JP2011152812A - Vehicle motion control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle motion control device which controls motion of a vehicle so as to secure optimal motion performance, even when a motion range of a control object is large. <P>SOLUTION: This vehicle motion control device is composed of a yaw moment generating mechanism 10, a state sensor 20 and a control unit 30. The yaw moment generating mechanism 10 generates a yaw moment in the vehicle by determining a target state quantity of the vehicle. The state sensor measures or estimates a present state quantity and the present yaw moment of the vehicle by the yaw moment generating mechanism. The control unit 30 executes feedback control using a control rule U which takes into consideration virtual power (g) for multiplying a deviation between the target state quantity and the present state quantity of the vehicle by the present yaw moment. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a vehicle motion control device, and more particularly to a vehicle motion control device having a mechanism for generating a yaw moment in a vehicle.

  In general, when controlling the movement of a vehicle, yaw rate feedback is used to improve maneuverability (make the vehicle move responsively and responsively to the driver's steering wheel operation). Side slip angle feedback is often used to do this.

  In such general vehicle motion control, an estimated value calculated from the yaw rate and lateral acceleration is used for the side slip angle, and since the integral calculation is the main component, drift tends to occur. Can cause a phase error. For this reason, when performing side slip angle feedback, it is assumed that noise such as drift is included, and since the magnitude of the feedback gain is limited, the actual effect is that a great effect cannot be expected.

  One of the inventors of the present application has invented a control system as an attempt to solve the problem in the case of using such a side slip angle for control (Patent Document 1). According to this, the robustness with respect to the drift term at the time of side slip angle estimation can be improved, and the phase can be improved as compared with the case of simply performing side slip angle feedback.

  Furthermore, the inventors of the present application have invented a vehicle motion control device based on energy optimum control theory (Patent Document 2). Patent Document 1 does not disclose any control for a vehicle having a mechanism for generating a yaw moment. However, Patent Document 2 discloses a control device for an electric vehicle or an active suspension that can independently control the driving force of each wheel. A specific vehicle motion control is disclosed with an applied example.

  On the other hand, if the steering angle of the front wheels can be controlled with the steer-by-wire in consideration of the driver's intention, the driving operability and the steering responsiveness are improved, and thus there are many research examples (Non-Patent Document 1). Non-Patent Document 2). By the way, in recent years, not only electric drive vehicles and hybrid vehicles but also ultra-lightweight vehicles have been developed as environmental measures for vehicles such as automobiles. With ultra-lightweight vehicles, the driving performance, such as responsiveness and stability, will be worse when compared to a normal weight vehicle in terms of stability during emergency avoidance driving, crosswinds, and turning braking. It has been known. Therefore, if such deterioration in running performance can be recovered by steer-by-wire, it is possible to make a great contribution to environmental measures.

JP 2007-233985 A JP 2008-049996 A

Shiro Nakano, Takaharu Takamatsu, Osamu Nishihara, Hiromitsu Kumamoto, “Study on Steering Control in Steer-by-Wire” Vol. 31 No. 2, April 2000, p. 53-58 Sano Shoichi, Oyama Yasuharu, Kohei Sen, "Development of Optimal Control Law Utilizing Steer-by-Wire (1st Report)" Academic Lecture Preprints No. 148-07, October 2007, p. 1-6

  As described above, if, for example, the steering angle of the front wheels of a four-wheeled vehicle can be optimally controlled while considering the driver's intention by steer-by-wire, the motion performance of the vehicle is dramatically improved. However, when controlling by steer-by-wire, the front wheels have a steering angle range of about ± 30 deg, and find a method for rationally controlling the control variable range of such a large steering angle independently of the driver's steering. That was not easy.

  For example, research on motion control of steer-by-wire using a control method (Non-Patent Document 1) that combines feed-forward control and proportional control of driver steering or non-linear model predictive control (Non-Patent Document 2) has been studied. . However, with such a control method, the rear wheel steering angle control having a steering angle range of about ± 2 deg can be realized. However, for the steering angle control of the front wheels, the steering range is as large as ± 30 deg. It was difficult to improve athletic performance. Therefore, it has been desired to develop a vehicle motion control device that can fully utilize the steering range even for a control target having a large steering range such as a front wheel.

  In view of such circumstances, the present invention intends to provide a vehicle motion control device that controls the motion of a vehicle so as to achieve optimum motion performance even when the motion range of a controlled object is large.

  In order to achieve the above-described object of the present invention, a vehicle motion control device according to the present invention determines a target state quantity of a vehicle and generates a yaw moment in the vehicle, and a current state of the vehicle by the yaw moment generation mechanism. Control that performs feedback control using a state sensor that measures or estimates the state quantity and the current yaw moment, and a control law U that takes into account virtual power g that multiplies the deviation between the target state quantity and the current state quantity of the vehicle by the current yaw moment A part.

Here, the control unit only needs to include the partial differential term based on the state quantity of the virtual power g in the following equation in the control law U. That is,
However, R ₁ is the weighting coefficient, r _d the target state quantity, r is the current state of the vehicle, M is a current yaw moment.

  Further, the target state quantity and the current state quantity of the vehicle may be any yaw rate.

  The yaw moment generation mechanism may be a steering actuator.

Moreover, the control part should just obtain | require the control law U using the scalar function L of following Formula. That is,
However, R _a and R _b are weighting factors, P _u is control input power, and P is dissipated power.

Here, the control part should just have the control law U given by the following Formula. That is,
However, the control law U can be obtained by partially differentiating L by r and making it zero.

  The vehicle motion control device according to the present invention has an advantage that it is possible to control the motion of the vehicle so as to achieve an optimal motion performance even when the motion range of the controlled object is large.

FIG. 1 is a block diagram of vehicle control by steer-by-wire to which a vehicle motion control device of the present invention is applied. FIG. 2 is a three-degree-of-freedom vehicle motion model in the vehicle motion control device of the present invention. FIG. 3 is a graph showing the simulation result of the temporal change of the lateral displacement in the emergency avoidance lane change. FIG. 4 is a graph showing a simulation result of the temporal change of the lateral speed in the emergency avoidance lane change. FIG. 5 is a graph showing the simulation result of the time change of the yaw rate in the emergency avoidance lane change. FIG. 6 is a graph showing a simulation result of the time change beside the front wheel steering angle in the emergency avoidance lane change. FIG. 7 is a graph showing a simulation result of the time change of the control command in the emergency avoidance lane change. FIG. 8 is a graph showing the simulation result of the time change of the yaw rate in the turning braking stability. FIG. 9 is a graph showing a simulation result of the temporal change of the lateral speed in the turning braking stability.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. FIG. 1 is a block diagram of vehicle control by steer-by-wire to which a vehicle motion control device of the present invention is applied. As shown in the figure, the vehicle motion control device of the present invention mainly includes a yaw moment generation mechanism 10, a state sensor 20, and a control unit 30. The output of the state sensor 20 is connected to the control unit 30.

  As shown in the figure, the steering side of the steer-by-wire has a steering wheel 41, a steering shaft 42 connected to the steering wheel 41, a steering reaction force generating mechanism 43 provided on the steering shaft 42, and a steering reaction force generation. And a torque controller 44 of the mechanism 43.

  The steer-by-wire wheel side before steering includes a steering controller 51 that gives a control signal to the yaw moment generation mechanism 10 and a tire 52 connected to the yaw moment generation mechanism 10.

  The yaw moment generation mechanism 10 is for determining a target state quantity of the vehicle and generating a yaw moment in the vehicle. More specifically, the yaw moment generation mechanism 10 may be a steering actuator that changes the angle of the tire 52, for example. As the steering actuator, for example, any conventional or later-developed steering actuator such as a hydraulic type or an electric type can be applied. The yaw moment generation mechanism 10 changes the angle of the tire 52 to move the vehicle, that is, steer the vehicle.

  The state sensor 20 measures or estimates the current state quantity and the current yaw moment of the vehicle by the yaw moment generation mechanism 10. The state sensor 20 includes, for example, a steering torque sensor that detects torque generated in the steering shaft 42, a steering angle sensor that detects the steering angle of the steering wheel 41, a vehicle speed sensor that detects vehicle speed and acceleration, and a yaw rate generated in the vehicle. It consists of a yaw rate sensor to detect. The state sensor 20 includes not only a sensor that actually measures the current state quantity but also a sensor that estimates from other sensors by calculation or the like.

  The control unit 30 is a control mechanism for performing feedback control using a control law U that takes into account a virtual power g that multiplies the deviation between the target state quantity and the current state quantity of the vehicle by the current yaw moment. The virtual power g and the control law U will be described later in detail.

  The output of the state sensor 20 is input to the control unit 30. Further, the output of the control unit 30 is input to the steering controller 51. The output of the control unit 30 is also input to the torque controller 44 of the steering reaction force generating mechanism 43. The control unit 30 performs feedback control of the vehicle based on a control law for controlling the movement of the vehicle so as to obtain an optimum steering pattern in accordance with the output of the state sensor 20 that is input.

Now, the control law by the control unit 30 when the vehicle motion control device of the present invention is applied to such a steer-by-wire vehicle control mechanism will be described in more detail. FIG. 2 is a three-degree-of-freedom vehicle motion model in the vehicle motion control device of the present invention. For the sake of simplification, this figure is a vehicle model with three degrees of freedom of the vehicle body ignoring roll and pitch. The vehicle model in the illustrated example does not consider rolling motion and pitch motion, but considers load movement acting on each wheel due to acceleration acting on the center of gravity of the vehicle. In the figure, m is the vehicle mass, I _z is the vehicle yaw moment of inertia, l _f is the distance between the vehicle center of gravity and the front wheels, l _r is the distance between the vehicle center of gravity and the rear wheels, l _t is the tread, and V _x is the vehicle The longitudinal speed, V _y is the side slip speed of the vehicle, r is the yaw rate, β is the side slip angle, δ is the front wheel steering angle, and V is the vehicle speed.

When the lateral force generated by controlling the rudder angle is U, the nonlinear vehicle motion equation is expressed by the following equation.
Here, X and Y are the total sum of the front and rear forces of each wheel tire, as shown below.
Further, the sum of the dissipative power P (heat loss per unit time generated by slipping of the running tire) of each wheel tire is expressed by the following equation.
The control input power P _u is expressed by the following equation.

Here, in the control unit of the vehicle motion control device of the present invention, as an evaluation function related to followability, the deviation of the target yaw rate that is the target state quantity and the current yaw rate that is the current state quantity is multiplied by the current yaw moment, The virtual power g expressed by the formula is introduced.
However, R ₁ is the weighting coefficient, r _d is the target yaw rate, r is the current yaw rate of the vehicle, M is the current yaw moment.
The evaluation function is expressed by the following equation.
Here, the scalar function L is expressed by the following equation.
However, R _a and R _b are weighting factors, and P is dissipated power.
That is, L is expressed as follows from Equations 4 and 6.

For Equation 7, L is partially differentiated by r as follows so as to satisfy Euler's formula, which is a necessary condition for optimal control, and is set to zero.
Thereby, the optimal control law U of the following formula can be derived.
Here, the first term on the right side is a partial differential term is responsive improving section U _p of g increasing the control response capability. The second term on the right side is the stability improvement term U _m that is a partial differential term of the dissipated power P that brings about stability.

Since this input is a lateral force, in order to convert it into a steering angle input, it may be divided by the cornering stiffness at that time. Further, in order to obtain the partial differential of the lateral force and yaw moment due to the yaw rate, the lateral force generated by the tire may be approximated as follows from the tire characteristic equation based on Magic Formula.
_{However, D i = a 1 W i} -a 2 W i 2, W i is a tire _{load, a 1, a 2, B} , C are constants determined from the tire characteristic.

Here, determination of the target state quantity will be described. When the current state quantity of the vehicle measured by the target state quantity and the state sensor is the yaw rate, it is appropriate to use the equivalent amount of the steady yaw rate at the time of steady circle turning as the target yaw rate. In this case, since it is desirable to set the value in consideration of the nonlinearity of the tire characteristics, the description is made by diverting the Magic Formula as follows.
However,
It is.
This K _d is substituted into the following equation in which the response of the target yaw rate r _d is the first order delay of the actual steering angle δ.
However, _Td is a constant determined by the control system designer, and s is a Laplace operator.
This r _d becomes the final target yaw rate.

  In the vehicle motion control device of the present invention, the control unit may perform feedback control of the yaw moment generation mechanism using the control law U expressed by the above equation (8). The state quantity is not limited to the yaw rate, and may be a side slip speed or a side slip angle.

  Hereinafter, simulation results of emergency avoidance lane change and turning braking stability will be described by applying the vehicle motion control device of the present invention to a vehicle motion model having 6 degrees of freedom for the vehicle body and 4 degrees of freedom for the wheels. As an example, the vehicle specifications in which the volume of a 2-liter 1-box vehicle remains the same while the weight is reduced by half are used as a reference vehicle, and the control by the vehicle motion control device of the present invention and the effect of the conventional nonlinear model predictive control and no control are performed. Compared. The results are shown below.

  The emergency avoidance lane change assumes a situation in which a driver who finds an obstacle ahead in a high speed travel avoids the obstacle by a sudden steering operation. The simulation conditions are as follows. That is, sine wave-like steering with an amplitude of 120 deg is performed for 2 seconds from a straight traveling state at a vehicle speed of 100 km / h, and the straight traveling state is restored again. In addition, the accelerator and brake are not operated. Graphs of simulation results at this time are shown in FIGS.

  3 shows the lateral displacement, FIG. 4 shows the lateral velocity, FIG. 5 shows the yaw rate, FIG. 6 shows the front wheel rudder angle, and FIG. 7 shows the simulation result of each time change of the control command. In the figure, the solid line shows the control of the present invention, the alternate long and short dash line shows the nonlinear model predictive control, and the thin line shows the change when there is no control.

  From these simulation results, in the case of no control, the side slip increases and the yaw angle does not return to zero. In the case of nonlinear model predictive control, the yaw rate is saturated. However, in the control of the present invention, the yaw rate exceeding the target value is generated, and the lateral displacement at 1 sec, which is a standard of avoidance performance, is greatly generated, so it can be understood that the emergency avoidance performance is high. This is because in the control of the present invention, the yaw moment M is included in the partial differential term of g, which is the first term on the right side of Formula 8, and this term generates a yaw rate larger than the target value. is there. On the other hand, with respect to the lateral speed, the control of the present invention is somewhat larger than the nonlinear model predictive control, but is smaller than the case without control. As shown in FIG. 6, after the yaw rate larger than the target value is generated by the initial large steering angle, the steering angle is reversely steered before the steering angle has a large influence on the lateral speed. It is because it can prevent generating excessively. That is, it was confirmed by these simulations that the control of the present invention can improve the vehicle stability while generating a large lateral displacement at the time of emergency avoidance lane change.

In the control of the present invention, the steering that can be said to be emergent as shown in FIG. 6 is possible in the power form of virtual power g shown in Equation 4 in the L function shown in Equation 6 first. This is due to the introduction of virtual physical quantities. The virtual power is the power to change the current yaw rate to the target yaw rate, but since the yaw moment at this time is assumed not to change from the current value, it is not the actual power but the virtual power. is there. As a result, an effect of approaching the target value against the yaw moment of the tire that is currently occurring occurs. Such L function setting flexibility is also a feature of the control of the present invention. The second reason is that in the control of the present invention, the stability improvement term U _m that is a partial differential term of the dissipated power P that brings about stability and the response improvement term U _p that is a partial differential term of g that increases the steering response capability. By antagonizing.

Next, the simulation result of turning braking stability will be described. The turning braking stability is the stability when the accelerator is suddenly closed while the vehicle is turning, or when the gentle brake is applied. In such an operation during turning of the vehicle, a load is moved to the front wheel, and thus the tire lateral force of the front wheel is increased, oversteering is promoted, and the vehicle is suddenly cut off. A simulation was performed to reproduce such a phenomenon generally called tuck-in. The simulation conditions are as follows. That is, the simulation is started with an initial value of a vehicle speed of 100 km / h and a lateral acceleration of 8 m / s ^2. A braking force of 300 Nm is applied to the front wheels and a braking force of 200 Nm is applied to the rear wheels at 6 seconds after the yaw rate is stabilized. The graph of the simulation result at this time is shown in FIGS.

  FIG. 8 shows a yaw rate, and FIG. 9 shows a simulation result of each time change of the lateral velocity. In the figure, the solid line shows the control of the present invention, the alternate long and short dash line shows the nonlinear model predictive control, and the thin line shows the change when there is no control.

  From these simulation results, in the absence of control, tack-in occurs and the vehicle is in a state close to spin, whereas in the control of the present invention and the nonlinear model predictive control, tack-in can be suppressed. It can be seen that the control is more effective. In the control of the present invention, the effect of stabilizing the vehicle behavior at the time of tuck-in (the effect of suppressing the lateral speed) is excellent due to the effect of the stability improvement term.

  As described above, according to the vehicle motion control device of the present invention, control with higher stability and higher response performance is possible not only in the case of no control but also in comparison with the nonlinear model predictive control known as the prior art. It becomes possible.

  Note that the vehicle motion control device of the present invention is not limited to the illustrated examples described above, and it is needless to say that various changes can be made without departing from the scope of the present invention. In the illustrated example described above, the example in which the vehicle motion control device of the present invention is applied to a steer-by-wire vehicle control mechanism has been described. However, the vehicle motion control device of the present invention is not limited to this, and the vehicle active suspension control and each Application to wheel brake control, left and right driving force distribution control, etc. is also possible.

DESCRIPTION OF SYMBOLS 10 Yaw moment generation mechanism 20 State sensor 30 Control part 41 Steering wheel 42 Steering shaft 43 Steering reaction force generation mechanism 44 Torque controller 51 Steering controller 52 Tire

Claims (6)

A vehicle motion control device for controlling the motion of a vehicle, the vehicle motion control device comprising:
A yaw moment generating mechanism for determining a target state quantity of the vehicle and generating a yaw moment in the vehicle;
A state sensor for measuring or estimating a current state quantity and a current yaw moment of the vehicle by the yaw moment generation mechanism;
A control unit that performs feedback control using a control law U that takes into account a virtual power g that multiplies the deviation between the target state quantity and the current state quantity of the vehicle by the current yaw moment;
A vehicle motion control device comprising: 2. The vehicle motion control apparatus according to claim 1, wherein the control unit includes a partial differential term based on a state quantity of virtual power g of the following equation in its control law U:
Where R ₁ is a weighting factor, r _d is a target state quantity, r is a current state quantity of the vehicle, and M is a current yaw moment.
A vehicle motion control device.   3. The vehicle motion control device according to claim 1 or 2, wherein the target state quantity and the current state quantity of the vehicle are yaw rates.   4. The vehicle motion control device according to claim 1, wherein the yaw moment generation mechanism is a steering actuator. 5. 5. The vehicle motion control device according to claim 1, wherein the control unit obtains the control law U using a scalar function L of the following equation:
Where R _a and R _b are weighting factors, P _u is the control input power, and P is the dissipated power.
A vehicle motion control device. 6. The vehicle motion control apparatus according to claim 5, wherein the control unit has a control law U given by the following equation:
However, the control law U is obtained by partially differentiating L with r and setting this to 0.
A vehicle motion control device.