Lubricating System for a Two-Stroke Engine

Abstract

A lubricating system for a two-stroke engine is provided in which oil is more reliably pumped into the two-stroke engine. The oil travels through passages that are integrally cast into the cylinder and/or crankcase. The oil may be injected directly into the crankcase chamber or intake passage. The oil pump may be a rotary pump mounted on the crankcase concentric to the crankshaft. It is also possible to not use an oil pump, and have the oil drawn into the engine by vacuum created in the crankcase.

Description

This patent application claims the benefit of and priority of U.S. Provisional Patent Application Ser. No. 61/326,662, entitled “Lubricating. System for a Two Stroke Engine” by Nagesh Mavinahally, David Kostka, and Bernardo Herzer, filed on Apr. 22, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an internal combustion engine. In particular it pertains to a lubricating system for two stroke or two cycle engines.

2. Description of the Related Art

Conventional low cost two stroke engines, particularly the ones used in lawn and garden applications typically mix lubricating oil with the fuel to lubricate the internal parts of the engine. The disadvantage with pre-mixing is that the ratio of fuel to oil is very much dependent on the manufacturer, duty cycle of the engine, and model of the equipment. Having to use different ratios for different engines/models can confuse the user as to how much oil has to be mixed with the fuel. Secondly, if the ratio of fuel to oil is not correct the engine will either be overly lubricated or under lubricated, both of which are detrimental. A separate lubrication pump which eliminates the need for pre-mixing the oil with the fuel is known to be used in more expensive two-stroke engines, such as motorcycles and in some lawn and garden equipment, such as Mitsubishi's 23 cc trimmer engine. The disadvantage with current systems are that external fittings and hoses are used to inject oil into the intake manifold, which can leak oil at the hose or fitting junctions and add cost to the equipment because of additional parts. Also, in existing designs, the oil pump is driven by gears and the pump has a reciprocating plunger, which adds additional components and cost.

SUMMARY OF THE INVENTION

A new and improved method of lubricating engines is described in this invention. In an embodiment, the improved lubricating engine is applied to a hand-held gaseous fueled two-stroke engines, and lawn and garden engines in general.

The design described here eliminates the disadvantages of the current systems by not having external hoses, fewer parts, and therefore lowers the cost and increases the robustness of the lubrication system. In one of the embodiments, the oil passages from the oil tank to the oil pump and from pump to the engine (into intake passage or crankcase) are integrally cast into the cylinder and crankcase, thus eliminating the external oil pipes/hoses. In another embodiment, the oil pump is a rotary pump mounted on the crankcase concentric to the crankshaft. In yet another embodiment, there is no oil pump, the oil is drawn into the engine by vacuum created in the crankcase during the engine operating cycle.

The improved two stroke engine is especially well suited for hand held, lawn and garden equipment such as trimmers, blowers, chainsaws, generator engines, and mopeds.

The present invention reduces the number of parts and reduces the potential for oil leaks between the joints, particularly in the oil supply line, where the pressure is higher than atmospheric. The additional improvement to the oil pump design simplifies the construction and operation of the pump by driving the oil pump directly without the need for intermediate gears between the drive shaft (crankshaft) and the driven shaft (in the oil pump), or in the last embodiment, the elimination of the pump entirely.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the advantages thereof will be readily obtained as the same becomes better understood by reference to the detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 shows the front view of an embodiment of the engine with a front mounted oil pump.

FIG. 2 shows the top sectional view of an embodiment of the engine's crankcase, crankshaft, and the oil pump.

FIG. 3 shows the sectional side view of an embodiment of the engine having direct crankcase oil injection.

FIG. 4 shows the sectional side view of an embodiment of the engine having oil injection into intake passage.

FIG. 5 shows the sectional side of an embodiment of the engine having an oil pump concentrically driven off of the crankshaft.

FIG. 6 shows a Gerotor pump as an example of a rotary pump that may be used on an engine.

FIG. 7 shows the sectional side view of an embodiment of an engine having no oil pump but rather, a means for crankcase vacuum to draw the oil into the engine.

FIG. 8 shows an embodiment of an engine with an oil reservoir integral with the plastic housing.

FIG. 9 shows an embodiment of an engine with an oil reservoir integral with the flywheel housing.

DETAILED DESCRIPTION

FIG. 1 is an embodiment of the present invention. FIG. 1 shows an oil injected two-stroke engine 200 having an oil tank 220, and an oil pump 210 mounted on to the side of the crankcase 242 by screws. The pump 210 has a gear 212 and is driven by the crankshaft 208 having a gear 214. The gears 212 and 214 can be of pinion and worm type or any other type. The two-stroke engine 200 can be a liquid or gaseous fueled engine. The engine 200 has a cylinder 204, crankshaft 208, and intake manifold 218. The rest of the parts necessary for operation of the two-stroke engine, such as piston, connecting rod, muffler, fuel metering device, etc are very much similar to any two-stroke engine and can be constructed by anyone skilled in the art. The oil supply line 226 from the oil reservoir 220 feeds into the oil pump 210. The oil pump 210 may have an oil return line, not shown here, to return excess oil back into the oil reservoir 220.

FIG. 2 shows the partial top sectional view of the oil injected engine from FIG. 1, having an oil pump 210 injecting oil directly into the crankcase chamber 234. Also shown is the oil pump drive gear 214 which is located concentrically on the crankshaft 208. The oil supply passage 226 from the oil tank to the oil pump, which is cast integrally into the crankcase 242, is shown.

FIG. 3 shows an embodiment of the sectional side views of the engine from FIG. 1, showing the oil passage 224 in the oil pump 210 and the oil passage 227 in the crankcase 242. The oil passage 224 227 from the pump to the crankcase chamber 234 has a check valve 231. The check valve 231 has a spring 232 and a valve 230. The check valve is a one way valve allowing the oil to flow into the crankcase chamber 234, while preventing the crankcase gases from entering the oil pump 210. It also prevents the flow of oil into the crankcase when the engine is not operating. The spring loaded valve shown here is an example of a one way valve. It is understood there are many different types of check valves. Another example is a duck bill valve as used in many carburetors or fuel caps. It is shown in FIGS. 2 and 3 that the length of the oil passage from the oil pump 210 to the crankcase chamber 234 is very short and the passage 227 in the crankcase is directly in line with the outlet passage 224 in the pump 210. Also, it is shown that the oil supply line 226 from the oil reservoir 220 to the oil pump 210 is through a cast passage 226 in the crankcase 242. However, depending on the location of the oil reservoir, a portion of the cast passage 226 can be in the cylinder 204.

FIG. 4 shows another embodiment of the invention where the oil is injected into the intake passage 230. The construction of the engine 300 is similar to the engine of FIG. 3, however, the oil passage 222 from the pump to the intake passage 230 terminates at orifice 228 in the intake passage 230. A portion of the cast passage 222 could be in the crankcase 242 and another portion be in the cylinder 204.

FIG. 5 shows an engine 400 which is another embodiment where the oil pump 330 has a wobble plate or screw 314 concentrically mounted on the crankshaft 208. The oil pump 330 may have more than one wobble plate or teeth on the screw. Deeply cut grooves in place of wobble plates or screw teeth on the crankshaft 208 may also be used as a pump. The oil pump 330 has an oil inlet 326, which can be a cast passage. A check valve 331 may be integrated into the passage 326 or into the inlet to the pump 329. The outlet passage 324 from the oil pump 330 may feed the oil directly into the crankcase chamber 234 through passageway 229 and another check valve 332 at the outlet.

FIG. 6 shows an end view of a gerotor type pump which is yet another pump type that may be used in the embodiment depicted in FIG. 5.

All of the embodiments depicted in FIGS. 1 through 6 use pumps of the positive displacement type, and any type of pump may be used and deemed to be in the spirit and scope of the invention.

FIG. 7 shows another embodiment of an engine. FIG. 7 shows a partial cutaway of a two stroke engine 500 which lubricates the engine without the use of a pump. The system operates by making use of the alternating pressure and vacuum pulses present in the crankcase chamber 234 caused by the reciprocating action of the piston when the engine is operating. Oil is fed from a reservoir mounted on or integral to the engine through passageway 326 until it contacts the crankshaft at orifice 502. The orifice in the crankcase casting 502 is sized according to the oil requirements of the engine. Another passage in the crankshaft 501 connects to the orifice 502 and passageway 326 at preselected degrees of crankshaft rotation so that the flow of oil from the reservoir is connected to the crankcase chamber 234 when a vacuum is present in the crankcase chamber 234. At the exit of passageway 501 is a check valve assembly 531 consisting of a check ball 530, a spring 532 and a hollow retaining plug 533. The purpose of the check valve is to close the passageway when the engine is not operating. When the engine is operating and the crankshaft 208 is spinning, centrifugal force will cause the ball to retract from the seat in the passageway and flow of oil into the engine will be unobstructed. It is to be noted that the orientation of the exit of the passageway 501 allows centrifugal force to aid in the flow of oil during operation of the engine. With this invention it is also possible to vary the oil delivery rate to the engine according to it's needs by the size of the orifice 502, the timing and duration that the orifice 502 is making a connective path between passageways 326 and 501, and by the distance of the exit of passageway 501 from the rotational centerline of the crankshaft 208 thus affecting the amount of centrifugal force acting to aid the flow.

In another embodiment, as shown in FIG. 8, it may be preferable to have the oil reservoir 220 be an integral part of the plastic housing 410 of the small engine. The oil reservoir may also be integral part of the aluminum casting, such as crankcase or flywheel housing 412, as shown in FIG. 9. The oil reservoir may also be in the front on the front crankcase.

In FIGS. 8 and 9, it is preferable to have the shape of the reservoir 220 as a hemispherical doughnut such that the oil filter 252 is immersed in the oil at all attitudes. Secondly, the oil supply line 250 inside the oil reservoir 220 is flexible such that it is free to rotate and bend to keep the oil filter 252 in downward position at all attitudes of the engine, including but not limited to inverted attitude. That is, the flywheel housing 412 is in upward attitude. The shape of the oil reservoir 220 could also be spherical.

Operation

In a pre-mixed fuel, as in a conventional low cost two-stroke engine, the fuel-oil mixture and air is inducted into the crankcase chamber 234 and the oil present in the mixture lubricates the internal parts of the engine, mainly the bearings, the piston and the cylinder. The oil present in the mixture, is eventually burned with the fuel in the combustion chamber. The ratio of fuel to oil is dependent on the engine manufacturer and ranges anywhere from 20:1 to 50:1, which is quite a range and as such if the user mixes 50:1 oil in an engine that requires 20:1 ratio, the engine could easily starve for oil and lead to severe damage. On the other hand excessive oil in the fuel could build up carbon in the engine, particularly in combustion chamber and exhaust ports and lead to poor performance of the engines, and also require frequent removal of carbon build up in the engine. Also in engines equipped with an exhaust catalyst for the purpose of reducing harmful exhaust emissions, the catalyst can become damaged.

In an embodiment of the present invention, the lubricating oil is stored in an oil reservoir and with the injection of oil directly into the crankcase chamber, the time taken for purging the system, particularly when the oil is refilled into a completely empty reservoir, is very short and helps lubricate the engine quickly and prevent any damage that could potentially occur to the engine when a longer oil passage is used.

Therefore there are several significant advantages in using the new oil injected lubricating system in a two-stroke engine. The main advantages in oil injected two-stroke engines are: 1) The consumer does not have to worry about ratio of oil to fuel. 2) Any type of fuel can be used, including but not limited to LPG fuel. 3) The shape of the oil reservoir lets the user operate the engine in any attitude. 4) Internal cast passages eliminate potential leaks and extra parts. 5) Direct injection of oil into the crankcase purges the passage faster. 6) Integral oil tank eliminates extra parts (oil reservoir and fasteners). 7) Internal passages help warm the oil temperature and maintain the optimum viscosity of oil as it enters the crankcase chamber, at very cold ambient temperatures.

The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. While there have been described herein, what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Claims

1. (canceled)

2. A lubricating system for a two stroke engine comprising:

an oil pump mounted to the side of the crankcase of said two stroke engine;

an oil reservoir and oil supply passage from said oil reservoir to said oil pump, and

an oil outlet passage of said oil pump for the injection of oil from said oil pump into said crankcase, wherein said oil outlet passage is cast integrally into the crankcase.

3. The lubricating system of claim 2 further comprising an oil pump drive gear of said oil pump located concentrically on the crankshaft.

4. The lubricating system of claim 2 wherein said oil outlet passage of said oil pump injects oil into a crankcase chamber of said crankcase.

5. The lubricating system of claim 4 wherein said oil outlet passage of said oil pump is directly in line with a crankcase chamber inlet passage of said crankcase chamber.

6. The lubricating system of claim 4 further comprising a check valve for allowing one way flow of oil from said oil pump into said crankcase chamber.

7. The lubricating system of claim 2 wherein said oil outlet passage of said oil pump injects oil into an air/fuel intake port of said crankcase through an internally cast oil passage.

8. The lubricating system of claim 2 wherein said oil passage from said oil reservoir to said oil pump is cast integrally into said crankcase.

9. The lubricating system of claim 2 wherein said oil reservoir is shaped in a spherical to semi-spherical fashion with an oil supply line, that has an oil filter at the end, is inside said oil reservoir and said oil supply line is free to rotate, whereby said oil filter is kept immersed in the oil at all attitudes.

10. A lubricating system for a two stroke engine comprising:

a rotary oil pump concentrically mounted on a crankshaft of said engine;

an oil reservoir;

an oil supply passage from said oil reservoir to said rotary oil pump; and

an outlet passage from said oil pump to feed oil directly into a crankcase chamber of said crankcase.

11. The lubricating system of claim 10 further comprising of a check valve integrated into said oil supply passage.

12. The lubricating system of claim 10 further comprising of a check valve integrated into said outlet passage from said oil pump to said crankcase chamber.

13. The lubricating system of claim 10 wherein said rotary oil pump is a gerotor type pump.

14. The lubricating system of claim 10 wherein said oil reservoir is shaped in a spherical to semi-spherical fashion with an oil supply line, that has an oil filter at the end, is inside said oil reservoir and said oil supply line is free to rotate, whereby said oil filter is kept immersed in the oil at all attitudes.

15. A lubricating system for a two stroke engine comprising:

an oil reservoir;

an oil supply passage from said oil reservoir to a crankshaft of said engine, wherein said oil supply passage is cast integrally into a crankcase of said engine and said oil supply passage terminates at a oil supply passage ending orifice; and

a crankshaft passage within said crankcase, beginning at a crankshaft passage beginning orifice and terminating into a crankcase chamber of said crankcase, wherein said oil supply passage ending orifice connects to crankshaft passage beginning orifice at preselected degrees of crankshaft rotation such that the flow of oil from said oil reservoir into said crankcase chamber occurs through the presence of a vacuum in said crankcase chamber.

16. The lubricating system of claim 15 further comprising of a check valve at the exit of said crankshaft passage to close said crankshaft passage when said engine is not operating.

17. The lubricating system of claim 16 wherein said check valve is comprised of a checkball, a spring, and a hollow retaining plug, such that when said engine is operating and said crankshaft is spinning, centrifugal force causes the ball to retract from its seat in said crankshaft passage, unobstructing the flow of oil into said engine.

18. The lubricating system of claim 15 wherein said oil reservoir is shaped in a spherical to semi-spherical fashion with an oil supply line, that has an oil filter at the end, is inside said oil reservoir and said oil supply line is free to rotate, whereby said oil filter is kept immersed in the oil at all attitudes.