JP4539866B2 - Steering device - Google Patents

Description

  The present invention relates to a steering device including a steering actuator that independently steers front, rear, left and right wheels.

Conventionally, for example, Patent Document 1 discloses a vehicle steering system that suppresses vehicle deflection due to a left-right braking difference that occurs when a braking force is applied while traveling on a road surface having a different friction coefficient between left and right (so-called μ-split road). A device has been proposed.
In this steered device, the left-right braking force difference is estimated, and the braking force difference control amount is calculated in a direction to cancel the yaw moment caused by the left-right braking force difference. Then, the turning angle of the wheel is controlled by adding the braking force difference control amount to the turning control amount.
Patent Document 2 proposes a four-wheel independent steering device that controls the remaining steering actuator that has not failed to correct the deflection of the vehicle when the steering actuator has failed. .
JP-A-2005-112285 JP 2001-322557 A

  However, in such a steering device, when one wheel cannot be steered, the deceleration capability of the vehicle during braking is inferior to that during normal operation. In other words, the conventional steering device performs steering control so as to cancel the yaw moment by effectively using the non-steerable wheel when one wheel cannot be steered and brake braking is applied while traveling on a μ split road. Therefore, it is necessary to supplement the yaw canceling component that is originally generated on the wheel that cannot be steered by the steering control on the normal wheel side. For this reason, the deceleration direction component of the force generated at the wheel during braking decreases, and the deceleration of the vehicle (vehicle speed reduction rate: hereinafter referred to as deceleration G) decreases.

  An object of the present invention is to cope with the above-described problem, and suppresses the yawing of the vehicle by generating a force in a direction to suppress the yaw moment at the time of braking even for the wheel that has become unsteerable. The purpose is to increase the deceleration G of the vehicle.

  In order to achieve the above object, a feature of the present invention is to provide a steering actuator that includes a steering actuator that independently adjusts the steering angles of the front, rear, left and right wheels, and a steering control means that controls the steering actuator. In the device, a difference in friction coefficient between the steering abnormality detecting means for detecting a steering abnormality in which one of the left and right of the rear wheels becomes impossible to steer and the ground road surface between the left wheel and the right wheel is detected. When the left and right friction coefficient difference state detection means and the steering abnormality detection means detect any left or right turning abnormality of the rear wheel, the left and right friction coefficient difference state detection means detects the difference between the left and right wheels. When it is determined that the friction coefficient between the ground and the road surface is different, the steering actuators other than the wheels that cannot be steered are driven and controlled. For the direction of vehicle travel In that a abnormal turning control means for providing a slip angle to the vehicle body so that a predetermined wheel slip angle can be obtained.

  In the present invention configured as described above, the steering control means drives and controls the steering actuator. For example, the turning angle of the wheel is detected, and the turning actuator is driven and controlled so that the turning angle becomes the target turning angle. Then, the steering abnormality detection means detects that either the left or right rear wheel cannot be steered, and the left and right friction coefficient difference state detection means detects the friction coefficient between the left and right wheels and the ground road surface ( If it is determined that the friction coefficient between the left wheel and its ground contact surface and the friction coefficient between the right wheel and its ground contact surface) are different, the abnormal turning control means A steering actuator other than the disabled wheels is driven and controlled, and a slip angle is given to the vehicle body so that a wheel that has become unsteerable can obtain a predetermined wheel slip angle with respect to the vehicle traveling direction.

When braking is performed while traveling on a μ-split road where the left and right friction coefficients are different, a yaw moment is generated in the vehicle. According to the present invention, this yaw moment includes front and rear left and right wheels including wheels that cannot be steered. And the slip angle of the non-steerable wheel can be set so that a large deceleration G can be obtained. In other words, the left and right front and rear wheels including the wheels that cannot be steered during braking suppress the yaw moment generated in the vehicle, and in order to obtain a large deceleration G, only wheels that cannot be steered are provided in the predetermined direction in advance for braking. I can keep it.
In this case, a slip angle is generated in the vehicle body by drivingly controlling a steering actuator other than the non-steerable wheel so that a predetermined slip angle is generated in the non-steerable wheel.
Therefore, at the time of braking, even if the non-steerable wheel cannot be steered, it is generated in the vehicle on the left and right front and rear wheels including the non-steerable wheel by steering control of other normal wheels while maintaining the vehicle body slip angle. It is possible to suppress the yaw moment and obtain a large deceleration G.
For example, the optimal for the vehicle traveling direction for each left and right front and rear wheel that cancels each other the component forces in the yaw direction generated by the left and right front and rear wheels, including wheels that cannot be steered during braking, and obtains a substantially maximum deceleration G The angle is determined according to the difference in the left and right friction coefficients, and the normal steering actuator is driven and controlled so that the optimum angle of the wheel that cannot be steered becomes the wheel slip angle of the wheel that cannot be steered, thereby giving the vehicle body a slip angle. In actual braking, it is preferable to provide a braking-time turning control means for turning normal wheels in the obtained optimum direction.
As a result, even if one of the rear wheels becomes impossible to steer while traveling on the μ split road, the vehicle can be stopped quickly with the behavior of the vehicle stabilized, and safety is improved.

  Another feature of the present invention is that the abnormal-time steering control means is configured such that the friction coefficient of the target wheel slip angle of the wheel that has become non-steerable and the ground road surface of the non-steerable wheel is opposite to the left and right. When the friction coefficient with the ground road surface of the side wheel is large, the larger the difference is, the more outward the vehicle travel direction, the friction coefficient with the ground road surface of the non-steerable wheel is. When the coefficient of friction with the ground contact surface of the opposite side wheel is small, the larger the difference is, the more the target wheel slip angle setting means that is set inward from the vehicle traveling direction, and the rotation of the non-steerable wheel. A steering angle detecting means for detecting a steering angle; a target wheel slip angle set by the target wheel slip angle setting means; and a steering angle of a non-steerable wheel detected by the steering angle detection means. To determine the vehicle body slip angle Located in.

  According to this, since the target slip angle of the non-steerable wheel is appropriately set according to the difference between the friction coefficients of the left and right contact road surfaces, the reduction of the yaw moment generated in the vehicle and the generation of the high deceleration G are achieved. Even better.

  Hereinafter, a steering apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a turning device in a four-wheel independent turning vehicle according to the embodiment.

  This vehicle includes steering mechanisms 10A, 10B, 10C, and 10D for independently steering left and right front wheels Wfl and Wfr and left and right rear wheels Wrl and Wrr.

  The steered mechanisms 10A, 10B, 10C, 10D are assembled to the left and right front wheels Wfl, Wfr and the left and right rear wheels Wrl, Wrr, respectively, and rotate integrally around the vertical axis to thereby each wheel Wfl, Wfr, Wrl, Wrr. (Hereinafter, when these are generically referred to, they are simply referred to as wheels W.) knuckle 11a, 11b, 11c, and 11d are provided. Each knuckle 11a, 11b, 11c, 11d is supported by suspensions 12a, 12b, 12c, 12d. In this embodiment, a double wishbone type suspension is used, but other types such as a strut type suspension can also be adopted.

The suspensions 12a, 12b, 12c, and 12d include a pair of upper and lower suspension arms 12a1, 12b1, 12c1, and 12d1 that are pivotally supported on the left and right sides of the vehicle body BD so as to be swingable in the vertical direction and extend outward in the vehicle width direction.
The pair of upper and lower suspension arms 12a1, 12b1, 12c1, and 12d1 connect knuckles 11a, 11b, 11c, and 11d through ball joints 13a, 13b, 13c, and 13d provided at the tip portions of the suspension arms 12a1, 12b1, 12c1, and 12d1, respectively. Wfr, Wrl, Wrr are supported so as to be rotatable around the vertical axis.
Although not shown, between the lower arm of the suspension arms 12a1, 12b1, 12c1, and 12d1 and the vehicle body BD, a spring device that absorbs an impact received from the road surface and enhances riding comfort, and a vertical vibration of the spring device. A shock absorber for generating a damping force.

  The knuckles 11a and 11b of the left and right front wheels Wfl and Wfr extend rearward, and pins 14a and 14b are erected and fixed to the rear ends of the knuckles 11a and 11b with the vertical direction as the axial direction. The knuckles 11c and 11d of the left and right rear wheels Wrl and Wrr are extended forward, and pins 14c and 14d are vertically fixed to the front end portions of the knuckles 11a and 11b with the vertical direction as an axial direction.

  Each pin 14a, 14b, 14c, 14d is driven in the vehicle width direction by the steering actuators 15a, 15b, 15c, 15d via the drive arms 16a, 16b, 16c, 16d. The steering actuators 15a, 15b, 15c, 15d are housings 15a2, 15b2, 15c2 that convert the electric motor and the rotation mechanism of the motor into linear motion to drive the pins 15a1, 15b1, 15c1, 15d1 in the vehicle width direction. , 15d2 respectively. The pins 15a1, 15b1, 15c1, 15d1 protrude from guide holes 15a3, 15b3, 15c3, 15d3 provided in the housings 15a2, 15b2, 15c2, 15d2 along the vehicle width direction, and the guide holes 15a3, 15b3, 15c3 It is displaced in the vehicle width direction along 15d3. The drive arms 16a, 16b, 16c, and 16d are assembled so as to be rotatable around the axes of the pins 15a1, 15b1, 15c1, and 15d1 at the respective inner ends, and the pins 14a, 14b, 14c, and the like at the respective outer ends. It is assembled so as to be rotatable about the axis of 14d, and the pins 15a1, 14b, 14c, 14d and the knuckles 11a, 11b are swung on the horizontal plane by the displacement of the pins 15a1, 15b1, 15c1, 15d1 in the vehicle width direction. , 11c, 11d to steer each wheel Wfl, Wfr, Wrl, Wrr.

  In addition, the steering apparatus includes a steering handle 31 that is turned by a driver to steer the wheels Wfl, Wfr, Wrl, and Wrr. The steering handle 31 is fixed to the upper end of the steering shaft 32, and a reaction force actuator 33 including an electric motor and a speed reduction mechanism is connected to the lower end of the steering shaft 32. The reaction force actuator 33 applies a reaction force to the turning operation of the steering handle 31 by the driver.

  The vehicle further includes a steering control device 40 for controlling the steering actuators 15a, 15b, 15c, 15d and the reaction force actuator 33. The steering control device 40 is configured by a microcomputer as a main part, and includes a steering angle sensor 41, wheel steering angle sensors 42a, 42b, 42c, 42d, a steering torque sensor 43, a vehicle speed sensor 44, a yaw rate sensor 45, a lateral acceleration. The sensor 46 and wheel speed sensors 47a, 47b, 47c, 47d are connected. Further, the turning control device 40 includes drive circuits 50a, 50b, 50c, and 50d for driving the turning actuators 15a, 15b, 15c, and 15d, and a reaction force actuator 33 that applies a steering reaction force to the steering handle 31. A drive circuit 51 for driving is connected.

The steering angle sensor 41 is assembled to the steering shaft 32 connected to the steering handle 31, detects the rotation angle from the neutral position of the steering handle 31, and outputs it as the steering angle θ. The steering torque sensor 43 also detects torque applied to the steering handle 31 by being assembled to the steering shaft 32 and outputs the detected torque as steering torque T.
The wheel steering angle sensors 42a, 42b, 42c, 42d (hereinafter simply referred to as the wheel steering angle sensor 42) are referred to as the steering actuators 15a, 15b, 15c, 15d (hereinafter collectively referred to as the wheel steering angle sensors 42). (Referred to simply as a steering actuator 15) and turning angles δfl, δfr, δrl, δrr from the neutral position of each wheel Wfl, Wfr, Wrl, Wrr (referred to as δ).

The vehicle speed sensor 44 detects and outputs the vehicle speed V. The yaw rate sensor 45 detects and outputs the yaw rate γ of the vehicle. The lateral acceleration sensor 46 detects and outputs the lateral acceleration Gy of the vehicle.
The wheel speed sensors 47a, 47b, 47c, 47d detect the rotational speeds of the wheels Wfl, Wfr, Wrl, Wrr and output them as wheel speed signals ωfl, ωfr, ωrl, ωrr.

  The turning control device 40 stores in advance a target turning angle table of each wheel Wfl, Wfr, Wrl, Wrr corresponding to the steering angle θ and the vehicle speed V as a target turning angle table, and this target turning during traveling. The target turning angle of each wheel Wfl, Wfr, Wrl, Wrr is calculated with reference to the angle table. The steering actuators 15a, 15b, 15c, and 15d are feedback-controlled in accordance with deviations from the actual steering angles δfl, δfr, δrl, and δrr detected by the wheel steering angle sensors 42a, 42b, 42c, and 42d. Thus, each wheel Wfl, Wfr, Wrl, Wrr is set as a target turning angle.

Next, control when one of the rear wheels Wrl and Wrr becomes impossible to steer while traveling on the μ split road, which is a feature of the present invention, will be described.
First, the yaw moment of the vehicle generated during braking will be described.
FIG. 2 (a) shows a state in which braking is applied while the right ground road surface is traveling on a road surface (hereinafter referred to as a right high μ split road) having a larger friction coefficient μ with the wheel W than the left ground road surface. It represents the force acting on each wheel Wfl, Wfr, Wrl, Wrr. As can be seen from this figure, when brake braking force is applied to the wheels, each wheel Wfl, Wfr, Wrl, Wrr has not only the rearward braking force but also the yaw-direction component forces Yfl, Yfr, Yrl, Yrr indicated by the dashed arrows. Work. Therefore, on the right high μ split road, the yaw moment component Yfl, Yfr, Yrl, Yrr acting on each wheel Wfl, Wfr, Wrl, Wrr causes the vehicle to move to the right in the yaw moment (around the vertical axis passing through the center of gravity of the vehicle). Vehicle rotational force).

  Therefore, as shown in FIG. 2B, yawing of the vehicle is prevented by adjusting the turning angle of each wheel Wfl, Wfr, Wrl, Wrr. In other words, the turning angle of each wheel W is adjusted so that the component forces Yfl, Yfr, Yrl, Yrr in the yaw direction of each wheel Wfl, Wfr, Wrl, Wrr cancel each other (so that the sum of the dashed arrow vectors becomes 0). To do. At the same time, the turning angle is set so that the deceleration G is maximized, that is, the sum of the backward (directly downward direction) components of the solid line arrow vector in FIG.

  The optimum turning angle of each wheel W is set so that the yaw-direction component forces Yfl, Yfr, Yrl, Yrr generated on each wheel W cancel each other and the maximum deceleration G is obtained. The left μl between the left wheels Wfl and Wrl and the ground road surface and the right μr between the right wheels Wrl and Wrr and the ground road surface are obtained by convergence calculation. Accordingly, during traveling, the left and right friction coefficients μl and μr are always estimated, and the optimum turning angle of each wheel W is calculated based on the estimated friction coefficients μl and μr. In this case, the convergence calculation may be performed while the vehicle is running, but in order to reduce the computational burden on the microcomputer in the steering control device 40, the convergence is preliminarily determined based on the friction coefficients (μl, μr) in various cases. The optimum turning angle of the four wheels W is obtained by calculation, the result is stored in a storage element as a calculation map, and the optimum turning angle of each wheel W is calculated with reference to the calculation map during traveling. It may be.

Next, consider a case where one of the rear wheels Wrl and Wrr is in a state in which it cannot be steered.
For example, as shown in FIG. 3 (a), when the right rear wheel Wrr cannot be steered and is locked inward (toe-in) with respect to the longitudinal direction of the vehicle body while traveling on the right high μ split road. Causes an inward force to the non-steerable wheel Wrr, and a yaw moment is generated in the vehicle. Therefore, the left rear wheel steering actuator 15c is driven and controlled so that the left rear wheel Wrl is also steered inward, thereby generating an inward force on the left rear wheel Wrl and an inward force of the non-steerable wheel Wrr. To cancel the yaw moment of the vehicle and make the vehicle body slip angle zero.

When braking is applied to each wheel W in this state, as shown in FIG. 3B, the yaw-direction component Yfl is applied to each wheel Wfl, Wfr, Wrl, Wrr due to the difference in friction coefficients μl, μr of the left and right ground contact surfaces. , Yfr, Yrl, Yrr are generated. In this case, the right rear wheel Wrr, which is a wheel that cannot be steered, cannot be steered outward, so it is conceivable to cancel the yaw moment of the vehicle using the other three wheels Wfl, Wfr, Wrl.
However, the yaw direction component forces Yfl, Yfr, Yrl, Yrr generated at the respective wheels Wfl, Wfr, Wrl, Wrr using the normal three wheels Wfl, Wfr, Wrl while keeping the vehicle body slip angle at 0 in this way. When the steering control is performed so as to cancel each other, the deceleration G cannot be increased. This is because the yaw-direction canceling component Yrr that is originally generated on the non-steerable wheel Wrr must be compensated on the normal wheels Wfl, Wfr, Wrl side.

Therefore, in the present embodiment, as shown in FIGS. 3C and 3D, in preparation for brake braking, a slip angle β is added to the vehicle body BD in advance to turn the non-steerable wheel Wrr in a direction to cancel the yaw moment. To solve the above problem.
That is, instead of controlling the non-steerable wheel Wrr to the optimum steering angle according to the friction coefficient (μl, μr), the non-steerable wheel Wrr can obtain the optimum wheel slip angle α * with respect to the vehicle traveling direction. The direction of the vehicle body BD is adjusted by controlling the turning angles δfl, δfr, δrl of the normal wheels Wfl, Wfr, Wrl.

FIG. 3C shows the state of each wheel Wfl, Wfr, Wrl, Wrr when the vehicle is traveling with the vehicle body slip angle β so that the non-steerable wheel Wrr has the optimum wheel slip angle α *. In this case, the non-steerable wheel Wrr on the high μ road side is directed outward (toe-out) with respect to the vehicle traveling direction, and the left rear wheel Wrl that is opposite to the non-steerable wheel Wrr is also toe-out in the same manner.
The vehicle body slip angle β in the right direction with respect to the traveling direction of the vehicle includes a leftward turning angle δK (hereinafter referred to as a failure steering angle δK) of the non-steerable wheel Wrr detected by the wheel rudder angle sensor 42d, and a non-steerable wheel. It is obtained by the sum of Wrr and the outward optimum wheel slip angle α * with respect to the vehicle traveling direction.
β = δK + α *

The optimum wheel slip angle α * of the non-steerable wheel Wrr is derived according to the friction coefficient (μl, μr). In the present embodiment, the friction coefficient on the non-steerable wheel side is μA, and the friction on the opposite left and right wheels side is determined. When the coefficient is μB, it is determined from the value of μA / μB as shown in the map of FIG.
As can be seen from this map, the optimum wheel slip angle α * is greater with respect to the vehicle traveling direction as the friction coefficient on the non-steerable wheel side is larger than the friction coefficient on the opposite left and right wheels and the difference in friction coefficient is larger. The optimum wheel slip angle α * increases as the friction coefficient on the non-steerable wheel side is smaller than the friction coefficient on the opposite left and right wheels and the difference in friction coefficient is larger. It is set inwardly with respect to the direction.
Then, as shown in FIG. 3C, the vehicle travels at the calculated vehicle body slip angle β. That is, in preparation for brake braking, the direction of the non-steerable wheel Wrr is directed in the direction in which the yaw moment is canceled by the four wheels W during braking. In this case, the left and right front wheels Wfl, Wfr are steered to the left at the steered angles δfl, δfr equal to the vehicle body slip angle β.

  When brake braking is applied from this state, the normal three wheels Wfl, Wfr, Wrl are controlled to a target turning angle determined according to the friction coefficient (μl, μr) as shown in FIG. That is, while maintaining the vehicle body slip angle β, the yaw-direction component forces Yfl, Yfr, Yrl, which are generated on the wheels Wfl, Wfr, Wrl, Wrr by the four wheels Wfl, Wfr, Wrl, Wrr including the non-steerable wheel Wrr, The normal wheels Wfl, Wfr, and Wrl are steered so that Yrr cancels each other and the deceleration G becomes the largest in the four wheels. In this case, the target turning angles of the wheels Wfl, Wfr, Wrl may be obtained by convergence calculation based on the friction coefficients (μl, μr), but the four wheels Wfl corresponding to various friction coefficients (μl, μr). , Wfr, Wrl, Wrr may be obtained with reference to a calculation map storing the optimum turning angle.

During this braking operation, the non-steerable wheel Wrr cannot be steered, but the vehicle body slip angle β is already adjusted, and the four wheels Wfl, Wfr, Wrl, Wrr including the non-steerable wheel Wrr are used. The wheel slip angle α * is set so that the yaw-direction component forces Yfl, Yfr, Yrl, Yrr generated in each wheel Wfl, Wfr, Wrl, Wrr cancel each other, and the deceleration G becomes the largest in the four wheels. There is no need to steer.
Therefore, not only the normal three wheels Wfl, Wfr, Wrl but also the non-steerable wheels Wrr can be effectively used to eliminate the yaw moment of the vehicle and generate a large deceleration G. As a result, the behavior of the vehicle can be stabilized at the time of braking, and the vehicle can be stopped quickly, thereby improving safety.

Next, consider a case where the right rear wheel Wrr is greatly broken toward the outside during right high μ split traveling.
FIG. 4A shows the state of each wheel W when the right rear wheel Wrr is largely toe out and locked during right high μ split travel.
In this case, the left rear wheel Wrl, which is the left and right opposite wheel of the non-steerable wheel Wrr, is toe-out by the steering actuator 15c to set the vehicle body slip angle to 0. However, since the toe-out angle of the non-steerable wheel Wrr is large, When the difference in friction coefficient is large, the steering control of the left rear wheel Wrl cannot be corrected. Therefore, the vehicle body BD is inclined in a direction in which the slip angle of the non-steerable wheel Wrr is naturally reduced.

Therefore, in this embodiment, as in the previous example, the turning angles of the normal wheels Wfl, Wfr, Wrl are set so that the non-steerable wheel Wrr can obtain the optimum wheel slip angle α * with respect to the vehicle traveling direction. The direction of the vehicle body BD (vehicle slip angle β) is adjusted by controlling. That is, the yaw moment generated in the vehicle is canceled by the four wheels Wfl, Wfr, Wrl, Wrr including the non-steerable wheel Wrr at the time of brake braking, and the deceleration G is maximized by the four wheels Wfl, Wfr, Wrl, Wrr. In such a direction, only the non-steerable wheel Wrr is directed in advance for braking.
In this case, the vehicle body BD is directed leftward and the non-steerable wheel Wrr is directed outward with respect to the vehicle traveling direction. The left-side vehicle body slip angle β with respect to the vehicle traveling direction is defined as a failure steering angle δK directed to the right of the non-steerable wheel Wrr and an optimum wheel slip angle α * facing outward with respect to the vehicle traveling direction of the non-steerable wheel Wrr. It is calculated by the difference between
β = δK−α *
Therefore, as shown in FIG. 4 (c), when each wheel W is adjusted to the optimum turning angle according to the friction coefficient (μl, μr) during braking, the non-steerable wheel Wrr cannot be steered. The four wheels Wfl, Wfr, Wrl, Wrr including the non-steerable wheels Wrr cancel the yaw direction component forces Yfl, Yfr, Yrl, Yrr generated in each wheel Wfl, Wfr, Wrl, Wrr, and the four wheels. The largest deceleration G can be obtained. As a result, both the stability of the vehicle behavior during braking and good deceleration performance can be achieved, and safety is improved.

Next, consider a case in which the left rear wheel Wrl has failed toward the outside during right high μ split traveling.
FIG. 5A shows the state of each wheel W when the left rear wheel Wrl is toe-out and locked during right-high μ split traveling.
In this case, the vehicle body slip angle can be reduced to 0 by turning the right rear wheel Wrr, which is opposite to the left and right wheels of the non-steerable wheel Wrl, to the out by the steering actuator 15d.
However, as shown in FIG. 5B, at the time of braking, it is difficult to generate the counterclockwise yaw direction component Yrl with the non-steerable wheel Wrl. In order to prevent vehicle yawing, the other three wheels Wfl , Wfr, Wrr need to adjust the turning angle so that the yaw moment of the vehicle is canceled.
Therefore, as the other three wheels Wfl, Wfr, Wrr compensate for the shortage of the yaw direction component of the non-steerable wheel Wrl, the deceleration direction component (the backward component of the solid arrow) decreases, and the deceleration G decreases. .

Therefore, in the present embodiment, as shown in FIG. 5C, as in the previous example, the normal wheels are set so that the non-steerable wheel Wrl can obtain the optimum wheel slip angle α * with respect to the vehicle traveling direction. The direction of the vehicle body (vehicle body slip angle β) is adjusted by controlling the turning angles of Wfl, Wfr, and Wrr. That is, during braking, the yaw moment generated in the vehicle is canceled by the four wheels Wfl, Wfr, Wrl, Wrr including the non-steerable wheel Wrl, and the deceleration G is the largest at the four wheels Wfl, Wfr, Wrl, Wrr. In such a direction, only the non-steerable wheel Wrl is directed in advance.
In this case, the vehicle body BD is directed rightward and the non-steerable wheel Wrr is directed inward with respect to the vehicle traveling direction. The vehicle body slip angle β in the right direction with respect to the vehicle traveling direction is defined as a failure steering angle δK facing left of the non-steerable wheel Wrl and an optimum wheel slip angle α * facing inward with respect to the vehicle traveling direction of the non-steerable wheel Wrl. It is calculated by the sum of
β = δK + α *
In this case, the left and right front wheels Wfl, Wfr are steered to the left at the steered angles δfl, δfr equal to the vehicle body slip angle β.
Therefore, at the time of brake braking, as shown in FIG. 5D, each wheel W is adjusted to the optimum turning angle according to the friction coefficient (μl, μr), but the non-steerable wheel Wrl cannot be steered. The four wheels Wfl, Wfr, Wrl, and Wrr including the non-steerable wheels Wrl cancel the yaw direction component forces Yfl, Yfr, Yrl, and Yrr generated in the wheels Wfl, Wfr, Wrl, and Wrr, and the four wheels. The largest deceleration G can be obtained. As a result, both the stability of the vehicle behavior during braking and good deceleration performance can be achieved, and safety is improved.

Next, means for detecting a difference state between the left and right friction coefficients will be described.
Various techniques for detecting (including estimating) the friction coefficient between the road surface and the wheel are known.
For example, a method for obtaining a road surface friction coefficient from a slip state of a wheel when a braking force is applied (Japanese Patent Laid-Open No. 2001-315633), or a method for obtaining a road surface friction coefficient from a temporal change in wheel speed during automatic brake braking (Japanese Patent Laid-Open No. 2001). -354129). Therefore, the difference between the left and right friction coefficients can be detected by separately obtaining the road surface friction coefficient for the left wheel and the right wheel using such a technique.
In addition, as a means for accurately estimating the road surface friction coefficient in the four wheels, the wheel speed vibration Δω is obtained based on the wheel speed signal ω of each wheel output from the wheel speed sensor provided in the four wheels. The road surface friction coefficient is determined by calculating the road surface μ gradient and the wheel vibration level from the fast vibration Δω and estimating the road surface friction coefficient between each wheel and the road surface based on the calculated road surface μ gradient and the wheel vibration level. An apparatus is known (Japanese Patent Laid-Open No. 2002-274356).
Further, as a technique for detecting the μ split road, a means for individually detecting the wheel speeds of the four wheels and a slip detecting means for detecting that the slip state of each wheel has exceeded the reference state are provided. When the order of the wheels is the first and second for the left front wheel and the left rear wheel (or the right front wheel and the right rear wheel), and the speed difference between the left and right front wheels and the speed difference between the left and right rear wheels are greater than the set value In addition, it is also known that it is determined that the vehicle is traveling on a μ split road (Japanese Patent Laid-Open No. 5-178181).

In addition, since the friction coefficient varies depending on the ground contact state of the wheels, for example, it is possible to provide an air pressure sensor for each tire and estimate the difference state and degree of difference between the left and right friction coefficients from the balance of air pressure between the left and right wheels.
In this embodiment, any of these techniques may be used, and it may be selected according to the required accuracy. Moreover, it is not limited to these techniques.

Next, the steering control process at the time of rear wheel failure executed by the steering control device 40 when one of the rear wheels Wrl and Wrr becomes impossible to steer will be described.
FIG. 6 shows a rear wheel failure turning control routine executed by the turning control device 40, and is stored as a control program in a storage element (not shown) of the turning control device 40.
This rear wheel failure turning control routine is started by an ignition-on operation and is repeatedly executed at a predetermined short cycle.

  When this control routine is started, first, parameters necessary for steering control are read (S11). In the present embodiment, the vehicle speed V detected from the vehicle speed sensor 44, the steering angle θ detected from the steering angle sensor 41, and the actual turning angles δfl, δfr detected from the wheel steering angle sensors 42a, 42b, 42c, 42d. , Δrl, δrr, yaw rate γ detected from the yaw rate sensor 45, lateral acceleration Gy detected from the lateral acceleration sensor 46, wheel speeds ωfl, ωfr, ωrl, ωrr output from the wheel speed sensors 47a, 47b, 47c, 47d. Is read.

Subsequently, it is determined whether one side of the rear wheels Wrl and Wrr is not steerable (S12). This determination is based on the actual turning angles δrl and δrr detected by the wheel rudder angle sensors 42c and 42d even though the turning control command 40 is output to the turning actuators 15c and 15d. When is not changed, it is determined that the turning actuators 15c and 15d are not capable of turning. That is, the steering control device 40 executes a normal steering control routine for driving and controlling the steering actuator 15 in accordance with the rotation operation of the steering handle 31 in parallel with this control routine. The absolute value of the difference between the steered angle δfl *, δfr *, δrl *, δrr * and the actual steered angle δfl, δfr, δrl, δrr (| δfl * -δfl |, | δfr * -δfr |, | δr1 * When −δr1 |, | δrr * −δrr |) is maintained for a predetermined time at a predetermined value or more, it is determined that steering is impossible.
In step S12, if a steerable state is not detected, this control routine is once ended.
This control routine is repeatedly executed, and if the determination in step S12 is “YES”, that is, if it is determined that one side of the rear wheel is not steerable, the process proceeds to step S13.
Hereinafter, a wheel that has become non-steerable is referred to as a non-steerable wheel WK, and a wheel on the opposite side of the non-steerable wheel WK is referred to as a left-right opposite wheel W0.

In step S13, the coefficient of friction (μl, μr) between the left and right wheels W and the ground road surface is estimated. For example, the left wheel Wfl, Wrl and the right wheel Wfr, Wrr are determined from temporal changes in the wheel speeds ωfl, ωfr, ωrl, ωrr detected from the wheel speed sensors 47a, 47b, 47c, 47d when braking occurs on the wheel W. And calculate the slip ratio obtained by averaging the front and rear wheels separately. Then, the left and right friction coefficients (μl, μr) are estimated from the wheel slip ratio. Since the technique for estimating the friction coefficient from the wheel slip rate is well known, further explanation is omitted.
In this case, in step S13, such calculation processing is not performed at this time, but the friction coefficient (μl, μr) is calculated and stored in advance every time braking is applied, and the latest friction stored is stored. Coefficient (μl, μr) data is read out.
Subsequently, based on the estimated friction coefficients (μl, μr), it is determined whether or not the vehicle is traveling on the μ split road (S14). For example, whether the difference (| μl−μr |) or the ratio (μl / μr or μr / μl) between the friction coefficient μl on the left wheel Wfl, Wrl side and the friction coefficient μr on the right wheel Wfr, Wrr side is equal to or higher than a reference value Judgment by

If it is determined that the road is not a μ-split road (S14: NO), the wheel W0 on the opposite side of the non-steerable wheel WK is steered in the opposite direction to the non-steerable wheel WK (S15). That is, the actual rudder angle (failure rudder angle δK) of the non-steerable wheel WK is detected by the wheel rudder angle sensor 42, and the left and right opposite wheels W0 are steered in the opposite direction with the same size as the failed rudder angle δK. As a result, the vehicle body BD can travel while being directed in the vehicle traveling direction, and yawing of the vehicle is prevented even during braking.
On the other hand, if it is determined in step S14 that the road is a μ split road, next, an optimum vehicle body slip angle β is calculated (S16).

  This optimum vehicle body slip angle β is obtained by determining the direction of each wheel Wfl, Wfr, Wrl, Wrr that does not cause yawing and lateral displacement and also maximizes the deceleration G when brake braking is applied. This is the vehicle body slip angle for turning the non-steerable wheel WK in the opposite direction. That is, with the four wheels including the wheel WK that cannot be steered, the yaw direction component and the lateral component force generated in each wheel Wfl, Wfr, Wrl, Wrr cancel each other, and the maximum deceleration G can be obtained. The direction of the four wheels Wfl, Wfr, Wrl, Wrr is obtained, and the vehicle body slip angle is such that the non-steerable wheel WK faces in the optimum direction obtained there.

For example, as shown in FIG. 8, among the forces generated on the wheels W, the sum of the yaw direction component forces Yfl, Yfr, Yrl, Yrr is 0, and the sum of the lateral direction component forces Sfl, Sfr, Srl, Srr is The optimum turning angle δfl *, δfr *, δrl *, δrr * for the four wheels Wfl, Wfr, Wrl, Wrr that maximizes the sum of the deceleration direction component forces Gfl, Gfr, Grl, Grr Calculate by convergence calculation using (μl, μr).
In this case, the optimum turning angles δfl *, δfr *, δrl *, δrr * of the four wheels Wfl, Wfr, Wrl, Wrr at various patterns of friction coefficients (μl, μr) are obtained in advance by convergence calculation. The result is stored as a calculation map in a storage element in the steering control device 40, and the optimum steering angle δfl *, δfr * of each wheel Wfl, Wfr, Wrl, Wrr is referred to during calculation while referring to the calculation map. , Δrl *, δrr * may be calculated.

FIG. 7 shows, as an example, a calculation map for calculating the optimum direction of the non-steerable wheel WK based on the friction coefficients (μl, μr). In this example, the optimum wheel slip angle α * with respect to the vehicle traveling direction of the non-steerable wheel WK is determined from the value of μA / μB (μA: friction coefficient on the non-steerable wheel WK side, μB: on the left and right opposite wheel W0 side. Coefficient of friction).
Then, the optimum vehicle body slip angle β is obtained by adding or subtracting the failure steering angle δK of the non-steerable wheel WK detected by the wheel steering angle sensor 42 and the optimum wheel slip angle α * with respect to the vehicle traveling direction of the non-steerable wheel WK. Desired.
When the calculation process in step S16 ends, the other three wheels W are steered so that the calculated optimum vehicle body slip angle β is reached. 3 (c), 4 (b), and 5 (c) are examples showing the state.

Next, in step S18, it is determined whether or not braking has been applied to the wheel W. This determination is made by reading a brake signal from a brake control device (not shown).
While the brake is not applied, the above process is repeated. When brake braking is applied (S18: YES), for example, as shown in FIGS. 3 (d), 4 (c), and 5 (d), the steering actuator 15 is driven to optimize the normal wheel W. Turn to the turning angle. That is, the steering is performed using the optimum turning angles δfl *, δfr *, δrl *, δrr * of the wheels Wfl, Wfr, Wrl, Wrr calculated in the process of obtaining the optimum vehicle body slip angle β in step S16 as the target turning angle. The actuator 15 is driven and controlled.

Therefore, the vehicle has the yaw-direction component forces Yfl, Yfr, Yrl, Yrr and the lateral component forces generated on the wheels Wfl, Wfr, Wrl, Wrr by the four wheels Wfl, Wfr, Wrl, Wrr including the non-steerable wheels WK. Sfl, Sfr, Srl, Srr cancel each other, and the largest deceleration G is obtained with the four wheels Wfl, Wfr, Wrl, Wrr.
As a result, both the stability of the vehicle behavior during braking and good deceleration performance can be achieved, and safety is improved.

As mentioned above, although the steering apparatus of this embodiment was demonstrated, this invention is not limited to the said embodiment, A various change is possible unless it deviates from the objective of this invention.
For example, in the rear wheel turning steering control routine in the present embodiment, the target vehicle body slip angle β is obtained so that not only the yaw direction component force but also the lateral component force is 0, the lateral component force For example, it is possible to adopt an omitted form, and it is not necessary to make the total component force zero, and calculate a target vehicle body slip angle β that can obtain a large deceleration G to the extent that yawing of the vehicle is not generated. Also good.

It is a whole lineblock diagram of a steering device concerning an embodiment of the present invention. It is explanatory drawing explaining the direction and the force which generate | occur | produce on a wheel at the time of a wheel normal. It is explanatory drawing explaining the direction of the wheel at the time of a right rear wheel failure, and the force which generate | occur | produces on a wheel, (a), (b) is a reference example for contrasting with this embodiment, (c), (d) is This embodiment is represented. It is explanatory drawing explaining the direction of the wheel at the time of a right rear wheel failure, and the force which generate | occur | produces on a wheel, (a) is a reference example for contrasting with this embodiment, (b), (c) is this embodiment. To express. It is explanatory drawing explaining the direction of the wheel at the time of a left rear wheel failure, and the force which generate | occur | produces on a wheel, (a), (b) is a reference example for contrasting with this embodiment, (c), (d) is This embodiment is represented. It is a flowchart showing the steering control routine at the time of rear-wheel failure. The calculation map which derives | leads-out the optimal wheel slip angle of a wheel which cannot be steered according to a friction coefficient is represented. It is explanatory drawing explaining the force which generate | occur | produces on a wheel.

Explanation of symbols

10A, 10B, 10C, 10D: Steering mechanism, 11a, 11b, 11c, 11d ... Knuckle, 12a, 12b, 12c, 12d ... Suspension, 15a, 15b, 15c, 15d ... Steering actuator, 40 ... Steering control device 41 ... Steering angle sensor, 42a, 42b, 42c, 42d ... Wheel steering angle sensor, 44 ... Vehicle speed sensor, 45 ... Yaw rate sensor, 46 ... Lateral acceleration sensor, 47a, 47b, 47c, 47d ... Wheel speed sensor, Wfl , Wfr, Wrl, Wrr ... wheels.

Claims (2)

A steering actuator that independently adjusts the steering angle of the front, rear, left and right wheels;
A steering apparatus comprising a steering control means for driving and controlling the steering actuator,
A steering abnormality detection means for detecting a steering abnormality in which either one of the left and right rear wheels cannot be steered;
A left-right friction coefficient difference state detecting means for detecting a difference state of a friction coefficient between the left wheel and the right wheel on the ground road surface;
When either the left or right steering abnormality of the rear wheel is detected by the steering abnormality detection means, the friction coefficient between the left and right wheels on the ground road surface is detected by the left and right friction coefficient different state detection means. When it is determined that the wheels are different, the steering actuators other than the wheels that cannot be steered are driven and controlled, and the wheels that cannot be steered are predetermined wheels with respect to the vehicle traveling direction. A turning device comprising: an abnormal turning control means for giving a slip angle to a vehicle body so as to obtain a slip angle. The abnormal turning control means is
The difference between the target wheel slip angle of the wheel that has become non-steerable and the friction coefficient of the non-steerable wheel with the ground contact surface is larger than the friction coefficient with the ground contact surface of the left and right opposite wheels. If the degree of friction is smaller than the friction coefficient with the grounding road surface of the wheel on the opposite side, the friction coefficient with the grounding road surface of the wheel on the opposite side is smaller. Target wheel slip angle setting means for setting the degree of difference toward the inner side of the vehicle traveling direction as the degree of difference increases,
A steering angle detecting means for detecting a turning angle of the non-steerable wheel, a target wheel slip angle set by the target wheel slip angle setting means, and a non-steering impossible detected by the steering angle detecting means. The steering apparatus according to claim 1, wherein the vehicle body slip angle is determined based on a wheel turning angle.

Images