JP2008049963A - Vehicular steering control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular steering control device for improving steering feeling in response to vehicle speed. <P>SOLUTION: A vehicle steering device 1 mainly comprises a steering gear box 2, a friction characteristic variable mechanism 3, wheel speed sensors 4a-4d, a steering torque sensor 5, a steering angle sensor 6 and an ECU 7. In a steering force transmission system, the steering gear box 2 is connected to a steering wheel 8 through a steering shaft 9, and the friction characteristic variable mechanism 3 for changing friction characteristic of a rank and pinion mechanism is fitted to the steering gear box 2. The ECU 7 sets the friction torque corresponding to the car speed and the steering angle by using a friction characteristic map setting the friction torque corresponding to the car speed and the steering angle and a bad road map setting the friction torque in the case of running in a bad road at low speed, and changes the friction characteristic with the friction characteristic variable mechanism 3 according to the set friction torque. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vehicle steering apparatus capable of changing a friction characteristic in a steering force transmission system of a vehicle.

2. Description of the Related Art Conventionally, as a vehicle steering apparatus that can change the friction characteristic of a vehicle, as described in Japanese Patent Application Laid-Open No. 2005-228561, one that changes a friction characteristic according to a driving operation situation is known. When this device detects that the driver is operating the steering wheel with one hand, the frictional characteristic variable mechanism provided in the steering force transmission system is used to control the steering torque relative to the steering torque compared to when the steering wheel is operated with both hands. The friction characteristic is changed so that the steering angle is increased.
JP 2006-142912 A

  However, in the vehicle steering apparatus described in Patent Document 1, the friction characteristic is changed according to the driving operation status of the driver, but the friction characteristic is not changed according to the vehicle speed of the vehicle. Therefore, the steering feeling cannot be improved finely according to the vehicle speed.

  Therefore, an object of the present invention is to provide a vehicle steering apparatus that improves the steering feeling in accordance with the vehicle speed of the vehicle.

  A vehicle steering apparatus according to the present invention includes a vehicle speed detection unit that detects a vehicle speed of a vehicle, a friction characteristic variable unit that is provided in a steering force transmission system and that can change a friction characteristic in the steering force transmission system, and a vehicle speed detection unit. And a control means for changing the friction characteristic by the friction characteristic variable means according to the vehicle speed detected in step (b).

  In this vehicle steering apparatus, the friction characteristic of the steering force transmission system is changed according to the vehicle speed detected by the vehicle speed detection means. Therefore, by changing the friction characteristic in the steering force transmission system according to the vehicle speed, the hysteresis width in the steering characteristic can be adjusted, and the steering feeling can be improved according to the vehicle speed of the vehicle. For example, by increasing the friction and increasing the hysteresis width during high-speed driving, it is possible to improve the stability of the rudder during high-speed driving and improving the steering wheel return performance by reducing the friction during low-speed driving. It becomes possible to make it.

  The vehicle steering apparatus according to the present invention further includes a steering angle detection unit that detects a steering angle of the vehicle, and the control unit has a smaller steering angle detected by the steering angle detection unit than a large steering angle. It is preferable to reduce the friction. In this vehicle steering apparatus, when the vehicle steering angle detected by the steering angle detection means is small, the friction characteristic is changed so that the friction in the steering force transmission system is small, and the hysteresis width in the steering characteristic is small. For this reason, yaw is likely to be generated even with a small steering torque in the vicinity of the straight traveling neutrality, so that the correction steering can be easily performed in the vicinity of the straight traveling neutrality. In particular, when the friction of the steering force transmission system is increased during high-speed traveling, it becomes easier to perform corrective steering near the straight-running neutral position.

  In addition, the vehicle steering apparatus according to the present invention includes a traveling state determination unit that determines a traveling state of the vehicle, the control unit determines that the traveling state determined by the traveling state determination unit is a bad road, and the vehicle speed. When the vehicle speed detected by the detection means is lower than a predetermined value, it is preferable to increase the friction compared to the friction according to the vehicle speed. Here, the predetermined value is a value indicating an upper limit value of a vehicle speed range in which the vehicle is traveling at a low speed. Therefore, the case where the vehicle speed is lower than the predetermined value means a case where the vehicle is traveling at a low speed. In this vehicle steering device, when the vehicle travels on a rough road at a low speed, the friction of the steering force transmission system increases. Then, the clearance of gears and the like constituting the steering force transmission system (for example, when a rack and pinion mechanism is adopted as the steering force transmission system), the clearance between the rack and the pinion is reduced. For this reason, it is possible to reduce the rattling noise of the steering force transmission system caused by traveling on a rough road. If the friction of the steering force transmission system is reduced when traveling at low speed, the clearance of the gears etc. constituting the steering force transmission system will increase and the rattling noise will increase. In order to reduce the clearance, it is necessary to increase the friction of the steering force transmission system.

  According to the present invention, it is possible to improve the steering feeling according to the vehicle speed by changing the friction characteristic in the steering force transmission system according to the vehicle speed.

  Hereinafter, an embodiment of a vehicle steering apparatus according to the present invention will be described with reference to the drawings.

  With reference to FIG.1 and FIG.2, the vehicle steering apparatus 1 which concerns on this Embodiment is demonstrated. FIG. 1 is a diagram illustrating a configuration of a vehicle steering apparatus according to the present embodiment. FIG. 2 is a diagram illustrating a configuration of a friction characteristic variable mechanism of the vehicle steering apparatus.

  The vehicle steering device 1 transmits the steering force generated by the driver's steering operation to the vehicle steering wheels 10a and 10b via the steering force transmission system. Furthermore, the vehicle steering device 1 changes the friction characteristic of the steering force transmission system according to the vehicle speed and the traveling state. Therefore, as shown in FIG. 1, the vehicle steering apparatus 1 mainly includes a steering gear box 2, a friction characteristic variable mechanism 3, wheel speed sensors 4a to 4d, a steering torque sensor 5, a steering angle sensor 6, and an ECU (Electronic). Control Unit) 7.

  In the steering force transmission system, the steering gear box 2 is connected to the handle 8 via the steering shaft 9. A steering torque sensor 5 and a steering angle sensor 6 are disposed on the steering shaft 9. The steering gear box 2 is composed of a rack and pinion mechanism, and left and right steering wheels 10a and 10b are attached to both ends of the steering gear box 2 via tie rods or the like. The steering gear box 2 is provided with a friction characteristic variable mechanism 3 that changes the friction of the rack and pinion mechanism. Wheel speed sensors 4a to 4d are disposed on the front and rear wheels 10a to 10d including the steering wheels 10a and 10b, respectively.

  As shown in FIG. 2, the friction characteristic variable mechanism 3 is provided in the steering gear box 2 including the rack 11 and the pinion 12 as main components, and the friction characteristic is changed by changing the magnitude of the gear friction in the steering gear box 2. It can be changed. The friction characteristic variable mechanism 3 includes a motor 13. The motor 13 functions as an actuator that adjusts increase / decrease in coulomb friction and elastic friction in gear friction, and adjusts the pressing force of the rack guide 14 against the rack 11 to increase / decrease coulomb friction and elastic friction. The rack guide 14 is a member that is installed on the opposite side of the pinion 12 across the rack 11 and supports the rack 11 by pressing it toward the pinion 12.

  The rotating shaft 17 of the motor 13 passes through a base member 16 fixed to the gear housing 15 of the steering gear box 2, and a screw that engages with the base member 16 is engraved on the peripheral surface thereof. Therefore, when the motor 13 is driven, the rotating shaft 17 rotates and advances and retreats with respect to the rack guide 14. A plate 18 is attached to the tip of the rotating shaft 17. A spring 19 is contracted between the plate 18 and the rack guide 14. The spring 19 is a biasing unit that biases the rack guide 14 toward the pinion 12.

  When the plate 18 moves forward so as to approach the rack guide 14 by driving the motor 13, the pressing force of the rack guide 14 against the rack 11 increases, and the Coulomb friction and the elastic friction increase. On the other hand, when the plate 18 is moved away from the rack guide 14 by driving the motor 13, the pressing force of the rack guide 14 against the rack 11 is reduced, and the Coulomb friction and the elastic friction are reduced.

  The rack guide 14 is provided with an O-ring 20 on the outer periphery thereof and is fitted in the gear housing 15. The O-ring 20 functions as an elastic support member that adjusts the radial clearance of the rack guide 14 and supports the rack guide 14. The radial clearance of the rack guide 14 is caused by elastic deformation of the O-ring 20, and the elastic friction between the rack 11 and the pinion 12 gradually increases as the rack guide 14 moves with the stroke of the rack 11. The rate of increase in elastic friction with respect to the rack stroke is the elastic friction gradient. By changing the distance between the steering gear box 2 and the rack guide 14, the radial clearance of the rack guide 14 caused by elastic deformation of the O-ring 20 can be changed, and the inclination angle of the elastic friction gradient can be adjusted. .

FIG. 3 is a diagram showing the relationship between pinion torque and rack stroke. As shown in FIG. 3, in the general friction characteristic when the friction characteristic is fixed (hereinafter referred to as “general friction characteristic”), when torque is applied to the pinion 12 (handle 8), the Coulomb friction C ₀ and rack 11 while being elastically frictional E ₀ is gradually stroke. Then, the friction characteristics when the variable mechanism 3 of the motor 13 to advance the plate 18 to increase the friction between the rack 11 and the pinion 12, a large elastic friction Ea than larger Coulomb friction Ca and elastic frictional E ₀ than Coulomb friction C ₀ Occurs. For this reason, the pinion torque with respect to the rack stroke increases, and the handle 8 becomes heavy. Furthermore, friction characteristics when the variable mechanism 3 of the motor 13 to retract the plate 18 to reduce friction between the rack 11 and the pinion 12, a small elastic friction Eb than smaller Coulomb friction Cb and elastic frictional E ₀ than Coulomb friction C ₀ Occurs. Therefore, the pinion torque with respect to the rack stroke is reduced and the handle 8 is lightened.

  The wheel speed sensors 4a to 4d are sensors that detect the rotational speeds of the wheels 10a to 10d, respectively. The wheel speed sensors 4a to 4d transmit the detected values to the ECU 7 as wheel speed signals. In the ECU 7, the vehicle speed is obtained from the detection values of the wheel speed sensors 4a to 4d.

  The steering torque sensor 5 is a sensor that detects the steering torque input from the handle 8. The steering torque sensor 5 transmits the detected value to the ECU 7 as a steering torque signal.

  The steering angle sensor 6 is a sensor that detects the rotation angle and rotation direction of the steering shaft 9 (the steering angle and steering direction of the handle 8). The steering angle sensor 6 transmits the detected value to the ECU 7 as a steering angle signal.

  The ECU 7 is an electronic control unit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The ECU 7 is connected to the friction characteristic variable mechanism 3, the wheel speed sensors 4a to 4d, the steering torque sensor 5, and the steering angle sensor 6. The ECU 7 changes the friction characteristics of the friction characteristic variable mechanism 3 based on the wheel speed signals from the wheel speed sensors 4a to 4d, the steering torque signal from the steering torque sensor 5, and the steering angle signal from the steering angle sensor 6. Control for. For this purpose, the ECU 7 holds a friction characteristic map and a rough road map in which a friction torque according to the vehicle speed and the steering angle is set.

  FIG. 4 is a diagram showing a friction characteristic map and a rough road map. As shown in FIG. 4, the friction characteristic map shows the relationship between the steering angle and the friction torque when the vehicle is traveling at high speed, medium speed, and low speed. Each vehicle speed is set appropriately. In the low-speed friction characteristic map, a friction torque smaller than the friction torque of the general friction characteristic is set, and in the high-speed friction characteristic map, a friction torque larger than the friction torque of the general friction characteristic is set. In this friction characteristic map, the friction torque is set so as to be intermediate between the high speed friction characteristic map and the low speed friction characteristic map. In the friction characteristic map corresponding to each vehicle speed, a larger friction torque is set as the steering angle increases. In addition, the friction characteristic map corresponding to each vehicle speed is set to a friction torque that decreases rapidly as it approaches near straight neutrality (steering angle is near 0 degrees and steering is in a neutral state). It is smaller than the characteristic friction torque. In the rough road map, only the friction torque when traveling at a low speed is set, and a larger friction torque is set than the friction torque in the low-speed friction characteristic map in the entire steering angle region. Since the friction characteristic map is set only for three vehicle speeds of high speed, medium speed, and low speed, the other vehicle speeds are linearly interpolated in the ECU 7 using the high speed, medium speed, and low speed friction characteristic maps. Thus, a friction characteristic map of the corresponding vehicle speed is obtained.

  First, the ECU 7 acquires the vehicle speed, steering angle, and steering torque of the vehicle from the wheel speed signal, the steering angle signal, and the steering torque signal. Then, the ECU 7 selects either the friction characteristic map or the rough road map based on the vehicle speed, the steering angle, and the steering torque. When the steering angle is equal to or less than the straight travel threshold, the steering torque variation is equal to or greater than the variation threshold, and the vehicle speed is equal to or less than the low speed threshold, the rough road map is selected. On the other hand, if any one of the steering angle is equal to or less than the straight travel threshold and the steering torque variation is equal to or greater than the variation threshold and the vehicle speed is equal to or less than the low speed threshold, the friction characteristic map is selected according to the vehicle speed. Here, the straight-ahead threshold is a maximum value of the steering angle at which it is determined that the driver is driving the vehicle straight. The fluctuation threshold is a minimum value of the steering torque input to the steering shaft 9 from the road surface that is determined to be a bad road via the steering wheels 10a and 10b. That is, when the steering angle is equal to or less than the straight travel threshold and the steering torque variation is equal to or greater than the variation threshold, an external force is applied to the steered wheels 10a and 10b depending on the road surface condition (bad road) even though the vehicle is traveling straight, and the steering shaft 9 is a case where torque is generated. The low speed threshold is the maximum value in the vehicle speed range in which it is determined that the vehicle is traveling at a low speed. Therefore, when the vehicle speed is equal to or lower than the low speed threshold, the vehicle is traveling at a low speed, and when the vehicle speed is higher than the low speed threshold, the vehicle is traveling at a medium speed or high speed. And ECU7 extracts the friction torque according to a steering angle based on the selected map.

  Then, the ECU 7 controls the rotation of the motor 13 of the friction characteristic variable mechanism 3 so that the friction of the steering force transmission system becomes the extracted friction torque. Specifically, the ECU 7 holds a friction torque map (not shown) showing the relationship between the friction torque and the distance between the plate 18 and the rack guide 14, and the friction torque extracted based on this friction torque map. The motor current required to obtain the interval is calculated. The ECU 7 controls the rotation of the motor 13 by sending the motor current to the motor 13 and adjusts the distance between the plate 18 and the rack guide 14 to adjust the friction torque.

  FIG. 5 is a diagram showing the relationship between steering torque and yaw rate in general friction characteristics. FIG. 6 is a diagram showing the relationship between the steering torque and the yaw rate when the friction is increased when the friction characteristic is variable. FIG. 7 is a diagram showing the relationship between the steering torque and the yaw rate when the friction is reduced when the friction characteristic is variable. FIG. 8 is a diagram showing the relationship between steering torque and steering angle in general friction characteristics. FIG. 9 is a diagram showing the relationship between the steering torque and the steering angle when the friction is reduced when the friction characteristic is variable. FIG. 10 is an enlarged view of the case where the steering torque in FIG. FIG. 11 is an enlarged view of the case where the steering torque in FIG. FIG. 12 is an enlarged view of the case where the steering torque in FIG.

  When traveling at high speed, the friction between the rack 11 and the pinion 12 is increased by using the friction characteristic variable mechanism 3 so that the friction torque with respect to the steering force transmission system increases according to the high-speed friction characteristic map. As is clear from the comparison between FIG. 5 and FIG. 6, the hysteresis width increases as the friction increases. Therefore, when the steering torque is increased, the yaw rate does not fluctuate greatly even if the steering torque is changed to some extent, the steering can be stabilized during high-speed turning, and the driver's steering holding power can be reduced.

  When the vehicle is in the vicinity of straight running neutral at high speed (steering angle is near 0 degree), the friction characteristic variable mechanism 3 is used to reduce the friction torque against the steering force transmission system according to the high speed friction characteristic map. The friction with the pinion 12 is reduced. As is clear from a comparison of FIGS. 10, 11 and 12, when the friction is reduced, the yaw rate comes out faster when the steering torque is started (steering torque is near 0). For this reason, the yaw rate can be obtained even with a slight steering torque, and it becomes possible to easily perform the correction steering in the vicinity of the straight traveling neutrality. As is clear from a comparison between FIG. 10 and FIG. 11, when the friction is increased, the yaw rate rises when the steering torque is started (steering torque is near 0). For this reason, the yaw rate is not generated unless a large steering torque is applied, and it becomes difficult to perform corrective steering in the vicinity of the straight traveling neutrality.

  When traveling on a good road at low speed, the friction between the rack 11 and the pinion 12 using the friction characteristic variable mechanism 3 is reduced so that the friction torque with respect to the steering force transmission system is reduced according to the low speed friction characteristic map. Make it smaller. When the friction is reduced, a clean steering feeling without a feeling of friction can be obtained. Further, as apparent from the comparison between FIG. 5 and FIG. 7, when the friction is reduced, the hysteresis width is reduced. Therefore, the yaw rate responds sensitively with only a slight change in the steering torque, and the vehicle can be turned quickly. In general, when driving at low speed, the lateral load acting on the vehicle is reduced, so that the restoring force of the steered wheels is reduced and the steering wheel is difficult to return. Therefore, in the case of general friction characteristics, as shown in FIG. 8, the steering angle does not sufficiently return even when the steering torque returns to near neutral (steering torque is near 0) during low-speed traveling. However, when the friction is reduced during low-speed running, the hysteresis width is remarkably reduced as shown in FIG. 9, so the steering angle when the steering torque returns to near neutral (steering torque is near 0) is reduced, and the steering wheel Return performance is improved.

  On the other hand, when traveling on a rough road at low speed, the friction between the rack 11 and the pinion 12 using the friction characteristic variable mechanism 3 is increased so that the friction torque with respect to the steering force transmission system increases according to the rough road map. Increase In order to reduce friction in the low-speed friction characteristic map, the clearance between the rack 11 and the pinion 12 is increased, and the rattling noise between the rack 11 and the pinion 12 is increased. Therefore, when the friction is increased in accordance with the rough road map, the pressing force of the rack 11 against the pinion 12 is increased, the clearance between the rack 11 and the pinion 12 is decreased, and the rattling noise between the rack 11 and the pinion 12 is decreased.

  Next, the operation of the vehicle steering device 1 will be described. In particular, the processing of the ECU 7 will be described with reference to the flowchart of FIG. FIG. 13 is a flowchart showing a process flow of the ECU 7. The control process of FIG. 13 is repeatedly performed by the ECU 7.

  The wheel speed sensors 4a to 4d detect wheel speeds of the wheels 10a to 10d and send wheel speed signals to the ECU 7. The steering torque sensor 5 detects the steering torque of the steering shaft 9 and sends a steering torque signal to the ECU 7. The steering angle sensor 6 detects the steering angle of the steering shaft 9 and sends a steering angle signal.

  The ECU 7 receives a wheel speed signal from the wheel speed sensors 4a to 4d, a steering angle signal from the steering angle sensor 6, and a steering torque signal from the steering torque sensor 5 at regular intervals, and receives each signal. Based on this, the vehicle speed, steering angle and steering torque are acquired (S1). Then, the ECU 7 determines whether or not the steering angle is equal to or less than the straight travel threshold and the steering torque fluctuation is equal to or greater than the fluctuation threshold (S2). The ECU 7 determines that the road is a good road if the steering angle information is not more than the straight threshold and not more than the fluctuation threshold (S3).

  If it is determined that the road is good, the ECU 7 selects a friction characteristic map corresponding to the vehicle speed (S4). On the other hand, if it is determined that the road is rough, the ECU 7 determines whether or not the vehicle speed is equal to or lower than the low speed threshold (S6). If the vehicle speed is not below the low speed threshold, the ECU 7 determines that the vehicle is not traveling at low speed and selects a friction characteristic map corresponding to the vehicle speed (S4). It is determined that there is a rough road map and a rough road map is selected (S7). Then, the ECU 7 determines a friction torque corresponding to the steering angle based on the selected maps. Further, the ECU 7 obtains an interval between the plate 18 and the rack guide 14 corresponding to the friction torque based on the friction torque map so that the friction of the steering force transmission system becomes the obtained friction torque, and sets the interval. Calculate the required motor current. Then, the ECU 7 sends this motor current to the motor 13 to control the rotation of the motor 13, and adjusts the friction torque by changing the distance between the plate 18 and the rack guide 14 (S8).

  The motor 13 is driven by receiving a motor current from the ECU 7 and rotates the rotary shaft 17. The rotation of the rotary shaft 17 causes the plate 18 to advance and retreat, and the urging force of the spring 19 is adjusted, whereby the pressing force of the rack 11 against the pinion 12 is increased or decreased. In this manner, the friction between the rack 11 and the pinion 12 is changed by the friction characteristic variable mechanism 3.

  According to the vehicle steering apparatus 1, the hysteresis width in the steering characteristic can be adjusted by changing the friction characteristic of the steering force transmission system based on the vehicle speed and the steering angle. Thereby, it becomes possible to improve the steering feeling according to the vehicle speed and the steering angle of the vehicle.

  In particular, when traveling at high speed, by increasing the friction of the friction characteristic variable mechanism 3 based on the high-speed friction characteristic map, the hysteresis width becomes large, and it becomes possible to stabilize the steering during high-speed turning. Further, when the vehicle is near the neutral position during high-speed traveling, the friction of the friction characteristic variable mechanism 3 is reduced based on the high-speed friction characteristic map, so that the yaw rate comes out faster when the steering torque is started, and the vehicle goes straight. It becomes possible to easily perform correction steering near the neutral position. Further, when traveling on a good road during low-speed traveling, by reducing the friction based on the low-speed friction characteristic map, the hysteresis width is reduced, the vehicle can be turned quickly and the steering wheel return performance is improved. By increasing the friction based on the rough road map during rough roads and low speeds, it is possible to reduce the rattling noise between the rack 11 and the pinion 12 in the steering gear box 2 that occurs particularly during rough roads and low speeds. It becomes possible.

  As mentioned above, although embodiment which concerns on this invention was described, this invention is implemented in various forms, without being limited to the said embodiment.

  For example, in the present embodiment, the friction characteristic map and the rough road map set the friction torque corresponding to the vehicle speed and the steering angle, but the friction torque corresponding to the vehicle speed and the yaw rate may be set. In this case, the vehicle includes a yaw rate sensor, and a signal detected by the yaw rate sensor is sent to the ECU as a yaw rate signal. The ECU obtains a friction torque corresponding to the vehicle speed and the yaw rate, and changes the friction characteristic of the friction characteristic variable mechanism.

  In the present embodiment, only three friction characteristic maps are set, i.e., high speed, medium speed, and low speed, and the rough road map sets the friction torque only for low speed. However, the friction characteristic map and the rough road map are set for more vehicle speeds. The vehicle speed may be divided into a plurality of vehicle speed ranges, and a friction characteristic map and a rough road map may be set for each vehicle speed range.

  Further, in the present embodiment, the steering angle and the steering torque fluctuation are used as the rough road determination criteria, but it is only necessary to be able to determine that the vehicle is traveling on a rough road. For example, a vibration sensor that detects the vibration of the vehicle is provided. You may determine a bad road using the vibration detected by this vibration sensor.

  The friction torque set in the friction characteristic map and the rough road map is a relative magnitude based on the vehicle speed and the steering angle. Therefore, in practice, specific friction torques corresponding to the friction characteristic map and the rough road map are determined in consideration of the characteristics of the vehicle and the steering force transmission system.

It is a figure showing composition of a vehicle steering device concerning this embodiment. It is the figure which showed the structure of the friction characteristic variable mechanism of a vehicle steering device. It is the figure which showed the relationship between a pinion torque and a rack stroke. It is the figure which showed the friction characteristic map and the rough road map. It is the figure which showed the relationship between the steering torque in a general friction characteristic, and a yaw rate. It is the figure which showed the relationship between the steering torque when increasing friction, and a yaw rate. It is the figure which showed the relationship between the steering torque when making friction small, and a yaw rate. It is the figure which showed the relationship between the steering torque and steering angle in a general friction characteristic. It is the figure which showed the relationship between the steering torque when a friction was made small, and a steering angle. FIG. 6 is an enlarged view of the case where the steering torque in FIG. 5 is around 0 (near the straight neutral position). FIG. 7 is an enlarged view of the case where the steering torque in FIG. FIG. 8 is an enlarged view of the case where the steering torque in FIG. 7 is around 0 (near the straight neutral position). It is a flowchart which shows the flow of a process of ECU.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle steering device, 2 ... Steering gear box, 3 ... Friction characteristic variable mechanism, 4a-4d ... Wheel speed sensor, 5 ... Steering torque sensor, 6 ... Steering angle sensor, 7 ... ECU, 8 ... Steering wheel, 9 ... Steering Shaft, 10a to 10d ... wheel, 11 ... rack, 12 ... pinion, 13 ... motor, 14 ... rack guide, 15 ... gear housing, 16 ... base member, 17 ... rotary shaft, 18 ... plate, 19 ... spring, 20 ... O-ring.

Claims (3)

Vehicle speed detecting means for detecting the vehicle speed of the vehicle;
Friction characteristic variable means provided in the steering force transmission system and capable of changing the friction characteristic in the steering force transmission system;
A vehicle steering apparatus comprising: control means for changing a friction characteristic by the friction characteristic changing means according to a vehicle speed detected by the vehicle speed detection means. Steering angle detection means for detecting the steering angle of the vehicle,
2. The vehicle steering apparatus according to claim 1, wherein the control unit reduces the friction when the steering angle detected by the steering angle detection unit is small compared to when the steering angle is large. A traveling state determining means for determining a traveling state of the vehicle;
The control means determines that the traveling state determined by the traveling state determination means is a rough road, and the vehicle speed detected by the vehicle speed detection means is lower than a predetermined value, compared to the friction according to the vehicle speed. The vehicle steering apparatus according to claim 1, wherein friction is increased.

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