Abstract:
The present invention generally relates to providing an air supply for components associated with an engine. More particularly, the present invention relates to a system and method for using compressed air generated by a split-cycle engine to power components such as valves or air springs associated with the split-cycle engine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/176,263 filed May 7, 2009, the contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to providing an air supply for components associated with an engine. More particularly, the present invention relates to a system and method for using compressed air generated by a split-cycle engine to power components such as valves or air springs associated with the split-cycle engine. 
     BACKGROUND OF THE INVENTION 
     For purposes of clarity, the term “conventional engine” as used in the present application refers to an internal combustion engine wherein all four strokes of the well known Otto or Diesel cycles (the intake, compression, expansion and exhaust strokes) are contained in each piston/cylinder combination of the engine. Each stroke requires one half revolution of the crankshaft (180 degrees crank angle (CA)), and two full revolutions of the crankshaft (720 degrees CA) are required to complete the entire Otto or Diesel cycle in each cylinder of a conventional engine. 
     Also, for purposes of clarity, the following definition is offered for the term “split-cycle engine” as may be applied to engines disclosed in the prior art and as referred to in the present application. 
     A split-cycle engine comprises: 
     a crankshaft rotatable about a crankshaft axis; 
     a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston is operable to reciprocate through an intake stroke and a compression stroke during a single rotation of the crankshaft; 
     an expansion (power) piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston is operable to reciprocate through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft; and 
     a crossover passage interconnecting the compression and expansion cylinders, the crossover passage including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve operable to define a pressure chamber therebetween. 
     U.S. Pat. No. 6,543,225 granted Apr. 8, 2003 to Carmelo J. Scuderi (herein the “Scuderi patent”), U.S. Pat. No. 6,952,923 granted Oct. 11, 2005 to David P. Branyon et al. (herein the “Branyon patent”), and U.S. Pat. No. 7,353,786 granted Apr. 8, 2008 to Scuderi et al. (herein the “Air-Hybrid patent”) each contain an extensive discussion of split-cycle and similar type engines. In addition the Scuderi, Branyon, and Air-Hybrid patents disclose details of prior versions of engines of which the present invention comprises a further development. The Scuderi, Branyon, and Air-Hybrid patents are each hereby incorporated by reference in their entirety. 
     Referring to  FIG. 1 , a prior art split-cycle engine of the type similar to those described in the Branyon and Scuderi patents is shown generally by numeral  50 . The split-cycle engine  50  replaces two adjacent cylinders of a conventional engine with a combination of one compression cylinder  66  and one expansion cylinder  68 . The four strokes of the Otto or Diesel cycle are “split” over the two cylinders  66  and  68  such that the compression cylinder contains the intake and compression strokes and the expansion cylinder  68  contains the expansion and exhaust strokes. The Otto or Diesel cycle is therefore completed in these two cylinders  66 ,  68  once per crankshaft  52  revolution (360 degrees CA). 
     During the intake stroke, intake air is drawn into the compression cylinder  66  through an inwardly opening (opening inward into the cylinder) poppet intake valve  82 . During the compression stroke, the compression piston  72  pressurizes the air charge and drives the air charge through one or more crossover passages  78 , which act as the intake passages for the expansion cylinder  68 . 
     The volumetric compression ratio of the compression cylinder of a split-cycle engine is herein referred to as the “compression ratio” of the split-cycle engine. The volumetric compression ratio of the expansion cylinder of a split-cycle engine is herein referred to as the “expansion ratio” of the split-cycle engine. Due to very high compression ratios (e.g., 40 to 1, 80 to 1, or greater), outwardly opening (opening outward away from the cylinder) poppet crossover compression (XovrC) valves  84  at the inlet of each of the one or more crossover passages  78  are used to control flow from the compression cylinder  66  into the one or more crossover passages  78 . Due to very high expansion ratios (e.g., 40 to 1, 80 to 1, or greater), outwardly opening poppet crossover expansion (XovrE) valves at the outlet of each of the one or more crossover passages  78  control flow from the one or more crossover passages  78  into the expansion cylinder  68 . The actuation rates and phasing of the XovrC and XovrE valves  84 ,  86  are timed to maintain pressure in the one or more crossover passages  78  at a high minimum pressure (typically 20 bar or higher at full load) during all four strokes of the Otto or Diesel cycle. 
     One or more fuel injectors  90  (one for each crossover passage  78 ) inject fuel into the pressurized air at the exit end of the one or more crossover passages  78  in correspondence with the XovrE valve(s)  86  opening, which occurs shortly before the expansion piston  74  reaches its top dead center position. The fuel-air charge fully enters the expansion cylinder  68  shortly after the expansion piston  74  reaches its top dead center position. As expansion piston  74  begins its descent from its top dead center position, and while the XovrE valve(s)  86  is/are still open, the spark plug  92  is fired to initiate combustion (typically between 10 to 20 degrees CA after top dead center of the expansion piston  30 ). The XovrE valve(s)  86  is/are then closed before the resulting combustion event can enter the one or more crossover passages  78 . The combustion event drives the expansion piston  74  downward in a power stroke. Exhaust gases are pumped out of the expansion cylinder  68  through an inwardly opening poppet exhaust valve  88  during the exhaust stroke. 
     With the split-cycle engine concept, the geometric engine parameters (i.e., bore, stroke, connecting rod length, compression ratio, etc.) of the compression and expansion cylinders are generally independent from one another. For example, the crank throws  56 ,  58  for the compression cylinder  66  and expansion cylinder  68  respectively may have different radii and may be phased apart from one another with top dead center (TDC) of the expansion piston  74  occurring prior to TDC of the compression piston  72 . This independence, among other factors, enables the split-cycle engine to potentially achieve higher efficiency levels and greater torques than typical four stroke engines. 
     Considerable research has been devoted to air hybrid engines, which store energy for later use in the form of compressed air. The split-cycle engine  50  shown in  FIG. 1  can be combined with an air tank and various control features to provide an air hybrid system. 
       FIG. 2  illustrates an exemplary prior art split-cycle air-hybrid engine. Referring to  FIG. 2  in detail, a prior art split-cycle engine  50  is shown of the type described in  FIG. 1 . One or more of the one or more crossover passages  78  are connected to an air tank  94  via a control valve  93 . Valve  93  is opened and closed at appropriate times to control the flow of air between the air tank  94  and the one or more crossover passages  78 . Compressed air from the one or more crossover passages  78  is stored in the air tank at certain times such as, for example, when the vehicle is braking. The compressed air in the air tank  94  is fed back into the one or more crossover passages  78  at a later time in order to drive the crankshaft  54  in a pre-compressed air power (PAP) mode. The PAP mode can include a pre-compressed combustion-air power mode, wherein pre-compressed air and fuel are mixed and the fuel/air mixture is combusted to drive the power piston down during an expansion stroke. Further, the PAP mode can include various air motoring (AM) modes, wherein pre-compressed air is utilized to drive the power piston down during an expansion stroke without a corresponding combustion event occurring in the expansion cylinder. The Air-Hybrid patent describes details of the PAP modes of operation and other aspects of a split-cycle air hybrid engine similar to the one shown in  FIG. 2 . 
     The actuation mechanisms (not shown) for valves  82 ,  84 ,  86 ,  88  may be cam driven or camless. In general, a cam driven mechanism includes a camshaft mechanically linked to the crankshaft. A cam is mounted to the camshaft, and has a contoured surface that controls the profile of the valve lift (i.e. the valve lift from its valve seat, versus rotation of the crankshaft). A cam driven actuation mechanism is efficient and fast, but has limited flexibility. 
     Also in general, camless actuation systems for valves are known, and include systems that have one or more combinations of mechanical, hydraulic, pneumatic, and/or electrical components or the like. Camless systems allow for greater flexibility during operation, including, but not limited to, the ability to change the valve lift height and duration and/or deactivate the valve at selective times. Pneumatically actuated camless valves are generally advantageous for various reasons such as their compact packaging, low energy consumption requirements, and relatively low cost. 
     Dynamic actuation of the crossover valves  84 ,  86  of split-cycle engine  50  is very demanding. This is because the crossover valves  84  and  86  must achieve sufficient lift to fully transfer the fuel-air charge in a very short period of crankshaft rotation (generally in a range of about 30 to 60 degrees CA) relative to that of a conventional engine, which normally actuates the valves for a period of at least 180 degrees CA. This means that the crossover valves  84 ,  86  must actuate about four to six times faster than the valves of a conventional engine. 
     Valve springs (not shown) for the valves  82 ,  84 ,  86 ,  88  are used to keep the valves  82 ,  84 ,  86 ,  88  closed when they are not being actuated. Any suitable valve springs can be used for the intake valve  82  and the exhaust valve  88  such as mechanical springs or air springs. However, the crossover valves  84 ,  86  preferably use air springs because standard mechanical springs can have difficulty closing the crossover valves  84 ,  86  quickly enough to meet the aforementioned demanding crossover valve actuation requirements. 
     Pneumatic actuators, air springs, and other pneumatically powered components generally require a steady source of cool, dry, compressed air at a constant pressure that is free of particulates. These components generally need a steady source of such compressed air because, inter alia, compressed air tends to leak. Accordingly, there is a need in the art for providing such a compressed air source with an engine, more particularly with a split-cycle engine. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the aforementioned needs/problems in the art by providing an air supply for components associated with a split-cycle engine. More particularly, the present invention processes air generated by a split-cycle engine to power components of the split-cycle engine such as valves and air springs. 
     These and other advantages can be accomplished in an exemplary embodiment of the present invention by providing a system for supplying compressed air to a component requiring a supply of compressed air. The system can comprise an engine comprising a crankshaft rotatable about a crankshaft axis, a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston is operable to reciprocate through an intake stroke and a compression stroke during a single rotation of the crankshaft, an expansion (power) piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston is operable to reciprocate through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft, and a crossover passage interconnecting the compression and expansion cylinders, the crossover passage including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve operable to define a pressure chamber therebetween. The system can be operable to supply the component with compressed air compressed by the compression piston. 
     These and other advantages can be accomplished in a further exemplary embodiment of the present invention by providing a system for supplying compressed air to a component requiring a supply of compressed air. The system may comprise an engine, comprising a crankshaft rotatable about a crankshaft axis, a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston is operable to reciprocate through at least an intake stroke and a compression stroke, and an air tank operable to store compressed air compressed by the compression piston. The system may be configured to supply compressed air from the air tank to the component and to an expansion cylinder for performing at least an expansion stroke and an exhaust stroke. 
     These and other advantages of the present invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a prior art split-cycle engine. 
         FIG. 2  is a cross-sectional view of a prior art split-cycle air-hybrid engine. 
         FIG. 3  is a schematic view of a system for supplying compressed air to components associated with a split-cycle engine according to a first embodiment of the present invention. 
         FIG. 4  is a schematic view of a system for supplying compressed air to components associated with a split-cycle air-hybrid engine according to a second embodiment of the present invention. 
         FIG. 5  is a cross-sectional view of an air spring for a crossover valve of a split-cycle engine, which is supplied with compressed air according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     Referring now to the first embodiment of  FIG. 3  in detail, numeral  50  generally indicates a diagrammatic representation of a split-cycle engine of the type shown in  FIG. 1 . According to the present invention, compressed air generated by the split-cycle engine  50  is supplied to air actuators  234  for actuating the valves  82 ,  84 ,  86 ,  88  and to air springs  238  for supporting the valves  82 ,  84 ,  86 ,  88 . 
     Compression cylinder  66  draws in intake air during the intake stroke of the engine  50 . The compression piston  72  pressurizes the air charge and drives the air charge into the one or more crossover passages  78 . One or more check valves  228  in the one or more crossover passages  78  (preferably one check valve  228  in each crossover passage  78 ) control flow of compressed air into an air processing system  210  through one or more air input lines  224 . The air input lines  224  can preferably connect directly from the crossover passage(s)  78  to the air processing system  210 . Though check valves are utilized for this embodiment, other appropriately designed valves may also be used, e.g., poppet valves. Alternatively, one or more small orifices (preferably one orifice in each crossover passage  78 ) can be used in place of the one or more check valves  228 . Orifice(s) can generally be advantageous because of their potentially improved cost and packaging considerations in relation to check valves. 
     Alternatively to air supply line  224  or in combination with air supply line  224 , a second air supply line  226  can be used to supply compressed air to the air processing system  210 . The second air supply line  226  connects the compression cylinder  66  directly (i.e., not through one or more crossover passages  78 ) to the air processing system  210  as shown in  FIG. 3  via a check valve  230 . In other words, the compression piston  72  pressurizes an air charge and drives some or all of the air charge into the air supply line  226  through valve  230 , thereby bypassing the one or more crossover passages  78 . Alternatively, a poppet valve or an orifice can be used in place of the check valve  230 . Again, orifices may generally be advantageous because of potentially improved cost and packaging considerations. 
     After the compressed air enters the air processing system  210  via one or both of air input lines  224 ,  226 , the compressed air travels through an air input line  216 , which runs successively through various components of the air processing system  210 . Specifically, the compressed air is run successively through an air cooler  218  that cools the compressed air, an air filter  220  that removes particulates from the compressed air, and an air dryer  222  that removes water vapor from the compressed air. Next, the processed compressed air is stored in an air accumulator  212 . Alternative air processing systems  210  can also be used that include additional elements such as a pre-filter at air entry, a fine filter as a last stage, or elements in a different order, as is well known in the art. 
     Air accumulator  212  is connected to air supply lines  240 ,  242 . Air supply lines  240 ,  242  supply the processed compressed air to the components that require a supply of compressed air, for example, pneumatic actuators  234  for actuating pneumatically any of the valves  82 ,  84 ,  86 ,  88  or air springs  238  for supporting any of the valves  82 ,  84 ,  86 ,  88 . Air supply lines  240 ,  242  each run through air pressure regulators  232 ,  236 . Air pressure regulators  232  can regulate the pressure supplied to the pneumatic actuators  234  such that the pressure of the air supplied to the pneumatic actuators  234  is substantially constant. Similarly, air pressure regulators  236  regulate the pressure supplied to the air springs  238  such that the pressure of the air supplied to the air springs  238  is substantially constant. Air pressure regulators  232  and/or air pressure regulators  236  can optionally be variable pressure regulators, which could be advantageous in that this could allow a reduction in air pressure at low engine speeds, thereby reducing friction. 
     Individual pneumatic actuators  234  and individual air springs  238  each utilize separate air pressure regulators because each component can have different air pressure requirements. One of ordinary skill in the art would of course readily appreciate that groups of components with the same air pressure requirements could use a single air pressure regulator for the group. 
     Second Embodiment 
       FIG. 4  shows a second air-hybrid embodiment of the present invention. In this second embodiment, the split-cycle engine  50  is a split-cycle air hybrid engine. That is, the split-cycle engine further includes an air tank  94  (shown schematically) similar to the air tank detailed in  FIG. 2 . Compressed air from the one or more crossover passages  78  is fed into the air tank  94  through valve  93 , which can be a solenoid valve or any other appropriate type of valve. The air tank  94  is thereby used to store energy in the form of compressed air. At an appropriate time, the compressed air stored in the air tank  94  can be fed back into the one or more crossover passages  78  in order to power the crankshaft  54 . Further implementation details of operations modes of the air hybrid configuration are provided in the Air-Hybrid patent. 
     An air input line  227  connects the air tank  94  to the air processing system  210  (of the type described in reference to the first embodiment) via a check valve  247 . Compressed air can enter the air processing system via the air input lines  224 ,  226  (as in the first embodiment). However, in this second embodiment, compressed air can be fed into the air processing system  210  directly from the air tank  94  via air input line  227 . Air input line  226  can optionally be used as a further supply of compressed air for the air processing system  210 . The air processing system  210  of the second embodiment otherwise operates in the same manner as in the first embodiment to supply processed compressed air to components such as air actuators  234  and air springs  238 . 
     Much of the compressed air stored in air tank  94  can be used to drive the expansion piston  74  of the engine  50 . The air tank  94  is preferably insulated in order to prevent energy loss during this process. On the other hand, the air accumulator  212 , which can have a substantially smaller volume than the air tank  94 , does not necessarily require such insulation because the air accumulator  212  stores cooled air for alternative purposes. 
     Referring to  FIG. 5 , a cross sectional view of an air spring  238  for a crossover valve  84 ,  86  of the split-cycle engine  50  is shown. Air spring  238  comprises an air spring cylinder  246  within which an air spring piston  248  reciprocates. The air spring piston  248  and a sealing element (not shown) create a substantial seal within the air spring cylinder  246 . The air spring  238  is connected to air supply line  240 , which supplies the processed compressed air to a pressurized air spring chamber  244  created by the aforementioned substantial seal. The air spring further includes an ambient air chamber  250 , which is connected to external ambient air via an air passage  252 . The compressed air in the air spring chamber  244  applies pressure to the crossover valve  84 / 86  to stay in its closed position, as shown. 
     The invention disclosed herein uses compressed air generated by a split-cycle engine to power various components of the split-cycle engine. This powers the components in a convenient, cost reducing, and efficient manner. While various embodiments are shown and described herein, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.