Patent Description:
Conventionally, in an internal combustion engine, a valve stem seal is used so as to hermetically seal a space between a valve stem and a valve guide of an intake/exhaust valve which reciprocates between the cam side and the cylinder side. The valve stem seal suppresses damage of the valve guide and the valve stem caused due to small amounts of oil leakage (an amount of lubricating oil supplied between the valve stem and the valve guide) during the operation of the internal combustion engine. Further, to prevent problems such as generation of white smoke caused due to large amounts of oil leakage, the valve stem seal supplies a lubricating oil, which allows the valve stem to smoothly reciprocate, between the valve guide and the valve stem while adjusting an amount of oil leakage, and the valve stem seal prevents inflow of the lubricating oil into a port or a cylinder (combustion chamber).

<FIG> is a cross-sectional view showing a conventional valve stem seal <NUM> together with a valve stem <NUM> in a state where the valve stem seal <NUM> is attached to a valve guide <NUM>. The valve stem seal <NUM> includes a reinforcing ring <NUM> made of metal, and an elastic body portion <NUM> which is integrally formed with the reinforcing ring <NUM> and is formed of an elastic body made of rubber or the like.

The reinforcing ring <NUM> includes a cylindrical portion 101a extending in the direction of an axis x. The elastic body portion <NUM> integrally includes a sealing portion 102a and a fitting portion 102b. The sealing portion 102a includes a back pressure lip 102c so as to prevent a back pressure from the cylinder side from transmitting to the cam side. The fitting portion 102b is a portion which functions when the valve stem seal <NUM> is fitted on the valve guide <NUM>, and the fitting portion 102b covers the cylindrical portion 101a of the reinforcing ring <NUM> from the inside.

<FIG> is a cross-sectional view showing a conventional valve stem seal <NUM> together with a valve stem <NUM> in a state where the valve stem seal <NUM> is attached to a valve guide <NUM>. The valve stem seal <NUM> includes a reinforcing ring <NUM> made of metal, and an elastic body portion <NUM> which is integrally formed with the reinforcing ring <NUM>, and is formed of an elastic body made of rubber or the like.

The reinforcing ring <NUM> includes a cylindrical portion 201a extending in the direction of an axis x, and the cylindrical portion 201a is directly fitted on the valve guide <NUM>.

A valve stem seal has been also proposed where, different from the conventional valve stem seals shown in <FIG> and <FIG>, a reinforcing ring includes: a cylindrical portion extending toward the cam side along an axis; and a radial direction portion extending from one end of the cylindrical portion along the radial direction, the cylindrical portion is made to strike a recessed portion of a cylinder head, and the radial direction portion is pressed and fixed by a valve spring (for example, see Patent Literature <NUM>).

Patent Literature <NUM>: <CIT>
Patent Literature <CIT> discloses a valve stem seal assembly in an internal combustion engine which seals a space formed between a valve stem and a valve guide. In addition, the valve stem seal assembly includes a seal support and a resilient seal. The seal support includes a cylindrical body portion and a radially extending flange portion. The cylindrical body portion extends in the axial direction of the seal support, the radially extending flange portion extends in the radial direction of the seal support. The radially extending flange portion is pressed by a valve spring. Patent Literature <CIT> discloses a seal assembly which seals a space formed between a piston rod and a rod guide. In addition, the seal assembly includes a seal portion and a reinforcing ring. The reinforcing ring has a radially extending flat portion. The radially extending flat portion extends in the radial direction of the reinforcing ring. Patent Literature <CIT> discloses a valve stem oil seal comprising a cup-shaped case engageable with a valve guide of a piston-type internal combustion engine, the seal sealing a space formed between a valve stem and the valve guide. In addition, the valve stem oil seal includes a seal element and a brass washer. The brass washer has a radially extending flat portion. The radially extending flat portion extends in the radial direction of the brass washer. Patent Literature <CIT> discloses a valve stem seal assembly which seals a space formed between a valve stem and a valve guide. In addition, the valve stem seal assembly includes a metal ring and a seal portion. The metal ring includes a cylindrical portion and a radially extending portion. The cylindrical portion extends in the axial direction of the metal ring, the radially extending portion extends in the radial direction of the metal ring. The radially extending portion is pressed by a spring. Patent Literature <CIT> discloses a valve stem seal which seals a space formed between a valve stem and a valve stem guide. In addition, the valve stem seal includes a metallic ring and a rubber-like elastic body. The metallic ring includes a cylindrical portion and a flange portion. The cylindrical portion extends in the axial direction of the metallic ring, the flange portion extends in the radial direction of the metallic ring. Patent Literature <CIT> discloses a cylinder head assembly for an internal combustion engine including a cylinder head at least partially defining a flow path through the engine. A valve having a valve stem is coupled to the cylinder head and movable relative to the cylinder head to selectively open the combustion chamber to one of the intake port and the exhaust port. A valve spring is positioned between the valve and the cylinder head and biases the valve to a closed position. A valve guide contacts an outer surface of a valve stem. A valve stem seal is coupled to an end of the valve guide adjacent the valve spring. A lower collar is coupled to the valve stem seal. The lower collar is formed to fit an outer surface of the valve stem seal. The valve stem seal is axially positioned by the lower collar. The lower collar includes a lower flange that extends radially outward between the valve spring and a support surface of the cylinder head. A thermally insulating washer <NUM> is further positioned between the lower flange of the lower collar and the support surface. Patent literature <CIT> discloses an anti-loosening function of a valve stem seal. This function is provided to an attachment ring made of metal by integrally forming a pressed down part as a radial flange which is pressed down by a spring retainer urged by a valve spring and is thus fixed to a cylinder head. The valve stem seal is attached to a valve stem guide.

Recently, due to miniaturization of internal combustion engines for the purpose of further improving vehicle fuel economy, due to provision of a turbocharger or the like, there is a tendency that a pressure from the cylinder side (back pressure) caused by an increase in port pressure increases. Accordingly, there has been a demand for a valve stem seal which can tolerate an increase in back pressure.

However, in the valve stem seal <NUM> shown in <FIG>, the fitting portion 102b of the elastic body portion <NUM> is fitted on the valve guide <NUM>. Accordingly, to prevent elastic deformation in the fitting portion 102b caused by a back pressure causing the valve stem seal <NUM> to be removed from the valve guide <NUM>, it is necessary to increase a length of the cylindrical portion 101a in the direction of the axis x by an amount corresponding to at least a length of the fitting portion 102b.

Further, in the valve stem seal <NUM> shown in <FIG>, the cylindrical portion 201a is directly fitted on the valve guide <NUM> so that the removal of the cylindrical portion 201a caused by a back pressure is prevented. However, a fitting load when mounting the valve stem seal <NUM> is large so that operation of fitting the valve stem seal <NUM> is difficult. Further, the valve guide <NUM> is required to have a length which is at least a length of the cylindrical portion 201a.

Further, in the valve stem seal shown in Patent Literature <NUM>, the reinforcing ring is pressed by the valve spring so that the removal of the reinforcing ring is prevented. However, a space for accommodating the valve stem seal is required by an amount corresponding to a height of the cylindrical portion.

That is, in each of the above-mentioned valve stem seals, the reinforcing ring includes the cylindrical portion extending along the axis so that a height of the reinforcing ring in the direction of the axis increases. In view of the above, there is a demand for the reduction of the installation space for the valve stem seal.

Accordingly, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a valve stem seal which can prevent the removal thereof due to an increase in back pressure, can be easily assembled to a valve guide, and can reduce the installation space.

To achieve the above-mentioned object, the present invention is directed to a valve stem seal for hermetically sealing a space formed between a valve stem of a valve which establishes and interrupts communication between a cylinder and a port and a valve guide into which the valve stem is inserted in a reciprocally movable manner, the valve stem seal being characterized by including: a reinforcing ring formed into an annular shape centered about an axis, and extending in a radial direction of a ring of the reinforcing ring; and an elastic body portion formed into an annular shape centered about the axis, attached to the reinforcing ring, and including a seal lip which abuts on the valve stem.

It is preferable that the reinforcing ring includes a portion to be pressed which is disposed between an inner wall of a cylinder head and a valve spring, and is pressed by the valve spring.

To further achieve the above-mentioned object, the present invention is directed to a hermetic sealing structure for hermetically sealing a space formed between a valve stem of a valve and a valve guide, the valve establishing and interrupting communication between a cylinder and a port, the valve guide having one end facing a cam side and another end facing a cylinder side, and the valve stem being inserted into the valve guide in a reciprocally movable manner, the hermetic sealing structure being characterized by including: a cylinder head; a valve guide arranged on the cylinder head; the valve stem inserted into the valve guide in a reciprocally movable manner; a valve spring mounted on the cylinder head, and biasing the valve stem in a direction where communication between the cylinder and the port is interrupted; and a valve stem seal provided on the valve guide on a side of one end, wherein the valve stem seal includes: a reinforcing ring formed into an annular shape centered about an axis, and extending in a radial direction of a ring of the reinforcing ring; and an elastic body portion formed into an annular shape centered about the axis, attached to the reinforcing ring, and including a seal lip which abuts on the valve stem, and the reinforcing ring is disposed between an inner wall of the cylinder head and the valve spring, and is fixed to the cylinder head by pressure from the valve spring.

It is preferable that an accommodating portion for accommodating the reinforcing ring is formed on the cylinder head.

It is preferable that one end of the valve guide is disposed at a position more toward the cylinder side than the accommodating portion.

It is preferable that the elastic body portion include a back pressure lip which is disposed on a side closer to the valve guide than the seal lip, and abut on the valve stem, and the back pressure lip is disposed in a space formed between one end of the valve guide and the accommodating portion.

According to the present invention, the removal of a valve stem seal due to an increase in back pressure can be prevented, the valve stem seal can be easily assembled to a valve guide, and the installation space for the valve stem seal can be reduced.

Preferred embodiments of the present invention will be described with reference to drawings. The embodiments described hereinafter are merely for the sake of example, and can take any of various modes within the scope of the present invention.

<FIG> is a cross-sectional view showing a schematic configuration of a hermetic sealing structure <NUM> which includes a valve stem seal <NUM> according to a first embodiment of the present invention. <FIG> is a cross-sectional view showing a cross section of the valve stem seal <NUM> taken along the direction of an axis x. <FIG> is a cross-sectional view showing a part of the hermetic sealing structure <NUM> which includes the valve stem seal <NUM> shown in <FIG> in an enlarged manner.

The hermetic sealing structure <NUM> is used in a valve system of an internal combustion engine. The hermetic sealing structure <NUM> includes: a cylinder head <NUM>; a valve guide <NUM> arranged on the cylinder head <NUM>; a valve <NUM> inserted into the valve guide <NUM> in a reciprocally movable manner; a valve spring <NUM> mounted on the cylinder head <NUM>, and biasing the valve <NUM> in the direction where communication between a cylinder and a port P is interrupted; and a valve stem seal <NUM> provided on one end side of the valve guide <NUM>.

The valve stem seal <NUM> is provided for hermetically sealing a space formed between the valve guide <NUM> and a valve stem <NUM> of the valve <NUM> in an internal combustion engine. The valve guide <NUM> has one end thereof facing the cam side and another end thereof facing the cylinder side. The valve <NUM> establishes and interrupts communication between the cylinder and the port P, and the valve stem <NUM> of the valve <NUM> is inserted into the valve guide <NUM> in a reciprocally movable manner. In a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, the valve stem seal <NUM> is fixed to the cylinder head <NUM> at one end of the valve guide <NUM>, to be more specific, on one end side of the valve guide <NUM> which faces the cam side.

As shown in <FIG>, the valve stem seal <NUM> includes: a reinforcing ring <NUM> made of metal which is formed into an annular shape centered about the axis x, and extends in the radial direction of a ring of the reinforcing ring <NUM>; and an elastic body portion <NUM> in an annular shape centered about the axis x, the elastic body portion <NUM> being formed of an elastic body attached to the reinforcing ring <NUM>.

The reinforcing ring <NUM> is manufactured by press working or by forging, for example. The elastic body portion <NUM> is made of a rubber material such as fluororubber, for example, and is molded by crosslinking (vulcanization) molding using a molding die. In performing crosslinking molding, the reinforcing ring <NUM> is disposed in the molding die so that the elastic body portion <NUM> is bonded to the reinforcing ring <NUM> by crosslinking bonding thus being integrally formed with the reinforcing ring <NUM>.

The reinforcing ring <NUM> has a hollow disk shape. The reinforcing ring <NUM> is formed such that a main surface thereof has a flat surface extending along the direction orthogonal to the axis x, and a thickness of the reinforcing ring <NUM> is uniform. That is, the reinforcing ring <NUM> is not bent along any portion thereof, and a main surface of the reinforcing ring <NUM> simply has one flat surface. The reinforcing ring <NUM> includes a portion to be pressed <NUM> which is disposed between an inner wall of the cylinder head <NUM> and the valve spring <NUM>, and is pressed by the valve spring <NUM>.

The elastic body portion <NUM> includes a seal base portion <NUM> in an annular shape centered about the axis x, the elastic body portion <NUM> abutting on the valve stem <NUM> on the inner periphery side of the elastic body portion <NUM>. The seal base portion <NUM> integrally includes: a seal lip <NUM> abutting on the valve stem <NUM> which extends in the direction of the axis x, and is made to insert through the elastic body portion <NUM>; and a back pressure lip <NUM> disposed on the side closer to the valve guide <NUM> (cylinder side) than the seal lip <NUM> is.

As shown in <FIG>, the seal lip <NUM> extends upward from the seal base portion <NUM>, and an upper end portion of the seal lip <NUM> on the inner periphery side has a distal end portion in an annular shape centered about the axis x. The distal end portion projects inward in the radial direction toward the axis x. That is, a cross-sectional shape of the distal end portion is a wedge shape which projects toward the inner periphery side. As described later, in a use state, the seal lip <NUM> abuts on the valve stem <NUM> at the distal end portion of the seal lip <NUM>.

The back pressure lip <NUM> is a lip extending toward the valve guide <NUM> from the lower side of the seal base portion <NUM>. To be more specific, the back pressure lip <NUM> is a lip which is formed into an annular shape centered about the axis x, is disposed at a position below the seal lip <NUM>, and abuts on the valve stem <NUM>.

The elastic body portion <NUM> is fastened toward the valve stem <NUM> by a spring <NUM>. The spring <NUM> is fitted on the outer periphery side of the seal base portion <NUM>. The spring <NUM> biases the seal lip <NUM> in the direction toward the axis x thus applying a force to the distal end portion of the seal lip <NUM> for fastening the valve stem <NUM> such that the distal end portion follows the displacement of the valve stem <NUM>.

The elastic body portion <NUM> is attached to an inner peripheral edge portion of the reinforcing ring <NUM> at a portion of an outer peripheral surface of the elastic body portion <NUM> disposed below the spring <NUM> and above the back pressure lip <NUM>.

As shown in <FIG>, the cylinder head <NUM> has the port P, to be more specific, an intake port and an exhaust port. As shown in <FIG>, an accommodating portion <NUM> in an annular shape centered about the axis x is formed on an inner wall <NUM> of the cylinder head <NUM> which faces the cam side, the accommodating portion <NUM> accommodating the reinforcing ring <NUM> of the valve stem seal <NUM>. The accommodating portion <NUM> has: a side surface portion 32a in an annular shape which extends from the inner wall <NUM> toward the cylinder side; and a bottom surface portion 32b which extends from an end portion of the side surface portion 32a on the cylinder side toward the axis x.

A groove 32c in an annular shape centered about the axis x is formed on the bottom surface portion 32b. In the groove 32c, an O-ring <NUM> is disposed which provides sealing between the cylinder head <NUM> and the reinforcing ring <NUM>. Usually, an outer diameter of the O-ring <NUM> slightly projects from the bottom surface portion 32b in the direction of the axis x. However, when the reinforcing ring <NUM> is attached, the O-ring <NUM> is elastically deformed until the O-ring <NUM> becomes coplanar with the bottom surface portion 32b of the accommodating portion <NUM> thus performing a sealing function.

As shown in <FIG>, a cross-sectional shape of the valve guide <NUM> is a cylindrical shape extending in the direction of the axis x, and the valve guide <NUM> is fixed to the cylinder head <NUM> by press fitting. The valve guide <NUM> has a guide hole <NUM> which is a through hole into which the valve stem <NUM> of the valve <NUM> is inserted in a reciprocally movable manner in the direction of the axis x, and which extends in the direction of the axis x. The guide hole <NUM> extends between one end of the valve guide <NUM> on the cam side and another end of the valve guide <NUM> on the cylinder side, and an inner diameter of the guide hole <NUM> is larger than an outer diameter of the valve stem <NUM>.

The valve <NUM> is a valve used for controlling the intake and exhaust of an internal combustion engine by opening and closing a port with respect to the combustion chamber, the port communicating to a combustion chamber. When power is transmitted to one end of the valve stem <NUM> on the cam side by a cam not shown in the drawing, the valve <NUM> reciprocates in the direction of the axis x. As shown in <FIG>, the valve <NUM> includes the valve stem <NUM> in a rod shape, and a valve head <NUM> integrally formed on a lower end of the valve stem <NUM> on the cylinder side.

The valve stem <NUM> is inserted into the guide hole <NUM> of the valve guide <NUM>. A retainer <NUM> for supporting an upper end portion of the valve spring <NUM> is fixed to an upper end of the valve stem <NUM> on the cam side.

The valve spring <NUM> is disposed between the reinforcing ring <NUM> and the retainer <NUM>, and biases the valve <NUM> in the closing direction where communication between the cylinder and the port P is interrupted. The valve spring <NUM> is compressed such that power of the cam is transmitted to the valve stem <NUM> so that the valve stem <NUM> is pushed down toward the cylinder side by way of the retainer <NUM> whereby the valve head <NUM> enters the combustion chamber. When the action of the cam is released, the valve spring <NUM> is restored by an elastic force thereof thus pushing up the retainer <NUM> toward the cam side so that the valve <NUM> interrupts communication between the cylinder and the port P.

Next, the hermetic sealing structure <NUM> using the valve stem seal <NUM> is described.

As shown in <FIG>, the valve guide <NUM> is fixed to the cylinder head <NUM> by press fitting, and the valve stem <NUM> is inserted into the guide hole <NUM> of the valve guide <NUM>. An upper end portion of the valve guide <NUM> on the cam side is disposed at a position more toward the cylinder side than the bottom surface portion 32b of the accommodating portion <NUM> of the cylinder head <NUM>. With such a configuration, a space S is formed between the upper end portion of the valve guide <NUM> on the cam side and the accommodating portion <NUM>, to be more specific, the bottom surface portion 32b of the accommodating portion <NUM>.

The valve stem seal <NUM> is concentrically attached to the valve stem <NUM>, and the reinforcing ring <NUM> is accommodated in the accommodating portion <NUM> of the cylinder head <NUM>. To be more specific, a peripheral surface of the reinforcing ring <NUM> on the outer side in the radial direction abuts on the side surface portion 32a, and a surface of the reinforcing ring <NUM> which faces the bottom surface portion 32b abuts on the bottom surface portion 32b and the O-ring <NUM> (sealing member). Further, the back pressure lip <NUM> is positioned in the above-mentioned space S. On a surface of the reinforcing ring <NUM> which faces the cam side (portion to be pressed <NUM>), a spring washer <NUM> functioning as a support member which supports a lower end portion of the valve spring <NUM> is provided. A shape in cross section taken along the axis x (hereinafter also referred to as "cross-sectional shape") of the spring washer <NUM> is a substantially L shape. The spring washer <NUM> includes a cylindrical portion 33a in a cylindrical shape extending in the direction of the axis x, and a flange portion 33b extending from an end portion of the cylindrical portion 33a on the cylinder side toward the outside in the radial direction.

A peripheral surface of the flange portion 33b on the outer side in the radial direction abuts on the side surface portion 32a of the accommodating portion <NUM>, and an upper surface of the flange portion 33b is coplanar with the inner wall <NUM> of the cylinder head <NUM>. That is, a total thickness of the reinforcing ring <NUM> and the spring washer <NUM> is equal to a height of the side surface portion 32a of the accommodating portion <NUM>.

The lower end portion of the valve spring <NUM> is supported by the flange portion 33b of the spring washer <NUM>. The reinforcing ring <NUM> is disposed between the inner wall <NUM> of the cylinder head <NUM> and the valve spring <NUM>, and is fixed to the cylinder head <NUM> by pressure from the valve spring <NUM>. That is, when the valve stem seal <NUM> is in a use state, the reinforcing ring <NUM> is accommodated in the accommodating portion <NUM> of the cylinder head <NUM>, and is pressed toward the bottom surface portion 32b by the valve spring <NUM> by way of the spring washer <NUM>. Further, the valve spring <NUM> is always disposed above the reinforcing ring <NUM> and hence, there is no possibility that the reinforcing ring <NUM> separates from the accommodating portion <NUM>. Accordingly, the valve stem seal <NUM> is fixed in the accommodating portion <NUM> of the cylinder head <NUM>.

According to the valve stem seal <NUM> having the above-mentioned configuration, the reinforcing ring <NUM> is formed into an annular shape centered about the axis x, and extends in the radial direction of a ring of the reinforcing ring <NUM>. Accordingly, a size of the valve stem seal <NUM> in the height direction along the axis x can be reduced compared to a conventional valve stem seal.

According to the hermetic sealing structure <NUM> having the above-mentioned configuration, the reinforcing ring <NUM> is disposed between the inner wall <NUM> of the cylinder head <NUM> and the valve spring <NUM>, and is fixed to the cylinder head <NUM> by pressure from the valve spring <NUM>. Accordingly, the valve stem seal <NUM> can be easily assembled, and the removal of the valve stem seal <NUM> can be eliminated and hence, the hermetic sealing structure <NUM> can stably maintain hermetic sealability for a long period of time. Further, the reinforcing ring <NUM> extends in the radial direction so that a size of the valve stem seal <NUM> in the direction of the axis x is small and hence, a size of the hermetic sealing structure <NUM> per se in the height direction can be reduced. Accordingly, a space on the cylinder head <NUM> side can be also saved thus contributing to the miniaturization of an internal combustion engine.

Further, the accommodating portion <NUM> for accommodating the reinforcing ring <NUM> is formed on the cylinder head <NUM>. Accordingly, an assembling operation of the hermetic sealing structure <NUM> can be more simplified and, at the same time, a stable attachment state of the valve stem seal <NUM> can be achieved.

Further, the end portion of the valve guide <NUM> on the cam side is disposed at a position more toward the cylinder side than the accommodating portion <NUM> so that the back pressure lip <NUM> can be disposed in the space S formed between the one end of the valve guide <NUM> on the cam side and the accommodating portion <NUM>. Accordingly, even when the valve stem seal <NUM> includes the back pressure lip <NUM>, a height of the entire hermetic sealing structure <NUM> in the direction of the axis x can be suppressed and hence, the miniaturized hermetic sealing structure <NUM> can be achieved.

Next, with reference to <FIG> and <FIG>, a valve stem seal <NUM> and a hermetic sealing structure <NUM> according to a second embodiment of the present invention are described. Hereinafter, only parts which make the present embodiment different from the first embodiment are described. Configurations which are equal to the corresponding configurations of the first embodiment are given the same symbols, and the description of such configurations is omitted.

<FIG> is a cross-sectional view of the valve stem seal <NUM> taken along an axis x. <FIG> is a cross-sectional view showing a part of the hermetic sealing structure <NUM> which includes the valve stem seal <NUM> shown in <FIG> in an enlarged manner.

In an elastic body portion 8a of the valve stem seal <NUM>, a covering portion <NUM> includes a sealing portion which provides sealing between a cylinder head <NUM> and a reinforcing ring <NUM> at a position where the reinforcing ring <NUM> opposedly faces an inner wall of the cylinder head <NUM>. That is, as shown in <FIG>, the elastic body portion 8a includes the covering portion <NUM> as the sealing portion extending in the radial direction, the covering portion <NUM> covering a main surface of the reinforcing ring <NUM> which faces downward, to be more specific, a surface of the reinforcing ring <NUM> which opposedly faces a bottom surface portion 32b of an accommodating portion <NUM> of the cylinder head <NUM> in a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>. The covering portion <NUM> is formed with a uniform thickness and, in the same manner as a seal lip <NUM> and a back pressure lip <NUM>, is integrally formed with a seal base portion <NUM>.

As shown in <FIG>, in a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, the covering portion <NUM> is positioned in the accommodating portion <NUM> of the cylinder head <NUM>, and provides sealing between the cylinder head <NUM> and the reinforcing ring <NUM> at a position where the covering portion <NUM> opposedly faces the bottom surface portion 32b.

In <FIG>, the covering portion <NUM> covers an entire main surface of the reinforcing ring <NUM> which faces downward. However, provided that sealability between the cylinder head <NUM> and the reinforcing ring <NUM> can be ensured, it is sufficient for the covering portion <NUM> to cover at least a portion of the main surface of the reinforcing ring <NUM> which is brought into contact with the bottom surface portion 32b of the accommodating portion <NUM>.

In <FIG>, different from the first embodiment, a groove in an annular shape is not formed and an O-ring is not disposed on the bottom surface portion 32b of the accommodating portion <NUM>. However, to enhance sealability between the cylinder head <NUM> and the reinforcing ring <NUM>, the groove may be formed on the bottom surface portion 32b, and the O-ring may be disposed in the groove.

In the second embodiment, the elastic body portion <NUM> includes the covering portion <NUM> as the sealing portion. Accordingly, it becomes unnecessary to provide the groove and the sealing member to the cylinder head <NUM> for ensuring sealing between the reinforcing ring <NUM> and the cylinder head <NUM>. For this reason, it is possible to reduce the number of operation steps for constructing the hermetic sealing structure <NUM>.

Next, with reference to <FIG> and <FIG>, a valve stem seal <NUM> and a hermetic sealing structure <NUM> according to a third embodiment of the present invention are described. Hereinafter, only parts which make the present embodiment different from the above-mentioned embodiments are described. Configurations which are equal to the corresponding configurations of the above-mentioned embodiments are given the same symbols, and the description of such configurations is omitted.

As shown in <FIG>, in a state where the valve stem seal <NUM> is attached to a cylinder head <NUM>, a recessed portion <NUM> forming a portion to be pressed which is pressed by a valve spring <NUM> is formed on a main surface of a reinforcing ring 7b of the valve stem seal <NUM> which faces upward.

The recessed portion <NUM> is formed at a peripheral edge portion of the reinforcing ring <NUM> which is disposed on the outer side in the radial direction. The recessed portion <NUM> is formed with a smaller thickness than other portions of the reinforcing ring <NUM> thus forming a stepped portion on the reinforcing ring <NUM>. Accordingly, the reinforcing ring <NUM> has a smaller thickness on the outer side in the radial direction than on the inner side in the radial direction. To be more specific, the recessed portion <NUM> includes: a side surface portion 72a in an annular shape which extends toward a covering portion <NUM> from a front surface 71a of a portion of the reinforcing ring <NUM> other than the recessed portion <NUM> which faces upward; and a bottom surface portion 72b which extends from the side surface portion 72a in an annular shape in the direction of separation from the axis x, that is, toward the outside in the radial direction.

In the same manner as the second embodiment, an elastic body portion 8b includes the covering portion <NUM> which covers a main surface of the reinforcing ring <NUM> on the lower side.

As shown in <FIG>, in the hermetic sealing structure <NUM>, different from the above-mentioned embodiments, the valve stem seal <NUM> directly supports an end portion of the valve spring <NUM> on the cylinder side. That is, the above-mentioned spring washer is not provided, and the valve spring <NUM> is supported by the bottom surface portion 72b of the recessed portion <NUM> of the reinforcing ring <NUM>.

The bottom surface portion 72b of the recessed portion <NUM> is disposed at a position more toward the cylinder side than an inner wall <NUM> of the cylinder head <NUM> which faces the cam side. Accordingly, the movement of the valve spring <NUM> on the outer side in the radial direction is restricted by the side surface portion 32a of the accommodating portion <NUM> and the side surface portion 72a of the recessed portion <NUM>.

As shown in <FIG>, the surface of the reinforcing ring <NUM> which faces the cylinder side is covered by the covering portion <NUM> which is the sealing portion. However, the reinforcing ring <NUM> may be directly brought into contact with the bottom surface portion 32b of the accommodating portion <NUM>. Further, a groove in an annular shape is not formed and an O-ring is not disposed on the bottom surface portion 32b of the accommodating portion <NUM>. However, to enhance sealability between the cylinder head <NUM> and the reinforcing ring <NUM>, the groove may be formed on the bottom surface portion 32b, and the O-ring may be disposed in the groove.

In the third embodiment, the recessed portion <NUM> is formed on the front surface 71a of the reinforcing ring <NUM>. Accordingly, in a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, it is possible to support the valve spring <NUM> while movement of the valve spring <NUM>, particularly in the radial direction, is restricted without using a spring washer.

Next, with reference to <FIG> and <FIG>, a valve stem seal <NUM> and a hermetic sealing structure <NUM> according to a fourth embodiment of the present invention are described. Hereinafter, only parts which make the present embodiment different from the above-mentioned embodiments are described. Configurations which are equal to the corresponding configurations of the above-mentioned embodiments are given the same symbols, and the description of such configurations is omitted.

As shown in <FIG>, a cross-sectional shape of a reinforcing ring 7c of the valve stem seal <NUM> taken along the axis x is a substantially crank shape. In the same manner as the third embodiment, the reinforcing ring <NUM> includes a recessed portion <NUM> which is a portion to be pressed by a valve spring <NUM>. On a back surface 71b of the reinforcing ring 7c which faces downward, that is, on a surface of the reinforcing ring 7c which opposedly faces a bottom surface portion 32b of an accommodating portion <NUM> in a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, the reinforcing ring 7c includes a recessed portion <NUM> in an annular shape at a portion of the reinforcing ring 7c on an inner side in the radial direction.

The recessed portion <NUM> includes: a slope portion 73a in an annular shape which is inclined upward toward the axis x from a portion of the back surface 71b other than the recessed portion <NUM>; and a bottom surface portion 73b which extends toward the axis x from the slope portion 73a in an annular shape.

The elastic body portion <NUM> includes a covering portion <NUM> which covers the back surface 71b. The covering portion <NUM> covers the bottom surface portion 73b of the recessed portion <NUM> in the recessed portion <NUM>, and a distal end of the covering portion <NUM> on the outer side in the radial direction extends to the slope portion 73a. That is, the covering portion <NUM> does not cover the entire back surface 71b of the reinforcing ring <NUM>.

A distal end portion of the covering portion <NUM> on the outer side in the radial direction includes a protrusion 85a which projects downward. The protrusion 85a projects downward from the back surface 71b in the direction of the axis x. In a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, the protrusion 85a abuts on an inner wall of the cylinder head <NUM>, to be more specific, the bottom surface portion 32b of the accommodating portion <NUM>.

As shown in <FIG>, in a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, the back surface 71b of the reinforcing ring 7c and the covering portion <NUM> of the elastic body portion <NUM> are brought into contact with the inner wall of the cylinder head <NUM>. To be more specific, the reinforcing ring <NUM> abuts on the bottom surface portion 32b of the accommodating portion <NUM> of the cylinder head <NUM> at a portion of the reinforcing ring <NUM> where the recessed portion <NUM> is not formed, that is, at the portion of the back surface 71b which is not covered by the covering portion <NUM>. The covering portion <NUM> which covers the back surface 71b in the recessed portion <NUM> abuts on the bottom surface portion 32b of the accommodating portion <NUM> of the cylinder head <NUM>. Further, the protrusion 85a of the covering portion <NUM> projects toward the cylinder side from the back surface 71b as described above. Accordingly, in a state where the valve stem seal <NUM> is attached to the cylinder head <NUM>, the protrusion 85a of the covering portion <NUM> abuts on the bottom surface portion 32b of the accommodating portion <NUM> thus elastically deforming.

As shown in <FIG>, a groove in an annular shape is not formed and an O-ring is not disposed on the bottom surface portion 32b of the accommodating portion <NUM>. However, to enhance sealability between the cylinder head <NUM> and the reinforcing ring <NUM>, the groove may be formed on the bottom surface portion 32b which is not covered by the covering portion <NUM> and with which the back surface 71b of the reinforcing ring <NUM> is brought into contact, and the O-ring may be disposed in the groove.

In the fourth embodiment, the covering portion <NUM> which is the sealing portion includes the protrusion 85a which abuts on the inner wall of the cylinder head <NUM>, particularly, on the bottom surface portion 32b of the accommodating portion <NUM>. Accordingly, when the valve stem seal <NUM> is attached to the cylinder head <NUM>, the protrusion 85a elastically deforms so that higher sealability can be ensured between the cylinder head <NUM> and the reinforcing ring <NUM>.

Claim 1:
A hermetic sealing structure (<NUM>, <NUM>, <NUM>, <NUM>) for hermetically sealing a space formed between a valve stem (<NUM>) of a valve (<NUM>) and a valve guide (<NUM>), the valve (<NUM>) establishing and interrupting communication between a cylinder and a port (P), the valve guide (<NUM>) having one end facing a cam side and another end facing a cylinder side, and the valve stem (<NUM>) being inserted into the valve guide (<NUM>) in a reciprocally movable manner, the hermetic sealing structure (<NUM>, <NUM>) being characterized by comprising:
a cylinder head (<NUM>);
a valve guide (<NUM>) arranged on the cylinder head (<NUM>);
the valve stem (<NUM>) inserted into the valve guide (<NUM>) in a reciprocally movable manner;
a valve spring (<NUM>) mounted on the cylinder head (<NUM>), and biasing the valve stem (<NUM>) in a direction where communication between the cylinder and the port (P) is interrupted; and
a valve stem seal (<NUM>, <NUM>, <NUM>, <NUM>) provided on the valve guide (<NUM>) on a side of the one end, wherein
the valve stem seal (<NUM>, <NUM>, <NUM>, <NUM>) includes: a reinforcing ring (<NUM>) formed into an annular shape centered about an axis (x), and extending in a radial direction of a ring of the reinforcing ring (<NUM>); and an elastic body portion (<NUM>) formed into an annular shape centered about the axis (x), attached to the reinforcing ring (<NUM>), and including a seal lip (<NUM>) which abuts on the valve stem (<NUM>), and
the reinforcing ring (<NUM>) includes a portion to be pressed (<NUM>, <NUM>) which is disposed between an inner wall (<NUM>) of the cylinder head (<NUM>) which faces the cam side and the valve spring (<NUM>), and is fixed to the cylinder head (<NUM>) by pressure from the valve spring (<NUM>), wherein the reinforcing ring (<NUM>) has a hollow disk shape,
characterized in that the elastic body portion (<NUM>) is integrally formed with the reinforcing ring (<NUM>).