Oil Mist Separator

Abstract

 An oil mist separator including a tubular volume chamber into which a gas is introduced, a tubular valve body that is so disposed as to slidably move relative to one axial end portion of the volume chamber, a plurality of communication passages defined by the one axial end portion of the volume chamber and the valve body, and an impact wall disposed in an opposed relation to the communication passages such that the gas flowed out through the communication passages is impacted against the impact wall, wherein the communication passages are configured such that as the pressure of the gas flowing into the volume chamber is increased, a sectional area of each of the communication passages becomes larger.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an oil mist separator.

[0002] Oil mist separators which are adapted to separate an oil component from a gas containing the oil component are well known in the art.

[0003] Japanese Patent Application Unexamined Publication No. 2009-522486 (Japanese translation of PCT international application No. PCT/KR2006/005691) discloses an oil mist separator disposed in a baffle compartment of a cylinder head cover of an engine into which blow-by gas flows.

[0004] The oil mist separator of the above conventional art includes a partition wall disposed on a passageway in which the blow-by gas flows. The partition wall is formed with a through hole. A cover is so disposed as to close the through hole and connected with the partition wall through elastic members. When the blow-by gas impacts against the cover, an oil component contained in the blow-by gas is separated from the blow-by gas. The cover is allowed to move apart by a predetermined distance from the cover according to a pressure of the blow-by gas which is applied to the cover. Thus, a flow passage of the blow-by gas can be ensured in the oil mist separator.

SUMMARY OF THE INVENTION

[0005] However, in the above-described conventional art, the flow rate of the blow-by gas flowing into the oil mist separator is not always kept constant. Further, the flow velocity of the blow-by gas at the time at which the blow-by gas impacts against the cover is variable. Therefore, in a case where the flow velocity of the blow-by gas upon impacting against the cover is decreased, there tends to occur a failure in effectively trapping oil mist.

[0006] It is an object of the present invention to solve the above-described problems encountered in the technologies of the conventional art and to provide an oil mist separator having an excellent performance.

[0007] In one aspect of the present invention, there is provided an oil mist separator comprising:

a tubular volume chamber into which a gas is introduced, the volume chamber having one axial end portion;

a tubular valve body having one closed end, the valve body including a bottom wall which covers one end face of the one axial end portion of the volume chamber and a tubular side wall which covers an outer circumferential surface of a side wall of the one axial end portion of the volume chamber, the valve body being so disposed as to slidably move relative to the one axial end portion of the volume chamber such that a distance between the bottom wall and the one end face of the one axial end portion of the volume chamber is increased in accordance with increase in pressure of the gas flowing into the volume chamber,

a plurality of communication passages which are defined by the one axial end portion of the volume chamber and the valve body, through which the gas introduced into the volume chamber is flowed out from the volume chamber and the valve body; and

an impact wall which is disposed in an opposed relation to the communication passages such that the gas flowed out through the communication passages is impacted against the impact wall;

wherein the communication passages are configured such that as the pressure of the gas flowing into the volume chamber is increased, a sectional area of each of the communication passages becomes larger.

[0008] With the above construction of the oil mist separator according to the present invention, in a case where a pressure of the blow-by gas introduced into the volume chamber is increased and a flow rate of the blow-by gas to be flowed out from the side of one axial end of the volume chamber through the communication passages is increased, the sectional area of each of the communication passages serving as an outlet through which the blow-by gas is flowed out from the volume chamber is increased in accordance with the increase in the flow rate of the blow-by gas. Therefore, flow velocity of the blow-by gas which is flowed out from the communication passages can be kept substantially constant regardless of change in the flow rate of the blow-by gas introduced.

[0009] Further, the one axial end portion of the volume chamber may be formed into a cylindrical shape and the valve body may be formed into a cylindrical shape having one closed end. The communication passages may be arranged in the one axial end portion of the volume chamber in a circumferential direction of the one axial end portion thereof at constant intervals therebetween.

[0010] Furthermore, the communication passages may be defined by a side wall of the valve body and a plurality of through holes formed in the side wall of the one axial end portion of the volume chamber. When the valve body is moved in such a direction that the bottom wall thereof is spaced apart from the one end face of the volume chamber, a portion of each of the through holes which is covered with the side wall of the valve body may be exposed to thereby increase a sectional area of each of the communication passages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a plan view generally showing an oil mist separator according to the present invention.

[0012] FIG. 2 is a sectional view of the oil mist separator according to a first embodiment of the present invention, taken along line A-A shown in FIG. 1.

[0013] FIG. 3 is an explanatory diagram schematically showing the oil mist separator according to the first embodiment of the present invention.

[0014] FIG. 4A is an enlarged explanatory diagram of an essential part of the oil mist separator according to the first embodiment of the present invention, which shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is low.

[0015] FIG. 4B is an enlarged explanatory diagram similar to FIG. 4A, but shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is high.

[0016] FIG. 5 is a graph in which a characteristic curve of the oil mist separator according to the first embodiment of the present invention and that of an oil mist separator of a comparative embodiment are compared with each other, each of the characteristic curves showing a relationship between oil mist trap efficiency and blow-by gas flow rate.

[0017] FIG. 6 is a graph in which a characteristic curve of the oil mist separator according to the first embodiment of the present invention and that of an oil mist separator of a comparative embodiment are compared with each other, each of the characteristic curves showing a relationship between oil mist trap efficiency and oil mist particle size.

[0018] FIG. 7 is a graph in which a characteristic curve of the oil mist separator according to the first embodiment of the present invention and that of an oil mist separator of a comparative embodiment are compared with each other, each of the characteristic curves showing a relationship between pressure loss and blow-by gas flow rate.

[0019] FIG. 8A is an enlarged explanatory diagram of an essential part of the oil mist separator according to a second embodiment of the present invention, which shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is low.

[0020] FIG. 8B is an enlarged explanatory diagram similar to FIG. 8A, but shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is high.

[0021] FIG. 9A is an enlarged explanatory diagram of an essential part of the oil mist separator according to a third embodiment of the present invention, which shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is low.

[0022] FIG. 9B is an enlarged explanatory diagram similar to FIG. 9A, but shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is high.

[0023] FIG. 10A is an enlarged explanatory diagram of an essential part of the oil mist separator according to a fourth embodiment of the present invention, which shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is low.

[0024] FIG. 10B is an enlarged explanatory diagram similar to FIG. 10A, but shows the oil mist separator in such a condition that a flow rate of blow-by gas flowing thereinto is high.

[0025] FIG. 11 is a sectional view of an essential part of the oil mist separator according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] An oil mist separator 100 according to a first embodiment of the present invention will be explained hereinafter by referring to FIG. 1 to FIG. 4. FIG. 1 is a plan view of the oil mist separator 100 but common to oil mist separators 200, 300, 400 and 500 of second to fifth embodiments as explained later. FIG. 2 is a sectional view of the oil mist separator 100, taken along line A-A shown in FIG. 1. FIG. 3 is an explanatory diagram schematically showing the oil mist separator 100. FIG. 4 is an enlarged explanatory diagram showing an essential part of the oil mist separator 100.

[0027] The oil mist separator 100 is disposed in a flow path through which blow-by gas generated in an engine of an automobile flows. As shown in FIG. 2, the oil mist separator 100 includes a generally dish-shaped upper casing 2 and a flat plate-shaped lower casing 3 which is connected with a lower surface of the upper casing 2. The upper casing 2 and the lower casing 3 cooperate to define a space 4 therebetween in which an oil component contained in the blow-by gas is separated from the blow-by gas.

[0028] Specifically, the upper casing 2 is made of a resin material and includes a flat plate-shaped upper wall 5, a generally cylindrical side wall 6 that extends around a periphery of the upper wall 5 to surround the upper wall 5, a cylindrical impact wall 7 that projects from a lower wall surface of the upper wall 5, and a cylindrical blow-by gas discharging portion 8 communicated with the space 4. The impact wall 7 extends in a same direction as that of the side wall 6 and has a length shorter than that of the side wall 6 to thereby generate a clearance between an axial end of the impact wall 7 and the base wall 10 of the lower casing 3. The impact wall 7 has a plurality of projections 9 on an inner circumferential wall surface thereof which linearly extend along the projecting direction (i.e., an axial direction of the impact wall 7), that is, along an up-and-down direction in FIG. 2.

[0029] The lower casing 3 is made of a resin material and includes a flat plate-shaped base wall 10 that cooperates with the upper wall 5 of the upper casing 2 to define the space 4 therebetween, a lower casing-side cylindrical volume chamber 11 having one axial end portion 11a from which the blow-by gas is introduced into the space 4, and a cylindrical oil drain portion 12 from which the oil separated from the blow-by gas is drained to an outside of the oil mist separator 100.

[0030] The lower casing-side volume chamber 11 is disposed on an inside of the impact wall 7 formed in the upper casing 2. The lower casing-side volume chamber 11 is arranged to be in coaxial relation to the impact wall 7.

[0031] A volume chamber forming member 13 is connected to a lower portion of the lower casing 3 so as to join with the lower casing-side volume chamber 11. The volume chamber forming member 13 is made of a resin material and has a stepped cylindrical shape. The volume chamber forming member 13 includes a larger diameter portion 13a that is disposed on the side of one end of the volume chamber forming member 13, and a smaller diameter portion 13b that is disposed on the side of the other end of the volume chamber forming member 13. The larger diameter portion 13a is connected to an underside of the base wall 10 of the lower casing 3. The smaller diameter portion 13b serves as an inlet for introducing the blow-by gas into the oil mist separator 100. That is, the lower casing-side volume chamber 11 and the volume chamber forming member 13 cooperate with each other to define a cylindrical volume chamber 14 into which the blow-by gas is introduced.

[0032] One axial end portion 11a of the lower casing-side volume chamber 11 (i.e., one axial end portion of the volume chamber 14) is formed into a cylindrical shape and communicated with the space 4 defined between the upper casing 2 and the lower casing 3. The one axial end portion 11a is disposed on the side of an upper end of the lower casing-side volume chamber 11 as shown in FIG. 2. The one axial end portion 11a is covered with a valve body 15. The valve body 15 is made of a resin material and formed into a cylindrical shape having one closed end.

[0033] The valve body 15 includes a circular bottom wall 16 that covers one axial end face of the lower casing-side volume chamber 11 (i.e., one axial end face of the volume chamber 14). The valve body 15 also includes a tubular side wall 17 that covers an outer circumferential surface of a side wall of the one axial end portion 11a of the lower casing-side volume chamber 11 (i.e., an outer circumferential surface of one axial end portion of the volume chamber 14), and a cylindrical valve stem 18 that is disposed at a central portion of the bottom wall 16.

[0034] The valve stem 18 is inserted into an insertion hole 20 of a valve body supporting portion 19 and projected from the valve body supporting portion 19 into an inside space of the lower casing-side volume chamber 11. The valve body supporting portion 19 is disposed at a center of an end face (one axial end face) of the one axial end portion 11a of the lower casing-side volume chamber 11. The valve body supporting portion 19 is connected with four leg portions 21 which extend radially inwardly from an inner circumferential periphery of the side wall of the one axial end portion 11a of the lower casing-side volume chamber 11.

[0035] A retainer 22 is mounted to the valve stem 18 and holds a spring 23 that is made of a metal material. The spring 23 is installed between the retainer 22 and a lower surface of the valve body supporting portion 19 and serves as a biasing member which always biases the valve body 15 toward the end face of the one axial end portion 11a of the lower casing-side volume chamber 11. That is, the spring 23 always biases in such a direction as to close apertures formed on the end face of the one axial end portion 11a of the lower casing-side volume chamber 11 (i.e., in such a direction that the bottom wall 16 of the valve body 15 approaches the one axial end face of the lower casing-side volume chamber 11).

[0036] The one axial end portion 11a of the lower casing-side volume chamber 11 is provided at the periphery thereof with a plurality of elliptic through holes 25 which are arranged in a circumferential direction of the lower casing-side volume chamber 11 at constant intervals therebetween. In this embodiment, six elliptic through holes 25 are formed and each of the elliptic through holes 25 extends from the one axial end face of the lower casing-side volume chamber 11 in an axial direction of the lower casing-side volume chamber 11. In other words, in this embodiment, each of the elliptic through holes 25 is provided in the form of a cutout having a U-shaped profile. The elliptic through hole 25 is formed by cutting the side wall of the lower casing-side volume chamber 11. That is, the elliptic through hole 25 is a cutout formed at the periphery of the one axial end portion 11a of the lower casing-side volume chamber 11.

[0037] When the bottom wall 16 of the valve body 15 is kept in contact with the one axial end face of the lower casing-side volume chamber 11, the through holes 25 are partly covered with the side wall 17 of the valve body 15, respectively. In other words, the through holes 25 have a same length which extends in the axial direction of the lower casing-side volume chamber 11 (i.e., in the up-and-down direction in FIG. 2 and FIG. 4) and is longer than an axial length of the side wall 17 of the valve body 15.

[0038] The through holes 25 formed in the one axial end portion 11a of the lower casing-side volume chamber 11 and the side wall 17 of the valve body 15 cooperate with each other to define six communication passages 26 which allow fluid communication between the inside space of the lower casing-side volume chamber 11 and the space 4 defined between the upper casing 2 and the lower casing 3. The communication passages 26 are arranged in the circumferential direction of the lower casing-side volume chamber 11 at constant intervals therebetween.

[0039] An operation of the thus constructed oil mist separator 100 is now explained by referring to FIG. 3. As shown in FIG. 3, blow-by gas introduced into the volume chamber 14 passes through the communication passages 26 and flows into a space between the lower casing-side volume chamber 11 and the impact wall 7. The flow of blow-by gas then impacts against the inner circumferential wall surface of the impact wall 7 which is opposed to the communication passages 26. The provision of the projections 9 on the inner circumferential wall surface of the impact wall 7 allows the flow of blow-by gas to be impacted against the irregular inner circumferential wall surface of the impact wall 7, so that separation of oil mist present in the blow-by gas from the blow-by gas can be promoted. The blow-by gas free from the oil component passes through the clearance between the impact wall 7 and the lower casing 3 and then flows into the blow-by gas discharging portion 8. The oil component separated from the blow-by gas drops down to the base wall 10 along the inner circumferential wall surface of the impact wall 7, flows over the base wall 10 and enters into the oil drain portion 12. Then, the oil component is drained from the oil drain portion 12 to an outside of the oil mist separator 100.

[0040] In a case where the blow-by gas is impacted against the impact wall 7 to separate the oil component contained in the blow-by gas from the blow-by gas, a flow velocity of the blow-by gas is well controlled to attain a good separation performance. For instance, in a case where the oil mist separator has the communication passages 26 each having a constant and large sectional area, the flow velocity of the blow-by gas upon impacting against the impact wall 7 becomes relatively small when the flow velocity of the blow-by gas from an engine is reduced in accordance with engine operating conditions, thereby causing deterioration in the performance of separation of the oil component contained in the blow-by gas. On the other hand, in a case where the oil mist separator has the communication passages 26 each having a constant and small sectional area, the flow velocity of the blow-by gas upon passing through the communication passages 26 becomes relatively large even when the flow velocity of the blow-by gas from the engine is reduced in accordance with the engine operating conditions. However, in such a case, pressure loss across the communication passages 26 tends to occur.

[0041] Whereas, in the oil mist separator 100 of the first embodiment described above, the valve body 15 is used for controlling the flow velocity of the blow-by gas which is introduced into the oil mist separator 100. When a pressure of the blow-by gas flowing into the volume chamber 14 is increased, the valve body 15 is urged to slidably move in such a direction as to be spaced apart from the one axial end of the lower casing-side volume chamber 11 against the biasing force of the spring 23. That is, when the pressure of the blow-by gas flowing into the volume chamber 14 is increased, the valve body 15 is allowed to move such that a distance between the bottom wall 16 and the one end face of the one axial end portion 11a of the lower casing-side volume chamber 11 is increased. As a result, a portion of each of the through holes 25 of the one axial end portion 11a of the lower casing-side volume chamber 11 which is covered with the side wall 17 of the valve body 15 is exposed to thereby increase a sectional area of each of the communication passages 26.

[0042] Specifically, when the flow rate of blow-by gas flowing into the volume chamber 14 is low, a lift amount of the valve body 15 relative to the one axial end portion 11a of the lower casing-side volume chamber 11 becomes small as shown in FIG. 4A, so that the portion of each of the through holes 25 which is covered with the side wall 17 of the valve body 15 also becomes small, thereby providing a small sectional area of each of the communication passages 26. On the other hand, when the flow rate of blow-by gas flowing into the volume chamber 14 is high, the lift amount of the valve body 15 relative to the one axial end portion 11a of the lower casing-side volume chamber 11 becomes large as shown in FIG. 4B, so that the portion of each of the through holes 25 which is covered with the side wall 17 of the valve body 15 also becomes large, thereby providing an increased sectional area of each of the communication passages 26. That is, as the pressure of the blow-by gas flowing into the volume chamber 14 becomes higher, the sectional area of each of the communication passages 26 that allows fluid communication of the blow-by gas between the inside space of the volume chamber 14 and the space 4 defined between the upper casing 2 and the lower casing 3 is increased.

[0043] The oil mist separator 100 according to the first embodiment as described above can attain the following function and effect. In a case where a pressure of the blow-by gas introduced into the volume chamber 14 is increased and a flow rate of the blow-by gas to be flowed out from the side of the one axial end of the volume chamber 14 through the communication passages 26 is increased, the sectional area of each of the communication passages 26 serving as an outlet through which the blow-by gas is flowed out from the volume chamber 14 is increased by the increase in flow rate of the blow-by gas. Therefore, flow velocity of the blow-by gas which is flowed out from the communication passages 26 can be kept substantially constant regardless of the flow rate of the blow-by gas.

[0044] Accordingly, the flow velocity of the blow-by gas upon impacting against the impact wall 7 can be kept constant irrespective of the flow rate of the blow-by gas which flows into the oil mist separator 100. As a result, when the blow-by gas is impacted against the impact wall 7, the oil component contained in the blow-by gas can be stably separated from the blow-by gas.

[0045] Further, since the sectional area of each of the communication passages 26 varies in accordance with the flow rate of the blow-by gas which flows into the oil mist separator 100, it is possible to suppress increase in pressure loss which is caused due to increase in flow rate of the blow-by gas which enters into the oil mist separator 100.

[0046] FIG. 5 to FIG. 7 are graphs showing various characteristic curves in which characteristics of the oil mist separator 100 according to the first embodiment of the present invention and those of an oil mist separator of a comparative embodiment are compared with each other. In each of FIG. 5 to FIG. 7, each solid line indicates a characteristic curve of the oil mist separator 100 according to the first embodiment and each broken line indicates a characteristic curve of the oil mist separator of the comparative embodiment.

[0047] The oil mist separator of the comparative embodiment has substantially the same construction as that of the oil mist separator 100 except that a sectional area of each of the communication passages serving as the outlet for the blow-by gas flowing out of the volume chamber is kept constant without varying in accordance with the flow rate of the blow-by gas flowing into the volume chamber and is almost equal to that of each of the communication passages of the oil mist separator 100 which is provided corresponding to a medium value of the flow rate of the blow-by gas flowing into the volume chamber.

[0048] FIG. 5 shows characteristic curves of the oil mist separator 100 according to the first embodiment and the oil mist separator of the comparative embodiment, each showing a relationship between flow rate of blow-by gas flowing into the oil mist separator and efficiency of trapping or separating oil mist present in the blow-by gas. In the oil mist separator 100 according to the first embodiment described above, the sectional area of each of the communication passages 26 varies in accordance with the flow rate of the blow-by gas flowing into the volume chamber 14, so that the flow velocity of the blow-by gas upon impacting the impact wall 7 can be kept substantially constant. Therefore, as seen from FIG. 5, even in such a condition that the flow rate of the blow-by gas is low, an oil component contained in the blow-by gas can be efficiently separated from the blow-by gas.

[0049] FIG. 6 shows characteristic curves of the oil mist separator 100 according to the first embodiment and the oil mist separator of the comparative embodiment, each showing a relationship between particle size of oil mist which is separated from the blow-by gas in the oil mist separator and efficiency of trapping the oil mist (that is, efficiency of separating the oil mist from the blow-by gas) under a condition that the flow rate of the blow-by gas flowing into the oil mist separator is kept constant and low. In the oil mist separator 100 according to the first embodiment as described above, when the flow rate of the blow-by gas flowing into the oil mist separator is low, the sectional area of each of the communication passages 26 is small. Therefore, it is possible to suppress drop in flow velocity of the blow-by gas flowing out of the communication passages 26 and thereby efficiently trap the oil mist having a small particle size as seen from FIG. 6.

[0050] FIG. 7 shows characteristic curves of the oil mist separator 100 according to the first embodiment and the oil mist separator of the comparative embodiment, each showing a relationship between flow rate of the blow-by gas flowing into the oil mist separator and pressure loss in the oil mist separator. In the oil mist separator 100 according to the first embodiment as described above, the sectional area of each of the communication passages 26 varies in accordance with the flow rate of the blow-by gas flowing into the volume chamber 14. Accordingly, it is possible to effectively suppress further pressure loss which will occur when the flow rate of the blow-by gas flowing into the volume chamber 14 is increased.

[0051] The second, third, fourth and fifth embodiments of the present invention will be explained hereinafter by referring to FIGS. 8A-8B, FIGS. 9A-9B, FIGS. 10A-10B and FIG. 11. In FIGS. 8A-8B, FIGS. 9A-9B, FIGS. 10A-10B and FIG. 11, like reference numerals denote like parts, and therefore, detailed explanations therefor are omitted.

[0052] FIGS. 8A-8B are explanatory diagrams showing an essential part of an oil mist separator 200 according to the second embodiment of the present invention. The oil mist separator 200 according to the second embodiment has substantially the same construction as that of the oil mist separator 100 according to the first embodiment except that each of the communication passages 26 is defined by the U-shaped through hole 25 formed in the one axial end portion 11a of the lower casing-side volume chamber 11 and a reversed U-shaped cutout 31 formed in the side wall 17 of the valve body 15.

[0053] In the second embodiment, similar to the first embodiment, when the flow rate of the blow-by gas flowing into the oil mist separator 200 is low, the sectional area of each of the communication passages 26 is small. On the other hand, when the flow rate of the blow-by gas flowing into the oil mist separator 200 is high, the sectional area of each of the communication passages 26 is large. Specifically, when the flow rate of the blow-by gas flowing into the oil mist separator 200 is low, the valve body 15 is placed in a non-lifted position as shown in FIG. 8A. In the non-lifted position, the valve body 15 is not lifted up relative to the one axial end portion 11a of the lower casing-side volume chamber 11 and each of the communication passages 26 has a circular profile shape as shown in FIG. 8A. In contrast, when the flow rate of the blow-by gas flowing into the oil mist separator 200 is high, the valve body 15 is placed in a lifted position as shown in FIG. 8B. In the lifted position, the valve body 15 is lifted up relative to the one axial end portion 11a of the lower casing-side volume chamber 11 and each of the communication passages 26 has an elliptic profile shape as shown in FIG. 8B.

[0054] The oil mist separator 200 according to the second embodiment can attain the same function and effect as those of the oil mist separator 100 according to the first embodiment.

[0055] In addition, in the second embodiment, it is necessary to align the through holes 25 of the lower casing-side volume chamber 11 and the cutout 31 of the valve body with each other. Therefore, there is provided a positioning mechanism (not shown) which performs positioning of the valve body 15 relative to the lower casing-side volume chamber 11 in order to prevent rotation of the valve body 15 relative to the lower casing-side volume chamber 11 in the circumferential direction of the lower casing-side volume chamber 11. For instance, the positioning mechanism is so constructed as to always keep engagement between a projection (not shown) formed on the side of the valve body 15 and a recessed portion (not shown) formed on the side of the lower casing-side volume chamber 11 regardless of the lift amount of the valve body 15 relative to the one axial end portion 11a of the lower casing-side volume chamber 11.

[0056] FIGS. 9A-9B are explanatory diagrams showing an essential part of an oil mist separator 300 according to the third embodiment of the present invention. The oil mist separator 300 according to the third embodiment has substantially the same construction as that of the oil mist separator 100 according to the first embodiment except that a plurality of through holes 34, 34 are formed in the one axial end portion 11a of the lower casing-side volume chamber 11 instead of the elliptic through holes 25 in the first embodiment. The through holes 34, 34 are arranged in two rows in the circumferential direction of the lower casing-side volume chamber 11 at constant intervals therebetween. The through holes 34, 34 of one of the two rows are spaced from the through holes 34, 34 of the other of the two rows and aligned therewith along the axial direction of the lower casing-side volume chamber 11. Further, in the oil mist separator 300 according to the third embodiment, the through holes 34, 34 and the side wall 17 of the valve body 15 cooperate with each other to define the communication passages 26 which are provided in the one axial end portion 11a of the lower casing-side volume chamber 11 in the circumferential direction of the lower casing-side volume chamber 11 at constant intervals therebetween.

[0057] In the third embodiment, when the flow rate of the blow-by gas flowing into the oil mist separator 300 is low, the valve body 15 is placed in the non-lifted position as shown in FIG. 9A. In the non-lifted position, the through holes 34, 34 of one of the two rows (i.e., the through holes 34, 34 of the upper row as shown in FIG. 9A) arranged in the circumferential direction of the lower casing-side volume chamber 11 are covered with the side wall 17 of the valve body 15, so that the effective sectional area of each of the communication passages 26 becomes smaller. When the flow rate of the blow-by gas flowing into the oil mist separator 300 is high, the valve body 15 is placed in the lifted position as shown in FIG. 9B. In the lifted position, the through holes 34, 34 of both the two rows are free from being covered with the side wall 17 of the valve body 15, so that the effective sectional area of each of the communication passages 26 becomes larger.

[0058] Accordingly, the oil mist separator 300 according to the third embodiment can attain the same function and effect as those of the oil mist separator 100 according to the first embodiment.

[0059] FIGS. 10A-10B are explanatory diagrams showing an essential part of an oil mist separator 400 according to the fourth embodiment of the present invention. The oil mist separator 400 according to the fourth embodiment has substantially the same construction as that of the oil mist separator 100 according to the first embodiment except that a plurality of through holes 37 having a reversed triangular profile shape are formed in the one axial end portion 11a of the lower casing-side volume chamber 11 instead of the U-shape profiled through holes 25 of the first embodiment. With the configuration of the through holes 37 having a reversed triangular profile shape, as the flow rate of the blow-by gas flowing into the oil mist separator 400 is increased, a rate of increase in sectional area of each of the communication passages 26 becomes higher.

[0060] The oil mist separator 400 according to the fourth embodiment can attain the same function and effect as those of the oil mist separator 100 according to the first embodiment.

[0061] FIG. 11 is a sectional view of an essential part of an oil mist separator 500 according to the fifth embodiment of the present invention, taken along line A-A shown in FIG. 1.

[0062] The oil mist separator 500 according to the fifth embodiment has substantially the same construction as that of the oil mist separator 100 according to the first embodiment except for arrangement of the spring 23 for biasing the valve body 15. In the oil mist separator 500, the spring 23 is installed between the upper wall 5 of the upper casing 2 and the bottom wall 16 of the valve body 15 as shown in FIG. 11. The spring 23 has one end engaged with a projection 40 which is formed on a lower surface of the upper wall 5 of the upper casing 2, and the other end engaged with a projection 41 which is formed on an upper surface of the bottom wall 16 of the valve body 15. Thus, the spring 23 is held between the upper casing 2 and the valve body 15.

[0063] The oil mist separator 500 according to the fifth embodiment can attain the same function and effect as those of the oil mist separator 100 according to the first embodiment. In addition, with the arrangement of the spring 23 between the upper casing 2 and the valve body 15, the retainer 22 used in the oil mist separator 100 according to the first embodiment can be omitted.

[0064] Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.

Claims

1. An oil mist separator comprising:

a tubular volume chamber (14) into which a gas is introduced, the volume chamber (14) having one axial end portion (11a);

a tubular valve body (15) having one closed end, the valve body including a bottom wall (16) which covers one end face of the one axial end portion (11a) of the volume chamber (14) and a tubular side wall (17) which covers an outer circumferential surface of a side wall of the one axial end portion (11a) of the volume chamber, the valve body (15) being so disposed as to slidably move relative to the one axial end portion (11a) of the volume chamber (14) such that a distance between the bottom wall (16) and the one end face of the one axial end portion (11a) of the volume chamber (14) is increased in accordance with increase in pressure of the gas flowing into the volume chamber (14),

a plurality of communication passages (26) which are defined by the one axial end portion (11a) of the volume chamber (14) and the valve body (15), through which the gas introduced into the volume chamber is flowed out from the volume chamber (14) and the valve body (15); and

an impact wall (7) which is disposed in an opposed relation to the communication passages (26) such that the gas flowed out through the communication passages is impacted against the impact wall;

wherein the communication passages (26) are configured such that as the pressure of the gas flowing into the volume chamber (14) is increased, a sectional area of each of the communication passages becomes larger.

2. The oil mist separator as claimed in claim 1, wherein the one axial end portion (11a) of the volume chamber (14) is formed into a cylindrical shape, the valve body (15) is formed into a cylindrical shape having one closed end, and the communication passages (26) are arranged in a circumferential direction of the one axial end portion (11a) of the volume chamber (14) at constant intervals therebetween.

3. The oil mist separator as claimed in claim 1 or 2, wherein the communication passages (26) are defined by the side wall (17) of the valve body (15) and a plurality of through holes (25; 34; 37) formed in the side wall of the one axial end portion (11a) of the volume chamber (14), and wherein when the valve body (15) is moved such that the bottom wall (16) is spaced apart from the one end face of the volume chamber (14), a portion of each of the through holes (25; 34; 37) which is covered with the side wall (17) of the valve body (15) is exposed to thereby increase a sectional area of each of the communication passages (26).

4. The oil mist separator as claimed in one of claims 1 to 3, wherein the communication passages (26) are further defined by a plurality of cutouts (31) which are formed in the side wall (17) of the valve body (15) in alignment with the through holes (25) formed in a side wall of the one axial end portion (11a) of the volume chamber (14) in an axial direction of the one axial end portion (11a) of the volume chamber (14).

5. The oil mist separator as claimed in claim 3, wherein the through holes (34, 34) formed in the side wall of the one axial end portion (11a) of the volume chamber (14) are arranged in two rows in the circumferential direction of the one axial end portion (11a) of the volume chamber (14) at constant intervals therebetween, the through holes (34, 34) of one of the two rows being spaced from the through holes (34, 34) of the other of the two rows and aligned therewith along an axial direction of the one axial end portion (11a) of the volume chamber (14).

6. The oil mist separator as claimed in claim 3, wherein each of the through holes (37) formed in the side wall of the one axial end portion (11a) of the volume chamber (14) is configured such that as a flow rate of the blow-by gas flowing into the oil mist separator is increased, a rate of increase in sectional area of each of the communication passages (26) becomes higher.

7. The oil mist separator as claimed in claim 1, further comprising a biasing member (23) which always biases the valve body (15) toward the one axial end portion (11a) of the volume chamber (14).

8. The oil mist separator as claimed in claim 7, wherein the biasing member (23) is installed between the valve body (15) and the one axial end portion (11a) of the volume chamber (14).

9. The oil mist separator as claimed in claim 7, further comprising a casing (2) in which the valve body (15) is disposed, wherein the biasing member (23) is installed between the casing and the bottom wall (16) of the valve body (15).

10. The oil mist separator as claimed in claim 1, wherein the impact wall (7) has a cylindrical shape and has a plurality of projections (9) which extend in an axial direction of the impact wall, and the impact wall (7) is arranged in coaxial relation to the one axial end portion (11a) of the volume chamber (14).

Drawing