US2062821A - Scavenging and supply of combustion air to two-cycle engines - Google Patents

Description

1936- I E. B. POLLISTER' 2,062,821

SCAVENGING AND SUPPLY OF COMBUSTION AIR TO TWO-CYCLE ENGINES Filed Sept. 4, 1931 INVENTOR. MIRD B.POLL1S7R By /W /,zz

LA TTORNEYS.

Patented Dec. 1, 1936 UNITED STATES PATENT OFFICE SCAVENGING AND SUPPLY OF COMBUS- TION AIR TO TWO-CYCLE ENGINES Application September 4, 1931, Serial No. 561,130

9 Claims.

The object of the invention is the improvement in general efi'iciency of two-cycle internal-combustion engines, more particularly high speed, injection type engines, through improved scavenging accomplished by the use of air from different pretssure sources, as hereinbelow more fully set or h.

In engines of. the type to which this invention particularly relates and which have exhaust and scavenging ports uncovered by the piston and which use scavening air at the usual scavenging pressure, and whether or not such air also serves for super-charging, the scavenging is apt to be either imperfect or else wasteful of air, because of the shortness of the time available, and where such cylinders have also been served with air of higher pressure, for super-charging, the manner of introduction of the air for this purpose has not been such as appreciably to accelerate the scavenging nor be efficient for the scavenging purpose. According to my invention a limited injection of. air at an adequately high pressure is made to supplement a larger volume of air from a lower pressure source in such way as to clear the combustion space and particularly the upper part or clearance end thereof with unusual rapidity so that efiective scavenging is accomplished in spite of the high speed and large piston displacement and without excessive power cost for this work. This is accomplished by the provision of a source of air of considerably higher pressure than ordinarily used for scavenging, and of special scavenging ports for such high pressure air which are uncovered by the piston on its out or down stroke and which are disposed at an acute angle, pointing upward or toward the clearance space, the action of such ports being appropriately timed so that one or more high velocity jets issue therefrom coincidently with or during the flow of the normal or low pressure scavenging air, stimulating the movement of the latter, and at the same time, because of their acute angle, driving the combustion products from the upper part of the cylinder downwards toward the exhaust ports, the effect being generally equivalent to the use of a larger air volume from a single source of scavenging air at a pressure higher than that of the low-pressure air in this invention; but without the attendant expense incident to such larger quantity and higher pressure. Within the scope of the invention the same high pressure means can also be used for supercharging the engine when or if desired, as by appropriately designing the air admission timing.

Fig. 1 of the drawing is a more or less diagrammatic section of. an engine cylinder embodying one of the possible forms of the invention, at

present preferred, and Fig. 2 is a section on the line II-II of Fig. 1, showing also, in diagram, the air sup-ply sources for the high and low pressure ducts.

The engine cylinder I has exhaust discharge means in the form of a tier of ports 2 uncovered on the downstroke of the piston 3 and on the opposite side a series of admission ports for scavenging air, also uncovered by the piston, the engine being assumed to be of, the fuel injection type. As illustrated the normal scavenging ports are arranged in two tiers although this is by no means indispensable. The lower tier 4 is located to be uncovered by the piston after the exhaust port is open on the downward stroke, and the upper tier 5 is uncovered before the exhaust is opened and these ports are preferably controlled automatically, as by the pivoted louvers 6 or light and easily moved horizontally-pivoted vanes opening toward the cylinder whenever the pressure therein is less than that of the air on the outside of the louvers. Both tiers are supplied with scavenging air by a duct or receiver 1 which is connected with an appropriate source 8 of low pressure air, at say a pressure of one to three pounds above atmosphere. 7

A separate source 9, of air at a higher pressure say about six to eight pounds above atmosphere, supplies a duct or receiver l0 having a port or tier of ports H discharging into the cylinder in proximity to the lower pressure ports 6 and 5. The location of this discharge is subject to variation to suit conditions in hand, and, likewise, it may be controlled in any usual appropriate manner, as by the piston, or by timed or automatic valves. In the preferred embodiment however, the ports II are located in the opposite half of the cylinder from the exhaust port or ports 2 and above but adjacent the upper tier of scavenging ports 5, and formed at an angle with the cylinder axis more acute than that of the less inclined ports 5, so as to discharge toward the upper end of the cylinder, and their aggregate cross area-is materially less than that of the low pressure ports. For example, with high-pressure air at a pressure of between six and eight pounds the aggregate area of the high-pressure ports is usually about eight percent of that of the other ports. An automatic valve l2 (which may be like one of the louvers 6 previously described), opening toward the cylinder, when the pressure therein permits, is

illustrated as the means for controlling the high pressure air flow from duct l0, and when thus controlled the high pressure air ports discharge whenever their air supply pressure exceeds that within the cylinder, and some of the high pressure air in this case serves for super-charging. But while the exhaust port is open these jets serve for scavenging only and their efiicient action is the result not of their volume but of their velocity, and the fact that their path due to the velocity enables the air to reach and sweep the upper end of the cylinder, and to direct and stimulate the flow of the part of the air from ports 5 in a similar path. Accordingly, the amount of such higher-pressure air need be but small and, in any event, the power cost of producing it is more than compensated by the increased speed and thoroughness of the scavenging action, which results in increased capacity and better efficiency of the engine.

Although so illustrated, the invention is not limited to application to a single cylinder or any particular type of two-cycle engine and the ducts I and may therefore be understood as supplying high and low pressure air respectively to as many cylinders as may be desired.

Reference is made to Patent No. 1,978,816, October 30, 1934, issued on a co-pending application of mine.

It will be understood that my invention is not limited to the details of construction and operation described above and illustrated in the drawing except as appears hereinafter in the claims.

I claim:

1. The method of scavenging a two-cycle engine cylinder having overrun exhaust and scavenging ports which consists in coincidently directing low pressure air across the lower part of the cylinder and a smaller volume of air at higher pressure and velocity upwardly into the upper part of said cylinder, bothwhile the exhaust port is open and both from substantially the same part of the entrance side of the cylinder.

2. The method of scavenging a two-cycle engine cylinder having overrun exhaust and scavenging ports which consists in directing low pressure air into the lower part thereof and, simultaneously, a relatively small volume of air at high velocity upwardly toward the upper end of the cylinder, the point of entrance of the high velocity air into the cylinder being substantially above the entrance of the low pressure air.

3. The method of scavenging a two-cycle engine cylinder having overrun exhaust and scavenging ports which consists in coincidently directing low pressure air across the lower part of the cylinder and a smaller volume of air at higher pressure and velocity upwardly into the upper part of said cylinder, both while the exhaust port is open and both from the side of the cylinder opposite the exhaust port or ports.

4. scavenging means for a two-cycle engine cylinder comprising in combination with an exhaust port open when the piston is near the end of its outward stroke, one or more scavenging air ports uncovered by the piston in that position, one or more supplemental and upwardly directed air admission ports of less aggregate cross area, both said scavenging and supplemental air admission ports being at the opposite side of the cylinder from said exhaust port, and means to supply low and high pressure air for scavenging to said scavenging and supplemental ports respectively, the said high pressure air means supplying air through said supplemental port or ports during the discharge of air through said scavenging air port or ports.

5. scavenging means for a two-cycle engine cylinder comprising in combination with an exhaust port open when the piston is near the end of its outward stroke, a tier of scavenging air ports uncovered by the piston in that position, one or more supplemental and upwardly directed air admission ports of less aggregate cross area, sources of low and high pressure air connected respectively to said scavenging and supplemental ports and means for admitting the higher pressure air through said supplemental port or ports during the discharge of air through the other ports.

6. In a two-cycle internal combustion engine the combination of an exhaust port, an air admission port located to be uncovered by the piston after the exhaust port is opened and a source of supply of low pressure air connected to said admission port, a restricted air admission port, a source of higher pressure air, a duct connecting the same with said restricted port, the latter arranged at an angle so acute as to direct the high pressure air discharge towards the top of the cylinder and means for admitting the higher pressure air through said restricted port during the discharge of air through the first mentioned air port.

7. In a two-cycle internal combustion engine, the combination of an exhaust port, an air admission port located to be uncovered by the piston after the exhaust port is opened, a source of supply of low pressure air connected to said admission port, a second air admission port, located above the piston when the same is covering the exhaust port and in substantially the same angular position in the cylinder wall as the first mentioned air admission port, and a second source of air supply, of higher pressure, connected to said second port to supply scavenging air therethrough during the flow of low pressure air through the first mentioned air admission port, the second mentioned air admission port being of restricted cross-section so as to discharge a relatively small volume of air and so formed as to discharge the same towards the upper part of the cylinder.

8. In a two-cycle internal combustion engine, the combination of a source of low pressure air, a source of higher pressure air, a duct receiving air from the first of said sources and a duct receiving air from the second of said sources; a cylinder, a piston working therein and exhaust gas discharge means; a plurality of ports in the wall of the cylinder constituting outlets from the low pressure air duct and a plurality of ports in the cylinder wall constituting outlets from the high pressure air duct and discharging into the cylinder while said low pressure ports are discharging into the cylinder, the said high pressure ports being arranged to discharge into the cylinder above the piston when the latter is in the position, on its inward stroke, at which the outflow of exhaust gases ceases, and said low pressure ports being disposed to discharge their air toward the upper part of the cylinder and said high pressure ports being adapted to discharge their air at an angle with the cylinder axis more acute than that at which the low pressure ports discharge.

9. In a two-cycle internal combustion engine, the combination of an engine cylinder having an exhaust port in a side wall thereof to be covered and uncovered by the piston, an air admission port located to be uncovered by the piston before said exhaust port is opened, means to supply scavenging air to said air admission port, a second air admission port also located to be uncovered by the piston as the piston approaches the end of its combustion stroke, said second air admission port being arranged at an acute angle so as to direct the air entering therethrough to-

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