Patent Description:
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 <NUM>).

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. Patent Document <NUM> discloses a pressure release valve provided in a fuel tank that stores liquid fuel supplied to a fuel cell that constitutes a power source of a portable electronic device. Patent Document <NUM> describes a servo poppet valve that includes a valve housing having a flow passage therethrough, a poppet valve element disposed in the flow passage, and a first spring washer disposed between the valve housing and the poppet valve element. The poppet valve element is movable between an open position and a closed position, and the first spring washer biases the poppet valve element toward the closed position. Patent Document <NUM> relates to a self storage battery and describes a first safety valve being self-resetting, and reuseable after a battery internal pressure is increased. Patent Document <NUM> discloses a spring-loaded safety valve with a cup-shaped closure piece mounted on a cylindrical housing. Patent Document <NUM> discloses a pressure relief valve for venting expanding fluids contained in railway tank cars, tank trucks and similar containers. Patent Document <NUM> describes a pressure relief valve, comprising a vent path formed in an axial portion of the insertion portion and a slit formed in a peripheral wall portion of the insertion portion so as to communicate with the vent path.

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.

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. The casing includes a fastening portion in which a fastener is arranged to fix the casing to the pack case. The fastening portion includes a discharge passage to release gas that is discharged from the discharge hole.

A pressure relief valve for a battery pack according to one embodiment will now be described.

As shown in <FIG>, the pressure relieve valve for a battery pack (hereafter, referred to as the pressure relief valve <NUM>) is attached to a pack case <NUM> of a battery pack <NUM>. The battery pack <NUM> includes batteries (not shown) in the pack case <NUM>. 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 <NUM>. The pack case <NUM> includes a port <NUM> through which gas is discharged out of the pack case <NUM>.

The pressure relief valve <NUM> opens and closes the port <NUM> of the pack case <NUM>. Under atmospheric pressure, the pressure relief valve <NUM> releases gas from the pack case <NUM> when the pressure in the pack case <NUM> reaches a set upper limit pressure. The pressure relief valve <NUM> is attached and fastened to the pack case <NUM> by fasteners <NUM> such as bolts.

As shown in <FIG>, the pressure relief valve <NUM> includes a casing <NUM> and a cover <NUM>. The casing <NUM> includes a casing body <NUM> that is circular as viewed from the cover <NUM>. The casing body <NUM> includes a discharge hole <NUM> (refer to <FIG>) connected to the port <NUM> of the pack case <NUM>.

Further, the casing <NUM> includes a valve mechanism <NUM> that opens and closes the discharge hole <NUM>. The valve mechanism <NUM> includes a valve seat <NUM>, surrounding the discharge hole <NUM>, and a flap type valve member <NUM>. The valve member <NUM> has the form a disc. Two arms <NUM> extend radially outward from a central portion of the valve member <NUM> on the surface of the valve member <NUM>. A shaft hole (not shown) extends through the proximal end of each arm <NUM>, and one of two ends of a rotational shaft <NUM> is inserted through the shaft hole. The two ends of the rotational shaft <NUM> are rotatably supported by a shaft support <NUM> formed in the casing <NUM>.

A biasing portion <NUM> is supported by the casing body <NUM>. The biasing portion <NUM> is a double torsion spring that is a combination of two torsion coil springs. The biasing portion <NUM> includes an extension <NUM> that extends from between the two torsion coil springs. The distal end of the extension <NUM> is fixed to the central part of the valve member <NUM> to apply the biasing force of the biasing portion <NUM> to the valve member <NUM>.

When the pressure in the pack case <NUM> reaches a set upper limit pressure, the valve member <NUM> is pivoted about the proximal ends of the arms <NUM>, which are supported by the shaft support <NUM>, against the biasing force of the biasing portion <NUM>. This separates part of the valve member <NUM> from the valve seat <NUM> and releases gas from the pack case <NUM> through the discharge hole <NUM>.

Further, the casing <NUM> includes two fastening portions <NUM>. The casing <NUM> includes the casing body <NUM> and the two fastening portions <NUM> that are connected to the casing body <NUM> and located at the outer side of the casing body <NUM>. The two fastening portions <NUM> are positioned to be symmetric in the radial direction with respect to the center of the casing body <NUM>. The fastening portions <NUM> each include a fastening hole <NUM>, into which the corresponding fastener <NUM> is inserted, and a connection hole <NUM>, which serves as a discharge passage. The fastening hole <NUM> receives the corresponding fastener <NUM> that fixes the casing <NUM> to the pack case <NUM>. The connection hole <NUM> is closer to the casing body <NUM> than the fastening hole <NUM>. That is, the connection hole <NUM> is located between the casing body <NUM> and the fastening hole <NUM>. The cover <NUM> covers the connection hole <NUM>. Further, the casing body <NUM> includes a circumferential wall <NUM> surrounding the valve mechanism <NUM>. The circumferential wall <NUM> includes cutaway portions 49A at parts corresponding to the fastening portions <NUM>.

The casing body <NUM> also includes engagement pieces <NUM> that are press-fitted into receptacles 21B formed in the cover <NUM>. The engagement pieces <NUM> are press-fitted into the receptacles 21B of the cover <NUM> to position the cover <NUM> relative to the casing <NUM> in the circumferential direction.

As shown in <FIG>, the cover <NUM> includes an accommodation compartment 21A that accommodates the casing <NUM> excluding the fastening portions <NUM>. As shown in <FIG>, the cover <NUM> has a lower end that is open in a direction opposite to a Z-direction. The outer diameter of the casing body <NUM>, excluding the fastening portions <NUM>, is smaller than the inner diameter of the cover <NUM>. This forms a gap between the cover <NUM> and the casing <NUM>. The gap defines a passage <NUM> through which gas passes. The cover <NUM> includes a bottom end 21C inserted into the connection holes <NUM>. Gaps <NUM> are formed between the bottom end 21C of the cover <NUM> and the surface of the pack case <NUM> so that the gas passed through the passage <NUM> is discharged out of the pressure relief valve <NUM> via the gaps <NUM>. The gaps <NUM> are located between the fastening portions <NUM> and the pack case <NUM>.

The casing <NUM> includes a coupling portion <NUM> inserted into the port <NUM> of the pack case <NUM>. The coupling portion <NUM> is cylindrical and includes the discharge hole <NUM> at its inner side. A first seal member <NUM> and a second seal member <NUM> are arranged on the outer circumferential surface of the coupling portion <NUM>. The first seal member <NUM> has a circular cross section and is disposed between the casing <NUM> and the inner circumferential surface of the port <NUM> of the pack case <NUM>. The second seal member <NUM> contacts the surface of the pack case <NUM> when the pressure relief valve <NUM> is attached to the pack case <NUM>.

The valve member <NUM> is formed by combining a first valve body <NUM> and a second valve body <NUM>. The first valve body <NUM> and the second valve body <NUM> are coupled by fitting a fitting portion <NUM> of the first valve body <NUM> into a fitted portion <NUM> of the second valve body <NUM>. An annular third seal member <NUM> is disposed between the first valve body <NUM> and the second valve body <NUM>.

With reference to <FIG>, the third seal member <NUM> will now be described in detail. The third seal member <NUM> includes an inner end <NUM> accommodated in a groove <NUM> of the second valve body <NUM>. The end <NUM> includes two lips <NUM>. The lips <NUM> are pressed against the second valve body <NUM>. Further, the third seal member <NUM> includes an outer end <NUM> disposed between the second valve body <NUM> and a projection 26A of the valve seat <NUM> when the pressure relief valve <NUM> closes. The end <NUM> of the third seal member <NUM> includes a sub-lip <NUM>. The sub-lip <NUM> extends outward from the second valve body <NUM> and closes the space between the valve member <NUM> and the casing <NUM> to limit the entry of dust into the valve member <NUM>.

An annular rib <NUM>, which serves as a projection, is formed on the rim of the second valve body <NUM>. The annular rib <NUM> is arranged at a position located outward from the projection 26A in the radial direction of the discharge hole <NUM>. As shown in <FIG>, the annular rib <NUM> projects in the direction opposite to the Z-direction. As shown in <FIG>, the annular rib <NUM> contacts the third seal member <NUM> and presses the third seal member <NUM> from the side opposite to the projection 26A, which is projected in the Z-direction. Thus, when the valve member <NUM> is located at the closed position, pressing force is applied from two locations to the third seal member <NUM> between the valve seat <NUM> and the second valve body <NUM>. The separated locations where pressing force is applied to the third seal member <NUM> lowers the planar pressure produced by contact of the third seal member <NUM> and the valve seat <NUM>.

The operation of the pressure relief valve <NUM> will now be described with reference to <FIG> and <FIG>. The broken lines shown in <FIG> represent the cover <NUM>. The passage <NUM> is formed between the entire outer circumferential surface of the casing <NUM>, excluding the fastening portions <NUM>, and the inner circumferential surface of the cover <NUM>. Thus, when the internal pressure of the pack case <NUM> reaches the upper limit pressure and opens the valve member <NUM>, gas spreads out radially from the pack case <NUM> through the discharge hole <NUM>, as shown by the arrows in <FIG>, and passes through the passage <NUM> before flowing out. The gas flowing toward the fastening portions <NUM> passes through the cutaway portions 49A and enters the connection holes <NUM>.

As shown in <FIG>, the gas passed through the connection hole <NUM> passes through the gaps <NUM> between the fastening portions <NUM> and the pack case <NUM> and then flows out of the pressure relief valve <NUM>. As the open valve mechanism <NUM> lowers the internal pressure of the pack case <NUM> to less than the predetermined upper limit pressure, the biasing force of the biasing portion <NUM> acts to have the valve member <NUM> contact the valve seat <NUM>.

The above embodiment has the advantages described below.

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 <NUM> is formed by the cover <NUM> and the entire outer circumference of the casing body <NUM>, excluding the fastening portions <NUM>. Instead, the passage <NUM> can correspond to a section smaller than the entire outer circumference of the casing body <NUM>, excluding the fastening portions <NUM>. Further, when the fastening portions <NUM> are arranged at locations separated from the outer circumferential surface of the casing body <NUM>, the passage <NUM> may be formed by the cover <NUM> and the entire outer circumference of the casing body <NUM>.

In the above embodiment, the valve member <NUM> includes the annular rib <NUM> that presses the end <NUM> of the third seal member <NUM>. However, the annular rib <NUM> may be omitted if sticking of the third seal member <NUM> to the valve seat <NUM> or the like can be avoided by adjusting the biasing force of the biasing portion <NUM>. Alternatively, instead of, or in addition to, the annular rib <NUM>, a non-sticking treatment may be performed on the third seal member <NUM> or at least one of the valve member <NUM> and the valve seat <NUM> to avoid the third seal member <NUM> sticking to the valve seat <NUM> or the like.

In the above embodiment, the lower end of the cover <NUM> attached to the casing <NUM> is separated from the pack case <NUM> so that gas passes through the connection holes <NUM> and then flow out from the lower end of the cover <NUM>. Instead, or in addition, the casing <NUM> or the cover <NUM> may include a hole for passage of the gas.

In the above embodiment, the discharge passages formed in the fastening portions <NUM> correspond to the connection holes <NUM> extending through the fastening portions <NUM>. Instead, a discharge passage may be formed by gaps or the like between the fastening portions <NUM> and the cover <NUM>.

In the above embodiment, the fastening portions <NUM> include the connection holes <NUM>. However, the connection holes <NUM> may be omitted from the fastening portions <NUM>. Even in this case, the passage <NUM> is still formed at parts excluding the fastening portions <NUM>. Thus, the flow resistance of the passage can be lowered as the gas discharged from the pack case <NUM> passes.

Claim 1:
A pressure relief valve (<NUM>) for a battery pack (<NUM>), wherein the pressure relief valve (<NUM>) is configured to be attached to a port (<NUM>) formed in a pack case (<NUM>) of a battery pack (<NUM>), the pressure relief valve (<NUM>) comprising:
a casing (<NUM>) including a discharge hole (<NUM>) and a valve mechanism (<NUM>) configured to open and close the discharge hole (<NUM>), wherein the discharge hole (<NUM>) is connected to the port (<NUM>) when the pressure relief valve (<NUM>) is attached to the port (<NUM>); and
a cover (<NUM>) attached to the casing (<NUM>), wherein a passage (<NUM>) is formed between the cover (<NUM>) and the casing (<NUM>) to release gas that is discharged from the discharge hole (<NUM>),
wherein the valve mechanism (<NUM>) includes a valve member (<NUM>) configured to close the discharge hole (<NUM>) and a biasing portion (<NUM>) that biases the valve member (<NUM>) to a closed position where the valve member (<NUM>) closes the discharge hole (<NUM>); characterized in that, the pressure relief valve (<NUM>) comprises a fastener; in that
the casing (<NUM>) includes a fastening portion (<NUM>) in which said fastener (<NUM>) is arranged to fix the casing (<NUM>) to the pack case (<NUM>); and in that
the fastening portion (<NUM>) includes a discharge passage (<NUM>) to release gas that is discharged from the discharge hole (<NUM>).