Patent Description:
A high-pressure tank storing high pressure gas such as hydrogen is installed in a vehicle using a gaseous fuel such as a natural gas vehicle or a hydrogen fuel cell vehicle. In particular, as a high-pressure tank storing high pressure hydrogen gas, a high-pressure tank corresponding to type <NUM> is used.

In general, the high-pressure tank of type <NUM> is manufactured by forming a composite material layer on a surface of a liner made of a plastic material by a filament winding technique. The liner is manufactured by combining a metal boss and a knob to a plastic material such as polyolefin-based resin or polyamide-based resin. The composite material layer is formed by winding a composite fiber in which a carbon fiber or a glass fiber is mixed with a polymer resin such as an epoxy resin on the surface of the liner.

In the case of a high-pressure tank of a one port type, a port that is a head boss to which a valve for an entry of gas such as hydrogen is coupled is formed on one side, and a knob that is a tail boss for the purpose of fixing the tank is formed on the other side. A method in which a metallic knob cap is externally coupled to the knob has been conventionally used.

The knob cap serves to be coupled to a fixing shaft and fix the tank in order to prevent the tank from shaking during a filament winding process. Since the entire knob cap is made of metal, the knob cap became a factor hindering a weight reduction of the high-pressure tank.

<CIT> discloses a pressure container including a knob cap.

The present invention has been made in an effort to provide a knob cap for a high-pressure tank having advantages of enabling a weight reduction and securing a structural stability.

An exemplary embodiment of the present invention provides a knob cap for a high-pressure tank having advantages of installing a reinforcing cap having impact resistance so as to improve a protective effect against an external impact.

Another embodiment of the present invention provides a knob cap for a high-pressure tank including a coupling groove portion corresponding to a knob of a liner of the high-pressure tank formed in a lower surface of a body; a peripheral wing portion extending outward in a lower end of an outer circumferential surface of the body to be in contact with a surface of the liner; and a thickness conversion portion formed in the outer circumferential surface of the body to change a thickness between a center line and the outer circumferential surface. Furthermore, the body includes: a hollow fixing groove formed in a center of the upper surface of the body, a fixing shaft being able to be coupled to the hollow fixing groove when performing a filament winding process; and one or more inner grooves extending downward from an upper surface of the body and surrounding the hollow fixing groove.

According to the present invention, a metal insert formed of a metal material coupled to the knob may be inserted into the coupling groove portion of the body.

According to the present invention, the metal insert may be formed in the shape of a cup having a hollow in which a thread is formed on an inner circumferential surface.

According to the present invention, a reinforcing cap including a coupling protrusion coupled to the inner groove and in a shape of a disc with a hollow may be coupled to the upper surface of the body.

According to the present invention, the metal material of the metal insert may include aluminum, and the body may be formed of fiber-reinforced plastic reinforced with a glass fiber or a carbon fiber.

According to the present invention, the thickness conversion portion may be in the form of stairs in which a step is formed.

According to the present invention, in the thickness conversion portion, the outer circumferential surface may be in the form of an inclined surface in which a thickness of the body decreases toward an upper side, or in the form of a curved groove or a V-shaped groove concave toward a center line.

A metal bushing may be coupled to the fixing groove.

According to the knob cap for the high-pressure tank according to the present invention having the configuration as described above, it is possible to form the knob cap of a plastic material such as fiber-reinforced plastic, thereby increasing the effect of a weight reduction of the high-pressure tank.

According to the present invention, it is possible to control a generation of strong internal stress in the high-pressure tank by forming the thickness conversion portion in the form of stairs on the outer circumferential surface of the knob cap, thereby preventing damage to the knob cap and the high-pressure tank.

According to the present invention, it is possible to install the reinforcing cap having an impact resistance outside the knob cap, thereby protecting the knob cap from a drop test and an external impact.

Since the present invention may have various changes and may have various forms, embodiments will be described in detail in the detailed description. However, this is not intended to limit the present invention to the specific form of disclosure, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each of the drawings, like reference numerals have been used for like elements.

The above terms are used only for the purpose of distinguishing one element from another element. The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.

<FIG> is a diagram of a configuration of a liner of a high-pressure tank according to the present invention.

The high-pressure tank storing high-pressure gas such as hydrogen includes a liner <NUM> and a composite material layer formed by winding a fiber-reinforced composite material on an outer surface of the liner by a filament winding technique. The liner <NUM> stores high-pressure gas in an internal space and maintains tightness of the gas, and the composite material layer serves to support a stress acting in a circumferential direction of the liner due to an internal pressure of the gas.

The liner <NUM> uses a plastic material such as polyolefin-based resin or polyamide-based resin for a weight reduction, and is manufactured through blow molding, rotational molding, or injection molding.

A composite material layer <NUM> (see <FIG>) is formed by wrapping a fiber-reinforced composite material in which a carbon fiber or a glass fiber is mixed with a polymer resin such as an epoxy resin on the surface of the liner <NUM>, to maintain strength.

The high-pressure tank <NUM> manufactured as described above is used for compressing and storing various fluids including liquefied petroleum gas (LPG), compressed natural gas (CNG), light hydrocarbons (methane, propane, and butane) and hydrogen gas.

A valve is coupled to one side of the liner <NUM> and a port <NUM> through which a gaseous fuel may enter and exit is formed therein, and a knob <NUM> for the purpose of fixing is provided on the other side. A knob cap <NUM> as shown in <FIG> and <FIG> is coupled to the knob <NUM>.

<FIG> and <FIG> are respectively a perspective view and a cross-sectional view illustrating a knob cap for a high-pressure tank according to an embodiment of the present invention.

The knob cap <NUM> according to an embodiment of the present invention includes a body <NUM> coupled to the knob <NUM> of the liner <NUM> of the high-pressure tank <NUM>. According to an embodiment of the present invention, the body <NUM> may be formed of a plastic material, and may further include a metal insert <NUM> made of a metal material.

According to an embodiment of the present invention, as the plastic material of the knob cap body <NUM>, fiber-reinforced plastic containing a fiber in a plastic resin is used. As the plastic resin, a polyolefin-based resin (HDPE series) or polyamide series (PA6, PA66, etc.) and a compound material based thereon or a combination of the above resin may be used, and a carbon fiber or a glass fiber in the form of a long fiber or a short fiber may be used as the fiber. The fiber-reinforced plastic according to the present invention may be long fiber thermoplastic (LFT) or short fiber thermoplastic (SFT). When the fiber-reinforced plastic is applied, it is advantageous that a weight specific gravity of the fiber is composed of <NUM> % and <NUM> %.

According to the knob cap <NUM> according to the present invention, the metal insert <NUM> made of a metal, for example, aluminum (Al), may be provided to a part to which the knob <NUM> of the liner <NUM> of the high-pressure tank is coupled. The body <NUM> is formed of a plastic material and is coupled to the metal insert <NUM>, thereby improving a durability of the part to which the knob <NUM> of the liner <NUM> is coupled along with a weight reduction. When the knob cap <NUM> according to an embodiment of the present invention includes the metal insert <NUM>, the knob cap <NUM> may be manufactured by an insert injection molding method in which the metal insert <NUM> is inserted into a mold and a plastic material is injected.

Referring to <FIG> and <FIG>, in the knob cap <NUM> according to an embodiment of the present invention, a coupling groove <NUM> is formed in the center of a lower surface of the body <NUM> in correspondence to the knob <NUM>, and the metal insert <NUM> is provided to the coupling groove <NUM>.

The metal insert <NUM> is a part to which the knob <NUM> of the liner <NUM> is inserted and coupled, and may be formed in the form of a hollow cup in which a thread is formed on an inner circumferential surface. Therefore, the metal insert <NUM> may be coupled with the knob <NUM> of the liner <NUM> in which a thread is formed on an outer circumferential surface, in a screw fastening manner. Since the metal insert <NUM> is integrally molded with the body <NUM>, the knob cap <NUM> may be coupled to the knob <NUM> of the liner <NUM> in a screw fastening manner. The metal insert <NUM> increases the durability of the knob cap <NUM>.

The body <NUM> of the knob cap <NUM> includes a peripheral wing portion <NUM> extending outward from a lower end of the outer circumferential surface. The peripheral wing portion <NUM> extends by continuing in a curve with the outer circumferential surface of the body <NUM> and an outer surface of the liner <NUM>, and the entire bottom surface is closely attached to the liner <NUM>.

A plurality of inner grooves <NUM> are formed in the body <NUM> of the knob cap <NUM>. The inner groove <NUM> is a groove in the shape of a column that extends downward from an upper surface of the body <NUM>, that is, the upper end opened and extending downward. The inner groove <NUM> may be formed in the form of a circular column or a polygonal column. The plurality of inner grooves <NUM> surround a center line of the body <NUM> and are arranged in an annular shape, are spaced at equal intervals in a circumferential direction, and arranged to be spaced in a radial direction.

The inner groove <NUM> functions to prevent shrinkage from occurring when demolded from a mold after injection molding. That is, when the knob cap is demolded from the mold after molding, shape deformation may occur as an amount of cooling shrinkage in the central portion is relatively increased, and a plurality of inner grooves <NUM> function to prevent the shape deformation due to the shrinkage.

According to the present invention, a reinforcing material may be mounted on the inner groove <NUM>. That is, when there is concern about deterioration in physical properties due to the inner groove <NUM>, the reinforcing material having a shape, for example, a cylindrical shape, corresponding to the inner groove <NUM>, may be inserted into the inner groove <NUM> to prevent deterioration in physical properties.

According to the present invention, in the center of the upper surface of the body <NUM> of the knob cap <NUM>, a fixing groove <NUM> in the form of a hollow for fixing a fixing shaft (not shown) required for a filament winding process is formed. In the fixing groove <NUM>, a metal bushing <NUM> is installed inside to increase a bonding force with the fixing shaft.

The metal bushing <NUM> applied to the fixing groove <NUM> serves to strengthen the bonding force with the fixing shaft and to prevent damage due to strong tension during a filament winding operation.

According to an embodiment of the present invention, a thickness conversion portion <NUM> is formed on the outer circumferential surface of the body <NUM> of the knob cap <NUM>.

The thickness conversion portion <NUM> changes a thickness of the body defined between the center line and the outer circumferential surface so that the outer circumferential surface has a different thickness at least in part in a height direction. The center line is a line passing through the center of the knob cap in the height direction. The thickness conversion portion <NUM> improves a bearing capacity with respect to an internal stress.

According to an embodiment of the present invention, as shown in <FIG> and <FIG>, the thickness conversion portion <NUM> formed on the outer circumferential surface of the body <NUM> of the knob cap <NUM> may be in the shape of stairs in which a step <NUM> is formed. Since the thickness conversion portion <NUM> has the step <NUM>, the thickness conversion portion <NUM> has a reduction outer diameter portion <NUM> with a relatively reduced thickness on an upper end of the outer circumferential surface.

<FIG> and <FIG> illustrate that one step is formed, but the thickness may be reduced in such a way that steps are continuously formed.

The thickness conversion portion <NUM> formed on the outer circumferential surface of the knob cap <NUM> allows the composite material layer <NUM> to be reinforced when the high-pressure tank is manufactured. Since the composite material layer <NUM> is reinforced to make it possible to support the stress, the thickness conversion portion <NUM> functions to improve the structural stability of the knob cap <NUM>.

According to an embodiment of the present invention, the thickness conversion portion <NUM> is not limited to the shape of stairs and may be formed in various shapes.

<FIG> is a partial cross-sectional view for explaining implementation examples of the thickness conversion portion formed on an outer circumferential surface of the knob cap according to an embodiment of the present invention.

Referring to <FIG>, the thickness conversion portion <NUM> is formed in the form of an inclined surface. In the thickness conversion portion <NUM>, the outer circumferential surface forms the inclined surface and a thickness of the body decreases toward an upper side. Therefore, the inclined surface is located with an upper end close to a center line and a lower end relatively far from the center line. When the thickness conversion portion <NUM> shown in <FIG> is formed, at full height on the outer peripheral surface, the body has a trapezoidal cross section with a narrow upper end and a wide lower end.

Referring to <FIG>, the thickness conversion portion <NUM> may be formed in the shape of a curved groove. The curved groove is formed in a concave shape with a middle part toward the center line. Therefore, when the curved groove is formed in the outer circumferential surface, the thickness of the body is the thinnest in the middle part. Referring to of <FIG>, the thickness converting portion <NUM> may be in the form of a V-shaped groove in which a middle part is concave toward the center line. Therefore, the thickness of the body becomes the thinnest in the middle part. In <FIG>, the concave portion toward the center line is shown to be formed in the middle part, but its location may be changed. In addition, the inclined surface, the curved groove and the V-shaped groove may be formed over the entire outer circumferential surface of the body in the height direction, but may be formed in a part of the outer circumferential surface of the body. The thickness conversion portion <NUM> as described above improves a bonding force with the composite material layer <NUM> to serve to suppress deformation with respect to a stress acting in an outward direction of the liner <NUM>.

According to an embodiment of the present invention, it further includes a reinforcing cap <NUM> covering the upper surface of the knob cap <NUM>. The reinforcing cap <NUM> is formed in the form of a hollow thin disk having a larger diameter or width than that of the body <NUM> of the knob cap <NUM>. The reinforcing cap <NUM> includes a hollow <NUM>, and a coupling protrusion <NUM> corresponding to the inner groove <NUM> is formed on a lower surface thereof. The coupling protrusion <NUM> is inserted into and coupled to the inner groove <NUM>.

The reinforcing cap <NUM> is formed of an expanded polypropylene (EPP) foam and has an excellent recovery against repeated impact and deformation, maintains a high dimensional stability when exposed to an extreme temperature, and has an excellent impact resistance, a repeated buffering property, a flexibility and a chemical resistance. This reinforcing cap <NUM> may increase the ability to respond to a drop test and an external impact of the high-pressure tank <NUM>.

Hereinafter, with reference to Table <NUM> and <FIG> and <FIG>, a structural stability according to the effect of a weight reduction and stress distribution explanation results of the knob cap according to the present invention are compared.

The embodiment relates to an implementation of the knob cap shown in <FIG> and <FIG>, a reference example is the same as the embodiment, but relates to a form of a straight line in which the thickness conversion portion is not applied to the outer circumferential surface, and a comparative example relates to a conventional knob cap made of a metal material.

In the embodiment and the reference example, an aluminum (specifically, Al6061-T61) material was used for the metal insert, and long fiber thermoplastic was used for the body in which the metal insert was inserted into the coupling groove. Specifically, PA <NUM> was used as a mattress resin, and <NUM> wt% of GF was contained.

First, referring to [Table <NUM>], a weight reduction ratio is as follows.

As shown in [Table <NUM>], when the knob cap is formed through insert injection molding of the metal insert and plastic as in the embodiment of the present invention, the effect of the weight reduction equal to or greater than <NUM>% may be obtained compared to the comparative example, which acts as a factor that may increase a weight efficiency of a container product.

<FIG> is a diagram showing a stress distribution analysis result with respect to the knob cap for the high-pressure tank according to an embodiment of the present invention. <FIG> is a diagram showing a stress distribution analysis result with respect to the knob cap for the high-pressure tank according to a reference example.

It was assumed that a liner was molded by a blow molding method using a PA-based resin. The liner may be molded by rotation molding or injection molding. After forming the liner, the knob caps according to the embodiment and the reference example were attached to a screw-type protrusion, and the composite material layer was formed by a filament winding technique. A stress distribution analysis was performed assuming that gas such as hydrogen was injected at high pressure after complete curing, and whether the knob is deformed at a minimum design bursting pressure (<NUM>,<NUM> bar) was analyzed. Damage occurs when a stress value exceeds a tensile strength value of each material (see Al6061-T61: 310Mpa, PA6+GF50wt%: 230Mpa).

Upon comparing <FIG> and <FIG>, as shown in <FIG>, in the embodiment, it may be seen that a safety margin of +<NUM>% in a plastic material and +<NUM>% in an aluminum material were secured, and a sufficient structural stability was secured in the wing peripheral portion.

Claim 1:
A knob cap (<NUM>) for a high-pressure tank, the knob cap (<NUM>) comprising:
a coupling groove portion (<NUM>) corresponding to a knob (<NUM>) of a liner (<NUM>) of the high-pressure tank formed in a lower surface of a body (<NUM>);
a peripheral wing portion (<NUM>) extending outward in a lower end of an outer circumferential surface of the body (<NUM>) to be in contact with a surface of the liner (<NUM>);
a thickness conversion portion (<NUM>) formed in the outer circumferential surface of the body (<NUM>) to change a thickness between a center line and the outer circumferential surface; and
a hollow fixing groove (<NUM>) formed in a center of the upper surface of the body (<NUM>), a fixing shaft being able to be coupled to the hollow fixing groove (<NUM>) when performing a filament winding process,
characterised in one or more inner grooves (<NUM>) extending downward from an upper surface of the body (<NUM>) and surrounding the hollow fixing groove (<NUM>).