Internal Combustion Engine With Vented Piston Clearance Spaces And Method

Abstract

An internal combustion engine is provided with pistons having vent openings connecting the space between the first and second piston rings with the engine crankcase so as to vent to the crankcase hydrocarbon-rich gases which escape from the combustion chamber past the first piston ring. This method of venting the clearance space has been shown to reduce hydrocarbon emissions in some instances.

Description

BACKGROUND OF THE INVENTION

This invention relates to piston type internal combustion engines and more particularly to methods and means of venting the clearance spaces below the top compression rings for the purpose of reducing hydrocarbon emissions in such engines.

U.S. Pat. No. 3,335,643 Wentworth discloses the part that the crevice volumes beside and behind the top piston ring are believed to play in adding to the emission of unburned hydrocarbons in the exhaust gases of spark ignition internal combustion engines. Further discussion of these concepts is found in Society of Automotive Engineers, Paper No. 680,109 presented during the meeting of Jan. 8 th through 12 th, 1968. In paper it is hypothesized that unburned hydrocarbons entering the clearance space between the first and second compression rings of an engine piston are in part expanded back into the associated combustion chamber during lower pressure portions of its working cycle and some of these unburned hydrocarbons are swept out with the exhaust gases. While this is but one possible explanation of the observed effects, it seems likely that crevice volume effects contribute in some degree to the hydrocarbon emissions of most, if not all, gasoline fueled piston type internal combustion engines.

SUMMARY OF THE INVENTION

This invention proposes a method and means for reducing hydrocarbon emissions in the exhaust gases of internal combustion engines by venting the clearance space between the first and second compression rings of the engine pistons to a low pressure location, preferably the engine crankcase. Tests of this method in gasoline fueled four stroke spark ignition engines have in some cases shown substantial reductions in exhaust hydrocarbon emissions. These reductions are thought to result from a change in the action of unburned hydrocarbon-rich gases entering the clearance space between the first and second piston rings, which are vented into the crankcase and prevented from building up a pressure between the rings so that the re-expansion of such unburned hydrocarbons back into the combustion chamber at a later part of the cycle is avoided. Also, any increase in piston blowby which results from such venting is likely to result in residual exhaust products entering the clearance space between the rings toward the end of each combustion chamber expansion phase, sweeping out most of the unburned hydrocarbon-rich gases and leaving little to be returned to the combustion chamber on the expansion and exhaust strokes of the piston.

Further objects and advantages of the invention will be more clearly understood from the following description of a preferred embodiment taken together with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a fragmentary cross-sectional view of a four stroke gasoline fueled internal combustion engine of generally conventional construction but including pistons having venting means formed according to the invention,

FIG. 2 is an enlarged cross-sectional view showing more clearly the construction of the piston and venting means of FIG. 1 and

FIG. 3 is a side view taken generally in the plane indicated by the line 3--3 of FIG. 2 as viewed in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring in detail to the drawing, numeral 10 generally indicates a four stroke gasoline fueled internal combustion engine which is of the conventional V type but could equally well be of any other known cylinder arrangement. Engine 10 includes a cylinder block 12 having a plurality of cylinders 14 integrally formed therein and only one of which is illustrated.

Within each of the cylinders is a piston 16 connected by a connecting rod 18 with a throw 20 of crankshaft 22 which is rotatably supported by the cylinder block 12. The crankshaft is enclosed within the engine crankcase cavity 24, which is formed by the cylinder block 12 and oil pan 26 and connects with the lower open ends of the cylinders 14.

The upper ends of the cylinders 14 are closed by a conventional cylinder head 28 which coacts with the cylinders and pistons to define combustion chambers 30. Cylinder head 28 includes the usual intake ports and valves, not shown, as well as exhaust ports 32 and valves 34 to provide for the admission of fuel-air mixture to the combustion chambers and the discharge of exhaust products from the combustion chambers at the appropriate phases of each combustion chamber cycle. The valves are actuated by conventional valve gear such as rocker arms 36, push rods 38 and hydraulic lifters 40, all driven by a camshaft 42 carried in the cylinder block. Conventional coil springs 44 are used to seat the valves.

As best shown in FIGS. 2 and 3, the piston 16 includes integrally cast crown and skirt portions 46 and 48, respectively, joined by a thickened ring belt section 50. First, second and third axially spaced piston ring grooves 52, 54 and 56 are machined into the outer surface of the piston ring belt section adjacent the crown, leaving an ungrooved top land 58 with progressively smaller second and third lands 60, 62 between the various grooves. Within the first and second ring grooves 52, 54 are carried first and second compression rings 64 and 66, respectively, each of which are discontinuous at the usual end gaps 68. In the third ring groove 56 there is retained a conventional spring loaded rail type side sealing oil control ring 70 which engages the walls of cylinder 14 and acts to scrape oil from them in the usual manner. A plurality of radial oil drain holes 72 are provided in the piston, connecting the base of the third ring groove 56 with the piston interior which is open to the engine crankcase 24 and thus provides for the direct return to the crankcase of oil scraped from the cylinder walls by the oil ring 70.

The upper, ring belt, portion of the piston is smaller is diameter than the cylinder 14 so that a measurable clearance 74 exists between them. Since the piston rings 64, 66, 70 engage the cylinder wall, they coact with the piston and cylinder surfaces to enclose a first annular clearance space 76 between the first and second piston rings and a second annular clearance space 78 between the second compression ring and the oil ring 70. These annular clearance spaces are connected to the combustion chamber 30 by restricted flow paths through the end gaps 68 of the two compression rings as well as by very small leakage paths across the faces of these rings. The above described construction is conventional and is like that commonly used in current automotive engine practice.

The present invention differs from previous practice in the provision of means to vent the first annular clearance space 76 to a low pressure location. In the preferred embodiment disclosed, the clearance space is vented to the engine crankcase 24 by a pair of oppositely disposed drilled passages 80 which extend radially through the second ring land 60 and the ring belt section 50 so as to connect the clearance space 76 with the interior of the piston 16. Two passages 80 are provided on opposite sides of the piston so that if one of the passages is blocked by the movement of the piston outer diameter into engagement with the cylinder wall, the other passage will be spaced from the cylinder wall and open by reason of the differing diameters of the piston and cylinder.

With this arrangement the hydrocarbon-rich gases which escape from the combustion chamber past the top ring 64, either through the ring gap 68 or otherwise, are allowed to pass through passages 80 to the engine crankcase without building up a substantial pressure in the clearance space 76. This also prevents the build up of substantial pressures in the second annular clearance space 62.

Thus, it is thought that as pressures build up in the combustion chamber, on the compression stroke of the piston and continuing into the combustion phase of the expansion stroke, gases pass from the combustion chamber to the clearance space and are vented to the crankcase through the openings 80. In all likelihood, the gases entering the clearance space toward the end of each such period include substantial amounts of combustion products and thus have lower percentages of unburned hydrocarbons than the gases received earlier in each period. Thus, when the pressure in the combustion chamber is reduced during the latter portion of the expansion stroke and the beginning of the exhaust stroke, the pressure in the first annular clearance space is sufficiently low so as not to cause substantial return of the gases therein back to the combustion chamber. Furthermore, to the extent that there is some return of gases, these are not likely to be particularly rich in hydrocarbons. It is believed that in this way the venting of the first annular clearance space under the top ring causes reductions in hydrocarbon rich gases returned to the cylinder and a reduction in hydrocarbon emissions in the engine exhaust.

Whatever the mechanism by which the results are obtained, substantial reductions in exhaust emissions of hydrocarbons, averaging 16 percent in one instance, were obtained in actual vehicle tests using a production engine with the pistons modified as shown in the drawings. In other tests with different engines and under varying conditions, results varied from no change up to a 30 percent reduction in hydrocarbon emissions. Thus significant reductions are obtainable in certain instances but it would presently require engine testing to determine applicability to a particular engine design.

While the disclosed embodiment illustrates the continuous venting of the annular clearance space under the top ring groove directly to the engine crankcase, it should be obvious that many variations both in structure and in function are possible within the scope of the teachings presented herein. For example, the vent openings could be fitted with one-way valves or they could be arranged for coaction between the cylinder and the piston so that the vents were open only during certain portions of the piston travel. Some such arrangements have been tried with varying degrees of success. It is important, however, that whatever mechanism is used that it operate primarily to bleed gases from the clearance space into the engine crankcase and not provide a path through which substantial amounts of crankcase gases are drawn into the engine combustion chamber on the intake stroke, as this would undoubtedly result in excessive consumption of lubricating oil. While this factor may have an effect on the type and location of piston vent openings selected for a particular engine, the tests of the disclosed preferred embodiment did not show significant oil consumption problems.

Claims

We claim:

1. The method of reducing hydrocarbon emissions in the exhaust gases of a piston type four stroke non-rotary spark ignition internal combustion engine, said method including the step of directly venting to the engine crankcase the clearance space between the top and second piston rings of each engine piston during at least the latter part of the high pressure portions of each cycle of its respective combustion chamber, said venting step being accomplished without increasing the leakage path past the top piston ring and being characterized by the expulsion to the crankcase of a sufficient portion of the blowby gases entering said clearance space to prevent retention in said clearance space during the expansion and exhaust strokes of gas pressure significantly higher than that in the adjacent combustion chamber.

2. The method of claim 1 wherein said step of venting to the crankcase is performed continuously during engine operation.

3. The method of claim 2 wherein said venting of each said clearance space occurs through passage means provided in the wall of each piston at its second piston ring land.

4. In combination with a four stroke non-rotary spark ignition internal combustion engine having a crankcase, a plurality of cylinders having one of their ends open to the crankcase and closed at their other ends, pistons in the cylinders defining combustion chambers at the closed ends thereof and separating the combustion chambers from the crankcase and means permitting the cyclic admission of air and fuel to the combustion chambers and the discharge of exhaust gases therefrom said pistons each carrying first and second axially spaced gas sealing piston rings engaging said cylinder and defining a clearance space between said rings and between said piston and cylinder, each said first piston ring being disposed between a clearance space and a combustion chamber and having an end gas permitting limited passage of gas therethrough between each said combustion chamber and its respective clearance space and vent means through a wall of said piston and directly communicating said clearance space with the engine crankcase at least during the latter parts of the high pressure portions of the combustion chamber working cycle without increasing the gas leakage path past said first piston ring to said clearance space, said vent means being capable of expelling to said crankcase a sufficient portion of the gas entering said clearance space to prevent retention therein during the expansion and exhaust strokes of gas pressure significantly higher than in the adjacent combustion chamber.

5. The combination of claim 4 wherein said vent means comprise passage means extending radially through the piston wall between said first and second piston rings.

6. The combination of claim 5 wherein said vent means further comprise two of said passage means disposed on opposite sides of the piston.