JP4692170B2 - Vehicle steering system - Google Patents

Description

  The present invention belongs to a technical field of a vehicle steering apparatus that includes a device that can independently control at least the turning angles of front and rear wheels and that can arbitrarily set a vehicle body angle that is a direction of a vehicle body with respect to a traveling direction of the vehicle.

As a conventional vehicle steering device, for example, the direction of the vehicle body is changed while the traveling direction of the vehicle is constant during traveling, or the traveling direction of the vehicle is changed while the direction of the vehicle body remains unchanged. A technique for controlling the direction of the vehicle body in an arbitrary direction independent of the traveling direction of the vehicle has been proposed (see, for example, Patent Document 1 and Patent Document 2).
JP 2000-43748 A JP 2001-334951 A

  However, in the above prior art, since the rotation center of the rotation of the vehicle body during turning is always a fixed point, the vehicle has the same speed, the same turning radius, and the same rotation center position when turning left and right. When the vehicle turns around the same target body angle, the yaw rate experienced by the occupant in the left and right turns is the same, but there is a problem that the sensed lateral acceleration and the sensed longitudinal acceleration associated with the rotation of the vehicle differ between the left and right turns.

  For example, if the driver's position is set on the right side of the vehicle and the vehicle body is tilted to the inside of the turn, the driver will feel a sense of deceleration because the amount of rotation is small when turning right, and the amount of rotation is large when turning left. Creates a sense of acceleration. On the other hand, the passenger seat gives a feeling of acceleration when turning right and a feeling of deceleration when turning left. In particular, generating a large acceleration feeling when turning due to the rotation motion may give the driver a sense of incongruity.

  The present invention has been made paying attention to the problems of the prior art, and the object of the present invention is to provide a vehicle steering device that can reduce the feeling of acceleration given to the occupant regardless of the direction of the vehicle body when turning. Is to provide.

In order to achieve the above object, the present invention provides:
In a vehicle steering apparatus comprising a device capable of independently controlling at least the turning angles of the front and rear wheels and capable of arbitrarily setting a vehicle body angle that is a direction of the vehicle body with respect to the traveling direction of the vehicle,
A target turning radius calculating means for calculating a target turning radius according to the steering operation amount;
Target vehicle body angle calculating means for calculating a target vehicle body angle that is a target value of the vehicle body angle;
Target rotation center position setting means for setting the target rotation center position, which is the rotation center of the target vehicle body angle, to a position on the outer side of the turn from the vehicle occupant position;
Target turning center position calculating means for calculating a target turning center position based on the target turning radius and the target rotation center position;
Front and rear wheel steering angle calculation means for calculating a steering angle command value of front and rear wheels that realizes the target turning center position;
It is characterized by providing.

  Therefore, in the present invention, the target rotation center position, which is the rotation center of the target vehicle body angle, is set to a position outside the turn with respect to the vehicle occupant position. In other words, by moving the rotation center position to a position outside the turn from the vehicle occupant position, the driver always feels deceleration due to the rotation regardless of the direction of the vehicle body and the turn direction, and feels forward acceleration during the turn. Is to reduce. As a result, it is possible to reduce the uncomfortable feeling given to the occupant regardless of the direction of the vehicle body when turning.

  Hereinafter, the best mode for carrying out the present invention will be described based on Examples 1 to 3.

First, the configuration will be described.
FIG. 1 is an overall configuration diagram of a vehicle steering apparatus according to a first embodiment. The vehicle steering apparatus according to the first embodiment includes a steering wheel 1, front wheels 2, 2, rear wheels 3, 3, and a turning angle. This is a so-called steer-by-wire system that includes an actuator 4, a wheel speed sensor 5, and a drive motor 6, and in which the steering wheel 1 and the front wheels 2 and 2 are mechanically separated.

  The steering angle sensor 7 uses an encoder, a potentiometer, or the like to detect a driver's steering wheel operation amount. The vehicle body speed sensor 8 detects the vehicle body speed from each wheel speed obtained from each wheel speed sensor 5. The turning angle sensor 9 detects the turning angle of each wheel based on the operating angle of each turning angle actuator 4. The yaw rate sensor 10 detects the yaw rate of the vehicle.

  Detection signals from the steering angle sensor 7, the vehicle speed sensor 8, the turning angle sensor 9, and the yaw rate sensor 10 are input to the control unit 12 via an input / output (I / O) interface 11.

  The control unit 12 calculates the steering angle command value and the drive command value for each wheel based on the detection signal of each sensor, and sends the steering angle command value and the drive controller to the steering controller 13 via the I / O interface 11. The drive command values are output to 14 respectively.

  The turning controller 13 drives each turning angle actuator 4 based on each turning angle command value, and independently controls the turning angles of the four wheels. The drive controller 14 drives each drive motor 6 based on each drive command value, and independently controls the drive force of the four wheels.

  FIG. 2 is a plan view of the vehicle in the first embodiment. In FIG. 2, point O is the vehicle fixed coordinate origin. In the first embodiment, as the vehicle fixed coordinate origin O, an intersection of a line obtained by dividing the wheel base and the tread width into two equal parts is selected.

  In the following explanation, an arbitrary point is selected from the vehicle fixed coordinate system as the center of rotation, and the movement in which the center of rotation rotates in the ground coordinate system is “revolution”. In addition to the revolution, the vehicle fixed coordinate origin is the center of rotation. The movement that the vehicle body rotates around is called “rotation”.

[Front and rear wheel steering angle control processing]
FIG. 3 is a flowchart showing the flow of the front and rear wheel steering angle control processing executed by the control unit 12 of the first embodiment, and each step will be described below. In FIG. 3, step S1 is a steering angle sensor 7, step S2 is a target turning radius calculating means for calculating a target turning radius according to the steering angle, step S3 is a wheel speed sensor 5, a turning angle sensor 9, and step S4. Is a vehicle speed sensor 8, step S5 is a left / right turning judgment means for judging whether the vehicle is turning left or right with respect to the direction of the vehicle body, step S6 is a target body angle calculating means for calculating a target body angle, and step S7 is a target body angle. Target vehicle angular velocity calculating means for calculating the target vehicle angular velocity, Step S8 is a target rotation center position setting means for setting a target rotation center position that is a rotation center of the target vehicle body angle, Step S9 is a target turning radius, a target vehicle body angle, a target vehicle body Step S10 is a target turning center position calculating means for changing the turning center position based on the angular velocity and the rotation center position.Step S10 is based on the target turning center position and the target rotation center position. There are, corresponding to the front and rear wheel steering angle calculating means for calculating a front and rear wheel steering angle command value.

  In step S1, the steering angle δ of the steering wheel 1 is detected, and in step S2, an initial turning center radius R (target turning center) corresponding to the steering angle δ is calculated. As an example, FIG. 4 shows a method of setting the turning center radius R from the steering wheel 1 operated by the driver.

  The vehicle lateral direction is x and the vehicle right side is positive. Further, the vehicle front-rear direction is y, and the vehicle front is positive. The point P in FIG. 4 is the vehicle turning center, and the turning center y coordinate is set in advance on the rear wheel axle of the vehicle. An angle obtained by dividing the rotation angle of the steering wheel 1 operated by the driver by the steering gear ratio is defined as a turning angle δ. The turning angle δ is an angle formed by the vehicle fixed coordinate y direction from the center of the front wheel axle. The intersection of the line perpendicular to the turning angle δ and the turning center y coordinate is calculated as the turning center x coordinate. A turning radius R that is a distance from the turning center x, y to the vehicle fixed coordinate origin is calculated. Accordingly, when the steering wheel 1 is rotated to the right from the straight traveling time, the turning center x coordinate approaches 0 from infinity in the right direction. Conversely, when the steering wheel 1 is rotated to the left, the turning center x coordinate approaches 0 from infinity in the left direction.

In step S3, the turning angle of each wheel is output from the turning angle sensor 9 and the wheel speed of each wheel is output from the wheel speed sensor 5, and in step S4, the measured turning angle (δ _fl , δ of each wheel) is output. _fr , δ _rl , δ _rr ), obtain the direction of the wheel, average each wheel speed (V _fl , V _fr , V _rl , V _rr ), and approximate the vehicle speed V from the following equation (1) .
V = (δ _fl · V _fl + δ _fr · V _fr + δ _rl · V _rl + δ _rr · V _rr ) / 4… (1)

  In step S5, it is determined whether the vehicle is turning left or right. Judgment of left and right turning may be performed from the input of the steering wheel 1 or may be performed using a detector such as the yaw rate sensor 10.

  In step S6, the target vehicle speed α is set. The target vehicle body angle α can be set arbitrarily.

In step S7, the target vehicle body angle α is time-differentiated to calculate the target vehicle body angular velocity dα / dt. In step S8, the target rotation center position O ′ ^* is set from the target vehicle body angular velocity dα / dt. In the first embodiment, the target rotation center position O ′ ^* is set to the outside of the turning at the left-right symmetrical position with respect to the origin O.

In step S9, the speed V ′ of the target rotation center position O ′ ^* set in step S8 is obtained by coordinate conversion of the vehicle speed V. At this time, in order to obtain the target vehicle angular velocity dα / dt without changing the traveling direction of the target rotation center position O ′ ^*, a straight line connecting the rotation center position O ′ and the turning center position P as shown in FIG. In this case, it is possible to increase or decrease only the vehicle body angular velocity without changing the velocity vector of the rotation center position O ′ by setting the turning radius R ′ represented by the following equation (2).
R '= 1 / (1 / R + 1 / V' · dα / td) (2)
Here, R is the desired target turning radius, V ′ is the speed of the rotation center position O ′, and dα / dt is the target vehicle body angular velocity obtained from the target vehicle body angle.

  As shown in FIG. 6, the final target turning center position P ″ is calculated by performing coordinate conversion on the amount of α rotation of the vehicle body coordinate system relative to the initial coordinate system.

  In step S10, the steering angle command value of each wheel is calculated so as to geometrically satisfy the target turning center position P ". FIG. 7 shows the relationship between the target turning center position P" and the turning angle of each wheel. The turning angle of each wheel is calculated so as to form a right angle with the straight line connecting the point P and the turning center of each wheel, and the processing is terminated.

Next, the operation will be described.
[Problems of fixed rotation center position]
Normally, in the conventional vehicle steering apparatus, the vehicle rotation center O ′ is fixed to the vehicle fixed coordinate origin O as shown in FIG. When the rotation center position O ′ and the driver position have a distance L, L · d ² α / dt ² obtained by multiplying the distance L by the angular acceleration d ² α / dt ² generated by the rotation is the acceleration experienced by the driver. Appears as

  The simulation results of the above prior art will be shown below. FIG. 9 shows vehicle inputs when performing a simulation. When a target vehicle body angle is given so as to face inward in the turning direction at a steering angle input and a constant vehicle speed of 13 [km / h] (3.6 [m / sec]). A vehicle track is shown in FIG. The driver's position was calculated from the vehicle fixed coordinate O by setting the position in the x direction as 0.355 [m] and the y direction as -0.12 [m]. FIG. 11 shows the yaw rate, lateral acceleration, and longitudinal acceleration experienced by the driver. As shown in FIG. 11, it can be confirmed that the driver is receiving an acceleration feeling due to the rotation motion in the left turn.

[Rotation center position variable action]
On the other hand, in the vehicle steering system of the first embodiment, the target rotation center position O ′ ^* set in step S8 in FIG. 3 is set to a position outside the turn with respect to the occupant position. That is, when turning left, the rotation center position O ′ is set to a position outside the turning with respect to the driver (FIG. 12A), and when turning right, the rotation center position O ′ is located outside the turning than the passenger on the passenger seat. The position is set (FIG. 12 (b)). Thereby, the feeling of acceleration given to the driver can be reduced. As the rotation center position O ′ is arranged on the outer side of the turning of the vehicle, the necessary front and rear wheel turning angles with respect to the same target vehicle body angle α increase, but the feeling of deceleration, which is the backward acceleration, can be increased.

  FIGS. 13 and 14 show the simulation results of Example 1, and FIG. 15 shows the steering command value of the steering controller 13 when performing this operation. As the input of the vehicle, the same steering angle input, vehicle speed, and target vehicle body angle as those in the prior art shown in FIG. 9 are given. Further, as an example, the rotation center position O ′ is set to 0.72 [m] in the x direction and 0.0 [m] in the y direction when turning left from the vehicle fixed coordinates.

Next, the effect will be described.
The vehicle steering apparatus according to the first embodiment has the following effects.

(1) In a vehicle steering apparatus that includes a turning angle actuator 4 that can independently control the turning angle of each wheel and that can arbitrarily set a vehicle body angle that is the direction of the vehicle body relative to the traveling direction of the vehicle, The target turning radius calculating means (step S2) for calculating the target turning radius R, the target vehicle body angle calculating means (step S6) for calculating the target vehicle body angle α, and the target that is the center of rotation of the target vehicle body angle α. Based on the target rotation center position setting means (step S8) for setting the rotation center position O ′ ^* to a position outside the turning from the vehicle occupant position, the target turning radius R, and the target rotation center position O ′ ^* , Target turning center position calculating means (step S9) for calculating the target turning center position P "and front and rear wheel steering angle calculating means (step S10) for calculating the steering angle command values of the front and rear wheels that realize the target turning center position P". And comprising. Therefore, it is possible to reduce the uncomfortable feeling given to the occupant regardless of the direction of the vehicle body when turning.

(2) The target rotation center position setting means sets the target rotation center position O ' ^* to the outside of the left and right symmetrical positions with respect to the origin O, so that passengers are on both sides from the origin O. Can give deceleration to all occupants.

  The second embodiment is an example in which the rotation center position O ′ is switched between a case where the occupant is only the driver and a case where there are a plurality of occupants. Since the configuration is the same as that of the first embodiment, illustration and description of the overall configuration are omitted.

Next, the operation will be described. In the second embodiment, according to the position of the occupant, the target rotation center position O ′ ^* is set on the outer side of the turn at the symmetrical position with respect to the driver position. "Mode" and "Origin center mode" that is set to the outside of the turn at a symmetrical position with reference to any origin 0 or center of gravity on the vehicle. In the second embodiment, the driver determines the position of the occupant and operates a mode selection switch (mode selection means) or the like (not shown), so that the control unit 12 sets the “driver center mode” and “origin center mode”. Is switched.

  That is, in the “driver center mode”, as shown in FIG. 16, the rotation center position O ′ is set at a left-right symmetric position (hatched portion in the figure) with respect to the driver position. In the “origin mode”, as shown in FIG. 17, the rotation center position O ′ is set at a bilaterally symmetrical position (hatched portion in the figure) with respect to the vehicle fixed coordinate origin O.

Next, the effect will be described.
The vehicle steering apparatus according to the second embodiment has the following effects in addition to the effects (1) and (2) of the first embodiment.

(3) The target rotation center position setting means sets the target rotation center position O ′ ^* to the outside of the turn at a symmetrical position with respect to the driver's position, so only the driver gets on the left or right from the origin O. In this case, it is possible to give a feeling of deceleration in the same way on the left and right with the driver as the center.

  (4) The target rotation center position setting means can switch between `` origin center mode '' and `` driver center mode '', so when only the driver is on board or when another passenger is on board A more preferable mode can be selected.

  (5) Provided with a mode selection switch that selects either `` origin center mode '' or `` driver center mode '' by the driver's input operation. Since the “origin center mode” and the “driver center mode” are switched, the mode switching control can be realized with a simpler configuration.

  In the third embodiment, the control unit 12 determines the occupant position, and automatically switches between the “origin center mode” and the “driver center mode” according to the occupant arrangement. The determination of the occupant position is performed using a pressure-sensitive sensor embedded in the seat cushion of each seat, an infrared sensor for detecting the occupant, or image processing of a camera.

  Thereby, in Example 3, since a driver | operator can save the effort which switches a mode manually, a driver | operator's burden can be reduced with respect to Example 2. FIG.

Next, the effect will be described.
The vehicle steering apparatus according to the third embodiment has the following effects in addition to the effects (1) and (2) of the first embodiment and the effects (3) and (4) of the second embodiment.

(6) The target rotation center position setting means switches between the `` origin center mode '' and the `` driver center mode '' according to the occupant position. The target rotation center position O ′ ^* can be set.

(Other examples)
The best mode for carrying out the present invention has been described based on the first to third embodiments. However, the specific configuration of the present invention is not limited to the first to third embodiments. Design changes and the like within a range that does not depart from the gist are also included in the present invention.

  In the first embodiment, the vehicle steering device capable of independently controlling the turning angles of the four wheels is shown as an example. However, the present invention is also applied to the 4WS system capable of independently controlling the turning angles of the front and rear wheels. Applicable. In the first embodiment, the steer-by-wire system is used. However, the steering wheel 1 and the front wheels are mechanically connected, and the angle of the steering wheel operated by the driver and the turning angle of the front wheels can be changed. It can be applied to a front active steering system that can be used.

  In the first embodiment, an example in which the target rotation center position is set based on the vehicle fixed coordinate origin is shown, but the center of gravity of the vehicle may be used as a reference. In the “origin mode”, the center point of a plurality of passengers may be used as a reference for the target rotation center position.

1 is an overall configuration diagram of a vehicle steering apparatus according to a first embodiment. 1 is a plan view of a vehicle in Example 1. FIG. 6 is a flowchart showing a flow of front and rear wheel steering angle control processing executed by the control unit 12 of the first embodiment. It is explanatory drawing which shows the calculation method of the target turning radius R of Example 1. FIG. FIG. 6 is an explanatory diagram illustrating a method for calculating a target vehicle body angular velocity dα / td according to the first embodiment. It is explanatory drawing which shows the calculation method of the target turning center position P "of Example 1. FIG. It is a figure showing the relationship between the target turning center position P "of Example 1, and the turning angle of each wheel. It is a figure which shows rotation center position O 'of a prior art. It is a figure which shows the steering angle, vehicle speed, and target vehicle body angle which were input when performing simulation. It is a figure which shows the vehicle movement locus | trajectory by the simulation of a prior art. It is a figure which shows the yaw rate by the simulation of a prior art, a lateral acceleration, and a longitudinal acceleration. It is explanatory drawing which shows the autorotation center position setting method of Example 1. FIG. It is a figure which shows the vehicle movement locus | trajectory by the simulation of Example 1. FIG. It is a figure which shows the yaw rate by the simulation of Example 1, lateral acceleration, and longitudinal acceleration. It is a figure which shows the steering command value of each wheel calculated by Example 1. FIG. It is explanatory drawing which shows the autorotation center position setting method in the driver center mode of Example 2. FIG. It is explanatory drawing which shows the autorotation center position setting method in the origin center mode of Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2, 2 Front wheel 3, 3 Rear wheel 4 Steering actuator 5 Wheel speed sensor 6 Drive motor 7 Steering angle sensor 8 Car body speed sensor 9 Steering angle sensor 10 Yaw rate sensor 11 Input / output interface 12 Control unit 13 Steering controller 14 Drive controller

Claims (7)

In a vehicle steering apparatus comprising a device capable of independently controlling at least the turning angles of the front and rear wheels and capable of arbitrarily setting a vehicle body angle that is a direction of the vehicle body with respect to the traveling direction of the vehicle,
A target turning radius calculating means for calculating a target turning radius according to the steering operation amount;
Target vehicle body angle calculating means for calculating a target vehicle body angle that is a target value of the vehicle body angle;
Target rotation center position setting means for setting the target rotation center position, which is the rotation center of the target vehicle body angle, to a position on the outer side of the turn from the vehicle occupant position;
Target turning center position calculating means for calculating a target turning center position based on the target turning radius and the target rotation center position;
Front and rear wheel steering angle calculation means for calculating a steering angle command value of front and rear wheels that realizes the target turning center position;
A vehicle steering apparatus comprising: The vehicle steering apparatus according to claim 1,
The target rotation center position setting means sets the target rotation center position to the outside of the turn at a symmetrical position with respect to an arbitrary origin or center of gravity on the vehicle. The vehicle steering apparatus according to claim 1,
The target rotation center position setting means sets the target rotation center position to the outside of a turn at a symmetrical position with respect to the driver's position. The vehicle steering apparatus according to any one of claims 1 to 3,
The target rotation center position setting means sets the target rotation center position to an origin center mode in which the target rotation center position is set on the outer side of a left-right symmetrical position with respect to an arbitrary origin or center of gravity on the vehicle, and the target rotation center position. A vehicle steering apparatus characterized by being capable of switching between a driver center mode set outside a turn at a symmetrical position with respect to a driver's position. The vehicle steering device according to claim 4,
Comprising mode selection means for selecting one of the origin center mode and the driver center mode by a driver's input operation;
The target rotation center position setting means switches between the origin center mode and the driver center mode according to the mode selection state of the mode selection means. In the vehicle steering apparatus according to claim 4 or 5,
The target rotation center position setting means switches between the origin center mode and the driver center mode according to the occupant position. In a vehicle steering apparatus comprising a device capable of independently controlling at least the turning angles of the front and rear wheels and capable of arbitrarily setting a vehicle body angle that is a direction of the vehicle body with respect to the traveling direction of the vehicle,
Calculate the target turning radius according to the steering operation amount,
A target vehicle body angle that is a target value of the vehicle body angle is calculated,
The target rotation center position, which is the rotation center of the target vehicle body angle, is set to a position outside the turn from the vehicle occupant position,
Based on the target turning radius and the target rotation center position, the target turning center position is calculated,
A steering apparatus for a vehicle, wherein a steering angle command value for front and rear wheels that realizes the target turning center position is calculated.

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