The present invention relates to a signal transmission device which is used to electrically connect an auxiliary device provided on a steering wheel side of a vehicle to a wiring harness which is provided on the vehicle body side.
As a signal transmission device which supplies electricity to an auxiliary device provided on a rotating steering wheel, there is also available a signal transmission device which employs a sliding contact system. However, for example, in an air bag system mounted onto a steering wheel, such sliding contacts can be cut off instantaneously, proving fatal to the air bag system. For this reason, a highly reliable cable type of electric connecting device, a Steering Roller Connector (SRC) is employed.
Here, FIG. 1 is an exploded perspective view of a conventional column and FIG. 2 is a section view of the column shown in FIG. 1 taken along the axial direction of a steering unit including a steering roller connector. An SRC 1 comprises an outer cylinder 3 which is a fixed member, and an inner cylinder 5 which is a rotating member and is coaxial with the outer cylinder 3. Outer cylinder 3 and inner cylinder 5 define an annular storage chamber which houses an electrical cable 6 stored in a spiral manner. One end of the cable 6 is guided out from the outer cylinder 3 and is connected to a wiring harness provided on the vehicle body side, while the other end of the cable 6 is guided out from the inner cylinder 5 and is connected to an auxiliary device such as a horn switch, a steering switch, or a squib provided in an inflator. The SRC 1 can be fixed to a column 9 in such a manner that a fixing portion 7 provided on the outer periphery of the outer cylinder 3 is fixed to a screw hole 11 formed in the column 9.
The column 9 includes a pair of connector storage portions 13 which are respectively formed on the two side surfaces thereof; and, a lever unit, such as a turn signal lever 15 or a wiper control switch 17, is mounted into one of the corresponding connector storage portions 13. Also, a canceler 19 is assembled to the column 9.
The canceler 19 includes an engaging projection 27 on the upper surface thereof and, in order to prevent its relative rotation to the SRC 1, the engaging projection 27 is engaged with the lower surface of the inner cylinder 5 of the SRC 1. Also, the canceler 19 can be rotated integrally with the steering and thus, if the canceler 19 is rotated integrally with steering, then it not only transmits the rotation of the steering to the inner cylinder 5 of the SRC 1 but also brings a canceler portion 23 into contact with a return portion 25 provided in a turn signal cancel mechanism (not shown) to thereby return or cancel the turn signal lever 15 to its neutral position. Between the canceler 19 and a base plate 29 provided in the column 9, there is interposed a spring 31 which is used to energize the canceler 19 toward the SRC 1. With this structure, even when the SRC 1 is mounted at a position where the engaging projection 27 is not engaged, the canceler 19 can be moved in the steering axial direction against the energizing force of the spring 31, thereby being able to prevent itself against breakage.
However, in the above-mentioned conventional column structure, since the SRC 1 is disposed on the column 9, the canceler 19 is disposed on the lower surface of the column 9 in such a manner that it can be moved in the steering axial direction, and the spring 31 is used to energize the canceler 19 toward the SRC 1, a wide space is required which extends in the steering axial direction and is used to store these component parts. This not only increases the size of the column structure, but also increases the number of parts to be disposed in the steering axial direction, thus increasing the number of man-hours required for assembly. Also, when the SRC 1 is stored within the column 9, because of the limited space, the cancel system must be replaced with an electronic system, which further increases the number of parts required as well as the cost of the whole device.
Further, since the spring load of the spring 31 is applied to the sliding surfaces of the spring 31 and the canceler 19, there is a friction loss in rotation, which in turn degrades the operating feeling of the steering.