A rotation angle detector that is able to detect an absolute rotation angle of a detection body accurately and is able to reduce the installation space required. The rotation angle detector includes a first rotation angle detector connected to the detection body for generating a first detection signal having a cycle corresponding to the rotation of the detection body. The first rotation angle detector includes a first rotating body which is connected to the detection body and rotates together with the detection body. The detector includes a second rotation angle detector connected to the first rotation angle detector. The second rotation angle detector includes a second rotating body that rotates together with the first rotating body at a rate greater than that of the first rotating body, and generates a second detection signal having a cycle corresponding to the rotation of the second rotation body. The control device detects an absolute rotation angle of the detection body in accordance with the first detection signal and the second detection signal.
A method is provided for measuring an absolute steering angle .PHI. of a steering shaft for a vehicle, using a first rotatable body that rotates together with the steering shaft of the vehicle at a predetermined rotation ratio. The method includes obtaining a .PSI..sub.M ' value by measuring a relative rotational angle .PSI.' of the first rotatable body using an angle sensor having a measurement range of .OMEGA.. The method also includes obtaining a present value for a frequency i-value of the first rotatable body by comparing the present .PSI..sub.M ' value to a previous .PSI..sub.M ' value. The method also includes obtaining a present value for a absolute steering angle .PHI.1 of the steering shaft from a present value for an absolute rotational angle .PSI. of the first rotatable body by using the .PSI..sub.M ' value and the present i-value.
Supply and interruption of power source to the first angle sensor 2 and the second angle sensor 4 are alternately performed, by comparing the signal Vo1 or Vo2 which is outputted from the first angle sensor 2 or the second angle sensor 4 and amplified by the first signal amplifier 3 or the second signal amplifier 5 with the signal Vo1 or the signal Vo2 in a state where the abnormality such as the short-circuit does not occur between the wires, so that the determination is made as to whether or not the abnormality such as the short-circuit is present between the wires. The calculating section 6 can quickly detect an abnormality such as the short-circuit simply by supplying the power source to the first angle sensor 2 or the second angle sensor 4. In consequence, the abnormality of the rotational angle detecting device 1 can be detected before the steering wheel connected to the vehicular steering shaft is operated.
A rotation angle detection apparatus for reducing power consumption. A magnetoresistance element generates first and second analog signals, which change cyclically and continuously each time a steering shaft is rotated by 60 degrees. A microcomputer determines the rotation angle of the steering shaft from the output value and number of cycles of the analog signals.
A rotation-angle detecting device contains two rotators having the same number of teeth, which engage with a gear fixed to a rotation-detecting axle as a detected object. The detecting device further includes a controller. Receiving a rotation-angle signal from the rotators, the controller amplifies the signal, performs calculations, and stores the results. The controller converts each rotation-angle signal from each rotator into each periodic waveform output having the same crest value, and stores an initial phase difference value at initial setting. In driving operations, monitoring an evaluation value calculated with reference to the initial phase difference value, the controller determines that abnormalities occurred, if the evaluation value exceeds a predetermined abnormality-evaluation threshold.
An absolute steering angle of a steering shaft for a vehicle is measured using rotatable bodies that rotate together with the steering shaft at respective predetermined rotation ratios. A .PSI..sub.M' value is obtained by measuring a relative rotational angle .PSI.' of a first rotatable body and a .theta..sub.M' value is obtained by measuring the relative rotational angle .theta.' of a second rotatable body. .theta..sub.C's are obtained by calculating relative rotational angles .theta.'s of the second rotatable body corresponding to the .PSI..sub.M' value, using the relation between .PSI.' and .theta.'. A frequency i-value of the first rotatable body is obtained by comparing the .theta..sub.Cs to the .theta..sub.M' value. An absolute steering angle .PHI.1 of the steering shaft is obtained based on the relation between absolute rotational angles .PSI. and .PHI., after .PSI. is obtained using the i-value.
