Abstract:
A connector to be connected to a mating connector, includes a connector main body including a cylindrical member, a supporting member disposed in the cylindrical member, a terminal supported on the supporting member, and a fitting portion having an engaging portion; a movable sleeve including a diameter control portion; an elastic deformation member disposed to be elastically deformable in a radial direction thereof; an accommodating portion disposed between the connector main body and the movable sleeve for accommodating the elastic deformation member; and a transmission unit for transmitting a force in the axial direction from the movable sleeve to the elastic deformation member when the movable sleeve moves, and for transmitting a force in the radial direction from the elastic deformation member to the movable sleeve when the elastic deformation member returns to an original shape.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a connector. More specifically, the present invention relates to a connector such as an electrical connector for connecting devices electrically, in which a locking mechanism is provided for preventing the connector from coming off. 
     In a conventional connector such as an electrical connector, an optical connector, and so on, a locking mechanism is provided therein for preventing the connector connected to a mating connector from coming off the mating connector. For example, a connector having a circular cross-sectional shape such as a coaxial connector, a multi core connector, and so on, is equipped with the various locking mechanisms such as a screw-in style mechanism, a bayonet style mechanism, a push-pull style mechanism, and so on. 
     In the conventional connectors described above, the locking mechanism of the push-pull style includes a sleeve having a cylindrical shape on an outer circumference of a connector main body. The sleeve is capable of moving and sliding in a direction of an axis of the connector main body. When an operator unlocks the connector, the operator moves the sleeve in the direction of the axis by holding the sleeve with fingers thereof. When the fingers of the operator are released from the sleeve, the sleeve returns to an initial position automatically, thereby locking the connector. 
     In the conventional connector equipped with the locking mechanism of the push-pull style, when the connector is connected to the mating connector, the operator holds the sleeve of the connector with the fingers. Then, the operator applies a force so as to push the connector toward the mating connector in the direction of the axis. Accordingly, the sleeve moves to a distal end side of the connector in the direction of the axis. Thereby, the connector is unlocked and the connector becomes capable of connecting to the mating connector. As a result, the connector is connected to the mating connector as is. Further, the sleeve returns to the initial position as the fingers of the operator are released from the sleeve, thereby locking the connector. 
     When the operator extracts the connector from the mating connector, the operator holds the sleeve with the fingers thereof and applies a force so as to pull the connector out of the mating connector in the direction of the axis. Thereby, the sleeve moves to a proximal end side of the connector so that the connector is disengaged. Therefore, the connector is extracted from the mating connector as is. 
     As described above, in the conventional connector, the locking mechanism of the push-pull style enables to unlock the connector by simply holding the sleeve then applying the force in the direction that the connector is connected or extracted. Further, the locking mechanism of the push-pull style enables to lock the connector automatically by releasing the sleeve. On the other hand, when the connector is equipped with the locking mechanism of the screw-in style or the bayonet-style, it is necessary to rotate the sleeve thereof around the axis for locking or unlocking the connector. Therefore, the connector equipped with the locking mechanism of the push-pull style can be connected or extracted more easily, as compared to the connectors equipped with the locking mechanisms of the screw-in style and the bayonet-style. 
     As described above, the sleeve of the connector with the locking mechanism of the push-pull style automatically returns from a position being moved to the initial position as the operator releases the sleeve. It is attained since the connector is provided with a mechanism therein for returning the sleeve which is moved in the direction of the axis to the initial position. For example, when the connector includes a coil spring therein so that the coil spring is able to expand and contract in the direction of the axis, the sleeve returns to the initial position automatically. 
     More specifically, when the operator holds and moves the sleeve with the fingers thereof from the initial position in the direction of the proximal end side or the distal end side, the coil spring contracts with elasticity thereof. Further, when the operator releases the fingers from the sleeve, the coil spring expands with elasticity thereof. Accordingly, when a force generated by the expansion of the coil spring is applied to the sleeve, the sleeve returns to the initial position automatically. 
     Further, Patent Reference discloses a conventional connector having a mechanism for returning a locking sleeve to an initial position utilizing elasticity. 
     In the conventional connector disclosed in Patent Reference, the mechanism includes a locking sleeve and an elastic portion provided on other end of the locking sleeve. When a cam formed in the elastic portion contacts with a surface (a concaved portion with a slightly inclined surface) formed in an outer circumferential portion on the other end of a coupler, the elastic portion is deformed outward in a direction of a diameter thereof as the locking sleeve is moved from the initial position toward an end or the other end. Thereby, the locking sleeve returns to the initial position by utilizing the elasticity of the elastic portion. 
     Patent Reference Japanese Patent Publication No. 2003-516606 
     As described above, the conventional connector having the locking mechanism of the push-pull style includes the mechanism for returning the sleeve moved in the direction of the axis to the initial position. However, the mechanism described above has problems described below. 
     When the mechanism for returning the sleeve automatically to the initial position is configured with the coil spring as described above, the connector needs to include the coil spring, a spring washer, a space to expand and contract of the coil spring, and so on therein. As a result, a dimension of the connector in the direction of the axis becomes larger. Therefore, the connector becomes larger in size. 
     Further, as disclosed in Patent Reference, when the connector is equipped with the mechanism configured with the locking sleeve and the elastic portion provided on the other end of the locking sleeve, the connector becomes larger in size since the dimension of the connector in the direction of the axis also becomes larger. 
     More specifically, the elastic portion needs to have a certain length in the direction of the axis in order to obtain proper elasticity generated by deformation thereof. When the elastic portion has a short length as described in Patent Reference, the elastic portion tends to generate an excessive elastic force toward outside in the direction of the diameter. Consequently, a strong force is required to move the sleeve in the direction of the axis. As a result, it becomes difficult to lock and unlock easily. According to simulation, the elastic portion may need to be twice as long in the direction of the axis as disclosed in Patent Reference in order to obtain preferred operability for locking and unlocking. 
     Furthermore, in the conventional connector, when the mechanism for returning the sleeve to the initial position is configured with the locking sleeve and the elastic portion provided on the other end of the locking sleeve as disclosed in Patent Reference, it is difficult to provide the connector with proper durability and reduce the size of the connector. 
     More specifically, in the conventional connector disclosed in Patent Reference, the elastic portion has a shape of a collet chuck. Thereby, the elastic portion is capable of elastically deforming toward outside in the direction of the diameter. On the other hand, rigidity of the elastic portion becomes less strong consequently, since the elastic portion has a shape of a collet chuck. As a result, the connector is not able to obtain the sufficient durability. 
     Generally, when the connector is handled normally, the connector often receives an external force. For example, the elastic portion receives a force due to a forcible twisting upon extraction of the connector, or an external force generated as a cable connected to the other end of the connector is pulled in a direction crossing the direction of the axis of the connector. It is difficult for the elastic portion having the shape of the collet chuck to have sufficient durability against the forcible twisting or the external force described above. 
     In view of the problems described above, an object of the present invention is to provide a connector capable of reducing a size thereof, especially a size thereof in a direction of an axis thereof, as well as being equipped with a locking mechanism. 
     A further object of the present invention is to provide a connector having a locking mechanism including a sufficiently rigid movable sleeve arranged to be movable in the direction of the axis for locking and unlocking the connector, so that the connector is sufficiently durable and capable of preventing the movable sleeve thereof from being damaged or deformed due to the forcible twisting and so on. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In order to attain the objects described above, according to a first aspect of the present invention, a first connector is to be connected to a mating connector. 
     According to the first aspect of the present invention, the connector includes a connector main body including a cylindrical member formed in a cylindrical shape, a supporting member disposed in the cylindrical member, a terminal supported on the supporting member on a proximal end side of the cylindrical member and extending in an axial direction, and a fitting portion formed on a distal end side of the cylindrical member for receiving the mating connector and engaging with the mating connector. 
     According to the first aspect of the present invention, the fitting portion is arranged to be elastically deformable to increase a diameter thereof. Further, the fitting portion has an engaging portion on an inner circumference side thereof. When the mating connector starts entering the fitting portion, the fitting portion expands in the radial direction thereof, so that the mating connector is allowed to enter the fitting portion. Further, when the mating connector is completely inserted into the fitting portion, the fitting portion returns to an original shape thereof, and the engaging portion engages with an engaged portion formed on the mating connector. 
     According to the first aspect of the present invention, the connector further includes a movable sleeve formed in a ring shape and disposed on an outer circumference side of the connector main body to be movable along the axial direction thereof relative to the connector main body. The movable sleeve including a diameter control portion at the distal end side for controlling an expansion of the fitting portion in the radial direction. When the movable sleeve is situated at an initial position, the diameter control portion moves close to or contacts with an outer circumferential portion of the fitting portion, so that the fitting portion is not capable of expanding in the radial direction. Further, when the movable sleeve moves toward the distal end side or the proximal end side from the initial position along the axial direction, the diameter control portion moves away from the outer circumferential portion of the fitting portion, so that the fitting portion is capable of expanding in the radial direction. 
     According to the first aspect of the present invention, the connector further includes an elastic deformation member formed in a substantially ring shape and disposed to be elastically deformable in a radial direction thereof; and an accommodating portion disposed between an outer circumferential portion of the connector main body on the proximal end side and an inner circumferential portion of the movable sleeve on the proximal end side for accommodating the elastic deformation member in a state that the fitting portion is capable of expanding in the radial direction. 
     According to the first aspect of the present invention, the connector further includes a transmission unit for converting a force in the axial direction generated when the movable sleeve moves toward the distal end side or the proximal end side from the initial position along the axial direction into a force in the radial direction for deforming the elastic deformation member, and for transmitting the force in the radial direction to the elastic deformation member. The transmission unit is further provided for converting the force in the radial direction to restore the elastic deformation member from the deformed state into the force in the axial direction to return the movable sleeve moves from the distal end side or the proximal end side to the initial position along the axial direction, and for transmitting the force in the axial direction to the movable sleeve. 
     According to the first aspect of the present invention, when the connector is connected to the mating connector, an operator holds the movable sleeve with fingers, and pushes the connector towards the mating connector in a state that the distal end portion of the fitting portion of the connector contacts with a distal end portion of the mating connector. With the force in the axial direction, the movable sleeve of the connector moves from the initial position to the distal end side in the axial direction. 
     According to the first aspect of the present invention, the transmission unit is provided for converting the force in the axial direction generated when the movable sleeve moves toward the distal end side along the axial direction into the force in the radial direction, and for transmitting the force in the radial direction to the elastic deformation member. Accordingly, the elastic deformation member deforms in the radial direction. Further, when the movable sleeve moves from the initial position, the diameter control portion moves away from the outer circumferential portion of the fitting portion, so that the fitting portion is capable of expanding in the radial direction. 
     According to the first aspect of the present invention, when the fitting portion expands in the radial direction, the mating connector can be inserted into the fitting portion. When the mating connector enters up to a back side of the fitting portion and is completely inserted into the fitting portion, the fitting portion contracts and returns to the original shape. Accordingly, the engaging portion engages with the engaged portion of the mating connector. 
     According to the first aspect of the present invention, when the operator releases the fingers from the movable sleeve, the force in the axial direction to move the movable sleeve toward the distal end side in the axial direction disappears. As a result, the force in the radial direction transmitted to the elastic deformation member disappears, so that the elastic deformation member returns to the original shape thereof with own elastic force. 
     At this moment, the transmission unit is provided for converting the force in the radial direction to return the elastic deformation member to the original shape into the force in the axial direction to return the movable sleeve moves from the distal end side to the initial position along the axial direction, and for transmitting the force in the axial direction to the movable sleeve. Accordingly, the movable sleeve at the distal end side in the axial direction automatically returns to the initial position. 
     According to the first aspect of the present invention, when the connector is disconnected from the mating connector, the operator holds the movable sleeve with the fingers, and pulls the connector away from the mating connector. With the force in the axial direction, the movable sleeve of the connector moves from the initial position to the proximal end side in the axial direction. 
     According to the first aspect of the present invention, the transmission unit is provided for converting the force in the axial direction to move the movable sleeve toward the proximal end side along the axial direction into the force in the radial direction, and for transmitting the force in the radial direction to the elastic deformation member. Accordingly, the elastic deformation member deforms in the radial direction. Further, when the movable sleeve moves from the initial position, the diameter control portion moves away from the outer circumferential portion of the fitting portion, so that the fitting portion is capable of expanding in the radial direction. Accordingly, the engaging portion is disengaged from the engaged portion of the mating connector, and the mating connector is pulled out from the fitting portion. 
     According to the first aspect of the present invention, when the operator releases the fingers from the movable sleeve, the force in the axial direction to move the movable sleeve toward the proximal end side in the axial direction disappears. As a result, the force in the radial direction transmitted to the elastic deformation member disappears, so that the elastic deformation member returns to the original shape thereof with own elastic force. 
     At this moment, the transmission unit is provided for converting the force in the radial direction to return the elastic deformation member to the original shape into the force in the axial direction to return the movable sleeve moves from the proximal end side to the initial position along the axial direction, and for transmitting the force in the axial direction to the movable sleeve. Accordingly, the movable sleeve at the proximal end side in the axial direction automatically returns to the initial position. 
     As described above, in the first aspect of the present invention, utilizing the force in the radial direction to return the elastic deformation member thus deformed I to the original shape, it is possible to automatically return the movable sleeve moved to the distal end side or the proximal end side in the axial direction to the initial position. In other words, it is possible to automatically return the movable sleeve to the initial position with the simple configuration, in which the elastic deformation member is disposed between the movable sleeve and the connector main body. 
     Accordingly, as opposed to the conventional configuration, in which the coil spring is provided for automatically returning the movable sleeve to the initial position, or the movable member itself is configured to elastically deform, in the first aspect of the present invention, it is possible to reduce a dimension of the connector in the axial direction, thereby reducing a size of the connector. 
     Further, in the first aspect of the present invention, it is possible to automatically return the movable sleeve to the initial position with the simple configuration, in which the elastic deformation member is disposed between the movable sleeve and the connector main body. Accordingly, as opposed to the conventional configuration, it is not necessary to elastically deform the movable sleeve itself. As a result, it is possible to increase rigidity of the movable sleeve, thereby improving durability of the connector. 
     In order to attain the objects described above, according to a second aspect of the present invention, in the connector in the first aspect, the elastic deformation member may be formed in a C character shape. Accordingly, it is possible to produce the elastic deformation member capable of elastically deforming in the radial direction with the simple configuration or the simple part. 
     In order to attain the objects described above, according to a third aspect of the present invention, in the connector in the first aspect or the second aspect, the transmission unit may include a first inclined surface formed on the outer circumferential portion of the elastic deformation member, a second inclined surface formed on the outer circumferential portion of the elastic deformation member, and a sliding contact portion extending from the inner circumferential portion of the movable sleeve inwardly in the radial direction. 
     According to the third aspect of the present invention, the first inclined surface is inclined outwardly in the radial direction from a middle portion to a distal end portion of the elastic deformation member in the axial direction. Further, the second inclined surface is inclined outwardly in the radial direction from the middle portion to a proximal end portion of the elastic deformation member in the axial direction. Further, the sliding contact portion has an end portion arranged to slide against the first inclined surface of the elastic deformation member when the movable sleeve moves toward the distal end side from the initial position, and to slide against the second inclined surface of the elastic deformation member when the movable sleeve moves toward the proximal end side from the initial position. 
     According to the third aspect of the present invention, the first inclined surface and the second inclined surface are formed on the outer circumferential portion of the elastic deformation member, so that the outer circumferential portion of the elastic deformation member has a shape recessed at the middle portion in the axial direction. When the movable sleeve is situated at the initial position, the sliding contact portion of the movable sleeve is situated on the outer circumferential portion of the elastic deformation member at the middle portion thus recessed in the axial direction. In this state, the elastic deformation member, for example, does not deform at all in the radial direction, or deforms only slightly. 
     According to the third aspect of the present invention, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the distal end side in the axial direction, the sliding contact portion of the movable sleeve is moved toward the distal end side in the axial direction while sliding against the first inclined surface of the elastic deformation member. As described above, the first inclined surface is inclined outwardly in the radial direction from the middle portion to the distal end portion of the elastic deformation member in the axial direction. Accordingly, when the sliding contact portion of the movable sleeve is moved toward the distal end side in the axial direction, the sliding contact portion pushes the first inclined surface. As a result, the elastic deformation member deforms inwardly in the radial direction. 
     According to the third aspect of the present invention, when the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force outwardly in the radial direction. Accordingly, the force is applied to the sliding contact portion of the movable sleeve contacting with the first inclined surface of the elastic deformation member. As described above, the first inclined surface is inclined outwardly in the radial direction from the middle portion to the distal end portion of the elastic deformation member in the axial direction. Accordingly, the sliding contact portion is pushed toward the proximal end side in the axial direction. As a result, the movable sleeve is pushed back to the initial position from the distal end side in the axial direction. 
     According to the third aspect of the present invention, similarly, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the proximal end side in the axial direction, the sliding contact portion of the movable sleeve pushes the second inclined surface. As a result, the elastic deformation member deforms inwardly in the radial direction. When the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force outwardly in the radial direction. Accordingly, the force is applied to the sliding contact portion of the movable sleeve contacting with the second inclined surface of the elastic deformation member. Accordingly, the sliding contact portion is pushed, and the movable sleeve is pushed back to the initial position from the proximal end side in the axial direction. 
     In the third aspect of the present invention, as described above, after the elastic deformation member is deformed, when the elastic deformation member returns to the original shape to generate the force in the radial direction, the force in the radial direction is converted into the force in the axial direction. Then, the force in the axial direction is transmitted to the movable sleeve. Accordingly, it is possible to automatically return the movable sleeve to the initial position from the distal end side or the proximal end side in the axial direction with the simple configuration. 
     In order to attain the objects described above, according to a fourth aspect of the present invention, in the connector in the first aspect or the second aspect, the transmission unit may include a first inclined surface formed on the outer circumferential portion of the elastic deformation member, a second inclined surface formed on the outer circumferential portion of the elastic deformation member, a first sliding contact portion extending from the inner circumferential portion of the movable sleeve on the proximal end side inwardly in the radial direction, and a second sliding contact portion extending from the inner circumferential portion of the movable sleeve on the proximal end side inwardly in the radial direction. 
     According to the fourth aspect of the present invention, the first inclined surface is inclined inwardly in the radial direction from a middle portion to a distal end portion of the elastic deformation member in the axial direction. Further, the second inclined surface is inclined inwardly in the radial direction from the middle portion to a proximal end portion of the elastic deformation member in the axial direction. Further, the first sliding contact portion has an end portion arranged to slide against the second inclined surface of the elastic deformation member when the movable sleeve moves toward the distal end side from the initial position. Further, the second sliding contact portion has an end portion arranged to slide against the first inclined surface of the elastic deformation member when the movable sleeve moves toward the proximal end side from the initial position. 
     According to the fourth aspect of the present invention, the first inclined surface and the second inclined surface are formed on the outer circumferential portion of the elastic deformation member, so that the outer circumferential portion of the elastic deformation member has a shape protruded at the middle portion in the axial direction. When the movable sleeve is situated at the initial position, the middle portion thus protruded in the axial direction on the outer circumferential portion of the elastic deformation member is situated between the first sliding contact portion and the second sliding contact portion of the movable sleeve. In this state, the elastic deformation member, for example, does not deform at all in the radial direction, or deforms only slightly. 
     According to the fourth aspect of the present invention, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the distal end side in the axial direction, the first sliding contact portion of the movable sleeve is moved toward the distal end side in the axial direction while sliding against the second inclined surface of the elastic deformation member. As described above, the second inclined surface is inclined inwardly in the radial direction from the middle portion to the proximal end portion of the elastic deformation member in the axial direction. Accordingly, when the first sliding contact portion of the movable sleeve is moved toward the distal end side in the axial direction, the first sliding contact portion pushes the second inclined surface. As a result, the elastic deformation member deforms inwardly in the radial direction. 
     According to the fourth aspect of the present invention, when the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force outwardly in the radial direction. Accordingly, the force is applied to the first sliding contact portion of the movable sleeve contacting with the second inclined surface of the elastic deformation member. As described above, the second inclined surface is inclined inwardly in the radial direction from the middle portion to the proximal end portion of the elastic deformation member in the axial direction. Accordingly, the first sliding contact portion is pushed toward the proximal end side in the axial direction. As a result, the movable sleeve is pushed back to the initial position from the distal end side in the axial direction. 
     According to the fourth aspect of the present invention, similarly, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the proximal end side in the axial direction, the second sliding contact portion of the movable sleeve pushes the first inclined surface. As a result, the elastic deformation member deforms inwardly in the radial direction. When the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force outwardly in the radial direction. Accordingly, the force is applied to the second sliding contact portion of the movable sleeve contacting with the second inclined surface of the elastic deformation member. Accordingly, the second sliding contact portion is pushed, and the movable sleeve is pushed back to the initial position from the proximal end side in the axial direction. 
     In the fourth aspect of the present invention, as described above, when the elastic deformation member returns to the original shape to generate the force in the radial direction, the force in the radial direction is converted into the force in the axial direction. Then, the force in the axial direction is transmitted to the movable sleeve. Accordingly, it is possible to automatically return the movable sleeve to the initial position from the distal end side or the proximal end side in the axial direction with the simple configuration. 
     In order to attain the objects described above, according to a fifth aspect of the present invention, in the connector in the first aspect or the second aspect, the transmission unit may include a first inclined surface formed on the inner circumferential portion of the elastic deformation member, a second inclined surface formed on the inner circumferential portion of the elastic deformation member, and a sliding contact portion extending from the outer circumferential portion of the cylindrical member of the connector main body on the proximal end side outwardly in the radial direction. 
     According to the fifth aspect of the present invention, the first inclined surface is inclined inwardly in the radial direction from a middle portion to a distal end portion of the elastic deformation member in the axial direction. Further, the second inclined surface is inclined inwardly in the radial direction from the middle portion to a proximal end portion of the elastic deformation member in the axial direction. Further, the sliding contact portion has an end portion arranged to slide against the second inclined surface of the elastic deformation member when the movable sleeve moves toward the distal end side from the initial position, and to slide against the first inclined surface of the elastic deformation member when the movable sleeve moves toward the proximal end side from the initial position. 
     According to the fifth aspect of the present invention, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the distal end side in the axial direction, the sliding contact portion of the movable sleeve pushes the second inclined surface of the elastic deformation member. As a result, the elastic deformation member deforms outwardly in the radial direction. 
     According to the fifth aspect of the present invention, when the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force inwardly in the radial direction. Accordingly, the force is applied to the sliding contact portion of the movable sleeve contacting with the second inclined surface of the elastic deformation member. Accordingly, the sliding contact portion is pushed toward, and the movable sleeve is pushed back to the initial position from the distal end side in the axial direction. 
     According to the fifth aspect of the present invention, similarly, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the proximal end side in the axial direction, the sliding contact portion of the movable sleeve pushes the first inclined surface. As a result, the elastic deformation member deforms outwardly in the radial direction. When the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force inwardly in the radial direction. Accordingly, the force is applied to the sliding contact portion of the movable sleeve contacting with the second inclined surface of the elastic deformation member. Accordingly, the sliding contact portion is pushed, and the movable sleeve is pushed back to the initial position from the proximal end side in the axial direction. 
     In the fifth aspect of the present invention, as described above, when the elastic deformation member returns to the original shape to generate the force in the radial direction, the force in the radial direction is converted into the force in the axial direction. Then, the force in the axial direction is transmitted to the movable sleeve. Accordingly, it is possible to automatically return the movable sleeve to the initial position from the distal end side or the proximal end side in the axial direction with the simple configuration. 
     In order to attain the objects described above, according to a sixth aspect of the present invention, in the connector in the first aspect or the second aspect, the transmission unit may include a first inclined surface formed on the inner circumferential portion of the elastic deformation member, a second inclined surface formed on the inner circumferential portion of the elastic deformation member, a first sliding contact portion extending from the outer circumferential portion of the cylindrical member of the connector main body on the proximal end side inwardly in the radial direction, and a second sliding contact portion extending from the outer circumferential portion of the cylindrical member of the connector main body on the proximal end side inwardly in the radial direction. 
     According to the sixth aspect of the present invention, the first inclined surface is inclined outwardly in the radial direction from a middle portion to a distal end portion of the elastic deformation member in the axial direction. Further, the second inclined surface is inclined outwardly in the radial direction from the middle portion to a proximal end portion of the elastic deformation member in the axial direction. Further, the first sliding contact portion has an end portion arranged to slide against the first inclined surface of the elastic deformation member when the movable sleeve moves toward the distal end side from the initial position. Further, the second sliding contact portion has an end portion arranged to slide against the second inclined surface of the elastic deformation member when the movable sleeve moves toward the proximal end side from the initial position. 
     According to the sixth aspect of the present invention, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the distal end side in the axial direction, the first sliding contact portion of the movable sleeve pushes the first inclined surface of the elastic deformation member. As a result, the elastic deformation member deforms outwardly in the radial direction. 
     According to the sixth aspect of the present invention, when the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force inwardly in the radial direction. Accordingly, the force is applied to the first sliding contact portion of the movable sleeve contacting with the first inclined surface of the elastic deformation member. Accordingly, the first sliding contact portion is pushed, and the movable sleeve is pushed back to the initial position from the distal end side in the axial direction. 
     According to the sixth aspect of the present invention, similarly, when the operator holds the movable sleeve with the fingers, and applies a force to the movable sleeve to move the movable sleeve from the initial position toward the proximal end side in the axial direction, the second sliding contact portion of the movable sleeve pushes the second inclined surface. As a result, the elastic deformation member deforms outwardly in the radial direction. When the operator releases the fingers from the movable sleeve, the elastic deformation member returns to the original shape, and generates the force inwardly in the radial direction. Accordingly, the force is applied to the second sliding contact portion of the movable sleeve contacting with the second inclined surface of the elastic deformation member. Accordingly, the second sliding contact portion is pushed, and the movable sleeve is pushed back to the initial position from the proximal end side in the axial direction. 
     In the sixth aspect of the present invention, as described above, when the elastic deformation member returns to the original shape to generate the force in the radial direction, the force in the radial direction is converted into the force in the axial direction. Then, the force in the axial direction is transmitted to the movable sleeve. Accordingly, it is possible to automatically return the movable sleeve to the initial position from the distal end side or the proximal end side in the axial direction with the simple configuration. 
     In order to attain the objects described above, according to a seventh aspect of the present invention, a pair of connectors includes a first connector and a second connector both mutually and detachably connected. 
     According to the seventh aspect of the present invention, the first connector includes a first cylindrical member formed in a cylindrical shape, a first supporting member disposed in the first cylindrical member, a first terminal supported on the first supporting member and extending in an axial direction, and a fitting portion formed on a distal end side of the first cylindrical member for receiving the second connector and engaging with the second connector. 
     According to the seventh aspect of the present invention, the fitting portion is arranged to be elastically deformable to increase a diameter thereof. Further, the fitting portion has an engaging portion on an inner circumference side thereof. When the second connector starts entering the fitting portion, the fitting portion expands in the radial direction thereof, so that the second connector is allowed to enter the fitting portion. Further, when the second connector is completely inserted into the fitting portion, the fitting portion returns to an original shape thereof, and the engaging portion engages with an engaged portion formed on the second connector. 
     According to the seventh aspect of the present invention, the second connector includes a connector main body including a second cylindrical member formed in a cylindrical shape, a second supporting member disposed in the second cylindrical member, a second terminal supported on the second supporting member on a proximal end side of the second cylindrical member and extending in an axial direction, and the engaged portion formed on an outer circumferential portion of the cylindrical member on a distal end side thereof. 
     According to the seventh aspect of the present invention, the connector further includes a movable sleeve formed in a ring shape and disposed on an outer circumference side of the connector main body to be movable along the axial direction thereof relative to the connector main body. The movable sleeve including a diameter control portion for controlling an expansion of the fitting portion of the first connector in the radial direction. When the movable sleeve is situated at an initial position, the diameter control portion moves close to or contacts with an outer circumferential portion of the fitting portion, so that the fitting portion is not capable of expanding in the radial direction. Further, when the movable sleeve moves toward the distal end side or the proximal end side from the initial position along the axial direction, the diameter control portion moves away from the outer circumferential portion of the fitting portion, so that the fitting portion is capable of expanding in the radial direction. 
     According to the seventh aspect of the present invention, the connector further includes an elastic deformation member formed in a substantially ring shape and disposed to be elastically deformable in a radial direction thereof; and an accommodating portion disposed between an outer circumferential portion of the connector main body on the proximal end side and an inner circumferential portion of the movable sleeve on the proximal end side for accommodating the elastic deformation member in a state that the fitting portion is capable of expanding in the radial direction. 
     According to the seventh aspect of the present invention, the connector further includes a transmission unit for converting a force in the axial direction generated when the movable sleeve moves toward the distal end side or the proximal end side from the initial position along the axial direction into a force in the radial direction for deforming the elastic deformation member, and for transmitting the force in the radial direction to the elastic deformation member. The transmission unit is further provided for converting the force in the radial direction to restore the elastic deformation member from the deformed state into the force in the axial direction to return the movable sleeve moves from the distal end side or the proximal end side to the initial position along the axial direction, and for transmitting the force in the axial direction to the movable sleeve. 
     In the seventh aspect of the present invention, the elastic deformation member is disposed between the movable sleeve and the connector main body. Accordingly, it is possible to automatically return the movable sleeve of the second connector to the initial position from the distal end side or the proximal end side in the axial direction with the simple configuration. As a result, it is possible to reduce a size of the second connector and improve the durability thereof. 
     As described above, in the present invention, the connector includes the lock mechanism of the push-pull type, and it is possible to reduce the size of the connector through decreasing the dimension in the axial direction. Further, it is possible to increase the rigidity of the movable sleeve. Accordingly, it is possible to prevent deformation or damage due to twisting and the like, thereby making it possible to improve the durability of the connector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an electrical connector according to a first embodiment of the present invention; 
         FIG. 2  is a sectional view showing the electrical connector according to the first embodiment of the present invention, taken along a line II-II in  FIG. 1 ; 
         FIG. 3  is a perspective view showing an elastic deformation member of the electrical connector according to the first embodiment of the present invention; 
         FIG. 4  is a view showing measurements of various portions in the electrical connector at a proximal end portion thereof, according to the first embodiment of the present invention; 
         FIG. 5  is a perspective view showing a mating connector according to the first embodiment of the present invention; 
         FIG. 6  is a sectional view showing the mating connector according to the first embodiment of the present invention; 
         FIGS. 7(A) to 7(D)  are sectional views showing a process of connecting the electrical connector to the mating connector, according to the first embodiment of the present invention; 
         FIGS. 8(A) and 8(B)  are sectional views showing a process of extracting the electrical connector from the mating connector, according to the first embodiment of the present invention; 
         FIG. 9  is a sectional view showing an electrical connector according to a second embodiment of the present invention; 
         FIG. 10  is a sectional view showing an electrical connector according to a third embodiment of the present invention; 
         FIG. 11  is a sectional view showing an electrical connector according to a fourth embodiment of the present invention; 
         FIG. 12  is a sectional view showing an electrical connector according to a fifth embodiment of the present invention; 
         FIG. 13  is a sectional view showing a pair of electrical connectors according to a sixth embodiment of the present invention; 
         FIG. 14  is a sectional view showing a mating connector according to a modified example of the present invention; and 
         FIG. 15  is a sectional view showing a mating connector according to another modified example of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder, an electrical connector according to an embodiment of the present invention will be explained with reference to the accompanying drawings. 
     First Embodiment 
     A first embodiment of the present invention will be explained.  FIGS. 1 and 2  show an electrical connector according to a first embodiment of the present invention.  FIG. 3  shows an elastic deformation member provided to the electrical connector.  FIG. 3  shows measurements of various portions in the electrical connector at a proximal end portion thereof. 
     As shown in  FIG. 1 , the electrical connector  1  according to the first embodiment of the present invention is a coaxial connector equipped with a locking mechanism of push-pull style. The electrical connector  1  is configured substantially with a connector main body  11  and a movable sleeve  21  being movable in a direction of an axis, provided around an outer circumference of the connector main body  11 . 
     As shown in  FIG. 2 , the connector main body  11  includes a cylindrical member  12 . The cylindrical member  12  forms an outer shell of the connector main body  11 . In addition, the cylindrical member  12  functions as an external terminal contacting electrically with an external conductive member of a coaxial cable (not shown) connected to another end of the electrical connector  1 . The cylindrical member  12  is configured with a cylindrical portion  13  and a cylindrical portion  14  connected to each other. 
     In the embodiment, the cylindrical portion  13  and the cylindrical portion  14  have cylindrical shapes and are made from a metallic material, respectively. In other words, the cylindrical member  12  is configured by pushing a connecting portion  13 A at a proximal end of the cylindrical portion  13  and a connecting portion  14 A at a distal end of the cylindrical portion  14  into each other when the electrical connector  1  is manufactured. 
     A central terminal  15  is provided at the proximal end portion of inside the cylindrical member  12 . The central terminal  15  contacts with a central conductive member of the coaxial cable described above. The central terminal  15  is fixed in a position of a central axis of the cylindrical member  12  with a supporting member  16 . The supporting member  16  is made from an insulating material such as a resin. A tip portion of the central terminal  15  protrudes into a fitting portion  17 , which will be described later. 
     In the embodiment, the cylindrical member  12  includes the fitting portion  17  at a distal end portion thereof. The fitting portion  17  receives a mating connector  2  (refer to  FIG. 5 ) in order to connect to the mating connector  2 . The fitting portion  17  has a space inside thereof for receiving a distal end portion of the mating connector  2 . Further, the fitting portion  17  has an opening at the distal end of the electrical connector  1 . The fitting portion  17  has a shape of collet chucks. That is, the distal end portion of the fitting portion  17  is divided into a plurality of segments  19  by a dividing groove  18  formed in the distal end portion of the fitting portion  17  at a plurality of positions in a circumferential direction. Accordingly, the fitting portion  17  is capable of expanding a diameter thereof elastically in a direction of an arrow Dr shown in  FIG. 2 . 
     In the embodiment, the fitting portion  17  includes an engaging portion  20  in an inner circumferential portion thereof. The engaging portion  20  protrudes at the distal end portion of the fitting portion  17  toward inside in a direction of the diameter thereof. The engaging portion  20  engages an engaged portion  36  of the mating connector  2  when the mating connector  2  is connected to the fitting portion  17 . 
     The movable sleeve  21  is formed in a cylindrical shape and made from, for example, a metallic material, a resin material and the like. The movable sleeve  21  is attached to the connector main body  11  so as to surround the outer circumference of the connector main body  11  from the proximal end of the connector main body  11  to the distal end of the fitting portion  17 . Further, the movable sleeve  21  is movable against the connector main body  11  in the direction of the axis, in other words, in directions of arrows Db and Df shown in  FIG. 2 . 
     In addition, the movable sleeve  21  includes a diameter control portion  22  in a distal end portion of the inner circumference thereof. The diameter control portion  22  prevents the fitting portion  17  from expanding the diameter thereof as the movable sleeve  21  is situated in an initial position, while enabling the fitting portion  17  to expand the diameter thereof as the movable sleeve  21  is moved in a direction of the proximal end or in a direction of the distal end from the initial position. 
     In the embodiment, the diameter control portion  22  protrudes from the distal end portion of the movable sleeve  21  inwardly in the direction of the diameter thereof. When the movable sleeve  21  is in the initial position, an end portion of an inner circumferential surface of the diameter control portion  22  is situated close to an outer circumferential surface of the distal end portion of the fitting portion  17 . 
     More specifically, when the movable sleeve  21  is in the initial position, the end portion of the inner circumferential surface of the diameter control portion  22  faces the outer circumferential surface of the distal end portion of the fitting portion  17  with a narrow space in between, as well as surrounding the entire outer circumferential surface of the distal end portion of the fitting portion  17 . Therefore, the fitting portion  17  is not allowed to expand the diameter thereof since the outer circumferential surface of the distal end portion of the fitting portion  17  abuts against the end portion of the inner circumferential surface of the diameter control portion  22 . 
     When the movable sleeve  21  is in the initial position, the end portion of the inner circumferential surface of the diameter control portion  22  may contact with the outer circumferential surface of the distal end portion of the fitting portion  17  so as to be moved slidingly. 
     When the movable sleeve  21  is moved from the initial position to the distal end in the direction of the axis, the diameter control portion  22  is moved from the distal end portion of the fitting portion  17  in the direction of the arrow Df, being apart from the distal end portion of the fitting portion  17 . Therefore, a relatively larger space is generated between the distal end portion of the inner circumferential surface of the diameter control portion  22  and the outer circumferential surface of the distal end portion of the fitting portion  17 . Thereby, the fitting portion  17  is allowed to expand the diameter thereof. 
     In addition, when the movable sleeve  21  is moved from the initial position to the proximal end in the direction of the axis, the diameter control portion  22  is moved in the direction of the arrow Db from the distal end portion of the fitting portion  17 , being apart from the distal end portion of the fitting portion  17 . In this case, the distal end portion of the fitting portion  17  protrudes from the movable sleeve  21 , thereby the fitting portion  17  is allowed to expand the diameter thereof. 
     In the embodiment, the movable sleeve  21  further includes a holding portion  23  at an outer circumferential surface of a proximal end portion thereof. When an operator moves the movable sleeve  21 , the operator holds the holding portion  23  of the movable sleeve  21  with fingers. The holding portion  23  has an uneven surface in order to prevent the fingers from slipping. 
     Furthermore, the electrical connector  1  includes the elastic deformation member  24 , an accommodating portion  25  and a transmission unit  26  as a mechanism so that the movable sleeve  21  moved in the direction of the axis is able to return to the initial position automatically. The accommodating portion  25  accommodates the elastic deformation member  24  and the transmission unit  26  generates force bringing back the movable sleeve  21  to the initial position by utilizing elastic force of the elastic deformation member  24 . 
     As shown in  FIG. 2 , the elastic deformation member  24  is situated between the connector main body  11  and the movable sleeve  21  at the proximal end portion of the connector main body  11 . As shown in  FIG. 3 , the elastic deformation member  24  is made from a resin material and has a substantial ring shape, namely, has a C-letter shape as a whole with a separation space  24 A. The elastic deformation member  24  is capable of being deformed with elasticity thereof in a direction of a diameter thereof. 
     In other words, the elastic deformation member  24  is deformed so as to shrink the diameter thereof by changing a width the separation space  24 A as the elastic deformation member  24  receives an external force toward inside in the direction of the diameter from an outer circumference thereof. When it stops applying the external force after the elastic deformation member  24  is deformed, the elastic deformation member  24  restores the shape as shown in  FIG. 3 , expanding the diameter thereof by the elasticity thereof. 
     In the embodiment, the accommodating portion  25 , as shown in  FIG. 2 , is situated between the outer circumference in the proximal end portion of the connector main body  11  and an inner circumference in the proximal end portion of the movable sleeve  21 . More specifically, the accommodating portion  25  has a groove shape stretching in the circumferential direction around the outer circumferential surface in the proximal end portion of the cylindrical member  12  of the connector main body  11 . 
     In the embodiment, the accommodating portion  25  accommodates the elastic deformation member  24  therein so that the elastic deformation member  24  is able to be deformed inwardly in the direction of the diameter. The accommodating portion  25  has a dimension in the direction of the diameter (a groove depth) designed so that the elastic deformation member  24  is able to be deformed inwardly in the direction of the diameter by a certain amount. The dimension of the accommodating portion  25  in the direction of the diameter will be described later. Further, the accommodating portion  25  has a dimension in the direction of the axis designed so that the elastic deformation member  24  does not move in the direction of the axis while being deformed smoothly in the direction of the diameter. More specifically, the accommodating portion  25  has the dimension in the direction of the axis slightly larger than a dimension of the elastic deformation member  24  in the direction of the axis. 
     In the embodiment, the transmission unit  26  converts a force in the direction of the axis generated by moving the movable sleeve  21  from the initial position in a direction of the proximal end or in a direction of the distal end into a force in the direction of the diameter. Further, the transmission unit  26  transmits the force in the direction of the diameter thus converted to the elastic deformation member  24  for deforming the elastic deformation member  24 . 
     Additionally, the transmission unit  26  converts a force in the direction of the diameter generated when the elastic deformation member  24  thus deformed restores the shape thereof into a force in the direction of the axis. Further, the transmission unit  26  transmits the force in the direction of the axis thus converted to the movable sleeve  21  for bringing back the movable sleeve  21  from the proximal end or the distal end to the initial position. The transmission unit  26  includes at least two inclined surfaces  27 ,  28  formed on an outer circumferential surface of the elastic deformation member  24  and a sliding contact portion  29  provided in the movable sleeve  21 . 
     As shown in  FIG. 2 , the inclined surface  27  inclines by a predetermined angle toward outside in the direction of the diameter, from a middle portion to the distal end of the elastic deformation member  24  in the direction of the axis. Further, the inclined surface  27  extends around the entire outer circumferential surface of the elastic deformation member  24 . 
     In the embodiment, the inclined surface  28  inclines by a predetermined angle toward outside in the direction of the diameter, from the middle portion to the proximal end of the elastic deformation member  24  in the direction of the axis. The inclined surface  28  extends around the entire outer circumferential surface of the elastic deformation member  24 . With the inclined surfaces  27  and  28 , the elastic deformation member  24  has a shape constricted at the middle portion thereof in the direction of the axis. 
     In the embodiment, the sliding contact portion  29  protrudes from the inner circumference at a proximal end side of the movable sleeve  21  toward inside in the direction of the diameter. When the movable sleeve  21  is in the initial position, the sliding contact portion  29  is situated in a neutral position Po as shown in  FIG. 2 . When the sliding contact portion  29  is in the neutral position Po, an end portion of the sliding contact portion  29  is close to or contacts with the middle portion of the elastic deformation member  24  where the inclined surfaces  27  and  28  contacts with each other. At this point, the elastic deformation member  24  is not deformed or is slightly deformed in the direction of the diameter inwardly due to the contact of the sliding contact portion  29  and the like. 
     When the movable sleeve  21  is moved from the initial position in a direction of the distal end, the sliding contact portion  29  is moved from the neutral position Po to a pressing position Pf. The end portion of the sliding contact portion  29  contacts slidingly with the inclined surface  27  of the elastic deformation member  24  as the sliding contact portion  29  is moved from the neutral position Po to the pressing position Pf. Thereby, the sliding contact portion  29  presses the inclined surface  27  of the elastic deformation member  24 . As a result, the elastic deformation member  24  is considerably deformed inwardly in the direction of the diameter. 
     When the movable sleeve  21  is moved from the initial position in a direction of the proximal end, the sliding contact portion  29  is moved from the neutral position Po to a pressing position Pb. The end portion of the sliding contact portion  29  contacts slidingly with the inclined surface  28  of the elastic deformation member  24  as the sliding contact portion  29  is moved from the neutral position Po to the pressing position Pb. Thereby, the sliding contact portion  29  presses the inclined surface  28  of the elastic deformation member  24 . As a result, the elastic deformation member  24  is considerably deformed inwardly in the direction of the diameter. 
     In the embodiment, the sliding contact portion  29  may extend around the entire inner circumference of the movable sleeve  21  as an elongated protrusion. The sliding contact portion  29  also may be divided into a plurality of protruding pieces arranged in the inner circumference of the movable sleeve  21  with a constant or inconstant interval in the circumferential direction. 
     Hereunder, relation about measurements of various portions in the electrical connector  1  at a proximal end portion thereof will be explained. As shown in  FIG. 4 , when an inner diameter of the cylindrical member  12  where the accommodating portion  25  is situated is a; a thickness of the elastic deformation member  24  at the distal end portion or at the proximal end portion in the direction of the axis is b; and an inner diameter of the movable sleeve  21  where the sliding contact portion  29  is situated is c, relation among a, b and c satisfies a following expression (1):
 
 c&lt;a+ 2 b   (1)
 
     According to the expression (1) above, the movable sleeve  21  is controlled movement thereof in the direction of the axis, so that the diameter control portion  22  is able to admit or stop expanding the diameter of the fitting portion  17  appropriately. Consequently, it is possible to prevent the movable sleeve  21  from coming off the connector main body  11  due to the movement in the direction of the axis of the movable sleeve  21  beyond the control described above. 
     Therefore, as shown in  FIG. 4 , when the relation among a, b and c satisfies the expression (1), the sliding contact portion  29  is pressed against the inclined surface  27  of the elastic deformation member  24  as the movable sleeve  21  moves in the direction of the distal end from the initial position. Accordingly, the elastic deformation member  24  is considerably deformed inwardly in the direction of the diameter. 
     When an inner circumferential surface of the elastic deformation member  24  thus deformed contacts with a bottom surface of the groove shape of the accommodating portion  25 , the sliding contact portion  29  abuts against the distal end of the inclined surface  27  of the elastic deformation member  24 . As a result, the movable sleeve  21  is not allowed to move further in the direction of the distal end. Similarly, when the movable sleeve  21  moves in the direction of the proximal end from the initial position, the sliding contact portion  29  is pressed against the inclined surface  28  of the elastic deformation member  24 . 
     When the inner circumferential surface of the elastic deformation member  24  thus deformed contacts with the bottom surface of the groove shape of the accommodating portion  25 , the sliding contact portion  29  abuts against the proximal end of the inclined surface  28  of the elastic deformation member  24 . As a result, the movable sleeve  21  is not allowed to move further in the direction of the proximal end. 
     The electrical connector  1  configured as described above is manufactured as described below. First, as shown in  FIG. 2 , the central terminal  15  is attached to the cylindrical portion  13  with the supporting member  16 . Then the cylindrical portion  13  is inserted into the movable sleeve  21  from the proximal end of the movable sleeve  21 . At this time, the connecting portion  13 A of the cylindrical portion  13  is arranged so as to correspond to the sliding contact portion  29 . Next, the elastic deformation member  24  is inserted into the movable sleeve  21  from the proximal end of the movable sleeve  21  as being deformed inwardly in the direction of the axis. 
     In the embodiment, the elastic deformation member  24  is placed between the inner circumference of the movable sleeve  21  and an outer circumference of the connecting portion  13 A of the cylindrical portion  13 . Accordingly, the middle portion of the elastic deformation member  24  is situated at a corresponding position to the sliding contact portion  29 . Further, a distal end portion of the connecting portion  14 A of the cylindrical portion  14  is inserted into the movable sleeve  21  from the proximal end of the movable sleeve  21 . 
     At this time, the connecting portion  14 A is arranged so that the distal end portion of the connecting portion  14 A is situated into a space formed between the connecting portion  13 A of the cylindrical portion  13  and the elastic deformation member  24 . Then the connecting portion  14  thus arranged is inserted into the movable sleeve  21 . Thereby, the electrical connector  1  is assembled completely. 
     As described above, the cylindrical member  12  includes the cylindrical portion  13  and the cylindrical portion  14 . The cylindrical portion  13  provides a sidewall on a distal end side of the accommodating portion  25  and the cylindrical portion  14  provides a sidewall on the proximal end side of the accommodating portion  25 . The cylindrical portions  13  and  14  are connected to each other upon manufacturing the electrical connector  1 . Consequently, it is possible to easily manufacture the electrical connector  1  with the elastic deformation member  24  irremovable from the accommodating portion  25 . 
       FIGS. 5 and 6  show the mating connector  2  to be connected to the electrical connector  1 . As shown in  FIGS. 5 and 6 , the mating connector  2  includes an outer cylindrical member  31 . The outer cylindrical member  31  forms an outer shell of the mating connector  2 . In addition, the outer cylindrical member  31  functions as an external terminal. The outer cylindrical member  13  is made from a metallic material and has a tiered cylindrical shape. Other end of the mating connector  2  is directly attached to, for example, a housing of a device, a circuit board and so on (not shown). The outer cylindrical member contacts electrically, for example, with a ground of the device, the circuit board and so on. 
     In the embodiment, the mating connector  2  includes a mating terminal  32  inside the outer cylindrical member  31  thereof. The mating terminal  32  contacts electrically, for example, with a signal line of the device, the circuit board and so on. The mating terminal  32  is fixed in a position of a central axis of the outer cylindrical member  31  with a supporting member  33 . The supporting member  33  is made from an insulating material such as a resin. The mating terminal  32  includes a contact hole  34  at a tip portion thereof. The tip portion of the central terminal  15  of the electrical connector  1  enters the contact hole  34 . 
     In the embodiment, the outer cylindrical member  31  includes an insertion portion  35  at a distal end portion thereof. The insertion portion  35  is inserted and fitted into the fitting portion  17  of the electrical connector  1 . The mating connector  2  further includes the engaged portion  36 . The engaged portion  36  is situated at a position being apart from a distal end of the insertion portion  35  by a predetermined distance in a direction of a proximal end portion. The engaged portion  36  is a depression surrounding an entire outer circumference of the insertion portion  35 . A shape of the depression corresponds to a shape of the engaging portion  20  provided on the inner circumference of the fitting portion  17 . 
     When the insertion portion  35  of the mating connector  2  is inserted into the fitting portion  17  of the electrical connector  1  as the movable sleeve  21  of the electrical connector  1  is moved in the direction of the distal end from the initial position, an outer circumference surface of the insertion portion  35  contacts slidingly with an end surface of the engaging portion  20  of the electrical connector  1 . 
     Further, the fitting portion  17  expands the diameter thereof when the insertion portion  35  of the mating connector  2  is inserted into the fitting portion  17  of the electrical connector  1  further. Furthermore, when the insertion portion  35  of the mating connector  2  reaches inside of the fitting portion  17  of the electrical connector  1 , the engaging portion  20  of the electrical connector  1  enters the engaged portion  36  of the mating connector  2 . Thereby the engaging portion  20  and the engaged portion  36  engage each other. 
       FIGS. 7(A) to 7(D)  show a process of connecting the electrical connector  1  to the mating connector  2 .  FIGS. 8(A) and 8(B)  show a process of extracting the electrical connector  1  from the mating connector  2 . 
     As shown in  FIG. 7(A) , when the electrical connector  1  is connected to the mating connector  2 , the operator holds the holding portion  23  of the movable sleeve  21  with the fingers. Then, the operator applies force so that the electrical connector  1  is pushed toward the mating connector  2  as the distal end portion of the fitting portion  17  of the electrical connector  1  and the distal end portion of the insertion portion  35  of the mating connector  2  contact with each other. 
     With the force described above, the movable sleeve  21  of the electrical connector  1  is moved in the direction of the distal end from the initial position. When the movable sleeve  21  of the electrical connector  1  is moved in the direction of the distal end from the initial position, the diameter control portion  22  is moved being apart from the outer circumferential surface of the distal end portion of the fitting portion  17 . 
     Therefore, the fitting portion  17  is allowed to expand the diameter thereof. In addition, as the movable sleeve  21  is moved as described above, the sliding contact portion  29  is moved from the neutral position Po to the pressing position Pf (refer to  FIG. 2 ). Therefore, the end portion of the sliding contact portion  29  contacts slidingly with the inclined surface  27  of the elastic deformation member  24 . Thereby, the sliding contact portion  29  is pressed against the inclined surface  27 . As a result, the elastic deformation portion  24  is deformed inwardly in the direction of the diameter. 
     Next, as shown in  FIG. 7(B) , when the operator pushes the electrical connector  1  toward the mating connector  2  further, the insertion portion  35  of the mating connector  2  enters the fitting portion  17  of the electrical connector  1 . As the insertion portion  35  of the mating connector  2  enters the fitting portion  17  of the electrical connector  1  further, the fitting portion  17  expands the diameter thereof. 
     As shown in  FIG. 7(C) , when the insertion portion  35  of the mating connector  2  reaches inside of the fitting portion  17  of the electrical connector  1 , the central terminal  15  of the electrical connector  1  fits into the contact hole  34  of the mating terminal  32  of the mating connector  2 . Additionally, the engaging portion  20  engages the engaged portion  36 . The operator recognizes the electrical connector  1  is connected to the mating connector  2  certainly, with sound and vibration generated as the engaging portion  20  engages the engaged portion  36 . 
     Next, as shown in  FIG. 7(D) , as the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , the force moving the movable sleeve  21  toward the distal end from the initial position disappears. Accordingly, the force deforming the elastic deformation member  24  inwardly in the direction of the diameter also disappears. Therefore, the elastic deformation member  24  restores the shape thereof to an initial shape with the elasticity thereof. 
     For this reason, a force restoring the shape of the elastic deformation member  24  is applied to the sliding contact portion  29  of the movable sleeve  21  toward outside in the direction of the diameter, since the sliding contact portion  29  abuts against the inclined surface  27  of the elastic deformation member  24 . Therefore, the sliding contact portion  29  is pushed toward the proximal end in the direction of the axis. Consequently, the movable sleeve  21  thus pushed to the distal end side returns to the initial position thereof as the sliding contact portion  29  returns from the pressing position Pf to the neutral position Po (refer to  FIG. 2 ). 
     When the movable sleeve  21  returns to the initial position, the diameter control portion  22  comes closer to the outer circumferential surface of the distal end portion of the fitting portion  17 . Thereby, the fitting portion  17  is not allowed to expand the diameter thereof. Accordingly, the engaging portion  20  of the electrical connector  1  is fixed in a state of engaging the engaged portion  36  of the mating connector  2 . As a result, the electrical connector  1  and the mating connector  2  are locked as connecting to each other. 
     Next, as shown in  FIG. 8(A) , when the electrical connector  1  is extracted from the mating connector  2 , the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the electrical connector  1  is pulled so as to be apart from the mating connector  2 . 
     With the force described above, the movable sleeve  21  of the electrical connector  1  is moved in the direction of the proximal end from the initial position. When the movable sleeve  21  of the electrical connector  1  is moved in the direction of the proximal end from the initial position, the diameter control portion  22  is moved so as to be apart from the distal end portion of the fitting portion  17 . Thereby, the electrical connector  1  and the mating connector  2  are unlocked since the fitting portion  17  is allowed to expand the diameter thereof. 
     Further, as the movable sleeve  21  is moved as described above, the sliding contact portion  29  is moved from the neutral position Po to the pressing position Pb (refer to  FIG. 2 ). Therefore, the end portion of the sliding contact portion  29  contacts slidingly with the inclined surface  28  of the elastic deformation member  24 . Thereby, the sliding contact portion  29  is pressed against the inclined surface  28  of the elastic deformation member  24 . As a result, the elastic deformation portion  24  is deformed inwardly in the direction of the diameter. 
     Next, as shown in  FIG. 8(B) , when the operator pulls the electrical connector  1  so as to be apart from the mating connector  2  further, the engaging portion  20  of the electrical connector  1  expands the diameter of the fitting portion  17 , being removed from the engaged portion  36  of the mating connector  2 . As a result, the central terminal  15  of the electrical connector  1  comes off the contact hole  34  of the mating terminal  32  of the mating connector  2 . Further, the insertion portion  35  of the mating connector  2  is pulled out of the fitting portion  17  of the electrical connector  1 . Thereby, the electrical connector  1  is extracted from the mating connector  2 . 
     When the electrical connector  1  is extracted from the mating connector  2 , the force moving the movable sleeve  21  toward the proximal end disappears. Accordingly, the force deforming the elastic deformation member  24  inwardly in the direction of the diameter also disappears. Therefore, the elastic deformation member  24  restores the shape thereof to the initial shape with the elasticity thereof. 
     For this reason, a force restoring the shape of the elastic deformation member  24  is applied to the sliding contact portion  29  of the movable sleeve  21  toward outside in the direction of the diameter, since the sliding contact portion  29  abuts against the inclined surface  28  of the elastic deformation member  24 . Therefore, the sliding contact portion  29  is pushed toward the distal end in the direction of the axis. Consequently, the movable sleeve  21  thus pushed to the proximal end side returns to the initial position thereof as the sliding contact portion  29  returns from the pressing position Pb to the neutral position Po (refer to  FIG. 2 ). 
     As described above, according to the first embodiment of the present invention, the electrical connector  1  enables to obtain a function which automatically returns the movable sleeve  21  to the initial position with a simple configuration such that arranging the elastic deformation member  24  between the movable sleeve  21  and the connector main body  11 . Consequently, as compared to the case that having a coiled spring or having the movable sleeve capable of elastic deformation as a mechanism for returning automatically the movable sleeve to the initial position, the electrical connector  1  is able to have lesser dimension in the direction of the axis. As a result, it enables the electrical connector  1  to be downsized. 
     In addition, according to the first embodiment of the present invention, the electrical connector  1  enables to increase rigidity of the movable sleeve  21  thereof, since it is not necessary to deform the movable sleeve  21  elastically. Accordingly, it is possible to prevent the movable sleeve  21  from deformation or being damaged due to being twisted forcibly and the like. Consequently, the electrical connector  1  is able to obtain higher durability. 
     Second Embodiment 
     A second embodiment of the present invention will be explained next.  FIG. 9  is a sectional view showing an electrical connector according to a second embodiment of the present invention. In  FIG. 9 , components unchanged from the first embodiment have the same numeral references as  FIGS. 1 to 8(B)  and explanations thereof will be omitted. 
     As shown in  FIG. 9 , the electrical connector  41  according to the second embodiment of the present invention includes an elastic deformation member  42 ; an accommodating portion  43  and a transmission unit  44  as the mechanism for returning the movable sleeve  21  moved by the operator in the direction of the axis to the initial position automatically. The accommodating portion  43  accommodates the elastic deformation member  42  and the transmission unit  44  generates force bringing back the movable sleeve  21  to the initial position by utilizing elastic force of the elastic deformation member  42 . 
     The elastic deformation member  42  is made from a resin material and has a C-letter shape as a whole. The elastic deformation member  42  is capable of being deformed with elasticity thereof in a direction of a diameter thereof. These aspects are the same as aspects of the elastic deformation member  24  in the first embodiment. 
     The accommodating portion  43  is situated between the outer circumference in the proximal end portion of the connector main body  11  and the inner circumference in the proximal end portion of the movable sleeve  21 . The accommodating portion  43  includes grooves  43 A and  43 B. The groove  43 A stretches in the circumferential direction around the outer circumferential surface in the proximal end portion of the cylindrical member  12  of the connector main body  11 . 
     In the embodiment, the groove  43 B stretches in the circumferential direction around an inner circumferential surface in the proximal end portion of the movable sleeve  21  so as to face the groove  43 A. The accommodating portion  43  accommodates the elastic deformation member  42  therein so that the elastic deformation member  42  is able to be deformed toward inside in the direction of the diameter while being disabled to be moved in the direction of the axis. 
     In the embodiment, the transmission unit  44  converts the force in the direction of the axis generated by moving the movable sleeve  21  from the initial position in the direction of the proximal end or in the direction of the distal end into the force in the direction of the diameter. Further, the transmission unit  44  transmits the force in the direction of the diameter thus converted to the elastic deformation member  42  for deforming the elastic deformation member  42 . 
     Additionally, the transmission unit  44  converts the force in the direction of the diameter generated when the elastic deformation member  42  thus deformed restores the shape thereof into the force in the direction of the axis. Further, the transmission unit  44  transmits the force in the direction of the axis thus converted to the movable sleeve  21  for bringing back the movable sleeve  21  from the proximal end or the distal end to the initial position. The transmission unit  44  includes at least two inclined surfaces  45  and  46  formed on the outer circumferential surface of the elastic deformation member  42  and two sliding contact portions  47  and  48  provided in the movable sleeve  21 . 
     In the embodiment, the inclined surface  45  inclines by a predetermined angle toward inside in the direction of the diameter, from the middle portion to the distal end portion of the elastic deformation member  42  in the direction of the axis. The inclined surface  45  extends around the entire outer circumferential surface of the elastic deformation member  42 . 
     In the embodiment, the inclined surface  46  inclines by a predetermined angle toward inside in the direction of the diameter, from the middle portion to the proximal end portion of the elastic deformation member  42  in the direction of the axis. The inclined surface  46  extends around the entire outer circumferential surface of the elastic deformation member  42 . 
     In the embodiment, the elastic deformation member  42  has a shape expanded at the middle portion thereof in the direction of the axis, with the inclined surfaces  45  and  46 . Hereunder, a portion of the elastic deformation member  42  thus expanded in the middle portion thereof in the direction of the axis is called an expanded portion  42 A. 
     In the embodiment, the sliding contact portions  47  and  48  are provided in the inner circumference at a proximal end side of the movable sleeve  21 . The sliding contact portions  47  and  48  are situated in positions corresponding to the inclined surfaces  45  and  46  of the elastic deformation member  42 , respectively. 
     More specifically, the sliding contact portion  47  is provided in a circumferential end portion at the distal end in the direction of the axis of the groove  43 B formed in the inner circumferential surface in the proximal end portion of the movable sleeve  21 . Similarly, the sliding contact portion  48  is provided in the circumferential end portion at the proximal end in the direction of the axis of the groove  43 B formed in the inner circumferential surface in the proximal end portion of the movable sleeve  21 . 
     When the movable sleeve  21  is in the initial position, the expanded portion  42 A of the elastic deformation member  42  is situated between the sliding contact portions  47  and  48 . Further, end portions of the sliding contact portions  47  and  48  are close to or contact with the inclined surfaces  45  and  46 , respectively. At this point, the elastic deformation member  42  is not deformed; is slightly deformed inwardly in the direction of the diameter due to contact of an end portion of the expanded portion  42 A with a bottom surface of the groove  43 B; or is slightly deformed inwardly in the direction of the diameter due to contact of the sliding contact portions  47  and  48  with the inclined surface  45  and  46 , respectively. 
     When the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the movable sleeve  21  is pushed toward the distal end in the direction of the axis, the movable sleeve  21  is moved in the direction of the distal end from the initial position. Therefore, the sliding contact portion  48  is moved toward the distal end in the direction of the axis, contacting slidingly with the inclined surface  46 . 
     As a result, the elastic deformation member  42  is considerably deformed inwardly in the direction of the diameter since the inclined surface  46  is pushed against the sliding contact portion  48 . Further, when the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , a force toward outside in the direction of the diameter to restore the shape of the elastic deformation member  42  is applied to the sliding contact portion  48  which is in contact with the inclined surface  46 . Therefore, the sliding contact portion  48  is pushed toward the proximal end in the direction of the axis. Consequently, the movable sleeve  21  at the distal end side returns to the initial position thereof. 
     In addition, when the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the movable sleeve  21  is pushed toward the proximal end in the direction of the axis, the movable sleeve  21  is moved in the direction of the proximal end from the initial position. Therefore, the sliding contact portion  47  is moved toward the proximal end in the direction of the axis, contacting slidingly with the inclined surface  45 . 
     As a result, the elastic deformation member  42  is considerably deformed inwardly in the direction of the diameter since the inclined surface  45  is pushed against the sliding contact portion  47 . Further, when the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , a force toward inside in the direction of the diameter to restore the shape of the elastic deformation member  42  is applied to the sliding contact portion  47  which is in contact with the inclined surface  45 . Therefore, the sliding contact portion  47  is pushed toward the distal end in the direction of the axis. Consequently, the movable sleeve  21  at the distal end side returns to the initial position thereof. 
     It is possible that the electrical connector  41  according to the second embodiment of the invention is able to obtain the same functionality and effect with the electrical connector  1  in the first embodiment of the present invention. 
     Third Embodiment 
     A third embodiment of the present invention will be explained next.  FIG. 10  is a sectional view showing an electrical connector according to a third embodiment of the present invention. In  FIG. 10 , components unchanged from the first embodiment have the same numeral references as  FIGS. 1 to 8(B)  and explanations thereof will be omitted. 
     As shown in  FIG. 10 , the electrical connector  51  according to the third embodiment of the present invention includes an elastic deformation member  52  as a part of the mechanism for returning the movable sleeve  21  moved by the operator in the direction of the axis to the initial position automatically. In the embodiment, the elastic deformation member  52  is made from a metallic material by press working. 
     In the embodiment, the elastic deformation member  52  has a C-letter shape as a whole. The elastic deformation member  52  is capable of being deformed with elasticity thereof in the direction of the diameter thereof. The elastic deformation member  52  includes inclined surfaces  53  and  54  in the outer circumferential surface thereof. 
     In the embodiment, the inclined surface  53  inclines from the middle portion of the elastic deformation portion  52  to the distal end portion in the direction of the axis, and toward outside in the direction of a diameter. The inclined surface  54  inclines from the middle portion of the elastic deformation portion  52  to the proximal end portion in the direction of the axis, and toward outside in the direction of a diameter. Other configuration of the electrical connector  51  is the same with the configuration of the electrical connector  1  in the first embodiment of the present invention. 
     In addition, the electrical connector  51  has the same function with the electrical connector  1  in the first embodiment of the present invention, that is, the function to move the movable sleeve  21  to the initial position automatically, utilizing the force toward outside in the direction of the diameter generated as the elastic deformation member  52  restores the shape thereof after deformed inwardly in the direction of the diameter. 
     It is possible that the electrical connector  51  according to the third embodiment of the invention is able to obtain the same functionality and effect with the electrical connector  1  in the first embodiment of the present invention. 
     Fourth Embodiment 
     A fourth embodiment of the present invention will be explained next.  FIG. 11  is a sectional view showing an electrical connector according to a fourth embodiment of the present invention. In  FIG. 11 , components unchanged from the first embodiment have the same numeral references as  FIGS. 1 to 8(B)  and explanations thereof will be omitted. 
     As shown in  FIG. 11 , the electrical connector  61  according to the fourth embodiment of the present invention includes an elastic deformation member  62  made from a resin material and has a C-letter shape as a whole. The elastic deformation member  62  is capable of being deformed outwardly in the direction of the diameter with elasticity thereof. Further, the electrical connector  61  further includes an accommodating portion  63  for accommodating the elastic deformation member  62 . The accommodating portion  63  has a groove shape stretching in the circumferential direction in the inner surface of the movable sleeve  21  at the proximal end portion. 
     Furthermore, the electrical connector  61  includes a transmission unit  64  for generating a force bringing back the movable sleeve  21  to the initial position by utilizing elastic force of the elastic deformation member  62 . The transmission unit  64  includes at least inclined surfaces  65  and  66 , a sliding contact portion  67 . 
     In other words, the elastic deformation member  62  includes the inclined surfaces  65  and  66  formed on the inner circumference of the elastic deformation member  62 . The inclined surface  65  inclines from the middle portion of the elastic deformation portion  62  to the distal end portion in the direction of the axis, and toward inside in the direction of a diameter. 
     In the embodiment, the inclined surface  66  inclines from the middle portion of the elastic deformation portion  62  to the proximal end portion in the direction of the axis, and toward inside in the direction of a diameter. Further, the sliding contact portion  67  is provided in the outer circumferential surface at the proximal end side of the cylindrical member  12  of the connector main body  11 . The sliding contact portion  67  extends toward outside in the direction of the diameter. 
     In the embodiment, the sliding contact portion  67  may extend around the entire outer circumference at the proximal end side of the cylindrical member  12  as an elongated protrusion. The sliding contact portion  67  also may be divided into a plurality of protruding pieces arranged in the outer circumference at the proximal end side of the cylindrical member  12  with a constant or inconstant interval in the circumferential direction. 
     When the movable sleeve  21  is in the initial position, an end portion of the sliding contact portion  67  is close to or contacts with the middle portion in the direction of the axis of the elastic deformation member  62 , where the inclined surfaces  65  and  66  contacts with each other. At this point, the elastic deformation member  62  is not deformed or is slightly deformed in the direction of the diameter outwardly. 
     When the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the movable sleeve  21  is pushed toward the distal end in the direction of the axis, the movable sleeve  21  is moved in the direction of the distal end from the initial position. Therefore, the elastic deformation portion  62  is moved in the direction of the distal end. 
     Accordingly, the sliding contact portion  67  contacts slidingly with the inclined surface  66 . Thereby, the sliding contact portion  67  presses the inclined surface  66 . As a result, the elastic deformation member  62  is considerably deformed outwardly in the direction of the diameter. Further, when the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , a force toward inside in the direction of the diameter for restoring the shape of the elastic deformation member  62  is applied to the sliding contact portion  67  which is in contact with the inclined surface  66 . Therefore, the sliding contact portion  67  is pushed toward the proximal end in the direction of the axis. Consequently, the movable sleeve  21  moved to the distal end side returns to the initial position thereof. 
     In addition, when the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the movable sleeve  21  is pushed toward the proximal end in the direction of the axis, the movable sleeve  21  is moved in the direction of the proximal end from the initial position. Therefore, the elastic deformation portion  62  is moved in the direction of the proximal end. Accordingly, the sliding contact portion  67  contacts slidingly with the inclined surface  65 . Thereby, the sliding contact portion  67  presses the inclined surface  65 . As a result, the elastic deformation member  62  is considerably deformed outwardly in the direction of the diameter. 
     Further, when the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , a force toward inside in the direction of the diameter for restoring the shape of the elastic deformation member  62  is applied to the sliding contact portion  67  which is in contact with the inclined surface  65 . Therefore, the sliding contact portion  67  is pushed toward the distal end in the direction of the axis. Consequently, the movable sleeve  21  moved to the proximal end side returns to the initial position thereof. 
     It is possible that the electrical connector  61  according to the fourth embodiment of the invention is able to obtain the same functionality and effect with the electrical connector  1  in the first embodiment of the present invention. 
     Fifth Embodiment 
     A fifth embodiment of the present invention will be explained next.  FIG. 12  is a sectional view showing an electrical connector according to a fifth embodiment of the present invention. In  FIG. 12 , components unchanged from the first embodiment have the same numeral references as  FIGS. 1 to 8(B)  and explanations thereof will be omitted. 
     As shown in  FIG. 12 , the electrical connector  71  according to the fifth embodiment of the present invention includes an elastic deformation member  72 . In the embodiment, the elastic deformation member  72  is made from a resin material and has a C-letter shape as a whole. The elastic deformation member  72  is capable of being deformed with elasticity thereof in the direction of the diameter thereof outwardly. An accommodating portion  73  for accommodating the elastic deformation member  72  therein includes grooves  73 A and  73 B. 
     In the embodiment, the groove  73 A stretches in the circumferential direction around the outer circumferential surface in the proximal end portion of the cylindrical member  12  of the connector main body  11 . The groove  73 B stretches in the circumferential direction around an inner circumferential surface in the proximal end portion of the movable sleeve  21  so as to face the groove  73 A. 
     In the embodiment, the transmission unit  74  generates the force to move the movable sleeve  21  to the initial position, utilizing the elasticity of the elastic deformation member  72 . The transmission unit  74  includes at least inclined surfaces  75  and  76  and sliding contact portions  77  and  78 . That is, elastic deformation member  72  includes the inclined surfaces  75  and  76  on an inner circumference thereof. 
     In the embodiment, the inclined surface  75  inclines from the middle portion to the distal end portion of the elastic deformation member  72  in the direction of the axis, toward outside in the direction of the diameter. The inclined surface  76  inclines from the middle portion to the proximal end portion of the elastic deformation member  72  in the direction of the axis, toward outside in the direction of the diameter. 
     In the embodiment, the elastic deformation member  72  has a shape expanded at the middle portion thereof inwardly in the direction of the axis, with the inclined surfaces  75  and  76 . Hereunder, a portion of the elastic deformation member  72  thus expanded in the middle portion thereof in the direction of the axis is called an expanded portion  72 A. Further, the cylindrical member  12  of the connector main body  11  includes a groove  73 A in the inner circumference in the proximal end portion thereof. The sliding contact portion  77  is provided in a circumferential end portion at the distal end in the direction of the axis of the groove  73 A. The sliding contact portion  78  is provided in the circumferential end portion at the proximal end in the direction of the axis of the groove  73 A. 
     When the movable sleeve  21  is in the initial position, the expanded portion  72 A of the elastic deformation member  72  is situated between the sliding contact portions  77  and  78 . Further, end portions of the sliding contact portions  77  and  78  are close to or contact with the inclined surfaces  75  and  76 , respectively. At this point, the elastic deformation member  72  is not deformed; is slightly deformed in the direction of the diameter inwardly due to contact of an end portion of the expanded portion  72 A with a bottom surface of the groove  73 A; or is slightly deformed in the direction of the diameter inwardly due to contact of the sliding contact portions  77  and  78  with the inclined surface  75  and  76 , respectively. 
     When the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the movable sleeve  21  is pushed toward the distal end, the movable sleeve  21  is moved in the direction of the distal end from the initial position. Therefore, the sliding contact portion  77  is moved toward the distal end in the direction of the axis, contacting slidingly with the inclined surface  75 . As a result, the elastic deformation member  72  is considerably deformed outwardly in the direction of the diameter since the inclined surface  75  is pushed against the sliding contact portion  77 . 
     Further, when the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , a force toward inside in the direction of the diameter to restore the shape of the elastic deformation member  72  is applied to the sliding contact portion  77  which is in contact with the inclined surface  75 . Therefore, the sliding contact portion  77  is pushed toward the proximal end in the direction of the axis. Consequently, the movable sleeve  21  moved to the distal end side returns to the initial position thereof. 
     In addition, when the operator holds the holding portion  23  of the movable sleeve  21  with the fingers and applies force so that the movable sleeve  21  is pushed toward the proximal end, the movable sleeve  21  is moved in the direction of the proximal end from the initial position. Therefore, the sliding contact portion  78  is moved toward the proximal end in the direction of the axis, contacting slidingly with the inclined surface  76 . As a result, the elastic deformation member  72  is considerably deformed outwardly in the direction of the diameter since the inclined surface  76  is pushed against the sliding contact portion  78 . 
     Further, when the fingers of the operator are taken off from the holding portion  23  of the movable sleeve  21 , a force toward inside in the direction of the diameter to restore the shape of the elastic deformation member  72  is applied to the sliding contact portion  78  which is in contact with the inclined surface  76 . Therefore, the sliding contact portion  78  is pushed toward the distal end in the direction of the axis. Consequently, the movable sleeve  21  moved to the proximal end side returns to the initial position thereof. 
     It is possible that the electrical connector  71  according to the fifth embodiment of the invention is able to obtain the same functionality and effect with the electrical connector  1  in the first embodiment of the present invention. 
     Sixth Embodiment 
     A sixth embodiment of the present invention will be explained next.  FIG. 13  is a sectional view showing a pair of electrical connectors according to a sixth embodiment of the present invention. The pair of the electrical connectors includes a first electrical connector  81  (a first connector) and a second electrical connector  82  (a second connector) connected to each other. 
     The first connector  81  includes a cylindrical member  83  having a cylindrical shape; a central terminal  85  extending in the direction of the axis and fixed in the cylindrical member  83  with a supporting member  84 ; and a fitting portion  86  at a distal end portion of the cylindrical member  83 , for receiving the second connector  82  upon being connected to the second connector  82 . 
     In the embodiment, the fitting portion  86  is capable of expanding a diameter thereof elastically. Furthermore, the fitting portion  86  includes an engaging portion  87  in an inner circumference thereof. When the second connector  82  is inserted into the fitting portion  86 , the fitting portion  86  expands the diameter thereof. Thereby the second connector  2  is able to be inserted into the fitting portion  86  further. When the second connector  82  is completely inserted into the fitting portion  86 , the engaging portion  87  engages an engaged portion  95  provided in the second connector  82  as the fitting portion  86  restores a shape thereof to an initial shape. 
     In addition, the cylindrical member  83  further includes a reinforcement guide  88  on an outer circumference thereof. The reinforcement guide  88  has a cylindrical shape. 
     The second connector  82  is substantially configured with a connector main body  89  and a movable sleeve  90 . The movable sleeve  90  is able to move against the connector main body  89  in the direction of the axis. 
     The connector main body  89  includes a cylindrical member  91  having a cylindrical shape and a central terminal  93  fixed in the cylindrical member  91  at the proximal side of the cylindrical member  91  with a supporting member  92 . The central terminal  93  extends in the direction of the axis. Furthermore, the cylindrical member  91  includes an insertion portion  94  at a distal end portion thereof. 
     In the embodiment, the insertion portion  94  is inserted and fitted into the fitting portion  86  of the first connector  81 . The second connector  82  further includes the engaged portion  95 . The engaged portion  95  is situated at the proximal end on an outer circumferential surface of the insertion portion  94  of the cylindrical member  91 . 
     In the embodiment, the movable sleeve  90  is formed in a cylindrical shape. The movable sleeve  90  includes diameter control portions  96  and  97  in a distal end portion and a middle portion thereof in the direction of the axis, respectively. The diameter control portions  96  and  97  control expansion of a diameter of the fitting portion  86  of the first connector  81 . 
     When a distal end portion of the fitting portion  86  of the first connector  81  and a distal end portion of the insertion portion  94  of the second connector  82  contact with each other upon connecting the first connector  81  and the second connector  82  to each other, the diameter control portion  96  comes close or abuts to an outer circumference of the fitting portion  86  in a case that the movable sleeve  90  is situated in an initial position in the direction of the axis. 
     In the case described above, the fitting portion  86  is not allowed to expand the diameter thereof at the distal end. When the movable sleeve  90  is moved from the initial position to the distal end, the diameter control portion  96  becomes apart from the outer circumference of the fitting portion  86 . Thereby, the fitting portion  86  is allowed to expand the diameter thereof. 
     In addition, when the insertion portion  94  of the second connector  82  is inserted completely into the fitting portion  86  of the first connector  81  and the first connector  81  and the second connector  82  are connected to each other, in other words, when the engaging portion  87  engages the engaged portion  95 , the diameter control portion  97  comes close or abuts to the outer circumference of the fitting portion  86  in a case that the movable sleeve  90  is situated in the initial position in the direction of the axis. 
     In the case described above, the fitting portion  86  is not allowed to expand the diameter thereof at the distal end. When the movable sleeve  90  is moved to the proximal end, the diameter control portion  97  becomes apart from the outer circumference of the fitting portion  86 . Thereby, the fitting portion  86  is allowed to expand the diameter thereof. 
     The second connector  82  includes an elastic deformation member  98 ; an accommodating portion  99 ; and a transmission unit  100  as a mechanism for enabling the movable sleeve  90  moved in the direction either of the proximal end or the distal end to return automatically to the initial position. The accommodating portion  99  accommodates the elastic deformation member  98  and the transmission unit  100  generates force bringing back the movable sleeve  90  to the initial position by utilizing elastic force of the elastic deformation member  98 . 
     In the embodiment, the elastic deformation member  98  and accommodating portion  99  have the same configurations as the elastic deformation member  24  and accommodating portion  25  in the first embodiment, respectively. Further, the transmission unit  100  at least includes two inclined surfaces  101  and  102  formed on an outer circumference of the elastic deformation member  98  and a sliding contact portion  103  provided in the movable sleeve  90  having the same configurations with the inclined surfaces  27  and  28  and sliding contact portion  29  in the first embodiment of the present invention, respectively. 
     It is possible that the pair of the electrical connectors according to the sixth embodiment of the invention is able to obtain the same functionality and effect with the electrical connector  1  in the first embodiment of the present invention. 
     In the embodiments described above, according to the present invention, each of the electrical connectors  1 ,  41 ,  51 ,  61 ,  71 ,  81  and  82  is a coaxial connector having a single central terminal  15 ,  85  or  93 . Electrical connectors according to the present invention are not limited to the electrical connectors described above. An electrical connector according to the present invention may be a multi core connector having a plurality of terminals in an inner circumference of an external terminal. 
     Furthermore, in the embodiments described above, according to the present invention, each of the electrical connectors  1 ,  41 ,  51 ,  61 ,  71 ,  81  and  82  has a circular cross-sectional shape. The present invention is applicable to an electrical connector having a polygonal cross-sectional shape, for example, a tetragonal cross-sectional shape, not limited to the circular cross-sectional shape. 
     Additionally, as shown in  FIG. 14 , a mating connector  111  may include a reinforcement guide  112 . The reinforcement guide  112  has a cylindrical shape. The reinforcement guide  112  is settled so as to surround an entire outer circumference in a distal end portion of the movable sleeve  21  of the electrical connector  1  when the electrical connector  1  is connected to the mating connector  111 . The reinforcement guide  112  protects the electrical connector  1  and the mating connector  111  from an external force applied to the electrical connector  1  and the mating connector  111  due to being twisted forcibly and the like. Consequently, the electrical connector  1  and the mating connector  111  are able to obtain higher durability. 
     Furthermore, as shown in  FIG. 15 , a mating connector  121  may include a bulging portion  124  situated next to an engaged portion  123  in a distal end portion of an outer cylindrical member  122 . The bulging portion  124  bulges outwardly in the direction of the diameter throughout an entire outer circumference of the outer cylindrical member  122 . An outer diameter of the distal end portion of the outer cylindrical member  122  is smaller than an outer diameter of the insertion portion  35  of the outer cylindrical member  31  shown in  FIGS. 5 and 6 . 
     With the configuration as described above, it is also possible to enable the fitting portion  17  to expand the diameter thereof since the bulging portion  124  pushes the engaging portion  20  outwardly in the direction of the diameter as the mating connector  121  enters the fitting portion  17  of the electrical connector  1 . When the mating connector  121  completely enters the fitting portion  17  of the electrical connector  1 , the fitting portion  17  is allowed to shrink the diameter thereof so as to obtain an initial shape. Therefore, it is possible for the engaging portion  20  to engage the engaged portion  123  of the mating connector  121 . 
     In the embodiments described above, the present invention is applied to an electrical connector. It is possible to apply the present invention to an optical connector having an optical signal terminal, not limited to the embodiments described above. 
     Moreover, the present invention is able to modify as far as the modification is within the inventive concept readable from the claims and the specification as a whole. Therefore, the connector thus modified also falls within the inventive concept of the present invention. 
     The disclosure of Japanese Patent Application No. 2011-069657 filed on Mar. 28, 2011, is incorporated in the application by reference. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.