Lubrication system for an engine

A lubrication system for a small lightweight four-stroke engine is disclosed. The lubrication system, provided with a weight at one end of a flexible oil tube inserted into an oil reservoir, is capable of providing a sufficient lubrication to components of the engine which may operate in a horizontal posture, a vertical posture, or any posture therebetween.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a four-stroke internal combustion engine (ICE) and more particularly to an improved lubrication system for a small lightweight four-stroke engine.

2. Description of Related Art

Portable power tools such as lawn movers, line trimmers, chain saws were mostly powered by two-stroke ICEs in earlier days. Gradually, two-stroke engines were phased out due to heavy harmful exhaust emissions (e.g., hydrocarbon (HC)). Nowadays, almost all such portable power tools are powered by four-stroke ICEs.

Lubrication becomes a very serious problem since portable power tools are required to operate in a wide range of orientations (i.e., being tilted or even upside down). There have been numerous suggestions in prior patents for solving this problem. For example, U.S. Pat. No. 7,287,508 discloses an engine lubrication method which is incorporated herein by reference. Thus, continuing improvements in the exploitation of lubrication system for a small lightweight four-stroke engine are constantly being sought.

SUMMARY OF THE INVENTION

It is therefore one object of the invention to provide a lubrication system for a small lightweight four-stroke engine and the lubrication system, provided with a weight at one end of a flexible oil tube inserted into an oil reservoir, is capable of providing a sufficient lubrication to the engine which may operate in a horizontal posture, a vertical posture, or any posture therebetween.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1 to 10, a four-stroke internal combustion engine (ICE) in accordance with a preferred embodiment of the invention is shown. The engine is constructed as a lightweight housing and comprises the following components. Each component is discussed in detail below.

A crankcase10is provided. An oil reservoir30is provided. A check valve case20is provided in fluid communication with both the crankcase10and the oil reservoir30. A first branch tube60is in fluid communication with both the check valve case20and a gaseous oil tube42which is connected to a cam actuation section40. A first venturi61is provided proximate a joining portion of the cam actuation section40and the gaseous oil tube42. Note that the number of the first venturi61may be more than one depending on applications. A second branch tube70is provided between the crankcase10and a camshaft case41of the cam actuation section40and is in fluid communication therewith. A second venturi71is provided in the second branch tube70. The second branch tube70has a flexible oil tube73having a weight731at one end so that one end of the flexible oil tube73may be always immersed in the oil reservoir30, and a tubing member72connected to the flexible oil tube73and being in fluid communication therewith.

The crankcase10comprises a crank casing11formed with a cylinder block81which has a cylinder bore (not numbered) with a piston15slidably provided therein. A passage12is provided on the bottom of the crankcase10and is in fluid communication with the check valve case20. A crankshaft13, provided in the crankcase10, has two sets of bearings131and oil seals132at both ends. A connecting rod14is provided to interconnect the crankshaft13and the piston15.

The check valve case20is provided below the crankcase10. The check valve case20is connected to an oil mist return tube22which is extended from the bottom of the check valve case20into the oil reservoir30. A check valve21is provided in the check valve case20and has a retaining plate211and an elastic plate212being on the top surface of the retaining plate211. Oil mist from the crankcase10may deflect the elastic plate212to open the check valve21when the piston15moves downward. Hence, oil mist enters the check valve case20. Finally, oil mist flows to the oil reservoir30via the oil mist return tube22. At the same time, a small portion of oil mist enters the first branch tube60which is in fluid communication with the check valve case20(seeFIG. 3). To the contrary, the elastic plate212returns to its original position to block the check valve21when the piston15moves upward. Hence, oil mist is prevented from returning from the oil reservoir30to the crankcase10.

The oil reservoir30is provided below the check valve case20and is in fluid communication with the check valve case20via the oil mist return tube22. Liquid lubricating oil is filled in the oil reservoir30. The oil reservoir30has a volume larger than that of the check valve case20. Hence, flow rate of the oil mist may decrease greatly when it enter the oil reservoir30. As a result, heavy liquid oil particles in the oil mist fall into the oil reservoir30and light gaseous oil particles in the oil mist are accumulated on the oil level of the oil reservoir30. Further, gaseous oil may enter the gaseous oil tube42. An open end of the oil mist return tube22is provided above the center of the oil reservoir30.

The cam actuation section40comprises a lower camshaft case41and an upper space431. Two spaced ports432are provided between the camshaft case41and the space431. A pushing rod43passes through either port432. In addition to the pushing rods43, a camshaft44and a camshaft follower45are provided in the cam actuation section40. The camshaft44comprises a cam441and a reduction gear442coaxially and integrally formed therewith. The camshaft44and the camshaft follower45are engaged. The reduction gear442is in mesh with a lower gear46which is fixed in the crankshaft13. The cam actuation section40has a top end in fluid communication with a rocker arm case50and a bottom end provided with the gaseous oil tube42. The gaseous oil tube42has a bottom end disposed above the oil level of the oil reservoir30. Gaseous oil rather than liquid oil in the oil reservoir30may flow to the cam actuation section40via the gaseous oil tube42when the piston15moves downward. Oil mist in the camshaft case41is directed along an inner wall411of the camshaft case41to the ports432and a second branch tube inlet701when the reduction gear442rotates.

The engine may be implemented as an overhead valve (OHV) engine in the embodiment. Alternatively, the engine may be implemented as an overhead camshaft (OHC) engine equipped with a cam443, upper and lower pulleys444in which one of the pulleys444is secured to the cam443, and a belt47passing around the pulleys444in another embodiment (seeFIG. 10).

The rocker arm case50is provided in a plastic cylinder head cover80which is affixed to the cylinder block81. In the rocker arm case50a rocker arm mechanism51is provided. The rocker arm mechanism51comprises a rocker arm511, a valve512, and a compression spring513. The cam441may rotate to actuate the rocker arm mechanism51via the camshaft follower45and the pushing rods43.

A small portion of oil mist in the check valve case20enters the first venturi61via the first branch tube60. Liquid oil particles in the oil mist are nebulized by the first venturi61. As an end, oil mist with a small amount of liquid oil enters the camshaft case41.

The second branch tube70has a second branch tube inlet701provided in the camshaft case41near the port432. Excess oil mist in the cam actuation section40may enter the crankcase10via the second branch tube70when the piston15moves upward. As a result, excess oil mist and liquid oil are prevented from remaining in the cam actuation section40and the rocker arm case50. This has the benefit of reducing the consumption of lubricating oil.

The number of the second branch tube70may be more than one depending on applications. Excess oil mist enters the second branch tube70when the piston15moves upward. Also, lubricating oil in the oil reservoir30flows to the second branch tube70via the flexible oil tube73and the tubing member72. Oil mist in the second branch tube70and liquid oil in the tubing member72are mixed in the second venturi71. Further, the nebulized oil mist enters the crankcase10when the piston15moves upward.

An oil return section83is provided on the top of the cylinder head cover80and is separated from the rocker arm case50therebelow. The oil return section83comprises two oil return reservoirs831being in fluid communication with each other, and a plurality of channels832interconnecting the oil return section83and the rocker arm case50. Excess oil mist and liquid oil may enter at least one of the channels832irrespective of the posture of the engine (i.e., horizontal posture, vertical posture, or any posture therebetween). Therefore, the purpose of returning lubricating oil in the rocker arm case50can be achieved.

One end of the oil return section83is provided with an oil return line84which has one end in fluid communication with the crankcase10so that the oil return section83can communicate with the crankcase10. Excess oil mist and liquid oil in the rocker arm case50may return to the oil return section83via the channels832. Next, the excess oil mist and liquid oil are inhaled into the crankcase10via the oil return line84.

A liquid oil and gaseous oil separation chamber85is provided between the oil return section83and the rocker arm case50. A porous plate851for absorbing lubricating oil is provided on the top of the liquid oil and gaseous oil separation chamber85. A plurality of apertures852are provided on the bottom of the liquid oil and gaseous oil separation chamber85and are in fluid communication with the rocker arm case50. Thus, excess oil mist may enter the liquid oil and gaseous oil separation chamber85via the apertures852. Liquid oil particles in the oil mist are absorbed by the porous plate851. Next, the absorbed liquid oil is inhaled into the oil return section83via the channels832. Finally, it is sent to the crankcase10via the oil return line84. Gaseous oil is separated by the liquid oil and gaseous oil separation chamber85to form blow-by gas which is sent to an air filter (not shown) via a breather pipe86. Blowby gas with clean air passing through the air filter is inhaled into a combustion chamber87in an air intake cycle of the engine (seeFIG. 1). Finally, the blowby gas and clean air are consumed in the combustion cycle of the engine.

As shownFIG. 6, volume of the crankcase10is decreased when the piston15moves downward. And in turn, oil mist in the crankcase10enters the check valve case20. Diameter of the oil mist return tube22is much larger than that of the first branch tube60. Hence, a large portion of oil mist flows toward the oil reservoir30via the oil mist return tube22and only a small portion thereof flows to the first branch tube60. Liquid oil in the oil mist is formed after leaving the oil mist return tube22since the flow speed of the oil mist in the oil reservoir30decreases greatly. Hence, the heavy liquid oil drops into the oil reservoir30. Also, light gaseous oil is accumulated on the oil level of the oil reservoir30and is sent to the gaseous oil tube42. Also, oil mist may branch from the check valve case20to flow to the first venturi61via the first branch tube60. Oil mist is then mixed with gaseous oil sent from the gaseous oil tube42at the first venturi61. The nebulized lubricating oil mixture is sent to the cam actuation section40and the rocker arm case50in sequence for lubrication.

As shown inFIGS. 7,8, and9, volume of the crankcase10is increased when the piston15moves upward. And in turn, excess oil mist and liquid oil in the cam actuation section40are inhaled into the second branch tube70. Also, lubricating oil in the oil reservoir30is sucked into the flexible oil tube73. And in turn, lubricating oil flows to the second branch tube70via the tubing member72which is connected to the flexible oil tube73. Lubricating oil is nebulized in the second venturi71. The nebulized lubricating oil is then sent to the crankcase10. At the same time, oil mist and liquid oil in the rocker arm case50may enter the oil return reservoirs831via the channels832. All oil mist and liquid oil contained in the oil return section83will be inhaled into the oil return line84prior to entering the crankcase10.

Oil mist and liquid oil in the crankcase10will flow to the check valve case20when the piston15moves downward.