Patent Publication Number: US-2022223970-A1

Title: Pressure relief valve for battery pack

Description:
TECHNICAL FIELD 
     The present disclosure relates to a pressure relief valve for a battery pack. 
     BACKGROUND ART 
     A battery pack that accommodates batteries in a pack case is mounted on, for example, electric vehicles and hybrid vehicles. Each battery includes a pressure regulation mechanism that releases gas from the battery to maintain the pressure in the battery within a predetermined range. The pack case includes a port and a pressure relief valve arranged in the port. The port prevents the pressure from being raised excessively high by the gas emitted from the batteries. The pressure relief valve opens when the difference in pressure between the inner side and outer side of the pack case reaches a predetermined pressure difference (refer to, for example, Patent Document 1). 
     The pressure relief valve described in the above document includes a film-like sheet member and a reinforcement plate. Fine holes extend through the reinforcement plate. The sheet member and the reinforcement plate cover the port of the pack case in a state arranged one upon the other. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Laid-Open Patent Publication No. 2017-73195 
       
    
     SUMMARY OF THE INVENTION 
     Problems that the Invention is to Solve 
     When the amount of gas expected to be released from the pack case increases as the number of batteries increases in the pack case, it is desirable that the port of the pack case be enlarged in diameter. However, when the port is enlarged in diameter and the sheet member is enlarged accordingly, the sheet member may bend and adversely affect the seal of the pressure relief valve. 
     It is an objective of the present disclosure to provide a pressure relief valve for a battery pack that obtains a high sealing capability regardless of the diameter of the port formed in the battery pack. 
     Means for Solving the Problem 
     One aspect of the present disclosure provides a pressure relief valve for a battery pack. The pressure relief valve is configured to be attached to a port formed in a pack case of a battery pack. The pressure relief valve includes a casing including a discharge hole and a valve mechanism configured to open and close the discharge hole. The discharge hole is connected to the port when the pressure relief valve is attached to the port. The pressure relief valve includes a cover attached to the casing. A passage is formed between the cover and the casing to release gas that is discharged from the discharge hole. The valve mechanism includes a valve member configured to close the discharge hole and a biasing portion that biases the valve member to a closed position where the valve member closes the discharge hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a pressure relief valve for a battery pack according to one embodiment attached to a pack case of the battery pack. 
         FIG. 2  is an exploded perspective view of the pressure relieve valve in accordance with the embodiment of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the pressure relieve valve in accordance with the embodiment of  FIG. 1 . 
         FIG. 4  is a cross-sectional view of a valve member in the pressure relieve valve in accordance with the embodiment of  FIG. 1 . 
         FIG. 5  is a plan view showing the pressure relieve valve in accordance with the embodiment of  FIG. 1  in an open state. 
         FIG. 6  is a cross-sectional view showing the pressure relieve valve in accordance with the embodiment of  FIG. 1  in an open state. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     A pressure relief valve for a battery pack according to one embodiment will now be described. 
     As shown in  FIG. 1 , the pressure relieve valve for a battery pack (hereafter, referred to as the pressure relief valve  10 ) is attached to a pack case  12  of a battery pack  11 . The battery pack  11  includes batteries (not shown) in the pack case  12 . Each battery includes battery elements, such as a positive electrode and a negative electrode, in a battery case. A pressure regulation mechanism, such as a valve device, is arranged in the battery case to release gas from the battery case when the pressure in the battery case becomes excessively high. The gas discharged from the battery case by the pressure regulation mechanism fills the pack case  12 . The pack case  12  includes a port  13  through which gas is discharged out of the pack case  12 . 
     The pressure relief valve  10  opens and closes the port  13  of the pack case  12 . Under atmospheric pressure, the pressure relief valve  10  releases gas from the pack case  12  when the pressure in the pack case  12  reaches a set upper limit pressure. The pressure relief valve  10  is attached and fastened to the pack case  12  by fasteners  14  such as bolts. 
     As shown in  FIG. 2 , the pressure relief valve  10  includes a casing  20  and a cover  21 . The casing  20  includes a casing body  22  that is circular as viewed from the cover  21 . The casing body  22  includes a discharge hole  23  (refer to  FIG. 3 ) connected to the port  13  of the pack case  12 . 
     Further, the casing  20  includes a valve mechanism  25  that opens and closes the discharge hole  23 . The valve mechanism  25  includes a valve seat  26 , surrounding the discharge hole  23 , and a flap type valve member  27 . The valve member  27  has the form a disc. Two arms  28  extend radially outward from a central portion of the valve member  27  on the surface of the valve member  27 . A shaft hole (not shown) extends through the proximal end of each arm  28 , and one of two ends of a rotational shaft  29  is inserted through the shaft hole. The two ends of the rotational shaft  29  are rotatably supported by a shaft support  30  formed in the casing  20 . 
     A biasing portion  31  is supported by the casing body  22 . The biasing portion  31  is a double torsion spring that is a combination of two torsion coil springs. The biasing portion  31  includes an extension  32  that extends from between the two torsion coil springs. The distal end of the extension  32  is fixed to the central part of the valve member  27  to apply the biasing force of the biasing portion  31  to the valve member  27 . 
     When the pressure in the pack case  12  reaches a set upper limit pressure, the valve member  27  is pivoted about the proximal ends of the arms  28 , which are supported by the shaft support  30 , against the biasing force of the biasing portion  31 . This separates part of the valve member  27  from the valve seat  26  and releases gas from the pack case  12  through the discharge hole  23 . 
     Further, the casing  20  includes two fastening portions  34 . The casing  20  includes the casing body  22  and the two fastening portions  34  that are connected to the casing body  22  and located at the outer side of the casing body  22 . The two fastening portions  34  are positioned to be symmetric in the radial direction with respect to the center of the casing body  22 . The fastening portions  34  each include a fastening hole  35 , into which the corresponding fastener  14  is inserted, and a connection hole  36 , which serves as a discharge passage. The fastening hole  35  receives the corresponding fastener  14  that fixes the casing  20  to the pack case  12 . The connection hole  36  is closer to the casing body  22  than the fastening hole  35 . That is, the connection hole  36  is located between the casing body  22  and the fastening hole  35 . The cover  21  covers the connection hole  36 . Further, the casing body  22  includes a circumferential wall  49  surrounding the valve mechanism  25 . The circumferential wall  49  includes cutaway portions  49 A at parts corresponding to the fastening portions  34 . 
     The casing body  22  also includes engagement pieces  37  that are press-fitted into receptacles  21 B formed in the cover  21 . The engagement pieces  37  are press-fitted into the receptacles  21 B of the cover  21  to position the cover  21  relative to the casing  20  in the circumferential direction. 
     As shown in  FIG. 3 , the cover  21  includes an accommodation compartment  21 A that accommodates the casing  20  excluding the fastening portions  34 . As shown in  FIG. 3 , the cover  21  has a lower end that is open in a direction opposite to a Z-direction. The outer diameter of the casing body  22 , excluding the fastening portions  34 , is smaller than the inner diameter of the cover  21 . This forms a gap between the cover  21  and the casing  20 . The gap defines a passage  40  through which gas passes. The cover  21  includes a bottom end  21 C inserted into the connection holes  36 . Gaps  41  are formed between the bottom end  21 C of the cover  21  and the surface of the pack case  12  so that the gas passed through the passage  40  is discharged out of the pressure relief valve  10  via the gaps  41 . The gaps  41  are located between the fastening portions  34  and the pack case  12 . 
     The casing  20  includes a coupling portion  38  inserted into the port  13  of the pack case  12 . The coupling portion  38  is cylindrical and includes the discharge hole  23  at its inner side. A first seal member  42  and a second seal member  43  are arranged on the outer circumferential surface of the coupling portion  38 . The first seal member  42  has a circular cross section and is disposed between the casing  20  and the inner circumferential surface of the port  13  of the pack case  12 . The second seal member  43  contacts the surface of the pack case  12  when the pressure relief valve  10  is attached to the pack case  12 . 
     The valve member  27  is formed by combining a first valve body  44  and a second valve body  45 . The first valve body  44  and the second valve body  45  are coupled by fitting a fitting portion  46  of the first valve body  44  into a fitted portion  47  of the second valve body  45 . An annular third seal member  50  is disposed between the first valve body  44  and the second valve body  45 . 
     With reference to  FIG. 4 , the third seal member  50  will now be described in detail. The third seal member  50  includes an inner end  51  accommodated in a groove  48  of the second valve body  45 . The end  51  includes two lips  52 . The lips  52  are pressed against the second valve body  45 . Further, the third seal member  50  includes an outer end  53  disposed between the second valve body  45  and a projection  26 A of the valve seat  26  when the pressure relief valve  10  closes. The end  53  of the third seal member  50  includes a sub-lip  54 . The sub-lip  54  extends outward from the second valve body  45  and closes the space between the valve member  27  and the casing  20  to limit the entry of dust into the valve member  27 . 
     An annular rib  55 , which serves as a projection, is formed on the rim of the second valve body  45 . The annular rib  55  is arranged at a position located outward from the projection  26 A in the radial direction of the discharge hole  23 . As shown in  FIG. 4 , the annular rib  55  projects in the direction opposite to the Z-direction. As shown in  FIG. 4 , the annular rib  55  contacts the third seal member  50  and presses the third seal member  50  from the side opposite to the projection  26 A, which is projected in the Z-direction. Thus, when the valve member  27  is located at the closed position, pressing force is applied from two locations to the third seal member  50  between the valve seat  26  and the second valve body  45 . The separated locations where pressing force is applied to the third seal member  50  lowers the planar pressure produced by contact of the third seal member  50  and the valve seat  26 . 
     The operation of the pressure relief valve  10  will now be described with reference to  FIGS. 5 and 6 . The broken lines shown in  FIG. 5  represent the cover  21 . The passage  40  is formed between the entire outer circumferential surface of the casing  20 , excluding the fastening portions  34 , and the inner circumferential surface of the cover  21 . Thus, when the internal pressure of the pack case  12  reaches the upper limit pressure and opens the valve member  27 , gas spreads out radially from the pack case  12  through the discharge hole  23 , as shown by the arrows in  FIG. 5 , and passes through the passage  40  before flowing out. The gas flowing toward the fastening portions  34  passes through the cutaway portions  49 A and enters the connection holes  36 . 
     As shown in  FIG. 6 , the gas passed through the connection hole  36  passes through the gaps  41  between the fastening portions  34  and the pack case  12  and then flows out of the pressure relief valve  10 . As the open valve mechanism  25  lowers the internal pressure of the pack case  12  to less than the predetermined upper limit pressure, the biasing force of the biasing portion  31  acts to have the valve member  27  contact the valve seat  26 . 
     The above embodiment has the advantages described below. 
     (1) In the above embodiment, the pressure relief valve  10  biases the valve member  27  to the closed position with the biasing portion  31 . Thus, the above embodiment increases the sealing capability when the valve member  27  is located at the closed position as compared with when the port  13  is closed with a film-like valve member. Further, the cover  21 , which is arranged on the casing  20 , limits the entry of dust into the pack case  12  when the valve mechanism  25  opens. In the pressure relief valve  10 , which arranges the cover  21  on the casing  20 , the passage  40  that discharges gas is formed between the inner circumferential surface of the cover  21  and the outer circumferential surface of the casing body  22 . This lowers the flow resistance in the passage  40  from the port  13  of the pack case  12  to the outside of the pressure relief valve  10 . Thus, gas will flow out smoothly even when the port  13  of the pack case  12  is enlarged in diameter to increase the maximum amount of gas that can be discharged from the port  13 . 
     (2) In the above embodiment, in addition to the passage  40  between the casing  20  and the cover  21 , the fastening portions  34  include the connection holes  36  to discharge gas. Thus, in the above embodiment, the fastening portions  34  further lowers the flow resistance. 
     (3) In the above embodiment, the gas that passes through the connection holes  36  further passes through the gaps  41  between the fastening portions  34  and the pack case  12  before flowing out. This lowers the flow resistance acting on the gas discharged from the discharge hole  23 . 
     (4) In the above embodiment, when the valve member  27  is located at the closed position, the third seal member  50  contacts both of the valve seat  26  and the annular rib  55 , which is located farther from the discharge hole  23  than the valve seat  26 . This lowers the planar pressure produced when the third seal member  50  contacts the valve seat  26 . Thus, even when the valve member  27  is located at the closed position over a long period of time, the third seal member  50  will not become stuck to the valve seat  26  or the like. 
     (5) In the above embodiment, the passage  40  for gas is formed over the entire circumference of the casing body  22 , excluding the fastening portions  34 . This lowers the flow resistance when gas passes through the passage  40 . 
     OTHER EMBODIMENTS 
     The present embodiment may be modified as described below. The present embodiment and the following modifications can be combined as long as there is no technical contradiction. 
     In the above embodiment, the passage  40  is formed by the cover  21  and the entire outer circumference of the casing body  22 , excluding the fastening portions  34 . Instead, the passage  40  can correspond to a section smaller than the entire outer circumference of the casing body  22 , excluding the fastening portions  34 . Further, when the fastening portions  34  are arranged at locations separated from the outer circumferential surface of the casing body  22 , the passage  40  may be formed by the cover  21  and the entire outer circumference of the casing body  22 . 
     In the above embodiment, the valve member  27  includes the annular rib  55  that presses the end  53  of the third seal member  50 . However, the annular rib  55  may be omitted if sticking of the third seal member  50  to the valve seat  26  or the like can be avoided by adjusting the biasing force of the biasing portion  31 . Alternatively, instead of, or in addition to, the annular rib  55 , a non-sticking treatment may be performed on the third seal member  50  or at least one of the valve member  27  and the valve seat  26  to avoid the third seal member  50  sticking to the valve seat  26  or the like. 
     In the above embodiment, the lower end of the cover  21  attached to the casing  20  is separated from the pack case  12  so that gas passes through the connection holes  36  and then flow out from the lower end of the cover  21 . Instead, or in addition, the casing  20  or the cover  21  may include a hole for passage of the gas. 
     In the above embodiment, the discharge passages formed in the fastening portions  34  correspond to the connection holes  36  extending through the fastening portions  34 . Instead, a discharge passage may be formed by gaps or the like between the fastening portions  34  and the cover  21 . 
     In the above embodiment, the fastening portions  34  include the connection holes  36 . However, the connection holes  36  may be omitted from the fastening portions  34 . Even in this case, the passage  40  is still formed at parts excluding the fastening portions  34 . Thus, the flow resistance of the passage can be lowered as the gas discharged from the pack case  12  passes. 
     In the above embodiment, the valve member  27  is formed by the first valve body  44  and the second valve body  45 . Instead, the valve member  27  may be formed by a single element, and the valve member  27  may be attached to the third seal member  50 .