JP2007022170A - Vehicle steering device and method for suppressing vehicle deviation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the deviation of a vehicle at running straight in good performance without giving any unnecessary shock to the driver. <P>SOLUTION: A vehicle steering device 10 for steering a pair of steered wheels 2L and 2R of the vehicle 1 is equipped with a rack 15 to turn the steered wheels 2L and 2R, a motor-driven assisting unit 17 capable of giving a torque to the rack 15 independently of the driver operation, and a steering ECU 20. The steering ECU 20 can judge whether the vehicle 1 is in the straight running condition and also judge if in the steered condition, and when the vehicle is judged as running straight, calculates the corrective steering torque Tc for suppressing the deviation in running straight, and when judged as being steered, the ECU controls the assisting unit 17 so that the corrective steering torque Tc is given to the rack 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vehicle steering apparatus for steering a pair of steered wheels included in a vehicle, and a vehicle deflection suppression method for suppressing deflection when the vehicle travels straight.

  Conventionally, as a vehicle steering device for steering a steering wheel of a vehicle, there has been provided an assist unit capable of applying torque independently of a driver's operation to a steering rod for turning each steering wheel. It is known (for example, refer to Patent Document 1). In this vehicle operating device, the assist reaction torque is generated in the assist unit in a direction to suppress the vehicle behavior determined based on the detection value of the vehicle behavior detection means, and the assist reaction torque is generated regardless of whether the driver is steering or not. The running stability of the vehicle is improved by acting on the steered wheels. In addition, in order to reduce the troublesome steering operation when traveling straight on an inclined road, when the traveling road is an inclined road, the turning angle necessary for moving the vehicle straight on the inclined road is calculated and calculated. There is also known a vehicle steering apparatus that sets a control amount in accordance with the steering angle and controls the assist unit based on the set control amount (see, for example, Patent Document 2).

Furthermore, in order to prevent unnecessary shocks to the driver, when the driver's steering wheel grip force is small, auxiliary steering (torque application) by the steering wheel assist unit according to vehicle behavior or disturbance is prohibited. There is also known an electric steering device that performs this (see, for example, Patent Document 3). In addition, there is also known a technology that suppresses a sudden change in the torque applied by the assist torque at the time of normal recovery while stopping the application of torque by the assist unit when any abnormality occurs in the vehicle steering device (for example, patents). Reference 4). In this vehicle steering apparatus, the torque applied by the assist unit is gradually increased only when the steering wheel is operated by the driver after normal return.
JP 2000-025630 A JP 2003-267250 A JP 05-000675 A Japanese Patent Laid-Open No. 10-181616

  By the way, while the vehicle is traveling, a vehicle that should be supposed to go straight may tend to be deflected due to road surface conditions, suspension settings, and the like. In such a case, the driver basically applies a steering torque via the steering handle, so that the vehicle is kept in a straight traveling state. However, the assist unit is operated to transmit the torque to the steering wheel. It is possible to keep the vehicle straight. However, if such torque is generated in the assist unit at an arbitrary timing, an unnecessary shock may be given to the driver via the steering wheel.

  Therefore, an object of the present invention is to provide a vehicle steering apparatus and a vehicle deflection suppressing method that can satisfactorily suppress the deflection of the vehicle when traveling straight without giving unnecessary shock to the driver.

  A vehicle steering apparatus according to the present invention is a vehicle steering apparatus for steering a pair of steering wheels included in a vehicle. A steering rod for turning each steering wheel, and an operation of a driver with respect to the steering rod are independent of each other. The vehicle includes a torque applying means capable of applying torque to the vehicle, a straight traveling determining means for determining whether or not the vehicle is in a straight traveling state, a steering determining means for determining whether or not the vehicle is in a steering state, and a straight traveling determining means. When it is determined that the vehicle is in the straight traveling state, when the vehicle is determined to be in the steering state by the correction torque calculating means for calculating the correction steering torque for suppressing the deflection when the vehicle is traveling straight, and the steering determining means And a control means for controlling the torque applying means so that the correction steering torque calculated by the correction torque calculating means is applied to the steering rod.

  In this vehicle steering apparatus, when the straight traveling determination unit determines that the vehicle is in a straight traveling state, the correction torque calculation unit calculates a corrected steering torque for suppressing deflection when the vehicle is traveling straight ahead. Thus, by calculating the corrected steering torque when the vehicle is in the straight traveling state, it is possible to appropriately determine the corrected steering torque for suppressing the deflection when the vehicle is traveling straight. However, if the torque application means is activated immediately after the calculation of the corrected steering torque, the driver himself may be operating the steering handle to keep the vehicle straight if the vehicle is traveling straight at that time, There is a risk that a shock (discomfort) due to torque fluctuation may be given to a driver who performs such an operation. Therefore, in this vehicle steering apparatus, after the correction steering torque is calculated, when the steering determination unit determines that the vehicle is in a steering state, the correction steering calculated by the correction torque calculation unit on the steering rod by the control unit is performed. The torque applying means is controlled so that torque is applied. In this way, if the corrected steering torque is generated in the torque applying means during vehicle steering when the steering wheel is being operated by the driver, it is difficult for the driver to experience torque fluctuations, so an unnecessary shock is given to the driver. Therefore, it is possible to satisfactorily suppress the deflection of the vehicle when traveling straight.

  In this case, it is preferable that the control means controls the torque applying means so that the torque applied to the steering rod gradually approaches the corrected steering torque.

  According to this aspect, when the correction steering torque is generated in the torque applying means, it is possible to make it more difficult for the driver to experience the torque fluctuation, and to suppress the driver from unnecessary shocks very well. Can do.

  Further, the correction torque calculating means includes a steering torque applied to the steering rod by the driver when the vehicle is in a straight traveling state, and a torque applied to the steering rod by the torque applying means according to the steering torque. The vehicle flow correction steering torque is preferably calculated based on the above.

  According to this aspect, it becomes possible to determine the correction steering torque for suppressing the deflection when the vehicle is traveling straight forward extremely appropriately.

A vehicle deflection suppression method according to the present invention is applied to a vehicle steering apparatus including a torque applying unit capable of applying a torque independently of a driver's operation to a steering rod for turning each steering wheel of the vehicle. A vehicle deflection suppressing method for suppressing deflection during straight traveling of the vehicle,
(A) determining whether the vehicle is in a straight ahead state;
(B) calculating a correction steering torque for suppressing deflection when the vehicle is traveling straight when it is determined in step (a) that the vehicle is traveling straight;
(C) determining whether the vehicle is in a steering state;
(D) activating the torque applying means so that the correction steering torque calculated in step (b) is applied to the steering rod when it is determined in step (c) that the vehicle is in a steering state. Is included.

  According to the present invention, it is possible to satisfactorily suppress the deflection of the vehicle when going straight without giving unnecessary shock to the driver.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a main part of a vehicle equipped with a vehicle steering apparatus according to the present invention. As shown in the figure, the vehicle 1 is a hybrid power that drives a pair of left and right steering wheels 2L, 2R, which are front wheels in this embodiment, or a rear wheel (not shown), an electric motor, or a combination thereof. The vehicle includes a drive source (not shown) such as a unit, and includes a vehicle steering device 10 for steering the left steering wheel 2L and the right steering wheel 2R. The steered wheels 2L and 2R each include a wheel and a tire, and the wheels of the steered wheels 2L and 2R are supported by a knuckle 4 via a disk rotor 3 constituting a brake unit. A knuckle arm 5 is integrated with or connected to the knuckle 4, and the knuckle 4 is supported to the vehicle body via a strut bar, a lower arm, or the like that constitutes a suspension device of the vehicle 1. A brake caliper 6 for applying a braking force to the steering wheels 2L and 2R via the disc rotor 3 is disposed inside the wheels of the steering wheels 2L and 2R.

  On the other hand, the vehicle steering device 10 of the vehicle 1 includes a steering handle 11 operated by a driver. The steering handle 11 is fixed to one end of a steering shaft 12, and the other end of the steering shaft 12 is connected to a steering gear box 14. The steering gear box 14 includes a pinion gear (not shown) fixed to the end of the steering shaft 12 and a rack 15 as a steering rod that meshes with the pinion gear. It functions as a steering angle transmission mechanism that converts to. In addition, a transmission ratio variable mechanism (VGRS) 16 is incorporated in the steering shaft 12 so as to be positioned between the steering handle 11 and the steering gear box 14. The transmission ratio variable mechanism 16 has a function of changing a transmission ratio that is a ratio of the steering angle of the steered wheels 2L and 2R to the steering angle of the steering handle 11, and a drive source for changing the transmission ratio. The actuator 16a which uses the DC motor as a main component, and the reduction gear (differential device) 16b are included.

  The vehicle steering device 10 is configured as a so-called electric power steering unit, and can apply torque to the rack 15 (steering rod) independently of the operation of the driver and assists the linear motion of the rack 15. A unit (torque applying means) 17 is provided. In the present embodiment, the electric assist unit 17 is provided on the downstream side of the transmission ratio variable mechanism 16, that is, on the steering wheel 2L side.

  The electric assist unit 17 includes a motor 18 including a stator and a rotor, and is configured as a so-called ball screw type assist unit, for example. In the present embodiment, a ball screw nut (not shown) is fixed to the rotor of the motor 18, and this ball screw nut and the ball (not shown) and one end side of the rack 15 (in this embodiment, the steered wheel 2 </ b> L side). Torque is transmitted from the motor 18 to the rack 15 through the formed thread groove. The electric assist unit 17 is not limited to the rack assist type as described above, but may be a pinion assist type or a column assist type.

  The end of the rack 15 extending from the electric assist unit 17 is connected to the knuckle arm 5 of the left steering wheel 2L via a tie rod 19. Further, the end of the rack 15 extending from the steering gear box 14 toward the steering wheel 2R is connected to the knuckle arm 5 of the right steering wheel 2R via a tie rod 19.

  As shown in FIG. 1, the vehicle steering apparatus 10 configured as described above is controlled by a steering electronic control unit (hereinafter referred to as “steering ECU”) 20 as control means. That is, the transmission ratio variable mechanism 16 and the electric assist unit 17 included in the vehicle steering device 10 are controlled by the steering ECU 20. The steering ECU 20 includes a CPU that executes various arithmetic processes, a ROM that stores various control programs, a RAM that is used as a work area for data storage and program execution, an input / output interface, a memory, and the like.

  A steering angle sensor 21, a steering torque sensor 22, a VGRS operating angle sensor 23, an EPS torque sensor 24, a wheel speed sensor 25, and a yaw rate sensor 26 are connected to the input / output interface of the steering ECU 20. The steering angle sensor 21 detects the steering angle of the steering handle 11, and gives a signal indicating the detected value to the steering ECU 20. The steering torque sensor 22 detects the steering torque applied to the steering handle 11 from the driver, and gives a signal indicating the detected value to the steering ECU 20. The VGRS operating angle sensor 23 detects a change (increase) in the steering angle due to the operation of the transmission ratio variable mechanism 16 and gives a signal indicating the detected value to the steering ECU 20.

  The EPS torque sensor 24 detects the assist torque by the electric assist unit 17 and gives a signal indicating the detected value to the steering ECU 20. The wheel speed sensor 25 is provided in all the wheels including the steered wheels 2L and 2R. Each wheel speed sensor 25 detects the rotational speed of the corresponding wheel, and gives a signal indicating the detected value to the steering ECU 20. The yaw rate sensor 26 detects the rotational angular velocity (yaw rate) around the vertical axis of the vehicle 1 and gives a signal indicating the detected value to the steering ECU 20. The steering ECU 20 controls the transmission ratio variable mechanism 16 and the electric assist unit 17 based on signals from the sensors 21 to 26 and the like.

  In the vehicle 1 including the above-described vehicle steering device 10, when the steering handle 11 is operated by a driver, the assist torque corresponding to the vehicle speed determined from the steering torque detected by the steering torque sensor 22 and the detection value of the wheel speed sensor 25. Is determined. That is, when the steering handle 11 is operated, the steering ECU 20 determines the assist torque by the electric assist unit 17 according to the steering torque by the driver and the vehicle speed of the vehicle 1 using a predetermined map, and the EPS torque sensor 24. The electric assist unit 17 is controlled so that the detected value coincides with the assist torque. As a result, the vehicle 1 can reduce the driver's steering burden and give the driver a smooth and responsive steering feeling.

  In the vehicle 1, the steering ECU 20 determines a transmission ratio between the steering angle and the turning angle corresponding to the vehicle speed of the vehicle 1, for example, obtained from the detection value of each wheel speed sensor 25, and the transmission ratio is realized. Thus, the transmission ratio variable mechanism 16 is controlled. As a result, the turning angle of the pair of steered wheels 2L and 2R is set by the transmission ratio variable mechanism 16, and the steering performance during low-speed traveling and the steering stability during medium-high speed traveling are ensured satisfactorily. Is possible.

  By the way, during the traveling of the vehicle 1 including the vehicle steering device 10 as described above, the vehicle 1 that should originally go straight may tend to be deflected due to road surface conditions, suspension settings, and the like. For example, when the travel path of the vehicle 1 is a cant road that is inclined substantially uniformly in the vehicle width direction, or when there is a slight deviation in the setting of the suspension, there is a deflection in a straight traveling state (so-called vehicle Flow) is likely to occur. In such a case, if the driver applies a steering torque via the steering handle 11, the vehicle is kept straight, but this increases the driver's steering burden and provides a comfortable driving environment. There is a risk that it will not be obtained.

  For this reason, in the vehicle 1 of the present embodiment, the routine shown in FIG. 2 is executed in order to suppress the deflection of the vehicle 1 during straight traveling. The routine shown in FIG. 2 is repeatedly executed by the steering ECU 20 every predetermined time while the vehicle 1 is traveling. When it is time to execute this routine, the steering ECU 20 determines whether or not the vehicle 1 is in a straight traveling state (S10). In S10, for example, the state where the steering torque by the driver detected by the steering torque sensor 22 is smaller than a predetermined value and the change amount of the steering angle detected by the steering angle sensor 21 is smaller than the predetermined value is constant. When continuing for more than time, it is determined that the vehicle 1 is in a straight traveling state. When it is determined in S10 that the vehicle 1 is not in the straight traveling state (No in S10), the processing after S12 is skipped, and the steering ECU 20 executes the processing after S10 again at the next execution timing.

When it is determined in S10 that the vehicle 1 is in the straight traveling state (Yes in S10), the steering ECU 20 acquires the steering torque Td by the driver detected by the steering torque sensor 22 at that stage, and the EPS torque sensor 24. The assist torque Ta detected by the electric assist unit 17 is acquired (S12). Then, the steering ECU 20 calculates a corrected steering torque Tc for suppressing deflection when the vehicle 1 is traveling straight, based on the acquired steering torque Td and assist torque Ta.
Tc = previous value + Td + Ta (1)
(S14). However, the initial value of the correction steering torque Tc is zero.

  Here, the steering torque applied to the rack 15 as the steering rod by the driver when the vehicle 1 is determined to be in the straight traveling state in S10, and the electric assist unit 17 as the steering rod according to the steering torque. The sum of the torque applied to the rack 15 is a torque required to keep the vehicle 1 in a straight traveling state, that is, to correct the deflection of the vehicle 1. Therefore, the correction steering torque Tc for suppressing the deflection when the vehicle 1 is traveling straight ahead can be determined extremely appropriately by performing the arithmetic processing according to the above equation (1).

  When the corrected steering torque Tc is calculated, the steering ECU 20 determines whether or not the steering wheel 11 is operated by the driver and the vehicle 1 is in a steering state (S16). In S16, for example, the steering angle detected by the steering angle sensor 21 is not less than a predetermined value, the steering torque detected by the steering torque sensor 22 is not less than a predetermined value, and the rotational speed of the steering handle 11 is It is determined that the vehicle 1 is in a steering state when at least one of the conditions of being equal to or greater than a predetermined value is satisfied. When the steering ECU 20 determines that the vehicle 1 is in a steering state (Yes in S16), the steering ECU 20 stores the value of the corrected steering torque Tc calculated in S14 in a predetermined storage area (S18), and then calculates in S14. The electric assist unit 17 is operated so that the corrected steering torque Tc is applied to the rack 15 as a steering rod (S20).

  That is, if the electric assist unit 17 is operated immediately after the corrected steering torque Tc is calculated in S14, if the vehicle 1 is traveling straight at that time, the driver himself / herself steers the steering wheel to keep the vehicle 1 in a straight traveling state. 11 may be operated, and a shock (discomfort) due to torque fluctuation may be given to a driver who performs such an operation. For this reason, in the vehicle 1, when the corrected steering torque Tc is calculated, when the vehicle 1 is determined to be in a steering state, the steering assist ECU 17 applies the corrected steering torque Tc to the rack 15 by the steering ECU 20. Is controlled. Thus, when the steering wheel 11 is operated by the driver and the vehicle is steered, if the corrected steering torque Tc is generated in the electric assist unit 17, it is difficult for the driver to experience torque fluctuations, which is unnecessary for the driver. It is possible to satisfactorily suppress the deflection of the vehicle 1 when going straight without giving a shock.

  In S20, the steering ECU 20 controls the electric assist unit 17 so that the torque applied to the rack 15 gradually approaches the corrected steering torque Tc. As a result, when the electric assist unit 17 generates the corrected steering torque Tc, it is possible to make it more difficult for the driver to experience the torque fluctuation, and to suppress the driver from unnecessary shocks extremely well. it can. When the process of S20 is executed, the steering ECU 20 executes the processes after S10 again when the next execution timing has come.

  On the other hand, when it is determined in S16 that the vehicle 1 is not in the steering state (No in S16), the steering ECU 20 stores the value of the corrected steering torque Tc without storing the value of the corrected steering torque Tc calculated in S14. Is held at the previous value (S22). That is, when it is determined in S16 that the vehicle 1 is not in the steering state, the corrected steering torque Tc is not applied by the electric assist unit 17, and in this case, the value of the corrected steering torque Tc is held at the previous value. . Then, after executing the process of S22, the steering ECU 20 executes the processes after S10 again at the stage when the next execution timing has come.

  The means for applying the corrected steering torque Tc to the rack 15 as a steering rod is not limited to the electric assist unit 17 as described above. That is, the means for generating the above-described corrected steering torque Tc may be the transmission ratio variable mechanism 16, for example, sending a steering reaction force (handling of the steering wheel) arranged on the upstream side of the transmission ratio variable mechanism 16 or the like. A torque generating source such as a reaction force motor may be used.

It is a schematic block diagram which shows the principal part of the vehicle provided with the vehicle steering device by this invention. 2 is a flowchart showing a routine for suppressing deflection when the vehicle of FIG. 1 is traveling straight ahead.

Explanation of symbols

  1 vehicle, 2L, 2R steering wheel, 3 disc rotor, 4 knuckle, 5 knuckle arm, 6 brake caliper, 10 vehicle steering device, 11 steering handle, 12 steering shaft, 14 steering gear box, 15 rack, 16 transmission ratio variable mechanism , 17 Electric assist unit, 18 motor, 19 tie rod, 20 steering ECU, 21 steering angle sensor, 22 steering torque sensor, 23 VGRS operating angle sensor, 24 EPS torque sensor, 25 wheel speed sensor, 26 yaw rate sensor.

Claims (4)

In a vehicle steering apparatus for steering a pair of steering wheels included in a vehicle,
A steering rod for turning each steering wheel;
Torque applying means capable of applying torque to the steering rod independently of a driver's operation;
Straight traveling determination means for determining whether or not the vehicle is in a straight traveling state;
Steering determination means for determining whether or not the vehicle is in a steering state;
Correction torque calculation means for calculating a correction steering torque for suppressing deflection when the vehicle is traveling straight when the vehicle is determined to be in a straight traveling state by the straight traveling determination means;
Control means for controlling the torque application means so that the correction steering torque calculated by the correction torque calculation means is applied to the steering rod when the steering determination means determines that the vehicle is in a steering state. A vehicle steering apparatus comprising:   2. The vehicle steering apparatus according to claim 1, wherein the control unit controls the torque applying unit such that a torque applied to the steering rod gradually approaches the corrected steering torque. 3.   The correction torque calculation means is applied to the steering rod by the torque application means according to the steering torque applied to the steering rod by the driver when the vehicle is in a straight traveling state. The vehicle steering apparatus according to claim 1, wherein the vehicle flow correction steering torque is calculated based on a torque obtained from the vehicle. The present invention is applied to a vehicle steering apparatus including a torque applying means capable of applying a torque independently of a driver's operation to a steering rod for turning each steered wheel of the vehicle, and suppresses deflection when the vehicle goes straight. A vehicle deflection suppressing method,
(A) determining whether the vehicle is in a straight traveling state;
(B) calculating a correction steering torque for suppressing deflection when the vehicle is traveling straight when it is determined in step (a) that the vehicle is traveling straight;
(C) determining whether the vehicle is in a steering state;
(D) When it is determined in step (c) that the vehicle is in a steering state, the torque applying means is operated so that the corrected steering torque calculated in step (b) is applied to the steering rod. And a vehicle deflection suppressing method.

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