Spring for fuel cell stack, method for designing and selecting spring, and fuel cell stack

Abstract

The application discloses a spring for a fuel cell stack and a design selection method and a fuel cell stack, and belongs to the technical field of fuel cells. The design selection method of the spring for the fuel cell stack comprises the following steps: obtaining the ranges of the spring diameter D, the maximum compression amount h of the spring and the thickness t of the spring according to the performance requirements of the fuel cell stack on the spring; taking the boundary condition of the spring geometric parameter diameter D as an input constraint function, establishing the response surface of the assembly force F and the optimal deformation amount δ of the fuel cell stack through the ranges of the spring diameter D, the maximum compression amount h of the spring and the thickness t of the spring, and obtaining the optimal D, h and t with the relative maximum of the flexible coefficient in the spring buffering and compensation process as a target condition. The application quantifies the displacement and assembly force of the fuel cell stack buffering and compensation in the life cycle of the fuel cell stack, can guarantee the sealing performance of the fuel cell stack, and can prevent the fuel cell stack from being affected by the assembly force and the performance and service life of the fuel cell stack.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cells, and particularly relates to a spring for a fuel cell stack and a design selection method thereof and a fuel cell stack. BACKGROUND

[0002] A proton exchange membrane fuel cell (PEMFC) is an electrochemical device that directly converts chemical energy of fuel into electrical energy, and has the advantages of high energy conversion rate, low emission, small pollution, low noise, and convenient maintenance. Generally, a single fuel cell is mainly composed of a membrane electrode assembly and a bipolar plate with a gas flow channel stacked alternately, wherein the membrane electrode assembly (MEA) is usually prepared by a hot pressing process from a gas diffusion layer, a catalyst layer, and a polymer electrolyte membrane. In order to enable the fuel cell to obtain higher performance, it is necessary to have as small a contact resistance as possible between the bipolar plate and the membrane electrode, and therefore a certain force needs to be applied to the stack so that the gas diffusion layer is compressed, while ensuring that the sealant line is compressed to achieve the sealing effect.

[0003] A fuel cell stack is usually composed of tens to hundreds of single cells connected in series. During the entire life cycle of the fuel cell stack, the temperature during operation can be as high as 80 DEG C, and the low-temperature storage temperature can be as low as -40 DEG C. With the change of temperature, expansion and contraction occur in the interior of the stack; at the same time, there is also a pneumatic load during the operation of the stack, both of which change the assembly force of the stack. Under the action of long-term load, the key components of the stack, the membrane electrode and the sealant line, will produce a certain relaxation. During the relaxation process, the assembly force in the stack will decrease while the compression rate in the stack remains unchanged. Eventually, the contact resistance between the gas diffusion layer and the polar plate will increase, the sealing reliability will decrease, and the performance and life of the stack will be affected. In order to solve the above problems, the design of the stack usually needs to use springs such as disc springs (referred to as disc springs) for buffering and compensation, so that the total compression amount of the gas diffusion layer and the sealant line in the stack is increased, the compression amount of the disc spring is released, and at the same time the assembly force in the stack is reduced, and the compression force of the disc spring is released.

[0004] A disc spring is a spring formed by a circular disc with a hole in the center into a conical disc shape. Unlike traditional springs, disc springs have special functions. For example, disc springs can bear large loads with small deformation, have short travel, require small space, are easy to use in combination, are easy to maintain and replace, are high in economic safety, and have long service life. At the same time, disc springs are also considered to be difficult to design, and subtle size differences have a great impact on the load when used in combination, and can also cause the phenomenon of reverse displacement and load relationship. Therefore, based on the important role of disc springs in fuel cell stacks and the characteristics of disc springs themselves, the selection and design of springs such as disc springs in fuel cell stacks are particularly important. However, no research on the design and selection of springs for fuel cell stacks has been found in the related art. SUMMARY

[0005] In view of the above problems, the present application aims to solve one of the technical problems in the related art at least to some extent. To this end, the present application provides a spring for fuel cell stack, a design selection method thereof and a fuel cell stack, which can fill the gap in the research on the design selection of the spring for the fuel cell stack, guarantee the sealing and performance of the fuel cell stack, and overcome the shortcomings in the prior art.

[0006] To solve the above technical problems, the present application is implemented as follows:

[0007] According to one aspect of the present application, the embodiments of the present application provide a design selection method of a spring for fuel cell stack, which comprises:

[0008] According to the performance requirement of the spring for the fuel cell stack, the range of the spring diameter D, the range of the maximum compression amount h of the spring and the range of the thickness t of the spring are obtained; the response surface of the assembly force F and the optimal deformation amount δ of the fuel cell stack is established by taking the boundary condition of the spring geometric parameter diameter D as the input constraint function, the optimal spring diameter D, the maximum compression amount h of the spring and the thickness t of the spring are obtained by taking the relative maximum of the flexible coefficient in the spring buffering and compensation process as the target condition.

[0009] Further, the obtaining of the range of the spring diameter D, the range of the maximum compression amount h of the spring and the range of the thickness t of the spring according to the performance requirement of the spring for the fuel cell stack comprises: establishing the matching principle of the fuel cell stack and the spring; based on the matching principle, establishing the consideration dimension of the fuel cell stack and the spring.

[0010] Further, the establishing of the matching principle of the fuel cell stack and the spring comprises: the matching of the static assembly force of the fuel cell stack and the compression of the spring; the matching of the dynamic assembly force compensation and the buffering performance of the fuel cell stack; the matching of the spring and the boundary condition of the fuel cell stack.

[0011] Further, the establishing of the consideration dimension of the fuel cell stack and the spring comprises: (1) the value of the assembly force F of the fuel cell stack divided by the number m of the spring distribution in the plane as the working compression force selection criterion of the spring; (2) under the premise of satisfying condition (1), the greater the flexible coefficient of the spring in the optional buffering and compensation range of the fuel cell stack, the better; (3) from the perspective of the contact boundary condition, the geometric parameter diameter D of the spring is suitable to approach the width of the reaction area of the bipolar plate, so as to uniformly apply the assembly force.

[0012] Further, on the premise of satisfying the consideration dimension condition (1) and the consideration dimension condition (2), the range of the spring diameter D, the range of the spring thickness t, and the range of the maximum compression amount h of the spring are sequentially proposed.

[0013] Further, the working compression force of the spring is the compression force corresponding to the spring δ = 0.75h; and / or the diameter D of the spring is not affected by the thickness t of the spring and the maximum compression amount h of the spring.

[0014] Further, the method specifically comprises: obtaining a buffer expected value of the compression amount of the fuel cell stack and a buffer expected value of the assembly force of the fuel cell stack; obtaining a compensation expected value of the compression amount of the fuel cell stack and a compensation expected value of the compression force; establishing a matching relationship between the spring diameter and the bipolar plate size to determine the range of the spring diameter D and the range of the number of springs distributed in the plane; establishing a functional relationship between the static assembly force of the fuel cell stack and the number of springs distributed in the plane to determine the compression force range of a single spring; obtaining the range of the spring thickness t according to the range of the spring diameter D and the compression force range of a single spring; arranging the straight-line springs in the vertical direction to increase the buffer and compensation capacity of the springs through the straight-line springs, and determining the range of the maximum compression amount h of the springs and the number of straight-line disc springs according to the compensation expected value of the compression amount of the fuel cell stack; and obtaining the optimal spring diameter D, the maximum compression amount h of the springs, and the spring thickness t with the maximum flexibility coefficient as the target condition according to the range of the spring diameter D, the range of the maximum compression amount h of the springs, and the range of the spring thickness t.

[0015] Further, the obtaining of the range of the spring thickness t according to the range of the spring diameter D and the compression force range of a single spring comprises: for the disc spring without supporting surface, the range of the spring thickness t can be obtained according to the following formula:

[0016]

[0017] In the formula:

[0018]

[0019] In the formula, F is the load of a single disc spring, C is the spring index, D is the spring diameter (the outer diameter of the disc spring), d is the inner diameter of the spring (the disc spring), t is the thickness of the spring (the disc spring), h0 is the calculated value of the deformation amount when the disc spring is flattened, δ is the deformation amount of the spring (the disc spring), E is the elastic modulus, and μ is the Poisson's ratio.

[0020] Further, the obtaining the buffer expected value of the compression amount of the fuel cell stack and the buffer expected value of the assembly force of the fuel cell stack comprises: establishing a mapping relationship between the length of the fuel cell stack and the expansion coefficient of the bipolar plate and the operating temperature to obtain the buffer expected value of the compression amount of the fuel cell stack; and establishing a mapping relationship between the aerodynamic load of the fuel cell stack and the reaction area to obtain the buffer expected value of the assembly force of the fuel cell stack.

[0021] Further, the obtaining the compensation expected value of the compression amount of the fuel cell stack and the compensation expected value of the compression force comprises: considering the creep of the assembly force locking device of the fuel cell stack under long-term force and the relaxation of the adhesive line under long-term load to obtain the compensation expected value of the compression amount of the fuel cell stack and the compensation expected value of the compression force.

[0022] According to another aspect of the present application, the embodiments of the present application further provide a spring for a fuel cell stack, which is designed and selected by using the design and selection method of the spring for a fuel cell stack as described above and applied to the fuel cell stack; the spring for a fuel cell stack is made of metal, resin or modified resin; and the spring for a fuel cell stack comprises a disc spring.

[0023] Further, the spring for a fuel cell stack is made of a plurality of single modified resin layers which are laminated and formed; and the modified resin layers comprise at least two fiber reinforced resin layers.

[0024] Further, the at least two fiber reinforced resin layers comprise at least two of a carbon fiber reinforced epoxy resin layer, a glass fiber reinforced epoxy resin layer, a basalt fiber reinforced epoxy resin layer, a wood fiber reinforced epoxy resin layer and an aramid fiber reinforced epoxy resin layer.

[0025] Further, the spring for a fuel cell stack is provided with a protective coating on the outer surface.

[0026] Further, the total thickness of the carbon fiber reinforced epoxy resin layer is 0.2-0.6 times the thickness of the spring for a fuel cell stack, and the total thickness of the glass fiber reinforced epoxy resin layer is 0.8-0.4 times the thickness of the spring for a fuel cell stack.

[0027] Further, the thickness of the single modified resin layer is 0.1-0.2 mm.

[0028] According to another aspect of the present application, the embodiments of the present application further provide a fuel cell stack, which comprises a core assembly and a spring designed and selected by using the design and selection method of the spring for a fuel cell stack as described above or the spring for a fuel cell stack as described above.

[0029] The technical scheme of the present application has at least the following beneficial effects:

[0030] In the embodiment of the present application, the design and selection method of the spring for the fuel cell stack is provided, the constraint function is input by the performance requirement of the fuel cell stack to the spring and the geometric parameter spring diameter D boundary condition, the response surface of the assembly force F and the optimal deformation amount δ of the fuel cell stack is established by the spring diameter D, the maximum compression amount h of the spring and the spring thickness t, and the design process of the optimal D, h and t is obtained, and the design objective function is the relative maximum of the flexibility coefficient in the spring buffering and compensation process. Therefore, by the design and selection method, the displacement and assembly force of the fuel cell stack in the whole life cycle of the fuel cell stack are quantified, the attenuation of the assembly force caused by the relaxation of the sealing glue line can be compensated, and the sealing property and performance of the fuel cell stack can be ensured; at the same time, the fuel cell stack can be buffered when subjected to thermal expansion and cold shrinkage and aerodynamic load, and the performance and service life of the fuel cell stack can be prevented from being affected by the excessive assembly force.

[0031] The spring for the fuel cell stack in some preferred embodiments of the present application can be made of non-metallic materials, which meets the demand of light weight of the fuel cell module and relieves the problems of large mass and insulation of the metal disc spring used in the fuel cell stack.

[0032] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and / or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A spring for a fuel cell stack provided for some exemplary embodiments of the present application is shown in the figure;

[0034] Figure 2 A first Force-Displacement curve of a spring for a fuel cell stack provided for some exemplary embodiments of the present application is shown in the figure;

[0035] Figure 3 A first Force-Flexibility curve of a spring for a fuel cell stack provided for some exemplary embodiments of the present application is shown in the figure;

[0036] Figure 4 A second Force-Displacement curve of a spring for a fuel cell stack provided for some exemplary embodiments of the present application is shown in the figure;

[0037] Figure 5A second Force-Flexibility graph of a spring for a fuel cell stack provided for illustrative embodiments of the present application;

[0038] Figure 6 A third Force-Flexibility graph of a spring for a fuel cell stack provided for illustrative embodiments of the present application;

[0039] Figure 7 A fourth Force-Flexibility graph of a spring for a fuel cell stack provided for illustrative embodiments of the present application;

[0040] Figure 8 A third Force-Displacement graph of a spring for a fuel cell stack provided for illustrative embodiments of the present application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0042] Springs play an important role in fuel cell stacks. Different fuel cell stacks need to match springs of different models or sizes to use the most suitable springs for buffering and compensation, to ensure the sealing reliability of the fuel cell stack, and thus to ensure the performance and service life of the fuel cell stack. However, before the filing date of the present application, no research on the design and selection of springs for fuel cell stacks has been found in the related art, and thus research and development are needed to fill the gap in this regard. In addition, when springs are applied in fuel cell stacks, not only the model or size of the spring needs to be considered, but also the material of the spring needs to be considered. The existing springs used in fuel cell stacks are basically made of metal, which has many "bottleneck" problems such as large mass, poor corrosion resistance, poor fatigue characteristics, and cannot adapt to the development trend of "lightweight" in the fuel cell industry. In addition, in the application process of fuel cells, the stack needs to be insulated from the outside to avoid threats to personal safety. Based on the consideration of strength, the end plates clamped at both ends of the spring are also made of metal, and there are small gaps at the positions where the spring is arranged and connected and where the spring contacts the end plate, which easily causes water to remain and reduces the insulation effect of the stack. Therefore, it is necessary to research and develop non-metallic springs for fuel cell stacks to meet the demand of fuel cell modules for lightweight.

[0043] Therefore, the technical scheme provided by the embodiments of the present application can improve the sealing, safety and reliability of the fuel cell stack, and help to prolong the service life of the fuel cell stack.

[0044] Please refer to Figures 1 to 7 In some embodiments of the present application, a design and selection method of a spring for a fuel cell stack is provided, and the design and selection method of the spring comprises:

[0045] According to the performance requirements of the spring for the fuel cell stack, the range of the diameter D of the spring, the range of the maximum compression amount h of the spring and the range of the thickness t of the spring are obtained;

[0046] Taking the boundary condition of the diameter D of the spring as an input constraint function, the response surface of the assembly force F and the optimal deformation amount δ of the fuel cell stack is established by the range of the diameter D of the spring, the range of the maximum compression amount h of the spring and the range of the thickness t of the spring, and the optimal diameter D of the spring, the maximum compression amount h of the spring and the thickness t of the spring are obtained under the condition that the relative maximum of the flexible coefficient in the spring buffering and compensation process is taken as the target condition.

[0047] The embodiments of the present application can quantify the displacement and assembly force of the fuel cell stack during the buffering and compensation of the fuel cell stack during the entire life cycle of the fuel cell stack by providing the design and selection method of the spring for the fuel cell stack, so that the attenuation of the assembly force caused by the relaxation of the sealant line can be compensated, and thus the sealing and performance of the fuel cell stack can be guaranteed.

[0048] The embodiments of the present application can buffer the fuel cell stack when it is subjected to thermal expansion and contraction and aerodynamic load, and prevent the fuel cell stack from affecting the performance and service life of the fuel cell stack due to excessive assembly force.

[0049] Therefore, by adopting the technical scheme provided by the embodiments of the present application, the sealing, safety and reliability of the fuel cell stack can be improved, and the service life of the fuel cell stack can be prolonged.

[0050] Optionally, the spring for the fuel cell stack can be a disc spring, which is referred to as a disc spring.

[0051] Figure 1 The geometric parameter diagram of the spring is shown, and reference is made to Figure 1 As shown in the figure, the spring for the fuel cell stack is a disc spring, the diameter (outer diameter) of the spring (disc spring) is denoted as D, the inner diameter of the spring is denoted as d, the total deflection of the spring, i.e. the maximum compression amount of the spring, is denoted as h, the thickness of the spring is denoted as t, and the free height of the spring is denoted as H, and H=h+t.

[0052] Figures 2 to 7 The diagram displays the Force-Displacement (compression force - compression amount) curve and the Force-Flexibility (compression force - flexibility) curve of the spring. (See reference.) Figures 2 to 7 As shown, for the spring described above, since D≈2d and H=h+t, the control parameters for the force-displacement and force-flexibility relationship curves of the spring are actually only the diameter D, thickness t, and maximum compression h. Therefore, for a certain fuel cell stack, the assembly force F and the optimal deformation δ are the input parameters, and D, t, and h can have countless combinations to satisfy the required F and δ relationships.

[0053] Specifically, the design and selection method for the springs used in this fuel cell stack will be described in detail below.

[0054] In some embodiments, the ranges for the spring diameter D, the maximum spring compression h, and the spring thickness t, based on the performance requirements of the fuel cell stack for the spring, include:

[0055] Establish matching principles between fuel cell stacks and springs;

[0056] Based on the aforementioned matching principle, the consideration dimensions for fuel cell stacks and springs are established.

[0057] The matching principle between the fuel cell stack and the spring mainly includes three aspects:

[0058] (1) The static assembly force of the fuel cell stack is matched with the compression of the spring; in this case, the force-displacement curve of the spring can be taken into consideration.

[0059] (2) Matching of dynamic assembly force compensation and buffering performance of fuel cell stack; in this case, the Force-Flexibility curve of spring can be used as the object of consideration.

[0060] (3) Matching of springs with the boundary conditions of fuel cell stacks. That is, disc springs can be used in fuel cells because of their advantages in boundary conditions, namely, the large and uniform contact area with the inner end plate of the disc spring.

[0061] The force-displacement curve can be divided into four stages:

[0062] 1) 0-0.25h stage: the elastic coefficient increases gradually accelerated, the acceleration slope is less than stage 2) and stage 3) but more than stage 4), the compression force increases (decreases) rate is the largest in the four stages, the stage buffer and compensation will cause the largest assembly force fluctuation in the four stages, so this stage is not recommended to use.

[0063] 2) 0.25h-0.5h stage: the elastic coefficient increases sharply accelerated, the acceleration slope reaches the maximum in the four stages, based on the principle of trying to use the buffer and compensation ability of the sharp increase of such flexibility, therefore, this stage is also not recommended to use.

[0064] 3) 0.5h-0.75h stage: the flexibility coefficient increases relative to stage 2) slow down, however, the acceleration slope is still second only to stage 2); the flexibility coefficient at the end of stage 3) has approached stage 4), and the elastic limit of the spring is also not much different.

[0065] 4) 0.75h-h stage: the flexibility coefficient increases in the four stages is the smallest, the flexibility coefficient reaches the maximum in the value, because the flexibility coefficient increases the smallest stage, the assembly force also reaches the minimum, so the compression force fluctuation is the smallest when the compression amount changes in this interval.

[0066] In summary, when the disc spring has a certain pre-compression force and the pre-compression force is compensated and buffered near the pre-compression force, 0.75h near the working point of the disc spring should be selected, 0.75h corresponds to the working compression force of the disc spring, and the buffer amount of 0.75h-h is the smallest fluctuation of the disc spring compression force. When the disc spring compensates the compression force, the 0.5-0.75h stage can provide the second only to 0.75-h compensation stability, and under the same compression compensation amount, the compression force fluctuation increases only more than stage 4).

[0067] In some embodiments, the dimensions of the fuel cell stack and the spring are established, mainly including:

[0068] (1) The value of the assembly force F of the fuel cell stack divided by the number m of spring distribution in the plane as the working compression force selection criterion of the spring;

[0069] (2) Under the premise of meeting condition (1), the greater the flexibility coefficient of the spring in the buffer and compensation range of the fuel cell stack is, the better;

[0070] (3) From the perspective of contact boundary conditions, the geometric parameter diameter D of the spring is suitable to approach the width of the bipolar plate reaction area, so that the assembly force is uniformly applied.

[0071] Wherein, the working compression force of the spring is the compression force corresponding to the disc spring δ = 0.75h. Thus, the above consideration dimension (1) can be that the value of the assembly force F of the fuel cell stack divided by the number of spring distribution in the plane m is selected as the compression force corresponding to the spring δ = 0.75h.

[0072] According to the present embodiment, in the design and selection process of the spring for the fuel cell stack, first, the performance requirements of the fuel cell stack on the disc spring and the constraint function with the boundary condition of the geometric parameter D as the input are used to establish the response surface of F and δ through the range of D, h and t, and the optimal design process of D, h and t is obtained, and the design objective function is the relative maximum of the flexibility coefficient in the disc spring buffering and compensation process.

[0073] Specifically, under the premise of meeting the consideration dimension condition (1) and the consideration dimension condition (2), the range of the spring diameter D, the range of the spring thickness t, and the range of the maximum compression amount h of the spring are sequentially proposed; and a group of D, h and t is selected as the optimal design under the target condition of the maximum flexibility coefficient.

[0074] It should be noted that the above boundary condition of the geometric parameter D, or from the perspective of the contact boundary condition, the geometric parameter diameter D of the spring is suitable for approaching the width of the reaction area of the bipolar plate, mainly referring to that the diameter D of the spring or the number of spring distribution in the plane needs to be adapted to the shape and size of the bipolar plate. For example, when a rectangular bipolar plate is used, the diameter D of the spring can be adapted to the width of the bipolar plate, that is, the diameter D of the spring can approach (equal to or slightly less than) the width of the bipolar plate, and a plurality of uniformly arranged springs can be distributed along the length direction of the bipolar plate, and the number of spring distribution in the plane is determined according to the length of the bipolar plate, which is beneficial to uniformly apply the assembly force.

[0075] The determination of the range of the spring diameter D, the range of the maximum compression amount h of the spring and the range of the spring thickness t will be described below.

[0076] [Range of spring diameter D]

[0077] The determination of the range of the spring diameter D can be mainly carried out from two aspects, one is the matching of the parameter diameter D and the fuel cell stack, and the other is the relationship between the parameter diameter D and the physical properties of the disc spring.

[0078] Regarding the matching of the parameter diameter D and the fuel cell stack:

[0079] The selection of the diameter D of the disc spring is related to the size of the bipolar plate. Generally, the number of disc spring distribution in the plane m x D should match the length of the bipolar plate, and the diameter D of the disc spring approaches the reaction width of the bipolar plate.

[0080] Exemplarily, the width of the bipolar plate is in the range of 100-130 mm, the length is in the range of 300-420 mm, the diameter D of the disc spring can be selected in the range of 80-120 mm, and the number of the disc springs distributed in the length direction of the bipolar plate can be 3-4.

[0081] More specifically, taking the width of the bipolar plate as 105 mm and the length as 420 mm as an example, the diameter D of the disc spring should be selected in the range of 80-100 mm, the number of the disc springs should be selected as 3-4, the assembly force of the stack is 30 kN, and the compression force of a single disc spring is in the range of 7500-10000 N.

[0082] The relationship between the parameter diameter D and the physical properties of the disc spring is as follows:

[0083] In the case that the parameter diameter D and the fuel cell stack are matched, the diameter D as the first proposed parameter is not constrained by the other two parameters, the thickness t and the maximum compression amount h. Therefore, as long as the geometric constraints of the fuel cell stack on D are taken as the selection parameter range of D, and the influence of D on the consideration dimension condition (1) and the consideration dimension condition (2) is explained.

[0084] As shown in Figure 2 , the influence of the parameter diameter D on the consideration dimension condition (1) can be seen from Figure 2 , the greater the diameter D, the smaller the stiffness of the disc spring, and the smaller the diameter D, the greater the stiffness of the disc spring.

[0085] As shown in Figure 3 , the influence of the parameter diameter D on the consideration dimension condition (2) can be seen from Figure 3 , the greater the diameter D, the greater the flexibility of the disc spring, and the smaller the diameter D, the smaller the flexibility of the disc spring.

[0086] Therefore, the diameter D affects the maximum and minimum values of the flexibility coefficient, and has little effect on the incremental development trend of the flexibility coefficient, which matches the phenomenon in the consideration dimension condition (1).

[0087] Therefore, for a stack with a size of 105 mm x 420 mm, the reasonable range of the diameter D of the disc spring is 80-100 mm.

[0088] [Range of spring thickness t]

[0089] The determination of the range of the spring thickness t can be mainly carried out from two aspects, one is the relationship between the parameter thickness t and the physical properties of the disc spring, and the other is the matching of the parameter thickness t and the fuel cell stack.

[0090] The relationship between the parameter thickness t and the physical properties of the disc spring is as follows:

[0091] As shown in Figure 4As shown, the influence of parameter thickness t on the consideration dimension condition (1) can be seen from... Figure 4 It can be seen that the larger the thickness t, the greater the stiffness of the disc spring, and the smaller the thickness t, the smaller the stiffness of the disc spring. A deeper numerical pattern is that when the diameter is 90mm, h is 2.3mm, and the thicknesses are 3.2mm and 3.5mm respectively, the maximum deformation h corresponding to the compression force is the same, and the compression amount is also close to the same.

[0092] like Figure 5 As shown, the influence of parameter thickness t on the consideration dimension condition (2) can be seen from... Figure 5 It can be seen that the larger the thickness t, the smaller the flexibility of the disc spring, and the smaller the thickness t, the larger the flexibility of the disc spring. Under the premise that the diameter D and the maximum compression h are the same, for the shape of the flexible curve, the thickness t determines the left and right movement of the flexible curve in the horizontal position of the coordinate axis, while having little effect on the shape of the curve.

[0093] Therefore, it can be seen that the thickness t does not affect the maximum and minimum values ​​of the flexibility coefficient, has little impact on the incremental development trend of the flexibility coefficient, and only affects the compressive force corresponding to the flexibility coefficient, which matches the phenomenon in the consideration dimension condition (1).

[0094] Regarding the matching of parameter thickness t with fuel cell stack:

[0095] For a fuel cell stack with an assembly force of 30kN, when the disc spring diameter D is in the range of 80-100mm, according to the disc spring's compressive force-compressive displacement relationship:

[0096]

[0097] In the formula:

[0098]

[0099] Wherein, F—load of a single disc spring, C—spring index, D—spring diameter (outer diameter of disc spring), d—inner diameter of spring (disc spring), t—thickness of spring (disc spring), h0—calculated value of deformation when the disc spring is compressed, δ—deformation of spring (disc spring), E—elastic modulus, μ—Poisson's ratio.

[0100] Therefore, it can be calculated that the reasonable range for thickness t is between 3.0 and 3.5 mm, and the assembly force increases by about 5 kN for every 0.5 mm increase in thickness.

[0101] [Range of maximum spring compression h]

[0102] The range of the maximum compression h of the spring can be determined from two aspects: first, the relationship between the maximum compression h of the spring and the physical properties of the disc spring itself; and second, the matching of the maximum compression h of the spring with the fuel cell stack.

[0103] Regarding the relationship between the maximum compression h of the spring and the physical properties of the disc spring itself:

[0104] The maximum compression h and the diameter D have a numerical relationship as h = tanα × (Dd). Under the premise that α is constant, the diameter D determines the maximum flexibility coefficient of the disc spring, and the thickness t determines the maximum compressive force of the disc spring (the cross-sectional shape determines the shape of the compression curve of the disc spring, so there are engineering applications of variable cross-section optimization design when there are requirements for the shape of the disc spring compression curve and a certain design capability).

[0105] like Figure 6 As shown in Figure 6, when the diameter D and thickness t are constant, the parameter sensitivity of α can be considered. It can be seen from Figure 6 that when h decreases (increases), both the maximum flexibility and the maximum compressive force decrease (increase), and the flexibility curve becomes smoother (steeper). The difference between the peaks and troughs of the flexibility curve decreases (increases). The smoothing of the flexibility curve indicates that the relative displacement assembly force is more uniformly compensated within the 0-h range of the disc spring. For example, taking a disc spring with a diameter D = 80 mm and a thickness t = 3.0 mm as an example, the flexibility coefficient curves under different maximum compression h values ​​are shown below. Figure 6 As shown, when the maximum compression h = 1.5 mm, its performance is optimal under an assembly force of 0-22.5 kN, and the optimal matching assembly force is 15 kN when δ = 0.75 h; when the maximum compression h = 2.0 mm, its performance is optimal within the assembly force range of 22.5-27 kN, and the matching assembly force is 22.5 kN when δ = 0.75 h; when h = 2.3 mm, its performance is optimal within the range of 27-37.5 kN, and the matching assembly force is 30 kN when δ = 0.75 h.

[0106] Regarding the matching of the maximum compression parameter h with the fuel cell stack:

[0107] By adjusting the value of the maximum compression h, the difference between the peaks and troughs of the compliance curve can be changed, as can the smoothness of the curve. During the compensation phase, a gentle compliance curve means that, for the same displacement, the decrease in assembly force is relatively uniform across the three stages: 0.75h-0.5h, 0.5h-0.25h, and 0.25h-0h. There is no phenomenon where the assembly force decreases less in one stage and more drastically in the next. The advantage of this in general applications is that it provides stable compensation force across the entire working range. The disadvantage is in the buffering stage. A gentle compliance curve means that the assembly force increases more when buffering the same displacement. A steep compliance curve in the compensation phase means that the assembly force changes less when buffering a certain amount of displacement from 0.5h to 0.75h, but the compensation performance drops sharply in the latter two stages. A steep compliance curve in the buffering stage means that the assembly force changes less when buffering the same displacement. The quality of the different compensation characteristics brought about by h ultimately depends on the operating environment. In fuel cell applications, the shape of the disc spring's flexibility coefficient-deformation or stiffness coefficient-assembly force curve needs to match the decay history of the assembly force within the fuel cell stack. In other words, the impact of the assembly force decay on the fuel cell stack performance must be within acceptable limits. Further dividing the decay range into several intervals, each assembly force interval corresponds to a different time amplitude due to the mechanical properties of the stack's internal materials. The optimal assembly force compensation performance of the disc spring should correspond to the assembly force interval with the largest time amplitude within the stack.

[0108] Among them, the optimal assembly force compensation performance of the disc spring refers to the fact that within the assembly force range with the largest time amplitude, the larger the flexibility coefficient (stiffness coefficient) of the disc spring, the better (the smaller the better).

[0109] In summary, when the compensation displacement range of the fuel cell stack is 0-7.8mm, the reasonable value range of h is 2.3-2.8mm when there are four disc springs in a straight line.

[0110] Based on the above, the ranges of spring diameter D, spring thickness t, and maximum spring compression h were obtained. Thus, the spring diameter D, spring thickness t, and maximum spring compression h can be optimized to obtain the optimal flexibility coefficient curve.

[0111] Specifically, methods for obtaining the optimal flexibility coefficient curve may include: first determining the compensation capacity h of the disc spring to a certain value (e.g., 2.3 mm), such as... Figure 7 As shown, the peak value of the flexibility coefficient can be adjusted by the diameter D, and the maximum assembly force can be adjusted by the thickness t to match the assembly force (30kN) of the fuel cell stack. Analysis of the diameter D and thickness t shows that the value of the diameter D can adjust the vertical movement of the flexibility curve in the force-flexibility coefficient coordinate system, and the value of the thickness t can adjust the horizontal movement of the flexibility coefficient curve in the force-flexibility coefficient coordinate system.

[0112] Therefore, under the determined F and delta requirements, the position of the flexibility coefficient curve in the force and flexibility coefficient coordinate system can be adjusted by reducing the relative design point, increasing the diameter D and increasing the thickness t to achieve the optimization of the design.

[0113] Reference Figure 8 As shown, in the range of the obtained spring diameter D, the range of the spring thickness t and the range of the spring maximum compression h, that is, D = 80-90mm, t = 3.0-3.5mm, h = 2.3-2.8mm, three optimal solutions can be output: D80_h2.3_t3.0, D90_h2.3_t3.2, D100_h2.3_t3.5. Since the maximum compression h is 2.3mm, the matching compensation and buffer interval is the same, and Figure 8 It can be seen that the starting and ending points of the compression displacement-compression force curves of the three disc spring designs are basically overlapped, and the fuel cell stack assembly forces they can match are all around 36kN. However, the maximum flexibility coefficient distribution compression force intervals are different, as shown in Figure 7 As shown, D90_h2.3_t3.2 is optimal in the 0-34kN assembly force range, D80_h2.3_t3.0 is optimal in the 34-37.5kN assembly force range, and D100_h2.3_t3.5 has the lowest flexibility coefficient peak-to-valley difference and the largest applicable assembly force compensation range.

[0114] In some embodiments, the design selection method of the fuel cell stack spring specifically comprises the following steps:

[0115] S1, obtaining the buffer expected value of the fuel cell stack compression and the buffer expected value of the fuel cell stack assembly force; specifically comprising:

[0116] S11, establishing a mapping relationship between the fuel cell stack length and the bipolar plate expansion coefficient and the operating temperature to obtain the buffer expected value of the fuel cell stack compression;

[0117] S12, establishing a mapping relationship between the fuel cell stack aerodynamic load and the reaction area to obtain the buffer expected value of the fuel cell stack assembly force.

[0118] S2, obtaining the compensation expected value of the fuel cell stack compression and the compensation expected value of the compression force; specifically comprising:

[0119] Considering the creep of the fuel cell stack assembly force locking device under long-term stress and the relaxation of the glue line under long-term load, the compensation expected value of the fuel cell stack compression and the compensation expected value of the compression force are obtained.

[0120] S3, establishing a matching relationship between the spring diameter and the bipolar plate size to determine the range of the spring diameter D and the range of the number of springs m in the plane.

[0121] S4, establishing a functional relationship between the static assembly force of the fuel cell stack and the number of springs in the plane to determine the range of the compression force of a single spring; and determining the range of the spring thickness t according to the range of the spring diameter D and the range of the compression force of a single spring;

[0122] S5, arranging the straight-line springs in the vertical direction to increase the buffering and compensation capacity of the springs through the straight-line springs, and determining the range of the maximum compression amount h of the springs and the number of straight-line disc springs according to the expected value of the compression amount of the fuel cell stack.

[0123] The straight-line spring can be a plurality of springs arranged in a stack in the vertical direction.

[0124] S6, obtaining the optimal spring diameter D, the maximum compression amount h of the springs and the spring thickness t according to the range of the spring diameter D, the range of the maximum compression amount h of the springs and the range of the spring thickness t, with the maximum flexibility coefficient as the target condition.

[0125] According to the embodiment, the diameter of the spring is generally close to the reaction width of the bipolar plate.

[0126] According to the embodiment, the diameter D of the spring is not affected by the thickness t of the spring and the maximum compression amount h of the spring.

[0127] According to the embodiment, the compression force of a single spring is the compression force corresponding to the disc spring δ = 0.75h.

[0128] According to the embodiment, the number of straight-line disc springs is an even number.

[0129] In some embodiments, a spring for a fuel cell stack is also provided, which is designed and selected by the design and selection method of the spring for a fuel cell stack described above and applied to the fuel cell stack.

[0130] Optionally, the spring for a fuel cell stack includes a disc spring.

[0131] Optionally, the material of the spring for a fuel cell stack is metal, resin or modified resin. Preferably, the material of the spring for a fuel cell stack is resin or modified resin.

[0132] In some embodiments, the material of the spring for a fuel cell stack is modified resin.

[0133] The spring design selection method provided by the embodiment of the present application is not only suitable for the design selection of springs made of metal materials, but also suitable for the design selection of springs made of non-metal materials, especially for the design selection of springs made of non-metal materials. On the one hand, the problems of large mass, insulation or corrosion of the springs made of metal materials used in the existing fuel cell stacks can be overcome. On the other hand, the problems of selection difficulty or unsuitable size of the springs made of non-metal materials used in the fuel cell stacks can be overcome, which affects the sealing performance or service life of the fuel cell stack.

[0134] In the embodiment of the present application, the material of the spring is preferably one or more modified resins, which can meet the demand of light weight of the fuel cell module and alleviate the problems of large mass and insulation of the metal disc springs used in the existing fuel cell stacks.

[0135] In some embodiments, the spring for the fuel cell stack is made of a plurality of single-layer modified resin layers which are laminated and formed.

[0136] In some embodiments, the at least two fiber-reinforced resin layers include at least two of a carbon fiber-reinforced epoxy resin layer, a glass fiber-reinforced epoxy resin layer, a basalt fiber-reinforced epoxy resin layer, a wood fiber-reinforced epoxy resin layer and an aramid fiber-reinforced epoxy resin layer. For example, the spring for the fuel cell stack can be made of a plurality of any two or more modified resin layers of carbon fiber-reinforced epoxy resin layer, glass fiber-reinforced epoxy resin layer, basalt fiber-reinforced epoxy resin layer, wood fiber-reinforced epoxy resin layer or aramid fiber-reinforced epoxy resin layer which are laminated and formed. In addition, in other embodiments, the modified resin layer can also use other types of modified resins, which will not be described in detail here.

[0137] Optionally, the spring, i.e. the disc spring, is made of a laminated structure of carbon fiber-reinforced epoxy resin layer and glass fiber-reinforced epoxy resin layer with each anisotropy.

[0138] Optionally, the disc spring has a standard cross section, the outer layer of the cross section is a carbon fiber-reinforced epoxy resin layer, the inner layer uses a glass fiber-reinforced epoxy resin layer, and the material lay-up mode is a symmetrical structure on the cross section.

[0139] In some embodiments, the outer surface of the spring for the fuel cell stack is provided with a protective coating, which can be an insulation layer. For example, if there is an insulation requirement, a durable glass fiber insulation coating can be coated on the outer surface of the disc spring.

[0140] In some embodiments, the total thickness of the carbon fiber reinforced epoxy resin layer is 0.2-0.6 times the thickness of the spring for the fuel cell stack, and the total thickness of the glass fiber reinforced epoxy resin layer is 0.8-0.4 times the thickness of the spring for the fuel cell stack.

[0141] In some embodiments, the thickness of a single layer of the modified resin layer is 0.1-0.2 mm.

[0142] In some embodiments, a fuel cell stack is provided, comprising a stack core assembly, and a spring designed and selected by the design and selection method for the spring for the fuel cell stack described above or the spring for the fuel cell stack described above.

[0143] In summary, based on the above settings, according to the technical scheme provided by the embodiments of the present application, the disc spring for the fuel cell stack is used, the density is only 1.5-2 g / cm 3 , compared with steel, the weight reduction of the same size can reach 80%, which can meet the demand of fuel cell module for light weight. The disc spring for the fuel cell stack has a glass fiber insulation coating on the outer surface, which can meet the demand of fuel cell stack for insulation. The embodiments of the present application quantify the displacement and assembly force of the stack during the entire life cycle of the stack, so that the attenuation of the assembly force caused by the relaxation of the sealant line is compensated, and the sealing performance and performance of the stack are guaranteed. The embodiments of the present application can buffer the stack when it is subjected to thermal expansion and contraction and pneumatic load, and prevent the stack from affecting the performance and service life of the stack due to excessive assembly force.

[0144] The parts not described in detail in the specification of the present application are known to those skilled in the art.

[0145] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled person in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0146] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for designing and selecting springs for fuel cell stacks, characterized in that, The method includes: Based on the performance requirements of the fuel cell stack for the spring, the ranges of the spring diameter D, the maximum spring compression h, and the spring thickness t are obtained, including: establishing the matching principle between the fuel cell stack and the spring; and establishing the consideration dimensions for the fuel cell stack and the spring based on the matching principle. Using the boundary condition of the spring's geometric parameter diameter D as the input constraint function, the assembly force F and the optimal deformation δ of the fuel cell stack are established through the range of spring diameter D, the range of the maximum spring compression h, and the range of spring thickness t. With the maximum flexibility coefficient during the spring buffering and compensation process as the objective condition, the optimal spring diameter D, the maximum spring compression h, and the spring thickness t are obtained. The matching principles include: The static assembly force of the fuel cell stack is matched with the compression force of the spring; Matching of dynamic assembly force compensation and buffering performance in fuel cell stacks; Matching the spring with the boundary conditions of the fuel cell stack; Furthermore, the dimensions to be considered include: (1) The assembly force F of the fuel cell stack divided by the number of springs m distributed in the plane is used as the selection criterion for the working compression force of the spring. (2) Under the premise of satisfying condition (1), the larger the spring flexibility coefficient is within the selectable buffer and compensation range of fuel cell stack, the better; (3) From the perspective of contact boundary conditions, the geometric parameter diameter D of the spring is suitable to be close to the width of the bipolar plate reaction region so that the assembly force is applied uniformly.

2. The design and selection method for springs used in fuel cell stacks according to claim 1, characterized in that, Based on the premise of satisfying consideration dimension conditions (1) and consideration dimension conditions (2), the range of spring diameter D, the range of spring thickness t, and the range of maximum spring compression h are proposed in turn.

3. The design and selection method for springs used in fuel cell stacks according to claim 1, characterized in that, The working compression force of the spring is taken as the compression force corresponding to spring δ = 0.75h; And / or, the diameter D of the spring is not affected by the spring thickness t and the maximum compression h of the spring.

4. The design and selection method for springs used in fuel cell stacks according to any one of claims 1-3, characterized in that, The method specifically includes: Obtain the expected buffer values ​​for fuel cell stack compression and fuel cell stack assembly force; Obtain the expected compensation values ​​for the compression amount and compression force of the fuel cell stack; Establish a matching relationship between the spring diameter and the bipolar plate size to determine the range of the spring diameter D and the range of the number of springs distributed in the plane; Establish a functional relationship between the static assembly force of the fuel cell stack and the number of springs distributed in the plane to determine the range of compressive force of a single spring; The range of spring thickness t is obtained based on the range of spring diameter D and the range of single spring compression force. In the vertical direction, inline springs are set to increase the buffering and compensation capacity of the springs. Based on the expected compensation value of the fuel cell stack compression, the range of the maximum compression h of the springs and the number of inline disc springs are determined. Based on the ranges of spring diameter D, maximum spring compression h, and spring thickness t, and with the maximum flexibility coefficient as the objective condition, the optimal spring diameter D, maximum spring compression h, and spring thickness t are obtained.

5. The design and selection method for springs used in fuel cell stacks according to claim 4, characterized in that, The expected values ​​for the buffered compression of the fuel cell stack and the expected values ​​for the buffered assembly force of the fuel cell stack are obtained as follows: Establish the mapping relationship between fuel cell stack length and bipolar plate expansion coefficient and operating temperature to obtain the buffer expected value of fuel cell stack compression. Establish the mapping relationship between the aerodynamic load of the fuel cell stack and the reaction area to obtain the expected buffer value of the fuel cell stack assembly force; And / or, the acquisition of the expected compensation values ​​for the compression amount and the expected compensation values ​​for the compression force of the fuel cell stack includes: considering the creep of the fuel cell stack assembly force locking device under long-term stress and the relaxation of the adhesive line under long-term load conditions, to obtain the expected compensation values ​​for the compression amount and the expected compensation values ​​for the compression force of the fuel cell stack.

6. A spring for a fuel cell stack, characterized in that, The spring for the fuel cell stack is designed and selected using the design and selection method for the spring for the fuel cell stack according to any one of claims 1-5, and is applied to the fuel cell stack; the material of the spring for the fuel cell stack is metal, resin or modified resin; the spring for the fuel cell stack includes a disc spring.

7. The spring for a fuel cell stack according to claim 6, characterized in that, The springs used in the fuel cell stack are made by laminating multiple single-layer modified resin layers. The modified resin layer comprises at least two types of fiber-reinforced resin layers.

8. The spring for a fuel cell stack according to claim 7, characterized in that, The at least two fiber-reinforced resin layers include at least two of the following: carbon fiber reinforced epoxy resin layer, glass fiber reinforced epoxy resin layer, basalt fiber reinforced epoxy resin layer, wood fiber reinforced epoxy resin layer, and aramid fiber reinforced epoxy resin layer. And / or, the outer surface of the spring for the fuel cell stack is provided with a protective coating; And / or, the total thickness of the carbon fiber reinforced epoxy resin layer is 0.2 to 0.6 times the thickness of the spring for the fuel cell stack, and the total thickness of the glass fiber reinforced epoxy resin layer is 0.8 to 0.4 times the thickness of the spring for the fuel cell stack; And / or, the thickness of a single layer of the modified resin is 0.1 mm to 0.2 mm.

9. A fuel cell stack, characterized in that, It includes a core assembly, and a spring designed and selected using the design and selection method for springs used in fuel cell stacks as described in any one of claims 1-5, or a spring used in fuel cell stacks as described in any one of claims 6-8.

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