Driving force control system

Abstract

The present application relates to a driving force control system. A state quantity acquisition section acquires a state quantity of each wheel in a vehicle. A driving stiffness acquisition section acquires a driving stiffness of each wheel based on the acquired state quantity. A driving force setting section sets a driving force of each wheel that reduces a total of wheel losses in a plurality of wheels based on the driving stiffness of each wheel. A driving control section drives each wheel in accordance with the set driving force of each wheel.

Description

Technical Field

[0001] This invention relates to a drive force control system that independently controls the driving force of multiple wheels in a vehicle. Background Technology

[0002] Japanese Patent Application Publication No. 2019-64415 discloses a drive force control method that uses an estimated maximum road surface μ to distribute the driving force of a vehicle. This drive force control method includes: a first estimation step, in a first driving state where the vehicle is steadily accelerating and traveling straight, estimating the maximum road surface μ based on the slip ratio and driving stiffness corresponding to the driving force; a second estimation step, in a second driving state where the vehicle is being steered, estimating the maximum road surface μ based on the steering reaction force; and a third estimation step, in a third driving state where the outside air temperature is above a predetermined temperature, estimating a pre-set maximum road surface μ. Summary of the Invention

[0003] During braking, wheel slippage causes driving losses between the wheel and the road surface. In battery-electric vehicles, these driving losses are a major cause of unnecessary power consumption; in internal combustion engine vehicles, they are a major cause of fuel consumption deterioration. Therefore, the object of this invention is to provide a technique for efficiently distributing driving force to each wheel.

[0004] The drive force control system of one aspect of the present invention is a system that independently controls the drive force of multiple wheels in a vehicle, comprising: a state quantity acquisition unit that acquires the state quantity of each wheel; a drive stiffness acquisition unit that acquires the drive stiffness of each wheel based on the acquired state quantity; a drive force setting unit that sets the total drive force of each wheel to reduce wheel wear of the multiple wheels based on the drive stiffness of each wheel; and a drive control unit that drives each wheel according to the set drive force of each wheel. Attached Figure Description

[0005] Hereinafter, the features, advantages, technical and industrial importance of exemplary embodiments of the present invention will be described with reference to the accompanying drawings, in which the same reference numerals denote the same constituent elements, wherein:

[0006] Figure 1 This is a diagram schematically illustrating the configuration of a vehicle according to an embodiment.

[0007] Figure 2 This is a diagram used to illustrate the driving losses that occur in the wheels.

[0008] Figure 3 This is a diagram showing the functional blocks of the drive force control system installed in a vehicle.

[0009] Figure 4 This is a flowchart of the method for allocating driving force in the implementation method. Detailed Implementation

[0010] Figure 1 The configuration of vehicle 1 according to the embodiment is schematically shown. Vehicle 1 has multiple wheels and multiple electric motors provided on the multiple wheels, and has the function of independently controlling the driving force of the multiple wheels. The multiple wheels include a left front wheel 2FL, a right front wheel 2FR, a left rear wheel 2RL, and a right rear wheel 2RR. The multiple 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. Hereinafter, unless otherwise specified, each wheel will be referred to as a wheel 2, and each electric motor will be referred to as an electric motor 3.

[0011] Vehicle 1 in this embodiment is an electric vehicle that uses an electric motor 3 as its driving force source, but it can also be a vehicle that uses only an internal combustion engine as its driving force source. Selected vehicles include, for example, battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or fuel cell electric vehicles (FCEVs). Vehicle 1 can be a driver-driven vehicle or an autonomous vehicle. Furthermore, even when vehicle 1 uses an internal combustion engine as its driving force source, it has the function of independently controlling the driving force of multiple wheels 2.

[0012] Vehicle 1 is equipped with a control device 10 having a processor, a storage device, and an input / output interface. The input / output interface acquires sensor signals measured by various sensors from sensor class 12 installed on vehicle 1. The storage device stores control programs and setting tables for setting the driving force of each wheel 2 to control each electric motor 3. The processor reads the control program from the storage device and executes it, thereby achieving optimal control of the driving force to be distributed to multiple wheels 2.

[0013] Sensor class 12 includes units for measuring state quantities of vehicle 1. In one embodiment, sensor class 12 includes a unit for measuring the temperature of each wheel 2. The unit for measuring wheel temperature may be a temperature sensor disposed inside the wheel 2. Additionally, sensor class 12 includes units for measuring the load on each wheel 2 or for measuring state quantities used to estimate the load on each wheel 2. The unit for measuring wheel load may be a load sensor for measuring wheel load, and the unit for measuring state quantities used to estimate wheel load may be a travel sensor for measuring suspension travel. In this case, the processor may have the function of estimating wheel load based on travel. Furthermore, sensor class 12 includes units for measuring state quantities used to estimate the slip angle of each wheel 2. The unit for measuring state quantities used to estimate slip angle may be a wheel speed sensor for measuring wheel speed and a lateral acceleration sensor for detecting lateral acceleration. In this case, the processor may have the function of estimating slip angle based on the integral value of vehicle speed and lateral acceleration. Alternatively, the processor may also have the function of estimating slip angle based on measurements from GPS and tire angle gauges.

[0014] Figure 2 This is a diagram used to illustrate the driving losses generated in the wheel. Here, it is assumed that the wheel's rotational speed (wheel speed) is V. T The vehicle's speed relative to the ground (road speed) is V. B According to the law of action and reaction, the driving force F X Reaction force F from the road surface X equal.

[0015] Calculate the distance d that the wheel travels in time Δt as follows: T and the distance d that the road surface moves. B .

[0016] Wheel travel distance d T =V T ×Δt

[0017] Road surface movement distance d B =V B ×Δt

[0018] If we study the amount of work done, then the amount of work done by the wheel is the driving force F. X × Wheel travel distance d T The amount of work done on the road surface is the road surface reaction force F. X × Road surface movement distance d B Therefore, the power of the wheel (work done by the wheel / Δt) is equal to the driving force F. X ×wheel speed V T The power of the road surface (work done by the road surface / Δt) is the road surface reaction force F. X × Road speed V BTherefore, the loss P between the wheel and the road surface... X In other words,

[0019] P X =F X ×V T -F X ×V B

[0020] =F X ×(V) T -V B )

[0021] =F X ×{(V T -V B ) / V B}×V B

[0022] Here, (V) T -V B ) / V B It is the slip ratio SR, and therefore can be expressed as the following formula.

[0023] P X =F X ×SR×V B …(1) The loss P X This becomes the driving loss (wheel loss) generated in one wheel.

[0024] Therefore, the loss P in each wheel 2 X It can be expressed as the following formula.

[0025] P Xi =F Xi ×SR×V B …(2)

[0026] Here, "i" is a number used to distinguish wheel 2, 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 set as F, then F becomes the following formula.

[0027] F = ΣF Xi =F1+F2+F3+F4…(3)

[0028] Figure 3 This represents a function block of the drive force control system installed in the vehicle. The drive force control system 20 has the function of independently controlling the drive force of multiple wheels 2, and includes a state quantity acquisition unit 22, a drive stiffness acquisition unit 30, a drive force setting unit 32, and a drive control unit 34. Each function in the drive force control system 20 can be implemented by the control device 10.

[0029] The state quantity acquisition unit 22 acquires the state quantity of each wheel 2 based on sensor signals (measured values) provided by the various sensors included in the sensor class 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 .

[0030] Temperature acquisition unit 24 can obtain the wheel temperature T from the measurement value of the temperature sensor installed inside the wheel 2. i The load acquisition unit 26 can calculate and acquire the load W of wheel 2 based on the measurement value of the stroke sensor. i Furthermore, the slip angle acquisition unit 28 can calculate and obtain the slip angle SA based on the measurements from the wheel speed sensor and the lateral acceleration sensor. i .

[0031] In regions with low slip ratio SR, the driving force F X The relationship between the driving stiffness and the slip ratio SR is approximately linear; this proportionality constant is called the driving stiffness DS. Therefore, the driving stiffness DS in each wheel 2... i Defined as follows.

[0032] F Xi =DS i ×SR…(4)

[0033] The drive stiffness acquisition unit 30 acquires the drive stiffness DS of each wheel 2 based on the state quantities acquired by the state quantity acquisition unit 22. i In this embodiment, the drive stiffness acquisition unit 30 is based on the acquired wheel temperature T. i Wheel load W i and wheel slip angle SA i To obtain the driving stiffness DS of each wheel 2 i The drive stiffness acquisition unit 30 can derive the drive stiffness DS of each wheel 2 using units such as setting tables that specify the relationship with each state quantity. i .

[0034] DS i =f(T) i W i SA i (5)

[0035] The drive stiffness acquisition unit 30 can acquire the drive stiffness DS of each wheel 2 using a known setting table that specifies the relationship between wheel temperature, wheel load, wheel slip angle, and drive stiffness. i .

[0036] The drive force setting unit 32 is based on the drive stiffness DS of each wheel 2 i To set the total driving force F of each wheel 2 to reduce wheel wear in multiple wheels 2. Xi .

[0037] According to equations (2) and (4), the loss P in each wheel 2 Xi It can be expressed as follows.

[0038] P Xi =F Xi ×(F Xi / DS i )×V B

[0039] =F Xi 2 ×V B / DS i …(6)

[0040] Therefore, the total wheel wear P of all wheels 2 is calculated by equation (7).

[0041] (Equation 1)

[0042]

[0043] The driving force setting unit 32 sets the driving force F of each wheel 2 in a manner that minimizes the total wheel losses P calculated by formula (7). Xi Specifically, the drive force setting unit 32 distributes the required drive force F of the vehicle 1, derived from the accelerator opening and vehicle speed, to each wheel 2 in a manner that minimizes the total drive loss (wheel loss) P of all wheels 2, and sets the drive force F of each wheel 2. Xi The drive control unit 34 drives each wheel 2 according to the set drive force of each wheel 2. Specifically, the drive control unit 34 controls each electric motor 3 according to the set drive force of each wheel 2. Thus, according to the embodiment, the drive force setting unit 32 sets the drive force F of each wheel 2 in a way that reduces the total wheel wear P. Xi Therefore, if it is a battery-powered electric vehicle, unnecessary power consumption can be avoided, and if it is an internal combustion engine vehicle, fuel consumption can be avoided.

[0044] Furthermore, the result of distributing the driving force is that, from the viewpoint of vehicle stability, oversteer is not preferable. Therefore, the driving force setting unit 32 can determine whether the set driving force F has been applied to each wheel 2. Xi Will over-switching occur under certain circumstances?

[0045] Figure 4 This is a flowchart of the method for distributing driving force according to the implementation method. The state quantity acquisition unit 22 acquires the state quantity of each wheel 2 (S10). In this implementation, the state quantity acquisition unit 22 can acquire the wheel temperature T at a predetermined period. i Wheel load W i and wheel slip angle SA i The drive stiffness acquisition unit 30 acquires the drive stiffness DS of each wheel 2 based on the acquired state quantities. i (S12). The drive stiffness acquisition unit 30 can acquire the drive stiffness DS using a setting table or the like. i The drive force setting unit 32 is based on the drive stiffness DS of each wheel 2. i To set the total driving force of each wheel 2 to reduce wheel wear of multiple wheels 2 (S14).

[0046] At this time, the drive force setting unit 32 determines whether the vehicle 1 will become oversteer when the set drive force is applied to each wheel 2 (S16). Here, the drive force setting unit 32 calculates the turning power CP of each wheel 2 when the set drive force is applied. i For example, the drive force setting unit 32 can use a setting table that specifies the relationship between state quantities and turning power to derive the turning power CP of each wheel 2. i Then, the drive force setting unit 32 uses, for example, equation (8) to calculate the stability coefficient K of the vehicle 1.

[0047] (Formula 2)

[0048]

[0049] CP i : Normalized CP of the i-th wheel

[0050] e i : CP amplification of the i-th wheel

[0051] C i The equivalent CP of the i-th wheel

[0052] C F The average equivalent CP of the two front wheels

[0053] C R The average equivalent CP of the two rear wheels

[0054] I: Wheelbase

[0055] g: acceleration due to gravity

[0056] The stability coefficient K is a characteristic value representing the steering state of the vehicle. A positive value indicates understeer, and a negative value indicates oversteer. In the case of understeer (N in S16), stable driving of the vehicle 1 can be achieved. Therefore, the drive control unit 34 controls each electric motor 3 according to the drive force of each wheel 2 set by the drive force setting unit 32 (S20).

[0057] On the other hand, when the vehicle becomes oversteerable (Y in S16), the drive force setting unit 32 determines that stable driving cannot be achieved if the set drive force is applied to each wheel 2, and changes the set drive force of each wheel 2, resetting it (S18). Specifically, the drive force setting unit 32 resets the set drive force in such a way that the vehicle 1 exhibits understeer characteristics. The drive control unit 34 controls each electric motor 3 according to the drive force of 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.

[0058] The present invention has been described above based on embodiments. These embodiments are merely illustrative, and those skilled in the art will understand that various modifications exist in the combination of the constituent elements and processing procedures; furthermore, such modifications are also within the scope of the present invention.

Claims

1. A drive force control system that independently controls the drive force of multiple wheels in a vehicle, characterized in that, have: The state quantity acquisition unit acquires the state quantities of each wheel; The drive stiffness acquisition unit obtains the drive stiffness of each wheel based on the acquired state variables. The drive force setting unit sets the total drive force of each wheel to reduce wheel wear by adjusting the drive stiffness of each wheel; and The drive control unit drives each wheel according to the set driving force of each wheel.

2. The driving force control system according to claim 1, characterized in that, The state quantity acquisition unit has: The temperature acquisition unit acquires the wheel temperature of each wheel; The load acquisition unit acquires the wheel load of each wheel; and The slip angle acquisition unit acquires the wheel slip angle of each wheel. The drive stiffness acquisition unit obtains the drive stiffness of each wheel based on the obtained wheel temperature, wheel load, and wheel slip angle.

3. The driving force control system according to claim 1, characterized in that, The drive force setting unit outputs the drive force of each wheel that minimizes the total wheel wear among the multiple wheels.

4. The driving force control system according to claim 1, characterized in that, If the vehicle becomes oversteerable when the set driving force is applied to each wheel, the driving force setting unit changes the set driving force.

5. The driving force control system according to claim 4, characterized in that, The drive force setting unit changes the set drive force in such a way that the vehicle is in an understeer state.

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