JP2017186960A - Structure of housing of exhaust selector valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure required high heat resistance while suppressing an increase of a cost caused by a use of a high-grade material for a housing 5, in an exhaust selector valve 4 which is arranged at an exhaust system of an engine 1 having, for example, a turbo supercharger (as one example, an HP turbo 3).SOLUTION: A seal member 51a between an exhaust system and the other component is formed at an insert member 51 which is interference-fit to a main body member 50 of a housing 5. A thermal expansion coefficient of the insert member 51 is set larger than that of the main body member 50, and a fastening margin between both the members is set so as not to reach zero even if a temperature of the insert member 51 is lowered ahead when temperatures of both the members are lowered during an operation of the engine 1.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a housing structure of an exhaust gas switching valve provided in an exhaust system of an engine or the like, and particularly relates to a structure suitable for a gasoline engine provided with a turbocharger.

  Conventionally, a turbocharger that supercharges intake air by using exhaust energy is sometimes used in an engine mounted on a vehicle or the like. In recent years, for example, as described in Patent Document 1, there is a diesel engine in which two large and small turbochargers are switched to operate, and the exhaust passage has a high pressure located upstream of the exhaust flow. A turbocharger of a stage and a low-pressure turbocharger located downstream thereof are arranged.

  A bypass passage is provided that branches from a passage for introducing exhaust gas to the high-pressure turbocharger and bypasses the exhaust flow downstream of the high-pressure turbocharger. A switching valve is provided. With this exhaust gas switching valve, the flow of exhaust gas can be changed to go to either the high-pressure stage turbocharger or the bypass passage. And the sealing surface between the parts which comprise an exhaust passage is formed in the housing of the exhaust gas switching valve.

JP 2012-12990 A

  By the way, in recent years, in order to improve the fuel efficiency of automobiles, gasoline engines are increasingly equipped with turbochargers, and the exhaust temperature is higher than that of diesel engines. It is necessary to increase the heat resistance of the housing. Here, as a material for the turbo housing, austenitic heat-resistant cast steel having excellent high-temperature strength and thermal fatigue characteristics is generally used. However, such a high-grade material is expensive and causes an increase in cost. .

  Therefore, as a housing for the exhaust gas switching valve, it is conceivable to form only the seal surface where heat resistance is a problem with the high-grade material as described above. In this case, an insert member for forming the seal surface is used. The problem is how to assemble the body member of the housing. For example, when the main body member is made of an inexpensive ferritic heat-resistant cast steel with relatively low heat resistance, its thermal expansion coefficient is smaller than that of the insert member, so the temperature of the housing decreases during engine operation. This is because a gap may be formed between the insert member and the insert member.

  In view of such points, an object of the present invention is to provide high heat resistance that is required while suppressing an increase in cost due to the use of a high-grade material for a housing, for example, in an exhaust gas switching valve used in an engine equipped with a turbocharger. Is to ensure.

  In order to achieve the above object, the present invention is directed to a structure of an exhaust switching valve housing that is provided in an exhaust system of an engine and changes an exhaust flow. And it is set as the structure which provides the sealing surface between other parts of an exhaust system in the insert member inserted by the interference fit in the main body member of a housing, and sets the thermal expansion coefficient of this insert member larger than the main body member, The tightening allowance of the insert member to the main body member was set so as not to become zero even if the temperature of the insert member first decreased when the temperature of both members decreased during the operation of the engine.

  That is, during the operation of the engine, high-temperature exhaust is received, the temperature of the housing becomes higher than the normal temperature, and the main body member and the insert member are each thermally expanded. Here, when the engine load increases and the temperature of the exhaust system rises, the amount of thermal expansion of the insert member temporarily increases temporarily, which is coupled with the fact that the coefficient of thermal expansion is larger than that of the main body member. Thus, the tightening allowance between both members is increased, and no gap is generated.

  On the other hand, for example, when the temperature of the exhaust system decreases as the engine load decreases, the amount of thermal expansion of the insert member whose temperature decreases first decreases (that is, contracts). Therefore, there is a possibility that a clearance between the main body member is reduced and a gap is generated.

  On the other hand, according to the above-described configuration, when the temperature of the insert member decreases first, the maximum value of the difference in contraction amount that can occur between the main body member and the temperature of the insert member that decreases with a delay is measured in advance. The fastening allowance to the main body member of the insert member is set so as to be larger than this maximum value obtained by calculation. Therefore, even if the amount of shrinkage of the insert member whose temperature decreases first increases as described above, there is no concern that a gap will be formed between the body member and the body member.

  According to the structure of the housing, the insert member formed with the seal surface is formed of a high-grade material such as austenitic heat-resistant cast steel, for example, while sufficiently ensuring the heat resistance of the seal surface. An increase in cost can be suppressed by using no expensive high-grade material for the main body member.

  If the structure of the housing according to the present invention is used, the seal surface between the exhaust switching valve and the other parts of the exhaust system is formed in a separate insert member. Therefore, the insert member is made of an expensive high-grade material. By forming, the required high heat resistance can be ensured, and an increase in cost can be suppressed by not using a high-grade material for the main body member of the housing. In addition, there is no possibility that a gap is generated in the fitting portion between the insert member and the main body member.

1 is a schematic configuration diagram of an intake / exhaust system of an engine according to an embodiment of the present invention. It is a front view which shows the structure of the housing of an exhaust gas switching valve. It is a timing chart which shows the change of the interference to the housing body member of an insert member.

  Hereinafter, an embodiment in which an exhaust gas switching valve according to the present invention is disposed in an exhaust system of an engine 1 mounted on an automobile will be described as an example. Examples of the engine 1 include an in-cylinder direct injection type multi-fuel engine and a diesel engine in addition to the in-cylinder direct injection type or intake port injection type gasoline engine.

−Turbo system for exhaust system−
FIG. 1 schematically shows a two-stage turbo system installed in an engine 1 according to the present embodiment. This system is composed of two turbochargers 2 and 3 in a low-pressure stage and a high-pressure stage in series. It is arranged to be operated in accordance with the operating state of the engine 1. That is, first, in the intake system of the engine 1, that is, the intake passage 11, a compressor impeller 21 of a low-pressure stage turbocharger 2 (hereinafter also referred to as LP turbo 2) is disposed upstream of the flow of intake air. The intake air flowing through the intake passage 11 is compressed.

  The LP turbo 2 is, for example, a large-capacity high-speed turbocharger, and a compressor impeller of a relatively small-capacity high-pressure turbocharger 3 (hereinafter also referred to as an HP turbo 3) on the downstream side thereof. 31 is disposed. The HP turbo 3 is a low-speed turbocharger that has a high supercharging capability in the low and medium speed range of the engine 1, and further compresses the intake air compressed by the LP turbo 2. An intercooler 12 is disposed on the downstream side of the HP turbo 3 in order to cool the intake air that has been compressed and thus increased in temperature.

  Further, the intake passage 11 bypasses the compressor impeller 31 of the HP turbo 3 and adjusts the flow rate of the intake air flowing through the intake bypass passage 13 and the intake bypass passage 13 for flowing the intake air from the upstream side to the downstream side. A possible intake switching valve 14 is provided. As the opening degree of the intake switching valve 14 is increased, the flow rate of intake air that bypasses the compressor impeller 31 is increased. As the opening degree is decreased, the flow rate of intake air that is bypassed is decreased.

  On the other hand, in the exhaust system of the engine 1, that is, the exhaust passage 15, the turbine wheel 32 of the HP turbo 3 is disposed downstream of the exhaust manifold (not shown) and rotates in response to the exhaust flow. Then, the compressor impeller 31 is rotated via the turbine shaft 33. A turbine wheel 22 of the LP turbo 2 is disposed in the exhaust passage 15 on the downstream side of the turbine wheel 32, and rotates by receiving the exhaust gas that has passed through the HP turbo 3. The impeller 21 is rotated.

  Further, an exhaust bypass passage 16 branched from the exhaust passage 15 and bypassing the turbine wheel 32 of the HP turbo 3 is provided, and an exhaust switching valve 4 is disposed at a branch portion of the exhaust bypass passage 16. Specifically, as shown in FIG. 2, the exhaust gas switching valve 4 includes a housing 5 attached to a portion where the exhaust bypass passage 16 branches from the exhaust passage 15, and a valve body 6 accommodated in the housing 5. The body 6 opens and closes an opening 5d communicating with the exhaust bypass passage 16 (hereinafter referred to as a bypass opening 5d).

  That is, when the valve body 6 is fully closed, the flow rate of the exhaust gas to the exhaust bypass passage 16 becomes zero, and the flow of the exhaust gas flows toward the turbine wheel 32 of the HP turbo 3. When the valve body 6 is opened from this state, the flow rate of the exhaust (that is, the exhaust that bypasses the HP turbo 3) toward the exhaust bypass passage 16 increases as the opening degree increases. As shown in FIG. 1, the exhaust passage 15 is also provided with an exhaust bypass passage 17 that bypasses the turbine wheel 22 of the LP turbo 2, and a wastegate valve 18 is provided here.

  For example, the opening degree of the intake switching valve 14 and the exhaust switching valve 4 is controlled based on the operating state of the engine 1 in accordance with a signal from the ECU 100 which is a controller of the engine 1, and the LP turbo 2 and the HP turbo 3. The operation of can be switched. For example, in the operating region where the engine speed is particularly low, the intake switching valve 14 and the exhaust switching valve 4 are fully closed, and both the LP turbo 2 and the HP turbo 3 supercharge the intake air. At this time, the wastegate valve 18 is also closed.

  Thus, as the engine speed increases, the exhaust gas switching valve 4 is opened, and the degree of supercharging by the HP turbo 3 gradually decreases and the degree of supercharging by the LP turbo 2 gradually increases. Further, when the engine speed or the engine load rises to reach a middle / high speed operation region, the intake switching valve 14 is also opened to switch to the supercharged state mainly by the LP turbo 2, and the HP turbo 3 does not perform supercharging substantially. Idle state. Then, the wastegate valve 18 is opened in a predetermined operation region of high load and high rotation.

−Exhaust switching valve structure−
As shown in FIG. 2 as a single unit removed from the exhaust passage 15, the exhaust switching valve 4 of the present embodiment is a butterfly valve, and the housing 5 has components (exhaust system) constituting the upstream side of the exhaust passage 15. A flange surface 5a (shown in front in FIG. 2) to be joined to the other component is formed. The flange surface 5a is basically rectangular, and one of the four corners (upper right corner in FIG. 2) extends outward.

  In addition, the flange surface 5a is formed with an opening 5b having a circular shape in a cross section at a substantially central portion thereof and an opening extending in the extending direction from the opening 5b. Is communicated with the upstream side of the first side (hereinafter referred to as upstream side opening 5b). The upstream opening 5 b is formed by a bifurcated communication passage 5 c provided in the housing 5, and has a cross section that is continuous with the circular bypass opening 5 d that is continuous with the exhaust bypass passage 16 and the inlet of the turbine wheel 32 of the HP turbo 3. Each communicates with the trapezoidal turbo opening 5e. Bolt holes 5f are opened at the four corners of the flange surface 5a.

  And the disc-shaped valve body 6 which opens and closes the said bypass opening 5d is screwed by the spindle 7, and it rotates integrally. The support shaft 7 extends in the left-right direction in FIG. 2, and a lever 71 is attached to a distal end portion (right end portion in FIG. 2). That is, the distal end portion of the support shaft 7 passes through a cylindrical portion that protrudes from the outer periphery of the housing 5 along the flange surface 5a and protrudes outward, and is connected to the lever 71 (not shown). It is designed to be rotated by.

  In this embodiment, the peripheral edge of the upstream opening 5b that opens to the flange surface 5a of the housing 5 is formed by an insert member 51 that is separate from the main body member 50 of the housing 5. In the present embodiment, as an example, the main body member 50 is formed of a relatively inexpensive, for example, ferritic heat-resistant cast steel, and the insert member 51 that receives high-temperature exhaust is relatively expensive but has excellent high-temperature strength and thermal fatigue characteristics. Austenitic heat-resistant cast steel.

  The insert member 51 is fitted into the main body member 50 by interference fitting such as press fitting and shrink fitting, and a surface 51a that is a part of the flange surface 5a of the housing 5 is a component that constitutes the upstream side of the exhaust passage 15. It becomes the sealing surface 51a between. That is, in this embodiment, the required high heat resistance can be ensured by forming the seal surface 51a on the insert member 51 made of a high-grade material excellent in high-temperature strength and thermal fatigue characteristics.

  In general, austenitic heat-resistant cast steel has a larger coefficient of thermal expansion than ferritic heat-resistant cast steel. Therefore, during operation of the engine 1, the main body member 50 and the insert member 51 are affected by a change in the temperature of the housing 5. The allowance for changes will be changed. That is, while the engine 1 is in operation, the amount of heat of the exhaust gas changes in accordance with the increase or decrease of the load, and the temperature of the housing 5 changes in response to this, as shown schematically in FIG. The fastening allowance between the main body member 50 and the insert member 51 changes.

  More specifically, at time t0 to t1 in FIG. 3, when the amount of heat of the exhaust increases due to an increase in engine load and the temperature of the housing 5 of the exhaust switching valve 4 rises, the main body member 50 and the insert member 51 are each thermally expanded. Will do. At this time, due to the fact that the temperature of the insert member 51 that is more easily affected by the exhaust heat becomes higher first and the thermal expansion coefficient of the insert member 51 is larger, both the members 50 and 51 are temporarily provided. The allowance between is increased.

  That is, the thermal expansion amount of the insert member 51 temporarily becomes larger than that of the main body member 50, and the tightening allowance for fitting the both members 50 and 51 increases as shown in the figure. Then, at subsequent times t1 to t2, the temperature of the main body member 50 gradually increases, so that the difference in thermal expansion amount from the insert member 51, that is, the tightening margin gradually decreases. Thereafter, when the engine 1 is in a steady state with little change in the load and the number of revolutions (time t2 to t3), the tightening allowance generally does not change.

  On the other hand, for example, when the load on the engine 1 decreases and the temperature of the housing 5 decreases at time t3 to t4, the thermal expansion amounts of the main body member 50 and the insert member 51 are both small (that is, the members 50 and 51 are contracted). To do). At this time, as in the case of the increase in the load, the temperature of the insert member 51 that is more easily affected by the exhaust heat is lowered first, and the thermal expansion coefficient of the insert member 51 is large. Therefore, the tightening margin between the members 50 and 51 is reduced.

  That is, the amount of shrinkage of the insert member 51 where the temperature first decreases temporarily increases, so that the tightening allowance for fitting with the main body member 50 decreases, and the tightening allowance as shown by the phantom line in FIG. Is originally smaller than zero, there is a possibility that a gap may be formed between the main body member 50 and the main body member 50. If this happens, the high-temperature and high-pressure exhaust gas leaks from the gap, so that the function of the exhaust gas switching valve 4 is impaired.

  In contrast, in the present embodiment, when the temperature of the main body member 50 and the insert member 51 of the housing 5 decreases as the load of the engine 1 decreases as described above, the insert whose temperature first decreases. The maximum value of the difference in shrinkage that can occur between the member 51 and the main body member 50 whose temperature decreases with a delay is obtained in advance by experiments and calculations, and the insert member 51 is applied to the main body member 50 so as to be larger than this. The tightening allowance is set.

  That is, as shown by the solid line in FIG. 3, the tightening margin is originally set to be large, so that the temperature of the housing 5 decreases at the time t3 to t4, and the main body member 50 and the insert member 51 are thereby contracted. In doing so, even if the amount of contraction of the insert member 51 temporarily increases, the allowance for fitting with the main body member 50 is not lost, and no gap is generated between the members 50 and 51.

  Therefore, while the housing 5 of the exhaust gas switching valve 4 according to the present embodiment forms the main body member 50 of a relatively inexpensive material such as ferritic heat-resistant cast steel, the insert member 51 fitted therein is, for example, It is made of high-grade material such as austenitic heat-resistant cast steel. And by forming the sealing surface 51a between the housing 5 and the components of the exhaust passage 15 in the insert member 51, sufficient heat resistance can be ensured while suppressing an increase in cost.

  In addition, the insert member 51 having a high thermal expansion coefficient can be fitted into the main body member 50 relatively easily by an interference fit, and the operating state of the engine 1 changes, and the temperature of the housing 5 is increased due to an increase or decrease in the amount of exhaust heat. Even if it changes, there is no possibility that a gap will occur in the fitting part of the main body member 50 and the insert member 51, and there is no fear that high-temperature and high-pressure exhaust will leak.

-Other embodiments-
The configuration of the present invention is not limited to the above-described embodiment, but includes other various forms. In other words, in the above-described embodiment, the present invention is applied to the housing 5 of the exhaust gas switching valve 4 that changes the flow of exhaust gas to the HP turbo 3 or the exhaust bypass passage 16. The present invention can be applied to the structure of the housing.

  Needless to say, the present invention is not limited to the two-stage turbo system as in the above-described embodiment. For example, the exhaust system is provided with one turbocharger or one electric or mechanically driven supercharger. In this case, the present invention can also be applied to a housing of an exhaust gas switching valve that changes the flow of exhaust gas to the supercharger or the bypass passage.

  Furthermore, the present invention is not limited to an exhaust system provided with a supercharger as described above, and can be applied to an exhaust system switching valve of an exhaust system not provided with a supercharger. For example, the present invention can be applied as a structure of an EGR valve housing.

  INDUSTRIAL APPLICABILITY The present invention can be applied to an engine exhaust gas switching valve, and is particularly effective when applied to an exhaust system equipped with a turbocharger that tends to have a high exhaust temperature, such as a downsizing gasoline engine. .

1 Engine 4 Exhaust gas switching valve 5 Housing 50 Main body member 51 Insert member 51a Seal surface 15 Exhaust passage (other parts of exhaust system)

Claims (1)

A structure of a housing of an exhaust gas switching valve that is provided in an engine exhaust system and changes an exhaust flow,
A seal surface between other parts of the exhaust system is formed on the insert member fitted into the body member of the housing with an interference fit,
When the thermal expansion coefficient of the insert member is larger than that of the main body member, and the tightening allowance of the insert member to the main body member decreases during the operation of the engine, the temperature of the insert member first decreases. Even if it is set so that it may not become zero, the structure of the housing of the exhaust gas switching valve characterized by the above-mentioned.

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