JP4577020B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a vehicle steering apparatus equipped with a steering actuator that applies an assist steering force.

2. Description of the Related Art Conventionally, there is known a vehicle steering device in which a steering actuator is arranged in a steering system, and assist steering force for assisting a driver's steering force is applied by driving the steering actuator or automatic steering is performed (for example, patents). Reference 1). The technique of Patent Document 1 is to suppress the rotation of the steering wheel from being delayed due to the torsion of the torsion bar with respect to the drive of the actuator and the vibration of the rotation during the automatic steering in such an automatic steering device. The control is performed in consideration of the twist angle.
JP 2003-237607 A

  By the way, due to such torsion of the torsion bar, friction between the gears constituting the steering system, etc., a deviation occurs between the steering of the driver and the actual change of the steering angle of the steered wheels. Specifically, when the driver starts rotating the steering wheel or when the direction of rotation is switched to the opposite direction, the steering torque is consumed by the torsion bar itself or by the steering system. Until the actual steering angle change is delayed.

  Accordingly, an object of the present invention is to provide a vehicle steering apparatus capable of suppressing such a shift in steering feeling.

In order to solve the above problems, a vehicle steering apparatus according to the present invention includes a transmission mechanism that transmits a driver's steering input to a steering wheel via a torsion bar and a rack and pinion mechanism. A steering angle detecting means for detecting the steering angle by the steering wheel, a steering torque detecting means for detecting the steering torque by the driver, a rack stroke movement amount determining means for estimating or detecting the rack stroke movement amount, and a transmission mechanism. The electric actuator capable of adjusting the rack stroke movement amount with respect to the steering input by the driving force, and the target rack stroke movement amount and the rack stroke movement amount determination means corresponding to the steering state determined from the detected steering angle and steering torque controls the operation of the actuator such that the rack stroke movement amount matches, Wherein the Tsu comprises a controller for the change with time of click stroke movement amount correction based on the ratio of the target rack stroke movement amount of time change amount.

  This electric actuator is of a type in which the steering gear ratio can be arbitrarily changed or an assist steering force is applied. The former is a VGRS (Variable Gear Ratio Steering) system provided with a gear ratio variable mechanism that changes the rotation ratio of the input shaft and the output shaft, and the latter is an EPS (Electric Power Steering) system.

  The conventional system of this type is intended to provide a desired gear ratio and assist steering force by driving an actuator in accordance with the vehicle speed, steering angle, and steering torque. In the vehicle steering apparatus according to the present invention, the steering state by the driver is obtained from the steering angle and the steering torque. The target rack stroke movement amount is set from this steering state. On the other hand, the rack stroke movement amount determination means detects the actual movement amount of the rack stroke directly or indirectly by detecting the movement amount of the member directly connected thereto, or a torsion bar or the like. Judgment is made by estimating in consideration of twist. Then, the driving of the actuator is controlled so that the actual rack stroke movement amount thus determined matches the set target rack stroke movement amount.

  If this actuator directly drives the rack bar in the EPS system, the actual drive amount of the actuator and the actual movement amount of the rack bar have a one-to-one relationship, which is preferable.

According to the present invention, by performing correction control based on the ratio of the time change amount of the rack stroke movement amount and the time change amount of the target rack stroke movement amount, a desired rack stroke amount can be obtained according to the operation state. By controlling the drive of the actuator, the driver's steering input and the rack stroke amount can be substantially matched, and the delay in the steering angle change at the steering start time and the switchback time can be suppressed. A feeling improves. Then, by measuring or estimating the rack stroke amount directly or indirectly and controlling the movement amount so as to be in a desired state, a smooth rack stroke can be realized, and the steering feeling can be improved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

  FIG. 1 is a perspective view showing the configuration of an embodiment of a vehicle steering apparatus according to the present invention. One end of a steering column 2 is coupled to a steering wheel 1 that is a steering wheel that receives a steering input from a driver, and the other end of the steering column 2 is connected to a steering gear 3. A steering angle sensor 4 (integrated with a combination switch in the column cover) for detecting the steering angle of the steering wheel 1 is incorporated in a coupling portion between the steering wheel 1 and the steering column 2.

  The steering angle sensor 4 can detect a steering amount (steering angle) and a steering direction, and includes two sets of magnetoresistive elements for detecting the rotation of a magnet built in the detection gear, and the detection gear rotates. Based on the magnetic change caused by this, the amount and direction of rotation of the steering wheel 1 are detected. The output signal of the steering angle sensor 4 is input to an electronic control unit (ECU) 5 that is a steering control device. The ECU 5 is constituted by a CPU, a ROM, a RAM, and the like, and controls the operation of the steering device in accordance with a predetermined program built therein.

  The steering column 2 includes a torque sensor 6 on the side of the steering wheel 1 in the substantially central portion, and a VGRS mechanism 7 on the side of the steering gear 3 in the central portion. The VGRS mechanism 7 variably controls a transmission ratio (steering gear ratio) that is a ratio of a steered wheel (not shown) to a steered angle with respect to the steering angle of the steering wheel 1.

  Inside the torque sensor 6, the input shaft on the steering wheel 1 side and the output shaft on the steering gear 3 side are connected by a torsion bar, and a rotation angle sensor (resolver sensor) is attached to each of the input shaft and the output shaft. ing. Each rotation angle sensor detects the rotation angle of the input shaft and the rotation angle of the output shaft. When the steering wheel 1 is steered, the torsion bar is twisted and a relative difference occurs between the angles detected by the two rotation angle sensors, and the steering torque can be calculated from the difference. The torque sensor 6 is also connected to the ECU 5, and the ECU 5 calculates torque based on the detection results of the two rotation angle sensors. That is, the torque sensor 6 and the ECU 5 function as steering torque detection means.

  A partial cross-sectional perspective view of the VGRS mechanism 7 is shown in FIG. The VGRS of this embodiment uses a wave gear. As wave gears, those of Harmonic Drive Systems are well known. As shown in FIG. 2, the VGRS mechanism 7 fixes a transmission ratio when the VGRS mechanism 7 has a failure, a differential mechanism portion 7 a having a wave gear, a DC brushless motor 7 b that is a drive actuator of the VGRS mechanism 7. , A spiral cable 7d provided so that electric power can be supplied even if the shaft of the steering column 2 rotates, and a rubber coupling 7e. In FIG. 2, the right side is the steering wheel 1 side, and the left side is the steering gear 3 side.

  The cases of the differential mechanism portion 7a, the DC brushless motor 7b, and the lock mechanism portion 7c are fixed to the input shaft on the steering wheel 1 side. The output shaft of the differential mechanism portion 7a is fixed to the output shaft on the steering gear 3 side, and the DC brushless motor 7b is driven to operate the differential mechanism portion 7a to variably control the transmission ratio. The lock mechanism 7c locks the motor shaft of the DC brushless motor 7b so that it does not rotate when the VGRS mechanism 7 fails (fails) or when the ignition switch is OFF. The DC brushless motor 7b and the lock mechanism 7c are also connected to the ECU 5 described above, and the operation of the VGRS mechanism 7 is controlled by the ECU 5.

  A cross-sectional view of the steering gear 3 is shown in FIG. As described above, the steering gear 3 of the present embodiment incorporates a rack-type electronically controlled power steering (EPS) mechanism, and incorporates a DC brushless motor 3a serving as an EPS drive source. In FIG. 3, only the periphery of the DC brushless motor 3a is shown enlarged. The steering gear 3 is attached to an intermediate portion of a pair of steering wheels (not shown), and both ends of the steering shaft 3b inside thereof are connected to a hub carrier of the steering wheels (not shown) via tie rods 3c. Yes. A rack gear 3d is formed on one end side of the steering shaft 3b and meshes with a pinion gear (not shown) formed at the tip of the input shaft 3e. The input shaft 3e is connected to the output side of the steering column 2. When the steering wheel 1 is rotated by the driver, the rotational motion is converted into a linear motion by the pinion gear and the rack gear 3d, and the steering shaft 3b is moved in the axial direction (left-right direction in FIG. 3) to steer the steering wheel. The

  The DC brushless motor 3a described above includes a stator fixed to the case of the steering gear 3 and a rotor that rotates inside the stator. The rotor is integrated with a cylindrical member, and the steering shaft 3b includes the cylindrical member. It penetrates the inside. Note that both ends of the cylindrical member are instructed to be rotatable by bearings. A ball screw groove 3f is formed in a part on the outer peripheral surface of the steering shaft 3b, and a ball nut 3g is fixed to a part on the inner periphery of the above-described cylindrical member. A plurality of bearing balls are housed between the pair of ball screw grooves 3f and the ball nut 3g, and the DC brushless motor 3a is driven to rotate the rotor, thereby assisting the movement of the steering shaft 3b in the axial direction. .

  The steering gear 3 also includes a rotational position sensor 3h that detects the rotational position of the DC brushless motor 3a. The DC brushless motor 3a and the rotational position sensor 3h are also connected to the ECU 5 described above, and the operation of the EPS is controlled by the ECU 5. The DC brushless motor 3a, the ball screw mechanism, and the ECU 5 inside the steering gear 3 function as power steering means. Further, a pinion rotation angle sensor 8 for detecting the rotation angle of the pinion gear is attached to the pinion gear, and an output signal thereof is input to the ECU 5 described above.

  A method for controlling the steering apparatus will be described below. FIG. 4 is a flowchart of the main control portion, and FIGS. 5 and 6 are flowcharts of the portion branched from the main control. This control is repeatedly executed by the ECU 5 at a predetermined timing while the vehicle is powered on.

  First, by reading the outputs of the steering angle sensor 20, the steering torque sensor 21, the pinion angle sensor 31, and the vehicle speed sensor 40, the steering angle MA, the steering torque MT, the pinion rotation angle θp, and the vehicle speed V, which are vehicle state quantities, are read. (Step S1). Next, it is determined whether or not the steering is maintained (step S2). Specifically, when the steering angle MA is approximately 0, the pinion rotation angle θp is approximately 0, and the steering torque MT is less than the threshold value A, the steering angle and the turning angle are in the neutral state, and the steering state What is necessary is just to determine that it is not a steering maintenance state.

If it is determined that the steering state is maintained, an initial value of 0 is set to a variable N that represents the number of times of control flow passage of the startup control described later, and 0 is set to the steering angle storage value θ1 (step S3). Then, each vehicle state quantity (steering angle MA, pinion rotation angle θp, vehicle speed V 1 , steering torque MT ) is read again (step S4). Finally, the steering angle MA is determined to be positive or negative (step S5). If MA is substantially 0, that is, if the steering holding state continues, the process returns to step S4 as it is. When MA is positive, that is, when the steering input is in the left direction, the steering coefficient K1 is set to 1 meaning that the vehicle is turning left (step S6). On the other hand, when MA is negative, that is, when the steering input is in the right direction, the steering coefficient K1 is set to -1 which means that the vehicle is turning right (step S7). After step S6 or S7 ends, the process proceeds to step S8 to determine whether N is 0 or not.

When N is 0, the process proceeds to step S9, and the target pinion rotation angle θi is set based on the steering angle MA and the steering torque MT among the read vehicle state quantities. Next, the current steering angle MA is stored in the steering angle memory value θ1, the current pinion angle θp is stored in the pinion angle memory value θ2, and the current steering coefficient K1 is stored in the steering coefficient memory value K0 (step S10). Then, an absolute value e of a deviation between the target pinion rotation angle θi and the actual pinion rotation angle θp is obtained (step S11). By multiplying the absolute value e of this deviation by the steering system number K1, Is is set as a control signal (hereinafter referred to as actuator control signal) to the DC brushless motor 7b which is a drive actuator of the VGRS mechanism 7 (step S12), and By outputting Is set to the DC brushless motor 7b as a control signal (step S13), the DC brushless motor 7b is driven to obtain the target pinion rotation angle θi. Here, since the pinion rotation angle and the rack stroke have a one-to-one correspondence, controlling the actual pinion rotation angle based on the target pinion angle results in the actual rack stroke based on the target rack stroke. It is substantially synonymous with controlling.

  Next, the vehicle state quantities (steering angle MA, pinion rotation angle θp, vehicle speed V) are read again (step S14), and it is determined whether or not the value of the control variable N has reached 2 (step S15). If N has not reached 2 (0 or 1), the process proceeds to step S16, where θp−θ2 is divided by MA−θ1, that is, the time variation of the pinion angle and the steering angle. It is determined whether or not the absolute value of the ratio with the time variation exceeds a range obtained by multiplying the steady gradient B by a predetermined coefficient K3. When the condition is satisfied, the control process at the time of rising ends. If the upper limit is not satisfied, the control variable N is set to 1 (step S17), the process returns to step S5, and the process at the time of rising is continued.

  If N is not 0 (in the case of 1 or 2) in step S8, the process proceeds to step S20 of the processing flow shown in FIG. In step S20, the sign of MA−θ1 is determined. If it is positive, 1 is set to the steering coefficient K2 (step S21). If negative, it is further determined whether or not K1 × K0 is positive (step S22). The case where K1 × K0 is negative is a case where both have different signs, which means that the steering torque direction is reversed from the previous time step. In this case, since it is in a turning-back state, the process at the time of rising ends.

  If K1 × K0 is positive in step S22, that is, if the sign is the same, the process proceeds to step S23 and -1 is set to the steering coefficient K2. After steps S21 and S23 are completed, the process proceeds to step S24 to determine whether or not the value of the control variable N is 2.

  If N is not 2 (0 or 1), it is determined whether or not the value of K1 × K2 is positive (step S25). The case where the product of K1 and K2 is positive is when both have the same sign. When MA is positive and increasing, and when MA is negative and decreasing, that is, the absolute value of MA is increasing. Means the case. If positive, the process proceeds to step S11 in FIG. If negative, the variable N is set to 2 (step S26), and the process proceeds to step S28.

  Similarly, when N is 2, it is determined whether or not the value of K1 × K2 is positive (step S27). If it is positive, the process similarly proceeds to step S11 in FIG. If negative, the process proceeds to step S28. In step S28, the ratio of θ1 to θ2 is set to C, and C × MA is set as the target pinion angle θi (step S29). Further, K2 is set to K1 (step S30), and the process returns to step S9 in FIG.

  If N is determined to be 2 in step S15 of FIG. 4, the process proceeds to step S18 to determine whether K1 × MA is positive. The case where K1 × MA is positive means that the steering direction is the same as the previous time. In this case, the process returns to step S5. If it is determined that the steering direction has been reversed, the process at the time of rising ends.

  When it is determined in step S2 that the steering angle MA or the pinion rotation angle θp is not substantially 0 (the former means that the steering angle is not in the neutral state, the latter means that the turning angle is not in the neutral state), or the steering torque. When it is determined that the MT is equal to or greater than the threshold A (meaning that the vehicle is in the steering state), the process proceeds to the control flow at the time of switching shown in FIG.

  In the control at the time of switching back, first, 0 is set to the steering coefficient K5 (step S31). Then, the sign of MA-θ1 is determined (step S32). If it is positive or 0, 1 is set to the steering coefficient K4 (step S33). If negative, -1 is set to the steering coefficient K4 (step S34). After steps S33 and S34 are completed, the process proceeds to step S35 to determine whether or not the product of K4 and K5 is positive. The initial value of K5 is 0, but the previous value of K4 is stored as will be described later while the process of the switching control flow is continued. Since K4 corresponds to the difference between the current value and the previous value of the steering torque as described above, a positive product of K4 and K5 means that the direction of change in the steering torque is the same as the previous value. It will be. In this case, since it is not at the time of the switching operation, the process is terminated as it is. If the product is negative or 0, the actual process is entered as the switchback operation.

Specifically, first, the target pinion rotation angle θi is set based on the steering angle MA and the steering torque MT among the read vehicle state quantities (step S36). Next, the current steering angle MA is stored in the steering angle memory value θ1, the current pinion angle θp is stored in the pinion angle memory value θ2, and the current steering coefficient K4 is stored in the steering coefficient memory value K5 (step S37). Then, the absolute value e of the deviation between the target pinion rotation angle θi and the actual pinion rotation angle θp is obtained (step S38). By multiplying the absolute value e of this deviation by the steering system number K4, Is is set as a control signal (hereinafter referred to as actuator control signal) to the DC brushless motor 7b which is a drive actuator of the VGRS mechanism 7 (step S39), and By outputting Is set to the DC brushless motor 7b as a control signal (step S40), the DC brushless motor 7b is driven to obtain the target pinion rotation angle θi.

  Next, the vehicle state quantities (steering angle MA, pinion rotation angle θp, vehicle speed V) are read again (step S41), and θp−θ2 is divided by MA−θ1, that is, the time variation of pinion angle and steering. It is determined whether or not the absolute value of the ratio with the time change amount of the corner exceeds the range obtained by multiplying the gradient C at the time of correction by a predetermined coefficient K6 (step S42). When the condition is satisfied, the control process at the time of switching ends. If the condition is not satisfied, the process returns to step S32, and the process at the time of switching is continued.

  FIG. 7 is a corresponding line diagram showing a comparison between the steering angle (MA) and the rack stroke (RS) during the conventional control and the control according to the present embodiment. In the case of the conventional control example, even when the steering wheel 1 is operated due to torsion of the torsion bar or other friction of the steering system at the time of starting up or switching back, the movement of the rack bar in the target direction is delayed. Will occur. For this reason, as indicated by a broken line in the figure, the trackability of the rack stroke (RS) with respect to the change of the steering angle (MA) is not good. In the case of the present embodiment, by controlling the operation of the DC brushless motor 7b, which is the drive actuator of the VGRS mechanism 7, so that the pinion rotation angle becomes the target angle, the steering angle (MA ) Quickly follows the rack stroke (RS). As a result, the steered wheels can be smoothly steered with respect to the steering of the steering wheel 1 at the start of steering (arrow A in the figure) and the turn-back time (arrows B and C in the figure), thereby improving the steering feeling. To do.

  In the above control example, the example in which the correction control of the pinion rotation angle is performed at the time of switching back and at the time of rising is described, but the same correction control as at the time of rising may be performed at the time of switching back. FIG. 8 shows a corresponding line diagram comparing the relationship between the steering angle (MA) and the rack stroke (RS) with and without correction control at the time of switching back.

  At the time of the switch back operation, the torsion bar twist generated at the start of steering is eliminated, and the twist in the reverse direction is further generated. When correction control is not performed, the angle on the steering gear 3 side of the torsion bar does not change greatly during this time even if the steering wheel 1 is rotated in reverse. For this reason, as indicated by a broken line in the figure, the actual movement amount of the rack stroke is small, and the response to the change in the steering angle of the steered wheels with respect to the switchback steering is delayed. In addition, even if the steering wheel 1 is returned to the neutral position, it takes time for the steered wheels to return to the neutral state, so there is a discrepancy between the steered angle and the actual steered angle, and the driver feels strange when steering. You will feel it. On the other hand, when the correction control is performed, as shown by the solid line in the figure, the rack stroke according to the steering torque can be generated, so that the followability of the rack stroke change is improved, It is possible to suppress the actual turning angle from deviating from the steering angle. As a result, the steering performance is improved and the driver's uncomfortable feeling during steering operation is reduced.

  In the present embodiment, the target pinion angle θi is set appropriately, and angle correction control is performed using an actuator so that the actual pinion angle matches this, whereby the characteristic of the rack stroke with respect to the steering angle MA is set appropriately. It becomes possible to do. Since the correction amount at this time can be adjusted by changing the driving amount of the actuator, an appropriate steering feeling can be produced according to the driving situation. The above-mentioned gradients B and C are not set as constants, but more accurate control can be performed by performing control by estimating from the measured values at the time of steering excluding the start-up time and the return time point.

  Here, an example of driving the DC brushless motor 7b, which is a drive actuator of the VGRS mechanism 7, has been described, but instead of this, or in addition to this, a DC brushless motor 3a serving as an EPS drive source may be used. . Moreover, it is good also as a structure only of EPS or only VGRS, and when providing a VGRS mechanism, a power steering apparatus may employ | adopt a hydraulic power steering apparatus. The EPS mechanism does not necessarily need to be of a type that directly drives the rack bar, and a type that drives the steering shaft or pinion gear can also be used.

  In addition to measuring the pinion rotation angle, the stroke amount of the rack bar may be directly measured by a sensor, or the stroke amount may be calculated from the driving amount of the DC brushless motor 3a disposed on the rack bar. In addition, based on the torsional rigidity of the torsion bar, the amount of displacement due to the torsion is obtained, or the deviation of the stroke amount with respect to the steering angle is estimated from models including other steering systems, and control is performed to correct it. Also good.

1 is a perspective view showing a configuration of an embodiment of a vehicle steering apparatus according to the present invention. It is a partial cross section perspective view of the VGRS mechanism 7 of the apparatus of FIG. It is sectional drawing of the steering gear 3 of the apparatus of FIG. It is a flowchart which shows the process of the main control part of the steering apparatus of FIG. It is a flowchart which shows the process of the part branched from the process of FIG. It is a flowchart which shows the process of another part branched from the process of FIG. It is a corresponding line figure which compares and shows the relation of steering angle (MA) and rack stroke (RS) at the time of the control at the time of conventional control, and this embodiment. It is a corresponding line figure which compares and shows the relation of steering angle (MA) and rack stroke (RS) with the case where correction control at the time of switch back is performed, and the case where it does not perform.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering column, 3 ... Steering gear, 3a ... Brushless motor, 3b ... Steering shaft, 3c ... Tie rod, 3d ... Rack gear, 3e ... Input shaft, 3f ... Ball screw groove, 3g ... Ball nut, 3h ... rotational position sensor, 4 ... steering angle sensor, 5 ... ECU, 6 ... torque sensor, 7 ... VGRS mechanism, 7a ... differential mechanism, 7b ... brushless motor, 7c ... lock mechanism, 7d ... spiral cable, 7e ... Rubber coupling, 8 ... pinion rotation angle sensor, 20 ... steering angle sensor, 21 ... steering torque sensor, 31 ... pinion angle sensor, 40 ... vehicle speed sensor.

Claims (4)

In a vehicle steering apparatus including a transmission mechanism that transmits a steering input of a driver to a steered wheel via a torsion bar and a rack and pinion mechanism,
Steering angle detection means for detecting the steering angle by the driver;
Steering torque detection means for detecting steering torque by the driver;
Rack stroke movement amount judging means for estimating or detecting the rack stroke movement amount;
An electric actuator disposed in the transmission mechanism and capable of adjusting a rack stroke movement amount with respect to a steering input by the driving force;
The operation of the actuator is controlled so that the target rack stroke movement amount according to the steering state determined from the detected steering angle and steering torque matches the rack stroke movement amount determined by the rack stroke movement amount determination means, and the rack stroke A control device that performs correction based on a ratio of a time change amount of the movement amount and a time change amount of the target rack stroke movement amount ;
A vehicle steering apparatus comprising:   The vehicle steering apparatus according to claim 1, wherein the electric actuator is capable of arbitrarily changing a steering gear ratio.   The vehicle steering apparatus according to claim 1, wherein the electric actuator applies an assist steering force.   4. The vehicle steering apparatus according to claim 3, wherein the actuator directly drives a rack bar.

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