JP2009149201A - Vehicle control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle control device capable of performing a highly accurate ABS control in all road surface conditions. <P>SOLUTION: In this vehicle control device, a slip ratio is acquired from a slip ratio arithmetic part 14 at a prescribed time interval, and at the same time, a road surface μ is acquired from a road surface arithmetic part 16. In a target slip ratio arithmetic part 15, a slip ratio increment to be a difference between the slip ratio acquired the last time and the slip ratio acquired this time and a road surface μ increment to be a difference between a friction coefficient acquired the last time and a friction coefficient acquired this time are calculated, and a change rate of the road surface μ increment in relation to the slip ratio increment is calculated. When the change rate enters a prescribed change rate range, the slip ratio acquired just near the range is set to be a target slip ratio of one's own vehicle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vehicle control device mounted on an electric vehicle such as an electric vehicle in which four wheels are independently driven by a motor.

  2. Description of the Related Art Conventionally, a vehicle control device that performs anti-lock brake control (hereinafter referred to as ABS control) that prevents a wheel from being locked during sudden braking and maintains vehicle stability and steering performance in an automobile is known. (See Patent Document 1 and Non-Patent Document 1). In such a vehicle control apparatus, a plurality of road surface μ-slip ratio maps indicating the relationship between the coefficient of friction between the tire of the host vehicle and the road surface (hereinafter referred to as road surface μ) and the slip ratio of the wheels are stored as tire data. is doing. Here, the slip ratio of the wheel is a value calculated based on the wheel speed and the vehicle body speed.

  Then, the vehicle control device calculates the road surface μ of the own vehicle, selects tire data corresponding to the road surface μ at that time from the plurality of stored tire data of the road surface μ-slip ratio, and the tire data , The slip ratio at which the road surface μ is maximum is set as the target slip ratio, and braking of the brake is controlled so that the slip ratio of the wheel is close to the target slip ratio. As a result, even during sudden braking, the vehicle is decelerated safely without locking the wheels while preventing a decrease in cornering force.

FIG. 6 is a characteristic diagram showing the relationship between the road surface μ and the slip ratio, and shows an example of the tire data described above. As shown in FIG. 6, when the driver performs a braking operation, the slip ratio S gradually increases, and the road surface μ also increases with this. However, the correspondence between the road surface μ and the slip ratio is not constant. When a certain slip ratio is reached, the road surface μ becomes a maximum value, and then the road surface μ gradually decreases. Such a relationship between the road surface μ and the slip ratio can vary depending on the type of tire used and the road surface condition. Each curve shown in FIG. 6 shows a difference in characteristics depending on the type of tire and the road surface condition. A range below the slip ratio where the road surface μ becomes a maximum value is referred to as a stable region, and a range exceeding the slip rate is referred to as an unstable region.
JP-A-62-99249 Research on ABS for Sankaido Automobile (Nippon ABS Co., Ltd.)

  As described above, in the conventional vehicle control device, tire data corresponding to the tire type, road surface μ, etc. of the own vehicle is selected from a plurality of tire data stored in advance. However, in this method, since tire data is selected based on information with a small amount of tire data, the acquired tire data may not always be suitable for the actual situation. As described above, since the relationship between the road surface μ and the slip ratio varies depending on the type of tire and the road surface condition, the target slip ratio changes each time. Therefore, depending on the road surface condition, the acquired tire data may not be appropriate, the ABS control may not work well, and the brake braking may not be properly controlled.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a vehicle control device capable of performing high-precision ABS control in all road surface conditions.

  In order to achieve the above object, an invention according to claim 1 is a vehicle control device mounted on an electric vehicle that independently drives four wheels by a motor, and includes a slip ratio calculation unit that calculates a slip ratio of the own vehicle. A wheel torque calculator that calculates the wheel torque of the host vehicle based on the torque of a motor that rotates the wheels of the host vehicle, a variable wheel load calculator that calculates a load acting on the wheel of the host vehicle, A friction coefficient calculation unit that calculates a friction coefficient between the wheel of the vehicle and the road surface based on a wheel torque and a load acting on the wheel of the vehicle, and slips from the slip rate calculation unit at a predetermined time interval. The friction coefficient is obtained from the friction coefficient calculation unit at the same time, the difference between the slip ratio acquired last time and the slip ratio acquired this time (hereinafter referred to as slip ratio increment), the friction coefficient acquired last time and the current acquisition time friction The difference between the number of frictions (hereinafter referred to as friction coefficient increment) and the rate of change of the friction coefficient increment relative to the slip rate increment are calculated. When the rate of change falls within a predetermined rate of change range, The gist is to include a target slip ratio setting unit that sets the acquired slip ratio as the target slip ratio of the host vehicle.

  The invention according to claim 2 is the invention according to claim 1, wherein when the change rate of the friction coefficient increment with respect to the slip rate increment falls within a predetermined change rate range, the target slip ratio setting unit acquires the slip ratio acquired last time. The gist is to set the average slip ratio acquired this time as the target slip ratio of the vehicle.

  According to the vehicle control apparatus of the present invention, when the change rate of the road surface μ increment with respect to the slip rate increment calculated at a predetermined time interval falls within the predetermined change rate range, the most recently acquired slip rate is used as the target slip rate. Therefore, regardless of the road surface condition at that time, the slip ratio at which the road surface μ always has the maximum value can be set as the target slip ratio. According to this, since a plurality of tire data is stored in advance and the target slip ratio can be set more finely than the method of selecting tire data that applies to the tire type or road surface μ of the own vehicle, High-accuracy ABS control can be performed according to all road surface conditions. In addition, since it is not necessary to store a plurality of tire data, the storage area can be used effectively. Furthermore, it is possible to save time and labor for newly adding tire data or updating the contents of stored tire data.

  In addition, when the average of the slip ratio acquired last time and the slip ratio acquired this time is set as the target slip ratio, it is originally set even if the slip ratio acquired this time is not accurate due to the influence of noise etc. A slip ratio closer to the slip ratio to be set can be set as the target slip ratio.

  Therefore, according to the vehicle control device according to the present invention, it is possible to perform highly accurate ABS control in any road surface condition.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a vehicle control device according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a vehicle control device 1 according to the present embodiment. The vehicle control device 1 is mounted on an electric vehicle (not shown) (hereinafter also referred to as a host vehicle), and includes a hydraulic pressure sensor 2, a motor torque sensor 3, a front and rear G sensor 4, a lateral G sensor 5, a vehicle body speed sensor 6, and a wheel speed sensor 7. The main control device 11 is connected to the braking device 17.

  The main control device 11 is a computer device that executes arithmetic processing and data input / output in accordance with a preset program. For example, a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), A microcomputer having a hardware configuration such as an input / output interface (I / O interface) can be used.

  Of these hardware configurations, the ROM stores a program necessary for the operation of the main controller 11. The RAM is used as a work area by the CPU. CPU develops the program memorize | stored in ROM on RAM, and executes it sequentially, wheel torque calculating part 12, variable wheel load calculating part 13, slip ratio calculating part 14, target slip ratio calculating part 15, road surface μ calculation Each function of the unit 16 is realized.

  FIG. 2 is a plan view showing an actual coordinate system and various physical quantities used in this embodiment. In FIG. 2, fl is a tire for the left front wheel of the own vehicle, fr is a tire for the right front wheel of the own vehicle, rl is a tire for the left rear wheel of the own vehicle, and rr is a tire for the right rear wheel of the own vehicle. The real coordinate system used in the present embodiment has the center of gravity of the host vehicle as the origin, the axis parallel to the road surface and the axis extending in the front-rear direction of the host vehicle is the x axis, is parallel to the road surface, and the left-right direction of the host vehicle The axis extending in the direction is the y-axis. β is a slip angle of the own vehicle, and is represented by an angle formed by the traveling direction vector v of the own vehicle and the x axis. The counterclockwise direction in FIG. 2 is the positive direction of the slip angle, and the clockwise direction is the negative direction of the slip angle. δ is a steering angle of the host vehicle, and is represented by an angle formed by a plane perpendicular to the rotation axis of the wheel and the x axis. FIG. 2 shows the steering angle of the left front wheel as an example of the steering angle. The direction in which the wheel moves when the steering wheel of the host vehicle rotates to the left is the positive direction of the steering angle, and the direction of movement of the wheel when the steering wheel of the host vehicle rotates to the right is the negative direction of the steering angle. “lf” is a value representing the x coordinate of the rotation axis of the front wheel as an absolute value, and “lr” is a value representing the x coordinate of the rotation axis of the rear wheel as an absolute value. d is the distance between the rotation centers of the front wheels (or rear wheels).

  Each wheel of the host vehicle is provided with a hydraulic brake (not shown) (hereinafter referred to as a brake). The oil pressure sensor 2 is provided for each brake, detects the oil pressure acting on each brake, and outputs a signal related to the result to the wheel torque calculator 12.

  The motor torque sensor 3 is provided in each motor and detects a current i flowing through each motor. And motor torque is calculated based on the electric current which flows into a motor, and the following formula | equation (1).

Tm = i · k (1)
Tm: Motor torque, i: Current flowing through the motor, k: Torque coefficient Here, the sign of the current i is the positive direction when flowing to the motor during acceleration or low-speed running, and the negative direction when flowing through the motor during deceleration. . Since the vehicle also activates the regenerative brake when decelerating, a current in the direction opposite to that during acceleration or low-speed traveling flows through the motor when decelerating. The torque coefficient is a constant determined by the motor. The motor torque sensor 3 outputs a signal related to the calculated motor torque to the wheel torque calculator 12.

  The front-rear G sensor 4 detects the acceleration in the x-axis direction out of the acceleration of the host vehicle, and outputs a signal related to the result to the variable wheel load calculation unit 13.

  The lateral G sensor 5 detects the acceleration in the y-axis direction out of the acceleration of the host vehicle, and outputs a signal related to the result to the slip ratio calculation unit 14 and the variable wheel load calculation unit 13.

  The vehicle body speed sensor 6 detects the vehicle body speed of the host vehicle (the speed of the portion other than the wheels), and outputs a signal related to the result to the slip ratio calculation unit 14 and the slip ratio calculation unit 14.

  The wheel speed sensor 7 is provided at each wheel of the host vehicle, detects the rotation speed of the wheel provided with the wheel speed sensor 7, that is, the wheel speed of the host vehicle, and outputs a signal related to the result to the slip ratio calculation unit 14. To do.

  Each of the sensors repeatedly performs detection and signal output every 0.001 seconds while the power source and power source of the vehicle are in operation by the driver.

  Next, the function and processing operation of each part constituting the vehicle control device 1 will be described with reference to the flowchart shown in FIG. In addition, the vehicle control apparatus 1 performs the process demonstrated below for every wheel. Here, as an example, processing related to the left front wheel will be described. Further, the execution procedure of each step can be changed within a range where logical matching can be achieved, and a plurality of processes may be executed in parallel.

  In step S1, the slip ratio calculation unit 14 determines whether or not the brake is operated based on a signal given from the hydraulic pressure sensor 2 provided on the left front wheel, and waits until the brake is operated.

  In step S2, the slip ratio calculation unit 14 calculates the slip ratio of the left front wheel based on signals given from the vehicle speed sensor 6 and the wheel speed sensor 7 provided on the left front wheel, and outputs a signal related to the result as a target. The result is output to the slip ratio calculation unit 15. The slip ratio calculation unit 14 repeatedly calculates the slip ratio every 0.01 seconds.

  In step S3, the variable wheel load calculation unit 13 calculates the load Ffl acting on the left front wheel based on the signals given from the front and rear G sensor 4 and the lateral G sensor 5 and the following equation (2): A signal related to the result is output to the road surface μ calculator 16.

Ffl = m ・ g ・ lr / 2 / (lf + lr) -m ・ αx ・ h / 2 / (lf ・ lr) -m ・ αy ・ h ・ lr / d / (lf + lr)… （2）
m: mass of own vehicle, g: acceleration of gravity, h: distance from center of gravity of own vehicle to road surface, αx: front and rear G of own vehicle, αy: lateral G of own vehicle
The load Ffr acting on the right front wheel is the following equation (3), the load Frl acting on the left rear wheel is the following equation (4), and the load Frr acting on the right rear wheel is the following equation (5). Respectively.

Ffr = m ・ g ・ lr / 2 / (lf + lr) -m ・ αx ・ h / 2 / (lf ・ lr) + m ・ αy ・ h ・ lr / d / (lf + lr) (3)
Frl = m ・ g ・ lf / 2 / (lf + lr) + m ・ αx ・ h / 2 / (lf ・ lr) -m ・ αy ・ h ・ lf / d / (lf + lr) (4)
Frr = m ・ g ・ lf / 2 / (lf + lr) + m ・ αx ・ h / 2 / (lf ・ lr) + m ・ αy ・ h ・ lf / d / (lf + lr)… （5）
The variable wheel load calculation unit 13 repeatedly executes the calculation of the wheel load for each wheel every 0.01 seconds.

  In step S4, the wheel torque calculation unit 12 calculates the wheel torque of the left front wheel based on the signal given from the motor torque sensor 3 and the following equation (6).

Tt = (Tm−lm) dω / dt (6)
Tt: Wheel torque, lm: Inertia moment of wheel, ω: Angular velocity of wheel Note that the sign of ω is the positive direction when the vehicle is moving forward and the negative direction when the vehicle is moving backward. The wheel torque calculation unit 12 outputs a signal related to the calculated left front wheel torque to the road surface μ calculation unit 16. Further, the wheel torque calculation unit 12 repeatedly executes the calculation of the wheel torque for each wheel every 0.01 seconds.

  In step S5, the road surface μ calculator 16 determines the road surface μ of the left front wheel (of the vehicle) based on the signals given from the wheel torque calculator 12 and the variable wheel load calculator 13 and the following equation (7). Road surface μ) is calculated.

μ = (Tt · rt) / Fz1 (7)
Fz1: Load acting on the wheel (here, load Ffl acting on the left front wheel), rt: Wheel radius The road surface μ calculation unit 16 generates a signal related to the road surface μ of the left front wheel, and sends it to the target slip ratio calculation unit 15 Output. The road surface μ calculation unit 16 repeatedly calculates the road surface μ for each wheel every 0.01 seconds.

  In step S6, the target slip ratio calculation unit 15 determines whether 0.01 seconds have elapsed since the end of the previous step S10, and waits until 0.01 seconds have elapsed if not. When 0.01 second has elapsed, it is determined in step S7 whether the number of repetitions n = 2. Here, the number n of repetitions refers to the number of times the change rate calculation process has been executed in step S10 described later. If n = 2 is not satisfied, n is incremented by 1 in step S8, and the process returns to step S2. If n = 2 in step S7, the process proceeds to step S9, and the repetition count n is returned to 1.

  Subsequently, in step S10, the target slip ratio calculation unit 15 acquires the slip ratio calculated by the slip ratio calculation unit 15 and the road surface μ calculated by the road surface μ calculation unit 16 every 0.01 seconds. . The slip ratio and road surface μ acquired at this time are temporarily stored in a predetermined storage area. And the difference (henceforth slip ratio increment) of the slip ratio acquired last time and the slip ratio acquired this time is calculated about the slip ratio acquired from the slip ratio calculating part. Further, with respect to the road surface μ acquired from the road surface μ calculation unit 16, a difference between the road surface μ acquired last time and the road surface μ acquired this time (hereinafter referred to as road surface μ increment) is calculated. Then, a change rate of the road surface μ increment with respect to the slip rate increment is calculated (hereinafter referred to as a change rate calculation process).

  Here, the rate of change of the road surface μ increment with respect to the slip rate increment will be described. FIG. 4 is an explanatory diagram showing the relationship between the slip rate increment and the road surface μ increment in 0.01 seconds, where the horizontal axis represents the slip rate S and the vertical axis represents the road surface μ. As shown in FIG. 4, the difference between the slip rate S1 acquired last time and the slip rate S2 acquired this time 0.01 seconds later is the slip rate increment Δx. Also, at the same time interval, the difference between the road surface μ1 acquired last time and the road surface μ2 acquired this time 0.01 seconds later is the road surface μ increment Δy. Therefore, by calculating Δy / Δx, the rate of change v of the road surface μ increment Δy with respect to the slip rate increment Δx is obtained. It can be considered that the smaller the change rate v, the smaller the road surface μ increment Δy with respect to the slip rate increment Δx, that is, closer to the inflection point of the convex curve indicating the change of the road surface μ. The number of repetitions n in step S7 described above is for determining whether the slip ratio and the road surface μ have been acquired for the previous and current two times. Therefore, if n = 1, only the previous slip rate S1 and road surface μ1 are acquired.

  Next, in step S11, the target slip ratio calculation unit 15 determines whether or not the calculated change rate v is within a preset change rate range. Here, the relationship between the change rate v and the change rate range will be described. FIG. 5 is an explanatory diagram showing a state when the change rate calculation process is performed at intervals of 0.1 seconds. The target slip ratio calculation unit 15 performs the change rate calculation processing for calculating the change rate v of the road surface μ increment Δy with respect to the slip ratio increment Δx at intervals of 0.01 seconds (s) described above at intervals of 0.1 second (s). Repeatedly, it is determined every 0.1 seconds whether or not the calculated change rate v is within a preset change rate range (hereinafter referred to as change rate determination processing).

  As described above, when the driver performs a braking operation, the slip ratio S gradually increases, and the road surface μ also increases. When a certain slip ratio is reached, the road surface μ has a maximum value. As shown in FIG. 5, in the section where the road surface μ is the maximum value (enlarged portion in FIG. 5), the road surface μ increment Δy with respect to the slip ratio increment Δx is zero, so the rate of change v is also zero. Therefore, a predetermined range including a range near the rate of change of zero, specifically, a range before and after the rate of change zero (plus, minus) is set in advance as the rate of change range, and every 0.1 second. By determining whether or not the change rate v obtained by the change rate calculation process is within this change rate range, it is possible to specify a section where the road surface μ is a maximum value.

  In this embodiment, the change rate range set in advance is a range in the vicinity where the change rate is zero, and the change rate range has a certain width. Does not change so steeply, one point where the change rate v becomes zero may be set as the change rate range. Further, when the rate of change v becomes a negative value, that is, a section where the road surface μ slightly exceeds the maximum value may be set as the rate of change range. In FIG. 5, the calculated slip rate S is drawn at equal intervals according to the time interval, but actually, the calculated slip rate S is different even if the time interval is the same. Is.

  On the other hand, when the change rate v is not within the preset change rate range in step S11 in FIG. 3, the road surface μ is not in the section where the maximum value is reached. After 1 second, the process returns to step S2. In step S11, when the rate of change v is within a preset rate of change range, it is considered that the road surface μ has reached the maximum value, and the process proceeds to step S13. In step S13, the target slip ratio calculation unit 15 sets the slip ratio acquired in the current (most recent) step S2 as the target slip ratio of the left front wheel of the host vehicle. The target slip ratio of the left front wheel set here is a slip ratio at which the road surface μ of the left front wheel becomes a maximum value. The target slip ratio calculation unit 15 generates a signal related to the target slip ratio of the left front wheel and outputs the signal to the braking device 17. Thereafter, the vehicle control device 1 ends this process. In addition, although description is abbreviate | omitted, the process which sets a target slip ratio is performed in the same procedure also about another wheel.

  The braking device 17 controls the braking torque of each wheel based on the signal given from the target slip ratio calculating unit 15 so that the slip ratio of each wheel is close to the target slip ratio of that wheel (ABS control). Further, in the target slip ratio calculation unit 15, after setting the target slip ratio by the procedure as described above, if the slip ratio calculated in the slip ratio calculation unit 15 exceeds the target slip ratio, it is set first. By controlling the braking torque so as to be equal to or less than the target slip ratio, the vehicle can be stably braked out of the unstable region (FIG. 6).

  As described above, in the vehicle control apparatus 1 according to the present embodiment, when the change rate v of the road surface μ increment with respect to the slip rate increment calculated at a predetermined time interval is within the predetermined change rate range, it is acquired most recently. Since the slip ratio is set as the target slip ratio, the slip ratio at which the road surface μ always has the maximum value can be set as the target slip ratio regardless of the road surface condition at that time. According to this, since a plurality of tire data is stored in advance and the target slip ratio can be set more finely than the method of selecting tire data that applies to the tire type or road surface μ of the own vehicle, High-accuracy ABS control can be performed according to all road surface conditions. In addition, since it is not necessary to store a plurality of tire data, the storage area can be used effectively. Furthermore, it is possible to save time and labor for newly adding tire data or updating the contents of stored tire data.

  In the above embodiment, when the rate of change v enters the preset rate of change range in step S11 of FIG. 3, the slip rate acquired in the current (most recent) step S2 is set as the target slip rate. However, the average of the slip ratio acquired last time and the slip ratio acquired this time may be set as the target slip ratio. Thus, when the average value of the calculated two slip ratios before and after is set as the target slip ratio, even if the slip ratio acquired this time is not accurate due to the influence of noise or the like, the slip ratio should be set originally. A near slip ratio can be set as the target slip ratio.

  In the above-described embodiment, an example in which the time interval for executing the change rate calculation process is 0.01 second and the time interval for executing the change rate determination process is 0.1 second is shown. It is not limited to the example of this embodiment, It can set suitably. However, if the time interval for executing the change rate calculation process is short, it is possible that an accurate road surface μ cannot be obtained due to the influence of noise or the like. Therefore, the time interval for executing the change rate calculation process is at least 0.01. It is preferable to set it as second or more.

The block diagram which shows the structure of the vehicle control apparatus which concerns on embodiment. The top view which shows the real coordinate system used in embodiment, and various physical quantities. The flowchart which shows the procedure of the process by a vehicle control apparatus. Explanatory drawing which shows the relationship between the slip rate increment in 0.01 second, and road surface micro increment. Explanatory drawing which shows a mode when a change rate calculation process is implemented at an interval of 0.1 second. The characteristic view which shows the relationship between road surface micro | micron | mu and a slip ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vehicle control apparatus 2 ... Hydraulic pressure sensor 3 ... Motor torque sensor 4 ... Front-back G sensor 5 ... Lateral G sensor 6 ... Vehicle body speed sensor 7 ... Wheel speed sensor 11 ... Main controller 12 ... Wheel torque calculation part 13 ... Variable wheel load Calculation unit 14 ... Slip rate calculation unit 15 ... Target slip rate calculation unit 16 ... Road surface μ calculation unit 17 ... Braking device

Claims (2)

A vehicle control device mounted on an electric vehicle that independently drives four wheels by a motor,
A slip ratio calculation unit for calculating the slip ratio of the own vehicle;
A wheel torque calculator that calculates the wheel torque of the host vehicle based on the torque of the motor that rotates the wheel of the host vehicle;
A variable wheel load calculation unit for calculating a load acting on the wheel of the host vehicle
A friction coefficient calculation unit for calculating a friction coefficient between the wheel of the host vehicle and the road surface based on the wheel torque of the host vehicle and a load acting on the wheel of the host vehicle;
At a predetermined time interval, the slip ratio is acquired from the slip ratio calculation unit, and at the same time, the friction coefficient is acquired from the friction coefficient calculation unit. The difference between the slip ratio acquired last time and the slip ratio acquired this time (hereinafter referred to as slip ratio). Increment) and the difference between the friction coefficient acquired last time and the friction coefficient acquired this time (hereinafter referred to as friction coefficient increment), and the rate of change of the friction coefficient increment relative to the slip rate increment is calculated. When the vehicle enters a predetermined change rate range, a target slip rate setting unit that sets the most recently acquired slip rate as the target slip rate of the host vehicle,
A vehicle control device comprising:   When the change rate of the friction coefficient increment with respect to the slip rate increment falls within a predetermined change rate range, the target slip ratio setting unit calculates the average of the slip ratio acquired last time and the slip ratio acquired this time as a target of the vehicle. The vehicle control device according to claim 1, wherein the vehicle control device is set as a slip ratio.

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