Patent Description:
The present invention relates to the field of battery, and particularly relates to a cap plate and a secondary battery.

At present, a secondary battery generally uses a case made of aluminium alloy or plastic. In order to improve energy density of the secondary battery, people generally decreases a thickness of the case; however, if the thickness of the case is decreased, rigidity of the case will be small, which leads to an opening of the case contracting inwardly (referring to <FIG>, shape of the contracted opening is shown by a dotted line). The rigidity of the plastic case made by injection molding is lower than the rigidity of the case made of the aluminium alloy, so the opening of the plastic case contracts inwardly more seriously under the influence of residual stress. In the process of assembling a cap plate and the case of the secondary battery, due to the contracted opening of the case, it is difficult to insert the cap plate into the case, which will increase difficulty of assembling the cap plate and the case and reduce assembling efficiency. <CIT> discloses a closure assembly for sealing a container lid and base. <CIT> refers to a battery housing, comprising a cap plate, having an inclined portion, coupled and welded to an opening of a case.

The scope of the present invention is defined by claims <NUM> and <NUM>. In view of the problem existing in the background, an object of the present invention is to provide a cap plate of a secondary battery and a secondary battery, which can decrease difficulty of assembling the cap plate and the case and improve assembling efficiency.

In order to achieve the above object, in a first aspect, the present invention provides a cap plate of a secondary battery as defined in the independent claim, which includes a main portion and a first protruding portion. The main portion includes a first exterior surface, a second exterior surface and a third exterior surface which are formed along a periphery of the main portion, the third exterior surface is a curved surface and connects the first exterior surface and the second exterior surface. The first protruding portion is provided below the main portion and includes a fourth exterior surface extending downwardly from a bottom end of the third exterior surface, the fourth exterior surface is inclined inwardly relative to the third exterior surface.

In order to achieve the above object, in a second aspect, the present invention provides a secondary battery, which comprises the cap plate according to the first aspect of the present invention and a case. The case includes an opening in a top thereof, a shape of the opening is fitted with a shape of the periphery of the main portion; the cap plate is provided to the opening of the case, and the main portion of the cap plate is fixed to an inner wall of the case. The first protruding portion of the cap plate is received in the case, and a gap is provided between the fourth exterior surface of the first protruding portion and the inner wall of the case, a dimension of the gap increases gradually along a downward direction.

The present invention has the following beneficial effects: in the process of assembling the case and the cap plate, because the fourth exterior surface is inclined inwardly relative to the third exterior surface, even though the opening of the case contracts, the first protruding portion also can be inserted into the opening. After inserting the first protruding portion into the opening, the fourth exterior surface of the first protruding portion contacts the inner wall of the case; with a downward movement of the cap plate, the fourth exterior surface will apply an outward force to the inner wall of the case, the inner wall will be stretched outwardly gradually under the influence of the outward force, and the opening of the case will be expended gradually; when the first protruding portion has been inserted into the case completely, the opening of the case can be completely expanded by the first protruding portion, when the cap plate is continuously moved downwardly, the main portion of the cap plate can be allowed to directly insert into the opening. Therefore, the secondary battery of the present invention can reduce difficulty of assembling the cap plate and the case, improve assembling efficiency.

Reference numerals in figures are represented as follows:.

Hereinafter a cap plate and a secondary battery according to the present invention will be described in detail in combination with the figures.

Firstly, a cap plate according to a first aspect of the present invention will be described.

Referring to <FIG>, a cap plate <NUM> according to the present invention includes a main portion <NUM> and a first protruding portion <NUM>. The main portion <NUM> includes a first exterior surface <NUM>, a second exterior surface <NUM> and a third exterior surface <NUM> which are formed along a periphery of the main portion <NUM>, the third exterior surface <NUM> is a curved surface and connects the first exterior surface <NUM> and the second exterior surface <NUM>. The first protruding portion <NUM> is provided below the main portion <NUM> and includes a fourth exterior surface <NUM> extending downwardly from a bottom end of the third exterior surface <NUM>, the fourth exterior surface <NUM> is inclined inwardly relative to the third exterior surface <NUM>.

Preferably, the third exterior surface <NUM> is a curved surface parallel to an up-down direction Z. Specifically, referring to <FIG>, the third exterior surface <NUM> can be generated by a first generatrix L2 rotating around an axis L1, the first generatrix L2 and the axis L1 are parallel to the up-down direction Z. Preferably, the first generatrix L2 rotates around the axis L1 by <NUM> degrees. The first exterior surface <NUM> and the second exterior surface <NUM> are planes parallel to the up-down direction Z. Furthermore, the third exterior surface <NUM> is tangential to the first exterior surface <NUM> and the second exterior surface <NUM>.

The cap plate <NUM> is a constituent member of a secondary battery. Specifically, the cap plate <NUM> is used for assembling with a case <NUM> of the secondary battery. The main portion <NUM> of the cap plate <NUM> can be inserted into an opening of the case <NUM> and fixed to an inner wall <NUM> of the case <NUM>. When the main portion <NUM> of the cap plate <NUM> is inserted into the opening of the case <NUM>, the third exterior surface <NUM> will be fixed to a corner of the inner wall <NUM>.

A line generated at an intersection of the third exterior surface <NUM> and a plane perpendicular to the up-down direction Z is a circular arc, and a radius of the circular arc ranges from <NUM> to <NUM>. The third exterior surface <NUM> can be formed by providing a rounded corner in the main portion <NUM>. In the forming process of the case <NUM>, the corner of the inner wall <NUM> is configured as a rounded corner; in order to ensure sealing performance between the cap plate <NUM> and the case <NUM>, the line generated at the intersection of the third exterior surface <NUM> and the plane perpendicular to the up-down direction Z is configured as the circular arc, and the radius of the circular arc is less than or equal to a radius of the rounded corner of the inner wall <NUM>.

When the main portion <NUM> of the cap plate <NUM> is inserted into the case <NUM>, the case <NUM> and main portion <NUM> can be welded together by a laser emitted from the outside of the case <NUM>. In the process of welding the case <NUM> and main portion <NUM>, when the laser moves along the third exterior surface <NUM>, a distance between focus of the laser and the third exterior surface <NUM> will change along the circular arc, which will affect welding quality. Because the radius of the circular arc ranges from <NUM> to <NUM>, variation of the welding quality caused by the distance between focus of the laser and the third exterior surface <NUM> will be little, thereby ensuring sealing performance and strength of the welding zone.

Referring to <FIG> and <FIG>, lengths of lines respectively generated at intersections of the fourth exterior surface <NUM> and planes perpendicular to the up-down direction Z gradually decrease from top to bottom. In the process of inserting the first protruding portion <NUM> into the case <NUM>, the fourth exterior surface <NUM> contacts the inner wall <NUM> of the case <NUM>; with a downward movement of the first protruding portion <NUM>, the support force of the first protruding portion <NUM> with respect to the case <NUM> will increase gradually. Because the lengths of the lines respectively generated at the intersections of the fourth exterior surface <NUM> and the planes perpendicular to the up-down direction Z gradually decrease from top to bottom, with the downward movement of the first protruding portion <NUM>, a contacting area between the fourth exterior surface <NUM> and the inner wall <NUM> of the case <NUM> will increase gradually, thereby preventing deformation of the first protruding portion <NUM> caused by the excessive support force.

The lines respectively generated at the intersections of the fourth exterior surface <NUM> and the planes perpendicular to the up-down direction Z are circular arcs. Specifically, the fourth exterior surface <NUM> is generated by a second generatrix L3 rotating around the axis L1, and a top end of the second generatrix L3 is connected with a bottom end of the first generatrix L2. The second generatrix L3 is inclined inwardly relative to the first generatrix L2, in other words, the second generatrix L3 is inclined towards the axis L1, so the fourth exterior surface <NUM> is inclined inwardly relative to third exterior surface <NUM>. An angle between the second generatrix L3 and the axis L1 ranges from <NUM> degrees to <NUM> degrees. Similarly, the second generatrix L3 rotates around the axis L1 by <NUM> degrees.

The main portion <NUM> of the cap plate <NUM> may be a flat plate in shape of quadrilateral. Specifically, referring to <FIG>, the first exterior surface <NUM> is provided as two in number, the second exterior surface <NUM> is provided as two in number, the first exterior surfaces <NUM> and the second exterior surfaces <NUM> are alternately provided along the periphery of the main portion <NUM>, the third exterior surfaces <NUM> each are provided between each first exterior surface <NUM> and each second exterior surface <NUM> adjacent to the first exterior surface <NUM>; each third exterior surface <NUM> is positioned at the corner of the main portion <NUM>, the bottom end of each third exterior surface <NUM> is connected with one corresponding fourth exterior surface <NUM>. In other words, the third exterior surface <NUM> is provided as four in number. The third exterior surface <NUM> may be formed by providing the rounded corner on the flat plate. Because the bottom end of each third exterior surface <NUM> is connected with one corresponding fourth exterior surface <NUM>, the fourth exterior surface <NUM> is provided as four in number; correspondingly, the first protruding portion <NUM> is provided as four in number and respectively formed at four corners of the main portion <NUM>. Preferably, the two first exterior surfaces <NUM> are perpendicular to a transverse direction X, and the two second exterior surfaces <NUM> are perpendicular to a longitudinal direction Y. Referring to <FIG> and <FIG>, the four first protruding portions <NUM> respectively apply force to the four corners of the inner wall <NUM>. When a first protruding portion <NUM> applies force to a corresponding corner of the inner wall <NUM>, the force can be decomposed into a component F<NUM> and a component F<NUM> in two directions, which in turn can wholly expand the opening of the case <NUM> more easily. If the fourth exterior surface <NUM> of the first protruding portion <NUM> applies force to other position of the inner wall <NUM>, direction of the force is single, which will easily lead to the opening of the case <NUM> only being partly expanded. Preferably, the number of the first protruding portions <NUM> is equal to the number of the corners of the inner wall <NUM>, if the number of the first protruding portions <NUM> is less than the number of the corners of the inner wall <NUM>, the opening of the case <NUM> will only be partly expanded, which will lead to the main portion <NUM> of the cap plate <NUM> being inserted into the opening of the case <NUM> difficultly.

Referring to <FIG>, the cap plate <NUM> further includes a second protruding portion <NUM> provided below the main portion <NUM>, the second protruding portion <NUM> includes a fifth exterior surface <NUM> extending downwardly from a bottom end of the first exterior surface <NUM>, the fifth exterior surface <NUM> is inclined inwardly relative to the first exterior surface <NUM>. An end of the second protruding portion <NUM> in the longitudinal direction Y is connected with the first protruding portion <NUM>, and the fifth exterior surface <NUM> of the second protruding portion <NUM> is connected with the fourth exterior surface <NUM> of the first protruding portion <NUM>. The fifth exterior surface <NUM> is a plane, a line generated at an intersection of the fifth exterior surface <NUM> and the fourth exterior surface <NUM> can be acted as the second generatrix L3. The angle between the second generatrix L3 and the axis L1 is equal to an angle between the fifth exterior surface <NUM> and the axis L1. Preferably, two ends of the second protruding portion <NUM> in the longitudinal direction Y are respectively connected with two first protruding portions <NUM>, and the fifth exterior surface <NUM> of the second protruding portion <NUM> is connected with the fourth exterior surfaces <NUM> of the two first protruding portions <NUM>. A length of the first exterior surface <NUM> is smaller than a length of the second exterior surface <NUM>. Referring to <FIG>, in the process of placement of the case <NUM> lonely, a long wall of the case <NUM> extending in the transverse direction X generally deforms inwardly more than a short wall of the case <NUM> extending in the longitudinal direction Y; referring to <FIG>, in the process of inserting the first protruding portion <NUM> into the case <NUM>, the long wall of the case <NUM> needs to be stretched to a large extent, so a force (which is a reaction with respect to the component F<NUM> shown in <FIG>) in the transverse direction X applied to the first protruding portion <NUM> is large; a part of the force in the transverse direction X can be applied to the second protruding portion <NUM>, which can effectively prevent deformation of the first protruding portion <NUM>.

Referring to <FIG>, a groove <NUM> recessed upwardly is provided in a bottom surface of the main portion <NUM>. The groove <NUM> can reduce weight of the cap plate <NUM>, save interior space of the secondary battery, thereby improving energy density. An inner peripheral wall of the groove <NUM> can be provided with ribbed plates, which can improve strength of the cap plate <NUM>. Alternatively, referring to <FIG>, the main portion <NUM> also can be a solid structure.

Referring to <FIG>, the cap plate <NUM> further includes a third protruding portion <NUM> provided to the main portion <NUM> and protruding outwardly. The third protruding portion <NUM> extends outwardly from the first exterior surfaces <NUM>, the second exterior surfaces <NUM> and the third exterior surfaces <NUM>. Preferably, the periphery of the main portion <NUM> is encircled by the third protruding portion <NUM>. Alternatively, the third protruding portion <NUM> also can only extend outwardly from the first exterior surfaces <NUM>. In the prior art, the inner wall <NUM> of the case <NUM> is generally provided with a step, the step is used to prevent the cap plate <NUM> being excessively inserted into the case <NUM>; compared to the step of the prior art, the third protruding portion <NUM> provided to the periphery of the main portion <NUM> not only can prevent the cap plate <NUM> being excessively inserted into the case <NUM>, but also further decrease a thickness of the case <NUM> and improve the energy density of the secondary battery.

The cap plate <NUM> can be made of plastic. Compared to the cap plate <NUM> made of aluminium alloy, forming method of the cap plate <NUM> made of the plastic is simple and weight of the plastic is small.

Secondly, a secondary battery according to a second aspect of the present invention will be described.

Referring to <FIG>, a secondary battery according to the present invention comprises the cap plate <NUM> according to the first aspect of the present invention and the case <NUM>. Both the cap plate <NUM> and the case <NUM> are made of plastic, the plastics used for making the cap plate <NUM> and the case <NUM> can be same or different. The case <NUM> includes the opening in a top thereof, a shape of the opening is fitted with a shape of the periphery of the main portion <NUM>; the cap plate <NUM> is provided to the opening of the case <NUM>, and the main portion <NUM> of the cap plate <NUM> is fixed to the inner wall <NUM> of the case <NUM>, the third exterior surface <NUM> is fixed to the corner of the inner wall <NUM>. The first protruding portion <NUM> of the cap plate <NUM> is received in the case <NUM>, and a gap is provided between the fourth exterior surface <NUM> of the first protruding portion <NUM> and the inner wall <NUM> of the case <NUM>, a dimension of the gap increases gradually along a downward direction.

Preferably, the corner of the inner wall <NUM> is configured as the rounded corner.

Referring to <FIG> and <FIG>, the secondary battery further comprises an electrode assembly <NUM> and an electrode terminal <NUM>, the electrode assembly <NUM> is received in the case <NUM>, the electrode terminal <NUM> is fixed to the main portion <NUM> of the cap plate <NUM> and electrically connected with the electrode assembly <NUM>. The electrode assembly <NUM> comprises a positive electrode plate, a negative electrode plate and a separator separating the positive electrode plate and the negative electrode plate.

Because the case <NUM> is thin and made of plastic, referring to a dotted line shown in <FIG>, the opening of the case <NUM> will contract inwardly under the influence of residual stress, which leads to a dimension of the opening being smaller than a dimension of the main portion <NUM> of the cap plate <NUM>.

In the process of assembling the case <NUM> and the cap plate <NUM>, the first protruding portion <NUM> needs to be inserted into the corner of the inner wall <NUM> firstly. Because the fourth exterior surface <NUM> is inclined inwardly relative to the third exterior surface <NUM>, the fourth exterior surface <NUM> is offset inwardly from top to bottom; even though the opening of the case <NUM> contracts, the first protruding portion <NUM> also can be inserted into the opening. Referring to <FIG>, after inserting the first protruding portion <NUM> into the opening, the fourth exterior surface <NUM> of the first protruding portion <NUM> contacts the inner wall <NUM> of the case <NUM>; with a downward movement of the cap plate <NUM>, the fourth exterior surface <NUM> will apply an outward force (such as the component F<NUM> and the component F<NUM> shown in <FIG>) to the inner wall <NUM> of the case <NUM>, the inner wall <NUM> will be stretched outwardly gradually under the influence of the outward force, and the opening of the case <NUM> will be expended gradually; referring to <FIG>, when the first protruding portion <NUM> has been inserted into the case <NUM> completely, the opening of the case <NUM> can be completely expanded by the first protruding portion <NUM>, when the cap plate <NUM> is continuously moved downwardly, the main portion <NUM> of the cap plate <NUM> can be allowed to directly insert into the opening. Therefore, the secondary battery of the present invention can reduce difficulty of assembling the cap plate <NUM> and the case <NUM>, improve assembling efficiency.

Referring to <FIG> and <FIG>, the first protruding portion <NUM> is identical with the corner of the inner wall <NUM> of the case <NUM> in number. When the first protruding portion <NUM> applies force to the corner of the inner wall <NUM>, the force can be decomposed into the component F1 and the component F2 in two directions, which can wholly expand the opening of the case <NUM> more easily. If the fourth exterior surface <NUM> of the first protruding portion <NUM> applies force to other position of the inner wall <NUM>, the direction of the force is single, which will easily lead to the opening of the case <NUM> only being partly expanded. In addition, the number of the first protruding portions <NUM> needs to be equal to the number of the corners of the inner wall <NUM>, if the number of the first protruding portions <NUM> is less than the number of the corners of the inner wall <NUM>, the opening of the case <NUM> will be partly expanded, which will lead to the main portion <NUM> of the cap plate <NUM> being inserted into the opening of the case <NUM> difficultly. The second protruding portion <NUM> of the cap plate <NUM> can improve the strength of the first protruding portion <NUM> and help expand the opening of the case <NUM>.

Preferably, lengths of the lines respectively generated at the intersections of the fourth exterior surface <NUM> and the planes perpendicular to the up-down direction Z gradually decrease from top to bottom, so the first protruding portion <NUM> can be inserted into the case <NUM> easily. Furthermore, in the process of inserting the first protruding portion <NUM> into the case <NUM>, the fourth exterior surface <NUM> contacts the inner wall <NUM> of the case <NUM>; with the downward movement of the first protruding portion <NUM>, the support force of the first protruding portion <NUM> with respect to the case <NUM> will increase gradually. Because the lengths of the lines respectively generated at the intersections of the fourth exterior surface <NUM> and the planes perpendicular to the up-down direction Z gradually decrease from top to bottom, with the downward movement of the first protruding portion <NUM>, the contacting area between the fourth exterior surface <NUM> and the inner wall <NUM> of the case <NUM> will increase gradually, thereby preventing deformation of the first protruding portion <NUM> caused by the excessive support force.

Preferably, the angle between the second generatrix L3 and the axis L1 ranges from <NUM> degrees to <NUM> degrees. If a length of the first protruding portion <NUM> extending in the up-down direction Z is constant, with increasing of the angle, the length of the second generatrix L3, an area of the fourth exterior surface <NUM> and a volume of the first protruding portion <NUM> will increase correspondingly; if the angle is larger than <NUM> degrees, the first protruding portion <NUM> will occupy excessive space, which reduces the energy density of the secondary battery. In addition, in the process of assembling the cap plate <NUM> and the case <NUM>, if the angle is too large, the first protruding portion <NUM> may damage the electrode assembly <NUM>, thereby leading to short circuit; when the cap plate <NUM> moves a unit distance downwardly, if the angle is too large, the opening of the case <NUM> will deform excessively, which damages the case <NUM> easily. In addition, if the angle is too small, the first protruding portion <NUM> cannot be easily inserted into the opening of the case <NUM>, which leads to difficulty of assembling.

Referring to <FIG> and <FIG>, the third protruding portion <NUM> is attached to a top surface <NUM> of the case <NUM>. The third protruding portion <NUM> can have a positioning function in the assembling process, prevent the main portion <NUM> of the cap plate <NUM> from inserting the case <NUM> excessively.

There is an interference fit between the main portion <NUM> of the cap plate <NUM> and the inner wall <NUM> of the case <NUM>. The interference fit can ensure that there is no space between the main portion <NUM> and the inner wall <NUM> of the case <NUM>, and improve sealing performance. In addition, the opening of the case <NUM> can be expanded by the first protruding portion <NUM>, so the interference fit will not increase difficulty of assembling.

The first exterior surfaces <NUM>, the second exterior surfaces <NUM> and the third exterior surfaces <NUM> of the main portion <NUM> of the cap plate <NUM> can be fixed to the inner wall <NUM> of the case <NUM> by laser welding, and a height of welding zone between the main portion <NUM> and the case <NUM> in the up-down direction Z ranges from <NUM> to <NUM>. When the main portion <NUM> is inserted into the case <NUM>, the case <NUM> and main portion <NUM> can be welded together by the laser emitted from the outside of the case <NUM>. For the cap plate <NUM> made of plastic and the case <NUM> made of plastic, the prior art generally melt an edge of the case <NUM> and an edge of the cap plate <NUM> by a hot plate, and then securely connects the edge of the case <NUM> and the edge of the cap plate <NUM> under exterior pressure; however, when the hot plate are separated from the case <NUM> or the cap plate <NUM>, the plastic will easily generate filaments due to adhering to the hot plate, and the filaments will enter the case <NUM> easily and pierce the separator, which leads to short circuit of the electrode assembly <NUM>; at the same time, with this connecting way in the prior art, connecting area, connecting strength and sealing performance between the case <NUM> and the cap plate <NUM> are not desirable. The welding way of the present invention will not generate filaments in the case <NUM>, which can ensure the sealing performance and no foreign matter existing in the case <NUM>.

The case <NUM> is made of plastic and a wall thickness of the case <NUM> ranges from <NUM> to <NUM>. The prior art generally securely connects the case <NUM> made of metal and the cap plate <NUM> made of metal by butt welding, in order to ensure welding strength, a gap between the case <NUM> and cap plate <NUM> must be small. In the present invention, the case <NUM> is made of plastic and the wall thickness is small, and the opening of the case <NUM> will contract inwardly easily under the influence of the residual stress after injection molding, so the case <NUM> cannot be attached to the cap plate <NUM> closely, which may lead to low welding strength or weak welding; in addition, if the case <NUM> made of plastic and the cap plate <NUM> made of plastic are connected by butt welding, it will lead to a small welding area and cannot ensure welding strength. By welding the periphery of the main portion <NUM> of the cap plate <NUM> (specifically, the first exterior surface <NUM>, the second exterior surface <NUM> and the third exterior surface <NUM>) to the case <NUM> and ensuring that the height of welding zone between the periphery of the main portion <NUM> of the cap plate <NUM> and the case <NUM> in the up-down direction Z ranges from <NUM> to <NUM>, it can increase connecting area, prevent low welding strength and weak welding.

Preferably, the groove <NUM> recessed upwardly is provided in the bottom surface of the main portion <NUM>. The groove <NUM> can increase interior space of the secondary battery and improves energy density.

Claim 1:
A cap plate (<NUM>) configured to be comprised by a secondary battery, wherein
the cap plate (<NUM>) is rectangular and includes a main portion (<NUM>) and a first protruding portion (<NUM>);
the main portion (<NUM>) includes a first exterior surface (<NUM>), a second exterior surface (<NUM>) and a third exterior surface (<NUM>) which are formed along a periphery of the main portion (<NUM>), the third exterior surface (<NUM>) is a curved surface and connects the first exterior surface (<NUM>) and the second exterior surface (<NUM>);
the first exterior surface (<NUM>) is planar and is provided as two in number, the second exterior surface (<NUM>) is planar and is provided as two in number, the first exterior surfaces (<NUM>) and the second exterior surfaces (<NUM>) are alternately provided along the periphery of the main portion (<NUM>), the third exterior surfaces (<NUM>) is provided as four in number, the third exterior surfaces (<NUM>) each are provided between each first exterior surface (<NUM>) and each second exterior surface (<NUM>) adjacent to the first exterior surface (<NUM>), the third exterior surfaces (<NUM>) each is positioned at a corner of the cap plate (<NUM>);
the first protruding portion (<NUM>) is provided as four in number and positioned below the main portion (<NUM>), and each first protruding portion (<NUM>) includes a fourth exterior surface (<NUM>) extending downwardly from a bottom end of one corresponding third exterior surface (<NUM>), each fourth exterior surface (<NUM>) is inclined inwardly relative to the one corresponding third exterior surface (<NUM>);
the secondary battery further comprises a case (<NUM>);
the case (<NUM>) includes an opening in a top thereof, a shape of the opening is fitted with a shape of the periphery of the main portion (<NUM>);
the cap plate (<NUM>) is provided to the opening of the case (<NUM>), and the main portion (<NUM>) of the cap plate (<NUM>) is fixed to an inner wall (<NUM>) of the case (<NUM>);
the first protruding portion (<NUM>) of the cap plate (<NUM>) is received in the case (<NUM>), and a gap is provided between the fourth exterior surface (<NUM>) and the inner wall (<NUM>) of the case (<NUM>), a dimension of the gap increases gradually along a downward direction;
the opening of the case (<NUM>) is expanded when the first protruding portion (<NUM>) of the cap plate (<NUM>) is received in the case (<NUM>).