JP2015033941A - Steering control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove affection of an off-set error of a torque sensor without imparting discomfort to a driver during steering, in a steering control device in which servo control is implemented.SOLUTION: Target creation means (21, 22) creates a target steering torque (Ts) which is a target value of a steering torque applied to a steering shaft connected with a steering member from a road surface load (Tx) by estimating the road surface load (Tx) applied to a steering wheel from the road surface. Deviation calculation means (23) determines a torque deviation (ΔT) which is the deviation of the detected steering torque (Ts) from the target steering torque. Command value creation means (24) creates a command value (Tb) for servo-controlling a motor applying an assist torque to the steering shaft in accordance with the torque deviation. Dead zone imparting means 243 imparts a dead zone to an internal value used in the command value creation means so that the command value created when the detected steering torque is within the range of the off-set error becomes the value inside the dead zone.

Description

  The present invention relates to a steering control device that generates an assist torque that applies a desired reaction force to a steering wheel during steering by servo control of a motor.

  2. Description of the Related Art Conventionally, there is known an electric power steering device that detects a steering torque by a torque sensor provided on a steering shaft and sets a current command value for driving a motor that generates an assist torque according to the detected steering torque. Yes.

  By the way, if the detected value of the torque sensor includes an offset error due to a temperature change or an assembly error, the detected value of the torque sensor does not become zero even if the actual steering torque is zero. Unnecessary assist torque is generated based on the offset error. As a result, there is a problem that the left and right steering feelings are different and unnecessary current consumption occurs in the motor.

  In contrast, by adding a dead band to the steering torque detected by the torque sensor or providing a dead band in the conversion characteristics for converting the steering torque into a current command value, the influence of the offset error of the torque sensor is eliminated. A technique is known in which the current command value is also zero when the actual torque is zero (see, for example, Patent Document 1).

Japanese Patent No. 3740439

  In the prior art, the current command value (motor current) is directly obtained from the steering torque. Separately, the target steering torque is obtained based on the steering torque or the like, and the deviation between the target steering torque and the actual steering torque is obtained. It is known to obtain a current command value for servo-controlling a motor so that becomes zero. In the case where the conventional technology is applied to a device that performs such servo control, a dead zone is given to the detected steering torque, or a dead zone is provided in the conversion characteristics when the steering torque is converted to the target steering torque. Become.

  However, even if a dead zone is applied to either the steering torque or the target steering torque, the servo control does not necessarily operate to make the assist torque zero when the dead zone is applied, and is based on an offset error. There was a problem that generation of unnecessary assist torque could not be prevented.

  In particular, when the target steering torque is set to zero, the servo control does not set the assist torque to zero, but operates so as to generate an assist torque that eliminates resistance during steering. For this reason, when steering is performed such that the target steering torque passes through a state where the target steering torque is zero, if the dead zone acts, the resistance during steering disappears, and when the dead zone is passed, the resistance during steering is restored. There was also a problem that caused the driver to feel uncomfortable.

  In order to solve the above problems, an object of the present invention is to eliminate the influence of an offset error of a torque sensor in a steering control device that performs servo control without causing the driver to feel uncomfortable during steering.

The steering control device of the present invention includes target generation means, deviation calculation means, command value generation means, and dead zone provision means.
The target generation means estimates a road load applied to the steered wheel from the road surface, and generates a target steering torque that is a target value of a steering torque applied to the steering shaft connected to the steering member from the estimated road load. The deviation calculating means obtains a torque deviation which is a deviation of the detected steering torque with respect to the target steering torque, using the detected value of the steering torque as the detected steering torque. The command value generating means generates a command value for servo-controlling a motor that applies assist torque to the steering shaft according to the torque deviation. Then, the dead band providing means adds a dead band to the internal value used by the command value generating means so that the command value generated when the detected value of the steering torque is within the range of the offset error becomes a value within the dead band. To do.

  According to such a configuration, it is possible to make the command value zero when the detected value of the steering torque is within the range of the offset error without giving the driver a sense of incongruity during steering, and unnecessary assist based on the offset error. The generation of torque can be suppressed.

It is a block diagram which shows schematic structure of an electric power steering system. It is a block diagram which shows the outline of the control mechanism of ECU. It is a block diagram which shows the structure of a base assist part. It is a block diagram which shows the control structure of an assist controller. (A) is a block diagram which shows the control structure of general PID control, (b) is a graph which shows the input-output characteristic of a dead zone calculator. 4 is a graph illustrating waveforms of steering torque, target steering torque, estimated load, and assist command. It is a graph which illustrates the waveform of each part in a comparative example. It is a graph which illustrates the waveform of each part in a comparative example. It is a graph which illustrates the waveform of each part in a comparative example. (A) is a block diagram which shows arrangement | positioning of a dead zone calculator in a modification, (b) is a graph which illustrates the waveform of the assist command at that time. It is a block diagram which shows schematic structure of the steer-by-wire system of 2nd Embodiment. It is a graph which shows the characteristic of a target steering angle calculating part.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
<Overall configuration>
As shown in FIG. 1, the electric power steering system 1 of the present embodiment assists an operation of a handle (steering member) 2 by a driver with a motor 6. The handle 2 is fixed to one end of a steering shaft 3, and a torque sensor 4 is connected to the other end of the steering shaft 3, and an intermediate shaft 5 is connected to the other end of the torque sensor 4. In the following description, the entire shaft body from the steering shaft 3 through the torque sensor 4 to the intermediate shaft 5 is also collectively referred to as a steering shaft. Hereinafter, the rotation angle of the steering shaft is also referred to as a steering angle, and the rotation angular velocity of the steering shaft is also referred to as a steering speed.

  The torque sensor 4 is a sensor for detecting the steering torque Ts. Specifically, a torsion bar that connects the steering shaft 3 and the intermediate shaft 5 is provided, and a torque applied to the torsion bar is detected based on a twist angle of the torsion bar.

  The motor 6 assists the steering force of the handle 2 and its rotation is transmitted to the intermediate shaft 5 via the speed reduction mechanism 6a. That is, the speed reduction mechanism 6a is constituted by a worm gear provided at the tip of the rotating shaft of the motor 6 and a worm wheel provided coaxially on the intermediate shaft 5 in mesh with the worm gear. The rotation of the motor 6 is transmitted to the intermediate shaft 5. Conversely, when the intermediate shaft 5 is rotated by the operation of the handle 2 or the reaction force from the road surface (road surface reaction force), the rotation is transmitted to the motor 6 via the speed reduction mechanism 6a, and the motor 6 also rotates. .

  The motor 6 is a brushless motor in the present embodiment, and includes a rotation sensor such as a resolver, and is configured to output the rotation state of the motor 6. The motor 6 of the present embodiment is configured to be capable of outputting at least the motor speed ω (information indicating the rotational angular speed) as the rotational state from the rotation sensor.

  The other end of the intermediate shaft 5 opposite to the end to which the torque sensor 4 is connected is connected to the steering gear box 7. The steering gear box 7 is configured by a gear mechanism including a rack and a pinion gear, and a rack tooth meshes with a pinion gear provided at the other end of the intermediate shaft 5. Therefore, when the driver turns the handle 2, the intermediate shaft 5 rotates (that is, the pinion gear rotates), thereby moving the rack to the left and right. Tie rods 8 are attached to both ends of the rack, and the tie rods 8 reciprocate left and right together with the rack. Accordingly, the tie rod 8 pulls or pushes the knuckle arm 9 ahead, thereby changing the direction of each tire 10 that is a steered wheel.

A vehicle speed sensor 11 for detecting the vehicle speed V is provided at a predetermined part of the vehicle.
With this configuration, when the driver rotates (steers) the handle 2, the rotation is transmitted to the steering gear box 7 via the steering shaft 3, the torque sensor 4, and the intermediate shaft 5. Then, in the steering gear box 7, the rotation of the intermediate shaft 5 is converted into the left and right movement of the tie rod 8, and the left and right tires (steering wheels) 10 are steered by the movement of the tie rod 8.

  The ECU 15 is operated by electric power from an in-vehicle battery (not shown), and assist torque based on the steering torque Ts detected by the torque sensor 4, the motor speed ω of the motor 6, and the vehicle speed V detected by the vehicle speed sensor 11. Command Ta is calculated. Then, by applying a drive voltage Vd corresponding to the calculation result to the motor 6, the assist amount of the force with which the driver turns the steering wheel 2 (and thus the force to steer both tires 10) is controlled.

  In this embodiment, since the motor 6 is a brushless motor, the drive voltage Vd output (applied) from the ECU 15 to the motor 6 is specifically the three-phase (U, V, W) drive voltages Vdu, Vdv, Vdw. is there. The rotational torque of the motor 6 is controlled by applying the drive voltages Vdu, Vdv, Vdw of each phase from the ECU 15 to the motor 6 (energizing the drive current of each phase). A method for driving a brushless motor with a three-phase drive voltage (for example, PWM drive) and a drive circuit (for example, a three-phase inverter) for generating the three-phase drive voltage are well known. Omitted.

  The ECU 15 controls the motor 6 by directly controlling the drive voltage Vd applied to the motor 6, but the steering system mechanism 100 driven by the motor 6 as a result by controlling the motor 6. It can be said that the control object of the ECU 15 is the steering system mechanism 100. The steering system mechanism 100 indicates the entire mechanism excluding the ECU 15 in the system configuration diagram shown in FIG. 1, that is, the entire mechanism that transmits the steering force of the handle 2 from the handle 2 to each tire 10.

<ECU>
ECU15, as shown in FIG. 2, the base assist unit 20 that generates a base command Tb ^*, a correction unit 30 for generating a correction command Tr, the assist torque command by adding the correction command Tr based command Tb ^* An adder 41 that generates Ta, and a current feedback (FB) unit 42 that energizes and drives the motor 6 by applying a drive voltage Vd to the motor 6 based on the assist torque command Ta.

Based on the steering torque Ts and the vehicle speed V, the base assist unit 20 generates a base command Tb ^* for assisting the operation of the steering wheel 2. The base assist unit 20 makes it easier for the driver to grasp the vehicle state and the road surface state by allowing the reaction (reaction force) corresponding to the vehicle state and the road surface state to be transmitted quasi-steadily to the driver. In addition, it is a block for realizing an improvement in feel during steering by adjusting the hand feeling (sensory hardness, stickiness, weight from the steering wheel to the tire) given to the driver.

  The correction unit 30 adjusts the vehicle control characteristics with respect to the steering operation of the driver and the transmission of the steering mechanism so as to follow the driver's intention (specifically, the vehicle is properly converged or a smooth vehicle turn is generated). It is a block for. The correction unit 30 generates a correction command Tr for suppressing (converging) the above-described unstable behavior based on the steering torque Ts, the motor speed ω, and the vehicle speed V.

The adder 41 generates an assist torque command Ta by adding the base command Tb ^* generated by the base assist unit 20 and the correction command Tr generated by the correction unit 30.
Based on the assist torque command Ta, the current FB unit 42 is configured so that an assist torque (assist steering force) corresponding to the assist torque command Ta is applied to the steering shaft (particularly on the tire 10 side with respect to the torque sensor 4). A drive voltage Vd is applied. Specifically, a target current (target current for each phase) to be energized to each phase of the motor 6 is set based on the assist torque command Ta. Then, by detecting and feeding back the energization current Im of each phase and controlling the drive voltage Vd (controlling the energization current) so that the detected value (the energization current Im of each phase) matches the target current, A desired assist torque is generated for the steering shaft.

  The correction unit 30 and the current FB unit 42 are known techniques (see, for example, Japanese Patent Application Laid-Open No. 2013-52793), and thus description thereof is omitted here. The following description relates to the main part of the present invention. The base assist unit 20 will be described in detail.

<Base assist part>
As shown in FIG. 3, the base assist unit 20 includes a load estimator 21, a target generation unit 22, a deviation calculator 23, and an assist controller 24.

The load estimator 21 estimates a road load based on the base command Tb ^* and the steering torque Ts. Specifically, the load estimator 21 includes an adder 211 that adds the base command Tb ^* and the steering torque Ts, and a low-pass filter (LPF) 212 that extracts a band component of a predetermined frequency or less from the addition result. The frequency component extracted by the LPF 212 is output as the estimated load Tx. Usually, since the driver mainly operates by relying on the steering reaction force information of 10 Hz or less, the frequency component of approximately 10 Hz or less is allowed to pass (extract) and the frequency component higher than 10 Hz is cut off.

The target generator 22 is an assist map set to realize desired steering characteristics based on the road surface load (estimated load Tx) estimated by the load estimator 21 and the traveling speed (vehicle speed V) of the host vehicle. Is used to generate a target steering torque Ts ^* that is a target value of the steering torque. However, at vehicle speeds other than the mapped vehicle speed V, the target steering torque is obtained by interpolation from the map value.

The assist map is obtained by mapping the relationship between the estimated load Tx and the target steering torque for each of a plurality of preset vehicle speeds V. The characteristic is that the target steering torque Ts ^* is also obtained when the estimated load Tx is zero. The absolute value of the target steering torque Ts ^* is set so as to increase as the absolute value of the estimated load Tx increases. The increase rate has a tendency that the increase rate is large near Tx = 0, and the increase rate tends to decrease as Tx increases. Note that the symbols such as the steering torque Ts, the estimated load Tx, and the target steering torque Ts ^* correspond to the operation direction (left and right) of the steering wheel.

The deviation calculator 23 calculates a torque deviation ΔT (= Ts ^* −Ts) that is a difference between the steering torque Ts and the target steering torque Ts ^* .
<< Assist controller >>
The assist controller 24 performs so-called servo control based on the torque deviation ΔT so that ΔT = 0. Thus, to produce a base command Tb ^* for generating the assist torque as the steering torque Ts is to follow the target steering torque Ts ^* (also referred to as assist amount).

  Specifically, as shown in FIG. 4, the assist controller 24 includes a gain adder 241 that applies a PID gain to the torque deviation obtained by the deviation calculator 23, and an integration target value TM that is an output of the gain adder 241. Are integrated with each other, a dead zone calculator 243 for adding a dead zone to the internal value of the integrator 242, and a limit calculator 244 for limiting the internal value of the integrator 242.

Here, the control structure of the gain applicator 241 and the integrator 242 will be described. In general, the control structure of PID control is represented by a block diagram shown in FIG. 5A, and its transfer characteristic is represented by equation (1). Where Kp is the gain of the proportional element (proportional gain), Ki is the gain of the integral element (integral gain), Kd is the gain of the differential element (differential gain), s is the Laplace operator, and D is the pseudo differential (s / (τs + 1) ) Indicates a function that executes the operation of ² ).

In order to discretize the equation (1), the bilinear transformation equation represented by the equation (2) is substituted into the equation (1) and rearranged to obtain the equation (3). However, ts represents a calculation cycle.

Further, regarding Tb ^* and ΔT, if the current value is represented by the subscript n and the previous value is represented by the subscript n-1, the expression (3) is modified to obtain the expression (4).

The gain structure 241 and the integrator 242 are realized by modifying the control structure represented by the equation (4) so that the integral operation portions are collectively arranged in the subsequent stage, which is a block diagram in the figure. The control structures other than the dead zone calculator 243 and the limit calculator 244 shown in FIG.

The limit calculator 244 is connected so that the output of the dead zone calculator 243 is set as a limit target value and the output after the limit becomes the base command Tb ^* . The limit calculator 244 is a well-known device that outputs the limit value if the limit target value is equal to or less than the guard value, and outputs the limit value when the limit value exceeds the guard value.

  The dead zone calculator 243 is connected so that the output of the adder that adds the integration target value TM and the previous value of the assist command in the integrator 242 is the target input u. Then, as shown in FIG. 5B, when the target input u is | u | <Td, y = 0 is output, and when | u |> Td, y that increases in proportion to the input is output. ing.

<< Setting method of dead band >>
Here, a method of setting the boundary value Td that determines the width of the dead zone (−Td to Td) will be described.

Assuming that the steering torque Ts includes an offset δ, the dead zone width (boundary value Td) is set so that the base command Tb ^* based on the offset δ is not output in a steady state when the steering force is not applied in the steering wheel neutral state. Set.

  First, in the steering wheel neutral state and the steady state, the differential term of equation (4) does not contribute and is ignored, so equation (4) is simplified as equation (5).

If the neutral point of the assist map used by the target generator 22 the gain in the vicinity of (Tx = 0) and K, the target steering torque Ts ^* is previous value ^Tb _{* n-1} of the assist command, the steering torque _Ts n (= [delta] _n ) and the gain K is expressed by the equation (6). Further, the torque deviation ΔT _n is expressed by equation (7).

In the equation obtained by substituting the equation (7) into the equation (5), the offset δ does not change (that is, δ _n = δ _n-1 = δ), the previous value Tb ^* _{n−1 of} the assist command, and the previous value Tb ^{* .} _{When n-2} is arranged as being removed by the dead zone (that is, Tb ^* _n-1 = Tb ^* _n-2 = 0), Equation (8) is obtained.

That is, since the value obtained using the equation (8) is the maximum value of the assist command before the dead zone process caused by the offset δ, this value may be set as the dead zone boundary value ± Td.

<Operation>
FIG. 6 illustrates a result obtained by simulation of how the target steering torque Ts ^* , the estimated load Tx, and the base command Tb ^* change with respect to the steering torque Ts. However, it is assumed that the calculation cycle ts = 800 [μsec], the integral gain Ki = −360 [sec−1], the assist map gain K = 0.14, and the torque sensor zero point deviation δ = 0.3 [Nm]. The boundary value Td was set to Td = 0.074 [Nm] based on the equation (8).

As shown in FIG. 6, in the section where the torque deviation ΔT (= Ts ^* −Ts) is −0.3 to 0.3 [Nm], the assist command is Tb ^* = 0 (for example, surrounded by a dotted line in the figure). You can see that the deadband processing is working correctly.

  Here, for comparison, not the internal value of the assist controller 24, but the signal at the point P1 shown in FIG. 3 (the steering torque Ts supplied to the load estimator 21 and the deviation calculator 23), and the signal at the point P2 ( FIGS. 7 to 9 show simulation results when the dead zone is given to the steering torque Ts) supplied to the deviation calculator 23 and the signal (torque deviation ΔT) at the point P3.

  When a dead zone is given to the signal at the point P1, noise is superimposed on the assist command Tb *. This is because, as shown in FIG. 7, the waveform of the estimated load Tx changes discontinuously (non-linearly) at the timing of entering the dead zone and the timing of leaving the dead zone (see the portion surrounded by the dotted line in the figure). ). As a result, when there is another control using the estimated load Tx (for example, sprung mass damping control disclosed in Japanese Patent No. 4715351), the control is performed due to the influence of the high frequency noise included in the estimated load Tx. The accuracy will be reduced.

When a dead zone is given to the signal at the point P2, as shown in FIG. 8, when the steering torque Ts changes from positive to negative, the base command Tb ^* changes from negative to positive in the direction that hinders steering. Assist torque is generated, giving the driver a sense of incongruity (friction).

When the dead zone is given to the signal at the point P3, as shown in FIG. 9, when the steering torque Ts changes from positive to negative, the base command Tb ^* is the value when the dead zone is entered (here, Therefore, when the steering torque Ts becomes negative, the assist torque is generated in a direction that hinders the steering. After that, when the steering torque Ts leaves the dead zone, the base command Tb ^* follows the steering torque Ts. As a result, the torque suddenly becomes negative and assist torque is generated in a direction to assist steering. This gives the driver a sense of incongruity that causes a catch in the dead zone.

<Effect>
According to the present embodiment, instead of setting a dead zone for the target steering torque Ts ^* , a dead zone is provided for the internal value of servo control (the value after integration), so that the base command Tb ^* is changed to the steering torque Ts. Therefore, the influence of the offset of the torque sensor 4 can be eliminated without causing the driver to feel uncomfortable.

Further, according to the present embodiment, the change in the waveform of the estimated load Tx at the timing when the dead zone is switched / inactivated is gentle compared to the base command Tb ^*, and the waveform of the estimated load Tx has a high-frequency component. Is suppressed. For this reason, it can suppress that the other control (for example, vibration suppression control) using estimated load Tx exerts the bad influence by high frequency noise.

<Modification>
In the above-described embodiment, the dead zone calculator 243 is disposed between the adder that adds the integration target value TM and the previous value Tb ^* _{n−1 of the} assist command and the limit calculator 244, and the dead zone is output from the adder. Is configured to be granted. On the other hand, as shown in FIG. 10A, the dead zone calculator 243 may be arranged to give a dead zone to the previous value Tb ^* _{n−1 of the} assist command that is input to the adder. Good.

In this case, as shown in FIG. 10B, the waveform of the base command Tb ^* is not exactly Tb ^* = 0 within the dead zone, and slightly changes according to the change in the torque deviation ΔT. This is substantially the same as in the above embodiment, and the same effect can be obtained.

[Second Embodiment]
Next, a second embodiment will be described.
In the first embodiment, an example in which the present invention is applied to an electric power steering configured such that a steering wheel and a tire (steering wheel) are mechanically interlocked is shown. On the other hand, this embodiment shows an example applied to a so-called steer-by-wire system having a configuration in which a handle (steering shaft) and a tire (steering mechanism) are mechanically separated.

<Overall configuration>
As shown in FIG. 11, the steer-by-wire system 1 a of this embodiment includes a handle 2, a steering shaft 3, a torque sensor 4, an intermediate shaft 5, and a motor (hereinafter referred to as “reaction force motor”) 61. However, the intermediate shaft 5 is configured such that one end thereof is connected to the torque sensor 4 and the other end thereof is connected to the reaction force motor 61 so as not to be mechanically interlocked with the tire 10. The torque sensor 4 includes a torsion bar that connects the steering shaft 3 and the intermediate shaft 5 and is configured to detect a twist angle θt of the torsion bar.

  Further, in the steer-by-wire system 1a, the steering gear box 7 is omitted from the configuration shown in FIG. 1, and instead, a motor (hereinafter referred to as “steering motor”) that moves the tie rod 8 to the left and right is provided. In other words, the direction of each tire 10 that is the tire 10 is changed by operating the tie rod 8 or the knuckle arm 9 ahead thereof by the steering motor 62.

  The reaction force motor 61 outputs the motor rotation angle θmr and the motor current Imr as the motor rotation state, and similarly, the steering motor 62 outputs the motor rotation angle θmf and the motor current Imf as the motor rotation state. It is configured. Further, a vehicle speed sensor (not shown) for detecting the vehicle speed V is provided at a predetermined portion in the vehicle.

  The ECU 15a generates a drive voltage Vr to be applied to the reaction force motor 61 based on the twist angle θt detected by the torque sensor 4, the motor current Imr of the reaction force motor 61, the motor current Imf of the steering motor 62, and the vehicle speed V. Thus, the steering force control unit 70 that controls the reaction force felt by the driver during steering, the twist angle θt detected by the torque sensor, the motor rotation angle θmr of the reaction force motor 61, the motor current Imr, and the steering motor 62 And a steering angle control unit 80 for controlling the direction (steering angle) of the tire 10 by generating a drive voltage Vf to be applied to the steering motor 62 based on the motor rotation angle θmf and the motor current Imf. The ECU 15a is operated by electric power from an in-vehicle battery (not shown).

<Steering force control unit>
The steering force control unit 70 includes a load estimator 71, a target steering torque calculation unit 72, a steering torque detection unit 73, a deviation calculation unit 74, a torque servo controller 75, and a reaction force motor drive control unit 76. . However, the target steering torque calculation unit 72, the deviation calculation unit 74, the torque servo controller 75, and the reaction force motor drive control unit 76 are the same as the target generation unit 22, the deviation calculation unit 23, the assist controller 24, and the current FB unit 42, respectively. Since it is configured, description thereof is omitted. However, the reaction force motor drive control unit 76 uses the motor current Imr of the reaction force motor 61 instead of the motor current Im, and generates a drive voltage Vr for driving the reaction force motor 61 instead of the drive voltage Vd.

  The load estimator 71 estimates a road surface load (estimated load) Tx based on the motor current Imf of the steering motor 62. Specifically, an estimated load Tx (= Kf · Imf) is obtained by multiplying the motor current Imf by the gain Kf. The steering torque detection unit 73 is a known unit that obtains the steering torque Ts from the twist angle θt output from the torque sensor 4.

<Steering angle control unit>
The steering angle controller 80 includes a steering wheel angle detector 81, a target steering angle calculator 82, a steering angle detector 83, a deviation calculator 84, an angle servo controller 85, and a steering motor drive controller 86. ing.

The handle angle detector 81 calculates the handle angle θs by adding the motor rotation angle θmr of the reaction force motor 61 and the twist angle θt detected by the torque sensor 4.
The target steering angle calculator 82 calculates the target steering angle θf ^* of the tire 10 based on the steering wheel angle θs obtained by the steering wheel angle detector 81 and the vehicle speed V detected by the vehicle speed sensor. Note that the conversion gain from the steering wheel angle θs to the target steering angle θf ^* is set to be large so that a small turning angle can be made even with a small steering angle at low speeds, and in order to reduce the sensitivity of the vehicle lateral movement with respect to the steering wheel angle θs at high speeds. It is set to small. When represented by the gear ratio θs / θf that is the reciprocal of the conversion gain, as shown in FIG. 12, the gear ratio θs / θf is set to a small value at a low speed and to a large value at a high speed.

The steering angle detector 83 multiplies the motor rotation angle θmf of the steering motor 62 by a predetermined gain to convert it into a steering angle θf that represents the direction of the tire 10.
The deviation calculator 84 calculates a steering angle deviation Δθ (= Tf ^* −Tf) which is a difference between the target steering angle θf ^* obtained by the target steering angle computing unit 82 and the steering angle θf obtained by the steering angle detecting unit 83. Calculate.

The angle servo controller 85 is configured in the same manner as the assist controller 24 and uses a steering angle deviation Δθ instead of the torque deviation ΔT so that the steering angle θf matches the target steering angle θf ^* . A current command value Imf ^* for realizing PID control is calculated. However, the dead band computing unit constituting the angle servo controller 85 is based on the offset error that appears in the handle angle θs obtained by the handle angle detector 81 (and thus the offset error of the twist angle θt detected by the torque sensor 4). A boundary value Td is set.

  The steering motor drive control unit 86 is configured in the same manner as the current FB unit 42, and uses the motor current Imf of the steering motor 62 instead of the motor current Im and drives the steering motor 62 instead of the drive voltage Vd. A drive voltage Vf is generated.

<Effect>
According to the present embodiment, as in the case of the first embodiment, the twist angle θt detected by the torque sensor 4, and thus the steering torque Ts obtained by the steering torque detector 73 and the handle angle θs obtained by the handle angle detector 81. The influence of the offset error of the twist angle θt detected by the torque sensor 4 can be removed without causing the driver to feel uncomfortable.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment. For example, the functions of one component may be distributed to a plurality of components, or the functions of a plurality of components may be integrated into one component. Further, at least a part of the configuration of the above embodiment may be replaced with a known configuration having the same function. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment.

  In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

  In addition to the above-described steering control device, the present invention has various modes such as various systems including the steering control device, a program for causing a computer to function as each means constituting the steering control device, and a steering control method. Can be realized.

DESCRIPTION OF SYMBOLS 1 ... Electric power steering system 1a ... Steer-by-wire system 2 ... Handle 4 ... Torque sensor 6 ... Motor 10 ... Tire 11 ... Vehicle speed sensor 15, 15a ... ECU20 ... Base assist part 21 ... Load estimator 22 ... Target generation part 23 ... Deviation calculator 24 ... assist controller 30 ... correction unit 41 ... adder 42 ... current FB unit 61 ... reaction force motor 62 ... steering motor 70 ... steering force control unit 71 ... load estimator 72 ... target steering torque calculation unit 73 ... steering Torque detector 74 ... Deviation calculator 75 ... Torque servo controller 76 ... Reaction force motor drive controller 80 ... Steering angle controller 81 ... Steering angle detector 82 ... Target steering angle calculator 83 ... Steering angle detector 84 ... Deviation calculation 85 ... Angle servo controller 86 ... Steering motor drive controller 1 00 ... Steering system mechanism 211 ... Adder 241 ... Gain applicator 242 ... Integrator 243 ... Dead band calculator 244 ... Limit calculator

Claims (6)

Target generation means (21, 22) that estimates a road load applied to the steering wheel from the road surface, and generates a target steering torque that is a target value of the steering torque applied to the steering shaft connected to the steering member from the estimated road load. , 71, 72) and
Deviation calculation means (23, 74) for obtaining a torque deviation which is a deviation of the detected steering torque with respect to the target steering torque, using the detected value of the steering torque as a detected steering torque;
Command value generating means (24, 75) for generating a command value for servo-controlling the motor (6, 61) for applying assist torque to the steering shaft according to the torque deviation;
A dead zone applying means for giving a dead zone to the internal value used by the command value generating means so that the command value generated when the detected value of the steering torque is within an offset error range is a value within the dead zone. (243)
A steering control device comprising: The command value generating means
Gain applying means (241) for applying a control gain to the torque deviation;
Integration means (242) for generating the command value by adding the output value of the gain applying means to the previous value of the command value;
With
2. The steering control device according to claim 1, wherein the dead zone applying unit sets the addition result in the integrating unit or the previous value of the command value as the internal value to which the dead zone is applied.   Any of an integral gain which is a gain of an integral element in the servo control, a calculation cycle which is a cycle in which the command value generation unit generates the command value, a conversion gain from the detected steering torque to the target steering torque, and the offset error The steering control device according to claim 2, wherein a width of the dead zone given by the dead zone giving means is set based on one or more of them. The integral gain is Ki, the calculation cycle is ts, the conversion gain is K, the offset error is δ, and a boundary value Td calculated using the following equation:
Td = tsKi (K−1) δ
The steering control device according to claim 3, wherein a width of the dead zone provided by the dead zone applying unit is set to −Td to Td. The steering shaft constitutes a steering mechanism for turning the steering wheel,
The steering control device according to any one of claims 1 to 4, wherein the target generation means (21, 22) generates the target steering torque based on a detected value of the steering torque. . The steering shaft is provided separately from a steering mechanism that steers the steering wheel,
The said target production | generation means (71, 72) produces | generates the said target steering torque based on the load of the motor (62) which comprises the said steering mechanism, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. The steering control device according to item.