PATENT ABSTRACT
The invention proposes an electrically operated power steering controller for inputting a driving electric current offset value of higher accuracy and being able to make an offset correction of a driving electric current by using this driving electric current offset value of higher accuracy, and an adjusting method of this driving electric current offset. Therefore, an electric motor driving electric current measuring device of accuracy higher than that of an electric motor driving electric current detector assembled into a controller CNT is prepared separately from this electric motor driving electric current detector. The driving electric current offset value of high accuracy is outputted by this electric motor driving electric current measuring device. An input device for receiving the driving electric current offset value of high accuracy from the driving electric current measuring device is arranged in an offset correcting device or an of f set signal generator within the controller.

PATENT DESCRIPTION
This is a continuation of application Ser. No. 10/979,242 filed Nov. 3, 2004. The entire disclosure of the prior application, application Ser. No. 10/979,242 is considered part of the disclosure of the accompanying continuation application and is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an electrically operated power steering controller for controlling the operation of an electric motor for generating auxiliary steering torque and an adjusting method of its driving electric current offset. 
   2. Background Art 
   The electrically operated power steering controller disclosed in FIG. 2 of JP08-175405A includes an offset correcting means as well as a target signal generating means, an electric current detecting means and a drive control means. This electrically operated power steering controller controls the operation of the electric motor for generating the auxiliary steering torque. The target signal generating means calculates a driving electric current target value with respect to the electric motor, and generates a driving electric current target signal representing this driving electric current target value. The electric current detecting means detects the driving electric current value of the electric motor, and generates a driving electric current detecting signal representing this driving electric current value. 
   In this electrically operated power steering controller, the driving electric current of the electric motor is basically controlled by the driving control means such that the deviation between the driving electric current target value calculated by the target signal generating means and the driving electric current value detected by the electric current detecting means is zero. However, in the electrically operated power steering controller, the driving electric current value detected from the electric motor includes a driving electric current offset value even when the driving electric current target value with respect to the electric motor is zero. Therefore, the offset correcting means disclosed in the above prior art stores the driving electric current offset value when this driving electric current target value is zero, and makes an offset correction in consideration of this driving electric current offset value. 
   However, the offset correcting means disclosed in the above prior art stores the driving electric current offset value by using an output from the electric current detecting means for detecting the driving electric current value from the electric motor as it is. However, this electric current detecting means is a mass-produced product assembled into the electrically operated power steering controller, and its electric current detecting accuracy cannot be set to be so high from the restriction of cost. Therefore, the accuracy of the stored driving electric current offset value becomes low so that the accuracy of the offset correction also becomes low. 
   SUMMARY OF THE INVENTION 
   This invention proposes an improved electrically operated power steering controller able to introduce a more precise driving electric current offset value. 
   Further, this invention proposes an adjusting method of the driving electric current offset in the electrically operated power steering controller able to introduce a more precise driving electric current offset value into the electrically operated power steering controller. 
   According to a first aspect of this invention, it is proposed an electrically operated power steering controller for controlling the operation of an electric motor for generating auxiliary steering torque. The electrically operated power steering controller according to the first aspect includes driving electric current target signal generating means, driving electric current detecting means, offset correcting means and electric motor driving control means. The driving electric current target signal generating means generates a driving electric current target signal representing a driving electric current target value Itag for the electric motor. The driving electric current detecting means generates a driving electric current detecting signal representing a driving electric current value Imtr of the electric motor. The offset correcting means generates a corrected driving electric current signal representing a corrected driving electric current value Iamd provided by correcting the driving electric current value Imtr by using a driving electric current offset value Ioff of the electric motor when the driving electric current target value Itag is set to zero. The electric motor driving control means controls the operation of the electric motor on the basis of the driving electric current target signal and the corrected driving electric current signal. In the electrically operated power steering controller according to the first aspect, the offset correcting means has first and second input sections, the driving electric current detecting signal is inputted to the first input section, and input means for inputting a driving electric current offset signal representing the driving electric current offset value Ioff is connected to the second input section. 
   According to a second aspect of this invention, it is proposed an electrically operated power steering controller for controlling the operation of an electric motor for generating auxiliary steering torque. The electrically operated power steering controller according to the second aspect includes driving electric current target signal generating means, driving electric current detecting means, offset signal generating means, arithmetic means and electric motor driving control means. The driving electric current target signal generating means generates a driving electric current target signal representing a driving electric current target value Itag for the electric motor. The driving electric current detecting means generates a driving electric current detecting signal representing a driving electric current value Imtr of the electric motor. The offset signal generating means generates a driving electric current offset signal representing a driving electric current offset value Ioff of the electric motor when the driving electric current target value Itag is set to zero. The arithmetic means calculates an arithmetic value Iest=Itag−(Imtr−Ioff) on the basis of the driving electric current target signal, the driving electric current detecting signal and the driving electric current offset signal. The electric motor driving control means controls the operation of the electric motor on the basis of the arithmetic value. The electrically operated power steering controller according to the second aspect is constructed such that the driving electric current detecting signal and the driving electric current offset signal are supplied to the arithmetic means from routes different from each other, and input means for inputting the offset electric current signal representing the driving electric current offset value Ioff is connected to the offset signal generating means. 
   According to the first aspect, it is also proposed an adjusting method of a driving electric current offset in an electrically operated power steering controller including driving electric current target signal generating means, driving electric current detecting means, offset correcting means and electric motor driving control means. The driving electric current target signal generating means generates a driving electric current target signal representing a driving electric current target value Itag for an electric motor for generating auxiliary steering torque. The driving electric current detecting means generates a driving electric current detecting signal representing a driving electric current value Imtr of the electric motor. The offset correcting means generates a corrected driving electric current signal representing a corrected driving electric current value Iamd provided by correcting the driving electric current value Imtr by using a driving electric current offset value Ioff of the electric motor when the driving electric current target value Itag is set to zero. The electric motor driving control means controls the operation of the electric motor on the basis of the driving electric current target signal and the corrected driving electric current signal. In the electrically operated power steering controller according the first aspect, the offset correcting means has first and second input sections, the driving electric current detecting signal is inputted to the first input section, and input means for inputting an offset electric current signal representing the driving electric current offset value Ioff is connected to the second input section. The adjusting method according to the first aspect uses driving electric current measuring means different from the driving electric current detecting means. In the adjusting method according to the first aspect, the offset electric current signal representing the driving electric current offset value Ioff is inputted to the offset correcting means through the input means by this driving electric current measuring means. 
   According to the second aspect, it is also proposed an adjusting method of a driving electric current offset in an electrically operated power steering controller including driving electric current target signal generating means, driving electric current detecting means, offset signal generating means, arithmetic means and electric motor driving control means. The driving electric current target signal generating means generates a driving electric current target signal representing a driving electric current target value Itag for an electric motor for generating auxiliary steering torque. The driving electric current detecting means generates a driving electric current detecting signal representing a driving electric current value Imtr of the electric motor. The offset signal generating means generates a driving electric current offset signal representing a driving electric current offset value Ioff of the electric motor when the driving electric current target value Itag is set to zero. The arithmetic means calculates an arithmetic value Iest−Itag−(Imtr−Ioff) on the basis of the driving electric current target signal, the driving electric current detecting signal and the driving electric current offset signal. The electric motor driving control means controls the operation of the electric motor on the basis of the arithmetic value. The electrically operated power steering controller according to the second aspect is constructed such that the driving electric current detecting signal and the driving electric current offset signal are supplied to the arithmetic means from routes different from each other, and input means is connected to the offset signal generating means. The adjusting method according to the second aspect uses driving electric current measuring means different from the driving electric current detecting means, and the offset electric current signal representing the driving electric current offset value Ioff is inputted to the offset signal generating means through the input means by this driving electric current measuring means. 
   In the electrically operated power steering controller corresponding to the first aspect of this invention, the offset correcting means has the first and second input sections, and the driving electric current detecting signal is inputted to the first input section, and the input means for inputting the driving electric current offset signal representing the driving electric current off set value Ioff is connected to the second input section. Accordingly, the driving electric current offset signal representing the driving electric current offset value of high accuracy can be introduced from this input means irrespective of the driving electric current detecting means. Thus, the operation of the electric motor can be controlled with higher accuracy by using this driving electric current offset value of high accuracy. 
   Further, in the electrically operated power steering controller corresponding to the second aspect of this invention, the electrically operated power steering controller is constructed such that the driving electric current detecting signal and the driving electric current offset signal are supplied to the arithmetic means from routes different from each other, and the input means for inputting the driving electric current offset signal representing the driving electric current offset value Ioff is connected to the offset signal generating means. Accordingly, the driving electric current offset signal representing the driving electric current offset value of high accuracy can be introduced from this input means irrespective of the driving electric current detecting means. Thus, the operation of the electric motor can be controlled with higher accuracy by using this driving electric current offset value of high accuracy. 
   In the adjusting method of the driving electric current offset in the electrically operated power steering controller corresponding to the first aspect of this invention, the driving electric current measuring means different from the driving electric current detecting means is used, and the driving electric current offset signal representing the driving electric current offset value Ioff is inputted to the offset correction means through the input means by this driving electric current measuring means. Accordingly, the driving electric current offset signal representing the driving electric current offset value of high accuracy can be introduced into the electrically operated power steering controller by setting the measuring accuracy of the driving electric current measuring means to be higher than the detecting accuracy of the driving electric current detecting means. Thus, the electrically operated power steering controller can control the operation of the electric motor with higher accuracy by using this driving electric current offset value of higher accuracy. 
   Further, in the adjusting method of the driving electric current offset in the electrically operated power steering controller corresponding to the second aspect of this invention, the driving electric current measuring means different from the driving electric current detecting means is used, and the driving electric current offset signal representing the driving electric current offset value Ioff is inputted to the offset signal generating means through the input means by this driving electric current measuring means. Accordingly, the driving electric current offset signal representing the driving electric current offset value of high accuracy can be introduced into the electrically operated power steering controller by setting the measuring accuracy of the driving electric current measuring means to be higher than the detecting accuracy of the driving electric current detecting means. Thus, the electrically operated power steering controller can control the operation of the electric motor with higher accuracy by using this driving electric current offset value of higher accuracy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing an embodiment 1 of an electrically operated power steering controller in this invention; 
       FIG. 2  is a flow chart showing an adjusting method of a driving electric current offset of the electrically operated power steering controller of the embodiment 1; 
       FIG. 3  is a block diagram showing an embodiment 2 of the electrically operated power steering controller in this invention; and 
       FIG. 4  is a flow chart showing an adjusting method of the driving electric current offset of the electrically operated power steering controller of the embodiment 2. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Some embodiments of this invention will next be explained with reference to the drawings. 
   Embodiment 1 
   This embodiment 1 is an embodiment corresponding to a first aspect of this invention, and includes an electrically operated power steering controller in this invention, and an adjusting method of a driving electric current offset in the electrically operated power steering controller in this invention. 
     FIG. 1  is a block diagram showing the electrically operated power steering controller in this embodiment 1. This electrically operated power steering controller is mounted to an automobile, and includes a controller CNT, a direct current power source BAT, an electric motor MTR and an electric motor driving electric current measuring means MCM. The controller CNT, the direct current power source BAT and the electric motor MTR are mounted to the automobile, but the electric motor driving electric current measuring circuit MCM is arranged in a manufacturing factory or a repairing factory of the automobile or automobile parts. When an adjusting process of the driving electric current offset is executed with respect to the electrically operated power steering controller, the electric motor driving electric current measuring circuit MCM is combined with the controller CNT, the direct current power source BAT and the electric motor MTR. For example, the direct current power source BAT is a battery mounted to the automobile. 
   The electric motor MTR is assembled into a steering mechanism of the automobile, and gives auxiliary steering torque for assisting steering torque provided by a driver to the steering mechanism. The steering mechanism of the automobile has a steering handle operated by the driver, a steering shaft operated by this steering handle, and a gear box connected to this steering shaft. The steering mechanism steers a steering wheel of the automobile through the steering shaft and the gear box on the basis of the steering torque given to the steering handle. The electric motor MTR is connected to the steering shaft through a speed reduction gear, and gives the auxiliary steering torque for assisting the steering torque to the steering shaft. For example, a direct current electric motor is used as this electric motor MTR. 
   The controller CNT includes a power driving circuit  100  with respect to the electric motor MTR, and a control unit  200  for controlling the operation of this power driving circuit  100 . The power driving circuit  100  includes a switch circuit  110  connected to the direct current power source BAT and switching the polarities of its direct current voltage, a gate driving circuit  120  with respect to this switch circuit  110 , and an electric motor driving electric current detecting circuit  130 . 
   The switch circuit  110  includes two power switch elements  11 A,  11 B connected in series, and power switch elements  11 C,  11 D connected in series. The connecting portion between the power switch elements  11 A and  11 B constitutes a first output terminal  11   a . The connecting portion between the power switch elements  11 C and  11 D constitutes a second output terminal  11   b.    
   The electric motor MTR is connected between the first output terminal  11   a  and the second output terminal  11   b , and the operation of the electric motor MTR is controlled by the switch circuit  110  in a first or second control state. In the first control state, for example, the electric motor MTR is rotated in the positive direction in a controlled driving duty ratio. In the second control state, for example, the electric motor MTR is rotated in the reverse direction in the controlled driving duty ratio. 
   In the first control state, both the power switch elements  11 B,  11 C are turned off, and both the power switch elements  11 A,  11 D are periodically turned on in the controlled driving duty ratio. When the power switch elements  11 A,  11 D are turned on in this first control state, an electric current is flowed from the power switch element  11 A to the power switch element  11 D via the first output terminal  11   a , the electric motor MTR and the second output terminal  11   b . When the electric current flowed to the electric motor MTR is set to have a positive polarity in this first control state, the electric motor MTR is rotated in the positive direction in the driving duty ratio and is operated by the electric current of the positive polarity in the first control state. 
   In the second control state, both the power switch elements  11 A,  11 D are turned off, and both the power switch elements  11 B,  11 C are periodically turned on in the controlled duty ratio. when the power switch elements  11 B,  11 C are turned on in this second control state, the electric current is flowed from the power switch element  11 C to the power switch element  11 B via the second output terminal  11   b , the electric motor MTR and the first output terminal  11   a . When the electric current flowed to the electric motor MTR in this second control state is set to have a reverse polarity, the electric motor MTR is rotated in the reverse direction in the driving duty ratio and is operated by the electric current of the reverse polarity in the second control state. 
   For example, a power MOSFET is used in the power switch elements  11 A,  11 B,  11 C,  11 D. This power MOSFET has a gate for controlling its turning on and off operations, and attains a turning-on state when a driving pulse is given to the gate. A gate driving circuit  120  has driving pulse circuits  12 A,  12 B,  12 C, l 2 D for supplying the a driving pulse to the respective gates of the power switch elements  11 A,  11 B,  11 C,  11 D. 
   The electric motor driving electric current detecting circuit  130  generates a driving electric current detecting signal SImtr representing a driving electric current value Imtr of the electric motor MTR. This electric motor driving electric current detecting circuit  130  includes a detecting resistor RD and a driving electric current detecting means  13 . The detecting resistor RD is connected between the first output terminal  11   a  and the electric motor MTR. The driving electric current detecting means  13  detects the voltage generated at both the ends of a detecting resistor  21  on the basis of the driving electric current value Imtr of the electric motor MTR, and generates the driving electric current detecting signal SImtr representing the driving electric current value Imtr. 
   The electric motor driving electric current detecting circuit  130  is assembled into the controller CNT. The controller CNT is a mass-produced controller mounted to the automobile and including the electric motor driving electric current detecting circuit  130 . There is a restriction in cost of this controller CNT to mass-produce this controller CNT. Since this restriction of cost is similarly applied to the electric motor driving electric current detecting circuit  130 , the electric motor driving electric current detecting circuit  130  and an A/D converter  51  are also made at relatively low cost, and its detecting accuracy of the driving electric current value Imtr is not so high. 
   Similar to the electric motor driving electric current detecting circuit  130 , the electric motor driving electric current measuring circuit MCM measures the driving electric current value Imtr of the electric motor MTR. However, this electric motor driving electric current measuring circuit MCM is not mounted to the automobile, but is arranged in a manufacturing factory of the automobile or automobile parts or a repairing factory of the automobile. Only a small number of electric motor driving electric current measuring circuits MCM are arranged in the manufacturing factory of the automobile or the automobile parts, or the repairing factory, and are not restricted so much in cost. Accordingly, the electric motor driving electric current measuring circuit MCM is constructed so as to generate a driving electric current measuring signal SIPmtr in which the driving electric current value Imtr is measured with high accuracy in comparison with the electric motor driving electric current detecting circuit  130 . This electric motor driving electric current measuring circuit MCM has an electric motor driving electric current measuring means  300  and an A/D converter  301 . This electric motor driving electric current measuring means  300  is connected between the second output terminal  11   b  and the electric motor MTR, and outputs a driving electric current measuring signal (analog) of high accuracy. The A/D converter  301  of high accuracy is connected to the output of the electric motor driving electric current measuring means  300 , and this A/D converter  301  outputs the driving electric current measuring signal SIPmtr of high accuracy in which the driving electric current measuring signal of high accuracy is converted into a digital format. 
   The control unit  200  is constructed with a microcomputer  20  as a center. This microcomputer  20  includes a driving electric current target signal generating means  30 , an electric motor driving control means  40 , an offset correcting means  50 , an arithmetic means  60  and a ROM  70 , The ROM  70  is a read only memory for storing a program required in the microcomputer  20 . The operations of the driving electric current target signal generating means  30 , the electric motor driving control means  40 , the offset correcting means  50  and the arithmetic means  60  are respectively executed by using a CPU and a RAM of the microcomputer  20  on the basis of the program stored to the ROM  70 . 
   The driving electric current target signal generating means  30  calculates a driving electric current target value Itag with respect to the electric motor MTR, and generates a driving electric current target signal SItag representing this driving electric current target value Itag. This driving electric current target signal generating means  30  has two input sections  30   a ,  30   b  and one output section  30   c . A steering torque signal ST representing steering torque T from a steering torque sensor  31  is fetched into the input section  30   a  through an A/D converter  32 . Various kinds of signals are fetched from a network  33  within the automobile into the input section  30   b  through a control area network (CAN)  34 . A vehicle speed signal SV representing a vehicle speed V of the automobile, a steering angle signal Sθ representing the steering angle θ of a steering handle, and a steering speed signal Sωs representing a rotating speed ωs of the steering shaft of the steering mechanism are transmitted in the network  33 . The driving electric current target signal generating means  30  calculates the driving electric current target value Itag on the basis of the steering torque signal ST, the vehicle speed signal SV, the steering angle signal Sθ and the steering speed signal Sωs, and generates the driving electric current target signal SItag representing this driving electric current target value Itag in the output section  30   c . This driving electric current target signal SItag is supplied to the arithmetic means  60 . This arithmetic means  60  outputs a driving electric current arithmetic value Iest. 
   The electric motor driving control means  40  has one input section  40   a  and two output sections  40   b ,  40   c . The input section  40   a  is connected to the arithmetic means  60 . The output sections  40   b ,  40   c  are respectively connected to pulse width modulating circuits (PWM)  41 ,  42 . These pulse width modulating circuits  41 ,  42  give a controlled driving duty ratio to the respective driving pulse circuits  12 A to  12 D of the gate driving circuit  120 . The electric motor driving control means  40  controls the driving duty ratio outputted from the pulse width modulating circuits  41 ,  42  on the basis of the driving electric current arithmetic value Iest from the arithmetic means  60 , and controls the driving electric current value Imtr with respect to the electric motor MTR. 
   When the driving electric current target value Itag is given to the electric motor driving control means  40 , the electric motor driving control means  40  basically controls the operations of the pulse width modulating circuits  41 ,  42  and controls the driving electric current Imtr of the electric motor MTR by the gate driving circuit  120  such that the driving electric current value Imtr is equal to this driving electric current target value Itag. However, even when the driving electric current target value Itag is set to zero, the electric current of a predetermined driving electric current offset value Ioff is flowed to the electric motor MTR. Accordingly, the driving electric current value Imtr is corrected by the offset correction means  50 . 
   A corrected driving electric current value Iamd given from the offset correcting means  50  to the arithmetic means  60  is represented by the following formula (1).
 
 I amd= I mtr− I off   (1)
 
   The arithmetic means  60  calculates the driving electric current arithmetic value Iest by the following formula (2).
 
 I est= I tag− I amd= I tag− I mtr+ I off   (2)
 
   The offset correcting means  50  has two input sections  50   a ,  50   b , one input-output section  50   c  and one output section  50   d . The driving electric current detecting signal SImtr representing the driving electric current value Imtr from the electric motor electric current detecting circuit  130  is converted into a digital signal by an A/D converter  51  and is inputted to the input section  50   a . An input means  52  is connected to the input section  50   b . This input means  52  is an input means called a serial communication interface(SCI), and the driving electric current offset value Ioff of high accuracy from the electric motor driving electric current measuring circuit MCM is inputted in a digital format to this input means  52  through a communication means  53 . A nonvolatile memory (EEPROM)  55  is connected to the input-output section  50   c . The output section  50   d  supplies a correcting driving electric current signal SIamd representing the corrected driving electric current value Iamd to the arithmetic means  60 . 
   The offset adjusting process of the driving electric current is executed in the manufacturing factory of the automobile or the automobile parts, or the repairing factory by using the electric motor driving electric current measuring circuit MCM. In this offset adjusting process, the driving electric current offset value Ioff is really measured with the controller CNT and the electric motor MTR combined with this controller CNT as objects. This driving electric current offset value Ioff is adjusted such that the driving electric current target signal generating means  30  of the controller CNT sets the driving electric current target value Itag to zero. Then, the driving electric current value Imtr of the driving electric current flowed to the electric motor MTR at this time is really measured by the electric motor driving electric current measuring circuit MCM. The electric motor driving electric current measuring circuit MCM outputs the driving electric current measuring signal SIPmtr of high accuracy, but the driving electric current measuring signal SIPmtr provided by setting the driving electric current target value Itag to zero becomes a driving electric current offset signal SIoff representing the driving electric current offset value Ioff. 
   This driving electric current offset signal SIoff from the electric motor driving electric current measuring circuit MCM is supplied to the input means  52  through the communication means  53 , and is stored and held in the nonvolatile memory  55  through the offset correcting means  50 . This driving electric current offset value Ioff is held in the nonvolatile memory  55  until the driving electric current offset value Ioff is readjusted thereafter. 
   The RON  70  of the microcomputer  20  includes a program for fetching the driving electric current offset signal SIoff from the input means  52  to the of f set correcting means  50 , and a program for storing and holding the fetched driving electric current offset value Ioff in the nonvolatile memory  55 . The fetching operation of the driving electric current offset signal SIoff to the offset correcting means  50 , and the storing and holding operations of the offset value Ioff to the nonvolatile memory  55  are executed by using these programs of the ROM  70 . 
   After the offset adjusting process is terminated in the manufacturing factory of the automobile or the automobile parts, or the repairing factory, the offset correcting means  50  of the controller CNT mounted to the automobile calculates the corrected driving electric current value Iamd on the basis of the formula (1) in an operating state of the automobile. In this case, the driving electric current value Imtr is fetched from the driving electric current detecting signal SImtr from the driving electric current detecting circuit  130  assembled into the controller CNT. In this operating state of the automobile, the arithmetic means  60  calculates the driving electric current arithmetic value Iest by the formula (2), and the driving electric current value Imtr of the electric motor MTR is controlled on the basis of this driving electric current arithmetic value Iest. 
     FIG. 2  shows a flow chart of the adjusting process of the driving electric current offset in the embodiment 1. This flow chart of  FIG. 2  includes ten steps from step S 1  to step S 10 . As mentioned above, the adjusting process of this offset is executed in the manufacturing factory of the automobile or the automobile parts, or the repairing factory. The controller CNT is separated from the steering torque sensor  31 , the network  33  within the automobile, and the direct current power source BAT, and is connected to a direct current power source within a factory similar to the direct current power source BAT. 
   First, in the step S 1 , instructions of the offset adjustment are given from the communication means  53  to the controller CNT by using an instruction signal INS. These offset adjusting instructions are fetched to the microcomputer  20  through the input means  52  and the offset correcting means  50 . The microcomputer  20  stops control based on information from the steering torque sensor  31  and the network  33  within the automobile. In the next step $ 2 , the driving electric current target signal generating means  30  generates a driving target signal SItag with the driving electric current target value Itag as zero. 
   In the next step S 3 , the electric motor driving electric current measuring circuit MCM measures the driving electric current of the electric motor MTR corresponding to the driving electric current target value Itag=0, and generates an offset signal SIoff (digital) representing the driving electric current offset value Ioff of the electric motor MTR. In a step S 4 , this offset signal SIoff is inputted from the communication means  53  to the offset correcting means  50  through the input means  52 . 
   In the next step S 5 , the offset correcting means  50  stores the driving electric current offset value Ioff to the nonvolatile memory  55  on the basis of the fetched offset signal SIoff. In a step S 6 , the offset correcting means  50  calculates and outputs a corrected driving electric current value Iamd by using a detecting signal SImtr from the electric motor electric current detecting circuit  130  and the driving electric current offset value Ioff stored and held in the nonvolatile memory  55 . At this time, since the driving electric current target value Itag=0 is set, an arithmetic value Iest=TIamd=Imtr−Ioff is outputted from the arithmetic means  60 . 
   In the next step S 7 , the electric motor driving control means  40  controls the operation of the electric motor MTR through the pulse width modulating circuits  41 ,  42 , the gate driving circuit  120  and the switch circuit  110  on the basis of the arithmetic value Test from the arithmetic means  60 . In a step S 8 , the driving electric current value Imtr of the electric motor MTR is again measured by using the electric motor driving electric current measuring circuit MCM. 
   In the next step S 9 , it is judged whether the driving electric current value Imtr of the electric motor measured in the step S 8  lies within a predetermined tolerance or not. If this judging result is “yes”, the instructions of termination of the offset adjustment are given by an instruction signal INS from the communication means  53  in a step S 10 , and the offset adjusting process is terminated. In contrast to this, when the judging result of the step S 9  is “no”, it is returned to the step S 4 , and the adjustment of the driving electric current offset is again made. At the readjusting time, a driving electric current offset signal SIoff (n) based on the measuring result in the step S 8  is sent out in the step S 4 . In the step S 5 , a new driving electric current offset value Ioff is stored to the nonvolatile memory  55  on the basis of the driving electric current offset signal SIoff (n-1) sent out in the previous step S 4  and the above driving electric current offset signal SIoff (n). 
   As mentioned above, in the electrically operated power steering controller in the embodiment 1, the off set correcting means  50  has the first input section  50   a  and the second input section  50   b . The driving electric current detecting signal SImtr from the driving electric current detecting circuit  130  is inputted to the first input section  50   a . The input means  52  for inputting the driving electric current offset signal SIoff representing the driving electric current offset value Ioff is connected to the second input section  50   b . Accordingly, the driving electric current offset signal. SIoff repsenting the driving electric current offset value Ioff of high accuracy can be introduced from this input means  52  irrespective of the driving electric current detecting circuit  130 . Thus, the operation of the electric motor MTR can be controlled with higher accuracy by using this driving electric current offset value of high accuracy. 
   Further, in the embodiment 1, the driving electric current offset signal SIoff is fetched to the offset correcting means  50  by the program stored to the ROM  70  of the microcomputer  20 , and is stored and held in the nonvolatile memory  55 . Accordingly, the fetching operation of the driving electric current offset value Ioff and the storing and holding operations can be simply performed. In addition, the memory  55  is a nonvolatile memory and can reliably hold the driving electric current offset value Ioff until the driving electric current offset value Ioff is next rewritten. 
   Further, in the adjusting method of the driving electric current offset in the electrically operated power steering controller in the embodiment 1, the driving electric current measuring means  300  different from the driving electric current detecting means  13  is used and the offset electric current signal SIoff representing the driving electric current offset value Ioff is inputted to the offset correcting means  50  through the input means  52  by this driving electric current measuring means  300 . Accordingly, the driving electric current offset signal SIoff representing the driving electric current offset value Ioff of high accuracy can be introduced into the electrically operated power steering controller by setting the measuring accuracy of the driving electric current measuring means  300  to be higher than the detecting accuracy using the driving electric current detecting means  13  and the A/D converter  51 . Thus, the electrically operated power steering controller can control the operation of the electric motor with higher accuracy by using this driving electric current offset value of higher accuracy. 
   Further, in the adjusting method of the driving electric current offset of the electrically operated power steering controller in the embodiment 1, since the driving electric current offset signal SIoff is fetched to the offset correcting means  50  through the input means  52  as a digital signal, noise resisting characteristics of the driving electric current offset signal SIoff can be also improved. Embodiment 2. 
   This embodiment 2 is an embodiment corresponding to a second aspect of this invention, and includes an electrically operated power steering controller in this invention, and an adjusting method of the driving electric current offset in the electrically operated power steering controller in this invention. 
     FIG. 3  is a block diagram showing the electrically operated power steering controller in this embodiment 2. In the electrically operated power steering controller in this embodiment 2, an offset signal generating means  50 A is substituted for the offset correcting means  50  in the embodiment 1, and the driving electric current detecting signal SImtr reprenting the driving electric current value Imtr of the electric motor NTR from the electric motor driving electric current detecting means  13  is directly inputted to the arithmetic means  60 . The other constructions are the same as the embodiment 1. 
   In the offset signal generating means  50 A of  FIG. 3 , the input section  50   a  is omitted. This offset signal generating means  50 A of  FIG. 3  has an input section  50   b  connected to the input means  52 , an input-output section  50   c  connected to the nonvolatile memory  55 , and an output section  50   d  connected to the arithmetic means  60 . 
   In the adjusting process of the driving electric current offset similar to that in the embodiment 1, a driving electric current offset signal SIoff representing a driving electric current offset value Ioff measured with high accuracy by the electric motor driving electric current measuring means  300  is fetched from the input means  52  to the offset signal generating means  50 A in the input section  50   b  of the offset signal generating means  50 A, and is stored and held in the nonvolatile memory  55 . The offset signal generating means  50 A generates the driving electric current offset signal SIoff representing the driving electric current offset value Ioff of high accuracy in the output section  50   d  of this offset signal generating means  50 A, and supplies this driving electric current offset signal SIoff to the arithmetic means  60 . 
   In the embodiment 2, the arithmetic means  60  calculates a driving electric current arithmetic value lest on the basis of the following formula (3) by using a driving electric current target signal SItag representing a driving electric current target value Itag from the driving electric current target signal generating means  30 , a driving electric current detecting signal SImtr representing a driving electric current value Imtr from the driving electric current detecting means  13 , and the driving electric current offset signal SIoff representing the driving electric current offset value Ioff from the offset signal generating means  50 A.
 
 I est= I tag− I mtr+ I off   (3)
 
   In the adjusting process of the driving electric current offset, driving electric current target value Itag= 0  is set. Accordingly, the arithmetic value lest using the following formula (4) is calculated.
 
 I est=− I mtr+ I off   (4)
 
   The adjusting process of the driving electric current offset of the electrically operated power steering controller of this embodiment 2 is executed by the flow chart of  FIG. 4 . Similar to the embodiment it this adjusting process of the driving electric current offset is executed in the manufacturing factory of the automobile or the automobile parts, or the repairing factory. 
   Steps S 1  to S 4  of  FIG. 4  are the same as steps S 1  to S 4  of  FIG. 2 , and steps S 8  to S 10  of  FIG. 4  are also the same as steps S 8  to S 10  of  FIG. 2 . 
   In a step S 51  of  FIG. 4 , the offset signal generating means  50 A stores the driving electric current offset value Ioff of high accuracy from the driving electric current measuring means  300  to the nonvolatile memory  55 . In a step S 61 , the offset signal generating means  50 A generates the driving electric current off set signal SIoff representing the driving electric current offset value Ioff of high accuracy in the output section  50   d . In a step S 71 , the electric motor driving control means  40  drives the electric motor MTR by the difference between the arithmetic value lest based on the formula (4), i.e. , the driving electric current value Imtr and the driving electric current offset value Ioff of high accuracy. 
   As mentioned above, in the embodiment 2 of the electrically operated power steering controller in this invention, it is constructed such that the driving electric current detecting signal SImtr from the electric motor driving electric current detecting means  13  and the driving electric current offset signal SIoff from the offset signal generating means  50 A are supplied to the arithmetic means  60  from routes different from each other. Further, the input means  52  for inputting the driving electric current offset signal SIoff representing the driving electric current offset value Ioff is connected to the offset signal generating means  50 A. Accordingly, the driving electric current offset signal SIoff representing the driving electric current offset value Ioff of high accuracy can be introduced from this input means  52  irrespective of the driving electric current detecting means  13 . Thus, the operation of the electric motor can be controlled with higher accuracy by using this driving electric current offset value of high accuracy. 
   Further, similar to the embodiment 1, the driving electric current offset signal SIoff is fetched to the offset signal generating means  50 A by a program stored to the ROM  70  of the microcomputer  20  in the embodiment 2. Further, this driving electric current offset value Ioff is stored and held in the memory  55 . Accordingly, the fetching, storing and holding operations of the driving electric current offset value Ioff can be simply performed. In addition, the memory  55  is a nonvolatile memory and can reliably hold the driving electric current offset value Ioff until the driving electric current offset value Ioff is next rewritten. 
   Further, in the adjusting method of the driving electric current offset in the electrically operated power steering controller in the embodiment 2, the driving electric current measuring means  300  different from the driving electric current detecting means  13  is used, and the offset electric current signal SIoff representing the driving electric current offset value Ioff is inputted to the offset signal generating means  50 A through the input means  52  by this driving electric current measuring means  300 . Accordingly, the driving electric current offset signal SIoff representing the driving electric current offset value Ioff of high accuracy can be introduced into the electrically operated power steering controller by setting the measuring accuracy of the driving electric current measuring means  300  to be higher than the detecting accuracy using the driving electric current detecting means  13  and the A/D converter  51 . Thus, the electrically operated power steering controller can control the operation of the electric motor with higher accuracy by using this driving electric current offset value of higher accuracy. 
   Further, in the adjusting method of the driving electric current offset of the electrically operated power steering controller in the embodiment 2, since the driving electric current offset signal SIoff is fetched to the offset correcting means  50  through the input means  52  as a digital signal, noise resisting characteristics of the driving electric current offset signal SIoff can be also improved. Embodiment 3. 
   In the embodiments 1 and 2, the direct current electric motor is used as the electric motor MTR. However, in this embodiment 3, a three-phase brushless alternating current electric motor is used, and an electric motor driving electric current measuring circuit MCM is arranged in each phase, and driving electric current offset values Ioff-a, Ioff-b, Ioff-c of the respective phases are stored and held in the nonvolatile memory  55 . Further, in accordance with this construction, the electric motor driving electric current detecting circuit  130  also detects driving electric current values Imtr-a, Imtr-b, Imtr-c of the respective phases. The other constructions are the same as the embodiment 1 or 2. In accordance with this embodiment 3, the driving electric current can be controlled with high accuracy while the driving electric current offset value of each phase of the three-phase alternating current electric motor is independent in each phase and is corrected by the driving electric current offset values Ioff-a, Ioff-b, Ioff-c of high accuracy from the electric motor driving electric current measuring circuit MCM. 
   Embodiment 4 
   In the above embodiments 1 to 3, the driving electric current offset signal SIoff is supplied to the input means  52  through the communication means  53 . However, in the embodiment 4, a mode for supplying the driving electric current offset signal SIoff through a control network (CAN)  34  is set. In this case, no input means  52  is required so that cost can be reduced. 
   The electrically operated power steering controller and the adjusting method of its driving electric current offset in this invention are utilized in a power steering device of the automobile.