Two stroke, opposed piston engine with compression release brake arrangement and method

A two-stroke, opposed-piston engine includes a cylinder with an inlet piston controlled inlet port and an exhaust piston controlled exhaust port, the cylinder defining a combustion chamber with the inlet piston and the exhaust piston, a charge air channel in flow communication with the inlet port, a conduit extending directly from the combustion chamber to the charge air channel, and a valve arranged to selectively open and close flow communication through the conduit.

BACKGROUND AND SUMMARY

The present invention relates generally to two stroke, opposed piston engines and, more particularly, to compression release brake arrangements and methods for such engines.

In conventional diesel engines that have a single piston per cylinder, a compression release braking function or engine retarder brake can be achieved by opening the exhaust valves at the top of the compression stroke, resulting in adiabatic expansion of the compressed air, so the large amount of energy stored in that compressed air is not returned to the crankshaft, but is released into the atmosphere, http://en.wikipedia.org/wiki/Engine braking Normally during the compression stroke, energy is used as the upward-traveling piston compresses an in the cylinder; the compressed air then acts as a compressed spring and pushes the piston back down. However, with the engine retarder brake in operation, the compressed air is suddenly released just before the piston begins its downward travel. Having lost the energy stored within the compressed air, there is no ‘spring back’ from it so the engine must expend yet more energy pulling the piston back down again.

In typical opposed piston engine designs, it is not possible to open an exhaust valve at the top of the compression stroke because an exhaust port in the cylinder wall is closed by the exhaust piston. Accordingly, it is desirable to provide an apparatus and method for performing a compression release braking function in a two stroke, opposed piston engine.

In accordance with an aspect of the present invention, a two-stroke, opposed-piston engine comprises a cylinder including an inlet port and an exhaust port, an inlet piston movable in the cylinder between an inlet piston top dead center (IPTDC) position and an inlet piston bottom dead center (IPDBC) position, an exhaust piston movable in the cylinder between an exhaust piston top dead center (OPTDC) position and an exhaust piston bottom dead center (OPBDC) position, a charge air channel in fluid communication with the inlet port, a combustion chamber defined by the cylinder, the inlet piston, and the exhaust piston, the inlet piston permitting flow communication between the inlet port and the combustion chamber when the inlet piston is in the IPBDC position and blocking flow communication between the inlet port and the combustion chamber when the inlet piston is in the IPTDC position, the exhaust piston permitting flow communication between the exhaust port and the combustion chamber when the exhaust piston is in the OPBDC position and blocking flow communication between the exhaust port and the combustion chamber when the exhaust piston is in the OPTDC position, a conduit extending directly from the combustion chamber to the charge air channel, and a valve arranged to selectively open and close flow communication through the conduit.

In accordance with another aspect of the present invention, a two-stroke, opposed-piston engine comprises a cylinder with an inlet piston controlled inlet port and an exhaust piston controlled exhaust port, the cylinder defining a combustion chamber with the inlet piston and the exhaust piston, a charge air channel in flow communication with the inlet port, a conduit extending directly from the combustion chamber to the charge air channel, and a valve arranged to selectively open and close flow communication through the conduit.

In accordance with yet another aspect of the present invention, a method of operating a two-stroke, opposed-piston engine is provided, the engine comprising a cylinder with an inlet piston controlled inlet port and an exhaust piston controlled exhaust port, the cylinder defining a combustion chamber with the inlet piston and the exhaust piston, and a charge air channel in flow communication with the inlet port. The method comprises selectively opening and closing flow communication through a conduit extending directly from the combustion chamber to the charge air channel.

DETAILED DESCRIPTION

A two-stroke, opposed-piston engine21according to an aspect of the present invention is seen inFIGS. 1-4and comprises a cylinder23including an inlet port25and an exhaust port27. The inlet port25and the exhaust port27are typically in the form of a plurality of openings in the cylinder wall. The openings are typically elongated in a direction of a longitudinal axis of the cylinder23.

The inlet port25typically leads to an inlet gallery29in flow communication with a charge an channel31. A compressor of as turbocharger (not shown) and a supercharger or other form of blower (not shown), and one or more charge air coolers (not shown) are typically disposed upstream of the inlet gallery29to provide pressurized air to facilitate scavenging of the cylinder23.

The exhaust port27typically leads to an exhaust gallery33in flow communication with an exhaust channel35. A turbine of a turbocharger (not shown), an exhaust gas recirculation line (not shown) that connects to the charge air channel31are typically disposed downstrean of the exhaust gallery33, along with other exhaust aftertreatment devices (not shown) such as a diesel particulate filter, and a selective catalyst reduction catalyst.

An inlet piston37is movable in the cylinder23between an inlet piston top dead center (IPTDC) position (FIGS. 1 and 3) and an inlet piston bottom (lead center (IPDBC) position (FIGS. 2 and 4), and an exhaust piston39is movable in the cylinder between an exhaust piston top dead center (OPTDC) position (FIGS. 1 and 3) and an exhaust piston bottom dead center (OPBDC) position (FIGS. 2 and 4). The inlet piston37permits flow communication between the inlet port25and a combustion chamber41defined by the cylinder23, the inlet piston37when the inlet piston is in the IPBDC position and blocks flow communication between the inlet port and the combustion chamber when the inlet piston is in the IPTDC position. Similarly, the exhaust piston39permits flow communication between the exhaust port27and the combustion chamber41when the exhaust piston is in the OPBDC position and blocking flow communication between the exhaust port and the combustion chamber when the exhaust piston is in the OFTDC position.

It will be appreciated that, typically, the inlet piston37and the exhaust piston will completely block the inlet port25and the exhaust port27, respectively, at some point well before and after the IPDBC and OPDBC positions. WhileFIGS. 1-4show the inlet piston37and the exhaust piston39being in their respective top dead center positions and bottom dead center positions at the same time, the movement of the pistons will often be timed so that the exhaust port27opens before the inlet port25opens and closes before the inlet port closes. In this way, pressurized combustion gases in the combustion chamber41, and the exhaust piston39will start exiting the cylinder through the exhaust port27before charge air starts entering the cylinder through the inlet port25and further forces the combustion gases out of the cylinder, facilitating uniflow scavenging.

A valve45is arranged to selectively open and close flow communication through the conduit43. By selectively opening and closing it is intended to refer to opening and closing under control of an operator or a suitable controller (e.g., an ECU) programmed to open and close flow communication under particular circumstances, as opposed to opening and closing that occurs randomly or at all times. A compression release brake function can be provided by selectively opening flow communication through the conduit43via the valve45.

The valve45is ordinarily a poppet valve arranged to open and close port47in the wall49of the cylinder23that leads to the conduit43, however, the valve may be another form of valve that closes the conduit itself. A spring (not shown) will ordinarily be provided to urge a poppet or other form of valve45to a closed position as seen inFIGS. 1, 2, and 4. Ordinarily, but not necessarily, the valve45is arranged to selectively open and close flow communication through the conduit43only when the inlet piston37and the exhaust piston39are both in positions in which flow communication between the combustion chamber41and both the inlet port25and the exhaust port27is blocked by the inlet piston and the exhaust piston, respectively.

The valve43can be arranged to selectively open and close flow communication through the conduit45via a hear and camshaft arrange lent51driven by one or both of an inlet crankshaft53driven by the inlet piston37and an exhaust crankshaft55driven b the exhaust piston39, where the gear and camshaft arrangement in turn drives a rocker arm57that pivots to open and close the valve. The valve43can, alternatively, be arranged to selectively open and close flow communication through the conduit45via hydraulic, pneumatic, or electronic drives (not shown) that can be controlled by an operator or a controller such as an ECU.

As seen inFIG. 5, at least one of the inlet crankshaft53can include an inlet crank gear59and the exhaust crankshaft55can include an exhaust crank gear61. A camshaft63can include a cam drive gear65driven by the at least one of the inlet crank gear59and the exhaust crank gear61, and a cam67on the camshaft arranged to drive the rocker arm57to move the valve45to permit selective opening and closing of flow communication through the conduit43by the valve. Idler gears (not shown) will typically be disposed between gears mounted on the inlet crankshaft53and/or the exhaust crankshaft55such as the inlet crank gear59and/or the exhaust crank gear61.

The rocker arm57can comprise a surface69that contacts the valve45to move it between an extended position and a retracted position (shown in phantom inFIG. 5) as the cam67rotates. The rocker arm surface69that contacts the valve45can be a surface of a rocker arm piston71that is movable outwardly from a first position (shown in phantom inFIG. 5) to a second position. Rocker arms with movable pistons for opening valves in engines suitable or adaptable for use in connection with the present invention are disclosed in, e.g., U.S. Pat. No. 8,151,749 and U.S. App. Pub. US2013/0220249, which are both incorporated by reference.

A valve45arranged with a gear and camshaft arrangement51such as shown inFIG. 5permits flow communication through the conduit43only when the rocker arm piston71is at least partially moved away from the first position toward the second position. The rocker arm piston71may be any one of hydraulically driven, pneumatically driven, or electrically driven (e.g., via a solenoid) between the first and second positions. The rocker arm57can be connected to a source73(shown in phantom) of hydraulic or pneumatic fluid or electrical power. As seen inFIG. 6, the rocker arm piston71may be moved to positions between the first and second positions so that the degree of opening of the conduit43by the valve45can be increased or decreased as desired to vary the compression release brake function achieved.

A method aspect of the invention involves operating a two-stroke opposed-piston engine21that comprises a cylinder23with an inlet piston37controlled inlet port25and an exhaust piston39controlled exhaust port27. The cylinder23defines a combustion chamber41with the inlet piston37and the exhaust piston39. A charge air channel31is in flow communication with the inlet port25. The method comprises selectively opening (FIG. 3) and closing (FIGS. 1, 2, and4) flow communication through a conduit43extending directly from the combustion chamber41to the charge air channel31.

Ordinarily, flow communication through the conduit43will be selectively opened and closed only when the inlet piston37and the exhaust piston39are both in positions in which flow communication between the combustion chamber41and both the inlet port25and the exhaust port27is blocked.

The engine21can comprise air inlet crankshaft55driven by the inlet piston37and an exhaust crankshaft57driven by the exhaust piston39, and at least one of the inlet crankshaft includes an inlet crank gear59and the exhaust crankshaft includes an exhaust crank gear51. A camshaft63including a cam drive gear65driven by the at least one of the inlet crank gear59and the exhaust crank gear61, and a cam67on the camshaft arranged to drive a rocker arm57to move a valve45to permit the selective opening and closing of flow communication through the conduit43. The rocker arm57can comprise a surface69that contacts the valve45to move it between an extended position (FIG. 3) and a retracted position (FIGS. 1, 2, and 4) as the cam rotates. The rocker arm surface69that contacts the valve45can be a surface of a rocker arm piston71that is movable outwardly from a first position (FIGS. 1 and 2) to a second position (FIGS. 3 and 4).

The valve45ordinarily permits flow communication through the conduit43only when the rocker arm piston71is at least partially moved away from the first position toward the second position. The method comprises selectively moving the rocker arm piston between the first and second position, e.g., to perform a compression release braking function in response to an operator or controller generated command.

The valve45is movable between a fully closed position (FIGS. 1, 2, and 4) in which flow communication through the conduit4is completely blocked and a fully open position (FIG. 3) in which flow communication through the conduit is unobstructed by the valve, and to one or more partially open positions (FIG. 6) in which flow communication through the conduit is partially obstructed by the valve. The method can further comprise holding the rocker arm piston71in an intermediate position (FIG. 6) between the first position and the second position so that the valve45is in one of one or more partially open positions. The rocker arm piston71can further be moved between the intermediate position (FIG. 6) and the second position in which the valve45is positioned so that the conduit43is fully open (FIG. 5, solid lines) or the first position in which the valve is positioned so that the conduit is fully closed.

By providing a conduit43that leads directly from the combustion chamber41to the charge air channel31, instead of, for example, through the exhaust channel35, any actuators used to open and close flow communication through the conduit can be kept in a cooler environment. Additionally, noise from the compression release brake operation is muted because the compression release is not directly into the exhaust system. Further, heat dissipation from the brake operation is handled during, the scavenge event of the two stroke engine.

In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.