JP2005178574A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both reduction of a vehicle body slip angle and insurance of a target yaw rate. <P>SOLUTION: The steering device is provided with LSD 9 provided between a right side rear wheel 6a and a left side rear wheel 6b and capable of changing distribution of driving force transmitted from an engine to the rear wheels 6a, 6b; a front wheel steering actuator 7 for varying steering angles of the front wheels 4a, 4b; a rear wheel steering actuator 8 for varying steering angles of the rear wheels 6a, 6b; and a four-wheel steering controller 10 for outputting control instruction for varying the steering angle to the front wheel steering actuator 7 and the rear wheel steering actuator 8 in response to the traveling state. When engine torque is not varied, the four-wheel steering controller 10 outputs the control instruction for making the front wheel steering angle and the rear wheel steering angle large in proportion to a control current value of the LSD 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention belongs to a technical field of a steering device including a driving force distribution unit that distributes a driving force of an engine to left and right driving wheels, and a driving wheel steering mechanism that steers the driving wheels.

As a conventional steering device, a vehicle body slip angle is corrected by controlling a turning angle of a driving wheel according to a driving force distribution difference between left and right driving wheels, thereby reducing a sense of incongruity given to a driver. It is known (see, for example, Patent Document 1).
Here, the vehicle body slip angle refers to an angle formed by the traveling direction of the vehicle and the direction of the vehicle center plane when the vehicle in a turning state is viewed from above.
Japanese Patent Laid-Open No. 5-262253

  However, in the above-described prior art, when the target yaw rate is large, the yaw rate is decreased, and there is a problem in that reduction of the vehicle body slip angle and securing of the target yaw rate cannot be achieved at the same time.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a steering device capable of achieving both reduction of a vehicle body slip angle and securing of a target yaw rate.

  In order to achieve the above object, in the present invention, driving force distribution means provided between the left and right driving wheels and capable of changing the distribution of driving force transmitted from the engine to the driving wheels, and steering of the steered wheels The steered wheel steering mechanism for changing the angle, the drive wheel steered mechanism for changing the steered angle of the driving wheel, and the steered wheel steered mechanism and the drive wheel steered mechanism according to the traveling state, A steering control means for outputting a control command to be changed, wherein the steering control means outputs a control command for changing a turning angle in accordance with a difference in a driving force distribution amount between left and right drive wheels. I decided to output it.

  In the steering device according to the present invention, the steering wheel turning angle is controlled in addition to the driving wheel turning angle in accordance with the difference in the amount of distribution of the driving force, so that the vehicle body slip that makes the driver feel uncomfortable while ensuring the target yaw rate. The angle can be reduced.

  Hereinafter, the best mode for carrying out the present invention will be described based on Examples 1 to 3.

First, the configuration will be described.
FIG. 1 is a system block diagram of a vehicle to which the steering device of the first embodiment is applied. The steering device of the first embodiment includes a steering wheel 1, a column shaft 2, and a front wheel steering mechanism (steered wheel steering mechanism). 3, front wheels (steering wheels) 4a, 4b, rear wheel steering mechanism (drive wheel steering mechanism) 5, rear wheels (drive wheels) 6a, 6b, front wheel steering actuator 7, and rear wheel steering actuator 8 And a limited slip differential (driving force distribution means) 9, a four-wheel steering controller 10 (steering control means), a steering angle sensor 11, and wheel speed sensors 12a to 12d.

  The front wheel steering mechanism 3 converts the rotation input to the column shaft 2 from the steering wheel 1 into a lateral movement of the vehicle by a rack and pinion, and steers the front wheels 4a and 4b. Further, the rear wheel steering mechanism 5 converts the input of the rear wheel steering actuator 8 into vehicle lateral movement, and steers the rear wheels 6 and 6.

  The front wheel steering actuator 7 includes, for example, a motor and a speed reducer, and the rotation shaft of the motor is connected to the column shaft 2. The front wheel steering actuator 7 variably controls the steering gear ratio (θ / δ), which is the ratio of the steering angle θ to the front wheel steering angle δ, based on a command signal from the four-wheel steering controller 10.

  The rear wheel steering actuator 8 is configured by a motor, a reduction gear, and the like, like the front wheel steering actuator 7, and the rotation shaft of the motor is connected to the rack shaft of the rear wheel steering mechanism 5. The rear wheel steering actuator 8 variably controls the steering angles of the rear wheels 6 a and 6 b based on a command signal from the four-wheel steering controller 10.

  A limited slip differential (LSD) 9 is provided in the rear differential 13 and, for example, a friction type differential limiting device using a multi-plate clutch mechanism is used. The driving force distribution amount (the difference in driving force distribution amount between the rear wheel 6a and the rear wheel 6b) of the LSD 9 is controlled by a hydraulic control valve unit (not shown) that supplies hydraulic pressure to the multi-plate clutch. The hydraulic control valve unit is controlled based on a command current output from the four-wheel steering controller 10.

  The four-wheel steering controller 10 drives the LSD 9 based on the steering angle input from the steering angle sensor 11 and the vehicle body speed (= vehicle speed) estimated from the wheel speeds input from the wheel speed sensors 12a to 12d. Control power distribution. Further, the four-wheel turning controller 10 generates a target front wheel turning angle θf and a target rear wheel turning angle θr based on the steering angle, the vehicle body speed, and the driving force distribution amount of the LSD 9. The front wheel turning angle and the rear wheel turning angle fed back from the front wheel turning actuator 7 and the rear wheel turning actuator 8 are adjusted so that the target front wheel turning angle θf and the target rear wheel turning angle θr coincide with each other. A command current is output to the wheel steering actuator 7 and the rear wheel steering actuator 8.

Next, the operation will be described.
[Target turning angle setting control process]
FIG. 2 is a flowchart showing the flow of the target turning angle setting control process executed by the four-wheel turning controller 10, and each step will be described below.

  In step S1, the driving force distribution amount of the LSD 9 is set based on the output value of the steering angle sensor 11 and the vehicle body speed estimated from the outputs of the wheel speed sensors 12a to 12d. Then, a command current is output to the hydraulic control valve unit that drives the LSD 9, and the process proceeds to step S2.

  In step S2, the target rear wheel turning angle θr is determined from the command current value output to the LSD 9, and the process proceeds to step S3.

  In step S3, the target front wheel turning angle θf of the front wheels 4a and 4b is determined, and the process proceeds to step S4.

  In step S4, the front wheel turning actuator 7 and the rear wheel turning actuator 8 are set so that the actual front wheel turning angle and the actual rear wheel turning angle coincide with the target front wheel turning angle θf and the target rear wheel turning angle θr. The control current is output and this control is terminated.

[Determination of target turning angle based on driving force distribution]
If the equation of motion of the vehicle in the steady state is set as the following formulas 1 and 2,
mGy = Cf + Cr ... Formula 1
CfLf−CrLr = 0 Equation 2
M is the vehicle weight, Gy is the lateral G, Cf is the front wheel cornering force, Cr is the rear wheel cornering force, Lf is the front wheel base from the center of gravity to the front wheel, and Lr is the rear wheel from the center of gravity of the car to the rear wheel. It is a wheelbase.

When moment MLSD by LSD is added,
mGy = Cf + Cr ... Formula 1 '
Cf'Lf-Cr'Lr + MLSD = 0 ... Formula 2 '
Thus, the following formulas 3 and 4 are obtained. MLSD is a moment generated by LSD9.
Cf ′ = Cf−MLSD / (Lf−Lr) Equation 3
Cr ′ = Cr + MLSD / (Lf + Lr) Equation 4

here,
Cf = Kfβf Equation 5
Cr = Krβr Equation 6
Then,
Cf '= Kfβf' ... Formula 5 '
Cr '= Krβr' ... Formula 6 '
It becomes. Here, Kf is a front wheel cornering power, Kr is a front wheel cornering power, βf is a front wheel tire slip angle, and βr is a rear wheel tire slip angle.

At this time, the MLSD of Equation 4
Cr ′ ≧ Cr (Formula 7)
Therefore,
βr ′ ≧ βr (Formula 8)
Β ′ = βr ′ Equation 9
If so, the vehicle body slip angle β also increases.

Also, if Equation 4 is rewritten with Equations 6 and 6 ′,
Krβr ′ = Krβr + MLSD / L Equation 10
Therefore,
βr′−βr = MLSD / L · Kr Equation 11
Thus, (βr′−βr) becomes the control turning amount of the rear wheel turning angle.
That is, since the driving force distribution amount of the rear wheels 6a and 6b by the LSD 9 is proportional to the output current value, the target rear wheel turning angle θr can be determined based on the output current value.

  Further, the target front wheel turning angle θf changes the front wheel tire slip angle βf so that the front wheel cornering force Cf ′ does not change even when the four-wheel steering control is operated. That is, it should be increased by (β′−β).

However, the moment MLSD generated by the LSD 9 is calculated as follows.
MLSD = L · ΔFx / 2 × 2
ΔFx = Teng × Gmf × Tdist / R
L is a wheel base (L = Lf + Lr), Teng is an estimated engine torque value, Gmf is a gear ratio (T / M × Final), Tdist is a distribution torque, and R is a tire radius.
Here, when the engine torque does not change, the distribution torque Tdist is given in proportion to the control current value A of the LSD 9 as shown in the torque distribution characteristic diagram shown in FIG.
Further, the estimated engine torque value Teng is calculated from an accelerator opening-engine speed map or the like.

From the above,
MLSD = Kdist × Teng × Tdist Equation 12
Kdist is a constant and is the slope of the torque distribution characteristic shown in FIG.

From Equations 11 and 12, the target front wheel turning angle θf and the target rear wheel turning angle θr are expressed by the following equations.
θr = (Kdist × Teng / L · Kr × Ka) × A
θf = θr

[4-wheel steering control action based on driving force distribution]
The prior art (Japanese Patent Laid-Open No. 5-262253) describes a technique for improving turning performance by generating a driving force by a driving force distribution device such as an LSD and turning a rear wheel based on the generated driving force. Yes.

  However, in the configuration in which only the rear wheels are steered based on the driving force as in the prior art, it is difficult to achieve both reduction of the vehicle body slip angle and tracking of the target yaw rate. As shown in FIG. 4 (a), in the state where only the driving force distribution control is performed, the vehicle body slip angle becomes large, and the driver feels uncomfortable. In FIG. 4 (b), the rear wheel is steered to correct the vehicle body slip angle. However, when the target yaw rate is large, the yaw rate is reduced and the vehicle body slip angle cannot be reduced. .

  Further, in the prior art, as shown in FIG. 5 (b), when the target yaw rate is larger, the rear wheel is controlled in reverse phase to generate the yaw rate. Can't keep up. In other words, the yaw rate is increased by the driving force distribution control, but if the vehicle body slip angle is decreased by the steering control of the rear wheels, the yaw rate is decreased, and the securing of the target yaw rate and the reduction of the vehicle body slip angle are trade There was a problem of being in an off relationship.

  On the other hand, in the steering device of the first embodiment, as shown in FIG. 6B, the driving force distribution control is performed to change the turning angle of the rear wheels and the front wheels according to the driving force distribution amount of the rear wheels. The target yaw rate can be ensured by the front wheel steering control while the increase in the vehicle body slip angle caused by the above is canceled by the rear wheel steering control.

Next, the effect will be described.
In the steering device of the first embodiment, the following effects can be obtained.

  (1) The four-wheel steering controller 10 determines the target front wheel turning angle θf and the target rear wheel turning angle θr based on the control current value A of the LSD 9, and therefore ensures the target yaw rate and reduces the vehicle body slip angle. Both can be achieved (effect corresponding to claim 1).

  (2) The four-wheel steering controller 10 increases the target front wheel turning angle θf and the target rear wheel turning angle θr in proportion to the control current value A of the LSD 9 when the engine torque does not change. As the angle increases, a turning angle can be given to cancel it. Therefore, a running feeling with linearity is obtained, and the driver does not feel uncomfortable (effect corresponding to claim 2).

  (3) Since the four-wheel turning controller 10 matches the target front wheel turning angle θf with the target rear wheel turning angle θr, all the vehicle body slip angles can be canceled. Furthermore, the generated yaw rate does not change at all (effect corresponding to claim 7).

First, the configuration will be described.
In the first embodiment, the configuration in which the LSD driving force distribution is controlled by the four-wheel steering controller 10 is shown. However, the steering device of the second embodiment uses a rotation speed-sensitive differential limiting device as the driving force distribution device. This is different from the first embodiment.

  FIG. 7 is a system block diagram of a vehicle to which the steering device of the second embodiment is applied. The rear differential 13 is provided with a viscous LSD 14. As shown in FIG. 8, in the viscous LSD 14, the driving force distribution amount is determined by the wheel speed difference between the right rear wheel 6a and the left rear wheel 6b. That is, the target front wheel turning angle θf and the target rear wheel turning angle θr are determined by the wheel speed difference.

  Since (βr′−βr) is proportional to the moment MLSD of the viscous LSD 14 from the equations 11 and 12 of the first embodiment, the target front wheel turning angle θf and the target rear wheel turning angle θr are set to the right rear wheel 6a and the left side. It can be determined by the wheel speed difference of the rear wheel 6b. This wheel speed difference is obtained from the outputs of the wheel speed sensors 12c and 12d.

  When the engine torque does not change, the four-wheel turning controller 10 increases the target front wheel turning angle θf and the target rear wheel turning angle θr as the wheel speed difference between the right rear wheel 6a and the left rear wheel 6b increases.

Next, the operation will be described.
[4-wheel steering control action based on rear wheel speed difference]
As shown in FIG. 9 (a), when turning left, the wheel speed of the left rear wheel is smaller than the wheel speed of the right rear wheel. At this time, the driving force distribution proportional to the wheel speed difference is made by the viscous LSD 14, and more driving force is distributed to the left rear wheel side, so that the vehicle yaw rate is reduced.

  In the second embodiment, as shown in FIG. 9 (b), when the engine torque does not change, the larger the wheel speed difference, the larger the turning angle of the rear wheel and the front wheel. Vehicle yaw rate can be secured.

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

  (4) The four-wheel steering controller 10 determines the target front wheel turning angle θf and the target rear wheel turning angle θr based on the wheel speed difference between the right rear wheel 6a and the left rear wheel 6b. In the configuration using the differential limiting device (viscus LSD 14), the vehicle body slip angle can be reduced while ensuring the target yaw rate (effect corresponding to claim 3).

  (5) When the engine torque does not change, the four-wheel steering controller 10 increases both the target front wheel turning angle θf and the target rear wheel turning angle θr as the wheel speed difference increases. Along with this, it is possible to give a turning angle that cancels the turning angle, to obtain a running feeling with linearity, and to reduce a sense of incongruity given to the driver (effect corresponding to claim 4).

First, the configuration will be described.
The steering device of the third embodiment is different from the second embodiment in that a torque proportional LSD is used as a driving force distribution device, and the configuration of the other parts is the same as that of the second embodiment shown in FIG. Therefore, save the explanation.

  In the third embodiment, the relationship between the driving wheel speed difference and the driving force distribution amount shown in FIG. 8 of the second embodiment may be replaced with the relationship between the engine torque output and the driving force distribution amount as shown in FIG. it can. There are a plurality of practical methods for estimating the engine torque. For example, from the engine speed (FIG. 11 (a)) and the accelerator opening (FIG. 11 (b)), the engine torque shown in FIG. It is easy to estimate as follows.

  FIG. 11D shows a driving force distribution amount based on the engine torque. The target rear wheel turning angle θr and the target front wheel turning angle θf based on the driving force distribution amount are as shown in FIGS. 11E and 11F. To be determined. That is, the target front wheel turning angle θf and the target rear wheel turning angle θr are set to increase as the engine torque increases.

Next, the operation will be described.
[4-wheel steering control action based on engine torque]
As shown in FIG. 12 (a), when turning left, the wheel speed of the left rear wheel is smaller than the wheel speed of the right rear wheel. At this time, the driving force distribution proportional to the wheel speed difference is made by the torque proportional LSD, and more driving force is distributed to the left rear wheel, so that the vehicle yaw rate is reduced.

  In the third embodiment, as shown in FIG. 12 (b), the larger the engine torque, the larger the turning angles of the rear wheels and the front wheels. Therefore, the vehicle yaw rate can be ensured while reducing the vehicle body slip angle.

Next, the effect will be described.
In the steering device of the third embodiment, the effects listed below can be obtained.

  (6) The four-wheel steering controller 10 determines the target front wheel turning angle θf and the target rear wheel turning angle θr according to the engine torque, and therefore, in the configuration using the torque proportional LSD as the driving force distribution device, The vehicle body slip angle can be reduced while ensuring the yaw rate as described above (effect corresponding to claim 5).

  (7) Since the four-wheel steering controller 10 increases both the target front wheel turning angle θf and the target rear wheel turning angle θr as the engine torque increases, the steering that cancels the increase as the vehicle body slip angle increases. A corner can be given, a running feeling with linearity can be obtained, and a sense of incongruity given to the driver can be reduced (effect corresponding to claim 6).

(Other examples)
The best mode for carrying out the present invention has been described based on the first to third embodiments. However, the specific configuration of the present invention is not limited to the first to third embodiments. The present invention is also applied to the case of the front wheel or the front and rear wheels, and design changes and the like within the scope not departing from the gist of the invention are also included in the present invention.

1 is a system block diagram of a vehicle to which a steering device according to a first embodiment is applied. 4 is a flowchart showing a flow of target turning angle setting control processing executed by a four-wheel turning controller 10; It is a torque distribution characteristic view. It is explanatory drawing which shows the problem of a prior art example. It is explanatory drawing which shows the problem of a prior art example. It is explanatory drawing which shows the effect | action of Example 1. FIG. FIG. 6 is a system block diagram of a vehicle to which a steering device of Embodiment 2 is applied. It is a characteristic view of the driving force distribution amount with respect to the rear wheel speed difference. It is explanatory drawing which shows the effect | action of Example 2. FIG. It is a characteristic view of the driving force distribution amount with respect to the engine torque output. It is explanatory drawing which shows the engine torque estimation method and the determination method of a target front wheel turning angle and a target rear wheel turning angle. It is explanatory drawing which shows the effect | action of Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Column shaft 3 Front wheel steering mechanism 4a Right front wheel 4b Front wheel 5 Rear wheel steering mechanism 6a Right rear wheel 6b Left rear wheel 7 Front wheel steering actuator 8 Rear wheel steering actuator 9 Limited slip differential 10 Wheel steering controller 11 Steering angle Sensors 12a to 12d Wheel speed sensor 13 Rear differential 14 Viscous LSD

Claims (7)

Drive force distribution means provided between the left and right drive wheels, and capable of changing the distribution of the drive force transmitted from the engine to the drive wheels to the left and right;
A steered wheel turning mechanism for changing the steered wheel turning angle;
A drive wheel turning mechanism for changing the turning angle of the drive wheel;
Steering control means for outputting a control command to change the steering angle to the steered wheel steering mechanism and the drive wheel steering mechanism according to the traveling state;
In a steering device with
The steering apparatus according to claim 1, wherein the steering control means outputs a control command for changing a steering angle in accordance with a difference in driving force distribution amount between left and right driving wheels. The steering apparatus according to claim 1, wherein
The steering wheel is a driven wheel to which no driving force is transmitted,
When the engine torque does not change, the steered control means outputs a control command for increasing both the steered wheels and the steered wheels as the driving force distribution amount difference between the left and right drive wheels increases. Steering device. The steering apparatus according to claim 1 or 2,
The driving force distribution means is a rotation speed sensitive operation limiting device,
The steering apparatus according to claim 1, wherein the steering control means outputs a control command for changing a steering angle in accordance with a wheel speed difference between left and right drive wheels. The steering apparatus according to claim 3, wherein
The steering control means outputs a control command for increasing both the steered wheel and the steered angle of the drive wheel as the wheel speed difference between the left and right drive wheels is larger when the engine torque does not change. Steering device. The steering apparatus according to claim 1 or 2,
The driving force distribution means is a torque proportional operation limiting device,
The steering apparatus according to claim 1, wherein the steering control means outputs a control command for changing a steering angle in accordance with an engine torque. The steering apparatus according to claim 5, wherein
The steering apparatus according to claim 1, wherein the steering control means outputs a control command to increase both the steering angles of the steered wheels and the drive wheels as the engine torque increases. The steering apparatus according to any one of claims 1 to 6,
The steering apparatus according to claim 1, wherein the steering control means outputs a control command for matching steering angles of steered wheels and drive wheels.

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