JP5001591B2 - Vehicle steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device of a vehicle for facilitating the operation of a vehicle by properly controlling a steering condition of a turning wheel to a steering wheel operation of a driver. <P>SOLUTION: A steering-held condition judging part 41 judges whether a rotary operation condition of a steering wheel 11 of the driver is a normal operation condition or a steering-held operation condition. In the normal operation condition, a target steering angle &delta;d exponentially changing relative to a steering angle &theta; is calculated by respective processing of a displacement-torque conversion part 42, a torque-lateral acceleration conversion part 43, and a steering angle conversion part 44. Meanwhile, in the steering-held operation condition, a target steering angle &delta;dh exponentially changing relative to the steering angle &theta; is calculated by respective processing of the conversion parts 42, 43, 44 using a steering-held steering angle &theta;h as a virtual original point. Thereby, in the steering-held operation condition, a transmission ratio can be reduced, and right and left front wheels FW1, FW2 can be properly steered according to a rotary operation of the steering wheel 11 by the driver. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

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 control device that steers the vehicle.

  In recent years, the development of this type of steering-by-wire steering system has been actively carried out. For example, the applicant of the present application has proposed a vehicle steering apparatus disclosed in Patent Document 1 below. This vehicle steering device can turn the vehicle in accordance with the driver's perceptual characteristics in response to the driver's steering wheel operation based on Weber-Fechner's law regarding human perceptual characteristics. Is. That is, according to Weber-Hefner's law, it is said that the amount of human sensation is proportional to the logarithm of the physical quantity of the given stimulus, and the physical quantity of the stimulus given to the human relative to the amount of human manipulation is If the amount of operation is changed exponentially in the case of displacement and exponentially when the amount of operation is torque, the relationship between the amount of operation and the physical amount can be matched to human perceptual characteristics.

  Therefore, in the vehicle steering device disclosed by the applicant of the present invention according to Patent Document 1 below, the amount of motion state of the vehicle (lateral acceleration, yaw rate, turning curvature) that can be perceived by the driver with respect to the steering wheel operation by the driver. Etc.) is changed exponentially or exponentially. In order to realize a vehicle motion state quantity that changes exponentially or exponentially, the steered wheels are steered non-linearly. As a result, the driver can operate the vehicle by operating the steering wheel in accordance with the perceptual characteristics, so even when the mechanical connection between the steering wheel and the steered wheels is removed, it is very easy. The vehicle can be turned.

  Here, when the steered wheels are non-linearly steered in response to the operation of the steering handle by the driver, the steered amount of the steered wheels with respect to the steered wheel is increased as the steered handle is operated. The transmission ratio representing the ratio of increases. In this state, the steered wheels are steered greatly in response to minute changes in the amount of steering wheel operation by the driver. For example, the driver operates the steering handle during turning of the vehicle to turn the steered wheels. When finely adjusting the steering wheel, it is necessary to carefully operate the steering wheel. On the other hand, when the steering wheel is operated near the neutral position, the transmission ratio is small. In this state, the change in the turning angle of the steered wheels with respect to the steering wheel operation by the driver is small, in other words, the steering response cannot be sufficiently ensured, so the driver needs to operate the steering wheel more. is there.

On the other hand, for example, a steering device disclosed in Patent Documents 2 and 3 below is known. And these conventional steering apparatuses change the output gain for turning a steered wheel according to the operation state of the steering wheel by a driver | operator.
JP 2005-193783 A Japanese Patent No. 3494212 JP 2000-203440 A

  By the way, in the conventional steering devices shown in Patent Documents 2 and 3, the output gain is changed according to the operating state of the steering wheel by the driver, but the steering represents the ratio of the steering angle to the steering angle. The gear ratio is directly determined by the vehicle speed. For this reason, in the conventional steering apparatus, the steered wheels transmit a certain amount of transmission with respect to the input steering wheel operation amount (steering angle) regardless of the operation state (for example, operation speed) of the steering wheel by the driver. Varies with ratio. For this reason, in the conventional steering device, when the steering wheel is operated in a steering range where the transmission ratio is large, it may be difficult to turn the vehicle in a manner intended by the driver.

    SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to appropriately control the steered state of the steered wheels with respect to the steering wheel operation by the driver, thereby facilitating driving of the vehicle. To provide an apparatus.

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 the steering actuator to nonlinearly control the steered wheels; and operates the steering control device with respect to the steering handle. An operation input value detecting means for detecting an operation input value of the user, a normal operation state representing an operation state of the steering wheel having a large change amount based on the detected change amount of the operation input value, and the change amount An operation state determining means for determining a steering operation state representing an operation state of the steering handle having a small size, and determining that the operation state of the steering handle is the steering operation state. When, as a transmission ratio that represents the ratio of the change amount of the steering angle of the steered wheels with respect to a change amount of the operation input value is smaller than that in the normal operating state, it is the detection of the target steering angle Steering angle calculation means for calculating using the operation input value, and controlling the steering actuator according to the calculated target turning angle to steer the steered wheel to the calculated target turning angle A detection reference for detecting the operation input value when the steering angle calculation unit determines that the steering handle is in a normal operation state by the operation state determination unit. A target turning angle in a normal operation state having a predetermined non-linear relationship with the detected operation input value is calculated with a point as an origin, and the operation state determination unit determines that the steering handle is in a steering holding operation state. Then, Calculating the target turning angle of the steering operation state that is in a predetermined nonlinear relationship with the detected operation input value using the operation input value at the time of determination as a virtual origin, and the turning control means includes: The turning actuator is controlled in accordance with the calculated target turning angle to turn the steered wheel to the calculated target turning angle .

In this case, the operation state determination means determines that the operation state of the steering wheel is a normal operation state if the time differential value of the detected operation input value is equal to or greater than a predetermined value, and the time If the differential value is less than the predetermined value, it may be determined that the operation state of the steering wheel is the steering operation state. The steering control device further includes vehicle speed detection means for detecting a vehicle speed of the vehicle, and the operation state determination means is configured such that the detected vehicle speed is equal to or higher than a predetermined vehicle speed and the time differentiation is performed. If the value is less than the predetermined value, it may be determined that the operation state of the steering wheel is the steering operation state. The steering wheel operated by a driver to steer the vehicle, a steering actuator for steering the steered wheel, and the steered wheel by driving the steered actuator according to the operation of the steering handle. In a steering device for a steering-by-wire vehicle having a steering control device that nonlinearly controls steering, the steering control device detects an operation input value of a driver for the steering handle. And a steering operation indicating the operation state of the steering handle having a large change amount and the operation state of the steering handle having a small change amount based on the detected change amount of the operation input value. An operation state determination unit that determines an operation state, and a change amount of the operation input value when the operation state of the steering handle is determined to be the steering holding operation state. Steering for calculating a target turning angle using the detected operation input value so that a transmission ratio representing a ratio of a change amount of the turning angle of the steered wheel to the steering wheel is smaller than that in the normal operation state. An angle calculating means, and a turning control means for controlling the turning actuator according to the calculated target turning angle and turning the turning wheel to the calculated target turning angle; The operation state determination means may determine the operation state of the steering wheel when the transmission ratio in the normal operation state of the steering wheel is larger than a predetermined transmission ratio.

  According to these, when the operation state determination means determines that the operation state of the steering handle by the driver is in the normal operation state, a target turning angle with a large transmission ratio is calculated, and the steered wheel is set to this target turning angle. Is steered. Thus, in the normal operation state, the driver can turn the steered wheel greatly by operating the small steering handle, and can easily turn the vehicle. On the other hand, when the operation state of the steering wheel is in the normal operation state, for example, the driver is operating the steering wheel in a steering range having a large transmission ratio, and the operation state of the steering wheel is maintained by the operation state determination means. When it is determined that the vehicle is in the state, a target turning angle that is smaller than that in the normal operation state is calculated, and the steered wheels are steered to the target turning angle. Thereby, in the steering operation state, the steered wheels can be gently steered according to the gentle steering handle operation by the driver. Therefore, for example, even when the operation amount of the steering wheel increases, the driver can easily steer the steered wheels and can easily drive the vehicle.

  Here, when turning the steered wheels, the detection input point of the operation input value is set as the origin in the normal operation state, while the operation input value at the start of the hold operation is set as the virtual origin in the steering operation state. The target turning angle that changes nonlinearly with respect to the operation input value can be calculated. In this case, in particular, by calculating a target turning angle that varies nonlinearly around the virtual origin, the transmission ratio in the vicinity of the virtual origin can be reduced. Thereby, in the steering operation state, the steered wheels can be gently steered according to the gentle steering handle operation by the driver. Therefore, for example, even when the operation amount of the steering wheel increases, the driver can easily steer the steered wheels and can easily drive the vehicle.

  Further, the operation state determination means can determine whether or not the operation state of the steering wheel is the steering operation state a plurality of times. In this way, by making the determination a plurality of times, even if the steering operation state has already been established and the transmission ratio increases nonlinearly as the operation amount of the steering wheel increases, a plurality of virtual neutral A point can be set. For this reason, the driver can turn the vehicle better and can easily drive the vehicle.

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 device for a steering-by-wire vehicle having a steering control device that drives an actuator to nonlinearly control the steered wheels, the steering control device is operated by a driver's operation input to the steering handle. An operation input value detecting means for detecting a value, and a time differential value of the detected operation input value, a transmission ratio representing a ratio of a change amount of the turning angle of the steered wheel to a change amount of the detected operation input value. A transmission ratio changing means for changing the detected operation input value and a target turning angle having a predetermined non-linear relationship with the detected operation input value, and the detected operation input value and the changed transmission ratio. A turning angle calculation means for calculating the turning wheel, and a turning control means for controlling the turning actuator according to the calculated target turning angle to turn the turning wheel to the calculated turning angle. It is also made up of.

  In this case, the transmission ratio changing means may change the transmission ratio based on the detected change amount of the operation input value when the time differential value of the detected operation input value is smaller than a predetermined value. . In addition, the transmission ratio changing unit is configured to display the detected operation input value when the operation of the steering wheel is continued in a state where the time differential value of the detected operation input value is smaller than a predetermined value. The transmission ratio may be changed to a large value according to the amount of change.

  According to these, the transmission ratio is changed according to the operation state of the steering wheel by the driver, that is, the time differential value of the operation input value or the change amount of the operation input value, and the target of the steered wheels is changed using the changed transmission ratio. The turning angle can be calculated. As a result, the transmission ratio can be changed to a smaller value as the time differential value of the operation input value becomes smaller. On the other hand, the transmission ratio can be changed to a larger value as the time differential value of the operation input value increases.

  In this way, since the steered wheel can be appropriately controlled according to the time differential value of the operation input value, for example, when the steering wheel is operated quickly near the neutral position such as slalom running By increasing the transmission ratio, the left and right front wheels FW1, FW2 can be steered with high responsiveness. On the other hand, for the gentle steering wheel operation within the operation range with a large transmission ratio, the transmission ratio can be reduced to gently steer the left and right front wheels FW1, FW2.

  For a gentle steering wheel operation, the transmission ratio can be changed based on the amount of change in the operation input value. According to this, for example, the steered gear ratio can be accurately changed without depending on the sampling rate of the operation input value detecting means. Furthermore, in a situation where the driver gradually operates the steering wheel, the transmission ratio can be changed to a large value according to the amount of operation of the steering wheel. Thereby, since the amount of change in the turning angle can be increased, the amount of operation of the steering wheel by the driver can be reduced, and the burden on the driver can be reduced.

  Another feature of the present invention is that the predetermined non-linear relationship is a predetermined exponent relationship with the operation input value detected by the operation input value detecting means. In this case, the turning angle calculation means represents the amount of motion state of the vehicle that can be perceived by the driver in relation to the turning of the vehicle, and has a predetermined exponent relationship with the detected operation input value. The expected motion state quantity may be calculated using the detected operation input value, and the target turning angle may be calculated using the calculated expected motion state quantity. The expected motion state quantity may be any one of a lateral acceleration, a yaw rate, and a turning curvature of the vehicle, for example. Furthermore, in this case, the operation input value detection means includes a displacement amount detection means for detecting the displacement amount of the steering handle, and an operation force conversion for converting the detected displacement amount into an operation force applied to the steering handle. It is good to comprise with a means.

  According to these, the operation input value (for example, the steering angle) of the driver with respect to the steering handle represents the motion state of the vehicle that can be perceived by the driver in relation to the turning of the vehicle, and It can be converted into a predicted motion state quantity (lateral acceleration, yaw rate, turning curvature, etc.) of the vehicle having a predetermined exponential relationship or a power relationship. Then, based on the converted expected motion state quantity, the target turning angle of the steered wheels necessary for the vehicle to move with the expected motion state quantity changes exponentially with respect to the operation input value of the steering wheel. Can be calculated to

  Therefore, when the steered wheels are steered to the target turning angle and the vehicle turns, the turn gives the driver the estimated motion state quantity as the “physical quantity of the given stimulus” according to the Weber-Hefner law. Given. Since the expected motion state quantity changes exponentially or exponentially with respect to the operation input value to the steering wheel, the driver perceives the motion state quantity that matches human perception characteristics. While the steering wheel can be operated. 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, the driver can operate the steering wheel in accordance with human perceptual characteristics, so that driving of the vehicle is simplified.

  Furthermore, another feature of the present invention is that a reaction force device is provided that applies a reaction force to the operation of the steering wheel. According to this, an appropriate reaction force can be applied to the operation of the steering wheel by the driver. In this case, for example, when it is determined by the operation state determination means that the steering wheel is in the normal operation state, the operation input value detected with the detection reference point for detecting the operation input value as the origin and a predetermined non-linear relationship It is possible to calculate the target reaction force in the normal operation state at Further, when it is determined by the operation state determination means that the steering handle is in the steering operation state, the operation input value detected when the steering operation state is determined is used as a virtual origin and a predetermined value. It is possible to calculate a target reaction force in the steering operation state that is in a non-linear relationship. As a result, a more appropriate reaction force can be applied to the operation of the steering wheel by the driver.

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 steering apparatus for a vehicle according to a first embodiment.

  This steering device includes a steering handle 11 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, and a lateral acceleration sensor 34.

  The steering angle sensor 31 is assembled to the steering input shaft 12, detects the rotation angle from the neutral position as the detection reference point 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). ) Is output. Here, in this specification, the neutral position refers to the positions of the steering handle 11, the steering input shaft 12, the steering output shaft 22, and the left and right front wheels FW1 and FW2 for maintaining the vehicle in a straight traveling state. 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 actual lateral acceleration G also represents leftward acceleration as a positive value and rightward acceleration as a negative value.

  These sensors 31 to 34 are connected to the electronic control unit 35. The electronic control unit 35 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 a program. Drive circuits 36 and 37 for driving the reaction force actuator 13 and the steering actuator 21 are connected to the output side of the electronic control unit 35, respectively. In the drive circuits 36 and 37, current detectors 36a and 37a for detecting a drive current flowing through the electric motor in the reaction force actuator 13 and the steering actuator 21 are provided. The drive current detected by the current detectors 36a and 37a is fed back to the electronic control unit 35 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 35. The electronic control unit 35 includes a sensory adaptation control unit 40 for determining the target turning angle δd of 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, and the target turning. The steering control unit 50 includes a steering control unit 50 that controls the steering of the left and right front wheels FW1 and FW2 based on the angle δd, and a reaction force control unit 60 that controls the application of a reaction force to the steering handle 11.

  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 to control the sensory adaptation control unit 40 and the reaction force control. Output to the unit 60. In the sensory adaptation control unit 40, the steering state determination unit 41 stops the turning operation of the steering handle 11 by the driver based on the input detected steering angle θ and the detected vehicle speed V input from the vehicle speed sensor 33. It is determined whether or not it is in a state of being gently rotated (hereinafter, this state is referred to as a steering operation state).

  More specifically, the steered state determination unit 41 determines the steered operation state of the steering handle 11 based on the steered operation state determination condition using the detected steering angle θ and the detected vehicle speed V. Here, the holding operation state determination condition is that when the absolute value of the detected steering angle θ is equal to or larger than the predetermined steering angle θg, the detected vehicle speed V is equal to or higher than the predetermined vehicle speed Vc, and the detected steering angle θ A value obtained by dividing the absolute value of the time differential value dθ / dt (hereinafter, this differential value is referred to as steering angular velocity dθ / dt) by the detected vehicle speed V, that is, | dθ / dt | / V is less than a predetermined value dθv set in advance. This is a condition for determining whether the state continues for a predetermined time th. The predetermined steering angle θg will be described later.

  Therefore, the steered state determination unit 41 determines that the steering handle 11 is in the steered operation state if the aforementioned steered operation state determination condition is satisfied. On the other hand, the steered state determination unit 41 does not satisfy the steered operation state determination condition, for example, a state in which the steering handle 11 is operated to rotate at a certain speed by the driver (hereinafter, this state is usually referred to as normal state). If it is referred to as an operation state), it is determined that the steering handle 11 is not in the steering holding operation state. In the following description, the first embodiment will be described from the case of the normal operation state in order to facilitate understanding.

When it is determined that the steering handle 11 is in the normal operation state, the steered state determination unit 41 supplies the detected steering angle θ input from the steering angle sensor 31 to the displacement-torque conversion unit 42. The displacement-torque converter 42 calculates a steering torque Td11 that is a linear function of the steering angle θ according to the following equation 1, and calculates a steering torque Td12 that is an exponential function of the steering angle θ according to the following equation 2. Here, the linear function of Expression 1 and the exponential function of Expression 2 are continuously connected at a predetermined steering angle θz. For example, the origin “0” at the steering angle θz in the exponential function of Expression 2 is used. The tangent line passing through is preferably adopted as the linear function of Equation 1. Note that Equation 1 is not limited to a linear function, and when the steering angle θ is “0”, the steering torque Td11 becomes “0” and is continuously connected to the exponential function of Equation 2. As long as it is a function, various functions can be adopted.
Td11 = (Tmax / θmax1) · θ Equation 1
Td12 ＝ To ・ exp (K1 ・ θ)… Formula 2

  However, Tmax in the formula 1 represents the absolute value of the maximum value of the torque that can change in the system. Further, θmax1 in the expression 1 represents the absolute value of the maximum steering angle of the steering wheel 11 in the normal operation state. Therefore, in the normal operation state, (Tmax / θmax1) in Equation 1 is set as a constant representing the slope of the linear function. In addition, To and K1 in Equation 2 are constants, and in particular, the constant To is the minimum steering torque that can be perceived by the driver. The constant K1 will be described later in detail. Further, the steering angle θ in the equations 1 and 2 represents the absolute value of the detected steering angle θ. If the detected steering angle θ is positive (Tmax / θmax1) and the constant To is positive. If the detected steering angle θ is negative (Tmax / θmax1) and the constant To is a negative value having the same absolute value as the positive (Tmax / θmax1) and the positive constant To.

Then, the displacement-torque converter 42 calculates the steering torque Td1 in the normal operation state according to the following equation 3 that adds the equation 1 and the equation 2.
Td1 ＝ KRs0 ・ Td11 + (1−KRs0) ・ Td12… Formula 3
However, KRs0 in Equation 3 is a coefficient for correcting the change characteristic of the detected steering angle θ, and has the characteristic as shown in FIG. Specifically, as shown in FIG. 3, the correction coefficient KRs0 is “1” when the steering angle θ input by the driver is less than the predetermined steering angle θz, and is equal to or greater than the predetermined steering angle θz. Is a correction coefficient whose value changes to a predetermined value. The predetermined value may be set as a numerical value between “0” and “1”. Here, the reason why the correction coefficient KRs0 is set to “1” when the steering angle is less than the predetermined steering angle θz is to change the steering torque Td1 in a linear function according to the equation 1 when the steering coefficient is less than the predetermined steering angle θz. Note that the steering torque Td1 is calculated using a conversion table having characteristics as shown in FIG. 4 in which the steering torque Td1 with respect to the steering angle θ is stored instead of the calculation of the expression 3 (the expressions 1 and 2). May be.

The calculated steering torque Td1 is supplied to the torque-lateral acceleration conversion unit 43. The torque-lateral acceleration conversion unit 43 calculates the expected lateral acceleration Gd that the driver expects by turning the steering wheel 11 according to the following formula 4 if the absolute value of the steering torque Td1 is less than the positive predetermined value Tg. If the absolute value of the steering torque Td1 is equal to or greater than the positive predetermined value Tg, the calculation is performed according to the following formula 5. Here, Expression 4 is a linear function expression of the steering torque Td1, and is a function in which the expected lateral acceleration Gd becomes “0” when the steering torque Td1 is “0”. Equation 5 is a power function of the steering torque Td1, and is continuously connected to Equation 4 at a predetermined value Tg.
Gd = a · Td1 (| Td1 | <Tg) Equation 4
Gd = C ・ Td1 ^K2 (Tg ≦ | Td1 |) Equation 5

  However, a in the formula 4 is a constant representing the slope of the linear function, and C and K2 in the formula 5 are constants. The steering torque Td1 in the equations 4 and 5 represents the absolute value of the steering torque Td1 calculated using the equation 3 (the equations 1 and 2), and the calculated steering torque Td1 is a positive value. If the constant a and constant C are positive values, and the calculated steering torque Td1 is negative, the constant a and constant C are negative values having the same absolute value as the positive constant a and constant C. And In this case as well, the expected lateral acceleration Gd is calculated using a conversion table having a characteristic as shown in FIG. 5 in which the expected lateral acceleration Gd with respect to the steering torque Td1 is stored instead of the calculations of the equations 4 and 5. It may be.

Here, the exponential function characteristic of Equation 5 will be described. When the steering torque Td is eliminated using the equation 2, the following equation 6 is obtained.
Gd = C · (To · exp (K1 · θ)) ^K2 = C · To ^K2 · exp (K1 · K2 · θ) = Go · exp (K1 · K2 · θ)
In Equation 6, Go is a constant C · To ^K2 , and Equation 6 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. Accordingly, if the driver can turn the steering handle 11 while perceiving a lateral acceleration equal to the expected lateral acceleration Gd when the steering torque Td is equal to or greater than the predetermined value Tg, the turning operation of the steering handle 11 is performed. And the vehicle steering can be made to correspond to human perceptual characteristics.

As described above, the expected lateral acceleration Gd shown in the equation 5 (that is, the equation 6) changes exponentially with respect to the steering angle θ, which is the operation amount of the steering wheel 11, and thus human perception. It suits the characteristics. 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 (7). Therefore, it can be seen from this that if the steering handle 11 can be rotated while perceiving a lateral acceleration equal to the expected lateral acceleration Gd, the driver can easily rotate the steering handle 11.
Gd = Go · exp (K0 · ω · t) (7)
However, K0 is a constant having a relationship of K0 = K1 · K2.

  Further, as shown in Equation 4, when the steering torque Td1 is less than the predetermined value Tg, the expected lateral acceleration Gd changes in a linear function. This is because, for example, when the steering torque Td1 is less than the predetermined value Tg, that is, when the steering angle θ is maintained in the vicinity of “0” (near the neutral position of the steering wheel 11), the expected lateral acceleration Gd is calculated according to the above equation 5, for example If calculated, the expected lateral acceleration Gd does not converge to “0”, which is not realistic. However, as described above, if the steering handle 11 is in the vicinity of the neutral position, that is, if the steering torque Td1 is less than the predetermined value Tg, the expected lateral acceleration Gd is calculated according to the above equation 4 to obtain the steering handle 11 in the normal operation state. Is rotated in the neutral position direction, the expected lateral acceleration Gd converges to “0”, which solves this problem.

  Next, how to determine the parameters K1, K2, and C (predetermined values K1, K2, and C) used in the expressions 1 to 7 will be described. In the description of how to determine the parameters K1, K2, and C, the steering torque Td1 and the expected lateral acceleration Gd in the expressions 1 to 6 are simply handled as the steering torque T and the lateral acceleration G. According to the above-mentioned 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 S is called the Weber ratio. The present inventors confirmed that the above-mentioned Weber-Hefner's law is established with respect to steering torque and lateral acceleration, and in order to determine the Weber ratio, the following experiments were conducted for men and women, age, and vehicle driving. I went to various people with different 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. Value.

  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, under the above situation, when F is the detection force that can withstand lateral force from the outside at a certain time and maintain the posture, and ΔF is the minimum force change amount that can perceive the change from the detection force F The ratio value ΔF / F, the Weber ratio, was measured for various humans. According to the result of this experiment, the Weber ratio ΔF / F was a substantially constant value 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 8 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 9 is established.
K1 = ΔT / (T · Δθ) = Kt / Δθ Equation 9

If the maximum setting value of the steering torque T is Tmax, the following expression 10 is established from the expressions 1 and 2.
Tmax ＝ To ・ exp (K1 ・ θmax1) ... Equation 10
If this equation 10 is modified, the following equation 11 is established.
K1 = log (Tmax / To) / θmax1 Equation 11
Then, the following equation 12 is derived from the equations 9 and 11.
Δθ = Kt / K1 = Kt · θmax1 / log (Tmax / To) (12)
In Equation 11, Kt is the Weber ratio of the steering torque T, To corresponds to the minimum steering torque that can be perceived by humans, and these values Kt, Tmax, To, and θmax1 are constants that can be set in advance. Therefore, the differential value Δθ can be calculated using the equation (11). The predetermined value (coefficient) K1 can also be calculated based on the equation 9 using the differential value Δθ and the Weber ratio Kt.

In addition, when the formula 5 is differentiated and the formula 5 is considered in the differentiated formula, the following formula 13 is established.
ΔG = C · K2 · T ^K2-1 · ΔT = G · K2 · ΔT / T Equation 13
When Expression 12 is modified and the Weber ratio ΔT / T related to the steering torque obtained by the above experiment is set to Kt, and the Weber ratio ΔF / F related to the lateral acceleration is set to Ka, the following Expressions 14 and 15 are established.
ΔG / G = K2 · ΔT / T Equation 14
K2 = Ka / Kt ... Formula 15
In this equation 15, 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. The coefficient K2 can also be calculated based on 15.

Further, if the maximum set value of the lateral acceleration is Gmax and the maximum set value of the steering torque is Tmax, the following expression 16 is derived from the above expression 5.
C = Gmax / Tmax ^K2 Equation 16
In Equation 16, Gmax and Tmax are constants that can be set in advance, and K2 is calculated by Equation 15, so that a constant (coefficient) C can also be calculated.

  As described above, the maximum steering angle θmax1, 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 related to the steering torque T, and the lateral acceleration G If the Weber ratio Ka is set, the coefficients K1, K2, and C in Equations 1 to 6 can be calculated. Therefore, in the displacement-torque conversion unit 42 and the torque-lateral acceleration conversion unit 43, the steering torque Td and the expected lateral acceleration Gd that match the driver's perceptual characteristics can be calculated using the equations 1-6.

  Returning to the description of FIG. 2 again, the expected lateral acceleration Gd calculated by the torque-lateral acceleration conversion unit 43 is supplied to the turning angle conversion unit 44. The turning angle conversion unit 44 calculates the target turning angle δd of the left and right front wheels FW1, FW2 necessary for generating the expected lateral acceleration Gd, and changes according to the vehicle speed V as shown in FIG. And a table representing a change characteristic of the target turning angle δd 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 44 refers to this table and calculates a target turning angle δd corresponding to the input expected lateral acceleration Gd and the detected vehicle speed V input from the vehicle speed sensor 33. Here, the lateral acceleration G (expected lateral acceleration Gd) and the target turning angle δd stored in the table are both positive, but the expected lateral acceleration Gd supplied from the torque-lateral acceleration conversion unit 43 is negative. If so, the output target turning angle δd is also negative.

Here, since the target turning angle δd is a function of the vehicle speed V and the lateral acceleration G as shown in the following equation 17, it is also calculated by executing the operation of the following equation 17 instead of referring to the table. Can do.
δd = L · (1 + A · V ² ) · Gd / V ² Equation 17
However, L in the formula 17 is a predetermined value indicating the wheel base, and A is a predetermined value indicating the motion performance of the vehicle.

The calculated target turning angle δd is supplied to the turning angle correction unit 51 of the turning control unit 50. The turning angle correction unit 51 receives the expected lateral acceleration Gd from the torque-lateral acceleration conversion unit 43 and also the actual lateral acceleration G detected by the lateral acceleration sensor 34, and calculates the following equation (18). The target turning angle δd input after execution is corrected, and the corrected target turning angle δda is calculated.
δda = δd + K3 · (Gd−G) Equation 18
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 generating the expected lateral acceleration Gd are ensured with high accuracy.

  The calculated corrected target turning angle δda is supplied to the drive control unit 52. The drive control unit 52 inputs the actual turning angle δ detected by the turning angle sensor 32, and the electric power in the turning actuator 21 is turned 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 52 also inputs a drive current that flows from the drive circuit 37 to the electric motor, and feedback-controls the drive circuit 37 so that a drive current having a magnitude corresponding to the steering torque appropriately flows to the electric motor. To do. 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 operation state of the steering wheel 11 by the driver is the steering operation state will be described. As described above, the steered state determination unit 41 satisfies the steered operation state determination condition when the steered handle 11 is turned more than a predetermined steering angle θg as a result of the turning operation. Then, it is determined that the steering handle 11 is in the steering holding operation state. Here, the steering state of the left and right front wheels FW1 and FW2 when the steering handle 11 is steered by a driver to a predetermined steering angle θg or more in the normal operation state will be described.

By substituting Equation 6 into Equation 17 and rearranging, Equation 19 below is established.
δd = (L · (1 + A · V ² ) / V ² ) · Go · exp (K1 · K2 · θ) Equation 19
However, the coefficients K1 and K2 in Equation 19 are calculated according to Equation 9 and Equation 15. According to the equation 19, the target turning angle δd changes exponentially with respect to the steering angle θ as shown in FIG. 7, and in particular, the steering angle θ exceeds the predetermined steering angle θg. As the absolute value increases, the ratio of the change amount of the absolute value of the target turning angle δd to the change amount of the steering angle θ (hereinafter, this change amount ratio is referred to as a transmission ratio) increases. As described above, when the steering handle 11 is turned within the steering range where the transmission ratio becomes large, the target turning angle δd greatly changes with respect to the turning operation of the steering handle 11, and therefore, for example, the left and right front wheels It becomes difficult to finely adjust the steered state of FW1 and FW2.

Therefore, when the above-described steering operation state determination condition is satisfied, the steering state determination unit 41 sets the steering angle θ as the steering steering angle θh when the condition is satisfied, and this steering steering angle θh and the detected steering angle θ are supplied to the displacement-torque converter 42. The displacement-torque conversion unit 42 calculates the steering torque Td2 according to the following formulas 20 to 22 similar to the above formulas 1 to 3, using the set steered steering angle θh as a virtual origin.
Td21 = (Tmax / θmax2) · (θ−θh) Equation 20
Td22 = To · exp (K1 · (θ−θh)) Equation 21
Td2 = KRs0 · Td21 + (1-KRs0) · Td22 + Tk Equation 22

  Here, θmax2 in the equation 20 represents the absolute value of the maximum steering angle of the steering handle 11 in the steering holding state. Further, Tk in the equation 22 represents the steering torque at the steering steering angle θh in the normal operation state, and is calculated according to the equation 3 (the equations 1 and 2). KRs0 in the equation 22 is also a coefficient for correcting the change characteristic of the detected steering angle θ similar to the equation 3. In this case, KRs0 is less than “1” because the steering handle 11 is turned over a predetermined value θz.

Then, the displacement-torque converter 42 calculates the steering torque Tdh in the steering holding operation state according to the following equation (23).
Tdh = (1−F) · Td1 + F · Td2 Equation 23
However, F in the equation 23 is a variable for determining the ratio of the steering torque Td1 and the steering torque Td2, and as shown in FIG. 8, the steering angular velocity dθ / dt that constitutes the holding operation state determination condition. It has a characteristic that changes in accordance with the absolute value of and the change of (1 / V). That is, the variable F changes from “1” to “0” as the absolute value of the steering angular velocity dθ / dt increases, and also changes from “1” to “0” as the detected vehicle speed V decreases. To do. As a result, the steering torque Tdh calculated according to the equation 23 increases the ratio of the steering torque Td2 when the steering operation state determination condition is satisfied. On the other hand, when the above condition is not satisfied, ie, when the absolute value of the steering angular velocity dθ / dt is large or the detected vehicle speed V decreases, the ratio of the steering torque Td1 increases continuously. In this case as well, the steering torque Tdh is calculated using a conversion table having a characteristic as shown by a solid line in FIG. 9 in which the steering torque Tdh with respect to the steering angle θ is stored instead of the calculation of the equation 23. May be.

The calculated steering torque Tdh is supplied to the torque-lateral acceleration conversion unit 43. The torque-lateral acceleration conversion unit 43 calculates the expected lateral acceleration Gdh expected when the driver finely adjusts the turning state of the left and right front wheels FW1 and FW2 in the steering operation state according to the following equation 24.
Gdh = C ・ Tdh ^K2 ... Formula 24
However, the steering torque Tdh in the equation 24 represents the absolute value of the steering torque Tdh calculated using the equation 23. If the calculated steering torque Tdh is positive, the constant C is a positive value. If the calculated steering torque Tdh 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 Gdh is calculated using a conversion table having a characteristic as shown by a solid line in FIG. 10 in which the estimated lateral acceleration Gdh with respect to the steering torque Tdh is stored instead of the calculation of the equation 24. You may do it. Here, Gk in FIG. 10 represents the steering torque Tk, that is, the expected lateral acceleration at the steering-holding steering angle θh.

Then, the torque-lateral acceleration conversion unit 43 supplies the calculated expected lateral acceleration Gdh to the turning angle conversion unit 44. The turning angle conversion unit 44 calculates the target turning angle δdh according to the following formula 25 using the supplied expected lateral acceleration Gdh.
δdh = δk + L · (1 + A · V ² ) · Gdh / V ² ... Formula 25
However, δk in the equation 25 is the target turning angle at the predicted lateral acceleration Gk calculated according to the equation 17, in other words, the target turning at the steering holding angle θh calculated according to the equation 19. Represents a corner.

Here, when the steering handle 11 is held within the steering range where the transmission ratio is large, the following Expression 26 is derived by modifying the Expression 25 in the same manner as the Expression 17.
δdh = δk + (L · (1 + A · V ² ) / V ² ) · Go · exp (K1 · K2 · (θ−θh)
According to Expression 26, the target turning angle δdh varies exponentially with respect to the steering angle θ, with the steered steering angle θh as a virtual origin, as shown by a solid line in FIG. Thereby, when the steering wheel 11 is gently operated in the vicinity of the steering steering angle θh, the amount of change in the target turning angle δdh is small, in other words, the transmission ratio is small. Therefore, the driver can finely adjust the steering state of the left and right front wheels FW1, FW2 very well after switching from the normal operation state to the steering operation state.

  On the other hand, when the steered steering state is switched to the normal steered state, in other words, when the steered operation state determination condition is not satisfied, as described above, the value of the variable F in the equation 23 is continuously “ Changes to "0". As a result, the steering torque Tdh calculated by the displacement-torque converter 42 greatly depends on the steering torque Td1 in the normal operation state. As a result, the target turning angle δdh in the steering operation state calculated by the turning angle conversion unit 44 is changed to the target turning angle δd in the normal operation state.

Here, the displacement-torque converter 42 continuously changes the ratio of the steering torque Td1 and the ratio of the steering torque Td2 to the steering torque Tdh, that is, the value of the variable F is continuously changed from “1” to “0”. When the change is made, the limit expressed by the following equation 27 is set.
| Td1−Tdh | <ε Equation 27
However, ε in Equation 27 is a preset constant. Then, the displacement-torque converter 42 continuously changes the value of the variable F from “1” to “0” to satisfy the target turning angle δdh from the target turning angle δdh when the relationship expressed by the equation 27 is satisfied. Change to angle δd. In this way, by restricting a rapid change from the target turning angle δdh to the target turning angle δd, when switching from the steered operation state to the normal operation state, in other words, from the target turning angle δdh to the target turning angle. Even in the case of switching to the angle δd, a sudden change in the left and right front wheels FW1, FW2 can be effectively prevented, and the driver can be prevented from feeling uncomfortable.

The target turning angle δdh calculated in this way is supplied to the turning angle correction unit 51 of the turning control unit 50 in the same manner as in the normal operation state described above, and follows the following equation 28 similar to the above equation 18. The corrected target turning angle δdha is corrected.
δdha = δdh + K4 · (Gdh−G) Equation 28
However, the coefficient K4 is a predetermined positive constant. The actual lateral acceleration G is detected by the lateral acceleration sensor 34, and the expected lateral acceleration Gdh is calculated by the torque-lateral acceleration conversion unit 43. Then, the corrected target turning angle δdha calculated in this way is supplied to the drive control unit 52, and the left and right front wheels FW1, FW2 are turned to the corrected target turning angle δdha.

  Next, the reaction force control unit 60 will be described. The steering angle θ detected by the steering angle sensor 31 is supplied to the steered state determination unit 61. The steered state determination unit 61, like the steered state determination unit 41 of the sensory adaptation control unit 40, converts the detected steering angle θ into displacement-torque conversion in the normal operation state based on the aforementioned steered operation state determination condition. When the steering operation state is established, the steering steering angle θh and the detected steering angle θ set are supplied to the displacement-torque conversion unit 62.

If the detected steering angle θ is supplied, the displacement-torque converter 62 calculates the reaction force torque Tz1 according to the following formulas 29 to 31 similar to the above formulas 1 to 3. Also in the calculation of the reaction torque Tz1, Equation 29 is not limited to a linear function. When the steering angle θ is “0”, the reaction force torque Tz11 becomes “0”, and As long as the function is continuously connected to the exponential function, various functions can be adopted.
Tz11 = (Tmax / θmax1) · θ Equation 29
Tz12 ＝ To ・ exp (K1 ・ θ) ... Equation 30
Tz1 ＝ KRs0 ・ Td11 + (1−KRs0) ・ Td12… Formula 31

  Also in this case, Tmax and θmax1 in the equation 29 are set values similar to those in the equation 1. In addition, To and K1 in Equation 30 are the same constants as in Equation 2. Further, KRs0 in the equation 31 is a coefficient for correcting the change characteristic of the detected steering angle θ, as in the equation 3, and has a characteristic as shown in FIG. Further, the steering angle θ in the equations 29 and 30 represents the absolute value of the detected steering angle θ. If the detected steering angle θ is positive (Tmax / θmax1) and the constant To If the detected steering angle θ is negative (Tmax / θmax1) and the constant To is a positive value having the same absolute value as the positive (Tmax / θmax1) and the positive constant To . In this case as well, the reaction force torque Tz1 is calculated using a conversion table having a characteristic as shown in FIG. 4 in which the reaction force torque Tz with respect to the steering angle θ is stored instead of the calculations of the equations 29 to 31. It may be.

On the other hand, the displacement-torque conversion unit 62, if the steered steering angle θh and the detected steering angle θ set by the steered state determination unit 61 are supplied, the following formulas 32-34 similar to the formulas 20-22 described above. According to the above, the reaction torque Tz2 is calculated.
Tz21 = (Tmax / θmax2) · (θ−θh) Equation 32
Tz22 = To · exp (K1 · (θ−θh)) Equation 33
Tz2 ＝ KRs0 ・ Tz21 + (1−KRs0) ・ Tz22 + Tk… Formula 34
Here, θmax2 in the equation 32 represents the absolute value of the maximum steering angle of the steering wheel 11 in the steering holding state similar to the equation 20. Tk in the equation 34 represents the steering torque of the steering steering angle θh in the normal operation state, and is calculated according to the equation 31 (the equations 29 and 30). Also, KRs0 in the equation 34 is a coefficient for correcting the change characteristic of the detected steering angle θ similar to the equation 31. In this case, KRs0 is less than “1” because the steering handle 11 is turned over a predetermined steering angle θg.

Then, the displacement-torque converter 42 calculates the steering torque Tzh in the steering holding operation state according to the following equation 35 similar to the equation 23.
Tzh = (1−F) ・ Tz1 + F ・ Tz2 Equation 35
However, F in the equation 35 is also a variable for determining the ratio of the steering torque Td1 and the steering torque Td2 as in the equation 23. As shown in FIG. It has characteristics that change in accordance with changes in the absolute value of the steering angular velocity dθ / dt and (1 / V). As a result, the variable F changes from “1” to “0” as the absolute value of the steering angular velocity dθ / dt increases, and from “1” to “0” as the detected vehicle speed V decreases. Change.

  Therefore, the steering torque Tzh calculated according to the equation 35 also increases the ratio of the steering torque Tz2 when the steering operation state determination condition is satisfied. On the other hand, the steering torque Tzh does not hold the above condition, that is, when the absolute value of the steering angular velocity dθ / dt is large or the detected vehicle speed V decreases, the ratio of the steering torque Tz1 increases continuously. In this case, the steering torque Tzh may be calculated using a conversion table having characteristics as shown in FIG. 9 in which the steering torque Tzh with respect to the steering angle θ is stored, instead of the calculation of the equation 35. .

  The reaction force torque Tz1 or the reaction force torque Tzh calculated in this way is supplied to the drive control unit 63. The drive control unit 63 inputs a drive current that flows from the drive circuit 36 to the electric motor in the reaction force actuator 13, and the drive circuit so that the drive current corresponding to the reaction force torque Tz1 or the reaction force torque Tzh flows to the electric motor. 36 is feedback controlled. By the drive control of the electric motor in the reaction force actuator 13, the electric motor applies a reaction force torque Tz1 or a reaction force torque Tzh to the steering handle 11 via the steering input shaft 12.

  Accordingly, in the normal operation state, the driver turns the steering handle 11 while applying the reaction torque Tz1 equal to the steering torque Td1 to the steering handle 11. Further, in the steering holding state, the driver turns the steering handle 11 while applying a reaction force torque Tzh equal to the steering torque Tdh to the steering handle 11. Thereby, the driver perceives the reaction force torque Tz1 or reaction force torque Tzh according to the above-mentioned Weber-Hefner's law with respect to the steering angle θ, that is, while receiving a sense suitable for human perception characteristics, The steering handle 11 can be turned.

  As can be understood from the above description, according to the first embodiment, when the steering wheel determination unit 41 determines that the steering wheel 11 is in the normal operation state, the steering angle θ with respect to the steering wheel 11 is The displacement-torque conversion unit 42 and the torque-lateral acceleration conversion unit 43 convert the predicted lateral acceleration Gd. Then, based on the converted expected lateral acceleration Gd, the turning angle conversion unit 44 uses the target turning angle δd for the vehicle to move at the expected lateral acceleration Gd as an index with respect to the steering angle θ of the steering handle 11. It can be calculated to change functionally (non-linearly).

  Therefore, when the left and right front wheels FW1 and FW2 are steered to the target turning angle δd and the vehicle turns, the turn causes the driver to assume the “physical quantity of the given stimulus” according to the Weber-Hefner law. An acceleration Gd is given. Since the expected lateral acceleration Gd changes exponentially with respect to the steering angle θ of the steering wheel 11, the driver perceives a lateral acceleration that matches human perception characteristics. While the steering wheel 11 can be operated. 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.

  On the other hand, when the steering handle 11 is turned in a steering range with a large transmission ratio in the normal operation state, it is difficult to finely adjust the turning state of the left and right front wheels FW1, FW2. On the other hand, the steered state determination unit 41 sets the steered steering angle θh based on the establishment of the steered operation state determination condition, that is, if the steering handle 11 is gently rotated by the driver. Can be set to a virtual origin. The torque-lateral acceleration conversion unit 43 calculates the expected lateral acceleration Gdh, and the turning angle conversion unit 44 calculates the target turning angle δdh based on the expected lateral acceleration Gdh, based on the steered steering angle θh. As a result, the transmission ratio can be reduced. Therefore, the driver can turn the vehicle very easily and in accordance with the perceptual characteristics even within the steering range where the steering angle θ of the steering handle 11 is large, and the driving of the vehicle becomes simple.

b. Second Embodiment In the first embodiment, when the steering state determination units 41 and 61 determine that the operation state of the steering handle 11 by the driver is the steering operation state, the steering steering angle θh is set. The virtual origin was set once, and the transmission ratio in the vicinity of the steering steering angle θh was reduced. On the other hand, when the steering operation state is determined a plurality of times during the steering operation state, the steering steering angle may be set again as a virtual origin for each determination. Is possible. Hereinafter, although this 2nd Embodiment is described, the same code | symbol is attached | subjected to the same part as the said 1st Embodiment, and the detailed description is abbreviate | omitted.

  The computer program in the second embodiment is different from the computer program in the first embodiment in that the steering steering angle is set a plurality of times in the steering operation state. Therefore, in the following description, description of the normal operation state that is exactly the same as that in the first embodiment will be omitted, and the steering operation state will be described in detail.

  In the second embodiment, the computer program executed by the electronic control unit 35 is shown by the functional block diagram of FIG. Then, if the steering operation state determination condition is satisfied in the normal operation state, the steering maintenance state determination unit 41 of the sensory adaptation control unit 40 performs the first steering maintenance steering angle θh1 as in the first embodiment. And the steered steering angle θh1 and the detected steering angle θ are supplied to the displacement-torque converter 42. As a result, the displacement-torque converter 42 calculates the steering torque Tdh1 according to the equations 20 to 23 using the steering steering angle θh1 as a virtual origin, and the calculated steering torque Tdh1 is the torque-lateral acceleration converter 43. To supply.

  In the torque-lateral acceleration conversion unit 43, the expected lateral acceleration Gdh1 is calculated according to the equation 24 using the supplied steering torque Tdh1, and the turning angle conversion unit 44 uses the calculated expected lateral acceleration Gdh1. The target turning angle δdh1 is calculated according to the equation 25. Accordingly, when the steering operation state is shifted from the normal operation state, that is, when the first steering steering angle θh1 is set, in the vicinity of the steering steering angle θh1 as in the first embodiment. The transmission ratio is reduced. Therefore, it becomes easy to finely adjust the steered state of the left and right front wheels FW1, FW2.

Incidentally, even in the steering holding state, the target turning angle δdh1 changes exponentially with respect to the steering angle θ. For example, when the driver keeps turning the steering wheel 11 gently. In some cases, the transmission ratio increases, making it difficult to fine-tune the steered state of the left and right front wheels FW1, FW2. For this reason, the steered state determining unit 41 has already determined that the steered state is in the steered operation state, and the steered handle 11 is gently rotated to the steering range where the transmission ratio becomes large, thereby determining the steered state determining condition. When is satisfied, a plurality of steering steering angles are set each time the condition is satisfied. Hereinafter, the case where the nth steering holding angle θh _n is set will be described in detail.

Holding steering state determining section 41, when the steering holding operation state determination condition to the n-th time satisfied, sets the detected steering angle θ at the established time the steering hold the steering angle [theta] h _n, the steering hold the steering angle [theta] h _n, and The detected steering angle θ is supplied to the displacement-torque converter 42. Displacement - in the torque converter 42, as a virtual origin of the supplied steering hold the steering angle [theta] h _n, to calculate the steering torque Tdh _n according to the equation 20 to 23 similar to that formula 36-39.
Td _n 1 = (Tmax / θmax _n ) · (θ−θh _n ) Equation 36
Td _n 2 = To · exp (K1 · (θ−θh _n )) Equation 37
Td _n = KRs0 ・ Td _n 1+ (1−KRs0) ・ Td _n 2 + Tk Equation 38
Tdh _n = (1−F) · Td _(n−1) + F · Td _n ... Equation 39
However, θmax _n in the equation 36 represents the maximum steering angle of the steering handle 11 in the n-th steering operation state. Td _(n-1) in the equation 39 represents the steering torque calculated according to the equations 36 to 38 with the setting of the _{(n-1) th} steering holding angle θh _(n-1) . In this case, the steering torque Tdh _n is calculated using a conversion table having characteristics as shown by a solid line in FIG. 13 in which the steering torque Tdh _n with respect to the steering angle θ is stored instead of the calculation of the equation 39. It may be.

The calculated steering torque Tdh _n is torque - is supplied to the lateral acceleration conversion unit 43. The torque-lateral acceleration conversion unit 43 calculates the expected lateral acceleration Gdh _n that the driver expects when finely adjusting the steered state of the left and right front wheels FW1, FW2 in the n-th steering operation state according to the following equation 40: calculate.
Gdh _n = C · Tdh _n ^K2 ... Formula 40
However, the steering torque Tdh _n in the formula 40 are those representing the absolute value of the steering torque Tdh _n calculated by using the equation 39, the constant C if it is positive steering torque Tdh _n is obtained by the calculated with a positive value, the steering torque Tdh _n that the calculation is a negative value having the same absolute value constant C and the positive constant C if it is negative. Also in this case, instead of the calculation of the equation 40, using the conversion table of the characteristics shown by the anticipated lateral acceleration Gdh 14 _{which n} storing in solid lines to the steering torque Tdh _n, anticipated lateral acceleration Gdh _n May be calculated. Here, Gk _n in the Figure 14, represents the anticipated lateral acceleration in the steering torque Tk _n ie steering hold the steering angle [theta] h _n.

Then, the torque-lateral acceleration conversion unit 43 supplies the calculated expected lateral acceleration Gdh _n to the turning angle conversion unit 44. The turning angle conversion unit 44 calculates a target turning angle δdh _n according to the following formula 41 using the supplied expected lateral acceleration Gdh _n .
δdh _n = δk _(n−1) + L · (1 + A · V ² ) · Gdh _n / V ^{2 (} Formula 41)
However, δk _(n−1) in the equation 41 is the steering steering angle θh _n calculated according to the equation 41 when the steering steering angle θh _(n−1) is set for the _{(n−1) th time.} Represents the target turning angle corresponding to.

As described above, even when the steering steering angle is set n times, the target steering angle δdh _n is obtained by using the steering steering angle θh _n as a virtual origin as shown in FIG. It varies exponentially with respect to θ. When the steering wheel 11 is gently operated near the steering steering angle θh _n , the amount of change in the target turning angle δdh _n is small, in other words, the transmission ratio is small. Therefore, the driver can finely adjust the steering state of the left and right front wheels FW1, FW2 very well.

On the other hand, when switching from the n-th steered steering state to the normal steering state, the value of the variable F in the equation 39 continuously changes to “0” as in the first embodiment described above. Thus, the displacement - the steering torque Tdh _n which is calculated by the torque converter 42, so highly dependent on the steering torque Td in the n-1 th holding steering operation state of the _(n-1). As a result, the target turning angle δdh _n in the steered operation state calculated by the steered angle conversion unit 44 is continuous with the target turning angle δdh _(n-1) in the _{(n−1) th} steered operation state. Changed to By such changes are repeated, it is continuously changed from the target turning angle Derutadh _n to the target turning angle δd in the normal operation state.

Here, the displacement - the torque converter 42, similarly to the first embodiment, i.e., continuously changing the ratio of the ratio between the steering torque Td _n of the steering torque Td with respect to the steering torque Tdh _{n (n-1)} In order to continuously change the value of the variable F from “1” to “0”, it is preferable to set the limit represented by the equation 27. Thus, by limiting the rapid change of the ratio of the ratio between the steering torque Td _n of the steering torque Td _(n-1), when switching from the fixed steering operation state to the normal operation state, in other words, the target turning angle δdh _{Even in the} case of switching from _n to the target turning angle δd, a sudden change in the left and right front wheels FW1, FW2 can be effectively prevented, and the driver can be prevented from feeling uncomfortable.

The target turning angle δdh _n calculated in this way is supplied to the turning angle correction unit 51 of the turning control unit 50 as in the case of the normal operation state described above, and the corrected target turning angle according to the equation 28. It is corrected to δdh _n a. Then, thus calculated corrected target turning angle δdh _n a is supplied to the drive control unit 52, front left and right wheels FW1, FW2 are turned into the corrected target turning angle δdh _n a.

Also in the reaction force control unit 60, when the steered steering angle θh _n is set by the steered state determination unit 61, the displacement-torque conversion unit 62 corresponds to the steered steering angle θh _n and The reaction torque Tzh _n is calculated according to the following formulas 42 to 45 similar to the formulas 35 to 38.
Tz _n 1 = (Tmax / θmax _n ) · (θ−θh _n ) Equation 42
Tz _n 2 = To · exp (K1 · (θ−θh _n )) Equation 43
Tz _n = KRs0 • Tz _n 1 + (1−KRs0) • Tz _n 2 + Tk Equation 44
Tzh _n = (1−F) · Tz _(n−1) + F · Tz _n ... Formula 45

Then, the drive control unit 63 feedback-controls the drive circuit 36 so that the drive current corresponding to the calculated reaction force torque Tzh _n flows, and the reaction force torque Tzh _{n is} applied to the steering handle 11 via the steering input shaft 12. Is granted. Accordingly, the driver turns the steering handle 11 while applying a reaction torque Tzh _n equal to the steering torque Tdh _n to the steering handle 11. As a result, the driver moves the steering wheel 11 while perceiving the reaction torque Tzh _n whose relationship with the steering angle θ follows the Weber-Hefner law described above, that is, while receiving a sense that matches human perception characteristics. Can be rotated.

  As can be understood from the above description, also in this second embodiment, the transmission ratio of the left and right front wheels FW1, FW2 can be increased in the normal operation state, and the driver turns the vehicle very easily. be able to. On the other hand, when the transition is made from the normal operation state to the steering operation state, the transmission ratio can be reduced, and the driver can turn the vehicle very easily. Even if the steering operation state is already satisfied, if the steering operation state determination condition is satisfied, a plurality of steering steering angles can be set, so that the driver can turn the vehicle better. Can drive the vehicle easily.

c. Third Embodiment In the first embodiment and the second embodiment, the steering operation state is maintained by the steering state determination unit 41 in a situation where the steering handle 11 is being rotated within the steering range where the transmission ratio is large. When it is determined that the determination condition is satisfied, the steering steering angle θh is set to a virtual origin. Thereby, in the steering maintenance state, the transmission ratio can be reduced, and the turning state of the left and right front wheels FW1, FW2 can be finely adjusted very easily.

  On the other hand, when the steering handle 11 is turned in the steering range where the transmission ratio becomes large, the ratio of the actual turning angle δ to the detected steering angle θ, that is, the turning gear ratio may be changed. Good. That is, the transmission ratio can be generally expressed as the reciprocal of the steered gear ratio. For this reason, the transmission ratio can be changed by appropriately changing the steered gear ratio. The third embodiment will be described below.

  The configuration of the vehicle steering apparatus in the third embodiment is the same as that in the first embodiment, but the computer program executed by the electronic control unit 35 is the same as in the first and second embodiments. Slightly different.

  In the third embodiment, the computer program executed by the electronic control unit 35 is shown by the functional block diagram of FIG. In this case, the sensory adaptation control unit 40 is configured with the steered state determination unit 41 in the first embodiment and the second embodiment omitted. That is, in the third embodiment, the displacement-torque converter 42 is configured to directly input the detected steering angle θ from the steering angle sensor 31. Thereby, each process in the displacement-torque conversion part 42, the torque-lateral acceleration conversion part 43, and the turning angle conversion part 44 becomes the same as that of the case of the normal operation state in the said 1st Embodiment and 2nd Embodiment.

  Specifically, the displacement-torque converter 42 calculates the steering torque Td1 according to the above equations 1 to 3, and supplies it to the torque-lateral acceleration converter 43. The torque-lateral acceleration conversion unit 43 calculates the expected lateral acceleration Gd according to the equations 4 and 5 using the supplied steering torque Td1. Then, the calculated expected lateral acceleration Gd is supplied to the turning angle conversion unit 44, and the turning angle conversion unit 44 refers to the table shown in FIG. Thus, the target turning angle δd of the left and right front wheels FW1, FW2 necessary for generating the expected lateral acceleration Gd is calculated.

The target turning angle δd calculated in this way is supplied to the turning angle correction unit 53 of the turning control unit 50. The turning angle correction unit 53 receives the detected steering angle θ from the steering angle sensor 31, and the target turning is performed according to the time differential value of the inputted detected steering angle θ, that is, the steering angular velocity dθ / dt. A control target turning angle δs _n for controlling the turning operation of the left and right front wheels FW1, FW2 steered to the angle δd is calculated. That is, the turning angle correction unit 51 calculates the target turning angle for control δs _n according to the following equation 46.
δs _n = (dθ / dt) / Gra0 + δs _(n-1) Equation 46
However, Gra0 in the formula 46 represents the steered gear ratio and has characteristics as shown in FIG. Specifically, as shown in FIG. 17, the steered gear ratio Gra0 has a change characteristic that decreases as the absolute value of the steering angular velocity dθ / dt of the steering wheel 11 by the driver increases. is there. Further, δs _(n−1) in the equation 46 represents the control target turning angle calculated last time.

Then, the target turning angle for control δs _n calculated in this way is supplied to the drive control unit 52. The drive control unit 52 inputs the actual turning angle δ detected by the turning angle sensor 32 and also inputs the target turning angle δd from the turning angle conversion unit 44, and the left and right front wheels FW1 and FW2 are sequentially supplied. is the feedback control of the rotation of the electric motor in the turning actuator 21 so as to be steered to the control target turning angle .delta.s _n. This feedback control is repeatedly executed until the actual turning angle δ of the left and right front wheels FW1, FW2 reaches the target turning angle δd, whereby the left and right front wheels FW1, FW2 are turned to the target turning angle δd. .

Thus, when the steering operation of the left and right front wheels FW1, FW2 is controlled, the left and right front wheels FW1, FW2 are steered reflecting the steering angular velocity dθ / dt of the steering handle 11 by the driver. That is, according to the above equation 46, when the absolute value of the steering angular velocity dθ / dt is large, the steered gear ratio Gra0 becomes small, in other words, the transmission ratio becomes large. δs _n is greatly calculated according to the absolute value of the steering angular velocity dθ / dt. As a result, the turning operation speed of the left and right front wheels FW1, FW2 is increased, and the left and right front wheels FW1, FW2 are quickly turned to the target turning angle δd. On the other hand, when the absolute value of the steering angular velocity dθ / dt is small, the steered gear ratio Gra0 becomes large, in other words, because the transmission ratio becomes small, the calculated target turning angle for control δs _n is the steering angular velocity dθ. It is calculated smaller depending on the absolute value of / dt. Thereby, the turning operation speed of the left and right front wheels FW1, FW2 is reduced, and the turning state of the left and right front wheels FW1, FW2 is easily finely adjusted.

  Further, in the reaction force control unit 60 in the third embodiment, since the steered state determination unit 61 in the first embodiment and the second embodiment is omitted, the reaction force control unit 60 also has the first. As in the case of the normal operation state in the embodiment and the second embodiment, the reaction force torque Tz1 is calculated. In addition, the program processing executed by the electronic control unit 35 is the same as in the first and second embodiments. And in the functional block diagram of FIG. 16, the same code | symbol as the said 1st Embodiment and 2nd Embodiment is attached | subjected, and the detailed description is abbreviate | omitted.

  As can be understood from the above description, in the third embodiment, the steering operation of the left and right front wheels FW1, FW2 can be appropriately controlled according to the steering angular velocity dθ / dt. When the steering handle 11 is quickly operated in the vicinity of the neutral position, such as slalom running, the left and right front wheels FW1, FW2 can be steered with high responsiveness. On the other hand, in the steering range where the transmission ratio is large, the left and right front wheels FW1, FW2 can be gently steered in response to the turning operation of the steering handle 11 having a small absolute value of the steering angular velocity dθ / dt.

  In the third embodiment, the steering operation of the left and right front wheels FW1 and FW2 is always controlled by reflecting the steering angular velocity dθ / dt of the steering handle 11 by the driver. However, when a pulse output type sensor is used as the steering angle sensor 31, for example, when the driver gently turns the steering handle 11, the steering angle correction unit 53 appropriately calculates the steering angle sensor 31. The pulse may not be output. In this case, the steering angular velocity dθ / dt cannot be calculated accurately, and there is a possibility that the left and right front wheels FW1, FW2 cannot be appropriately steered. Hereinafter, a first modification of the third embodiment in consideration of this point will be described.

In the first modification, in addition to the steering control of the left and right front wheels FW1 and FW2 according to the steering angular velocity dθ / dt, in particular, when the absolute value of the steering angular velocity dθ / dt is small, the detected steering angle θ is set. The corresponding left and right front wheels FW1, FW2 are controlled to be steered. Specifically, in this first modification, the turning angle correction unit 53 calculates the current steering angle θ _n based on the number of pulses input from the pulse output type steering angle sensor 31. Then, the turning angle correction unit 53 calculates the steering angular velocity dθ _n / dt of the steering handle 11 by the driver using the calculated steering angle θ _n . If the absolute value of the calculated steering angular velocity dθ _n / dt is equal to or greater than a predetermined steering angular velocity S set in advance, the turning angle correction unit 53 follows the above equation 46 using the calculated steering angular velocity dθ _n / dt. Then, the control target turning angle δs _n is calculated. That is, in this case, since the steering handle 11 is rotated by the driver to some extent, the left and right front wheels FW1 and FW2 are steered according to the steering angular velocity dθ _n / dt.

On the other hand, if the absolute value of the calculated steering angular velocity dθ _n / dt is less than the predetermined steering angular velocity S set in advance, the turning angle correction unit 53 sets the control target turning angle δs _n according to the following equation 47. calculate.
δs _n = (θ _n −θc) / Gra1 + δsc Equation 47
However, θc in the equation 47 represents a steering angle when the absolute value of the steering angular velocity dθ _n / dt is less than the predetermined steering angular velocity S, and δsc represents a predetermined absolute value of the steering angular velocity dθ _n / dt. This represents the target turning angle for control when the steering angular velocity S is less than. Further, Gra1 in the equation 47 is a constant representing the steered gear ratio. According to this, in the state where the steering handle 11 is gently rotated by the driver, the control target turning angle δs _n is calculated depending on the change of the detected steering angle θ _n . Therefore, as long as the driver continues the turning operation of the steering wheel 11 gently, the target turning angle for control δs _n can be calculated appropriately. This is the case where the pulse output type steering angle sensor 31 is employed. Even so, the left and right front wheels FW1, FW2 can be appropriately steered.

By the way, in the first modified example, when the absolute value of the steering angular velocity dθ _n / dt is less than the predetermined steering angular velocity S, the steered gear ratio Gra1 is constant. In this case, in order to turn the left and right front wheels FW1 and FW2 to the target turning angle δd, the driver needs to turn the steering handle 11 more frequently. Therefore, the steered gear ratio Gra1 can be changed in accordance with the amount of rotation operation. Hereinafter, a second modification of the third embodiment will be described.

In the second modification, the steered gear ratio Gra1 in the equation 46 has characteristics as shown in FIG. More specifically, as shown in FIG. 18, the steered gear ratio Gra1 has a change characteristic that decreases as the absolute value of (θ _n −θc) increases. Thus, the transmission ratio can be changed to a large value by changing the steered gear ratio Gra1 to a small value, and the amount of turning operation of the steering handle 11 by the driver can be reduced. Therefore, in the second modification, in addition to the effects of the third embodiment and the first modification, it is possible to reduce the burden on the operation of the steering handle 11 by the driver.

d. Fourth Embodiment Next, a fourth embodiment of the present invention using a yaw rate instead of the lateral acceleration as the motion state quantity in the first to third embodiments will be described. In the fourth embodiment, as indicated by a broken line in FIG. 1, instead of the lateral acceleration sensor 34 in the first embodiment, a yaw rate sensor that detects an actual yaw rate γ that is a motion state quantity that can be perceived by the driver. 38. Other configurations are the same as those in the first embodiment, but the computer program executed by the electronic control unit 35 is slightly different from that in the first embodiment.

  In the fourth embodiment, a computer program executed by the electronic control unit 35 is shown by a functional block diagram of FIG. In this case, in the sensory adaptation control unit 70, the steered state determination unit 71 uses the detected steering angle θ and the detected vehicle speed V to determine whether the steering handle 11 is in the steered operation state, as in the first embodiment. Whether or not the steering operation state determination condition is different from the condition of the first embodiment. That is, the steering operation state determination condition in the fourth embodiment is that when the absolute value of the detected steering angle θ is equal to or greater than the predetermined steering angle θg, the detected vehicle speed V is equal to or greater than the predetermined vehicle speed Vc, and the steering This is a condition in which the state where the absolute value of the angular velocity dθ / dt is less than a preset predetermined value dθv continues for a predetermined time th.

  The steered state determination unit 71 supplies the detected steering angle θ to the displacement-torque conversion unit 72 that functions in the same manner as the displacement-torque conversion unit 42 of the first embodiment if it is in the normal operation state. If the steering operation state is maintained, the set steering steering angle θh and the detected steering angle θ are supplied. As a result, the displacement-torque converter 72 calculates the steering torque Td1 according to the above equations 1 to 3 when the detected steering angle θ is supplied, and the above equation when the steering steering angle θh and the detected steering angle θ are supplied. The steering torque Tdh is calculated according to 20-23.

In the fourth embodiment, a torque-yaw rate conversion unit 73 is provided instead of the torque-lateral acceleration conversion unit 43 of the first embodiment. This torque-yaw rate conversion unit 73 uses the steering torque Td1 calculated by the displacement-torque conversion unit 72 in the normal operation state to steer the expected yaw rate γd that the driver expects by turning the steering handle 11. If the absolute value of the torque Td1 is less than the positive predetermined value Tg, the following equation 48 is used. If the absolute value of the steering torque Td1 is greater than the positive predetermined value Tg, the following equation 49 is used. Here, Expression 47 is a linear function expression of the steering torque Td1 as in the first embodiment, and is a function in which the expected yaw rate γd becomes “0” when the steering torque Td1 is “0”. Further, Expression 48 is a power function of the steering torque Td1 as in the first embodiment, and is continuously connected to Expression 47 at a predetermined value Tg.
γd = a · Td1 (| Td | <Tg) Equation 47
γd = C · Td1 ^K2 (Tg ≦ | Td |) Equation 48

The torque-yaw rate conversion unit 73 uses the steering torque Tdh calculated by the displacement-torque conversion unit 72 in the steering operation state, and the driver expects the steering handle 11 to rotate by the steering operation in the steering operation state. The expected yaw rate γdh is calculated according to the following equation 49.
γdh = C ・ Tdh ^K2 … Formula 49

  However, a in Expression 47 is a constant representing the slope of the linear function, and C and K2 in Expressions 48 and 49 are constants as in the first embodiment. Further, the steering torque Td1 in the formulas 47 and 48 represents the absolute value of the steering torque Td1 calculated using the formula 3 (the formulas 1 and 2), and the calculated steering torque Td1 is If positive, the constants a and C are positive values, and if the calculated steering torque Td1 is negative, the constants a and C are negative and have the same absolute value as the positive constants a and C. Value.

  The steering torque Tdh in the equation 49 represents the absolute value of the steering torque Tdh calculated using the equation 23. If the calculated steering torque Tdh is positive, the constant C is a positive value. If the calculated steering torque Tdh 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, instead of calculating the equations 47 to 49, the expected yaw rates γd and γdh are calculated using a conversion table having characteristics as shown in FIG. 20 in which the expected yaw rates γd for the steering torques Td1 and Tdh are stored. You may make it do.

  Further, the turning angle conversion unit 74 calculates the target turning angles δd and δdh of the left and right front wheels FW1 and FW2 necessary for generating the expected yaw rates γd and γdh, and the vehicle speed V as shown in FIG. And a table representing the change characteristics of the target turning angles δd and δdh with respect to the expected yaw rates γd and γdh. 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 74 refers to this table and calculates the target turning angles δd and δdh corresponding to the input expected yaw rates γd and γdh and the detected vehicle speed V input from the vehicle speed sensor 33. The yaw rate γ (expected yaw rate γd, γdh) and target turning angles δd, δdh stored in the table are both positive, but the expected yaw rates γd, γdh supplied from the torque-yaw rate converting unit 73 are If it is negative, the output target turning angles δd and δdh are also negative.

Here, since the target turning angles δd and δdh are functions of the vehicle speed V and the yaw rate γ as shown in the following formulas 50 and 51, the calculation of the following formulas 50 and 51 is executed instead of referring to the table. Can also be calculated.
δd = L · (1 + A · V ² ) · γd / V Equation 50
δdh = δk + L · (1 + A · V ² ) · γdh / V (Formula 51)
However, L in the formulas 50 and 51 is a predetermined value indicating the wheel base, and A is a predetermined value indicating the motion performance of the vehicle. Further, δk in the equation 51 represents a target turning angle when the steering steering angle θh is calculated according to the equation 50.

Then, the calculated target turning angles δd and δdh are supplied to the turning angle correction unit 54 of the turning control unit 50. The turning angle correction unit 54 receives the expected yaw rate γd and γdh from the torque-yaw rate conversion unit 73 and also the actual yaw rate γ detected by the yaw rate sensor 38, and calculates the following formulas 52 and 53. The corrected target turning angles δda and δdha are calculated by correcting the input target turning angles δd and δdh.
δda = δd + K5 · (γd−γ) (Formula 52)
δdha = δdh + K5 · (γdh−γ) Equation 53

  However, the coefficient K5 is a predetermined positive constant, and when the actual yaw rate γ is less than the expected yaw rates γd and γdh, the coefficient K5 is corrected so that the absolute values of the corrected target turning angles δda and δdha are increased. . When the actual yaw rate γ exceeds the expected yaw rates γd, γdh, the absolute values of the corrected target turning angles δda, δdha are corrected. By this correction, the turning angle δ of the left and right front wheels FW1, FW2 necessary for the expected yaw rates γd, γdh is ensured with higher accuracy.

  The other program processing executed by the electronic control unit 35 is the same as that in the first embodiment. In the functional block diagram of FIG. 19, the same reference numerals as those in FIG. 2 of the first embodiment are given, and the description thereof is omitted.

  Also in the above-described fourth embodiment, when the steering state determination unit 71 determines that the steering handle 11 is in the normal operation state, the steering angle θ with respect to the steering handle 11 becomes the displacement-torque conversion unit 72. And the torque-yaw rate conversion unit 73 converts the estimated yaw rate γd. Based on the converted expected yaw rate γd, the turning angle conversion unit 74 uses the exponential function of the target turning angle δd for the vehicle to move at the expected lateral acceleration Gd with respect to the steering angle θ of the steering wheel 11. It can be calculated so as to change (non-linearly).

  Therefore, when the left and right front wheels FW1 and FW2 are steered to the target turning angle δd and the vehicle turns, this turn gives the driver an expected yaw rate as the “physical quantity of the given stimulus” according to the Weber-Hefner law. γd is given. Since the expected yaw rate γd changes exponentially with respect to the steering angle θ of the steering wheel 11, the driver perceives a lateral acceleration that matches human perception characteristics. While the steering wheel 11 can be operated. 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, the steered state determination unit 71 determines the steered steering angle θh as a virtual origin based on the establishment of the steered operation state determination condition, that is, if the steering handle 11 is gently rotated by the driver. Can be set to The torque-yaw rate conversion unit 73 calculates the expected yaw rate γdh with reference to the steering steering angle θh, and the turning angle conversion unit 74 can calculate the target turning angle δdh based on the expected yaw rate γdh, As a result, the transmission ratio can be reduced. Therefore, the driver can turn the vehicle very easily and in accordance with the perceptual characteristics even within the steering range where the steering angle θ of the steering handle 11 is large, and the driving of the vehicle becomes simple.

e. Fifth Embodiment Next, a fifth embodiment of the present invention using a turning curvature instead of the lateral acceleration as the motion state quantity in the first to third embodiments will be described. The fifth embodiment is also configured as shown in FIG. 1 as in the first embodiment. However, the computer program executed by the electronic control unit 35 is slightly different from the case of the first embodiment.

  In the fifth embodiment, the computer program executed by the electronic control unit 35 is shown by the functional block diagram of FIG. In this case, in the sensory adaptation control unit 80, the steered state determination unit 81 uses the detected steering angle θ and the detected vehicle speed V to determine whether the steering handle 11 is in the steered operation state, as in the first embodiment. Whether or not the steering operation state determination condition is different from the condition of the first embodiment. That is, the steering operation state determination condition in the fifth embodiment is that when the absolute value of the detected steering angle θ is equal to or greater than the predetermined steering angle θg, the detected vehicle speed V is equal to or greater than the predetermined vehicle speed Vc, and the steering This is a condition in which the state where the absolute value of the angular velocity (dθ / dt) · V is less than a predetermined value dθv set in advance continues for a predetermined time th.

  Then, the steered state determination unit 81 supplies the detected steering angle θ to the displacement-torque conversion unit 82 that functions in the same manner as the displacement-torque conversion unit 42 of the first embodiment in the normal operation state. If the steering operation state is maintained, the set steering steering angle θh and the detected steering angle θ are supplied. As a result, the displacement-torque converter 82 calculates the steering torque Td1 according to the above equations 1 to 3 when the detected steering angle θ is supplied, and the equation when the steering steering angle θh and the detected steering angle θ are supplied. The steering torque Tdh is calculated according to 20-23.

In the fifth embodiment, a torque-turning curvature conversion unit 83 is provided instead of the torque-lateral acceleration conversion unit 43 of the first embodiment. The torque-turning curvature conversion unit 83 uses the steering torque Td1 calculated by the displacement-torque conversion unit 82 in the normal operation state to calculate the expected turning curvature ρd that the driver expects by turning the steering handle 11. If the absolute value of the steering torque Td1 is less than the positive predetermined value Tg, the following formula 54 is used. If the absolute value of the steering torque Td1 is not less than the positive predetermined value Tg, the calculation is performed according to the following formula 55. Here, Expression 54 is a linear function expression of the steering torque Td1 as in the first embodiment, and is a function in which the expected yaw rate γd becomes “0” when the steering torque Td1 is “0”. Further, Expression 55 is a power function of the steering torque Td1 as in the first embodiment, and is continuously connected to Expression 54 at a predetermined value Tg.
ρd = a · Td1 (| Td | <Tg) Equation 54
ρd = C · Td1 ^K2 (Tg ≦ | Td |) Equation 55

Further, the torque-turning curvature conversion unit 83 uses the steering torque Tdh calculated by the displacement-torque conversion unit 82 in the steering operation state, and the driver expects the steering handle 11 to rotate in the steering operation state. The expected turning curvature ρdh is calculated according to the following formula 56.
ρdh = C ・ Tdh ^K2 … Formula 56

  However, a in the equation 54 is a constant representing the slope of the linear function, and C and K2 in the equations 55 and 56 are constants as in the first embodiment. The steering torque Td1 in the formulas 54 and 55 represents the absolute value of the steering torque Td1 calculated using the formula 3 (the formulas 1 and 2), and the calculated steering torque Td1 is If positive, the constants a and C are positive values, and if the calculated steering torque Td1 is negative, the constants a and C are negative and have the same absolute value as the positive constants a and C. Value.

  Further, the steering torque Tdh in the equation 56 represents the absolute value of the steering torque Tdh calculated using the equation 23. If the calculated steering torque Tdh is positive, the constant C is a positive value. If the calculated steering torque Tdh 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, instead of calculating the equations 54 to 56, the expected turning curvature ρd using a conversion table having characteristics as shown in FIG. 23 storing the expected turning curvatures ρd and ρdh with respect to the steering torques Td1 and Tdh. , Ρdh may be calculated.

  Further, the turning angle conversion unit 84 calculates the target turning angles δd and δdh of the left and right front wheels FW1 and FW2 necessary for generating the expected turning curvatures ρd and ρdh. As shown in FIG. There is a table that changes in accordance with V and represents the change characteristics of the target turning angles δd and δdh with respect to the expected turning curvatures ρd and ρdh. 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 84 refers to this table and calculates the target turning angles δd and δdh corresponding to the input expected turning curvatures ρd and ρdh and the detected vehicle speed V input from the vehicle speed sensor 33. Further, although the turning curvature ρ (expected turning curvature ρd, ρdh) and the target turning angles δd, δdh stored in the table are both positive, the expected turning curvature supplied from the torque-turning curvature converting unit 83 is used. If ρd and ρdh are negative, the output target turning angles δd and δdh are also negative.

Here, since the target turning angles δd and δdh are functions of the vehicle speed V and the turning curvature ρ as shown in the following equations 57 and 58, instead of referring to the table, the calculation of the following equations 57 and 58 is performed. It can also be calculated by execution.
δd = L · (1 + A · V ² ) · ρd Equation 57
δdh = δk + L · (1 + A · V ² ) · ρdh Equation 58
However, L in the formulas 57 and 58 is a predetermined value indicating the wheel base, and A is a predetermined value indicating the motion performance of the vehicle. Further, δk in the equation 58 represents a target turning angle when the steering steering angle θh is calculated according to the equation 57.

Then, the calculated target turning angles δd and δdh are supplied to the turning angle correction unit 55 of the turning control unit 50. The turning angle correction unit 55 receives the expected turning curvatures ρd and ρdh from the torque-turning curvature conversion unit 83 and also receives the actual turning curvature ρ from the turning curvature calculation unit 56. The turning curvature calculation unit 56 uses the lateral acceleration G detected by the lateral acceleration sensor 34, the yaw rate γ detected by the yaw rate sensor 38, and the vehicle speed V detected by the vehicle speed sensor 33, and the following equation 59 By executing this calculation, the actual turning curvature ρ is calculated and output to the turning angle correction unit 55.
ρ = G / V ² or ρ = γ / V Equation 59

Then, the turning angle correction unit 55 calculates the corrected target turning angles δda and δdha by correcting the input target turning angles δd and δdh by executing calculations of the following formulas 60 and 61.
δda = δd + K6 · (γd−γ) Equation 60
δdha = δdh + K6 · (γdh−γ) ... Formula 61
However, the coefficient K6 is a positive constant determined in advance, and when the actual turning curvature ρ is less than the expected turning curvatures ρd and ρdh, the correction target turning angles δda and δdha are corrected so that the absolute values become larger. Is done. Further, when the actual turning station rate ρ exceeds the expected turning curvatures ρd and ρdh, the absolute values of the corrected target turning angles δda and δdha are corrected. By this correction, the turning angles of the left and right front wheels FW1 and FW2 necessary for the expected turning curvatures ρd and ρdh are more accurately ensured.

  The other program processing executed by the electronic control unit 35 is the same as that in the first embodiment. And in the functional block diagram of FIG. 22, the same code | symbol as FIG. 2 of the said 1st Embodiment is attached | subjected, and the description is abbreviate | omitted.

  Also in the fifth embodiment described above, when the steered state determination unit 81 determines that the steering handle 11 is in the normal operation state, the steering angle θ with respect to the steering handle 11 is changed to the displacement-torque conversion unit 82. Then, the torque-yaw rate conversion unit 83 converts the predicted turning curvature ρd. Then, based on the converted expected turning curvature ρd, the turning angle conversion unit 84 uses the target turning angle δd for the vehicle to move with the expected turning curvature ρd as an index with respect to the steering angle θ of the steering handle 11. It can be calculated to change functionally (non-linearly).

  Therefore, when the left and right front wheels FW1 and FW2 are steered to the target turning angle δd and the vehicle turns, the turn makes the prospective turn as the “physical quantity of the given stimulus” according to the Weber-Hefner law. The curvature ρd is given. The expected turning curvature ρd changes exponentially (or exponentially) with respect to the steering angle θ of the steering handle 11, so that the driver perceives a turning curvature that matches human perception characteristics. While the steering wheel 11 can be operated. 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, the steered state determination unit 81 determines the steered steering angle θh as a virtual origin based on the establishment of the steered operation state determination condition, that is, if the steering handle 11 is gently rotated by the driver. Can be set to The torque-turning curvature conversion unit 83 calculates the expected turning curvature ρdh, and the turning angle conversion unit 84 calculates the target turning angle δdh based on the expected turning curvature ρdh, based on the steered steering angle θh. As a result, the transmission ratio can be reduced. Therefore, the driver can turn the vehicle very easily and in accordance with the perceptual characteristics even within the steering range where the steering angle θ of the steering handle 11 is large, and the driving of the vehicle becomes simple.

  Furthermore, in carrying out the present invention, the present invention is not limited to the first to fifth embodiments and the respective modifications, and various modifications can be made without departing from the object of the present invention.

  For example, in the first to fifth embodiments and the modified examples, 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.

  In the first to fifth embodiments and the modifications, 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.

  Further, in the first to fifth embodiments, the lateral acceleration, the yaw rate, and the turning curvature are each independently used as the motion state quantity of the vehicle that can be perceived by a human. However, the vehicle steering control may be performed by switching the amount of motion state of these vehicles by a selection operation by the driver or by automatically switching according to the traveling state of the vehicle. When switching automatically according to the running state of the vehicle, for example, the turning curvature is used as the motion state quantity when the vehicle is running at low speed, the yaw rate is used as the motion state quantity when the vehicle is running at medium speed, and the vehicle is running at high speed. Sometimes, lateral acceleration is used as the motion state quantity. According to this, appropriate steering control of the vehicle is performed according to the running state of the vehicle, and the driving of the vehicle becomes easier.

1 is a schematic view of a vehicle steering apparatus common to first to fifth embodiments of the present invention. FIG. 2 is a functional block diagram functionally representing computer program processing executed by the electronic control unit of FIG. 1 according to the first embodiment of the present invention. It is a graph which shows the change with respect to the steering angle of correction coefficient KRs0. It is a graph which shows the relationship between the steering angle and steering torque in a normal operation state. It is a graph which shows the relationship between the steering torque in a normal operation state, 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 showing the relationship between the steering angle in a normal operation state, and a target turning angle. 5 is a graph showing a change characteristic of a variable F for determining a steering torque in a steering holding operation state. It is a graph which shows the relationship between the steering angle and steering torque in a steering maintenance operation state. It is a graph which shows the relationship between the steering torque in a steering maintenance operation state, and estimated lateral acceleration. It is a graph showing the relationship between the steering angle and target turning angle in a steering maintenance operation state. FIG. 9 is a functional block diagram functionally representing computer program processing executed by the electronic control unit of FIG. 1 according to the second embodiment of the present invention. It is a graph which concerns on 2nd Embodiment and shows the relationship between the steering angle and steering torque in a steering maintenance operation state. It is a graph which concerns on 2nd Embodiment and shows the relationship between the steering torque in a steering maintenance operation state, and estimated lateral acceleration. It is a graph which concerns on 2nd Embodiment and represents the relationship between the steering angle in a steering maintenance operation state, and a target turning angle. FIG. 10 is a functional block diagram functionally representing computer program processing executed by the electronic control unit of FIG. 1 according to the third embodiment of the present invention. It is a graph which shows the relationship between a steering angular velocity and a steering gear ratio. It is a graph which shows the relationship between a steering angle change and a steering gear ratio. FIG. 10 is a functional block diagram functionally representing computer program processing executed by the electronic control unit of FIG. 1 according to a fourth embodiment of the present invention. 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. FIG. 10 is a functional block diagram functionally representing computer program processing executed by the electronic control unit of FIG. 1 according to a fifth embodiment of the present invention. 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.

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 ... Vehicle speed sensor, 34 ... Lateral acceleration sensor, 35 ... Electronic control unit, 38 ... Steering torque sensor, 39 ... Yaw rate sensor, 40 ... Sensory adaptation control unit, 41, 71, 81 ... Steering state determination unit, 42, 72, DESCRIPTION OF SYMBOLS 82 ... Displacement-torque conversion part, 43 ... Torque-lateral acceleration conversion part, 44, 74, 84 ... Steering angle conversion part, 73 ... Torque-yaw rate conversion part, 83 ... Torque-turning curvature conversion part, 50 ... Steering Control part, 51, 53, 54, 55 ... Steering angle correction part, 60 ... Reaction force control part, 61 ... Steering state determination part, 62 ... Displacement-torque conversion part

Claims (12)

A steering handle operated by a driver to steer the vehicle, a steering actuator for steering the steered wheel, and the steered wheel by driving the steered actuator according to the operation of the steering handle In a steering-by-wire vehicle steering apparatus provided with a steering control apparatus that performs steering control automatically, the steering control apparatus includes:
An operation input value detecting means for detecting an operation input value of a driver for the steering wheel;
Based on the detected change amount of the operation input value, a normal operation state indicating the operation state of the steering handle having a large change amount, and a steering operation state indicating the operation state of the steering handle having a small change amount, An operation state determination means for determining
When it is determined that the operation state of the steering wheel is the steering holding operation state, a transmission ratio indicating a ratio of a change amount of the turning angle of the steered wheel with respect to a change amount of the operation input value is the normal operation state. Turning angle calculation means for calculating a target turning angle using the detected operation input value so as to be smaller than the time,
A steering control unit configured to control the steering actuator according to the calculated target turning angle and to turn the steered wheel to the calculated target turning angle ;
The turning angle calculation means is
When it is determined by the operation state determination means that the steering handle is in a normal operation state, a predetermined non-linear relationship is established with the detected operation input value using the detection reference point for detecting the operation input value as an origin. A target turning angle in a certain normal operation state is calculated, and when the operation state determination unit determines that the steering handle is in the holding operation state, an operation input value when the steering operation state is determined is calculated. Calculate the target turning angle of the steering operation state that has a predetermined nonlinear relationship with the detected operation input value as a virtual origin,
The steering control means is
A steering-by-wire vehicle steering apparatus, wherein the steering actuator is controlled in accordance with the calculated target turning angle to turn the steered wheels to the calculated target turning angle . The steering apparatus for a steering-by-wire vehicle according to claim 1,
The operation state determination means includes
If the time differential value of the detected operation input value is greater than or equal to a predetermined value set in advance, it is determined that the operation state of the steering wheel is a normal operation state, and if the time differential value is less than the predetermined value. A steering-by-wire vehicle steering apparatus that determines that an operation state of the steering wheel is a steering holding operation state. In the steering device for a steering-by-wire vehicle according to claim 2,
The steering control device further includes:
Vehicle speed detecting means for detecting the vehicle speed of the vehicle,
The operation state determination means includes
If the detected vehicle speed is equal to or higher than a predetermined vehicle speed and the time differential value is less than the predetermined value, it is determined that the operation state of the steering wheel is a steering operation state. Type vehicle steering device. A steering handle operated by a driver to steer the vehicle, a steering actuator for steering the steered wheel, and the steered wheel by driving the steered actuator according to the operation of the steering handle In a steering-by-wire vehicle steering apparatus provided with a steering control apparatus that performs steering control automatically, the steering control apparatus includes:
An operation input value detecting means for detecting an operation input value of a driver for the steering wheel;
Based on the detected change amount of the operation input value, a normal operation state indicating the operation state of the steering handle having a large change amount, and a steering operation state indicating the operation state of the steering handle having a small change amount, An operation state determination means for determining
When it is determined that the operation state of the steering wheel is the steering holding operation state, a transmission ratio indicating a ratio of a change amount of the turning angle of the steered wheel with respect to a change amount of the operation input value is the normal operation state. Turning angle calculation means for calculating a target turning angle using the detected operation input value so as to be smaller than the time,
A steering control unit configured to control the steering actuator according to the calculated target turning angle and to turn the steered wheel to the calculated target turning angle;
The operation state determination means includes
A steering-by-wire vehicle steering apparatus, wherein an operation state of the steering wheel is determined when the transmission ratio in a normal operation state of the steering wheel is larger than a predetermined transmission ratio. A steering handle operated by a driver to steer the vehicle, a steering actuator for steering the steered wheels, and driving the steered actuators in response to the operation of the steering handle to make the steered wheels nonlinear In a steering-by-wire vehicle steering apparatus provided with a steering control apparatus that performs steering control automatically, the steering control apparatus includes:
An operation input value detecting means for detecting an operation input value of a driver for the steering wheel;
A transmission ratio changing means for changing a transmission ratio representing a ratio of a change amount of the turning angle of the steered wheel to a change amount of the detected operation input value based on a time differential value of the detected operation input value;
A turning angle calculation means for calculating a target turning angle having a predetermined nonlinear relationship with the detected operation input value using the detected operation input value and the changed transmission ratio;
Steering-by-wire comprising steering control means for controlling the steering actuator in accordance with the calculated target turning angle and turning the steered wheels to the calculated target turning angle. Type vehicle steering device. The transmission ratio changing means is
The steering-by-wire vehicle according to claim 5 , wherein when the time differential value of the detected operation input value is smaller than a predetermined value, the transmission ratio is changed based on a change amount of the detected operation input value. Steering device. The transmission ratio changing means is
When the operation of the steering wheel is continued in a state where the time differential value of the detected operation input value is smaller than a predetermined value, the transmission ratio is set according to the amount of change in the detected operation input value. The steering apparatus for a steering-by-wire vehicle according to claim 6 , wherein the steering apparatus is changed to a large value. Wherein the predetermined non-linear relationship, vehicle steering apparatus of a steer-by-wire system according to claim 1 or claim 5 which is a predetermined exponential relationship between the detected operation input value by the operation input value detecting means. The steering device for a steering-by-wire vehicle according to claim 8 ,
The turning angle calculation means includes
A vehicle motion state quantity that can be perceived by the driver in relation to the turning of the vehicle, and a predicted motion state quantity of the vehicle having a predetermined exponent relationship with the detected operation input value. A steering-by-wire vehicle steering apparatus characterized in that the target turning angle is calculated using a predicted motion state quantity calculated using the value. In the steering device for a steering-by-wire vehicle according to claim 9 ,
The predicted motion state quantity is a steering-by-wire vehicle steering apparatus that is one of a lateral acceleration, a yaw rate, and a turning curvature of the vehicle. The steering device for a steering-by-wire vehicle according to claim 8 ,
The operation input value detection means,
A displacement amount detecting means for detecting a displacement amount of the steering wheel;
A steering-by-wire vehicle steering apparatus comprising: an operation force converting means for converting the detected displacement amount into an operation force applied to the steering handle. The steering-by-wire vehicle steering apparatus according to any one of claims 1 to 11 , 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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