Internal-combustion engines – Two-cycle – Pump compression
Patent
1996-11-26
1998-05-26
Okonsky, David A.
Internal-combustion engines
Two-cycle
Pump compression
123 70R, F02B 2512
Patent
active
057551910
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a two-stroke, reciprocating-piston internal combustion engine with a charging cylinder arranged parallel with or inclined relative to the main cylinder, in which a single- or double-action pump piston is driven by a crankshaft and designed as a cylinder slide piston with overflow apertures, and the main cylinder has an outlet channel controlled by the main piston.
An internal combustion engine is known from U.S. Pat. No. 2,247,147 and No. 2,417,185, in which the outlet channel is, in the way known per se, exclusively opened and closed by the top edge of the main piston. For this reason, the control times for the opening and for the closing of the outlet channel are necessarily the same- and the control cross sections are the same as well, even though the control times and the control cross sections should be substantially lower for the closing of the outlet channel, so that fewer fresh gases can escape from the main cylinder into the outlet channel when the charge changes. WO 90/0884 A1 shows a two-stroke internal combustion engine with crankcase flushing, in which a connection duct is arranged from the crankcase to the outlet channel, through which fresh gas is conveyed and intended to penetrate the cylinder against the exhaust gas flow. Since the control of the connection duct is dependent on the position of the piston window, the connection duct is opened in part of the same period of time as the outlet slot. Therefore, a symmetric control diagram exists. The fresh gases thus flow into the outlet channel at an unfavorable point in time because the flow of exhaust gas still has a high intensity at such time. By the high vacuum prevailing at the orifice of the connection duct, the fresh gas charge is dragged along from the crankcase and necessarily mixed with the exhaust gas. The flushing pressure of a crankcase-flushed two-stroke engine, which pressure is known to be very low, leads to the fact that the flow of fresh gas is not capable of making its way against the direction of the flow of exhaust has, which has a larger volume.
It is known that in internal combustion engines with a single outlet slot control, as it is used with most two-stroke engines, a relatively large proportion of the intake charge escapes through the orifice of the outlet channel before said orifice is closed by the top edge of the piston at the end of the change in charge. This impairs the volumetric efficiency and limits the maximally attainable mean operating pressure of such an internal combustion engine to a relatively low level. A further drawback, which becomes increasingly more important, is the fact that circulation losses in the exhaust gas falsify the measurement of the oxygen content by means of a lambda probe in the exhaust gas duct, and make a catalytic conversion of the nitrogen oxides more difficult. Furthermore, the late closing of the outlet channel also impairs the quality of the mixture formation. So that no parts of the fuel can penetrate the outlet channel, the fuel or the fuel/air mixture has to be admitted into the main cylinder relatively late. Therefore, in an internal combustion engine in which the fuel is directly injected into the main cylinder, only short times are available for the preparation of the mixture until ignition time. In addition, there is the drawback that the turbulences of the charging air have subsided as well. This impairs the formation of the mixture especially at high numbers of revolution and thus the quality of the combustion. Heretofore, resonance exhaust systems have been used in order to counteract the occurrence of charging losses with a retrogressive exhaust gas vibration. This mode of operation, however, has little efficiency; it is limited to a very narrow band of numbers of revolution, and thus inadequate for an internal combustion engine that is expected to operate economically in all load and rpm-ranges.
The invention is based on the problem of eliminating said deficiencies. Without arranging any additional costly control elements such as valves o
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