JP2006224936A - System for controlling vehicle posture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle posture control system for optimizing turnability. <P>SOLUTION: The vehicle posture control system 2 includes: a right and left torque transmission control part 4 for transmitting a driving torque to right and left drive wheels 18; and a variable steering ratio control part 6 for varying a steering ratio between the steering wheel angle of a steering wheel 20 and the steering angle of front wheels 14. When the steering characteristic of the vehicle 10 is understeering, the right and left torque transmission control part 4 performs understeering control to increase a driving torque difference between the right and left drive wheels 18. The variable steering ratio control part 6 controls the steering ratio, based on the driving torque difference between the right and left drive wheels 18. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle control system that controls the attitude of a vehicle.

  Conventionally, a left and right torque transmission control device has been used to transmit drive torque according to a vehicle state to left and right drive wheels (see Patent Document 1). In such a left-right torque transmission control device, for example, when the vehicle's steer characteristic is understeer on a low μ road or the like, the understeer is set so that the driving torque of the turning outer drive wheel is larger than the driving torque of the turning inner drive wheel in order to eliminate the understeer. Implement control. Conversely, when the vehicle's steer characteristic becomes oversteer, oversteer control is performed in which the drive torque of the turning inner drive wheel is larger than the drive torque of the turning outer drive wheel to eliminate the oversteer. Such control can improve the turning performance of the vehicle.

  Conventionally, a variable steering ratio control device has been used to vary the steering ratio between the steering wheel angle of the steering wheel and the turning angle of the steering wheel in accordance with the vehicle state (see Patent Document 2). In such a variable steering ratio control device, for example, by performing quick control to make the steering response quick by making the turning angle relatively large with respect to the steering wheel angle, the turning performance of the vehicle can be improved. Conversely, by performing slow control that makes the steering angle relatively small with respect to the steering wheel angle and slows down the steering response, it is possible to improve the stability of the vehicle particularly during high-speed traveling.

JP 2004-52901 A JP 2003-32049 A

  In recent years, attitude control using both a left-right torque transmission control device and a variable steering ratio control device is being performed on a vehicle. However, in the technologies that have been considered so far, the left / right torque transmission control device and the variable steering ratio control device are operated independently. .

  For example, in the situation where the drive torque difference between the left and right drive wheels is large in order to eliminate understeer by the left and right torque transmission control device, when the variable steering ratio control device quick control is performed, the steered wheels are actually There is a risk that the vehicle may become uncontrollable if it is cut more than the turning angle at which it can turn.

Also, in vehicles equipped with a conventional variable steering ratio control device and not equipped with a left / right torque transmission control device, if understeer occurs during turning due to insufficient grip force on the steering wheel, slow control is performed and The turning angle of the steered wheels is not made larger than the radius at which the vehicle can turn. This control is important for ensuring vehicle stability when the gripping force of the steered wheels is restored. However, in a vehicle equipped with a variable steering ratio control device and a left and right torque transmission control device, understeering by the left and right torque transmission control device is sufficiently possible to eliminate understeering, that is, driving between the left and right drive wheels. If the slow control of the variable steering ratio control device is performed under a situation where the torque difference is small, the steered wheel is difficult to cut, and the effect of improving the turning performance by the understeer control is halved.
The present invention has been made in view of the above-described problems, and an object thereof is to provide a vehicle attitude control system that optimizes turning performance.

According to the first aspect of the present invention, a left / right torque transmission control unit that transmits drive torque to the left / right drive wheels, and a variable steering ratio that makes the steering ratio between the steering wheel steering angle and the steering wheel turning angle variable. A vehicle attitude control system including a control unit, wherein the left and right torque transmission control unit performs understeer control to increase a drive torque difference between the left and right drive wheels when the steering characteristic of the vehicle is understeer, The variable steering ratio control unit controls the steering ratio based on a driving torque difference between the left and right driving wheels. The drive torque difference between the left and right drive wheels is increased by the left and right torque transmission control device when the vehicle's steering characteristic becomes understeer, so that the drive torque difference can be eliminated by the left and right torque transmission control device (hereinafter referred to as “understeer”). "The room for canceling understeer by the left and right torque transmission control device" is simply referred to as "the room for canceling understeer"). The variable steering ratio control unit controls the steering ratio between the steering wheel angle and the turning angle based on the difference in driving torque as such an indicator. It becomes possible to obtain.
The “steering ratio” means the relative ratio of the steering wheel angle to the steering angle (steering angle / cutting angle), as is generally well known.

  According to a second aspect of the present invention, a drive torque difference between the left and right drive wheels or a value correlated with the drive torque difference is supplied to the variable steering ratio control unit. The variable steering ratio control unit can directly recognize the magnitude of the room for resolving understeer by directly supplying the drive torque difference between the left and right drive wheels or the correlation value thereof from the left and right torque transmission control unit. Therefore, the turning effect optimization effect can be enhanced.

  According to a third aspect of the present invention, the variable steering ratio control unit sets the target value of the steering ratio by correcting a reference value of the steering ratio based on a driving torque difference between the left and right driving wheels. And an actuator for making the steering ratio coincide with the target value by changing the turning angle relative to the steering wheel angle. Since the target value for the actuator that changes the turning angle relative to the steering wheel angle is obtained by correcting the reference value of the steering ratio based on the drive torque difference between the left and right drive wheels, the target value is The value reflects the room for resolving understeer. Therefore, when the steering characteristic of the vehicle is understeer, the steering ratio is matched with the target value by the actuator, so that it is possible to realize the optimum turning performance.

  According to a fourth aspect of the present invention, when the drive torque difference between the left and right drive wheels is greater than or equal to a threshold value, the correction means increases the target value more than when the drive torque difference is less than the threshold value. Set. In other words, when the drive torque difference between the left and right drive wheels is greater than or equal to the threshold value, that is, when the room for eliminating understeer is small, the target value is when the drive torque difference is less than the threshold value, that is, when the room for eliminating understeer is large. It is set larger than the target value. Therefore, when the room for understeer cancellation becomes small during the understeer control of the left and right torque transmission control unit, the steering ratio is increased to match the target value. As a result, the turning angle becomes relatively small with respect to the steering wheel angle, so that a situation in which the vehicle becomes uncontrollable due to excessive turning of the steering wheel can be prevented. On the other hand, if there is sufficient room for understeer elimination during the understeer control of the left and right torque transmission control unit, the steering ratio is made to coincide with the target value and decreases. As a result, the turning angle becomes relatively large with respect to the steering wheel angle, so that the turning of the steering wheel can be assisted and high turning performance can be obtained. For example, the steering handle operating burden when turning right or left at the intersection is reduced. be able to.

  According to a fifth aspect of the present invention, the correction means includes a reference gain setting means for setting a reference gain larger as the understeer of the vehicle becomes stronger, and a drive torque difference between the left and right drive wheels is equal to or greater than a threshold value. While setting the reference gain as a correction gain, a correction gain setting means for setting a correction gain smaller than the reference gain when the drive torque difference is less than the threshold, and the correction set by the correction gain setting means Target value setting means for setting the target value by multiplying the reference value by a gain.

  Thus, in the invention according to claim 5, when the difference between the driving torques of the left and right driving wheels is less than the threshold value, that is, when there is a large room for eliminating the understeer, the driving gain difference is equal to or more than the threshold value. In other words, it is set to be smaller than a reference gain that is used as a correction gain when there is little room for canceling understeer. Therefore, the target value of the steering ratio obtained by multiplying the correction gain by the reference value increases when the room for understeer cancellation decreases, and conversely decreases when the room increases. For this reason, if the room for understeer cancellation becomes small during the understeer control of the left and right torque transmission control unit, the turning angle is made relatively small with respect to the steering wheel angle so that the steered wheels are not overcut. it can. On the other hand, if there is sufficient room for understeer removal during the understeer control of the left and right torque transmission control unit, the turning angle can be made relatively large with respect to the steering wheel angle to assist the turning of the steered wheels. .

  Furthermore, in the invention described in claim 5, the reference gain is set to be larger as the understeer of the vehicle becomes stronger. Therefore, by multiplying the reference value by a correction gain using the reference gain as it is, the reference gain is increased as the understeer becomes stronger. A target value can be acquired. Therefore, when the understeer becomes strong in a state where there is little room for eliminating the understeer, the steering ratio is made to coincide with the target value that increases following the strength, so that the steering wheel can be sufficiently prevented from being broken.

  According to the invention described in claim 6, when the drive torque difference between the left and right drive wheels is greater than or equal to a threshold value, the correction means sets the correction gain larger than when the drive torque difference is less than the threshold value. Correction gain setting means; and target value setting means for setting the target value by multiplying the reference value by the correction gain set by the correction gain setting means.

  Thus, in the invention described in claim 6, when the difference in driving torque between the left and right driving wheels is greater than or equal to the threshold value, that is, when the room for eliminating the understeer is small, the correction gain is less than the threshold value. In other words, it is set larger than the correction gain when there is a large room for understeer elimination. Therefore, the target value of the steering ratio obtained by multiplying the correction gain by the reference value increases when the room for understeer cancellation decreases, and conversely decreases when the room increases. For this reason, if the room for understeer cancellation becomes small during the understeer control of the left and right torque transmission control unit, the turning angle is made relatively small with respect to the steering wheel angle so that the steered wheels are not overcut. it can. On the other hand, if there is sufficient room for understeer removal during the understeer control of the left and right torque transmission control unit, the turning angle can be made relatively large with respect to the steering wheel angle to assist the turning of the steered wheels. .

  According to the seventh aspect of the present invention, the reference value is stored in the correction means as a value correlated with the vehicle speed. Since the target value for the actuator is obtained by correcting a reference value that correlates with the vehicle speed, it is possible to change the steering ratio matched with the target value in accordance with the vehicle speed. Therefore, for example, at low speeds, the steering ratio is controlled so that the turning angle is relatively large with respect to the steering wheel angle to improve turning performance. Conversely, at high speeds, the turning angle is relatively high with respect to the steering wheel angle. It is possible to improve the stability by controlling the steering ratio so as to decrease.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a four-wheel drive vehicle 10 to which a vehicle attitude control system 2 according to a first embodiment of the present invention is applied.

First, the vehicle 10 will be described.
In the vehicle 10, torque output from a power source 11 such as an internal combustion engine or an electric motor is transmitted to the left and right front wheels 14 via the transaxle 12, thereby driving each front wheel 14. The output torque of the power source 11 is transmitted to the left and right rear wheels 18 via the transaxle 12, the propeller shaft 15, the front and rear torque transmission control device 16 and the left and right torque transmission control device 4 of the vehicle attitude control system 2 in order. Thereby, each rear wheel 18 is driven. Here, the torque distribution ratio between the front wheel 14 and the rear wheel 18 is determined by the operating state of the front-rear torque transmission control device 16, and the torque distribution ratio between the left rear wheel 18 and the right rear wheel 18 is the left-right torque. It depends on the operating state of the transmission control device 4. The front-rear torque transmission control device 16 adjusts the engagement force of the built-in clutch, so that only the front wheel 14 is moved from a complete four-wheel drive state in which the torque of the power source 11 is equally distributed to the front and rear wheels 14, 18. It is a device that switches to a two-wheel drive state in which the vehicle 10 is driven according to the traveling state of the vehicle 10.

  In the vehicle 10, the rotational motion given to the steering handle 20 by the driver is transmitted to the steering gear 24 via the first steering shaft 21, the variable steering ratio control device 6 of the vehicle attitude control system 2, and the second steering shaft 22. Communicated. The rotational motion transmitted to the steering gear 24 is converted into a linear motion of the tie rod 25 by the steering gear 24. The left and right front wheels 14 connected to the tie rod 25 via the knuckle arm 26 are cut to the left and right following the reciprocating linear motion of the tie rod 25.

  Next, the vehicle attitude control system 2 including the left / right torque transmission control device 4 and the variable steering ratio control device 6 will be described. In the following description, “electronic control unit” is abbreviated as “ECU”.

The left and right torque transmission control device 4 includes a transmission control mechanism unit 30, a transmission control circuit unit 32, and the like.
The transmission control mechanism unit 30 includes a differential mechanism 35 interposed between the left and right rear axles 34 that rotate integrally with the left and right rear wheels 18 and the front and rear torque transmission control device 16, and an electric motor 36 including a DC motor and the like. have. The differential mechanism 35 is configured by combining a plurality of gears, for example, as shown in FIG. 2 in order to produce a differential between the left and right rear axles 34, and the input torque from the front-rear torque transmission control device 16 is output torque of the electric motor 36. Output to the left and right rear axles 34 at a distribution ratio according to Tm. That is, in the transmission control mechanism unit 30, the driving torque Td of each rear wheel 18 changes according to the output torque Tm of the electric motor 36.

  As shown in FIG. 1, the transmission control circuit unit 32 includes a drive circuit 37 composed of a bridge circuit or the like, and an ECU 38 composed of a microcomputer or the like. The ECU 38 controls the supply current Cm supplied to the electric motor 36 by the drive circuit 37 based on the traveling state of the vehicle 10, thereby changing the output torque Tm of the electric motor 36 and consequently the driving torque Td of each rear wheel 18. Hereinafter, details of control by the ECU 38 will be described.

FIG. 3 schematically shows the contents of control by the ECU 38 in a functional block diagram. As shown in the figure, in the lead control process 40, a lead control target torque Tmol for improving control responsiveness is calculated based on the steering wheel angle θh, the steering speed Vh, and the vehicle speed Vc of the steering handle 20. The handle angle θh is a value given to the ECU 38 from a rotation angle sensor that detects the rotation angle of the first steering shaft 21 that rotates together with the steering handle 20. The steering speed Vh is a value obtained by differentiating the steering wheel angle θh with time by the ECU 38. Furthermore, the vehicle speed Vc is based on the output value of a wheel speed sensor that detects the rotational speed Vt of each of the wheels 14 and 18 (hereinafter, “the rotational speed Vt of each of the wheels 14 and 18” is simply referred to as “wheel speed Vt”). This is a value given to the ECU 38 from the ECU for calculating the vehicle speed Vc.
In the straight safety control process 41, a straight safety control target torque Tmos for improving the straight running stability of the vehicle 10 by limiting the differential between the left and right rear axles 34 is calculated based on the steering wheel angle θh and the vehicle speed Vc. To do.

In the yaw rate control process (hereinafter, “yaw rate control” is abbreviated as “YR control”) 42, a YR control target for improving turning performance based on the steering wheel angle θh, the vehicle speed Vc, the yaw rate Y, and the accelerator opening degree O. Torque Tmoy is calculated.
Specifically, first, in the vehicle model calculation process 43, the vehicle model is calculated based on the steering wheel angle θh and the vehicle speed Vc, and the target yaw rate Yo is calculated.

  In the next steer characteristic determination process 44, the steer characteristic of the vehicle 10 is determined based on the target yaw rate Yo calculated in the vehicle model calculation process 43 and the yaw rate Y given from the yaw rate sensor to the ECU 38, and the determination result is expressed. A steer characteristic index Nys is calculated. Specifically, when the target yaw rate Yo is smaller than the actual yaw rate Y, it is determined that the steering is oversteer, and the steer characteristic index Nys is set to a larger positive value as the oversteer becomes stronger. Further, when the target yaw rate Yo is larger than the actual yaw rate Y, it is determined as understeer, and the steer characteristic index Nys is set to a smaller negative value as the understeer becomes stronger. Furthermore, when the target yaw rate Yo is substantially equal to the actual yaw rate Y, it is determined that the vehicle is neutral steer, and the steer characteristic index Nys is set to zero.

  In addition, when the accelerator opening degree O becomes excessive when the vehicle 10 turns, the steering characteristic of the vehicle 10 tends to be understeer. Therefore, in the steering characteristic determination process 44 of the present embodiment, the steering characteristic index Nys is a positive value even when the accelerator opening degree O given from the accelerator sensor to the ECU 38 at the time of turning determined from the yaw rate Y is equal to or greater than the threshold value Oth. Set to.

  In the subsequent target torque calculation process 45, the YR control target torque Tmoy is calculated based on the steer characteristic index Nys calculated in the steer characteristic determination process 44. More specifically, when the steering characteristic index Nys is a positive value, the drive torque Tdi of the turning inner rear wheel 18 increases and the driving torque Tdo of the turning outer rear wheel 18 decreases as the value increases. The YR control target torque Tmoy is set. Further, when the steer characteristic index Nys is a negative value, the YR control is performed so that the drive torque Tdo of the outer turning rear wheel 18 increases and the driving torque Tdi of the inner turning rear wheel 18 decreases as the value decreases. A target torque Tmoy is set. Furthermore, when the steering characteristic index Nys is 0, the YR control target torque Tmoy is set so that the driving torque Td of each rear wheel 18 is maintained as it is.

  The target torques Tmol, Tmos, and Tmoy calculated in the above lead control process 40, direct safety control process 41, and YR control process 42 are superimposed and calculated in the command torque calculation process 46, whereby the command for the output torque Tm of the electric motor 36 is calculated. Torque Tmo is calculated. In the command current calculation process 47, the command torque Tmo calculated in the command torque calculation process 46 is converted into a command current Cmo for the supply current Cm to the electric motor 36, and this command current Cmo is given to the drive circuit 37. As a result, the supply current Cm is matched with the command current Cmo, so that the output torque Tm of the electric motor 36 is controlled to match the command torque Tmo. Therefore, for example, when the determination result in the steer characteristic determination process 44 is understeer, the drive torque Td of the outer wheel 18 outside the turn is more than the inner rear wheel 18 by the command torque Tmo reflecting the YR control target torque Tmoy. Increases, and the drive torque difference ΔTd between the wheels increases. In this case, since the rotational speed of the rear outer wheel 18 is higher than the rotational speed of the rear inner wheel 18, the steering characteristic of the vehicle 10 moves toward the neutral steer side where the understeer is eliminated.

  Further, the command torque Tmo calculated in the command torque calculation process 46 is used in the drive torque difference calculation process 48. Specifically, in the drive torque difference calculation process 48, the drive torque difference ΔTd between the left and right rear wheels 18 realized by matching the output torque Tm of the electric motor 36 with the command torque Tmo reflecting the control target torque Tmoy. Is estimated and calculated based on the command torque Tmo. Then, the calculated drive torque difference ΔTd is supplied to the variable steering ratio control device 6. Here, the driving torque difference ΔTd is a value represented by a difference (Tdo−Tdi) between the driving torque Tdo of the rear outer wheel 18 and the driving torque Tdi of the inner rear wheel 18.

As shown in FIG. 1, the variable steering ratio control device 6 includes a variable control mechanism unit 50, a variable control circuit unit 52, and the like.
The variable control mechanism 50 includes a gear mechanism 53 interposed between the steering shafts 21 and 22 and an electric motor 54 including a three-phase brushless motor. In addition to the steering wheel angle θh of the steering handle 20 input from the first steering shaft 21, the gear mechanism 53 reduces the rotational angle θm of the electric motor 54 by reducing the rotational angle θm with the mechanical gear ratio Gvm inherent to the gear mechanism 53. Transmission to the two steering shafts 22. That is, the gear mechanism 53 outputs to the second steering shaft 22 a rotation angle (θh + Gvm · θm) obtained by adding a multiplication value of the mechanical gear ratio Gvm and the rotation angle θm to the handle angle θh. Therefore, the apparent gear ratio Gv between the input and output of the gear mechanism 53 can be expressed by (1 + Gvm · θm / θh). Therefore, the turning angle θt of the front wheel 14 is a value θh · Gv · Gs obtained by multiplying the apparent gear ratio Gv of the gear mechanism 53 and the gear ratio Gs of the steering gear 24 by the steering wheel angle θh, that is, (θh + Gvm · θm). ) · Gs. Therefore, in the present embodiment, the steering ratio R, which is the relative ratio (θh / θt) of the steering wheel angle θh to the turning angle θt, changes according to the rotation angle θm of the electric motor 54. Here, each gear ratio Gvm, Gv, Gs is a value represented by a relative ratio of output to input (output / input).

  The variable control circuit unit 52 includes a drive circuit 55 formed of a bridge circuit or the like and an ECU 56 formed of a microcomputer or the like. The ECU 56 changes the rotation angle θm of the electric motor 54 and consequently the steering ratio R by controlling the current Im supplied to the electric motor 54 by the drive circuit 55 based on the traveling state of the vehicle 10. Hereinafter, the control content by ECU56 is demonstrated in detail.

FIG. 4 schematically shows the contents of control by the ECU 56 in a functional block diagram. As shown in the figure, in the lead steer control process (hereinafter, “lead steer control” is abbreviated as “LS control”) 60, the LS control target angle θmol for improving the control responsiveness is set to the steering speed Vh and the vehicle speed. Calculated based on Vc. The steering speed Vh is a value obtained by time-differentiating the steering wheel angle θh given from the rotation angle sensor of the first steering shaft 21 to the ECU 56 by the ECU 56. The vehicle speed Vc is a value given to the ECU 56 from the ECU that calculates the vehicle speed Vc described above.
In the turning angle calculation process 61, the turning angle θt of the front wheel 14 is calculated based on the steering wheel angle θh and the rotation angle θm of the electric motor 54. The rotation angle θm is a value given to the ECU 56 from a rotation angle sensor built in the electric motor 54.

  In the intelligent front steering control process (hereinafter, “intelligent front steering control” is abbreviated as “IFS control”) 62, the IFS control target angle θmoi and the correction gain Κu for optimizing the turning performance of the vehicle 10 are Is calculated based on the plurality of state quantities. Here, the plurality of state quantities are a drive torque difference ΔTd, a cutting angle θt of the front wheel 14, a steering wheel angle θh, a vehicle speed Vc, a wheel speed Vt, a yaw rate Y, a lateral acceleration LA, a brake state value B, and a slip angle θs. is there. The drive torque difference ΔTd is a value calculated by the drive torque difference calculation process 48 and given from the ECU 38 of the left / right torque transmission control device 4 to the ECU 56. Further, the turning angle θt is a value calculated by the turning angle calculation processing 61, and the wheel speed Vt, the yaw rate Y, the lateral acceleration LA, and the brake state value B are the wheel speed sensor, the yaw rate sensor, the lateral acceleration sensor, and the brake. This is a value given from the sensor to the ECU 56. Furthermore, the slip angle θs is a value given to the ECU 56 from the ECU that calculates the slip angle θs based on the output values of the yaw rate sensor and the lateral acceleration sensor.

  In the variable gear ratio control process (hereinafter, “variable gear ratio control” is abbreviated as “VGR control”) 63, the cut angle θt calculated in the cut angle calculation process 61 and the correction gain Κu calculated in the IFS control process 62 are displayed. Based on the steering wheel angle θh and the vehicle speed Vc, the VGR control target angle θmov for making the apparent gear ratio Gv of the gear mechanism 53 variable is calculated.

In the command angle calculation process 64, the target angles θmol, θmoi, and θmov calculated in the control processes 60, 62, and 63 of LS, IFS, and VGR are overlapped to calculate the command angle θmo with respect to the rotation angle θm of the electric motor 54. Is calculated.
In a feedforward control process (hereinafter “feedforward control” is abbreviated as “FF control”) 65, an FF control target current Imov is calculated based on the command angle θmo calculated in the command angle calculation process 64. In the feedback control process (hereinafter, “feedback control” is abbreviated as “FB control”) 66, the command angle θmo calculated in the command angle calculation process 64 and the rotation fed back from the rotation angle sensor of the electric motor 54. The FB control target current Imob is calculated based on the angle θm. In the command current calculation process 67, the command current Imo with respect to the supply current Im to the electric motor 54 is calculated by superimposing the target currents Imov and Imob calculated in the FF and FB control processes 65 and 66, respectively. Since the supply current Im is matched with the command current Imo by the drive circuit 55 to which the command current Imo is applied, the rotation angle θm of the electric motor 54 is controlled so as to match the command angle θmo.

FIG. 5 is a functional block diagram showing the specific contents of the IFS control processing 62. As shown in the figure, in the crossing road determination processing 70, it is determined whether or not the vehicle 10 is in a braking state on the crossing road based on the turning angle θt, the vehicle speed Vc, the wheel speed Vt, and the brake state value B. Here, the crossing road means a traveling road in a μ split state in which the road surface resistance value μ is significantly different between the left wheels 14 and 18 side and the right wheels 14 and 18 side.
In the vehicle model calculation processing 71, a vehicle model is calculated based on the steering wheel angle θh and the vehicle speed Vc, and a target yaw rate Yo and a target slip angle θso are calculated.

  In the oversteer control process (hereinafter, “oversteer control” is abbreviated as “OS control”) 72, the yaw rate Y and slip angle θs and the state values target values Yo and θso calculated in the vehicle model calculation process 71 are used. Then, the feedback calculation regarding the yaw rate Y, the slip angle θs, and the yaw angle θy is performed to calculate the OS control target angle θmoo for eliminating the oversteer. Here, the feedback calculation related to the yaw angle θy is performed with the affirmative determination in the crossing path determination processing 70 as a trigger, as shown in FIG.

  In the steer characteristic calculation process 73, the steer characteristic of the vehicle 10 is determined based on the steering wheel angle θh, the vehicle speed Vc, the yaw rate Y, and the target yaw rate Yo calculated in the vehicle model calculation process 71, and the steer characteristic representing the determination result. The index Nis is calculated. Specifically, if the determination result is oversteer, the steer characteristic index Nis is set to a larger positive value as the oversteer becomes stronger. If the determination result is understeer, the steer characteristic index Nis is set to a smaller negative value as the understeer becomes stronger. Furthermore, when the determination result is neutral steer, the steer characteristic index Nis is set to zero.

  In an understeer control process (hereinafter, “understeer control” is abbreviated as “US control”) 74, a US control correction gain Κu and a US control target angle θmou for eliminating understeer while avoiding interference with the YR control process 42. Is calculated based on a plurality of state quantities of the vehicle 10. Here, the plurality of state quantities are given from the steering wheel angle θh and the steering speed Vh obtained by differentiating the steering wheel angle θh, the steering characteristic index Nis calculated by the steering characteristic calculation processing 73, and the left and right torque transmission control device 4. The driving torque difference ΔTd.

  Specifically, first, in the reference gain calculation process 75, the steer characteristic index Nis and the steering characteristic index Nis and the steering speed correlation index Nih and the reference gain map Mgb representing the correlation between the reference gain Κb are used. A reference gain Κb suitable for the steering speed correlation index Nih is calculated. Here, the reference gain map Mgb is a three-dimensional map as shown in FIG. 6, for example, stored in the ECU 56, and is configured to increase the reference gain Κb as the steering characteristic index Nis decreases. Thus, the reference gain Κb is set to a larger value as the understeer becomes stronger, especially when the determination result in the steer characteristic calculation process 73 is understeer. The steering speed correlation index Nih is positive when the steering direction of the steering wheel 20 estimated from the steering wheel angle θh is the cut-in side, and negative when the steering direction is the reverse side. It is added to the size. Therefore, as shown in FIG. 6, the reference gain Κb is set to be larger as the steering speed Vh is higher toward the cut-in side, and is set to be smaller as the steering speed Vh is higher toward the reverse side.

  In the next gain correction process 76, the correction gain map Mgcu representing the correlation among the drive torque difference ΔTd, the reference gain Κb, and the US control correction gain Κu is used, which is suitable for the drive torque difference ΔTd and the reference gain Κb at the time of execution of the process. The US control correction gain Κu is calculated. Here, the correction gain map Mgcu is a three-dimensional map as shown in FIG. 7 stored in the ECU 56, and is configured such that the US control correction gain Κu changes according to the drive torque difference ΔTd. As a result, when the drive torque difference ΔTd is equal to or greater than the threshold value ΔTdth, that is, when there is little room for canceling the understeer by the YR control process 42, the reference gain Κb is directly used as the US control correction gain Κu. Further, when the drive torque difference ΔTd is less than the threshold value ΔTdth, that is, when there is a large room for eliminating the understeer by the YR control process 42, the US control correction gain Κu is set to a value smaller than the reference gain Κb.

In the subsequent gain limiting process 77, the US control correction gain Κu calculated in the gain correction process 76 is limited according to the handle angle θh and output. Specifically, when the steering wheel angle θh does not reach the left and right critical angles θhl, the US control correction gain Κu is output as it is. When the steering wheel angle θh has reached the critical angle θhl, the US control correction gain Κu is reduced to a predetermined limit value Κul and output.
Further, in the gain conversion processing 78, the US control correction gain Κu after the gain limiting processing 77 is converted into the US control target angle θmou.

  The OS / US control selection process 79 selects which of the OS and US control processes 72 and 74 described above is reflected in the IFS control target angle θmoi based on a plurality of state quantities of the vehicle 10. Then, the selection flag F representing the selection result is set. Here, the plurality of state quantities are the vehicle speed Vc, the yaw rate Y, the lateral acceleration LA, and the steering characteristic index Nis calculated by the steering characteristic calculation process 73.

  In the target angle calculation process 80, the IFS control target angle is based on the target angles θmoo, θmou obtained in the OS and US control processes 72 and 74 and the selection flag F set in the OS / US control selection process 79. θmoi is calculated. Specifically, when the selection flag F is for selecting the OS control process 72, the OS control target angle θmoo is set as the IFS control target angle θmoi. If the selection flag F is for selecting the US control process 74, the US control target angle θmou is set as the IFS control target angle θmoi. Furthermore, when the selection flag F selects neither the control process 72 or 74 of OS and US, the IFS control target angle θmoi is set to 0.

  FIG. 8 is a functional block diagram showing the specific contents of the VGR control process 63. As shown in the figure, in the reference ratio calculation process 90, a reference steering ratio Rb suitable for the vehicle speed Vc at the time of processing is calculated using a reference ratio map Mrb representing the correlation between the vehicle speed Vc and the reference steering ratio Rb. . Here, the reference ratio map Mrb is a two-dimensional map as shown in FIG. 9 stored in the ECU 56, and is configured such that the reference steering ratio Rb increases as the vehicle speed Vc increases.

In the ratio correction process 91, the target steering ratio Ro is calculated by multiplying the US control correction gain Κu after the gain limiting process 77 by the reference steering ratio Rb calculated in the reference ratio calculation process 90. Here, the one-dot chain line and the two-dot chain line in FIG. 10 show examples of calculation of the target steering ratio Ro in the case of (I) and (II) below, and in the case of (I) below than the case of (II) below. It can be seen that the target steering ratio Ro is increased.
(I) Since the room for understeer elimination is small, the reference gain Κb following the understeer strength is set as the US control correction gain Κu in the gain correction processing 76, and the US control correction gain Κu in the gain limiting processing 77 Is output as is.
(II) Since the room for understeer elimination is large, the US control correction gain Κu is set smaller than the reference gain Κb in the gain correction processing 76, and the US control correction gain Κu is output as it is in the gain restriction processing 77. If.

In the target angle calculation process 92, the target steering ratio Ro calculated in the ratio correction process 91 is converted into a VGR control target angle θmov based on the steering wheel angle θh and the turning angle θt. Since the rotation angle θm of the electric motor 54 matches the command angle θmo reflecting the VGR control target angle θmov, for example, in the case of (I), the cutting angle θt follows the strength of the understeer. It is made relatively small with respect to the handle angle θh. Therefore, when the left and right torque transmission control device 4 advances YR control toward the understeer canceling state in a state where there is little room for canceling the understeer, it is possible to prevent a situation in which the vehicle 10 becomes uncontrollable due to the front wheel 14 being cut too much. it can. In the case of (II), the turning angle θt is relatively increased with respect to the steering wheel angle θh, so that the cutting of the front wheel 14 can be assisted. Therefore, when the left and right torque transmission control device 4 is advancing YR control to the understeer canceling side in a state where there is a large room for canceling understeer, a situation where the YR control is hindered by the US control of the variable steering ratio control device 6 is prevented. can do.
As described above, according to the first embodiment, it is possible to obtain the optimum turning performance according to the room for eliminating the understeer.

  In the first embodiment described above, the rear wheel 18 corresponds to the “drive wheel” recited in the claims, and the left / right torque transmission control device 4 includes the “left / right torque transmission control unit” recited in the claims. The front wheel 14 corresponds to the “steering wheel” recited in the claims, and the variable steering ratio control device 6 corresponds to the “variable steering ratio control unit” recited in the claims. Further, the reference steering ratio Rb corresponds to the “reference value” described in the claims, the target steering ratio Ro corresponds to the “target value” described in the claims, and the processing 75, 76, 90 of the ECU 56 is performed. , 91 corresponds to the “correction means” recited in the claims, and the electric motor 54 corresponds to the “actuator” recited in the claims. Further, the part for executing the process 75 of the ECU 56 corresponds to the “reference gain setting means” described in the claims, and the part for executing the process 76 of the ECU 56 is the “correction gain setting means” described in the claims. The portion for executing the processes 90 and 91 of the ECU 56 corresponds to “target value setting means” described in the claims.

(Second embodiment)
The second embodiment of the present invention is a modification of the first embodiment, and the description of the components that are substantially the same as those of the first embodiment is omitted by providing the same reference numerals.
FIG. 11 schematically shows the control contents of the ECU 102 constituting the variable control circuit unit 101 of the variable steering ratio control apparatus 100 according to the second embodiment in a functional block diagram. In this ECU 102, the IFS control process 62 is not performed.

  Further, in the ECU 102, in the VGR control processing 110, based on the driving torque difference ΔTd given from the left and right torque transmission control device 4, the turning angle θt calculated by the turning angle calculation processing 61, the steering wheel angle θh, and the vehicle speed Vc. Then, the VGR control target angle θmov is calculated.

Specifically, as shown in FIG. 12, first, a reference ratio calculation process 90 similar to that of the first embodiment is performed to calculate a reference steering ratio Rb.
On the other hand, in the correction gain calculation process 120, a VGR control correction gain Κv suitable for the drive torque difference ΔTd at the time of processing is calculated using a correction gain map Mgcv representing the correlation between the drive torque difference ΔTd and the VGR control correction gain Κv. calculate. Here, the correction gain map Mgcv is a two-dimensional map as shown in FIG. 13 stored in the ECU 102, and is configured such that the VGR control correction gain Κv changes according to the drive torque difference ΔTd. Thus, when the drive torque difference ΔTd is less than the threshold value ΔTdth, that is, when there is a large room for understeer cancellation by the YR control processing 42 of the left and right torque transmission control device 4, the VGR control correction gain Κv is set to 1. Further, when the drive torque difference ΔTd is equal to or greater than the threshold value ΔTdth, that is, when there is little room for canceling the understeer by the YR control process 42, the value increases as the VGR control correction gain Κv is greater than 1 and the drive torque difference ΔTd is increased. Set to

In the ratio correction process 121, the target steering ratio Ro is calculated by multiplying the reference steering ratio Rb and the VGR control correction gain Κv calculated in the reference ratio calculation process 90 and the correction gain calculation process 120. Here, the one-dot chain line and the two-dot chain line in FIG. 14 show examples of calculating the target steering ratio Ro in the cases (i) and (ii) below, and in the case (i) below than the case (ii) below. It can be seen that the target steering ratio Ro is increased.
(I) The case where the VGR control correction gain Κv is set to be larger than 1 in the correction gain calculation processing 120 because the room for understeer elimination is small.
(II) A case where the VGR control correction gain Κv is set to 1 in the correction gain calculation processing 120 due to a large room for eliminating understeer.

  Since the target steering ratio Ro calculated in the ratio correction process 121 is converted into the VGR control target angle θmov by the target angle calculation process 92 similar to that in the first embodiment, a command reflecting the VGR control target angle θmov is included. The rotation angle θm of the electric motor 54 is matched with the angle θmo. Therefore, for example, in the case of (I), the turning angle θt is relatively small with respect to the handle angle θh, and in the case of (II), the cutting angle θt is relatively large with respect to the handle angle θh. Is done. Therefore, the same effect as the first embodiment can be obtained.

  In the second embodiment described above, the variable steering ratio control device 100 corresponds to the “variable steering ratio control unit” recited in the claims, and the part that executes the processing 90, 120, 121 of the ECU 102 is patented. This corresponds to “correction means” recited in the claims. Further, the part for executing the process 120 of the ECU 102 corresponds to “correction gain setting means” described in the claims, and the part for executing the processes 90 and 121 of the ECU 102 is “target value setting” described in the claims. It corresponds to “means”.

Although several embodiments of the present invention have been described so far, the present invention should not be construed as being limited to these embodiments.
For example, torque transmission to the left and right rear wheels 18 in a two-wheel drive vehicle may be controlled by the left and right torque transmission control device 4.

  Further, in the left and right torque transmission control device 4, instead of distributing and transmitting the torque from the power source 11 to the left and right rear wheels 18, torque transmission to the rear wheels 18 is performed by a wheel-in motor built in each rear wheel 18. You may make it perform. In this case, in place of the electric motor 36, the hole-in motor of each rear wheel 18 is controlled by the ECU 38.

Furthermore, the left and right torque transmission control device 4 may not perform the lead control process 40 and the direct safety control process 41.
Furthermore, the variable steering ratio control device 6 may not execute the LS control process 60.

Furthermore, instead of the drive torque difference ΔTd, physical quantities correlated to the drive torque difference ΔTd, such as the drive torque Td of each rear wheel 18, the rotational speed Vt of each rear wheel 18, and the command torque Tmo, are applied to the left-right torque transmission control device. 4 may be supplied to the variable steering ratio control device 6. In this case, the variable steering ratio control device 6 calculates the drive torque difference ΔTd based on the correlation physical quantity of the drive torque difference ΔTd given from the left and right torque transmission control device 4.
In addition, the ECU 38 of the left and right torque transmission control device 4 and the ECU 56 or 102 of the variable steering ratio control device 6 may be combined into one ECU.

1 is a schematic configuration diagram illustrating a four-wheel drive vehicle to which a vehicle attitude control system according to a first embodiment is applied. It is a schematic block diagram which shows an example of the differential mechanism in the left-right torque transmission control apparatus of FIG. It is a functional block diagram which shows the control content by ECU of the left-right torque transmission control apparatus of FIG. It is a functional block diagram which shows the control content by ECU of the variable steering ratio control apparatus of FIG. It is a functional block diagram which shows the specific content of the IFS control process of FIG. FIG. 6 is a schematic diagram showing a reference gain map used in the reference gain calculation process of FIG. 5. FIG. 6 is a schematic diagram showing a correction gain map used in the gain correction process of FIG. 5. It is a functional block diagram which shows the specific content of the VGR control process of FIG. It is a schematic diagram which shows the reference ratio map utilized by the reference ratio calculation process of FIG. It is a schematic diagram which shows the example of calculation of the target steering ratio by the ratio correction process of FIG. It is a functional block diagram which shows the control content of ECU of the variable steering ratio control apparatus by 2nd embodiment. It is a functional block diagram which shows the specific content of the VGR control process of FIG. FIG. 13 is a schematic diagram illustrating a correction gain map used in the correction gain calculation process of FIG. 12. It is a schematic diagram which shows the example of calculation of the target steering ratio by the ratio correction process of FIG.

Explanation of symbols

2 Vehicle attitude control system, 4 Left / right torque transmission control device (left / right torque transmission control unit), 6 Variable steering ratio control device (variable steering ratio control unit), 10 Vehicle, 14 Front wheel (steering wheel), 18 Rear wheel (drive) Wheel), 20 steering handle, 30 transmission control mechanism section, 32 transmission control circuit section, 35 differential mechanism, 36 electric motor, 38 ECU, 40 lead control processing, 41 straight safety control processing, 42 YR control processing, 44 steering characteristic Determination processing, 45 Target torque calculation processing, 48 Drive torque difference calculation processing, 50 Variable control mechanism section, 52 Variable control circuit section, 53 Gear mechanism, 54 Electric motor (actuator), 56 ECU (correction means, reference gain setting means, Correction gain setting means, target value setting means), 60 LS control processing, 62 IFS control processing, 63 VGR Control processing, 73 steering characteristic calculation processing, 74 US control processing, 75 reference gain calculation processing, 76 gain correction processing, 90 reference ratio calculation processing, 91 ratio correction processing, 92 target angle calculation processing, 100 variable steering ratio control device (variable) Steering ratio control unit), 101 variable control circuit unit, 102 ECU (correction means, correction gain setting means, target value setting means), 120 correction gain calculation processing, 121 ratio correction processing

Claims (7)

A vehicle attitude control system including a left and right torque transmission control unit that transmits driving torque to left and right driving wheels, and a variable steering ratio control unit that varies a steering ratio between a steering wheel steering angle and a steering wheel turning angle. There,
The left and right torque transmission control unit performs an understeer control for increasing a drive torque difference between the left and right drive wheels when the steering characteristic of the vehicle is understeer.
The variable steering ratio control unit controls the steering ratio based on a driving torque difference between the left and right driving wheels.   2. The vehicle attitude according to claim 1, wherein the left-right torque transmission control unit supplies a drive torque difference between the left and right drive wheels or a value correlated with the drive torque difference to the variable steering ratio control unit. Control system. The variable steering ratio controller is
Correction means for setting a target value of the steering ratio by correcting a reference value of the steering ratio based on a driving torque difference between the left and right driving wheels;
An actuator for matching the steering ratio with the target value by changing the turning angle relative to the steering wheel angle;
The vehicle attitude control system according to claim 1 or 2, characterized by comprising:   The correction means sets the target value larger when the drive torque difference between the left and right drive wheels is greater than or equal to a threshold value than when the drive torque difference is less than the threshold value. Vehicle attitude control system described in 1. The correction means includes
A reference gain setting means for setting a reference gain to be larger as the understeer of the vehicle becomes stronger;
Correction that sets the reference gain as a correction gain when the drive torque difference between the left and right drive wheels is greater than or equal to a threshold value, while setting the correction gain smaller than the reference gain when the drive torque difference is less than the threshold value Gain setting means;
Target value setting means for setting the target value by multiplying the reference value by the correction gain set by the correction gain setting means;
The vehicle attitude control system according to claim 4, comprising: The correction means includes
A correction gain setting means for setting a correction gain larger when the drive torque difference between the left and right drive wheels is greater than or equal to a threshold, than when the drive torque difference is less than the threshold;
Target value setting means for setting the target value by multiplying the reference value by the correction gain set by the correction gain setting means;
The vehicle attitude control system according to claim 4, comprising: The vehicle attitude control system according to any one of claims 3 to 6, wherein the reference value is stored in the correction unit as a value correlated with a vehicle speed.

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