JP3590608B2 - Vehicle turning control device and steering limit determination method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a turning control device that controls a braking force of a wheel during turning of a vehicle and corrects the turning motion to stabilize the turning motion, and that a steering angle is limited with respect to a road surface in turning control and the like. And a method for determining a steering limit.
[0002]
[Prior art]
As a control technique for obtaining stability during turning of the vehicle, for example, Japanese Patent Application Laid-Open No. H8-310360 and Patent No. 3175369 are disclosed. FIG. 9 is an operation block diagram showing a control function in the turning control device for a vehicle disclosed in Japanese Patent Application Laid-Open No. 8-310360. In the figure, various sensors 1 include, for example, a wheel speed sensor that detects a wheel speed Vw (i), a yaw rate sensor that detects a yaw rate γ, an acceleration sensor that detects a longitudinal acceleration Gx and a lateral acceleration Gy, and a steering angle of a steering wheel. It shows a group of sensors such as a steering angle sensor for detecting θ and a pedal stroke sensor for detecting the stroke St of the brake pedal, and information of the vehicle detected by the various sensors 1 is input to the control means 2.
[0003]
The information input to the control means 2 is smoothed by the filter 3 and input to the vehicle motion state calculation means 4 and the driving operation determination means 5. The vehicle motion state calculation means 4 calculates the vehicle motion state such as the vehicle speed Vb and the center-of-gravity slip angular speed dβ based on the signals of the wheel speed Vw (i), the longitudinal acceleration Gx, the lateral acceleration Gy, and the yaw rate γ. The driving operation determining means 5 determines the operating condition of the steering wheel or the brake pedal by the driver based on the steering angle signal θ and the stroke signal St of the brake pedal. The result of the determination by the operation determining means 5 is input to the turning determining means 6, and the turning direction is determined.
[0004]
The steering angle θ and the vehicle speed Vb, which are the results of calculation and judgment by the vehicle motion state calculating means 4 and the driving operation judging means 5, are input to the target yaw rate calculating means 7, and the target yaw rate γt of the vehicle is calculated. Further, the target yaw rate γt and the actual yaw rate γ are input to the required yaw moment calculating means 8, a deviation Δγ and a deviation derivative Δγs of both are obtained, and a required yaw moment γd is calculated from these values. The yaw moment control means 9 generates a signal for controlling the braking force so that the actual yaw rate γ matches the target yaw rate γt in accordance with the required yaw moment γd, and supplies the control signal to the control signal selection means 10. The control signal selecting means 10 distributes this signal to each pressure unit 11 for the front wheel and the rear wheel on the outside of the turning motion to be controlled, and controls the braking force.
[0005]
FIG. 10 shows a technique disclosed in Japanese Patent No. 3175369, which controls the motion of a vehicle by controlling a steering angle δf of a front wheel and a steering angle δr of a rear wheel. It is. The vehicle control device disclosed in this publication includes a controller 12, a steering angle sensor 13, steering torque sensors 14, pressure sensors 15, 16, a yaw rate sensor 17, a lateral acceleration sensor 18, a vehicle speed sensor 19, and front wheels. The actuator includes a steering angle actuator 20, a rear wheel steering angle actuator 21, and a throttle opening degree actuator 22.
[0006]
The steering angle sensor 13 indicates the steering angle θh of the steering wheel, the steering torque sensor 14 indicates the steering torque Th applied to the steering wheel, and the pressure sensors 15 and 16 indicate the left chamber pressure Pl and the right chamber of the power cylinder provided in the steering device. The pressure Pr, the yaw rate sensor 17 detects the yaw rate γ of the vehicle body, the lateral acceleration sensor 18 detects the lateral acceleration Gy at the center of gravity of the vehicle, and the vehicle speed sensor 19 detects the vehicle speed V, and gives them to the controller 12. The controller 12 receives the signals of these sensors, operates the front wheel steering angle actuator 20 and the rear wheel steering angle actuator 21 to perform steering, and operates the throttle opening actuator 22 to control the output of the internal combustion engine. I do.
[0007]
For example, the steering angle control of the front wheels by the controller 12 is performed based on information indicating at least one of the steering of the driver and the actual motion of the vehicle when the front wheels do not exceed the turning limit. When the front wheel exceeds the turning limit, the front wheel steering angle δf is decreased to control the wheel to recover from exceeding the turning limit. That is, the front wheel steering angle reduction amount Δδf is calculated according to the degree of excess of the turning limit of the front wheel, and the calculation result is output to the front wheel steering angle actuator 20 to recover from exceeding the turning limit. The front wheel steering angle reduction amount Δδf is calculated as follows.
[0008]
First, a front wheel restoring moment (road surface reaction torque) Mf is calculated based on the steering torque Th, the left chamber pressure Pl and the right chamber pressure Pr of the power cylinder, and the current if supplied to the front wheel steering angle actuator 20. You. Next, the front wheel cornering force Ff is calculated based on the time derivative of the lateral acceleration Gy and the yaw rate γ. Subsequently, by dividing the differential value ΔMf of the absolute value of the front wheel restoring moment Mf by the differential value ΔFf of the absolute value of the front wheel cornering force Ff, an increase rate ΔMf / ΔFf of the front wheel restoring moment is calculated. Further, the front wheel steering angle decrease amount Δδf corresponding to the calculated increase rate ΔMf / ΔFf of the front wheel restoring moment is determined using a characteristic map as shown in FIG.
[0009]
In such an apparatus, the relationship between the cornering force Ff and the turning limit is as shown in FIG. FIG. 12 shows the cornering force Ff on the horizontal axis and the restoring moment Mf on the vertical axis. As shown in the figure, the restoring moment Mf increases with an increase in the cornering force Ff, but when the cornering force Ff exceeds a certain value, the restoring moment Mf tends to decrease with an increase in the cornering force Ff. In the technology disclosed in Japanese Patent No. 3175369, whether or not the steering is at a limit with respect to the road surface is detected using this relationship. If the limit is exceeded, the front wheel steering angle δf is reduced by Δδf, and the front wheel is decreased. When the decrease in the steering angle δf is insufficient, the throttle opening actuator 22 is operated to decelerate.
[0010]
[Problems to be solved by the invention]
As described above, in the related art described above, the former calculates the target yaw rate γt using the steering angle θ and the vehicle speed Vb, and controls the turning of the vehicle based on the deviation from the actual yaw rate. The determination of the limit is performed by detecting a state in which the actual yaw rate does not follow the steering angle, and therefore is not detected until the cornering force is completely saturated. Also, in the latter, it is determined whether the steering is at a limit with respect to the road surface from the relationship between the cornering force and the restoring moment, and the determination can be made before the cornering force is saturated, but the cornering force Ff is determined from the value of each sensor. Since it is an estimated value and the restoration moment Mf is also an estimated value, it has been difficult to accurately detect the degree of excess of the turning limit.
[0011]
The present invention has been made in order to solve such a problem, and a state where steering is limited with respect to a road surface is easily determined by using a road surface reaction force torque before a cornering force is saturated. It is an object of the present invention to obtain a vehicle turning control device capable of improving the turning performance of a vehicle by controlling the turning of the vehicle based on the above, and a steering limit determination method.
[0012]
[Means for Solving the Problems]
The turning control device for a vehicle according to the present invention includes a steering angle detecting unit that detects a steering angle of the vehicle,Vehicle motion state detecting means for detecting the turning motion of the vehicle, target vehicle motion setting means for setting a target turning motion of the vehicle from the steering angle, and a road surface for detecting a road reaction torque received by the steered wheels of the vehicle from the road surface The reaction torque detection means detects a road reaction torque peak point at which the absolute value of the road reaction torque changes from an increase to a decrease with respect to an increase in the absolute value of the steering angle, and the absolute value of the steering angle is A steering limit judging means for judging a steering limit when the steering angle is greater than an absolute value of a steering angle at a peak point of a road surface reaction torque or a value lower than the predetermined ratio, a detection result of the vehicle motion state detecting means, and a target vehicle motion setting Turning motion control means for controlling the turning motion of the vehicle from the set value of the means.When the steering limit determining means determines that the steering limit is reached, the turning motion control means changes the control content in a direction to promote the turning motion.
[0013]
Further, the turning motion control means inputs outputs from the vehicle motion state detecting means, the target vehicle motion setting means, and the steering limit determining means, and inputs a required control amount (Mu). , Mo) for calculating the required yaw moment, and the required control amount (Mu) , Mo), control start / end determination means for determining the start and end of the vehicle turning motion, and determining whether to perform under-steering suppression control or over-steering suppression control, and the rate of increase or decrease of the brake fluid pressure of each wheel. The braking force adjustment amount calculating means calculates the rate of increase or decrease of the brake fluid pressure of each wheel for each wheel, and distributes the braking force to each wheel accordingly.
Further, the steering device is an electric power steering device, and includes a steering torque detecting unit, a motor current detecting unit, and a motor rotational acceleration detecting unit. The road surface reaction torque is a steering torque value, and the motor current is a torque constant. , And the rotational acceleration of the motor.
[0014]
In the steering limit determination method according to the present invention, the steering angle of the vehicle, a road surface reaction torque received by the steered wheels of the vehicle from the road surface, and an absolute value of the road surface reaction force torque with respect to an increase in the absolute value of the steering angle. Detects each peak point of road surface reaction torque that turns from increasing to decreasing,The absolute value of the road surface reaction torque at the peak point of the road surface reaction torque or the absolute value of the steering angle at the absolute value of the road surface reaction torque at a value lower by a predetermined ratio than the absolute value is set as a limit steering angle, and the steering angle is set. Is determined to be the steering limit when the absolute value of the steering angle exceeds the limit steering angle, and the control content is changed in a direction to promote the turning motion.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
1 to 8 illustrate a vehicle turning control device and a steering limit determination method according to a first embodiment of the present invention. FIG. 1 is a block diagram showing an entire configuration of the vehicle turning control device, and FIG. Is a functional block diagram illustrating the operation of the ECU, FIG. 3 is a functional block diagram illustrating the electric power steering device, FIG. 4 is a flowchart illustrating the operation of the steering limit determination, and FIG. 5 is used as a map. FIG. 6 is a block diagram illustrating a method of calculating a control amount of the required yaw moment calculating means, and FIG. 7 is a diagram illustrating a relationship between a side slip angle of a tire, a cornering force, and a self-aligning torque. FIG. 8 is a characteristic diagram showing a relationship between the steering angle and the road surface reaction torque.
[0016]
In the turning control device for a vehicle shown in FIG. 1, reference numeral 23 denotes an ECU for controlling turning motion of the vehicle. The ECU 23 includes a steering angle sensor 24 as steering angle detecting means for a steering wheel, and a yaw rate sensor for detecting turning motion of the vehicle. 25 and a lateral acceleration sensor 26, an M / C pressure sensor 27 for detecting a master cylinder pressure of the brake, a wheel speed sensor 28 for detecting the speed of each wheel, and signals from road surface reaction torque detecting means 29 to be described later. The ECU 23 outputs the calculation results based on these signals to the hydraulic unit 30 as the valve drive signal Md (i). Here, since the yaw rate detected by the yaw rate sensor 25 is the actual yaw rate applied to the vehicle, it is hereinafter referred to as the actual yaw rate.
[0017]
The hydraulic unit 30 is connected via a pressure pipe between the master cylinder 31 connected to the brake pedal and the wheel cylinders 32a to 32d of the respective wheels, and a command from the ECU 23 is transmitted to the master cylinder 31 by the driver. The pressure of the wheel cylinders 32a to 32d of each wheel is individually controlled independently of the operation of. The road surface reaction torque detecting means 29 can be constituted by, for example, a strain measuring means such as a load cell or a strain gauge provided on one or both sides of the front wheel side of a rack connecting the front wheels of the vehicle and the steering shaft. In this method, the force of the road surface reaction torque from the tires of the front wheels, that is, the steered wheels, acting as a compressive force on the rack is detected as a rack distortion amount. In a vehicle equipped with an electric power steering device, a road surface reaction torque can be obtained as follows.
[0018]
FIG. 3 is a functional block diagram in the case where the electric power steering device is provided. The steering torque detecting means 41 detects the steering torque by the driver, and the steering is assisted by the motor 42. The motor speed detecting means 43 detects the rotation speed of the motor 42, and the motor acceleration detecting means 44 detects the acceleration. The motor current determination means 45 calculates the target torque by inputting the steering torque, the motor speed, the motor acceleration, and the vehicle speed, and calculates a target current value corresponding to the target torque. The target current value and the actual current of the motor 42 detected by the motor current detecting means 46 are input to a subtractor 47, and the difference between the two is obtained. The motor driving means 48 sets the motor driving means 48 so that the difference becomes zero. The voltage applied to 42 is determined. A current corresponding to the voltage is applied to the motor 42 to assist the steering according to the driver's steering torque.
[0019]
The road surface reaction torque detection unit 29 receives the output of the steering torque detection unit 41, the output of the motor acceleration detection unit 44, and the output of the motor current detection unit 46, and calculates the road surface reaction force torque. The calculation of the road surface reaction torque is as follows. First, the equation of motion of the steering mechanism is expressed by the following equation.
J × dωs / dt = Thdl + Tmtr−Tfric−Treact (1)
Here, J is the moment of inertia of the steering mechanism, dωs / dt is the rotational acceleration of the steering shaft, Thdl is the steering torque, Tmtr is the motor output torque in terms of the steering shaft, Tfric is the friction torque of the steering mechanism, and Treact is the steering shaft in terms of steering shaft. This is the road reaction torque.
[0020]
When this equation (1) is solved with the road surface reaction torque Treact, the following equation is obtained, and the road surface reaction torque is obtained.
Treact = Thdl + Tmtr−J × dωs / dt−Tfric (2)
In the calculation of the road surface reaction force torque Treact, a value Tsens detected by the steering torque detecting means 41 is used as the steering torque Thdl, and the motor output torque Tmtr is set to the motor current Imtr detected by the motor current detecting means 46. It can be obtained by multiplying by a constant Kt. Further, the rotational acceleration dωs / dt of the steering shaft is proportional to the motor acceleration detected by the motor acceleration detecting means 44, and the output of the motor acceleration detecting means 44 can be used.
[0021]
The friction torque Tfric acts as a relay with respect to the rotational speed of the steering mechanism. As is well known, the relay can be equivalently represented by gain and phase by an equivalent linearization method in control engineering. . A filter is used as the most general method for adjusting the gain and the phase. Therefore, (2) can be replaced by the following equation (3).
Treact = LPF (Tsens + Kt × Imtr−J · dω) (3)
Here, the LPF is a primary low-pass filter. In this way, the road surface reaction force torque Treact can be calculated from each measured value. The time constant of the first-order low-pass filter is determined such that the corner frequency is between 0.05 and 1.0 Hz.
[0022]
The function of the ECU 23 for controlling the turning motion of the vehicle is as shown in the functional block diagram of FIG. 2, and the signal information input from the various sensors (24 to 28) is The smoothing process is performed based on the constant. The vehicle motion state detecting means 34 receives the wheel speed Vw (i), the lateral acceleration Gy, and the actual yaw rate γ, detects the vehicle speed Vb and the turning motion, and outputs the vehicle speed Vb together with the lateral acceleration Gy and the actual yaw rate γ. I do. The vehicle speed Vb can be calculated, for example, by selecting the wheel speed that is the second highest rotating speed among the wheel speeds, and can be corrected based on sensor information during turning. (I) of the wheel speed Vw (i) indicates each wheel, and i = 1 indicates the left front wheel, 2 indicates the right front wheel, 3 indicates the left rear wheel, and 4 indicates the right rear wheel.
[0023]
The target vehicle motion setting means 35 sets a target turning motion, detects a steering angle θ to detect an operation of a steering wheel, and sets a target yaw rate γt as a turning motion of the vehicle according to a driving state to the following ( The values are obtained and output by equations 4) and (5).
γt = LPF {Vb / (1 + A × Vb2) × (δ / L)} (4)
δ = θ / ρ (5)
Here, A is a stability factor, L is a wheelbase, δ is a front wheel steering angle, and ρ is a steering gear ratio.
[0024]
The steering limit determining unit 36 receives the road surface reaction torque Treact and the steering angle θ to determine the steering limit, and calculates and outputs a steering limit correction amount Kpo corresponding to the amount exceeding the steering limit by a method described later. The required yaw moment calculating means 37 inputs the data calculated and output by the vehicle motion state detecting means 34, the target vehicle motion setting means 35, and the steering limit determining means 36, and requests understeering (hereinafter referred to as US) suppression. The yaw moment Mu and the oversteering (hereinafter referred to as OS) suppression request yaw moment Mo, that is, the required control amount, are calculated by a method described later.
[0025]
The control start / end determination means 38 inputs the required control amounts Mu and Mo and determines the start and end of the vehicle turning motion, and determines whether to perform the US suppression control or the OS suppression control. That is, when the US suppression request yaw moment Mu exceeds the US suppression control start threshold Mstu, the US suppression control is selected, and the signal Cuson = 1 is output. When the OS suppression request yaw moment Mo exceeds the OS suppression control start threshold Msto, the OS suppression control is selected, a signal Coson = 1 is output, and the US suppression control and the OS suppression control simultaneously satisfy the start condition. In this case, the OS suppression control is performed with priority. When the US suppression request yaw moment Mu falls below the US suppression control start threshold value Mstu, and when the OS suppression request yaw moment Mo falls below the OS suppression control start threshold value Msto, the suppression control ends.
[0026]
The braking force adjustment amount calculation means 39 calculates the rate of increase or decrease of the brake fluid pressure of each wheel, that is, the time change amount dPw (i) of the increase or decrease. In this calculation procedure, first, wheels to be controlled are selected according to the turning direction of the vehicle as follows. When implementing US suppression control, select the rear wheels, or the front and rear wheels, that are inside the turn, on the side that increases the braking force, and select some or all of the other wheels on the side that decreases the braking force. I do. Further, when performing the OS suppression control, the front wheels or the front wheels and the rear wheels outside the turn are selected to increase the braking force, and some or all of the other wheels are set to decrease the braking force. select.
[0027]
Next, an increase / decrease rate dPw (i) of the brake fluid pressure of each wheel is set for each wheel. When the US suppression control is performed, the setting of dPw (i) is such that the wheel selected on the increasing side of the braking force is set to a value proportional to the US suppression request yaw moment Mu, and is selected on the decreasing side of the braking force. The calculated wheel is calculated as a value proportional to a value obtained by inverting the US suppression request yaw moment Mu negatively. When performing the OS suppression control, the wheel selected on the increasing side of the braking force is set to a value proportional to the OS suppression request yaw moment Mo, and the wheel selected on the decreasing side of the braking force is set to the OS suppression request yaw moment. It is calculated as a value proportional to the value obtained by inverting Mo.
[0028]
The brake fluid pressure increase / decrease rate dPw (i) thus selected and calculated for each wheel is input to the slip controller 40, and the slip controller 40 corresponds to the brake fluid pressure increase / decrease rate dPw (i) for each wheel. A valve drive signal Md (i) for adjusting the brake fluid pressure is output. If the wheel slip Sw (i) is within the permissible slip ratio Slm, the valve drive signal Md (i) increases the brake fluid pressure of the wheel to be pressure-increased in accordance with the brake fluid pressure increase / decrease rate dPw (i). If the slip rate is equal to or more than the allowable slip rate Slm, the brake fluid pressure is controlled in the pressure decreasing direction so that the wheel slip Sw (i) converges within the allowable slip rate Slm.
[0029]
The valve drive signal Md (i) output from the slip controller 40 is supplied to the hydraulic unit 30 described with reference to FIG. 1 to drive the hydraulic unit 30, control the brake fluid pressure of each wheel, and distribute the braking force to each wheel. Is performed. The distribution of the braking force controls the motion of the vehicle so that the actual yaw rate approaches the target yaw rate. In this way, the motion of the vehicle according to the driver's will is independently controlled according to the road conditions and the characteristics of the vehicle. Therefore, the required yaw moment calculation means 37, the control start / end determination means 38, the braking force adjustment amount calculation means 39, the slip controller 40, and the hydraulic unit 30 constitute a turning motion control means.
[0030]
FIG. 4 is a flowchart showing a method of calculating the steering limit correction amount Kpo by the above-mentioned steering limit determining means 36, and this flowchart is repeated every predetermined time. ST1 to ST3 surrounded by a dotted frame in FIG. 4 indicate operation blocks, respectively. ST1 is a step of detecting a peak point of the road surface reaction torque Treact, and an absolute value | Treakpk | The absolute value θpk0 of the steering angle at the peak point is stored. ST2 is a step of detecting the limit steering angle, and detects and stores the limit steering angle θpk indicating that the steering angle is close to the limit with respect to the road surface. ST3 is a step of judging a steering limit, and judging from the limit steering angle θpk whether or not the steering angle of the vehicle is a limit with respect to the road surface, and determining whether the steering angle exceeds the threshold value θpk which is the limit steering angle. , The steering limit correction amount Kpo is calculated.
[0031]
The operation of each step will be described in detail. First, in the block for detecting the peak point of the road surface reaction force torque Treact in ST1, in ST11, the steering angle θ is input and the absolute value | θ | exceeds the predetermined value θpkmin. Is determined. Here, if | θ |> θpkmin holds, the process proceeds to ST12, where the absolute value | Treact | of the road surface reaction force torque Treact | is compared with the previously stored road surface reaction torque peak value Treapkk, and | Treact |> Treapkk If the condition is satisfied, the process proceeds to ST13. In ST13, the absolute value | θ | of the steering angle is stored as the peak steering angle θpk0, and the absolute value | Treact | of the road surface reaction torque is stored as the current road surface reaction torque peak value Treapkk.
[0032]
The predetermined value θpkmin in ST11 is set as the minimum value of the steering angle at the peak value of the road surface reaction torque, and is stored, so that in the block of ST1, only when the steering angle is operated at θpkmin or more, the road surface reaction is reduced. The absolute value of the force torque and the absolute value of the steering angle at that time are stored as respective peak values. The routine is repeated, and when the steering angle is changing in a direction to increase, the values of θpk0 and Treakpk are continuously updated for each routine, and when the steering angle is no longer changed, θpk0 and Treakpk are not updated. The stored θpk0 is the peak steering angle, and Treakpk is the peak value of the road surface reaction torque. If the steering angle θ becomes a predetermined value or more, the road surface reaction torque decreases rather as described later. Therefore, the block in ST1 functions as a road surface reaction torque peak point detecting means for the steering angle.
[0033]
If ST11 or ST12 is not satisfied, or if ST1 is completed, the process proceeds to block ST2 for detecting the limit steering angle, and in ST21, the absolute value | θ | of the steering angle is compared with the stored peak steering angle θpk0. Is done. In this comparison, when | θ | <θpk0, that is, when the steering angle becomes smaller than the absolute value of the steering angle stored in the block of ST1, the process proceeds to ST22, where the peak steering angle θpk0 and the limit steering angle θpk are set. Is stored instead of the steering angle absolute value | θ |, 0 is stored instead of the road surface reaction torque peak value Treacpk, and the stored value of the road surface reaction torque peak value and the limit steering angle are stored. Is reset. Here, the maximum value of the physical steering angle absolute value or the maximum value of the calculated steering angle absolute value is used as | θ | max.
[0034]
If the comparison result in ST21 is | θ | ≧ θpk0, the process proceeds to ST23, where the absolute value | Treact | of the road surface reaction torque is compared with the product of the road surface reaction torque peak value Treacpk and the coefficient Krt. Krt is a positive coefficient equal to or less than 1, and is a coefficient for determining how much the road surface reaction torque is reduced with respect to the road surface reaction torque peak value Treacpk as the limit steering angle. For example, when Krt = 0.8, a value in which the absolute value of the road surface reaction torque is 20% lower than the peak value of the road surface reaction force torque is set as the limit steering angle, and a margin is given.
[0035]
If the result of comparison in ST23 is | Treact | ≧ Treakpk × Krt, the process proceeds to ST24, where the maximum steering angle absolute value | θ || θ | max is stored in the limit steering angle θpk, and the limit steering angle θpk is Reset. If the result of the comparison is | Treact | <Treakpk · Krt, the operation proceeds to ST25, where the absolute steering angle value | θ | is compared with the limit steering angle θpk. If | θ | <θpk, the limit steering angle is determined in ST26. The steering angle absolute value | θ | is stored in θpk. That is, the minimum steering angle absolute value | θ | when the condition | Treact | <Treakpk × Krt is satisfied is stored as the limit steering angle θpk.
[0036]
That is, when | θ | ≧ θpk0 is satisfied in ST21, the steering angle is increased, and when the steering angle is increased and | Treact | <Treakpk × Krt is satisfied in ST23, the steering angle is determined as described below. Since the torque peak point has been exceeded, the absolute value | θ | of the steering angle in this routine becomes the minimum value of the steering angle when the road surface reaction torque exceeds the peak point, and this is the limit steering angle θpk. The value of the limit steering angle θpk is valid only while the condition | Treact | <Treakpk × Krt holds, otherwise | θ | max is stored. Even if ST25 is not satisfied, the steering angle exceeds the peak point of the road surface reaction torque, so that θpk is not reset and the process proceeds to ST3.
[0037]
In ST3, which is a block for determining the steering limit, in ST31, the absolute value of the steering angle | θ | is compared with a value obtained by adding a steering limit determination end offset θofofs to the limit steering angle θpk. Here, if | θ | ≦ θpk + θofofs, the non-steering limit state is determined in ST32, and 0 is stored in the steering limit correction amount Kpo. If | θ |> θpk + θofofs, the process proceeds to ST33, where the absolute value of the steering angle | θ | is compared with a value obtained by adding the steering limit determination start offset θonofs to the limit steering angle θpk. Here, if | θ |> θpk + θonofs, the process proceeds to ST34, where it is determined that the steering is in the steering limit state, and Fkpo (| θ |) is stored in the steering limit correction amount Kpo.
[0038]
This Fkpo (| θ |) is defined as a function of | θ |, and for example, a characteristic diagram as shown in FIG. 5 is calculated as a map. This map shows the value of Fkpo (| θ |) with (| θ | −θpk) / θpk as the horizontal axis. Therefore, the smaller the limit steering angle θpk is, the more sensitive the steering limit correction amount Kpo is to the steering angle absolute value | θ |, and the smaller the limit steering angle θpk is, the smaller the friction coefficient of the road surface is. As the road surface becomes smaller, a larger steering limit correction amount can be obtained for smaller steering. Here, the steering limit determination end offset θofofs and the steering limit determination start offset θonofs are offset values that set a control margin, and may be the same value or 0.
[0039]
As described above, by repeating this routine, the peak point of the road surface reaction torque is detected in the block of ST1, and the absolute value of the steering angle when the road surface reaction torque is determined to be the peak in the block of ST2. | Θ | is detected as the limit steering angle θpk. In the block of ST3, the steering limit is determined by adding the steering limit determination end offset θofofs and the steering limit determination start offset θonofs to the limit steering angle θpk. , The steering limit correction amount Kpo is determined. As described above, the steering limit determining unit 36 has a function as a road surface reaction torque peak point detecting unit, a unit for setting a margin for the road surface reaction force torque, a steering limit determining unit, and a steering limit correction amount setting unit. Will be.
[0040]
Next, a method of calculating the required control amount by the required yaw moment calculating means 37 will be described with reference to FIG. In the figure, the road surface μ correcting means 50 inputs the target yaw rate γt obtained by the above formulas (4) and (5) and clips it to a value corresponding to the road surface friction coefficient μ, thereby obtaining an OS (oversteer). Target yaw rate γto is calculated. A subtractor 51 calculates a difference between the target yaw rate γt and the actual yaw rate γ, calculates a deviation γer0u of US (understeer), and a subtractor 52 calculates a difference between the actual yaw rate γ and the target yaw rate γto for the OS. Is calculated. Subsequently, the turning direction code conversion units 53a and 53b receive the deviation γer0u for the US and the deviation γer0o for the OS, respectively, perform sign processing, and convert the deviation γeru for the US and the deviation γero for the OS.
[0041]
In the case of the US deviation γeru, this sign processing reverses the sign of γer0u during a left turn where the actual yaw rate becomes negative when the yaw rate during a right turn is positive, and when the actual yaw rate is positive ( (Right turn) does not reverse. On the other hand, in the case of the OS deviation γero, the sign of γer0o is inverted when the actual yaw rate is positive, and is not inverted when the actual yaw rate is negative. In this way, when the absolute value of the actual yaw rate of the vehicle is smaller than the absolute value of the target yaw rate, regardless of the turning direction, the US deviation γeru is set to be positive when the vehicle is under-steering, and , The OS deviation γero is set to be positive.
[0042]
The US deviation γeru and the OS deviation γero are input to the PD controllers 54a and 54b, respectively. The PD controllers 54a and 54b multiply the US deviation γeru and the OS deviation γero by the gains Krpu and Krpo in the gain multipliers 55a and 55b, and the differentiators 56a and 56b use the US deviation γeru and the OS deviation γeru. Time derivative of the deviation γero. Further, the time-differentiated deviations are multiplied by gains Krdu and Krdo by gain multipliers 57a and 57b, respectively, and the outputs of gain multipliers 55a and 55b and the outputs of gain multipliers 57a and 57b are respectively added to adders 58a and 58b. 58b, and the respective suppression request yaw moments Mu and Mo are obtained.
[0043]
That is, each of the suppression request yaw moments (request control amounts) Mu and Mo is
Mu = Krpu × γeru + Krdu × (dγeru / dt) (6)
Mo = Krpo × γero + Krdo × (dγero / dt) (7)
Is required. Here, the gains Krpu and Krdu, and Krpo and Krdo are gain coefficients read from a map set in advance based on the vehicle speed Vb, the steering angle θ of the steering wheel, the angular speed dθ of the steering wheel, and the lateral acceleration Gy.
[0044]
The steering multiplier correction amount Kpo calculated by the steering limit determining means 36 is input to the gain multipliers 55a and 57a of the US deviation PD controller 54a, and the gain coefficients Krpu and Krdu are determined by the steering limit correction amount Kpo. Are also changed in size. For example, when the steering limit correction amount Kpo is 0.5, Krpu and Krdu each have a value of 1 + 0.5 = 1.5 times. Also, the weighting of the steering limit correction amount Kpo of Krpu and Krdu can be individually set. When the weighting factors are 1.0 and 1.2, respectively, Krpu is 1 × (1 + 0.5) = 1. Five times, Krdu becomes 1.2 × (1 + 0.5) = 1.8 times.
[0045]
Here, since the steering limit correction amount Kpo is reflected only in the calculation of the US suppression request moment Mu, the correction based on the steering limit determination is performed only in the case of understeering, and the gain coefficient is changed in a direction in which the gain coefficient increases. Therefore, it acts in a direction to further suppress understeering of the vehicle. The US suppression request moment Mu is also input to the control start / end determination means 38, and is also used for the determination of the start / end of the US suppression control, so that it also acts in the direction in which the start of the US suppression control is performed earlier. Therefore, the turning motion is promoted, and the turning performance can be improved.
[0046]
The detection of the peak value of the road reaction torque will be described below with reference to FIGS. 7 and 8. FIG. 7 shows the relationship between the cornering force and the self-aligning torque with respect to the side slip angle βf of the wheel (tire). When the side slip angle βf of the wheel is near zero, both the cornering force and the self-aligning torque increase with the increase of βf, but the self-aligning torque shows a peak value when βf = βft, and the value of βf increases beyond βft. It will decrease. When the value of βf is near βft, the cornering force increases almost in proportion to the value of βf. When the value of βf increases to βfc, the cornering force becomes saturated.
[0047]
The force that returns the steering wheel from the road surface to the steering system, i.e., the relationship between the road surface reaction torque Treact and the steering angle θ, is determined by the side slip angle βf when the cornering force is in the linear range and the vehicle exhibits the US characteristics. Since the steering angle θ is substantially proportional to the steering angle θ, the result is as shown in FIG. In the vicinity of the peak value of the road surface reaction torque Treact, the cornering force is in the linear range, and the correction based on the steering limit determination is performed only in the case of the understeering, so that the control can be performed according to the relationship of FIG.
[0048]
Since the road surface reaction torque Treact is a moment around the kingpin, the shape of the characteristic is different from that of the wheel self-aligning torque, but the peak point is generated when the side slip angle βf = βft is substantially the same, and is increased to βft or more. It will decrease. Therefore, the peak steering angle θpk0 obtained by the steering limit determination means 36 is the steering angle when the side slip angle is βft. The road surface reaction torque Treact at the side slip angle βfc at which the cornering force is saturated is determined by the values of the pneumatic trail and the caster trail when the side slip angle βf is substantially zero.
[0049]
Accordingly, the margin of the steering limit determination with respect to the cornering force saturation point is determined by determining how much the road surface reaction torque is reduced with respect to the road surface reaction torque peak value Treacpk set by the steering limit determination unit 36 as the limit steering angle. It can be set according to the characteristics of the vehicle by the coefficient Krt that determines whether to do so. For example, when the pneumatic trail and the caster trail when the sideslip angle βf is substantially 0 are set to be substantially the same, the road surface reaction force torque Treact at the sideslip angle βfc is substantially half of the road surface reaction force torque peak value Treakpk. Value.
[0050]
From the above, if the coefficient Krt is set to around 0.5, it can be set so that the determination of the steering limit is not performed until immediately before the cornering force is saturated. Also, the road surface reaction torque peak value Treapkk changes depending on the friction coefficient of the road surface. However, the road surface reaction force torque peak value Treapkk is obtained by determining whether the measured value of the road surface reaction force torque is increased or decreased with respect to the increase or decrease of the steering angle. In the determination of the steering limit, a predetermined ratio to the road surface reaction force torque peak value Treapk is set as a threshold value, so that stability can be obtained without depending on the road surface friction coefficient.
[0051]
【The invention's effect】
As described above, according to the turning control device for a vehicle of the present invention, the steering angle detecting means for detecting the steering angle of the vehicle, the vehicle motion state detecting means for detecting the turning motion of the vehicle, and the vehicle based on the steering angle Target vehicle motion setting means for setting a target turning motion ofA road reaction torque detecting means for detecting a road reaction torque received by the steered wheels of the vehicle from a road surface; a road surface reaction in which the absolute value of the road reaction torque changes from an increase to a decrease with an increase in the absolute value of the steering angle; A steering limit determination that detects a force torque peak point and determines that the steering angle is a steering limit when the absolute value of the steering angle is greater than the absolute value of the steering angle at the road surface reaction torque peak point or at a value lower than the peak value by a predetermined ratio. Means, turning motion control means for controlling the turning motion of the vehicle from the detection result of the vehicle motion state detecting means and the set value of the target vehicle motion setting means,When the steering limit determining unit determines that the steering limit is reached, the turning motion control unit changes the control content in a direction that promotes the turning motion, so that it is easy to determine that the steering angle has reached near the limit. In addition, it is possible to reliably detect, and it is possible to improve the turning performance of the vehicle by detecting that the steering angle has reached the vicinity of the limit.
[0054]
Further, the steering limit determination method according to the present invention includes:Road surface reaction torque calculated from each measured value of steering torque, motor current and motor acceleration,Detecting the peak point of the road surface reaction torque where the absolute value of the road surface reaction torque changes from an increase to a decrease with respect to the increase in the absolute value of the steering angle,The absolute value of the road surface reaction torque at the peak point of the road surface reaction torque or the absolute value of the steering angle at the absolute value of the road surface reaction torque at a value lower by a predetermined ratio than the absolute value is set as a limit steering angle, and the steering angle is set. When the absolute value of the steering angle exceeds the limit steering angle, it is determined that the steering limit is reached, and the control content is changed in a direction that promotes the turning motion.Therefore, it is possible to easily and accurately detect that the steering angle has reached the vicinity of the limit.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of a vehicle turning control device according to Embodiment 1 of the present invention.
FIG. 2 is a block diagram illustrating an operation of an ECU of the vehicle turning control device according to the first embodiment of the present invention.
FIG. 3 is a block diagram of an electric power steering device used in the vehicle turning control device according to the first embodiment of the present invention;
FIG. 4 is a flowchart illustrating an operation of a steering limit determination method according to the first embodiment of the present invention.
FIG. 5 is a characteristic diagram of a steering limit correction amount used in the steering limit determination method according to the first embodiment of the present invention.
FIG. 6 is a block diagram of a required yaw moment calculating means of the vehicle turning control device according to the first embodiment of the present invention;
FIG. 7 is a characteristic diagram showing a relationship between a side slip angle of a tire and a cornering force of the turning control device for a vehicle according to the first embodiment of the present invention.
FIG. 8 is a characteristic diagram illustrating a relationship between a steering angle and a road surface reaction torque of the turning control device for a vehicle according to the first embodiment of the present invention.
FIG. 9 is a block diagram showing a conventional vehicle turning control device.
FIG. 10 is a block diagram showing a conventional vehicle turning control device.
FIG. 11 is a characteristic diagram illustrating a conventional vehicle turning control device.
FIG. 12 is a characteristic diagram illustrating a conventional vehicle turning control device.
[Explanation of symbols]
23 ECU, 24 steering angle sensor (steering angle detecting means),
25 yaw rate sensor, 26 lateral acceleration sensor,
27 M / C pressure sensor, 28 wheel speed sensor,
29 road surface reaction torque detecting means, 30 hydraulic unit,
31 master cylinder, 34 vehicle motion state detecting means,
35 target vehicle motion setting means, 36 steering limit determining means,
37 required yaw moment calculation means, 38 control start / end determination means,
39 braking force adjustment amount calculation means, 40 slip controller,
41 steering torque detecting means, 42 motor, 43 motor speed detecting means,
44 motor acceleration detecting means, 45 motor current determining means,
46 motor current detecting means, 48 motor driving means,
50 road surface μ correction means, 53a, 53b turning direction code conversion unit,
54a, 54b PD controller,
55a, 55b, 57a, 57b gain multiplier,
56a, 56b Differentiator, 58a, 58b Adder.

Claims (4)

Steering angle detecting means for detecting a steering angle of the vehicle, vehicle motion state detecting means for detecting a turning motion of the vehicle, target vehicle motion setting means for setting a target turning motion of the vehicle from the steering angle , and steered wheels of the vehicle Road surface reaction torque detecting means for detecting a road surface reaction torque received from the road surface, a road surface reaction torque peak point at which the absolute value of the road surface reaction torque turns from an increase to a decrease with respect to an increase in the absolute value of the steering angle. A steering limit determining means for detecting, when the absolute value of the steering angle is greater than the absolute value of the steering angle at the peak value of the road reaction torque or at a value lower by a predetermined ratio than the peak value, the steering limit determining means; comprising a turning motion controlling means for controlling the detection result and the turning movement of the vehicle from a set value of the target vehicle motion setting means state detecting means, the steering limit decision means steering limit When it is determined that it is, the turning motion control means for a vehicle turning control device, characterized in that to change the control contents in the direction that promotes turning motion. The turning motion control means inputs the outputs from the vehicle motion state detecting means, the target vehicle motion setting means, and the steering limit determining means and receives a required control amount (Mu). , Mo) calculating means for calculating the required control amount (Mu). , Mo), control start / end determination means for determining the start and end of the vehicle turning motion, and determining whether to perform under-steering suppression control or over-steering suppression control; 2. A brake force adjustment amount calculating means for calculating, wherein an increase / decrease rate of the brake fluid pressure of each wheel is set for each wheel, and the braking force is distributed to each wheel according to the set rate. Turning control device for vehicles. The steering device is an electric power steering device, and includes a steering torque detection unit, a motor current detection unit, and a motor acceleration detection unit. The road surface reaction torque is obtained by multiplying the steering torque value and the motor current by a torque constant. The turning control device for a vehicle according to claim 1, wherein the turning control device is calculated from the calculated value and a rotational acceleration of the motor. The steering angle of the vehicle, the road surface reaction torque received by the steered wheels of the vehicle from the road surface, and the road surface reaction torque at which the absolute value of the road surface reaction torque changes from an increase to a decrease with an increase in the absolute value of the steering angle. A peak point of the road surface reaction torque, and limits an absolute value of the steering angle at an absolute value of the road surface reaction torque at a peak point of the road surface reaction torque or a predetermined ratio lower than the absolute value of the road surface reaction force torque. Setting a steering angle, determining that the steering limit is reached when the absolute value of the steering angle exceeds the limit steering angle, and changing the control content in a direction that promotes the turning motion. Judgment method.

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