JP4280695B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a steering wheel operated by a driver to steer a vehicle, a steering actuator for steering a steered wheel, and a steered wheel by driving and controlling the steered actuator according to the operation of the steering handle. The present invention relates to a steering device for a steering-by-wire vehicle including a steering control device for steering the vehicle.

  In recent years, the development of this type of steering-by-wire steering system has been actively carried out. For example, Patent Document 1 below detects a steering angle and a vehicle speed, calculates a transmission ratio that decreases as the steering angle increases and increases as the vehicle speed increases, and divides the steering angle by this transmission ratio, thereby dividing the front wheel A steering device is shown in which a turning angle (amount of rack shaft displacement) is calculated and the front wheels are turned to the calculated turning angle. Further, in this steering device, the steering response and followability of the front wheels are improved by correcting the calculated turning angle in accordance with the steering speed obtained by time-differentiating the detected steering angle. Further, by calculating the target yaw rate using the detected vehicle speed and the detected steering angle, and correcting the calculated turning angle according to the difference between the calculated target yaw rate and the detected actual yaw rate, the vehicle behavior state Steering control that takes into account is also realized.

  Further, in Patent Document 2 below, the steering torque and the steering angle of the steering wheel are detected, two turning angles that increase as the steering torque and the steering wheel steering angle increase are calculated, and these calculated turning angles are added. A steering device is shown in which the front wheels are steered at the steered angle. In this steering device, the vehicle speed is also detected, and both turning angles are corrected based on the detected vehicle speed, so that the turning characteristics are changed according to the vehicle speed.

JP 2000-85604 A Japanese Patent Laid-Open No. 11-124047

  However, in any of the above conventional devices, the steering angle and the steering torque, which are the operation input values to the steering wheel by the driver, are detected, and the steering angle of the front wheels is directly determined using the detected steering angle and steering torque. Thus, the front wheels are steered to the calculated turning angle. However, the steering control of these front wheels, although the mechanical connection between the conventional steering wheel and the steered wheels is removed, the steering method of the front wheel with respect to the steering wheel operation is as follows: The basic technical idea of determining the steering angle of the front wheels according to the force is exactly the same, and in these steering methods, the steering angle of the front wheels is not determined according to human sensory characteristics So it was difficult to drive the vehicle.

  That is, in the conventional apparatus, the turning angle that cannot be perceived by the driver is determined directly in response to the operation of the steering wheel, and the vehicle turns by turning the front wheels according to the turning angle. . The driver senses the lateral acceleration, yaw rate, and turning curvature of the vehicle due to the turning of the vehicle by touch or vision, and feeds back to the operation of the steering handle to turn the vehicle in a desired manner. In other words, since the turning angle of the front wheels with respect to the steering wheel operation by the driver is a physical quantity that cannot be perceived by humans, the turning angle that is directly determined by the driver's steering operation is the driver's perception. It was not determined according to the characteristics, and this made it difficult to drive the vehicle.

  Further, in the above-described conventional device, the determined turning angle is corrected according to the difference between the target yaw rate calculated using the detected vehicle speed and the detected steering wheel angle and the detected actual yaw rate. This is merely correction of the turning angle in consideration of the behavior state of the vehicle, and does not determine the turning angle according to the yaw rate that the driver will perceive by operating the steering wheel. Accordingly, in this case as well, the turning angle determined for the driver's steering operation is not determined in accordance with the driver's perceptual characteristics, making it difficult to drive the vehicle.

  Further, in a steering-by-wire type steering apparatus such as the above-described conventional apparatus, the driver's steering feeling may change as the vehicle speed changes, and the driver may feel uncomfortable. That is, in the above-described conventional steering-by-wire type steering device, the transmission ratio can be changed as the vehicle speed changes, but the change in the gear ratio is simply changed. is there. In other words, since it is not changed according to the driver's perceptual characteristics, the driver may feel discomfort regarding the steering characteristics as the transmission ratio is changed.

  In order to cope with the above problem, the present inventors have worked on research on a vehicle steering apparatus that can steer a vehicle in accordance with human perceptual characteristics in response to a steering wheel operation by a driver. Regarding such human perceptual characteristics, according to Weber-Fechner's law, it is said that the human sensory quantity is proportional to the logarithm of the physical quantity of the given stimulus. In other words, if the physical quantity of a stimulus given to a human is changed exponentially or exponentially with respect to the human's manipulated variable, the relationship between the manipulated variable and the physical quantity can be matched to the human perceptual characteristics. it can. The present inventors have applied the Weber-Hefner's law to the steering operation of a vehicle and discovered the following.

  When driving a vehicle, the vehicle turns by operating the steering handle, and the vehicle's motion state quantities such as lateral acceleration, yaw rate, and turning curvature change as the vehicle turns, and the driver senses the motion state quantity of the vehicle. And it feels more visually. Therefore, if the vehicle motion state quantity that can be perceived by the driver is changed exponentially or by a power function in response to the driver's operation on the steering wheel, the driver can adjust to the perceptual characteristics. The vehicle can be driven by operating the steering wheel.

  The present invention is based on the above discovery, and an object thereof is to facilitate driving of the vehicle by steering the vehicle in accordance with human perceptual characteristics, and uniform steering characteristics and steering response in all vehicle speed ranges. It is an object of the present invention to provide a steering-by-wire vehicle steering apparatus that can achieve high performance.

In order to achieve the above object, the present invention is characterized in that a steering handle operated by a driver to steer a vehicle, a steering actuator for turning a steered wheel, and an operation of the steering handle. A steering-by-wire vehicle steering apparatus comprising: a steering control device that drives and controls the steering actuator to steer the steered wheels, wherein the steering control device detects vehicle speed of the vehicle. And an operation input value detection means for detecting an operation input value of the driver for the steering wheel, and an operation input value for the steering wheel that represents a motion state of the vehicle that can be perceived by the driver in relation to turning of the vehicle. A motion state quantity calculating means for calculating a predicted motion state quantity of a vehicle having a predetermined exponential relationship or a power relation with the operation input value; and the vehicle speed detecting means Therefore when the detected vehicle speed is increased, the motion state quantity changing means for changing reduced anticipated motion state quantity calculated by the motion state quantity calculating means, because the vehicle is moving at anticipated motion state quantity in which the have changed A turning angle calculation means for calculating a turning angle of the steered wheels necessary for the vehicle using the changed estimated motion state quantity and the detected vehicle speed, and depending on the calculated turning angle, The present invention resides in that the steered wheel is composed of steered control means for controlling the steered wheel to steer the steered wheel to the calculated steered angle.

Another feature of the present invention is that a steering handle operated by a driver to steer the vehicle, a steering actuator for turning a steered wheel, and the steering according to an operation of the steering handle. In a steering-by-wire vehicle steering apparatus including a steering control apparatus that drives and controls an actuator to steer a steered wheel, the steering control apparatus includes a vehicle speed detection unit that detects a vehicle speed of the vehicle, and the steering An operation input value detecting means for detecting an operation input value of the driver with respect to the steering wheel, and a motion state of the vehicle that can be perceived by the driver in relation to the turning of the vehicle. The motion state quantity calculating means for calculating the expected motion state quantity of the vehicle having an exponential relation or a power relation using the operation input value and the vehicle speed detecting means. Depending on the vehicle speed, the movement state quantity changing means for changing the magnitude of the expected movement state quantity calculated by the movement state quantity calculating means, and the vehicle necessary for the vehicle to move with the changed expected movement state quantity. A turning angle calculation means for calculating a turning angle of a turning wheel by using the changed estimated motion state quantity and the detected vehicle speed, and the turning actuator according to the calculated turning angle. Steering control means for controlling and turning the steered wheels to the calculated turning angle, and a maximum value of an operation input value input by a driver to the steering handle is detected by the vehicle speed detecting means. The maximum operation input value changing means for changing the speed based on the vehicle speed is also included. In this case, before Symbol maximum operation input value changing means, when the vehicle speed detected by the vehicle speed detecting means increases, may be changed reduce the maximum value of the operation input value. Furthermore, another feature of the present invention is that a steering handle operated by a driver to steer the vehicle, a steering actuator for steering a steered wheel, and the steering according to an operation of the steering handle. In a steering-by-wire vehicle steering apparatus including a steering control apparatus that drives and controls an actuator to steer a steered wheel, the steering control apparatus includes a vehicle speed detection unit that detects a vehicle speed of the vehicle, and the steering An operation input value detecting means for detecting an operation input value of the driver with respect to the steering wheel, and a motion state of the vehicle that can be perceived by the driver in relation to the turning of the vehicle. A motion state quantity calculating means for calculating a predicted motion state quantity of a vehicle having an exponential relationship or a power relationship using the operation input value and detected by the vehicle speed detecting means. The movement state quantity changing means for changing the magnitude of the expected movement state quantity calculated by the movement state quantity calculating means according to the vehicle speed, and the vehicle necessary to move with the changed expected movement state quantity. A turning angle calculation means for calculating a turning angle of the steered wheel using the changed estimated motion state quantity and the detected vehicle speed, and the turning actuator according to the calculated turning angle And a turning control means for turning the steered wheels to the same calculated turning angle, and the turning angle calculating means has a vehicle speed detected by the vehicle speed detecting means less than a predetermined vehicle speed. When the value of the turning angle of the steered wheel calculated using the detected vehicle speed exceeds the maximum value that can be steered by the steered wheel, an operation input value input by the driver to the steering handle Steering of the steered wheels with respect to the maximum value of There based on the relationship that matches the maximum value that can be steered in the steering wheel, it is also possible to calculate the turning angle of the steered wheels.

  In these cases, the expected motion state quantity is selected from, for example, a lateral acceleration, a yaw rate, and a turning curvature of the vehicle based on the vehicle speed detected by the vehicle speed detecting means. Further, in this vehicle steering device, a reaction force device for applying a reaction force to the operation of the steering wheel may be further provided.

  Further, the operation input value detecting means is constituted by, for example, a displacement amount sensor for detecting the displacement amount of the steering handle, and the motion state amount calculating means is provided with the detected displacement amount to the steering handle. It is good to comprise with the operation force conversion means which converts into the operation force, and the exercise state quantity conversion means which converts the converted operation force into the expected movement state quantity. Further, the operation input value detection means is constituted by, for example, an operation force sensor that detects an operation force applied to the steering handle, and the motion state quantity calculation means uses the detected operation force as the expected motion. It is good to comprise with the movement state quantity conversion means converted into a state quantity.

  In the present invention configured as described above, first, the operation input value of the driver with respect to the steering wheel represents the motion state of the vehicle that can be perceived by the driver in relation to the turning of the vehicle. It is converted into a predicted motion state quantity (lateral acceleration, yaw rate, turning curvature, etc.) of the vehicle that has a predetermined exponential relationship or power relationship with the value. At this time, the magnitude of the expected motion state quantity of the vehicle is changed to be smaller when the vehicle speed is increased, for example, according to the vehicle speed of the vehicle. Then, based on the converted expected motion state quantity and the vehicle speed of the vehicle, the turning angle of the steered wheels necessary for the vehicle to move with the expected motion state quantity expected by the driver is calculated. The steered wheels are steered at the calculated steered angle.

  Therefore, when the vehicle turns by turning the steered wheels, the driver is given the expected motion state quantity as the “physical quantity of the applied stimulus” according to the Weber-Hefner law. Since it changes exponentially or exponentially with respect to the operation input value, the driver can operate the steering wheel while perceiving the amount of motion state that matches human perception characteristics. The lateral acceleration and yaw rate can be sensed tactilely by the driver in contact with each part in the vehicle. Further, the turning curvature can be visually perceived by the driver due to changes in the situation within the field of view of the vehicle. As a result, according to the present invention, the driver can operate the steering wheel in accordance with human perceptual characteristics, so that driving of the vehicle is simplified.

  Further, the turning angle of the steered wheels is calculated based on the expected motion state quantity and the vehicle speed. More precisely, since the expected motion state quantity is calculated using the operation input value, the turning angle is calculated based on the operation input value and the vehicle speed. For this reason, for example, when the expected motion state quantity is large (that is, the operation input value is large) and the vehicle speed is increasing, the calculated turning angle may exceed the maximum value that the steered wheels can steer. There is. In other words, the turning operation range of the steering wheel may be limited by the turning angle that is not perceived by the driver. For this reason, the driver may feel uncomfortable regarding the steering characteristics of the steering wheel. On the other hand, by changing the expected motion state quantity according to the vehicle speed, for example, by changing the expected motion state quantity to be smaller when the vehicle speed increases, the turning operation range of the steering handle by the driver is reduced to the full vehicle speed range. Can be assured equally. As a result, the driver can expect the amount of motion state of the vehicle by rotating the steering handle within the rotation operation range that is equally secured in the entire vehicle speed range. Therefore, even when the vehicle speed changes, uniform steering characteristics can be ensured, and the driver does not feel uncomfortable.

  On the other hand, in a case where the steering operation range of the steering wheel is secured equally over the entire vehicle speed range, when the driver rotates the steering wheel, there is a possibility of perceiving a response delay in the steering control of the steered wheels. There is. That is, as the turning operation range becomes larger, the driver needs to increase the operation input value necessary for turning the vehicle with the expected motion state quantity, and accordingly, the steering control of the steered wheels is performed. You may perceive a response delay. For this reason, by changing the maximum value of the operation input value input by the driver to the steering wheel according to the change in the vehicle speed (for example, by changing it small), driving from the neutral position to the maximum value of the operation input value changed. The relationship between the operation input value by the person and the expected motion state quantity calculated using the operation input value can be appropriately set according to the vehicle speed. Therefore, in the turning control of the steered wheels in response to the turning operation of the steering handle, it is possible to prevent the driver from perceiving a response delay.

  Further, as described above, the turning angle of the steered wheels is calculated based on the operation input value and the vehicle speed, and thus is calculated even when the vehicle speed is extremely small (for example, low-speed movement for garage entry). There is a possibility that the turning angle exceeds the maximum value of the turning angle that the system can take. In this case, even if the driver operates the steering wheel, the steered wheels may not be steered any further, and the vehicle may not turn at the amount of motion state expected by the driver. As a result, the driver may feel uncomfortable regarding the steering characteristics of the steering wheel. On the other hand, when the vehicle speed is lower than the predetermined vehicle speed, the turning angle of the steered wheel with respect to the maximum value of the operation input value input by the driver to the steering handle is the maximum value (maximum steered angle) that the steered wheel can steer. ) To calculate the turning angle, the calculated value of the turning angle can be obtained within a range that the steered wheels can turn. Therefore, if the driver operates the steering handle, the steered wheels are always steered in accordance with the operation, so that the driver can turn with the motion state amount that anticipates the vehicle, and does not feel uncomfortable.

  In addition, another feature of the present invention is that, in addition to the above-described configuration, the motion state quantity detection means for detecting an actual motion state quantity that is the same type as the expected motion state quantity and represents the actual motion state of the vehicle, and the calculation. And a correction means for correcting the calculated turning angle in accordance with a difference between the estimated motion state quantity and the detected actual motion state quantity. According to this, the steered wheel is steered more accurately to the steered angle necessary for the vehicle to move with the calculated expected motion state quantity. As a result, the driver can operate the steering wheel while perceiving the amount of motion state that accurately matches the human perceptual characteristics, so that the driving of the vehicle is further simplified.

a. First Embodiment Hereinafter, a vehicle steering apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a vehicle steering apparatus according to the first embodiment.

  The steering apparatus includes a steering handle 11 as an operation unit that is turned by a driver to steer left and right front wheels FW1 and FW2 as steered wheels. The steering handle 11 is fixed to the upper end of the steering input shaft 12, and the lower end of the steering input shaft 12 is connected to a reaction force actuator 13 including an electric motor and a speed reduction mechanism. The reaction force actuator 13 applies a reaction force to the turning operation of the steering handle 11 by the driver.

  In addition, the steering device includes a steering actuator 21 including an electric motor and a speed reduction mechanism. The turning force by the turning actuator 21 is transmitted to the left and right front wheels FW1 and FW2 via the turning output shaft 22, the pinion gear 23, and the rack bar 24. With this configuration, the rotational force from the steering actuator 21 is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the rotation of the pinion gear 23. Due to the displacement in the axial direction, the left and right front wheels FW1, FW2 are steered left and right.

  Next, an electric control device that controls the rotation of the reaction force actuator 13 and the turning actuator 21 will be described. The electric control device includes a steering angle sensor 31, a turning angle sensor 32, a vehicle speed sensor 33, a lateral acceleration sensor 34, and a yaw rate sensor 35.

  The steering angle sensor 31 is assembled to the steering input shaft 12, detects the rotation angle from the neutral position of the steering handle 11, and outputs it as the steering angle θ. The steered angle sensor 32 is assembled to the steered output shaft 22, detects the rotational angle from the neutral position of the steered output shaft 22, and corresponds to the actual steered angle δ (the steered angle of the left and right front wheels FW1, FW2). ). Note that the steering angle θ and the actual turning angle δ are represented by setting the neutral position to “0”, the left rotation angle as a positive value, and the right rotation angle as a negative value. The vehicle speed sensor 33 detects and outputs the vehicle speed V. The lateral acceleration sensor 34 detects and outputs the actual lateral acceleration G of the vehicle. The yaw rate sensor 35 detects and outputs the actual yaw rate γ of the vehicle. Note that, in both the actual lateral acceleration G and the actual yaw rate γ, the leftward acceleration and yaw rate are positive, and the rightward acceleration and yaw rate are negative.

  These sensors 31 to 35 are connected to the electronic control unit 36. The electronic control unit 36 includes a microcomputer including a CPU, a ROM, a RAM, and the like as main components, and controls the operations of the reaction force actuator 13 and the turning actuator 21 by executing programs. Drive circuits 37 and 38 for driving the reaction force actuator 13 and the steering actuator 21 are connected to the output side of the electronic control unit 36, respectively. In the drive circuits 37 and 38, current detectors 37a and 38a for detecting a drive current flowing in the electric motors in the reaction force actuator 13 and the steering actuator 21 are provided. The drive current detected by the current detectors 37a and 38a is fed back to the electronic control unit 36 in order to control the drive of both electric motors.

  Next, the operation of the first embodiment configured as described above will be described with reference to the functional block diagram of FIG. 2 showing functions realized by computer program processing in the electronic control unit 36. The electronic control unit 36 includes a reaction force control unit 40 for controlling the reaction force applied to the steering handle 11, and the left and right front wheels FW1 and FW2 corresponding to the driver's sensory characteristics based on the turning operation of the steering handle 11. A sensory adaptation control unit 50 for determining the target turning angles δg, γδ, δρ, and a steering for controlling the steering of the left and right front wheels FW1, FW2 based on the determined target turning angles δg, γδ, δρ. And a control unit 60.

When the steering handle 11 is turned by the driver, the steering angle sensor 31 detects the steering angle θ, which is the rotation angle of the steering handle 11, and uses the detected steering angle θ as the reaction force control unit 40 and the sense. Each is output to the matching control unit 50. In the reaction force control unit 40, the displacement-torque conversion unit 41 calculates a reaction force torque Tz that is an exponential function of the steering angle θ by using the following equation (1).
Tz ＝ To ・ exp (K1 ・ θ)… Formula 1
However, To and K1 in the formula 1 are constants, and these values will be described in detail when the sensory adaptation control unit 50 described later is described. Further, the steering angle θ in the equation 1 represents the absolute value of the detected steering angle θ. If the detected steering angle θ is positive, the constant To is set to a negative value, and the detected steering angle θ is If negative, the constant To is a positive value having the same absolute value as the negative constant To. Note that the reaction torque Tz may be calculated using a conversion table having characteristics as shown in FIG. 3 in which the reaction force torque Tz with respect to the steering angle θ is stored instead of the calculation of the expression 1.

  The calculated reaction force torque Tz is supplied to the drive control unit 42. The drive control unit 42 inputs a drive current flowing from the drive circuit 37 to the electric motor in the reaction force actuator 13 and feedback-controls the drive circuit 37 so that a drive current corresponding to the reaction force torque Tz flows through the electric motor. . By the drive control of the electric motor in the reaction force actuator 13, the electric motor applies a reaction force torque Tz to the steering handle 11 via the steering input shaft 12. Therefore, the driver feels the reaction force torque Tz that changes exponentially with respect to the steering angle θ, in other words, while applying a steering torque equal to the reaction force torque Tz to the steering handle 11, It will rotate. The relationship between the steering angle θ and the reaction torque Tz also follows the above-mentioned Weber-Hefner law, and the driver rotates the steering handle 11 while receiving a sense from the steering handle 11 that matches human perception characteristics. Can be operated.

On the other hand, with respect to the steering angle θ input to the sensory adaptation control unit 50, the displacement-torque conversion unit 51 calculates the steering torque Td according to the following equation 2 similar to the equation 1.
Td ＝ To ・ exp (K1 ・ θ)… Formula 2
Also in this case, To and K1 in the formula 2 are constants similar to those in the formula 1. However, the steering angle θ in Equation 2 represents the absolute value of the detected steering angle θ. If the detected steering angle θ is positive, the constant To is set to a positive value, and the detected steering angle is If θ is negative, the constant To is a negative value having the same absolute value as the positive constant To. In this case as well, the steering torque Td may be calculated by using a conversion table having characteristics as shown in FIG. 3 in which the steering torque Td with respect to the steering angle θ is stored instead of the calculation of the expression (2). .

  The calculated steering torque Td is supplied to the torque-lateral acceleration conversion unit 52, the torque-yaw rate conversion unit 53, and the torque-turning curvature conversion unit 54. Here, the torque-lateral acceleration conversion unit 52, the torque-yaw rate conversion unit 53, and the torque-turning curvature conversion unit 54 each convert the supplied steering torque Td according to the vehicle speed V detected by the vehicle speed sensor 33. To do. That is, when the detected vehicle speed V is high (hereinafter, referred to as high speed traveling), the torque-lateral acceleration conversion unit 52 is expected that the driver expects the supplied steering torque Td by the turning operation of the steering handle 11. Convert to lateral acceleration Gd. Further, when the detected vehicle speed V is large to some extent (hereinafter referred to as “medium speed traveling”), the torque-yaw rate conversion unit 53 expects the supplied steering torque Td by the driver turning the steering wheel 11. Convert to expected yaw rate γd. Further, when the detected vehicle speed V is small (hereinafter, referred to as low speed traveling), the torque-turning curvature conversion unit 54 is expected that the driver expects the supplied steering torque Td by the turning operation of the steering handle 11. Convert to turning curvature ρd. Hereinafter, first, the case where the left and right front wheels FW1 and FW2 are steered based on the expected lateral acceleration Gd converted by the torque-lateral acceleration conversion unit 52 during high-speed traveling will be described.

The torque-lateral acceleration conversion unit 52 sets the expected lateral acceleration Gd to “0” as shown in the following equation 3 when the absolute value of the steering torque Td is less than a predetermined positive value To, and the absolute value of the steering torque Td is If it is greater than or equal to a small positive value To, conversion (calculation) is performed according to Equation 4 below.
Gd = 0 (| Td | <To) Equation 3
Gd = C · Td ^K2 (To ≦ | Td |) Equation 4
However, C and K2 in the formula 4 are constants. Further, the steering torque Td in the equation 4 represents the absolute value of the steering torque Td calculated using the equation 2, and if the calculated steering torque Td is positive, the constant C is a positive value. If the calculated steering torque Td is negative, the constant C is set to a negative value having the same absolute value as the positive constant C. In this case as well, the expected lateral acceleration Gd is calculated by using a conversion table having characteristics as shown in FIG. 4 in which the expected lateral acceleration Gd with respect to the steering torque Td is stored instead of the calculations of the expressions 3 and 4. It may be.

Here, Formula 4 will be described. When the steering torque Td in the equation 4 is eliminated using the equation 2, the following equation 5 is obtained.
Gd = C · (To · exp (K1 · θ)) ^K2 = C · To ^K2 · exp (K1 · K2 · θ) = Go · exp (K1 · K2 · θ)
In Equation 5, Go is a constant C · To ^K2 , and Equation 5 indicates that the expected lateral acceleration Gd varies exponentially with respect to the steering angle θ of the steering wheel 11 by the driver. The expected lateral acceleration Gd is a physical quantity that can be perceived by the driver due to the contact of a part of the driver's body with a predetermined part in the vehicle, and follows the aforementioned Weber-Hefner law. Therefore, if the driver can turn the steering handle 11 while perceiving a lateral acceleration equal to the expected lateral acceleration Gd, the relationship between the turning operation of the steering handle 11 and the steering of the vehicle becomes a human perceptual characteristic. Can be matched.

As described above, the expected lateral acceleration Gd shown in the equation 4 (that is, the equation 5) changes exponentially with respect to the steering angle θ that is the operation amount of the steering wheel 11, and thus human perception characteristics. It is suitable for. Furthermore, the simplest method for the turning operation of the steering handle 11 by the driver is to turn the steering handle 11 at a constant speed ω (θ = ω · t). The acceleration Gd changes exponentially with respect to time t as shown in the following equation (6). Therefore, it will be understood that if the steering handle 11 can be rotated while the lateral acceleration equal to the expected lateral acceleration Gd is perceived, the driver can easily rotate the steering handle 11.
Gd = Go · exp (K0 · ω · t) (6)
However, K0 is a constant having a relationship of K0 = K1 · K2.

Further, as shown in Equation 3, when the steering torque Td is less than the predetermined value To, the expected lateral acceleration Gd is kept at “0”. This is because, even when the steering angle θ is “0”, that is, when the steering wheel 11 is kept at the neutral position, the steering torque Td becomes a positive predetermined value To by the calculation of the above equation 2, and this steering torque Td ( = To) is applied to the calculation of Equation 4, the expected lateral acceleration Gd becomes a positive value C · To ^K2 , which is not realistic. However, as described above, if the steering torque Td is less than the predetermined value To, the expected lateral acceleration Gd is “0”, so this problem is solved.

In this case, the minimum steering torque that can be perceived by the driver is the predetermined value To, the minimum perceived lateral acceleration that the driver can perceive is Go, and the predetermined value To has a relationship of Go = C · To ^K2. By doing so, the expected lateral acceleration Gd of the vehicle until the steering torque Td reaches a predetermined value To, that is, until the driver feels the lateral acceleration generated in the vehicle by turning the steering handle 11 of the driver. Is kept at “0”. According to this, only when the steering handle 11 is steered at the minimum steering torque To or more, the left and right front wheels FW1, FW2 are steered by the steered angle required to generate the expected lateral acceleration Gd. Will correspond exactly to the steering of the vehicle.

  Next, how to determine the parameters K1, K2, and C (predetermined coefficients K1, K2, and C) used in the expressions 1 to 5 will be described. In the description of how to determine the parameters K1, K2, and C, the steering torque Td is treated as the steering torque T, and the expected lateral acceleration Gd is treated as the lateral acceleration G. According to the aforementioned Weber-Hefner law, “the ratio ΔS / S between the minimum physical quantity change ΔS perceivable by humans and the physical quantity S at that time is constant regardless of the value of the physical quantity S, and the ratio ΔS / S is called the Weber ratio. In order to determine the Weber ratio, the present inventors confirmed that the Weber-Hefner's law was established with respect to the steering torque Td, the expected lateral acceleration Gd, the expected yaw rate γd, and the expected turning curvature ρd. Experiments were conducted on various humans with different genders, ages, and driving histories.

  Regarding the steering torque, a torque sensor is assembled to the steering handle of the vehicle, and an inspection torque is applied to the steering handle from the outside and the inspection torque is changed in various manners against this inspection torque. We measured the ability of the human to adjust the steering torque to adjust the steering handle so that it does not rotate by applying an operating force to the steering handle. That is, in the above situation, the value of the ratio ΔT / T, that is, Weber, where T is the detected steering torque at a certain time and ΔT is the minimum amount of change in steering torque that can be perceived as a change from the detected steering torque T. The ratio was measured for various humans. According to the results of this experiment, the Weber ratio ΔT / T is almost constant for various humans regardless of the direction of operation of the steering wheel, the state of the hand holding the steering wheel, and the magnitude and direction of the inspection torque. The value α was obtained.

  Regarding the lateral acceleration, a wall member is provided on the side of the driver's seat, and a force sensor for detecting the pressing force of the human shoulder is assembled to the wall member to allow the human to grasp the steering handle and to the wall member force sensor. The wall is applied to the wall member with the inspection force from the outside in the lateral direction, and the wall is against the inspection force while changing the inspection force in various modes. We adjusted the lateral force adjustment ability of the human to push the member so that the wall member does not move, that is, maintain the posture. That is, when F is the detection force that can withstand lateral force from the outside at a certain time and maintain the posture under the above situation, and ΔF is the minimum force change amount that can perceive the change from the detection force F The ratio value ΔF / F, that is, the Weber ratio was measured for various humans. According to the results of this experiment, the Weber ratio ΔF / F was a substantially constant value β for various people regardless of the magnitude and direction of the reference force applied to the wall member.

On the other hand, when the formula 2 is differentiated and the formula 2 is considered in the differentiated formula, the following formula 7 is established.
ΔT ＝ To ・ exp (K1 ・ θ) ・ K1 ・ Δθ = T ・ K1 ・ Δθ
When the equation 7 is modified and the Weber ratio ΔT / T related to the steering torque obtained by the experiment is Kt, the following equation 8 is established.
K1 = ΔT / (T · Δθ) = Kt / Δθ Equation 8

If the maximum steering torque is Tmax, the following formula 9 is established from the above formula 2.
Tmax ＝ To ・ exp (K1 ・ θmax) ... Equation 9
If Equation 9 is modified, the following Equation 10 is established.
K1 = log (Tmax / To) / θmax Equation 10
Then, the following formula 11 is derived from the formula 8 and the formula 10.
Δθ = Kt / K1 = Kt · θmax / log (Tmax / To) (Formula 11)
In Equation 11, Kt is the Weber ratio of the steering torque T, θmax is the maximum value of the steering angle, Tmax is the maximum value of the steering torque, and To is the minimum steering torque that can be perceived by humans as described above. Since these values Kt, θmax, Tmax, and To are constants determined by experiments and systems, the differential value Δθ can be calculated using the equation (11). The predetermined value (coefficient) K1 can also be calculated based on the equation 8 using the differential value Δθ and the Weber ratio Kt.

In addition, when the expression 4 is differentiated and the expression 4 is considered in the differentiated expression, the following expression 12 is established.
ΔG = C · K2 · T ^K2-1 · ΔT = G · K2 · ΔT / T Equation 12
When Expression 12 is modified and the Weber ratio ΔT / T related to the steering torque obtained by the above experiment is Kt, and the Weber ratio F / F related to the lateral acceleration is Ka, the following Expressions 13 and 14 are established.
ΔG / G = K2 · ΔT / T Equation 13
K2 = Ka / Kt ... Formula 14
In this equation 14, Kt is the Weber ratio related to the steering torque, and Ka is the Weber ratio related to the lateral acceleration, both of which are given as constants. Therefore, using these Weber ratios Kt and Ka, the above equation is used. 14 can also calculate the coefficient K2.

If the maximum value of the lateral acceleration is Gmax and the maximum value of the steering torque is Tmax, the following equation 15 is derived from the equation 4.
C = Gmax / Tmax ^K2 Equation 15
In Equation 15, Gmax and Tmax are constants determined by experiments and systems, and K2 is calculated by Equation 14, so that a constant (coefficient) C can also be calculated.

  As described above, the maximum value θmax of the steering angle θ, the maximum value Tmax of the steering torque T, the maximum value Gmax of the lateral acceleration G, the minimum steering torque To, the minimum sensed lateral acceleration Go, the Weber ratio Kt regarding the steering torque T, and the lateral If the Weber ratio Ka relating to acceleration is determined by experiments and systems, the coefficients K1, K2, and C in the equations 1 to 4 can be determined in advance by calculation. Therefore, in the displacement-torque conversion units 41 and 51 and the torque-lateral acceleration conversion unit 52, the reaction force torque Tz, the steering torque Td, and the torque- The lateral acceleration conversion unit 52 can calculate the expected lateral acceleration Gd.

  Returning to the description of FIG. 2 again, the expected lateral acceleration Gd calculated by the torque-lateral acceleration conversion unit 52 is supplied to the turning angle conversion unit 55. The turning angle conversion unit 55 calculates the target turning angle δg of the left and right front wheels FW1 and FW2 necessary to generate the calculated expected lateral acceleration Gd, and corresponds to the vehicle speed V as shown in FIG. And a table representing a change characteristic of the target turning angle δg with respect to the expected lateral acceleration Gd. This table is a set of data collected by running the vehicle while changing the vehicle speed V and actually measuring the turning angle δ and the lateral acceleration G of the left and right front wheels FW1, FW2. Then, the turning angle conversion unit 55 refers to this table and calculates a target turning angle δg corresponding to the input expected lateral acceleration Gd and the detected vehicle speed V input from the vehicle speed sensor 33. The lateral acceleration G (expected lateral acceleration Gd) and the target turning angle δg stored in the table are both positive, but the expected lateral acceleration Gd supplied from the torque-lateral acceleration converting unit 52 is negative. If so, the output target turning angle δg is also negative.

Since the target turning angle δg is a function of the vehicle speed V and the lateral acceleration G as shown in the following formula 16, it can be calculated by executing the calculation of the following formula 16 instead of referring to the table. it can.
δg = L · (1 + A · V ² ) · Gd / V ² Equation 16
However, L in said Formula 16 is a predetermined predetermined value which shows a wheel base, and A is a predetermined predetermined value showing the exercise | movement performance of a vehicle.

The calculated target turning angle δg is supplied to the turning angle correction unit 61 of the turning control unit 60. The turning angle correction unit 61 receives the expected lateral acceleration Gd from the torque-lateral acceleration conversion unit 52 and also the actual lateral acceleration G detected by the lateral acceleration sensor 34, and calculates the following equation (17). The corrected target turning angle δda is calculated by correcting the input target turning angle δg.
δda = δg + K3 · (Gd−G) Equation 17
However, the coefficient K3 is a positive constant determined in advance, and when the actual lateral acceleration G is less than the expected lateral acceleration Gd, the coefficient K3 is corrected so that the absolute value of the corrected target turning angle Δda becomes larger. When the actual lateral acceleration G exceeds the expected lateral acceleration Gd, the correction target turning angle δda is corrected to be smaller. By this correction, the turning angles of the left and right front wheels FW1, FW2 necessary for the expected lateral acceleration Gd are more accurately ensured.

  The calculated corrected target turning angle δda is supplied to the drive control unit 63. The drive control unit 63 inputs the actual turning angle δ detected by the turning angle sensor 32, and electrically drives the turning actuator 21 so that the left and right front wheels FW1, FW2 are turned to the corrected target turning angle δda. Feedback control of motor rotation. The drive control unit 63 also inputs a drive current that flows from the drive circuit 38 to the electric motor, and feedback-controls the drive circuit 38 so that a drive current having a magnitude corresponding to the steering torque appropriately flows to the electric motor. . By the drive control of the electric motor in the steering actuator 21, the rotation of the electric motor is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the pinion gear 23. The left and right front wheels FW1, FW2 are steered to the corrected target turning angle δda by the displacement of the rack bar 24 in the axial direction.

Next, the case where the left and right front wheels FW1 and FW2 are steered based on the expected yaw rate γd converted by the torque-yaw rate conversion unit 53 shown in FIG. If the absolute value of the steering torque Td is less than a predetermined positive value To, the torque-yaw rate conversion unit 53 calculates the expected yaw rate γd that the driver expects by turning the steering wheel 11 as shown in the following formula 18. If “0” is set and the absolute value of the steering torque Td is equal to or greater than the positive small predetermined value To, the calculation is performed according to the following Equation 19.
γd = 0 (| Td | <To) Equation 18
γd = C1 · Td ^K2 (To ≦ | Td |) Equation 19
However, K2 in Equation 19 is a constant as in Equation 4, and C1 is a variable that changes according to the vehicle speed V. Also in this case, the steering torque Td in the equation 19 represents the absolute value of the steering torque Td calculated using the equation 2, and if the calculated steering torque Td is positive, the variable C1 is a positive value, and if the calculated steering torque Td is negative, the variable C1 is a negative value having the same absolute value as the positive variable C1. In this case, the expected yaw rate γd may be calculated using a conversion table having a characteristic as shown in FIG. 6 in which the expected yaw rate γd with respect to the steering torque Td is stored instead of the calculations of the equations 18 and 19. Good.

Here, the equation 19 will be described. When the steering torque Td is eliminated by using the formula 2, the following formula 20 is obtained.
γd = C1 · (To · exp (K1 · θ)) ^K2 = C1 · To ^K2 · exp (K1 · K2 · θ) = γo · exp (K1 · K2 · θ) ... Equation 20
In Equation 20, since the variable C1 becomes a constant when the vehicle speed V is constant, γo becomes a constant C1 · To ^K2 , and Equation 20 shows that the expected yaw rate γd is the steering angle θ of the steering wheel 11 by the driver. Indicates an exponential change. The expected yaw rate γd is a physical quantity that can be perceived by the driver by the driver's vision or contact with a predetermined part in the vehicle, and follows the aforementioned Weber-Hefner law. Therefore, if the driver can turn the steering handle 11 while perceiving the yaw rate equal to the expected yaw rate γd, the relationship between the turning operation of the handle and the steering of the vehicle is made to correspond to the human perceptual characteristics. Can do.

Further, even when the left and right front wheels FW1, FW2 are steered based on the expected yaw rate γd during medium speed traveling, as shown in the equation 18, if the steering torque Td is less than the predetermined value To, the expected yaw rate γd Is kept at “0”. As a result, when the steering handle 11 is maintained at the neutral position, the expected yaw rate γd is “0” as in the case of high-speed traveling, and realistic steering characteristics can be obtained. In this case, the minimum steering torque that can be perceived by the driver is the predetermined value To, the minimum perceived yaw rate that the driver can perceive is γo, and the predetermined value To has a relationship of γo = C1 · To ^K2. Then, the expected yaw rate γd of the vehicle is “0” until the steering torque Td reaches a predetermined value To, that is, until the driver feels the yaw rate generated in the vehicle by the operation of the steering handle 11 of the driver. Is kept. According to this, the left and right front wheels FW1 and FW2 are steered by the turning angle necessary to generate the expected yaw rate γd only when the steering handle 11 is steered at the minimum steering torque To or more. It corresponds exactly to the steering of.

  The expected yaw rate γd calculated by the torque-yaw rate conversion unit 53 is supplied to the turning angle conversion unit 56. The turning angle conversion unit 56 calculates the target turning angle δγ of the left and right front wheels FW1, FW2 necessary to generate the calculated expected yaw rate γd, and according to the vehicle speed V as shown in FIG. It has a table that changes and represents the change characteristic of the target turning angle δγ with respect to the expected yaw rate γd. This table is a set of data collected by actually measuring the turning angle δ and the yaw rate γ of the left and right front wheels FW1 and FW2 while running the vehicle while changing the vehicle speed V. Then, the turning angle conversion unit 56 refers to this table and calculates the target turning angle δγ corresponding to the input expected yaw rate γd and the detected vehicle speed V input from the vehicle speed sensor 33. The yaw rate γ (estimated yaw rate γd) and the target turning angle δγ stored in the table are both positive, but are output if the expected yaw rate γd supplied from the turning angle conversion unit 56 is negative. The target turning angle δγ is also negative.

Since the target turning angle δγ is also a function of the vehicle speed V and the yaw rate γ as shown in the following equation 21, it is also calculated by executing the calculation of the following equation 21 instead of referring to the table. Can do.
δγ = L · (1 + A · V ² ) · γd / V Equation 21
However, also in the formula 21, L is a predetermined value indicating the wheel base, and A is a predetermined value indicating the motion performance of the vehicle.

  Here, the target turning angle δγ calculated by the turning angle conversion unit 56 according to the equation 21 changes based on the expected yaw rate γd calculated by the equation 19, and also changes based on the detected vehicle speed V. Therefore, when the target turning angle δγ is calculated based on the expected yaw rate γd during medium-speed traveling, the amount of turning operation of the steering wheel 11 by the driver (that is, as the detected vehicle speed V increases) The absolute value of the target turning angle δγ with respect to the steering angle θ) increases. Now, consider a vehicle steering system in which when the steering wheel 11 is turned to the maximum steering angle θmax, the left and right front wheels FW1, FW2 are steered to the maximum turning angle δmax that can be steered. The maximum turning angle Δmax is a maximum value that can be taken when the vehicle is traveling at a predetermined small vehicle speed Vs. In this vehicle steering device, when the target turning angle δγ is calculated at a certain vehicle speed V, the left and right front wheels FW1, FW2 are turned to the maximum before the driver turns the steering handle 11 to the maximum steering angle θmax. There may be an angle δmax.

  In other words, when the estimated yaw rate γd is adopted as the motion state quantity, the maximum steering angle θ at which the driver can turn the steering handle 11 may be smaller than the maximum steering angle θmax determined by the system. is there. More specifically, as is clear from the equation 21, the calculated target turning angle δγ gradually increases with respect to the detected vehicle speed V as the detected vehicle speed V increases. As a result, when the driver turns the steering handle 11, the dynamic range of the steering angle θ relative to the maximum steering angle θmax, that is, the turning operation range in which the steering handle 11 can be turned is narrowed. The steering angle adjustment sensation (so-called steering angle resolution) of the left and right front wheels FW1 and FW2 with respect to the 11 turning operation is deteriorated. For this reason, when the driver operates the steering handle 11 to rotate, the driver feels uncomfortable with the steering feeling. Therefore, the torque-yaw rate converter 53 appropriately changes the parameter C1 (variable C1) according to the detected vehicle speed V, and determines the magnitude of the expected yaw rate γd calculated according to the equation 19 (or the equation 20). Change appropriately according to V. Then, the steering sensation of the steering wheel 11 at the time of medium speed traveling is matched with the driver's sensory characteristics (more specifically, sensory characteristics at high speed traveling). This will be described in detail below.

Now, assuming that the maximum value of the steering torque is Tmax and the maximum yaw rate generated in the vehicle when the maximum steering torque Tmax is applied to the steering wheel 11 is γmax, the following equation 22 is established from the equation 19.
γmax = C1 · Tmax ^K2 ... Formula 22
If this equation 22 is modified, the following equation 23 is established.
C1 = γmax / Tmax ^K2 Equation 23
Here, the maximum steering torque Tmax is a constant determined by the system. Therefore, to change the parameter C1 according to the detected vehicle speed V, the maximum yaw rate γmax in the equation 23 is replaced with a function γmax (V) with respect to the detected vehicle speed V as shown in the following equation 24. Then, the magnitude of the function γmax (V) is changed according to the detected vehicle speed V. That is, the function γmax (V) is calculated according to the following equation 25.
C1 = γmax (V) / Tmax ^K2 Equation 24
γmax (V) = γmax (Vo) · (Vo / V) ... Formula 25

  However, γmax (Vo) is the maximum value of the yaw rate that can be generated when the vehicle turns at a predetermined vehicle speed Vo, and is a constant determined in advance by experiments and systems. According to the equation 25, as the detected vehicle speed V increases, the value of the function γmax (V) is calculated to be small, and the parameter C1 is calculated to be small according to the equation 24. Therefore, the expected yaw rate γd calculated by the equation 19 (or the equation 20) becomes a small value as the detected vehicle speed V increases. As a result, the calculated absolute value of the target turning angle δγ is suppressed as the detected vehicle speed V increases, and as a result, a wide dynamic range of the steering angle θ with respect to the maximum steering angle θmax is ensured. it can. Therefore, the target turning angle δγ of the left and right front wheels FW1, FW2 can be smoothly changed to the maximum turning angle δmax with respect to the turning operation of the steering handle 11 during medium speed traveling, and the steering feel of the steering handle 11 can be changed. Can be adjusted to the sensory characteristics of the driver.

Further, when the minimum yaw rate that can be perceived by the driver is γo and the minimum steering torque that can be perceived by the driver is To, the following formula 26 is derived from the formula 19.
γo ＝ C1 ・ To ^K2 … Formula 26
Then, when the formula 26 is modified, the following formula 27 is derived.
To = (γo / C1) ^{(1 / K2)} ... Equation 27
Here, according to the equation 27, when the minimum perceptual yaw rate γo is a constant, the value of the parameter C1 calculated according to the equation 24 is calculated to be smaller as the vehicle speed V increases. Torque To increases with increasing vehicle speed V. As a result, the minimum perceived steering torque To that can be perceived by the driver increases as the detected vehicle speed V increases, so the driver may feel uncomfortable. Therefore, even if the detected vehicle speed V increases, the minimum perceived yaw rate γo in the equation 27 is set to the detected vehicle speed V as shown in the following equation 28 in order to keep the minimum perceived steering torque To uniform. Replace with the function γo (V). Then, the magnitude of the function γo (V) is changed according to the detected vehicle speed V. That is, the function γo (V) is calculated according to the following equation 29.
To = (γo (V) / C1) ^{(1 / K2)} ... Equation 28
γo (V) = γo (Vo) · (Vo / V) ... Equation 29
However, γo (Vo) is the minimum yaw rate that the driver can perceive when the vehicle turns at a predetermined vehicle speed Vo, and is a constant determined in advance by experiment. According to the equation 29, as the detected vehicle speed V increases, the value of the function γo (V) is calculated to be small, and an increase in the minimum perceived steering torque To calculated according to the equation 28 can be suppressed. This also makes it possible to match the steering sensation of the steering wheel 11 to the driver's sensory characteristics during medium speed traveling.

The target turning angle δγ calculated as described above is also supplied to the turning angle correction unit 61 of the turning control unit 60. The turning angle correction unit 61 receives the expected yaw rate γd from the torque-yaw rate conversion unit 53 and also the actual yaw rate γ detected by the yaw rate sensor 35, and performs the calculation of the following equation 30 to perform correction. A target turning angle δda is calculated.
δda = δγ + K4 · (γd−γ) Equation 30
However, the coefficient K4 is a predetermined positive constant, and when the actual yaw rate γ is less than the expected yaw rate γd, the coefficient K4 is corrected so that the absolute value of the corrected target turning angle δda becomes larger. When the actual yaw rate γ exceeds the expected yaw rate γd, the absolute value of the corrected target turning angle δda is corrected. By this correction, the turning angles of the left and right front wheels FW1, FW2 necessary for the expected yaw rate γd are ensured with high accuracy.

  Then, the calculated corrected target turning angle δda is supplied to the drive control unit 63. The drive control unit 63 inputs the actual turning angle δ detected by the turning angle sensor 32, and electrically drives the turning actuator 21 so that the left and right front wheels FW1, FW2 are turned to the corrected target turning angle δda. Feedback control of motor rotation. Thereby, the rotation of the electric motor is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the pinion gear 23. The left and right front wheels FW1, FW2 are steered to the corrected target turning angle δda by the displacement of the rack bar 24 in the axial direction.

Next, the case where the left and right front wheels FW1 and FW2 are steered based on the expected turning curvature ρd converted by the torque-turning curvature converting unit 54 shown in FIG. If the absolute value of the steering torque Td is less than the positive predetermined value To, the torque-turning curvature conversion unit 54 calculates the expected turning curvature ρd that the driver expects through the turning operation of the steering handle 11. If the absolute value of the steering torque Td is not less than the positive small predetermined value To, the calculation is performed according to the following equation 32.
ρd = 0 (| Td | <To) Equation 31
ρd = C2 · Td ^K2 (To ≦ | Td |) Equation 32
However, K2 in Equation 32 is a constant as in Equation 4, and C2 is a variable that changes according to the vehicle speed V. Also in this case, the steering torque Td in the equation 32 represents the absolute value of the steering torque Td calculated using the equation 2, and if the calculated steering torque Td is positive, the variable C2 is a positive value, and if the calculated steering torque Td is negative, the variable C2 is a negative value having the same absolute value as the positive variable C2. In this case, the expected turning curvature ρd is calculated using a conversion table having characteristics as shown in FIG. 8 in which the expected turning curvature ρd with respect to the steering torque Td is stored in place of the calculations of the equations 31 and 32. May be.

Here, Equation 32 will be described. When the steering torque Td is eliminated using the above equation 2, the following equation 33 is obtained.
ρd ＝ C2 ・ (To ・ exp (K1 ・ θ)) ^K2 ＝ C2 ・ To ^K2・ exp (K1 ・ K2 ・ θ) ＝ ρo ・ exp (K1 ・ K2 ・ θ)
In Expression 33, if the vehicle speed V is constant, the variable C2 is a constant. Therefore, ρo is a constant C2 · To ^K2 , and Expression 33 indicates the expected turning curvature ρd with respect to the steering angle θ of the steering wheel 11 by the driver. Indicates that is changing exponentially. The expected turning curvature ρd is a physical quantity that can be perceived by the driver by the driver's vision, and is in accordance with the aforementioned Weber-Hefner law. Therefore, if the driver can turn the steering handle 11 while visually recognizing the turning curvature equal to the expected turning curvature ρd, the relationship between the turning operation of the handle and the steering of the vehicle corresponds to the human perceptual characteristics. Can be made.

Further, when the left and right front wheels FW1 and FW2 are steered based on the expected turning curvature ρd during low-speed traveling, as shown in the equation 31, if the steering torque Td is less than the predetermined value To, the expected turning curvature ρd is kept at “0”. As a result, when the steering handle 11 is maintained at the neutral position, the expected turning curvature ρd is “0” as in the case of high speed traveling or medium speed traveling, and realistic steering characteristics are obtained. Can do. In this case, the minimum steering torque that can be perceived by the driver is the predetermined value To, the minimum visual turning curvature that the driver can visually recognize is ρo, and the predetermined value To has a relationship of ρo = C1 · To ^K2. By doing so, the expected turning curvature ρd of the vehicle is “0” until the steering torque Td reaches a predetermined value To, that is, until the driver feels turning of the vehicle by turning the steering handle 11 of the driver. Is kept. According to this, the left and right front wheels FW1 and FW2 are steered by the turning angle necessary for turning the vehicle with the expected turning curvature ρd only when the steering handle 11 is steered at the minimum steering torque To or higher. The rudder control accurately corresponds to the steering of the vehicle.

  The expected turning curvature ρd calculated by the torque-turning curvature conversion unit 54 is supplied to the turning angle conversion unit 57. The turning angle conversion unit 57 calculates the target turning angle δρ of the left and right front wheels FW1 and FW2 necessary to generate the calculated expected turning curvature ρd, and corresponds to the vehicle speed V as shown in FIG. And a table representing a change characteristic of the target turning angle δρ corresponding to the expected turning curvature ρd. This table is a set of data collected by actually measuring the turning angle δ and the turning curvature ρ of the left and right front wheels FW1 and FW2 while the vehicle is running while changing the vehicle speed V. Then, the turning angle conversion unit 57 refers to this table and calculates the target turning angle δρ corresponding to the input expected turning curvature ρd and the detected vehicle speed V input from the vehicle speed sensor 33. The turning curvature ρ (expected turning curvature ρd) and the target turning angle δρ stored in the table are both positive, but the expected turning curvature ρd supplied from the turning angle conversion unit 57 is negative. In this case, the output target turning angle δρ is also negative.

Since the target turning angle δρ is also a function of the vehicle speed V and the turning curvature ρ as shown in the following equation 34, it is also calculated by executing the calculation of the following equation 34 instead of referring to the table. be able to.
δρ = L · (1 + A · V ² ) · ρd Equation 34
However, also in the equation 34, L is a predetermined value indicating the wheel base, and A is a predetermined value indicating the motion performance of the vehicle.

  Here, the target turning angle δρ calculated by the turning angle conversion unit 57 according to the equation 34 changes based on the expected turning curvature ρd calculated by the equation 32 and also changes based on the detected vehicle speed V. . For this reason, when the target turning angle δρ is calculated based on the expected turning curvature ρd during low-speed traveling, the amount of turning operation of the steering wheel 11 by the driver (that is, as the detected vehicle speed V increases) The absolute value of the target turning angle δρ with respect to the steering angle θ) increases. As in the case of the medium speed traveling described above, the left and right front wheels FW1, FW2 are turned when the steering wheel 11 is rotated to the maximum steering angle θmax while the vehicle is traveling at a predetermined small vehicle speed Vs. Consider a steering apparatus for a vehicle that is steered to the maximum steerable angle δmax that can be steered. In this vehicle steering apparatus, when the target turning angle δρ is calculated at a certain vehicle speed V, the left and right front wheels FW1, FW2 are turned to the maximum before the driver turns the steering handle 11 to the maximum steering angle θmax. There may be an angle δmax.

  In other words, even when the expected turning curvature ρd is adopted as the motion state quantity, the maximum steering angle θ at which the driver can turn the steering handle 11 is smaller than the maximum steering angle θmax determined by the system. There is. Specifically, as is clear from the equation 34, as the detected vehicle speed V increases, the calculated target turning angle δρ increases in a quadratic function with respect to the detected vehicle speed V. As a result, when the driver rotates the steering handle 11, the dynamic range of the steering angle θ with respect to the maximum steering angle θmax is narrowed, and the steering angle resolution of the steering handle 11 is deteriorated. For this reason, when the driver operates the steering handle 11 to rotate, the driver feels uncomfortable with the steering feeling. Therefore, the torque-turning curvature converter 54 appropriately changes the parameter C2 (variable C2) according to the detected vehicle speed V, and sets the magnitude of the expected turning curvature ρd calculated according to the equation 32 (or the equation 33). It changes suitably according to the detected vehicle speed V. The steering feeling of the steering wheel 11 during low-speed traveling is also matched with the driver's sensory characteristics (more specifically, sensory characteristics during high-speed driving). This will be described in detail below.

Now, assuming that the maximum value of the steering torque is Tmax and the maximum turning curvature at which the vehicle turns when the maximum steering torque Tmax is applied to the steering handle 11 is ρmax, the following Expression 35 is established from Expression 32 above.
ρmax = C2 / Tmax ^K2 Equation 35
If this equation 35 is modified, the following equation 36 is established.
C2 = ρmax / Tmax ^{K2 (} Formula 36)
Here, the maximum steering torque Tmax is a constant determined by the system. Therefore, in order to change the parameter C2 according to the detected vehicle speed V, the maximum turning curvature ρmax in the equation 36 is replaced with a function ρmax (V) with respect to the detected vehicle speed V as shown in the following equation 37. Then, the magnitude of the function ρmax (V) is changed according to the detected vehicle speed V. That is, the function ρmax (V) is calculated according to the following equation 38.
C2 = ρmax (V) / Tmax ^K2 Equation 37
ρmax (V) = ρmax (Vo) · (Vo / V) ² ... Formula 38

  However, ρmax (Vo) is the maximum value of the turning curvature when the vehicle turns at a predetermined vehicle speed Vo, and is a constant determined in advance by experiments and systems. According to the equation 38, as the detected vehicle speed V increases, the value of the function ρmax (V) is calculated to be small, and the parameter C2 is calculated to be small according to the equation 37. Therefore, the expected turning curvature ρd calculated by the equation 32 (or the equation 33) becomes a small value as the detected vehicle speed V increases. As a result, the calculated absolute value of the target turning angle δρ is suppressed as the detected vehicle speed V increases, and as a result, a wide dynamic range of the steering angle θ with respect to the maximum steering angle θmax is ensured. it can. Accordingly, the target turning angle δρ of the left and right front wheels FW1, FW2 can be smoothly changed to the maximum turning angle δmax with respect to the turning operation of the steering handle 11 during low-speed traveling, and the steering feel of the steering handle 11 can be improved. It can be matched to the driver's sensory characteristics.

Further, when the minimum turning curvature that can be visually recognized by the driver is ρo and the minimum steering torque that can be perceived by the driver is To, the following Expression 39 is derived from Expression 32.
ρo ＝ C2 ・ To ^K2 … Formula 39
Then, when the equation 39 is modified, the following equation 40 is derived.
To = (ρo / C2) ^{(1 / K2)} ... Equation 40
Here, according to the equation 40, when the minimum visual turning curvature ρo is a constant, the value of the parameter C2 calculated according to the equation 37 is calculated to decrease as the vehicle speed V increases. The steering torque To increases as the vehicle speed V increases. As a result, the minimum perceived steering torque To that can be perceived by the driver increases as the detected vehicle speed V increases, so the driver may feel uncomfortable. For this reason, even if the detected vehicle speed V increases, the minimum visible turning curvature ρo in the equation 40 is determined as shown in the following equation 41 in order to keep the minimum perceived steering torque To uniform. Replace with the function ρo (V) for. Then, the magnitude of the function ρo (V) is changed according to the detected vehicle speed V. That is, the function ρo (V) is calculated according to the following equation 42.
To = (ρo (V) / C2) ^{(1 / K2)} Equation 41
ρo (V) = ρo (Vo) · (Vo / V) ² (Formula 42)
However, ρo (Vo) is the minimum turning curvature that the driver can visually recognize when the vehicle turns at a predetermined vehicle speed Vo, and is a constant determined in advance by experiments. According to the equation 42, as the detected vehicle speed V increases, the value of the function ρo (V) is calculated to be small, and an increase in the minimum perceived steering torque To calculated according to the equation 41 can be suppressed. This also makes it possible to match the steering sensation of the steering wheel 11 during low-speed traveling with the driver's sensory characteristics.

The target turning angle δρ calculated as described above is also supplied to the turning angle correction unit 61 of the turning control unit 60. The turning angle correction unit 61 receives the expected turning curvature ρd from the torque-turning curvature conversion unit 54 and also receives the actual turning curvature ρ from the turning curvature calculation unit 62. The turning curvature calculation unit 62 uses the lateral acceleration G detected by the lateral acceleration sensor 34 or the yaw rate γ detected by the yaw rate sensor 35 and the detected vehicle speed V detected by the vehicle speed sensor 33, and the following equation 43 By executing this calculation, the actual turning curvature ρ is calculated and output to the turning angle correction unit 61.
ρ = G / V ² or ρ = γ / V Equation 43

And the turning angle correction | amendment part 61 performs the calculation of following formula 44, and calculates correction | amendment target turning angle (delta) da.
δda = δρ + K5 · (ρd−ρ) Equation 44
However, the coefficient K5 is a predetermined positive constant, and when the actual turning curvature ρ is less than the expected turning curvature ρ, the coefficient K5 is corrected so that the absolute value of the corrected target turning angle δda becomes larger. When the actual turning station rate ρ exceeds the expected turning curvature ρd, the absolute value of the corrected target turning angle δda is corrected to the smaller side. By this correction, the turning angles of the left and right front wheels FW1, FW2 necessary for the expected turning curvature ρd are more accurately ensured.

  Then, the calculated corrected target turning angle δda is supplied to the drive control unit 63. The drive control unit 63 inputs the actual turning angle δ detected by the turning angle sensor 32, and electrically drives the turning actuator 21 so that the left and right front wheels FW1, FW2 are turned to the corrected target turning angle δda. Feedback control of motor rotation. Thereby, the rotation of the electric motor is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the pinion gear 23. The left and right front wheels FW1, FW2 are steered to the corrected target turning angle δda by the displacement of the rack bar 24 in the axial direction.

  As can be understood from the above description, according to the first embodiment, the steering angle θ as the operation input value of the driver with respect to the steering handle 11 is converted into the steering torque Td by the displacement-torque converter 51. The converted steering torque Td is supplied to the torque-lateral acceleration conversion unit 52, the torque-yaw rate conversion unit 53, or the torque-turning curvature conversion unit 54 in accordance with the vehicle speed V detected by the vehicle speed sensor 33, and the expected lateral Converted to acceleration Gd, expected yaw rate γd, or expected turning curvature ρd. The converted expected lateral acceleration Gd, estimated yaw rate γd, or estimated turning curvature ρd is supplied to the turning angle conversion units 55, 56, and 57, respectively, and the conversion units 55, 56, and 57 each have a target turning angle δg, The target turning angle δγ or the target turning angle δρ is calculated.

  Then, the calculated target turning angle δg, target turning angle δγ or target turning angle δρ is supplied to the turning angle correction unit 61 and corrected to the corrected target turning angle δda. When the corrected target turning angle δda is supplied to the drive control unit 63, the left and right front wheels FW1, FW2 are steered to the corrected target turning angle δda. In this case, the steering torque Td is a physical quantity that can be perceived by the driver from the steering handle 11 due to the action of the reaction force actuator 13 and changes exponentially with respect to the steering angle θ. The steering handle 11 can be turned according to the human perceptual characteristic while feeling the reaction force according to the Weber-Hefner law. Further, the actual lateral acceleration G, the actual yaw rate γ or the actual turning curvature ρ generated in the vehicle by the steering of the left and right front wheels FW1 and FW2 is a physical quantity that can be perceived, and these values G, γ, and ρ are the expected lateral acceleration Gd. , The expected yaw rate γd or the expected turning curvature ρd.

  Further, the expected lateral acceleration Gd, the expected yaw rate γd, or the expected turning curvature ρd is also a power function with respect to the steering torque Td calculated from the steering angle θ input by the driver (for example, transforming Expression 4 into Expression 5). Thus, it changes exponentially with respect to the steering angle θ. Therefore, the driver can turn the vehicle by turning the steering handle 11 according to the human perceptual characteristics while perceiving the lateral acceleration, the yaw rate, and the turning curvature according to the Weber-Hefner law. As a result, the driver can operate the steering handle 11 in accordance with human perceptual characteristics, and thus driving of the vehicle is simplified.

  Further, in order to match the steering sensation of the steering wheel 11 with human sensation characteristics (specifically, sensation characteristics during high-speed driving) in all vehicle speed ranges of the vehicle, the turning angle conversion units 56 and 57 according to the detected vehicle speed V. Can calculate the absolute value of the expected yaw rate γd or the expected turning curvature ρd small. That is, during high-speed traveling, the turning angle conversion unit 55 calculates the target turning angle δg by adopting the estimated lateral acceleration Gd as the motion state quantity. As is clear from Equation 16, the target turning angle δg is calculated as a small absolute value as the detected vehicle speed V increases. As a result, the target turning angle δg is always smaller than the maximum turning angle δmax of the left and right front wheels FW1, FW2 determined by the system, so that the driver can steer to the maximum steering angle θmax determined by the system. The handle 11 can be rotated.

  On the other hand, at the time of medium speed running or low speed running, the turning angle conversion units 56 and 57 adopt the expected yaw rate γd or the expected turning curvature ρd as the motion state quantity, and the target turning angle δγ or the target turning angle. The steering angle δρ is calculated. The target turning angle δγ or the target turning angle δρ has a large absolute value as the detected vehicle speed V increases, as is apparent from the equation 21 or 34. As a result, the target turning angle δγ or the target turning angle δρ may be larger than the maximum turning angle δmax of the left and right front wheels FW1, FW2 determined by the system, and the driver is determined by the system. In some cases, the steering handle 11 cannot be rotated to the maximum steering angle θmax. For this reason, the torque-yaw rate conversion unit 53 or the torque-turning curvature conversion unit 54 changes the expected yaw rate γd or the expected turning curvature ρd according to the detected vehicle speed V, and more specifically, calculates smaller as the detected vehicle speed V increases. To do.

  As a result, the absolute value of the target turning angle δγ or the target turning angle δρ calculated by the turning angle conversion units 56 and 57 is suppressed as the detected vehicle speed V increases. Therefore, the driver can turn the steering wheel 11 to the maximum steering angle θmax determined by the system even during medium speed driving or low speed driving, and the driver feels uncomfortable regarding the steering feeling over the entire vehicle speed range. Can be prevented. Furthermore, by ensuring the same amount of turning operation of the steering handle 11 over the entire vehicle speed range, a wide dynamic range of the steering angle θ with respect to the maximum steering angle θmax can be ensured. Accordingly, the target turning angle δg, target turning angle δγ, or target turning angle δρ of the left and right front wheels FW1, FW2 can be smoothly changed to the maximum turning angle δmax with respect to the turning operation of the steering handle 11. The steering sensation of the steering wheel 11 can be matched to the driver's sensory characteristics. Therefore, the driving of the vehicle is further simplified.

  Further, the turning angle correction unit 61 corrects the actual lateral acceleration G, the actual yaw rate γ, or the actual turning curvature ρ actually generated in the vehicle so as to accurately correspond to the steering angle θ of the steering handle 11. As a result, an actual lateral acceleration G, an actual yaw rate γ, or an actual turning curvature ρ that accurately corresponds to the steering angle θ of the steering handle 11 is generated in the vehicle. As a result, the driver can operate the steering wheel 11 while perceiving the lateral acceleration, the yaw rate, and the turning curvature that more accurately match the human perceptual characteristics, so that the driving of the vehicle becomes easier.

  In the first embodiment, the expected lateral acceleration Gd is calculated according to the equations 3 and 4, and in particular, C in the equation 4 is calculated as a constant. As is apparent from the equation 16, since the absolute value of the target turning angle δg decreases with an increase in the detected vehicle speed V, the steering characteristics when the vehicle is traveling at high speed, that is, when the estimated lateral acceleration Gd is adopted. This is to make it a standard. However, as described above, as in the case of medium-speed traveling or low-speed traveling, it is also possible to implement C in Equation 4 as a variable for the detected vehicle speed V even during high-speed traveling. In this case, for example, if C is changed so as to increase with respect to the detected vehicle speed V, a decrease in the absolute value of the target turning angle δg can be appropriately suppressed, and driving is performed in the entire vehicle speed range. A person can perceive a more suitable steering characteristic.

b. Second Embodiment In the first embodiment described above, the expected yaw rate at the time of medium speed traveling and at the time of low speed traveling is set so as to make the steering feeling uniform in all vehicle speed ranges, in other words, to match the steering feeling at high speed traveling. The absolute values of γd and expected turning curvature ρd were changed in small increments as the detected vehicle speed V increased. As a result, a wide dynamic range of the steering angle θ with respect to the maximum steering angle θmax is ensured in all vehicle speed ranges, thereby preventing the uncomfortable feeling of steering from occurring. By the way, when the steering handle 11 can be turned to the maximum steering angle θmax determined by the system in the entire vehicle speed range, the amount of turning operation required for turning the vehicle increases. For this reason, the driver may feel that the left and right front wheels FW1 and FW2 cause a response delay and are steered when the vehicle is turned with the motion state amount estimated by the turning operation of the steering handle 11. Below, 2nd Embodiment which reduces the response delay of the steering control which this driver | operator perceives is described. In the vehicle steering apparatus according to the second embodiment, the computer program executed by the electronic control unit 36 is slightly different, but the configuration of the steering apparatus is the same as that of the first embodiment. For this reason, the detailed description of the configuration of the steering device is omitted.

  In the second embodiment, as in the first embodiment, the displacement-torque converter 41 of the reaction force controller 40 is an exponential function of the steering angle θ of the steering wheel 11 detected by the steering angle sensor 31. The reaction torque Tz is calculated according to Equation 1 above. The calculated reaction force torque Tz is supplied to the drive control unit 42, and the electric motor in the reaction force actuator 13 is driven and controlled by the drive control unit 42. As a result, the electric motor applies reaction force torque Tz to the steering handle 11 via the steering input shaft 12.

  Further, the displacement-torque conversion unit 51 of the sensory adaptation control unit 50 also uses the steering torque Td, which is an exponential function of the steering angle θ of the steering handle 11 detected by the steering angle sensor 31, as in the first embodiment. Calculate according to Equation 2. When the steering torque Td is calculated, the torque-lateral acceleration conversion unit 52 determines the expected lateral acceleration if the vehicle is traveling at a high speed according to the vehicle speed V detected by the vehicle speed sensor 33, as in the first embodiment. Gd is calculated, and the torque-yaw rate conversion unit 53 calculates the expected yaw rate γd when driving at medium speed, and the torque-turning curvature conversion unit 54 calculates the expected turning curvature ρd when driving at low speed. The calculated expected lateral acceleration Gd, expected yaw rate γd, and expected turning curvature ρd are respectively supplied to the turning angle conversion units 55, 56, and 57, and the turning angle conversion units 55, 56, and 57 are respectively The target turning angle δg, the target turning angle δγ, and the target turning angle δρ are calculated according to the formulas 16, 21, and 34.

  Incidentally, the target turning angle δg, the target turning angle δγ, and the target turning angle δρ calculated according to the equations 16, 21, and 34 are abrupt with respect to the increase in the detected vehicle speed V as described in the first embodiment. Increase is suppressed. Thus, the left and right front wheels FW1, FW2 can be steered by changing the steering angle θ of the steering handle 11 to the maximum steering angle θmax determined by the system. However, when the maximum steering angle θmax is a unique value, the driver needs to turn the steering handle 11 more in order to turn the vehicle. This will be described in detail below.

Now, let us consider a state in which the vehicle is turning at high speed in the φ direction (the direction φ of the translational movement of the vehicle) with respect to the longitudinal direction of the vehicle at the vehicle speed V. At this time, if the speed component of the vehicle speed V in the x direction (for example, the longitudinal direction of the vehicle) is Vx, and the speed component of the vehicle speed V in the y direction (for example, the lateral direction of the vehicle) is Vy, the direction φ is approximate. Is represented by the following formula 45.
φ ≒ Vy / Vx = V · sinφ / V · cosφ = tanφ (| φ | << 1)
The direction φ can also be expressed by the following equation 46 using the yaw rate γ (= Gd / V).
φ = φo + ∫γdt Equation 46
However, φo is a predetermined constant. Here, if the yaw rate γ, that is, Gd / V in the equation 46 is constant, the time change dφ / dt in the direction φ of the translational motion of the vehicle becomes the same (constant) with respect to the detected vehicle speed V. For this reason, the following formula 47 is established.
dφ / dt = Gd / V Equation 47

Here, for example, when traveling at high speed, the expected lateral acceleration Gd is calculated according to the above equation 4, and when the steering torque Td in the equation 4 is eliminated and arranged using the equation 2, the following equation 48 is established. To do.
Gd = C.Td ^K2 = C. (To.exp ((log (Tmax / To) /. Theta.max) .theta.) ^K2 Equation 48
When N = C · To · log (Tmax / To) in the equation 48 and the equation 48 is linearly approximated, the following equation 49 is established.
Gd = (N / θmax) · θ Equation 49
Therefore, when the equation 49 is substituted into the equation 47, the following equation 50 is established.
dφ / dt = (N / θmax · V) · θ Equation 50
At this time, N in the formula 50 is a constant (constant at a certain vehicle speed during medium speed traveling or low speed traveling), and if the maximum steering angle θmax is a constant determined by the system, the vehicle speed V increases. As a result, the value of dφ / dt decreases. In other words, as the vehicle speed V increases, the amount of movement of the vehicle in the left-right direction (Vy direction) decreases per unit time, and the driver has a delayed response to the turning state of the vehicle with respect to the turning operation of the steering handle 11. Perceive that it has occurred.

Therefore, θmax · V in the equation 50 is set to a constant value with respect to the change in the detected vehicle speed V. That is, the maximum steering angle θmax in the equation 50 is replaced with the function θmax (V) with respect to the detected vehicle speed V, and the magnitude of the function θmax (V) is changed according to the detected vehicle speed V according to the following equation 51.
dφ / dt = (N / θmax (V) · V) · θ Equation 51
θmax (V) = θmax (Vo) · (Vo / V) Equation 52
However, θmax (Vo) is the maximum value of the steering angle θ that the driver can turn to turn the vehicle at a predetermined vehicle speed Vo, and is a constant determined in advance by experiments and the system. According to the equation 52, as the detected vehicle speed V increases, the value of the function θmax (V) is calculated to be small, and θmax (V) · V in the equation 51 is constant with respect to the change in the detected vehicle speed V. Can be a value. Therefore, dφ / dt calculated according to the equation 51 is constant with respect to the change in the vehicle speed V. In other words, even when the vehicle speed V changes, the movement amount per unit time in the left-right direction of the vehicle is the same, and the driver delays the response to the turning state of the vehicle with respect to the turning operation of the steering handle 11. Do not perceive.

  Regarding the calculation of the function θmax (V), instead of the calculation of the equation 52, the function θmax (V) with respect to the detected vehicle speed V is referred to by referring to a table showing the change characteristic with respect to the vehicle speed V as shown in FIG. It is also possible to calculate a value. According to this, the value of the function θmax (V) suitable for the motion state of the vehicle can be calculated by preparing a table representing various change characteristics.

  In this way, the parameter K1 is calculated using the maximum value of the steering angle θ calculated by the function θmax (V), and the displacement-torque converters 41 and 51 use the equations 1 and 2 to perceive the driver's perception characteristics. The reaction force torque Tz and the steering torque Td that match the above are calculated. As in the first embodiment, the expected lateral acceleration Gd, the expected yaw rate γd, and the expected turning curvature ρd are calculated, and the target turning angle δg, the target turning angle δγ, and the target turning angle δρ are calculated. Then, the left and right front wheels FW1 and FW2 are steered with the corrected target turning angle δda obtained by correcting the calculated target turning angle δg, target turning angle δγ, and target turning angle δρ.

  As can be understood from the above description, according to the second embodiment, in addition to the effects of the first embodiment, the maximum steering angle θmax is changed with the change of the vehicle speed V. A person can turn the steering handle 11 without perceiving a response delay in the turning state of the vehicle with respect to the turning operation (steering angle θ). Therefore, the driving of the vehicle is further simplified.

  In the first or second embodiment, as the motion state quantity of the vehicle, the torque-lateral acceleration conversion unit 52 calculates the expected lateral acceleration Gd during high-speed traveling, and the torque-yaw rate conversion unit during medium-speed traveling. 53 calculated the expected yaw rate γd, and the torque-turning curvature converter 54 calculated the expected turning curvature ρd during low-speed running. And turning angle conversion part 55,56,57 implemented so that target turning angle | corner (delta) g, (delta) gamma, and (delta) ρ might be calculated using the estimated estimated lateral acceleration Gd, estimated yaw rate (gamma) d, or estimated turning curvature (rho) d. . However, it is also possible to employ any one of the expected lateral acceleration Gd, the expected yaw rate γd, or the expected turning curvature ρd as the motion state quantity of the vehicle. By the way, for example, when the estimated lateral acceleration Gd or the estimated yaw rate γd is adopted as the motion state quantity, the target turning angle δg or the target turning angle δγ calculated during low-speed traveling is the maximum turning angle δmax. May be calculated in excess of.

  That is, a specific example where the expected lateral acceleration Gd is employed will be described. As described above, the target turning angle δg calculated according to the equation 16 using the expected lateral acceleration Gd is the detected vehicle speed V. While it is calculated to be small as the vehicle speed increases, it is greatly calculated as the detected vehicle speed V decreases. For this reason, the target turning angle δg may be calculated exceeding the maximum turning angle δmax when traveling at a low speed, particularly when the detected vehicle speed V is extremely small. In this case, the steering handle 11 is at the maximum. There is a possibility that the target turning angle δg exceeds the maximum turning angle δmax before the steering angle θmax (or the maximum steering angle θmax changed based on the function θmax (V)) is turned. As a result, the left and right front wheels FW1, FW2 are not steered any further in response to the turning operation of the steering handle 11 by the driver, and the driver may feel uncomfortable. Further, even when the estimated yaw rate γd is adopted as the motion state quantity, the target turning angle δγ calculated according to the equation 21 is the maximum turning when the detected vehicle speed V is extremely small as in the case of the estimated lateral acceleration Gd. The angle δmax may be exceeded, and the driver may feel uncomfortable.

  Thus, when the estimated lateral acceleration Gd or the estimated yaw rate γd is employed as the motion state quantity in this way, by setting a limit value (lower limit value) for the vehicle speed V in the equation 16 or the equation 21, The above problems can be solved. Hereinafter, this modification will be specifically described.

  When the estimated lateral acceleration Gd is adopted as the motion state quantity of the vehicle, the torque-lateral acceleration conversion unit 52 calculates the estimated lateral acceleration Gd according to the above formula 3 or 4. Then, the turning angle conversion unit 55 calculates the target turning angle δg according to the equation 16 using the calculated expected lateral acceleration Gd. At this time, the turning angle conversion unit 55 calculates the target turning angle δg using the vehicle speed V input from the vehicle speed sensor 33. If the turning angle conversion unit 55 exceeds the maximum turning angle δmax, the maximum steering angle of the steering handle 11 is calculated. A predetermined limit value (lower limit value) is set for the vehicle speed so that the target turning angle δg with respect to θmax is equal to the maximum turning angle δmax, and more specifically, different from the predetermined small vehicle speed Vs described above. A predetermined small vehicle speed Vs1 is set, and the target turning angle δg is calculated. The relationship between the vehicle speed Vs and the vehicle speed Vs1 is preferably Vs <Vs1. Thus, if the predetermined limit value (lower limit value) Vs1 is set as appropriate, when the detected vehicle speed V is less than the predetermined limit value (lower limit value) Vs1, the target turning angle δg is a value within the maximum turning angle δmax. It becomes. Therefore, even when the vehicle speed V is very small (for example, movement such as garage entry), the driver can rotate the steering handle 11 to the maximum steering angle θmax in a state that matches the human perceptual characteristics. And never feel uncomfortable.

  Even when the estimated yaw rate γd is adopted as the motion state quantity of the vehicle, the steered angle conversion unit 56 determines a predetermined limit value (lower limit value) for the vehicle speed as in the case of the estimated lateral acceleration Gd described above. Vs1 is set, and the target turning angle δγ is calculated according to the equation 21. Thereby, when the detected vehicle speed V is less than the predetermined limit value (lower limit value) Vs1, the target turning angle δγ becomes a value within the maximum turning angle δmax. Therefore, the steering sensation of the steering handle 11 can be matched to the human perceptual characteristics, and the driver can turn the steering handle 11 up to the maximum steering angle θmax without feeling uncomfortable.

  Here, in the implementation of this modification, as in the second embodiment, in order to prevent the occurrence of a response delay in the turning state of the vehicle with respect to the turning operation of the steering handle 11, the function θmax (V) is used. It is preferable to set a range (that is, an upper limit value and a lower limit value) that can be taken by the maximum steering angle θmax. The setting of the upper limit value and the lower limit value will be specifically described. As described above, the maximum steering angle θmax is calculated according to the function θmax (V) expressed by the equation 52. Therefore, the upper limit value and the lower limit value of the maximum steering angle θmax can be set by limiting the input range of the detected vehicle speed V in the equation 52. That is, the upper limit value of the maximum steering angle θmax can be set by appropriately setting the lower limit value of the detected vehicle speed V. In addition, the lower limit value of the maximum steering angle θmax can be set by appropriately setting the upper limit value of the detected vehicle speed V.

  At this time, in particular, as the lower limit value of the detected vehicle speed V for setting the upper limit value of the maximum steering angle θmax, as described above, a predetermined limit value for the vehicle speed V set by the turning angle conversion units 55 and 56 ( Lower limit value) Vs1 can be applied. Thus, for example, when the vehicle speed V is extremely small, if the steering handle 11 is turned to the maximum steering angle θmax, that is, the upper limit value determined according to the vehicle speed V, the left and right front wheels FW1, FW2 are moved to the maximum turning angle δmax. Can be steered. Therefore, the driver can turn the steering handle 11 up to the maximum steering angle θmax in a state suitable for human perceptual characteristics, and perceive the steering response delay of the left and right front wheels FW1, FW2 with respect to the turning operation of the steering handle 11. do not do.

  Next, a modification in which the steering torque T is used as the operation input value of the steering handle 11 will be described. In this modified example, as shown by a broken line in FIG. 1, a steering torque sensor 39 is provided that detects a steering torque T that is assembled to the steering input shaft 12 and applied to the steering handle 11. Other configurations are the same as those in the first embodiment, but the computer program executed by the electronic control unit 36 is slightly different from that in the first embodiment.

  In the case of this modification, in the functional block diagram of FIG. 2 representing the computer program, the displacement-torque conversion unit 51 is not provided, and the torque-lateral acceleration conversion unit 52, the torque-yaw rate conversion unit 53, and the torque The turning curvature conversion unit 54 calculates the expected lateral acceleration Gd, the expected yaw rate γd, and the expected turning curvature ρd by executing the calculations of Equations 4, 19, and 32 using the steering torque T detected by the steering torque sensor 39. In this case as well, instead of executing the calculations of Equations 4, 19, and 32, the expected lateral acceleration Gd, the expected yaw rate γd, and the expected turning curvature ρd are calculated using the tables representing the characteristics shown in FIGS. You may make it calculate. Other program processes executed by the electronic control unit 36 are the same as those in the first embodiment.

  According to this modification, the steering torque T as an operation input value of the driver for the steering handle 11 is converted into the expected lateral acceleration by the torque-lateral acceleration conversion unit 52, the torque-yaw rate conversion unit 53, and the torque-turning curvature conversion unit 54. Converted to Gd, expected yaw rate γd, and expected turning curvature ρd. The converted expected lateral acceleration Gd, estimated yaw rate γd, and expected turning curvature ρd are calculated by the turning angle conversion units 55, 56, and 57 as the target turning angle δg, the target turning angle δγ, and the target turning angle δρ. . Then, the left and right front wheels FW1, FW2 are steered to the corrected target turning angle δda by the turning angle correction unit 61 and the drive control unit 63. Also in this case, the steering torque T is a physical quantity that can be perceived by the driver from the steering handle 11, and the expected lateral acceleration Gd, the expected yaw rate γd, and the expected turning curvature ρd with respect to the steering torque T are exponential functions (for example, 4 is changed to an exponential function with respect to the steering angle θ by transforming 4 into Formula 5, so that the driver can feel the reaction force according to Weber-Hefner's law, and 11 can be rotated. Accordingly, also in this modified example, as in the case of the first embodiment, the driver rotates the steering handle 11 according to the human perceptual characteristics while feeling the lateral acceleration according to the Weber-Hefner law, Since the vehicle can be turned, the same effect as in the case of the first embodiment is expected.

  Also in this modified example, a wide dynamic range with respect to the maximum value of the turning operation amount can be secured by ensuring the same amount of turning operation of the steering handle 11 over the entire vehicle speed range. Accordingly, the target turning angle δg, target turning angle δγ, or target turning angle δρ of the left and right front wheels FW1, FW2 can be smoothly changed to the maximum turning angle δmax with respect to the turning operation of the steering handle 11. The steering sensation of the steering wheel 11 can be matched to the driver's sensory characteristics. Therefore, the driving of the vehicle is further simplified.

  Furthermore, the vehicle steering control according to the first embodiment and the vehicle steering control according to the modification may be switchable. That is, both the steering angle sensor 31 and the steering torque sensor 39 are provided, and the expected lateral acceleration Gd and the expected yaw rate γd using the target steering torque Td calculated by the displacement-torque conversion unit 51 as in the first embodiment. And the case where the expected turning curvature ρd is calculated and the case where the expected lateral acceleration Gd, the expected yaw rate γd and the expected turning curvature ρd are calculated using the steering torque T detected by the steering torque sensor 39 can be used by switching. You can also. In this case, the switching may be performed automatically according to the driver's intention or according to the motion state of the vehicle.

d. Other Modifications Further, the implementation of the present invention is not limited to the first or second embodiment and the modifications described above, and various modifications can be made without departing from the object of the present invention.

  For example, in the first or second embodiment and the modification, the steering handle 11 that is turned to steer the vehicle is used. However, instead of this, for example, a joystick-type steering handle that is linearly displaced may be used, or any other one that can be operated by the driver and instructed to steer the vehicle is used. May be.

  Further, in the first or second embodiment and the modification, the left and right front wheels FW1 and FW2 are steered by rotating the steered output shaft 22 using the steered actuator 21. However, instead of this, the left and right front wheels FW1, FW2 may be steered by linearly displacing the rack bar 24 using the steering actuator 13.

It is the schematic of the steering apparatus of the vehicle common to 1st or 2nd embodiment of this invention. FIG. 3 is a functional block diagram functionally representing computer program processing executed by the electronic control unit of FIG. 1 according to the first or second embodiment of the present invention. It is a graph which shows the relationship between a steering angle and a steering torque. It is a graph which shows the relationship between steering torque and estimated lateral acceleration. It is a graph which shows the relationship between a prospective lateral acceleration and a target turning angle. It is a graph which shows the relationship between steering torque and estimated yaw rate. It is a graph which shows the relationship between an expected yaw rate and a target turning angle. It is a graph which shows the relationship between steering torque and prospective turning curvature. It is a graph which shows the relationship between a prospective turning curvature and a target turning angle. It is a graph showing the change characteristic with respect to vehicle speed in the maximum steering angle according to the second embodiment of the present invention.

Explanation of symbols

FW1, FW2 ... front wheels, 11 ... steering handle, 12 ... steering input shaft, 13 ... reaction actuator, 21 ... steering actuator, 22 ... steering output shaft, 31 ... steering angle sensor, 32 ... steering angle sensor, 33 DESCRIPTION OF SYMBOLS ... Vehicle speed sensor 34 ... Lateral acceleration sensor 35 ... Yaw rate sensor 36 ... Electronic control unit 39 ... Steering torque sensor 40 ... Reaction force control part 50 ... Sensory adaptation control part 51 ... Displacement-torque conversion part 52 ... torque-lateral acceleration conversion unit, 53 ... torque-yaw rate conversion unit, 54 ... torque-turning curvature conversion unit, 55, 56, 57 ... turning angle conversion unit, 60 ... turning control unit, 61 ... turning angle correction Part

Claims (9)

A steering wheel operated by a driver to steer the vehicle, a steering actuator for steering the steered wheel, and the steered actuator according to the operation of the steering handle to drive and control the steered wheel. In a steering device for a steering-by-wire vehicle equipped with a steering control device for steering, the steering control device,
Vehicle speed detecting means for detecting the vehicle speed of the vehicle;
An operation input value detecting means for detecting an operation input value of a driver for the steering wheel;
A vehicle motion state that can be perceived by the driver in relation to the turning of the vehicle, and an operation input value for the steering handle and a predicted motion state amount of the vehicle that is in a predetermined exponential relationship or a power relationship with the operation input value. A motion state quantity calculating means for calculating using values,
When the vehicle speed detected by the vehicle speed detecting means increases, the motion state quantity changing means for changing the expected motion state quantity calculated by the motion state quantity calculating means to be small ;
A turning angle calculation for calculating a turning angle of the steered wheels necessary for the vehicle to move with the changed expected motion state quantity using the changed expected motion state quantity and the detected vehicle speed. Means,
A steering-by-wire system comprising: a steering control unit configured to control the steering actuator according to the calculated turning angle and to turn the steered wheels to the calculated turning angle. Vehicle steering device. A steering wheel operated by a driver to steer the vehicle, a steering actuator for steering the steered wheel, and the steered actuator according to the operation of the steering handle to drive and control the steered wheel. In a steering device for a steering-by-wire vehicle equipped with a steering control device for steering, the steering control device,
Vehicle speed detecting means for detecting the vehicle speed of the vehicle;
An operation input value detecting means for detecting an operation input value of a driver for the steering wheel;
A vehicle motion state that can be perceived by the driver in relation to the turning of the vehicle, and an operation input value for the steering handle and a predicted motion state amount of the vehicle that is in a predetermined exponential relationship or a power relationship with the operation input value. A motion state quantity calculating means for calculating using values,
According to the vehicle speed detected by the vehicle speed detecting means, an exercise state quantity changing means for changing the magnitude of the expected exercise state quantity calculated by the exercise state quantity calculating means;
A turning angle calculation for calculating a turning angle of the steered wheels necessary for the vehicle to move with the changed expected motion state quantity using the changed expected motion state quantity and the detected vehicle speed. Means,
Steering control means for controlling the steered actuator according to the calculated steered angle and steering the steered wheel to the steered angle calculated by the same,
Steering-by-wire comprising a maximum operation input value changing means for changing a maximum value of an operation input value inputted by a driver to the steering wheel based on a vehicle speed detected by the vehicle speed detecting means. Type vehicle steering device. The steering-by-wire vehicle steering apparatus according to claim 2 , wherein the maximum operation input value changing means changes the maximum value of the operation input value to be small when the vehicle speed detected by the vehicle speed detection means increases. A steering wheel operated by a driver to steer the vehicle, a steering actuator for steering the steered wheel, and the steered actuator according to the operation of the steering handle to drive and control the steered wheel. In a steering device for a steering-by-wire vehicle equipped with a steering control device for steering, the steering control device,
Vehicle speed detecting means for detecting the vehicle speed of the vehicle;
An operation input value detecting means for detecting an operation input value of a driver for the steering wheel;
A vehicle motion state that can be perceived by the driver in relation to the turning of the vehicle, and an operation input value for the steering handle and a predicted motion state amount of the vehicle that is in a predetermined exponential relationship or a power relationship with the operation input value. A motion state quantity calculating means for calculating using values,
According to the vehicle speed detected by the vehicle speed detecting means, an exercise state quantity changing means for changing the magnitude of the expected exercise state quantity calculated by the exercise state quantity calculating means;
A turning angle calculation for calculating a turning angle of the steered wheels necessary for the vehicle to move with the changed expected movement state quantity using the changed expected movement state quantity and the detected vehicle speed. Means,
A steering control unit configured to control the steering actuator according to the calculated turning angle to steer the steered wheel to the calculated turning angle;
The turning angle calculation means is
When the vehicle speed detected by the vehicle speed detection means is less than a predetermined vehicle speed, and the value of the turning angle of the steered wheel calculated using the detected vehicle speed exceeds the maximum value that can be steered by the steered wheel, The turning of the steered wheels is based on a relationship in which the turning angle of the steered wheels with respect to the maximum operation input value input by the driver to the steering handle coincides with the maximum value that the steered wheels can steer. A steering-by-wire vehicle steering apparatus characterized by calculating an angle. In the steering device for a steering-by-wire vehicle according to any one of claims 1 to 4 ,
The steering-by-wire vehicle steering apparatus, wherein the estimated motion state quantity is selected from a lateral acceleration, a yaw rate, and a turning curvature of the vehicle based on the vehicle speed detected by the vehicle speed detecting means. In the steering device for a steering-by-wire vehicle according to any one of claims 1 to 5 ,
The operation input value detection means includes a displacement amount sensor that detects the displacement amount of the steering wheel,
The motion state quantity calculating means includes an operation force conversion means for converting the detected displacement amount into an operation force applied to the steering handle, and an exercise state for converting the converted operation force into the expected motion state quantity. A steering-by-wire vehicle steering apparatus comprising a quantity conversion means. In the steering device for a steering-by-wire vehicle according to any one of claims 1 to 5 ,
The operation input value detection means includes an operation force sensor that detects an operation force applied to the steering handle,
A steering-by-wire vehicle steering apparatus, wherein the motion state quantity calculating means is composed of motion state quantity conversion means for converting the detected operating force into the expected motion state quantity. The steering apparatus for a steering-by-wire vehicle according to any one of claims 1 to 7 , further comprising:
A motion state quantity detection means for detecting an actual motion state quantity that is the same type as the calculated expected motion state quantity and represents the actual motion state of the vehicle;
A steering-by-wire type vehicle characterized by comprising correction means for correcting the calculated turning angle in accordance with a difference between the calculated expected motion state quantity and the detected actual motion state quantity. Steering device. The steering device for a steering-by-wire vehicle according to any one of claims 1 to 8 , further comprising:
A steering-by-wire vehicle steering apparatus, comprising a reaction force device that applies a reaction force to the operation of the steering wheel.

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