DE102016225446B4 - Pressure tank with reinforcing fibers - Google Patents

Abstract

A pressure tank (110) is described with at least one curved wall (201), wherein the curved wall (201) forms a cavity for receiving a medium. The wall (201) has a first layer with fibers (211, 212) and an overlying second layer with fibers (211, 212). In this case, at least fibers (211, 212) of the first layer have a Poisson number which is less than 0.05, in particular less than zero.

Description

The invention relates to a pressure tank, in particular for receiving a fuel for a vehicle.

A road vehicle may comprise a fuel cell based on a fuel such as e.g. Hydrogen generates electrical energy for operation, in particular for the drive, of the vehicle. The fuel may be stored in one or more pressurized tanks of the vehicle with a pressurized tank having walls enclosing a cavity for receiving the fuel.

A filled pressure tank is exposed to the pressure forces of the fuel contained in the pressure tank and is typically designed for a certain nominal pressure. For example, a pressure tank can be designed to permanently store fuel at a pressure of 350, 500, 700 bar or more (baru stands for "bar" overpressure relative to the atmospheric pressure or ambient pressure). The walls of a pressure tank must therefore be designed for the respective nominal pressure. For example, a pressure tank must be designed for a minimum burst pressure, which is a multiple of the nominal pressure. For example, the common approval requirements require a safety factor of 2.25 μm for hydrogen containers with carbon fiber reinforcement, which must exceed the minimum burst pressure above the nominal pressure. The required wall thickness typically increases with increasing nominal pressure or minimum burst pressure.

As the wall thickness increases, the capacity of a pressure tank (for a given limited space) decreases and / or the weight of a pressure tank increases. As a result, the range and efficiency of a vehicle are compromised.

The present document deals with the technical problem of providing a pressure tank for receiving a fuel, which has the smallest possible wall thickness for a given nominal pressure.

The object is solved by the independent claim. Advantageous embodiments are described i.a. in the dependent claims.

In one aspect, a pressure tank having at least one domed wall is described. In this case, the wall forms a cavity for receiving a medium, in particular for receiving a fuel. The fuel may e.g. Comprise compressed hydrogen. The wall can at least partially form a cylinder. The cylinder can be closed by dome-shaped end walls. The pressure tank can be designed for a certain nominal pressure (above atmospheric pressure). The nominal pressure causes forces on the inside of the at least one wall. The forces on the inside cause stresses within the at least one wall of the pressure tank.

The wall may comprise a first layer of fibers and an overlying second layer of fibers. The fibers may be in a matrix, e.g. embedded in a resin. In other words, the wall can be constructed of several layers of a fiber composite material. In this case, the first layer is arranged closer to the inside of the wall than the second layer. Furthermore, due to the curvature of the wall, the second layer may have a larger surface area than the first layer. The first layer is thus closer to the cavity in which the medium can be stored while the second layer is closer to the environment (where atmospheric pressure typically exists).

Due to the curvature of the wall, the fibers of the first layer normally have a higher tensile stress than the fibers of the overlying second layer. However, at least fibers of the first layer may have a Poisson's number that is less than 0.05, in particular less than zero. At least fibers of the first layer may thus exhibit auxetic behavior, i. a negative Poisson number. In other words, longitudinal stretching of the fibers also causes an increase in the cross-sectional area of the fibers. Thus it can be effected that tensile stresses on the fibers of the different layers can be distributed as uniformly as possible over the cross section of the wall. In particular, such a difference between the tensile stress on fibers of the first layer and the tensile stress on fibers of the second layer can be reduced (possibly reduced to substantially zero). A uniform or at least a more uniform stress on the fibers of the different layers then allows the use of walls with a reduced wall thickness.

Fibers of the first layer may comprise carbon fibers based on polyacrylonitrile (PAN). Such carbon fibers may nanoscopically have a negative Poisson's ratio of about -0.4, with the distance of the graphene planes from each other increasing with the longitudinal strain. However, due to the porosity of the PAN-based carbon fibers, which is typically 30%, microscopically, when viewed on the fiber, a positive Poisson's value of about 0.2 results. The carbon fibers may therefore have been densified in the course of manufacture in order to have a reduced pore content. In particular, the carbon fibers may have a porosity of 20%, more preferably 10%, or less. By reducing the porosity of the PAN-based carbon fibers, the Poisson's number of fibers can be reduced (ie by reducing the porosity, the auxetic behavior on the nano-scale (distances of the graphene planes to each other) on the micro-scale (fiber cross-section ) be transmitted.).

Alternatively or additionally, fibers of the first layer may comprise a helical auxetic yarn.

In particular, a fiber of the first layer may comprise a first fiber component and a second fiber component, wherein the first fiber component (in particular a first fiber or a first fiber bundle) in a ground state helically or helically around the second fiber component (in particular around a second fiber or around a second fiber bundle) is wound. In this case, the first fiber component and / or the second component, e.g. Carbon, Kevlar, glass, plastic, polyamide and / or polyester include. Preferably, the first fiber component may have a higher modulus of elasticity than the second fiber component. By using such auxetic yarn, fiber layers with auxetic behavior can be provided to effect uniform loading of the layers of a multilayer wall.

The transverse expansion behavior (ie in particular the Poisson's ratio) of the fibers of the first layer and of the second layer is preferably such that in a curved section of the wall, stresses in the first layer and in the second layer are substantially equal when the pressure tank is loaded with its minimum burst pressure , In this case, the transverse expansion behavior (in particular the Poisson's number) can be adapted to the curvature, in particular to a curvature radius.

The alignment of the stresses in the different layers can be effected, as described in this document, by using fibers with auxetic behavior. In particular, forces on the second layer may be caused by auxetic fibers in the first layer due to the radial expansion of the fibers of the first layer to cause uniform stress on the layers of the multilayer, curved, wall. In other words, the auxetic behavior causes a (slight) thickening of the wall with increasing pressure, which causes the outer layers (which would be less burdened than the inner layers without auxetic behavior) to carry more of the load and, ideally, a uniform fiber load of all layers is reached for the bursting pressure.

As stated above, the first layer and the second layer typically comprise a matrix (e.g., resin) in which the fibers are disposed. A material of the matrix may have a negative Poisson number. Thus, the uniformity of the stress distribution within a multilayer wall can be further increased.

According to a further aspect, a vehicle (in particular a road motor vehicle, for example a passenger car or a lorry) is described which comprises the pressure tank described in this document.

It should be understood that the devices and systems described herein may be used alone as well as in combination with other devices and systems described in this document. Furthermore, any aspects of the devices and systems described in this document may be combined in a variety of ways. In particular, the features of the claims can be combined in a variety of ways.

• 1 eine beispielhafte Drucktank-Anordnung;
• 2 einen beispielhaften Querschnitt eines Drucktanks; und
• 3 ein beispielhaftes auxetisches Garn.

Furthermore, the invention will be described in more detail with reference to exemplary embodiments. Show

• 1 an exemplary pressure tank assembly;
• 2 an exemplary cross section of a pressure tank; and
• 3 an exemplary auxetic yarn.

As stated above, the present document is concerned with reducing the wall thickness of a pressure tank. In particular, the present document is concerned with a pressurized container system (= compressed hydrogen storage system (= CHS system)) for a motor vehicle. The pressure vessel system is used to store under ambient conditions gaseous fuel or fuel. The pressure vessel system can be used, for example, in a motor vehicle that is operated with compressed natural gas (CNG) or liquefied (LNG) natural gas or with hydrogen.

Such a pressure vessel system comprises at least one pressure vessel. The pressure vessel may be, for example, a cryogenic pressure vessel (= CcH2) or a high-pressure gas vessel (= CGH2).

High pressure gas containers are formed, substantially at ambient temperatures Permanently store fuel at a nominal operating pressure (also called nominal working pressure or NWP) of about 350 bar (= over-pressure versus atmospheric pressure), more preferably about 700 bar or more. A cryogenic pressure vessel is suitable to store the fuel at the aforementioned operating pressures even at temperatures well below the operating temperature of the motor vehicle.

1 shows an exemplary pressure tank assembly 100 with a first pressure tank 110 and a second pressure tank 120 that can be used to fuel (especially hydrogen) for a fuel consumer (eg a fuel cell) 101 to provide a vehicle. The pressure tanks 110 . 120 are over lines 112 . 122 with the fuel consumer 101 connected.

The pressure tanks 110 . 120 can end pieces on the front ends 111 . 114 respectively. 121 . 124 exhibit in the manufacture of the pressure tanks 110 . 120 for holding the pressure tanks 110 . 120 can be used. Furthermore, at the end pieces 111 . 121 an opening can be provided through which fuel from a pressure tank 110 . 120 can be performed (eg via a valve to a line 112 . 122 ). At an opening of a pressure tank 110 . 120 can also be a pressure relief device 113 . 123 can be arranged, which can trigger in the presence of a certain trigger condition (eg, when a certain temperature) to fuel from the pressure tank 110 . 120 in the environment of the pressure tank 110 . 120 let off, and so the pressure in the pressure tank 110 . 120 to reduce.

A pressure tank 110 . 120 (Also referred to as a pressure vessel) may include a liner. The liner forms the hollow body in which the fuel is stored. The liner may for example be made of aluminum or steel or of their alloys. Further preferably, the liner may be made of a plastic. It can also be a linerless pressure vessel 110 . 120 be provided.

A pressure vessel 110 . 120 typically includes at least one fiber reinforced layer. The fiber-reinforced layer may preferably completely surround a liner at least in regions. The fiber reinforced layer is often referred to as a laminate or armor. In this document, the term "fiber reinforced layer" or "layer (s) with fibers" is most commonly used. Fiber-reinforced plastics (also abbreviated to FVK or FKV) are usually used as the fiber-reinforced layer, for example carbon fiber reinforced plastics (CFRP) and / or glass fiber reinforced plastics (GRP). A fiber-reinforced layer suitably comprises reinforcing fibers embedded in a plastic matrix. In particular, matrix material, type and proportion of reinforcing fibers and their orientation can be varied so that the desired mechanical and / or chemical properties are established. Preferably, continuous fibers are used as reinforcing fibers, which can be applied by winding and / or braiding. A fiber-reinforced layer usually has several layer layers or several (partial) layers.

The fiber reinforced layer typically has cross and circumferential layers. In order to compensate for axial stresses, cross layers (helical layers) are wound or braided over the entire winding core surface. In the generally cylindrical peripheral area usually so-called peripheral layers ("hoop layers") are provided, which provide a gain in the circumferential direction. The circumferential positions extend in the circumferential direction U of the pressure vessel and are at an angle of about 90 ° (+/- 5 °) to the pressure vessel longitudinal axis AA (axis 207 in 2 ) oriented.

Advantageously, at least two layers of the fiber-reinforced layer can be arranged in a balanced angle composite (AWV, English: Balanced Ply Laminate). A balanced angle composite can be described as a composite of two unidirectional layers, whereby in addition to the scrim also, for example, tissue and wound cross-layers come into question. The reinforcing fibers of these unidirectional layers have fiber angles to the tissue normal or longitudinal axis AA (axis 207 in 2 ), which have the same amount but different signs.

2 shows a cross section of a pressure tank 110 , The pressure tank 110 includes in the illustrated area a circular wall 201 with a certain wall thickness 206 , The one in the pressure tank 110 located fuel has a certain pressure, by the voltages σ 203 in the circumferential direction within the wall 201 caused. The tensions σ 203 In the circumferential direction typically take from the inside out, ie with increasing radial distance 202 from a central axis 207 of the pressure tank 110 from. 2 shows an example voltage curve 205 the hoop stresses in the radial direction through the cross section of the wall 201 of the pressure tank 110 ,

A pressure tank 110 has a certain volume and is typically for a burst pressure p _max designed. Furthermore, the material of the wall 201 for a certain maximum voltage σ _max be designed. From the required bursting pressure, the maximum voltage and from the surface A of the wall 201 can then be a required Wall thickness 206 the Wall 201 be determined. For example, for a cylindrical tank the required wall thickness 206 be calculated according to the boiler formula as S _min = p _max * r _m / σ _mean , where r _{m is} the average radius of the tank and σ _means the average (tangential) tension in the tank wall 201 equivalent. As is apparent from the voltage curve 205 in 2 results, the maximum voltage is σ _max only on the inside of the wall 201 before while the material is on the outside of the wall 201 a lower voltage σ 203 is exposed, so that without the present invention for the tangential stress applies: σ _medium <σ _max .

The wall 201 a pressure tank 110 can be made of a fiber composite material. The fiber composite has fibers 211 . 212 , for example made of carbon or carbon, on, in a matrix 213 , For example, from a plastic material such as a synthetic resin, are arranged. The fibers 211 . 212 can, as in 2 exemplified, in different directions within the wall 201 run. In 2 are fibers 211 shown extending along a direction perpendicular to the image plane, and fibers 212 represented that run within the image plane.

The forces on the inside of the wall 201 cause tension in the fibers 211 . 212 , In particular, axial stresses (ie in the longitudinal direction of the tank) cause stresses in the respective longitudinal direction of the fibers 211 and tangential stresses (ie in the circumferential direction of the tank) stresses in the respective longitudinal direction of the fibers 212 , As stated above, the longitudinal stresses take on the fibers 212 typically with increasing radial distance 202 to the central axis 207 from.

This document proposes fibers 211 . 212 to use that have auxetic behavior. Auxetic materials have a negative Poisson number, ie an elongation ε _x in the longitudinal direction likewise causes an expansion ε _r in the lateral or radial direction, where ε _r = -ν · ε _x , where v is the transverse expansion coefficient or Poisson's ratio. On the other hand, for the longitudinal strain ε _x = σ _x / E, where E is the modulus of elasticity of a fiber 211 . 212 in the longitudinal direction. A longitudinal tension σ _x thus causes a fiber 211 . 212 with an auxetic behavior an elongation ε _r = -ν / E · σ _x transverse to the longitudinal direction of the fiber 211 . 212 , in particular an expansion in the radial direction of the wall 201 of the pressure tank 110 ,

As a result of the strain ε _{r of} the fibers 211 . 212 on the inside of the wall 201 Additional forces are applied to the fibers on the outside 211 . 212 causes. For example, the wall 201 of the pressure tank 110 several layers of fibers 211 . 212 have, which are arranged one above the other in the radial direction (from the inside of the wall 201 to the outside of the wall 201 ). The elongation ε _{r of} the fibers 211 . 212 One layer then causes additional forces on the next, further outermost layer.

The use of fibers 211 . 212 with auxetic behavior can thus be used to stress (in particular the tangential stresses) within a wall 201 a pressure tank 110 distribute more evenly. In particular, it can be effected that all layers of a wall 201 at the bursting pressure uniformly the maximum stress σ _{max are} exposed, as in 2 exemplified by the voltage curve 208 is shown. Due to the uniform load of the wall material can turn the wall thickness 206 around the difference 204 be reduced.

The difference 204 to the wall thickness 206 can be reduced, for example, can be determined as follows. The integral of the original voltage curve 205 (using conventional fibers 211 . 212 ) in the radial direction over the entire wall thickness 206 gives a first voltage integral. The difference 204 can then be determined such that the integral of the balanced voltage waveform 208 (when using auxetic fibers 211 . 212 ) in the radial direction over the difference 204 reduced wall thickness corresponds to the first voltage integral. This consideration, which is preferably made separately for the axial and the tangential stresses, has been summarized in the above remarks for the sake of simplicity.

The fibers 211 . 212 For example, with auxetic behavior, carbon fibers based on polyacrylonitrile (PAN) may be included. It has been observed that carbon fibers based on PAN have an auxetic behavior, in particular when porosity is reduced within the individual carbon fibers. The reduction of the porosity can be achieved by a (in particular mechanical) compression of the fibers 211 . 212 during the production of the fibers 211 . 212 be achieved.

It should be pointed out that a reduction in the Poisson's number (even if the possion number remains positive) leads to a more uniform distribution of fiber utilization. In other words, the in 2 illustrated voltage curve 205 can already be made more uniform by reducing the Poisson's number, so that the voltage 203 on the fibers 211 . 212 in an outer layer of a wall 201 of the pressure tank 110 works, to the tension 203 is approximated on the fibers 211 . 212 in an inner layer of the wall 201 acts.

3 shows an exemplary fiber 300 with auxetic behavior. In particular shows 3 a so-called auxetic yarn 300 (in English "helical auxetic yarn") as it is eg in US8002879B2 is described. The yarn 300 includes a first fiber component 301 (eg, a first fiber and / or a first fiber bundle) and a second fiber component 302 (eg a second fiber and / or a second fiber bundle), wherein the first fiber component 301 around the second fiber component 302 wrapped around (in the form of a helix, also called screw, helix, cylindrical spiral or helix). For the sake of simplicity, this form should be referred to as "helical". The first fiber component 301 may comprise a material having a relatively high modulus of elasticity, such as a carbon fiber, a wire, a glass fiber, etc. The second fiber component 302 preferably has a lower modulus of elasticity in the longitudinal direction than the first fiber component 301 and may include, for example, siloxanes, silicones, gums, etc.

In the upper part of 3 will the yarn (or the fiber) 300 in the relaxed state or in the ground state shown. If the yarn 300 is loaded with a tensile force, then becomes the first fiber component 301 elongated and the second fiber component 302 Wraps around the first fiber component 301 , This has the consequence that the width 305 of the yarn 300 increased, as from the lower part of 3 evident. Thus, the yarn points 300 out 3 an auxetic behavior, since the elongation in the longitudinal direction also to an elongation in the radial direction of the yarn 300 leads.

It can thus auxetic yarns 300 in the composite or in the composite material of a pressure tank 110 can be used to cause an auxetic effect and to counteract (in particular radial) uneven fiber loading or fiber utilization.

The auxetic yarn 300 comprises at least two twisted fibers and / or fiber bundles 301 . 302 , which preferably have a different stiffness. By stretching these twisted fibers or fiber bundles 301 . 302 it comes to an effective thickening, if parameters of the yarn 300 be selected accordingly. Parameters with which the auxetic behavior of the yarn 300 can be adjusted, are: the stiffness (modulus of elasticity) of the fibers or fiber bundles 301 . 302 , the diameter of the fibers or fiber bundles 301 . 302 and / or the pitches and gradients through the fibers or fiber bundles 301 . 302 Helices formed in the unstretched state. Exemplary materials for the fibers or fiber bundles 301 . 302 are: carbon, kevlar, glass, plastics, biogenic materials, etc.

The total Poisson number for the composite in the wall 201 a pressure tank 110 ie for the fibers 211 . 212 and for the matrix 213 , can be determined via a mixture rule. In the mixing rule, the volume weighted average of the respective Poisson numbers of fiber 211 . 212 and matrix 213 educated. The volume fraction of the matrix 213 is about 35% to 40% and the volume fraction of the fibers 211 . 212 is about 60% -65%. The total Poisson's number of the composite thus typically becomes predominantly the Poisson's number of fibers 211 . 212 affected. Thus, the use of fibers leads 211 . 212 with auxetic behavior also typically leads to auxetic behavior of the composite.

In addition to the use of fibers 211 . 212 with auxetic behavior can also be the matrix 213 of the fiber composite have an auxetic behavior. So can the uniformity of the material load over the entire cross-section 206 a wall 201 a pressure tank 110 be further improved.

The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and figures are intended to illustrate only the principle of the proposed devices and systems.

Claims (10)

A pressure tank (110) having at least one domed wall (201) forming a cavity for receiving a medium; in which - The wall (201) has a first layer with fibers (211, 212) and an overlying second layer with fibers (211, 212); and - At least fibers (211, 212) of the first layer have a Poisson number which is less than 0.05, in particular less than zero. Pressure tank (110) according to Claim 1 wherein fibers (211, 212) of the first layer comprise carbon fibers based on polyacrylonitrile. Pressure tank (110) according to Claim 2 wherein the carbon fibers have a reduced pore density, in particular a porosity of 20% or less. A pressure tank (110) according to any one of the preceding claims, wherein fibers (211, 212) of the first layer comprise a helical auxetic yarn (300). Pressure tank (110) according to one of the preceding claims, wherein - a fiber (211, 212) of the first layer comprises a first fiber component (301) and a second fiber component (302); and - the first fiber component (301) is helically wound around the second fiber component (302) in a ground state. Pressure tank (110) according to Claim 5 wherein the first fiber component (301) has a higher modulus of elasticity than the second fiber component (302). Pressure tank (110) according to one of Claims 5 to 6 wherein the first fiber component (301) and / or the second component (302) comprise carbon, kevlar, glass and / or plastic, in particular polyamide and / or polyester. A pressure tank (110) according to any one of the preceding claims, wherein a transverse expansion behavior of the fibers (211, 212) of the first layer and the second layer is such that stresses (203) in the first layer and in a curved portion of the wall (201) Substantially equal to the second layer when the pressure tank (110) is loaded with a minimum burst pressure. A pressure tank (110) according to any one of the preceding claims, wherein the first layer and the second layer comprise a matrix (213) in which the fibers (211, 212) are disposed. Pressure tank (110) according to Claim 9 wherein a material of the matrix (213) has a negative Poisson number.

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