JP2000025630A - Vehicular steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the irregular behavior of a vehicle caused by the external disturbance of a lateral wind without requiring a driver's possitive steering by acting an auxiliary reaction torque to the direction restraining a vehicular behavoir to a running wheel regardless of the existence/absence of a driver's steering. SOLUTION: The auxiliary reaction torques T1, T2, T3 for respective components are found out, by making each of a steering angular velosity ω, lateral acceleration G and yaw rate γ to an address, from respective data tables set per a car speed V (S21-23) and they are added (S24). Further, the auxiliary reaction torque more than needed is removed (S25) and a target auxiliary reaction torque decision value TA is decided. Thereby, when the yaw rate γ or lateral acceleration G are generated to the vehicle by the external disturbance such as the lateral wind, a front wheel is steered automatically so as to always running the vehicle straightly for the external disturbance and the irregular behavoir can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system,
More specifically, the present invention relates to a steering device in which a steering torque for turning in a direction for suppressing the vehicle body behavior in accordance with the vehicle body behavior of the vehicle is applied to a steering wheel.

[0002]

2. Description of the Related Art Conventionally, for example, the one described in Japanese Patent Publication No. 50-35884 is known. This relates to an electric booster, and the output of the motor for assisting the steering torque is increased or decreased by changing the amplification of the detection signal of the steering torque by human power according to the detection signal such as the vehicle speed or road condition, so that the optimum steering is always performed. The torque is obtained. That is,
When the steering handle is manually operated, the output increasing / decreasing function of the electric motor is configured to operate.

[0003]

However, when a disturbance such as a cross wind is applied to the vehicle, the steering device does not generate a steering torque by human power, so that there is no effect of suppressing the disturbance such as a cross wind. The same applies to a manual steering device without a booster. Therefore, when such a disturbance is received, the driver must steer the steering wheel in a direction to suppress the disturbance. SUMMARY OF THE INVENTION It is an object of the present invention to provide a vehicle steering system capable of improving the vehicle's disturbance suppression performance against disturbances such as crosswinds.

[0004]

In order to achieve the above object, a vehicle steering apparatus according to the present invention is provided with a manual steering means for manually turning a steered wheel of a vehicle, and a manual steering means. Steering torque detecting means for detecting the steering torque, auxiliary steering torque determining means for determining an auxiliary steering torque based on the detected value of the steering torque detecting means, and an electric motor for applying an auxiliary steering torque to the steered wheels. A vehicle steering device having control means for controlling the electric motor based on the value determined by the auxiliary steering torque determining means; a vehicle behavior detecting means for detecting the behavior of the vehicle; Auxiliary reaction torque determining means for determining an auxiliary reaction torque based on the detected value, wherein the control means determines the value of the auxiliary reaction torque determining means and the auxiliary operation torque. To provide a vehicle steering system, characterized in that is adapted to control the drive torque of the motor based on the determined value of the torque determining means.

[0005] The steering apparatus for a vehicle according to the present invention adds the torque value determined based on the vehicle body behavior to the steering actuator, so that the steering wheel can not only obtain the torque value determined by the vehicle speed or the rack reaction force, but also Further, since the steering actuator adds a torque value ranging from positive to negative, it is possible to easily turn the steering wheel up or down. In other words, by adding the torque value due to the disturbance to the steering actuator, the steering wheel can be steered in a direction to suppress the disturbance.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show a vehicle steering apparatus according to an embodiment of the present invention. FIG. 1 is a schematic overall configuration diagram, FIG. 2 is a circuit block diagram of a control system, FIG. 3 is a control block diagram, and FIG. FIG. 5 is a data table used for the control processing, and FIG. 6 is a graph for explaining the operation in comparison with the related art.

In FIG. 1, reference numeral 11 denotes a steering handle that can be steered by a driver, and the steering handle 11 is provided on a steering shaft 11a. Steering shaft 1
1a is rotatably supported by the vehicle body and is connected to a reaction motor (steering torque generating means) 12. The reaction force motor 12 is connected to a control device 13, and the control device 1
The steering torque is applied to the steering wheel 11 by being energized from the steering wheel 3, in other words, a steering force of the steering wheel 11 is generated.

The steering shaft 11a has a first steering angle sensor 14 composed of an analog sensor such as a potentiometer, a second steering angle sensor 15 composed of a digital sensor such as an encoder, and a steering torque composed of a differential transformer and the like. A sensor 16 is provided. The reaction motor 12 is provided with a current sensor 41 for detecting an energizing current value. The sensors 14, 15, 16, 41
3 is connected.

The first steering angle sensor 14 is a steering wheel 1
The rotation angle of the steering shaft 11a, that is, the steering angle θ of the steering handle 11 is detected with reference to the predetermined position (eg, the neutral position) of the first steering wheel 11 and a detection signal representing the steering angle θ is output to the control device 13. Further, the second steering angle sensor 15 outputs a pulse signal of a predetermined number of pulses for the unit steering angle of the steering handle 11 to the control device 13. Similarly, the steering torque sensor 16 detects the steering torque and outputs the steering torque. Is output, and the current sensor 41 outputs the detection signal
, A detection signal corresponding to the output torque is output. Although detailed description is omitted, the control device 13 calculates the steering angle of the steering wheel 11 from the output signals of the sensors 14 and 15 and the steering torque from the output signal of the sensor 16.

Reference numerals 17L and 17R denote a pair of left and right steered wheels. These steered wheels 17L and 17R are connected to a steering mechanism 19 via tie rods 18L and 18R, respectively. The steering mechanism 19 includes a worm shaft 20 having a spiral groove, a ball nut 21 screwed into the groove of the worm shaft 20 via a number of balls, and a transmission gear 22 coupled to the ball nut 21 so as to be integrally rotatable.
Having.

The worm shaft 20 is supported by a housing (not shown) or the like so as to prohibit rotation and to be movable in the axial direction.
Both ends are connected to the steered wheels 17L, 17R via the tie rods 18L, 18R described above. In the worm shaft 20, the ball rolls in the groove and circulates between the ball nut 21 and moves in the axial direction by the rotation of the ball nut 21 to steer the steered wheels 17L and 17R. The transmission gear 22 meshes with the drive gear 23 and rotates integrally with the ball nut 21 by the rotation of the drive gear 23.

The drive gear 23 is fixed to a rotating shaft 24, and the rotating shaft 24 is integrally and concentrically connected to output shafts of two steering motors 25L and 25R. Steering motor 25L, 2
5R are connected to the control device 13, respectively, and the steering motors 25L, 25R are provided with current sensors 40L, 40R for detecting a current value. These current sensors 40L and 40R are connected to the control device 13 and output detection signals indicating the values of currents flowing to the steering motors 25L and 25R.

Further, axial force sensors 26L, 26R are respectively attached to the tie rods 18L, 18R,
In FIG. 1, an absolute position sensor 27 composed of an analog type sensor such as a potentiometer (not shown in FIG. 1 because it is included in the ball nut 21) is provided, and the steering motors 25L and 25R are each provided with a digital type sensor such as an encoder. Steering angle sensors 28L and 28R are provided. As shown in FIG. 2, these sensors 26L, 26R, 27, 28
L and 28R are connected to the control device 13.

The axial force sensors 26L and 26R detect the turning reaction force of the steered wheels 17L and 17R, respectively, and output a detection signal representing the turning reaction force to the control device 13. Similarly, the absolute position sensor 27 is a rotation angle of the ball nut 21 based on the neutral position, that is, a steering angle based on the neutral position of the steered wheels 17L and 17R, similarly to the first steering angle sensor 14 described above. Is output, and the steering angle sensor 28
Similarly to the second steering angle sensor 15, L and 28R output pulse signals of a predetermined number of pulses for the unit rotation angle of the output shaft of each of the steering motors 25L and 25R, ie, the unit steering angle of the steered wheels 17L and 17R. Output to the control device 13. Similarly to the steering angle of the steering wheel 11, the steering angles of the steered wheels 17L and 17R are calculated from the detection signals of the sensors 27 and 28.

In FIG. 1, reference numeral 29 denotes a display, 30 denotes an ignition switch, and 31 denotes a battery. Display 2
9 is connected to the control device 13 and based on the output signal of the control device 13, the steering angle θ of the steering wheel 11 and the steered wheels 17L,
The relative deviation from the steering angle δ of 17R is displayed.

As shown in FIG. 2, the control device 13 has two controllers 13a and 13b containing a one-chip microcomputer, a memory, an A / D converter, a clock and the like, and these controllers 13a and 13b are connected to each other. Is done. These controllers 13a and 13b are connected to watchdog timers 32a and 32b, respectively, and are connected to the sensors 14, 15, 16, 26, 27, and 27 described above.
28, 40 and 41 (alphabetic subscripts are omitted) are connected. Further, a vehicle speed sensor 33, a yaw rate sensor 34, and a lateral acceleration sensor 88 are connected to these controllers 13a and 13b, and a reaction motor driving circuit 35, steering motor driving circuits 36L and 36R, and the above-described display 29 are also provided. Connected in parallel.

As is well known, the vehicle speed sensor 33 detects the vehicle speed V and outputs a detection signal indicating the vehicle speed V, and the yaw rate sensor 34 detects the yaw angular speed (yaw rate) of the vehicle and outputs a signal indicating the yaw angular speed. The lateral acceleration sensor 88 detects a lateral acceleration (lateral G) acting on the vehicle body in the vehicle width direction and outputs a detection signal indicating the lateral G. The yaw rate sensor 34 and the lateral acceleration sensor 88 correspond to vehicle body behavior detecting means.

Each of the controllers 13a and 13b (hereinafter represented by numbers without a suffix) processes the above-mentioned detection signals of the respective sensors in parallel according to a predetermined routine, and sends the signals to the respective motor drive circuits 35, 36L and 36R. A PWM drive signal is output to the display 29. The watchdog timers 32a and 32b are connected to the controllers 13a and
By monitoring the execution interval of the routine of 13b or the cycle of the built-in timer, an abnormality of the controllers 13a and 13b is determined. Although detailed description is omitted, these controllers 1
3a and 13b mutually perform a failure diagnosis, determine a failure based on the determination result of the watchdog timers 32a and 32b, and when a failure occurs, cut off the part diagnosed as a failure and continue the control.

The motor drive circuits 35, 36L and 36R are each configured by connecting FETs in a bridge shape. The reaction motor drive circuit 35 is connected to the reaction motor 12, and the steering motor drive circuits 36L and 36R are connected to the steering motor 25L. , 25R. These motor drive circuits 35, 36L, 36
R receives a PWM signal from the controller 13, and supplies a current having a duty factor corresponding to the PWM signal to the motors 12, 25L, and 25R.

In this embodiment, a steering wheel 11 and steering wheels 17L and 17R are mechanically separated from each other by a CBW (CONTROL).
A steering system of the (BY WIRE) type is exemplified, and its control method is shown in the block diagram of FIG. As shown in the figure, the steering device detects a steering state of the steering handle 11,
Based on the steering angle θ of the steering handle 11, the steered wheels 17L,
The steering angle of 17R is feedback-controlled, and the yaw rate of the vehicle body, lateral G, and the steering reaction force of the steered wheels 17L and 17R are detected. The steering reaction force of the steering wheel 11 is controlled based on the steering angle θ.

Here, in the control of the steering reaction force, a steering angle component T1 of the steering reaction force is calculated by converting the steering angle θ by a function f1, and similarly determined by a function f2 from the steering speed dθ / dt. From the damping component T2 and the yaw rate γ
3, the first vehicle body behavior suppression component T3, the second vehicle body behavior suppression component T4, the steered wheels 17L,
The road surface component T5 is calculated by the function f5 from the steering reaction force R of 17R. Although these functions adopt linear functions whose inclination changes according to the vehicle speed as shown in FIGS. 5A, 5B, 5C, 5D, and 5E, it is also possible to employ a linear function that does not change according to the vehicle speed or a function having another characteristic. . Note that S is a Laplace operator.

The components T1 and T of the steering reaction force
The target steering reaction force is determined from the following equation based on 2, T3, T4, and T5, and the output torque of the reaction motor, that is, the steering reaction force of the steering wheel, is feedback-controlled to the target steering reaction force Ts. Ts = T1 + T3 + T4 + T5 + T2 However, in the above equation, the direction of the resistance to the steering of the steering handle 11 in the forward direction is expressed as positive.

In FIG. 3, a function L indicates a limiter, and the limiter L defines the magnitude of the target steering reaction force as an absolute value to be equal to or less than a predetermined value as described later. Although each of the above functions can be understood as a transfer function from FIG. 3, the transfer function can also be achieved by a linear function, and its value is given an appropriate weight according to the specifications of the vehicle in practical use. Can be set as appropriate, and can also be configured to be determined by a map search by expressing it in a table or map.

In the steering apparatus of this embodiment, the processing shown in the flowchart of FIG. 4 is repeatedly executed at a predetermined cycle in the control device 13 to control the steering reaction force.
As shown in the figure, the output signal of each sensor is read in step 1, and the yaw rate, lateral G, turning reaction force, vehicle speed, steering torque, steering angle and the like of the vehicle body are calculated from the output signal of the sensor in step 2. Subsequently, in step 3, the respective steering reaction components T1, T2, T3, T4, and T5 are calculated using a data table as shown in FIG. 5, and then in step 4, the target steering reaction force Ts is calculated according to the above equation.

Next, at step 5, the target steering reaction force T
It is determined whether or not s exceeds a predetermined value Tmax. If the target steering reaction force Ts exceeds the predetermined value Tmax, the value is set as the upper limit in step 6 to the above value Tmax. In the next step 7, similarly, the target steering reaction force Ts is set to a predetermined value (-Tma
x) is determined, and if the target steering reaction force Ts is small, the lower limit is set to the above value (-Tmax). The processing from step 5 to step 8 corresponds to the limiter L in FIG. 3 described above.

Subsequently, in step 9, the reaction force motor 12 is energized, and the output torque of the reaction force motor 12, ie, the steering reaction force applied to the steering wheel 11, is feedback-controlled to the target steering reaction force Ts.

As described above, the steering apparatus of this embodiment is
The steering torque applied to the steering wheel 11 by the reaction motor 12 has a steering reaction component T3 corresponding to the yaw rate of the vehicle body and a steering reaction component T4 corresponding to the lateral G. The torque (steering reaction force) tries to steer the steering handle 11 in a direction to suppress the yaw rate and the lateral G. For this reason, when a vehicle body behavior such as a yaw rate or a side G occurs in the vehicle body due to disturbance such as a cross wind, the steering handle 11 is steered even if the driver releases the vehicle, and the vehicle body behavior can be stabilized. . In addition, even when the driver holds the steering wheel 11, the same effect can be obtained even if the driver leaves the movement of the steering wheel 11 by the torque.

More specifically, when the vehicle is going straight ahead, the driver holds the steering handle 11 neutrally and lightly, and the vehicle body behavior detecting means detects that the traveling direction of the vehicle changes when it receives a crosswind. Steering torque for returning to the straight running state is generated, the steering handle 11 is moved, an actual steering angle is generated, and the vehicle returns to straight running. Then, even in such a case, even in the steering in the general traveling, the driver can use the reaction force motor 1.
From 2, the steering torque acting on the steering wheel 11 allows the user to experience the behavior of the vehicle body, that is, the yaw rate and the lateral G generated in the vehicle body, thereby obtaining a better steering feeling. If the driver steers or steers against this torque, the driver can freely move the vehicle.

Explaining in comparison with the prior art, the steering apparatus according to the present invention is characterized in that when the vehicle body behavior occurs due to a cross wind disturbance, the steering reaction force includes only the yaw rate component as the vehicle body behavior and the steering reaction force When only G is included, the trajectory as shown in FIG. 6A can be maintained even when the driver does not perform any operation, that is, in the state of the hand-free driving. However, the traveling direction of a normal vehicle is greatly affected by disturbance as shown in FIG.

As shown in FIG. 6 (b), even when the driver holds the steering wheel 11, the present invention can be applied to the case where the control is performed based on only the yaw rate and the case where the control is performed based on only the lateral G. The influence of the disturbance on the traveling direction can be made smaller than that of a normal vehicle. FIG. 6 shows a state in which the vehicle travels straight, the horizontal axis represents the straight traveling direction of the vehicle, and the vertical axis represents the deviation amount in a direction orthogonal to the traveling direction.

Further, even during normal turning travel, etc.
The turning generates a lateral G and a yaw rate.
The steering torque is generated by the reaction force motor 12 in a direction to suppress the like, that is, the steering torque is generated so as to return the vehicle to the straight traveling state. Therefore, when returning to straight running, the driver gradually returns the steering handle 11 in accordance with the steering torque, so that the vehicle returns to the straight running state. In addition, when the vehicle suddenly shows an oversteer tendency, a strong return force acts, so that the countersteer becomes easy, and in the drift tendency, the return force is weak, so that it is easy to make more cuts.

In the above-described embodiment, the steering reaction force based on both the yaw rate and the lateral G of the vehicle body is applied to the steering wheel 11.
It is needless to say that the present invention can also be achieved by applying a steering reaction force based on either one.

FIGS. 7 and 8 show a steering device according to another embodiment of the present invention. FIG. 7 is a schematic diagram of the entire structure, and FIG. 8 is a control block diagram. In this embodiment, the same portions as those in the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the steering wheel 11 is connected to a steering mechanism 19 via a steering shaft 11a and a joint 91, and the steering wheel 11 and the steering wheel 17 are connected.
L and 17R are mechanically connected. The steering mechanism 19 is composed of a rack-and-pinion type mechanism. The pinion is provided with a sensor 94 for detecting a steering torque and a steering angle. The rack can transmit power bidirectionally via an electric motor 95 and a ball screw mechanism 90. Connect to The electric motor 95 is connected to a motor drive circuit 96.
To generate steering assist torque. The electric motor 95 corresponds to a steering torque generating means.

The motor drive circuit 96 is connected to the controller 13, and the controller 13
4 and the lateral acceleration sensor 88 are connected. As described in the previous embodiment, the yaw rate sensor 34 detects the yaw rate of the vehicle body, the lateral acceleration sensor 88 detects the lateral G,
The controller 13 outputs a control signal to the motor drive circuit 96 based on the detection signal input from each sensor, and
5 is energized.

In this embodiment, the steering handle 11
And the steering wheel 17 are mechanically connected to each other.
Of the motor 95 to assist the steering with the output torque of the electric motor 95. Therefore, in this steering device, not only the steering assist characteristic but also the steering reaction force of the steering wheel 11 is determined by the control of the electric motor 95.

Also in this embodiment, as shown in FIG. 8, the steering torque, the yaw rate and the lateral G are detected, and the output torque of the electric motor 95 is controlled based on these detected values. That is, two components determined by the steering torque, a component determined by the transfer function from the yaw rate, and the lateral G
And the target torque is defined as the sum obtained by adding the component determined by the transfer function to the target torque, and the output torque of the electric motor 95 is feedback-controlled to the target torque. Therefore, similarly to the above-described embodiment, when the yaw rate and the lateral G of the vehicle body occur, the steered wheels 17 are steered in a direction to suppress the yaw rate and the lateral G regardless of whether the steering handle 11 is steered. That is, the steering handle 11 is steered, and the vehicle behavior can be stabilized.

Also in this embodiment, since the transfer function b applied to the (steering reaction force) component corresponding to the steering angle is changed between the yaw rate and the lateral G, as described in the official gazette described as the prior art. Stabilization can be achieved. Similarly, as shown in FIG. 5, when a linear function is used as the transfer function, the steering torque component can be adjusted by changing the slope, so that the degree of freedom in selecting the characteristic is increased, and the stability is improved. Is easy. Other configurations and operations are the same as those of the above-described embodiment, and detailed description thereof is omitted, but the system can be simplified as compared with the first embodiment.

In FIG. 8, J1 is the inertia of the steering wheel 11, J2 is the inertia of the steering wheel 17,
J3 is the rotor inertia, J is (J2 + J3), a is the steering speed gain of the steering wheel 11, b is the torque gain,
K1 is a torque constant, K2 is a tire constant, KE is an induced voltage constant, Kγ is a yaw rate reaction force coefficient, KG is a lateral G reaction force coefficient, and S is a Laplace operator.

In each of the above-described embodiments, only the control of the power system will be described. However, the control of the steering angle can be performed together with the control of the power system. It goes without saying that the present invention is also applicable to a steering device employing a hydraulic cylinder.

[0041]

As described above, according to the vehicle steering apparatus of the present invention, the steering torque for turning in the direction for suppressing the behavior of the vehicle body is applied to the steering wheel irrespective of the presence or absence of the driver's steering. Because of this, regardless of whether the driver actively steers or not, it can suppress the behavior of the vehicle body due to disturbance such as crosswind and improve the stability of the vehicle, and also acts on the steering wheel with the driver's intention The steering wheel can be held or steered against the steering torque to be performed, and the degree of freedom of driving does not decrease. Further, the effect that the driver can sense the behavior of the vehicle with the torque of the steering wheel can be obtained. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram schematically showing a vehicle steering system according to one embodiment of the present invention.

FIG. 2 is a circuit block diagram of a control system of the steering device.

FIG. 3 is a control block diagram of the steering device.

FIG. 4 is a flowchart showing a control process of the steering device.

FIG. 5 is a data table used for the control processing.

FIG. 6 is a graph illustrating the operation of the present invention in comparison with the related art.

FIG. 7 is a schematic overall view showing a vehicle steering system according to another embodiment of the present invention.

FIG. 8 is a control block diagram of the steering device.

[Explanation of symbols]

11: steering handle, 12: reaction motor (steering torque generating means), 13: control device (control means), 17L,
17R: steered wheels, 33: vehicle speed sensor, 34: yaw rate sensor (vehicle behavior detecting means), 88: lateral acceleration sensor (vehicle behavior detecting means), 95: electric motor (steering torque) Generating means).

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[Procedure amendment]

[Submission date] June 24, 1999 (1999.6.2
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Vehicle steering system

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vehicle steering system,
In particular, the present invention relates to a steering device that generates an auxiliary steering torque by an electric motor.

[0002]

2. Description of the Related Art As a so-called power steering device for reducing a driver's steering force, for example, Japanese Patent Publication No. 50-33
A type as described in Japanese Patent No. 584 is known. This is designed to assist the steering force of the steering wheel with the output torque of the electric motor. The amplification of the detection signal of the steering torque applied by the driver to the steering wheel is detected by detecting the vehicle speed and road conditions. The output torque of the auxiliary motor is increased or decreased by changing the output torque according to the signal, so that an optimum steering torque can always be obtained.

[0003]

When the vehicle receives a strong crosswind or travels on a rutted road while traveling, the vehicle may be deflected in a direction deviating from the target traveling line. Also, the coefficient of friction between tires and road surfaces such as snowy roads (μ)
The road surface reaction force decreases when the vehicle travels on a low road surface (hereinafter referred to as a low μ road) or at low speed.

In the case of the above-described conventional power steering device, the electric motor generates the auxiliary steering torque only after the driver turns the electric power steering device. No auxiliary steering torque is generated. Therefore, in order to suppress the deflection of the vehicle, the driver himself must operate the steering wheel. On the other hand, the power steering device generally requires a larger steering force as the lateral acceleration and the yaw rate of the vehicle increase. Therefore, when the vehicle is deflected due to a disturbance, the steering torque required for the correction becomes larger as the deflection becomes larger.

[0005] In addition to this, a general power steering device requires only a small steering force of a driver during normal driving, but it is difficult to transmit information on the vehicle behavior from the steering wheel, so that the vehicle behavior rapidly increases. The information in the case of a change has been obtained only from the driver's sight and bodily sensation. For this reason, the correction operation is delayed, and the operation amount tends to increase.

Further, since the return of the steering wheel is caused by the road surface reaction force, the return of the steering wheel becomes slow when the road surface reaction force is reduced when traveling on a low μ road such as a snowy road or at low speed. As a result, the driver himself must return the steering wheel, which tends to increase the steering wheel operation load.

The present invention has been devised to remedy such disadvantages of the prior art, and its main objects are as follows.
The ability to suppress deflection when disturbance such as crosswinds or running on rutted roads acts on the vehicle is improved, and the stability of the vehicle can be improved.The steering operation load is reduced even on low μ roads such as snowy roads and low-speed driving. It is an object of the present invention to provide a vehicle steering system improved in such a manner.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a manual steering means for manually turning a steered wheel of a vehicle, and a steering torque applied to the manual steering means. A steering torque detecting means for detecting, an auxiliary steering torque determining means for determining an auxiliary steering torque based on a detection value of the steering torque detecting means, an electric motor for applying an auxiliary steering torque to the steered wheels; A vehicle steering device having a control means for controlling the electric motor based on a value determined by the torque determining means; a vehicle behavior detecting means for detecting a behavior of the vehicle; and a detection value detected by the vehicle behavior detecting means. Auxiliary reaction torque determining means for determining the auxiliary reaction torque based on the control means,
A vehicle steering device is provided, wherein the driving torque of the electric motor is controlled based on a value determined by the auxiliary reaction torque determining means and a value determined by the auxiliary steering torque determining means. Achieved by

With this configuration, the irregular behavior of the vehicle caused by the disturbance can be detected from the yaw rate or the lateral acceleration of the vehicle, and the torque facing the detected yaw rate or the lateral acceleration can be generated by the electric motor for generating the auxiliary steering torque. Therefore, vehicle behavior due to disturbance can be suppressed. Further, even when traveling on a low μ road such as a snowy road or at a low speed, the steering wheel can be returned by the auxiliary reaction torque determined from the yaw rate or the lateral acceleration.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific embodiments shown in the accompanying drawings.

FIG. 1 shows the configuration of a vehicle steering system to which the present invention is applied. This device comprises a manual steering force generator 1 as a manual steering means and an electric auxiliary steering force generator 2. The manual steering force generator 1 is freely movable on a steering shaft 4 integrally connected to a steering wheel 3. Pinion 6 connected via connecting shaft 5 having a joint
And a rack 7 that meshes with the pinion 6 and can reciprocate in the vehicle width direction.
The knuckle arms of the left and right front wheels 9 are connected via the. As a result, a normal rack-and-pinion steering operation can be performed.

On the other hand, an electric motor 10 is provided on the outer periphery of the rack 7 coaxially. The electric motor 10 has a rack 7 inserted into a hollow rotor and a drive helical gear 11 attached to the rotor. The drive helical gear 11 has a ball screw mechanism extending parallel to the rack 7. The driven helical gear 13 attached to the shaft end of the screw shaft 12 is meshed. The nut 14 of the ball screw mechanism is fixed to the rack 7. Thus, the electric assist steering force generator 2 is configured.

As the steering torque detecting means, a torque sensor 15 for outputting a signal corresponding to the steering torque of the steering shaft 4 and a signal corresponding to the rotational angular velocity of the steering wheel 3 are output to the steering shaft 4. And an angular velocity sensor 16 are mounted.

[0014] Further, a lateral acceleration sensor 17 for outputting a signal corresponding to the lateral acceleration of the vehicle and a yaw rate sensor for outputting a signal corresponding to the yaw angular velocity of the vehicle are provided at appropriate places on the vehicle body as vehicle behavior detecting means. 18 and
A vehicle speed sensor 19 for outputting a signal corresponding to the traveling speed of the vehicle is mounted.

In this embodiment, the steering wheel 3 and the front wheel 9 which is the steered wheel are mechanically connected, and the output of each of the sensors 15 to 19 is controlled by the control unit 20.
The output torque of the electric motor 10 is controlled by giving the control signal obtained by the processing described above to the electric motor 10 via the drive circuit 21.

FIG. 2 is a schematic block diagram showing a control system to which the present invention is applied. Each signal output of the torque sensor 15, the steering wheel angular velocity sensor 16, the lateral acceleration sensor 17, the yaw rate sensor 18, and the vehicle speed sensor 19 is input to the control unit 20. These signal inputs are input to the auxiliary steering torque determining means 22 and the auxiliary reaction force torque determining means 23, respectively, and processed to determine the output torque target value of the electric motor 10. This output torque target value is converted into a target current value of the electric motor 10 by the target current determining means 24, and the electric motor 10 is controlled via the drive circuit 21.

In the auxiliary steering torque determining means 22,
A target value of the auxiliary steering torque for the normal steering force assist is determined. For this determination means, for example, a known electric power steering control for realizing a desired steering torque can be applied, and therefore a detailed description thereof is omitted here.

In the auxiliary reaction torque determining means 23,
Based on the respective signal outputs from the sensors 16 to 19, the target auxiliary reaction torque is obtained by an algorithm described later.

In the target current determining means 24, the motor 10
The output torque target value is converted into a target drive current value in accordance with the known characteristics (torque constant) of the current and the output torque.

In the auxiliary reaction torque calculating means 23 in the control unit 20, the processing shown in the flowchart of FIG. 3 is repeatedly executed at a predetermined cycle. First, Step 1
In step 2, the output signal of each sensor is read, the auxiliary reaction force torque TA is determined in step 2, and the target auxiliary reaction torque determination value is output in step 3.

This processing will be described in more detail with reference to FIGS. First, in step 1 described above, as shown in the flowchart of FIG.
1), steering wheel angular velocity ω (step 12), lateral acceleration G
(Step 13), a process of reading the yaw rate γ (Step 14) is performed.

Next, in step 2 described above, as shown in the flowchart of FIG. 5, FIG. 7 (a), FIG.
With each of the steering angular velocity ω, the lateral acceleration G, and the yaw rate γ as an address as shown in FIG. 7C as an address, an auxiliary reaction torque T1 (damping torque) for each component is obtained from each data table set for each vehicle speed V. (Components), T2 (lateral G torque component), and T3 (yaw rate torque component) (steps 21 to 23), and these auxiliary reaction torque components T1, T2, and T3 are added (step 24). Furthermore,
It is determined whether or not the target steering reaction force value TA exceeds a maximum value (Tmax) in order to eliminate an excessive auxiliary reaction force torque, and if the target steering reaction force value TA exceeds the maximum value, the target is determined. The steering reaction force value TA is set to the above Tmax. If the target steering reaction force value TA does not exceed the maximum value (Tmax), the target steering reaction force value TA is similarly set to the negative maximum value (−Tm).
ax) is determined, and the target steering reaction force value TA is determined.
Is greater than the negative maximum value, the target steering reaction force value TA
Is set to the above-mentioned Tmax value (step 2
5) is performed to determine the target auxiliary reaction torque determination value TA.

FIG. 6 is a control block diagram of the above step 2, and steps 21 to 25 correspond to the respective blocks in FIG.

The target auxiliary reaction torque determining value TA determined in this way is added to the separately determined target auxiliary steering torque determining value, converted into a target current value by the target current determining means 24, and output. .

By performing the above processing, as shown in FIG. 8, when the vehicle 26 comes off the traveling line 27 due to the crosswind, the yaw rate γ of the vehicle 26 at this time is determined.
Alternatively, the lateral acceleration G is detected, and the yaw rate γ and the lateral acceleration G are canceled out, that is, the vehicle 26 at that time is canceled.
The electric motor 10 is driven in such a direction as to return the deflection to the traveling line 27.

FIG. 9 is a graph comparing the characteristics (solid line) of a vehicle equipped with a steering device to which the present invention is applied and the characteristics of a conventional steering device (dashed line) when crosswind is received during traveling.
(A), FIG. 9 (b), and FIG. 9 (c). When a disturbance such as a cross wind is received, the behavior of a vehicle equipped with a conventional steering device in which the above control is not performed is compared with the behavior of a vehicle equipped with a steering device to which the present invention is applied. Further, it can be seen that the lateral shift amount is both suppressed.

For this reason, when the yaw rate γ or the lateral acceleration G occurs in the vehicle 26 due to a disturbance such as a crosswind, the front wheels are so arranged that the vehicle 26 always travels straight against the disturbance even if the driver is in a released state. 9 is automatically steered, and irregular behavior can be stabilized. Also, when the driver is holding the steering wheel 3, the same effect can be obtained if the driver leaves the movement of the steering wheel 3 by the auxiliary reaction torque.

When the vehicle is traveling on a rutted road surface or a puddle road surface, the steering wheel 3 can be easily taken. In such a case, the yaw rate γ or the lateral acceleration can be obtained in the same manner as in the crosswind traveling. G is vehicle 26
Therefore, by executing the above control, the trajectory is automatically corrected so that the vehicle 26 goes straight.

Further, even when the yaw rate γ or the lateral acceleration G occurs during a normal turning operation or the like, the electric motor 10 generates the steering torque in a direction for suppressing them, that is, in a direction for returning the vehicle to the straight traveling state. This serves the same function as the self-aligning torque, and the steering wheel can be returned to neutral by the auxiliary reaction torque even when the reaction force from the road surface is reduced especially on low μ roads such as snowy roads and low-speed driving. Therefore, the driver's steering load, particularly the steering load at the time of turning back, can be reduced, and steering when returning to straight running can be easily performed.

Further, when the vehicle suddenly shows an oversteering tendency, a strong return force acts in accordance with the yaw rate γ at that time, so that countersteering becomes easy.

In addition, in general driving steering,
Since the auxiliary reaction torque can be added to the road surface reaction force by the auxiliary reaction torque determining means and the degree of reduction of the steering torque can be adjusted by the auxiliary steering torque determining means, the steering feel for the driver can be improved.

In the above configuration, the vehicle behavior detecting means is a vehicle behavior detecting means using both the lateral acceleration sensor and the yaw rate sensor. However, the same operation and effect can be obtained by using either the lateral acceleration sensor or the yaw rate sensor. .

[0033]

As described above, according to the present invention, the auxiliary reaction torque in the direction for suppressing the vehicle behavior acts on the steered wheels regardless of the presence or absence of the driver's steering. Irregular behavior of the vehicle due to disturbance such as a rutted road can be suppressed without requiring the driver to actively steer, and the running stability of the vehicle can be improved. Moreover, since the auxiliary reaction torque based on the detection value of the vehicle behavior detection means is added to the road surface reaction force, the load of the steering operation, particularly the operation of returning the steering, can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram schematically showing a vehicle steering system to which the present invention is applied.

FIG. 2 is a circuit block diagram of a control system of the steering device.

FIG. 3 is a flowchart showing control processing of the steering device.

FIG. 4 is a flowchart showing a control process of the steering device.

FIG. 5 is a flowchart showing control processing of the steering device.

FIG. 6 is a circuit block diagram of a control system of the steering device and a data table used for the control processing.

FIGS. 7A, 7B, and 7C are enlarged views of a data table used for the control processing.

FIG. 8 is a schematic diagram showing the movement of the vehicle when a crosswind is received during straight running.

9A, 9B, and 9C are graphs comparing the characteristics of a vehicle equipped with a vehicle steering device to which the present invention is applied and the characteristics of a vehicle equipped with a conventional steering device.

[Description of Signs] 1 Manual steering force generator 2 Electric auxiliary steering force generator 3 Steering wheel 4 Steering shaft 5 Connecting shaft 6 Pinion 7 Rack 8 Tie rod 9 Front wheel 10 Electric motor 11 Drive helical gear 12 Screw shaft 13 Driven helical gear 14 Nut 15 Torque sensor 16 Angular velocity sensor 17 Lateral acceleration sensor 18 Yaw rate sensor 19 Vehicle speed sensor 20 Control unit 21 Drive circuit 22 Auxiliary steering torque determining means 23 Auxiliary reaction torque determining means 24 Target current determining means 26 Vehicle 27 Straight running line

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

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──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) B62D 13:00

Claims (3)

[Claims] 1. A manual steering device for manually turning a steered wheel of a vehicle, a steering torque detecting device for detecting a steering torque applied to the manual steering device, and a detection value of the steering torque detecting device. Auxiliary steering torque determining means for determining an auxiliary steering torque based on the motor, an electric motor for applying the auxiliary steering torque to the steered wheels, and a control means for controlling the electric motor based on a value determined by the auxiliary steering torque determining means A vehicle steering device having: a vehicle behavior detecting means for detecting a behavior of the vehicle; an auxiliary reaction torque determining means for determining an auxiliary reaction torque based on a detection value detected by the vehicle behavior detecting means; Wherein the control means controls the drive torque of the electric motor based on the determined value of the auxiliary reaction torque determining means and the determined value of the auxiliary steering torque determining means. A vehicle steering system characterized in that: 2. The vehicle steering system according to claim 1, wherein said vehicle behavior detecting means includes a yaw rate sensor. 3. The vehicle steering system according to claim 1, wherein the vehicle behavior detecting means includes a lateral acceleration sensor.