Patent Application
20130125865
This invention relates to improvements in an oil separator disposed inside a cylinder head cover of an internal combustion engine to separate oil mist from blowby gas discharged outside through the cylinder head cover.
For example, in an automotive internal combustion engine, blowby gas containing unburned components and leaked from a combustion chamber to a crankcase is introduced through an engine intake system into the combustion chamber to burn the unburned components together with fresh air taken in from outside, as well known. Blowby gas passing through the inside of the crankcase contains oil mist, and therefore an oil separator is disposed at a part of the cylinder head cover as disclosed in Japanese Patent Provisional Publication Nos. 2005-120855 and 2009-121281 in order to prevent oil mist from being carried to the engine intake system. After oil mist is separated and removed by this oil separator, blowby gas is taken out from the inside of the cylinder head cover. In general, two blowby gas passages are connected to the cylinder head cover, in which fresh air is introduced through one of them under a normal operating condition, while blowby gas flows through both of them under a high engine load operating condition. Accordingly, two oil separators are respectively provided in the two blowby gas passages.
The oil separator disclosed in the Patent Provisional Publications is a so-called inertial collision-type oil separator, in which a partition wall formed with many passage holes is disposed inside an oil separator chamber, and a collision plate is disposed adjacent to this partition wall in such a manner as to be opposite to the passage holes. The flow velocity of blowby gas containing oil mist becomes high when blowby gas passes through the passage holes of the partition wall, so that blowby gas strikes against the collision plate at a high speed after getting out of the flow passages so that oil mist adheres onto the collision plate and recovered. The collision plate is formed at its bottom section with a slit-like opening through which oil grown as large droplets upon being separated by the collision plate is flown along the bottom surface of the oil separator to a downstream side and then dropped into a valve operating chamber through the bottom end discharge outlet of a drain pipe disposed at the bottom wall of the oil separator.
Here, in general, the passage holes formed in the above partition wall is circular in cross-section as disclosed in Japanese Patent Provisional Publication No. 2005-120855. In this regard, Japanese Patent Provisional Publication No. 9-96209 discloses an oil separator using passage holes which are rectangular or hexagonal in cross-section though the oil separator is different in basic configuration from that of the above two Japanese Patent Provisional Publications.
In order to further improve a trapping performance (efficiency) for oil mist in the inertia collision-type oil separator, it is required to increase the flow velocity of blowby gas ejected from the passage holes by decreasing the cross-sectional area of the passage holes.
However, if the cross-sectional area of each passage hole is thus decreased, a pressure loss between the upstream side and downstream sides of the partition wall unavoidably rises according to decrease in passage hole cross-sectional area. As a result, this pressure loss lowers the pressure within the oil separator chamber at the downstream side of the partition wall, so that oil tends to reversely flow from the side of the valve operating chamber through the drain pipe to the side of the oil separator chamber, which is problematic.
In other words, it is difficult to make the trapping performance of oil mist compatible with the pressure loss at sufficient levels, the trapping performance and the pressure loss being in the relationship of trade-off in configuration of conventional oil separators.
In order to overcome difficulties encountered in conventional oil separators, the present invention has been made. The present invention resides in an oil separator for an internal combustion engine, disposed inside a cylinder head cover to separate oil mist from blowby gas to be discharged out of the cylinder head cover. The oil separator comprises a section defining an elongate separator chamber and having first and second ends. The section includes a blowby gas inlet located at side of the first end, and a blowby gas outlet located at side of the second end. A partition wall is disposed to divide the separator chamber into an inlet chamber at side of the blowby gas inlet and an outlet chamber at side of the blowby gas outlet. The partition wall is formed with a plurality of passage holes each of which pierces the partition wall. A collision plate is disposed inside the outlet chamber and located opposite to the passage holes of the partition wall. The collision plate has a lower section located at a lower part of the outlet chamber, the lower section of the collision plate defining a slit-like opening located at the lower part of the outlet chamber and extends throughout at least a part of width of the collision plate. Additionally, a drain section is provided to discharge oil separated from blowby gas from the lower part of the outlet chamber into a valve operating chamber. In the above oil separator, each of the passage holes of the collision plate is triangular in cross-section.
Specifically, with an oil separator provided with a partition wall formed with general passage holes circular in cross-section, under the actions of contraction generated at the inlet opening portion of each passage hole and a boundary layer at the wall surface of each passage hole due to viscosity of fluid, flow of blowby gas concentrates to the cross-sectional center of the passage hole so that blowby gas flows through a cross-sectional central part of the passage hole, thereby narrowing a substantial passage area. This raises a pressure loss across the partition wall at a remarkable high level.
In contrast, according to the present invention or the oil separator provided with the partition wall formed with the passage holes triangular in cross-section, an area where the flow rate of blowby gas is high can become broader in each passage hole than that in each passage hole circular in cross-section. In other words, a uniform flow velocity distribution of blowby gas can be obtained in each passage hole as compared with the conventional oil separator provided with the partition wall formed with passage holes circular in cross-section. This increases the substantial passage area of each passage hole, thereby lowering a pressure loss across the partition wall. Additionally, according to experiments conducted by the present inventors, as discussed after, the oil separator of the present invention exhibited such results that the pressure loss is lowered while improving the trapping efficiency of oil mist. Although the mechanism for so improving the trapping efficient is strictly unclear, it is assumed that blowby gas containing oil mist flows through each passage hole without being excessively locally concentrated and with a relatively uniform flow velocity distribution to strike against a collision plate, and therefore oil mist can be totally effectively separated.
Preferably, in the present invention, each of the passage holes is in the shape of isosceles triangle in cross-section, in which the cross-sectional isosceles triangle having a base parallel with a lower edge of the collision plate. Blowby gas passed through the plurality of the passage holes in the partition wall strikes against the collision plate and flows through the opening formed at the lower section of the collision plate toward the downstream side, and therefore blowby gas is directed downward as a whole. As a result, the flow velocity distribution in each passage hole spreads along the base of the isosceles triangle which base extends laterally, so that the distribution becomes more uniform. It is not preferable that the isosceles triangle has an excessively small vertical angle in order to prevent the passage hole from becoming slit-shaped. Typically, the triangle may be equilateral triangle; however, it will be understood that the equilateral triangle may not be accurate equilateral triangle.
Preferably, in the present invention, a plurality of the passage holes are aligned along a direction in which the base of the isosceles triangle extends, in which the respective cross-sectional triangles of the two passage holes adjacent to each other are vertically reversed to each other. With this configuration, the opposite sides of the respective triangles of the two adjacent passage holes are parallel with each other, which is advantageous from the viewpoint of securing a strength of the partition wall. Accordingly, the passage holes can be effectively arranged in a limited region of the partition wall.
Preferably, in the present invention, each of the passage holes has a length of not less than two times an equivalent diameter of the passage hole. In other words, each passage hole is sufficiently elongate so that flow of blowby gas, particularly oil mist, can certainly strike against the collision plate without excessively spreading.
Thus, according to the present invention, by forming the passage holes triangular in cross-section, the trapping performance of oil mist and the pressure loss across the oil separator can be compatible at high levels.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.
In the drawings, like reference numerals designate like parts and elements throughout all figures, in which:
Referring now to
In such a configuration, fresh air is introduced through the fresh air inflow opening 8 according to a pressure difference between the upstream and downstream sides of the throttle valve so as to ventilate the inside of the crankcase 4 and the inside of the valve operating chamber 6. Blowby gas inside the crankcase 4 and the valve operating chamber 6 is introduced together with this fresh air through the PCV valve 10 in the blowby gas outflow opening 9 into the downstream side of the throttle valve.
Additionally, the oil separator 1 is disposed inside the cylinder head cover 7 provided with the blowby gas outflow opening 9 in order to remove oil mist mixed in this blowby gas.
It is to be noted that dark arrows in
The oil separator 1 in this instance elongates in a direction perpendicular to the row of engine cylinders (or in a width direction of the engine). An elongate separator chamber 23 having a rectangular cross-section perpendicular to the longitudinal direction thereof is defined between the housing section 21 and the separator cover 22. A blowby gas inlet 24 is formed in the separator cover 22 and located at one end section of the separator chamber 23 in the longitudinal direction whereas a blowby gas outlet 25 is formed in the ceiling portion of the housing section 21 and located at the other end section of the separator chamber 23 in the longitudinal direction. Accordingly, blowby gas flows inside the separator chamber 23 basically linearly along the longitudinal direction of the separator chamber 23.
The blowby gas inlet 24 is formed in the separator cover 22 and has an opening which is rectangular in cross-section. In other words, in this embodiment, the blowby gas inlet 24 is opened or connected to the bottom part of the separator chamber 23, so that the separator chamber 23 is in communication with the valve operating chamber 6 through this blowby gas inlet 24. The blowby gas outlet 25 is located at the ceiling portion of the housing section 21 and formed piecing the ceiling portion of the housing section 21 in this embodiment. As discussed above, in case that the oil separator 1 is disposed on the side of the blowby gas outflow opening 9, the blowby gas outlet 25 serves as the blowby gas outflow opening 9, in which the PCV valve (not shown) is installed in the blowby gas outlet 25. It is to be noted that the blowby gas outlet 25 may be located at an end part (whose relatively upper position) of the elongate separator chamber 23.
A plate-shaped partition wall 27 is disposed perpendicular to the longitudinal direction of the separator chamber 23 or the separator cover 22, and located generally at an intermediate part of the separator chamber 23 in the longitudinal direction. This partition wall 27 divides the separator chamber 23 into an inlet chamber 28 at the side of the blowby gas inlet 24 and an outlet chamber 29 at the side of the blowby gas outlet 25. In this instance, this partition wall 27 is formed integral with the separator cover 22 and extends upward to reach the ceiling portion of the housing section 21. In contrast, the partition wall 27 may be formed integral with the housing section 21 or the cylinder head cover 7. The partition wall 27 is formed with a plurality of passage holes 30 which serve as orifices for increasing the flow velocity of blowby gas, as discussed in detail after. The partition wall 27 is formed with two cutout portions 31 which are located at the opposite corners of the lower end section thereof, in order to allow oil droplets formed in the inlet chamber 28 to flow to the side of the outlet chamber 29.
A collision plate 32 is disposed in the outlet chamber 29 and located adjacent to and parallel with the partition wall 27 in the outlet chamber 29. The collision plate 32 is opposite to or faces the passage holes 30 in the partition wall 27 at a suitable distance from the partition wall 27 so as to separate oil mist from blowby gas flowing at a high speed through the passage holes 30. In this instance as shown, the collision plate 32 is formed integral with the separator cover 22 similarly to the partition wall 27, and extends upward to reach the ceiling portion of the housing section 21. In contrast, the collision plate 32 may be formed integral with the housing section 21. It will be understood that the surface of the collision plate 32 may be formed uneven, for example, by forming a plurality of vertically extending grooves at the surface of the collision plate 32. A lower section of the collision plate 32 defines a slit-like opening 33 whose lower end is defined by the separator cover 22. The upper end of the opening 33 is defined by a lower edge of the collision plate 32 which extends parallel with the upper surface of the separator cover 22. In this instance as shown, the collision plate 32 is formed integral with the separator cover 22 in such a manner as to stand from the upper surface of the separator cover 22, and therefore the opening 32 is formed to be opened like a window at a lower central section of the collision plate 32 in the width direction so that lower opposite end sections of the collision plate 32 in the width direction remain to support the main body of the collision plate 32. For example, in case of forming the collision plate 32 integral with the housing section 21, the opening 33 may be formed extending throughout the whole width of the collision plate 32. Oil separated at the surface of the collision plate 32 flows downward and flows through the opening 33, and then flows along the upper surface of the separator cover 22 defining the separator chamber 23 so as to be carried to the downstream side.
A drain pipe 35 is formed integral with the separator cover 22 and located to be opened to the bottom part of the outlet chamber 29, serving as a drain section for discharging collected oil to the side of the valve operating chamber 6. The drain pipe extends downward into the valve operating chamber 6 and has a small discharge opening through which oil is discharged.
With the above-configured oil separator 1, the passage of blowby gas flowing from the blowby gas inlet 24 through the separator chamber 23 to the blowby gas outlet 25 is narrowed in passage area by the passage holes 30 piercing through the partition wall 27 so as to form a high speed gas flow of blowby gas, and then strikes against the surface of the collision plate 32. As a result, oil mist contained in blowby gas is separated and adhered to the surface of the collision plate 32. The thus trapped oil mist gradually grows to large liquid droplets and drop from the lower edge 32a of the collision plate 32 to the upper surface of the separator cover 22 defining the bottom part of the separator chamber 23, followed by flowing along the upper surface of the separator cover 22 to the downstream side. Finally, liquid oil drops from the drain pipe 35 into the valve operating chamber 6. Since the liquid oil is collected inside the drain pipe 35 to a certain level of the drain pile 35, blowby gas can be prevented from its reverse flow through the discharge opening at the lower end of the drain pipe 35 (i.e., inflow of blowby gas from the valve operating chamber 6 in
Here, when blowby gas flows through the passage holes 30 of the partition wall 27, the passage holes 30 serving as flow resistance develop a pressure loss. As this pressure loss is larger, the pressure difference between the inlet chamber 28 and the outlet chamber 29 or the pressure difference between the valve operating chamber 6 and the outlet chamber 29 becomes larger, so that the reverse flow of blowby gas tends to be caused through the drain pipe 35. When such reverse flow of blowby gas is caused, oil inside the drain pipe 35 will be scattered into the outlet chamber 29 and carried to the blowby gas outflow opening 9.
As discussed above, by alternately locating the right triangle and the reversed triangle, the width or area of a portion 27a (referred to as a foot portion, for convenience) remaining between the adjacent two cross-sectional triangles (or passage holes 30) is secured to be constant and wide, which is advantages from the viewpoint of obtaining a sufficient strength of the partition wall 27. In other words, the inclined side 30b of one cross-sectional triangle and the inclined side 30c of the other cross-sectional triangle of the adjacent two cross-sectional triangles are parallel with each other, and therefore no narrow foot portion (27a) having a low strength is locally formed. Accordingly, many passage holes 30 having the rectangular cross-section can be formed within a limited area of the partition wall 27 without lowering the strength of the partition wall 27.
In this embodiment, the passage hole 30 has an equivalent diameter (or diameter of a circle having the same area) of 3 mm in cross-section perpendicular to the thickness direction of the partition wall 27, and a passage length (or thickness of the partition wall 27) of 10 mm. It will be understood that the dimensions of the passage hole 30 are not limited to these, the passage hole 30 may have the equivalent diameter of about 1 to 5 mm. If the equivalent diameter of the triangular passage hole 30 is smaller than 1 mm, it is substantially difficult to machine or form the passage hole 30. If the equivalent diameter is larger than 5 mm, the passage hole 30 cannot sufficiently serve as an orifice so that a sufficiently high flow velocity of blowby gas cannot be obtained thereby lowering the trapping performance of oil mist. The passage length of the passage hole 30 is preferably not less than two times the equivalent diameter in order to allow oil mist to flow straight with a sufficient inertia. The total number of the passage holes 30 in the partition wall 27 is generally about 3 to 20 though it is different according to displacement of the internal combustion engine, dimensions of the oil separator 1, and/or the like.
It is to be noted that the above passage hole 30 triangular in cross-section (referred to as “triangular passage hole”) is low in pressure loss and high in the trapping efficiency of oil mist as compared with general passage holes circular in cross-section (referred to as “circular passage hole”).
In general, as the gas flow rate increases, the flow rate of gas passing through the passage hole 30 becomes high. Therefore, as the gas flow rate increases, the trapping efficiency of oil mist increases while the pressure loss simultaneously increases. However, as shown in the graph of
Specifically, with general circular passage holes, flow of gas concentrates to the cross-sectional center of the passage hole under the action of contraction formed around the inlet of the passage hole and under the action of boundary layer at the wall surface of the passage hole due to viscosity of fluid, and therefore blowby gas substantially flows through the vicinity of the center axis of the circular passage hole thereby narrowing the substantial cross-sectional area of the passage hole thus making a pressure loss remarkable.
In contrast, the following is assumed in case of the oil separator using the triangular passage holes: A region where flow velocity is high is widened in each passage hole as compared with the case of the oil separator using the circular passage holes. In other words, in the case of the oil separator using the triangular passage holes, a more uniform flow velocity distribution can be obtained in each passage hole than the case of the oil separator using the circular passage holes, thereby increasing the substantial passage hole area in each passage hole thus to lower the pressure loss. Additionally, blowby gas containing oil mist can strike against the collision plate through the triangular passage hole in a relatively uniform flow velocity distribution without being excessively locally concentrated. Hence, oil mist can be effectively separated as a whole through the triangular passage hole.
As shown in
In contrast, in the triangular passage hole 30 in Example, as shown in
It is to be noted that the above-discussed effects can be obtained only in case of using the triangular passage holes 30 and therefore cannot be obtained even in cases of using passage holes having other complicated shapes in cross-section.
By using the thus configured partition walls 27B, 27C, 27D, measurements of the trapping efficiency of oil mist and the pressure loss between the upstream and downstream sides of the oil separator 1 were carried out to obtain results shown in
As will be apparent from
Meanwhile, in case of an oil separator using passage holes rectangular in cross-section or passage holes hexagonal in cross-section as disclosed in Japanese Patent Provisional Publication No. 9-96209, blowby gas flow concentrates in the vicinity of the cross-sectional center of each passage hole similarly in case of using the circular passage holes, thereby exhibiting the characteristics similar to that of the oil separator using the circular passage holes.
It is to be noted that the same performance as that of the oil separator using the triangular passage holes in Example can be obtained even if the three tip end portions (corresponding to the three vertical angles of the triangle) of each triangular passage hole are rounded with an arc (in cross-section) whose radium is 0.5 mm as shown in
The triangular passage holes whose tip end portions are rounded advantageous from the viewpoint of manufacturing technique for forming the triangular passage holes in the partition wall. Specifically, in case of producing the partition wall formed with the triangular passage holes by die-forming of a molten material or by secondary machining, it is generally not easy to accurately form the three tip end portions (having an acute angle in cross-section) of the triangular passage hole. Accordingly, by employing the triangular passage holes formed by slightly rounding the three tip end portions of the triangular passage holes as shown in
Although the invention has been described above by reference to a certain embodiment and Example of the invention, the invention is not limited to the embodiment and Example described above. Modifications and variations of the embodiment and Example described above will occur to those skilled in the art, in light of the above teachings. For example, while the triangle of the triangular passage hole 30 has been shown and described as being the equilateral-triangle, it may be isosceles triangle whose base is parallel with the lower edge 32a of the collision plate 32, providing the same effects as apparent from the gas flow velocity distribution in
While the housing section 21 has been shown as taking the shape of complete rectangular parallelepiped in
The entire contents of Japanese Patent Applications P2011-253428 (filed Nov. 21, 2011) are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-253428 | Nov 2011 | JP | national |
