodiment, the pressure of compressed natural gas exiting the last cylinder piston assembly of the compressor is between about 2000 and 5000 psi when a drive shaft of the drive system is rotating between about 50 and 500 RPM.

In certain embodiments, the drive system of the compressor104comprises, for each cylinder piston assembly, an eccentric connected to the drive shaft and a connecting rod, a driving member connected to the connecting rod, a piston push rod connected to the driving member and engaging the piston of the assembly. The rotation of the drive shaft rotates the eccentric and oscillates the connecting rod. Oscillation of the connecting rod oscillates the driving member and oscillation of the driving member moves the piston to compress natural gas within the cylinder of the assembly. The pistons of the cylinder piston assemblies and the piston push rods of the drive system may comprise organic seals. Further, each driving member of the drive system may be connected on opposite sides of the corresponding piston push rod. Further, each piston push rod of the drive system may be supported by upper and lower bushings, the upper bushing located above the connection of the driving member and the lower bushing located below the connection of the driving member.

The compressor104generally has a compact mechanical design so that it fits onboard a vehicle. One of the features that contributes to the compressor104having a compact design is the design and arrangement of the mechanical components that convert the rotational energy of the motor to linear motion to motivate the pistons. The linear motivation of the pistons is made possible by use of a driving member. The driving member acts like a walking beam such that the force is turned 180 degrees. Further, the compressor104may include a physical separation of oil and gas within the compressor.

The compressor104may also comprise organic seals on the pistons reciprocating inside the cylinders of the piston cylinder assemblies, as well as the piston push rods. The life of the organic seals may be increased by a water cooling system that circulates cooling water pass the sidewalls of the cylinders in which the heat or compression is generated, by limiting the amount of sideways motion on the organic seals, and by the pistons having a slow reciprocating speed such as, for example, between 50 and 500 RPM or, in at least one embodiment, 200 RPM. The lack of sideways motion for the organic seals may be accomplished, at least in part, by holding the piston on both ends with lower and upper guide bearings. The piston push rod may also not be lubricated with oil but is sealed with a dry organic seal, thus oil is prohibited from mixing with the compressed natural gas.

As discussed above, the natural gas compression systems and compressor assemblies of the present application may be configured for use in a vehicle. For example, the compression systems and compressor assemblies may be used in trucks, pickup trucks, vans, sedans, forklifts, tow motors, or any vehicle having an engine capable of operating using compressed natural gas. For example, the compression systems and compressor assemblies may be located in the bed of a pickup truck, in the rear or under the seats in a van or truck, or in the trunk of a sedan. The compression systems and compressor assemblies may be, for example, OEM conversions or aftermarket conversions.

All components of the natural gas compression system100may be located in the vehicle. For example, the compressor assembly170may be sized and configured such that it fits in a small or medium sized vehicle, e.g., in the trunk of a small car such as a Ford Focus. In certain embodiments, the compressor assembly170is sized such that it occupies no more than between about 2000 and 12,000 in3, between about 4000 and 10000 in3, between about 5000 and 8000 in3, about 7000 in3, and about 8000 in3. In one embodiment, the compressor assembly170is compact and has dimensions not greater than 14 in×14 in×36 in (35.6 cm×35.6 cm×91.4 cm) so that it may fit in a small to medium sized vehicle. However, It should be understood that one or more portions of the natural gas compression system100may be disposed outside of the vehicle, e.g., in the garage or carport. For example, the compressor assembly170and water circulation system may be disposed outside of the vehicle.

FIG. 2Aillustrates a natural gas compression system200according to an embodiment of the present application. As shown, the system200comprises a CNG storage tank212and a compressor assembly270having an electric motor260, a torque multiplier or gear reducer202, a natural gas compressor204, and an intercooler206. The electric motor260drives the compressor204which compresses the natural gas and delivers the compressed natural gas to be stored in the CNG storage tank212. Although not shown inFIG. 2A, the intercooler206is part of a water circulation system that further comprises a pump and a radiator to circulate and cool the water. In certain embodiments, the pump and/or radiator of the vehicle may be used.

FIG. 2Aillustrates an exemplary arrangement of the compressor assembly207and the CNG tank212of the natural gas compression system200. As shown, the system200is arranged such that it is capable of fitting in a vehicle, e.g., in the trunk of an automobile. For example, the volume290represents the dimensions and volume of an exemplary trunk in a small vehicle, such as a Ford Focus. In certain embodiments, the volume290is sized such that it occupies no more than between about 25,000 and 50,000 in3, between about 30,000 and 40,000 in3, between about 33,000 and 37,000 in3, and about 35,000 in3. In one embodiment, the volume290has a length, width, and height not exceeding 48 in×35 in×20.5 in (122 cm×95 cm×52 cm). As illustrated inFIG. 2A, the natural gas compression system200is sized and arranged to fit within the volume290. The compressor assembly207is compact and has a small footprint so that it takes up a small volume of space, such as in the trunk of a vehicle or as a wall-mounted appliance. In certain embodiments, the compressor assembly207is sized such that it occupies no more than between about 2000 and 12,000 in3, between about 4000 and 10000 in3, between about 5000 and 8000 in3, about 7000 in3, and about 8000 in3. In one embodiment, the compressor assembly207has dimensions not greater than 14 in×14 in×36 in (35.6 cm×35.6 cm×91.4 cm).

FIGS. 2B and 2Cillustrate the compressor assembly270of the natural gas compression system200. The compressor204is a residential automotive natural gas compressor. In certain embodiments, the compressor204is capable of compressing natural gas to a pressure between about 2000 and 5000 psi and has a capacity of between about ½ and 3 GGE (Gasoline Gallon Equivalent) of CNG per hour (between about 63 and 380 standard cubic feet of natural gas @ 200° F.). In one embodiment, the capacity of the compressor204is between about ½ and 1½ GGE of CNG per hour. As described above, the compressor204may be installed in the vehicle or where a vehicle may be stored or refueled, e.g., on or near a structure such as a garage, carport, etc.

As illustrated inFIG. 2C, a piston drive assembly224of the compressor204is contained within a housing. The housing comprises a lower casing226and an upper casing222that are sealed with a gasket or other seal230. The compressor204further comprises a cylinder head or cylinder cap top plate220that is securely attached to an upper casing222. As discussed below, the cylinder head220forms at least a portion of the compression cylinders and comprises conduits for the flow of natural gas between cylinders. The term “conduit” as used herein may be any passage, tube, channel, pipe, feature, element (e.g., a brazed element or plate), or the like capable of carrying a fluid, whether liquid or gas, from one point to another. The cylinder head220is sealed with the upper casing222using a gasket228(e.g., organic rubber), however other suitable seals may be used.

In certain embodiments, the housing is a two piece die-cast aluminum housing. The two piece die-cast aluminum housing offers an inexpensive, lightweight means of encasing the parts of the compressor204. The housing of the compressor may also be configured such that its exterior forms other portions of the compressor assembly or compression system such as, for example, the torque multiplier or water pump housing, thereby providing a modular low cost construction.

As illustrated inFIG. 2C, the intercooler206(FIG. 2B) of the compressor assembly270includes a tank housing290and conduits236attached to the cylinder head220. As described in more detail below, natural gas exits the compression cylinders of the compressor204between the various stages of compression through the conduits236and passes through the water bath in the tank housing290to cool the gas. The intercooler housing290encloses the conduits236which, as shown, is a series of tubes bent in such a manner as to be compactly coiled within the housing. In certain embodiments, the natural gas travels through the tank housing290in stainless steel tubing which facilitates the transfer of heat from the compressed gas to the intercooler water bath. Thus, the intercooler206is a circulating bath which takes water to the area of the compressor204where heat is generated due to the friction of organic seals against the cylinder walls.

As illustrated inFIG. 2C, the electric drive motor260and the torque multiplier202are connected to the piston drive assembly224and mounted to the upper casing222with a motor mount232and a gasket or other seal234. The torque multiplier202is used at the interface of the electric motor260and compressor crankshaft. The torque multiplier202couples the compressor crankshaft with the drive motor260and serves at least two primary purposes. First, the torque multiplier202reduces the motor output speed to a suitable speed for the compressor204. For example, the torque multiplier202may be configured to reduce the output speed of the motor260such that the input speed to the compressor204is between about 50 RPM and about 500 RPM. In one embodiment, the torque multiplier202is a planetary gearbox and has an 18:1 reduction in output speed which permits the use of a 3600 rpm motor while providing a desired input speed of about 200 rpm to the compressor204. Second, through this reduction in speed, an equivalent multiplication of torque is provided by the torque multiplier202. The increase in torque permits the compressor204to overcome the large piston forces generated due to the low shaft speed. As such, the torque multiplier202allows the use of low torque/high speed motors which are typically compact and inexpensive. Exemplary embodiments of the torque multiplier202include a worm drive with worm and helical gear, in-line cycloidal, planetary gearboxes, and belt and pulley systems.

FIGS. 3-6illustrate the compressor204with the cylinder head220removed. The compressor204has a piston drive assembly224(FIG. 2C) inside the housing of the compressor. As shown, the piston drive assembly224comprises five linearly arranged cylinder/piston assemblies. The largest cylinder/piston assembly is labeled300inFIG. 3. The cylinder/piston assemblies are sized in order from largest to smallest following the sequence of300,302,304,306, and308. Each compression cylinder/piston assembly is considered a stage of compression. As such, the compressor204comprises five stages of compression ranging from a first stage of compression produced by cylinder/piston assembly300to a fifth stage of compression produced by cylinder/piston assembly308. However, in certain embodiments, the compressor may have more or less cylinder/piston assemblies and stages of compression, e.g.,1,2,3,4,6, or more. Each cylinder/piston assembly300,302,304,306, and308comprises a piston, cylinder, and at least one seal and is non-lubricated in that no additional lubricants are used during compression of the gas within the cylinder.

In certain embodiments, the diameters of the cylinder/piston assemblies300,302,304,306, and308range between about 5 and ¼ inches and the volumes range between about 12 and ¼ in2. In one embodiment, the cylinder/piston assemblies300,302,304,306, and308have the following diameters and volumes:

FIG. 3illustrates five connecting rods of the piston drive assembly224connected to the crankshaft310, one for each cylinder/piston assembly. The connecting rods for cylinder/piston assemblies300,302,304,306, and308are shown and labeled320,322,324,326, and328, respectively. Further, the pan of the lower compressor housing226is filled with oil for lubrication of the piston drive assembly224. The approximate oil level fill line452is shown inFIGS. 4 and 5.

FIG. 4is a cross-sectional side view of the natural gas compressor204taken along line4-4ofFIG. 3. Here, the five linearly arranged cylinder/piston assemblies are illustrated and they have a common linear planar top surface. As shown, the pistons of the five cylinder/piston assemblies300,302,304,306, and308are at various points of compression within the compression cylinders. This is because the pistons are timed to balance the load on the motor and for gas delivery to the subsequent downstream stages.FIG. 4also illustrates five piston push rods, each connected to a piston of a cylinder/piston assembly. The piston push rods for cylinder/piston assemblies300,302,304,306, and308are shown and labeled420,422,424,426, and428, respectively.

FIG. 4further illustrates features which separate the areas in which oil and gas are located within the compressor204. The line450inFIG. 4represents the separation of oil and gas within the compressor housing. The natural gas undergoing compression is separated from flowing into oil-filled areas of the compressor204with the use of dry organic seals. In certain embodiments, the dry organic seal is a PEEK, PTFE or inorganic filled PTFE seal. The dry organic seals may be used in a variety of locations within the compressor, such as on the piston push rods and pistons.

For example, the location of a dry organic seal408on the piston push rod420of the first stage cylinder/piston assembly300is illustrated inFIG. 4. Because the organic seal408does not need oil to lubricate the piston push rod420, oil is prohibited from mixing with the natural gas, potentially causing the hazard of contaminated gas fouling the vehicle's fuel system. The other four stages of the compressor204also comprise at least one dry organic seal on the piston push rod in the same or similar location as seal408. Further, located below the dry organic seal408on the piston push rod420is an oil wiper410. The oil wiper410removes oil from the piston push rod420as it moves. The other four stages of the compressor204also comprise at least one oil wiper on the piston push rod in the same or similar location as oil wiper410.

The cylinder/piston assemblies300,302,304,306, and308are also non-lubricated and use dry organic seals. For example, as illustrated inFIG. 4, the seal460on the piston of the first stage cylinder/piston assembly300is a dry organic seal. The other four stages of the compressor204also comprise at least one dry organic seal on the piston in the same or similar location as seal460.

To increase the efficiency and life cycle of the compressor204, the linear speeds of the pistons are generally reduced to well within acceptable pressure-velocity (PV) ranges for dry organic seals. For example, in certain embodiments, the driveshaft310has a slow rotational speed of about 200 rpm and the piston push rod420has a stroke of about 1¼ inches producing a linear speed of the pistons below 42 ft/min. This yields a maximum PV value of under 150,000 psi*ft/min for the highest pressure seal in the fifth stage cylinder/piston assembly308. In one embodiment, the PV values for stages 1-5 in psi*ft/min are about 1800, 5600, 17000, 50000, and 150000 respectively. With these reduced PV values, the compressor204is able to deliver consistent performance over a life cycle of 3000-5000 hours with little or no maintenance. This is in direct comparison to conventional compressor units which operate on a very short stroke and very high speed, often 1800 rpm or greater, which produces unnecessarily high wear on seals, poor thermal efficiency, and leads to short life spans and decreased performance. The decreased speed allows the compressor204to operate without any cylinder lubricants or other additives. This eliminates the potential hazard of contaminated gas fouling the vehicle's fuel system.

FIG. 5is a cross-sectional front view of the compressor204shown inFIG. 3taken along line5-5and illustrates the features of the piston drive assembly224for the first stage of the compressor, although the description of the drive system applies to the other four stages of the compressor as well. As shown, the piston500of the cylinder/piston assembly300is actuated by the piston push rod420to the move the piston in a direction D1within the cylinder560to compress the natural gas. The piston push rod420is supported by two guide bushings, an upper guide bushing502separated from a lower guide bushing504.

As illustrated inFIG. 5, The piston push rod420is articulated up and down in the direction D1by a driving member506. A first end of the driving member506is connected to the connecting rod320and a second end of the driving member is connected to the piston push rod420. As shown inFIG. 3, the driving member506is generally connected on opposite sides of the piston push rod420to minimize side load on the push rod. The driving member is also connected to the lower housing226by a pivoting member520. Oscillation of the connecting rod320moves the first end of the driving member506in a direction D2. The pivoting member520permits the driving member506to act as a walking beam such that movement of the first end in the direction D2moves the second end of the driving member a corresponding amount in a direction D3, which moves the piston push rod420up and down in the direction D1. The use of the driving member or walking beam506permits the compressor204to convert rotational forces to linear forces with a compact geometry favorable for installation, such as in a vehicle or mounted to a structure.

As illustrated inFIG. 5, the pivoting member520will also pivot or oscillate back and forth in a direction D4as the connecting rod320oscillates to facilitate movement of the driving member506. As shown, the pivoting member is connected at or near the center of the driving member. Further, the connecting rod320is connected to the crankshaft or drive shaft310of the compressor204by an eccentric512and an eccentric bearing510. As the eccentric512rotates with the drive shaft310, the connecting rod320oscillates back and forth to move the first end of the driving member506in the direction D2. The fill level for the oil used as lubrication of the piston drive assembly224is illustrated as line452inFIG. 5.

The conversion of rotational energy from the motor260to linear motion to motivate the pistons is handled with the eccentric bearing, driving member, and guide bushings for each cylinder/piston assembly300,302,304,306, and308. For example, in certain embodiments, the eccentric512provides an offset equal to one half stroke which is translated to one end of the driving member506via the connecting rod320. The driving member506then serves two purposes. First, the driving member506acts like a walking beam such that the force is turned 180 degrees allowing for a more compact design. Second, the position of the pivotal connection of the driving member506to the piston push rod420may be modified to allow for differential or unequal stroke lengths, for all or some of the pistons. The position of the pivotal connections between the driving member506and the connecting rod320and/or pivoting member520may also be modified in certain embodiments to modify the stroke length of the piston. Changing the stroke length allows for a change in cylinder/piston diameter, which changes the piston rod loading and flow pattern of the natural gas, which in turn affects the balance of the load on the motor and cooling of the compressor. The active end of the driving member506is generally pivotally coupled to the piston push rod420with a pin. The piston push rod420provides the motivating force of compression for the compression pistons.

As discussed above, the piston push rod420is guided by the upper guide bushing502and the lower guide bushing504. In certain embodiments, the upper and lower guide bushings502,504are greater than 1.5 inches apart. The guide bushings can be a variety of different types of bushings, including lubricated bronze, polymeric or ferrous bushings. As illustrated inFIG. 5, the upper and lower guide bushings502,504are located above and below the connection of the driving member506to the piston push rod420, respectively, to prohibit side loading on the piston, a cause of failure in many compressor designs. Side loading occurs when the transition from rotational motion to linear motion produces a force vector perpendicular to the desired motion. However, this arrangement prohibits side loading of the piston because the guide bushings502,504are on either side of the applied load providing a large lever arm that reduces the wear on either bushing.

The driving member, pivoting member, connecting rod, eccentric, driveshaft, and the lower portion of the piston push rod which extends between the two guide bushings are generally lubricated by a splash and/or a pressure lubrication system. In certain embodiments when a pressurized lubrication system is used, the lower portion of the piston push rod may comprise an oil pump which pressurizes the lubrication system. For example,FIG. 5illustrates an oil pump516that acts as a displacement plunger type pump. As shown, oil enters a chamber via a check valve during the piston up stroke. On the piston down stroke, the piston push rod420displaces the oil through passages to lubricate components of the compressor.

Further, in certain embodiments, at least one piston of the compressor may not be connected to the push-rod, but rather the push-rod acts as a pusher only and does not assist in pulling the piston back. For example, as shown inFIGS. 4 and 6, the pistons of cylinder/piston assemblies304,306, and308are not attached to the piston push rods424,426, and428respectively. Instead, the push rods424,426, and428are used to push the piston and compress the gas in the cylinder, then the pressure of the inlet gas returns the piston. Decoupling the push rod and the piston allows for the self-alignment of the piston within the cylinder and prohibits side-load and misalignment from the push rod being transmitted to the piston. As shown inFIGS. 4 and 5, the pistons of cylinder/piston assemblies300and302are attached to the piston push rods420and422respectively. More or less of the cylinder/piston assemblies may be connected to the corresponding piston push rod in other embodiments.

FIG. 6is a cross-sectional front view of the compressor204shown inFIG. 3taken along line6-6illustrating the stage5or highest pressure piston/cylinder assembly308. As shown, the seal between the piston610and cylinder612comprises a plurality of stacked seals600. As shown, the stacked seals600are U-cup shaped seals with alternating layers of sealing material. The sealing material may be organic and/or organic inorganic-filled material. The fillers in the sealing material may be materials with high thermal conductive that facilitate the removal of heat, such as, for example, carbon or graphite. The stacked seals600also permit the pressure of the natural gas within the cylinder612to spread the seals out evenly and engage tightly around the circumference of interior cylinder wall. Multiple seals provide more contact area to reduce the pressure on any one seal and to distribute the load. Greater surface contact reduces the pressure on any one seal also increases the lifetime of the seals due to less wear.

FIGS. 7A-7Care various views of the compressor204of the compressor assembly270with the cylinder head220secured to the upper housing222.FIG. 7Ais a perspective view of the compressor204showing the intercooler tank290with the top plate of the tank removed exposing the conduits236.FIG. 7Bis a perspective view of the compressor204with the intercooler tank290and top plate710of the cylinder head220removed exposing a cooling channel716of the cylinder head.FIG. 7Cis a cross sectional side view of the compressor204taken along line7C-7C inFIG. 7A.

FIGS. 7A-7Cillustrate the flow of natural gas NG through the various stages of compressor204. As illustrated inFIG. 7C, the natural gas NG enters the low pressure side of the cylinder head220through an inlet702. The natural gas NG generally comes from a home natural gas supply at a pressure between about ½ and 5 psig, and in certain embodiments between about ½ and 3 psig. The natural gas NG travels through a conduit730into the compression chamber of the first stage cylinder/piston assembly300where it is compressed by the piston to between about 20 and 40 psig (e.g., about 30 psig). The compressed natural gas NG exits the first stage compression chamber through a conduit732, into a conduit740of the intercooler206(FIG. 7B), then through a conduit734into the compression chamber of the second stage cylinder/piston assembly302where it is compressed by the piston to between about 100 and 140 psig (e.g., about 120 psig). The compressed natural gas exits the second stage compression chamber through a conduit736, into a conduit742of the intercooler206(FIG. 7B), then through a conduit738into the compression chamber of the third stage cylinder/piston assembly304where it is compressed by the piston to between about 350 and 450 psig (e.g., 389 psig or about 400 psig). This process continues for stages4and5—the compressed natural gas enters the compression chamber and is compressed by the reciprocating piston and travels through conduits in the cylinder head and intercooler to the next stage. The respective inlet and outlet gas pressures for stages4and5are: stage4inlet pressure of between about 350 and 450 psig (e.g., 389 psig or about 400 psig) and outlet pressure of between about 1100 and 1300 psig (e.g., 1192 psig or about 1200 psig); stage5inlet pressure of between about 1100 and 1300 psig (e.g., 1192 psig or about 1200 psig) and outlet pressure of between about 3200 and 4000 psig (e.g., about 3600 psig). The compressed natural gas NG exits the stage5compression chamber, through a conduit750, and out an outlet708of the high pressure side of the cylinder head220to the CNG tank onboard the vehicle.

In certain embodiments, the compressor of the present application may be configured to recirculate natural gas that has seeped past or “blown by” the seals of the pistons of the compressor. For example,FIG. 8schematically illustrates a compressor800according to an embodiment of the present application. As shown, the compressor800has three cylinder/piston assemblies and a lower passageway850that receives natural gas808that has blown past the pistons and into the compressor housing820. The lower passageway850is positioned above the dry organic seal840and oil wiper842such that the blow by gas808is not contaminated with oil. A valve806controls the flow of the blow by natural gas808and mixture of the same with incoming natural gas. In operation, natural gas enters the compressor800through an inlet valve804and combines with the blow by natural gas808. The combined natural gas802then enters the first stage compression chamber through inlet valve830. Once compressed, the natural gas exits the first stage through an outlet valve832and enters the next stage. This sequence proceeds until the last stage where the compressed natural gas822exits the compressor to a CNG storage tank.

As illustrated inFIGS. 7A-7C, the compression chambers of the cylinder/piston assemblies and compressed natural gas is cooled by the water in multiple ways. For example, as illustrated inFIGS. 7A and 7Band discussed above, the series of intercooler conduits236that extend between each stage of the compressor204are submerged in a water bath allowing removal of heat from the compressed gas.

As illustrated inFIG. 7B, the cylinder head220may comprise one or more cooling channels or conduits that carry water to cool the compression chambers of the cylinder/piston assemblies and compressed natural gas. As shown, water W1enters an inlet704and extends through the cooling channel or passage716in the cylinder head220to cool the compression chambers of the cylinder/piston assemblies and compressed natural gas flowing through the head. The water W1then exits the outlet706.

As illustrated inFIG. 7C, the cylinders of the cylinder/piston assemblies300,302,304,306, and308are water jacketed. As shown, water W2enters an inlet712and flows around each cylinder of the cylinder piston assemblies300,302,304,306, and308to a outlets714and715(FIG. 7B). The water jacket carries heat away from the cylinders or compression chambers, the sources of heat due to the compression of the natural gas.

The heated water from the various cooling systems discussed above is generally sent through a water-air radiator where the water may be cooled for recirculation. The radiator may be a unit dedicated to the compressor, or the compressor may make use of the vehicle's own cooling system. For example, the heated water may be circulated through the vehicle's radiator and returned to the compressor bypassing the engine block, thermostat, and water pump.

As illustrated inFIGS. 7A-7C, the compact, planar, in-line arrangement of the cylinder head220brings the cylinder valves closer to the pistons thus reducing the gas flow paths and dead-volume in the system and maintaining gas flow through the compressor204. This layout is possible through the use of the water cooling systems above by eliminating the need for large fins on individual heads separated by an air gap. The arrangement of the cylinder head220also maximizes the surface area of the intercooler. The volumetric specific heat of water is 4200 times greater than air allowing the compressor package to be reduced in size while maintaining thermal performance. Water cooling also allows cooling to be directed where needed which reduces the thermal gain on various components such as seals, cylinder walls, valves, and plumbing. This has the benefit of allowing for densification of the gas for a more complete fueling of the vehicle, while reducing the wear on seals and other rubbed surfaces. As the water-cooling has intimate contact with the cylinder walls, the temperature-controlled environment further prolongs the life of the seals.

As described herein, when one or more components are described as being connected, joined, affixed, coupled, attached, or otherwise interconnected, such interconnection may be direct as between the components or may be in direct such as through the use of one or more intermediary components. Also as described herein, reference to a “member,” “connector”, “component,” or “portion” shall not be limited to a single structural member, component, or element but can include an assembly of components, members or elements.

While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the invention to such details. Additional advantages and modifications will readily appear to those skilled in the art. For example, where components are releasably or removably connected or attached together, any type of releasable connection may be suitable including for example, locking connections, fastened connections, tongue and groove connections, etc. Still further, component geometries, shapes, and dimensions can be modified without changing the overall role or function of the components. Therefore, the inventive concept, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.