Rotary connector

Abstract: The object is to provide a rotary connector in which the flat cable is not damaged when the rotary connector is correctly assembled, and the flat cable can be cut off easily when the user operates the steering wheel to which the rotary connector is incorrectly assembled, thus an accidental firing of the air bag is prevented. The rotary connector has a flat cable 4 with one end connected to a terminal strap 14 and the other end connected to a supporting member 11. The flat cable 4 is in the shape of a spiral and is accommodated in a space G defined by a stator housing 1 and a rotor housing 2 rotatably assembled to the stator housing 1. The terminal strap 14 is located between an inner wall 7c of the stator housing 1 and a guide 9 disposed near the inner wall 7c. The guide 9 has a small-width strap 9d with a curved surface in contact with the flat cable 4. The flat cable 4 is routed through the gap between the inner wall 7c of the stator housing 1 and the small-width strap 9d into a space G in the stator housing 1.

Description: The present invention relates to a rotary connector through which electric power is supplied to an air bag or the like provided, for example, at a pad of a steering wheel of an automobile. Recently, a technique has been implemented in which when an accident occurs, an air bag pops out to protect the passenger from the impact. This type of air bag, particularly the one provided at the pad of the steering wheel, requires electric power to be supplied from the vehicle side through a rotatable portion of the steering wheel to the inflater of the air bag system mounted on the pad side. One commonly used means for supplying electric power is a rotary connector that incorporates a flat cable usually wound in a spiral fashion. A variety of this type of rotary connectors have been proposed. For example, discloses a rotary connector that calls a US-A-4 928 901 cable reel. This rotary connector includes a stator housing, a rotor housing rotatably assembled to the stator housing, and a flat cable accommodated in a spiral fashion in a space defined by the stator housing and the rotor housing. The rotary connector further includes a cutter and a cutting element provided at an end of the flat cable, the cutter and cutting element being used to cut the flat cable. A rotary connector is assembled at a neutral position thereof from which the steering wheel can be rotated by two rotations leftward and rightward, respectively. If the rotary connector is assembled off the neutral position by mistake, the steering wheel cannot be rotated by two rotations leftward and rightward, respectively. This prevents the driver from steering the vehicle with maximum operability. In order to solve the problem, the aforementioned cutter and cutting member are used to cut off the flat cable, ensuring that the steering wheel can be rotated by two rotations leftward and rightward, respectively, from the neutral position. However, the aforementioned conventional rotary connector suffers from the problem that even if the rotary connector is assembled correctly to the steering wheel, the cutter and cutting member used for cutting the cable still remain in contact with the flat cable and therefore may damage the flat cable. An object of the present invention is to provide a rotary connector in which the flat cable is not damaged when the rotary connector is assembled correctly and the flat cable can be cut off easily if the user operates the steering wheel to which the rotary connector is assembled incorrectly. The present invention was made in order to achieve the aforementioned objects. The present invention of the aforementioned construction offers the following advantages. The invention defined in Claim 1 is directed to a rotary connector having a flat cable with one end connected to a terminal strap and the other end connected to a supporting member, the flat cable being in the shape of a spiral and being accommodated in a space defined by a stator housing and a rotor housing rotatably assembled to the stator housing. The terminal strap is located between an inner wall of the stator housing and a guide disposed near the inner wall; the guide has a strap with a width smaller than the width of the guide, called small width strap, with a curved surface in contact with the flat cable; and the flat cable is routed passing between the inner wall of the stator housing and the small-width strap into the space. Therefore, when the user operates the steering wheel to which the rotary connector is incorrectly assembled, the flat cable is pulled taut at both ends thereof, so that a stress is concentrated on the contact portion at which the flat cable is in contact with the small-width strap. As a result, the flat cable is cut off at the contact portion. When the user operates the steering wheel of an automobile to which the rotary connector has been incorrectly assembled, the small-width strap will cut off the flat cable at the connection of the flat cable so that the user is allowed to operate the steering wheel in the same manner when the rotary connector has been assembled correctly. The invention of Claim 2 further defines the rotary connector according to Claim 1, wherein the stator housing has a projection formed on the inner wall near the small-width strap. This construction allows the flat cable, which has been cut off, to strike the projection, thereby preventing the short-circuit of the cut end of flat cable to the terminal of the terminal strap which would otherwise inadvertently fire the air bag. The invention of Claim 3 further defines the rotary connector according to Claim 1 or Claim 2, wherein the stator housing has a projection formed on the inner wall between the terminal strap and the small-width strap. Therefore, the construction prevents the cut end of the connection of the flat cable from entering the gap between the small-width strap and the inner wall to reach the terminal strap. Thus, the construction prevents the short-circuit of the conductive wires of the cut-off flat cable to the terminals of the terminal strap which would otherwise inadvertently fire the air bag. The invention of Claim 4 further defines the rotary connector according to Claim 1, Claim 2, or claim 3, wherein the guide has a recess near a location facing the projection. The projection cooperates with the recess to change the direction of the flat cable, thereby preventing the cut end of the flat cable from entering the gap beyond the guide to come into contact with the terminal. Thus, the construction prevents the short-circuit of the conductive wires of the cut-off flat cable to the terminals of the terminal strap which would otherwise inadvertently fire the air bag. The invention of Claim 5 further defines the rotary connector according to Claim 2 or Claim 4, wherein the projection has an inclined surface on a side remote from the terminal strap. The construction allows the cut end of the flat cable to move to the center of the rotary connector while rotating, after the flat cable has been cut off. Thus, the construction prevents the cut end of the flat cable from entering the gap between the guide and the inner wall of the side housing. Attached drawings illustrate an embodiment of the present invention, in which: Fig. 1 is a partially cross-sectional perspective view of an embodiment of the invention; Fig. 2 is a cross-sectional view of the embodiment of the invention taken along the diameter; Fig. 3 is an enlarged perspective view of a stator housing having a flat cable according to the embodiment of the invention; Fig. 4 is a top plan view of the stator housing having the flat cable according to the embodiment of the invention and. Fig. 5 is an enlarged view of a part depicted at H of Fig. 4. Referring to the drawings, reference numerals 1,2,3, and 4 denote a stator housing, rotor housing, attachment, and flat cable. Reference numerals 5 and 6 denote connectors. These structural elements will be described. A rotary connector includes the stator housing 1, rotor housing 2 rotatably assembled to the stator housing 1, and the flat cable 4 in the shape of a spiral. The flat cable 4 is housed in a space G defined by the stator housing 1 and the rotor housing 2. The stator housing 1 is a stationary component that is screwed down on the combination switch (not shown) of, for example, an automobile. The stator housing 1 includes a side housing 7 and a bottom housing 8 combined with the side housing 7. For more detail, the side housing 7 has a fitting hole 7a and the bottom housing has a fitting projection 8a. The fitting projection 8a is fitted into the fitting hole 7a, thereby assembling the bottom housing 8 to the side housing 7. The side housing 7 and bottom housing 8 may be formed in one piece, thereby providing a single piece stator housing 1. The side housing 7 and the bottom housing 8 have base portions 7b and 8b, respectively, that are flush with each other when they are assembled together. Thus, when the stator housing 1 has been fixed to the combination switch, both the base portions 7b and 8b abut the combination switch. Therefore, if an external force is exerted on the bottom housing 8 in a direction shown by arrow A of Fig. 2, the base portion 8b abuts the combination switch, so that the bottom housing 8 is prevented from being deformed in the direction shown by the arrow A as well as the fitting projection 8a of the bottom housing 8 is prevented from dropping out of the fitting hole 7a of the side housing 7. As shown in Fig. 2, the bottom housing 8 has a guide 9 that holds an end of the flat cable 4 and guides the flat cable 4 in a space G defined by the stator housing 1 and the rotor housing 2. There is provided a slide sheet 15 on top of the bottom housing 8. The rotor housing 2 is rotatably fitted into the stator housing 1 and is coupled to the steering wheel (not shown) by means of a coupling pin 10 having a resilient cover 10a fitted thereover. The rotor housing 2 has projections 2b and a stepped portion 2c on its inner circumferential surface 2a. The projections 2b fit into fitting portions 3a formed on an attachment 3. The stepped portions 2c abut projecting straps 3b formed on the attachment 3. The rotor housing 2 has a cord cover 12 that covers cords 6a of connectors 6 led out of the rotor housing 2 and secures a later-described supporting member 11 to the rotor housing 2. The cord cover 12 is inserted into the top surface of the rotor housing 2 and is fixed by heat bonding or ultrasonic bonding. The rotor housing 2 has a caution label 13 stuck on the top surface of the rotor housing 2 as shown in Fig. 2. The caution label 13 lists cautions about the handling of the rotary connector. The supporting member 11 is a component that supports one end of the flat cable 4 as shown in Fig. 2. The supporting member 11 is also a member that prevents the flat cable 4 from buckling, thereby protecting the flat cable 4 from breakage and damage. The attachment 3 is a member that couples the stator housing 1 to the rotor housing 2. The attachment 3 has the fitting portions 3a and projecting straps 3b. The fitting portions 3a resiliently engage the projections 2b of the rotor housing 2, and the projecting straps 3b abut the stepped portions 2c of the rotor housing 2. The attachment 3 slides on the inner surface of the bottom housing 8, serving as a radial (direction of radius) bearing. As shown in Fig. 4, the flat cable 4 includes a plurality of conductive wires 4a and sheets of resin film 4b between which the plurality of conductive wires 4a are sandwiched. The plurality of conductive belt-shaped wires 4a are arranged at predetermined intervals and are sandwiched between two sheets of insulating resin film 4b. The flat cable 4 has one end fixed to a terminal strap 14 that is electrically connected to a connector 5 and the other end fixed to the supporting member 11 mounted to the rotor housing 2. The conductive wires 4a have front and back surfaces bonded to two sheets of resin film 4b. The conductive wires 4a are flat belt-shaped and have one ends thereof connected to the air bag apparatus accommodated in the steering wheel and the other ends thereof electrically connected to a power supply and sensors of the air bag apparatus. The conductive wires 4a include a total of three wires; two wires for the air bag and one wire for a horn. The number of conductive wires is not limited to three and may be selected in accordance with the design purpose. The resin film 4b is of the construction in which two laminated films of, for example, polyethylene terephthalate are contact bonded by heat or bonded by an adhesive such that the plurality of conductive wires 4a are insulated from each other. The flat cable 4 is housed in a doughnut-shaped space G defined by the stator housing 1 and the rotor housing 2. The flat cable 4 is rotatable leftward and rightward, at least two complete rotations in each direction. One end of the flat cable 4 is electrically connected to the connector 5 of the stator housing 1 via the terminal strap 14, and the other end of the flat cable 4 is connected to the connectors 6 of the rotor housing 2 via the supporting member 11. As shown in Figs. 2 and 4, the supporting member 1 1 connected to the flat cable 4 is fastened to the outer wall of a hollow shaft 2d of the rotor housing 2. As shown in Figs. 3 and 4, the terminal strap 14 located at the other end of the flat cable 4 is disposed between an inner wall 7c of the side housing 7 and the guide 9 near the upper outer periphery of the bottom housing 8. The terminal strap 14 is an resin material in which conductors (not shown) are insert molded. The conductors have lateral ends connected to the respective conductive wires 4a and downward ends connected to the respective ends of the terminals (not shown) of the connector 5. The terminal strap 14 is mounted to the bottom surface of the bottom housing 8. As shown in Figs. 3 and 4, the terminal strap 14 engages a bottom surface 9a of a recess formed in the guide 9 and is received between projections 7d and 7e formed on the inner wall 7c of the side housing 7. The projections 7d, 7e, and 7f are vertically extending on the inner wall 7c of the side housing 7. As shown in Figs. 3 and 4, the projection 7d cooperates with the bottom surface 9a of the guide 9 to support the terminal strap 14 therebetween. As shown in Figs. 3, 4, and 5, a projection 7e opposes a guide strap 9b of the guide 9 and is aligned with an edge of a recess 9c formed in a surface of the guide strap 9b facing the inner wall 7c. The projection 7e cooperates with the guide strap 9b to support the end of the flat cable 4, and cooperates with the recess 9c to prevent the cut end of the flat cable 4 from again entering a gap between the guide 9 and the inner wall 7c after the flat cable 4 has been cut off at the connection C connected to the terminal strap 14. In this manner, the construction prevents the cut end of the flat cable 4 from short-circuiting. The projection 7e has a side surface 7g closer to the small-width strap 9d. The side surface 7g is inclined to make an acute angle with the flat cable 4. As shown in Fig. 5, when a flat cable 4c that has been cut off enters a space between the inner wall 7c and the guide strap 9b, the cut end of the flat cable 4c strikes the side surface 7g and slips to a base portion 7h of the projection 7e where the tip of the flat cable 4c is finally stopped. In this manner, the flat cable 4c is prevented from entering the gap between the guide 9 and the inner wall 7c. As shown in Fig. 5, the projection 7f prevents a flat cable 4e from again entering the gap between the guide 9 and inner wall 7c after the flat cable 4 has been cut off, ensuring that the flat cable 4e will not be short-circuited to inadvertently fire the air bag. The projection 7f should be provided at a location near the small-width strap 9d, including a location 7i shown by a phantom line adjacent to the small-width strap 9d and a location 7j further away from the small-width strap 9d as shown in Fig. 5. The projections 7f, 7i, and 7j may have inclined side surfaces such as a surface 7k formed on the projection 7j shown by phantom lines in Fig. 5. The surface 7k guides the flat cable 4e, which moves toward the guide 9 in a direction shown by arrow I, toward the center of the rotary connector. The side surface 7k is formed on a side of the projections 7f, 7i, and 7j remote from the guide 9. The side surface 7k may be a flat surface or a curved surface. The guide 9 is a projected strap provided at a location over the connector 5 of the bottom housing 8. The guide 9 includes guide strap 9b, recess 9c, small-width strap 9d, and the recess having the bottom surface 9a. The guide 9 extends along the inner wall 7c of the side housing 7, generally describing an arc. The bottom surface 9a of the recess is a bottom surface of a groove with which the projection 7d and the terminal strap 14 are engaged. When the user rotates the steering wheel, the guide strap 9b guides the flat cable 4 in such a way that the flat cable 4 connected to the terminal strap 14 expands or contracts within the side housing 7 while maintaining its spiral shape. Just like the projections 7e and 7f, when the flat cable 4 has been cut off at the connection C connected to the terminal strap 14, the recess 9c serves to prevent the reentering of the flat cable 4 between the inner wall 7c and the guide 9 which would otherwise cause a short-circuit. The recess 9c is a substantially U-shaped groove having a side wall 9e. The side wall 9e is closer to the terminal strap 14 and is aligned with the tip of the side surface 7g of the projection 7e. The side wall 9e is inclined such that the side wall 9e makes an acute angle with the flat cable 4. When a flat cable 4d again enters the gap between the inner wall 7c and the guide strap 9b as shown in Fig. 5 after the flat cable 4 has been cut, the tip of the flat cable 4d strikes the side wall 9e and slides on the side wall 9e toward a recess 9c. The tip of the cable 4d is stopped at the recess 9c. Thus, the flat cable 4d is prevented from entering the gap between the guide 9 and the inner wall 7c. The small-width strap 9d is a projecting strap formed at the lower end of the guide strap 9b and is in contact with the flat cable 4. The small-width strap 9d has a shorter vertical width than the guide strap 9b. When the user operates the steering wheel to which the rotary connector is incorrectly assembled, the small-width strap 9d exerts a concentrated stress on the flat cable 4 that is in contact with the small-width strap 9d, thereby cutting off the flat cable 4 at the connection C connected to the terminal strap 14. The small-width strap 9d has a rounded tip portion such that the friction resistance between the flat cable 4 and the small-width strap 9d is small when the rotary connector is assembled correctly. The small-width strap 9d may be at a vertically upper end or middle of the guide strap 9b, provided that the small-width strap 9d is at the tip of the guide strap 9b. The small-width strap 9d should be located where the small-width strap 9d presses the conductive wires 4a hard, so that the flat cable 4 can be cut off efficiently at the connection C connected to the terminal strap 14. The rotary connector having the flat cable 4 operates as follows: The rotary connector has the connectors 6 connected to, for example, an air bag apparatus (not shown) on the steering wheel side and the other connector 5 to, for example, air bag controller (not shown) on the vehicle side. Thus, in the event of crash of the vehicle, the electrical signal generated by the air bag controller is sent to the air bag apparatus provided at the steering pad via the flat cable 4 of the rotary connector, thereby firing the inflater to inflate the air bag. When the user operates the steering wheel, the steering wheel rotates together with the rotor housing 2 and attachment 3, so that the flat cable 4 slides. When the rotary connector is correctly mounted to the steering wheel, the steering wheel and flat cable 4 rotate leftward and rightward from the position at which the vehicle runs straightly, rotating through two complete rotations in each direction. No load is exerted on the contact portion D between the flat cable 4 and the small-width strap 9d of the guide 9. Additionally, the flat cable 4 is not damaged because the small-width strap 9d has a curved surface. For example, Fig. 4 illustrates the rotary connector when the user operates the steering wheel rightward in the direction shown by arrow E more than one rotation, if the rotary connector has been inadvertently assembled with the steering wheel rotated rightward by one complete rotation from the neutral position. Rotating the steering wheel causes the flat cable 4 to be taut. The flat cable 4 near the guide 9 is pulled in the direction shown by arrow B as shown in Figs. 3 and 4, so that a stress is concentrated on the contact portion D at which the flat cable 4 is in contact with the small-width strap 9d. The small-width strap 9d has a shorter vertical dimension than the guide 9, so that the stress exerted on the flat cable 4 at the contact portion D is large. When the user operates the steering wheel further in the direction shown by arrow E, for example, to make a right turn, the flat cable 4 is cut off at the weakest portion, i.e., the connection portion C connected to the terminal strap 14. Since the flat cable 4 is cut off, the steering wheel can be operated in the same manner that the rotary connector is assembled correctly. When the steering wheel has been rotated more than one complete rotation rightward in the direction shown by arrow E after the flat cable 4 has been cut off, the cut end of the connection portion C is pulled in the direction shown by arrow B, passing between the guide 9 and the inner wall 7c to the space G in the side housing 7. When the user rotates the steering wheel in a direction shown by arrow F shown in Fig. 4, the cut end of the connection portion C of the flat cable 4 also moves in the direction shown by arrow F. The cut end of the connection portion C of the flat cable 4 strikes the projection 7f, which prevents the flat cable 4 from entering the gap between the guide 9 and the inner wall 7c. Thus, even if the cut end of the connection portion C passes between the small-width strap 9d and the inner wall 7c into the space between the side wall 9e and the inner wall 7c, the projection 7e cooperates with the recess 9c to prevent the cut end of the connection portion C from entering further through the gap to a position where the cut end of the connection portion C may reach the terminal strap 14. Thus, the construction prevents the short-circuit of the conductive wires 4a of the flat cable 4 to the terminals of the terminal strap 14, which would otherwise cause the air bag system to go off spontaneously. Description of References 1: stator housing, 2: rotor housing 4. 4c, 4d, 4e: flat cables 7c: inner wall 7e, 7f, 7i, 7j: projections 7g, 7k: side surfaces 9: guide 9c: recess 9d: small-width strap 11: supporting member 14: terminal strap G: space

Claims: A rotary connector having a flat cable (4) with one end connected to a terminal strap (14) and the other end connected to a supporting member (11), the flat cable (4) being in the shape of a spiral and being accommodated in a space (G) defined by a stator housing (1) and a rotor housing (2) rotatably assembled to the stator housing (1), characterized in that : the terminal strap (14) is located between an inner wall (7c) of the stator housing (1) and a guide (9) disposed near the inner wall (7c); the guide (9) has a strap (9d) with a width smaller than the width of the guide (9) with a curved surface in contact with the flat cable (4); and the flat cable (4) is routed to pass through a gap between the inner wall (7c) of the stator housing (1) and the strap (9d) with a width smaller than the width of the guide (9) into the space (G) in the stator housing. The rotary connector according to Claim 1, wherein the stator housing (1) has a projection (7f, 7i, 7j) formed on the inner wall (7c) near the small-width strap (9d). The rotary connector according to Claim 1 or Claim 2, wherein the stator housing (1) has a projection (7e) formed on the inner wall (7c) between the terminal strap (14) and the small-width strap (9d). The rotary connector according to Claim 3, wherein the guide (9) has a recess (9c) near a location facing the projection (7e). The rotary connector according to Claim 2 or Claim 4, wherein the projection (7e, 7j) has an inclined surface on a side thereof remote from the terminal strap (14).

Inventors: MATSUMOTO TSUYOSHI, MATSUMOTO, TSUYOSHI, Matsumoto, Tsuyoshi, c/o Niles Parts Co., Ltd.
Applicants: NILES PARTS CO LTD, NILES PARTS CO., LTD.
Application year: 2000
Main classification: H01R35
IPC codes: H01R35