Flow passage switching valve

A flow passage switching valve provided with a swing arm type valve element comprises a housing formed with a first passage communicated with an inlet port, a second passage communicated with an outlet port, a bypass passage for providing communication between the first passage and the second passage, an introduction port through which a fluid flowing in the first passage is introduced into an external part, and a discharge port through which the fluid introduced into the external part is discharged into the second passage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flow passage switching valve for switching a flow passage of a fluid and, more particularly, to a flow passage switching valve provided with a valve element of a swing arm type.

2. Description of Related Art

For diesel engines, an exhaust gas recirculation (EGR) system has been adopted heretofore to reduce NOx in exhaust gas. When high-temperature exhaust gas is directly recirculated to an intake side of this EGR system, the high-temperature, expanded exhaust gas is supplied to an intake manifold. This increases the ratio of exhaust gas in a cylinder. Accordingly, the amount of air in the cylinder decreases, leading to lowering of combustion efficiency and also deterioration of exhaust gas components such as NOx.

To avoid the above problems, an EGR-cooler-attached EGR system has been developed. This system is structured such that an EGR cooler for cooling exhaust gas (EGR gas) by heat exchange with cooling water is disposed in part of an EGR passage to cool high-temperature exhaust gas (EGR gas), and the thus cooled gas is recirculated to an intake manifold. When the temperature of cooling water is low at engine start or at cold temperatures, on the other hand, exhaust gas (EGR gas) is likely to be excessively cooled, which causes lowering of combustion efficiency in a cylinder and deterioration of exhaust gas components. Accordingly, at engine start or cold temperatures at which the temperature of cooling water is lower than usual, the above EGR-cooler-attached EGR system is structured to allow exhaust gas (EGR gas) to flow in a bypass passage connected thereto to bypass the passage of the EGR cooler.

Further, a flow passage switching valve has been used to switch the flow of exhaust gas from one direction to either one of two directions or from two directions to one direction in order to switch the EGR cooler between use or nonuse. As such flow passage switching valve, many valves using butterfly valve elements have been put to practical use.

This flow switching valve using the butterfly valve element is however difficult to provide high dimensional accuracy, which may cause accumulation of deposits, leading to fixation of the valve element or interference to movement of the valve element to a full closed position.

Under the circumstances, using a flow passage switching valve provided with a valve element of a swing arm type in the EGR system has been proposed. One of the flow passage switching valves using such swing arm type valve element is a three-way switching valve with a rotatable cantilevered valve shaft and a flat valve seat to cause a valve element to come into surface contact with the valve seat, thereby improving the closability of fluid.

If used in the EGR-cooler-attached EGR system, however, even the above flow passage switching valve using the swing arm type valve element needs a pipe for EGR cooler and a bypass pipe to bypass the EGR cooler. This makes it difficult to reduce a mounting space of the system in an engine room.

Further, the above flow passage switching valve using the swing arm type valve element is likely to cause stagnation of exhaust gas around a support shaft (a bearing) due to a positional relationship between a path in each direction and the support shaft (the bearing). This also likely causes accumulation of deposits or stagnation of condensed water around the support shaft (the bearing). There is also a problem that the accumulation of deposits and stagnation of condensed water may increase resistance of operation of the valve element.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and has an object to provide a flow passage switching valve capable of simplifying a system in which the flow passage switching valve is to be used and preventing accumulation of products derived from exhaust gas on or around a bearing.

To achieve the purpose of the invention, there is provided a flow passage switching valve comprising: a housing formed with an inlet port through which a fluid discharged from an engine flows in the housing and an outlet port through which the fluid flows out of the housing; a valve element of a swing arm type for allowing and interrupting communication between the inlet port and the outlet port to switch a flow passage; a valve shaft fixed to the swing arm type valve element; a bearing which rotatably supports the valve shaft; and an actuator for rotating the valve shaft to swing the swing arm type valve element; wherein the housing is formed with: a first passage communicated with the inlet port; a second passage communicated with the outlet port; a bypass passage which provides communication between the first passage and the second passage; an introduction port through which the fluid having flowed in the first passage is introduced into an external part attachable to the flow passage switching valve; and a discharge port through which the fluid introduced into the external part is discharged into the second passage.

Further, according to another aspect, the present invention provides a flow passage switching valve comprising: a housing formed with an inlet port through which a fluid discharged from an engine flows in the housing and an outlet port through which the fluid flows out of the housing; a valve element of a swing arm type for allowing and interrupting communication between the inlet port and the outlet port to switch a flow passage; a valve shaft fixed to the swing arm type valve element; a bearing which rotatably supports the valve shaft; and an actuator for rotating the valve shaft to swing the swing arm type valve element; wherein the housing is formed with: a first passage communicated with the inlet port; a second passage communicated with the outlet port; a bypass passage which provides communication between the first passage and the second passage; an introduction port through which the fluid having flowed in the first passage is introduced into an external part attachable to the flow passage switching valve; a discharge port through which the fluid introduced into the external part is discharged into the second passage; the bypass passage is vertically formed; and the valve element is placed in the first passage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of a preferred embodiment of the present invention will now be given referring to the accompanying drawings. In the present embodiment, the flow passage switching valve of the present invention will be explained as an EGR cooler bypass valve used in an EGR-cooler-attached EGR system.

The EGR cooler bypass valve in the present embodiment is described below referring toFIGS. 1 to 4.FIG. 1is a front view of the EGR cooler bypass valve in the present embodiment;FIG. 2is a side view of the EGR cooler bypass valve ofFIG. 1;FIG. 3is a sectional view of the EGR cooler bypass valve ofFIG. 1; andFIG. 4is a cross-sectional view of the EGR cooler bypass valve ofFIG. 1, showing a schematic structure of a bearing and peripheral parts thereof.

The EGR cooler bypass valve1includes a housing10in which flow passages are formed, a swing valve20for switching between the passages formed in the housing10, a valve shaft21to which the swing valve20is fixed, and an actuator30for rotating the valve shaft21to actuate (swing) the swing valve20.

The housing10is made of aluminum, formed in nearly rectangular parallelepiped shape. This housing10is formed with an inlet port11through which EGR gas flows in the housing10, an outlet port12through which EGR gas (or EGR cooled gas) flows out of the housing10, an introduction port13through which the EGR gas is introduced into the EGR cooler, and a discharge port14through which the EGR cooled gas having passed through the EGR cooler is discharged from the EGR cooler. The inlet port11is formed opening in the top of the housing10and the outlet port12is formed opening in the bottom of the housing10. The introduction port13and the discharge port14are formed opening in the side of the housing10.

Formed in the housing10are a first passage15providing communication between the inlet port11and the introduction port13, a second passage16providing communication between the outlet port12and the discharge port14, and a bypass passage17providing communication between the first passage15and the second passage16. On the other hand, a partition wall19is formed between the first passage15and the second passage16to have a slanting surface defining the first passage15, so that the thickness of the partition wall19is reduced toward the introduction port13.

Herein, the bypass passage17is vertically formed so that the inlet port11, the outlet port12, and the bypass passage17are linearly arranged (i.e. linearly communicated with each other). The housing10is further provided with an attaching part41for attaching thereto the EGR cooler. This attaching part41is formed with six screw holes42(corresponding to a “fastening portion” of the present invention), whereby directly attaching the EGR cooler to the EGR cooler bypass valve1.

The swing valve20is placed in the first passage15and fixed at an end portion to the valve shaft21arranged to be horizontal when the valve1is mounted in an engine room, that is, horizontal inFIG. 1. To be more specific, the swing valve20is fixed to the valve shaft21with an end portion20aof the swing valve20protruding from the valve shaft21, so that the valve shaft21is positioned closer to the partition wall19than the swing valve20is while the bypass passage17is closed. In other words, the valve shaft21is positioned under the lower surface of the swing valve20in the present invention, and a clearance between the end portion20aof the swing valve20and the partition wall19is slight while the introduction port13is closed. The swing valve20and the valve shaft21are made of materials (stainless steel in the present embodiment) harder than the material of the housing10. These swing valve20and valve shaft21are applied with oil repellent coating to prevent adhesion of deposits.

The valve shaft21is supported in the housing10by means of a bearing22as shown inFIG. 4. This bearing22includes a bush24and three seal plates25to rotatably support the valve shaft21. At one end of the bearing22, an E-ring23is fitted on the valve shaft21. This E-ring23serves to prevent movement (displacement) of the valve shaft21in a thrust direction. One end of the valve shaft21protrudes outside the housing10and is coupled with a link member31as shown inFIG. 1. This link member31is connected with an end of a rod32of the actuator30.

The actuator30is formed with a diaphragm chamber37in which a diaphragm36is placed and urged downward (in a direction that pushes out the rod32) by a spring35as shown inFIG. 2. The diaphragm36is coupled with the rod32. Such actuator30is configured so that when a negative pressure is introduced into the diaphragm chamber37, the diaphragm36is moved upward against the urging force of the spring35, thereby pulling the rod32toward the actuator side (to move upward).

With this structure, when the actuator30start operating (i.e. when a negative pressure is introduced into the diaphragm chamber37), the rod32is pulled up, rotating the valve shaft21through the link member31. The swing valve20fixed to the valve shaft21thus swings for opening/closing operations. When the actuator30is operated, the swing valve20is swung to a position where a clearance between the outer periphery of the swing valve20and the inner wall surface of the first passage15is very slight, closing the introduction port13. This slight clearance generated between the outer periphery of the swing valve20and the inner wall surface of the first passage15, which is similarly generated even in a conventionally used butterfly valve, does not cause leakage that may cause a practical problem.

When the actuator30is not operated, on the other hand, the swing valve20is held in contact with a valve seat18formed around an end of the bypass passage17on the first passage15side, as shown inFIG. 1. This valve seat18is formed at a slant with respect to the horizontal direction inFIG. 1so that a rotation angle of the swing valve20is less than 90°. Accordingly, deposits are hard to adhere to the valve seat18. The valve seat18is also formed to receive the swing valve20in surface contact relation. Thus, the swing valve20can be held in surface contact with the valve seat18while the actuator30is not operated, thereby closing the bypass passage17.

The above EGR cooler bypass valve1is directly attached to an EGR cooler (corresponding to an “external part” of the invention)40as shown inFIG. 5. Specifically, the EGR cooler40is fastened to the housing10by bolts through bolt holes43of the EGR cooler40aligned with the screw holes42of the attaching part41of the housing10. Using the EGR cooler bypass valve1can eliminate the need for extra pipes for connection of the EGR cooler40.FIG. 5is an explanatory view showing a configuration that the EGR cooler is attached to the EGR cooler bypass valve.

The EGR cooler bypass valve1, to which the EGR cooler40is attached as shown inFIG. 5, is disposed at a predetermined position in an EGR pipe between an exhaust manifold and an intake manifold of an engine. In other words, the inlet port11of the EGR cooler bypass valve1is connected to the exhaust manifold through the EGR pipe, while the inlet port12is connected to the intake manifold through the EGR pipe. In this way, the configuration of the EGR-cooter-attached EGR system using the EGR cooler bypass valve1can eliminate the need for pipes for EGR cooler and bypass pipes that have conventionally been required. Thus, the piping configuration of the EGR system can be facilitated. The EGR-cooler-attached EGR system using the EGR cooler bypass valve1is therefore extremely easy-to-mount in an engine room.

The operation of the EGR cooler bypass valve1having the above structure will be explained below. Firstly, when the cooling water temperature in the engine is a predetermined value or less (i.e. during a cold period), a negative pressure is introduced into the diaphragm chamber37of the actuator30to operate the actuator30. Then, the swing valve20is swung to open the bypass passage17and close the introduction port13. In the first passage15, accordingly, the inlet port11is brought into communication with the bypass passage17, closing off communication with the introduction port13. EGR gas having flowed from the EGR pipe into the first passage15of the EGR cooler bypass valve1through the inlet port11is allowed to pass through the bypass passage17into the second passage16. The EGR gas having flowed in the second passage16then flows out of the valve1through the outlet port12to the intake manifold. As above, during the cold period, the EGR gas is directly supplied to the intake manifold without passing through the EGR cooler40. At that time, the EGR gas is unlikely to pass through between the valve shaft21and the partition wall19. This is because the clearance between the end portion20aof the swing valve20and the partition wall19is sufficiently slight to prevent leakage of EGR gas to the introduction port13. This makes it possible to prevent accumulation of deposits on or around the valve shaft21and the bearing22.

Since the low-temperature EGR gas flows in the EGR cooler bypass valve1during the engine cold period, condensed water is apt to be generated in the first passage15. In the EGR cooler bypass valve1, however, the bypass passage17is formed vertically so that almost the condensed water generated in the first passage15is discharged to the second passage16through the bypass passage17. Further, condensed water that does not flow in the second passage16through the bypass passage17is discharged along the partition wall19out of the valve1through the introduction port13. This is because the partition wall19has a slanting surface on the first passage15side so that the thickness is gradually reduced toward the introduction port13. Since the valve shaft21is horizontally provided, the condensed water adhering to such valve shaft21will drop down by its own weight onto the partition wall19without entering the bearing22. Consequently, the condensed water is unlikely to stagnate in the first passage15.

Since the swing valve20is placed in the first passage15in which condensed water is unlikely to stagnate and the valve shaft21is horizontally placed, it is surely possible to prevent the condensed water from entering the bearing22. This makes it possible to reliably prevent corrosion of the housing10and hence avoid an increase in operation resistance of the valve shaft21resulting therefrom.

In the EGR cooler bypass valve1, furthermore, the inlet port11, the bypass passage17, and the outlet port12are linearly arranged. This configuration enables the EGR gas having flowed in the housing10through the inlet port11to smoothly pass through the bypass passage17without stagnating in the first passage15and then flow out of the valve1through the outlet port12. It is therefore possible to prevent accumulation of deposits on or around the valve shaft21and the bearing22. In the EGR cooler bypass valve1, the valve seat18is formed at a slant, so that deposits are hard to adhere to the valve seat18.

In the EGR cooler bypass valve1, further, the E-ring23is fitted on the valve shaft21to prevent displacement of the valve shaft21(the swing valve20) in the thrust direction. Accordingly, the introduction port13can be closed while a slight clearance is always kept between the outer periphery of the swing valve20and the inner surface of the first passage15at a slight level. This makes it possible to minimize leakage of EGR gas to the EGR cooler40.

When the cooling water temperature reaches a predetermined value (after a warm-up period), the introduction of negative pressure into the diaphragm chamber37of the actuator30is stopped. Then, the swing valve20comes into surface contact with the valve seat18to close the bypass passage17and open the introduction port13. In the first passage15, accordingly, the communication between the inlet port11and the bypass passage17is closed whereas the communication between the inlet port11and the introduction port13is provided. The EGR gas having flowed from the EGR pipe into the first passage15of the EGR cooler bypass valve1through the inlet port11is supplied to the EGR cooler40through the introduction port13. The EGR gas cooled by the EGR cooler40then flows in the second passage16through the discharge port14and out of the valve1through the outlet port12, and is supplied to the intake manifold. After the warm-up period, as above, the EGR gas cooled by the EGR cooler40is supplied to the intake manifold.

Herein, in the EGR cooler bypass valve1, the swing valve20is brought into surface contact with the valve seat18to close the bypass passage17. The bypass passage17can therefore reliably be shut off. Even when deposits adhere to the valve seat18during the cold period, the deposits just adhered are so soft as to be crushed by the swing valve20when brought into surface contact with the valve seat18after the warm-up period. This makes it possible to surely prevent leakage of high-temperature EGR gas to the bypass passage17. In other words, the EGR gas after the warm-up period can be introduced into the EGR cooler40.

Since the valve seat18is formed at a slant, the swing valve20in surface contact with the valve seat18is also in a slanting position. Accordingly, the EGR gas can smoothly be introduced into the EGR cooler40without stagnating in the first passage15. Because the valve shaft21is placed under the swing valve20, it can prevent the EGR gas from passing to the vicinity of the valve shaft21and the bearing22. It is therefore possible to prevent accumulation of deposits on or around the valve shaft21and the bearing22.

As described above, the EGR cooler bypass valve1in the present embodiment includes the housing10provided with the first passage15communicated with the inlet port11, the second passage16communicated with the outlet port12, the bypass passage17providing communication between the first passage15and the second passage16, the introduction port13through which the EGR gas flowing in the first passage15is introduced into the EGR cooler40, the discharge port14through which the EGR gas introduced into the EGR cooler40is discharged into the second passage16, and the attaching part41with the screw holes42whereby the EGR cooler40is attached to the valve1to connect the passage of the EGR cooler40with the introduction port13and the discharge port14. This configuration enables direct attaching of the EGR cooler40to the EGR cooler bypass valve1without needing extra pipes for EGR cooler. The bypass passage17for bypassing the EGR gas so as not to pass through the EGR cooler40is further formed in the housing10, so that no conventional bypass pipe is needed. The EGR cooler bypass valve1in the present embodiment as described above does not require any pipes for EGR cooler and any bypass pipes that have conventionally been required. Consequently, the EGR-cooler-attached EGR system can be simplified in structure.

In the EGR cooler bypass valve1in the present embodiment, the bypass passage17is formed vertically and the swing valve20is placed in the first passage15. During the engine cold period in which condensed water is apt to be generated in the first passage15, accordingly, the generated condensed water can be discharged to the second passage16through the bypass passage17. For this reason, the condensed water is unlikely to stagnate in the first passage15in which the swing valve20is placed, which makes it possible to reliably prevent the condensed water from entering the bearing22. This can avoid corrosion of the housing10around the bearing22, whereby reliably preventing an increase in operation resistance of the valve shaft21.

The present invention may be embodied in other specific forms without departing from the essential characteristics thereof.

For instance, the inlet port11, the bypass passage17, and the outlet port12are arranged linearly in the above embodiment. If this arrangement causes difficulty in mounting the valve1in the engine room, different arrangements may be adopted as shown inFIGS. 6 to 8.

Specifically, as shown inFIG. 6, the position of the inlet port11remains unchanged (in the top of the housing) but the outlet port12is formed in the side wall of the housing, opposing the discharge port14. As another alternative, as shown inFIG. 7, the position of the outlet port12remains unchanged (in the bottom of the housing) but the inlet port11is formed in the side wall of the housing, opposing the introduction port13. Further, as another alternative, as shown inFIG. 8, the inlet port11is formed in the side wall of the housing, opposing the introduction port13and the outlet port12is formed in the housing, opposing the discharge port14.

The above embodiment shows the case where the valve1is oriented so that the first passage15is on an upper side. Alternatively, the valve1may be oriented in an inverted position as shown inFIG. 9so that the first passage15is on a lower side (the second passage16is on the upper side). It is to be noted that the flow passage switching valves shown inFIGS. 6 to 8may similarly be inverted.

In the above embodiment, the shape of the swing valve and the shape (in section) of the first passage are rectangle, but they may be configured in any shape; for example, semi-elliptic as shown inFIG. 10.