JP2013032085A - Electric power steering control device - Google Patents

Abstract

An electric power steering device capable of correctly estimating road surface reaction torque is provided.
SOLUTION: Three sensors (torque sensor 4 and rotational angular velocity sensor 13) whose detected values change according to a handle torque that is a torque input by a driver, a motor torque that is a torque generated in a motor, and a road surface reaction force torque, respectively. , A motor current sensor 14), and a road surface reaction force estimator 101 that receives the detection values of these three sensors and outputs a road surface reaction force torque estimation value Tl_est based on these detection values. This road surface reaction force estimator 101 has a response that outputs an output value that is substantially equal to an input value for an input of an estimated value, and a separation that outputs substantially zero for an input other than the estimated value. An estimator having a characteristic, in which an estimated value is road surface reaction torque.
[Selection] Figure 2

Description

  The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus that determines an assist torque based on a road surface reaction torque.

  The electric power steering apparatus includes a motor, and generates assist torque in the motor. An apparatus that determines the assist torque based on road surface reaction torque is known (for example, Patent Document 1).

  In Patent Document 1, assist torque is determined based on vehicle speed, steering torque, road surface reaction force, and the like. The road surface reaction force is estimated by passing a steering shaft reaction force torque Ttran determined from the following equation through a low-pass filter. In the following equation, Thdl is the steering torque, Tassist is the assist torque, and J · dw / dt is the inertia term of the motor.

  Ttran = Thdl + Tassist−J · dw / dt

JP 2003-312521 A

  As described above, the invention of Patent Document 1 uses the steering torque Thdl, the assist torque Tassist, and the motor inertia term J · dw / dt to estimate the road surface reaction force. Even if the force is 0), the estimated value is not likely to be zero. That is, the invention of Patent Document 1 has a problem that the road surface reaction force cannot be estimated correctly.

  The present invention has been made based on this situation, and an object thereof is to provide an electric power steering apparatus capable of correctly estimating road surface reaction torque.

  In order to achieve the object, the invention according to claim 1 includes a motor, estimates a road surface reaction torque that is a torque input to the tire from the road surface, and uses at least the estimated road surface reaction torque in the motor. It is an invention of an electric power steering device that determines assist torque to be generated. The electric power steering apparatus according to the present invention includes first, second, and second detection values that change depending on a handle torque that is a torque input by a driver to a handle, a motor torque that is a torque generated in a motor, and a road surface reaction force torque, respectively. A third sensor and a road surface reaction force estimator that receives detection values of the first, second, and third sensors and outputs a road surface reaction force torque estimation value based on these detection values are provided. This road surface reaction force estimator has the responsiveness of outputting an output value approximately equal to the input value for the input of the estimated value, and the separability of outputting approximately zero for the input other than the estimated value An estimator having a road surface reaction force torque as an estimated value is used.

  As described above, the road surface reaction force estimator of the present invention has responsiveness of outputting an output value substantially equal to the input value with respect to the input of the estimated value, and the estimated value is the road surface reaction force torque. It is said that. Therefore, an output value substantially equal to the input value is output for the input of the road surface reaction torque, while substantially zero is output for the other inputs. Therefore, the road surface reaction torque can be correctly estimated.

  Examples of the first, second, and third sensors include a torque sensor that detects a steering torque, a rotational angular velocity sensor that detects a rotational angular velocity of a motor, and a motor current that detects a current flowing through the motor. A detection sensor can be used.

  Further, as in claim 3, it is particularly preferable to have the responsiveness with respect to an input of 20 Hz or less of the estimated value and that the separability is -40 dB or less.

  Moreover, as a road surface reaction force estimator provided with the said responsiveness and separability, the estimator designed by the H∞ control theory like Claim 4 can be used, for example. In the invention according to claim 2, the road surface reaction force estimator generates a control input u from the control output u and the external input w, and a generalized plant that outputs the controlled variable z and the observation output y. Is designed based on the H∞ control theory using a controller that feeds back to a generalized plant. The external input w is a handle torque, a motor torque, and a road surface reaction force torque. 2. The detected value of the third sensor, the controller is the road surface reaction force estimator, the control input u is the road surface reaction force torque estimated value output by the road surface reaction force estimator, and the control amount z is the road surface reaction force torque and the road surface. It is set as the difference e with the reaction force torque estimated value. The response from the handle torque, the motor torque, and the road surface reaction force torque that are external inputs w to the difference e between the road surface reaction force torque and the road surface reaction force torque estimated value that is the control amount z is substantially zero. A road surface reaction force estimator has been designed.

1 is a schematic diagram showing an overall configuration of an electric power steering apparatus to which the present invention is applied. It is a block diagram which shows the structure and function of the control apparatus 1 of FIG. It is a figure explaining the separability and responsiveness in the road surface reaction force estimator 101. It is a model figure which shows the general generalized plant for estimator design. It is a figure which shows the generalized plant used in order to design the road surface reaction force estimator 101 of this embodiment. FIG. 6 is a Bode diagram of a road surface reaction force estimator 101 designed using the generalized plant of FIG. 5. (A) is a Bode diagram which shows the characteristic of the road surface reaction force estimator 101, (b) is a figure which shows the step response of the road surface reaction force estimator 101. It is a flowchart which the road surface reaction force estimator 101 performs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an overall configuration of an electric power steering apparatus to which the present invention is applied.

  As shown in FIG. 1, a steering shaft 3 is connected to a steering wheel (hereinafter referred to as a handle) 2, and the steering shaft 3 rotates integrally with the handle 2. A speed reduction mechanism 5 is attached to the steering shaft 3. The speed reduction mechanism 5 decelerates the rotation of the motor 6 and transmits it to the intermediate shaft 7. The motor 6 generates steering assist torque (hereinafter referred to as assist torque) that assists the driver's steering force, and is connected to the steering shaft 3 via the speed reduction mechanism 5.

  The torque sensor 4 includes a torsion bar (not shown), and the steering shaft 3 and the intermediate shaft 7 are connected by the torsion bar. When the steering shaft 3 rotates with respect to the intermediate shaft 7, the torsion bar is twisted according to the rotation. The torque sensor 4 is provided with a sensor that detects the twist, and sequentially supplies the detected twist to the control device 1.

  The end of the intermediate shaft 7 opposite to the steering shaft 3 is connected to a pinion shaft 9 of a rack and pinion gear device 8. The gear device 8 is constituted by the pinion shaft 9 and the rack shaft 10. A pair of tires 11 as left and right steered wheels are connected to both ends of the rack shaft 10 via tie rods and knuckle arms (not shown). Accordingly, when the rotational motion of the pinion shaft 9 is converted into the linear motion of the rack shaft 10, the left and right tires 11 are steered by an angle corresponding to the linear motion displacement of the rack shaft 10.

  The rotation angular velocity sensor 13 and the motor current detection sensor 14 sequentially detect the rotation angular velocity dThc of the motor 6 and the current flowing through the motor 6, respectively, and sequentially send signals indicating the detected rotation angular velocity dThc and the motor current value Cur to the control device 1. Supply. Further, a signal indicating torque (hereinafter referred to as steering torque) Ts detected by the torque sensor 4 is also input to the control device 1. The steering torque Ts, the rotational angular velocity dThc of the motor 6, and the motor current value Cur are all detected because their detected values change according to the handle torque Th, the motor torque Tm, and the road surface reaction force torque Tl. The torque sensor 4, the rotational angular velocity sensor 13, and the motor current detection sensor 14 that correspond to the first, second, and third sensors in the claims.

  Next, the configuration, function, and the like of the control device 1 will be described with reference to FIG. The control device 1 includes a microcomputer, and some or all of the functions are realized by the microcomputer.

  The control device 1 includes a road surface reaction force estimator 101, a current command value converter 102, and a current control unit 103. The road surface reaction force estimator 101 is based on the steering torque Ts supplied from the torque sensor 4, the rotational angular velocity dThc of the motor 6 supplied from the rotational angular velocity sensor 13, and the motor current value Cur supplied from the motor current detection sensor 14. The estimated value of the road surface reaction force torque Tl (hereinafter referred to as the road surface reaction force torque estimated value) Tl_est is sequentially estimated. A method for estimating the road surface reaction force torque estimated value Tl_est in the road surface reaction force estimator 101 will be described later. The road surface reaction force estimator 101 outputs the estimated road surface reaction force torque estimated value Tl_est to the current command value converter 102 as an assist command value that is a command value of the assist torque generated by the motor 6.

  The current command value converter 102 converts the assist command value into a current command value based on a previously stored map or relational expression. The current control unit 103 includes a known motor drive circuit such as a bridge circuit composed of four MOSFETs, for example, and the motor current value detected by the motor current detection circuit 14 is supplied from the current command value converter 102. The feedback control of the motor drive circuit is performed so that the current command value becomes the same. The motor current detection circuit 14 described above detects the current flowing through the motor 6 by detecting the voltage across the current detection resistor provided between the motor drive circuit and the ground line.

  Next, a method for designing the road surface reaction force estimator 101 will be described. The road surface reaction force estimator 101 estimates a road surface reaction force torque estimated value Tl_est based on three input values, that is, the steering torque Ts, the rotational angular velocity dThc of the motor 6, and the motor current value Cur. Designed to satisfy performance and responsiveness.

  Here, first, separation and response in the road surface reaction force estimator 101 will be described with reference to FIG. Separation means that the output of the road surface reaction force estimator 101 becomes substantially zero when a value other than the road surface reaction force torque Tl, such as the handle torque Th and the motor torque Tm, is input. FIGS. 3A and 3B conceptually show input and output when the handle torque Th is input and when the motor torque Tm is input, respectively. Each of the sensors 4, 13, and 14 is used when the handle torque Th is input (FIG. 3A) and when the motor torque Tm is input (FIG. 3B). A detected value corresponding to the torque is input to the road surface reaction force estimator 101. However, when the steering wheel torque Th or the motor torque Tm is input, the output of the road surface reaction force estimator 101 is substantially zero. This is separability.

  On the other hand, responsiveness means that the gain from a true value to an estimated value is 1. Even when the road surface reaction force torque Tl is input, the sensors 4, 13, and 14 each input a detection value corresponding to the road surface reaction force torque Tl to the road surface reaction force estimator 101. In this case, the road surface reaction force estimation is performed. The device 101 outputs a value substantially equal to the input road surface reaction torque Tl.

  In the present embodiment, the road surface reaction force estimator 101 having such characteristics is designed based on the H∞ control theory. The H∞ control theory is called a generalized plant and targets a general-purpose control model having four inputs / outputs of a control input u, an external input w, an observation output y, and a controlled variable z (see FIG. 4). The purpose of the control is to keep the control amount z as small as possible with respect to the external input w. Therefore, by applying appropriate feedback from the observation output y to the control input u, the transfer function G from the external input w to the control amount z The controller K is designed to reduce the H∞ norm, in other words, to reduce the response from the external input w to the control amount z.

  FIG. 5 shows a generalized plant used for designing the road surface reaction force estimator 101 in this embodiment. In the electric power steering apparatus, torque is input from three torque input locations such as a handle (input by a driver), a motor, and a road surface. Therefore, the generalized plant in this embodiment uses an external input w as a handle torque Th and a motor. The torque Tm and the road surface reaction force torque Tl are used. The control input u is an output from the road surface reaction force estimator 101, that is, a road surface reaction force torque estimated value Tl_est estimated by the road surface reaction force estimator 101.

  The observation output y is the motor current value Cur, the rotational angular velocity dThc of the motor 6, and the steering torque Ts. Three types of values are used as the observation output y. In the electric power steering device, there are three torque input locations, such as the handle (input by the driver), the motor, and the road surface. This is because three or more types of observation output values are required for estimation. In this embodiment, the motor current value Cur, the rotational angular velocity dThc of the motor 6, and the steering torque Ts are used as the three types of observed output values for the following reason. In a vehicle equipped with an electric power steering device, the steering torque Ts is usually the sensor detection value closest to the driver, the rotational angular velocity dThc of the motor 6 is the sensor detection value closest to the road surface, and the motor current value Cur is the motor. This is because the sensor detection value closest to is.

  In the present embodiment, the remaining control amount z is the difference e between the road surface reaction force Tl and the road surface reaction force torque estimated value Tl_est, which is an estimator output. The reason why the control amount z is the difference e between the road surface reaction force Tl and the estimator output (Tl_est) will be described next.

  If only the road surface reaction force torque Tl is input and the handle torque Th and the motor torque Tm are both zero, the road surface reaction force estimator 101 can correctly estimate the road surface reaction force torque Tl. The estimator output (Tl_est) is Tl. Therefore, the difference e is zero. On the other hand, the steering wheel torque Th and the motor torque Tm are input, but if the road surface reaction force torque Tl is zero, the road surface reaction force estimator 101 is estimated if the road surface reaction force torque Tl can be correctly estimated. Output (Tl_est) becomes zero. Therefore, also in this case, the difference e is zero. That is, in any case, when the road surface reaction force estimator 101 can correctly estimate the road surface reaction force torque Tl, the difference e is zero.

  As described above, in the H∞ control theory, from the external input w (in this embodiment, the handle torque Th, the motor torque Tm, the road surface reaction torque Tl) to the control amount z (in this embodiment, the road surface reaction torque Tl). And the controller K (the road surface reaction force estimator 101) is designed so as to lower the response up to the difference e) between the estimator output Tl_est and the estimator output Tl_est. Therefore, the road surface reaction force estimator 101 that can correctly estimate the road surface reaction force torque Tl can be designed by setting the control amount z as the difference e between the road surface reaction force Tl and the estimator output (Tl_est). In this embodiment, the cut-off frequency (more specifically, the cut-off frequency of the frequency response from the road surface reaction force to the road surface reaction force estimator 101) is set to 20 [Hz] in consideration of the noise of the observation amount. Yes. FIG. 6 shows a Bode diagram of the road surface reaction force estimator 101 designed in this way.

  Next, it will be shown that the road surface reaction force estimator 101 designed as described above can correctly estimate the road surface reaction force torque Tl. In the following description, in order to make the description easy to understand, it is assumed that DC components are input to each observation output y, that is, the motor current value Cur, the rotational angular velocity dThc of the motor 6, and the steering torque Ts. However, the behavior at each frequency can be easily determined from the Bode diagram of FIG.

Assuming that the DC gain of the steering torque Ts is α, the DC gain of the rotational angular velocity dThc of the motor 6 is β, and the DC gain of the motor current Cur is γ, the output of the road surface reaction force estimator 101 can be expressed as Equation 1. Note that α and γ have opposite signs to β, as can be seen from FIG. 6, the phase of the motor current value Cur and the steering torque Ts is 180 ° with respect to the rotational angular velocity dThc of the motor 6. This is because it is reversed.
(Formula 1) -αTs + βdThc-γCur

  Here, gains α and β determined from the Bode diagram of FIG. 6 are gains such that the absolute values of αTs and βdThc are equal, and gain γ is given so that 2αTs = γCur. In addition, the detected current Cur when the handle torque Th is input or when the road surface reaction force torque Tl is input is only the current generated by the counter electromotive force, and therefore the detected current Cur when the motor torque Tm is input. Is sufficiently small, and γCur≈0. Based on these facts, (1) only the handle torque Th is input, (2) only the motor torque Tm is input, and (3) only the road surface reaction force torque Tl is input are considered. .

First, consider the case where (1) only the handle torque Th is input. When the handle torque Th is an input, the torsion torque Ts and the rotational angular velocity dThc of the motor 6 are both positive, but the detected current Cur is negative because it is a counter electromotive force. Further, as described above, since the absolute values of αTs and βdThc are equal to each other, Equation 1 is only γCur as shown in Equation 2, and γCur is substantially zero. That is, when only the handle torque Th is input, the output of the road surface reaction force estimator 101 is substantially zero.
(Formula 2) −αTs + βdThc−γ (−Cur) = γCur≈0

Next, consider (2) the case where only the motor torque Tm is input. When the motor torque Tm is an input, the signs of the torsion torque Ts and the rotational angular velocity dThc of the motor 6 are opposite to each other. Further, the detection current Cur is positive. Therefore, Formula 1 becomes Formula 3. As described above, since γ is given so that 2αTs = γCur, the output becomes zero.
(Expression 3) −α (−Ts) + βdThc−γCur = 2αTs−γCur≈0

Next, consider (3) the case where only road surface reaction torque Tl is input. Even when the road surface reaction torque Tl is input, the torsion torque Ts and the rotational angular velocity dThc of the motor 6 have opposite signs. Further, the detection current Cur is negative because it is a back electromotive force. Further, since the detected current Cur in the case of the counter electromotive force is substantially zero, γCur can be ignored. Therefore, Formula 1 becomes Formula 4. Therefore, when the road surface reaction force torque Tl is input, the road surface reaction force estimator 101 outputs a non-zero value of 2αTs.
(Formula 4) −α (−Ts) + βdThc−γCur = 2αTs + γCur = 2αTs

  FIG. 7A is a Bode diagram showing the frequency characteristics of the road surface reaction force estimator 101, and FIG. 7B is a view showing the step response of the road surface reaction force estimator 101. In FIG. 7, the solid line indicates the case where the handle torque Th is input, the dotted line indicates the case where the motor torque Tm is input, and the broken line indicates the case where the road surface reaction force torque Tl is input.

  As can be seen from FIG. 7A, the frequency response from the handle torque Th to the road surface reaction force estimator 101 has a gain of about −60 dB at a frequency of 20 Hz or less, and from the motor torque Tm to the road surface reaction force estimator 101. In the frequency response, the gain at a frequency of 20 Hz or less is about −90 dB, and the gain is small enough to be regarded as substantially zero. Further, the frequency response from the handle torque Th and the motor torque Tm to the road surface reaction force estimator 101 is smaller at a frequency of 20 Hz or more than at a gain of 20 Hz or less. Therefore, with respect to the handle torque Th and the motor torque Tm (that is, inputs other than the input to be estimated), it can be said that the gains from those inputs to the road surface reaction force estimator 101 are −40 dB or less at all frequencies. . From this, it can be seen that the road surface reaction force estimator 101 of this embodiment has separability. 7B also shows that the road surface reaction force estimator 101 does not react to the input of the handle torque Th and the motor torque Tm.

  On the other hand, as can be seen from FIG. 7A, the gain at a frequency of 20 Hz or less when the road surface reaction torque Tl is input is 0 dB, that is, a gain of 1 time. Further, as can be seen from FIG. 7B, when the road surface reaction torque Tl is input, the amplitude “1” is output with almost no time delay. From this, it can be seen that the road surface reaction force estimator 101 has responsiveness to the road surface reaction force torque Tl. As can be seen from the Bode diagram of FIG. 7A, at 20 Hz or more, the gain is reduced from 20 Hz or less for any torque Th, Tm, or Tl. This is because the cut-off frequency is set to 20 Hz in consideration of the observed amount of noise as already described.

  The road surface reaction force estimator 101 having the above-described characteristics estimates the road surface reaction force torque Tl according to the flow shown in FIG.

  First, a value necessary for calculating the road surface reaction force torque estimated value Tl_est is read from each sensor (step S1). That is, the steering torque Ts is read from the torque sensor 4, the rotational angular velocity dThc of the motor 6 is read from the rotational angular velocity sensor 13, and the motor current value Cur is read from the motor current sensor 14.

  Next, a road surface reaction force torque estimated value Tl_est is calculated using values (Ts, dThc, Cur) read by the steering S1 (step S2). Specifically, the road surface reaction force torque estimated value Tl_est is calculated based on Ts, dThc, Cur read in step S1 and the Bode diagram shown in FIG. , Γ are determined respectively. Then, the road surface reaction force torque estimated value Tl_est is calculated by substituting these α, β, and γ and Ts, dThc, and Cur read in step S1 into Equation 1.

  The road surface reaction force torque estimated value Tl_est calculated in this way is output to the current command value converter 102 as an assist command value as described above, and is used for assist torque control.

  As described above, according to the present embodiment described above, the road surface reaction force estimator 101 outputs an output value substantially equal to the input value when the road surface reaction force torque Tl is input, while the handle torque Th and the motor torque Tm are output. In contrast, approximately zero is output. Therefore, the road surface reaction torque Tl can be correctly estimated. As a result of correctly estimating the road surface reaction torque Tl, a natural feeling of steering can be realized.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following embodiment is also contained in the technical scope of this invention, and also the summary other than the following is also included. Various modifications can be made without departing from the scope.

  In the above-described embodiment, the torque sensor 4, the rotational angular velocity sensor 13, and the motor current detection sensor 14 are used as the first, second, and third sensors. The steering torque Ts detected by these sensors and the rotation of the motor 6 are used. Although the angular velocity dThc and the motor current value Cur are input to the road surface reaction force estimator 101 to estimate the road surface reaction force torque estimation value Tl_est, the present invention is not limited to this. As the sensor detection values input to the road surface reaction force estimator 101, various detection values can be used as long as the detection values change according to the handle torque Th, the motor torque Tm, and the road surface reaction force torque Tl. In addition to the steering torque Ts, the rotational angular velocity dThc of the motor 6, and the motor current value Cur, for example, the steering wheel rotational angle, the steering wheel rotational angular velocity, the motor rotational angle, the intermediate torque (the torque of the intermediate shaft 7), the rack stroke, and the rack stroke. There are speed, tire rotation angle, tire rotation angular speed, detection voltage of the motor 6, and the like. From these, at least three detection values may be used.

  Here, if the steering wheel rotation angle is used instead of the steering torque Ts in the above-described embodiment, the steering wheel rotation angle is a sensor detection value at a position closer to the steering wheel than the steering torque Ts. Further improvement in the estimation accuracy of Tl can be expected. Further, even if the rack stroke is replaced with the motor rotational angular velocity dThc, the rack stroke is a sensor detection value at a position closer to the road surface than the motor rotational angular velocity dThc, and therefore further improvement in the estimation accuracy of the road surface reaction force torque Tl is expected. it can. Of course, if the steering wheel rotation angle is used instead of the steering torque Ts and the rack stroke is used instead of the motor rotation angular velocity dThc, the estimation accuracy can be further improved.

  In the above-described embodiment, the road surface reaction force torque estimated value Tl_est is directly used as the assist command value. However, the present invention is not limited to this. For example, the road surface reaction force torque estimated value Tl_est and the steering torque Ts may be added, or a correction value for stabilization control may be added thereto. Further, the road surface reaction force torque estimated value Tl_est may be multiplied by a gain. Further, the road surface reaction force torque estimated value Tl_est may be used to calculate a correction coefficient or a correction amount for correcting an assist command value determined by a parameter other than the road surface reaction force torque estimated value Tl_est, such as the steering torque Ts. As long as the road surface reaction torque estimation value Tl_est is used, the assist command value determination method can be variously changed.

  In the above-described embodiment, the road surface reaction force estimator 101 is designed based on the H∞ control theory. However, the road surface reaction force estimator 101 may be designed by other methods such as a μ design method. .

1: Control device, 2: Steering wheel (handle), 3: Steering shaft, 4: Torque sensor, 5: Reduction mechanism, 6: Motor, 7: Intermediate shaft, 8: Gear device, 9: Pinion shaft, 10: Rack shaft, 11: tire, 12: vehicle speed sensor, 13: rotation angle sensor, 14: motor current detection circuit, 41: torque sensor, 42: motor rotation angular velocity sensor, 43: motor current sensor, 101: estimator, 102: Current command value converter, 103: current control unit

Claims (4)

An electric power steering apparatus that includes a motor, estimates a road surface reaction torque that is a torque input to a tire from a road surface, and determines an assist torque to be generated by the motor using at least the estimated road surface reaction torque ,
First, second, and third sensors whose detected values change according to a handle torque that is a torque input to the handle by a driver, a motor torque that is a torque generated in the motor, and the road surface reaction force torque;
A road surface reaction force estimator that receives detection values of the first, second, and third sensors and outputs a road surface reaction force torque estimation value based on the detection values;
As the road surface reaction force estimator, it has a responsiveness to output an output value substantially equal to the input value for an input of an estimated value, and a separability to output approximately zero for an input other than the estimated value An electric power steering apparatus comprising: an estimator including: an estimator whose estimated value is the road surface reaction torque. In claim 1,
As the first, second, and third sensors, a torque sensor that detects a steering torque, a rotational angular velocity sensor that detects a rotational angular velocity of the motor, and a motor current detection sensor that detects a current flowing through the motor are used. Electric power steering device. In claim 1 or 2,
An electric power steering apparatus having the responsiveness to an input of 20 Hz or less of an estimated value and having the separability of -40 dB or less. In any one of Claims 1-3,
The road surface reaction force estimator is
A generalized plant that outputs a controlled variable z and an observed output y from a control input u and an external input w, and a controller that generates the control input u from the observed output y and feeds back to the generalized plant is used. ∞ Designed based on control theory,
The external input w is the handle torque, motor torque, road surface reaction torque,
The observation output y is a detection value of the first, second and third sensors,
The controller is the road reaction force estimator,
The control input u is a road surface reaction force torque estimated value output by the road surface reaction force estimator,
The control amount z is the difference e between the road surface reaction force torque and the road surface reaction force torque estimated value,
The response from the handle torque, the motor torque, and the road surface reaction force torque that is the external input w to the difference e between the road surface reaction force torque and the road surface reaction force torque estimated value that is the control amount z is substantially zero. Thus, the road surface reaction force estimator is designed.

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