JP5293144B2 - Vehicle steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device for a vehicle, capable of performing a reaction force control reflecting a road surface state, while maintaining steering feeling in an excellent state. <P>SOLUTION: In a target yaw rate setting part 40 included in a control device 20 of this steering device, target torque Th* is calculated based on gain G set by relating to a deviation &Delta;&gamma; subtracted with a yaw rate detection value &gamma; from a yaw rate target value &gamma;* so that the rate of a current component made to flow to an actuator 2 for steering contributed to a calculation of the target torque Th* or the target value Im* component may be increased as the deviation &Delta;&gamma;is increased. As a result, when a vehicle is in an under steering state, a reaction force torque for making a driver exactly recognize a low &mu; road without deteriorating steering feeling can be imparted. When the vehicle is in an over steering state, the reaction force torque as a guidance torque for urging the driver to perform a counter operation can be imparted. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a vehicle steering apparatus such as a steer-by-wire system in which mechanical coupling between a steering wheel and a steering mechanism is eliminated.

  In recent years, as a vehicle steering device, the mechanical coupling between the steering wheel and the steering mechanism is eliminated, the steering wheel operating angle is detected by a sensor, and the steering actuator controlled according to the output of the sensor is driven. A steer-by-wire system has been proposed in which force is transmitted to the steering mechanism. In such a steer-by-wire system, the ratio of the steering angle of the steering wheel to the operation angle of the steering wheel (steering angle ratio) can be freely determined.

  In such a steer-by-wire system, a reaction force actuator for applying an operation reaction force to the steering wheel is provided. This reaction force actuator is controlled according to the operating angle of the steering wheel and the vehicle speed. As a result, an operation reaction force similar to that of a conventional vehicle steering apparatus in which the steering wheel and the steering mechanism are mechanically coupled is applied to the steering wheel. In this way, a bilateral servo system is configured that returns the external force applied to the steering mechanism side to the steering wheel.

  However, the reaction force by the reaction force actuator controlled to be generated according to the operation angle of the steering wheel may be different from the operation reaction force in the conventional vehicle steering apparatus generated by friction between the wheels and the road surface. . In this case, the driver feels uncomfortable.

Therefore, conventionally, there is a vehicle steering apparatus that obtains an operation reaction force corresponding to the friction in accordance with a change in behavior in the lateral direction of the vehicle based on an actual yaw rate or a differential value thereof (see, for example, Patent Document 1). In addition, there is a vehicle steering apparatus that performs control so that the operation reaction force increases as the deviation between the standard yaw rate and the actual yaw rate increases in response to the change in friction caused by the change in the tire grip state (for example, Patent Document 2). See).
JP 2003-11838 A JP 2006-264392 A

  However, in the configuration described in Patent Document 1 and Patent Document 2, that is, the configuration in which the magnitude of the operation reaction force is controlled according to the vehicle behavior such as the yaw rate, the force applied to the steering mechanism side from the road surface is accurately determined. There is a problem that it cannot return (reproduce) to the steering wheel.

  In this respect, since the current (hereinafter referred to as “steering current”) that flows to the motor that drives the steering mechanism corresponds to the external force from the road surface, the magnitude of the reaction force is controlled according to the steering current. For example, a reaction force according to the road surface condition should be generated. However, this steering current contains many components other than external force from the road surface such as noise components and vibration components. Therefore, if the magnitude of the reaction force is always controlled according to the steering current, the steering feeling will be worsened. End up.

  Therefore, the present invention has an object to provide a vehicle steering apparatus capable of performing reaction force control in which an external force applied from the road surface to the steering mechanism side is reflected according to the road surface condition while maintaining a good steering feeling. And

A first aspect of the present invention is a vehicle steering apparatus that generates a reaction force against an operation of an operation member operated by a driver,
Yaw rate detection means for detecting the yaw rate of the vehicle;
Target yaw rate calculating means for calculating the yaw rate target value of the vehicle;
A steering actuator for changing the turning angle of the vehicle;
Steering drive control means for calculating a current target value for driving the steering actuator based on the operation amount of the operating member, and for causing a current to flow to the steering actuator based on the calculated current target value;
A reaction force actuator for generating the reaction force;
A torque target value for driving the reaction force actuator is calculated based on the current passed through the steering actuator or the current target value, and the reaction force drive is used to drive the reaction force actuator based on the torque target value. Control means;
With
The reaction force drive control means uses T as a target torque value corresponding to the torque target value, and is proportional to a component proportional to the manipulated variable, a component proportional to the yaw rate detection value, and a differential value of the yaw rate detection value. A torque value corresponding to a vehicle behavior component indicating the behavior of the vehicle including any one or more of the components is Ta, and a torque value corresponding to the current flowing to the steering actuator or the current target value is Tb, The gain that determines the ratio that contributes to the calculation of the torque target value is G (where G is a real number between −1 and 1), and the gain G is calculated from the yaw rate target value calculated by the target yaw rate calculation means. When the difference obtained by subtracting the yaw rate detection value detected by the yaw rate detection means becomes greater than zero, it becomes positive and the difference becomes larger. The target torque value T that satisfies T = (1−G) · Ta + (1 + G) · Tb is set so that the difference becomes smaller when the difference becomes smaller than zero and becomes smaller as the difference becomes smaller. It is characterized by calculating | requiring .

According to the first aspect of the present invention, as the difference between the yaw rate target value calculated by the target yaw rate calculation means and the detected yaw rate increases, the current component that flows to the steering actuator that contributes to the calculation of the torque target value or Since the torque target value is calculated in association with the difference so that the ratio of the current target value component becomes large, the vehicle becomes under steered as the difference becomes larger (as the yaw rate target value becomes larger than the yaw rate detection value). Therefore, in this state, it is possible to give a reaction force torque that allows the driver to accurately recognize that the road is a low μ road without deteriorating the steering feeling in accordance with the current.
According to the first aspect of the invention, the torque target value is calculated so that the proportion of the vehicle behavior component contributing to the calculation of the torque target value increases as the difference is negative and decreases. Since the vehicle is in an oversteer state as the value becomes larger than the yaw rate target value, a reaction force torque can be applied as a guidance torque that prompts the driver to perform a counter operation in this state.
Furthermore, according to the first aspect of the present invention, the reaction torque as described above can be given to the driver with a simple configuration, and for example, if various parameters are set (tuned) on the dry road surface, the reaction torque can be reduced. Since it is not necessary to newly perform tuning on the μ road from the beginning and it is not necessary to set a new reaction torque component for the low μ road, the number of tuning steps on the low μ road can be greatly reduced.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram for explaining the configuration of a vehicle steering apparatus according to an embodiment of the present invention. FIG. 1 shows the configuration of a steer-by-wire system as a vehicle steering apparatus. The vehicle steering apparatus includes a steering wheel 1 as an operation member that a driver operates for steering, a steering actuator 2 that is driven according to a rotation operation of the steering wheel 1, and driving of the steering actuator 2. And a steering gear 3 that transmits force to the front left and right wheels 4 as steering wheels.

  There is no mechanical connection between the steering wheel 1 and the steering mechanism 5 including the steering actuator 2 and the like, so that the operating torque applied to the steering wheel 1 is transmitted to the steering mechanism 5. The wheel 4 is steered when the steering actuator 2 is driven and controlled according to the (operation angle or operation torque).

  The steering actuator 2 is constituted by an electric motor such as a brushless motor, for example. The steering gear 3 has a motion conversion mechanism that converts the rotational motion of the output shaft of the steering actuator 2 into linear motion of the steering rod 7 (linear motion in the vehicle left-right direction). The movement of the steering rod 7 is transmitted to the wheel 4 via the tie rod 8 and the knuckle arm 9, and the turning angle of the wheel 4 changes. The steering gear 3 may have any other known configuration as long as it can transmit the movement of the steering actuator 2 to the wheels 4 so that the turning angle changes. Further, in a state where the steering actuator 2 is not driven, the wheel alignment is set so that the wheel 4 is returned to the straight steering position by the self-aligning torque.

  The steering wheel 1 is connected to a rotating shaft 10 that is rotatably supported on the vehicle body side. The rotary shaft 10 is provided with a reaction force actuator 19 formed of an electric motor such as a brushless motor having an output shaft integrated therewith. The reaction force actuator 19 applies a reaction force torque Th to the rotary shaft 10. The reaction force actuator 19 may have any other known configuration as long as it generates a reaction force torque acting on the steering wheel 1.

  The rotary shaft 10 is provided with an angle sensor 11 that detects an operation angle (rotation angle) δh of the steering wheel 1. In addition, the vehicle steering apparatus is provided with a steering angle sensor 13 for detecting a steering angle (steering angle of the steering mechanism 5) δ of the vehicle. The steering angle sensor 13 includes a potentiometer that detects the operation amount of the steering rod 7 corresponding to the steering angle. Further, the vehicle steering apparatus is provided with a vehicle speed sensor 14 for detecting the vehicle speed V and a yaw rate sensor 15 for detecting the yaw rate γ of the vehicle.

  These angle sensor 11, rudder angle sensor 13, vehicle speed sensor 14, and yaw rate sensor 15 are respectively connected to a control device 20 constituted by a microcomputer. The control device 20 controls the steering actuator 2 and the reaction force actuator 19 via drive circuits 22 and 23 that typically include a bridge circuit composed of a plurality of MOSFETs and a PWM modulator.

  FIG. 2 is a block diagram showing a functional configuration of the control device provided in the vehicle steering device. As shown in FIG. 2, this control device has a target torque setting unit 30, a reaction force control unit 34, a target yaw rate setting unit 40, and a target turning angle setting unit 50 as functions realized by software processing. The steering control unit 54 and the subtracters 42 and 52 are provided.

The target turning angle setting unit 50 sets a target turning angle δ ^* corresponding to the operation angle δh of the steering wheel 1 detected by the angle sensor 11. The target turning angle δ ^* may be set according to the operation angle δh and the vehicle speed V (for example, by using a predetermined transfer function Kδ (V)).

The subtractor 52 obtains a deviation Δδ between the target turning angle δ ^* set by the target turning angle setting unit 50 and the steering angle δ detected by the steering angle sensor 13, and uses the deviation Δδ as a turning control unit. 54.

The turning control unit 54 calculates a target turning current Im ^* such that the deviation Δδ (= δ ^* −δ) becomes zero, and is calculated so that the target turning current Im ^* flows through the steering actuator 2. The steered command value Ds is given to the drive circuit 22. That is, a current flowing through the steering actuator 2 that is a motor is detected by a current sensor (not shown), and the turning control unit 54 performs a calculation such as a proportional integration calculation based on a deviation between the detected current value and the target turning current Im ^*. To calculate the steering command value Ds and give it to the drive circuit 22. The drive circuit 22 drives the steering actuator 2 in accordance with the steering command value Ds. As a result, the turning angle δ of the steering mechanism 5 is brought close to the target turning angle δ ^* .

The target yaw rate setting unit 40 obtains a target yaw rate γ ^* as a vehicle behavior target value based on the operation angle δh and the vehicle speed V. Specifically, the target yaw rate setting unit 40 determines whether the vehicle travels based on the operation angle δh and the vehicle speed V, and a stability factor that is a function of the wheel base, the steering gear ratio, and the vehicle speed. A target yaw rate γ ^* , which is a yaw rate that can improve stability, is determined. The target yaw rate setting unit 42 may determine the target yaw rate γ ^* using detected values of acceleration in the longitudinal direction and the lateral direction of the vehicle output from an acceleration sensor (not shown). Since many examples of such target yaw rate calculation methods (calculation formulas) are well known, detailed description thereof is omitted here.

The target torque setting unit 30 includes an operation angle δh detected by the angle sensor 11, a vehicle speed V detected by the vehicle speed sensor 14, a vehicle yaw rate γ detected by the yaw rate sensor 15, and the target yaw rate setting unit 40. Based on the desired target yaw rate γ ^* and the target turning current Im ^* calculated by the turning control unit 54, the target torque Th ^* to be generated by the reaction force actuator 19 is set. Unlike the conventional case, the target torque Th ^* is calculated as an appropriate value so that the driver can be informed of the vehicle behavior, the road surface condition, and the like appropriately according to the driving condition and the road surface condition. This calculation method will be described in detail later. As long as the yaw rate γ of the vehicle can be detected, for example, the yaw rate sensor 15 may be omitted, and the yaw rate γ of the vehicle may be calculated based on the detection value of the lateral G sensor or the like.

The reaction force control unit 34 calculates a target motor current corresponding to the target torque Th ^* set by the target torque setting unit 30, and the reaction force command calculated so that the target motor current flows through the reaction force actuator 19. The value Dr is given to the drive circuit 22. That is, the current flowing through the reaction force actuator 19 that is a motor is detected by a current sensor (not shown), and the reaction force control unit 34 performs a calculation such as a proportional integration calculation based on a deviation between the detected current value and the target motor current. A reaction force command value Dr is calculated and applied to the drive circuit 23. The drive circuit 23 drives the reaction force actuator 19 according to the reaction force command value Dr. As a result, the reaction force torque Th applied to the rotary shaft 10 by the reaction force actuator 19 is brought close to the target torque Th ^* .

  Thus, the reaction force actuator 19 operates so as to apply a reaction force torque Th corresponding to the operation angle δh and the vehicle speed V to the steering wheel 1. As a result, a bilateral servo system that returns an external force applied to the steering mechanism 5 to the steering wheel 1 is configured. Next, the configuration of the target torque setting unit 30 will be described in detail with reference to FIG.

  FIG. 3 is a block diagram showing a detailed configuration of the target torque setting unit. As shown in FIG. 3, the target torque setting unit 30 includes an operation angle proportional component calculation unit 61, a yaw rate proportional component calculation unit 62, a yaw rate differential component calculation unit 63, a steering current proportional component calculation unit 64, A differentiator 65, adders 66 and 67, a vehicle behavior gain setting unit 68, a steering current gain setting unit 69, and a gain setting unit 70 are provided.

The operation angle proportional component calculation unit 61 is an operation angle that is a torque component proportional to the operation angle in the target torque Th ^* based on the operation angle δh detected by the angle sensor 11 and the vehicle speed V detected by the vehicle speed sensor 14. A proportional component Tθ is calculated. Specifically, the operation angle proportional component Tθ is calculated by multiplying the operation angle δh by a proportional coefficient K1 (V) determined in advance as a function of the vehicle speed. The proportionality coefficient K1 (V) is typically determined so as to increase as the vehicle speed increases.

The yaw rate proportional component calculation unit 62 multiplies the vehicle yaw rate γ detected by the yaw rate sensor 15 by a predetermined proportionality coefficient K2, thereby obtaining a yaw rate proportional component that is a torque component proportional to the yaw rate in the target torque Th ^* . Tγ is calculated.

The differentiator 65 calculates the yaw rate differential value γ ′ by differentiating the yaw rate γ detected by the yaw rate sensor 15. The yaw rate differential component calculation unit 63 multiplies the yaw rate differential value γ ′ calculated by the differentiator 65 by a predetermined proportionality coefficient K3 to obtain a torque component proportional to the yaw rate differential value in the target torque Th ^* . A certain yaw rate differential component Tγ ′ is calculated.

The turning current proportional component calculation unit 64 is proportional to the turning current at the target torque Th ^* by multiplying the target turning current Im ^* calculated by the turning control unit 54 by a predetermined proportionality coefficient K4. A steering current component Tb that is a torque component to be calculated is calculated. The steered current proportional component calculation unit 64 replaces the target steered current Im ^* with a steered current detected by a current sensor (not shown) provided in the steering actuator 2 (actually passed to the motor). May be used.

The adder 66 includes an operation angle proportional component Tθ calculated by the operation angle proportional component calculation unit 61, a yaw rate proportional component Tγ calculated by the yaw rate proportional component calculation unit 62, and a yaw rate calculated by the yaw rate differential component calculation unit 63. The differential component Tγ ′ is added and given to the vehicle behavior gain setting unit 68 as a vehicle behavior component Ta that is a torque component corresponding to the behavior of the vehicle at the target torque Th ^* .

The vehicle behavior gain setting unit 68 calculates a value obtained by multiplying the vehicle behavior component Ta given from the adder 66 by (1−G), and gives it to the adder 67. This G is a gain set by a gain setting unit 70 described later. Further, the turning current gain setting unit 69 uses this gain G to calculate and add a value obtained by multiplying the turning current component Tb calculated by the turning current proportional component calculation unit 64 by (1 + G). This is given to the device 67. The adder 67 adds the value given from the vehicle behavior gain setting unit 68 and the value given from the steering current gain setting unit 69, and outputs the result as the target torque Th ^* . That is, based on these, the target torque Th ^* is calculated as in the following equation (1). However, G is a real number that satisfies −1 ≦ G ≦ 1.
Th ^* = (1-G) .Ta + (1 + G) .Tb (1)

The gain setting unit 70 calculates the gain G used in the above equation (1) based on the deviation Δγ (= γ ^* −γ) calculated by the subtractor 42. As shown in FIG. 4, G is in the range of −1 ≦ G ≦ 1, and as Δγ becomes larger than zero, G becomes a positive value and becomes larger, and Δγ is larger than zero. It is determined that G becomes a negative value and decreases as the value decreases. That is, when Δγ is zero, G becomes zero, and the contribution ratios of the vehicle behavior component Ta and the steering current component Tb in the equation (1) for calculating the target torque Th ^* are equal, and Δγ is zero. The contribution ratio of the steering current component Tb increases as the ratio increases (the contribution ratio of the vehicle behavior component Ta decreases simultaneously), and the contribution ratio of the vehicle behavior component Ta increases as Δγ decreases from zero.

By setting the gain G in this way, it is possible to calculate the target torque Th ^* that can appropriately notify the driver of the vehicle behavior, the road surface condition, and the like according to the traveling state and the road surface condition. This will be described in detail below. Generally, when the yaw rate deviation Δγ is large, the vehicle behavior is greatly deviated from the target stable vehicle behavior. Specifically, when Δγ (= γ ^* −γ) is positive, the vehicle is in an understeer state, and when Δγ is negative, it is an oversteer state.

First, when the vehicle is in an understeer state, the gain G is set so as to increase as Δγ increases as described above. Therefore, the ratio of the steering current component Tb that allows the driver to accurately recognize the road surface condition is as follows. The ratio increases and the proportion of the vehicle behavior component Ta decreases. As a result, the target torque Th ^* allows the driver to accurately recognize the road surface condition, but on the other hand, as described above, the noise component or vibration component that is included in the steering current in a large amount is included in the driver. Is given as torque. However, when the vehicle is in an understeer state, this is a case where the road friction μ is small. Therefore, the steering current value is also small, and the target torque Th ^* is also small as a whole from the above equation (1). ing. As a result, the steering feeling is not deteriorated by suppressing the influence of the noise component and the vibration component, and the driver feels that the road friction μ is small because the reaction force is small. can do.

Further, when the vehicle is in an oversteer state, the gain G is set to be small as described above, so the ratio of the steering current component Tb is small. As a result, the target torque Th ^* does not cause the driver to accurately recognize the road surface condition, but since the ratio of the vehicle behavior component Ta increases, the target torque Th ^* increases as a whole from the above equation (1). . As a result, the reaction force increases and the driver is prompted to perform a counter operation on the steering wheel 1. That is, the target torque Th ^* is given as guidance torque that prompts the driver to perform a counter operation. Therefore, the vehicle is prevented from spinning and the vehicle is stabilized.

As described above, according to the vehicle steering apparatus of the present embodiment, the deviation Δγ between the yaw rate target value γ ^* calculated by the target yaw rate setting unit 40 functioning as the target yaw rate calculation means and the yaw rate detection value γ is large. The above formula is based on the gain G set in association with the deviation Δγ so that the ratio of the current component flowing through the steering actuator 2 that contributes to the calculation of the target torque Th ^* or the target value Im ^* component increases. The target torque Th ^* is calculated by (1). As a result, when the vehicle is in an understeer state, it is possible to give a reaction force torque that allows the driver to accurately recognize that the road is a low μ road without deteriorating the steering feeling.

  In addition, when the vehicle is in an oversteer state, the vehicle steering apparatus has a higher proportion of the vehicle behavior component Ta than the above equation (1). Force torque can be applied.

  Further, the vehicle steering apparatus needs to newly perform tuning on the low μ road from the beginning if various parameters (for example, the proportional coefficients K1 to K4) are appropriately set (tuned) on the dry road surface. In addition, since it is not necessary to set a new reaction torque component for the low μ road, the number of tuning steps on the low μ road can be greatly reduced.

In addition, this invention can be implemented with various forms other than the case of the said one Embodiment. For example, although the operation angle δh is used in the above embodiment, instead of this, a variable indicating the steering state, for example, an operation torque by an operator detected by a torque sensor (not shown) is used, and the target rotation is based on this operation torque. The configuration may be such that the steering angle δ ^* and the target yaw rate γ ^* are obtained.

  Further, in the above embodiment, the steer-by-wire system has been described as an example, but the same control in the present invention is performed by inserting a gear device between the steering wheel and the steering wheel, and operating and turning angles. The present invention can also be applied to a variable gear ratio type steering device in which the above relationship is variable. In this configuration, the steering wheel and the steering wheel are mechanically coupled to each other via the variable transmission ratio unit. In addition, the present invention can be implemented by making various design changes.

It is the schematic which shows the structure of the steering apparatus for vehicles which concerns on one Embodiment of this invention with the vehicle structure relevant to it. It is a block diagram which shows the functional structure of the control apparatus with which the vehicle steering device which concerns on the said embodiment is equipped. It is a block diagram which shows the detailed structure of the target torque setting part in the said embodiment. It is a figure which shows the relationship between the yaw rate deviation (DELTA) gamma and the gain G in the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 5 ... Steering mechanism, 10 ... Rotating shaft, Th ^* ... Target torque, Im ^* ... Target steering current, γ ... Actual yaw rate, γ ^* ... Target yaw rate, Δγ ... Yaw rate deviation, δ ... Steering angle, δh: Operating angle, V: Vehicle speed, G: Gain

Claims (1)

A vehicle steering apparatus that generates a reaction force against an operation of an operation member operated by a driver,
Yaw rate detection means for detecting the yaw rate of the vehicle;
Target yaw rate calculating means for calculating the yaw rate target value of the vehicle;
A steering actuator for changing the turning angle of the vehicle;
Steering drive control means for calculating a current target value for driving the steering actuator based on the operation amount of the operating member, and for causing a current to flow to the steering actuator based on the calculated current target value;
A reaction force actuator for generating the reaction force;
A torque target value for driving the reaction force actuator is calculated based on the current passed through the steering actuator or the current target value, and the reaction force drive is used to drive the reaction force actuator based on the torque target value. Control means;
With
The reaction force drive control means uses T as a target torque value corresponding to the torque target value, and is proportional to a component proportional to the manipulated variable, a component proportional to the yaw rate detection value, and a differential value of the yaw rate detection value. A torque value corresponding to a vehicle behavior component indicating the behavior of the vehicle including any one or more of the components is Ta, and a torque value corresponding to the current flowing to the steering actuator or the current target value is Tb, The gain that determines the ratio that contributes to the calculation of the torque target value is G (where G is a real number between −1 and 1), and the gain G is calculated from the yaw rate target value calculated by the target yaw rate calculation means. When the difference obtained by subtracting the yaw rate detection value detected by the yaw rate detection means becomes greater than zero, it becomes positive and the difference becomes larger. The target torque value T that satisfies T = (1−G) · Ta + (1 + G) · Tb is set so that the difference becomes smaller when the difference becomes smaller than zero and becomes smaller as the difference becomes smaller. A vehicle steering apparatus, characterized in that:

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