As a conventional art, a general configuration of the conventional electric power steering apparatus will be described with reference to FIG. 1. As shown in FIG. 1, a column shaft (a steering shaft) 2 connected to a steering wheel 1 is connected to steered wheels 8L and 8R through reduction gears 3, universal joints 4a and 4b, a pinion-and-rack mechanism 5, and tie rods 6a and 6b, further via hub units 7a and 7b . In addition, the column shaft 2 is provided with a torque sensor 10 for detecting a steering torque Tr of the steering wheel 1 and a steering angle sensor 14 for detecting a steering angle θh of the steering wheel 1, and a motor 20 for assisting a steering torque of the steering wheel 1 is connected to the column shaft 2 through the reduction gears 3. The electric power is supplied to a control unit (ECU) 100 for controlling the electric power steering apparatus from a battery 13, and an ignition key signal is inputted into the control unit 100 through an ignition key 11. The control unit 100 calculates a steering assist command value of an assist (steering assist) command on the basis of the steering torque Tr detected by the torque sensor 10 and a vehicle speed Vs detected by a vehicle speed sensor 12, and controls a current supplied to the motor 20 by means of a voltage control value E obtained by performing compensation or the like to the steering assist command value. As well, a steering angle sensor 14 is not indispensable and may not be provided. It is possible to obtain the steering angle θ from a rotational position sensor such as a resolver which is connected to the motor 20.
The controller area network (CAN) 50 to send/receive various information and signals on the vehicle is connected to the control unit 100, and it is also possible to receive the vehicle speed Vs from the CAN 50. Further, a Non-CAN 51 is also possible to connect to the control unit 100, and the Non-CAN 51 sends and receives a communication, analogue/digital signals, electric wave or the like except for the CAN 50.
In the electric power steering apparatus having a torsion bar to the column shaft (the handle shaft) 2, for example, as shown in FIG. 2, various sensors are mounted on the column shaft between which the torsion bar 23 is interposed, and various angles are detected. That is, a Hall IC sensor 21 as an angle sensor and a 20° rotor sensor 22 of a torque sensor input-side rotor are mounted on an input shaft 2A of the steering wheel 1 side of the handle shaft 2. The Hall IC sensor 21 outputs an AS_IS angle θn of 296° period. The 20° rotor sensor 22 that is mounted to the steering shaft 1 side closer than the torsion bar 23 outputs a column input-side angle signal θh1 of 20° period, and the column input-side angle signal θh1 is inputted into a steering angle calculating section 50. A 40° rotor sensor 24 of a torque sensor output-side rotor is mounted on an output shaft 2B of the handle shaft 2, a column output-side angle signal θc1 from the 40° rotor sensor 24 is outputted, and the column output-side angle signal θc1 is inputted into the steering angle calculating section 50. The column input-side angle signal θh1 and the column output side angle signal θc1 are calculated with an absolute angle at the steering angle calculating section 50, a handle angle θh and a column angle θc with the absolute angle are outputted from the steering angle calculating section 50. A mechanism diagram that shows a relationship among a torsion bar torsional angle Δθ, the handle angle θh and the column angle θc is shown in FIG. 3.
As another prior art, it is known that the power steering apparatus, which has a parking assist apparatus which easily assists a double parking or a parallel parking, steering-controls by performing a velocity proportional-integrational control (a velocity PI-control) to a deviation between a target steering angle and a steering angle. The above technique is disclosed in, for example, Japanese Unexamined Patent Publication No. 2003-341543 (Patent Document 1).
In the electric power steering apparatus of the vehicle having the automatic mode (a parking assist function) and the assist mode, it is known that a steering angle control section including a position control system that a velocity control loop system is a minor loop, and comprises a rate limiter which smooths the target steering angle and is constituted by a first-order or second-order low pass filter (LPF). This technique is disclosed in, for example, Japanese Unexamined Patent Publication No. 2013-252729 A (Patent Document 2) and Japanese Unexamined Patent Publication No. 2014-054885 A (Patent Document 3).