A tank comprises: a liner including a circular cylindrical body part having a center axis and a dome part placed at each of opposite ends of the body part; and a reinforcing layer placed on the liner and containing fiber. The reinforcing layer includes a hoop layer placed on the body part and a helical layer placed across an area on the hoop layer and on the dome part. The hoop layer includes a hoop body layer and a hoop end layer connected to the hoop body layer and located at an end portion of the hoop body layer in an axis direction along the center axis. The hoop end layer has a shape projecting externally further in a radial direction of the body part than the hoop body layer, and includes an apex portion located at the outermost position in the radial direction and a tilted surface extending from the apex portion toward an outer surface of the dome part and having a shape conforming to the shape of the outer surface.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese patent application No.2022-5772 filed on Jan. 18, 2022, the disclosure of which is hereby incorporated in its entirety by reference into the present application.

BACKGROUND

Field

The present disclosure relates to a technique relating to a tank for storing a fluid therein.

Related Art

A tank conventionally known stores therein fuel used for natural gas cars, fuel cell cars, etc. (Japanese Patent Application Publication No. 2016-223569). The conventional tank includes a liner and a reinforcing layer placed on the liner. The reinforcing layer includes a sheet layer (also called a hoop layer) placed on a straight part of the liner, and a helical layer placed on the sheet layer and on a dome part of the liner. The helical layer is formed by helical winding of a fiber on the sheet layer and on the dome part. Opposite end portions of the sheet layer is processed into shapes conforming to an outer surface of the dome part.

The helical winding for forming the helical layer is performed while tension is applied to the fiber. According to the conventional technique, however, it is impossible in some cases to apply intended tension on the opposite end portions of the sheet layer. In such cases, increasing the strength of the tank may be impossible due to a clearance formed between the sheet layer and the helical layer.

SUMMARY

According to a first aspect of the present disclosure, a tank for storing a fluid therein is provided. The tank comprises: a liner including a circular cylindrical body part having a center axis and a dome part placed at each of opposite ends of the body part; and a reinforcing layer placed on the liner and containing fiber. The reinforcing layer includes a hoop layer placed on the body part and a helical layer placed across an area on the hoop layer and on the dome part. The hoop layer includes a hoop body layer and a hoop end layer connected to the hoop body layer and located at an end portion in an axis direction along the center axis. The hoop end layer has a shape projecting externally further in a radial direction of the body part than the hoop body layer, and includes an apex portion located at the outermost position in the radial direction and a tilted surface extending from the apex portion toward an outer surface of the dome part and having a shape conforming to the shape of the outer surface.

DETAILED DESCRIPTION

FIG.1is a sectional view of a tank10according the present embodiment.FIG.1shows a section (predetermined section) defined by cutting the tank10along a plane passing through a center axis AX of a body part42of the tank10and parallel to the center axis AX. The tank10is used for storing a high-pressure fluid therein. In the present embodiment, the tank10stores high-pressure fuel gas used for fuel cell cars, for example. The tank10includes a liner40, a reinforcing layer50placed on the liner40, a first ferrule part14, and a second ferrule part15. The first ferrule part14includes an opening14afor forming communication between the interior and exterior of the tank10. The second ferrule part15does not include the opening14a.

The liner40is a hollow container in which a storage chamber25is formed for storing a fluid therein. The liner40is made of resin with gas barrier properties such as polyamide resin, for example. The liner40may be made of metal instead of the resin. The liner40includes the circular cylindrical body part42having the center axis AX, and dome parts44and46in a pair placed at opposite ends of the body part42. One of the dome parts44and46in a pair is also called a first dome part44, and the other is also called a second dome part46. The first dome part44is connected to one end portion of the body part42in an axis direction DAx along the center axis AX. The second dome part46is connected to the other end portion of the body part42in the axis direction DAx. Each of the first dome part44and the second dome part46has a dome shape having an outer diameter reduced with a greater distance from the body part42in the axis direction DAx.

The reinforcing layer50is a layer for reinforcing the liner40. The reinforcing layer50covers an outer surface of the liner40. The reinforcing layer50contains a fiber. In the present embodiment, the reinforcing layer50is composed of a carbon fiber bundle impregnated in advance with thermosetting resin such as epoxy resin.

FIG.2is a view for explaining the tank10further.FIG.2schematically shows a region of the tank10inFIG.1covering a boundary between the body part42and the first dome part44. A region covering a boundary between the body part42and the second dome part46has a corresponding structure. For this reason, a detailed configuration of the tank10will be described below using the region covering the boundary between the body part42and the first dome part44.

The reinforcing layer50includes a hoop layer53placed on the body part42, and a helical layer58placed across an area on the hoop layer53and on the dome part44. A winding direction of a fiber to form the hoop layer53is a direction along a peripheral direction of the body part42. Specifically, the winding direction of the fiber of the hoop layer53and the axis direction DAx form an angle that is approximately 90°. In the present embodiment, the hoop layer53is formed by preparing a cylindrical member by winding a sheet-like fiber impregnated with thermosetting resin on a member different from the liner40, and placing the cylindrical member at the body part42of the liner40. A method of forming the hoop layer53will be described later in detail. The helical layer58is formed by winding a fiber bundle impregnated with thermosetting resin in such a manner as to cover the hoop layer53, the first dome part44, and the second dome part46while tension set in advance is applied to the fiber bundle. The helical layer58is formed by winding the fiber bundle repeatedly on the tank10using at least one of low-angle helical winding and high-angle helical winding. A method of forming the helical layer58will be described later in detail.

The hoop layer53includes a hoop body layer51having a constant thickness and a hoop end layer52. In a radial direction of the body part42, a distance between an outer surface42faof the body part42and an outer surface of the hoop body layer51, namely, the thickness of the hoop body layer51is defined as a thickness Tb. The hoop end layer52includes two layers located at opposite end portions of the hoop body layer51in the axis direction DAx. While the description herein is intended for one hoop end layer52belonging to the two hoop end layers52at the opposite end portions, the same configuration is also applied to the other hoop end layer52. The hoop end layer52is connected to the hoop body layer51and located at an end portion of the hoop layer53in the axis direction DAx.

The hoop end layer52has a convex shape projecting externally further in the radial direction of the body part42than the hoop body layer51. More specifically, the hoop end layer52includes an apex portion54plocated at the outermost position of the hoop end layer52in the radial direction, specifically, an intermediate portion54of the greatest thickness of the hoop end layer52, a hoop base end portion55connecting the intermediate portion54and the hoop body layer51, and a hoop tip portion57located on the opposite side of the hoop base end portion55across the intermediate portion54in the axis direction DAx. The hoop base end portion55has a thickness that is gradually increased further with a shorter distance from the hoop body layer51toward the intermediate portion54in the axis direction DAx. An outer surface of the hoop base end portion55is a tilted surface tilted from the axis direction DAx and having a curved surface shape, for example. The hoop tip portion57has a thickness that is gradually reduced further with a greater distance from the intermediate portion54, namely, with a shorter distance to the dome part (here, the first dome part44) in the axis direction DAx. A tilted surface53facorresponding to an outer surface of the hoop tip portion57extends from the apex portion54ptoward an outer surface44faof the dome part (here, the first dome part44), and is tilted from the axis direction DAx. A boundary between the tilted surface53faand the outer surface44faforms a smooth curved surface without generating a step height. Specifically, the tilted surface53fahas a shape formed by extending the outer surface44fain such a manner as to be defined in the same way as the shape of the outer surface44fa, and has a curved surface shape conforming to the shape of the outer surface44fa. In the present embodiment, the tilted surface53faand the outer surface44faof the dome part (here, the first dome part44) on the same side relative to the axis direction DAx form an isotonic curved surface. In a certain section of the tank10shown inFIG.2, a distance Lt along the tilted surface53fais preferably equal to or greater than a width Wt of the fiber bundle used for forming the helical layer58. The distance Lt is a distance determined along the tilted surface53fafrom the apex portion54pto an end portion57pof the tilted surface53faadjacent to the dome part (here, the first dome part44). With this configuration, it is possible to place the fiber bundle along its entire width on the tilted surface53faduring helical winding, allowing a greater amount of pressing force responsive to intended tension on the fiber bundle to be applied to the tilted surface53fa. This achieves an increased degree of tight contact between the helical layer58and the hoop end layer52.

Preferably, a maximum thickness of the hoop end layer52, namely, a distance Ta between the apex portion54pand the outer surface42faof the body part42in the radial direction of the body part42is equal to or greater than 1.05 times the thickness Tb of the hoop body layer51. This allows the tilted surface53fato be tilted more largely from the axis direction DAx to a degree by which distribution of force of pressing the fiber bundle toward the hoop end layer52is suppressed during helical winding. The distance Ta is also preferably equal to or less than 1.10 times the thickness Tb. This makes it possible to restrict a degree of external projection of the hoop end layer52in the radial direction, thereby achieving reduction in the occurrence of strain on a fiber bundle80forming the helical layer58.

FIG.3is a process view showing a method of manufacturing the tank10. According to the manufacturing method of the present embodiment, after a hoop layer forming step is performed in which the hoop layer53is placed on the liner40, a helical layer forming step is performed in which the helical layer58is placed on the hoop layer53and on the dome parts44and46.

In the hoop layer forming step, a winding step is performed first in which a sheet fiber is wound on a mandrel (cored bar) having higher stiffness than the liner40(step P10).

FIG.4is an explanatory view of the step P10. In the step P10, a mandrel70is prepared first. The mandrel70is a member different from the liner40and to become a mold for a hoop layer62before processing. The mandrel70has a circular columnar shape formed by using stainless steel or metal such as iron or copper, for example. The mandrel70has an outer diameter slightly larger (by about 0.5 mm, for example) than that of the body part42of the liner40. A length of the mandrel70along the axis AX is larger than the length of the body part42of the liner40. In the present embodiment, the stiffness of the mandrel70is higher than that of the liner40.

After the mandrel70is prepared, a sheet fiber60impregnated with thermosetting resin is wound several times in a peripheral direction of the mandrel70using a sheet winding method (hereinafter called an “SW method”), thereby completing the hoop layer62before processing. In the present embodiment, the sheet fiber60has a width same as the length of the body part42of the liner40in the axis direction DAx. During winding of the sheet fiber60on the mandrel70, tension set in advance is applied to the sheet fiber60. According to the SW method, tension per unit width to be applied to the sheet fiber60is about twice as high as tension to be applied to a fiber bundle by a common filament winding method (hereinafter called an “FW method”), for example.

Subsequent to completion of formation of the hoop layer62before processing, a step of extracting the mandrel70from the hoop layer62before processing is performed (a step P20inFIG.2). The step P20is also called an extraction step.

FIG.5is a sectional view of the hoop layer62before processing from which the mandrel70was extracted by the extraction step. As shown inFIG.5, after extraction of the mandrel70, the hoop layer62before processing has a circular cylindrical shape.

After implementation of the extraction step, the hoop layer62before processing is processed to form a hoop layer63before placement as a cylindrical member including the hoop body layer51and the hoop end layer52(a step P30inFIG.2). The step P30is also called a processing step.

FIG.6is a sectional view of the hoop layer63before placement. In the processing step, the hoop layer62before processing is processed by cutting or grinding into a shape conforming to the shape of the hoop layer53.

After implementation of the processing step, a step of fitting the liner40into the hoop layer63before placement is performed (a step P40inFIG.2). The step P40is also called a fitting step. As a result of implementation of the fitting step, the hoop layer63before placement is placed on the body part42of the liner40to become the hoop layer53.

FIG.7is a schematic view showing a state where the hoop layer53is formed on the body part42of the liner40by the fitting step. In a step performed after implementation of the fitting step, the interior of the liner40is pressurized through the first ferrule part14to form tight contact of the outer surface42faof the body part42of the liner40with an inner surface of the hoop layer53(a step P50inFIG.2). The step P50is also called a pressurizing step.

After implementation of the pressurizing step, with the interior of the liner40kept in the pressurized state, a helical layer forming step is performed (a step P60). In the helical layer forming step, a fiber bundle impregnated with thermosetting resin is first wound several times by helical winding on the liner40using the FW method to form the helical layer58composed of a plurality of layers. The helical winding is performed using at least one of high-angle helical winding and low-angle helical winding. In the present embodiment, the helical layer58is formed using high-angle helical winding and low-angle helical winding in combination.

FIG.8is a view for explaining the low-angle helical winding.FIG.9is a view for explaining the high-angle helical winding. As shown inFIG.8, according to the low-angle helical winding, the fiber bundle80is wound repeatedly in a spiral pattern in such a manner as to stretch between the two dome parts44and46. In a layer formed by the low-angle helical winding, an angle α1formed between a winding direction of the fiber bundle80and the axis direction DAx is any angle in an exemplary range from 5 to 40° (for example, 15°).

As shown inFIG.9, in a layer formed by the high-angle helical winding, an angle α2formed between a winding direction of the fiber bundle80and the axis direction DAx is larger than the angle al determined by the low-angle helical winding. The angle α2is any angle in an exemplary range from 65° to 87° (for example, 80°).

After implementation of the helical layer forming step, a thermal hardening process is performed for hardening the hoop layer53and the helical layer58integrally by applying heat (a step P70inFIG.2). After implementation of the thermal hardening process, the liner40is released from the pressurized state (a step P80). As a result of a series of the steps described above, formation of the tank10is completed.

FIG.10is a view for explaining a tank10tof a reference example.FIG.10is a view corresponding toFIG.2. The tank10tdiffers from the tank10of the embodiment shown inFIG.2in the shape of a hoop end layer52t. The other structures are common between the tank10tand the tank10, so that description of the common structures will be omitted, if appropriate.

The hoop end layer52tof the tank10tdoes not project externally further in the radial direction of the body part42than the hoop body layer51but is reduced in thickness with a shorter distance from the hoop body layer51toward the dome part (inFIG.10, the first dome part44). An outer surface of the hoop end layer52thas a curved surface shape and forms a tilted surface53tfatilted from the axis direction DAx. In each of the certain sections shown inFIGS.2and10, the tilted surface53tfais tilted more gently than the tilted surface53fa. Specifically, at each point of the axis direction DAx in each of the certain sections, a tangent to the tilted surface53tfaand the axis direction DAx form an angle smaller than an angle formed between a tangent to the tilted surface53faand the axis direction DAx.

In winding the fiber bundle80by helical winding on the tilted surface53tfaof the hoop end layer52t, a winding direction FD of the fiber bundle80and a tangent to a portion of the hoop end layer52ton which the fiber bundle80is wound form an angle β1that is reduced considerably from 90°. Hence, in pressing the fiber bundle80toward the hoop end layer52t, it is impossible in some cases to apply intended tension due to distribution of force of pressing the hoop end layer52twith the fiber bundle80. This reduces a degree of tight contact between the hoop end layer52tand the helical layer58to cause a clearance in a region Rg between the hoop end layer52tand the helical layer58. This clearance may cause a void or separation between the hoop end layer52tand the helical layer58. The occurrence of the void or the separation reduces the strength of the tank10t. In filling the storage chamber25with high-pressure fuel gas, this may cause a crack, etc. at a shoulder portion of the reinforcing layer50located in a boundary area between the hoop layer53tand each of the dome parts44and46due to stress (shearing force, for example) occurring at the shoulder portion.

FIG.11is a view for explaining the helical layer forming step further.FIG.11is a view corresponding toFIG.2. In winding the fiber bundle80by helical winding on the tilted surface53faof the hoop end layer52of the present embodiment, the winding direction FD of the fiber bundle80and a tangent to a portion of the hoop end layer52on which the fiber bundle80is wound form an angle β2that is settable as an angle larger than β1shown inFIG.10and more approximate to 90°. Specifically, the shape of the hoop end layer52projecting externally further in the radial direction than the hoop body layer51allows the tilted surface53fato be tilted more largely from the axis direction DAx than the shape of the hoop end layer52tshown inFIG.10not projecting externally further in the radial direction than the hoop body layer51. As a result, in winding the fiber bundle80by helical winding on the tilted surface53faof the hoop end layer52, it becomes possible to suppress distribution of force of pressing the fiber bundle80toward the hoop end layer52, allowing intended tension to be applied to the fiber bundle80. This achieves an increased degree of tight contact between the helical layer58and the hoop layer53by the application of pressing force responsive to the intended tension from the fiber bundle80toward the hoop end layer52, thereby reducing the probability of the occurrence of a clearance between the helical layer58and the hoop layer (in particular, the hoop end layer52). Thus, it becomes possible to suppress reduction in the strength of the tank10.

As shown inFIG.2, according to the above-described embodiment, the tilted surface53faand the outer surface44faof the dome part44form an isotonic curved surface. This achieves reduction in imbalance of tension to be applied to the fiber bundle80of the reinforcing layer50formed on the tilted surface53faand on the outer surface44fa, allowing the tank10to have strength increased to a greater degree. As shown inFIGS.4to7, according to the above-described embodiment, the hoop layer53is formed by thermally hardening the hoop layer63before placement that is a cylindrical member formed by winding the sheet fiber60on the mandrel70different from the liner40. This facilitates formation of the hoop layer53by using the hoop layer63before placement.

B. Other Embodiments

In the above-described embodiment, the hoop layer53is formed by thermally hardening the hoop layer63before placement prepared using the sheet fiber60. However, the hoop layer53is not limited to this. For example, the hoop layer53may be formed by winding a fiber impregnated with thermosetting resin by hoop winding on the body part42of the liner40. A winding direction of the fiber by hoop winding conforms to the peripheral direction of the body part42. In forming the hoop layer53by hoop winding of the fiber, the hoop body layer51and the hoop end layer52may be formed by changing the number of layers to be stacked or by stacking the fiber to a certain thickness and then performing cutting or grinding in such a manner as to form the stacked fiber into the shape of the hoop layer53.

The present disclosure is not limited to the above-described embodiments but is feasible in the form of various configurations within a range not deviating from the substance of the disclosure. For example, technical features in the embodiments corresponding to those in each of the aspects described in SUMMARY may be replaced or combined, where appropriate, with the intention of solving some or all of the aforementioned problems or achieving some or all of the aforementioned effects. Unless being described as absolute necessities in the present specification, these technical features may be deleted, where appropriate. For example, the present disclosure may be realized in the following aspects.

(1) According to a first aspect of the present disclosure, a tank for storing a fluid therein is provided. The tank comprises: a liner including a circular cylindrical body part having a center axis and a dome part placed at each of opposite ends of the body part; and a reinforcing layer placed on the liner and containing fiber. The reinforcing layer includes a hoop layer placed on the body part and a helical layer placed across an area on the hoop layer and on the dome part. The hoop layer includes a hoop body layer and a hoop end layer connected to the hoop body layer and located at an end portion in an axis direction along the center axis. The hoop end layer has a shape projecting externally further in a radial direction of the body part than the hoop body layer, and includes an apex portion located at the outermost position in the radial direction and a tilted surface extending from the apex portion toward an outer surface of the dome part and having a shape conforming to the shape of the outer surface. According to this aspect, the shape of the hoop end layer projecting externally further in the radial direction than the hoop body layer allows the tilted surface to be tilted more largely from the axis direction than the shape of the hoop end layer not projecting externally further in the radial direction than the hoop body layer. As a result, in winding the fiber by helical winding on the tilted surface of the hoop end layer, it becomes possible to suppress distribution of force of pressing the fiber toward the hoop end layer, allowing intended tension to be applied to the fiber. This achieves an increased degree of tight contact between the helical layer and the hoop layer by the application of pressing force responsive to the intended tension from the fiber toward the hoop end layer, thereby reducing the probability of the occurrence of a clearance between the helical layer and the hoop layer (in particular, the hoop end layer).

(2) In the above-described aspect, in a section defined by cutting the tank along a plane passing through the center axis and parallel to the center axis, a distance along the tilted surface may be equal to or greater than a width of a fiber bundle used for forming the helical layer. This aspect allows application of a greater amount of pressing force to the tilted surface that is responsive to intended tension applied to the fiber bundle during helical winding, thereby achieving an increased degree of tight contact between the helical layer and the hoop end layer. Thus, it becomes possible to further reduce the probability of the occurrence of a clearance between the helical layer and the hoop layer (in particular, the hoop end layer).

(3) In the above-described aspect, a distance between the apex portion and an outer surface of the body part in the radial direction may be equal to or greater than 1.05 times and equal to or less than 1.10 times the thickness of the hoop body layer. This aspect allows the tilted surface to be tilted more largely from the axis direction to a degree by which distribution of force of pressing the fiber toward the hoop end layer is suppressed during helical winding. Furthermore, a degree of external projection of the hoop end layer in the radial direction is restricted, thereby achieving reduction in the occurrence of strain on the helical layer.

(4) In the above-described aspect, the tilted surface and the outer surface of the dome part may form an isotonic curved surface. This aspect achieves reduction in imbalance of tension to be applied to the fiber of the reinforcing layer formed on the tilted surface and on the outer surface of the dome part, allowing the tank to have strength increased to a greater degree.

(5) In the above-described aspect, the hoop layer may be composed of a cylindrical member formed by winding the fiber on a member different from the liner. This aspect facilitates formation of the hoop layer by using the cylindrical member.

The present disclosure is feasible in various aspects. In addition to the above-described aspects, the present disclosure may be realized in aspects including a method of manufacturing a tank and a vehicle including the tank, for example.