JP2009056888A - Vehicle steering system - Google Patents

Abstract

To realize a steer-by-wire type steering system using a transmission ratio variable device and a power steering device in a manner capable of applying an appropriate operation reaction torque to a steering wheel.
A vehicle steering device according to the present invention performs steering reaction force control with a transmission ratio variable device when no abnormality is detected in either the transmission ratio variable device or the power steering device, and the power steering device steers the steering. It is characterized by performing angle control. When an abnormality is detected in the transmission ratio variable device in a situation where no abnormality is detected in the word steering device, the transmission ratio variable mechanism of the transmission ratio variable device is locked and the control of the power steering device is controlled by the steering angle control. Gradually shift to torque control.
[Selection] Figure 4

Description

  The present invention relates to a vehicle steering apparatus that performs torque control and steering angle control using a transmission ratio variable device and a power steering device.

Conventionally, when a transmission ratio variable device fails, there is known a vehicle steering device that controls a power steering device based on an operation amount of a steering wheel, instead of controlling the power steering device based on an operation force of the steering wheel. (For example, refer to Patent Document 1).
JP 2007-90947 A

  By the way, in the technique described in Patent Document 1, in the event that the motor of the transmission ratio variable device has failed, before performing locking by the lock mechanism, instead of torque control of the power steering device based on the operating force of the steering wheel, steering is performed. A steer-by-wire steering system is realized by controlling the steering angle of the power steering device based on the operation amount of the wheel. However, in a state where the steer-by-wire type steering system is realized, the motor of the transmission ratio variable device has failed, so that it is not possible to apply an appropriate operation reaction torque to the steering wheel.

  An object of the present invention is to provide a vehicle steering device that realizes a steer-by-wire steering system using a transmission ratio variable device and a power steering device in a manner that can provide an appropriate operation reaction torque to a steering wheel. And

  Another object of the present invention is to provide a vehicle steering device that can appropriately prevent sudden change in torque due to switching from steering angle control to torque control when an abnormality occurs in the transmission ratio variable device.

  In order to achieve the above object, the vehicle steering apparatus according to the first invention performs steering reaction force control by the transmission ratio variable device when no abnormality is detected in either the transmission ratio variable device or the power steering device. The steering angle control is performed by the power steering device.

A second aspect of the present invention is the vehicle steering apparatus according to the first aspect,
If an abnormality is detected in the transmission ratio variable device under the condition that no abnormality is detected in the power steering device, the transmission ratio variable mechanism of the transmission ratio variable device is locked and the control of the power steering device is controlled from the steering angle control to the torque. It is characterized by gradually shifting to control.

A third invention is the vehicle steering system according to the second invention,
The stepwise transition from the steering angle control to the torque control of the power steering device is based on the difference between the target value of the steering angle control and the target value of the torque control when an abnormality is detected in the transmission ratio variable device. The method includes gradually changing a target current of an actuator of the power steering apparatus.

A fourth invention is a vehicle steering apparatus according to the second or third invention,
The target value for torque control of the power steering apparatus is determined using at least one parameter as a vehicle speed.

A fifth invention is the vehicle steering apparatus according to the fourth invention,
A target value for torque control of the power steering apparatus is determined by correcting a friction reaction force torque component.

A target steering reaction force determining means for determining a target steering reaction force for a vehicle steering apparatus according to a sixth invention;
Target steering angle determining means for determining a target steering angle;
Target assist torque determining means for determining the target assist torque;
Steering reaction force control means for controlling the transmission ratio variable device so as to realize the target steering reaction force;
Assist torque control means for controlling the power steering device so that the target assist torque is realized;
Steering angle control means for controlling the power steering device so that the target steering angle is realized,
The steering reaction force control means and the steering angle control means function when the transmission ratio variable device is normal,
The assist torque control means functions when an abnormality is detected in the transmission ratio variable device;
When the control of the power steering device shifts from the steering angle control by the steering angle control means to the torque control by the assist torque control means due to an abnormality of the transmission ratio variable device, the power steering device caused by the transition It is characterized by suppressing a sudden change in torque generated.

  According to the present invention, it is possible to realize a steer-by-wire steering system using a transmission ratio variable device and a power steering device in a mode in which an appropriate operation reaction torque can be applied to the steering wheel. Moreover, in one Example, the sudden change of the torque resulting from switching from steering angle control to torque control at the time of abnormality occurrence of the transmission ratio variable device can be appropriately prevented.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall view schematically showing an embodiment of a vehicle steering apparatus according to the present invention. The vehicle steering apparatus 10 includes a steering column 12 including a steering wheel 11 operated by a driver. The steering column 12 rotatably supports a steering shaft 14 that serves as a rotating shaft of the steering wheel 11. The steering shaft 14 is connected to an intermediate shaft (intermediate shaft) 16 via a rubber coupling 13 or the like. The intermediate shaft 16 is connected to the pinion 17, and the pinion 17 is meshed with the steering rack (steering rod) 18 in the steering gear box 31. One end of a tie rod 19 is connected to each end of the steering rack 18 and a steered wheel (not shown) is connected to the other end of each tie rod 19 via a knuckle arm or the like (not shown). Further, the intermediate shaft 16 or the steering shaft 14 is provided with a steering angle sensor 74 that generates a signal corresponding to the steering angle of the steering wheel 11 and a torque sensor 15 that generates a signal corresponding to the steering torque generated in the steering shaft. . The torque sensor 15 may be disposed closer to the steered wheels than the transmission ratio variable device 30, but is preferably disposed near the steering wheel 11 from the transmission ratio variable device 30.

  The vehicle steering device 10 includes a power steering device 20. The power steering apparatus 20 includes, as main components, a steering assist actuator 22 (hereinafter referred to as “assist motor 22”) and a rotation angle of the assist motor 22 (hereinafter also referred to as “steering motor rotation angle”). Is provided with a rotation angle sensor 24 for detecting. The assist motor 22 is composed of, for example, a three-phase AC motor. The assist motor 22 is provided coaxially with the steering rack 18 in the steering gear box 31 and assists the movement of the steering rack 18 by its driving force. The configuration itself of the power steering apparatus 20 may be arbitrary, for example, may be a configuration as disclosed in Japanese Patent Application Laid-Open No. 2007-90947. The assist motor 22 of the power steering device 20 is controlled by an ECU 80 described later. The control mode of the assist motor 22 will be described later.

  The vehicle steering device 10 includes a transmission ratio variable device 30. FIG. 2 is a cross-sectional view of the main components of the transmission ratio variable device 30. The transmission ratio variable device 30 includes an input shaft 60, an output shaft 62, a differential mechanism 40, an actuator 34 (hereinafter referred to as “VGRS motor 34”), and a rotation angle (hereinafter referred to as “reaction force motor rotation angle”) of the VGRS motor 34. A rotation angle sensor 76 for detecting ”and a lock mechanism 50. Note that the VGRS motor 34 is constituted by, for example, a three-phase AC motor. The differential mechanism 40 includes a driven gear 38, a stator gear 42, a wave generator 46, and a flexible gear 48, as will be described later.

  The lower end of the intermediate shaft 16 is connected to the upper end of the input shaft 60. A stator gear 42 is provided at the lower end of the input shaft 60. A pinion 17 is provided below the output shaft 62. A driven gear 38 is provided above the output shaft 62. Gears having different numbers of teeth (the number of teeth of the driven gear 38 <the number of teeth of the stator gear 42) are formed on the inner peripheral surfaces of the driven gear 38 and the stator gear 42, respectively. Inside the driven gear 38 and the stator gear 42, a flexible gear 48 that meshes simultaneously with each gear is provided. That is, the teeth formed inside the driven gear 38 and the stator gear 42 mesh with the teeth formed outside the flexible gear 48 (the number of teeth is the same as the number of teeth of the driven gear 38). The inner side of the flexible gear 48 is fitted on the outer ring of the wave generator 46. A case 34 a of the VGRS motor 34 is fixed to the housing 32. The VGRS motor 34 has a motor shaft 35, and the motor shaft 35 is connected to the cam of the wave generator 46. An input shaft 60 is rotatably inserted into the motor shaft 35. That is, the input shaft 60 and the motor shaft 35 are configured to be able to rotate independently of each other.

  FIG. 3 is a cross-sectional view of the locking mechanism 50 cut along line AA in FIG. The lock mechanism 50 is mounted around the motor shaft 35 of the VGRS motor 34. The lock mechanism 50 includes a lock lever (lock arm) 52 that can rotate around the rotation pin 54. The rotation pin 54 is fixed to the housing 32 of the transmission ratio variable device 30. As a result, the lock lever 52 is supported at a portion that cannot rotate with respect to the vehicle body such as the housing 32. At the tip of the lock lever 52, an engaging portion 52a that engages with a concave portion 37 of the lock holder 36 described later is provided.

  A substantially ring-shaped lock holder 36 is provided on the motor shaft 35 of the VGRS motor 34. The lock holder 36 is formed of a hard material, and is provided so as not to rotate with respect to the motor shaft 35 so as to rotate together with the motor shaft 35. On the periphery of the lock holder 36, a recess 37 is formed in which the engaging portion 52a of the lock lever 52 is engaged.

  The lock lever 52 is urged toward the lock holder 36 by a return spring 53 provided around the rotation pin 54. That is, the return spring 53 urges the lock lever 52 to rotate toward the lock holder 36 (motor shaft 35). When the engagement portion 52 a of the lock lever 52 is fitted into the recess 37, the lock lever 52 is held in the recess 37 by the elastic force of the return spring 53. Thereby, the locked state is realized.

  When the locked state is realized, the motor shaft 35 of the VGRS motor 34 is fixed to the housing 32 of the transmission ratio variable device 30 by the engagement of the lock lever 52 and the lock holder 36. In other words, the rotation of the motor shaft 35 of the VGRS motor 34 is locked by the engaging portion 52a of the lock lever 52 fitted in the recess 37 of the lock holder 36, and cannot be rotated with respect to the housing 32 (vehicle body). It becomes a state. In this case, when the steering wheel 11 rotates, the input shaft 60 (stator gear 42) rotates, and the driven gear 38 rotates through the flexible gear 48. At this time, a rotational reaction force is transmitted to the motor shaft 35 via the flexible gear 48. However, since the motor shaft 35 is in a non-rotatable state by the lock lever 52, the motor shaft 35 is not rotated. It is not rotated by force (that is, the rotation of the steering wheel 11 is reliably transmitted to the steered wheels even in the locked state).

  The lock mechanism 50 is electromagnetically operated by a solenoid 56. For example, when the solenoid 56 is energized when the ignition is on (when the system is normal), the lock lever 52 rotates against the urging force from the return spring 53 due to the suction force generated by the solenoid 56, and the lock lever 52 The engaging portion 52 a is detached from the recess 37 of the lock holder 36. Thereby, the unlocked state is realized. When the unlocked state is realized, a state in which the differential mechanism 40 functions is formed.

  Note that the transmission ratio variable device 30 itself has a VGRS motor 34 that can transmit rotational torque (steering reaction force) to the input shaft 60 (and consequently the steering shaft 14 and the steering wheel 11), the input shaft 60, and the output shaft 62. As long as it includes a differential mechanism 40 that absorbs the rotational difference between the input shaft 60 and the lock mechanism 50 that directly connects the input shaft 60 and the output shaft 62 when locked, and a VGRS motor. Configurations such as 34 and differential mechanism 40 may be configurations other than those described above as long as equivalent functions can be realized.

  Next, main operations of the above-described vehicle steering device 10 will be described. The vehicle steering apparatus 10 includes an ECU 80 that performs various controls described below. The ECU 80 may be a single ECU that controls the steering system, or may be realized in cooperation with two or more ECUs. Information or data for realizing various controls described below is input to the ECU 80, and more specifically, the torque sensor 15, the rotation angle sensor 24, the steering angle sensor 74, and the rotation angle sensor 76 are input to the ECU 80. Various sensor values are input from a vehicle speed sensor (not shown) or the like. Further, the ECU 80 includes a current sensor (not shown) for detecting an operating current (hereinafter referred to as “reaction motor current”) of the VGRS motor 34 of the transmission ratio variable device 30, and an assist motor 22 of the power steering device 20. Is connected to a current sensor (not shown) for detecting the operating current (hereinafter referred to as “steering motor current”), and signals representing the reaction force motor current and the steering motor current are input. In addition, the transmission ratio variable device 30 and the power steering device 20 are connected to the ECU 80 as control targets.

  FIG. 4 is a diagram schematically showing the control contents realized by the ECU 80 when the system is normal. When the system is normal, that is, when no abnormality is detected in either the transmission ratio variable device 30 or the power steering device 20, the ECU 80 performs steering reaction force control by the transmission ratio variable device 30 and the power steering device 20 controls the steering angle. Take control. The steering reaction force control and the steering angle control are realized by a steering reaction force control unit 82 and a steering angle control unit 84 of the ECU 80, as schematically shown in FIG.

  FIG. 5 is a functional block diagram of the steering reaction force control unit 82 and the steering angle control unit 84 of the ECU 80.

As shown in FIG. 5, the steering angle control unit 84 sets the target yaw rate (γ *) based on the steering angle (handle angle) θ input from the steering angle sensor 74 and the vehicle speed v input from the vehicle speed sensor. Calculated. Note that the symbol * indicates a target value. Next, a target turning motor rotation angle (θ _esp *) is calculated based on the target yaw rate (γ *). Next, based on the difference between the turning motor rotation angle (θ _esp ) input from the rotation angle sensor 24 and the target turning motor rotation angle (θ _esp *), the target turning motor current (I _esp *) is calculated. Is done. Next, the motor drive duty (DUTY _esp ) is calculated based on the difference between the steered motor current (detected value) and the target steered motor current (I _esp *). At this time, the motor drive duty (DUTY _esp ) is determined in consideration of the turning motor rotation angle (θ _esp ) from the rotation angle sensor 24. The assist motor 22 of the power steering apparatus 20 is controlled in accordance with the motor drive duty (DUTY _esp ) calculated and output in this manner, _thereby realizing steering angle control.

As shown in FIG. 5, in the steering reaction force control unit 82, the target steering torque (Tr *) is determined based on the steering angle (handle angle) θ input from the steering angle sensor 74 and the vehicle speed v input from the vehicle speed sensor. ) Is calculated. Next, the target reaction force motor current (I _vgrs *) is calculated based on the difference between the steering torque (Tr) input from the torque sensor 15 and the target steering torque (Tr *). Next, the motor drive duty (DUTY _vgrs ) is calculated based on the difference between the reaction force motor current (detected value) and the target reaction force motor current (I _vgrs *). At this time, the motor drive duty (DUTY _vgrs ) is determined in consideration of the turning motor rotation angle (θ _vgrs ) from the rotation angle sensor 76. The VGRS motor 34 of the transmission ratio variable device 30 is controlled according to the motor drive duty (DUTY _vgrs ) calculated and output in this manner, _thereby realizing steering reaction force control.

  Thus, according to the present embodiment, the transmission ratio variable device 30 conventionally used for steering angle control is used for steering reaction force control, and the power steering device 20 conventionally used for torque assist control is used for steering angle control. Thus, a so-called steer-by-wire type steering system using the differential mechanism 40 of the transmission ratio variable device 30 can be realized.

  Next, the fail safe in the vehicle steering apparatus 10 of the present embodiment will be described.

  Table 1 below is a table that represents a possible failure state in the vehicle steering apparatus 10 of the present embodiment and a control mode corresponding thereto.

In the vehicle steering apparatus 10 of the present embodiment, as shown in Table 1, two failure states I and II are assumed. The failure state I is a state in which a failure is detected in at least one of the rudder angle sensor 74, the VGRS motor 34, and the rotation angle sensor 76 of the VGRS motor 34. More generally, the failure state I refers to a failure state in which torque assist control by the power steering device 20 is possible but steering reaction force control by the transmission ratio variable device 30 is not possible. Therefore, depending on the mode of torque assist control by the power steering device 20 and the mode of steering reaction force control by the transmission ratio variable device 30, the failure detection part may be different from that shown in Table 1.

  When the failure state I is detected, as shown in Table 1, a lock state is formed by the lock mechanism 50 of the transmission ratio variable device 30 (control of the transmission ratio variable device 30 is prohibited), and torque generated by the power steering device 20 Assist control is executed. That is, the control of the transmission ratio variable device 30 shifts from the normal steering reaction force control to the control prohibited state, and the control of the power steering device 20 shifts from the normal steering angle control to the torque assist control.

  The failure state II is a state in which a failure is detected in at least one of the torque sensor 15, the assist motor 22, and the rotation angle sensor 24 of the assist motor 22. Note that when both the above-described failure state I and failure state II are detected, the failure state II has priority. When the failure state II is detected, as shown in Table 1, the control of the power steering device 20 and the transmission ratio variable device 30 are both prohibited.

  FIG. 6 is a flowchart showing a process related to the above-described failure state I and realized by the ECU 80 of the present embodiment. The processing routine of FIG. 6 may be repeatedly executed at predetermined intervals until, for example, after the ignition switch of the vehicle is turned on, the processing routine is turned off.

In step 100, it is determined whether or not the system is normal. When the system is normal, the processing of steps 102 to 106 is executed, and the steering angle control is realized as described above (see FIG. 5). That is, a target turning angle (target turning motor rotation angle θ _esp *) corresponding to the steering angle θ or the like is calculated (step 102), and according to a deviation between the target turning angle and the actual turning angle (θ _esp ). Then, the target current I0 * is calculated (step 104), and the calculated target current I0 * is used as the target turning motor current (I _esp *) (step 106). On the other hand, if the system is not normal, the process proceeds to step 108.

In step 108, it is determined whether or not the cause of the system abnormality is the failure state I. If it is in the fault state I, the process proceeds to step 112. If it is not the fault state I (typically, it is in the fault state II), the process proceeds to step 110. In step 110, the target turning motor current (I _esp *) is set to zero (that is, control of the power steering device 20 is prohibited).

In step 112, the target current I0 * is calculated according to the output value from the torque sensor 15 and the vehicle speed from the vehicle speed sensor. Note that a map used in normal torque assist control may be used to calculate the target current I0 *. For example, a map as shown in FIG. 7 is used. In this case, it is determined whether the vehicle speed belongs to a high speed range, a medium speed range, or a low speed range, and a base assist current IT _base * corresponding to the torque value is calculated using a curve corresponding to the speed range to which the vehicle speed belongs. The Here, target current I0 * is calculated as target current I0 * = base assist current IT _base *.

  In step 120, the current correction value ΔI is calculated. This process will be described later with reference to FIG.

In step 130, using the target current I0 * calculated in step 112 and the current correction value ΔI calculated in step 120, the target turning motor current I _esp * is I _esp * = I0 * −ΔI. Is calculated as That is, the target current I0 * is corrected by the current correction value ΔI, and the final target turning motor current I _esp * is derived.

  FIG. 8 is a flowchart illustrating an example of a calculation process of the current correction value ΔI.

  In step 122, it is determined whether or not the failure state I is detected for the first time in the current cycle. If the failure state I is detected for the first time in the current cycle, the process proceeds to step 124. Otherwise, that is, if the failure state I is detected continuously from the previous cycle, the process proceeds to step 126. move on. When the process proceeds to step 124, the lock mechanism 50 of the transmission ratio variable device 30 is locked as described above, and the control of the transmission ratio variable device 30 is disabled.

In step 124, the current correction value ΔI = IT * of the current cycle−I0 * of the previous cycle is calculated. The IT * of the current cycle is the target current IT * calculated in step 112 of the current cycle. The previous cycle I0 * is the target current I0 * calculated in step 104 of the previous cycle (that is, the target turning motor current I _esp * of the previous cycle). The current correction value ΔI may be calculated as current correction value ΔI = (current cycle IT * −previous cycle I0 *) × K. In this case, K is a constant of 0 <K <1.

  In step 126, the current correction value ΔI is calculated as current correction value ΔI = ΔI × K of the previous cycle. Here, K is a constant of 0 <K <1.

  In step 128, it is determined whether or not the absolute value of the current correction value ΔI calculated in step 126 is less than a predetermined value. The predetermined value is a value for determining whether or not the current correction value ΔI is a value that is substantially large enough to have a correction significance, and therefore corresponds to the minimum resolution of the duty that can be set by the duty control of the assist motor 22. It may be a value to be. In this step 128, when the absolute value of the current correction value ΔI is less than the predetermined value, the process proceeds to step 129. In other cases, the current cycle calculation process is terminated as it is.

In step 129, the current correction value ΔI calculated in step 126 is set to zero. When the current correction value ΔI is set to 0, I _esp * = I 0 * in the process of step 130 in FIG. Therefore, the transition from the steering angle control to the torque assist control is completed.

In this way, according to the process shown in FIG. 8, the current correction value ΔI is initially set to the difference between the target current I0 * of the previous cycle and the target current IT * of the current cycle (or a value K times the difference). The value gradually decreases with time. Accordingly, the current correction value ΔI used in step 130 of FIG. 6 described above initially sets the difference (or K times the difference) between the target current I0 * of the previous cycle and the target current IT * of the current cycle. The value gradually decreases with time. Therefore, in the present embodiment, the target steering motor current I _esp * is not immediately set to the target current IT * in the cycle in which the failure state I is detected, but the target steering motor current I _esp * The cycle target current I0 * (target turning motor current I _esp *) is gradually changed to the target current IT *. Accordingly, when the failure state I is detected, if the control of the power steering device 20 is immediately switched from the steering angle control to the torque assist control, a sudden change may occur in the torque generated by the assist motor 22 at the time of the switching. In the example, such a sudden change can be prevented, and the control of the power steering device 20 can be switched from the steering angle control to the torque assist control in a manner that does not give the user a sense of incongruity. That is, in the configuration in which the control of the power steering device 20 is switched (shifted) from the steering angle control to the torque control when the abnormality of the transmission ratio variable device 30 occurs, the steering torque is generated even when the abnormality of the transmission ratio variable device 30 occurs. Although the steering operation of the user can still be supported, when switching from the steering angle control to the torque control, the generated torque of the power steering apparatus 20 may change suddenly due to the switching, which may give the user a sense of incongruity. In this embodiment, such a sense of incongruity can be prevented by gradually switching the control of the power steering device 20 from the steering angle control to the torque assist control.

  In the process shown in FIG. 8, the value of the current correction value ΔI is reduced exponentially with the passage of time. However, the reduction mode is arbitrary as long as it is gradually reduced with the passage of time. For example, the value of the current correction value ΔI may be reduced by a certain amount with the passage of time.

  FIG. 9 is a diagram showing the relationship between the vehicle speed and the steering gear ratio of the vehicle steering device 10. In FIG. 9, a curve indicated as a normal characteristic indicates a characteristic curve that may be employed when the system is normal. Such characteristics are realized by the steering angle control of the power steering apparatus 20 as described above. By the way, as described above, when the failure state I is detected and the lock state is formed by the lock mechanism 50 of the transmission ratio variable device 30, the steering gear ratio of the vehicle steering device 10 is fixed. At this time, in order to ensure vehicle stability during high-speed traveling, it is preferable to set the steering gear ratio at the time of fixing to a characteristic such as an abnormal characteristic I in FIG. However, in the case of this abnormal characteristic I, there is a problem that the differential angle of the VGRS motor 34 when the system is normal is large and the accuracy of the steering reaction force control is deteriorated.

  Therefore, preferably, the transmission ratio variable device 30 is configured so that the steering gear ratio at the time of fixing becomes a characteristic such as the characteristic II at the time of abnormality in FIG. The target current IT * is calculated by the method described below.

  FIG. 10 is a flowchart showing another example of a method for calculating the target current IT *. The process shown in FIG. 10 may be applied as the process of step 112 in FIG. 6 described above.

In step 200, the base assist current IT _base * is calculated according to the torque value from the torque sensor 15 and the vehicle speed from the vehicle speed sensor, using the map shown in FIG.

  In Step 202, based on the torque value from the torque sensor 15 and the vehicle speed from the vehicle speed sensor, the torque assist correction amount IT_1 * is calculated using the map shown in FIG. As shown in FIG. 11, the map used for calculating the torque assist correction amount IT_1 * is created so that the assist torque decreases as the vehicle speed increases. That is, the amount of reduction in assist torque with respect to the detection value of the torque sensor 15 increases as the vehicle speed increases.

  In step 204, the viscosity acting on the operation of the steering wheel 11 using the map shown in FIG. 12 based on the steering angular velocity (time differential value of the steering angle) from the steering angle sensor 74 and the vehicle speed from the vehicle speed sensor. The reaction force correction amount IT_2 * is calculated. As shown in FIG. 12, the map used to calculate the viscosity reaction force correction amount IT_2 * is created so that the assist torque decreases (the viscosity reaction force increases) as the vehicle speed increases. That is, the amount of reduction of the assist torque with respect to the steering angular speed increases at a high speed that tends to be unstable.

  In step 204, based on the vehicle speed from the vehicle speed sensor, the friction reaction force torque correction amount IT_3 * acting on the operation of the steering wheel 11 is calculated using the map shown in FIG. Specifically, the friction reaction force torque corresponding to the vehicle speed is calculated using the map shown in FIG. 13, and the friction reaction force torque correction amount IT_3 * corresponding to the calculated friction reaction force torque is calculated. The map shown in FIG. 13 is created so that a larger frictional reaction force is added at high speed, which tends to be unstable.

In step 208, the target current IT * is calculated as IT * = IT _base * + IT_1 * + IT_2 * + IT_3 * based on the values obtained in steps 200 to 206 described above. When IT * becomes negative, IT * = 0 may be set.

  As described above, according to the processing shown in FIG. 10, even when the steering gear ratio when the failure state I is detected has a characteristic disadvantageous for high-speed stability (for example, the abnormal-time characteristic II in FIG. 9), By increasing the friction, viscosity, and spring characteristics of torque assist control of the power steering device 20, vehicle stability during high-speed traveling can be ensured. As a result, it is possible to ensure the vehicle stability during high-speed traveling while improving the accuracy of the steering reaction force control by the transmission ratio variable device 30 when the system is normal.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

1 is an overall view schematically showing an embodiment of a vehicle steering apparatus according to the present invention. 3 is a cross-sectional view of main components of the transmission ratio variable device 30. FIG. It is sectional drawing of the locking mechanism 50 cut | disconnected by line AA of FIG. It is a figure which shows typically the control content implement | achieved by ECU80 at the time of a system normal. 3 is a functional block diagram of a steering reaction force control unit 82 and a steering angle control unit 84 of an ECU 80. FIG. 4 is a flowchart showing processing related to a failure state I. It is a figure which shows an example of a normal time map. It is a flowchart which shows an example of the calculation process of electric current correction value (DELTA) I. It is a figure which shows the relationship between a vehicle speed and the steering gear ratio of the steering device 10 for vehicles. It is a flowchart which shows another example of the calculation method of target current IT *. It is a figure which shows the map used for calculation of torque assist correction amount IT_1 *. It is a figure which shows the map used for calculation of viscosity reaction force correction amount IT_2 *. It is a figure which shows the map used for calculation of friction reaction force torque correction amount IT_3 *.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle steering device 11 Steering wheel 12 Steering column 13 Rubber coupling 14 Steering shaft 15 Torque sensor 16 Intermediate shaft 17 Pinion 18 Steering rack 19 Tie rod 20 Power steering device 22 Assist motor 24 Rotation angle sensor 30 Transmission ratio variable device 31 Steering gear Box 32 Housing 34 VGRS motor 35 Motor shaft 36 Lock holder 37 Recess 38 Driven gear 40 Differential mechanism 42 Stator gear 46 Wave generator 48 Flexible gear 50 Lock mechanism 52 Lock lever 52a Engaging portion 53 Return spring 54 Rotating pin 56 Solenoid 60 Input shaft 62 Output shaft 74 Rudder angle sensor 76 Rotation angle sensor 80 ECU
82 Steering reaction force control unit 84 Steering angle control unit

Claims (6)

  When no abnormality is detected in either the transmission ratio variable device or the power steering device, the steering reaction force control is performed by the transmission ratio variable device, and the steering angle control is performed by the power steering device. apparatus.   If an abnormality is detected in the transmission ratio variable device under the condition that no abnormality is detected in the power steering device, the transmission ratio variable mechanism of the transmission ratio variable device is locked and the control of the power steering device is controlled from the steering angle control to the torque. The vehicle steering apparatus according to claim 1, wherein the vehicle steering apparatus is gradually shifted to control.   The stepwise transition from the steering angle control to the torque control of the power steering device is based on the difference between the target value of the steering angle control and the target value of the torque control when an abnormality is detected in the transmission ratio variable device. The vehicle steering apparatus according to claim 2, comprising gradually changing a target current of an actuator of the power steering apparatus.   4. The vehicle steering apparatus according to claim 2, wherein the target value for torque control of the power steering apparatus is determined using at least one parameter as a vehicle speed. 5.   The vehicle steering apparatus according to claim 4, wherein a target value for torque control of the power steering apparatus is determined by correcting a friction reaction force torque component. A target steering reaction force determining means for determining a target steering reaction force;
Target steering angle determining means for determining a target steering angle;
Target assist torque determining means for determining the target assist torque;
Steering reaction force control means for controlling the transmission ratio variable device so as to realize the target steering reaction force;
Assist torque control means for controlling the power steering device so that the target assist torque is realized;
Steering angle control means for controlling the power steering device so that the target steering angle is realized,
The steering reaction force control means and the steering angle control means function when the transmission ratio variable device is normal,
The assist torque control means functions when an abnormality is detected in the transmission ratio variable device;
When the control of the power steering device shifts from the steering angle control by the steering angle control means to the torque control by the assist torque control means due to an abnormality of the transmission ratio variable device, the power steering device caused by the transition A vehicular steering apparatus characterized by suppressing a sudden change in torque generated.