JPH11303619A - Muffler for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the opening of a valve disc the larger sufficiently as the rotation frequency of an internal combustion engine is made the larger, in a muffler for internal combustion engine having a valve disc which can open and close a bypass flow passage. SOLUTION: A valve disc 32 which can open and close a bypass inner pipe 28 is supported swayable to the stay 35 of the bypass inner pipe 28, through a swelling form of bent plate spring 37 whose cross section is swelled to the exhaust gas downstream side. Since the bent plate spring 37 is in the swelling form in the cross section, until the valve disc 32 reaches to a specified opening from the blocking position, the opening load necessary to open the valve disc 32 is relatively large (1 and 2). But since the cross section of the bent plate spring 37 is moved from the swelling form to an about linear form, when the opening of the valve disc 32 exceeds the specific opening, the opening load is reduced (3). After the bent plate spring 37 is mad to an about linear form in the cross section, the opening load is made larger slowly, as the opening of the valve disc 32 is made larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffler for an internal combustion engine, and more particularly, to a muffler for an internal combustion engine having a valve body capable of opening and closing a bypass flow path.

[0002]

2. Description of the Related Art Conventionally, there has been known a muffler for an internal combustion engine having a valve element capable of opening and closing a bypass flow passage. Such a muffler suppresses a rise in back pressure by opening the bypass flow passage when the rotation speed of the internal combustion engine is high to reduce exhaust resistance, and conversely, when the rotation speed of the internal combustion engine is low, the bypass flow passage The purpose is to improve sound silencing by closing the door.

[0003] For example, Japanese Patent Application Laid-Open No. Hei 9-170425 discloses that, as shown in FIG.
An inlet pipe 118 and an outlet pipe 120 are inserted into different expansion chambers 102 and 104 in a housing 116 partitioned into 106, and two inner pipes 126 and 128 connecting the two expansion chambers 102 and 104 are connected in parallel. A muffler in which a valve body 132 is provided on one of the inner pipes 128 (hereinafter referred to as a bypass inner pipe) is disclosed. As shown in FIGS. 13 (a) and 13 (b), the valve body 132 has the open end 12 of the bypass inner pipe 128.
It is swingably attached to a fixed shaft 136 supported near 8a, is urged toward the open end 128a by a coil spring 142, and is configured to close the open end 128a in close contact with the flange 138.

[0004] According to this, when the rotational speed of the internal combustion engine is low, the pressure in the bypass inner pipe 128 increases.
The difference (F _U −F _L ) between the acting force acting on the valve body 32, ie, the upstream acting force F _U, and the acting force acting on the valve element 32 due to the pressure in the expansion chamber 104, ie, the downstream acting force _FL, is determined by the difference of the coil spring 142. Less than the biasing force. For this reason, the opening end 128a is closed, and the noise reduction is improved. On the other hand, when the rotation speed of the internal combustion engine increases and the pressure in the bypass inner pipe 128 increases, and the difference (F _U -F _L ) becomes larger than the urging force of the coil spring 142, the valve body 132 moves from the open end 128a. Separated,
The bypass inner pipe 128 is in a communicating state, and suppresses a rise in back pressure.

[0005]

By the way, the characteristics of the coil spring 142 are as follows, assuming that the initial opening load required to open the valve body 132 in the closed state is F _P0.
The biasing force exerted on the valve body 132 by the force increases substantially in proportion to the opening degree of the valve body 132. That is, the characteristic of the coil spring 142 is represented as a primary straight line as shown in FIG.

On the other hand, in the internal combustion engine muffler of this kind, as described above, the difference in increased engine speed of the internal combustion engine to a predetermined rotational speed (F _U -F _L) biasing force or initial opening of the coil spring 142 When the degree load F _P0 or more, the valve body 132
Opens the open end 128a of the bypass inner pipe 128 against the urging force of the coil spring 142. However, when the valve body 132 opens the bypass inner pipe 128, the pressure in the bypass inner pipe 128 decreases, so that the upstream-side acting force F _U does not sufficiently increase. As a result, the difference (F _U
-F _L ) has a problem that the opening load of the coil spring 142 required to sufficiently increase the opening of the valve body 132 cannot be satisfied. That is, in this type of conventional muffler for an internal combustion engine, there is a problem that it is difficult to sufficiently increase the opening of the valve body 132.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and in a muffler for an internal combustion engine having a valve element capable of opening and closing a bypass passage, the valve element opens as the rotation speed of the internal combustion engine increases. It is intended to provide a device capable of sufficiently increasing the degree.

[0008]

Means for Solving the Problems and Effects of the Invention In order to solve the above-mentioned problems, the invention according to claim 1 is directed to an exhaust gas passage leading from an inlet pipe to an outlet pipe, and the inlet pipe is provided separately from the exhaust gas passage. A muffler for an internal combustion engine provided with a bypass passage leading to the outlet pipe from the valve body, and a biasing body for biasing the valve body to close the bypass passage, the valve body being capable of opening and closing the bypass passage. Wherein the urging element is required to open the valve body by an opening exceeding a predetermined opening than an opening load required to open the valve by a predetermined opening. It is characterized by having a characteristic region where the opening load is lower.

In this muffler for an internal combustion engine, as in the case where the rotational speed of the internal combustion engine is low, the acting force exerted on the valve body by the pressure upstream of the valve body, that is, the upstream acting force F _U , the difference (F _U -F _L) is the initial opening force or initial opening required to open the valve body in the closed state pressure is the applied force or downstream side acting force F _L on the valve body If it is less than the load F _0, the valve element is to keep the state of closing the bypass passage, thereby improving the sound deadening qualities.

On the other hand, the rotation speed of the internal combustion engine is increased, when the difference (F _U -F _L) is in the initial opening force F ₀ or more, the valve body bypass flow against the urging force of the urging body Since the road is opened, an increase in back pressure can be suppressed. At this time, when the valve element opens the bypass flow path, the pressure on the upstream side of the valve element and hence the upstream acting force F _U do not sufficiently increase, and as a result, the difference (F _U)
−F _L ) is not large enough. However, the biasing element has a smaller opening load required to open the valve body by an opening amount exceeding the predetermined opening degree than an opening load required to open the valve body by the predetermined opening degree. Has a low characteristic region, after the valve element is opened by a predetermined opening, the difference (F _U -F _L )
Even if is not sufficiently large, the valve element can easily open greatly beyond a predetermined opening degree. Therefore, according to the muffler for an internal combustion engine, it is possible to sufficiently increase the opening degree of the valve body as the rotational speed of the internal combustion engine increases.

In the muffler for an internal combustion engine according to the second aspect, the urging member is a curved plate spring, and a cross section of the muffler cut perpendicularly to a plate surface along a bending axis when the curved plate spring bends is an exhaust gas. And a cross section of the curved plate spring changes from the bulged shape to a substantially linear shape when the opening degree of the valve body exceeds a predetermined opening degree.

In this case, the degree of bending of the curved leaf spring increases as the degree of opening of the valve element increases. When the opening of the valve body exceeds a predetermined opening, the cross section of the curved leaf spring changes from the bulging shape to a substantially linear shape. When this curved leaf spring bends with its cross section expanded, a large opening load is required because a force is applied to restore the original expanded shape, but the cross section changes to a substantially linear shape. In the case of bending after bending, such a force does not work, so that only a small opening load is required. That is, the opening load required to open the valve body decreases at a predetermined opening. Therefore, the opening degree required to open the valve body by an opening degree exceeding the predetermined opening degree is greater than the opening degree load required to open the valve body by the predetermined opening degree. The load has a lower characteristic region. Therefore, the muffler for an internal combustion engine according to the second aspect has the same operation and effect as the first aspect.

According to a third aspect of the present invention, there is provided a muffler for an internal combustion engine, wherein a plurality of curved leaf springs according to the second aspect are stacked. When the thickness of the curved leaf spring is set to a predetermined thickness, the durability when repeatedly bent is improved when a plurality of curved leaf springs are formed, compared to when the curved leaf spring is composed of one piece. I do. Further, the initial opening load can be increased.

According to a fourth aspect of the present invention, there is provided a muffler for an internal combustion engine, wherein the curved plate spring according to the second or third aspect is attached to the bypass flow passage and the valve body via a cushioning material.
When the valve body reaches a predetermined opening degree, the cross section of the curved leaf spring changes to a substantially linear shape, but when the valve body closes thereafter, the cross section returns from the substantially linear shape to the bulging shape. When the shape of the curved leaf spring returns in this way, a collision may occur at a location where the curved leaf spring is attached to the bypass flow path and at a location where the curved leaf spring is attached to the valve body, and a collision noise may be generated. here,
Since the curved plate spring is attached to the bypass flow passage and the valve via the cushioning material, it is possible to suppress the generation of the collision sound.

The cross section when the valve element is cut perpendicularly to the plate surface along the bending axis may have any shape as long as it expands toward the downstream side of the exhaust gas. Or a folded line shape. Further, the biasing body may be provided at one place between the bypass flow passage and the valve body, or may be provided at a plurality of places.

[0016]

[First Embodiment] FIG. 1 is a schematic structural view of a muffler for an internal combustion engine according to the present embodiment. The muffler for an internal combustion engine includes a housing 6 in which both ends of a cylindrical outer wall 1 are closed by a front end wall 2 and a rear end wall 4. The inside of the housing 6 is partitioned by a first partition 8 and a second partition 10,
A first expansion chamber 12 is formed surrounded by the first partition 8, the second partition 10, and the outer wall 1. A second expansion chamber 14 is formed surrounded by the front end wall 2, the first partition 8 and the outer wall 1, and a resonance chamber 16 is formed surrounded by the rear end wall 4, the second partition 10 and the outer wall 1. Is formed.

On the other hand, an inlet pipe 18 connected to an exhaust pipe of an internal combustion engine (not shown) via a catalyst device or the like penetrates the front end wall 2 and the first partition 8 and has a tip end in the first expansion chamber 1.
2 are provided so as to open. The outlet pipe 20 has one end opened to the second expansion chamber 14 and the first
The second extension chamber 14 is provided so as to penetrate the partition 8, the second partition 10, and the rear end wall 4 so that the other end reaches the outside, that is, communicates the second extension chamber 14 with the outside. Further, the second partition 10 has
First and second communication between the first expansion chamber 12 and the resonance chamber 16
Resonance pipes 22, 24 are attached. Furthermore, although not shown, a plurality of punching holes are formed in the first partition 8.

FIG. 2 is an assembled perspective view of the bypass inner pipe with the valve body attached thereto, FIG. 3 is a front view of the same, FIG. 4 is a plan view of the same, and FIG. 5 is a sectional view taken along line AA of FIG. The bypass inner pipe 28 is a substantially rectangular pipe, and a stay 35 is provided near an opening end 28a opened to the second expansion chamber 14 side. The stay 35 is formed so as to swell to the exhaust gas downstream side in accordance with the shape of a curved leaf spring 37 described later, and has a screw insertion hole 36 for supporting the curved leaf spring 37. The valve element 32 is connected to the open end 2 of the bypass inner pipe 28.
8a is formed in a substantially square plate shape so as to substantially close 8a. At the center of the upper end of the valve body 32, an attachment portion 33 having a shape bulging downstream of the exhaust gas in accordance with the shape of the curved leaf spring 37.
Are formed. The attachment portion 33 is provided with a screw insertion hole 34 for supporting the curved leaf spring 37. The area S (see FIG. 3) of the gap between the valve element 32 and the bypass inner pipe 28 is designed as a part of the opening area of the punching hole provided in the first partition 8.

As shown in FIG. 2, the curved leaf spring 37 is formed by stacking two sheets. The curved plate spring 37 has an upper center fixed to the bypass inner pipe 28 side and a lower center fixed to the valve body 32 side. Specifically, the curved leaf spring 37
A first fixing screw 41 inserted through a screw insertion hole 38 provided at the upper center and a screw insertion hole 36 of the stay 35 is screwed to a first screw nut 42, and a screw insertion hole 39 provided at the lower center is provided. By screwing a second fixing screw 43 inserted through the screw insertion hole 34 of the valve body 32 to the second screw nut 44, the bypass inner pipe 28 and the valve body 32 are bridged. The curved leaf spring 37 has a bulged shape in which the cross section when the curved leaf spring 37 is cut along the bending axis C (see FIG. 3) perpendicular to the plate surface and swells toward the exhaust gas downstream side, here a substantially arc shape. It is formed so that it becomes.

FIG. 6 is a graph showing the characteristics of the curved leaf spring. 6, a perspective view when the valve body 32 is in the initial state, that is, when the valve body 32 is in a closed state, a perspective view when the valve body 32 is opened at a predetermined opening degree and the curved plate spring 37 is bent in a bulged shape,
Is a perspective view when the valve body 32 opens beyond a predetermined opening and the curved leaf spring 37 shifts to a substantially linear shape and is bent, and FIG. It is a perspective view when 37 is bent in a substantially linear shape. In FIG. 6, since the curved leaf spring 37 has a cross-sectional swelling shape from the opening of the valve body 32 to the predetermined opening degree, the opening load required to open the valve body 32 is relatively small. large. When the opening degree of the valve body 32 exceeds a predetermined opening degree, the cross-section of the curved leaf spring 37 shifts from the bulging shape to a substantially linear shape, so that the opening load decreases. afterwards,
In other words, after the curved leaf spring 37 has a substantially linear cross section, the opening load increases as the opening of the valve body 32 increases, but the gradient is smaller than in the case where the opening of the valve body 32 increases.

Next, the operation of the muffler for an internal combustion engine of this embodiment will be described with reference to FIG. Exhaust gas from the internal combustion engine is introduced into the first expansion chamber 12 via the inlet pipe 18. The exhaust gas introduced into the first expansion chamber 12 is once expanded in the first expansion chamber 12 and then through the inner pipe 26 (or through the bypass inner pipe 28 when the valve body 32 is open). , Is introduced into the second expansion chamber 14 and expanded again. In addition, the first and second resonance pipes 2
When the gas is introduced into the resonance chamber 16 through 2 and 24, it resonates at a predetermined frequency, interferes with the pressure wave of the first expansion chamber 12, and the exhaust sound is muted. Thus, the exhaust gas in the second expansion chamber 14 in which the pressure pulsation of the exhaust gas has been smoothed and silenced is discharged to the outside via the outlet pipe 20. In addition,
As shown by the dashed arrow in FIG.
The flow path from 8 to the outlet pipe 20 via the first expansion chamber 12, the inner pipe 26, and the second expansion chamber 14 corresponds to the exhaust gas flow path of the present invention. In addition, as shown by an alternate long and short dash line arrow in FIG. 1, the first expansion chamber 12, the bypass inner pipe 28, the second expansion chamber
The flow path leading to the outlet pipe 20 via the outlet pipe corresponds to the bypass flow path of the present invention.

Here, when the pressure in the first expansion chamber 12 is still low, for example, when the rotation speed of the internal combustion engine is low, the pressure in the first expansion chamber 12 (= the pressure in the bypass inner pipe 28) is increased as shown in FIG. pressure) difference acting force or downstream side acting force F _L pressure acting force or upstream side acting force F _U and the second expansion chamber 14 on the valve element 32 is on the valve element 32 (F _U -F _L )
Is less than the initial opening load F _{0 of the} curved leaf spring 37. Therefore, the bypass inner pipe 28 is closed by the valve body 32, and the noise reduction performance is improved.

On the other hand, the operating state of the internal combustion engine changes, for example, the rotational speed of the internal combustion engine increases, and the amount of exhaust gas increases.
The pressure in the first expansion chamber 12 increases, and the difference (F _U −
When F _L ) reaches the initial opening load F ₀ of the curved leaf spring 37, the valve element 32 opens the bypass inner pipe 28, and in addition to the exhaust gas flow path indicated by the broken line arrow in FIG. A bypass flow path indicated by an arrow is separately formed, and an increase in back pressure is suppressed. At this time, the valve body 32 opens the bypass inner pipe 28, the pressure of the first expansion chamber 12 does not rise sufficiently, does not increase and thus the upstream side acting force F _U is sufficiently, as a result, the difference (F _U -F _L ) is not large enough. However, as shown in FIG. 6, the curved leaf spring 37 exceeds the opening load required to open the valve body 32 by the predetermined opening (opening load in FIG. 6). There is a characteristic that the opening load (opening load in FIG. 6) required to open the valve body 32 by the opening is lower.
For this reason, after the valve body 32 is opened by the predetermined opening,
Even if the difference (F _U -F _L ) is not sufficiently large, the valve element 32 tends to open greatly beyond a predetermined opening.

The above, according to the internal combustion engine muffler of the first embodiment, the difference between the upstream side acting force F _U and the downstream-side operating force F _L with respect to the valve body 32 (F _U -F _L) is initial opening force since the valve body 32 reaches the F ₀ is in the tendency to open the bypass inner pipe 28 the valve body 32 after opening the can, the valve body 32 can be opened sufficiently large, can be very effectively suppress an increase in back pressure . Furthermore, since the curved plate spring 37 is constructed by superposing two sheets, as compared with the case of composed of one, it is possible to increase the initial opening force F ₀ order to improve durability strength.

[Second Embodiment] FIGS. 7A and 7B are explanatory views showing a main part of a second embodiment. FIG. 7A is a perspective view when a valve body is closed, and FIG. It is a perspective view when the cross section of a leaf spring changes from a bulging shape to a substantially linear shape. Second
The muffler for an internal combustion engine according to the embodiment is substantially similar to the muffler according to the first embodiment except that a valve element 82 is attached to an opening end 28b of the bypass inner pipe 28 on the upstream side of the exhaust gas flow.
The configuration is the same as that of the embodiment. Therefore, here, only the mounting structure of the valve element 82 will be described.

The curved plate spring 87 has a stay 8 whose upper center is provided at the opening end 28b on the upstream side of the bypass inner pipe 28.
5 and the lower center is fixed to the valve body 82.
Then, the cross section of the curved leaf spring 87 cut perpendicularly to the plate surface along the bending axis C when the curved leaf spring 87 bends has a bulging shape (here, a substantially arc shape) bulging toward the downstream side of the exhaust gas.
It is formed so that it becomes. When the degree of opening of the valve body 82 exceeds a predetermined degree of opening, the curved leaf spring 87 changes its cross section from a bulging shape to a substantially linear shape as shown in FIG. 7B. For this reason, the characteristic of the curved leaf spring 87 is substantially the same as the graph of FIG. Therefore, the muffler for an internal combustion engine of the second embodiment also has the same operation and effect as the first embodiment.

The embodiments of the present invention are not limited to the above-described embodiments, and it goes without saying that various forms can be adopted as long as they fall within the technical scope of the present invention. For example, in the above embodiment, the bypass inner pipe 2
Although 8 has a rectangular cross section, it is not particularly limited to this, and may have, for example, a substantially circular cross section. In this case, the valve element 32,
Preferably, 82 has the same shape.

Further, the valve body and the bypass inner pipe may be configured to be in close contact with each other via a wire mesh as a cushioning material. For example, as shown in FIG. 8, in the first embodiment, a ring-shaped wire mesh 45 is provided along the inner periphery of the bypass inner pipe 28, and the valve element 32 and the bypass inner pipe 28 are connected to the wire mesh 45.
May be configured so as to be in close contact with each other.

Further, a cushioning material may be provided between the curved leaf spring and the stay and between the curved leaf spring and the valve body. For example,
As shown in FIG. 9, in the first embodiment, the curved plate spring 3
7 and the stay 35, and the curved leaf spring 37 and the valve body 32
Wire mesh 4 as a cushioning material between the
6, 47 may be provided. In this case, the curved leaf spring 37 changes its cross section into a substantially linear shape when the valve body 32 reaches a predetermined opening degree and bends. However, when the valve body 32 is closed thereafter, the cross section changes from a substantially linear shape to a bulging shape. Return. Thus, the curved leaf spring 3
When the shape of 7 returns to the original shape, the curved leaf spring 37 and the stay 35,
In addition, a collision occurs between the curved plate spring 37 and the attachment portion 33 of the valve body 32. However, since the wire meshes 46 and 47 are present, generation of a collision sound can be suppressed.

Further, the curved leaf springs may be provided at a plurality of positions between the bypass inner pipe and the valve body. For example, in the first embodiment, two or more curved leaf springs 37 may be provided as shown in FIG. Since the curved leaf spring 37 has a substantially arc-shaped cross section, when one curved leaf spring 37 is provided, there is a possibility that the curved spring 37 may be slightly displaced along the arc about a line connecting the first fixing screw 41 and the second fixing screw 43 as an axis. In that case, the valve element 3
2 and the area of the gap between the bypass inner pipe 28 will change. In this case, if the gap area is designed as a part of the opening area of the punching hole of the first partition 8, there is a possibility that the designed noise reduction performance may not be obtained. In this regard, if two or more curved leaf springs 37 are provided, the curved leaf springs 37
Can be prevented, and the gap area can be prevented from being changed, and the designed noise reduction performance can be obtained.

Further, the curved leaf spring is not particularly limited as long as its cross section when cut perpendicularly to the plate surface along the bending axis has a shape bulging toward the exhaust gas downstream side. Specifically, it may be formed into a substantially U-shaped cross section as shown in FIG. 11A or a substantially U-shaped cross section as shown in FIG. 11B. Also, as shown in FIG. 11C, the curved leaf spring may be formed so that the radius of curvature changes in the vertical direction (in this figure, the radius of curvature gradually increases from the top to the bottom). It is preferable that the swelling portions of the stays and the valve body have a shape adapted to the curved leaf spring 37.

The structure of the present invention is not limited to the manner of dividing the inside of the housing 6 of the above embodiment, the number of inner pipes, and the way of installation, but a muffler having an exhaust gas flow path and a bypass flow path. It can be applied to any muffler.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a muffler for an internal combustion engine according to a first embodiment.

FIG. 2 is an assembled perspective view of a bypass inner pipe with a valve body attached.

FIG. 3 is a front view of a bypass inner pipe with a valve body attached.

FIG. 4 is a plan view of a bypass inner pipe with a valve body attached.

FIG. 5 is a sectional view taken along line AA of FIG. 3;

FIG. 6 is an explanatory diagram showing characteristics of a curved leaf spring.

FIG. 7 is an explanatory diagram illustrating a main part of a second embodiment.

FIG. 8 is an explanatory diagram in a case where a valve body and a bypass inner pipe are brought into close contact with each other.

FIG. 9 is an explanatory diagram in the case where a curved leaf spring is attached to a stay or a valve via a cushioning material.

FIG. 10 is a front view when two curved leaf springs are provided.

FIG. 11 is a perspective view of a curved leaf spring applicable to the present invention.

FIG. 12 is a schematic configuration diagram of a conventional muffler for an internal combustion engine.

FIG. 13 is an explanatory diagram of a bypass inner pipe to which a conventional valve element is attached.

FIG. 14 is a graph showing characteristics of a conventional spring for biasing a valve element.

[Explanation of symbols]

18 ... inlet pipe, 20 ... outlet pipe, 26 ... inner pipe, 28 ... bypass inner pipe, 32 ... valve element, 33 ... attachment part, 3
5 ... stay, 37 ... curved leaf spring, 41 ... first
Fixing screw, 43: second fixing screw, C: bending axis.

Claims (4)

[Claims] 1. A muffler for an internal combustion engine, comprising: an exhaust gas flow path leading from an inlet pipe to an outlet pipe; and a bypass flow path leading from the inlet pipe to the outlet pipe separately from the exhaust gas flow path. And a biasing element that biases the valve element so as to close the bypass flow path. The urging element requires a predetermined opening degree to open the valve element. A muffler for an internal combustion engine, characterized in that an opening load required to open the valve body by an opening exceeding a predetermined opening is lower than a required opening load. 2. A muffler for an internal combustion engine, comprising: an exhaust gas passage leading from an inlet pipe to an outlet pipe; and a bypass passage leading to the outlet pipe from the inlet pipe separately from the exhaust gas passage. And a biasing element for biasing the valve element so as to close the bypass flow path, wherein the biasing element is a curved leaf spring, and when the curved leaf spring is bent. The cross section when cut perpendicularly to the plate surface along the bending axis is a bulging shape bulging to the downstream side of the exhaust gas, and when the opening degree of the valve body exceeds a predetermined opening degree, the cross section of the curved leaf spring is A muffler for an internal combustion engine, wherein the muffler transitions from the bulged shape to a substantially linear shape. 3. The muffler for an internal combustion engine according to claim 2, wherein a plurality of said curved leaf springs are stacked. 4. The muffler for an internal combustion engine according to claim 2, wherein the curved plate spring is attached to the bypass passage and the valve body via a buffer material.