JP2014227115A - Steering controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve feeling according to a steering state without depending on a state of adjusting a mechanical impedance.SOLUTION: A BPF 31 extracts a signal component in a specific band (10 to 40 Hz according to the present embodiment) that is a range where vibration representing a state of a road surface (road information) from a steering torque Ts. A filter gain calculation unit 32 generates a transmission control gain G by which an output from the BPF 31 is multiplied, according to a rigidity equivalent coefficient K supplied from a base assist unit 20 using a gain adjustment map. Specifically, the transmission control gain G is increased if the rigidity coefficient decreases, and the transmission control gain G is decreased if the rigidity coefficient increases. A corrected torque calculation unit 33 generates a corrected torque command Tr by multiplying the output from the BPF 31 (signal component in the specific band) by an output from the filter gain calculation unit 32 (transmission control gain G).

Description

  The present invention relates to a steering control device that adjusts a feel during steering by assist torque.

  Conventionally, as one of the steering control devices for assisting the steering force applied to the steering member (steering wheel) of the vehicle, the target steering torque is generated by using the reference steering model that defines the relationship between the steering angle and the steering torque in the steering member. In addition, there is known one that drives a steering assist motor that generates assist torque (auxiliary steering torque) based on a deviation between a target steering torque and a detected value of the steering torque. In this device, the mechanical impedance that characterizes the reference steering model is also changed in accordance with the vehicle speed and the steering angle (see, for example, Patent Document 1).

Japanese Patent No. 4232471

  By the way, the mechanical impedance affects the force sense of the driver who operates the handle. For example, when the handle is lightened, the mechanical impedance (particularly, the stiffness coefficient) is adjusted in the direction of decreasing. However, in this case, there is a problem that not only the steering wheel becomes light, but also the response when the steering wheel is turned off (rudder slipping) deteriorates the feel during steering, giving the driver a sense of incongruity. .

  In order to solve the above-described problems, an object of the present invention is to realize a feel corresponding to a steering state regardless of how the mechanical impedance is adjusted.

  The steering control device of the present invention includes basic torque generation means, adjustment torque generation means, correction torque generation means, and command value generation means. The basic torque generating means generates a basic torque that is a target value of the steering torque generated according to the assist torque. The adjustment torque generating means generates an adjustment torque that is a target value of the steering torque for adjusting the mechanical impedance that defines the relationship between the steering torque detected by the steering shaft and the steering angle. The correction torque generation means generates a correction torque that is a target value of the steering torque for adjusting the vibration transmission characteristic from the steering wheel to the steering member. The command value generating means generates a command value for controlling the motor from the basic torque, the adjustment torque, and the correction torque. However, the correction torque generation means changes the vibration transfer characteristic according to the adjustment contents of the mechanical impedance in the adjustment torque generation means.

  According to such a configuration, the deterioration of the feeling (particularly response) during steering and the uncomfortable feeling given to the driver caused by the adjustment of the mechanical impedance are suppressed by adjusting the correction torque (and hence the vibration transmission characteristic) linked to the mechanical impedance. can do. Such an effect of the present invention is the result of an experiment in which the characteristics discovered by experiments conducted by the present inventors, that is, the vibration applied to the steering member affects the driver's feeling (for example, rigidity) (see FIG. 6)) for the first time.

  Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiments described later as one aspect, and do not limit the technical scope of the present invention. . The present invention can be realized in various forms such as a program for causing a computer to function as each means constituting the steering control device, a steering control method, and the like in addition to the above-described steering control device.

It is a block diagram showing schematic structure of an electric power steering system. It is a block diagram showing schematic structure of the control mechanism of ECU. It is a block diagram showing the structure of a base assistance part and a correction | amendment part. It is a graph which illustrates the characteristic of a gain adjustment map. It is a Bode diagram showing how the transmission characteristic from the steering torque to the steering angle changes by changing the transmission control gain according to the gain adjustment map. It is a graph which shows the experimental result of the influence which the vibration added to a steering member has on perception of rigidity.

Embodiments of the present invention will be described below with reference to the drawings.
<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, the rotation angular velocity of the steering shaft is also referred to as steering speed, and the rotation angular acceleration of the steering shaft is also referred to as steering acceleration.

  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. Instead of the motor speed ω, a steering speed obtained by multiplying the motor speed ω by the gear ratio of the speed reduction mechanism 6a may be used.

  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 the rack teeth mesh 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-right movement of the tie rod 8, and the left and right tires 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 steering characteristic by controlling the motor 6 by directly controlling the drive voltage Vd applied to the motor 6. It can be said that the steering system mechanism 100 to be driven is controlled, and therefore the control target of the ECU 15 can be said to be 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>
Next, a schematic configuration (control mechanism) of the ECU 15 is shown in a block diagram of FIG. Note that, in the control mechanism of the ECU 15 shown in FIG. 2, each part except the current feedback (FB) unit 42 and part of the functions of the current FB unit 42 are actually determined by a CPU (not shown) included in the ECU 15. This is realized by executing a control program. That is, FIG. 2 shows various functions realized by the CPU divided into functional blocks. However, it is only an example that the control mechanism shown in each figure is realized by software, and the whole or a part of the control mechanism shown in FIG. 2 or the like is realized by hardware such as a logic circuit. Needless to say, it may be.

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

The base assist unit 20 realizes the characteristic of the steering reaction force (steering torque) according to the road surface reaction force (road surface load), that is, the reaction (reaction force) corresponding to the road surface load is transmitted quasi-steadily to the driver. This makes it easier for the driver to grasp the vehicle and road surface conditions, and adjusts the hand feeling (sensory hardness, stickiness, and weight from the steering wheel to the tire) according to the steering state. This is a block for realizing an improvement in the feel during steering. Based on the steering torque Ts, the motor speed ω, and the vehicle speed V, the base assist unit 20 assists the operation of the steering wheel 2 so as to realize the transmission feeling according to the road surface load and the feel according to the steering state. The base assist command Tb ^* is generated.

  The correction unit 30 is a block for making sure that the road surface condition (road information) is accurately transmitted to the steering wheel and for compensating for a feel during steering that cannot be adjusted by the base assist unit 20 alone. The correction unit 30 generates the above-described correction torque command Tr based on the steering torque Ts and the mechanical impedance adjustment value (here, the stiffness equivalent coefficient K) supplied from the base assist unit 20.

The adder 41 generates an assist torque command Ta by adding the base assist command Tb ^* generated by the base assist unit 20 and the correction torque 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.

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

<Base assist part>
As shown in FIG. 3, the base assist unit 20 includes a load estimator 21, a basic load amount calculation unit 22, a driver work rate calculation unit 23, a stiffness adjustment amount calculation unit 24, and a viscosity adjustment amount calculation unit 25. The inertia adjustment amount calculation unit 26, the differentiator 261, the target calculation unit 27, the deviation calculation unit 28, and the controller unit 29 are provided.

The load estimator 21 estimates the road load based on the base assist command Tb ^* (corresponding to the assist torque) and the steering torque Ts. The basic load amount calculation unit 22 is a basic component that is a basic component of the target value of the steering torque 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. Torque Tf ^* is generated.

  The driver power calculation unit 23 calculates the driver power W by multiplying the steering speed obtained by multiplying the motor speed ω by the gear ratio of the speed reduction mechanism 6a by the steering torque Ts. However, the steering torque Ts and the motor speed ω (and thus the steering speed) both have opposite polarities when the handle 2 is rotated clockwise and when it is rotated counterclockwise. Further, the steering torque Ts has a reverse polarity value when the steering wheel 2 is rotated clockwise from the neutral position and counterclockwise when the position of the handle 2 where Ts = 0 is set to the neutral position. The neutral position is a position where the vehicle is moved straight during normal driving when the tire is gripped, and a neutral position is a direction in which the tire slides when a spin is caused by oversteer. Here, it is assumed that it is positive when rotating left and negative when rotating right.

  Therefore, when the steering torque Ts and the motor speed ω have the same polarity and the driver power W is positive, it is a value generated by the operation of turning the steering wheel, and the polarity of the steering torque Ts and the motor speed ω is different. When the driver power W is negative, it indicates that the value is generated by the operation of turning back the steering wheel. If the driver power W is zero, the steering power is maintained.

  That is, when the steering wheel is cut to the left or right from the neutral position, the polarities of the steering torque Ts and the motor speed ω are the same, so the driver power W has a positive value. If it is held with the steering wheel turned off (steering state), the motor speed ω is zero, so the driver power is zero. When the steering wheel is turned back from this state of steering holding, the polarity of the motor speed ω is reversed from that when the steering wheel is turned, and the polarity of the steering torque Ts and the motor speed ω are different from each other. Is a negative polarity value. Note that the steering torque Ts increases as the tire direction deviates from the traveling direction of the vehicle, and increases as the motor speed ω steers more rapidly, and depends on the degree of these operations (operation amount). The absolute value of the driver work rate W takes a large value.

  Since the steering speed is a value proportional to the motor speed ω, the motor speed ω may be regarded as the steering speed, and the motor speed ω multiplied by the steering torque Ts may be used as the driver work rate W.

The differentiator 261 generates a motor acceleration α corresponding to the steering acceleration by differentiating the motor speed ω corresponding to the steering speed.
The stiffness adjustment amount calculation unit 24 is one of adjustment components (adjustment torque) included in the target steering torque Ts ^* based on the driver power W, the estimated load Tx, and the vehicle speed V, and is a steering system that is given to the driver during steering. A rigidity adjustment torque Tk ^* for adjusting the rigidity feeling of the mechanism 100 is generated. Specifically, the stiffness adjustment amount calculation unit 24 includes a stiffness coefficient calculation unit 24a and a multiplier 24b. The stiffness coefficient calculation unit 24a is a stiffness equivalent coefficient K (corresponding to the stiffness coefficient of mechanical impedance) that is a gain for adjusting the stiffness feeling (spring feeling) given to the driver during steering operation according to the driver power W and the vehicle speed V. Value) to be generated using a stiffness adjustment map prepared in advance. The multiplier 24b generates the stiffness adjustment torque Tk ^* by multiplying the stiffness equivalent coefficient K by the estimated load Tx. That is, the stiffness equivalent coefficient K can be said to be an adjustment gain for the road surface load (estimated load Tx). The stiffness equivalent coefficient K is supplied to the correction unit 30 as a mechanical impedance adjustment amount.

The viscosity adjustment amount calculation unit 25 is one of adjustment components included in the target steering torque Ts ^* based on the driver power W, the motor speed ω, and the vehicle speed V, and the viscosity of the steering system mechanism 100 given to the driver during steering. A viscosity adjustment torque Tc ^* for adjusting the sexual feeling is generated. Specifically, the viscosity adjustment amount calculation unit 25 includes a viscosity coefficient calculation unit 25a and a multiplier 25b. The viscosity coefficient calculation unit 25a generates a viscosity coefficient C used for adjusting the feeling of viscosity given to the driver during the steering operation using the prepared viscosity adjustment map according to the driver power W and the vehicle speed V. . The multiplier 25b multiplies the viscosity coefficient C by the motor speed ω (corresponding to the steering speed) to generate the viscosity adjustment torque Tc ^* . That is, the viscosity coefficient C can be said to be an adjustment gain with respect to the motor speed ω (and hence the steering speed).

The inertia adjustment amount calculation unit 26 is one of adjustment components included in the target steering torque Ts ^* based on the driver power W and the motor acceleration α, and adjusts the inertial feeling of the steering system mechanism 100 given to the driver during steering. Inertia adjustment torque Ti ^* is generated. Specifically, the inertia adjustment amount calculation unit 26 includes an inertia coefficient calculation unit 26a and a multiplier 26b. The inertia coefficient calculation unit 26a generates an inertia coefficient I for adjusting the feeling of inertia given to the driver at the time of operating the steering wheel using a prepared inertia adjustment map according to the driver power W. The multiplier 26b calculates the inertia adjustment torque Ti ^* by multiplying the motor acceleration α generated by the differentiator 261 by the inertia coefficient I. That is, it can be said that the inertia coefficient is an adjustment gain with respect to the motor acceleration α (and hence the steering acceleration). Here, the driver power W is used as a parameter for changing the inertia coefficient I, but the vehicle speed V may be used in addition to the driver power W as in the stiffness equivalent coefficient K and the viscosity coefficient C.

The target calculator 27 calculates the target steering torque Ts ^* by adding the basic torque Tf ^* , the rigidity adjustment torque Tk ^* , the viscosity adjustment torque Tc ^* , and the inertia adjustment torque Ti ^* . The deviation calculator 28 calculates a torque deviation which is a difference between the steering torque Ts and the target steering torque Ts ^* . The controller unit 29 includes a differentiator, an integrator, and the like, and generates an output for adjusting the feeling of transmission according to the road load applied to the driver during the steering operation and the feel according to the steering state quantity.

Based on the torque deviation (the difference between the steering torque Ts and the target steering torque Ts ^* ), the controller unit 29 performs control so that the torque deviation becomes zero, that is, the steering torque Ts follows the target steering torque Ts ^*. Thus, a base assist command Tb ^* for generating an assist torque (also referred to as an assist amount) for realizing a feeling of transmission according to the road surface load and a feel according to the steering state amount is generated.

  Incidentally, the mechanical impedance (stiffness coefficient, viscosity coefficient, inertia coefficient) defines the relationship between the force F applied to the object and the displacement amount x of the object, and is represented by the relational expression (1). In particular, in the case of rotational motion, F is regarded as the torque applied to the object, and x is regarded as the amount of rotation of the object.

Here, x represents a steering angle (motor rotation angle), a first derivative value represents a steering speed (motor speed ω), and a second derivative represents a steering acceleration (motor acceleration α). In other words, the stiffness adjustment amount calculation unit 24, the viscosity adjustment amount calculation unit 25, and the inertia adjustment amount calculation unit 26 obtain torque necessary for adjusting the feel given to the driver when operating the handle according to the equation (1). However, in this embodiment, since the estimated load Tx is used instead of the steering angle x for calculating the stiffness adjustment torque Tk ^* , the stiffness equivalent coefficient K corresponding to the stiffness coefficient is used instead of the stiffness coefficient. . The relationship between the steering angle x and the stiffness equivalent coefficient K can be easily obtained from a relational expression representing the characteristics of the steering system mechanism 100.

<Correction unit>
The correction unit 30 includes a bandpass filter (BPF) 31, a filter gain calculation unit 32, and a correction torque calculator 33.

  The BPF 31 extracts a signal component in a specific band (10 to 40 Hz in the present embodiment), which is a region where a vibration representing a road surface state (road information) is generated, from the steering torque Ts. The filter gain calculation unit 32 generates a transmission control gain G by which the output of the BPF 31 is multiplied according to the stiffness equivalent coefficient K using a gain adjustment map prepared in advance. The correction torque calculator 33 generates a correction torque command Tr by multiplying the output of the BPF 31 (a signal component in a specific band) by the output of the filter gain calculation unit 32 (transmission control gain G). That is, the transmission characteristic of the torque (and hence vibration) from the tire to the steering wheel is adjusted by the transmission control gain G.

  By the way, as shown in FIG. 6, the rigidity perception of the driver at the time of steering changes depending on the presence or absence of vibration applied to the steering wheel and the frequency of vibration. In particular, when vibration is applied when the actual stiffness value (actual stiffness value) is small, the stiffness value (perceived stiffness value) felt by the driver tends to feel greater than the actual stiffness value. In addition, the frequency band of vibration that causes such an action overlaps with a region in which vibration representing road information is generated. That is, it can be seen that by adjusting the transmission characteristics in this region, it is possible to change the feeling of rigidity during steering, for example, response when the steering wheel is cut.

  FIG. 6 shows an experimental apparatus (reaction device) in which a handle is directly connected to a motor drive shaft, and the operator changes the stiffness value at the time of steering and the applied vibration frequency by motor control. This is the result of investigating the subjectively sensed stiffness value (rigidity magnitude). However, 4 types of rigidity values (2, 3, 4, 5 [Nm / rad]) and 6 types of vibration frequencies (0 (no vibration), 10, 20, 30, 40, 50 [Hz]) are used. The vibration amplitude was changed to a magnitude proportional to the steering angle.

  For any combination of the above stiffness and vibration frequency (for example, stiffness value: 3 [Nm / rad], vibration frequency 30 Hz, etc.), the subject felt subjectively after reciprocating a predetermined number of times in a range of ± 20 deg. The magnitude of the stiffness was answered using VAS (Visual Analog Scale). Here, 7 test subjects were asked to steer all combinations of the stiffness values and vibration frequencies a predetermined number of times in a random order, and the results were averaged to obtain the perceived stiffness values shown in FIG. .

  As shown in FIG. 4, the gain adjustment map is set to have an approximately inversely proportional relationship in which the transmission control gain G decreases as the stiffness equivalent coefficient K increases. However, the upper limit value of the transmission control gain G is set to 1, and here, G = 1 is set when the stiffness equivalent coefficient K ≦ 1.

  That is, when the stiffness equivalent coefficient K is small, that is, when the base assist unit 20 is adjusted so that the stiffness coefficient of the mechanical impedance is small, the transmission control gain G is set to a large value. Thereby, even when the handle becomes light, the response when the handle is cut is compensated. On the contrary, when the rigidity equivalent coefficient K is large, that is, when the base assist unit 20 is adjusted so as to increase the rigidity coefficient of the mechanical impedance, the transmission control gain G is set to a small value. Thereby, transmission of the signal component of the specific band from the tire to the steering wheel is suppressed.

Note that the gain adjustment map shown in FIG. 4 is merely an example, and may be set as appropriate so as to realize desired characteristics.
<Effect>
As described above, the electric power steering system 1 is configured to adjust the transmission characteristic of the signal component in the specific band in conjunction with the adjustment content of the mechanical impedance, and when the stiffness coefficient decreases, the transmission control gain When G is increased and the stiffness coefficient is increased, the transmission control gain G is decreased.

  Therefore, according to the electric power steering system 1, even when the stiffness coefficient of the mechanical impedance is decreased due to an increase in the assist amount, the response when the steering wheel is turned off can be compensated, and the feeling during steering is deteriorated. It is possible to prevent the driver from feeling uncomfortable (rudder or the like). Further, when the stiffness coefficient of the mechanical impedance is increased, excessive vibration (torque fluctuation) is not applied to the steering wheel, so that the driver can be prevented from feeling uncomfortable.

  That is, the signal component (10 Hz or less) for controlling the mechanical impedance mainly acts on a force sense, and creates a basic weight and response in the steering feeling. On the other hand, the signal component (10 to 40 Hz) for transmitting the road surface condition (road information) mainly acts on the sensory receptors on the skin. However, it has been clarified by experiments of the present inventors that the stimulation to the skin also acts on force sense such as response (generates an illusion). It can be said that a desired feel is realized by using this to compensate the force sense using the component acting on the tactile sense when the component acting on the sense of force decreases.

  FIG. 5 is a Bode diagram in which torque transmission characteristics from the road surface load (estimated load Tx) to the steering angle are obtained by simulation. Specifically, the transmission control gain G was set to G0, G1, and G2 in FIG. FIG. 5 shows that the gain in the 10-20 Hz band, which is a part of the road information area, increases as the transmission control gain G increases, that is, the torque fluctuation (vibration) transmitted from the road surface to the steering wheel. It turns out that it becomes more noticeable.

  Also, when the mechanical impedance decreases, the assist works in the direction to cancel the road surface reaction force, and the road surface state becomes difficult to be transmitted, but the specific frequency used for compensation of the stiffness coefficient overlaps with the road information area, The signal component representing the road information is also transmitted to the steering wheel, so that the driver can perceive the road surface condition.

<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 the above embodiment, the driver power W and the vehicle speed V, which are the products of the steering torque Ts and the steering speed (motor speed ω), are used as parameters for changing the mechanical impedance. However, the present invention is not limited to this. Instead of the driver power W, a steering angle or the like may be used.

  In the above embodiment, the transmission control gain G is changed according to the stiffness equivalent coefficient K, but is changed according to the viscosity coefficient C and the inertia coefficient I, or according to any two or all of K, C, and I. It may be changed.

In the above embodiment, the load estimator 21 generates the estimated load Tx from the base assist command Tb ^* and the steering torque Ts, but the energization current Im detected by the current FB unit 42 instead of the base assist command Tb ^*. May be used.

In the above embodiment, the basic torque Tf ^* is generated from the estimated load Tx. However, the basic torque Tf ^* may be generated from the steering angle.
In the above embodiment, the basic torque Tf ^* and the mechanical impedance adjustment torques Tk ^* , Tc ^* , and Ti ^* are obtained separately and then added to generate the target steering torque Ts ^* . As described in Document 1, the present invention may be applied to a system configured to obtain a target steering torque Ts ^* from a steering angle using a standard steering model reflecting mechanical impedance. In this case, the transmission control gain G may be changed according to the mechanical impedance used in the reference steering model.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering system 20 ... Base assist part 21 ... Load estimator 22 ... Basic load amount calculating part 23 ... Driver work rate calculating part 24 ... Rigidity adjustment amount calculating part 24a ... Stiffness coefficient calculating part 24b, 25b, 26b ... Multiplication 25 ... Viscosity adjustment amount calculation unit 25a ... Viscosity coefficient calculation unit 26 ... Inertia adjustment amount calculation unit 26a ... Inertia coefficient calculation unit 27 ... Target calculation unit 28 ... Deviation calculation unit 29 ... Controller unit 30 ... Correction unit 31 ... Band pass filter 32 ... Filter gain calculation unit 33 ... Correction torque calculation unit 41 ... Adder 42 ... Current feedback (FB) unit, 100 ... Steering system mechanism 261 ... Differentiator

Claims (7)

A steering control device (15) for controlling steering characteristics by outputting an assist torque according to a steering torque applied to a steering shaft (3.5) coupled to a steering member (2) by a motor (6),
Basic torque generating means (21, 22) for generating a basic torque that is a target value of the steering torque to be generated according to the assist torque;
Adjustment torque generating means (23, 24) for generating an adjustment torque that is a target value of the steering torque for adjusting the mechanical impedance that defines the relationship between the steering torque detected by the steering shaft and the steering angle;
Correction torque generating means (30) for generating a correction torque which is a target value of the steering torque for adjusting a vibration transmission characteristic from the steering wheel to the steering member;
Command value generating means (27, 28, 29, 41, 42) for generating a command value for controlling the motor from the basic torque, the adjustment torque, and the correction torque;
With
The steering control device, wherein the correction torque generation means changes the vibration transmission characteristic according to the adjustment contents of the mechanical impedance in the adjustment torque generation means.   2. The steering control device according to claim 1, wherein the adjustment torque generating unit generates the adjustment torque according to a steering state amount representing an operation applied to the steering member.   The command value generating means generates a target steering torque from the basic torque, the adjustment torque, and the correction torque, and the command value is for causing the steering torque to follow the target steering torque. The steering control device according to claim 1 or 2. The correction torque generating means
A filter (31) for extracting a signal component of a specific band set in advance from the steering torque;
Gain adjusting means (32, 33) for outputting the correction torque obtained by multiplying the output of the filter by an adjustment gain set according to the magnitude of the mechanical impedance;
The steering control device according to any one of claims 1 to 3, further comprising:   The steering control device according to claim 4, wherein the specific band is 10 to 40 Hz.   The steering control device according to claim 4 or 5, wherein the gain adjustment means increases the adjustment gain when the mechanical impedance decreases.   The steering control device according to any one of claims 1 to 6, wherein at least one of a stiffness coefficient, a viscosity coefficient, and an inertia coefficient is used as the mechanical impedance.