Driving force control system

Abstract

This invention provides a method for independently controlling the driving force of multiple wheels. [Solution] The state quantity acquisition unit 22 acquires the state quantity of each wheel in the vehicle. The driving stiffness acquisition unit 30 acquires the driving stiffness of each wheel based on the acquired state quantity. The driving force setting unit 32 sets the driving force of each wheel based on the driving stiffness of each wheel to minimize the total wheel loss of the multiple wheels. The drive control unit 34 drives each wheel according to the set driving force of each wheel.

Description

Technical Field

[0001] The present invention relates to a driving force control system that independently controls the driving force of a plurality of wheels in a vehicle.

Background Art

[0002] Patent Document 1 discloses a driving force control method for distributing driving force of a vehicle using an estimated maximum road surface μ. This driving force control method comprises: a first estimation step of estimating the maximum road surface μ based on a driving stiffness corresponding to a slip rate and the driving force when the vehicle is in a first driving state where the vehicle is performing steady acceleration straight running; a second estimation step of estimating the maximum road surface μ based on steering reaction force when the vehicle is in a second driving state where steering is performed; and a third estimation step of estimating a preset maximum road surface μ when the vehicle is in a third driving state where an outside air temperature is equal to or higher than a determination temperature.

Prior Art Literature

Patent Literature

[0003]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] When wheels are driven or braked, driving loss occurs due to slip between the wheels and the road surface. The driving loss occurring in each wheel becomes a factor that causes unnecessary power consumption in the case of an electric vehicle, and becomes a factor that causes deterioration of fuel efficiency in the case of an internal combustion engine vehicle. Accordingly, an object of the present invention is to provide a technique for efficiently distributing driving force to each wheel.

Means for Solving the Problem

[0005] A driving force control system according to one aspect of the present invention is a system for independently controlling the driving force of multiple wheels in a vehicle, comprising: a state quantity acquisition unit that acquires state quantities for each wheel; a driving stiffness acquisition unit that acquires the driving stiffness of each wheel based on the acquired state quantities; a driving force setting unit that sets the driving force of each wheel to reduce the total wheel loss in the multiple wheels based on the driving stiffness of each wheel; and a driving control unit that drives each wheel according to the set driving force of each wheel. [Brief explanation of the drawing]

[0006] [Figure 1] This diagram schematically shows the configuration of a vehicle according to the embodiment. [Figure 2] This diagram illustrates the drive losses that occur in the wheels. [Figure 3] This diagram shows the functional blocks of the drive force control system installed in the vehicle. [Figure 4] This is a flowchart of the method for distributing driving force according to the embodiment. [Modes for carrying out the invention]

[0007] Figure 1 schematically shows the configuration of vehicle 1 according to an embodiment. Vehicle 1 is equipped with a plurality of wheels and a plurality of electric motors provided on the plurality of wheels, and has the function of independently controlling the driving force of the plurality of wheels. The plurality of wheels include the left front wheel 2FL, the right front wheel 2FR, the left rear wheel 2RL, and the right rear wheel 2RR, and the plurality of electric motors include an electric motor 3FL that rotates the left front wheel 2FL, an electric motor 3FR that rotates the right front wheel 2FR, an electric motor 3RL that rotates the left rear wheel 2RL, and an electric motor 3RR that rotates the right rear wheel 2RR. In the following, unless otherwise specified, each wheel will be referred to as wheel 2 and each electric motor will be referred to as electric motor 3.

[0008] Vehicle 1 in this embodiment is an electric vehicle that uses an electric motor 3 as a driving force source, but it may also be a vehicle that uses only an internal combustion engine as a driving force source. Examples of electric vehicles include battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or fuel cell electric vehicles (FCEVs). Vehicle 1 may be a vehicle driven by a driver or an autonomous vehicle. Even when vehicle 1 uses an internal combustion engine as a driving force source, it is equipped with a function to independently control the driving force of multiple wheels 2.

[0009] Vehicle 1 is equipped with a control device 10 having a processor, a memory device, and an input / output interface. The input / output interface receives sensor signals measured by various sensors from sensors 12 provided on vehicle 1. The memory device stores control data such as control programs and maps for setting the driving force of each wheel 2 and controlling each electric motor 3. The processor reads the control program from the memory device and executes it, thereby realizing control that optimally distributes the driving force to the multiple wheels 2.

[0010] The sensors 12 have means for measuring state quantities of the vehicle 1. In the embodiment, the sensors 12 have means for measuring the temperature of each wheel 2. The means for measuring the wheel temperature may be a temperature sensor provided inside the wheel 2. The sensors 12 also have means for measuring the load on each wheel 2 or means for measuring a state quantity for estimating the load on each wheel 2. The means for measuring the wheel load may be a load sensor that measures the wheel load, and the means for measuring the state quantity for estimating the wheel load may be a stroke sensor that measures the stroke amount of a suspension. In this case, the processor may have a function of estimating the wheel load from the stroke amount. The sensors 12 further have means for measuring a state quantity for estimating the slip angle of each wheel 2. The means for measuring the state quantity for estimating the slip angle may be a wheel speed sensor that measures the wheel speed and a lateral acceleration sensor that detects the lateral acceleration. In this case, the processor may have a function of estimating the slip angle from an integrated value of the vehicle speed and the lateral acceleration. Note that the processor may also have a function of estimating the slip angle from measurement values of a GPS and a tire angle meter.

[0011] Figure 2 is a diagram for explaining drive loss occurring in a wheel. Here, the rotational speed of the wheel (wheel speed) is V T , and the ground speed of the vehicle (road surface speed) is V B It is assumed that According to the law of action and reaction, the driving force F X and the road surface reaction force F X are equal to each other. The movement distance d of the wheel in time Δt T and the movement distance d of the road surface B are calculated as follows. Wheel movement distance d T = V T × Δt Road surface movement distance d B = V B × Δt

[0012] When examining the amount of work, the amount of work done by the wheel is the driving force F X × wheel movement distance d T , and the amount of work done on the road surface is the road surface reaction force F X × road surface movement distance d BTherefore, the power of the wheel (work done by the wheel / Δt) is equal to the driving force F. X ×Wheel speed V T Therefore, the power of the road surface (work done on the road surface / Δt) is equal to the road surface reaction force F. X × road speed V B Therefore, the loss P between the wheel and the road surface is... X teeth, P X =F X ×V T -F X ×V B =F X × (V T -V B ) =F X ×{ (V T -V B ) / V B}×V B Here, (V T -V B ) / V B Because the slip ratio is SR, P X =F X ×SR×V B ...(1) This is expressed as: This loss P X This represents the drive loss (wheel loss) that occurs in a single wheel.

[0013] Therefore, the loss P in each wheel 2 X teeth, P Xi =F Xi ×SR×V B ...(2) This can be expressed as follows. Here, "i" is a number used to distinguish the two wheels; for example, "1" represents the left front wheel 2FL, "2" represents the right front wheel 2FR, "3" represents the left rear wheel 2RL, and "4" represents the right rear wheel 2RR. If the required driving force in vehicle 1 is F, F = ΣF Xi =F1+F2+F3+F4···(3) This is the result.

[0014] Figure 3 shows the functional blocks of a drive force control system mounted on a vehicle. The drive force control system 20 has the function of independently controlling the driving force of multiple wheels 2 and comprises a state quantity acquisition unit 22, a driving stiffness acquisition unit 30, a drive force setting unit 32, and a drive control unit 34. Each function of the drive force control system 20 may be realized by a control device 10.

[0015] The state quantity acquisition unit 22 acquires the state quantities of each wheel 2 based on sensor signals (measured values) provided by various sensors included in the sensors 12. The state quantity acquisition unit 22 includes a temperature acquisition unit 24, a load acquisition unit 26, and a slip angle acquisition unit 28. The temperature acquisition unit 24 acquires the wheel temperature T of each wheel 2. i The load acquisition unit 26 acquires the wheel load W of each wheel 2. i The slip angle acquisition unit 28 acquires the wheel slip angle SA of each wheel 2. i Obtain it.

[0016] The temperature acquisition unit 24 obtains the wheel temperature T from the temperature sensor installed inside the wheel 2. i The load acquisition unit 26 obtains the load W of the wheel 2 from the measured value of the stroke sensor. i The slip angle acquisition unit 28 may calculate and obtain the slip angle SA from the measured value of the wheel speed sensor and the measured value of the lateral acceleration sensor. i You may calculate and obtain it.

[0017] In the region where the slip ratio SR is small, the driving force F X The driving stiffness DS has an almost linear relationship with the slip ratio SR, and the proportionality constant at this time is called the driving stiffness DS. Therefore, the driving stiffness DS at each wheel 2 is i It is defined as follows: F Xi =DS i ×SR ···(4)

[0018] The driving stiffness acquisition unit 30 acquires the driving stiffness DS of each wheel based on the state quantity acquired by the state quantity acquisition unit 22. iThe driving stiffness acquisition unit 30 acquires the wheel temperature T. i Wheel load W i and wheel slip angle SA i Based on this, the driving stiffness DS of each wheel i The driving stiffness acquisition unit 30 acquires the driving stiffness DS of each wheel 2. i This can be derived using means such as a map that defines the relationship with each state variable. DS i =f(T i ,W i ,SA i ) ···(5) The driving stiffness acquisition unit 30 uses a known map that defines the relationship between wheel temperature, wheel load, wheel slip angle, and driving stiffness to acquire the driving stiffness DS for each wheel 2. i You may obtain it.

[0019] The driving force setting unit 32 sets the driving stiffness DS of each wheel 2. i Based on this, the driving force F of each wheel is determined to minimize the total wheel loss in multiple wheels 2. Xi Set it. From equations (2) and (4), the loss P in each wheel 2 is Xi This can be expressed as follows: P Xi =F Xi × (F Xi / DS i )×V B =F Xi 2 ×V B / DS i ...(6) Therefore, the total wheel loss P for all wheels 2 is calculated by equation (7).

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[0020] The driving force setting unit 32 sets the driving force F of each wheel so that the total wheel loss P calculated by equation (7) is minimized. Xi Specifically, the drive force setting unit 32 distributes the required drive force F of the vehicle 1, derived based on the accelerator opening and vehicle speed, to each wheel 2 such that the total drive loss (wheel loss) P in all wheels 2 is minimized, and sets the drive force F of each wheel. Xi The drive control unit 34 sets the driving force F of each wheel 2 according to the set driving force of each wheel 2. Specifically, the drive control unit 34 controls each electric motor 3 according to the set driving force of each wheel 2. Thus, according to this embodiment, the drive force setting unit 32 sets the driving force F of each wheel 2 to minimize the total wheel loss P. Xi By setting this, electric vehicles can avoid unnecessary power consumption, and internal combustion engine vehicles can avoid a decrease in fuel efficiency.

[0021] Furthermore, the distribution of driving force resulting in oversteer is undesirable from the standpoint of vehicle stability. Therefore, the driving force setting unit 32 sets the driving force F Xi The system may have a function to determine whether or not oversteer occurs when a certain force is applied to each of the two wheels.

[0022] Figure 4 is a flowchart of the method for distributing driving force according to the embodiment. The state quantity acquisition unit 22 acquires the state quantity of each wheel 2 (S10). In the embodiment, the state quantity acquisition unit 22 acquires the wheel temperature T at a predetermined period. i Wheel load W i and wheel slip angle SA i The driving stiffness acquisition unit 30 may acquire the driving stiffness DS of each wheel 2 based on the acquired state quantity. i The driving stiffness acquisition unit 30 acquires the driving stiffness DS using a map, etc. (S12). i The driving force setting unit 32 sets the driving stiffness DS of each wheel 2. i Based on this, the driving force of each wheel 2 is set to minimize the total wheel loss in the multiple wheels 2 (S14).

[0023] At this time, the driving force setting unit 32 determines whether or not the vehicle 1 will oversteer when the set driving force is applied to each wheel 2 (S16). Here, the driving force setting unit 32 determines the cornering power CP of each wheel 2 when the set driving force is applied. i The following is derived. For example, the driving force setting unit 32 uses a map that defines the relationship between state variables and cornering power to determine the cornering power CP of each wheel 2. i The following can be derived. Then the drive force setting unit 32 calculates the stability factor K of the vehicle 1 using, for example, equation (8).

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[0024] The stability factor K is a characteristic value that indicates the steering state of the vehicle. A positive value indicates an understeer state, and a negative value indicates an oversteer state. When an understeer state occurs (N in S16), stable driving of the vehicle 1 can be achieved, so the drive control unit 34 controls each electric motor 3 according to the driving force of each wheel 2 set by the driving force setting unit 32 (S20).

[0025] On the other hand, if an oversteer condition occurs (Y in S16), the drive force setting unit 32 determines that stable driving cannot be achieved by applying the set drive force to each wheel 2, and changes and resets the set drive force for each wheel 2 (S18). Specifically, the drive force setting unit 32 changes and resets the set drive force so that the vehicle 1 exhibits understeer characteristics. The drive control unit 34 controls each electric motor 3 according to the drive force for each wheel 2 reset by the drive force setting unit 32 (S20). As a result, the drive force control system 20 can achieve stable driving of the vehicle 1.

[0026] The present invention has been described above based on the embodiments. The embodiments are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of each component and each processing process, and that such modifications also fall within the scope of the present invention. [Explanation of symbols]

[0027] 1...Vehicle, 2...Wheels, 3...Electric motor, 10...Control device, 12...Sensors, 20...Drive force control system, 22...Status quantity acquisition unit, 24...Temperature acquisition unit, 26...Load acquisition unit, 28...Slip angle acquisition unit, 30...Driving stiffness acquisition unit, 32...Drive force setting unit, 34...Drive control unit.

Claims

1. A drive force control system that independently controls the driving force of multiple wheels in a vehicle, A state quantity acquisition unit that acquires the state quantity of each wheel, A driving stiffness acquisition unit acquires the driving stiffness of each wheel based on the acquired state quantities, A driving force setting unit sets the driving force of each wheel to minimize the total wheel loss across multiple wheels, based on the driving stiffness of each wheel. A drive control unit drives each wheel according to the set driving force for each wheel, A drive force control system equipped with the following features.

2. The state quantity acquisition unit, A temperature acquisition unit that acquires the wheel temperature of each wheel, A load acquisition unit that acquires the wheel load of each wheel, It has a slip angle acquisition unit that acquires the wheel slip angle of each wheel. The driving stiffness acquisition unit acquires the driving stiffness of each wheel based on the acquired wheel temperature, wheel load, and wheel slip angle. The driving force control system according to feature 1.

3. The aforementioned driving force setting unit derives the driving force for each wheel that minimizes the total wheel losses across multiple wheels. The driving force control system according to feature 1.

4. The aforementioned drive force setting unit modifies the set drive force if applying the set drive force to each wheel would cause the vehicle to oversteer. The driving force control system according to feature 1.

5. The aforementioned drive force setting unit modifies the set drive force so that the vehicle enters an understeer state. The driving force control system according to feature 4.

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