JP2020032850A - Vehicle control apparatus - Google Patents

Abstract

To provide a vehicle control apparatus capable of accurately determining a road surface state even during a steady running motion.SOLUTION: A vehicle control apparatus includes: an inclination calculation part which calculates a coefficient of driving force by dividing the driving force, acting on a wheel possessed by a vehicle, by a ground load acting on the wheel, which calculates a slip ratio by using wheel speeds of front and rear wheels, and which calculates an inclination of a linear line providing a relationship between the coefficient of driving force and the slip ratio; and a road surface state determination part which determines a road surface state during a vehicle running motion by comparing the inclination, calculated in a range of a predetermined slip ratio or below, with a reference inclination.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for a vehicle.

  2. Description of the Related Art Conventionally, there has been known a technique of calculating a slope of a tire characteristic curve, which is a rate of change of a road surface friction coefficient as a road surface state with respect to a slip ratio, and comparing the slope with a preset threshold to determine a road surface state. (See, for example, Patent Document 1). In this technology, a front wheel speed, a rear wheel speed, a rear wheel acceleration, a front wheel speed difference value, a rear wheel speed difference value, and a rear wheel acceleration difference value are calculated, and further, a ground contact load acting on a drive wheel. The front wheel contact load is calculated, and the slope of the tire characteristic curve is calculated based on these values.

JP 2009-1158 A

  However, when the vehicle is traveling steadily, the amount of change in the slip ratio and the amount of change in the road surface friction coefficient are small, and the slope of the tire characteristic curve is uncertain, and the road surface state cannot be accurately determined. There is.

  The present invention has been made in view of the above, and an object of the present invention is to provide a vehicle control device capable of accurately determining a road surface state even during steady running.

  In order to solve the above-described problems and achieve the object, a control device for a vehicle according to the present invention calculates a driving force coefficient by dividing a driving force acting on a wheel of the vehicle by a ground contact load acting on the wheel. Calculating a slip ratio using the wheel speeds of the front and rear wheels, calculating a slope of a straight line that gives a relationship between the driving force coefficient and the slip ratio, and calculating in a region equal to or less than a predetermined slip ratio. A road surface state determination unit that determines a road surface state during travel of the vehicle by comparing the inclination with a reference inclination.

  According to the present invention, a driving force coefficient is calculated by dividing a driving force acting on a wheel by a ground contact load of the wheel, a slip ratio is calculated using wheel speeds of front and rear wheels, and a driving force coefficient and a slip ratio are calculated. The slope of the straight line that gives the relationship with the vehicle is determined, and the slope calculated in an area equal to or less than a predetermined slip ratio is compared with the reference slope to determine the road surface state during which the vehicle is traveling. The road surface condition can be accurately determined without inclining the inclination.

FIG. 1 is a block diagram illustrating a functional configuration of a control device for a vehicle according to an embodiment. FIG. 2 is a diagram illustrating a driving force coefficient. FIG. 3 is a diagram illustrating the relationship between the slip ratio and the road surface friction coefficient. FIG. 4 is a flowchart showing an outline of processing executed by the vehicle control device according to the embodiment. FIG. 5 is a diagram illustrating an outline of a road surface state determination process performed by a road surface state determination unit provided in the vehicle control device according to the embodiment.

  Hereinafter, a slip ratio calculating device according to an embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited by the embodiment.

  FIG. 1 is a block diagram illustrating a functional configuration of a main part of a vehicle control device according to an embodiment. The vehicle control device 1 includes an ECU (Electronic Control Unit) 11, an acceleration sensor 12, a front wheel speed sensor 13, a rear wheel speed sensor 14, an engine control unit 15, and a brake control unit 16. The acceleration sensor 12 detects the acceleration of the vehicle and outputs a detection signal to the ECU 11. The front wheel speed sensor 13 detects the front wheel speed and outputs a detection signal to the ECU 11. The ECU 11 receives a sensor signal from each sensor, an engine (motor) total driving force 21, and a deceleration signal 22. The engine control unit 15 and the brake control unit 16 output signals for controlling the engine and the brake of the vehicle based on various information acquired by the ECU 11. Note that sensors and control targets other than those described above may be connected to the ECU 11.

  The ECU 11 includes a slope calculation unit 17 and a road surface state determination unit 18. The inclination calculating section 17 includes a driving force coefficient calculating section 171 for calculating a driving force coefficient, and a slip rate calculating section 172 for calculating a slip rate.

  The driving force coefficient calculation unit 171 calculates the ground contact load W acting on the front wheels of the vehicle using the acceleration acquired from the acceleration sensor 12. Further, the driving force coefficient calculation unit 171 obtains a driving force F acting on the front wheels using the total engine driving force. When calculating the driving force F, the driving force coefficient calculation unit 171 may remove the inertia loss. The driving force coefficient calculation unit 171 calculates a quotient F / W obtained by dividing the obtained driving force F by the contact load W as a driving force coefficient μd. As shown in FIG. 2, the driving force coefficient μd is an index indicating a road surface characteristic when the road surface friction coefficient μ is set to 1. In FIG. 2, the force exerted on the road surface by the vehicle 100 is described by a vector, so the force acting on the vehicle 100 is in the opposite direction to the vector of FIG. 2.

The slip ratio calculation unit 172 calculates the front wheel average wheel speed vf and the rear wheel average wheel speed based on the information on the front wheel speed and the rear wheel speed acquired from the front wheel speed sensor 13 and the rear wheel speed sensor 14 during a predetermined period, respectively. vr is calculated, and the slip ratio λ is calculated in accordance with the following equation (1) using these vr.
λ = (vf−vr) / vf (1)
When calculating the formula (1), the slip ratio calculating unit 172 may execute the turning correction by geometrically adjusting the rotation speed.

  The ECU 11 is configured using a microcomputer having a CPU (Central Processing Unit) and a RAM (Random Access Memory). The ECU 11 performs various calculations using input data, data and programs stored in the RAM in advance, and outputs a command signal based on the calculation results to a control target.

  FIG. 3 is a diagram illustrating the relationship between the slip ratio and the road surface friction coefficient. The relationship between the slip ratio and the road surface friction coefficient differs depending on the type of road surface on which the vehicle travels. Specifically, in FIG. 3, curve C1 is a road surface of dry asphalt, curve C2 is a road surface of asphalt wet with a thin water film, curve C3 is a road surface of asphalt wet with a thick water film, and curve C4 is fresh snow. A curved road surface, a curve C5 is a road surface on which snow is solidified, and a curve C6 is a road surface on which ice is stretched smoothly. The curves C1 to C6 are almost straight lines in a region D (small slip region) where the slip ratio is 10% or less. Therefore, the area D can be regarded as an area where the road surface friction coefficient changes substantially linearly with respect to the slip ratio. The maximum value of the road surface friction coefficient in each curve is a value obtained by normalizing the maximum static friction force for each road surface by a load. Hereinafter, the region D is defined as a road surface state determination target region.

  Next, an outline of a process executed by the vehicle control device 1 will be described with reference to a flowchart of FIG.

  First, the driving force coefficient calculator 171 calculates a driving force coefficient μd = F / W (step S1). Specifically, the driving force coefficient calculation unit 171 calculates the ground contact load W acting on the front wheels of the vehicle using the acceleration acquired from the acceleration sensor 12, and calculates the driving force acting on the front wheels using the total engine driving force 21. After calculating F, the driving force coefficient μd = F / W is calculated by dividing the driving force F by the contact load W.

  In parallel with step S1, the slip ratio calculation unit 172 calculates the slip ratio λ based on the above-described equation (1) (step S2).

  After steps S1 and S2, the inclination calculating unit 17 calculates the point (λ, μd) and the origin (0, 0) by using the driving force coefficient μd calculated in step S1 and the slip ratio λ calculated in step S2. Is calculated (step S3).

  Thereafter, the road surface state determination unit 18 determines the road surface state on which the vehicle travels by using the slope SL calculated by the slope calculation unit 17 (Step S4). Hereinafter, an outline of the processing of the road surface state determination unit 18 will be described with reference to FIG. FIG. 5 shows a region where the slip ratio λ is 0.01 to 0.03 (1 to 3%).

The straight line L0 is a straight line that gives a reference slope, and is a straight line corresponding to a case where the road surface friction coefficient μ is 1. The straight line L0 passes through the point P and the origin. At the point P, since the slip ratio λ is 0.03 and the driving force coefficient μd is 1.0, the slope (reference slope) SL0 of the straight line L0 is
SL0 = 1.0 / 0.03 = 30.

  On the other hand, points Q and R are points indicating examples of the calculated values calculated by the slope calculator 17. At the point Q, since the slip ratio λ is 0.01 and the driving force coefficient μd is 0.8, the slope SL1 of the straight line L1 passing through the point Q and the origin is SL1 = 0.8 / 0.01 = 80. At the point R, since the slip ratio λ is 0.02 and the driving force coefficient μd is 0.2, the slope SL2 of the straight line L2 passing through the point Q and the origin is SL2 = 0.2 / 0.02 = 10.

The road surface condition determination unit 18 calculates a value of a ratio between the slope of the calculated value and the reference slope.
When the slope of the operation value is SL1, the value of the ratio is SL1 / SL0 = 80/30 ≒ 2.667. In this case, the road surface state determination unit 18 determines that the vehicle is in a road surface state where the road surface friction coefficient μ is larger than 1.
On the other hand, when the slope of the calculated value is SL2, the value of the ratio is SL2 / SL0 = 10/30 ≒ 0.333. When the slope of the calculated value is SL2, the road surface state determination unit 18 determines that the road surface during traveling is in a road surface state where the road surface friction coefficient μ is smaller than 1.

  The road surface state determination unit 18 may compare the reference inclination with the inclination of the calculated value, estimate the road surface friction coefficient μ during traveling from the value of the ratio, and determine the road surface state based on the estimation result. . In this case, the road surface state determination unit 18 stores in advance the correspondence between the ratio value and the road surface friction coefficient μ, and estimates the road surface friction coefficient μ from the ratio value calculated using the calculated value.

  According to the embodiment described above, the driving force coefficient is calculated by dividing the driving force acting on the wheel by the contact load of the wheel, the slip ratio is calculated using the wheel speeds of the front and rear wheels, and the driving force is calculated. In order to determine the road surface condition during which the vehicle is traveling by calculating the slope of a straight line that gives the relationship between the coefficient and the slip rate, and comparing the slope calculated in an area equal to or less than a predetermined slip rate with a reference slope, Even when the driving force is generated, the inclination does not become unstable while the driving force is being generated, and the road surface state can be accurately determined.

  Further, according to the embodiment, a slight slip of the wheel that always occurs regardless of the road surface friction coefficient can be captured, and the road surface state can be determined before the wheel starts to slip significantly.

  In addition, according to the embodiment, in the micro slip region, utilizing the fact that the relationship between the slip ratio and the driving force coefficient changes substantially linearly, the slope of the straight line in this region is compared with the reference slope to obtain the road surface condition. , The road surface condition can be determined with high accuracy.

(Other embodiments)
In the above description, the case where the vehicle runs with two-wheel drive has been described, but the present invention can also be applied to a vehicle that can run with four-wheel drive. However, the calculation result of the slip ratio when traveling with four-wheel drive is less than that when traveling with two-wheel drive. Therefore, when traveling with four-wheel drive, the relative speed ratio (slip ratio) with the road surface cannot be calculated.

Therefore, when the vehicle is running in four-wheel drive, the slip ratio calculation unit 172 calculates the front wheel road surface friction coefficient μf, the rear wheel road surface friction coefficient μr, and the front and rear wheel speed difference ΔN, respectively, based on the calculation result. To calculate the slip ratio λ of the front and rear wheels. At this time, the slip ratio calculation unit 172 calculates the slip ratio λ by a different calculation shown below according to the magnitude of the front wheel road surface friction coefficient μf and the rear wheel road surface friction coefficient μr.
When μf> μr λ = μr × ΔN / (μf−μr) + ΔN
When μf <μr λ = μf × ΔN / (μr−μf) + ΔN

  With this, in a four-wheel drive vehicle, when applying a slip feedback system that distributes driving force to the rear wheel when the front wheel slips, before the front wheel slips greatly beyond the driving force that can be transmitted by the front wheel during slippery traveling, By distributing the driving force to the rear wheels, traveling stability can be improved. In addition, fuel efficiency can be improved without distributing excessive driving force to the rear wheels.

  The present invention is not limited to the above-described embodiment, and can be freely modified without departing from the gist of the present invention.

1 vehicle control device 11 ECU
DESCRIPTION OF SYMBOLS 12 Acceleration sensor 13 Front wheel speed sensor 14 Rear wheel speed sensor 15 Engine control unit 16 Brake control unit 17 Inclination calculation unit 18 Road surface determination unit 21 Total driving force of engine (motor) 22 Deceleration signal 100 Vehicle 171 Driving force coefficient calculation Section 172 slip ratio calculation section C1 to C6 curves L0, L1, L2 straight lines

Claims (1)

A driving force coefficient is calculated by dividing a driving force acting on a wheel of the vehicle by a ground contact load acting on the wheel, a slip ratio is calculated using wheel speeds of front and rear wheels, and the driving force coefficient and the slip are calculated. A slope calculation unit that calculates a slope of a straight line that gives a relationship with the rate,
A road surface state determination unit that determines a road surface state during travel of the vehicle by comparing the inclination calculated in an area equal to or less than a predetermined slip ratio with a reference inclination;
A control device for a vehicle comprising:

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