DUAL CRANKSHAFT, OPPOSED-PISTON ENGINE WITH VARIABLE PORT TIMING

A dual-crankshaft, opposed-piston, internal combustion engine includes one or more ported cylinders. Each cylinder has exhaust and intake ports, and the cylinders are juxtaposed and oriented with exhaust and intake ports mutually aligned. The crankshafts are rotatably mounted at respective exhaust and intake ends of the cylinders. A pair of pistons is disposed for opposed sliding movement in the bore of each cylinder. All of the pistons controlling the exhaust ports are coupled by connecting rods to the crankshaft mounted near at the exhaust ends of the cylinders, and all of the pistons controlling the intake ports are coupled by connecting rods to the crankshaft mounted near at the intake ends of the cylinders. The crankshafts are connected by a timing adjustment mechanism operative to change the rotational timing between the crankshafts, thereby to change the timing of exhaust and/or intake port timing.
Inventor: Brendan Lenski
Disclosure Numbers: D306
Date of This Draft: 06/09/2016
Prepared by: Joel F. Lemke

ABSTRACT
A dual-crankshaft, opposed-piston, internal combustion engine includes one or more ported cylinders. Each cylinder has exhaust and intake ports, and the cylinders are juxtaposed and oriented with exhaust and intake ports mutually aligned. The crankshafts are rotatably mounted at respective exhaust and intake ends of the cylinders. A pair of pistons is disposed for opposed sliding movement in the bore of each cylinder. All of the pistons controlling the exhaust ports are coupled by connecting rods to the crankshaft mounted near at the exhaust ends of the cylinders, and all of the pistons controlling the intake ports are coupled by connecting rods to the crankshaft mounted near at the intake ends of the cylinders. The crankshafts are connected by a timing adjustment mechanism operative to change the rotational timing between the crankshafts, thereby to change the timing of exhaust and/or intake port timing.

BACKGROUND
The subject matter relates to a dual-crankshaft, opposed-piston engine equipped with a mechanism for varying timing between the crankshafts. More particularly, the subject matter relates to an opposed-piston engine with two crankshafts coupled by a gear train, in which at least one of the crankshafts is coupled to the gear train by a timing control mechanism that acts between the crankshaft and the gear train to vary the timing of port operations in the engine.
In an opposed-piston engine, a pair of pistons is disposed for opposed sliding motion in the bore of at least one ported cylinder. Each cylinder has exhaust and intake ports, and the cylinders are juxtaposed and oriented with exhaust and intake ports mutually aligned. Of two crankshafts, one each is rotatably mounted at respective exhaust ends and intake ends of the cylinders, and each piston is coupled to drive a respective one of the two crankshafts. The reciprocal movement of each piston in the cylinder controls the operation of a respective one of the two ports formed in the cylinder’s sidewall. Each port is located at a fixed position where it is opened and closed by a respective piston at predetermined points during each cycle of engine operation.
It is desirable to be able to vary the timing of port openings and closings during engine operation in order to dynamically adapt the time that a port remains open to changing speeds and loads that occur during engine operation. The objective is to maximize the amount of air trapped in the cylinder during the compression stroke during various phases of engine operation.
In a dual-crankshaft, opposed-piston engine architecture, the trapped compression ratio (trapped CR) can be varied by adjusting the phase offset between the exhaust and intake crankshafts (typically called the “exhaust crank lead”). Increasing the exhaust crank lead from a nominal value results in decreasing the trapped compression ratio along with a corresponding increase in the exhaust blowdown time-area, that is, the time-integrated area that the exhaust port is open before the intake port opens. Conversely, decreasing the exhaust crank lead results in increasing the trapped compression ratio along with a corresponding decrease in the exhaust blowdown time-area.
Concurrently decreasing the trapped compression ratio and increasing the exhaust blowdown time-area is advantageous for standard engine operation at high engine speeds and high engine loads. At these conditions, lower trapped compression ratios are typically desired because of NOx emission considerations (lower CR typically leads to lower NOx emission), while larger blowdown time-areas are required because of the decreased wall-clock time available to blow down the cylinder contents into the exhaust manifold prior to the intake ports opening.
Similarly, the concurrently increasing trapped compression ratio and decreasing exhaust blowdown time-area is advantageous at lower speeds and lower loads, where higher compression ratios are advantageous for cold-start and engine efficiency considerations and where less exhaust blowdown time-area is required.
One way to change the port timing in a cylinder of an opposed-piston engine is to advance or retard the operational cycle of at least one of the opposed pistons. The change acts to produce a shift in the timings of the openings and closings of the port controlled by the piston with respect to the engine operating cycle. In order to obtain such a variation according to the invention, at least one crankshaft of the pair of crankshafts is utilized for advancing or retarding the operational cycle of the piston with respect to the engine operating cycle. In particular, the timing between the crankshafts is varied in order to obtain a change in timing between the movements of the opposed pistons

D-306 Fig 1D-306 Figure 2D-306 Figure 3

FIGURES
FIG. 1 isometric view of an opposed-piston engine, with casing parts removed to show ported cylinders.
FIG. 2 is an isometric view of the opposed-piston engine of FIG. 1, with cylinders removed to show pistons;
FIG. 3 is an isometric view of the opposed-piston engine of FIG. 2 showing a timing adjustment mechanism operative to change the rotational timing between the crankshafts.

DESCRIPTION
FIG. 1 illustrates a dual-crankshaft, opposed-piston, internal combustion engine 10 with two crankshafts 12 and 14. The engine includes one or more ported cylinders. For example, the engine can include one, two, three, or more cylinders. Each cylinder 30 has exhaust and intake ports 32 and 33, and the cylinders 30 are juxtaposed and oriented with exhaust and intake ports mutually aligned. The crankshafts 12 and 14 are rotatably mounted at respective exhaust and intake ends of the cylinders 30, and so the crankshafts 12 and 14 can be respectively indicated as the exhaust crankshaft 12 and the intake crankshaft 14. As per FIGS. 1 and 2 a pair of pistons 42, 43 is disposed for opposed sliding movement in the bore of each cylinder 30. All of the pistons 42 controlling the exhaust ports 32 are coupled by connecting rods to 52 the exhaust crankshaft 12; all of the pistons 43 controlling the intake ports 33 are coupled by connecting rods 53 to the intake crankshaft 14. The crankshafts 12 and 14 are connected by a gear train including the gears 60-64. Preferably, each of the cranks on the exhaust crankshaft 12 leads the crank coupled to the same cylinder 30 of the intake crankshaft 14 by a predetermined angle Ø. Preferably, although not necessarily, driving power is taken from the exhaust crankshaft 12, while the intake crankshaft 14 is coupled to run auxiliary devices such as pumps, a supercharger, and a compressor.
The engine architecture illustrated in FIG. 1 is modified to equip the engine with a timing adjustment mechanism operative to change the rotational timing between the crankshafts, thereby to change the timing of exhaust and/or intake port timing. The modification is illustrated in FIGS. 2 and 3.
As per FIGS. 2 and 3, the end portion 65 of the exhaust crankshaft 12 has a set of splines 66 oriented in an axial direction of the exhaust crankshaft that engage and rotate a corresponding set of splines 67 formed on a circumferential surface corresponding to the inside diameter of a sleeve 68. A set of splines 69 formed on a circumferential surface corresponding to the outside diameter of the sleeve 68 and oriented in a helical direction centered on the axis of the exhaust crankshaft 12 engage and rotate a corresponding set of splines 70 formed on a circumferential central surface of the gear 60 that is driven by the crankshaft 12. The sleeve 68 is positioned coaxially with and between the crankshaft 12 and the gear 60 and is capable of being moved axially along the crankshaft 12 in either of the directions indicated by the arrow 72. Movement of the sleeve 68 in one direction causes the helical sets of splines 69 and 70 to advance (or retard) the relative rotation between the gear 60 and the crankshaft 12, thereby changing the predetermined angle Ø between the exhaust and intake crankshafts 12 and 14; changing the predetermined angle Ø advances (or retards) the exhaust port timing. Although this example illustrates modification only of the exhaust crankshaft 12, it should be evident that a corresponding modification can also be made to the intake crankshaft 14. The sleeve 68 is capable of being moved axially on the end 65 of the exhaust crankshaft 12 by one or more mechanisms. For example, an actuator can be mounted at one end of the sleeve 68 and driven at that position by hydraulic, pneumatic, electrical, or mechanical means. In some aspects, the actuator is driven by an electrically-actuated servo motor, in conjunction with a gear reduction device.