Electrical connectors – With relatively guided members and intermediate pliable... – Relatively movable about axis
Reexamination Certificate
1999-06-08
2001-07-10
Paumen, Gary F. (Department: 2833)
Electrical connectors
With relatively guided members and intermediate pliable...
Relatively movable about axis
Reexamination Certificate
active
06257909
ABSTRACT:
This application is based on and claims the benefit of German Patent Application No. 198 25 692.2 filed Jun. 9, 1998, which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
The invention relates to a rotary joint with two housing parts rotatable in relation to each other, which are connected by a flexible flat conductor that extends in spires within an interstice between the housing parts and is attached at its end to a contact element, which connects a strand of the flat conductor with a circular conductor and which is arranged in a holder in a housing part.
The problem of suitable current or signal transmission between parts of an apparatus that can be rotated in relation to each other within a limited angular range is frequently encountered. For example, a permanent, reliable connection to supply power to deploy the airbag in a motor vehicle steering wheel is of decisive importance. Since sliding contacts are unsuitable for this purpose due to wear and fluctuating contact resistance, rotary joints with flat conductors have been developed to ensure safe connection.
The flat conductor (hereinafter referred to as FFC) is arranged in the interstice between two rotary joint housing parts rotatable in relation to each other and is attached at its ends to the two housing parts. It is normally made of one or several copper strips spaced at a distance from each other and embedded between two plastic strips. In the simplest case, the flat conductor extends helically like a clock spring. On relative rotation of the housing parts, the diameter and the spire number changes as a function of the direction of rotation. As an alternative, the spires of the flat conductor extend along the inner and outer radial walls of the interstice in opposite directions of rotation, whereby there is a reversing point between the two conductor segments. In this case, upon relative rotation of the housing parts of the joint, the conductor is unwound from one wall and taken up by the other. It is also well known to arrange guiding or elastic elements within the interstice and to make the flat conductor from an elastic material to ensure its safe guidance upon rotation of the housing parts and to prevent damage.
The exterior contacting of the rotary joint is generally effected by wires or stranded conductors with an approximately circular cross-section. Consequently, contact elements have to be provided, which electrically connect the circular conductors with the strands of the flat conductor. Such a contact element is described, for example, in DE 196 04 797 A1. Its design is complex, however, which is a disadvantage particularly if production lots are small, since forming dies are required to produce the contact element. Furthermore, the described contact element has relatively large dimensions and is arranged in the radial outer wall of the rotary joint. Since many functional elements are disposed on the steering wheel of a motor vehicle, the corresponding mounting space is frequently not available.
SUMMARY OF THE INVENTION
Against this background, it is an object of the invention to develop a rotary joint with a contact element for connecting the circular conductor and the flat conductor, which permits simple and low-cost production even for small production lots and which is distinguished by small dimensions.
This object is attained by the invention in that the contact element is made as a single-piece metal part, which has a surface to which the strand of the flat conductor is permanently fixed, the contact element is attached to the circular conductor by crimping, and each contact element is fixed within an associated holder.
The basic idea of the invention is to use a contact element made of a single-piece metal part, e.g., of copper, for connecting the flat conductor of the rotary joint with a circular conductor. The contact element has a preferably flat surface, e.g., a tongue, to which the strand of the flat conductor is permanently fixed. Fixation is by soldering or welding for example, e.g., spot welding or ultrasonic welding. Advantageously, the width of the surface approximately corresponds to, or slightly exceeds, the width of the strand of the flat conductor. Particularly suitable is a flat conductor made of ribbon-type copper conductors which are laminated with plastic foil. Alternatively, any other type of flat conductor may be used. The contact element is fixed to the circular conductor by crimping, preferably by bending tabs along the rim of the contact element around the circular conductor and by deforming them together with the circular conductor to create an easily produced connection that can be subjected to mechanical stress. To improve the stability under load, several pairs of tabs may be provided, which can be crimped to the conductive core of the circular conductor as well as to its insulation.
Since the contact elements are made of an electrically conductive material, each must be arranged within a respective holder of the rotary joint to insulate the strands with respect to each other, whereby the housing parts of the rotary joint are advantageously made of an insulating plastic material. The contact elements and holders are formed so as to provide permanent fixation through positive locking. This prevents any transfer of tensile loads between circular conductor and flat conductor. The number of contact elements corresponds to the number of flat conductor strands to be contacted, whereby either one or both ends of the flat conductor may be provided with such contact elements. Providing a corresponding number of holders in the rotary joint makes it possible to vary the number of contact elements used in order to adapt to flat conductors with different numbers of strands. The holders and thus the contact elements are advantageously arranged parallel and adjacent to each other.
Using single-piece metal parts as the contact elements makes it possible to produce the inventive rotary joints at low cost and with little complexity. Suitable contact elements are, for example, stampings that can be produced in large quantities at low cost. It is possible to use commercially available stampings, which are suitable for crimping to a circular conductor and for welding to a strand of a ribbon or flat conductor. A further advantage is the small size of the contact elements. Their maximum width can be limited to approximately the strand width of the flat conductor. With the flattened form, the maximum thickness is defined by the crimped area and corresponds approximately to the cross-section of the circular conductor. Consequently, the inventive rotary joint is particularly well suited for spatially tight mounting locations.
Due to the small dimensions of the contact elements, it is possible in one advantageous embodiment of the invention to arrange their holders in an extension of a housing part. Particularly advantageous is the arrangement of the extension on an axial end face of the rotary joint. Thus, the radial diameter of the rotary joint can be limited to the value required for receiving the spires of the flat conductor, while the contact elements are disposed above or below the plane of the spires. The transition of the flat conductor from the plane of its spires to the extension is advantageously accomplished by folding it along a line extending at a 45° angle to its longitudinal axis so that it bends at a right angle.
The contact element is preferably latched within its holder. Suitable for this purpose are, for example, barbed spring arms between which the crimping area of the contact element is inserted. The contact element is preferably inserted in its holder at a right angle to the longitudinal axis of the circular conductor.
It is furthermore proposed to seal the holder with a cover to prevent any unintended detachment of the contact element. The cover can be fixed on the rotary joint, for example, by latching or insertion into guides. To simplify assembly, a single cover is preferably used to seal all the holders at one end of the flat conductor. Even in conju
Reber Wolfgang
Schröer Frank
Alcatel
Nguyen Phuongchi
Paumen Gary F.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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