Energy Storage Devices

Abstract

To provide a power storage device which can improve safety when an abnormality of a power storage cell is detected or predicted.SOLUTION: A power storage device 20 comprises: a power storage cell 26 formed into a plate-like shape; and a cell binding part 60 which applies binding pressure to the power storage cell 26 in a plate thickness direction. When an abnormality of the power storage cell 26 has been detected or predicted, the cell binding part 60 is deformed so as to reduce the binding pressure.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electricity storage device. [Background technology]

[0002] 2. Description of the Related Art In an electricity storage device such as a lithium ion secondary battery, it has been proposed to apply a confining pressure to the electricity storage cell in order to prevent the electricity storage cell from shifting position and to ensure output performance (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-103083 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when an unexpected event such as overcharging or short circuit occurs, gas may be generated inside the storage cell due to decomposition of the electrolyte, etc. As in Patent Document 1, when a restraining pressure is applied to the storage cell, gas pressure may concentrate inside the storage cell, causing damage to the exterior body, which may result in the gas being released to the outside of the storage cell.

[0005] In consideration of the above, an object of the present invention is to provide an electricity storage device capable of improving safety when an abnormality in an electricity storage cell is detected or predicted. [Means for solving the problem]

[0006] The electric storage device according to claim 1 includes a plate-shaped electric storage cell, and a pressure applying device that applies a pressure to the electric storage cell in a thickness direction and that deforms when an abnormality in the electric storage cell is detected or predicted. By making it possible and transforming it, A cell restraining portion that reduces the restraining pressure; a restraint control unit that detects at least one of a temperature, a voltage, and water ingress in the power storage cell, and deforms the cell restraint unit to reduce the restraint pressure when an abnormality in the power storage cell is detected or predicted from the detection result; has.

[0007] In the electric storage device described in claim 1, the cell restraining portion applies restraining pressure to the plate-shaped electric storage cell in the plate thickness direction. This prevents the electric storage cell from shifting position and stabilizes the expansion and contraction of the electric storage cell due to charging and discharging, thereby ensuring output performance. Here, The restraint control unit detects at least one of a temperature, a voltage, and a flood in the power storage cell, and When an abnormality in the storage cell is detected or predicted, the cell restraint section of Transform Let me This reduces the confining pressure of the energy storage cell, thereby suppressing the concentration of gas pressure inside the energy storage cell and preventing damage to the exterior body, thereby improving safety.

[0008] The power storage device according to claim 2 has the configuration according to claim 1, wherein the power storage cell is , positive The battery includes an all-solid-state battery element in which an electrode layer, a solid electrolyte layer, and an anode layer are laminated, and an exterior body made of a laminate film that covers the all-solid-state battery element.

[0009] In the all-solid-state battery storage device according to claim 2, the storage cell constitutes an all-solid-state battery element having a solid electrolyte layer. It is known that the storage cell constituting such an all-solid-state battery element can be easily thinned compared to conventional lithium ion secondary batteries using liquid electrolytes, and contributes to miniaturization of the device. Here, by forming the exterior body from a laminate film, when gas is generated in the storage cell, the exterior body can be flexibly deformed in accordance with the device package. This makes it easy to disperse gas pressure, and effectively suppresses concentration of gas pressure. As a result, it is possible to improve safety while miniaturizing the storage device.

[0010] The energy storage device described in claim 3 has the configuration described in claim 1 or claim 2, and has a stack in which a plurality of the energy storage cells are stacked in a plate thickness direction, and the cell restraint portion applies the restraint pressure to the stack along the stacking direction.

[0011] The all-solid-state battery energy storage device according to claim 3 has a stack in which a plurality of energy storage cells are stacked in the plate thickness direction, and the cell restraining portion applies a restraining pressure to the stack in the stacking direction. Therefore, when an abnormality in the energy storage cell is detected or predicted, the restraining pressure on the stack is reduced to provide a gap between the electrodes of each energy storage cell. This suppresses heat transfer between the electrodes, improving safety.

[0012] The electric storage device according to claim 4 is the electric storage device according to claim 1, wherein the cell restraining portion is a first restraining portion arranged on one side in a plate thickness direction of the electric storage cell, and a second restraining portion arranged on the other side in the plate thickness direction of the electric storage cell, the first restraining portion and the second restraining portion being connected together, and the cell restraining portion is moved by driving an actuator. Transform A connecting portion that displaces the first restraining portion relative to the second restraining portion in a plate thickness direction, The restraint control unit is When an abnormality in the power storage cell is detected or predicted, the first restraining portion is displaced in a direction away from the second restraining portion. The connecting portion is deformed. , reducing the confining pressure.

[0013] In the all-solid-state battery power storage device described in claim 4, the power storage cell can be restrained from both sides in the plate thickness direction by the first restraining portion and the second restraining portion. The restraint control unit is When an abnormality in a storage cell is detected or predicted To, The actuator drives the connection part. of Transform By making 1st restraint section of Separated from the second restraint Let me With this configuration, it is possible to reliably reduce the confining pressure when an abnormality occurs. Effect of the Invention

[0016] As described above, the power storage device according to the present invention has an effect of improving safety when an abnormality in a power storage cell is detected or predicted. [Brief description of the drawings]

[0017] [Figure 1]1 is a schematic diagram showing a vehicle including an electricity storage device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view illustrating a schematic diagram of the electricity storage device illustrated in FIG. [Diagram 3] 3 is a vertical cross-sectional view showing a stacking structure of the electricity storage cell shown in FIG. 2. [Figure 4] 5A and 5B are schematic diagrams for explaining the operation of an actuator, in which (A) shows a restrained state of a storage cell, and (B) shows a state in which the restraint of the storage cell is released. FIG. [Diagram 5] FIG. 4 is a block diagram of a restraint pressure control ECU. [Figure 6] 4 is a flowchart showing an example of a restraint pressure control process executed by a restraint pressure control ECU. [Figure 7] 1A and 1B are schematic diagrams showing a cell restraint section according to a modified example of the present embodiment, in which (A) shows a restrained state of the storage cell, and (B) shows a state in which the restraint of the storage cell has been released. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an electricity accumulation device 20 according to one embodiment of the present invention will be described with reference to FIGS.

[0019] 1 includes an electricity storage device 20, a restraining pressure control ECU 40, and a drive source 50. The vehicle 10 includes an electric motor (not shown) as the drive source 50 for traveling, and the electric motor is driven by using electric power stored in the electricity storage device 20.

[0020] As shown in FIG. 2, the electricity storage device 20 has a laminate 24 that constitutes an electricity storage module, and a housing 22 in which the laminate 24 is housed.

[0021] The stack 24 includes a plurality of storage cells 26 formed in a plate shape, end plates 28 arranged at the ends of the stack 24, and sheet-shaped insulating members 29 arranged between the storage cells 26 and between the storage cells 26 and the end plates 28.

[0022] The plurality of storage cells 26 are stacked in the plate thickness direction. Two end plates 28 are disposed at one end and the other end in the stacking direction.

[0023] In addition, in the mounted state of the stack 24, a cell restraining portion 60 is attached for applying a predetermined restraining pressure to the stack 24 in the stacking direction (that is, the plate thickness direction of the electricity storage cells 26).

[0024] 3, each storage cell 26 is a lithium ion secondary battery, and a positive electrode layer 30P, a solid electrolyte layer 33, and a negative electrode layer 30N are laminated to form an all-solid-state battery element 30. Note that in FIG. 3, the lamination direction H1 of each layer of the all-solid-state battery element 30 and the surface direction W1 of each layer are shown.

[0025] The positive electrode layer 30P is composed of a positive electrode current collector layer 31 having a positive electrode current collector tab 31A, and a positive electrode active material layer 32. The negative electrode layer 30N is composed of a negative electrode active material layer 34 and a negative electrode current collector layer 35 having a negative electrode current collector tab 35A.

[0026] The material of the positive electrode current collector layer 31 is, for example, but not limited to, SUS, aluminum, copper, nickel, iron, titanium, or carbon.

[0027] The positive electrode active material layer 32 includes at least a positive electrode active material. The material of the positive electrode active material is, for example, lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), but is not limited to these.

[0028] The solid electrolyte layer 33 includes at least a solid electrolyte. The material of the solid electrolyte is not particularly limited, and any material that can be used as a solid electrolyte for an all-solid-state battery can be used.

[0029] The negative electrode active material layer 34 contains lithium titanate (LTO), a binder that bonds LTO particles together, and a conductive additive.

[0030] The material used for the negative electrode current collector layer 35 is, for example, the material used for the positive electrode current collector layer 31 .

[0031] In the power storage cell 26, a positive electrode current collector layer 31, a positive electrode active material layer 32, a solid electrolyte layer 33, a negative electrode active material layer 34, and a negative electrode current collector layer 35 are laminated in this order to form one all-solid-state battery element 30. Note that, although Fig. 3 illustrates a configuration in which one power storage cell 26 includes one all-solid-state battery element 30, the present invention is not limited to this, and one power storage cell may be formed of a laminate of a plurality of all-solid-state battery elements 30. In this case, the positive electrode current collector layer 31 and the negative electrode current collector layer 35 may be shared between adjacent all-solid-state battery elements, and a plurality of the all-solid-state battery elements may be laminated with the layers laminated in the opposite order.

[0032] The all-solid-state battery element 30 is covered with an exterior body 38. The exterior body 38 can be made of a laminate film, a square can, or the like, but in one example of this embodiment, the exterior body 38 is made of a laminate film. When the exterior body 38 is made of a laminate film, this is preferable because when gas is generated in the all-solid-state battery element 30, the exterior body 38 can be flexibly deformed to disperse the gas pressure.

[0033] The laminate film is composed of a resin-laminated metal foil having a resin film on one or both sides of the metal foil, for example, a resin film for imparting mechanical strength to one side of the metal foil, and a resin film having heat sealability to the opposite side.

[0034] The metal foil in the resin-laminated metal foil may be, for example, a foil made of aluminum, an aluminum alloy, etc. The resin film for maintaining mechanical strength may be, for example, a film made of polyester, nylon, etc. The resin film having heat sealability may be, for example, a film made of polyolefin, etc., specifically, for example, a film made of polyethylene, polypropylene, etc.

[0035] In the exterior body 38, two laminate films are arranged facing each other with the resin film having heat sealability on the inside, and the all-solid-state battery element 30 is placed in the gap between them. The four outer periphery sides of the laminate film are sealed by heat sealing to form a bag-shaped exterior body. As a result, the all-solid-state battery element 30 is housed in the exterior body 38 made of the laminate film.

[0036] In the electricity storage device 20, a plurality of electricity storage cells 26 are stacked in the plate thickness direction with a sheet-like insulating member 29 sandwiched therebetween. The stacked electricity storage cells 26 are sandwiched between two end plates 28 on both sides in the stacking direction to form a stack 24.

[0037] A cell restraining portion 60 is attached to the stack 24. The cell restraining portion 60 is attached so as to sandwich the stack 24 from both sides in the stacking direction, and applies a predetermined restraining pressure to the stack 24 from both sides in the stacking direction. As a result, the stacked plurality of energy storage cells 26 are integrated, and a predetermined restraining pressure is applied to each energy storage cell 26 along the plate thickness direction.

[0038] As shown in FIGS. 4(A) and 4(B), the cell restraining portion 60 includes a first restraining portion 62, a second restraining portion 64, and a connecting portion 66.

[0039] The first restraining portion 62 is disposed on one side in the stacking direction of the stack 24. The second restraining portion 64 is disposed opposite the first restraining portion 62 on the other side in the stacking direction of the stack 24. The connecting portion 66 extends in the stacking direction and connects the first restraining portion 62 and the second restraining portion 64. That is, the stack 24 is inserted into and clamped in the contained space formed by the first restraining portion 62, the second restraining portion 64, and the connecting portion 66.

[0040] The connecting portion 66 has a first connecting body 661 extending from an end of the first restraining portion 62 and a second connecting body 662 extending from an end of the second restraining portion 64. The first connecting body 661 and the second connecting body 662 are connected in the stacking direction via the actuator 54.

[0041] The actuator 54 has a motor 56 as a drive source provided in the second connecting body 662, and a shaft 58 connected to the output shaft of the motor 56. The shaft 58 has a male screw portion provided on the outer periphery that screws into a screw hole in the first connecting body 661, and the shaft 58 is rotated by the drive of the motor 56, so that the first connecting body 661 is displaced in the axial direction relative to the second connecting body 662. In other words, the connecting portion 66 is deformed by the drive of the actuator 54 so as to extend in the stacking direction of the stack 24. As a result, the first constraining portion 62 moves relative to the second constraining portion 64 in the stacking direction, and the constraining pressure applied to the stack 24 can be changed.

[0042] The driving of the actuator 54 is controlled by the restraining pressure control ECU 40 . The configuration of the restraining pressure control ECU 40 will be described below.

[0043] 5, the restraint pressure control ECU 40 includes, as hardware components, a CPU (Central Processing Unit) 41, a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a storage 44, a communication interface (I / F) 45, and an input / output interface (I / F) 46. The CPU 41, the ROM 42, the RAM 43, the storage 44, the communication I / F 45, and the input / output I / F 46 are connected via an internal bus 47 so as to be able to communicate with each other.

[0044] The CPU 41 is a central processing unit that executes various programs and controls each part. The CPU 41 reads the programs from the ROM 42 or the storage 44, and executes the programs using the RAM 43 as a working area. The CPU 41 controls each component and performs various calculation processes according to the programs recorded in the ROM 42 or the storage 44.

[0045] The ROM 42 stores various programs and various data. The RAM 43 temporarily stores programs or data as a working area. The storage 44 is configured by a storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various programs and various data.

[0046] The communication I / F 45 is an interface for the restraining pressure control ECU 40 to communicate with other devices.

[0047] The input / output I / F 46 is an interface for communicating with each device mounted on the vehicle 10. In this embodiment, an abnormality detection sensor 52 and an actuator 54 are connected to the input / output I / F 46.

[0048] The abnormality detection sensor 52 is a sensor for detecting or predicting an abnormality in the power storage cell 26, and may be configured as a single sensor or as a sensor group combining a plurality of sensors. The abnormality detection sensor 52 is configured to include at least one of a temperature sensor, a voltage sensor, and a water ingress detection sensor, for example. The temperature sensor may be provided so as to be able to detect the temperature of a single power storage cell 26, or may be provided so as to detect the temperature inside the housing 22 of the power storage device 20. The water ingress detection sensor is provided so as to detect, for example, the presence or absence of water ingress into the housing 22. These sensors detect or predict an abnormality or abnormality of the power storage cell 26 due to a fire occurring inside or outside the housing 22, water ingress into the housing 22, an abnormal temperature rise of the power storage cell 26, overcharging of the power storage cell 26, etc. abnormality It is possible to detect predictions of

[0049] The restraint pressure control ECU 40 also has, as functional components, an acquisition unit 410 and a restraint pressure control unit 420. The functions of the acquisition unit 410 and the restraint pressure control unit 420 are realized by the CPU 41 reading out and executing a program stored in the ROM 42.

[0050] The acquisition unit 410 has a function of acquiring a detection value of the anomaly detection sensor 52 .

[0051] The restraining pressure control unit 420 has a function of driving the actuator 54 when an abnormality in the power storage cell 26 is detected or predicted based on the detection value acquired by the acquisition unit 410. Specifically, the restraining pressure control unit 420 drives the actuator 54 to displace the first restraining portion 62 from the restraining position shown in Fig. 4(A) to the released restraint position shown in Fig. 4(B). At the released restraint position, the first restraining portion 62 is displaced in a direction away from the second restraining portion 64 along the stacking direction, relative to the restraining position. As a result, the restraining pressure applied to the stack 24 is reduced.

[0052] (operation) Next, an example of the restraint pressure control process executed by the restraint pressure control ECU 40 will be described with reference to the flowchart shown in Fig. 6. This restraint pressure control process is started, for example, when the ignition switch of the vehicle is turned ON, and is performed by the CPU 41 reading a program from the RO 42 or storage 44, expanding it in the RAM 43, and executing it.

[0053] 6, the CPU 41 acquires sensor information in step S101. Specifically, the CPU 41 acquires a detection value detected by the anomaly detection sensor 52 using the function of the acquisition unit 410.

[0054] In step S102, the CPU 41 determines whether the acquired detection value is an abnormal value. Whether the detection value is abnormal is determined based on a preset threshold. If the CPU 41 determines that an abnormal value has been detected, the process proceeds to step S103. On the other hand, if the CPU 41 determines that an abnormal value has not been detected, the process returns to step S101.

[0055] In step S103, the CPU 41 releases the energy storage cells 26. Specifically, the actuator 54 is driven based on the function of the binding pressure control unit 420. By driving the actuator 54, the first binding portion 62 of the cell binding unit 60 is displaced in a direction away from the second binding portion 64, thereby reducing the binding pressure on the stack 24 and, ultimately, the energy storage cells 26, and then the binding pressure control process is terminated.

[0056] The reduction in the confining pressure provides gaps between the stacked electricity storage cells 26. This suppresses heat transfer between the electrodes (positive electrode current collector tab 31A or negative electrode current collector tab 35A) of the electricity storage cell 26 in the event of an abnormal temperature rise in the electricity storage cell 26 due to a short circuit caused by flooding or a fire. Furthermore, in the event that a flammable gas or the like is generated inside the electricity storage cell 26, the exterior body 38 of the electricity storage cell 26 becomes deformable, making it possible to suppress concentration of gas pressure.

[0057] As described above, in the energy storage device 20 according to this embodiment, the cell restraining portion 60 applies a restraining pressure to the plate-shaped energy storage cell 26 in the plate thickness direction. This prevents the energy storage cell 26 from shifting out of position and stabilizes the expansion and contraction of the energy storage cell 26 due to charging and discharging, thereby ensuring output performance. Here, when an abnormality in the energy storage cell 26 is detected or predicted, the cell restraining portion 60 deforms to reduce the restraining pressure of the energy storage cell 26. This suppresses concentration of gas pressure inside the energy storage cell 26 and prevents damage to the exterior body 38, improving safety.

[0058] In the electricity storage device 20, the electricity storage cell 26 constitutes an all-solid-state battery element 30 having a solid electrolyte layer 33. The electricity storage cell 26 constituting such an all-solid-state battery element 30 is known to be easier to thin than a conventional lithium ion secondary battery using a liquid electrolyte, and can contribute to miniaturization of the device. Here, by forming the exterior body 38 from a laminate film, when gas is generated in the electricity storage cell 26, the exterior body 38 can be flexibly deformed in accordance with the device package. This makes it easy to disperse gas pressure, and can effectively suppress concentration of gas pressure. As a result, the safety of the electricity storage device 20 can be improved while miniaturizing the electricity storage device 20.

[0059] The electricity storage device 20 has a stack 24 including a plurality of electricity storage cells 26 stacked in the plate thickness direction, and the cell restraining portion 60 applies a restraining pressure to the stack 24 in the stacking direction. Therefore, when an abnormality in the electricity storage cell 26 is detected or predicted, a gap is provided between the electrodes of each electricity storage cell 26 by reducing the restraining pressure on the stack 24. This suppresses heat transfer between the electrodes and improves safety.

[0060] In the electricity storage device 20, the electricity storage cell 26 can be restrained from both sides in the plate thickness direction by the first restraining portion 62 and the second restraining portion 64. Furthermore, when an abnormality in the electricity storage cell 26 is detected or predicted, the actuator 54 is driven to deform the connecting portion 66. This causes the first restraining portion 62 to move away from the second restraining portion 64, thereby reducing the restraining pressure. This configuration ensures that the restraining pressure is reduced when an abnormality occurs.

[0061] (Modification of cell restraint part) Next, an electricity storage device 70 including a cell restraining unit 72 according to a modified example will be described with reference to Figures 7(A) and 7(B). Note that the same components as those in the first embodiment described above are given the same reference numbers and descriptions thereof will be omitted.

[0062] The cell restraining portion 72 according to the modified example is disposed inside the housing 22 on one side in the stacking direction of the stack 24 (energy storage cells 26). The shape of the cell restraining portion 72 is not particularly limited, but as an example, it is formed in a plate or rod shape extending along the surface direction of the stack 24, and both ends in the longitudinal direction are supported by the housing 22. When the stack 24 is accommodated inside the housing 22, this cell restraining portion 72 is pressed against the opposing surface of the housing 22, thereby applying a restraining pressure to the stack 24 along the stacking direction.

[0063] Here, the cell restraining portion 72 according to this modified example is characterized in that it is formed using a material that melts in a situation in which an abnormality in the power storage cell 26 is detected or predicted.

[0064] For example, the cell restraining portion 72 can be formed using a material that is melted when heated to a temperature equal to or higher than a threshold value. As a result, when the cell restraining portion 72 is heated due to a fire or an abnormal temperature rise of the power storage cell 26, the heated portion of the cell restraining portion 72 melts, and the support state by the housing 22 is released.

[0065] Furthermore, the cell restraining portion 72 may be formed using a material that melts when moisture of a threshold value or more penetrates into the cell restraining portion 72. In this case, if the inside of the housing 22 becomes flooded with water for some reason, the flooded portion of the cell restraining portion 72 melts, and the support state by the housing 22 is released. In other words, flooding of the inside of the housing 22 may cause a short circuit to the energy storage cell 26. Therefore, flooding of the inside of the housing 22 can be used to detect or predict an abnormal state of the energy storage cell 26.

[0066] When the cell restraining portion 72 is released from the support state by the housing 22 due to melting, the cell restraining portion 72 loses the reaction surface, and the restraining pressure on the stack 24 is reduced. This provides gaps between the energy storage cells 26, and the same effects as those of the above embodiment can be achieved. In addition, this modified example can be implemented without a high-precision sensor group or precise control processing, and therefore manufacturing costs can be reduced. [supplementary explanation]

[0067] Although the above describes the embodiments of the present invention, the present invention is not limited thereto. Each configuration of the present invention can be modified in various ways without departing from the spirit of the present invention. For example, in the above embodiments and modifications, the power storage device 20, 70 is configured to house a plurality of power storage cells 26, but the present invention is not limited thereto. A configuration in which a cell restraining portion is attached to a single power storage cell may also be used.

[0068] In addition, in the above embodiment and modified example, the case where the storage cell constitutes an all-solid-state battery element has been described, but this is not limiting. The configuration of the present invention can also be applied to a storage cell having a liquid electrolyte layer. [Explanation of symbols]

[0069] 20 Energy storage devices 22 Case 24 Laminate 26 Energy Storage Cell 30 All-solid-state battery element 30P positive electrode layer 30N negative electrode layer 33 Solid electrolyte layer 54 Actuator 60 Cell Restraint Section 62 1st restraint section 64 2nd restraint section 66 Connecting part 72 Cell Restraint Section

Claims

1. A storage cell formed in a plate shape; A cell restraining portion that applies a restraining pressure to the energy storage cell along a plate thickness direction and is deformable when an abnormality in the energy storage cell is detected or predicted, and reduces the restraining pressure by deforming; a restraint control unit that detects at least one of a temperature, a voltage, and water ingress in the power storage cell, and deforms the cell restraint unit to reduce the restraint pressure when an abnormality in the power storage cell is detected or predicted from the detection result; A power storage device having the above structure.

2. The storage cell is an all-solid-state battery element in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are laminated; The electricity storage device according to claim 1 , further comprising: an exterior body including a laminate film that covers the all-solid-state battery element.

3. A stack of a plurality of the storage cells in a plate thickness direction is provided, The power storage device according to claim 1 or 2, wherein the cell restraining portion applies the restraining pressure to the stack in a stacking direction.

4. The cell restraint portion is A first restraint portion arranged on one side in a plate thickness direction of the energy storage cell; A second restraint portion arranged on the other side in a plate thickness direction of the energy storage cell; a connecting portion that connects the first restraining portion and the second restraining portion and is deformed by driving an actuator to relatively displace the first restraining portion in a plate thickness direction with respect to the second restraining portion, The energy storage device according to claim 1 , wherein the restraint control unit, when an abnormality in the energy storage cell is detected or predicted, deforms the connecting portion so as to displace the first restraint portion in a direction away from the second restraint portion, thereby reducing the restraint pressure.

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