JP3678566B2 - Vehicle steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle steering apparatus capable of optimizing steering by a driver when vehicle behavior becomes unstable due to disturbance, steering by a driver, or the like.
[0002]
[Prior art and problems to be solved by the invention]
Japanese Patent Application Laid-Open No. 7-47970 discloses a device that changes the control characteristics according to the current driving technique of the driver when controlling the steering device according to the detection result of the running state of the vehicle. That is, the yaw rate of the vehicle is detected in order to detect the running state of the vehicle, and the torque required for steering is set according to the detected yaw rate and driving technique. For drivers with low driving skills, set the torque required for steering high to stabilize the vehicle behavior, and for drivers with high driving skills, set low torque for steering to provide information from the road surface. It is easy to recognize.
However, since the yaw rate does not change unless the steering angle has actually changed, control is delayed. For this reason, when a disturbance such as a decrease in the friction coefficient of the road is suddenly applied, or when excessive steering is performed at the time of course change for lane change etc., the behavior of the vehicle becomes unstable due to the delay of the control. Thus, when excessive steering is performed, steering for correcting the course is required. Also, when avoiding a front obstacle, if the torque required for steering is set high, the front obstacle may not be avoided because sudden steering is difficult.
[0003]
There are also devices that detect disturbance based on the driving state, rotational speed, current, etc. of the actuator for generating steering assist force and compensate for the influence of the disturbance (Japanese Patent Laid-Open Nos. 2-6272 and 3-182881). Issue gazette).
However, when based on the driving state, rotational speed, current, etc. of the actuator, the disturbance can be detected only after the vehicle behavior is actually unstable due to the influence of the disturbance. Therefore, when a sudden disturbance is applied, or when excessive steering is performed at the time of course change for lane change etc., the behavior of the vehicle becomes unstable due to control delay, and when excessive steering is performed Steering to correct the course is required. Moreover, it cannot cope with the unstable behavior caused by the steering wheel operation of the driver.
[0004]
Japanese Patent Laid-Open No. 2-117467 controls the steering torque generating motor according to the vehicle speed and the rudder angle, thereby suppressing the rotation of the steering shaft and preventing the side slip and the rollover due to a sudden steering operation during high speed driving. A steering safety device is disclosed.
However, since the control of the motor is based only on the vehicle speed and the rudder angle, rotation of the steering shaft is suppressed even when an abrupt steering operation is performed to avoid a front obstacle. Therefore, there is a possibility that a front obstacle cannot be avoided. Further, only by controlling the motor based only on the vehicle speed and the steering angle, a side slip or the like due to disturbance cannot be sufficiently prevented. Also, when a driver with advanced driving technology makes a spin turn to avoid danger, a large steering restraining force is applied, causing the vehicle behavior to be different from that intended by the driver.
[0005]
Japanese Patent Laid-Open No. 4-266538 detects the steering angle, brake hydraulic pressure, throttle opening, and the current vehicle motion state, and based on this detection information, the future vehicle motion state and the vehicle motion state that serves as a reference A vehicle motion characteristic correction device that controls the steering angle, brake hydraulic pressure, throttle opening, etc. so that the deviation between the estimated actual vehicle motion state and the standard vehicle motion state is reduced. Disclose.
However, this device requires a large number of sensors and actuators, and it is also necessary to control brake hydraulic pressure and throttle opening other than the steering device. This makes the system complex and expensive.
[0006]
It is an object of the present invention to provide a vehicle steering apparatus that can solve the above-described problems.
[0007]
[Means for Solving the Problems]
A vehicle steering apparatus according to the present invention includes a steering shaft that transmits a steering torque applied by a driver to a wheel, an actuator for generating torque that is added to the steering torque, and a means for detecting torque transmitted by the steering shaft. The vehicle speed detecting means, the steering angle detecting means, the means for obtaining the standard steering torque based on the detected vehicle speed and the steering angle, and the deviation between the detected torque and the standard steering torque is reduced. And a means for controlling the additional torque applied by the actuator.
The normative steering torque in the present invention is a state in which a vehicle (including steering) is geometrically modeled, and a vehicle environment such as a road surface does not cause disturbance to the vehicle, and does not exceed the motion limit of the vehicle. Thus, it means the torque that should be transmitted by the steering shaft when steering.
According to the configuration of the present invention, the additional torque can be applied by the actuator so that the deviation between the torque transmitted by the steering shaft and the standard steering torque is small. As a result, when the vehicle behavior becomes unstable due to disturbance, driver steering, etc., the torque transmitted by the steering shaft before the vehicle driving limit is exceeded, regardless of the driver's driving skill. It can be returned to a range that does not exceed the limit.
Further, when a disturbance is applied to the vehicle, the torque transmitted by the steering shaft changes before the vehicle behavior becomes unstable due to an actual change in the steering angle or the like. Therefore, even when a disturbance acts suddenly, the behavior of the vehicle becomes unstable by quickly controlling the additional torque applied by the actuator according to the detection result of the torque transmitted by the steering shaft. Can be prevented.
Further, since it is only necessary to detect the steering angle, the vehicle speed, and the torque transmitted by the steering shaft and control the actuator for generating additional torque, the configuration can be simplified and the cost can be reduced.
[0008]
In the present invention, when the absolute value of the deviation between the detected torque and the reference steering torque is equal to or greater than the set value and the absolute value of the detected change acceleration of the torque is equal to or greater than the set value, The absolute value of the additional torque applied by the actuator is larger than when the absolute value is less than the set value, and the absolute value of the deviation between the detected torque and the reference steering torque is greater than or equal to the set value, When the absolute value of the detected acceleration of change in torque is less than the set value, the absolute value of the additional torque applied by the actuator is made smaller than when the absolute value of the deviation is less than the set value. Is preferred.
When the driver intentionally steers suddenly or excessively steers more than necessary when changing the course, the cornering force becomes saturated and the road surface reaction force hardly rises when the rudder angle increases. In addition, when the frictional resistance of the road surface decreases, a moment that reduces the road surface reaction force acts. Therefore, if the driver intentionally steers suddenly, or if the driver steers more than necessary when changing course, or if the frictional resistance of the road surface decreases, the torque transmitted by the steering shaft and the standard steering torque The absolute value of the deviation becomes larger.
The absolute value of the detected acceleration of change in torque increases as the driver intentionally steers suddenly.
Therefore, when the absolute value of the deviation is equal to or greater than the set value and the absolute value of the detected change acceleration of the torque is equal to or greater than the set value, it can be determined that the driver has intentionally steered suddenly. In this case, by increasing the additional torque applied by the actuator, the driver's intentional steering is promoted, and the steering reflecting the driver's intention such as avoiding a front obstacle can be performed.
On the other hand, when the frictional resistance of the road surface decreases or the course is changed, the absolute value of the detected torque change acceleration is smaller than when the driver intentionally steers. Therefore, if the absolute value of the deviation between the detected torque and the standard steering torque is greater than or equal to the set value and the absolute value of the torque change acceleration is less than the set value, was steering excessively more than necessary when changing the course? Alternatively, it can be determined that the frictional resistance of the road surface has decreased. In this case, it is possible to stabilize the vehicle behavior by reducing the additional torque applied by the actuator.
[0009]
Further, as a part of the standard steering torque, the standard road surface reaction torque corresponding to the standard tire side slip angle obtained from the detected vehicle speed and the rudder angle is calculated as the stored standard tire side slip angle and the standard road surface reaction torque. It is preferable to be obtained from a linear relationship.
The relationship between the tire side slip angle and the road surface reaction torque is actually nonlinear. That is, as compared with the case where the relationship is regarded as linear, when the absolute value of the tire side slip angle increases, the absolute value of the road surface reaction torque decreases and the vehicle behavior tends to become unstable. Therefore, when the relationship is considered to be linear, the absolute value of the deviation between the torque transmitted by the steering shaft and the reference steering torque is calculated when the absolute value of the tire skid angle increases and the vehicle behavior tends to become unstable. Can be greater than the above set value. This makes it possible to stabilize the vehicle behavior by reducing the absolute value of the additional torque applied by the actuator when steering is excessively necessary when changing the course or when the frictional resistance of the road surface is reduced. In addition, when the driver intentionally steers suddenly, the additional torque applied by the actuator is increased to promote the driver's intentional steering and reflect the driver's intention such as avoiding obstacles ahead. Can be steered.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0011]
A rack and pinion type electric power steering apparatus 1 shown in FIG. 1 includes an input shaft 2 connected to a steering wheel H of a vehicle A, an output shaft 4 connected to the input shaft 2 via a torque sensor 3, and a steering angle. And a sensor 5. The input shaft 2 and the output shaft 4 constitute a steering shaft. Torque transmitted by the steering shaft is continuously detected by the torque sensor 3. The output shaft 4 is connected to a pinion 6, and a steering wheel 8 is coupled to a rack 7 that meshes with the pinion 6. Thus, the steering torque applied by the driver is transmitted to the wheels 8 via the steering wheel H, the input shaft 2, the torque sensor 3, the output shaft 4, the pinion 6 and the rack 7, and the vehicle A is steered.
[0012]
A part of the rack 7 is a ball screw 11, a gear is formed on the outer periphery of a ball nut 12 that meshes with the ball screw 11, and a drive gear 14 meshes with a gear 13 that meshes with the gear. The drive gear 14 is rotationally driven by a DC servo motor 15 which is an actuator for generating additional torque. As a result, the torque applied by the motor 15 is added to the steering torque by the driver and transmitted to the wheels 8.
[0013]
The torque sensor 3 and the motor 15 are connected to the control device 20. In addition, a steering angle sensor 5 that continuously detects the rotation angle of the steering shaft as a steering angle and a vehicle speed sensor 16 that continuously detects the vehicle speed of the vehicle A are connected to the control device 20.
[0014]
The control device 20 stores the relationship obtained in advance between the vehicle speed, the steering angle, and the reference steering torque, and stores the relationship, the steering angle detected by the steering angle sensor 5, and the vehicle speed detected by the vehicle speed sensor 16. Based on this, the standard steering torque is obtained. The reference steering torque may be obtained by calculation using a predetermined function from the vehicle speed and the steering angle. FIG. 2 is a block diagram showing functions of the control device 20.
That is, in the control device 20, the tire slip angle β as a standard is determined by the vehicle speed V detected by the vehicle speed sensor 16, the steering angle θ detected by the steering angle sensor 5, and the transfer function G (s). Desired. The transfer function G (s) is, for example, K / (s ² + 2ξs + ω ² ), where s is a Laplace operator, ξ is an attenuation coefficient, ω is an angular frequency, and K is a gain. And memorized. From the reference tire side slip angle β, the reference road surface reaction torque Tk is obtained from the relationship between the tire side slip angle β and the road surface reaction force torque Tk which has been obtained in advance through experiments and stored. The relationship between the stored tire side slip angle β and the road surface reaction force torque Tk is actually nonlinear as shown by a broken line in the figure, but in the present invention, it is linear as shown by a solid line in the figure.
Further, based on the rudder angular velocity obtained by the differentiation of the rudder angle θ detected by the rudder angle sensor 5 and the viscous friction coefficient Cs of the steering system between the steering wheel H and the wheel 8, it is based on the viscous friction of the steering system. A standard torque Tb is required. The viscous friction coefficient is obtained in advance by experiments and stored.
Further, from the steering angular acceleration obtained by the second order differential of the steering angle θ detected by the steering angle sensor 5 and the inertia moment Is of the steering system between the steering wheel H and the wheel 8, the inertia moment of the steering system is obtained. A torque Tc serving as a standard based on the above is obtained. The moment of inertia is obtained in advance by experiments and stored.
The sum (Tk + Tb + Tc) of the reference road surface reaction torque, the reference torque based on the viscous friction of the steering system, and the reference torque based on the moment of inertia is set as the reference steering torque.
Further, the control device 20 obtains a deviation ΔT between the torque T transmitted by the steering shaft detected by the torque sensor 3 and the reference steering torque. The torque T detected by the torque sensor 3 is the sum of the steering torque Td applied by the driver and the additional torque Ta applied by the motor 15. The control device 20 controls the additional torque Ta applied by the motor 15 so as to reduce the deviation ΔT. That is, the additional torque Ta corresponding to the deviation ΔT is calculated, and the motor 15 is driven so as to generate the calculated additional torque Ta.
[0015]
The calculation of the additional torque Ta is performed based on the driver's steering intention obtained based on the deviation ΔT and the change acceleration d ² T / dt ^{2 of the} torque T detected by the torque sensor 3.
That is, when the driver intentionally steers suddenly or performs steering more than necessary when changing the course, the cornering force is saturated and the road surface reaction force hardly rises as the steering angle θ increases. In addition, when the frictional resistance of the road surface decreases, a moment that reduces the road surface reaction force acts. For this reason, when the driver intentionally steers suddenly, when the course is changed excessively more than necessary, or when the frictional resistance of the road surface decreases, the torque T transmitted by the steering shaft and the standard steering The absolute value of the deviation ΔT from the torque increases. The absolute value of the detected change acceleration d ² T / dt ² of the torque T increases as the driver intentionally steers suddenly. Therefore, when the absolute value of the deviation ΔT between the detected torque T and the reference steering torque is equal to or larger than the set value, and the absolute value of the detected acceleration change D ² T / dt ² is equal to or larger than the set value. Therefore, it can be determined that the driver intentionally steers suddenly.
On the other hand, when the steering is changed excessively more than necessary when the course is changed, or when the frictional resistance of the road surface is reduced, the detected acceleration change of the torque T is compared to when the driver intentionally steers suddenly. The absolute value of d ² T / dt ² becomes small. Therefore, when the absolute value of the deviation ΔT between the detected torque T and the reference steering torque is equal to or larger than the set value, and the absolute value of the change acceleration d ² T / dt ² of the detected torque T is less than the set value, It can be determined that the steering has been excessively performed more than necessary when changing the course, or that the frictional resistance of the road surface has decreased. If steering is performed excessively more than necessary when changing the course, steering is required to correct the course, and the driver tries to suppress the excessive steering. When the frictional resistance of the road surface decreases, the driver's resistance to steering becomes small, so the driver tries to suppress steering.
[0016]
The flowchart of FIG. 3 shows the procedure for determining the steering intention of the driver.
First, it is determined whether or not the absolute value of the deviation ΔT is greater than or equal to a set value T1 (step 1). The set value T1 is set so that proper steering is performed within the motion limit of the vehicle if the absolute value of the deviation ΔT is less than the set value T1. If the absolute value of the deviation ΔT is less than the set value T1, it is determined that the driver's steering intention is normal (step 2). If the absolute value of the deviation ΔT is not less than the set value T1, it is determined whether or not the absolute value of the change acceleration d ² T / dt ² of the torque T detected by the torque sensor 3 is not less than the set value E1 (step 3). ). The set value E1 is set so as to correspond to the minimum value of the change acceleration d ² T / dt ² when the driver steers the vehicle suddenly. If the absolute value of the change acceleration d ² T / dt ² is greater than or equal to the set value E1, it is determined that the driver's steering intention is the promotion of steering (step 4). If the absolute value of the change acceleration d ² T / dt ² is less than the set value E1, it is determined that the driver's steering intention is suppression of steering (step 5).
[0017]
FIG. 4 shows the relationship between the deviation ΔT and the additional torque Ta applied by the motor 15. The solid line indicates the case where the driver's steering intention is normal, the one-dot chain line indicates the case where the driver's steering intention is the steering acceleration, This is a case where the driver's steering intention is to suppress steering. That is, when the steering intention is promoted, the absolute value of the additional torque Ta applied by the motor 15 is larger than in the normal case, and when the steering intention is suppressed, the additional torque applied by the motor 15 than in the normal case. The absolute value of Ta is reduced.
[0018]
According to the configuration of the present invention, the additional torque Ta can be applied by the motor 15 so that the deviation ΔT between the torque T transmitted by the steering shaft and the standard steering torque becomes small. As a result, when the vehicle behavior becomes unstable due to disturbance, driver steering, etc., the torque transmitted by the steering shaft before the vehicle driving limit is exceeded, regardless of the driver's driving skill. It can be returned to a range that does not exceed the limit.
When a disturbance is applied to the vehicle, the torque T transmitted by the steering shaft changes before the vehicle behavior becomes unstable due to an actual change in the steering angle or the like. Therefore, even when a disturbance is abruptly applied, the behavior of the vehicle is not affected by quickly controlling the additional torque Ta applied by the motor 15 according to the detection result of the torque T transmitted by the steering shaft. It can be prevented from becoming stable.
Further, since it is only necessary to detect the steering angle θ, the vehicle speed V, and the torque T transmitted by the steering shaft and control the motor 15, the configuration can be simplified and the cost can be reduced.
In addition, when the driver intentionally steers suddenly, the additional torque Ta applied by the motor 15 is increased, thereby promoting the driver's intentional steering and the driver's intention such as avoiding a front obstacle. Steering that reflects Further, when the frictional resistance of the road surface decreases, the vehicle behavior can be stabilized by reducing the additional torque Ta applied by the motor 15. Further, when steering is performed excessively more than necessary when the course is changed, the additional torque Ta applied by the motor 15 is reduced, so that the conventional steering correction of the course of the vehicle A as shown by the broken line in FIG. However, as indicated by the solid line, the behavior of the vehicle A can be stabilized and the course correction steering can be made unnecessary.
Further, as a part of the reference steering torque, the reference road surface reaction torque Tk corresponding to the reference tire side slip angle β obtained from the vehicle speed V and the steering angle θ is stored in the stored tire side slip angle β and road reaction force torque Tk. Is obtained from the linear relationship. As a result, compared with the case where the relationship between the tire side slip angle β and the road surface reaction force torque Tk is made non-linear accurately, steering is performed when the absolute value of the tire side slip angle β is large and the vehicle behavior tends to become unstable. The absolute value of the deviation ΔT between the torque T transmitted by the shaft and the reference steering torque can be made equal to or greater than the set value T1. That is, when the course is changed, steering is performed excessively more than necessary, or when the frictional resistance of the road surface is lowered and the vehicle behavior is likely to become unstable, the absolute value of the additional torque Ta applied by the motor 15 is reduced, The vehicle behavior can be stabilized, and when the driver intentionally steers suddenly, the additional torque applied by the actuator is increased to promote the driver's intentional steering. Steering that reflects the driver's intentions such as avoiding obstacles is possible.
[0019]
In addition, this invention is not limited to the said embodiment. For example, in the example shown in FIG. 4, the relationship between the deviation ΔT and the additional torque Ta applied by the motor 15 is linear, but may be nonlinear.
[0020]
【The invention's effect】
According to the present invention, when the behavior of the vehicle is likely to exceed the movement limit due to disturbance or the steering of the driver, the steering torque is positively controlled, so that even an inexperienced driver always keeps the vehicle appropriate like an expert driver. It is possible to provide a vehicle steering apparatus that can improve the safety by steering the vehicle back to the limit of motion and improving the safety at a low cost.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a configuration of a vehicle steering apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating functions of a control device for a vehicle steering apparatus according to an embodiment of the present invention. FIG. 4 is a flowchart showing a determination procedure of a driver's steering intention by the control device for a vehicle steering device according to the embodiment. The figure which shows the relationship of the additional torque which is given by the motor Figure 5 The figure which shows the course of the vehicle
2 Input shaft 3 Torque sensor 4 Output shaft 5 Steering angle sensor 15 Motor 16 Vehicle speed sensor 20 Control device

Claims (2)

A steering shaft that transmits the steering torque applied by the driver to the wheels;
An actuator for generating torque to be added to the steering torque;
A means for detecting torque transmitted by the steering shaft;
Vehicle speed detection means;
Rudder angle detection means;
Means for obtaining a reference steering torque based on the detected vehicle speed and steering angle;
Means for controlling an additional torque applied by the actuator so as to reduce a deviation between the detected torque and the reference steering torque ;
If the absolute value of the deviation between the detected torque and the reference steering torque is greater than or equal to the set value and the absolute value of the detected torque change acceleration is greater than or equal to the set value, the absolute value of the deviation is set. The absolute value of the additional torque applied by the actuator is larger than when the value is less than the value,
If the absolute value of the deviation between the detected torque and the reference steering torque is equal to or greater than the set value and the absolute value of the detected torque change acceleration is less than the set value, the absolute value of the deviation is set. The vehicle steering apparatus in which the absolute value of the additional torque applied by the actuator is made smaller than when the value is less than the value . As a part of the standard steering torque, the standard road surface reaction torque corresponding to the standard tire side slip angle obtained from the detected vehicle speed and rudder angle is a linear relationship between the stored standard tire side slip angle and the standard road surface reaction torque. The vehicle steering device according to claim 1, wherein the vehicle steering device is obtained from the following.

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