Blow-by Gas Recirculating Apparatus

The present invention relates to an apparatus for recirculating the blow-by gases in the crankcase of an internal combustion engine back to an air-mixture intake passage such as an intake manifold.

When the fuel is ignited and exploded in an engine combustion chamber, gases are produced therein and the pressure in the combustion chamber is increased. Some of the gases are forced under the increased pressure to flow through the gap between the piston and the cylinder wall into the crankcase. As this process is repeated during operation of the engine, these blow-by gases are accumulated to develop a high pressure in the crankcase and caused to leak between the crankcase and the oil pan into the atmosphere as undesired air pollutants.

To solve the above problem, there have been employed blow-by gas recirculating apparatus, known as a positive crankcase ventilation (PCV) system, for guiding unburned gases that have leaked into the crankcase back to the combustion chamber as blow-by gases and introducing air into the crankcase for crankcase ventilation.

Some blow-by gas recirculating apparatus include a breather chamber disposed in the cylinder head and connected to the air cleaner. During engine operation, air is supplied via the breather chamber into the crankcase.

In such blow-by gas recirculating apparatus, the pressure in the air cleaner is lower than that in the breather chamber while the engine is rotating at high speeds, causing blow-by gases to flow from the breather chamber into the air cleaner. The blow-by gases contain a large amount of oil mist as well as unburned gases, and such oil mist would be attached to the filter element in the air cleaner, thus contaminating the air filter.

U.S. Pat. No. 4,156,406 issued on May 29, 1979 discloses a gas-oil separator for separating oil and contaminants from gas-oil mixtures in an internal combustion engine. U.S. Pat. No. 4,345,573 issued on Aug. 24, 1982 discloses a blow-by gas treating and controlling system.

It is an object of the present invention to provide a blow-by gas recirculating apparatus including a breather chamber capable of separating gases including unburned gases from an oil mist.

According to the present invention, there is provided a blow-by gas recirculating apparatus for returning blow-by gases from the crankcase of an internal combustion engine to an intake passage thereof, the blow-by gas recirculating apparatus including a cylinder head, a cylinder head cover mounted on the engine cylinder head, a DOHC valve mechanism housed in the cylinder head, a shield panel attached to the cylinder head cover in substantially covering relation to the DOHC valve mechanism, and a breather chamber defined between the cylinder head cover and the shield panel and communicating with the interior of the cylinder head and an air intake unit, such as an air cleaner, of the internal combustion engine.

The breather chamber comprises first through third breather chamber sections interconnected by constricted passages. Therefore, while blow-by gases are flowing through the breather chamber, an oil mist can reliably be separated from the blow-by gases. Oil and gases including unburned gases can efficiently be separated even when the amount of blow-by gases is increased in case the engine of a larger displacement is employed. The breather chamber is relatively large in volume or capacity, and contains a gas layer. Therefore, it can minimize a temperature rise on the surface oaf the cylinder head cover, and sounds transmitted from the cylinder head can be attenuated by the gas layer in the breather chamber. The large-volume breather chamber is less subject to influences due to the temperature of the outer surface of the cylinder head cover. Even when the ambient air is of a low temperature, therefore, the passages in the breather chamber are less likely to be frozen. Where the cylinder head cover is formed of an aluminum alloy and the shield plate is formed of a steel sheet, the breather chamber can be kept at a high temperature by the difference between the heat capacities of these different materials. As a result, water and unburned fuel in the blow-by gases can be evaporated effectively for quick and reliable separation from the oil mist.

The above and another objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

FIG. 1 is a schematic front elevational view of an internal combustion engine incorporating a blow-by gas recirculating apparatus according to the present invention;

FIG. 2 is an enlarged longitudinal cross-sectional view of the engine shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along III--III of FIG. 2;

FIG. 4 is a cross-sectional view taken along IV--IV of FIG. 2;

FIG. 5 is a bottom view of a cylinder head cover of the engine of FIG. 1;

FIG. 6 is a plan view of a shield panel of the engine of FIG. 1;

FIG. 7 is a cross-sectional view taken along line VII--VII of FIG. 6; and

FIG. 8 is a cross-sectional view taken along line VIII--VIII of FIG. 6.

FIG. 1 schematically shows an internal combustion engine, generally denoted by the reference numeral 1, in which a blow-by gas recirculating apparatus of the invention is incorporated. The engine 1 has its cylinder axis N inclined to the vertical line. The engine 1 includes a crankcase 3 in which a crankshaft 2 is rotatably accommodated, an oil pan 4 attached to the bottom of the crankcase 3, a cylinder block 5 on the top of the crankcase 3, pistons 7 (only one shown in FIG. 1) slidably disposed in the cylinder block 5 and operatively connected to the crankshaft 2 by a connecting rod 6, a cylinder head 8 mounted on the upper end of the cylinder block 5, a cylinder head cover 9 mounted on the top of the cylinder head 8, and a valve mechanism 10 of the DOHC (double overhead cam) type housed in the cylinder head 8. The crankcase 3, the cylinder block 5, the cylinder head 8, and the cylinder head cover 9 are cast of an aluminum alloy.

An air cleaner case 11 is positioned upwardly and laterally of the engine 1. Fresh and cleaned air supplied from the air cleaner case 11 is delivered through an intake manifold 12 to combustion chambers 13 (only one shown in FIG. 1) in the engine 1. The air cleaner 11 is connected by a tube 16 to a breather chamber 15 of a relatively large volume or capacity defined longitudinally in the cylinder head cover 9 by a shield panel 14.

A trap chamber 17 is attached to a side of the crankcase 3. Upwardly from the trap chamber 17, there extends a blow-by gas supply pipe 18 connected to the intake manifold 12. The blow-by gas pipe 18 houses therein a PCV (positive crankcase ventilation) valve 19 for controlling the amount of blow-by gases supplied to the intake manifold 12 dependent on the difference between the pressure in the intake manifold 12 and the pressure in the crankcase 3.

When the engine 1 rotates in a low- or medium-speed range, the blow-by gases from the crankcase 3 and fresh air fed from the air cleaner case 11, as indicated by the arrow a, pass through the breather chamber 15 into the crankcase 3 and flow into the trap chamber 17 in which the oil mist is separated from the blow-by gases. Then, the blow-by gases flow through the PCV valve 19 into the intake manifold 12, in which the gases are mixed with an air-fuel mixture. The mixture is then supplied to the combustion chambers 13.

During high-speed rotation of the engine 1, vacuum is developed in the air cleaner case 11, and some of the blow-by gases in the crankcase 3 are forced to flow through the breather chamber 15 into the air cleaner case 11, as indicated by the arrow b.

FIGS. 2 through 4 illustrate the upper structure of the engine 1 in the cross section. The DOHC valve mechanism 10 includes two cam shafts 20 rotatably supported by respective bearings 21 in an upper portion of the cylinder head 8. The cam shafts 20 have one end disposed in a case 22 (FIG. 2) attached to an end of the engine 1. Gears 23 are fixedly mounted on the respective ends of the cam shafts 20 in the case 22. The gears 23 are operatively coupled by timing belts 24 to a gear (not shown) fixedly mounted on the crankshaft 2 so that the crankshaft 2 and the cam shafts 20 will rotate in synchronism. The cam shafts 20 have cam surfaces 20a slidably held against respective rocker arms 25 (FIG. 3) engaging the upper ends of valve stems 28 of valves 27 that are normally urged upwardly by respective springs 26. Therefore, the valves 27 are caused to be opened and closed in synchronism with rotation of the crankshaft 2. The valve mechanism 10 is composed primarily of the cam shafts 20, the rocker arms 25, the springs 26, and the valve stems 28.

The cylinder head 8 has a central array of tubular plug housings 30 in which respective ignition plugs 29 are disposed. The cylinder head cover 9 also has a central array of vertical plug access tubes 31 held in registry with the tubular plug housings 30, respectively.

The cylinder head cover 9 has an oil supply inlet 32 (FIG. 2) at one end remote from the case 22. The cylinder head cover 9 also has an integral rib or partition 33 projecting downwardly from the underside thereof. The shield panel 14 is held against the lower end of the rib 33 in covering relation to th valve mechanism 10.

The cylinder head cover 9 and the shield panel 14 which jointly define the breather chamber 15 will be described below in detail with reference to FIGS. 5 through 8.

As shown in FIG. 5, the plug access tubes 31 (there are four plug access tubes in the illustrated embodiment) are spaced longitudinally on the cylinder head cover 9. A rib 33 projecting downwardly from the inside of cover 9 includes an inner rib member 33a extending around the plug access tubes 31 and an outer rib member 33b extending around the inner member 33a in spaced relation thereto along the peripheral edge of the cylinder head cover 9. These inner and outer rub members 33a, 33b divide the breather chamber 15 into a first central breather chamber section 15a, a second side breather chamber section 15b, a third side breather chamber section 15c, and constricted passages 15d, 15e by which the first through third breather chamber sections 15a, 15b, 15c are interconnected. More specifically, the inner rib member 33a defines the first breather chamber section 15a therein, and the outer rib member 33b defines the second the third breather chamber sections 15b, 15c around the inner rib member 33c. The second and third breather chamber sections 15b, 15c are positioned one on each side of the first breather chamber section 15a. The rib 33 has threaded holes 34 in which screws (now shown) are threaded to attach the shield panel 14 to the rib 33. The outer rib member 33b has a hole 35 (also shown in FIG. 3) through which the third breather chamber section 15c communicates with the air cleaner case 12 via the tube 16.

FIGS. 6 through 8 illustrate the shield panel 14, which is formed of a steel sheet or the like. The shield panel 14 is of such a size as to cover about 80% of the entire area of the underside of the cylinder head cover 9. The shield panel 14 has attachment holes 36 registering with the threaded holes 34, respectively. The shield panel 14 includes a central portion 37 bulging downwardly to partly define the first breather chamber section 15a. The central bulging portion 37 has circular holes 38 defined at spaced intervals in its bottom for passage of the respective plug access tubes 31 of the cylinder head cover 9. The circular holes 38 have a diameter larger than the outside diameter of the plug access tubes 31. With the shield panel 14 attached to the cylinder head cover 9, there are gaps or clearances 39 (FIGS. 2 and 4) defined between the plug access tubes 31 and the edges of the circular holes 38. These gaps 39 provide communication between the breather chamber 15 and the interior of the cylinder head 8 in which the valve mechanism 10 is accommodated.

The shield panel 14 has a plurality of oil return holes 40 defined near one side thereof which is in the lowermost position when the engine 1 is mounted on an automobile (not shown) with its axis N inclined to the vertical line, as shown in FIG. 1. These oil return holes 40 are positioned in the second breather chamber section 15b. With the engine axis N inclined, the second breather chamber section 15b is in a lower position whereas the third breather chamber section 15c is in a higher position.

When the engine 1 rotates in a high-speed range, some of the blow-by gases in the crankcase 3 pass through the cylinder head 8 and the gaps 39 into the central section, i.e., the first breather chamber section 15a, of the breather chamber 15. The blow-by gases then flow from the first breather chamber section 15a to the constricted passage 15d to the second breather chamber section 15b to the constricted passage 15e to the third breather chamber section 15c, from which the blow-by gases flow through the hole 35 and the tube 16 into the air cleaner 11.

While the blow-by gases are passing through the breather chamber sections 15a, 15b, 15c and the constricted passages 15d, 15e, they are repeatedly expanded and compressed, and flow at different speeds, i.e., at a high speed in the constricted passages 15d, 15e and at a low speed downstream of the constricted passages 15d, 15e. Therefore, an oil mist is reliably separated from the blow-by gases while they are flowing through the breather chamber 15. The blow-by gases from which the oil mist has been removed are then introduced into the air cleaner case 11.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.