Vehicle control device of four-wheel independent drive vehicle for when one wheel is lost

Abstract

A target longitudinal force sum/yaw moment setting section is provided which is configured to determine and set a target longitudinal force sum to be exerted on drive wheels by drive sources and a target yaw moment of a vehicle. A failure detection section is provided which is configured to detect occurrence of a failure in the drive source of each of the drive wheels and a drive system including a control system of the drive source. A one-wheel-failure control section is provided which is configured to, when a failure of one of the wheels is detected by the failure detection section, drive the drive sources of all the remaining sound wheels so as to minimize a sum of squares of load factors of the sound wheels and to be matched with the target longitudinal force sum and the target yaw moment that are set.

Claims

1. A one-wheel-failure vehicle control device for a four-wheel independent drive vehicle including drive sources configured to independently drive respective four drive wheels serving as left and right front wheels and left and right rear wheels, the one-wheel-failure vehicle control device comprising: a target longitudinal force sum/yaw moment setting section configured to calculate and set a longitudinal force sum that is a present target sum of longitudinal forces to be exerted on all four drive wheels by the corresponding drive sources and a present target yaw moment of the vehicle; a failure detection section configured to detect an occurrence of a failure in the drive source of each of the drive wheels and a failure in a drive system including a control system of the drive source; and a one-wheel-failure control section configured to, when a failure in the drive source and the drive system of one of the wheels is detected by the failure detection section, drive the drive sources of all sound wheels except for the one wheel in which the failure of the drive source and the drive system is detected, wherein the one-wheel-failure control section minimizes a sum of squares of load factors of all the sound wheels using the longitudinal force sum set by target longitudinal force sum/yaw moment setting section prior to the failure as a target value to determine the longitudinal force for each of the sound wheels, where the load factor is defined as a ratio of a resultant force of longitudinal force and lateral force relative to vertical force acting on the respective wheel.

2. The one-wheel-failure vehicle control device for the four-wheel independent drive vehicle as claimed in claim 1, wherein the target longitudinal force sum/yaw moment setting section obtains a steering angle input from a steering device of the vehicle, and sets the target yaw moment by using a transfer function with respect to the steering angle input that is determined by using an equation of motion of the vehicle.

3. The one-wheel-failure vehicle control device for the four-wheel independent drive vehicle as claimed in claim 1, wherein a transfer characteristic of a yaw angular velocity with respect to a steering angle input obtained from a steering device of the vehicle is set and the target longitudinal force sum/yaw moment setting section calculates and sets the target yaw moment from the steering angle input by using the transfer characteristic.

4. The one-wheel-failure vehicle control device for the four-wheel independent drive vehicle as claimed in claim 1, wherein the one-wheel-failure control section estimates one of a longitudinal force, a lateral force, and a vertical force acting on each of the wheels by solving an equation of motion of the drive wheel or the vehicle, and determines the load factor by using a value obtained by the estimation.

5. The one-wheel-failure vehicle control device for the four-wheel independent drive vehicle as claimed in claim 4, wherein the vertical force acting on each of the wheels is estimated from a vehicle weight and distances between a center of gravity and front and rear axles.

6. The one-wheel-failure vehicle control device for the four-wheel independent drive vehicle as claimed in claim 1, wherein the one-wheel-failure control section detects one of a longitudinal force, a lateral force, and a vertical force acting on each of the wheels with a load sensor attached to a wheel supporting part, and determines the load factor by using a value obtained by the detection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views, and:

(2) FIG. 1 is a block diagram showing a conceptual configuration of a one-wheel-failure vehicle control device for a four-wheel independent drive vehicle according to an embodiment of the present invention;

(3) FIG. 2 is an explanatory diagram showing the dimensions and the working loads of various parts of the four-wheel independent drive vehicle in plan view;

(4) FIG. 3 is an explanatory diagram of a control operation performed by the one-wheel-failure vehicle control device;

(5) FIG. 4 shows graphs showing simulation results for a relationship between time, a yaw angular velocity, and a vehicle speed, and a relationship between time and a longitudinal force for each wheel when the one-wheel-failure vehicle control device is applied; and

(6) FIG. 5 shows graphs showing simulation results for a relationship between time, a yaw angular velocity, and a vehicle speed, and a relationship between time and a longitudinal force for each wheel when the one-wheel-failure vehicle control device is not applied.

DESCRIPTION OF EMBODIMENTS

(7) An embodiment of the present invention will be described with reference to the drawings. Referring to FIG. 1, a vehicle 1 to which a one-wheel-failure vehicle control device is applied is a four-wheel independent drive vehicle in which four drive wheels 2, 2, 3, 3 serving as left and right front wheels and left and right rear wheels are independently driven by respective motors 4 serving as drive sources. In the illustrated example, each motor 4 constitutes an in-wheel motor drive device 7, together with a wheel bearing 5 and a speed reducer or reduction gear 6 that transmits a rotation of the motor 4 to a rotating ring (not shown) of the wheel bearing 5. The motor 4 is not limited to a motor constituting the in-wheel motor drive device 7, and may be a motor that is installed on a chassis and drives the drive wheels 2, 3 via a drive shaft (not shown).

(8) The left and right drive wheels 2, 2 serving as the front wheels can be turned by a turning mechanism 8, and are steered with a steering wheel 9 serving as a steering input component through the turning mechanism 8. The turning mechanism 8 and the steering wheel 9 constitute a steering device 10. The steering device 10 in this example employs a steer-by-wire system including a turning motor (not shown) in the turning mechanism 8. The steering device 10 detects a steering angle of the steering wheel 9 by use of a steering detection sensor 11, and controls a rotation angle of the turning motor with a steering control section (not shown) on the basis of the detected steering angle. The steering control section is provided as a part of the functions of an ECU 21, which will be described later, or as a dedicated ECU. The steering device 10 may employ not only the steer-by-wire system but also a power steering or a system that mechanically transmits a rotation of the steering wheel 9 to the turning mechanism 8.

(9) The control system of the vehicle 1 is mainly composed of the ECU 21 and inverter devices 22, 22, 22, 22 that respectively drive the motors 4 for the drive wheels 2, 3. The ECU 21 is an electric control unit that performs cooperative control and central control of the entire vehicle, and is provided with a torque distribution section 23.

(10) The torque distribution section 23 receives input of an accelerating command from an accelerator manipulation component such as an accelerator pedal 13 and a decelerating command from a brake manipulation component such as a brake pedal 14, and distributes a drive command corresponding to a difference between the accelerating command and the decelerating command to the motors 4, 4, 4, 4 for the respective drive wheels 2, 3. The accelerating command and the decelerating command are commands for manipulation amounts such as depressing amount of pedals provided for the accelerator pedal 13 and the brake pedal 14 respectively. Basically, the torque distribution section 23 equally divides and provides the drive command to the respective motors 4 for the four wheels, but may be configured to have the function for adjusting the values of left and right driving forces in accordance with a steering angle input from the steering wheel 9. The drive command is a torque command, for example.

(11) The drive command that is distributed and outputted from the torque distribution section 23 is provided to the inverter device 22 for each wheel. Each inverter device 22 includes an inverter (not shown) that converts a direct-current power of a battery (not shown) into an alternating-current power for driving the corresponding motor 4, and a motor control circuitry (not shown) that controls the inverter. The motor control circuitry includes a microcomputer and a motor control program. The inverter device 22 controls the inverter in accordance with the provided drive command such as the torque command to control the power provided to the motor 4.

(12) The one-wheel-failure vehicle control device 24 is provided in the ECU 21 or provided as a dedicated ECU separate from the ECU 21, in the vehicle having the above-described configuration. The one-wheel-failure vehicle control device 24 includes a target longitudinal force sum/yaw moment setting section 25, a failure detection section 26, a one-wheel-failure control section 27, and a notification section 28.

(13) The target longitudinal force sum/yaw moment setting section 25 is configured to constantly calculate and set a longitudinal force sum that is a present target sum of longitudinal forces exerted on the drive wheels 2, 3 by the corresponding motors 4, and a present target yaw moment of the vehicle, for example, during driving of the motors 4. The failure detection section 26 is configured to detect an occurrence of a failure in the drive source 4 of any of the drive wheels 2, 3 and a failure in a drive system including the control system of that drive source 4. The one-wheel-failure control section 27 is configured to, when the failure of one wheel is detected by the failure detection section 26, distribute the drive command such as the torque command, in place of the distribution performed by the torque distribution section 23. The one-wheel-failure control section 27 provides the drive command to the motors 4 for driving all sound wheels, which will be described later, except for the one wheel in which the failure is detected, so as to be matched with the target longitudinal force sum and the target yaw moment set by the target longitudinal force sum/yaw moment setting section 25, and so as to minimize a sum of squares of load factors in all the sound wheels. The one-wheel-failure control section 27 does not function when two or more wheels have failed. The notification section 28 is configured to, when the failure is detected by the failure detection section 26, notify a driver of the drive wheel 2, 3 in which the failure has occurred and the type of the failure by displaying the failure drive wheel 2, 3 and the type of the failure on a monitor (not shown) in front of the driver's seat. In addition to this, the notification section 28 notifies the driver of the fact that, due to the occurrence of the failure in one wheel, the vehicle is running with the remaining three wheels, by displaying that fact on the monitor.

(14) Specific examples of the failures detected by the failure detection section 26 include faults in the inverter of each inverter device 22 and the motor control circuitry controlling the inverter, problems in the motor control program, breakage of cables, and damages to the components (gears and bearings) of each in-wheel motor drive device 7, including a slight damage.

(15) The one-wheel-failure control section 27 will be described in detail. First, a description of the principle applied thereto will be given. Based on the vehicle kinematic theory, a longitudinal force sum X and a yaw moment M that act on the vehicle, for example, when the right rear wheel has failed, are represented by the following formulas.

(16) [Math. 1]
X=X.sub.1+X.sub.2+X.sub.3+X.sub.fail(1)
M=(Y.sub.2+Y.sub.2)l.sub.f(Y.sub.2+Y.sub.fail)l.sub.fd.sub.f(X.sub.2X.sub.2)/2d.sub.f(X.sub.2X.sub.fail)/2(2)

(17) In the formulas, Xi and Yi respectively represent the longitudinal force and a lateral force acting on each wheel. Regarding the subscript i, 1 represents the left front wheel, 2 represents the right front wheel, 3 represents the left rear wheel, and fail represents the right rear wheel (the failed wheel) (see FIG. 2). lf and lr represent the distances from the vehicle's center of gravity G to front and rear axles respectively. df and dr represent the treads of the front and rear wheels respectively.

(18) To decrease the load factors of the sound wheels after occurrence of the failure, which are represented by the following formula, the following evaluation function J is introduced. The load factor is defined as a ratio of a resultant force of the longitudinal force X and the lateral force Y relative to a vertical force Z described below. The evaluation function is the sum of the squares of the load factors of the sound wheels.

(19) $\begin{array}{cc}\left[\mathrm{Math}.2\right]& \\ \mathrm{Load}\mathrm{factor}\left(=\sqrt{X_i^2+Y_i^2}/Z_i\right)/=\underset{i=1}{\overset{3}{.Math.}}{\left(\frac{\sqrt{X_i^2+Y_i^2}}{\mathrm{Zi}}\right)}^2& \left(3\right)\end{array}$

(20) In Formula (3), Zi represents a vertical force acting on each wheel. It is assumed that the longitudinal force sum X and the yaw moment M are given, and the longitudinal force Xi, the lateral force Yi, and the vertical force Zi that act on each wheel can be known. At this time, when a condition that the evaluation function (sum of squares of the load factors) of Formula (3) is minimized is added to Formulas (1) and (2), the longitudinal forces Xi (i=1 to 3) for the sound wheels are determined. That is, when the longitudinal force sum X and the yaw moment M before the occurrence of the failure are set as the target values, even if the failure occurs in the right rear wheel, it is possible to maintain the vehicle speed (corresponding to the longitudinal force sum) and the turning performance (corresponding to the yaw moment) before the occurrence of the failure so as to follow the target values, by providing, to the sound wheels, the longitudinal forces Xi determined by Formulas (1) to (3). The longitudinal forces provided to the sound wheels in this manner are determined such that the sum of the squares of the load factors of the sound wheels is minimized.

(21) The one-wheel-failure control section 27 is configured to perform control according to the above-described principle, receives inputs of the longitudinal force Xi, the lateral force Yi, and the vertical force Zi acting on each wheel, and determines the longitudinal forces Xi for all sound wheels by using Formulas (1) and (2) so as to give the longitudinal force sum X and the yaw moment M set as the targets by the target longitudinal force sum/yaw moment setting section 25 and so as to minimize the evaluation function of Formula (3). The determined longitudinal force Xi for each wheel is provided to the inverter device 22 for the respective wheel.

(22) In the one-wheel-failure control section 27, each of the longitudinal force Xi, the lateral force Yi, and the vertical force Zi may be estimated by using the equation of motion of wheels (drive wheels 2, 3). In the case where a load sensor 15 capable of measuring a load acting on a wheel is provided, these forces may be measured by using values detected by the load sensor 15. The load sensor 15 is provided, for example, to a wheel supporting part such as the wheel bearing 5 or a hub (not shown). One or more of the longitudinal force Xi, the lateral force Yi, and the vertical force Zi may be estimated by using the equation of motion, and the remaining forces may be measured by using the values detected by the load sensor 15. Instead of using the load sensor 15, the longitudinal force Xi, the lateral force Yi, and the vertical force Zi may be estimated by using an output from an attitude detection sensor (not shown) for detecting the attitude of the vehicle 1. For simplicity, assuming that a significant load shift does not occur in the longitudinal direction and the left-right direction, the vertical force Zi may be given by the following formulas in which a vehicle weight W is distributed on the basis of lf and lr.

(23) $\begin{array}{cc}\left[\mathrm{Math}.3\right]& \\ Z_1=Z_2=\frac{I_r}{I_f+I_r}\frac{W}{3}{Z}_3=Z_{\mathrm{fall}}=\frac{I_f}{I_f+I_r}\frac{W}{3}& \left(4\right)\end{array}$

(24) The target longitudinal force sum/yaw moment setting section 25 will be described in detail. The target longitudinal force sum X is set in accordance with depressing amounts (manipulation amounts) of the accelerator pedal 13 and the brake pedal 14. The target yaw moment M is set in accordance with a vehicle speed V and a steering angle .

(25) For example, the yaw moment M(s) is set by determining a transfer function (M(s)/(s)) with respect to the steering angle input (s) by using an equation of motion of the vehicle in the following manner. Alternatively, the transfer characteristic of the yaw angular velocity with respect to the steering angle is examined by actual running, and the examined transfer characteristic is set.

(26) From the equation of motion of the vehicle for a two-wheel model, the transfer characteristic of the yaw angular velocity r(s) with respect to the steering angle input (s) can be represented by the following formula. In the following formula, I represents a yaw moment of inertia, n represents a steering gear ratio, n represents a natural frequency of the vehicle, and represents a damping ratio. A represents a stability factor, l represents the distance between the front and rear axles, m represents the vehicle mass, and Kr represents the cornering power of the rear wheels.

(27) $\begin{array}{cc}\frac{r\left(s\right)}{\left(s\right)}=\frac{G_{}^r\left(0\right)}{n}\frac{1+T_{r}s}{1+\frac{2s}{{}_n}+\frac{s^2}{{}_n^s}}& \left[\mathrm{Math}.4\right]\end{array}$
Therefore, the target yaw moment M(s) may be set as

(28) $\frac{M\left(s\right)}{\left(s\right)}=[\frac{G_{}^r\left(0\right)}{n}\frac{s+T_r{s}^2}{1+\frac{2s}{{}_n}+\frac{s^2}{{}_n^s}}\mathrm{where}{G}_{}^r\left(0\right)-\frac{1}{1+{\mathrm{AV}}^2}\frac{V}{l}{T}_r=\frac{\mathrm{mLV}}{2{\mathrm{lK}}_r}$

(29) An example of the control operation performed with the above-described configuration will be described in conjunction with FIG. 3. FIG. 3 shows a block diagram including the control according to the present embodiment when the failure has occurred. For example, the detected values of the rotational speed (or the number of rotation) of the motors 4 for the four wheels are constantly monitored to detect whether or not the motor failure has occurred, and to identify the failed wheel (step S1). The failure detection and the identification mentioned above are performed by the failure detection section 26 shown in FIG. 1. When a failure has occurred, the driver is notified of the abnormality by the notification section 28, and the drive torque of the failed wheel or the occurrence of the failure is informed from the failure detection section 26 to the one-wheel-failure control section 27.

(30) The one-wheel-failure control section 27 obtains the longitudinal force Xi, the lateral force Yi and the vertical force Zi of the failed wheel, and the longitudinal forces Xi, the lateral forces Yi and the vertical forces Zi of the sound wheels either from the equation of motion or from the values measured by the load sensors 15 for the wheels or by the attitude sensor of the vehicle (step S2). After the longitudinal force Xi, the lateral force Yi, and the vertical force Zi of each wheel are obtained in this manner, the one-wheel-failure control section 27 calculates the longitudinal forces that are to be provided to all the sound wheels, so as to give the target longitudinal force sum and the target yaw moment set by the target longitudinal force sum/yaw moment setting section 25, and so as to minimize the sum of the squares of the load factors, that is, to minimize the value of the evaluation function (3) (step S3), and provides these calculated longitudinal forces to all the sound wheels as the drive commands for the motors 4, in place of the torque distribution section 23.

(31) The effects achieved by the control according to the present embodiment are verified by a simulation of the vehicle motion. The simulation assumes a situation where, during a circular turn in the counterclockwise direction at a speed of 50 km/h, a failure occurs in the right rear wheel so that a sudden braking force is unintendedly generated in the right rear wheel 3. To set values in the steady-state circular turn before the occurrence of the failure as the target values, X=M=0 is set. FIG. 5 shows the results obtained when the control according to the present embodiment is not applied. FIG. 4 shows the results obtained when the control according to the present embodiment is applied.

(32) As can be seen from FIG. 5, when the control is not applied, the yaw angular velocity and the vehicle speed drop after the failure because of the sudden occurrence of braking of the right rear wheel. However, as shown in FIG. 4, it can be confirmed that, by providing appropriate longitudinal forces to the sound wheels through the control according to the present embodiment, it is possible to maintain the yaw angular velocity and the vehicle speed at their values before the occurrence of the failure, thereby allowing the circular turn to be continued without a feeling of discomfort. Although the foregoing description assumes that the right rear wheel has failed, the same control can also be applied regardless of which wheel has failed.

(33) According to the one-wheel-failure vehicle control device 24 having this configuration, the target values for the longitudinal force sum and the yaw moment that act on a four-wheel independent drive vehicle are set as described above. Even when the motor for one wheel has failed and an unintended longitudinal force has been generated in the failed wheel, the motors for the remaining three wheels (sound wheels) are controlled to provide appropriate longitudinal forces to the sound wheels so as to follow the set target values. At this time, the longitudinal forces are determined so as to minimize the sum of the squares of the load factors of the sound wheels. Accordingly, even when one wheel has failed, it is possible to maintain the vehicle speed and the turning performance, thereby making it possible to continue to drive with the same level of safety as that before the occurrence of the failure. It is also possible to perform driving with the same feel as when the failure has not occurred. Furthermore, since the load factors of the wheels are taken into consideration in determination of the longitudinal forces, it is possible to prevent each wheel from exceeding a grip limit to start sliding.

(34) Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. Accordingly, such changes and modifications are, unless they depart from the scope of the present invention as delivered from the claims annexed hereto, to be construed as included within the scope.

REFERENCE NUMERALS

(35) 1 . . . vehicle

(36) 2, 3 . . . drive wheel

(37) 4 . . . motor (drive source)

(38) 10 . . . steering device

(39) 15 . . . load sensor

(40) 25 . . . target longitudinal force sum/yaw moment setting section

(41) 26 . . . failure detection section

(42) 27 . . . one-wheel-failure control section