This invention relates to a steering torque detecting apparatus, and more particularly to a steering torque detecting apparatus which is simplified in structure, readily assembled and exhibits high reliability.
Now, a conventional steering torque detecting apparatus will be described with reference to FIGS. 1 to 3. FIG. 1 shows a conventional steering system for an outboard motor. A steering handle 101 is provided so as to be rotatably operated in any desired direction. The rotation of the steering handle 101 is transmitted through a steering wire 102, a slide member 105, a steering rod 107 and an oscillation lever 109 to an outboard motor 111.
Steering force input to the steering wire 102, as shown in FIG. 2, is also transmitted through an interlocking element 113 and a transmission rod 115 to a torque sensor 117. The torque sensor 117 includes a sensor body 121 slidably arranged in a housing 119 as shown in FIG. 3. The sensor body 121 is normally held at a neutral position by means of a spring 123. The sensor body 121 is formed at a part thereof into a reduced diameter, resulting in providing a reduced diameter section 125, on which a strain sensor 127 is mounted. The sensor body 121 is also connected to the transmission rod 115. To the strain sensor 127 is connected a signal cable 129, which is arranged so as to externally extend through a through-hole 131 formed at the housing 119.
When the sensor body 121 which is connected to the transmission rod 115 as described above is forced in the longitudinal direction thereof against the spring 123, strain occurs on the reduced diameter section 125 of the sensor body 121. The so-produced strain is detected by the strain sensor 127 and then input to a controller 133 shown in FIG. 1. The controller 133 serves to calculate power assisting force depending upon a detection signal supplied from the strain sensor 127 to generate a control signal, which is then supplied to a drive motor 135, leading to rotation of the drive motor 135. The rotation of the drive motor 135 causes a pinion 137 (FIG. 2) to be rotated, so that a rack 139 is moved in a suitable direction.
Such movement of the rack 139 results in the power assisting force being applied through the steering rod 107 to the oscillation lever 109.
Unfortunately, it was found that the conventional steering torque detecting apparatus constructed as described above has the following problems.
First, the operation of mounting the strain sensor 127 on the torque sensor 117 is highly troublesome, because it must be carried out in a narrow space in the housing 119.
Another problem of the conventional steering torque detecting apparatus is that the strain sensor 127 is readily subject to a radio trouble or fault. This adversely decreases the level of output of the strain sensor to a degree sufficient to cause the apparatus to require an amplifier, resulting in the apparatus being highly large-sized and costly.