Patent Application
20160222877
The present teachings generally include an internal combustion engine assembly.
Internal combustion engines combust mixtures of air and fuel to generate mechanical power for work. The basic components of an internal combustion engine are well known in the art and preferably include an engine block, cylinder head, cylinders, pistons, valves, crankshaft and one or more camshafts. The cylinder heads, cylinders and tops of the pistons typically form variable volume combustion chambers into which fuel and air are introduced and combustion occurs as part of a thermodynamic cycle of the device. In all internal combustion engines, useful work is generated from the hot, gaseous products of combustion acting directly on moveable engine components, such as the top or crown of a piston. Generally, reciprocating motion of the pistons is transferred to rotary motion of a crankshaft via connecting rods. One known internal-combustion engine operates in a four-stroke combustion cycle, wherein a stroke is defined as a complete movement of a piston from a top-dead-center (TDC) position to a bottom-dead-center (BDC) position or vice versa, and the strokes include intake, compression, power and exhaust. Accordingly, a four-stroke engine is defined herein to be an engine that requires four complete strokes of a piston for every power stroke of a cylinder charge, i.e., for every stroke that delivers power to a crankshaft.
The overall efficiency of an internal combustion engine is dependent on its ability to maximize the efficiency of all the processes by minimizing the compromises that lead to energy losses to the environment. Dividing the traditional 4-stroke cycle amongst dedicated components allows the compression process to be made more efficient by attempting to approximate isothermal compression of a cylinder charge through mid-compression heat extraction, such as by using a heat exchanger. Likewise, a greater amount of energy may be obtained during expansion of a cylinder charge by moving towards an adiabatic expansion, and extending that expansion further to bring the working gases down to atmospheric pressure. In addition, maximizing the ratio of specific heats of the working gas while reducing each specific heat individually allows greater energy extraction over the expansion while minimizing the mechanical and flow losses associated with each dedicated component.
One known approach to meeting these challenges is a low temperature combustion (LTC) turbocharged diesel engine. The LTC turbocharged diesel relies on a two-stage compression process separated by charge cooling to approximate isothermal compression, reducing the work required to achieve a given air density, lean low temperature combustion to minimize heat losses while improving gas properties, and a two-stage expansion process to enhance work recovery from the hot post-combustion gases. Thermodynamically, the turbocharged diesel is a multi-shaft dual-compression, dual expansion engine that relies on a combination of rotating and reciprocating machines to execute two compressions prior to combustion and two expansions post-combustion. However, the overall efficiency may be limited by the ability to match and optimize the performance of these components over the operating domain. Air handling systems used to provide boosting on externally-charged multi-shaft engines may include more complex boosting systems using two and three stages of turbocharging or combinations of turbochargers and mechanically driven superchargers. In addition to the charging devices, the systems require heat exchangers, bypass valves and controls.
A single-shaft dual expansion internal combustion engine is described and includes an engine block, a cylinder head, a single crankshaft and a multi-link connecting rod assembly. The engine block includes first and second power cylinders and an expander cylinder. The cylinder head fluidly couples the first and second power cylinders and the expander cylinder. The first and second power pistons reciprocate in the first and second power cylinders, respectively, and connect to respective first and second crankpins of the crankshaft. The multi-link connecting rod assembly includes a rigid main arm extending orthogonally to a longitudinal axis of the crankshaft and supporting a first pivot pin located on a first end of the main arm, a second pivot pin located on a central portion of the main arm and a third pivot pin located on a second end of the main arm. The first pivot pin connects via a connecting rod to an expander piston reciprocating in the third cylinder. A third crankpin of the crankshaft acts as the second crankpin and has a throw that is rotated 180 degrees around the longitudinal axis of the crankshaft from a throw of the first crankpin. The third pivot pin couples to a first end of a swing arm, and a second end of the swing arm rotatably couples to a fourth pivot pin that couples to a distal end of a rotating arm that attaches to a rotating shaft coupled to rotation of the crankshaft.
The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers are used to identify like or identical components in the various views,
Each compound cylinder configuration includes one of the cylinder triplets 30 that includes first and second power cylinders 32, 34, respectively, and a third, expander cylinder 36. The first power cylinder 32 houses a first power piston 42 that rotatably couples to a first crankpin 26 of the crankshaft 20 through a first connecting rod 43 and is moveable therein to translate up and down in conjunction with rotation of the crankshaft 20, and also defines a first power cylinder center line 33. Similarly, the second power cylinder 34 houses a second power piston 44 that rotatably couples to a second crankpin 27 of the crankshaft 20 through a second connecting rod 45 and is moveable therein to translate up and down in conjunction with rotation of the crankshaft 20, and also defines a second power cylinder center line 35. The first and second power cylinders 32, 34, first and second power pistons 42, 44 and associated components are dimensionally equivalent, and the first and second crankpins 26, 27 are radially coincident, i.e., they rotatably couple to the crankshaft 20 at the same rotational angle. In one embodiment, the first and second power cylinder center lines 33, 35 define a plane that intersects with the crankshaft center line 24. Alternatively, and as shown the first and second power cylinder center lines 33, 35 define a plane that is offset from the crankshaft center line 24.
The expander cylinder 36 is adjacent to the first and second power cylinders 32, 34, and has a center line 37 that is parallel to the first and second power cylinder center lines 33, 35. An expander piston 46 is housed in the expander cylinder 36 and is moveable therein to translate up and down, and couples to a third connecting rod 47 that rotatably couples to the crankshaft 20 by a multi-link connecting rod assembly 50. The expander cylinder 36 is preferably considerably larger in volume than the individual power cylinders 32, 34, and is preferably in a range between 1.5 times and 4.0 times the volumetric displacement of one of the individual power cylinders 32, 34. Cylinder displacement for the expander cylinder 36 as defined based upon piston movement between TDC location and a BDC location is application-specific and is determined as described herein. Furthermore, the TDC location and the BDC location for the expander cylinder 36 may vary, as described herein.
The cylinder head 60 is an integrated device including cast portions, machined portions and assembled portions for controlling and directing flows of intake air, fuel and combustion gases into and out of the first and second power cylinders 32, 34 and the expander cylinders 36 to effect engine operation to generate mechanical power. The cylinder head 60 includes structural bearing supports for power cylinder camshaft(s) and expander camshaft(s). The cylinder head 60 includes first and second power cylinder intake runners 70, 74, respectively, which fluidly connect to first and second power cylinder intake ports 71, 75, respectively, with engine intake airflow controlled by first and second power cylinder intake valves 62, 64, respectively. As shown, there are two intake valves per cylinder, although any suitable quantity, e.g., one or three intake valves per cylinder, may be employed. Engine intake air originates from an ambient air source, which may pass through a pressurizing device such as a turbocharger or a supercharger prior to entering the first and second power cylinder intake runners 70, 74. The cylinder head 60 also includes first and second power cylinder exhaust ports 72, 76, with engine exhaust airflow controlled by first and second power cylinder exhaust valves 63, 65, respectively. As shown, there are two exhaust valves per cylinder, although any suitable quantity, e.g., one or three exhaust valves per cylinder, may be employed. The first and second power cylinder intake valves 62, 64 and exhaust valves 63, 65 are normally-closed spring-biased poppet valves that are activated by rotation of the power cylinder camshafts in one embodiment, and may alternatively include any other suitable valve and valve activation configuration.
The cylinder head supports elements necessary to initiate combustion, e.g., a spark plug and a fuel injector in one embodiment, for each of the first and second power cylinders 32, 34.
The first power cylinder exhaust port 72 fluidly couples via a first expander cylinder intake runner 73 to a first expander cylinder intake port 79, with flow controlled by a first expander cylinder intake valve 66 and the first power cylinder exhaust valve 63. The second power cylinder exhaust port 76 fluidly couples via a second expander cylinder intake runner 77 to a second expander cylinder intake port 80, with flow controlled by a second expander cylinder intake valve 67 and the second power cylinder exhaust valve 65. The cylinder head 60 also includes one or a plurality of expander cylinder exhaust port(s) 78, two of which are shown, with corresponding expander cylinder exhaust valve(s) 68 that fluidly connect to an expander cylinder exhaust runner 81 that leads to an exhaust system that may include exhaust purification devices, a turbocharger, exhaust sound tuning devices, etc. The first expander cylinder intake valve 66, the second expander cylinder intake valve 67 and the expander cylinder exhaust valve(s) 68 may be normally-closed spring-biased poppet valves that may be activated by rotation of the expander camshaft in one embodiment, and may alternatively include any other suitable camshaft configuration. The rotations of the power cylinder camshafts and the expander camshafts are preferably indexed and linked to rotation of the crankshaft 20. The first and second crankpins 26, 27 of the crankshaft 20 rotatably couple with the first and second power pistons 42, 44 through the first and second connecting rods 43, 45.
The multi-link connecting rod assembly 50 forms a multi-bar linkage that translates linear reciprocating motion of the expander piston 46 offset from the crankshaft center line 24 to rotary motion of the crankshaft 20 while minimizing side-loading of the expander piston 46. An offset 25 between the crankshaft center line 24 and the center line 37 of the expander cylinder 36 is shown with reference to
In one embodiment, the phasing authority of the phaser 90 is between 0° (Position 1) and 180° of rotation (Position 2). The effect of controlling phasing of the phaser 90 is to control rotational phasing of the rotating arm 58 in relation to rotational position of the crankshaft 20, and is described with reference to
The multi-link connecting rod assembly 50 mechanically couples the in-cylinder translation of the first and second power pistons 42, 44 with the in-cylinder translation of the expander piston 46 during rotation of the crankshaft 20 through the first, second and third crankpins 26, 27 and 28. The first pivot pin 53 and the second pivot pin 54 of the rigid main link arm 52 define a first linear distance. The second pivot pin 54 and the third pivot pin 55 define a second linear distance. This configuration including the main link arm 52 permits the stroke of the expander piston 46 to differ from a third crank throw length that is defined by the third crankpin 28 of the crankshaft 20. Preferably, the multi-link connecting rod assembly 50 amplifies the stroke of the expander piston 46 in relation to the crank throw length of the third crankpin 28, with the amplification factor determined by the geometry thereof including the first and second linear distances between the pivot pins. A magnitude of a linear travel distance of the expander piston 46 between a TDC point and a BDC point is determined based upon the following: The lever arm, i.e., a first linear distance and the second linear distance between the pivot pins, the third crank throw, the throw of the rotating anchor arm and fourth pivot pin 57, and the phasing of the rotating arm 58 with respect to the crankshaft 20 all affect the stroke of the expander piston 46.
Operation of the engine 10 described herein includes as follows. The first and second power cylinders 32, 34 both operate in four-stroke cycles including repetitively executed intake-compression-expansion-exhaust strokes over 720° of crankshaft rotation. The four-stroke cycle associated with the second power cylinder 34 is out of phase from the cycle associated with the first power cylinder 32 by 360° of crankshaft rotation. As such, when the first power cylinder 32 is in the intake stroke, the second power cylinder 34 is in the expansion stroke, and when the second power cylinder 34 is in the intake stroke, the first power cylinder 32 is in the expansion stroke. The expander cylinder 36 operates in a two-stroke cycle including an intake stroke and an exhaust stroke, wherein the intake stroke is alternately coordinated with the exhaust strokes from the first and second power cylinders 32, 34. As such, each of the power cylinders 32, 34 displaces its exhaust gas into the expander cylinder 42 in alternating fashion. This operation is shown graphically with reference to
The data includes volumetric displacement for the expander cylinder 36 (560), volumetric displacements for the first and second power cylinders 32, 34 (540, 550), operation of the first power cylinder 32 (510) including openings (1) and closings (0) of the intake valves 512 and the exhaust valves 514 and an associated combustion event 515, operation of the second power cylinder 34 (520) including openings (1) and closings (0) of the intake valves 522 and the exhaust valves 524 and an associated combustion event 525, operation of the first expander cylinder 36 (530) including openings (1) and closings (0) of the first intake valve 532, the second intake valve 531 and the exhaust valves 534, all of which is coincidently graphed in relation to engine crank angle 505 between a nominal −360° crank angle and a nominal +720° crank angle.
The configuration as shown employing a compound cylinder configuration includes one of the cylinder triplets that includes first and second power cylinders 32, 34, respectively, and a third, expander cylinder 36 and the multi-link connecting rod assembly 50 includes a rigid main link arm 52 including a first pivot pin 53, a second pivot pin 54, a third pivot pin 55, swing arm 56 that mechanically couples to a rotating phaser 90 via rotating arm 58. The multi-link connecting rod assembly 50 mechanically couples the in-cylinder translation of the first and second power pistons 42, 44 with the in-cylinder translation of the expander piston 46.
The effect of controlling phasing employing the phaser 90 to control rotational phasing of the rotating arm 58 in relation to rotational position of the crankshaft 20 is described with reference to
This arrangement permits the expander cylinder 36 and associated expander piston 46 to be significantly offset from the crankshaft center line 24 without operating issues associated with piston side loading. This arrangement allows the stroke of the expander piston 46 to be selected in relation to the crank throw, but does not limit the stroke to be equivalent to the crank throw.
Such configurations allows for more compact design of an embodiment of the single-shaft dual expansion internal combustion engine 10, including an overall shorter engine length, a shorter engine height, and better engine performance through lower gas transfer losses due to the minimization of the lengths of the intake runners 73, 77 for the expander cylinder 36.
While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.
