JP2014024414A - Vehicular power steering control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a driver to smoothly and naturally steer a vehicle from a curving road to a rectilinear road by properly reflecting not only a running road shape but also a driver's steering situation.SOLUTION: A basic assist torque Tb is designated based on vehicle velocity V and steering wheel torque Ts. A basic assist torque correction quantity ΔTa with which the basic assist torque Tb is corrected in a direction in which the steering wheel torque Ts at a neutral position of a steering angle δH at an exit of a curving road at which a transition is made from the curving road to a rectilinear road approaches to a nil is calculated based on a radius R of a curve of a frontal running road, the steering angle δH, and a driver's state of returning a steering wheel. The basic assist torque Tb is corrected with the basic assist torque correction quantity ΔTa, and outputted as a control quantity (assist torque Ta) to a motor drive unit 12a.

Description

  The present invention particularly relates to a power steering control device for a vehicle that realizes an appropriate steering feeling at a curve exit.

  2. Description of the Related Art Conventionally, in a vehicle, a steering assist device that performs various steering assists by generating various steering torques with a power steering motor has been proposed and put into practical use. For example, in Japanese Patent Application Laid-Open No. 2007-38696 (hereinafter referred to as Patent Document 1), steering that applies a steering torque to a steering mechanism so that a vehicle travels along a travel path based on an image obtained by imaging a travel path ahead of the vehicle. In the support device, when the vehicle exits the curve exit by detecting the curve exit on the road, increase the amount of change in the steering torque when turning back the steering wheel compared to the case other than when the vehicle exits the curve, A technique of a steering assist device is disclosed in which a delay in turning back a steering wheel at a curve exit is suppressed, and a vehicle is caused to travel following a traveling path.

JP 2007-38696 A

  By the way, with the technique of the steering assist device disclosed in the above-mentioned Patent Document 1, it is possible to keep the lane keep at the curve exit by suppressing the delay in turning back the steering wheel, but mainly consider the driver's steering intention. In such a case, the lane keep control that follows the shape of the road exit at the curve exit does not necessarily match the steering control desired by the driver, and the driver feels uncomfortable by the lane keep control as described above. There is a fear.

  The present invention has been made in view of the above circumstances, and a vehicle in which a driver can smoothly and naturally perform steering from a curve to a straight path by accurately reflecting not only the shape of the traveling road but also the steering state of the driver. An object of the present invention is to provide a power steering control device.

  One aspect of a power steering control device for a vehicle according to the present invention includes a basic assist torque setting unit that sets an assist torque of a steering torque as a basic assist torque according to a driving state of the vehicle, and a travel path that recognizes the shape of a forward travel path. The shape recognizing means, the steering torque at the neutral position of the steering angle at the curve exit that transitions from the curve to the straight path based on the curve radius and steering angle of the forward traveling road and the driver steering switchback state in the direction approaching 0 Assist torque correction amount calculating means for calculating a basic assist torque correction amount for correcting the basic assist torque, and steering control means for driving and controlling an actuator for assisting the steering torque by correcting the basic assist torque with the basic assist torque correction amount. And with.

  According to the power steering control device for a vehicle according to the present invention, the driver can smoothly and naturally steer from the curve to the straight path by accurately reflecting not only the shape of the traveling road but also the steering state of the driver. Become.

1 is a configuration explanatory diagram of a vehicle steering system according to an embodiment of the present invention. FIG. It is a functional block diagram of the steering control part which concerns on one Embodiment of this invention. It is a flowchart of the power steering control program which concerns on one Embodiment of this invention. It is a flowchart of a basic assist torque correction amount calculation routine according to an embodiment of the present invention. It is a flowchart of the curve radius correction value calculation routine which concerns on one Embodiment of this invention. It is explanatory drawing which shows an example of the characteristic of the basic assist torque which concerns on one Embodiment of this invention. It is explanatory drawing of the characteristic of the steering angle return gain which concerns on one Embodiment of this invention. It is explanatory drawing of the switchback determination value which concerns on one Embodiment of this invention. It is explanatory drawing of the curve radius calculation which concerns on one Embodiment of this invention. It is explanatory drawing of the change of the curve radius of the front traveling road which concerns on one Embodiment of this invention. 11A and 11B are explanatory diagrams of a curve radius correction value calculation process according to an embodiment of the present invention. FIG. 11A shows a current curve radius limiter process and a dead band process, and FIG. 11B shows a curve radius deviation limiter. FIG. 11C shows a curve radius correction value, and FIG. 11D shows an example of steering angle correction. FIG. 12A is an explanatory diagram of the effect of correction in the Lissajous diagram of the steering torque and the steering angle according to the embodiment of the present invention, and FIG. 12A shows a travel path that transitions from a (left) curve to a straight path, 12 (b) shows a traveling road that transitions from a (left) curve to a (right) curve, and FIG. 12 (c) shows steering when traveling on the traveling road shown in FIGS. 12 (a) and 12 (b). An example of a Lissajous diagram of torque and steering angle is shown.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes an electric power steering apparatus. In the electric power steering apparatus 1, a steering shaft 2 is rotatably supported on a vehicle body frame (not shown) via a steering column 3, and one end thereof is It extends to the driver's seat side, and the other end extends to the engine room side. A steering wheel 4 is fixed to an end portion of the steering shaft 2 on the driver's seat side, and a pinion shaft 5 is connected to an end portion extending to the engine room side.

  A steering gear box 6 extending in the vehicle width direction is disposed in the engine room, and a rack shaft 7 is inserted into and supported by the steering gear box 6 so as to be reciprocally movable. A rack (not shown) formed on the rack shaft 7 is engaged with a pinion (not shown) formed on the pinion shaft 5 to form a rack and pinion type steering gear mechanism.

  The left and right ends of the rack shaft 7 protrude from the end of the steering gear box 6, and a front knuckle 9 is connected to the end via a tie rod 8. The front knuckle 9 rotatably supports left and right wheels 10L and 10R as steering wheels, and is supported by a vehicle body frame via a king pin (not shown) so as to be steerable.

  Accordingly, when the steering wheel 4 is operated and the steering shaft 2 and the pinion shaft 5 are rotated, the rack shaft 7 is moved in the left-right direction by the rotation of the pinion shaft 5, and the front knuckle 9 is moved to the king pin (not shown). ) And the left and right wheels 10L, 10R are steered in the left-right direction.

  An electric motor 12 is connected to the pinion shaft 5 via an assist transmission mechanism 11, and the electric motor 12 assists the steering torque applied to the steering wheel 4. The electric motor 12 is drive-controlled through a motor drive unit 12a with a control amount (assist torque Ta in the present embodiment) set by a steering control unit 20 described later. Note that the control amount may be a current value corresponding to the assist torque Ta.

  The steering control unit 20 includes a vehicle speed sensor 31 that detects the vehicle speed V, a steering angle sensor 32 that detects the steering angle δH, a steering torque sensor 33 that detects the steering torque Ts applied to the steering wheel 4, and a stereo camera 34a. A front environment recognition device 34 is connected as a travel path shape recognition means for processing image information and recognizing a forward travel path shape.

  The stereo camera 34a is composed of a pair of (left and right) cameras using a solid-state image sensor, and each camera is attached with a certain baseline length in front of the ceiling in the vehicle interior, and has different viewpoints for objects outside the vehicle. The stereo image is taken from and the image data is output to the forward environment recognition device 34.

  The front environment recognition device 34 includes an image processing engine that performs high-speed processing on an image captured by the stereo camera 34a, and recognizes it based on the output result of the image processing engine and travel information of the host vehicle (travel information such as the host vehicle speed V). It is configured as a processing unit that performs processing. The image processing of the stereo camera 34a in the front environment recognition device 34 is performed as follows, for example.

  That is, the front environment recognition device 34 first obtains distance information from a corresponding positional shift amount for a pair of stereo images in the traveling direction of the host vehicle captured by the stereo camera 34a, and generates a distance image. Then, based on this data, a well-known grouping process is performed and compared with frames (windows) such as three-dimensional road shape data, side wall data, and three-dimensional object data stored in advance. Side wall data such as guardrails and curbs that exist along the road are extracted, and three-dimensional objects are classified and extracted as types of vehicles, crossing pedestrians, and other three-dimensional objects. As shown in FIG. 9, these data are calculated as data in a coordinate system in which the own vehicle is the origin, the longitudinal direction of the own vehicle is the Z axis, and the width direction is the X axis. Sidewall data of existing guardrails, curbs, etc., type of three-dimensional object, distance from own vehicle, speed (time differential value of distance + own vehicle speed V), acceleration (time differential value of speed), center position, both end positions Are output to the steering control unit 20 as three-dimensional object information. At this time, especially for the road shape, for example, a curved line (or straight line) in which the central portion between the left white line and the right white line is continuous is estimated as the forward travel path of the host vehicle and output to the steering control unit 20. In the present embodiment, the shape of the traveling road ahead of the host vehicle is recognized based on image information from the stereo camera 34a. However, image information from a monocular camera or color camera is also available. Needless to say, the present invention can also be applied to a vehicle driving support device that recognizes based on the above, and can also be applied to such a camera in combination with other recognition sensors such as millimeter wave radar and inter-vehicle communication. Moreover, you may make it recognize based on the road shape by the map information obtained based on a well-known navigation apparatus, or the map information provided by an infrastructure.

As for the road shape (front traveling road) recognized as described above, the coordinate position and the curve radius R at the coordinate position are calculated and output together as coordinate information. As shown in FIG. 9, the curve radius Rs at a predetermined distance in front (front gaze distance: own vehicle speed / set time) Zs is set to (Xs, Zs) as the coordinates of the distance Zs set in advance on the forward travel path. For example, it is calculated by the following equation (1).
Rs = (Xs ² + Zs ² ) / (2 · Xs) (1)

  The steering control unit 20 sets a basic assist torque Tb based on the vehicle speed V and the steering torque Ts, and transitions from a curve to a straight path based on the curve radius R of the forward travel path, the steering angle δH, and the driver steering switchback state. The basic assist torque correction amount ΔTa for correcting the basic assist torque Tb in a direction approaching 0 is calculated for the steering torque Ts at the neutral position of the steering angle at the curve exit to be corrected, and the basic assist torque Tb is corrected by the basic assist torque correction amount ΔTa. The control amount (assist torque Ta) is output to the motor drive unit 12a. In the embodiment of the present invention, as an example, the left turning direction is (+) and the right turning direction is (−), and although not specifically described below, these two directions are always considered and controlled. Is.

  Therefore, as shown in FIG. 2, the steering control unit 20 mainly includes a basic assist torque setting unit 21, a basic assist torque correction amount calculation unit 22, and an assist torque calculation unit 23.

  The basic assist torque setting unit 21 receives the vehicle speed V from the vehicle speed sensor 31 and the steering torque Ts from the steering torque sensor 33. The basic assist torque Tb is set based on the vehicle speed V and the steering torque Ts with reference to, for example, a map previously set by experiment / calculation as shown in FIG. Output to. The setting of the basic assist torque Tb described above is merely an example, and may be set using a known map / calculation formula based on other parameters, or a map / calculation formula having different characteristics. Thus, the basic assist torque setting unit 21 is provided as basic assist torque setting means.

  The basic assist torque correction amount calculation unit 22 determines the steering torque at the neutral position of the steering angle at the curve exit that makes a transition from the curve to the straight path based on the curve radius R and the steering angle δH of the forward traveling road and the driver steering switchback state. Is provided as an assist torque correction amount calculating means for calculating a basic assist torque correction amount ΔTa for correcting the basic assist torque Tb in a direction approaching 0, a rudder angle return gain setting unit 22a, a switchback determination value calculating unit 22b, A curve radius correction value calculation unit 22c and a basic assist torque correction amount calculation unit 22d are mainly configured.

  The steering angle return gain setting unit 22 a receives the steering angle δH from the steering angle sensor 32. Then, the steering angle return gain Gθ is set with reference to, for example, a map or table of the characteristics of the steering angle return gain corresponding to the steering angle δH set in advance by experiment, calculation, etc. as shown in FIG. And output to the basic assist torque correction amount calculation unit 22d. As will be described later, this steering angle return gain Gθ is a gain that is multiplied when calculating the basic assist torque correction amount ΔTa, and in this embodiment, the basic value increases as the absolute value | δH | of the steering angle increases. The steering angle return gain Gθ is set to be large so that the absolute value | ΔTa | of the assist torque correction amount is large. The steering angle return gain Gθ may be further variably set according to other parameters such as the vehicle speed V.

The switchback determination value calculation unit 22 b receives the steering angle δH from the steering angle sensor 32 and receives the steering torque Ts from the steering torque sensor 33. Then, for example, the switchback determination value Vj is calculated by any of the following formulas (2), (3), and (4), and is output to the basic assist torque correction amount calculation unit 22d.
SIGN (Ts · (dδH / dt))> 0: Vj = + 1 (2)
SIGN (Ts · (dδH / dt)) <0: Vj = −1 (3)
Ts · (dδH / dt) = 0: Vj = 0 (4)
Here, SIGN (Ts · (dδH / dt)) indicates the sign of Ts · (dδH / dt).

  That is, on the Lissajous diagram of the steering state drawn on the coordinates where the horizontal axis in FIG. 8 is the steering angle δH and the vertical axis is the steering torque Ts, the switchback determination value Vj expressed by the above equation (2) is The region in the second quadrant where the steering torque Ts becomes positive and the steering angle δH changes from negative to zero, and the steering holding state (shown by SH after the steering torque Ts is positive and the steering angle δH becomes 0) ( The area of the first quadrant up to (Equation (4) above), and the areas of the solid lines of the areas of the first and second quadrants and the third and fourth quadrants that are point-symmetric with respect to the origin O, It has become.

  Further, on the Lissajous diagram of FIG. 8, the switchback determination value Vj expressed by the above-described equation (3) is the first quadrant region from the steering holding state SH until the steering torque Ts becomes 0, The first quadrant area and the third quadrant broken line area are point-symmetric with respect to the origin O.

  The curve radius correction value calculation unit 22c receives the coordinates of the road shape (front traveling road) recognized by the forward environment recognition device 34 together with the curve radius R at the coordinates. Then, as shown in FIG. 10, the current curve radius R0 and the curve radius R1 after the set time (t seconds) are calculated on the basis of the coordinates of the forward traveling road inputted every moment and the curve radius R at the coordinates. The curve radius correction value Tr1 is calculated using the curve radius R0 and the curve radius R1, and is output to the basic assist torque correction amount calculation unit 22d.

Calculation of the curve radius correction value Tr1 executed by the curve radius correction value calculation unit 22c will be described with reference to the flowchart of FIG. 5 and FIG.
First, in step (hereinafter abbreviated as “S”) 301, a limiter process is performed with a preset upper limit value (RH) as shown in FIG. 11A for the calculated current curve radius R 0. Then, the case of a substantially straight road is excluded from the control target, and the dead zone process is performed with the preset threshold value RL, and the case where the curve is still turning and does not reach the curve exit is excluded from the control measures. .

  Next, in S302, the curve radius deviation ΔR (= R1-R0) is calculated by subtracting the current curve radius R0 from the curve radius R1 after the set time (t seconds).

  Next, the process proceeds to S303, where a limiter process is performed with a preset upper limit value ΔRH for the curve radius deviation ΔR, and the values from the carp inlet to the curve outlet that can be determined from the curve radius deviation ΔR are separated (see FIG. 11B). ) Multiplying this cut value by the current curve radius R0 subjected to the limiter / dead zone processing in S301, and cutting the value to the value of only the curve exit, and further, the limiter processing of the value of only this curve exit with the lower limit value 0 (Refer FIG.11 (c)).

  Next, proceeding to S304, the value subjected to the limiter process with the lower limit value 0 of S303 is subjected to absolute value processing, calculated as a curve radius correction value Tr1, and the routine is exited.

  In this way, the curve radius correction value calculation unit 22c determines the curve exit when the change in the curve radius of the forward travel path is small and the current curve radius is large, and the current curve at the curve exit is determined. The curve radius correction value Tr1 is calculated according to the degree of the curve exit obtained by multiplying the radius R0 and the curve radius deviation ΔR.

The basic assist torque correction amount calculation unit 22d receives the steering angle return gain Gθ from the steering angle return gain setting unit 22a, receives the switchback determination value Vj from the switchback determination value calculation unit 22b, and calculates the curve radius correction value calculation unit. The curve radius correction value Tr1 is input from 22c. Then, the basic assist torque correction amount ΔTa is calculated by the following equation (5) and output to the assist torque calculation unit 23.
ΔTa = Gθ · Tr1 · Vj (5)

The assist torque calculation unit 23 receives the basic assist torque Tb from the basic assist torque setting unit 21 and the basic assist torque correction amount ΔTa from the basic assist torque correction amount calculation unit 22d of the basic assist torque correction amount calculation unit 22. . Then, for example, the basic assist torque Tb is corrected with the basic assist torque correction amount ΔTa by the following equation (6), and is output to the motor drive unit 21 as a control amount (assist torque Ta).
Ta = Tb + ΔTa (6)
Thus, the assist torque calculation unit 23 is provided as steering control means.

Next, the power steering control executed by the steering control unit 20 will be described with reference to the flowcharts of FIGS.
First, in S101, necessary parameters, that is, the vehicle speed V, the steering angle δH, the steering torque Ts, the coordinates of the front traveling road shape, and the curve radius R at the coordinates are read.

  Next, the process proceeds to S102, where the basic assist torque setting unit 21 refers to the map set in advance as described above (for example, shown in FIG. 6) and based on the vehicle speed V and the steering torque Ts. Torque Tb is set.

  Next, in S103, the basic assist torque correction amount calculation unit 22 calculates the basic assist torque correction amount ΔTa according to the flowchart of FIG.

  Then, the process proceeds to S104, where the assist torque calculation unit 23 calculates the assist torque Ta by the above-described equation (6), and outputs it to the motor drive unit 12a to exit the program.

  As shown in the flowchart of FIG. 4, the calculation of the basic assist torque correction amount ΔTa executed in S103 is first performed in advance in S201 by the steering angle return gain setting unit 22a as shown in FIG. The steering angle return gain Gθ is set with reference to a map or table of the characteristics of the steering angle return gain corresponding to the steering angle δH set by experiment, calculation, or the like.

  Next, the process proceeds to S202, and the switchback determination value calculation unit 22b calculates the switchback determination value Vj by, for example, any one of the aforementioned formulas (2), (3), and (4).

  Next, proceeding to S203, the curve radius correction value calculation unit 22c calculates the current curve radius R0 and the curve radius R1 after the set time (t seconds) according to the flowchart of FIG. A curve radius correction value Tr1 is calculated using the radius R0 and the curve radius R1.

  In step S204, the basic assist torque correction amount calculation unit 22d calculates the basic assist torque correction amount ΔTa by the above-described equation (5), and exits the routine.

  As described above, according to the embodiment of the present invention, the basic assist torque Tb is set based on the vehicle speed V and the steering torque Ts, and the curve radius R, the steering angle δH, and the driver steering switchback state are set. Based on the basic assist torque Tb, the basic assist torque correction amount ΔTa for correcting the basic assist torque Tb in a direction approaching 0 is calculated for the steering torque Ts at the neutral position of the steering angle at the curve exit where the curve transitions from the curve to the straight path. It is corrected with the assist torque correction amount ΔTa and output as a control amount (assist torque Ta) to the motor drive unit 12a. For this reason, it becomes possible for the driver to smoothly perform the steering from the curve to the straight path smoothly and naturally without a sense of incongruity by accurately reflecting not only the traveling road shape but also the driver's steering situation.

  That is, in the steering characteristics, friction is set in consideration of reverse input from the tire side, vibration, and the like. For example, the traveling road changes from a left curve to a straight road as shown in FIG. When traveling from point A (left curve) → point B (curve exit) → point C (straight path), the relationship between the steering angle δH and the steering torque Ts is shown in FIG. Ideally, it should transition to point C.

  On the other hand, as shown in FIG. 12B, the traveling path changes from a left curve to a right curve at point A (left curve) → B ′ point (curve connecting portion) → C ′ point (right curve). In the case of traveling, the relationship between the steering angle δH and the steering torque Ts can be switched more smoothly when the transition from point A → point B ′ → point C ′ shown in FIG.

  In the present application, in order to solve such a problem, even if the steering waveform to the curve exit is the same, depending on the traveling path ahead, the straight path from the curve as shown in FIG. On the travel road that changes to, the basic assist torque correction amount ΔTa for correcting the basic assist torque Tb in the direction in which the steering torque Ts at the neutral position of the steering angle approaches 0 is calculated, and the basic assist torque Tb is calculated as the basic assist torque correction amount. It is corrected by ΔTa and output to the motor drive unit 12a as a control amount (assist torque Ta). That is, the characteristic of transition from point A → B ′ point → C ′ point in FIG. 12C is corrected to the characteristic of transition from A point → B, C point.

  In other words, as shown in FIG. 11D, the steering angle δH when the correction with the basic assist torque correction amount ΔTa is performed changes from δH0 to δH1 when the basic assist torque correction amount ΔTa is not corrected. When the basic assist torque correction amount ΔTa is corrected, the characteristic (broken line) becomes a characteristic (solid line) from δH0 to δH2. At this time, since the basic assist torque correction amount ΔTa is set not only according to the shape of the travel path but also according to the driver's steering situation, the driver's steering intention is mainly used not only to keep the lane keep good. Considering this, it is possible to control the steering at the curve exit naturally without a sense of incongruity.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 4 Steering wheel 5 Pinion shaft 11 Assist transmission mechanism 12 Electric motor 12a Motor drive part 20 Steering control part 21 Basic assist torque setting part (basic assist torque setting means)
22 Basic assist torque correction amount calculation unit (assist torque correction amount calculation means)
22a Steering angle return gain setting unit 22b Switchback determination value calculation unit 22c Curve radius correction value calculation unit 22d Basic assist torque correction amount calculation unit 23 Assist torque calculation unit (steering control means)
Reference Signs List 31 Vehicle speed sensor 32 Steering angle sensor 33 Steering torque sensor 34 Front environment recognition device
34a Stereo camera

Claims (5)

Basic assist torque setting means for setting the assist torque of the steering torque as the basic assist torque according to the driving state of the vehicle;
Traveling road shape recognition means for recognizing the shape of the forward traveling road;
The basic assist torque is corrected so that the steering torque at the neutral position of the steering angle at the curve exit that transitions from the curve to the straight path approaches 0 based on the curve radius and steering angle of the forward travel path and the driver steering return state. Assist torque correction amount calculating means for calculating a basic assist torque correction amount to be
Steering control means for driving and controlling an actuator for assisting steering torque by correcting the basic assist torque with the basic assist torque correction amount;
A vehicle power steering control device.   2. The power steering control device for a vehicle according to claim 1, wherein the assist torque correction amount calculating means sets the absolute value of the basic assist torque correction amount to be larger as the absolute value of the steering angle is larger.   3. The power steering control device for a vehicle according to claim 1, wherein the assist torque correction amount calculating means determines a return state of driver steering based on a steering torque and a steering speed.   4. The assist torque correction amount calculating means calculates an absolute value of the basic assist torque correction amount based on at least a change in a curve radius of the forward travel path. A power steering control device for a vehicle according to claim 1.   The assist torque correction amount calculating means determines the curve exit when the change in the curve radius of the forward travel path is small and the current curve radius is large, and according to the degree of the curve exit 5. The power steering control device for a vehicle according to claim 4, wherein an absolute value of the basic assist torque correction amount is calculated.

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