The present disclosure is related to internal combustion engines having primary and secondary intake ports. The present disclosure is further related to engines having a unidirectional valve disposed in the primary intake ports.
Two-stroke engines are commonly provided intake and exhaust ports in the cylinder wall through which intake gases are provided into the cylinder and exhaust gases are scavenged from the cylinder. The ports are covered and uncovered by pistons reciprocating in the cylinder and the open durations of the intake and exhaust ports overlap. During overlap and at some operating conditions, the respective pressures in the cylinder and the intake system are such that exhaust gases from the cylinder backflow through the intake ports into the intake system thereby negatively impacting scavenging effectiveness of the engine. It is known to provide reed valves in the intake system as close to the intake ports as possible to largely prevent backflow of exhaust gases into the intake system. Reed valves allow flow from the intake system into the cylinder; however, the valves close off flow when pressure in the cylinder is greater than the pressure in the intake, thereby preventing back flow into the intake. Reed valves, unfortunately, present a pressure drop in the intake system and thus reduce the peak torque that the engine may develop. It is desirable to improve scavenging effectiveness, but without increasing pressure drop in the intake.
It is desired to provide a larger intake port area than exhaust port area because the driving pressure on the exhaust gases is greater than the driving pressure on the intake gases. In an engine in which the ports are provided substantially evenly around the periphery, the total intake port height is greater than that of the exhaust port height to provide the desired flow area. However, such greater intake port height is inconsistent with the desired port timing in which the exhaust ports open and close prior to the opening and closing of the intake ports.
To address at least one issue associated describe above, an internal combustion engine is disclosed which has a cylinder, a crankshaft, a piston reciprocating in the cylinder with the piston coupled to the crankshaft via a rod, a first plurality of intake ports defined in the cylinder at a first predetermined distance from an axis of rotation of the crankshaft, and a second plurality of intake ports defined in the cylinder at a second predetermined distance from an axis of rotation of the crankshaft. The first and second pluralities of ports fluidly couple between a combustion chamber defined by a top of the piston and the cylinder In some embodiments, the first and second pluralities of ports are substantially evenly disposed around a periphery of the cylinder. Normally-closed unidirectional flow valves are disposed upstream of the first plurality of intake ports. The unidirectional valves open when pressure on the upstream side of the unidirectional valves exceeds the pressure on the downstream side of the unidirectional valves. In some embodiments, the unidirectional valves include a reed valve block having a frame with a plurality of openings, flexible petals adapted to cover the openings, and stops that limit the movement of the petals. The first plurality of intake ports do not overlap the second plurality of intake portions in a direction parallel to motion of the piston in the cylinder. In some situations, a high-pressure compressor is fluidly coupled to the first plurality of intake ports and a low-pressure compressor is fluidly coupled to the second plurality of intake ports. The second plurality of intake ports is closer to the crankshaft than the first plurality of intake ports.
In some examples, the piston is an intake piston and the engine further includes: a first plurality of exhaust ports defined in the cylinder at a third predetermined distance from the axis of rotation of the crankshaft, and an exhaust piston reciprocating in the cylinder with a top of the intake piston facing a top of the exhaust piston in an opposed-piston arrangement wherein the intake piston covers and uncovers the first and second pluralities of intake ports when the intake piston reciprocates in the cylinder and the exhaust piston covers and uncovers the first plurality of exhaust ports when the exhaust piston reciprocates in the cylinder. The engine may further include a second plurality of exhaust ports defined in the cylinder at a fourth predetermined distance from the axis of rotation of the crankshaft, a high-pressure compressor coupled to the first plurality of intake ports, a low-pressure compressor coupled to the second plurality of intake ports, a high-pressure turbine fluidly coupled to the first plurality of exhaust ports, and a low-pressure turbine fluidly coupled to the second plurality of exhaust ports wherein the high-pressure compressor is shaft-coupled to the high-pressure turbine and the low-pressure compressor is shaft-coupled to the low pressure turbine.
Also disclosed is an internal combustion engine having a cylinder, a crankshaft, a piston adapted to reciprocate in the cylinder with the piston coupled to the crankshaft via a rod, a plurality of primary intake ports defined in the cylinder at a first predetermined distance from an axis of rotation of the crankshaft, a plurality of secondary intake ports defined in the cylinder at a second predetermined distance from the axis of rotation of the crankshaft, a primary intake duct coupled to the primary intake ports, normally-closed valves disposed in the primary intake duct, and a secondary intake duct coupled to the secondary intake ports. In some embodiments, reed valves are disposed in the secondary intake duct. The reed valves may be disposed in a reed valve block. The primary intake duct is fluidly decoupled from the secondary intake duct at least for a portion of the lengths of the first and secondary intake on an end of the intake ducts proximate the intake ports.
Also disclosed in an internal combustion engine having a cylinder with a plurality of primary intake ports defined in the cylinder at first predetermined distance from a first end of the cylinder and a plurality of secondary intake ports defined in the cylinder at a second predetermined distance from the first end of the cylinder, a primary intake duct coupled to the primary intake ports, and a secondary intake duct coupled to the secondary intake ports. The primary intake duct is fluidly decoupled from the secondary intake duct at least for a portion of the lengths of the first and secondary intake ducts proximate the intake ports. The engine may also include an intake plenum fluidly coupled to the primary and secondary intake ducts and a unidirectional valve disposed in the primary intake duct located between the intake plenum and the primary intake ports. The engine further includes a reed valve block disposed in the primary intake duct. The reed valve block includes a frame having a plurality of openings and flexible reed petals adapted to occlude the openings.
As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.
In
A vee-configured engine 100 is shown in
Crankshafts 92 and 92′ of
Referring now to
In
An even further expanded state in cylinder 162 is shown in
In
In
In
In
The embodiment illustrated in
In
The port timings and areas that are shown in
According to an embodiment of the disclosure, reed valves are placed upstream of the primary intake ports. Thus, although the intake ports may be uncovered by the intake piston, flow through the intake ports is prevented by the reed valves. The effect of the reed valves on the effective intake port open area is shown by dotted line 310 (in regards to opening of the reed valves) and short dash-long dash line 312 (in regards to closing of the reed valves). The reed valves allow for a large port open area, but with a desirable open duration. The reed valve opening 310 and closing 312 are one example. Reed valves open and close based on the relative pressures on the upstream and downstream sides of the reed valve and the flow conditions past the reed valves. Thus, the opening 310 and the closing 312 of the reed valves as depicted in
While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.
The present application claims priority benefit from U.S. provisional patent application 61/478,736 filed 25 Apr. 2011.
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Number | Date | Country | |
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20120266851 A1 | Oct 2012 | US |
Number | Date | Country | |
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61478736 | Apr 2011 | US |