US2818052A

US2818052A - Crankcase ventilating system for internal combustion engines

Info

Publication number: US2818052A
Application number: US608501A
Authority: US
Inventors: Jr Horace G Trainer
Original assignee: International Harverster Corp
Current assignee: Navistar Inc
Priority date: 1956-09-07
Filing date: 1956-09-07
Publication date: 1957-12-31
Anticipated expiration: 1974-12-31

Description

Dec. 31, 1957 H. e. TRAINER, JR 2,813,052

CRANKCASE VENTILATING SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed Sept. 7, 1956 67466 6'. Pain; /5:

PQMLQ United States Patent 'CRANKCASE VENTILATING SYSTEM FOR INTERNAL COMBUSTION ENGINES Horace G. Trainer, In, Fort Wayne, Ind., assignor to International Harvester Company, a corporation of New Jersey Application September 7, 1956, Serial No. 608,501

9 Claims. (Cl. 123-119) This invention relates to internal combustion engines and more particularly to a new and improved system for continuously and efiiciently maintaining the crankcase and other mechanism compartments in communication therewith free of blow by gases or vapors under all load and speed operating conditions of the engine.

It is well established that if the blow by gas or vapor such as water and unburned fuel entering the lubricating oil containing crankcase and other mechanism compartments in communication therewith during the operation of the engine by leakage pass the cylinders is not continually removed the lubricating oil will become contaminated by dilution. To obviate this undesirable condition most present day engines are provided with ventilating or scavenging means for passing air through the engine crankcase to remove the oil diluence therefrom. Generally the current of air is developed by establishing communication between the crankcase interior and a source of vacuum or sub-atmospheric pressure and is usually accomplished by utilizing the suction existing in the engine intake manifold or the carburetor air intake whereby the condensible vapors which would otherwise dilute the oil are withdrawn from the crankcase.

In the majority of crankcase ventilating systems it has been practically impossible to insure a desired adequate flow of air through the crankcase under all conditions of engine operation since the volume of air flowing therethrough depends on the suction developed by the engine which in turn is proportional to the load and speed of the engine which are extremely variable. As stated hereinbefore, most common crankcase ventilating systems employ a conduit or duct leading from the engine crankcase to a point on the engine where the vacuum is greatest throughout the operating range of the engine. Such point of greatest vacuum in gasoline engines having a charge forming device or carburetor utilizing a throttle valve for regulating a quantity of combustible mixture delivered to the intake manifold is in the intake manifold or car-.

lburetor on the engine side of the throttle valve. When .an engine of the type to which the present invention pertains is running at idling speed and minimum load with the throttle valve in its closed or substantially closed position, the vacuum developed in the conduit down stream of the throttle valve is at its maximum value. However, during this phase of engine operation minimum leakage of gases and vapors from between the pistons and cylinder walls is experienced. Conversely, as the throttle valve is moved to its fully opened position as when the engine is operating under full load or the speed is increased the air pressure in the conduit leading from the carburetor to the engine approaches atmospheric pressure and at the same time the volume of blow by gases and vapors emitted into the crankcase chamber is increased. Thus it will be appreciated in prior crankcase ventilating systems of the type incorporating a connection between the engine crankcase chamber and the intake manifold which depend upon the difference in pressure between the .crankcase chamber and the intake manifold to maintain a circulation of gases and air from the crankcase chamber a serious problem exists. An efficient crankcase ventilating system should be one capable of circulating a sutficient amount of air through the crankcase chamber to insure adequate ventilation thereof when the blow by gases emitted to the crankcase is at a maximum as when the engine is operating under full load wide open throttle. However, since the amount of scavenging air flowing through the crankcase is dependent upon the differential in pressure between the crankcase chamber and the intake manifold as well as the cross-sectional area of the conduit interconnecting the intake and manifold crankcase chamber the conduit must be relatively large to compensate for the small differential in pressure at wide open throttle. In other words the conducting capacity of the passage or conduit connecting the crankcase chamber to the engine intake manifold should be great enough to accommodate the maximum volume of blow by gases as when the engine is operating at wide open throttle at full load when the vacuum condition in the intake manifold is lowest. However, inasmuch as the conducting capacity of the conduit depends upon the pressure differential between the intake manifold and the crankcase chamber and the cross-sectional area of the conduit, it will be appreciated that a conduit having relatively large cross-sectional area is required. By providing the proper size conduit in prior ventilating systems to insure adequate ventilation of the crankcase at wide open throttle the volume of air flowing through the crankcase at idle and low speed during which phase of engine operation the vacuum is at a maximum in the intake manifold and the resultant volume of air flowing through the conduit is very much greater than is necessary to adequately ventilate the crankcase. Thus, an unnecessary load on the air cleaning equipment is created and furthermore this very high volume of air injected into the engine intake manifold represents such a large percentage of the total air delivered to the engine as to seriously upset the performance and efficiency characteristics at the idle and in a lower load and speed ranges. By the same token, if the conducting capacity of the passage or conduit between the crankcase chamber and the intake manifold is reduced in cross-sectional area to a value where the total amount of air or gases that are drawn into the engine intake manifold from the crankcase chamber at idle or low load does not materially affect the engine operating characteristics the capacity of the ventilating system will usually be far too small to handle the high volume of blow by gases and efiiciently ventilate the crankcase chamber at high load or high speed when a diflerence in pressure between the two chambers is lowest. It is therefore the primary objective of the present invention to provide a crankcase ventilating system capable of rapidly moving blow by gases from the crankcase chamber and other mechanism chambers or compartments in communication therewith and to supply a continuous flow of fresh air through the crankcase which flow of fresh air is maintained throughout the entire operating range of the engine without adversely affecting the operating characteristics of the engine and without creating an unnecessary load on the air cleaning equipment.

It is another object of the invention to utilize two sources of vacuum for drawing the blow by gases or vapors from the engine crankcase chamber; the degree of vacuum present at one source of vacuum decreasing as the throttle valve of a carburetor approaches closed position while the vacuum at the other source of vacuum increases as the throttle valve approaches closed position.

A more specific object of the invention is to provide a vacuum-producing nozzle disposed within the inlet pipe of the engine air cleaner which nozzle is in communication with the crankcase chamber such that as the air entering the engine is increased the suction efiect produced by the nozzleon the crankcase chamber is correspondingly increased.

A still further object is to create a pressure-difierential 'between an air inlet and an air outlet of an engine crankcase chamber which pressure differential is effective throughout the entire operating range of the engine to induce circulation of. the deleterious fumes and vapors within the engine and to expel themwithout loss or escape of lubricant to the atmosphere.

The foregoing and other important objects and desirable features inherent in and encompassed by the invention, together with many of the purposes and uses thereof, will 'become readily apparent from a reading of the ensuing description'in conjunction with the annexed drawings, in which:

Figure '1 is a'plan view of an engine incorporating the Figure 2'is'a sectional view taken substantially along the "line 2 2 of Figure 1;

chamber air cleaner.

Referring to the drawings in detail, wherein like ref- 'erence characters represent like elements throughoutthe various views, an internal combustion engine is shown which includes a cylinder block structure 10. The cylinder :block structure is provided with six cylinder-bores 11 in which-pistons 12 are reciprocally mounted. Pistons 12'are drivingly connected to a crankcase 13 rotatively journalled in the cylinder block structure .10, by means of conventional connecting rods 14. Suitably secured to :the lower marginal edge of the cylinder block structure 10 is an oil pan 15 whichis adapted to contain lubricating oil and serve as an oil reservoir for the engine lubricating system. While the-invention is to be described in conjunction with an inline type engine hereinafter,,it-is to be understood that the invention could be applied to a V-type internal combustion engine without departing from the spirit and scope of the invention.

As best shown in Figure 2 a cylinder head 16 is secured to the uppermost surface of the cylinder block structure 10. Slidingly mounted in the cylinder head 16 are intake valves 17 for controlling the admission of air and fuel to the cylinder bores 11 from an intake manifold 18. Similarly mounted in the head 16 are exhaust valves, not shown. for permitting the flow of exhaust gases from the cylinder bores 11 to an exhaust manifold, not shown. A longitudinally extending wall 19 integrally formed with the cylinder block 10 extends along one side of the engine. The lower ends of a plurality of push 'rods or tappets 20 are slidably mounted in the wall 19 and have their upper ends operatively connected to the intake valves 17. The tappets 20 are actuated by a rotatable cam shaft 21 in a conventional manner. The camshaft 21 is rotatively supported by the block structure 10 below the. wall 19 and is driven by the crankshaft 13 by means of a'pair of meshing gears, not shown, secured to the cam shaft and crankshaft, respectively. From the foregoingit will be appreciated that the crankcase chamber 22 extends substantially the entire length of the engine and is defincd by the oil pan 15 and the cylinder block structure 10. Inasmuch as each of the six cylinder bores 12 opens into the crankcase chamber 22. the gas or vapor which inevitably leaks between the pistons 12 and the cylinder bores 11 during the operationof the engine accumulate within the crankcase chamber-27 to deteriorate the oil contained therein if not efficiently removed therefrom. A valve chamber, designated generally by numeral '23,"disposed above the crankcase chamber22 is. partially formed by Wall 19 and vertically aligned walls 24 and'25 of the cylinder block 10 andthe cylinderh'ead 16, respectively. A valve chamber coverassembly 26 is provided for closing the valve chamber 23. A plurality of apertures 27 (only one is shown in Figure 2) extend through the wall 19 for establishing communication between the valve chamber 23 and the crankcase chamber 22. The upper ends of the tappets or push rods 20 extend through enlarged openings 28 formed in a lateral projection of the wall 25 of the cylinder head 16 to provide communication between the valve chamber 23 and the space 29 outlined by the top of the cylinder head and a valve train cover 30 which is suitably fastened to the top of the cylinder head. From the foregoing it will be appreciated that the crankcase chamber 22, valve chamber 23 and space 29 extend longitudinally through the engine and are in communication with each other. Mounted on the valve train cover 30 is an air cleaner 31 which includes an upright section of tubing 32 to which is secured a shell-like casing 33 which closes the upper end of the air inlet tubing 32. The tubing 32 is provided with a series of ports or apertures 34 therethrough adjacent its upper end. The base or lower end portion of the casing 33 is formed to provide an annular oil reservoir 35, one wall 36 of which is radially spaced from the tube section 32 to provide an annular passage 37. Secured to the tube section 32 intermediate its ends thereof within the casing 33 is a sheet metal support 38. The support 38 is positioned within the casing 33 and is of such formation that a passage 39 is provided which is a continuation ofpassage 37. The space 40 enclosed by the casing 33 above the support 38 is preferably filled with suitable air-pervious filtering material such as steel wool, crinkle wire or the like. Air entering the space 29 first fiows upwardly through the passage 37 downwardly through the passage 39 and over the'oil contained within the oil reservoir 35 where any foreign substances or elements contained with the air are deposited in theoil. The air then flows upwardly through the filter medium to the ports 34 and then downwardly through the tube section 32 into the space 29. Any fine particles of dust or other abrasive elements still remaining in the air after it passes over the oil in the oil reservoir 35 are deposited on the filtering material within the space 40. .The air whichis ultimately drawn into the engine as scavenging air is substantially free of dust, dirt and other foreign elements which would destroy the lubrieating properties of the engine lubricating oil by contarninating the same.

An oil filler tube 41 is secured to the side of the cylinder .bl'ock.10 and has one end opening into the crankcase chamber 22 well above the normal oil level of the lubricating oil contained therein. The opposite end of the filler tube -41.is provided with a removable cap 42 for closing thetube in an air and dirt tight manner as in mostconventional engines. As stated hereinbefore, the present invention contemplates the continuous ventilation .of the interior'of the engine throughout the entire operating range. of the engine with respect to load and speed without experiencing erratic and inefficient engine performance. To accomplish this objective two sources of vacuum are utilized; the efiectiveness of each to draw air through the air cleaner 31 being dependent upon the position of the butterfly-type throttle plate 43 disposed within the air fuel discharge passage 44 of a conventional carburetor or charge forming device 45. The air'fuel passage 44 is connected to the intake manifold 18 which is, as stated hereinbefore, attachedto the cylinder head 16. The carburetor 45 is shown somewhat diagrammatically but it is understood that any type of carburetor such as an updraft or downdraft, two barrel or four barrel carburetor may be employed without departing from the spirit and scope of the invention. The air inlet 46 to the carburetor 45 is connected to the outlet pipe 47 of an air cleaner 48. The air cleaner 48 illustrated somewhat diagrammatically is an oil-washed type wherein the cleaning .or filtering element disposed within the .air cleaner'casing is continually beingwashed with oil C0ntained in a reservoir in the bottom of the air cleaner casing that is agitated by the incoming air. Fresh air enters the air cleaner 48 through a single relatively short air inlet pipe 49. It is to be understood that while the invention is shown in conjunction with an oil-washed type cleaner it is equally adaptable for use with other types of air cleaners.

The butterfly-type throttle plate 43 does not close to a position perpendicular to the axis of the air-fuel outlet passage 44 when in its closed position but is at a slight angle thereto as shown in Figure 2. This construction is conventional in the carburetor art and as the throttle plate 43 approaches its closed position as when the engine is operating under no load and at idling speed. The degree of vacuum or sub-atmospheric pressure present in the air-fuel outlet passage 44 down stream of the throttle plate 43 and in the intake manifold 18 increases. By the same token, the volume of air entering the air inlet pipe 49 of the air cleaner 48 decreases as the throttle plate 43 approaches its closed position as shown in Figure 2. As the throttle plate 43 is rocked from its closed position to its fully opened position the degree of vacuum present in the intake manifold 18 decreases and approaches the pressure of the air flowing through the outlet pipe 47 of the air cleaner 48. However, as the throttle plate 43 is moved toward its fully opened position the quantity and hence the velocity of air flowing through the air inlet pipe 49 of the air cleaner 48 increases. As stated hereinbefore, it is an important object of the present invention to utilize two sources of vacuum for continuously and efficiently sweeping the deleterious gases and vapors present within the crankcase chamber 22 and other mechanism compartments in communication therewith throughout the operating range of the engine. One source of vacuum is obtained by placing one end of a conduit 50 in communication with the interior of the intake manifold 18 and its opposite end in communication with the interior of the oil filler tube 41 which, as stated previously, is in communication with the interior of the crankcase chamber 22. In operation filtered air flows through the valve gear train cover 30 from the air cleaner 31 into the space 29 defined by the cover 30 and the cylinder head 16. The air then flows downwardly through openings 28 into the valve chamber 23. The air then flows downwardly through the openings 27 into the crankcase chamber 22 and then upwardly into the oil filler tube 41. The fresh air which is then mixed with crankcase gases and vapors then enters the conduit 56 and is emitted into the intake manifold 18 and mixes with the air-fuel mixture flowing from the carburetor 45 and ultimately reaches the engine cylinders 11. The amount of air and gases flowing through the conduit 50 depends upon the differential in pressure existing between the air entering the air cleaner 31 (atmospheric pressure) and the air pressure within the intake manifold and the cross-sectional area of the smallest restriction in the entire air passage from the air cleaner 31 to the intake manifold 18. Inasmuch as the emission of oildiluent gases and vapors into the crankcase chamber 22 is at a minimum when the engine is idling with the throttle valve plate 43 in its closed position relativelylittle air is needed to be circulated through the crankcase chamber 22 to rid the same of the gases and vapors. However, with the throttle valve plate 43 closed the degree of vacuum in the intake manifold 18 is greatest. Consequently a restriction 52 is formed in the conduit 50 to limit the air flowing therethrough and consequently the volume of scavenging air flowing through the crankcase 22. The cross-sectional area of the restriction 52 is dependent upon the particular engine, however, in most cases this is approximately of an inch in diameter. Thus, with the engine idling the conducting passage between the crankcase chamber 22 and the intake manifold 18 is such that the total amount of air or gases that are injected into the intake manifold 18 from the crankcase chamber 22 does not materially affect the engine operating characteristics but is sufficient to rid the crankcase chamber 22 of blow by gases and vapors.

The suction effect of the second source of vacuum depends upon the velocity of the air entering the air cleaner 48 which in turn, depends upon the position of the throttle valve plate 43. That is, the velocity is greatest when the throttle valve plate 43 is in its fully opened position and decreases as the throttle plate is moved toward its closed position. The second source of vacuum includes a conduit 53 having one end thereof in communication with the interior of the oil filler tube 41. The conduit 53 extends through the air inlet pipe 49 of the air cleaner 48 in an airtight manner and end section 54 projects into the interior of the air inlet pipe 49 so as to be in the path of the unfiltered air entering the air cleaner 48. The end section 54 projecting within the air inlet pipe 49 is in the form of a pitot tube, velocity pressure nozzle which has a beveled outlet 55 which faces downstream or in the same direction air flows through the air inlet pipe 49 when the engine is in operation. As in all pitot tube type nozzles as the velocity of the air flowing through the air inlet pipe 49 increases, the vacuum or sub-atmospheric pressure in the area of the beveled outlet 55 also increases. It will be appreciated therefore, that as the throttle valve plate 43 is moved toward its fully opened position, the velocity of the air flowing through the air inlet pipe 49 increases with a consequent increase in the vacuum in the area of the beveled outlet 55. Thus, with a differential in air pressure existing between the air at the bevel outlet 55 of the nozzle 54 and the air at the air inlet passage 37 of the air cleaner 31, air is caused to flow into the space 29 through the valve chamber 23 to the crankcase chamber 22 and then upwardly into the oil filler tube 41 into the conduit 53. The scavenging air discharged from the pitot tube type nozzle 54 when mixes with the unfiltered air entering the air cleaner 48. Any oil particles carried by the scavenging air are deposited on the body of filtering material contained within the air cleaner 48 to assist the oil contained within the air cleaner reservoir in cleansing the filtering material.

In operation, as soon as the engine is started with the throttle valve plate 43 in its closed position, the pressure in the engine intake manifold 18 will drop from atmospheric pressure to a sub-atmospheric pressure, while the pressure in the crankcase chamber 22 being continually in communication with air under atmospheric pressure, as pointed out hereinbefore, will remain substantially at atmospheric pressure. As a result of this low pressure or high vacuum condition in the intake manifold 18, air entering the space 29 from the air cleaner 31 is caused to flow through the valve chamber 23 and crankcase chamber 22 in the direction of the arrows, during which time it sweeps the deleterious gases and vapors present therein with it. The diluent-ladened air then flows upwardly into the oil filler tube 41 and passes through the conduit St). The scavenging air is then drawn into the intake manifold 18 where it combines with the idle airfuel mixture ilowing from the carburetor 45 to be ultimately burned in the engine combustion chambers. As pointed out hereinbefore, even with the throttle valve plate 43 in its closed position air enters the air cleaner 48 and since the pitot tube type nozzle 54 is always disposed within the air flowing to the air cleaner 48, a pressure differential will exist between the outlet 55 of the nozzle 54 and the crankcase chamber 22. Consequently, scavenging air will flow through the conduit 53 simultaneously with the flow of scavenging air through the conduit 50. However, because of the relatively low velocity of the air flowing through the air inlet pipe 49 the suction effect created thereby upon the nozzle 54 is practically negligible. Because of the restriction 52 in the conduit 56 the volume of air being swept through the crankcase chamber 22, while limited, is sufficient to carry away the piston blow b'y gases from the crankcase chamber and efficiently ventilate the same but is not great enough to seriously effect the idling characteristics ofthe engine.-

As the throttle valve plate 43 is rocked toward its fully opened position in order to increase engine speed or when the load on the engine is increased, the suction effective at the discharge end of the conduit 50 is progressively reduced while at the same time the rate of blow-by gases emitted into the crankcase chamber 22. is progressively increased. air is withdrawn from the crankcase chamber 22 through both conduits t] and 53 and although thatportion of the total flow of fresh air and blow-by gases andvapors from the crankcase chamber due to the suction effect present in the intake manifold 18' decreases asthethrot tle valve plate 43 is opened the total rate of scavenging air flowing from the crankcase actually increases. This is true because the velocity of air entering theair inlet pipe 49 of the air cleaner 48 increases causing the suction effect at the nozzle outlet 55 to increase. This suction efliect increase at the nozzle outlet 55 compensates for the loss or falling-olf of the suction effect in the intake manifold with regard to the rate of scavenging airibeing circulated through the engine crankcase chamber 22. It has been found that the cubic feet per minute of fresh air entering through the air cleaner 31 and circulated through the crankcase chamber 22 increases as the throttle valve plate 43 is moved toward its fully opened position to thus insure the riddance of blow-by gases and vapors from the crankcase chamber. From the foregoing it will. be appreciated that when the engine is operating crankcase vapors and gases are being withdrawn through both

conduits

50 and 53 and that part of the total amount of scavenging air flowing through any one particular conduit being dependent upon the position of the throttle valve plate 43. The blow-by gases and vapors are rapidly removed from the engine crankcase chamber 22 and a continuous flow of fresh air through the crankcase chamber 22 is maintained throughout the entire operating range of the engine without adversely effecting the performance and operating efficiency of the engine. Furthermore, the invention is readily incorporatable into existing internal combustion engines inexpensively and with very little or no changes or modifications in the various components of the engine such as the carburetor, air cleaner, etc. It is also obvious that no special complex valve means or the like are required to regulate and control the ventilating system.

The embodiment of the invention chosen for the purposes of illustration and description herein is that preferred for achieving the objects of the invention and developing the utility thereof in the most desirable manner, due regard being had to existing factors of economy, simplicity of design and construction and the improvements sought to be effected. It will be appreciated, therefore, that the particular structural and functional aspects emphasized hereinare not intended to exclude but rather to suggest such other adaptations and modifications of the invention as fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber provided with air inlet means and scavenging air outlet means and an air-fuel mixture passage having a movable throttle valve disposed therein for regulating the quantity of air-fuel mixture delivered to the engine; an air cleaner having an inlet pipe and an outlet pipe in communication with said air-fuel mixture passage; a second air cleaner connected to said air inlet means whereby air entering said crankcase chamber is filtered; a conduit having one end connected to said scavening air outlet means and its opposite end connected to said air-fuel mixture passage at a point downstream of As stated hereinbefore, scavenging" said throttle valve; and a second conduit having one end in communication with said scavenging air outlet means;

and means for subjecting the opposite end of said secondv conduit to a. source of variable sub-atmospheric air pressure, said sub-atmospheric air pressure substantially progressively increasing from a minimum value to a maximum value as said throttle valve is moved from its closed positiontoward its fully opened position including a nozzle projecting into said inlet pipe of said first-mentioned air cleaner sons to be in the path of the unfiltered air entering said air cleaner, said nozzle having a discharge opening facing downstream and lying in a plane disposed at an' angle with respect to a vertical plane perpendicular to-thelongitudinal axis of said inlet pipe.

2. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber and an air-fuel mixture passage, said air-fuel mixture passage having a throttle valve disposed therein for regulating the quantity of air-fuel mixture delivered to the engine, said crankcase chamber having fresh air inlet means and scavenging air outlet means;

means for subjecting said scavenging air outlet means to sub-atmospheric air pressure, said sub-atmospheric air pressure decreasing as said throttle valve is moved from its closed position to its fully opened position; and second means for subjecting said air outlet means to a variable sub-atmospheric pressure, said air pressure increasing as said throttle valve is moved from its closed position to its fully opened position;

3. In a ventilating system substantially as set forth in claim 2, in which, said first mentioned means for subjecting said scavenging air outlet means to a sub-atmospheric air pressure includes conduit'means extending between said airfuel mixture passage at a point downstream of said throttle valve and said scavenging air outlet means.

4. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber provided with fresh air inlet means and scavenging air outlet means and an air-fuel mixture passage having a movable throttle valve disposed therein for regulating the quantity of air-fuel mixture delivered to the engine; a conduit having one end connected to said scavenging air outlet means and its opposite end connected to said air-fuel mixture passage at a point downstream of said throttle valve; and a second conduit having one end in communication with said scavenging air outlet means; and means for subjecting the opposite end of said second conduit to a source of variable sub-atmospheric air pressure, said sub-atmospheric pressure substantially progressively increasing from a minimum value to a maximum value as said throttle valve is moved from its closed position toward its fully opened position.

5. In a ventilating system substantially as set forth in claim 4, in which, an air cleaner is provided having an inlet pipe and an outlet pipe in communication with said air-fuel mixture passage; and said means for subjecting one end of said second conduit to a source of variable sub-atmospheric air pressure includes a nozzle projecting into said inlet pipe so as to be in the path of the unfiltered air entering said air cleaner.

6. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber, said crankcase chamber having a fresh air inlet and a scavenging air outlet, said engine including a movable throttle valve for regulating the quantity of air-fuel mixture delivered to the engine; means for subjecting said scavenging air outlet to a source of variable sub-atmospheric pressure, said sub-atmospheric pressure substantially progressively increasing from a minimum value to a maximum value as said throttle valve is moved from its closed position toward its fully opened position; and second means for subjecting said scavenging air outlet to a source of variable sub-atmospheric pressure, said sub-atmospheric pressure decreasing as 9 said throttle valve is moved from its closed position to its fully opened position.

7. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber having air inlet and outlet means and an air-fuel mixture passage, said air-fuel mixture passage having a throttle valve disposed therein for regulating the quantity of air-fuel mixture delivered to the engine; means for establishing a variable pressure difierential between said air inlet and outlet means, said pressure difierential increasing as said throttle valve is moved from its closed position to its fully opened position; and second means for establishing a variable pressure differential between said air inlet and outlet means, said pressure difierential decreasing as said throttle valve is moved from its closed position to its fully opened position.

8. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber provided with fresh air inlet means and scavenging air outlet means and an air-fuel mixture passage for delivering air-fuel mixture to the engine; an air cleaner having an inlet pipe and an outlet pipe in communication with said air-fuel mixture passage; a conduit having one end in communication with said scavenging air outlet means and its opposite end ing air outlet means to a source of variable sub-atmospheric pressure, said sub-atmospheric pressure decreasing as the power output of the engine varies from a minimum value to a maximum value.

9. In a ventilating system for internal combustion engines or the like, the combination of an engine having a crankcase chamber provided with fresh air inlet means and scavenging air outlet means and an air-fuel mixture passage for delivering air-fuel mixture to the engine; an air cleaner having an inlet pipe and an outlet pipe in communication with said air-fuel mixture passage; a conduit having one end in communication with said scavenging air outlet means and its opposite ends subjected to a source of variable sub-atmospheric air pressure, said sub-atmospheric pressure substantially progressively increasing from a minimum value to a maximum value as the power output of the engine varies from a minimum value to a maximum value, said means including a nozzle projecting into said inlet pipe so as to be in the path of the unfiltered air entering said air cleaner; and a second conduit having one end connected to said airfuel mixture passage and its opposite end connected to said scavenging air outlet means.

References Cited in the file of this patent UNITED STATES PATENTS 2,252,974 Lowther Aug. 19, 1941 FOREIGN PATENTS 473,821 Canada May 22, 1951 661,649 Great Britain Nov. 21, 1951