JP2006044465A - Road surface friction coefficient detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a road surface friction coefficient detecting device capable of correctly detecting device capable of correctly detecting the friction coefficient of the road surface friction by sufficiently suppressing the deflection of a vehicle when detecting the road surface friction coefficient. <P>SOLUTION: The road surface friction coefficient detecting device has a motor capable of independently driving right and left wheels 2, 2 provided on a vehicle and a steering mechanism 4 capable of arbitrarily adjusting the steered angle of a steered wheel with respect to the steering angle of a steering wheel 41. The brake-driving force is given to the wheel 2 to slip the wheel 2, the road surface friction coefficient is calculated based on the brake-driving force when generating the slip, and the steered angle is controlled so as to suppress the deflection of the vehicle generated by giving the brake-driving force when giving the brake-driving force. Unstable vehicular state can be prevented even when the brake-driving force is given to detect the road surface friction coefficient. Therefore, a large brake-driving force can be given, and the road surface friction coefficient can be correctly detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a road surface friction coefficient detection device that detects a friction coefficient of a road surface on which a vehicle travels.

2. Description of the Related Art Conventionally, as a road surface friction coefficient detection device, as described in, for example, Japanese Patent Application Laid-Open No. 2002-160621, a road surface friction coefficient estimation device applied to a vehicle capable of executing anti-skid control, which has a predetermined braking force. It is known that a braking force is applied to a pair of left and right wheels until a predetermined slip state is reached or a road surface friction coefficient is estimated based on the braking force at that time. When applying braking force to a pair of wheels for estimating the friction coefficient of the road surface, this device sets the anti-skid control start threshold value low, starts anti-skid control early, and makes the vehicle suddenly It is intended to prevent an excessive yaw moment from occurring.
JP 2002-160621 A

  Such a road surface friction coefficient detecting device can be applied only to a vehicle capable of executing anti-skid control. Moreover, it is difficult to sufficiently suppress the deflection generated in the vehicle when detecting the road surface friction coefficient only by making the anti-skid control early. For this reason, it is difficult to increase the braking force of the wheels applied to detect the road surface friction coefficient, and it is difficult to accurately detect the road surface friction coefficient.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a road surface friction coefficient detection device capable of accurately detecting a road surface friction coefficient by sufficiently suppressing vehicle deflection when detecting the road surface friction coefficient.

  That is, the road surface friction coefficient detection device according to the present invention arbitrarily adjusts the turning angle of the steered wheel with respect to the steering angle of the steering means and the driving means that can drive the left and right wheels provided in the vehicle independently of each other. A steering mechanism, a road surface friction coefficient calculating means for applying a braking / driving force to the wheel to slip the wheel and calculating a road surface friction coefficient based on the braking / driving force when the slip is generated; And a steering angle control means for controlling the turning angle so as to suppress the deflection of the vehicle caused by the application of the braking / driving force when the driving force is applied.

  According to the present invention, when a braking / driving force is applied to detect the road surface friction coefficient, the turning angle can be controlled so as to suppress the deflection of the vehicle caused by the application of the braking / driving force. For this reason, even if the braking / driving force is applied to detect the road surface friction coefficient, the vehicle state can be prevented from becoming unstable. Therefore, it is possible to apply a strong braking / driving force, and it is possible to accurately detect the road surface friction coefficient.

  In the road surface friction coefficient detecting device according to the present invention, when the steering angle control means applies the braking / driving force, the steering angle is controlled so as to suppress a yaw moment of the vehicle caused by the braking / driving force. Is preferably controlled.

  In the road surface friction coefficient detecting device according to the present invention, when the rudder angle control means applies the braking / driving force, the steering angle is set so as to suppress a vehicle body slip angle caused by the braking / driving force. It is preferable to control.

  ADVANTAGE OF THE INVENTION According to this invention, the road surface friction coefficient detection apparatus which can fully suppress the deflection | deviation of a vehicle in the case of the detection of a road surface friction coefficient can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
(First embodiment)
FIG. 1 is a schematic configuration diagram of a road surface friction coefficient detecting device according to a first embodiment of the present invention.

  As shown in the figure, the road surface friction coefficient detection device 1 is a device mounted on a vehicle traveling on the road, and detects the friction coefficient of the road surface on which the vehicle travels. The road surface friction coefficient detecting device 1 includes a motor 3 that can independently drive left and right wheels 2 provided on a vehicle. The motor 3 is a driving means that is provided for each wheel 2 and can be independently driven. As the motor 3, for example, an in-wheel motor configured to be incorporated in the wheel 2 is used. In addition, although the road surface friction coefficient detection apparatus 1 which concerns on this embodiment is mounted in the vehicle which provided the motor 3 in all the four wheels, the road surface friction coefficient detection apparatus which concerns on this invention is such The present invention is not limited to this, and the present invention may be applied to a vehicle in which the motor 3 is provided only on the left and right front wheels or only on the rear left and right wheels.

  The road surface friction coefficient detection device 1 includes a steering mechanism 4 that can arbitrarily adjust the turning angle of the steered wheels with respect to the steering angle of the handle 41. The steering mechanism 4 turns the wheel 2 that is a steered wheel according to the steering amount by the operation of the handle 41 in normal times other than when the road surface friction coefficient is detected. A steering shaft 43 is connected to the handle 41. The steering shaft 43 is connected to the wheels 2 and 2 which are front wheels via a gear device 44 configured by a rack and pinion type or the like. The gear device 44 moves the tie rod 45 by turning input of the steering shaft 43 to steer the wheels 2 and 2.

  A steering sensor 47 and a transmission ratio variable mechanism 48 are provided in the middle of the steering shaft 43. The steering sensor 47 functions as a steering angle detection unit that detects the steering angle of the handle 41. The transmission ratio variable mechanism 48 can arbitrarily adjust the turning angle of the steered wheels with respect to the steering angle of the handle 41, and is connected to, for example, the input shaft connected to the handle 41 side and the gear device 44 side. And an output shaft that can arbitrarily rotate the input shaft and the output shaft. As a specific example, a motor and a speed reducer are provided between an input shaft and an output shaft, and the steering angle is arbitrarily adjusted with respect to the steering angle of the handle 41 by driving and controlling the motor. Used. Further, as the transmission ratio variable mechanism 48, as long as the turning angle can be arbitrarily adjusted with respect to the steering angle of the handle 41, the input shaft and the output shaft are mechanically separated from each other. A type may be used.

  Each wheel 2 of the vehicle is provided with a brake device 5. The brake device 5 brakes the wheel 2 and operates according to the hydraulic pressure transmitted through the hydraulic circuit 6. The hydraulic circuit 6 is provided with a brake fluid passage (not shown) and a pump (not shown) for forcibly applying hydraulic pressure. By operating this pump, a hydraulic pressure is generated in the flow path, and a braking force can be forcibly applied. Each wheel 2 of the vehicle is provided with a wheel speed sensor 7. The wheel speed sensor 7 is a wheel speed detection unit that detects the rotation speed of the wheel 2.

  The road surface friction coefficient detecting device 1 is provided with an ECU 10. The ECU 10 controls the entire apparatus, and includes, for example, a CPU, a ROM, a RAM, an input signal circuit, an output signal circuit, a power supply circuit, and the like. The ECU 10 is connected to the motor 3 and outputs a drive control signal to the motor 3 to control the drive of the motor 3. The ECU 10 is connected to the transmission ratio variable mechanism 48, outputs a steering control signal to the transmission ratio variable mechanism 48, and performs steering control to adjust the actual steering angle with respect to the steering angle of the handle 41. The ECU 10 is connected to the steering angle sensor 47 and inputs a detection signal of the steering angle sensor 47. The ECU 10 is connected to the wheel speed sensor 7 and inputs a detection signal from the wheel speed sensor 7.

  Further, the ECU 10 functions as road surface friction coefficient calculating means for forcibly applying a braking / driving force to the wheel 2 to cause the wheel 2 to slip and to calculate a road surface friction coefficient based on the braking / driving force when the slip is generated. To do. The ECU 10 also serves as a steering control means for controlling the turning angle so as to suppress vehicle deflection (yaw moment, vehicle body slip angle) caused by the application of the braking / driving force when the braking / driving force is applied. Function.

  Next, operation | movement of the road surface friction coefficient detection apparatus 1 which concerns on this embodiment is demonstrated.

  FIG. 2 is a flowchart showing the operation of the road surface friction coefficient detection apparatus 1 according to this embodiment. The control process in the flowchart of FIG. 2 is started, for example, when a vehicle ignition switch is turned on, and is repeatedly executed at predetermined time intervals. As shown in S10 of FIG. 2, first, it is determined whether or not a road friction coefficient detection condition is satisfied. The detection condition of the road surface friction coefficient is set, for example, that the vehicle is traveling at a vehicle speed equal to or higher than a predetermined speed and that the road surface state change is continued n times a predetermined number of times. When it is determined that the road friction coefficient detection condition is not satisfied, the control process is terminated.

  On the other hand, when it is determined that the road surface friction coefficient detection condition is satisfied, a braking / driving force applying process is performed (S12). This braking / driving force applying process is a process for forcibly applying either braking force or driving force to the specific wheel 2. When the braking force is applied, a hydraulic pressure control signal is output from the ECU 10 to the hydraulic circuit 6 to forcibly generate the hydraulic pressure and operate the brake device 5 of the wheel 2 to which the braking force is to be applied. Thereby, a braking force can be forcibly given to a specific wheel 2, and the wheel 2 can be made into a slip state.

  In addition, when a driving force is applied, a drive control signal is output from the ECU 10 to the motor 3, and the specific motor 3 is driven with a driving force larger than that of the other motors 3. Thereby, a big driving force is forcibly given to the specific wheel 2 and the wheel 2 can be made into a slip state.

  And it transfers to S14 and a steering angle control process is performed. This steering angle control process is a process of adjusting the steering angle so as to suppress the deflection of the vehicle caused by the application of the braking / driving force in S12. For example, the correction angle Δδ of the turning angle is calculated using the following equation (1).

  Then, as shown in the following equation (2), the correction angle Δδ is added to the turning angle δ according to the steering of the handle 41 to obtain a corrected turning angle δ ′.

  In equations (1) and (2), S is a Laplace operator, Grm is a yaw rate gain by direct moment application, Gr is a yaw rate gain by steering, Tr is a yaw rate time constant by steering, and Trm is a yaw rate time constant by direct moment application. , M is a moment generated by applying braking / driving force.

  The moment M due to the application of braking / driving force in the equations (1) and (2) can be calculated by the following equation (3).

  In this formula (3), Fi (i = 1 to 4: i = 1 is the left front wheel, i = 2 is the right front wheel, i = 3 is the left rear wheel, i = 4 is the right rear wheel, and so on. .) Is the braking / driving force applied to the wheel 2, Df is the front tread width, Dr is the rear tread width, Ji (i = 1 to 4) is the inertial mass of each wheel, and ωi (i = 1 to 4). ) Is the wheel angular velocity, Rf is the tire radius of the front wheel, and Rr is the tire radius of the rear wheel. Incidentally, although the road surface frictional force generated by each wheel 2 must be considered in the original case, here, the road surface friction coefficient must be taken into consideration. Here, based on the moment obtained from the inertial mass of each wheel 2 and the braking / driving force to be applied, it is a feedforward type. The steering correction angle is obtained.

  The correction angle Δδ in equation (1) can be derived based on the following equations (4) and (5).

  Equation (4) shows the yaw rate Yr (S) generated when the steered wheel is steered by the steered angle δ by the steering operation. Equation (5) shows the yaw rate Yrm (S) generated when the braking / driving force is forcibly applied.

  In the equations (4) and (5), Gr is a yaw rate gain by steering the steering wheel. This yaw rate gain Gr is calculated by equation (6). Grm is a yaw rate gain generated when a braking / driving force is forcibly applied. This yaw rate gain Grm is calculated by equation (7). ωn is a natural angular frequency and is calculated by the equation (8). Tr is a yaw rate time constant in a yaw rate generated by steering the steering wheel. This yaw rate time constant Tr is calculated by equation (9).

Trm is a yaw rate time constant in a yaw rate generated when a braking / driving force is forcibly applied. This yaw rate time constant Trm is calculated by equation (10).
ζ is an attenuation coefficient, and is calculated by equation (11).

  In these formulas (6) to (11), V is the vehicle speed, L is the wheel base of the vehicle, and kh is the stability factor. Kf and Kr are the front and rear wheel cornering power (for each wheel), m is the vehicle weight, I is the inertia moment in the yaw direction, Lf is the distance from the center of gravity of the vehicle to the front axis, and Lr is from the center of gravity of the vehicle to the rear axis. Is the distance.

  Here, the steering correction angle Δδ for suppressing the moment M due to the application of braking / driving force satisfies the following equation (12). That is, the sum of the yaw rate Yrm (Yrm derived from the equation (5)) generated by the moment M resulting from the application of the braking / driving force and the Yr (Yr derived from the equation (4)) generated by the corrected steering angle Δδ generated by the steering adjustment is obtained. By becoming zero, the yaw moment of the vehicle is suppressed.

  Then, the equation (1) described above can be obtained by solving the equation (12) with respect to Δδ.

  As described above, in the steering angle control process of S14, the output of the transmission ratio variable mechanism 48 is adjusted, and the correction angle Δδ is added as the turning angle of the steered wheels, so that the vehicle is deflected by forcibly applying the braking / driving force. Can be suppressed appropriately.

  And it transfers to S16 of FIG. 2 and a road surface friction coefficient calculation process is performed. The road surface friction coefficient calculation process is a process of calculating the road surface friction coefficient based on the braking / driving force when the wheel 2 is in a slip state by applying the braking / driving force in S12. After this road surface friction coefficient calculation process ends, the control process ends.

As described above, according to the road surface friction coefficient detection device 1 according to the present embodiment, when the braking / driving force is forcibly applied in order to detect the road surface friction coefficient, the vehicle frictional force generated by the braking / driving force is detected. The turning angle can be controlled to suppress the yaw moment and prevent the vehicle from deflecting. For this reason, even if the braking / driving force is applied to detect the road surface friction coefficient, the vehicle state can be prevented from becoming unstable. Therefore, it is possible to apply a strong braking / driving force, and it is possible to accurately detect the road surface friction coefficient.
(Second embodiment)
The road surface friction coefficient detection device according to the first embodiment described above controls the turning angle so as to suppress the yaw moment generated when the forced braking / driving force is applied and prevent the vehicle from deflecting. However, the road surface friction coefficient detecting device according to the present embodiment controls the turning angle so as to prevent the vehicle from deflecting by suppressing the vehicle body slip angle generated when the forced braking / driving force is applied. is there.

  The road surface friction coefficient detecting device according to the present embodiment has the same hardware configuration as the road surface friction coefficient detecting device according to the first embodiment shown in FIG. 1, and the road surface friction according to the first embodiment shown in FIG. Although the control processing is substantially the same as that of the coefficient detection device, the processing content of the steering angle control in S14 of FIG. 2 is different from that of the road surface friction coefficient detection device according to the first embodiment.

  The steering angle control process in the road surface friction coefficient detection device according to the present embodiment is performed as follows. For example, the correction angle Δδ of the turning angle is calculated using the following equation (13).

  Then, as shown in the following equation (14), this correction angle Δδ is added to the turning angle δ according to the steering of the handle 41 to obtain a corrected turning angle δ ′.

  In equations (13) and (14), S is a Laplace operator, Gβm is a vehicle body slip angle gain by direct moment application, Gβ is a vehicle body slip angle gain by steering, Tβ is a vehicle body slip angle time constant by steering, and M is a control. This is a moment generated by applying a driving force.

  The moment M due to the braking / driving force applied in the equations (13) and (14) can be calculated by the equation (3) described above.

  The correction angle Δδ in equation (13) can be derived based on the following equations (15) and (16).

  Equation (15) shows the vehicle body slip angle β (S) that is generated when the steered wheels are steered by the steered angle δ by the steering wheel operation. Equation (16) shows the vehicle body slip angle βm (S) that occurs when the braking / driving force is forcibly applied.

  In the expressions (15) and (16), Gβ is a vehicle body slip angle gain by steering the steering wheel. This yaw rate gain Gβ is calculated by equation (17). Gβm is a vehicle body slip angle gain generated when a braking / driving force is forcibly applied. The vehicle body slip angle gain Gβm is calculated by equation (18). ωn is a natural angular frequency and is calculated by the above-described equation (8). Tβ is a vehicle body slip angle time constant in the vehicle body slip angle generated by steering the steering wheel. The vehicle body slip angle time constant Tβ is calculated by the equation (19). ζ is an attenuation coefficient, and is calculated by the above-described equation (11).

  In these formulas (17) to (19), V is the vehicle speed, L is the wheel base of the vehicle, and kh is the stability factor. Kf and Kr are the front and rear wheel cornering power (for each wheel), m is the vehicle weight, I is the inertia moment in the yaw direction, Lf is the distance from the center of gravity of the vehicle to the front axis, and Lr is from the center of gravity of the vehicle to the rear axis. Is the distance.

  Here, the steering correction angle Δδ for suppressing the moment M due to the application of the braking / driving force satisfies the following equation (20). That is, the vehicle body slip angle βm (βm derived from the equation (16)) generated by the moment M due to the application of the braking / driving force and β (β derived from the equation (15)) generated by the corrected steering angle Δδ generated by the steering adjustment. When the sum becomes zero, the vehicle body slip angle of the vehicle is suppressed.

  Then, by solving the equation (20) for Δδ, the above-described equation (13) can be obtained.

  As described above, in the steering angle control process of S14, the output of the transmission ratio variable mechanism 48 is adjusted, and the correction angle Δδ is added as the turning angle of the steered wheels, so that the vehicle is deflected by forcibly applying the braking / driving force. Can be suppressed appropriately.

  As described above, according to the road surface friction coefficient detecting device according to the present embodiment, when the braking / driving force is forcibly applied to detect the road surface friction coefficient, the vehicle body slip angle generated by the application of the braking / driving force. It is possible to control the turning angle so as to prevent the vehicle from being deflected. For this reason, even if the braking / driving force is applied to detect the road surface friction coefficient, the vehicle state can be prevented from becoming unstable. Therefore, it is possible to apply a strong braking / driving force, and it is possible to accurately detect the road surface friction coefficient.

1 is a schematic configuration diagram of a road surface friction coefficient detection device according to a first embodiment of the present invention. It is a flowchart which shows operation | movement of the road surface friction coefficient detection apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Road surface friction coefficient detection apparatus, 2 ... Wheel, 3 ... Motor, 4 ... Steering mechanism, 5 ... Brake device, 6 ... Hydraulic circuit, 7 ... Wheel speed sensor, 10 ... ECU, 41 ... Handle, 43 ... Steering shaft, 44 ... Gear device, 47 ... Steering angle sensor, 48 ... Transmission ratio variable mechanism.

Claims (3)

Driving means capable of independently driving left and right wheels provided in the vehicle;
A steering mechanism capable of arbitrarily adjusting the turning angle of the steered wheels with respect to the steering angle of the steering wheel;
Road friction coefficient calculating means for applying a braking / driving force to the wheel to cause the wheel to slip and calculating a road surface friction coefficient based on the braking / driving force when the slip occurs;
Rudder angle control means for controlling the turning angle so as to suppress the deflection of the vehicle caused by the application of the braking / driving force when the braking / driving force is applied;
A road surface friction coefficient detecting device.   The steering angle control means controls the turning angle so as to suppress a yaw moment of a vehicle generated by applying the braking / driving force when the braking / driving force is applied. The road surface friction coefficient detecting device described.   The said steering angle control means controls the said steering angle so that the vehicle body slip angle produced by the application of the braking / driving force may be suppressed when the braking / driving force is applied. Road surface friction coefficient detection device.

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