Coil spring cassette

Abstract

A coil spring cassette with a cylindrical stator housing part and a rotor housing part, with a flexible flat cable, having at least one electrical conductor, and a flexible flat ribbon which with their respective ends are fastened on the one hand to the stator housing part and on the other hand to the rotor housing part and are wound so tightly on the respective housing parts that a U-shaped turning portion that reverses the direction of winding is formed between their ends, is characterized according to the invention in that at least three flexible flat cables and three flat ribbons, bearing on each of the lateral faces of the winding gap, cooperate in their sequence of superposition and in their respective internal configuration to form a desired waveguide geometry.

Description

[0001] Wicke If ede rkassette

[0002] The invention relates to a coil spring cassette with a fixed cylindrical stator housing part and a cylindrical rotor housing part arranged coaxially thereto and rotatable about its longitudinal axis, wherein a winding gap is formed which is delimited by the outer surface of the inner housing part and the inner surface of the outer housing part, in which at least one flexible flat cable having at least one electrical conductor and at least one flexible flat strip serving to mechanically stabilize the flat cable are arranged in such a way that their respective first ends are fastened to the stator housing part and their respective second ends are fastened to the rotor housing part,and that they are wound in opposite directions with a first section of their length against the outer surface of the inner housing part and with a second section of their length against the inner surface of the outer housing part, so that a U-shaped turning section reversing the winding direction is formed between the two sections of the flat cable and the flat strip.

[0003] Such coil spring cassettes are designed, for example, to reliably transmit power and / or data in motor vehicles between connection points that are rotatably mounted in the steering wheel and those that are fixed in the area of ​​the steering column. The connection points of such a device can be used to supply an airbag system, a steering wheel heater, a switching device, etc., with the voltage and signals necessary for their operation.

[0004] EP 0 556 779 B1 discloses such a coil spring cassette in which several flexible flat cables are accommodated within an annular cavity of a housing. One end of each flexible flat cable is secured to the stator part, and the other end is secured to a rotor part of the housing that is rotatable relative to the stator part. The flexible flat cables can each be wound with their two broad sides via a U-shaped turning section with at least one turn onto the axially aligned inner wall and, at a distance therefrom, conversely with at least one further turn onto the axially aligned outer wall of the housing.

[0005] If a plurality of flat cables is required to provide the required electrical connections, this plurality of flat cables is arranged in such a way that their respective end sections overlap on the outer surface of the inner housing part and on the inner surface of the outer housing part, and the U-shaped turning sections of each of the flat cables generate an elastic compressive force which ensures that the inside or outside wound areas of the other flat cables are securely attached to the housing surfaces.

[0006] If fewer flat cables are needed to provide the necessary electrical connections than are required to ensure proper mechanical function of the clock spring cassette, so-called dummy cables are used instead of additional flat cables. These are elastic flat strips that have equivalent mechanical properties to flat cables, but unlike flat cables, do not contain electrical conductors. Plastic strips, such as PET, are typically used as dummy cables. In practice, the use of at least four cables or dummy cables has proven advantageous to ensure proper mechanical function of the clock spring cassette.

[0007] Particularly when only a few electrical potentials are to be transmitted, considerable cost savings can be achieved by using dummy cables, for example by using only one flat cable and three significantly cheaper flat ribbons as dummy cables.

[0008] The increasing number of electronic functions in the steering wheel creates the need for fast, interference-free data transmission via a clock spring cassette. However, this is only possible to a limited extent due to the cable geometries of the flat cables currently in use. For fast data transmission, a cable system with an impedance matched to the impedance of the supply cables is necessary. Particularly for the transmission of fast signals, i.e. with data rates of up to 100 Mbit / s, e.g. on a so-called Automotive Ethernet, it is desirable to match the cable impedance of the clock spring to the cable impedance of a commonly used twisted pair cable, which is generally around 100 ohms. The characteristic impedance should also be influenced as little as possible by the rotation of the clock spring cassette.

[0009] To meet these electrical requirements, based on known standard values ​​for spacing and material thickness, a flat cable would have to have a thickness of more than 435 μm, which would not meet the mechanical requirements regarding flexibility. The flat cable must be extremely flexible and thus as thin as possible for use in the clock spring cassette, and also have a load capacity of 6 million bending cycles with a radius of 8 mm.

[0010] The coil spring cassette according to the present invention has the advantage over the prior art of providing a cable system suitable for fast data transmission with a matched impedance, whose flat cables also meet the high mechanical requirements. This is achieved according to the invention by at least three flexible flat cables and three flat ribbons cooperating in their superimposed sequence and their respective internal configuration to form a desired waveguide geometry when applied to each of the lateral surfaces of the coil gap.

[0011] In a preferred embodiment, it is provided that the first flat cable in the sequence has at least four electrical conductors and a thin metallic coating on its surface facing the second flat cable, that the second flat cable has an electrical conductor at ground potential, that the third flat cable has an electrical conductor for transmitting the supply voltage, and that a flat strip without electrical conductors is arranged between the first and second flat cables, and that two further flat strips without electrical conductors are arranged next to the third flat cable.

[0012] Further advantageous embodiments of the subject matter according to the invention are specified in the subclaims and are explained in more detail with reference to an embodiment shown in the drawings.

[0013] Fig. 1 : a cross-section through a layer of flexible flat cables and flat ribbons of an embodiment of a coil spring cassette according to the invention

[0014] Fig. 2: an embodiment of a clock spring cassette according to the

[0015] State of the art in cross-section

[0016] To clarify the general functioning of the systems concerned here

[0017] Fig. 2 shows a cross-sectional view of a prior art coil spring cassette with the aforementioned minimum number of four cables or dummy cables. This coil spring cassette essentially consists of a housing having a stator housing part 1 and a rotor housing part 2, and flexible flat cables 6 or flat strips 7 as dummy cables accommodated within an annular cavity of the housing forming a winding gap 5. In the known embodiment shown here, a flexible electrical flat cable 6 and three flat strips 7 without electrical conductors are present. The electrical flat cable 6 is shown in dashed lines in the drawing.

[0018] The rotor housing part 2, which is located on the outside in the embodiment shown, is rotatable about its longitudinal axis and thus about the stator housing part 1, which is arranged coaxially to the inside. The outer surface 3 of the stator housing part 1 and the inner surface 4 of the rotor housing part 2 form a winding gap 5 in which the flexible flat cable 6 is received. The flexible flat cable 6 is fastened with its first end to the stator housing part 1 and with its second end to the rotor housing part 2 and is arranged in the winding gap 5 such that it is wound in the opposite direction with a section of its length adjacent to its first end against the outer surface 3 of the stator housing part 1 and with a section of its length adjacent to its second end against the inner surface 4 of the rotor housing part 2.Between these two sections of the flat cable 6 is a U-shaped turning section 6' that reverses its winding direction. When the rotor housing part 2 rotates in one direction or the other, this U-shaped turning section 6' moves along the circumference of the winding gap 5, and the flat cable 6 is unwound on one side and wound up on the other. To mechanically stabilize the flat cable 6 and, in particular, to ensure that its end sections are firmly attached to the lateral surfaces 3, 4, three elastic flat bands 7 are accommodated in the winding gap 5 in the same way as the flat cable 6, namely such that the four U-shaped turning sections 6', 7' of the flat cable 6 and the three flat bands 7 are arranged at the same angular distance of approximately 90° from one another.

[0019] A coil spring cassette designed according to the invention is basically constructed in the same way, but differs from that described with reference to Fig. 2 in the number of flexible flat cables 6 or flat strips 7, which is at least six in total, and in particular in the internal structure of the flat cables 6 and a specific arrangement of the flat cables 6 and flat strips 7 relative to one another.

[0020] Fig. 1 shows a cross-section through a layering of three flexible flat cables 6, 8, 9 and three flat strips 7 of an embodiment of a coil spring cassette according to the invention, as it results when the same is applied to one of the lateral surfaces 3, 4 of the winding gap 5. The desired waveguide geometry results from the sequence of the superimposed flat cables 6, 8, 9 and flat strips 7 and their respective internal configuration.

[0021] The first flat cable 6, the actual data cable, has several electrical conductors 10a, 10b, 11a, 11b, 12 and, on its surface facing the second flat cable 8, a thin metallic coating, the so-called coupling surface 13. This coupling surface 13 can be applied to the flat cable 6, for example, using a thin-film PVD process. The second flat cable 8 has only one electrical conductor 14, which is at ground potential and extends practically across the entire width of the flat cable 8. Between the first and second flat cables 6, 8, a flat strip 7 is arranged as a dummy cable, which sets a specific distance between the electrical conductors 10a, 10b, 11a, 11b, 12 of the first flat cable 6 and the electrical conductor 14, which is at ground potential, of the second flat cable 8.The third flat cable 9 also has only one electrical conductor 15, via which the supply voltage of usually +12 volts is transmitted, and which also extends practically across the entire width of the flat cable 9. This third flat cable 9 is arranged directly next to the second electrical flat cable 8 without spacers. Two further flat strips 7 without electrical conductors are arranged next to the third flat cable 9. These serve to ensure sufficient spacing between the third flat cable 9 and the first flat cable 6, which, depending on the current rotational position of the clock spring cassette, comes back into contact with the first flat cable 6 after several revolutions.

[0022] The first flat cable 6 is constructed in detail as described below. All electrical conductors 10a, 10b, 11a, 11b, 12 are arranged approximately centrally in the flat cable 6 with respect to its thickness and surrounded by a sheath made of an insulating material. The actual data lines consist of two parallel conductors 10a, 10b, each having a width of 0.2 mm and a distance of 0.6 mm from each other. Externally adjacent to this pair of data lines 10a, 10b is a pair of electrical conductors 11a, 11b at ground potential. Further electrical conductors 12 can optionally be arranged externally adjacent to this pair of ground lines 11a, 11b.

Claims

Patent claims 1. A coil spring cassette comprising a stationary cylindrical stator housing part (1) and a cylindrical rotor housing part (2) arranged coaxially thereto and rotatable about its longitudinal axis, wherein a winding gap (5) is formed which is delimited by the outer circumferential surface (3) of the inner housing part (1) and the inner circumferential surface (4) of the outer housing part (3), in which at least one flexible flat cable (6) having at least one electrical conductor and at least one flexible flat strip (7) serving to mechanically stabilize the flat cable (6) are arranged in such a way that their respective first ends are fastened to the stator housing part (1) and their respective second ends are fastened to the rotor housing part (2),and that they are wound in opposite directions with a respective first section of their length against the outer surface (3) of the inner housing part (1) and with a respective second section of their length against the inner surface (4) of the outer housing part (2), so that a U-shaped turning section (6', 7') reversing the winding direction is formed between the respective two sections of the flat cable (6) and the flat strip (7), characterized in that at least three flexible flat cables (6, 8, 9) and three flat strips (7) cooperate in their sequence of superimposition and their respective internal configuration when resting against each of the surface areas (3, 4) of the winding gap (5) to form a desired waveguide geometry.

2. Clock spring cassette according to claim 1, characterized in that the first flat cable (6) in the sequence has at least four electrical conductors (10a, 10b, 11a, 11b) and a thin metallic coating (13) on its surface facing the second flat cable (8), that the second flat cable (8) has an electrical conductor (14) to ground potential, that the third flat cable (9) has an electrical conductor (15) for transmitting the supply voltage, and that a flat strip (7) without electrical conductors is arranged between the first and second flat cables (6, 8), and that two further flat strips (7) without electrical conductors are arranged next to the third flat cable (9).

3. Clock spring cassette according to claim 2, characterized in that the electrical conductors (10a, 10b, 11a, 11b) of the first flat cable (6) are arranged centrally with respect to its thickness, that a pair of conductors (10a, 10b) arranged immediately adjacent to one another are surrounded as data lines by a pair of electrical conductors (11a, 11b) at ground potential.

4. Clock spring cassette according to claim 3, characterized in that the electrical conductors (10a, 10b, 11a, 11b) of the first flat cable (6) each have a width of 0.2 mm and a distance of 0.6 mm from one another.

5. Clock spring cassette according to one of claims 2 to 4, characterized in that the electrical conductors (14, 15) of the second and / or the third flat cable (8, 9) extend over the entire width of the flat cables (8, 9).

6. Clock spring cassette according to one of claims 3 to 5, characterized in that further electrical conductors (12) are arranged externally adjacent to the pair of electrical conductors (11a, 11b) at ground potential.

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