JP2008126985A - Steering control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering control device for a vehicle capable of continuously generating feasible maximum lateral acceleration regardless of a coefficient of the friction of a road surface and improving obstacle avoiding performance. <P>SOLUTION: This steering control device is provided with: a target front wheel slip angle calculating means (step S200) which calculates as a target front wheel slip angle, a front wheel slip angle with a lateral force of a front wheel maximized based on a detected wheel load; a front wheel steering angle adjustment means (step S201) which adjusts a front wheel steering angle so that the front wheel slip angle follows the target front wheel slip angle; and a yaw movement adjustment means (step S202) which adjusts the yaw movement of a vehicle so that the yaw rate generation direction of the vehicle when turning is matched with the lateral movement direction thereof. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to the technical field of vehicle steering control devices.

  As a conventional technique for generating a large turning ability of a vehicle when an emergency avoidance of an obstacle or the like is performed, in a four-wheel steering vehicle, a gain from a steering angle to a front wheel steering angle is increased in an emergency situation, and a rear wheel is It is known that the initial lateral acceleration in an emergency is increased by setting the rear wheel steering angle to approximately the same amount as the front wheel steering angle in the initial operation. Note that in the steering switchback operation, the vehicle slip angle control is returned to ensure the turning stability (see, for example, Patent Document 1).

In addition, as a conventional technique for calculating a vehicle target trajectory and traveling along this vehicle target trajectory, the target trajectory is calculated under the limitations of a certain vehicle lateral jerk (jerk) and lateral acceleration, and the target trajectory is realized. A device that calculates a wheel steering angle is known (for example, see Patent Document 2).
JP 2000-177616 A JP 7-179140 A

  However, in the former of the above prior arts, until the steering is turned back, the rear wheel continues to be cut to the same amount as the front wheel in an amount corresponding to the steering angle. The vehicle travels and becomes close to a state where the vehicle is sliding. For this reason, the lateral force of the tire decreases as the traveling direction of the vehicle approaches the direction of the tire. That is, since the lateral force of the tire cannot be generated continuously, the turning ability of the vehicle cannot be fully exhibited. Therefore, there is room for improvement in the emergency avoidance exercise in a scene where it is desired to avoid by the maximum lateral movement of the vehicle, such as when an obstacle suddenly appears in front of the vehicle traveling direction.

  On the other hand, in the latter, in order to accurately calculate the absolute amount of lateral acceleration that can be achieved, it is necessary to estimate the road friction coefficient, and the target trajectory is affected by the estimation error of the road friction coefficient. There is a possibility that the maximum lateral movement avoidance performance of the vehicle cannot be fully exhibited.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to continuously generate the maximum possible lateral acceleration regardless of the road surface friction coefficient, and to obstruct the obstacle. An object of the present invention is to provide a vehicle steering control device capable of improving avoidance performance.

In order to achieve the above object, the present invention provides:
Front wheel steering means for steering the front wheels;
A yaw moment generating means capable of generating a yaw moment in the vehicle;
A wheel load detecting means for detecting the wheel load of each wheel;
A target front wheel slip angle calculating means for calculating, based on the detected wheel load, a front wheel slip angle at which the lateral force of the front wheel is maximum as a target front wheel slip angle;
Front wheel rudder angle adjusting means for adjusting the front wheel rudder angle so that the front wheel slip angle follows the target front wheel slip angle;
Yaw motion adjusting means for adjusting the yaw moment of the vehicle by adjusting the yaw moment that can be generated by the yaw moment generating means so that the direction of generation of the yaw rate of the vehicle during turning coincides with the direction of lateral movement;
It is characterized by providing.

In the vehicle steering control device of the present invention, the front wheel rudder angle adjustment means adjusts the front wheel rudder angle so that the front wheel slip angle follows the front wheel slip angle at which the lateral force of the front wheel is maximized. Regardless, the maximum possible lateral acceleration can be continuously generated.
Here, when the front wheel rudder angle is adjusted so that the front wheel slip angle becomes the maximum lateral force, the yaw moment in the direction opposite to the turning direction increases and the lateral movement performance deteriorates. In the means, since the yaw movement of the vehicle is adjusted so that the yaw rate of the vehicle at the time of turning coincides with the lateral movement direction, the yaw movement in which the vehicle faces the turning direction can be realized, and the lateral movement performance is deteriorated. In addition, it is possible to reduce both the uncomfortable feeling caused by the discrepancy between the turning motion and the vehicle body yaw motion.
As a result, the maximum possible lateral acceleration can be continuously generated regardless of the road surface friction coefficient, and the obstacle avoidance performance can be enhanced.

  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 a configuration diagram of an electric vehicle in which left and right rear wheels according to a first embodiment are independently driven by separate electric motors.

  The electric vehicle of the first embodiment includes electric motors 3RL and 3RR as driving force generation sources, and the rotation shafts of the motors 3RL and 3RR are rear wheels 2RL of the electric vehicle via speed reducers 4RL and 4RR. , 2RR. The output characteristics of the two motors 3RL and 3RR, the reduction ratios of the two reducers 4RL and 4RR, and the radii of the two wheels are all the same.

  Each of the motors 3RL and 3RR is a three-phase synchronous motor in which a permanent magnet is embedded in a rotor. Torque command values tTRL (left rear wheel), tTRR (right side) that drive circuits 5RL and 5RR that control power transfer with the lithium ion battery 6 receive the power running and regenerative torque of the motors 3RL and 3RR from the integrated controller 30 Adjust to match each of the rear wheels. The drive circuits 5RL and 5RR transmit the output torque of each motor 3RL and 3RR and the motor rotation speed detected by a rotation position sensor (not shown) attached to the motor rotation shaft to the integrated controller 30, respectively.

  The front wheels 2FL and 2FR are mechanically steered mechanically via the steering gear 14 by the rotational movement of the steering wheel 11 operated by the driver, and the steering gear 14 is entirely moved in the vehicle width direction by the auxiliary steering motor 12. Auxiliary steering is performed by displacing to. That is, the steering angles of the front wheels 2FL and 2FR are the sum of the main steering angle by the steering wheel 11 and the auxiliary steering angle by the auxiliary steering motor 12. The front wheel steering angle is controlled so as to coincide with the target front wheel steering angle tDF transmitted by the integrated controller 30 by adjusting the output of the auxiliary steering motor 12 by the control circuit 13. The auxiliary steering motor 12 and the steering gear 14 constitute front wheel steering means for steering the front wheels.

  The rear wheels 2RL and 2RR are steered by displacing the steering rack 15 as a whole in the vehicle width direction by the steering motor 16. The steering angle is controlled so that the control circuit 17 matches the target rear wheel steering angle tDR transmitted by the integrated controller 30 by adjusting the output of the steering motor 16. The steering rack 15 and the steering motor 16 constitute rear wheel steering means (yaw moment generating means) for steering the rear wheels.

  The integrated controller 30 includes an accelerator opening signal APO detected by an accelerator pedal sensor 23, a steering wheel rotation angle signal STR detected by a steering angle sensor 21 attached to the rotation shaft of the steering wheel 11, and a yaw rate sensor (yaw rate). The detecting means) 8 and the yaw rate signal γ detected by the acceleration sensor 8 and the acceleration sensor (lateral acceleration detecting means) 28 attached to the center of gravity position, the longitudinal acceleration signal ax and the lateral acceleration signal ay detected by the acceleration sensor (lateral acceleration detecting means) 28 are also attached to the center of gravity position. A vehicle slip angle signal β output from a slip angle sensor (vehicle side slip angle detecting means) 29 is input.

[Maximum lateral movement control processing]
FIG. 2 is a flowchart showing the flow of the maximum lateral movement control process calculated by the integrated controller 30 of the first embodiment, and each step will be described below. The integrated controller 30 includes peripheral components such as a RAM / ROM in addition to the microcomputer, and executes this control process at regular intervals, for example, every 5 ms.

In step S100, sensor signals and received signals from the drive circuits 5RL and 5RR are stored in RAM variables, and the process proceeds to step S101.
Specifically, the accelerator opening signal is stored in the variable APS (unit:%. 100% when fully opened), and the steering wheel rotation angle signal is stored in the variable STR (unit: rad, counterclockwise as positive). 1), the vehicle body yaw rate signal is stored in the variable γ (the left turn direction in FIG. 1 is positive), the vehicle body lateral acceleration signal is stored in ay (the left direction is positive), Acceleration signal is stored in ax (positive forward), body slip angle signal is stored in β (counterclockwise positive), front wheel speed signal is NFL, NFR (both units are rad / s) And the direction in which the vehicle moves forward is positive). For the signals received from the drive circuits 5RL and 5RR, the output torques of the motors 3RL and 3RR are stored in the variables TRL and TRR (both units are Nm, and the direction in which the vehicle is accelerated is positive), respectively. The rotational speeds of the motors 3RL and 3RR are stored in variables NRL and NRR (both units are rad / s, and the direction in which the vehicle moves forward is positive).

  Although the vehicle body side slip angle β is detected here, for example, as in the technique described in Japanese Patent Laid-Open No. 5-310142, a mathematical model of vehicle motion characteristics is obtained from the steering input, the driving force difference input, and the yaw rate detection value. You may estimate using the observer based on.

In step S101, the vehicle speed V (unit is m / s and the direction in which the vehicle moves forward is positive) is calculated from the number of rotations NFL and NFR of the driven wheel by the following formula, and the process proceeds to step S102. .
V = (NFL + NFR) / 2 × R
Where R is the radius of the wheel.

In step S102, the wheel loads Zfl, Zfr, Zrl, Zrr of the four wheels are obtained from the following formula, and the process proceeds to step s103 (wheel load detecting means).
Zfl = Zf-ΔZd-2ΔZc ・ (Zf-ΔZd) / (Zf + Zr)
Zfr = Zf-ΔZd + 2ΔZc ・ (Zf-ΔZd) / (Zf + Zr)
Zrl = Zr + ΔZd-2ΔZc ・ (Zr + ΔZd) / (Zf + Zr)
Zrr = Zr + ΔZd + 2ΔZc ・ (Zr + ΔZd) / (Zf + Zr)
Zf = mgLr / L
Zr = mgLf / L
ΔZd = m ・ ax ・ hcg / 2L
ΔZc = m ・ ay ・ hcg / 2Lt
Here, Lt is half of the tread distance, and hcg is the height of the center of gravity. Although ignored in the first embodiment, a delay in load change due to the suspension may be considered.

  In step S103, the front and rear wheel steering angle manipulated variable that moves maximum laterally is calculated according to the flowchart shown in FIG. 3, and the present control is terminated.

[Operation amount calculation control processing]
FIG. 3 is a flowchart showing the flow of the operation amount calculation subroutine executed in step S104 of the flowchart of FIG. 2, and each step will be described below.

  In step S200, from the left and right front wheel loads Zfl, Zfr, using the relationship between the wheel load and the tire slip angle at which the tire lateral force is maximum (hereinafter referred to as the maximum lateral force tire slip angle) shown in FIG. The target front wheel slip angle is calculated, and the process proceeds to step S201 (target front wheel slip angle calculating means). Here, the target front wheel slip angle may be, for example, an average value of the left and right target slip angles. The relationship between the wheel load shown in FIG. 4 and the maximum lateral force tire slip angle is based on the relationship between the tire slip angle and the tire lateral force for each wheel load shown in FIG. This is a summary of tire slip angles.

  FIG. 6 shows the relationship between the tire slip angle and the tire lateral force for each absolute value of the tire longitudinal force under the same wheel load. The black circles on each line are the points of the tire slip angle and the maximum tire lateral force that are the maximum tire lateral force. In the tire shown in FIG. 6, with the same wheel load, the maximum lateral force tire slip angle increases as the absolute value of the tire longitudinal force increases.

  Here, in Example 1, based on the relationship between the wheel load for each tire longitudinal force absolute value and the maximum lateral force tire slip angle shown in FIG. 7, the larger the tire lateral force absolute value of the front and rear wheels is, the larger the target slip angle is. Enlarge. Thereby, the maximum lateral force which changes according to the tire lateral force of the front and rear wheels can be generated with higher accuracy.

  FIG. 8 shows the relationship between the tire slip angle and the tire lateral force for each road friction coefficient under the same wheel load. The black circles on each line are the points of the tire slip angle and the maximum tire lateral force that are the maximum tire lateral force. In the tire shown in FIG. 8, with the same wheel load, the maximum lateral force tire slip angle increases as the road surface friction coefficient decreases.

  Therefore, as shown in FIG. 9, with the same wheel load, the maximum lateral force tire slip angle increases as the road surface friction coefficient decreases. For this reason, in Example 1, the target slip angle is increased as the road surface friction coefficient of the front and rear wheels is smaller. Thereby, the maximum lateral force which changes according to the road surface friction coefficient of the front and rear wheels can be generated with higher accuracy.

  Here, as a method for obtaining the road surface friction coefficient, for example, a method disclosed in Japanese Patent Laid-Open No. 6-258196 is used. In this method, the vibration acceleration G of the left and right front wheels is detected by an acceleration sensor, the power spectral density PSD of the acceleration G is calculated based on the result, and the road surface friction coefficient of the PSD value changes in one direction. On the other hand, the road surface friction coefficient is detected based on the PSD value within a frequency range in which the relationship of changing in one direction is established (corresponding to road surface friction coefficient estimating means).

ここで、Lfは重心位置と前輪車軸との間の長さである。
式(1)を用いて、車体すべり角βと車速Vとヨーレートγと目標前輪すべり角とから、目標前輪舵角tDFは算出される。 In step S201, a target front wheel steering angle tDF that realizes the target front wheel slip angle is calculated, and the routine proceeds to step S202 (front wheel steering angle adjusting means).
The relationship between the front wheel slip angle αf and the front wheel rudder angle DF is expressed by the following equation (1).

Here, Lf is the length between the position of the center of gravity and the front wheel axle.
Using the equation (1), the target front wheel steering angle tDF is calculated from the vehicle body slip angle β, the vehicle speed V, the yaw rate γ, and the target front wheel slip angle.

  In step S202, the target rear wheel steering angle tDR is calculated so that the direction of the yaw rate of the vehicle at the time of turning coincides with the lateral movement direction, and the process proceeds to return (yaw motion adjusting means).

  FIG. 10 shows the state of the force when turning left so that the slip angle of the front and rear wheels becomes the maximum lateral force, and FIG. 11 shows the vehicle turning trajectory (the vehicle travels from left to right). When turning left, the load on the right wheel, which is the outer ring, becomes larger than the left wheel, which is the inner ring, due to the load movement caused by the height of the center of gravity and centrifugal force. Therefore, as shown in FIG. 10, the tire lateral force indicated by the broken line is greater for the right wheel than for the left wheel. Further, depending on the steering angle of the front and rear wheels, the tire lateral force is divided into a vehicle body longitudinal component indicated by a solid line and a vehicle body lateral component indicated by a one-dot chain line. From the difference in lateral force between the left and right tires, the vertical component of the vehicle body is greater on the right side than on the left side.

  Due to the left-right difference in the vertical component of the vehicle body, a yaw moment opposite to the turning direction as shown in FIG. 10 is generated, and the vehicle has a lateral movement direction and a yaw rate opposite as shown in FIG. When this reverse yaw rate is sustained, the steering angle of the front and rear wheels continues to increase as shown in FIG. 11, and the yaw moment in the direction opposite to the turning direction increases as the vehicle body longitudinal component increases. The car body protrudes greatly outside the turn. Further, the lateral movement performance of the vehicle is reduced because the lateral force is reduced and the lateral movement amount is reduced. For example, when an obstacle is avoided, it becomes easy to collide with the obstacle.

  Therefore, in the first embodiment, in order to make the yaw rate of the vehicle and the lateral movement direction coincide with each other, the side slip angle of the rear wheel is reduced and the lateral force of the rear wheel is made smaller than the maximum value, thereby reversing the turning direction. Counteract yaw moment generated in the direction.

For example, when the vehicle slip angle is not changed as described below, a yaw change in the turning direction automatically occurs in accordance with the change in the traveling direction. Assuming that the vehicle slip angle β is sufficiently small, the relationship between the lateral acceleration ay at the center of gravity, the yaw rate γ, and the vehicle slip angle β is expressed by the following equation (2).

Using this equation (2), if the time change dβ / dt of the vehicle slip angle β is zero, the target yaw rate tγ is expressed by the following equation (3) from the vehicle speed V, the yaw rate γ, and the vehicle body lateral acceleration ay. The

In order to realize this target yaw rate, the target rear wheel steering angle tDR is determined using the PI controller shown in the following equation (4).

  Here, kP is a proportional gain of the PI controller, and kI is an integral gain of the PI controller. By this control, the yaw rate of the vehicle can be generated in the turning direction, and both the deterioration of the lateral movement performance and the uncomfortable feeling due to the mismatch between the turning motion and the vehicle body yaw motion can be reduced.

[Maximum lateral movement control action]
As a conventional technique for generating a large turning ability of a vehicle, such as when an obstacle is urgently avoided, an emergency driving support device for a vehicle described in JP-A-2000-177616 is known. In this prior art, in a four-wheel steering vehicle, the gain from the steering angle to the front wheel rudder angle is increased in an emergency situation, and the rear wheel rudder angle is substantially the same as the front wheel rudder angle in the initial steering operation. To increase the initial lateral acceleration in an emergency. Then, the steering slip-back operation returns to the control of the vehicle slip angle to ensure the turning stability.

  Further, as a conventional technique for calculating a vehicle target locus and traveling along the vehicle target locus, an automatic steering device for a vehicle described in JP-A-7-179140 is known. In this prior art, a target trajectory is calculated under the limitation of a certain vehicle lateral jerk and lateral acceleration, and the front and rear wheel steering angles for realizing the target trajectory are calculated.

However, the above prior art has the following problems.
In the prior art described in Japanese Patent Application Laid-Open No. 2000-177616, at the initial stage when the steering angle is generated, a lateral acceleration corresponding to the turning angle between the rear wheel and the front wheel is generated. However, until the steering is turned back, the rear wheel continues to be cut in the same amount as the front wheel in an amount corresponding to the steering angle, so the vehicle eventually moves in the direction of the tire and the vehicle slips sideways. It will be close to the state. For this reason, as the traveling direction of the vehicle changes to the direction of the tire, the lateral force of the tire decreases. After the traveling direction of the vehicle becomes the direction of the tire, the lateral force of the tire becomes zero. After the steering is turned back thereafter, a lateral force corresponding to the yaw movement of the vehicle is generated.

  As described above, in this conventional technology, since the lateral force of the tire cannot be generated continuously, the turning ability of the vehicle cannot be fully exhibited, and when an obstacle suddenly appears ahead in the vehicle traveling direction. There is room for improvement in emergency avoidance exercises in situations where you want to avoid the maximum lateral movement of the vehicle.

  On the other hand, in the prior art described in JP-A-7-179140, it is possible to generate a continuous lateral force by generating a target trajectory so as to move laterally while maintaining a maximum value of a realizable lateral acceleration. However, in order to accurately calculate the absolute amount of lateral acceleration that can be realized, a road surface friction coefficient is required. If there is an estimation error of the road surface friction coefficient, the target trajectory is greatly affected by the error.

  For example, when the actual road friction coefficient is smaller than the estimated value, the target trajectory has a turning radius that is larger than the turning radius that can be originally realized. There is room for improvement in emergency avoidance exercises when you want to avoid moving. In addition, if the actual road friction coefficient is larger than the estimated value, the target trajectory has a smaller turning radius than the originally feasible turning radius, which may cause saturation of the lateral force and make it difficult to achieve the target trajectory. There is.

  On the other hand, in Example 1, the front wheel slip angle is adjusted so that the front wheel slip angle follows the front wheel slip angle at which the front wheel lateral force is maximum, and the rear wheel lateral force is at the maximum from the slip angle. The rear wheel rudder angle is adjusted to reduce the rear wheel slip angle. Accordingly, the maximum lateral acceleration that can be realized can be continuously generated by performing a yaw motion that faces the turning direction, and thus the possibility of avoiding a front obstacle or the like is improved.

  The relationship between the tire slip angle and the lateral force at a certain wheel load is shown in FIG. 12 as a broken line, a solid line, and a one-dot chain line in descending order of the road surface friction coefficient. Since the absolute value of the maximum lateral force is determined substantially in proportion to the road surface friction coefficient, as shown in FIG. 12, the maximum lateral force is different at almost the same rate as the difference in the road surface friction coefficient. The control of the target track based on the absolute value is greatly affected by the difference in the friction coefficient of the road surface.

  On the other hand, when the tire slip angle is controlled to the tire slip angle α0 at which the lateral force is maximum in the relationship shown by the solid line as in Example 1, the estimation of the road surface friction coefficient is deviated, and actually the broken line or the alternate long and short dash line Even if the relationship is as shown in FIG. 4, the lateral force at the tire slip angle α0 can substantially realize the maximum tire lateral force at each road surface friction coefficient. In other words, a lateral force equivalent to the maximum lateral force can be automatically generated regardless of the road surface friction coefficient, so that the avoidance performance can be sufficiently exhibited without the lateral force being saturated and the vehicle motion becoming unstable. .

Next, the effect will be described.
In the vehicle steering control device according to the first embodiment, the following effects can be obtained.

  (1) Front wheel steering means (auxiliary steering motor 12, steering gear 14) for steering the front wheels, yaw moment generating means (steering rack 15, steering motor 16) capable of generating yaw moment in the vehicle, Wheel load detection means (step S102) for detecting the wheel load, and target front wheel slip angle calculation means (based on the detected wheel load) for calculating the front wheel slip angle at which the lateral force of the front wheel is maximum as the target front wheel slip angle ( Step S200), front wheel rudder angle adjusting means (step S201) for adjusting the front wheel rudder angle so that the front wheel slip angle follows the target front wheel slip angle, and the generation direction and lateral movement direction of the yaw rate of the vehicle during turning Yaw motion adjusting means (step S202) for adjusting the yaw motion of the vehicle by adjusting the yaw moment that can be generated by the yaw moment generating means so as to match. Accordingly, the maximum possible lateral acceleration can be continuously generated regardless of the road surface friction coefficient, and the obstacle avoidance performance can be enhanced.

  (2) As a yaw moment generating means, a rear wheel steering means (steering rack 15 and steering motor 16) for steering the rear wheel is provided, and the yaw motion adjusting means is more than the slip angle at which the lateral force of the rear wheel is maximized. The rear wheel rudder angle is adjusted so that the rear wheel slip angle becomes smaller. Thereby, in the front and rear wheel steering vehicle, the maximum possible lateral acceleration can be continuously generated regardless of the road surface friction coefficient, and the obstacle avoidance performance can be enhanced.

  (3) A yaw rate sensor 8 that detects the yaw rate of the vehicle and an acceleration sensor 28 that detects the lateral acceleration of the vehicle, and the yaw motion adjustment means sets the target yaw rate to a larger value as the lateral acceleration increases, The rear wheel rudder angle is adjusted so that the yaw rate follows the target yaw rate. Thereby, the yaw rate of the vehicle can be generated in the turning direction, and both the deterioration of the lateral movement performance and the uncomfortable feeling due to the mismatch between the turning motion and the vehicle body yaw motion can be reduced.

  (4) Since the target front wheel slip angle calculating means increases the target front wheel slip angle as the braking / driving torque of the front wheels increases, the maximum side force that changes according to the tire lateral force of the rear wheels can be generated more accurately.

  (5) The road surface friction coefficient estimating means for estimating the road surface friction coefficient is provided, and the target front wheel slip angle calculating means increases the target front wheel slip angle as the road surface friction coefficient is smaller. The changing maximum lateral force can be generated more accurately.

The second embodiment is an example in which the rear wheel steering angle is adjusted so that the vehicle body side slip angle substantially matches the vehicle traveling direction and the vehicle body direction.
The configuration is the same as that of the first embodiment except for the calculation in step S202 of the flowchart shown in FIG. Therefore, only the content of step S202 will be described, and the other description will be omitted.

  In step S202, the target rear wheel steering angle tDR is calculated so that the yaw rate of the vehicle at the time of turning does not turn in the reverse direction, and this control is finished.

ここで、kPはPI制御器の比例ゲイン、kIはPI制御器の積分ゲインである。目標車体すべり角は、車体が進行方向の近くに向くのであれば、ゼロである必要はない。 In the second embodiment, for example, the target vehicle body slip angle tβ is set to zero, and the target rear wheel steering angle tDR is determined using the PI controller shown in the following equation (5) so that the vehicle body slip angle becomes zero.

Here, kP is a proportional gain of the PI controller, and kI is an integral gain of the PI controller. The target vehicle body slip angle need not be zero if the vehicle body is oriented near the direction of travel.

  In the second embodiment, since the target rear wheel steering angle tDR is set so that the target vehicle body slip angle tβ becomes zero, the yaw rate of the vehicle can be generated in the turning direction. Therefore, it is possible to suppress the deterioration of the lateral movement performance and more reliably eliminate the uncomfortable feeling caused by the mismatch between the turning motion and the vehicle body yaw motion.

Next, the effect will be described.
In the vehicle steering control device of the second embodiment, the following effects are obtained in addition to the effects (1), (2), (4), and (5) of the first embodiment.

  (6) The vehicle includes a slip angle sensor 29 that detects the side slip angle of the vehicle, and the yaw motion adjusting means adjusts the rear wheel steering angle so that the vehicle side slip angle matches the vehicle traveling direction and the vehicle body direction. The deterioration of the movement performance can be suppressed, and the uncomfortable feeling caused by the discrepancy between the turning motion and the vehicle body yaw motion can be eliminated more reliably.

  The third embodiment is an example in which the discrepancy between the turning motion and the vehicle body yaw motion is prevented by adjusting the left / right driving force difference, and the left / right driving force difference between the motors 3RL and 3RR is used as the yaw moment generating means (left / right driving). Force difference generating means).

  Since the third embodiment is different from the first embodiment only in the operation amount calculation subroutine, other description is omitted.

[Operation amount calculation control processing]
FIG. 13 is a flowchart showing the flow of an operation amount calculation subroutine executed by integration of the third embodiment. Each step will be described below.

In step S300, a target left / right driving force difference tDD is calculated such that the direction of the yaw rate of the vehicle during turning matches the turning direction, and the process proceeds to step S301. In the first embodiment, for example, the target vehicle slip angle tβ is set to zero, and the target left / right driving force difference tDD is determined using the PI controller shown in the following equation (6) so that the vehicle slip angle becomes zero.

Here, kP is a proportional gain of the PI controller, and kI is an integral gain of the PI controller. The target vehicle body slip angle does not have to be zero if the vehicle body is close to the traveling direction. Then, from this target left / right driving force difference tDD and the driving torque command value tTD commanded from the host controller, the following formulas (7) and (8) are used to determine the motor torque command value tTRL (left rear wheel ), tTRR (right rear wheel) is calculated.
tTRL = tTD-tDD ・ R… (7)
tTRR = tTD + tDD ・ R… (8)

  However, the yaw motion control is not limited to such feedback control, and the target yaw rate is calculated as in the first embodiment, and the right and left driving force difference is appropriately set by feedforward according to the target yaw rate. Thus, the discrepancy between the turning direction and the yaw motion can be substantially eliminated without detecting the vehicle body slip angle.

  Since the target front wheel slip angle calculation in step S301 performs the same processing as step S200 in the first and second embodiments, the description thereof is omitted. Further, the calculation of the target front wheel steering angle in step S302 is the same as that in step S201 in the first embodiment and the second embodiment, and thus the description thereof is omitted.

  In step S303, a target rear wheel slip angle is calculated from the left and right rear wheel loads Zrl, Zrr using the relationship between the wheel load and the maximum lateral force tire slip angle shown in FIG. 4, and the process proceeds to step S304 ( Target rear wheel slip angle calculation means). For example, the target rear wheel slip angle may be an average value of the left and right target slip angles.

  Here, in Example 3, as with the front wheels, based on the relationship between the wheel load for each tire longitudinal force absolute value and the maximum lateral force tire slip angle shown in FIG. Increase the target slip angle. Thereby, the maximum lateral force which changes according to the tire longitudinal force of the front and rear wheels can be generated with higher accuracy.

  Further, in Example 3, as with the front wheels, based on the relationship between the wheel load for each road surface friction coefficient and the lateral force maximum tire slip angle shown in FIG. 9, the smaller the road surface friction coefficient of the front and rear wheels is, the smaller the target slip angle is. Enlarge. Thereby, the maximum lateral force which changes according to the road surface friction coefficient of the front and rear wheels can be generated with higher accuracy.

In step S304, a target rear wheel steering angle tDR that realizes the target rear wheel slip angle is calculated, and the process proceeds to return (rear wheel steering angle adjusting means). The relationship between the rear wheel slip angle αr and the rear wheel rudder angle DR is expressed by the following equation (9).

Here, Lr is the length between the position of the center of gravity and the rear wheel axle. Using the equation (9), the target rear wheel steering angle tDR is calculated from the vehicle body slip angle β, the vehicle speed V, the yaw rate γ, and the target rear wheel slip angle. As described above, since the difference between the left and right driving force acts in the direction of increasing the yaw rate, the lateral force of the rear wheel can be increased, and the lateral movement performance of the vehicle is improved.
Further, by adjusting the rear wheel so that the lateral force is maximized, the rise of the lateral force is accelerated, and the maximum lateral force can be surely output, and the lateral movement performance is improved.

[Maximum lateral movement control action]
Below, the effect | action of the maximum lateral movement control of Example 3 is shown using the result of a computer simulation.
FIG. 14 is a computer simulation result of the turning trajectory of the vehicle showing the maximum lateral movement control action of the third embodiment. As a conventional technique, Japanese Patent Laid-Open No. 2000-177616 sets the rear wheel steering angle to the same amount as the front wheel steering angle. A vehicle using the technology described in the publication is indicated by a wavy line. Further, the time change of the lateral force of the vehicle body is shown in the time chart of FIG.

  As shown in FIG. 15, in the early stage of turning, the lateral force is larger in the conventional technique than in the third embodiment because the yaw motion control is not performed. However, as time elapses, as shown in FIG. 14, in the related art, the traveling direction of the vehicle coincides with the direction of the tire. Therefore, the vehicle goes straight in an oblique direction. On the other hand, in Example 3, since the lateral force near the maximum lateral force can be generated continuously, as a result, the lateral movement amount becomes larger than that of the conventional technique, and the avoidance performance is improved.

Next, the effect will be described.
In the vehicle steering control apparatus according to the third embodiment, in addition to the effects (1), (4), and (5) of the first embodiment, the following effects can be obtained.

  (7) As the yaw moment generating means, left and right driving force difference generating means (motors 3RL, 3Rr) for generating a driving force difference between the left and right wheels are provided, and the yaw motion adjusting means is adjusted in the direction in which the yaw rate in the lateral movement direction increases. Since the driving force difference is generated, the lateral force of the rear wheels can be increased, and the lateral movement performance of the vehicle can be improved.

  (8) As the yaw moment generating means, left / right driving force difference generating means (motors 3RL, 3RR) for generating a driving force difference between the left and right wheels are provided, and the yaw motion adjusting means is adjusted in the direction in which the yaw rate in the lateral movement direction increases. Realized regardless of road friction coefficient in motor-driven electric vehicles, because the difference in driving force is generated and the rear wheel rudder angle is adjusted so that the rear wheel slip angle approaches the slip angle at which the rear wheel lateral force becomes maximum. The maximum possible lateral acceleration can be generated continuously, and the obstacle avoidance performance can be enhanced.

  (9) Based on the detected wheel load, target rear wheel slip angle calculating means (step S303) for calculating the rear wheel slip angle at which the lateral force of the rear wheel is maximum as the target rear wheel slip angle, and the rear wheel slip Rear wheel rudder angle adjusting means (step S304) for adjusting the rear wheel rudder angle so that the angle follows the target rear wheel slip angle. As a result, the lateral force rises quickly, and the maximum lateral force can be reliably produced, thereby improving the lateral movement performance.

  (10) Since the target rear wheel slip angle calculation means increases the target rear wheel slip angle as the braking / driving torque of the rear wheel increases, the maximum lateral force that changes according to the tire longitudinal force of the front and rear wheels is more accurately determined. Can occur.

  (11) A road surface friction coefficient estimating means for estimating the road surface friction coefficient is provided, and the target rear wheel slip angle calculating means increases the target rear wheel slip angle as the road surface friction coefficient is smaller. The maximum lateral force that changes accordingly can be generated more accurately.

(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.

  For example, the present invention is not limited to the electric vehicles as shown in the first to third embodiments, and can be realized as long as the vehicle has both front wheel steering means and other yaw moment generating means. Further, the left / right driving force difference may be any as long as it can generate braking / driving force independently on the left and right sides. For example, driving force distribution using a clutch or the like may be used. Further, the power source may be an engine, for example, and the effect can be obtained without being limited to the motor.

  Further, the maximum lateral movement control shown in the first to third embodiments may be executed in a scene in which the maximum turning motion is desired, for example, when an obstacle is urgently avoided or when the driver is steered greatly. For example, vehicle motion control that generates a yaw rate or a lateral force according to the steering angle of the driver may be performed.

It is a block diagram of the electric vehicle which drives independently the left-right rear wheel of Example 1 with a separate electric motor, respectively. 6 is a flowchart illustrating a flow of maximum lateral movement control processing calculated by the integrated controller 30 according to the first embodiment. 6 is a flowchart illustrating a flow of an operation amount calculation subroutine according to the first exemplary embodiment. It is a figure which shows the relationship between wheel load and side force maximum tire slip angle. It is a figure which shows the relationship between the tire slip angle for every wheel load, and a tire lateral force. It is a figure which shows the relationship between the tire slip angle for every tire longitudinal force absolute value, and a tire lateral force. It is a figure which shows the relationship between the wheel load for every tire longitudinal force absolute value, and a lateral force maximum tire slip angle. It is a figure which shows the relationship between the tire slip angle and tire lateral force for every road surface friction coefficient. It is a figure which shows the relationship between the wheel load for every road surface friction coefficient, and a lateral force maximum tire slip angle. It is a figure which shows the state of the force at the time of the left turn with the largest lateral force. It is a computer simulation result at the time of a lateral force maximum left turn. It is a figure which shows the relationship between the tire slip angle for every wheel load, and a tire lateral force. 12 is a flowchart illustrating a flow of an operation amount calculation subroutine according to the third embodiment. It is a computer simulation result of the turning locus | trajectory of the vehicle which shows the maximum lateral movement control effect | action of Example 3. FIG. 10 is a time chart of vehicle body lateral force showing the maximum lateral movement control action of the third embodiment.

Explanation of symbols

2FL, 2FR Front wheel 2RL, 2RR Rear wheel 3RL, 3RR Electric motor 4RL, 4RR Reducer 5RL, 5RR Drive circuit 6 Lithium ion battery 8 Yaw rate sensor 11 Steering wheel 12 Front wheel auxiliary steering motor 13 Front wheel control circuit 14 Front wheel steering gear 15 Rear Wheel steering gear 16 Rear wheel auxiliary steering motor 17 Rear wheel control circuit 21 Steering angle sensor 23 Accelerator pedal sensor 28 Acceleration sensor 29 Slip angle sensor 30 Integrated controller

Claims (11)

Front wheel steering means for steering the front wheels;
A yaw moment generating means capable of generating a yaw moment in the vehicle;
A wheel load detecting means for detecting the wheel load of each wheel;
A target front wheel slip angle calculating means for calculating, based on the detected wheel load, a front wheel slip angle at which the lateral force of the front wheel is maximum as a target front wheel slip angle;
Front wheel rudder angle adjusting means for adjusting the front wheel rudder angle so that the front wheel slip angle follows the target front wheel slip angle;
Yaw motion adjusting means for adjusting the yaw moment of the vehicle by adjusting the yaw moment that can be generated by the yaw moment generating means so that the direction of generation of the yaw rate of the vehicle during turning coincides with the direction of lateral movement;
A vehicle steering control device comprising: The vehicle steering control device according to claim 1,
Yaw rate detection means for detecting the yaw rate of the vehicle;
Lateral acceleration detecting means for detecting the lateral acceleration of the vehicle;
With
The yaw motion adjusting means sets the target yaw rate to a larger value as the lateral acceleration is larger, and adjusts the yaw moment that can be generated by the yaw moment generating means so that the yaw rate follows the target yaw rate. A vehicle steering control device. The vehicle steering control device according to claim 1 or 2,
Vehicle side slip angle detecting means for detecting the side slip angle of the vehicle,
The vehicle yaw motion adjusting means adjusts the yaw moment that can be generated by the yaw moment generating means so that the vehicle side-slip angle substantially matches the vehicle traveling direction and the vehicle body direction. . The vehicle steering control device according to any one of claims 1 to 3,
The yaw moment generating means includes a rear wheel steering means for steering a rear wheel,
The vehicle steering control device characterized in that the yaw motion adjusting means adjusts the rear wheel steering angle so that the rear wheel slip angle is smaller than the slip angle at which the lateral force of the rear wheel is maximum. The vehicle steering control device according to any one of claims 1 to 4,
The yaw moment generating means includes a left / right driving force difference generating means for generating a driving force difference between the left and right wheels,
The vehicle steering control device, wherein the yaw motion adjusting means generates a left / right driving force difference in a direction in which a yaw rate in a lateral movement direction increases. The vehicle steering control device according to claim 4,
The yaw moment generating means includes a left / right driving force difference generating means for generating a driving force difference between the left and right wheels,
The yaw movement adjustment means adjusts the rear wheel rudder angle so that the rear wheel slip angle approaches the slip angle at which the rear wheel slip force becomes maximum by generating a left-right driving force difference in the direction in which the yaw rate in the lateral movement direction increases. A vehicle steering control device. The vehicle steering control device according to claim 6,
A target rear wheel slip angle calculating means for calculating a rear wheel slip angle at which the lateral force of the rear wheel is maximum based on the detected wheel load as a target rear wheel slip angle;
Rear wheel rudder angle adjusting means for adjusting the rear wheel rudder angle so that the rear wheel slip angle follows the target rear wheel slip angle;
A vehicle steering control device comprising: The vehicle steering control device according to claim 7,
The target rear wheel slip angle calculating means increases the target rear wheel slip angle as the braking / driving torque of the rear wheel increases. In the vehicle steering control device according to claim 7 or 8,
A road surface friction coefficient estimating means for estimating a road surface friction coefficient;
The target rear wheel slip angle calculating means increases the target rear wheel slip angle as the road surface friction coefficient is smaller. The vehicle steering control device according to any one of claims 1 to 9,
The target front wheel slip angle calculating means increases the target front wheel slip angle as the braking / driving torque of the front wheels increases. The vehicle steering control device according to any one of claims 1 to 10,
A road surface friction coefficient estimating means for estimating a road surface friction coefficient;
The target front wheel slip angle calculating means increases the target front wheel slip angle as the road surface friction coefficient is smaller.

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