JP2006082726A - Control method for vehicle moving condition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control properly the moving condition of a vehicle on the basis of a presumed value by presuming properly the road surface friction coefficient between a tire and the road surface in accordance with the vehicle condition. <P>SOLUTION: The control gain g2 at the time of calculating the reaction force component based upon the yawrate is set on the basis of the addition gain obtained by adding together the first control gain μb calculated in a relatively short processing time and the second control gain μc calculated with a relatively high calculation accuracy. For the first control gain μb, the change width of the first control gain μa for a presumed road surface μ1 is set smaller than the change width of the second control gain μc for a presumed road surface μ2, and the upper limit Gup is set complying with the with-time change ▵μ of the presumed road surface μ1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle motion state control method.

Conventionally, an electric power steering device has been known as a vehicle steering device. In the electric power steering apparatus, a steering shaft coupled to a steering wheel and a steering mechanism for steering the steered wheels are mechanically coupled, and an electric motor for assisting a steering force is linked to the steering mechanism. In general, the drive torque command value (drive current value) of the electric motor is controlled such that the auxiliary steering force increases as the steering torque acting on the steering shaft increases.
As such an electric power steering device, for example, a drive torque command value is changed according to a change in a friction coefficient between a tire and a road surface estimated based on, for example, a wiper switch position, a steering torque, a vehicle speed, an outside air temperature, and the like. Thus, there is known an electric power steering device that sets the steering feeling of the steering wheel to be in a constant state regardless of the road surface state (see, for example, Patent Document 1).

For example, when estimating the road surface friction coefficient (road surface μ) according to the motion state of the vehicle, the estimated value of the road surface μ is calculated based on the detected value of the traveling state of the vehicle when the vehicle is traveling on a low μ road. Asymptotically approach the estimated value, and when the vehicle is traveling at high speed, depending on the detection result of the road surface condition, the road surface μ estimated value is set in advance, the road surface μ value of the asphalt road surface, or the vehicle traveling state There is known an electric power steering apparatus that gradually approaches one of estimated values estimated based on the detected value (see, for example, Patent Document 2).
Japanese Patent No. 2936706 JP 2002-145037 A

However, in the electric power steering apparatus according to the above prior art, when estimating the road surface μ based on the detected value of the running state amount of the vehicle, for example, the vehicle speed, the yaw rate, the lateral acceleration, etc. Thus, in a state where the running state of the vehicle greatly changes even if the road surface μ is slightly changed, the change in the vehicle state quantity such as the vehicle speed, the yaw rate, the lateral acceleration, etc. is small, and the road surface μ is accurately obtained based on these detected values. There arises a problem that it is difficult to calculate.
Further, in the electric power steering apparatus according to the above-described conventional technology, when the vehicle is traveling at a high speed, the estimation accuracy can be improved only by making the estimated value of the road surface μ asymptotic to the preset value of the road surface μ of the asphalt road surface. The problem that it cannot be made arises.

  The present invention has been made in view of the above circumstances, and it is possible to appropriately estimate the road surface friction coefficient between the tire and the road surface according to the vehicle state, and to appropriately control the motion state of the vehicle based on the estimated value. An object of the present invention is to provide a method for controlling a vehicle motion state.

  In order to solve the above-described problems and achieve the object, the vehicle motion state control method according to the first aspect of the present invention is a road surface friction coefficient (by a time priority estimation process in which a processing time is set relatively short. For example, the estimated road surface μ1) in the embodiment is estimated, the first gain (for example, the first control gains μa and μb in the embodiment) corresponding to the road surface friction coefficient is calculated, and the calculation accuracy is relatively high. The road surface friction coefficient (for example, the estimated road surface μ2 in the embodiment) is estimated by the accuracy priority estimation process set to be high, and the second gain (for example, the second control in the embodiment) according to the road surface friction coefficient is estimated. (Gain μc) is calculated, and a predetermined vehicle motion state is controlled based on an addition gain (for example, an addition gain gs in the embodiment) obtained by adding the first gain and the second gain. Control gain (eg, implementation form The control gain g2) in the state is changed.

  According to the vehicle motion state control method described above, the addition gain obtained by adding the first gain calculated in a relatively short processing time and the second gain calculated with relatively high calculation accuracy is used. Since the control gain for controlling the predetermined vehicle motion state is set based on this, the accuracy of the predetermined vehicle motion state can be improved without impairing the responsiveness to changes in the external environment such as the road surface state related to the road surface friction coefficient. Good and appropriate control can be performed.

  Furthermore, the vehicle motion state control method according to the second aspect of the present invention is characterized in that the maximum value of the first gain is set to a value smaller than the maximum value of the second gain.

  According to the vehicle motion state control method described above, it is possible to suppress an increase in the control gain error even when the estimation accuracy of the road surface friction coefficient estimated by the time priority estimation process deteriorates. it can.

  Furthermore, in the vehicle motion state control method according to the third aspect of the present invention, the change amount of the road surface friction coefficient estimated by the time priority estimation process (for example, in the embodiment) It is characterized in that it is set so as to change in a decreasing trend as the time change Δμ) increases.

  According to the vehicle motion state control method described above, the maximum value of the first gain is set in accordance with the amount of change in the road surface friction coefficient estimated by the time priority estimation process, so that the road surface friction coefficient is obtained by the time priority estimation process. Even if there is an erroneous determination, it is possible to prevent the control gain from fluctuating rapidly.

As described above, according to the vehicle motion state control method of the present invention as set forth in claim 1, a predetermined vehicle can be obtained without impairing responsiveness to changes in external conditions such as a road surface state related to a road surface friction coefficient. It is possible to execute appropriate control with high accuracy for the motion state.
According to the vehicle motion state control method of the second aspect of the present invention, even when the estimation accuracy of the road surface friction coefficient estimated by the time priority estimation process is deteriorated, the error of the control gain increases. Can be suppressed.
According to the vehicle motion state control method of the present invention, it is possible to prevent the control gain from fluctuating rapidly even if the road surface friction coefficient is erroneously determined by the time priority estimation process. Can do.

Hereinafter, a vehicle motion state control method according to an embodiment of the present invention will be described in a mode applied to, for example, reaction force control in an electric power steering apparatus.
The electric power steering apparatus according to this embodiment includes a manual steering force generation mechanism 1 as shown in FIG. 1, for example. This manual steering force generation mechanism 1 is a steering shaft integrally coupled to a steering wheel 3. 4 is connected to a pinion 6 of a rack and pinion mechanism via a connecting shaft 5 having a universal joint. The pinion 6 meshes with a rack 7a of a rack shaft 7 that can reciprocate in the vehicle width direction, and left and right front wheels 9, 9 as steered wheels are connected to both ends of the rack shaft 7 via tie rods 8, 8. ing. With this configuration, a normal rack and pinion type steering operation can be performed when the steering wheel 3 is steered, and the direction of the vehicle can be changed by turning the front wheels 9 and 9. The rack shaft 7 and the tie rods 8 and 8 constitute a steering mechanism.

  In addition, an electric motor 10 that supplies auxiliary steering force for reducing the steering force generated by the manual steering force generation mechanism 1 is disposed coaxially with the rack shaft 7. The auxiliary steering force supplied by the electric motor 10 is converted into thrust through a ball screw mechanism 12 provided substantially parallel to the rack shaft 7 and is applied to the rack shaft 7. For this purpose, a driving-side helical gear 11 is integrally provided on the rotor of the electric motor 10 through which the rack shaft 7 is inserted, and a driven-side helical gear 13 that meshes with the driving-side helical gear 11 is provided at one end of the screw shaft 12a of the ball screw mechanism 12. The nut 14 of the ball screw mechanism 12 is fixed to the rack 7.

The steering shaft 4 is provided with a steering speed sensor 15 for detecting the steering speed (angular speed) of the steering shaft 4, and is provided in a steering gear box (not shown) that houses the rack and pinion mechanism (6, 7a). Is provided with a steering torque sensor 16 for detecting the steering torque acting on the pinion 6. The steering speed sensor 15 outputs an electrical signal corresponding to the detected steering speed, and the steering torque sensor 16 outputs an electrical signal corresponding to the detected steering torque to the steering control device 20, respectively.
Further, a yaw rate sensor 18 for detecting the yaw rate of the vehicle and a vehicle speed sensor 19 for outputting an electrical signal corresponding to the vehicle speed are attached at appropriate positions of the vehicle body. The yaw rate sensor 18 outputs an electric signal corresponding to the detected yaw rate, and the vehicle speed sensor 19 outputs an electric signal corresponding to the vehicle speed to the steering control device 20, respectively.

  The steering control device 20 determines a target current to be supplied to the electric motor 10 based on a control signal obtained by processing input signals from these sensors 15, 16, 18, and 19, and the electric motor 10 through the drive circuit 21. , The output torque of the electric motor 10 is controlled, and the auxiliary steering force in the steering operation is controlled.

Next, with reference to the control block diagram of FIG. 2, the current control for the electric motor 10 in this embodiment will be described.
The steering control device 20 includes a base current determination unit 31, an inertia correction unit 32, a reaction force correction unit (reaction force component control means) 33, and a control gain calculation unit 40.
The base current determination unit 31 determines a base current value corresponding to the steering torque and the vehicle speed with reference to a base current table (not shown) based on the output signals of the steering torque sensor 16 and the vehicle speed sensor 19. Here, the base current table is set so that the base current increases as the steering torque increases, and the base current decreases as the vehicle speed increases.
In the inertia correction unit 32, inertia mass compensation of the electric motor 10 is performed on the base current determined by the base current determination unit 31.

The reaction force correction unit 33 subtracts a correction current corresponding to the reaction force component from the current after inertia mass compensation, calculates a target current for the electric motor 10, and outputs the target current to the drive circuit 21. The drive circuit 21 controls the supply current to the electric motor 10 to be a target current, supplies the electric current to the electric motor 10, and controls the output torque of the electric motor 10.
Therefore, in the electric power steering apparatus of this embodiment, the correction current set in the reaction force correction unit 33 can be referred to as a reaction force component for the steering assist force, and the base current set in the base current determination unit 31 is this It can be said that the steering assist force before canceling the reaction force component.
The reaction force correction unit 33 includes a damper correction unit 34 and a yaw rate reaction force correction unit 35.
The damper correction unit 34 calculates a first reaction force correction current based on the steering speed, and subtracts the first reaction force correction current from the current after the inertial mass compensation.

The yaw rate reaction force correction unit 35 calculates the second reaction force correction current Im2 based on the yaw rate, and subtracts the second reaction force correction current Im2 from the current output from the damper correction unit 34 to calculate the target current. .
The calculation of the second reaction force correction current Im2 in the yaw rate reaction force correction unit 35 will be described in detail.
The yaw rate correction current calculation unit 36 calculates a reference yaw rate correction current Imb with reference to a yaw rate correction current table (not shown) based on the output signal of the yaw rate sensor 18. Here, the yaw rate correction current table is set such that the reference yaw rate correction current Imb increases as the yaw rate increases (in other words, the reaction force component increases).

On the other hand, based on the output signal from the vehicle speed sensor 19, the offset torque corresponding to the vehicle speed is calculated with reference to the offset table 37. In the offset table 37, the offset torque is constant and sufficiently large in the region where the vehicle speed is low. When the vehicle speed exceeds a predetermined vehicle speed, the offset torque gradually decreases as the vehicle speed increases. Is set to be.
Then, the offset torque is subtracted from the steering torque detected by the steering torque sensor 16 to obtain a steering torque for ratio calculation (hereinafter referred to as offset steering torque), and the offset torque is obtained by referring to the steering torque ratio table 38. The corresponding ratio R is calculated. If the value obtained by subtracting the offset torque from the steering torque (ie, the offset steering torque) is negative, the offset steering torque is set to “0”.
In the steering torque ratio table 38, the ratio R is constant at 1.0 when the offset steering torque is smaller than T1, and the ratio R gradually increases as the offset steering torque increases when the offset steering torque is T1 or more and T2 or less. The ratio R is set to be constant at the lower limit value RL (1.0>RL> 0) when the offset steering torque becomes T2 or more.
Then, the product obtained by multiplying the reference yaw rate correction current Imb calculated by the reference yaw rate correction current calculation unit 36 by the ratio R calculated from the steering torque ratio table 38 and the control gain g2 described later is the second reaction force correction current. Im2 (Im2 = Imb · R · g2).

As described above, since the second reaction force correction current Im2 is determined by the yaw rate reaction force correction unit 35, the reaction force component based on the yaw rate is basically controlled to increase as the yaw rate increases. However, since the ratio R, which varies depending on the magnitude of the steering torque (more precisely, the offset steering torque), is multiplied, the steering torque is larger when the steering torque is larger than when the magnitude of the yaw rate is the same. The reaction force component is set smaller than when it is small. Here, the steering torque and the lateral acceleration in the vehicle have a substantially linear relationship, and the larger the steering torque, the larger the lateral acceleration, and the smaller the steering torque, the smaller the lateral acceleration. Therefore, when the steering torque is large, the reaction force component is set smaller than when the steering torque is small. In other words, when the lateral acceleration is large, the reaction force component is set smaller than when the lateral acceleration is small. Will be. That is, when the lateral acceleration is large, the reaction force component (second reaction force correction current Im2) based on the yaw rate is set to be smaller than that at normal time (when the lateral acceleration is small), so the target current of the motor 10 is increased, and the motor The output torque of 10 is increased, and the auxiliary steering force is increased. As a result, it is possible to prevent the steering wheel from becoming heavier than necessary during high-G turning and the like, and it becomes possible to operate with an appropriate steering force from normal steering to high-G turning, and a good steering fee. A ring can be realized.
In particular, in this embodiment, paying attention to the correlation between the steering torque and the lateral acceleration, the steering torque is used instead of the lateral acceleration, so that it is not necessary to use the lateral acceleration sensor, and the device configuration can be simplified. .

The reason why the ratio R is calculated based on the offset steering torque obtained by subtracting the offset torque from the steering torque detected by the steering torque sensor 16 is as follows.
In the steering torque ratio table 38, the ratio R is set to “1.0” in the region where the offset steering torque is T1 or less. Therefore, the steering torque corresponding to this region affects the setting of the reaction force component based on the yaw rate. Does not reach. In other words, the offset steering torque region below T1 is a dead zone.
On the other hand, since the offset torque is a variable set according to the vehicle speed, the offset steering torque changes according to the vehicle speed even if the steering torque is the same. FIGS. 3A and 3B are ratio characteristic diagrams in which the horizontal axis indicates the steering torque. FIG. 3A shows a case where the vehicle speed is high, and FIG. 3B shows a case where the vehicle speed is low. By using the offset steering torque in this way, the dead zone can be made variable according to the vehicle speed. That is, the dead zone at low vehicle speed (see FIG. 3B) can be made larger than the dead zone at high vehicle speed (see FIG. 3A).
As a result, a reduction effect on the reaction force component based on the yaw rate is exhibited from a relatively small steering torque at a high vehicle speed, and a reaction force based on the yaw rate until the steering torque becomes relatively large at a low vehicle speed. It is possible to make it difficult to reduce the components. In this way, for example, when turning an intersection at a low speed, the auxiliary steering force by the electric motor 10 can be reduced, and the steering wheel 3 can be easily returned.

Hereinafter, the control gain calculation unit 40 that calculates the control gain g2 used when calculating the second reaction force correction current Im2 will be described in detail.
The control gain calculation unit 40 includes an estimated speed priority processing unit 41 (for example, a calculation processing period of 10 ms) set with a relatively short processing time, and an estimated accuracy priority processing unit 42 set with a relatively high calculation accuracy. (E.g., a calculation processing period 1 s).
The estimated speed priority processing unit 41 includes, for example, a road surface μ simple estimation unit 51, a first control gain calculation unit 52, a μ estimated value change amount calculation unit 53, a gain fluctuation restriction unit 54, and a control gain restriction unit 55. , And an adder 56 and a device control gain limit calculator 57.
The estimation accuracy priority processing unit 42 includes, for example, a road surface μ high accuracy estimation unit 61 and a second control gain calculation unit 62.

  The road surface μ simple estimation unit 51 is simplified based on detection signals output from sensors that detect changes in road surface conditions, such as a wiper switch (not shown), an outside air temperature sensor (not shown), a raindrop sensor (not shown), and the like. Specifically, the road surface friction coefficient (road surface μ) is estimated, and the estimated road surface μ1 is output to the first control gain calculation unit 52 and the μ estimated value change amount calculation unit 53.

The first control gain calculation unit 52 stores a first control gain map (MAP1) indicating a predetermined relationship between the estimated road surface μ1 and the first control gain μa in advance, and is input from the road surface μ simple estimation unit 51. The first control gain map is searched based on the estimated road surface μ1, the first control gain μa is calculated, and output to the control gain limiter 55.
In the first control gain map (MAP1), when the estimated road surface μ1 is less than a predetermined value (for example, 0.1), the first control gain μa is a maximum value (for example, 0.25). As the estimated road surface μ1 increases from a predetermined value (for example, 0.1, etc.) to 1, the first control gain μa increases from the maximum value (for example, 0.25) to the maximum value (for example, 0, etc.). ) Is set to change to a decreasing trend.

The μ estimated value change amount calculation unit 53 calculates a time change Δμ of the estimated road surface μ1 input from the road surface μ simple estimation unit 51 for a predetermined time and outputs the time change Δμ to the gain fluctuation limiting unit 54.
The gain fluctuation restriction unit 54 stores a gain fluctuation restriction map indicating a predetermined relationship between the time change Δμ and the upper limit value Gup for the first control gain μa in advance, and is input from the μ estimated value change amount calculation unit 53. Based on the time change Δμ, the map is searched for the gain variation restriction map to calculate the upper limit value Gup and output to the control gain restriction unit 55.
In the gain variation restriction map, when the time change Δμ is less than a predetermined value (for example, 0.25), the upper limit value Gup is set to the maximum value (for example, 0.25), and the time change. As Δμ increases from a predetermined value (for example, 0.25) to 1, the upper limit value Gup changes in a decreasing trend from the maximum value (for example, 0.25) to the minimum value (for example, 0.05). It is set to be.

The control gain limiting unit 55 limits the first control gain μa input from the first control gain calculating unit 52 to a value equal to or less than the upper limit value Gup input from the gain fluctuation limiting unit 54. That is, when the first control gain μa exceeds the upper limit value Gup, the upper limit value Gup is set as a new first control gain μb, and when the first control gain μa is equal to or lower than the upper limit value Gup, a new value is set. The first control gain μa is set as the first control gain μb and output to the adder 56.
The adding unit 56 adds an addition gain gs obtained by adding a first control gain μb input from the control gain limiting unit 55 and a second control gain μc input from the estimation accuracy priority processing unit 42 described later. Output to the control gain limit calculation unit 57.

  The device control gain limit calculation unit 57 uses various control devices (for example, an electric power steering device, a vehicle behavior stabilization device, a four-way control device, etc.) to cooperatively control the vehicle motion state using the addition gain gs input from the addition unit 56. The wheel is limited to a predetermined upper limit value or less set for each wheel steering device or four-wheel drive device. That is, the device control gain limit calculation unit 57 stores a predetermined upper limit value set in advance for each of various control devices, and if the added gain gs exceeds the predetermined upper limit value for each control device, the control gain A predetermined upper limit value is set as g2, and when the addition gain gs is less than or equal to the predetermined upper limit value, the addition gain gs is set as the control gain g2, and each control device (for example, yaw rate reaction force correction of the electric power steering device) is set. Part 35 etc.).

In addition, the road surface μ high-precision estimation unit 61 recognizes an external state such as a road surface state based on a detection signal output from an external sensor such as a camera or a radar, or a vehicle motion parameter such as a yaw rate, speed, or steering torque. The road surface μ is estimated by an estimation process or the like in which adaptive control, an observer, or the like is applied to an appropriate vehicle motion model described by the following, and the estimated road surface μ2 is output to the second control gain calculation unit 62.
The second control gain calculation unit 62 stores a second control gain map (MAP2) indicating a predetermined relationship between the estimated road surface μ2 and the second control gain μc in advance, and is input from the road surface μ high accuracy estimation unit 61. The second control gain map is searched based on the estimated road surface μ2 to calculate the second control gain μc and output to the adder 56.

In the second control gain map (MAP2), when the estimated road surface μ2 is less than a predetermined value (for example, 0.1), the second control gain μc (for example, the second control gain μc> the first) The control gain μa) is set to a maximum value (for example, 2), and the second control gain μc is increased to a maximum value (for example, for example, as the estimated road surface μ2 increases from a predetermined value (for example, 0.1) to 1). 2) and the like (for example, 1 etc.).
The maximum value of the first control gain μa is set to a value smaller than the maximum value of the second control gain μc.

  In this electric power steering apparatus, the control gain g2 for calculating the reaction force component based on the yaw rate is set based on the addition gain gs obtained by adding the first control gain μb and the second control gain μc. Thus, for example, when the control gain g2 is output according to the calculation process cycle of the first control gain μb shorter than the calculation process cycle of the second control gain μc, the responsiveness is based only on the first control gain μb. The timing when the control gain g2 is emphasized and the control gain g2 is set and the timing when the accuracy is emphasized and the control gain g2 is set based on the first control gain μb and the second control gain μc are continuously switched.

As described above, according to the vehicle motion state control method of the present embodiment, the first control gain μb calculated in a relatively short processing time and the second control calculated in a relatively high calculation accuracy. Since the control gain g2 for calculating the reaction force component based on the yaw rate is set on the basis of the added gain gs obtained by adding the gain μc, the responsiveness to changes in external conditions such as road surface conditions is not impaired. In addition, it is possible to execute appropriate reaction force correction with high accuracy.
In particular, for the first control gain μb, first, the change width of the first control gain μa with respect to the estimated road surface μ1 is set to be smaller than the change width of the second control gain μc with respect to the estimated road surface μ2. Even when the estimation accuracy of the road surface μ1 is deteriorated, an increase in the error of the control gain g2 can be suppressed, and the upper limit value Gup is set according to the time change Δμ of the estimated road surface μ1. Thus, even if the road surface friction coefficient is erroneously determined by the time priority estimation process, it is possible to prevent the control gain g2 from fluctuating rapidly.

The present invention is not limited to the embodiment described above.
For example, the reaction force control device according to the present invention is not limited to application to the above-described electric power steering device, but is a vehicle steering device (SBW) for a steering-by-wire system and a vehicle for an active steering system. The present invention can also be applied to a vehicle steering device (VGS) for a vehicle steering system, a variable gear ratio steering system, and the like.
Note that the steering-by-wire system means that the operating element and the steering mechanism are mechanically separated, a reaction force motor that applies a reaction force to the operating element, and a steering wheel provided in the steering mechanism. The steering system includes a steering motor that generates a force for turning the vehicle.
The active steering system is a steering system that controls the front wheel steering angle and the rear wheel steering angle in accordance with the steering operation of the driver and the motion state of the vehicle.
The variable gear ratio steering system is a steering system in which the steering gear ratio can be changed according to the magnitude of the steering angle.

It is a lineblock diagram of an electric power steering device provided with a reaction force control device concerning one embodiment of the present invention. It is a block diagram of the current control with respect to the electric motor of the electric power steering apparatus which concerns on one Embodiment of this invention. It is a ratio characteristic figure at the time of high vehicle speed and low vehicle speed. It is a block diagram of the control gain calculation part shown in FIG.

Explanation of symbols

20 Steering control device 40 Control gain calculation unit 41 Estimated speed priority processing unit 42 Estimation accuracy priority processing unit

Claims (3)

A road surface friction coefficient is estimated by a time priority estimation process in which the processing time is set relatively short, and a first gain corresponding to the road surface friction coefficient is calculated.
A road surface friction coefficient is estimated by an accuracy priority estimation process set with a relatively high calculation accuracy, and a second gain corresponding to the road surface friction coefficient is calculated.
A vehicle motion state control method, wherein a control gain for controlling a predetermined vehicle motion state is changed based on an addition gain obtained by adding the first gain and the second gain. 2. The vehicle motion state control method according to claim 1, wherein the maximum value of the first gain is set to a value smaller than the maximum value of the second gain. The maximum value of the first gain is set so as to change in a decreasing tendency as the amount of change in the road surface friction coefficient estimated by the time priority estimation process increases. Control method of vehicle motion state.

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