JP2014139059A - Steering control device and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering control device enabling improvement of steering feeling.SOLUTION: An ECU 30 serving as a steering control device calculates motor output torque Tm to be generated by an assist motor 22 on the basis of a steering operation state of a driver and a driving state of a vehicle 1, estimates an estimation value Tvd of vehicle response reaction force that is transmitted to a steering from a road surface by a behavior of the vehicle 1 in response to the steering operation by the driver on the basis of steering torque Tsw caused by the steering operation by the driver of the vehicle 1, assist torque Ta and friction torque generated from the steering used by the driver to perform the steering operation to a steered wheel, calculates reaction force application torque Tadd transmitted to the steering in addition to actual vehicle response reaction force on the basis of the vehicle response reaction force estimation value Tvd, and controls the assist torque Ta for assisting the steering operation by the driver on the basis of a value obtained by subtracting reaction force application torque Tadd from the motor output torque Tm.

Description

  The present invention relates to a steering control device and a vehicle including the same.

  2. Description of the Related Art Conventionally, regarding a control technique of an electric power steering apparatus that assists a steering operation of a driver of a vehicle, for example, Patent Document 1 gives to a steering by an actuator based on information representing a vehicle state such as a vehicle speed and a steering angle. A technique for controlling the friction torque is disclosed. As a result, it is possible to generate a friction torque having an optimum magnitude and direction according to the vehicle state, and to reduce the steering force and to maintain stability during steering and holding.

JP 2009-126244 A

  However, in the prior art such as Patent Document 1, there is room for improvement in order to improve the steering feeling when the friction of the steering system is large because the friction torque is applied.

  The present invention has been made in view of the above, and an object of the present invention is to provide a steering control device capable of improving a steering feeling and a vehicle including the same.

  In order to solve the above-described problem, a steering control device according to the present invention is a steering control device that controls an assist torque generated by an actuator to assist a steering operation of a driver of a vehicle. Based on the operation state and the driving state of the vehicle, a reference torque to be generated by the actuator is calculated, the steering torque accompanying the steering operation of the driver of the vehicle, the assist torque, and the driver performing the steering operation. Based on the friction torque generated between the steering wheel and the steered wheels to be performed, the vehicle response reaction force transmitted from the road surface to the steering is estimated by the behavior of the vehicle generated according to the steering operation of the driver, and the estimated vehicle Based on the response reaction force, a reaction force application torque to be transmitted to the steering in addition to the actual vehicle response reaction force is calculated. Based on the value obtained by subtracting the force application torque, and controls the assisting torque.

  The steering control apparatus preferably calculates the estimated vehicle response reaction force by adding the assist torque to the steering torque and subtracting the friction torque.

  The steering control device preferably calculates the reaction force applying torque by multiplying the estimated vehicle response reaction force by a gain.

  In the steering control device, it is preferable that the gain is set to be larger as the absolute value of the estimated vehicle response reaction force is smaller and to be smaller as the absolute value of the estimated vehicle response reaction force is larger. .

  Similarly, in order to solve the above-described problem, a vehicle according to the present invention includes the above-described steering control device, and an electric power steering device including the actuator that generates the assist torque controlled by the steering control device. It is characterized by providing.

  In the steering control device and the vehicle according to the present invention, the torque generated around the axis of the steering shaft can be virtually amplified by the amount of the reaction force applying torque, so that the actual torque of the vehicle response can be increased. The linearity of the motor assist torque characteristic can be improved, and as a result, the steering feeling during the steering operation can be improved.

FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering apparatus having a steering control apparatus according to an embodiment of the present invention. FIG. 2 is a functional block diagram of the ECU as the steering control device in FIG. FIG. 3 is a flowchart of the reaction force application control performed by the ECU as the steering control device of the present embodiment. FIG. 4 is a flowchart showing a subroutine of friction torque estimation processing in step S101 of the flowchart of FIG. FIG. 5 is a diagram showing an example of a reaction force gain Kadd setting map used in step S105 of the flowchart of FIG. FIG. 6 is a diagram illustrating a difference in steering torque to yaw rate characteristics depending on the presence or absence of motor assist control and the magnitude of the vehicle response reaction force. FIG. 7 is a diagram showing a difference in characteristics between steering torque and motor assist torque depending on the magnitude of the vehicle response reaction force.

  Hereinafter, an embodiment of a steering control device according to the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

  First, the configuration of the steering control device according to this embodiment will be described with reference to FIGS. FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering apparatus having a steering control apparatus according to an embodiment of the present invention, and FIG. 2 is a functional block diagram of an ECU as the steering control apparatus in FIG. is there.

  As shown in FIG. 1, the vehicle steering device 10 is a device that is mounted on the vehicle 1 and steers steered wheels (not shown) of the vehicle 1 in accordance with the steering operation of the driver of the vehicle 1. . The vehicle steering apparatus 10 includes a steering column 12 including a steering wheel 11 operated by a driver. The steering column 12 rotatably supports a steering shaft 14 that serves as a rotating shaft of the steering wheel 11. The steering shaft 14 is connected to an intermediate shaft (intermediate shaft) 16 via a rubber coupling 13 or the like. The intermediate shaft 16 is connected to a pinion shaft (output shaft), and a pinion 17 of the pinion shaft is engaged with a steering rack (steering rod) 18 in a steering gear box 27. One end of a tie rod 19 is connected to each end of the steering rack 18 and a steered wheel (not shown) is connected to the other end of each tie rod 19 via a knuckle arm or the like (not shown).

  A steering angle sensor 26 that generates a signal corresponding to the steering angle of the steering wheel 11 and a signal corresponding to the steering torque Tsw applied to the steering shaft 14 are applied to the intermediate shaft 16 or the steering shaft 14 of the vehicle steering device 10. A torque sensor 15 is provided. The torque sensor 15 is provided on each of the intermediate shaft 16 (input shaft) and the pinion shaft (output shaft) coupled by, for example, a torsion bar, and a total of 2 that detects torque based on the rotation angle difference between these shafts. It may be composed of a single resolver sensor.

  The vehicle steering apparatus 10 includes an electric power steering apparatus 20. The electric power steering apparatus 20 includes, as main components, a steering assist actuator 22 (hereinafter referred to as “assist motor 22”) and a rotation angle (hereinafter also referred to as “motor rotation angle”) θ of the assist motor 22. Is provided with a rotation angle sensor 24 for detecting. The turning angle of the steered wheel can be obtained from the motor rotation angle θ detected by the rotation angle sensor 24. The assist motor 22 is composed of, for example, a three-phase AC motor. The assist motor 22 is provided coaxially with the steering rack 18 in the steering gear box 27, and assists the movement of the steering rack 18 by its driving force. The configuration itself of the electric power steering apparatus 20 may be arbitrary including an arrangement place. The assist motor 22 of the electric power steering device 20 is controlled by an ECU 30 described later. The control mode of the assist motor 22 will be described later.

  The vehicle steering apparatus 10 includes an ECU (Electronic Control Unit) 30. The ECU 30 controls each part of the vehicle 1 based on information such as the state of the vehicle 1 and the surrounding state of the vehicle 1. In particular, in the present embodiment, the ECU 30 steers the driver based on the physical quantity of the steering operation detected by various sensors such as the torque sensor 15, the rotation angle sensor 24, the rudder angle sensor 26, and the vehicle speed sensor (not shown). Control for adjusting the torque for assisting the operation (hereinafter referred to as “assist torque Ta”) and generating the assist torque Ta by the assist motor 22 of the electric power steering device 20 (hereinafter also referred to as “motor assist control”). Can be executed). That is, the ECU 30 functions as a steering control device that controls the assist torque Ta that is generated by the assist motor 22 and assists the steering operation of the driver of the vehicle 1.

  Further, the ECU 30 of the present embodiment virtually amplifies the vehicle response reaction force and adjusts the assist torque in consideration of the virtual amplification of the vehicle response reaction force (hereinafter referred to as “reaction force application control”). To be described). Here, the “vehicle response reaction force” is a rotating shaft of a steering wheel on which the steered wheels of the vehicle 1 are received from the road surface by the behavior of the vehicle 1 generated according to the driver's steering operation, and the driver performs the steering operation. It means the reaction force transmitted to a certain steering shaft.

  As shown in FIG. 2, the ECU 30 makes it possible to execute this reaction force application control, a motor output torque calculation unit 31, a friction torque estimation unit 32, a vehicle response reaction force estimation unit 33, a gain multiplier 34, a subtractor. 35, each function of the control command calculation unit 36 is realized.

  The motor output torque calculator 31 calculates a motor output torque Tm that is a reference value (reference torque) of torque to be generated by the assist motor 22 based on the steering operation state of the driver and the driving state of the vehicle 1. The motor output torque calculation unit 31 includes information such as the vehicle speed of the vehicle 1 detected by a vehicle speed sensor (not shown) and the steering torque Tsw accompanying the steering operation of the driver of the vehicle 1 detected by the torque sensor 15. Is entered. The motor output torque calculator 31 outputs the motor output torque Tm based on the input information using a known motor assist control method such as basic assist control or damping control. That is, the motor output torque Tm is equivalent to a control command value to the assist motor 22 in the conventional motor assist control.

  The friction torque estimation unit 32 estimates the friction torque based on the motor rotation angle θ detected by the rotation angle sensor 24. Here, the “friction torque” includes all mechanical friction generated between the steering wheel 11 on which the driver performs the steering operation and the steered wheels. The friction torque estimation unit 32 estimates the friction torque using a friction model using the motor rotation angle θ as input information, and outputs a friction torque estimated value Tf. A friction estimation method using the friction model will be described later with reference to FIG.

  The vehicle response reaction force estimation unit 33 estimates the vehicle response reaction force based on the steering torque Tsw detected by the torque sensor 15, the friction torque estimation value Tf that is the output of the friction torque estimation unit 32, and the assist torque Ta. The vehicle response reaction force estimated value Tvd is output.

Here, the vehicle response reaction force estimation method in the vehicle response reaction force estimation unit 33 will be described in detail. When the steering is continuously performed in one direction from the position where the steering angle is 0 degrees, the friction torque (friction torque estimated value Tf) is generated on the opposite side to the steering direction of the steering wheel 11, and therefore, the steering torque Tsw and the motor output torque Tm. And in the opposite direction. The vehicle response reaction force (vehicle response reaction force estimated value Tvd) is generated in the direction of the default position of the steering wheel 11 (the position at which the steering angle is 0 degrees). The assist torque Ta is generated in the same direction as the steering torque Tsw. The motor output torque Tm is a motor control command value in the conventional control method as described above, and has the same property as the assist torque Ta, and is generated in the same direction as the steering torque Tsw. Here, considering the state in which the driver moves the steering direction of the vehicle to a certain direction, the force for moving the steering direction is the steering torque Tsw generated by the driver and the assist torque Ta generated by the assist motor 22. . On the other hand, the force against the steering operation is a friction torque and a vehicle response reaction force. During the steering operation, the steering angle and the turning angle continuously change while maintaining a state where these four forces are balanced around the axis of the steering shaft 14 that is the rotation axis of the steering wheel 11. That is, the balance of force during the steering operation can be expressed by the following equation (1).
Steering torque Tsw + assist torque Ta = friction torque + vehicle response reaction force
... (1)

From the above equation (1), the vehicle response reaction force can be expressed by the following equation (2) using the steering torque Tsw, the assist torque Ta, and the friction torque Tf.
Vehicle response reaction force = steering torque Tsw + assist torque Ta−friction torque
... (2)

  Therefore, the vehicle response reaction force estimation unit 33 is based on the steering torque Tsw detected by the torque sensor 15, the previous value of the assist torque Ta output from the subtractor 35 in the previous process, and the output of the friction torque estimation unit 32. A vehicle response reaction force estimated value Tvd can be calculated by substituting a certain estimated friction torque value Tf into the equation (2).

  The gain multiplier 34 multiplies the vehicle response reaction force estimated value Tvd calculated by the vehicle response reaction force estimation unit 33 by the reaction force gain Kadd to calculate the reaction force application torque Tadd. Here, the “reaction force application torque” is a torque transmitted in addition to the actual vehicle response reaction force around the axis of the steering shaft 14, and is applied to virtually amplify the vehicle response reaction force transmitted to the steering. Torque. Since the reaction force applying torque Tadd is calculated by multiplying the vehicle response reaction force estimated value Tvd by the reaction force gain Kadd, the magnitude of the reaction force applying torque Tadd is basically the magnitude of the vehicle response reaction force estimated value Tvd. It is decided accordingly. That is, a virtual amplification amount of the vehicle response reaction force is determined according to the magnitude of the vehicle response reaction force estimated value Tvd estimated by the vehicle response reaction force estimation unit 33. For example, assuming that the virtual amplification amount of the vehicle response reaction force when the magnitude of the vehicle response reaction force estimated value Tvd is 100 is 50, when the vehicle response reaction force estimated value Tvd is 200, the vehicle response reaction force The virtual amplification amount can be set to 100.

  The subtractor 35 subtracts the reaction force application torque Tadd calculated by the vehicle response reaction force estimation unit 33 and the gain multiplier 34 from the motor output torque Tm calculated by the motor output torque calculation unit 31 to obtain an assist torque Ta. Output as.

  The control command calculation unit 36 outputs a control command value I to the assist motor 22 based on the assist torque Ta output from the subtractor 35. Specifically, the control command value I is an operating current value of the assist motor 22.

  The ECU 30 outputs this control command value I to the assist motor 22. The assist motor 22 is driven to generate a desired assist torque Ta around the axis of the steering shaft 14 in accordance with a control command value I input from the ECU 30. That is, the ECU 30 controls the assist torque Ta generated by the assist motor 22 based on a value obtained by subtracting the reaction force applying torque Tadd from the motor output torque Tm.

  The ECU 30 is physically an electronic circuit mainly including a well-known microcomputer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and an interface. The function of the ECU 30 described above is to load various application programs stored in the ROM into the RAM and execute them by the CPU, thereby operating various devices in the vehicle 1 under the control of the CPU, and data in the RAM and ROM. This is realized by reading and writing. Note that the ECU 30 is not limited to the above functions, and includes other various functions used as the ECU of the vehicle 1. Moreover, said ECU may be implement | achieved by single ECU which supervises a steering system, and may be implement | achieved in cooperation with 2 or more ECU.

Next, the operation of the steering control device according to the present embodiment will be described with reference to FIGS.
FIG. 3 is a flowchart of the reaction force application control performed by the ECU as the steering control device of this embodiment, and FIG. 4 is a flowchart showing a subroutine of the friction torque estimation process in step S101 of the flowchart of FIG. FIG. 5 is a diagram showing an example of a reaction force gain Kadd setting map used in step S105 of the flowchart of FIG. The reaction force application control process shown in the flowchart of FIG. 3 is executed by the ECU 30 at predetermined intervals, for example.

  The reaction force application control process of the steering control device (ECU 30) will be described with reference to the flowchart of FIG. 3. First, in step S101, the friction torque estimation unit 32 of the ECU 30 calculates the friction torque estimation value Tf. The friction torque estimating unit 32 executes the subroutine shown in FIG. 4 based on the motor rotation angle θ detected by the rotation angle sensor 24 and estimates the friction torque.

The subroutine of the friction torque estimation processing shown in FIG. 4, first, at step S201, whether the target motor rotational angle theta _t is initialized, that is, whether the period this is the first time period is determined. If the target motor rotation angle θ _t has not been initialized (No in step S201), the process proceeds to step S202, and if the current cycle is not the first cycle, that is, the target motor rotation angle θ _t is initialized before the previous cycle. If yes (Yes in step S201), the process directly proceeds to step S203.

In step S202, the initial value of the target motor rotational angle theta _t is, the motor rotational angle theta (current cycle value, hereinafter the same) is set to, the process proceeds to step S203. The initial value of the target motor rotational angle theta _t may be zero.

In step S203, it is determined whether or not the motor rotation angle θ, the deviation upper limit value Δ, and the current target motor rotation angle θ _t have a relationship of θ> θ _t + Δ. The deviation upper limit value Δ is calculated as Δ = T _f0 / K _f0 using the mechanical friction torque value T _f0 and the friction gradient K _f0 . The mechanical friction torque value T _f0 is a mechanical friction torque value between the steering wheel 11 and the steered wheel under a predetermined condition, and a value measured under the predetermined condition may be used. A value estimated based on a steering angle or the like may be used. The friction gradient K _f0 may be an arbitrary fixed value that is determined in consideration of the friction characteristics and rigidity of the steering system. Since T _f0 and K _f0 are positive values, the deviation upper limit Δ is a positive value.

As a result of the determination in step S203, if θ> θ _t + Δ (Yes in step S203), the process proceeds to step S204, and if θ ≦ θ _t + Δ (No in step S203), the process proceeds to step S205.

In step S204, the target motor rotation angle θ _t is changed to a new value by the equation θ _t = θ−Δ, using the motor rotation angle θ and the deviation upper limit value Δ. That is, when the deviation Δθ (= θ _t −θ) obtained by subtracting the motor rotation angle θ from the target motor rotation angle θ _t is Δθ <−Δ, the target motor rotation angle θ _t is θ _t = θ−Δ. Changed (updated) to When the process of step S204 is completed, the process proceeds to step S207.

In step S205, the motor rotation angle theta (the value in the current cycle), the upper limit value of the deviation delta, and the current target motor rotational angle theta _t, whether or not θ <θ _t -Δ the relationship is determined . If θ <θ _t −Δ (Yes in step S205), the process proceeds to step S206.

In step S206, the target motor rotation angle θ _t is changed to a new value by the equation θ _t = θ + Δ using the motor rotation angle θ and the deviation upper limit value Δ. That is, when the deviation Δθ (= θ _t −θ) obtained by subtracting the motor rotation angle θ from the target motor rotation angle θ _t is Δθ> Δ, the target motor rotation angle θ _t is changed to θ _t = θ + Δ ( Updated).

If θ ≧ θ _t −Δ in step S205 described above (No in step S205), the process proceeds to step S207 while the current target motor rotation angle θ _t is maintained unchanged. That is, when the deviation Δθ (= θ _t −θ) obtained by subtracting the motor rotation angle θ from the target motor rotation angle θ _t is −Δ ≦ Δθ ≦ Δ, the target motor rotation angle θ _t is maintained unchanged. Is done.

In step S207, using the updated or maintained the target motor rotational angle theta _t in step S201 to S206, the friction torque estimated value Tf is calculated by the following equation (3).
Tf = K _f0 (θ _t −θ) (3)

  In step S208, the estimated friction torque Tf calculated in step S207 is low-pass filtered. When the process of step S208 is completed, the process returns to the main flow and proceeds to step S102.

  In the friction torque estimation process shown in FIG. 4, the motor rotation angle θ used for calculating the friction torque estimation value Tf is replaced with the steering angle detected by the steering angle sensor 26, and the friction torque estimation value is calculated based on the steering angle. It is good also as a structure which calculates Tf.

  Returning to FIG. 3, in step S102, the steering torque Tsw is detected. The ECU 30 can obtain the steering torque Tsw based on information input from the torque sensor 15, for example. When the process of step S102 is completed, the process proceeds to step S103.

  In step S <b> 103, the motor output torque Tm is calculated by the motor output torque calculator 31. The motor output torque calculation unit 31 is based on input information such as the vehicle speed of the vehicle 1 detected by a vehicle speed sensor (not shown) and the steering torque Tsw detected in step S102, for example, basic assist control or damping control. The motor output torque Tm is output using a known control method of the electric power steering device 20. When the process of step S103 is completed, the process proceeds to step S104.

  In step S104, the vehicle response reaction force estimation unit 33 calculates a vehicle response reaction force estimated value Tvd. The vehicle response reaction force estimation unit 33 calculates the previous value of the friction torque estimated value Tf estimated in step S101, the steering torque Tsw detected in step S102, and the assist torque Ta calculated in the previous processing loop of this control flow. By substituting the value into the equation (2) as described above, the vehicle response reaction force estimated value Tvd is calculated. That is, the vehicle response reaction force estimated value Tvd is calculated by adding the assist torque Ta to the steering torque Tsw and subtracting the friction torque estimated value Tf (Tvd = Tsw + Ta−Tf). When the process of step S104 is completed, the process proceeds to step S105.

  In step S <b> 105, the reaction force gain Kadd is set by the gain multiplier 34. The reaction force gain Kadd is appropriately set according to the magnitude of the absolute value of the vehicle response reaction force estimated value Tvd calculated in step S104. For example, as shown in FIG. 5, the ECU 30 stores a setting map in which the vehicle response reaction force and the reaction force gain are associated with each other, and the vehicle response reaction force calculated in step S104 with reference to the setting map. A reaction force gain Kadd is set based on the estimated value Tvd. In the setting map of FIG. 5, the horizontal axis represents the vehicle response reaction force estimated value Tvd, and the vertical axis represents the reaction force gain Kadd. In the setting map of FIG. 5, the reaction force gain Kadd corresponding to the vehicle response reaction force estimated value Tvd is set as a curve having a convex shape in the positive direction of the vertical axis. That is, the smaller the absolute value of the vehicle response reaction force estimated value Tvd, the larger the reaction force gain Kadd, and the larger the absolute value of the vehicle response reaction force estimated value Tvd, the smaller the reaction force gain Kadd.

  The reaction force gain Kadd set in step S105 may be a constant value regardless of the magnitude of the vehicle response reaction force estimated value Tvd.

  In step S <b> 106, the reaction force applying torque Tadd is calculated by the gain multiplier 34. The gain multiplier 34 multiplies the vehicle response reaction force estimated value Tvd calculated in step S104 by the reaction force gain Kadd set in step S105 to calculate a reaction force application torque Tadd (Tadd = Kadd × Tvd). . When the process of step S106 is completed, the process proceeds to step S107.

  In step S107, the assist torque Ta is calculated by subtracting the reaction force application torque Tadd calculated in step S106 from the motor output torque Tm calculated in step S103 by the subtractor 35 (Ta = Tm-Tadd). The assist torque Ta calculated in step S107 is stored in the ECU 30 as the previous value of the assist torque Ta, and is used for calculating the vehicle response reaction force estimated value Tvd in step S104 at the next execution of this control flow. .

  In step S108, the control command calculation unit 36 calculates the control command value I for the assist motor 22 based on the assist torque Ta calculated in step S107. The ECU 30 outputs this control command value I to the assist motor 22. When the process of step S108 is completed, this control flow ends.

  Thus, in the present embodiment, the assist torque Ta is calculated by subtracting the reaction force applying torque Tadd from the motor output torque Tm that is a control command value of the conventional motor assist control. When the assist torque Ta calculated in this way is generated in the assist motor 22, the torque generated around the axis of the steering shaft 14 is the motor output torque Tm in the steering direction, and further in the direction opposite to the steering direction. This is equivalent to a state in which a reaction force obtained by summing the vehicle response reaction force generated when the vehicle is actually received from the road surface and the reaction force application torque Tadd virtually added by the assist motor 22 is generated. That is, in addition to the vehicle response reaction force actually transmitted from the road surface to the steering, the reaction force application torque Tadd is transmitted to the steering, and as a result, the vehicle response reaction force is virtually amplified by the reaction force application torque Tadd. It becomes a state.

  Thus, the effect by virtually amplifying the vehicle response reaction force will be described with reference to FIGS. FIG. 6 is a diagram showing the difference between steering torque and yaw rate characteristics depending on the presence or absence of motor assist control and the magnitude of vehicle response reaction force, and FIG. 7 is the characteristic of steering torque to motor assist torque depending on the magnitude of vehicle response reaction force. It is a figure which shows the difference.

  FIG. 6 shows the steering torque input by the driver on the horizontal axis, and the yaw rate output as the behavior of the vehicle 1 in accordance with the steering torque on the vertical axis. In FIG. 6, the steering torque to yaw rate characteristic with motor assist control is shown by a bold line graph. FIG. 6 shows two types of characteristics without motor assist control, depending on the magnitude of the vehicle response reaction force that the vehicle 1 actually receives. The characteristics when the vehicle response reaction force is large are indicated by solid lines. The characteristic when the vehicle response reaction force is small is shown by a dotted line graph.

  As shown by the solid and dotted lines in FIG. 6, in the absence of motor assist control, no steering is performed due to mechanical friction of the steering device until the steering torque reaches a predetermined value, and no yaw rate is generated. . When the steering torque exceeds a predetermined value, the steering is performed against friction and the yaw rate increases rapidly. That is, when there is no motor assist control, the steering torque-yaw rate characteristic becomes discontinuous due to the influence of friction and becomes a non-linear characteristic. Further, as shown by the dotted line graph in FIG. 6, the steering torque to yaw rate characteristic when the vehicle response reaction force is small is abruptly increased after generation of the yaw rate compared with the case where the vehicle response reaction force is large, and nonlinearity Has stronger characteristics.

  In the motor assist control, by applying motor assist torque by the assist motor 22, the nonlinear steering torque to yaw rate characteristic shown by the solid line and dotted line graph in FIG. 6 is changed to the target characteristic shown by the bold line graph, The linearity of the vehicle response to the steering torque can be improved.

  In FIG. 7, the horizontal axis represents the steering torque, and the vertical axis represents the motor assist torque that is applied to realize the target characteristics of FIG. 6 in the motor assist control. In FIG. 7, the steering torque to motor assist torque characteristic when the vehicle response reaction force is large is shown by a solid line graph, and the characteristic when the vehicle response reaction force is small is shown by a dotted line graph.

  Consider a case where the steering torque-yaw rate characteristic indicated by the solid line graph in FIG. 6 is changed to the target characteristic indicated by the thick line graph by motor assist control when the vehicle response reaction force is large. In this case, since the nonlinearity of the characteristic is relatively weak, as shown by a solid line graph in FIG. 7, the steering torque to motor assist torque characteristic is a characteristic close to linear.

  On the other hand, when the vehicle response reaction force is small, let us consider a case where the steering torque to yaw rate characteristic shown by the dotted line graph in FIG. 6 is changed to the target characteristic shown by the thick line graph by motor assist control. In this case, since the characteristic nonlinearity is strong, as shown by the dotted line graph in FIG. 7, the steering torque to motor assist torque characteristic also needs to be a characteristic with strong nonlinearity. In other words, as shown by the dotted line graph in FIG. 7, the steering torque to motor assist torque characteristic when the vehicle response reaction force is small is obtained when the vehicle response reaction force is large until the steering torque reaches a predetermined value. It changes with substantially the same inclination as the characteristic, and the nonlinearity is strong so that the inclination of the characteristic changes after the steering torque exceeds a predetermined value.

  As described above, when the nonlinearity of the steering torque to the motor assist torque characteristic by the motor assist control becomes strong, there is a contradiction such as a stepping of the steering torque on the return side or a sense of incongruity when the friction characteristic changes. There is an adverse effect on the steering feeling.

  Therefore, in this embodiment, the vehicle response reaction force is virtually increased by executing the reaction force application control together with the motor assist control. Thereby, the linearity of the steering torque to the motor assist torque characteristic can be improved, and the change to the target characteristic of the steering torque to the yaw rate characteristic can be realized without contradiction. As a result, it is possible to improve the steering feeling during the steering operation with motor assist control.

  Next, effects of the steering control device according to the present embodiment will be described.

  The ECU 30 as the steering control device of the present embodiment controls an assist torque Ta that is generated by the assist motor 22 and assists the steering operation of the driver of the vehicle 1. The motor output torque calculator 31 of the ECU 30 calculates a motor output torque Tm that is a reference torque to be generated by the assist motor 22 based on the steering operation state of the driver and the driving state of the vehicle 1. The vehicle response reaction force estimation unit 33 of the ECU 30 is generated between the steering torque Tsw accompanying the steering operation of the driver of the vehicle 1, the previous value of the assist torque Ta, and the steering wheel from which the driver performs the steering operation. Based on the friction torque (friction torque estimated value Tf), the vehicle response reaction force (vehicle response reaction force estimated value Tvd) transmitted from the road surface to the steering wheel is estimated by the behavior of the vehicle 1 generated according to the driver's steering operation. . Based on the vehicle response reaction force estimated value Tvd, the gain multiplier 34 of the ECU 30 calculates a reaction force application torque Tadd transmitted to the steering in addition to the actual vehicle response reaction force. The ECU 30 controls the assist torque Ta based on a value obtained by removing the reaction force applying torque Tadd from the motor output torque Tm.

  With this configuration, the assist torque Ta is subtracted by the reaction force applying torque Tadd. When the assist torque Ta calculated in this way is generated in the assist motor 22, the reaction force component transmitted around the steering shaft 14, which is the rotation axis of the steering, is the vehicle response actually transmitted from the road surface as described above. The reaction force is virtually amplified by the reaction force application torque Tadd. Thereby, as described with reference to FIGS. 6 and 7, since the linearity of the steering torque to the motor assist torque characteristic can be improved, the steering feeling during the steering operation with the motor assist control can be improved.

  Further, the vehicle response reaction force estimation unit 33 of the ECU 30 adds the previous value of the assist torque Ta to the steering torque Tsw and further subtracts the friction torque estimation value Tf, thereby calculating the vehicle response reaction force estimation value Tvd ( Tvd = Tsw + Ta−Tf).

  With this configuration, the vehicle response reaction force can be accurately estimated based on the relational expression of the force balance during the steering operation as described in accordance with the above formulas (1) and (2). It becomes possible to derive the reaction force application torque Tadd calculated based on the response reaction force estimated value Tvd with a more appropriate value. Thereby, the linearity of the steering torque to the motor assist torque characteristic changed by the reaction force applying torque Tadd can be further improved, and the steering feeling during the steering operation with the motor assist control can be further improved.

  The gain multiplier 34 of the ECU 30 calculates the reaction force applying torque Tadd by multiplying the vehicle response reaction force estimation value Tvd estimated by the vehicle response reaction force estimation unit 33 by the reaction force gain Kadd. The reaction force gain Kadd increases as the absolute value of the vehicle response reaction force estimated value Tvd estimated by the vehicle response reaction force estimation unit 33 decreases, and as the absolute value of the estimated vehicle response reaction force estimated value Tvd increases. Set small.

  With this configuration, the magnitude and change of the calculated reaction force application torque Tadd can be arbitrarily controlled by adjusting the setting of the reaction force gain Kadd. Accordingly, the reaction force application torque Tadd can be derived as an appropriate value, and the virtual amplification amount of the vehicle response reaction force can be appropriately controlled. Therefore, the steering torque changed by the reaction force application torque Tadd -The linearity of the motor assist torque characteristic can be further improved, and the steering feeling can be improved.

  As mentioned above, although embodiment of this invention was described, the said embodiment was shown as an example and is not intending limiting the range of invention. The above-described embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. The above-described embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof, as long as they are included in the scope and gist of the invention.

  For example, the assist motor 22 may be provided coaxially with the steering shaft 14 and the intermediate shaft 16, and may be configured to assist the rotation of the shaft with a driving force. In this case, the rotation angle sensor 24 is also disposed in the vicinity of the assist motor 22. The friction torque estimation unit 32 may estimate the friction torque using the steering angle detected by the steering angle sensor 26 instead of the rotation angle θ of the assist motor 22 detected by the rotation angle sensor 24.

  In the above embodiment, the vehicle response reaction force estimation unit 33 uses the previous value of the assist torque Ta when calculating the vehicle response reaction force estimation value Tvd using the equation (2). A past value other than the previous value of the assist torque Ta can also be used.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Vehicle steering device 20 Electric power steering device 22 Assist motor (actuator)
30 ECU (steering control device)
31 Motor output torque calculation unit 32 Friction torque estimation unit 33 Vehicle response reaction force estimation unit Ta assist torque Tm Motor output torque (reference torque)
Tsw Steering torque Tf Friction torque estimated value Tvd Vehicle response reaction force estimated value Tadd Reaction force applying torque

Claims (5)

A steering control device for controlling an assist torque generated by an actuator to assist a steering operation of a vehicle driver,
Based on the driver's steering operation state and the driving state of the vehicle, a reference torque to be generated by the actuator is calculated,
Based on the steering torque accompanying the steering operation of the driver of the vehicle, the assist torque, and the friction torque generated between the steering wheel and the steered wheel on which the driver performs the steering operation, the steering operation of the driver is performed. Estimating the vehicle reaction reaction force transmitted from the road surface to the steering wheel according to the behavior of the vehicle generated in response,
Based on the estimated vehicle response reaction force, a reaction force application torque to be transmitted to the steering in addition to the actual vehicle response reaction force is calculated,
A steering control device that controls the assist torque based on a value obtained by subtracting the reaction force applying torque from the reference torque.   The steering control device according to claim 1, wherein the estimated vehicle response reaction force is calculated by adding the assist torque to the steering torque and further subtracting the friction torque.   The steering control device according to claim 1, wherein the reaction force application torque is calculated by multiplying the estimated vehicle response reaction force by a gain.   4. The gain according to claim 3, wherein the gain is set to increase as the absolute value of the estimated vehicle response reaction force decreases, and to decrease as the absolute value of the estimated vehicle response reaction force increases. Steering control device. The steering control device according to any one of claims 1 to 4,
An electric power steering device having the actuator for generating the assist torque controlled by the steering control device;
A vehicle comprising:

Images