Patent Description:
Conventionally, there has been known a connector having a metal ball serving as a contact that is movably disposed between a connector terminal and a counter connector terminal for the purpose of reducing the sliding resistance of the counter connector terminal inserted into and pulled out from the connector terminal. The connector terminal is electrically connected to the counter connector terminal via the metal ball.

For instance, <CIT> discloses a connector in which a connector terminal <NUM> is electrically connected to a counter connector terminal <NUM> in a connector housing <NUM> made of a resin material, as shown in <FIG>. Three metal balls <NUM> held by a contact holder <NUM> and a diagonally wound coil spring <NUM> are disposed in the connector housing <NUM>, and the connector terminal <NUM> is pressed against the three metal balls <NUM> by the diagonally wound coil spring <NUM> and thereby electrically connected to the counter connector terminal <NUM> via the three metal balls <NUM>.

The three metal balls <NUM> are housed together with compression coil springs <NUM> separately in three contact housing portions <NUM> formed in the contact holder <NUM> as shown in <FIG>. When the counter connector terminal <NUM> is inserted into the connector housing <NUM>, the three metal balls <NUM> rotate and move in accordance with movement of the counter connector terminal <NUM> while elastically compressing the corresponding compression coil springs <NUM>. This structure reduces the sliding resistance during insertion of the counter connector terminal <NUM>.

Meanwhile, the three contact housing portions <NUM> formed in the contact holder <NUM> extend in parallel along an insertion direction D of the counter connector terminal <NUM> as shown in <FIG>. Thus, the three metal balls <NUM> cannot move in a direction perpendicular to the insertion direction D of the counter connector terminal <NUM> while being able to rotate and move along the insertion direction D.

Accordingly, when the counter connector terminal <NUM> moves relative to the connector terminal <NUM> in a direction different from the insertion direction D due to, for instance, receipt of a certain external force during insertion of the counter connector terminal <NUM> into the connector housing <NUM> or in the connected state between the connector terminal <NUM> and the counter connector terminal <NUM>, the sliding resistance cannot be reduced, which may result in lower reliability of electrical connection between the connector terminal <NUM> and the counter connector terminal <NUM>.

From <CIT> a terminal unit is known which comprises: a terminal case comprising an accommodation tubular part whose one end has a male terminal insertion port into which a male terminal is to be inserted; a terminal body comprising a terminal connection part accommodated inside the accommodation tubular part; a contactor holder that is accommodated inside the accommodation tubular part and is disposed so as to be overlapped with the terminal connection part; a contactor that is held by the contactor holder so as to be capable of rolling and moving in directions closer to/apart from one end of the terminal case and comes into contact with the terminal connection part and the male terminal; and a compression coil spring that is held by the contactor holder and energizes the contactor toward the one end of the terminal case.

The present invention has been made to overcome the conventional problem as above and aims at providing a connector that can establish electrical connection between a connector terminal and a counter connector terminal with high reliability no matter which direction the counter connector terminal moves relative to the connector terminal.

A connector according to the present invention is one having a counter connector terminal housing portion in which part of a counter connector terminal is to be inserted, the connector comprising:.

An embodiment of the present invention is described below based on the accompanying drawings.

<FIG> shows a connector <NUM> according to the embodiment and a counter connector terminal <NUM> to be inserted into the connector <NUM>. The connector <NUM> includes a connector terminal <NUM> to be electrically connected to the counter connector terminal <NUM>, and a shell <NUM> illustrated by broken lines is attached to the connector terminal <NUM>.

The counter connector terminal <NUM> is formed of a plug contact having a flat plate shape. The connector terminal <NUM> is formed of a socket contact having a flat plate shape as with the counter connector terminal <NUM>, and has a flat connection surface 12A.

For convenience, the flat connection surface 12A of the connector terminal <NUM> is defined as extending along an XY plane, the direction in which the counter connector terminal <NUM> is inserted with respect to the connector <NUM> is defined as a +Y direction, and the direction perpendicular to the connection surface 12A of the connector terminal <NUM> is defined as a Z direction.

As shown in <FIG>, a ball assembly BA used for electrically connecting the connector terminal <NUM> and the counter connector terminal <NUM> together is mounted on the connection surface 12A of the connector terminal <NUM>. The ball assembly BA includes three balls <NUM> that relay electrical connection between the connector terminal <NUM> and the counter connector terminal <NUM>, a ball retention member <NUM> that rotatably retains the three balls <NUM>, and a ball guide portion <NUM> that movably retains the ball retention member <NUM> along the connection surface 12A.

<FIG> shows an assembly view of the ball assembly BA. The three balls <NUM> are disposed on the +Z direction side of the connection surface 12A of the connector terminal <NUM>, the ball retention member <NUM> is disposed on the +Z direction side of the three balls <NUM>, and a spring member <NUM> and a cover member <NUM> that constitute the ball guide portion <NUM> are sequentially disposed on the +Z direction side of the ball retention member <NUM>.

The three balls <NUM> are arranged such that all the balls <NUM> are not aligned in a straight line in an XY plane. In other words, in one example of the embodiment, the three balls <NUM> are arranged such that the shape formed by connecting the centers of the balls <NUM> is a triangle in an XY plane. The three balls <NUM> have a spherical shape having the same diameter and are made of, for instance, electrically conductive metal. It is sufficient for the balls <NUM> that at least their surfaces are electrically conductive, and for instance, use may be made of balls in each of which an electrically conductive metal layer is formed on a surface of a spherical member made of a nonconductor.

As shown in <FIG>, the ball retention member <NUM> is formed of a plate member made of metal or another material, and includes a base portion 15A of disc shape extending along an XY plane and three projection portions 15B projecting in the +Z direction from a surface of the base portion 15A. The three projection portions 15B are arranged at positions of the three vertices of an equilateral triangle whose center corresponds to the center of the base portion 15A of disc shape. Each projection portion 15B has a cone surface 15C tapering toward the +Z direction and is provided with a circular opening 15D at its +Z directional end.

The ball retention member <NUM> as above is fabricated by, for example, shearing and drawing a flat metal plate, and the three balls <NUM> can be housed in three recess portions formed on the -Z direction side of the three projection portions 15B.

As shown in <FIG>, the spring member <NUM> is a plate-like member made of metal or another material, and includes a base portion 17A of equilateral triangular shape extending along an XY plane, three frame portions 17B of arc shape separately joined to the base portion 17A, and three return springs 17C extending separately from the three frame portions 17B. The spring member <NUM> is fabricated by, for example, shearing a flat metal plate.

The three frame portions 17B of arc shape are disposed at positions of the three vertices of the base portion 17A of equilateral triangular shape, and each frame portion 17B in combination with an arc edge portion of the base portion 17A forms a circular opening portion 17D. The spring member <NUM> is configured to be fitted to the ball retention member <NUM> by inserting the three projection portions 15B of the ball retention member <NUM> into the three opening portions 17D formed by the three frame portions 17B, and the base portion 17A and the three frame portions 17B constitute a fitting portion 17E that is fitted to the ball retention member <NUM>.

The three return springs 17C are formed of band members having the same shape, have a spiral shape extending around the outside of the base portion 17A and the three frame portions 17B, and are elastically deformable in an XY plane. Each return spring 17C includes a first end portion T1 joined to the corresponding frame portion 17B of the fitting portion 17E and a second end portion T2 that is a free end. The second end portion T2 is provided with a bent portion 17F bent toward the +Z direction.

Since the return springs 17C each have a spiral shape, a longer spring length can be ensured while an installation space for the spring member <NUM> is minimized, and a spring constant can be easily adjusted.

In the ball assembly BA, the ball retention member <NUM> is disposed such that the surface, on the -Z direction side, of the base portion 15A makes contact with the connection surface 12A of the connector terminal <NUM> with the balls <NUM> being housed in ball housing portions 15E of recess shape formed on the -Z direction side of the respective projection portions 15B, as shown in <FIG>.

The circular opening 15D formed at the +Z directional end of each projection portion 15B of the ball retention member <NUM> is situated higher than the height corresponding to the radius of the ball <NUM> and lower than the height corresponding to the diameter of the ball <NUM> in the +Z direction from the connection surface 12A of the connector terminal <NUM>, and has a smaller diameter than that of the ball <NUM>. Owing to this configuration, the ball <NUM> housed in the ball housing portion 15E can rotate within the ball housing portion 15E without coming out of the ball housing portion 15E.

Since the projection portion 15B of the ball retention member <NUM> has the opening 15D as above, the -Z directional end of the ball <NUM> housed in the ball housing portion 15E surrounded by the connection surface 12A of the connector terminal <NUM> and the projection portion 15B makes contact with the connection surface 12A, while the +Z directional end of the ball <NUM> protrudes from the opening 15D in the +Z direction, as shown in <FIG>.

The spring member <NUM> is disposed on the ball retention member <NUM>, and the three opening portions 17D formed by the three frame portions 17B make contact separately with the cone surfaces 15C of the three projection portions 15B of the ball retention member <NUM>, whereby the fitting portion 17E of the spring member <NUM> is fitted to the ball retention member <NUM>. The fitting portion 17E of the spring member <NUM>, the ball retention member <NUM>, and the three balls <NUM> are configured to be integrally movable in a two-dimensional manner along the connection surface 12A of the connector terminal <NUM>.

As shown in <FIG>, the cover member <NUM> is formed of a plate member made of, for example, metal and includes a cover body 18A in a frame shape extending along an XY plane, a pair of fixing portions 18B joined to the opposite ends, in the X direction, of the cover body 18A, and a pair of counter connector terminal guide portions 18C joined to the pair of fixing portions 18B.

The cover body 18A has the shape of a ring having in its center a circular opening portion 18D. A circular outer peripheral portion of the cover body 18A extends along an XY plane, while an inner peripheral portion of the cover body 18A adjacent to the opening portion 18D extends along an XY plane at a height situated on the +Z direction side of the outer peripheral portion. In other words, the cover body 18A has such a shape as to bulge in the +Z direction from the outer peripheral portion toward the inner peripheral portion as a whole. However, the thickness of the cover body 18A in the Z direction has a smaller dimension than the diameter of the ball <NUM>.

The ring-shaped cover body 18A is provided with insertion holes 18E penetrating the cover body 18A in the Z direction at rotational positions spaced at <NUM>-degree intervals about the central axis of the cover body 18A extending in the Z direction.

The pair of fixing portions 18B are used to fix the cover member <NUM> to the connection surface 12A of the connector terminal <NUM> and extend in the X direction along an XY plane separately from the +X directional end and the -X directional end of the cover body 18A.

The pair of counter connector terminal guide portions 18C joined to the pair of fixing portions 18B are used to guide the counter connector terminal <NUM> when the counter connector terminal <NUM> is inserted into the connector <NUM> as shown in <FIG>. Each counter connector terminal guide portion 18C extends in the +Y direction and the -Y direction from the corresponding fixing portion 18B and is formed of a pair of arm portions 18F that are curved in the Z direction.

As shown in <FIG>, the cover member <NUM> is disposed on the connection surface 12A of the connector terminal <NUM> to cover the spring member <NUM> that is fitted to the ball retention member <NUM> by the fitting portion 17E. In <FIG>, the cover member <NUM> is illustrated by dashed lines to show portions covered with the cover member <NUM>.

The three return springs 17C of the spring member <NUM> have a spiral shape extending along the outer peripheral portion of the ball retention member <NUM> on the connection surface 12A of the connector terminal <NUM> and are situated on the -Z direction side of the cover body 18A of the cover member <NUM>, and the +Z directional ends of the three balls <NUM> retained in the ball retention member <NUM> are exposed through the opening portion 18D of the cover member <NUM>. In addition, since the thickness of the cover body 18A in the Z direction has a smaller dimension than the diameter of the ball <NUM>, the +Z directional ends of the three balls <NUM> protrude in the +Z direction from the cover member <NUM>.

Further, as shown in <FIG>, the bent portion 17F formed at the second end portion T2 of each return spring 17C of the spring member <NUM> is inserted in the corresponding insertion hole 18E of the cover body 18A of the cover member <NUM>. Owing to this configuration, the positions of the second end portions T2 of the three return springs 17C are restricted.

Accordingly, when, for instance, the connector terminal <NUM> is disposed with the connection surface 12A being a horizontal surface and no external force other than gravity acts on the spring member <NUM>, the ball retention member <NUM>, and the three balls <NUM>, as shown in <FIG>, the three return springs 17C of the spring member <NUM> lie in a rotationally symmetrical arrangement along the connection surface 12A, and the ball retention member <NUM> is in an initial position P1 in which the center of the base portion 15A of disc shape substantially coincides with the center of the circular opening portion 18D of the cover member <NUM>.

The insertion hole 18E of the cover body 18A of the cover member <NUM> is formed to be larger than the bent portion 17F at the second end portion T2 of the return spring 17C as shown in <FIG> such that the bent portion 17F is inserted in the insertion hole 18E with an extra margin.

The shell <NUM> is formed of a plate member such as a bent metal plate as shown in <FIG> and includes a bottom plate portion 13A situated on the -Z direction side and extending along an XY plane, a top plate portion 13B situated on the +Z direction side and extending along an XY plane, a front plate portion 13C situated on the -Y direction side and extending along an XZ plane, and a rear plate portion 13D situated on the +Y direction side and extending along an XZ plane.

The front plate portion 13C and the rear plate portion 13D are respectively provided with opening portions 13E and 13F into which the counter connector terminal <NUM> is to be inserted. A terminal spring <NUM> extending while being bent in the -Z direction and the +Y direction is formed at the -Y directional end of the top plate portion 13B.

The height of the top plate portion 13B with respect to the bottom plate portion 13A in the Z direction has a larger dimension than the sum of the thickness of the connector terminal <NUM> in the Z direction, the thickness of the counter connector terminal <NUM> in the Z direction, and the diameter of the ball <NUM>.

The shell <NUM> is attached to the connector terminal <NUM> such that the connector terminal <NUM> is situated inside the shell <NUM> to be in contact with the bottom plate portion 13A of the shell <NUM>, and a counter connector terminal housing portion <NUM> to which the counter connector terminal <NUM> is to be inserted is formed between the terminal spring <NUM> and the connection surface 12A of the connector terminal <NUM>.

When the connector <NUM> is assembled, first, the ball retention member <NUM> is disposed on the connection surface 12A of the connector terminal <NUM> while the balls <NUM> are separately housed in the three ball housing portions 15E of the ball retention member <NUM> as shown in <FIG>. At this time, the base portion 15A of the ball retention member <NUM> makes contact with the connection surface 12A of the connector terminal <NUM>.

Next, the spring member <NUM> is disposed on the ball retention member <NUM> such that the three opening portions 17D of the spring member <NUM> make contact with the cone surfaces 15C of the corresponding projection portions 15B of the ball retention member <NUM>, and the fitting portion 17E of the spring member <NUM> is fitted to the ball retention member <NUM>.

Further, the cover member <NUM> is put over the ball retention member <NUM> and the spring member <NUM> as shown in <FIG>, and the bent portions 17F of the three return springs 17C of the spring member <NUM> are inserted into the corresponding insertion holes 18E of the cover body 18A of the cover member <NUM> as shown in <FIG>.

In this state, the pair of fixing portions 18B of the cover member <NUM> are, in plural positions, welded to the connection surface 12A of the connector terminal <NUM> by laser welding or another method, whereby the cover member <NUM> is fixed to the connector terminal <NUM>. Consequently, the fitting portion 17E of the spring member <NUM>, the ball retention member <NUM>, and the three balls <NUM> are integrally movable along the connection surface 12A of the connector terminal <NUM> within the cover member <NUM>, and the +Z directional ends of the three balls <NUM> retained in the ball retention member <NUM> are exposed through the opening portion 18D of the cover member <NUM>.

After the ball assembly BA is mounted on the connection surface 12A of the connector terminal <NUM> in this manner, the shell <NUM> is attached to the connector terminal <NUM> such that the surface, on the -Z directional side, of the connector terminal <NUM> makes contact with the bottom plate portion 13A of the shell <NUM>. Thus, the assembling operation of the connector <NUM> is completed.

It should be noted that since the insertion hole 18E of the cover member <NUM> is formed to be larger than the bent portion 17F of the return spring 17C as shown in <FIG>, the bent portion 17F can be inserted into the insertion hole 18E with an extra margin, which facilitates the assembling operation of the connector <NUM>.

Next, the operation of the connector <NUM> is described.

To electrically connect the counter connector terminal <NUM> to the connector terminal <NUM> of the connector <NUM>, the counter connector terminal <NUM> shown in <FIG> is moved from the -Y direction toward the +Y direction and inserted into the shell <NUM> of the connector <NUM>.

In this process, the counter connector terminal <NUM> is inserted into the shell <NUM> while being guided by the pair of counter connector terminal guide portions 18C of the cover member <NUM> shown in <FIG> to be parallel to the connection surface 12A of the connector terminal <NUM>, and a +Y directional end portion of the counter connector terminal <NUM> is inserted into the counter connector terminal housing portion <NUM> formed between the terminal spring <NUM> of the shell <NUM> shown in <FIG> and the connection surface 12A of the connector terminal <NUM> while elastically compressing the terminal spring <NUM> toward the +Z direction, and is thereby pressed by the terminal spring <NUM> against the connection surface 12A of the connector terminal <NUM> in the -Z direction.

As a consequence, the surface of the counter connector terminal <NUM> on the -Z direction side makes contact at a predetermined contact pressure with the +Z directional ends of the three balls <NUM> protruding from the cover member <NUM> in the +Z direction, the three balls <NUM> being retained in the ball retention member <NUM>, and this allows the -Z directional ends of the three balls <NUM> to contact the connection surface 12A of the connector terminal <NUM> at the predetermined contact pressure.

Thus, the counter connector terminal <NUM> and the connector terminal <NUM> are electrically connected to each other via the three balls <NUM>.

The three balls <NUM> contact the surface, on the -Z direction side, of the counter connector terminal <NUM> and the connection surface 12A of the connector terminal <NUM> at the predetermined contact pressure and, accordingly, are urged to move in the +Y direction while rotating with the insertion movement of the counter connector terminal <NUM> into the counter connector terminal housing portion <NUM>.

However, the positions of the second end portions T2 of the three return springs 17C are separately restricted because the bent portions 17F formed at the second end portions T2 of the respective return springs 17C of the spring member <NUM> are inserted in the corresponding insertion holes 18E of the cover member <NUM>. Accordingly, the ball retention member <NUM> being in the initial position P1 as shown in <FIG> before insertion of the counter connector terminal <NUM> moves together with the three balls <NUM> in the +Y direction along the connection surface 12A of the connector terminal <NUM> while elastically deforming each of the three return springs 17C.

The three balls <NUM> disposed between the counter connector terminal <NUM> and the connector terminal <NUM> thus move in the +Y direction while rotating, and this makes it possible to reduce the sliding resistance associated with insertion of the counter connector terminal <NUM> into the counter connector terminal housing portion <NUM>.

Likewise, the sliding resistance can be reduced also when the counter connector terminal <NUM> connected to the connector terminal <NUM> is pulled out from the counter connector terminal housing portion <NUM>.

Further, since the ball retention member <NUM> is held to be movable on the connection surface 12A of the connector terminal <NUM> not only in the Y direction but in a two-dimensional manner in an XY plane, when the counter connector terminal <NUM> is inserted into or pulled out from the counter connector terminal housing portion <NUM>, if the counter connector terminal <NUM> moves relative to the connector terminal <NUM> in a direction different from the Y direction, the three balls <NUM> also move in the same direction as the direction of movement of the counter connector terminal <NUM>, thereby reducing the sliding resistance.

Since the three return springs 17C of the spring member <NUM> lie in a rotationally symmetrical arrangement along the connection surface 12A of the connector terminal <NUM> when the ball retention member <NUM> is in the initial position P1, no matter which direction the ball retention member <NUM> is going to move in an XY plane, equal elastic forces act from the three return springs 17C to the ball retention member <NUM>, so that the ball retention member <NUM> can smoothly move regardless of the moving direction.

Thus, no matter which direction the counter connector terminal <NUM> moves relative to the connector terminal <NUM>, the sliding resistance can be effectively reduced.

Aside from that, the counter connector terminal <NUM> may move relative to the connector terminal <NUM> not only when it is inserted into or pulled out from the counter connector terminal housing portion <NUM> but also in the connected state with the connector terminal <NUM> because of an external force such as vibration acting on the connector <NUM>. Even in such cases, the ball retention member <NUM> can move together with the three balls <NUM> in the same direction as the direction of movement of the counter connector terminal <NUM> regardless of which direction the counter connector terminal <NUM> moves relative to the connector terminal <NUM>. Thus, the sliding resistance can be reduced, and the connector terminal <NUM> and the counter connector terminal <NUM> can be electrically connected to each other with high reliability.

Meanwhile, the three return springs 17C of the spring member <NUM> do not necessarily need to lie in a rotationally symmetrical arrangement along the connection surface 12A of the connector terminal <NUM> when the ball retention member <NUM> is in the initial position P1; as long as the three return springs 17C are arranged to surround the ball retention member <NUM>, substantially equal elastic forces act on the ball retention member <NUM> owing to the three return springs 17C, so that the ball retention member <NUM> can smoothly move, thus reducing the sliding resistance.

However, it is preferable that the three return springs 17C lie in a rotationally symmetrical arrangement as shown in <FIG> because this allows equal elastic forces to act on the ball retention member <NUM> in an XY plane regardless of which direction the ball retention member <NUM> moves.

When the connected state between the connector terminal <NUM> and the counter connector terminal <NUM> is released and the counter connector terminal <NUM> is pulled out from the counter connector terminal housing portion <NUM>, the ball retention member <NUM> returns to the initial position P1 shown in <FIG> along the connection surface 12A of the connector terminal <NUM> due to the action of the three return springs 17C.

Aside from that, in the connector <NUM> according to the embodiment, the spring member <NUM> is configured such that the center of gravity G of the spring member <NUM> is situated inside a region R of triangular shape surrounded by the centers 14A of the three respective balls <NUM> retained in the ball retention member <NUM> as shown in <FIG>. Owing to this configuration, the three balls <NUM> can rotate and smoothly move on the connection surface 12A of the connector terminal <NUM> together with the ball retention member <NUM> and the base portion 17A of the spring member <NUM> when the counter connector terminal <NUM> moves relative to the connector terminal <NUM>, so that the sliding resistance is effectively reduced, thus improving the reliability of electrical connection between the connector terminal <NUM> and the counter connector terminal <NUM>.

The center of gravity G of the spring member <NUM> does not necessarily need to be situated inside the region R surrounded by the centers 14A of the three respective balls <NUM> retained in the ball retention member <NUM> and may be situated outside the region R. However, when the center of gravity G of the spring member <NUM> is situated outside the region R, unequal forces tend to act on the three balls <NUM>, and this may make it difficult to smoothly rotate the three balls <NUM>; therefore, it is preferable that the center of gravity G of the spring member <NUM> be situated inside the region R. The expression "inside the region R" herein includes a position on the boundary of the region R.

While the three balls <NUM> are retained in the ball retention member <NUM> in the embodiment above, the number of the balls <NUM> is not limited to three, and two or four or more balls <NUM> may be retained.

Even when such plural balls <NUM> are retained in the ball retention member <NUM>, the center of gravity G of the spring member <NUM> is preferably situated inside the region R surrounded by the centers 14A of the plural respective balls <NUM>. When the number of the balls <NUM> is two, a straight line connecting the centers 14A of the two respective balls <NUM> is regarded as the "region R," and the center of gravity G of the spring member <NUM> is preferably situated on the straight line.

In the embodiment above, the three balls <NUM> are retained in the ball retention member <NUM>, and the spring member <NUM> has the three return springs 17C correspondingly; thus, the number of the return springs 17C is the same as the number of the balls <NUM>, but the invention is not limited thereto. However, the number of the return springs 17C is preferably greater than or equal to the number of the balls <NUM> because with this configuration, elastic forces acting from plural return springs 17C to plural balls <NUM> via the ball retention member <NUM> are more likely to be equal, and this allows the plural balls <NUM> to stably rotate regardless of the moving direction.

In the embodiment above, the terminal spring <NUM> of the shell <NUM> contacts the counter connector terminal <NUM> inserted in the counter connector terminal housing portion <NUM> and presses the counter connector terminal <NUM> against the connection surface 12A of the connector terminal <NUM>; however, the invention is not limited thereto.

Claim 1:
A connector (<NUM>) having a counter connector terminal housing portion (<NUM>) in which part of a counter connector terminal (<NUM>) is to be inserted, the connector comprising:
a connector terminal (<NUM>) having a connection surface (12A) in a flat shape that faces the counter connector terminal when inserted in the counter connector terminal housing portion;
a plurality of balls (<NUM>) in a spherical shape being disposed on the connection surface, at least surfaces of the plurality of balls having electrical conductivity;
a ball retention member (<NUM>) rotatably retaining the plurality of balls in such a manner part of the surfaces of the plurality of balls contacts the connection surface and another part of the surfaces of the plurality of balls that faces opposite from the connection surface protrudes;
a ball guide portion (<NUM>) fixed to the connector terminal and retaining the ball retention member such that the ball retention member is movable in a two-dimensional manner along the connection surface; and
a terminal spring (<NUM>) pressing the counter connector terminal when inserted in the counter connector terminal housing portion or the connection surface of the connector terminal in a direction closer together,
wherein the ball guide portion includes a plurality of return springs (17C) that are disposed to surround the ball retention member along the connection surface and act to return the ball retention member to an initial position (P1) on the connection surface,
the ball retention member moves in a two-dimensional manner along the connection surface in accordance with movement of the counter connector terminal when the counter connector terminal is inserted into the counter connector terminal housing portion and in a connected state between the counter connector terminal and the connector terminal, and the ball retention member returns to the initial position due to action of the plurality of return springs when the counter connector terminal is pulled out from the counter connector terminal housing portion, and
the counter connector terminal when inserted in the counter connector terminal housing portion is pressed against the connection surface by the terminal spring, contacts protruding parts of the surfaces of the plurality of balls retained in the ball retention member, and is electrically connected to the connector terminal via the plurality of balls.