BREATHER DEVICE

A breather device includes a case housing a device in an internal space and a valve tightly sealing the internal space. The valve includes a housing, a communication path, a ventilation passage, a seal portion, a valve element, and a spring. The valve element includes first and second valve members. The second valve member abuts against the first valve member to block a valve hole thereof. The spring includes first and second springs. The first spring pushes the first valve member against the seal portion in the housing of the valve. The second spring pushes the second valve member against the first valve member. The valve is brought into a closed valve state with the valve element pushed against the seal portion with the second valve member blocking the valve hole. The elastic force of the first spring in the closed valve state is larger than the second spring.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-031488 filed on Feb. 27, 2020, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a breather device that includes a case that defines a space and a valve that tightly seals the space. In the breather device, air can be taken into the case and can be exhausted from the case.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2009-106024 (JP 2009-106024 A) discloses a breather device that includes a case that houses a motor-generator in its internal space and a valve that allows air to be taken into the internal space of the case and exhausted from the internal space.

FIG. 10illustrates, as an example of a breather device according to the related art, a breather device510including two valve members that allow air to be taken in and exhausted, as with the breather device disclosed in JP 2009-106024 A. The breather device510includes a pipe521that penetrates a case511. The breather device510includes a cover529that covers the pipe521from the outside of the case511.

The breather device510includes a valve element560that insulates an internal space512and an external space513of the case511by blocking an opening end523A, which is positioned outside the case511, of a passage523in the pipe521. The valve element560is composed of two valve members, namely an exhaust valve member550in which a hole553is formed and an intake valve member540that abuts against the exhaust valve member550to block the hole553.

The breather device510includes a spring that biases the valve element560. The spring includes an outside spring562that pushes the exhaust valve member550against the pipe521so as to block the opening end523A and an inside spring561that pushes the intake valve member540against the exhaust valve member550. The outside spring562and the inside spring561are provided at positions facing each other with the valve element560interposed therebetween. The exhaust valve member550and the outside spring562are disposed between the cover529and the pipe521. The intake valve member540and the inside spring561are disposed in the passage523in the pipe521.

In the breather device510, when the pressure in the internal space512of the case511becomes higher, the intake valve member540and the exhaust valve member550are displaced toward the cover529along an axis C101that extends along the central axis of the passage523. Then, the internal space512and the external space513communicate with each other via the opening end523A of the pipe521to exhaust air from the internal space512to the external space513.

In the breather device510, when the pressure in the internal space512of the case511becomes lower, the intake valve member540is displaced toward the internal space512along the axis C101. Then, the internal space512and the external space513communicate with each other via the hole553of the exhaust valve member550to take air from the external space513into the internal space512.

In the breather device510, when the elastic force of the inside spring561at the time when there is no pressure difference between the inside and the outside is stronger than the elastic force of the outside spring562, the intake valve member540and the exhaust valve member550are displaced toward the cover529to allow communication between the internal space512and the external space513even when there is no pressure difference between the inside and the outside. In the breather device510, the case511is preferably tightly sealed when the pressure difference between the inside and the outside of the case511is small. Therefore, the elastic force of the inside spring561at the time when there is no pressure difference between the inside and the outside is set to be weaker than the elastic force of the outside spring562.

SUMMARY

There is a demand for the breather device to quickly resolve a pressure difference through exhaust when the pressure in the internal space of the case becomes high. When the breather device is placed in an environment in which the case may get wet with water, meanwhile, the pressure in the internal space may be lowered to be lower than the pressure in the external space when air in the case is cooled as the case gets wet with water. If the valve is opened because of the pressure difference at this time, water may enter the case. Therefore, it is not preferable for the breather device that air is taken in immediately when the pressure in the internal space becomes lower than the pressure in the external space since the case gets wet with water.

In the breather device510illustrated inFIG. 10, air tends to be taken in in a situation in which the pressure in the internal space is lowered to a smaller degree as the elastic force of the inside spring561at the time when there is no pressure difference between the inside and the outside is weaker. Therefore, water tends to enter the case when the pressure in the internal space is lowered since the case gets wet with water. The pressure difference at which air is taken in can be made larger by making the elastic force of the inside spring561stronger. In the breather device510, however, the elastic force of the inside spring561cannot be set to be stronger than the elastic force of the outside spring562. When the elastic force of the outside spring562is made stronger in order to make the elastic force of the inside spring561larger, the pressure difference at which air is exhausted becomes stronger, which makes it more difficult to resolve a situation in which the pressure in the internal space of the case is high.

When the pressure difference at which air is exhausted and the pressure difference at which air is taken in in the breather device are defined as a valve-opening pressure difference, the valve-opening pressure difference is determined by not only the spring load that affects the elastic force of the spring, but also the relationship between the spring load of the spring and the pressure receiving area that is the area of a surface of the valve element that receives the pressure. That is, the valve-opening pressure difference can be adjusted by changing the pressure receiving area. When the valve element is increased in size, for example, in order to increase the pressure receiving area, however, the size of the housing that houses the valve element is increased. When the valve element is reduced in size, for example, in order to reduce the pressure receiving area, meanwhile, the effect of fluctuations in the size of the valve element due to a manufacturing error on the valve-opening pressure difference tends to be large, and it is difficult to set the valve-opening pressure difference to a prescribed value.

In this manner, it has not been easy to set the pressure difference at which air is exhausted and the pressure difference at which air is taken in in accordance with the demand made for the breather device. Thus, the present disclosure provides a breather device that operates in accordance with the demand made for the breather device.

An aspect of the present disclosure relates to a breather device including a case and a valve. The case is configured to house a device in an internal space of the case. The valve is configured to tightly seal the internal space. The breather device is configured to open the valve based on a pressure difference between an external space and the internal space to take air from the external space into the internal space or exhaust air from the internal space to the external space, the external space being a space outside the case. The valve includes a housing, a communication path, a ventilation passage, a seal portion, a valve element, and a spring. The communication path is configured to allow communication between an inside of the housing and the internal space. The ventilation passage is configured to allow communication between the inside of the housing and the external space. The seal portion is provided in the housing and positioned between the communication path and the ventilation passage. The valve element is configured to block communication between the internal space and the external space through the inside of the housing by abutting against the seal portion. The spring is configured to bias the valve element. The valve element is composed of two valve members including a first valve member and a second valve member, the first valve member includes a valve hole that penetrates the first valve member, and the second valve member is configured to block the valve hole by abutting against the first valve member. The spring includes a first spring and a second spring. The first spring is configured to push the first valve member against the seal portion. The second spring is configured to push the second valve member against the first valve member. The first spring and the second spring are provided at positions facing each other with the valve element interposed between the first spring and the second spring. The valve is brought into a closed valve state, in which communication between the communication path and the ventilation passage through the inside of the housing is blocked, by the valve element being pushed against the seal portion with the second valve member blocking the valve hole of the first valve member, the first spring is disposed in a first space, the second spring is disposed in a second space, and an elastic force of the first spring in the closed valve state is larger than an elastic force of the second spring. The first space is a space positioned on the communication path side with respect to the valve element, and the second spring is a space positioned on the ventilation passage side with respect to the valve element, of spaces obtained by the valve element partitioning the inside of the housing when the valve is in the closed valve state.

In the breather device according to the aspect described above, when the pressure in the internal space of the case becomes lower and the force to draw the valve element toward the communication path exceeds the elastic force of the first spring, the valve element is displaced toward the communication path. Therefore, the first space and the second space communicate with each other with a gap formed between the first valve member and the seal portion. Consequently, communication between the internal space and the external space of the case is allowed, which allows air to be taken from the external space into the internal space. When the pressure in the internal space of the case becomes higher and the force to press the second valve member toward the ventilation passage exceeds the elastic force of the second spring, on the other hand, the second valve member is displaced toward the ventilation passage. Since the second valve member is moved away from the first valve member, the first space and the second space communicate with each other with the valve hole of the first valve member opened. Consequently, communication between the internal space and the external space of the case is allowed, which allows air to be exhausted from the internal space to the external space.

The valve is brought into the closed valve state with the valve element pushed against the seal portion with the second valve member blocking the valve hole of the first valve member. The closed valve state can be maintained when there is no pressure difference between the internal space and the external space, since the elastic force of the first spring that presses the first valve member, of the springs that are disposed at positions facing each other with the valve element interposed therebetween, is set to be larger than the elastic force of the second spring that presses the second valve member.

The first valve member is moved away from the seal portion less easily as the elastic force of the first spring in the closed valve state is stronger, for example. Therefore, the pressure difference required to take in air can be set to be larger by making the elastic force of the first spring stronger. On the other hand, the second valve member is moved away from the first valve member more easily as the elastic force of the second spring in the closed valve state is weaker. Therefore, the pressure difference required to exhaust air can be set to be smaller by making the elastic force of the second spring weaker.

That is, the closed valve state can be maintained when there is no pressure difference between the internal space and the external space since the elastic force of the first spring in the closed valve state is set to be larger than the elastic force of the second spring, and the valve-opening pressure difference that meets the demand can be set within such a range that the elastic force of the first spring is larger than the elastic force of the second spring.

With the breather device according to the aspect described above, as described above, the valve-opening pressure difference that meets the demand made for the breather device can be achieved by adjusting the elastic force of the spring without changing the pressure receiving area of the valve element. That is, it is possible to achieve the valve-opening pressure difference that meets the demand made for the breather device without increasing the size of the casing of the valve or without the valve-opening pressure difference being affected by a manufacturing error of the valve element.

In the breather device according to the aspect described above, the first valve member may be in a bottomed cylindrical shape in which the first valve member is open at one end and is blocked by a bottom plate at the other end. The valve hole of the first valve member may penetrate the bottom plate. The second valve member may be in a plate shape. The second valve member and the second spring may be disposed inside the first valve member. When an opening of the ventilation passage on the second space side is defined as a ventilation port, the seal portion may be a wall surface of the housing in which the ventilation port opens. The first valve member may be configured such that an end surface of the first valve member on an opening side abuts against the wall surface so as to surround the ventilation port when in the closed valve state.

With the breather device configured as described above, the second valve member and the second spring are disposed inside the first valve member in a tubular shape. Therefore, the second valve member is displaced inside the first valve member. That is, the first valve member functions as a guide that guides the second valve member that is displaced in accordance with the pressure difference between the internal space and the external space and the elastic force of the spring. Consequently, motion of the second valve member can be stabilized.

In the breather device according to the aspect described above, the first valve member may be in a bottomed cylindrical shape in which the first valve member is open at one end and is blocked by a bottom plate at the other end. The valve hole of the first valve member may penetrate the bottom plate. The second valve member may include a surface on the bottom plate side that projects in a spherical crown shape toward the bottom plate. The second valve member and the second spring may be disposed inside the first valve member. When an opening of the ventilation passage on the second space side is defined as a ventilation port, the seal portion may be a wall surface of the housing in which the ventilation port opens, and the first valve member may be configured such that an end surface of the first valve member on an opening side abuts against the wall surface so as to surround the ventilation port when in the closed valve state.

With the breather device configured as described above, the second valve member and the second spring are disposed inside the first valve member in a tubular shape. Therefore, the second valve member is displaced inside the first valve member. That is, the first valve member functions as a guide that guides the second valve member that is displaced in accordance with the elastic force of the spring and the pressure difference between the internal space and the external space. Consequently, motion of the second valve member can be stabilized.

Further, the second valve member has a surface that projects in a spherical crown shape. Therefore, a part of the second valve member can enter the valve hole when the second valve member abuts against the first valve member so as to block the valve hole. Therefore, the second valve member is easily accommodated at a prescribed position when the second valve member is pressed toward the first valve member. Consequently, the occurrence of a situation in which the valve hole is not blocked even when the second valve member abuts against the first valve member can be suppressed.

In the breather device according to the aspect described above, the first valve member may be in a bottomed cylindrical shape in which the first valve member is open at one end and is blocked by a bottom plate at the other end. The valve hole of the first valve member may penetrate the bottom plate. The second valve member may include a plate portion in a plate shape, a first projecting portion in a columnar shape that projects from a surface of the plate portion on the communication path side, and a second projecting portion in a columnar shape that projects from a surface of the plate portion on the ventilation passage side. The second valve member and the second spring may be disposed inside the first valve member. If an opening of the ventilation passage on the second space side is defined as a ventilation port, the seal portion may be a wall surface of the housing in which the ventilation port opens. When the valve is in the closed valve state, an end surface of the first valve member on an opening side may abut against the wall surface so as to surround the ventilation port, the first projecting portion may be inserted into the valve hole, and the second projecting portion may be inserted into the ventilation passage.

With the breather device configured as described above, displacement of the second valve member can be guided more easily, since the first projecting portion is inserted into the valve hole and the second projecting portion is inserted into the ventilation passage when the valve is in the closed valve state. Consequently, motion of the second valve member can be stabilized better.

In the breather device according to the aspect described above, the first valve member and the second valve member may be in a plate shape, and the seal portion may be a retention wall that partitions the inside of the housing into a portion on the internal space side and a portion on the external space side and that is provided with a through hole that allows communication between the portion on the internal space side and the portion on the external space side. The first valve member may be configured such that a surface of the first valve member on the retention wall side abuts against the retention wall such that the valve element blocks the through hole when in the closed valve state.

In the breather device according to the aspect described above, when an opening of the ventilation passage on the second space side is defined as a ventilation port and an opening of the ventilation passage on the external space side is defined as an open port, the ventilation passage may be shaped such that there are no line segments that are drawn between a point on an imaginary plane surrounded by a periphery of the ventilation port and a point on an imaginary plane surrounded by a periphery of the open port and that pass only in the ventilation passage.

With the breather device configured as described above, the ventilation passage is shaped so as not to allow one to see through from the open port to the ventilation port. Therefore, even if water droplets are carried by a flow of air to enter the ventilation passage from the open port in the case where air is taken in when the pressure in the internal space of the case becomes low, the water droplets that have entered the ventilation passage inevitably collide against the inner wall of the ventilation passage, which makes it difficult for the water droplets to reach the ventilation port. Consequently, entry of water into the internal space of the case during air intake can be suppressed.

In the breather device configured as described above, the ventilation passage may include a bent portion at which the ventilation passage is bent. The bent portion may be located between the ventilation port which is an opening on the second space side, and the open port which is an opening on the external space side.

With the breather device configured as described above, when line segments that may be drawn between a point on an imaginary plane surrounded by the periphery of the ventilation port of the ventilation passage and a point on an imaginary plane surrounded by the periphery of the open port are considered, there are no line segments that pass only in the ventilation passage because of the presence of the bent portion. Thus, even if water droplets enter the ventilation passage, the water droplets collide against the inner wall of the ventilation passage, which makes it difficult for the water droplets to reach the ventilation port. Thus, entry of water into the internal space of the case during air intake can be suppressed.

In the breather device configured as described above, the ventilation port may be positioned above the open port in a vertical direction.

With the breather device configured as described above, the ventilation port is positioned above the open port in the vertical direction. Thus, water droplets tend to fall before reaching the ventilation port even if water droplets enter the ventilation passage from the open port. That is, water droplets do not easily reach the ventilation port, which suppresses entry of water into the internal space of the case during air intake.

DETAILED DESCRIPTION OF EMBODIMENTS

A breather device according to a first embodiment of the present disclosure will be described below with reference toFIGS. 1 to 5.FIG. 1illustrates a breather device10mounted on a vehicle. The breather device10includes a case11that houses a transmission90of the vehicle. The case11defines an internal space12that is a space housing the transmission90. InFIG. 1, the space outside the case11is indicated as an external space13.

The breather device10includes a valve20attached to the case11. When the valve20is in the closed valve state, the internal space12is tightly sealed. The valve20opens based on the pressure difference between the internal space12and the external space13. The manner in which the valve20is opened will be discussed later. When the valve20is open, the breather device10can take air from the external space13into the internal space12as indicated by the dashed arrow inFIG. 1. When the valve20is open, in addition, the breather device10can exhaust air from the internal space12to the external space13as indicated by the continuous arrow inFIG. 1.

The structure of the valve20will be described with reference toFIGS. 2 to 4.

As illustrated inFIG. 2, the valve20includes a housing21and a valve element60disposed in the housing21.

The housing21is in a cylindrical shape. The housing21has an insertion portion22inserted into the case11and a body portion24that defines a space that houses the valve element60. The body portion24is positioned in the external space13. The diameter of the body portion24is larger than the diameter of the insertion portion22.

The valve20includes a communication path23that allows communication between the inside of the housing21and the internal space12. The communication path23is provided in the insertion portion22.FIG. 2indicates an axis C1that extends along the central axis of the communication path23.

The valve20includes a ventilation passage28that allows communication between the inside of the housing21and the external space13. The ventilation passage28is formed in a top plate27of the body portion24. The top plate27is positioned at an end of the body portion24on the opposite side from the insertion portion22in the direction in which the axis C1extends. An opening of the ventilation passage28on the side close to the space in the housing21is referred to as a ventilation port28A. The top plate27is a wall in which the ventilation port28A opens. An opening of the ventilation passage28on the external space13side is referred to as an open port28B. The central axis of the ventilation passage28coincides with the central axis of the communication path23.

The valve20includes a retention wall26that is a wall that partitions the space inside of the housing21into a portion on the internal space12side and a portion on the external space13side. The retention wall26is positioned in the body portion24. The retention wall26is provided with one through hole26B as a hole that allows communication between the portion on the internal space12side and the portion on the external space13side. The through hole26B is provided at the center of the retention wall26. The center of the through hole26B is positioned on the extension line of the axis C1. The retention wall26in which the through hole26B is formed is shaped to project into the housing21from the inner surface of a side wall25of the body portion24, which is in a cylindrical shape, to narrow the space in the housing21in the sectional structure illustrated inFIG. 2.

The valve element60is composed of a first valve member40in a circular plate shape and a second valve member50in a circular plate shape. The diameter of the first valve member40is larger than the inside diameter of the through hole26B, and smaller than the inside diameter of the body portion24. There is a gap between the first valve member40and the side wall25. A valve hole43is provided in the first valve member40as a hole that penetrates the first valve member40. The diameter of the second valve member50is larger than the inside diameter of the valve hole43, and smaller than the diameter of the first valve member40. In addition, the diameter of the second valve member50is smaller than the inside diameter of the through hole26B.

The second valve member50is disposed on the ventilation passage28side with respect to the first valve member40. The valve hole43can be blocked by a surface of the second valve member50on the first valve member40side as the surface abuts against the first valve member40.

The first valve member40is disposed on the communication path23side with respect to the retention wall26. The first valve member40is disposed such that the center of the valve hole43is positioned on the extension line of the axis C1. The through hole26B can be blocked by a surface of the first valve member40on the retention wall26side as the surface abuts against the retention wall26with the second valve member50blocking the valve hole43.

The inside diameter of the through hole26B is larger than the inside diameter of the communication path23. The inside diameter of the ventilation passage28is smaller than the inside diameter of the communication path23. The inside diameter of the valve hole43is equal to the inside diameter of the ventilation passage28. The valve20includes a spring that biases the valve element60. The valve20includes, as the spring, a first spring61and a second spring62provided at positions facing each other with the valve element60interposed therebetween. The first spring61pushes the first valve member40against the retention wall26. The second spring62pushes the second valve member50against the first valve member40.

In the valve20, the through hole26B is blocked by the valve element60when the valve element60is pushed against the retention wall26with the second valve member50blocking the valve hole43of the first valve member40. That is, the valve element60that is composed of the first valve member40and the second valve member50blocks communication between the internal space12and the external space13through the inside of the housing21by blocking the through hole26B as the valve element60abuts against the retention wall26. The retention wall26is a seal portion provided in the housing21and positioned between the communication path23and the ventilation passage28. The valve20is brought into the closed valve state, in which communication between the communication path23and the ventilation passage28through the inside of the housing21is blocked, when the valve hole43and the through hole26B are blocked.FIG. 2illustrates the valve20in the closed valve state. As discussed in detail later, the valve element60is biased by the first spring61and the second spring62such that the valve20is brought into the closed valve state when there is no pressure difference between the internal space12and the external space13. In the valve20, the spring loads of the first spring61and the second spring62are set such that the elastic force of the first spring61in the closed valve state is larger than the elastic force of the second spring62. Therefore, the closed valve state is maintained when there is no pressure difference between the internal space12and the external space13.

A space positioned on the communication path23side with respect to the valve element60, of spaces obtained by the valve element60partitioning the inside of the housing21when the valve20is in the closed valve state as illustrated inFIG. 2, is defined as a first space31. The first spring61is disposed in the first space31. A space positioned on the ventilation passage28side with respect to the valve element60, of the spaces obtained by the valve element60partitioning the inside of the housing21when the valve20is in the closed valve state, is defined as a second space32. The second spring62is disposed in the second space32.

FIG. 3illustrates the position of the valve element60at the time when air is taken from the external space13into the internal space12. When the pressure in the internal space12becomes lower and the force to draw the valve element60toward the communication path23exceeds the elastic force of the first spring61, the valve element60is displaced toward the communication path23. Since the first valve member40is moved away from the retention wall26, the first space31and the second space32communicate with each other with a gap formed between the first valve member40and the retention wall26as illustrated inFIG. 3. When the valve20is in this state, communication between the internal space12and the external space13is allowed. Since the pressure in the internal space12is low, air is taken from the external space13into the internal space12.

FIG. 4illustrates the position of the valve element60at the time when air is exhausted from the internal space12to the external space13. When the pressure in the internal space12becomes higher and the force to press the second valve member50toward the ventilation passage28exceeds the elastic force of the second spring62, the second valve member50is displaced toward the ventilation passage28. Since the second valve member50is moved away from the first valve member40, the first space31and the second space32communicate with each other with the valve hole43of the first valve member40opened as illustrated inFIG. 4. When the valve20is in this state, communication between the internal space12and the external space13is allowed. Since the pressure in the internal space12is high, air is exhausted from the internal space12to the external space13.

The relationship between the pressure difference between the pressure in the internal space12and the pressure in the external space13and the state of the valve20will be described with reference toFIG. 5. InFIG. 5, the pressure in the external space13is used as a reference, and the pressure difference is determined as “0” when the pressure in the internal space12is equal to the pressure in the external space13. The pressure difference has a negative value when the pressure in the internal space12is lower than the pressure in the external space13. Meanwhile, the pressure difference has a positive value when the pressure in the internal space12is higher than the pressure in the external space13.

In the breather device10, the valve element60is displaced toward the communication path23when the pressure difference is equal to or less than an intake pressure difference P1that has a value that is less than “0”. That is, a gap is formed between the first valve member40and the retention wall26as illustrated inFIG. 3. When the pressure difference is equal to or less than the intake pressure difference P1, air can be taken from the external space13into the internal space12by allowing communication between the first space31and the second space32. The breather device10requires the intake pressure difference P1to take in air.

In the breather device10, the second valve member50is displaced toward the ventilation passage28when the pressure difference is equal to or more than an exhaust pressure difference P2that has a value that is more than “0”. That is, the valve hole43of the first valve member40is opened as illustrated inFIG. 4. When the pressure difference is equal to or more than the exhaust pressure difference P2, air can be exhausted from the internal space12to the external space13by allowing communication between the first space31and the second space32. The breather device10requires the exhaust pressure difference P2to exhaust air.

In the breather device10, the housing21of the valve20is enclosed when the pressure difference is in a range including “0”. More particularly, the housing21is enclosed when the pressure difference is higher than the intake pressure difference P1and lower than the exhaust pressure difference P2. That is, the valve20is brought into the closed valve state with communication between the internal space12and the external space13blocked as illustrated inFIG. 2.

In the breather device10, as illustrated inFIG. 5, the intake pressure difference P1and the exhaust pressure difference P2are set such that the magnitude of the intake pressure difference P1is larger than the magnitude of the exhaust pressure difference P2, that is, the absolute value of “P1” is larger than the absolute value of “P2”. The intake pressure difference P1and the exhaust pressure difference P2can be set based on the relationship among the area with which the valve element60receives a pressure based on the pressure difference, the spring load of the first spring61, and the spring load of the second spring62.

In the valve20, when the area with which the valve element60receives a pressure from the second space32side is defined as a first pressure receiving area S1, the spring load of the first spring61is defined as a first spring load F1, and the spring load of the second spring62is defined as a second spring load F2, the magnitude of the intake pressure difference P1can be represented by the following (Expression 1).

That is, a relationship in which the magnitude of the intake pressure difference P1becomes larger as a value obtained by subtracting the second spring load F2from the first spring load F1is increased and the magnitude of the intake pressure difference P1becomes larger as the first pressure receiving area S1is reduced is established. The first spring load F1is larger than the second spring load F2so that the elastic force of the first spring61in the closed valve state is larger than the elastic force of the second spring62.

In the valve20, when the area with which the second valve member50receives a pressure from the first space31side is defined as a second pressure receiving area S2, the magnitude of the exhaust pressure difference P2can be represented by the following (Expression 2).

That is, a relationship in which the magnitude of the exhaust pressure difference P2becomes smaller as the second spring load F2is reduced and the magnitude of the exhaust pressure difference P2becomes smaller as the second pressure receiving area S2is increased is established.

In the valve20, the first pressure receiving area S1, the second pressure receiving area S2, the first spring load F1, and the second spring load F2are set based on the above (Expression 1) and (Expression 2) such that the intake pressure difference P1has a value that is less than “0”, the exhaust pressure difference P2has a value that is more than “0”, and the absolute value of the intake pressure difference P1is larger than the absolute value of the exhaust pressure difference P2. The first pressure receiving area S1and the second pressure receiving area S2can be changed in accordance with the shape of the housing21or the shape of the valve element60.

The functions of the first embodiment will be described. There is a demand for the breather device to quickly resolve a pressure difference through exhaust when the pressure in the internal space of the case becomes high. In the case where the breather device is placed in an environment in which the case may get wet with water, meanwhile, the pressure in the internal space may be lowered to be lower than the pressure in the external space when air in the case is cooled as the case gets wet with water. If the valve is opened because of the pressure difference at this time, water may enter the case. Therefore, it is not preferable for the breather device that air is taken in immediately when the pressure in the internal space becomes lower than the pressure in the external space since the case gets wet with water.

With the breather device10, the magnitude of the intake pressure difference P1can be set to be larger as the first spring load F1is increased using the relationship based on the above (Expression 1). As the first spring load F1is increased, the elastic force of the first spring61in the closed valve state is larger, and the first valve member40is less easily moved away from the retention wall26as a seal portion when the pressure in the internal space12is lowered to a small degree.

On the other hand, the magnitude of the exhaust pressure difference P2can be set to be smaller as the second spring load F2is reduced using the relationship based on the above (Expression 2). As the second spring load F2is smaller, the elastic force of the second spring62in the closed valve state is smaller, and the second valve member50is more easily moved away from the first valve member40even when the pressure in the internal space12is raised to a small degree.

The effects of the first embodiment will be described.

(1-1) In the breather device10, the first spring load F1and the second spring load F2are set such that the elastic force of the first spring61in the closed valve state is larger than the elastic force of the second spring62. The valve20can be maintained in the closed valve state when there is no pressure difference between the internal space12and the external space13, since the elastic force of the first spring61is larger than the elastic force of the second spring62in the closed valve state.

(1-2) With the breather device10, the magnitude of the intake pressure difference P1can be increased by increasing the first spring load F1. Further, the magnitude of the exhaust pressure difference P2can be reduced by reducing the second spring load F2. In addition, a value obtained by subtracting the second spring load F2from the first spring load F1is increased by reducing the second spring load F2, and therefore the magnitude of the intake pressure difference P1can be increased also by reducing the second spring load F2. Consequently, the magnitude of the intake pressure difference P1can be increased while setting the magnitude of the exhaust pressure difference P2to be small.

For the breather device10, for example, the exhaust pressure difference P2is preferably set to a value that is close to “0”, in order to facilitate immediate resolution of a situation in which the pressure in the internal space12is high when the pressure in the internal space12is raised. By way of example, the exhaust pressure difference P2is set to 2 to 5 [kPa]. In this manner, the magnitude of the intake pressure difference P1can be set to be large even when the magnitude of the exhaust pressure difference P2is small.

(1-3) The intake pressure difference P1and the exhaust pressure difference P2can be set using a relationship based on the above (Expression 1) and (Expression 2). Therefore, the valve20can be maintained in the closed valve state when there is no pressure difference between the internal space12and the external space13, and the intake pressure difference P1and the exhaust pressure difference P2that meet the demand can be set in such a range that the elastic force of the first spring61in the closed valve state is larger than the elastic force of the second spring62.

(1-4) The breather device10can achieve the intake pressure difference P1and the exhaust pressure difference P2that meet the demand made for the breather device10, by adjusting the first spring load F1and the second spring load F2without changing the first pressure receiving area S1or the second pressure receiving area S2.

For example, it is not necessary to reduce the first pressure receiving area S1in order to increase the magnitude of the intake pressure difference P1. When the size of the valve element is reduced in order to reduce the first pressure receiving area S1, the effect of fluctuations in the size of the valve element due to a manufacturing error on the intake pressure difference P1tends to be large, and it is difficult to set the intake pressure difference P1to a prescribed value.

In addition, for example, it is not necessary to increase the second pressure receiving area S2in order to reduce the magnitude of the exhaust pressure difference P2. When the size of the valve element is increased in order to increase the second pressure receiving area S2, the size of the housing that houses the valve element is also increased, which increases the size of the valve.

With the breather device10, on the contrary, the intake pressure difference P1and the exhaust pressure difference P2that meet the demand made for the breather device10can be achieved without causing the issues described above due to a change in the first pressure receiving area S1or the second pressure receiving area S2.

The first embodiment may be modified as follows. The first embodiment and the following modifications can be combined with each other unless such an embodiment and modifications technically contradict with each other. First, a first modification of the first embodiment will be described. A breather device110according to the first modification illustrated inFIG. 6is different from the breather device10according to the first embodiment in that a valve element160of a valve120is composed of a first valve member140in a bottomed cylindrical shape and a second valve member150in a plate shape.FIG. 6indicates an axis C2that extends along the central axis of a communication path123.

The first valve member140that constitutes the valve element160is in a cylindrical shape. The first valve member140is open at one end, and is blocked by a bottom plate141at the other end. A valve hole144is formed in the first valve member140as a hole that penetrates the bottom plate141. The first valve member140is disposed in a housing121such that the central axis of the cylinder coincides with the axis C2. The first valve member140is disposed with the bottom plate141positioned on the communication path123side and with an opening146positioned on the ventilation passage128side.

The second valve member150and a second spring162are disposed inside the first valve member140. The housing121is not provided with the retention wall26, unlike the breather device10. In the breather device110, the inner surface of a wall in which a ventilation port128A opens serves as a seal portion in place of the retention wall26. That is, an inner surface127A of a top plate127of the housing121serves as a seal portion. In the breather device110, the top plate127is a wall in which the ventilation port128A opens. The inner surface127A is a wall surface of the top plate127that is a wall in which the ventilation port128A opens. When the valve120is in the closed valve state, an end surface of the first valve member140on the opening146side abuts against the inner surface127A so as to surround the ventilation port128A. In the breather device110, a space positioned on the communication path123side with respect to the valve element160, that is, a space outside the first valve member140, is defined as a first space131. Meanwhile, a space positioned on the ventilation passage128side with respect to the valve element160, that is, a space inside the first valve member140, is defined as a second space132.

The breather device110illustrated inFIG. 6is different from the breather device10according to the first embodiment in the configuration of the valve element160and the position of the seal portion, but is the same as the breather device10in the arrangement of the valve members and the arrangement of the springs in the housing121. Therefore, the relationship of the above (Expression 1) and (Expression 2) is established. The intake pressure difference P1and the exhaust pressure difference P2can be set in the same manner as in the first embodiment. That is, the same effects as those of the first embodiment in (1-1) to (1-4) can be achieved.

In the breather device110, further, the second valve member150and the second spring162are disposed inside the first valve member140in a tubular shape. Therefore, the second valve member150is displaced inside the first valve member140. That is, the first valve member140functions as a guide that guides the second valve member150that is displaced in accordance with the pressure difference between the internal space12and the external space13and the elastic forces of the first spring161and the second spring162. Consequently, motion of the second valve member150can be stabilized.

Next, a second modification of the first embodiment will be described. A breather device210according to the second modification illustrated inFIG. 7is different from the breather device110illustrated inFIG. 6in the shape of a second valve member250. The second valve member250includes a first projecting portion252A and a second projecting portion253A in a circular column shape that project from the center of a plate portion251in a circular plate shape along the axis C2. The first projecting portion252A projects from a surface of the plate portion251on the communication path123side. The second projecting portion253A projects from a surface of the plate portion251on the ventilation passage128side. The diameters of the first projecting portion252A and the second projecting portion253A are smaller than the diameter of the plate portion251. The first projecting portion252A is inserted into a valve hole244. Further, the second projecting portion253A is inserted into the ventilation passage128.

The breather device210can achieve the same effects as those of the breather device110illustrated inFIG. 6. In the breather device210, further, displacement of the second valve member250is easily guided along the axis C2. Consequently, motion of the second valve member250can be stabilized better.

The effect of guiding the second valve member250can be achieved when the first projecting portion252A is inserted into the valve hole244or the second projecting portion253A is inserted into the ventilation passage128. In addition, the lengths of projection of the first projecting portion252A and the second projecting portion253A from the plate portion251are exemplary, and are changeable.

In addition, the shape of the first projecting portion252A may be any shape that enables insertion into the valve hole244, and is not limited to a circular column shape. Similarly, the shape of the second projecting portion253A may be any shape that enables insertion into the ventilation passage128, and is not limited to a circular column shape.

Furthermore, the first projecting portion252A may not necessarily project from the center of the plate portion251along the axis C2as long as the first projecting portion252A projects from a surface of the plate portion251on the communication path123side. Similarly, the second projecting portion253A may not necessarily project from the center of the plate portion251along the axis C2as long as the second projecting portion253A projects from a surface of the plate portion251on the ventilation passage128side.

Next, a third modification of the first embodiment will be described. A breather device310according to the third modification illustrated inFIG. 8is different from the breather device110illustrated inFIG. 6in that a second valve member350is in a spherical shape. Further, the diameter of a valve hole349that penetrates a bottom plate341of a first valve member340is increased from the first space131side toward the second space132.

The breather device310can achieve the same effects as those of the breather device110illustrated inFIG. 6. In the breather device310, further, the diameter of the valve hole349of the first valve member340is increased toward the second space132. Therefore, the second valve member350can be caused to abut against the inner wall of the valve hole349when the second valve member350in a spherical shape abuts against the first valve member340so as to block the valve hole349. Therefore, the second valve member350is easily accommodated at a prescribed position when the second valve member350is pressed toward the first valve member340. Consequently, the occurrence of a situation in which the valve hole349is not blocked even when the second valve member350abuts against the first valve member340can be suppressed.

It is not essential that the diameter of the valve hole349should be increased. Also, when the diameter of the valve hole349is not increased toward the second space132, a part of the second valve member can enter the valve hole in the case where the second valve member abuts against the first valve member so as to block the valve hole when the second valve member350is in a spherical shape. Consequently, the second valve member is easily accommodated at a prescribed position when the second valve member is pressed toward the first valve member.

When the second valve member is shaped to be swelled in a spherical crown shape on the bottom plate341side and have a surface that projects toward the bottom plate341, meanwhile, the same effect as that obtained with the second valve member350in a spherical shape described above can be achieved. That is, the second valve member is not limited to being in a spherical shape as illustrated inFIG. 8, and may be in the shape of a spherical segment such as a hemisphere.

While a first valve member in a cylindrical shape is adopted in the breather devices illustrated inFIGS. 6 to 8, the first valve member is not limited to a cylindrical shape as long as the first valve member is in a bottomed cylindrical shape including a bottom plate in which a valve hole is provided. The first valve member40and the second valve member50in a circulate plate shape according to the first embodiment are examples of valve members in a plate shape.

The shape of the housing21according to the first embodiment is exemplary. For example, the diameter of the insertion portion22and the diameter of the body portion24may be equal to each other. In addition, for example, the retention wall26may be positioned more on the communication path23side, or more on the ventilation passage28side.

The relationship among the respective inside diameters of the communication path23, the ventilation passage28, the through hole26B, and the valve hole43indicated in the first embodiment is exemplary. In the first embodiment, the central axis of the ventilation passage28coincides with the central axis of the communication path23. Further, the center of the through hole26B is positioned on the extension line of the axis C1that extends along the central axis of the communication path23. In addition, the first valve member40is disposed such that the center of the valve hole43is positioned on the extension line of the axis C1. It is not an essential requirement that all the central axes should coincide with each other. In addition, the center of the hole may be misaligned from the extension line of the axis C1.

The transmission90according to the first embodiment is an example of the device housed in the case11. The device housed in the case11is not limited to the transmission90, and may be a motor-generator, for example.

Next, a breather device according to a second embodiment of the present disclosure will be described with reference toFIG. 9. As illustrated inFIG. 9, a breather device410is configured such that the valve element160of a valve420is composed of the first valve member140and the second valve member150as in the breather device110illustrated inFIG. 6. The valve element160is not described in detail.

As illustrated inFIG. 9, the breather device410is mounted on a vehicle with an axis C3, which extends along the central axis of a communication path423, directed in the horizontal direction. In addition, an O-ring71is attached to an insertion portion422of a housing421to seal the boundary between the insertion portion422and a case411.

The case411includes a protruding portion414that shields the valve420from the lower side in the vertical direction. Further, the breather device410is different from the breather device110in that a lid portion429is attached to the housing421in place of the top plate127in the breather device110. A ventilation passage428that allows communication between the inside of the housing421and the external space13is provided in the lid portion429.

The ventilation passage428includes a bent portion428C that is located between a ventilation port428A, which is an opening on the second space132side, and an open port428B, which is an opening on the external space13side, and at which the passage is bent. Further, the ventilation port428A of the ventilation passage428is positioned above the open port428B in the vertical direction.

When line segments that may be drawn between a point on an imaginary plane surrounded by the periphery of a ventilation port428A of the ventilation passage428and a point on an imaginary plane surrounded by the periphery of the open port428B are considered, there are no line segments that pass only in the ventilation passage428because of the presence of the bent portion428C.

The functions and the effects of the second embodiment will be described.

(2-1) The breather device410achieves the same effects as those of (1-1) to (1-4) in the first embodiment. In addition, the breather device410also achieves the effect of stabilizing operation of the second valve member150as with the breather device110illustrated inFIG. 6.

(2-2) In the breather device410, the ventilation port428A is positioned above the open port428B in the vertical direction. Consequently, water droplets tend to fall before reaching the ventilation port428A even if water droplets enter the ventilation passage428from the open port428B. That is, water droplets do not easily reach the ventilation port428A, which suppresses entry of water into the internal space12of the case411during air intake.

(2-3) The ventilation passage428is shaped so as not to allow one to see through from the open port428B to the ventilation port428A with the presence of the bent portion428C. Therefore, even if water droplets are carried by a flow of air to enter the ventilation passage428from the open port428B in the case where air is taken in when the pressure in the internal space12of the case411becomes low, the water droplets that have entered the ventilation passage428inevitably collide against the inner wall of the ventilation passage428, which makes it difficult for the water droplets to reach the ventilation port428A. Consequently, entry of water into the internal space12of the case411during air intake can be suppressed.

(2-4) Since the case411includes the protruding portion414, adhesion of water droplets to the valve420can be suppressed when water droplets are splashed up from the lower side of the valve420in the vertical direction. Consequently, water droplets do not easily enter the ventilation passage428.

The second embodiment may be modified as follows. The second embodiment and the following modifications can be combined with each other unless such an embodiment and modifications technically contradict with each other. In the second embodiment, the breather device410is mounted on a vehicle with the axis C3directed in the horizontal direction. The posture in which the breather device410is mounted in not limited thereto. For example, the breather device410may be mounted with the axis C3intersecting the horizontal direction.

In the second embodiment, the ventilation passage428includes the bent portion428C. The present disclosure is not limited thereto. The ventilation passage428may be in any shape as long as there are no line segments that may be drawn between a point on an imaginary plane surrounded by the periphery of the ventilation port428A and a point on an imaginary plane surrounded by the periphery of the open port428B and that pass only in the ventilation passage428. For example, the ventilation passage428may be curved such that one cannot see through from the open port428B to the ventilation port428A. In addition, the ventilation passage428may include a labyrinth structure in which the passage is repeatedly bent several times between the ventilation port428A and the open port428B.

The valve in each of the breather devices illustrated inFIGS. 2 and 8may include the lid portion429. In addition, the valve in the breather device illustrated inFIG. 7may also be provided with a lid portion with a bent ventilation passage, as in the second embodiment, by shaping the ventilation passage for a predetermined range from the ventilation port so as to secure a space such that the first projecting portion252A does not interfere when the second valve member250is displaced.