Patent Publication Number: US-6708655-B2

Title: Variable compression ratio device for internal combustion engine

Description:
The Government of the United States of America has rights in this invention pursuant to Contract No. DE-FC05-970R22605 (LTCD) awarded by the U.S. Department of Energy. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to the field of internal combustion engines, and more specifically to engines operated under homogenous charge compression ignition principles and piston arrangements therefor. 
     BACKGROUND 
     An internal combustion engine combusts a fuel and air mixture within one or more combustion cylinders, and converts the energy from the combustion process into mechanical output energy. It has been known for many years to use spark ignition and combustion ignition concepts in internal combustion engines. In spark ignition engines, a mixture of fuel and air is provided to a combustion cylinder and compressed. A spark plug initiates combustion through the creation of an open spark sufficient to ignite the air and fuel mixture in the cylinder. Both two and four stroke operating sequences are known. 
     In a direct injection combustion ignition engine, such as a diesel engine, it also is common to use both two and four stroke operating sequences. Turbochargers are often used to supply a charge of air to the combustion cylinders at higher pressure and density than existing ambient conditions. On an upward stroke of the cylinder, the air intake ports are closed and the air is highly compressed. At the desired level of compression, fuel is sprayed into the cylinder by a fuel injector. The fuel ignites immediately, as a result of the heat and pressure inside the cylinder. The pressure created by the combustion of the fuel drives the piston downward in the power stroke of the engine. 
     Engine emission standards have led to the investigation of engine operating and compression ignition alternatives. In one such alternative, referred to as homogenous charge compression ignition (HCCI), significant reductions in emissions have been experienced during initial testing. In an engine operating under HCCI concepts, the air and fuel are intimately mixed, typically at a high air/fuel ratio, before maximum compression in the combustion cylinder. As a result, each droplet of fuel is surrounded by a quantity of combustion air in excess of that required for combustion. As compression occurs, the air temperature increases, and ultimately combustion is initiated at numerous locations throughout the cylinder. Typically, combustion commences at lower temperatures than for direct charge ignition, leading to reduced NOx emissions. 
     The use of homogenous charge compression ignition concepts has apparent benefits in substantial reduction of NOx emissions. However, two aspects of combustion control, used regularly in more conventional engines, are not available in an HCCI engine. The timing of ignition in an HCCI engine can be controlled neither indirectly by controlling the start of fuel injection, as in a direct injection engine, nor directly by controlling spark initiation, as in a spark ignition engine. Further, the rate of heat release can not be controlled via control of fuel injection, as in a direct injection engine, nor by flame propagation, as in a spark ignition engine. As a result, ongoing efforts for improving the HCCI concept include ways to control the ignition event in an HCCI engine. 
     To overcome these problems, attempts have been made to control the compression ratio in the combustion cylinder using a secondary cylinder in communication with the combustion cylinder. By varying the position and movement of a secondary piston in the secondary cylinder, the compression ratio in the combustion cylinder can be controlled. However, fully open secondary cylinders occupy significant space on the bottom deck of the cylinder head, making the placement, arrangement and operation of the standard aspiration valves more difficult. 
     U.S. Pat. No. 4,516,537 entitled, “A Variable Compression System For Internal Combustion Engines” discloses a spark ignition engine in which a secondary cylinder and piston are provided to vary the compression ratio and reduce knock at low speeds and/or heavy loads, while also increasing power and fuel efficiency at high speed and/or light loads. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, an internal combustion engine is provided with a combustion cylinder having an end, and a primary piston reciprocally disposed within the combustion cylinder. A cylinder head including a bottom deck at the end of the combustion cylinder. The cylinder head includes a secondary cylinder. A secondary piston is reciprocally disposed within the secondary cylinder. An actuator is coupled with the secondary piston for controlling a position of the secondary piston dependent upon a position of the primary piston, and thereby controlling commencement of a combustion event in the combustion cylinder. A communication port defined in the cylinder head establishes fluid flow communication between the combustion cylinder and the secondary cylinder. 
     In another aspect of the invention, a work machine is provided with a frame and an internal combustion engine carried by the frame. The internal combustion engine includes a combustion cylinder having an end, and a primary piston reciprocally disposed within the combustion cylinder. A cylinder head including a bottom deck at the end of the combustion cylinder. The cylinder head includes a secondary cylinder. A secondary piston is reciprocally disposed within the secondary cylinder. An actuator is coupled with the secondary piston for controlling a position of the secondary piston dependent upon a position of the primary piston, and thereby controlling commencement of a combustion event in the combustion cylinder. A communication port defined in the cylinder head establishes fluid flow communication between the combustion cylinder and the secondary cylinder. 
     In a further aspect of the invention, a method for operating an internal combustion engine is provided with steps of reciprocating a primary piston within a combustion cylinder having an end; reciprocating a secondary piston within a secondary cylinder adjacent the end, the reciprocating step being carried out such that the secondary piston has a position within the secondary cylinder which is dependent upon a position of the primary piston within the combustion cylinder; providing a combustable fuel to the combustion cylinder; communicating fluid flow between the secondary cylinder and the combustion cylinder, the communicating fluid flow step being carried out through a communication port having an opening in the combustion chamber and an opening in the secondary chamber, each the openings being narrower than the cylinders; and controlling commencement of a combustion event in the combustion cylinder through control of the position of the secondary piston. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional, partially fragmentary view of an embodiment of an internal combustion engine of the present invention within a work machine; 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG. 1; and 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, and more particularly to FIGS. 1 and 3, there is shown an embodiment of an internal combustion engine  10  of the present invention which is incorporated within a work machine such as an on-road vehicle, off-road vehicle, tractor, excavator or the like. An engine  10  according to the present invention is also suited to engines intended primarily for stationary single-speed operation installations, such as, for example, powering a generator. The work machine includes a frame  12  that carries internal combustion engine  10 , as designated schematically by phantom line  14 . 
     Engine  10  includes an engine block  16  that defines one or more combustion cylinders  18 , and typically defines a plurality of combustion cylinders  18 , which in preferred embodiments may be four, six, eight, twelve, sixteen or twenty combustion cylinders  18 . At an end  20  of combustion cylinders  18 , a head  22  is provided on block  16  above all cylinders  18 . 
     While in most applications of the present invention a plurality of cylinders  18  are provided in engine  10 , for purposes of simplicity, only one such cylinder  18  is shown in the drawings. A primary piston  24  is reciprocally disposed within combustion cylinder  18 , and movable between a top dead center position adjacent head  22  (as shown in FIG. 1) and a bottom dead center position at an opposing end of combustion cylinder  18 . Primary piston  24  includes a rod  26  coupled therewith on a side opposite from head  22 . 
     Primary piston  24  also includes a crown  28  having a predefined contour that assists in mixing the fuel and air mixture which is injected into combustion cylinder  18 . The particular contour of crown  28  may vary, depending on the particular application. By way of example, FIG. 1 shows a substantially flat crown  28 , and FIG. 3 shows a concave crown  28 . Fuel also can be provided premixed, as in a stationary natural gas engine. Primary piston  24  also includes one or more annular piston ring grooves  30  in the exterior periphery thereof, which each carry a respective piston ring  32  (FIG.  3 ). Piston rings  32  prevent blow-by of combustion products during a combustion cycle, as is known. Primary piston  24  may also be configured without piston ring grooves  30  and piston rings  32 , depending upon the particular application. 
     Head  22  includes a secondary cylinder  34  that is in communication with combustion cylinder  18 . A secondary piston  36  is reciprocally disposed in secondary cylinder  34 . Secondary cylinder  34  communicates with combustion cylinder  18  via a communication port  40  that establishes fluid flow communication between cylinders  18  and  34 . Communication port  40  has an opening  42  in a bottom deck  44  of head  22  at the top of combustion cylinder  18 , and an opening  46  in secondary cylinder  34 . Communication port  40  defines a passageway whereby pressure is equalized between cylinders  18  and  34 . Communication port  40 , particularly opening  42  thereof, is narrower in diameter than either combustion cylinder  18  or secondary cylinder  34 , and is open or unrestricted between openings  42  and  46 . 
     Head  22  also defines one or more intake ports  50 , and as shown includes a pair of intake ports  50 . Head  22  further defines one or more exhaust ports  52 , and as shown includes two exhaust ports  52 . A corresponding pair of intake valves  54  and exhaust valves  56  are reciprocally disposed in intake ports  50  and exhaust ports  52 . Intake valves  54  and exhaust valves  56  are actuated in known manner during operation of internal combustion engine  10 , as primary piston  24  reciprocates between the top dead center position and the bottom dead center position, and vice versa. 
     Secondary cylinder  34  is located at an outer area of combustion cylinder  18 , and communication port  40 , and particularly opening  42  thereof are located near a perimeter of combustion cylinder  18 . In this regard, opening  42  and communication port  40  are generally radially outwardly of intake ports  50  and exhaust ports  52 . By positioning secondary cylinder  34  near the periphery of combustion cylinders  18 , and providing communication port  40  of a narrower diameter than secondary cylinder  34 , a larger continuous uninterrupted area of head  22  is available for positioning and locating intake ports  50  and exhaust ports  52  in bottom deck  44  of head  22 . Further, more continuous area is provided and available for positioning and locating intake valves  54  and exhaust valves  56  and the necessary operators for the movement of valves  54  and  56 . 
     Secondary cylinder  34  is positioned adjacent combustion cylinder  18 , so as to affect the fluid dynamics and chemical kinetics of the fuel and air mixture during the combustion process when primary piston  24  is at or near the top dead center position as shown in FIG.  1 . 
     Secondary piston  36  is reciprocally disposed within secondary cylinder  34 , and movable between a top dead center position adjacent combustion cylinder  18  (as shown in FIG. 1) and a bottom dead center position at an opposite end of secondary cylinder  34 . Secondary piston  36  includes a crown  58  with a predefined contour, depending upon the particular application. In the embodiment shown, crown  58  is generally flat, but may also have a curved surface or compound curvature, depending upon the particular application. 
     Secondary piston  36  includes a pair of piston ring grooves  60  that respectively carry a pair of piston rings  62  (FIG.  3 ). Piston rings  62  are configured to inhibit blow-by of combustion products during combustion of the fuel and air mixture within combustion cylinder  18 . A rod  64  is coupled with secondary piston  36 , and is directly or indirectly coupled with an actuator  66  as indicated by line  68 . Secondary piston  36  is reciprocated within secondary cylinder  34  to affect the combustion timing of the fuel and air mixture within combustion cylinder  18 , as primary piston  24  reciprocates between a compression stroke and a return stroke within combustion cylinder  18 . 
     Actuator  66  controls the reciprocating position of secondary piston  36 , depending upon a position of primary piston  24 . Actuator  66  may be configured as a cam actuator, a hydraulic actuator, a solenoid actuator, or other actuation device, depending upon the particular application. When configured as a cam actuator, actuator  66  includes a cam (not shown) having a flat cam profile portion which causes secondary piston  36  to remain at the top dead center position to thereby “hang” at the top dead center position for a predetermined period of time. 
     As indicated above, actuator  66  also may be configured as a hydraulic actuator  66 A. When configured as a hydraulic actuator  66 A, rod  64  thus acts as a plunger shaft for reciprocating secondary piston  36  between the top dead center position and the bottom dead center position. A hydraulic fluid source  68  is connected to actuator  66 A and to a controller  70 . A return spring  72  urges rod  64  and secondary piston  36  toward the bottom dead center position. When configured as a hydraulic actuator, it will be appreciated that secondary piston  36  may be moved to or through any desired location within secondary cylinder  34 . Thus, the top dead center position and bottom dead center position of secondary piston  36  may vary. By varying the top dead center position of secondary piston  36 , the effective compression ratio of primary piston  24  and combustion chamber  18  may likewise be varied. 
     In the embodiments shown, secondary piston  36  and secondary cylinder  34  each have a generally cylindrical shape (i.e., generally circular cross-sectional shape). However, depending upon the particular application, it may also be possible to configure secondary piston  36  and secondary cylinder  34  with a different cross-sectional shape while still allowing effective reciprocation of the secondary piston within the secondary cylinder. 
     INDUSTRIAL APPLICABILITY 
     During use, primary piston  24  is reciprocated within combustion cylinder  18 , between the bottom dead center position and the top dead center position as shown in FIG. 1, and vice versa. As primary piston  24  moves from the bottom dead center position to the top dead center position, intake valves  54  are actuated to draw in combustion air and/or an air and fuel mixture. A separate fuel injector (not shown) may also be provided. When primary piston  24  is at or near the top dead center position, and preferably shortly before the top dead center position, secondary piston  36  is likewise actuated and moved to the top dead center position adjacent combustion cylinder  18 . This effectively causes a rapid decrease in the combined volumes of combustion cylinder  18  and its associated secondary cylinder  34 , communicated through communication port  40 , causing rapid compression of the air/fuel mixture. Sufficient energy is imparted to the fuel and air mixture within combustion cylinder  18  to cause the fuel and air mixture to combust. Secondary piston  36  is preferably held at the top dead center position for a predetermined period of time to maintain the total volume at a minimum. When actuator  24  is constructed as a cam actuator, this is accomplished through the cam profile. When configured as a hydraulic actuator, secondary piston  36  is simply held at the top dead center position by applying sufficient hydraulic pressure to rod  64 . 
     After combustion, primary piston  24  is moved from the top dead center position toward the bottom dead center position. Secondary piston  36  is concurrently moved toward its bottom dead center position to effectively increase the total volume communicating through communication port  40 . In the case of using hydraulic actuator  24 , the bottom dead center position of secondary piston  36  may also be varied to in turn vary the compression ratio of internal combustion engine  10 . The process repeats for each cycle of primary piston  24  between the bottom dead center position and top dead center position, and vice versa. 
     As primary piston  24  moves toward the bottom dead center position, exhaust valves  56  are actuated to allow exhaust gas to exit from combustion cylinder  18 . 
     By varying the timing of secondary piston  36 , it is possible to likewise vary the timing of the combustion sequence occurring within combustion cylinder  18 . Thus, it is possible to indirectly control the combustion sequence of the fuel and air mixture within combustion cylinder  18  using secondary piston  36 . Control of the position of secondary piston  36  may also be a function of engine operation and conditions, such as, for example, manifold pressure, temperature or the like. 
     Operation of engine  10  in accordance with the present invention is fuel independent, and any conventional fuel for internal combustion engines can be used. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.