Vehicle control system

Abstract

The present invention provides a vehicle control device that can increase opportunities for learning control while suppressing the increase in learning errors. [Solution] When driving with a tire load ratio difference of less than or equal to a predetermined load ratio difference, learning control is performed. This makes it possible to perform learning control over a wider range of driving forces compared to when learning control is performed when driving with a small tire slip ratio, which is considered to be within a range of minute driving forces. Furthermore, even when driving with a tire load ratio difference of less than or equal to a predetermined load ratio difference, if driving is not in the tire linear region, i.e., if driving is in the tire nonlinear region, learning control is not performed. This makes it possible to prevent or suppress the increase in learning error caused by the increase in the change in tire slip ratio when driving in the tire nonlinear region where the tire slip ratio is large. Thus, it is possible to increase the opportunities to perform learning control while suppressing the increase in learning error.

Description

Technical Field

[0006] , , ,

[0005] , ,

[0001] The present invention relates to a control device for a vehicle having front, rear, left, and right wheels.

Background Art

[0002] A control device for a vehicle including front, rear, left, and right wheels and a power source that generates power serving as the driving force of the wheels is well known. For example, the straight-ahead traveling state determination device for a vehicle described in Patent Document 1 is such a device. In this Patent Document 1, when it is determined that the vehicle is traveling straight in a steady state, a learning value is obtained based on the difference in wheel speed caused by variations in tire diameter, and the difference in wheel speed is corrected by this learning value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in order to reduce the learning error, in addition to the straight-ahead traveling determination, when it is determined that the tire slip ratio of each wheel is minute, learning control may be performed to correct the difference in wheel speed caused by the difference in tire diameter of the wheels by learning. However, when it is determined that the tire slip ratio is minute, the range of the driving force that can be learned is limited to the range of minute driving forces, so the frequency of performing the learning control may be reduced.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for a vehicle that can increase the opportunity to perform learning control while suppressing an increase in learning error.

Means for Solving the Problems

[0006] The gist of the first invention is a control device for a vehicle comprising (a) front and rear left and right wheels and a power source that generates power that becomes the driving force for the wheels, (b) a learning control unit that performs learning control to correct the difference in wheel speed caused by the difference in tire diameter of the wheels by learning, and (c) the learning control unit performs the learning control when it determines that the vehicle is running in a state in which the difference in tire load ratio, which is the value of the driving force with respect to the ground load of the wheels, is less than or equal to a predetermined load ratio difference, and that the vehicle is running in a tire linear region in which the value of the change in tire slip ratio with respect to the change in tire load ratio is small, while it does not perform the learning control when it determines that the vehicle is running in a state in which the difference in tire load ratio exceeds the predetermined load ratio difference, or when it determines that the vehicle is running in a tire nonlinear region in which the value of the change in tire slip ratio with respect to the change in tire load ratio is large. [Effects of the Invention]

[0007] According to the first invention, learning control is performed when the difference in tire load ratio is less than or equal to a predetermined load ratio difference during driving. This makes it possible to perform learning control over a wider range of driving forces compared to when learning control is performed during driving with a small range of driving force, which is defined as a range of minute driving forces. Furthermore, even when the difference in tire load ratio is less than or equal to a predetermined load ratio difference during driving, learning control is not performed if the vehicle is not driving in the linear tire region, i.e., if it is driving in the nonlinear tire region. This makes it possible to prevent or suppress the increase in learning error caused by the increase in the change in tire slip ratio during driving in the nonlinear tire region where the tire slip ratio is large. Thus, it is possible to increase the opportunities to perform learning control while suppressing the increase in learning error. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the schematic configuration of a vehicle to which the present invention is applied, and further illustrates the main parts of the control functions and control systems for various control functions in the vehicle. [Figure 2]This diagram illustrates the range of driving force that is subject to learning control. [Figure 3] This diagram illustrates the linear and nonlinear regions of tires. [Figure 4] This flowchart explains the key aspects of the control operation of an electronic control unit, specifically focusing on control operations that increase opportunities for learning control while suppressing the increase in learning errors. [Figure 5] This flowchart explains the control operation for determining a small load factor deviation, and is the subroutine corresponding to step S10 in the flowchart in Figure 4. [Figure 6] This flowchart explains the control operation for determining the tire linear region, and is the subroutine corresponding to step S20 in the flowchart in Figure 4. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0010] Figure 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied. Figure 1 also illustrates the main parts of the control functions and control systems for various controls in the vehicle 10. In Figure 1, the vehicle 10 comprises front and rear wheels 12, left and right wheels, and electric motors MG independently provided for each wheel 12. The electric motors MG are the power source of the present invention, generating power that becomes the driving force Fx of the wheels 12. The driving force Fx of the wheels 12 is the force at the wheels 12, which is the frictional force at the contact point of the wheels 12, i.e., the road surface grip force. The wheels 12 include the left front wheel 12fl, the right front wheel 12fr, the left rear wheel 12rl, and the right rear wheel 12rr. The electric motors MG include the left front motor MGfl, the right front motor MGfr, the left rear motor MGrl, and the right rear motor MGrr. Note that "front and rear" refers to the front and rear in the forward and backward direction of the vehicle 10, and "left and right" refers to the left and right with respect to the forward direction of the vehicle 10.

[0011] Vehicle 10 is an all-wheel drive vehicle in which the power distribution of the wheels 12 can be adjusted. Since vehicle 10 is equipped with four wheels, one at the front, one at the rear, one at the left, and one at the right, it is also a four-wheel drive vehicle. In this embodiment, all-wheel drive (AWD) and four-wheel drive (4WD) are synonymous. In addition to driving with AWD control (AWD state is also synonymous), which drives all of the wheels 12, vehicle 10 can also drive with two-wheel drive (=2WD) control (2WD state is also synonymous), which drives, for example, only the front wheels or only the rear wheels of the wheels 12.

[0012] The vehicle 10 also includes a drive shaft 14, a gear mechanism 16, a battery 20, and a power control unit 22. The drive shaft 14 and the gear mechanism 16 are components that constitute part of a power transmission device that transmits power from the electric motor MG to the wheels 12. The gear mechanism 16 is, for example, a reduction gear. The battery 20 is a rechargeable DC power source and is a high-voltage battery for driving. The battery 20 is electrically connected to the power control unit 22. The power control unit 22 includes, for example, an inverter. The power control unit 22 is electrically connected to the electric motor MG. The power control unit 22 is a power control device (PCU (Power Control Unit)) that controls the power exchanged between the battery 20 and the electric motor MG. When not specifically distinguished, the term "power" is synonymous with "electrical energy." When not specifically distinguished, the term "power" is synonymous with "driving force," "torque," and "force."

[0013] The electric motor MG is a known rotating electric machine, a so-called motor generator. The motor torque Tm of the electric motor MG is controlled by the power control unit 22 controlled by the electronic control device 50, which will be described later.

[0014] The drive shaft 14 includes the left front drive shaft 14fl, the right front drive shaft 14fr, the left rear drive shaft 14rl, and the right rear drive shaft 14rr. The gear mechanism 16 includes the left front gear mechanism 16fl, the right front gear mechanism 16fr, the left rear gear mechanism 16rl, and the right rear gear mechanism 16rr. One side of the left front drive shaft 14fl is connected to the left front electric motor MGfl via the left front gear mechanism 16fl, and the other side is connected to the left front wheel 12fl. The same applies to the connections between the right front drive shaft 14fr and the right front gear mechanism 16fr, the left rear drive shaft 14rl and the left rear gear mechanism 16rl, and the right rear drive shaft 14rr and the right rear gear mechanism 16rr.

[0015] The power control unit 22 includes the left front PCU 22fl, the right front PCU 22fr, the left rear PCU 22rl, and the right rear PCU 22rr. The left front PCU 22fl converts DC power from the battery 20 into AC power and supplies it to the left front motor MGfl, and converts AC power generated by the left front motor MGfl through regenerative braking into DC power and supplies it to the battery 20. The same applies to the functions of the right front PCU 22fr and the right front motor MGfr, the left rear PCU 22rl and the left rear motor MGrl, and the right rear PCU 22rr and the right rear motor MGrr.

[0016] Vehicle 10 is a vehicle in which the amount of change in the driving force Fx of the front, rear, left, and right wheels can be independently controlled, and is a battery electric vehicle (BEV) with independently driven front, rear, left, and right wheels. In vehicle 10, the distribution of driving force to the front, rear, left, and right wheels can be controlled according to the driving conditions.

[0017] Vehicle 10 further includes an electronic control unit 50 (refer to "ECU" in the figure) as a controller. The electronic control unit 50 is configured to include a so-called microcomputer having, for example, a CPU, a RAM, a ROM, an input / output interface, and the like. The CPU executes various controls of the vehicle 10 by performing signal processing according to a program stored in the ROM in advance while using the temporary storage function of the RAM, for example. The electronic control unit 50 is the control device of the present invention.

[0018] Various signals based on detection values from various sensors and the like provided in the vehicle 10 are respectively supplied to the electronic control unit 50. The various sensors and the like are, for example, a motor rotation sensor 30, a wheel speed sensor 32, an accelerator opening sensor 34, a brake sensor 36, a steering sensor 38, a G sensor 40, a yaw rate sensor 42, and the like. The various signals are, for example, a motor rotation speed Nm, a wheel speed ω, an accelerator opening θacc, a brake operation amount θbp, a steering angle θsw, a steering direction Dsw, a longitudinal acceleration Gx, a lateral acceleration Gy, a yaw rate Ryaw, and the like. The motor rotation sensor 30 includes a left front motor rotation sensor 30fl, a right front motor rotation sensor 30fr, a left rear motor rotation sensor 30rl, and a right rear motor rotation sensor 30rr. The wheel speed sensor 32 includes a left front wheel speed sensor 32fl, a right front wheel speed sensor 32fr, a left rear wheel speed sensor 32rl, and a right rear wheel speed sensor 32rr.

[0019] The motor rotation speed Nm is the rotation speed of the motor MG. The motor rotation speed Nm includes the left front motor rotation speed Nmfl, the right front motor rotation speed Nmfr, the left rear motor rotation speed Nmrl, and the right rear motor rotation speed Nmrr. The wheel speed ω is the rotation speed of the wheel 12. The wheel speed ω includes the left front wheel speed ωfl, the right front wheel speed ωfr, the left rear wheel speed ωrl, and the right rear wheel speed ωrr. The accelerator opening θacc is a signal corresponding to an acceleration required amount representing the magnitude of the driver's acceleration operation, and is the accelerator operation amount by the driver. The brake operation amount θbp is a signal representing the state in which the brake pedal for operating the wheel brake is being operated by the driver, and is also a signal representing the magnitude of the depression operation of the brake pedal. The wheel brake is a mechanical brake provided on each of the wheels 12 and actuated, for example, by hydraulic pressure, that is, a friction brake such as a disk brake or a drum brake. The steering wheel angle θsw is the steering angle of the steering wheel. The steering direction Dsw is the steering direction of the steering wheel. The longitudinal acceleration Gx is the acceleration in the longitudinal direction of the vehicle 10. The lateral acceleration Gy is the acceleration in the lateral direction of the vehicle 10. The yaw rate Ryaw is the rotational angular velocity around the vertical axis of the vehicle 10.

[0020] From the electronic control device 50, various command signals (such as the motor control command signal Sm, etc.) are output to each device (such as the power control unit 22, etc.) provided in the vehicle 10. The motor control command signal Sm is a torque instruction value for controlling the motor torque Tm. The motor control command signal Sm includes the left front motor control command signal Smfl, the right front motor control command signal Smfr, the left rear motor control command signal Smrl, and the right rear motor control command signal Smrr. The left front motor control command signal Smfl is a torque instruction value for controlling the left front motor torque Tmfl, which is the torque of the left front motor MGfl, and is output to the left front PCU 22fl. The same applies to the right front motor control command signal Smfr, the left rear motor control command signal Smrl, and the right rear motor control command signal Smrr.

[0021] The electronic control unit 50 includes a vehicle state acquisition unit 52, a drive control unit 54, and a learning control unit 56 in order to realize various controls in the vehicle 10.

[0022] The vehicle state acquisition unit 52 acquires an estimated value of the vehicle speed Vx of the vehicle 10 based on the wheel speed ω. For example, the vehicle state acquisition unit 52 acquires the lowest or second slowest value among the wheel speeds ω (ωfl, ωfr, ωrl, ωrr) as the estimated value of the vehicle speed Vx. When slip occurs in the wheels 12, the estimated value of the vehicle speed Vx becomes higher than the actual value of the vehicle speed Vx, resulting in a rise in the vehicle speed Vx. To prevent this rise in the vehicle speed Vx, the vehicle state acquisition unit 52 limits the upward slope of the estimated vehicle speed Vx by the velocity component obtained by integrating the longitudinal acceleration Gx. Alternatively, the vehicle state acquisition unit 52 may acquire the vehicle speed Vx used by, for example, a known traction control function or ABS function as the estimated value of the vehicle speed Vx. In this embodiment, hereafter, when simply referred to as vehicle speed Vx, it indicates the estimated value of the vehicle speed Vx, i.e., the estimated vehicle speed Vx.

[0023] The drive control unit 54 calculates the required drive torque Tdrvdem for the vehicle 10 based on, for example, the accelerator opening θacc and the vehicle speed Vx. The required drive torque Tdrvdem is the required value of the drive torque Tdrv, which is the torque at the wheels 12. The drive control unit 54 sets the torque distribution ratio of the front and rear left and right wheels based on, for example, several drive force-related values ​​such as the accelerator opening θacc, the vehicle speed Vx, the steering angle θsw, the steering direction Dsw, the longitudinal acceleration Gx, the lateral acceleration Gy, and the yaw rate Ryaw. Based on the required drive torque Tdrvdem and the torque distribution ratio, the drive control unit 54 calculates the required left front wheel torque Tdrvfldem, the required right front wheel torque Tdrvfrdem, the required left rear wheel torque Tdrvrldem, and the required right rear wheel torque Tdrvrrdem. The required left front wheel torque Tdrvfldem is the required value of the left front wheel drive torque Tdrvfl. The required right front wheel torque Tdrvfrdem is the required value for the right front wheel drive torque Tdrvfr. The required left rear wheel torque Tdrvrldem is the required value for the left rear wheel drive torque Tdrvrl. The required right rear wheel torque Tdrvrrdem is the required value for the right rear wheel drive torque Tdrvrr. The drive torque Tdrv is the sum of the left front wheel drive torque Tdrvfl, the right front wheel drive torque Tdrvfr, the left rear wheel drive torque Tdrvrl, and the right rear wheel drive torque Tdrvrr.

[0024] The drive control unit 54 outputs a left front motor control command signal Smfl to the left front PCU 22fl to achieve the requested left front wheel torque Tdrvfldem. The drive control unit 54 outputs a right front motor control command signal Smfr to the right front PCU 22fr to achieve the requested right front wheel torque Tdrvfrdem. The drive control unit 54 outputs a left rear motor control command signal Smrl to the left rear PCU 22rl to achieve the requested left rear wheel torque Tdrvrldem. The drive control unit 54 outputs a right rear motor control command signal Smrr to the right rear PCU 22rr to achieve the requested right rear wheel torque Tdrvrrdem.

[0025] The vehicle status acquisition unit 52 acquires an estimated value of the left front wheel drive torque Tdrvfl based on the left front motor control command signal Smfl output by the drive control unit 54. The vehicle status acquisition unit 52 acquires an estimated value of the right front wheel drive torque Tdrvfr based on the right front motor control command signal Smfr output by the drive control unit 54. The vehicle status acquisition unit 52 acquires an estimated value of the left rear wheel drive torque Tdrvrl based on the left rear motor control command signal Smrl output by the drive control unit 54. The vehicle status acquisition unit 52 acquires an estimated value of the right rear wheel drive torque Tdrvrr based on the right rear motor control command signal Smrr output by the drive control unit 54. In this embodiment, hereafter, when simply referred to as left front wheel drive torque Tdrvfl, it indicates an estimated value of the left front wheel drive torque Tdrvfl. The same applies to right front wheel drive torque Tdrvfr, left rear wheel drive torque Tdrvrl, and right rear wheel drive torque Tdrvrr.

[0026] The vehicle state acquisition unit 52 acquires an estimated value of the ground contact load Fz at the wheels 12. For example, the vehicle state acquisition unit 52 calculates the dynamic ground contact load at each of the wheels 12 based on the static ground contact load at each of the wheels 12 predetermined in the vehicle specifications 10, and the estimation of load transfer in the front, rear, left, and right directions. The vehicle state acquisition unit 52 acquires this dynamic ground contact load as an estimated value of the ground contact load Fz at each of the wheels 12. The vehicle state acquisition unit 52 estimates the load transfer in the front, rear, left, and right directions based on, for example, the front-rear acceleration Gx, the left-right acceleration Gy, and the driving torque Tdrv at each of the wheels 12. In this embodiment, the term "ground contact load Fz" refers to an estimated value of the ground contact load Fz. The ground contact load Fz includes the left front wheel ground contact load Fzfl, the right front wheel ground contact load Fzfr, the left rear wheel ground contact load Fzrl, and the right rear wheel ground contact load Fzrr.

[0027] The vehicle state acquisition unit 52 determines whether the wheel brakes are being applied based on the brake operation amount θbp. For example, the vehicle state acquisition unit 52 determines whether the brakes are off, meaning the wheel brakes are not being applied, based on the brake operation amount θbp.

[0028] The vehicle status acquisition unit 52 determines whether the vehicle 10 is traveling in a straight line based on the steering angle θsw, yaw rate Ryaw, etc. If the vehicle status acquisition unit 52 determines that the vehicle 10 is traveling in a straight line, it sets the straight-line determination flag to "on". If the vehicle status acquisition unit 52 determines that the vehicle 10 is not traveling in a straight line, it sets the straight-line determination flag to "off".

[0029] The learning control unit 56 performs learning control CNLrn, which corrects the difference in wheel speed ω caused by the difference in tire diameter of the wheels 12 through learning. The difference in tire diameter and wheel speed ω refers to, for example, the variation between the four wheels (front, rear, left, and right).

[0030] In the learning control CNlrn, the learning control unit 56 first calculates the rotation angle θ (=Σω) of each wheel 12 by integrating the individual wheel speeds ω of each wheel 12. The rotation angle θ includes the left front wheel rotation angle θfl (=Σωfl), the right front wheel rotation angle θfr (=Σωfr), the left rear wheel rotation angle θrl (=Σωrl), and the right rear wheel rotation angle θrr (=Σωrr). Next, the learning control unit 56 calculates the average rotation angle θave (=(θfl+θfr+θrl+θrr) / 4), which is the average value of the rotation angles θ of the wheels 12. Then, the learning control unit 56 determines whether the average rotation angle θave is greater than or equal to the learning completion threshold. This learning completion threshold is a predetermined threshold used, for example, to determine that the wheels 12 have rotated enough to perform the learning control CNlrn. If the learning control unit 56 determines that the average rotation angle θave is greater than or equal to the learning completion threshold, it calculates the correction coefficient K for each wheel 12 by dividing the average rotation angle θave in the wheel 12 by the rotation angle θ of each wheel 12 (=θave / θ). The correction coefficient K includes the left front wheel correction coefficient Kfl (=θave / θfl), the right front wheel correction coefficient Kfr (=θave / θfr), the left rear wheel correction coefficient Krl (=θave / θrl), and the right rear wheel correction coefficient Krr (=θave / θrr). Next, the learning control unit 56 multiplies the wheel speed ω of each wheel 12 by the corresponding correction coefficient K to calculate the corrected wheel speed ωc (ωfl×Kfl, ωfr×Kfr, ωrl×Krl, ωrr×Krr) of each wheel 12. The learning control unit 56 performs the learning control CNlrn by performing the above calculations.

[0031] To reduce learning errors, it is conceivable to perform the learning control CNlrn while driving in a state where wheel 12 slip is absent or minimal, in addition to the straight-line determination flag being "on". In other words, it is conceivable to perform the learning control CNlrn while driving in a range where the absolute value of the tire slip ratio S at wheel 12 is minimal. However, while driving in a range where the tire slip ratio S is minimal, the range of learnable driving force Fx is limited to the range of minimal driving force Fx. Therefore, the frequency of performing the learning control CNlrn may be reduced.

[0032] The learning control unit 56 calculates the value of the increase in wheel speed ω relative to vehicle speed Vx (=(ω-Vx) / Vx) as the tire slip ratio S of each wheel 12. The tire slip ratio S includes the left front wheel slip ratio Sfl (=(ωfl-Vx) / Vx), the right front wheel slip ratio Sfr (=(ωfr-Vx) / Vx), the left rear wheel slip ratio Srl (=(ωrl-Vx) / Vx), and the right rear wheel slip ratio Srr (=(ωrr-Vx) / Vx).

[0033] The learning control unit 56 calculates the tire load ratio μx (=Fx / Fz), which is the value of the driving force Fx relative to the ground contact load Fz at the wheel 12. The tire load ratio μx includes the left front wheel load ratio μxfl (=Fxfl / Fzfl), the right front wheel load ratio μxfr (=Fxfr / Fzfr), the left rear wheel load ratio μxrl (=Fxrl / Fzrl), and the right rear wheel load ratio μxrr (=Fxrr / Fzrr). As shown in equation (1) below, the wheel 12 accelerates due to the difference between the driving torque Tdrv and the product of the driving force Fx and the tire radius R. In equation (1) below, "I" is the inertia acting on the wheel 12, such as the electric motor MG, gear mechanism 16, drive shaft 14, and tire weight, and is a predetermined value. The learning control unit 56 calculates the driving force Fx using equation (1) below. Note that the tire radius R is the design value.

[0034] I×(dω / dt)=Tdrv-Fx×R (1)

[0035] Figure 2 illustrates the range of the driving force Fx for which learning control CNlrn is performed. Figure 2 shows an example of the relationship between the tire slip ratio S and the driving force Fx due to differences in ground contact load Fz. In Figure 2, the learning range for the comparative example shown by dashed line A is defined as the range of driving force Fx where there is a small slip, that is, the absolute value of the tire slip ratio S is small. The learning range for this embodiment shown by dashed line B is defined as the range of driving force Fx where the slip difference between the four wheels, that is, the difference in tire slip ratio S, is small. A small difference in tire slip ratio S means that the tire slip ratio S of the four wheels are approximately the same. When the driving force Fx is such that the tire load ratio μx of the four wheels are approximately the same, the tire slip ratio S of the four wheels are approximately the same. Therefore, learning control CNlrn is permitted when the tire load ratio μx of the four wheels are approximately the same, and the frequency of execution of learning control CNlrn is increased. The closer the distribution of the driving force Fx is to that which is proportional to the ground contact load Fz, the more the tire load ratio μx of the four wheels is equalized. When the driving force Fx is distributed in proportion to the ground contact load Fz, the frequency of execution of the learning control CNLrn can be greatly increased. In this embodiment, the learning range of the driving force Fx is wider than the range of the driving force Fx in which the absolute value of the tire slip ratio S is small. However, since the tire slip ratio S may become large, the learning control CNLrn is prohibited when driving in the nonlinear region of the tires.

[0036] Figure 3 illustrates the linear and nonlinear tire regions. Figure 3 shows an example of the relationship between the tire slip ratio S and the tire load ratio μx. In Figure 3, the linear tire region is the region where the change in the tire slip ratio S is small in relation to the change in the tire load ratio μx. The nonlinear tire region is the region where the change in the tire slip ratio S is large in relation to the change in the tire load ratio μx. Therefore, learning control CNlrn is disabled during driving in the nonlinear tire region.

[0037] The learning control unit 56 performs learning control CNlrn if it determines that the difference in tire load ratio μx across the wheels 12 is less than or equal to a predetermined load ratio difference Δμxf, and that the vehicle is traveling in the tire linear region. On the other hand, the learning control unit 56 does not perform learning control CNlrn if it determines that the difference in tire load ratio μx across the wheels 12 exceeds a predetermined load ratio difference Δμxf, or if the vehicle is traveling in the tire nonlinear region. The predetermined load ratio difference Δμxf is, for example, a predetermined threshold that allows the tire load ratio μx of the four wheels to be determined to be approximately the same.

[0038] The learning control unit 56 calculates the average load rate μxave (=(μxfl+μxfr+μxrl+μxrr) / 4), which is the average value of the tire load rates μx on the wheels 12. The learning control unit 56 also calculates the load rate deviation Δμx (=μx-μxave), which is the difference between the average load rate μxave on the wheels 12 and the load rate μx of each tire on the wheels 12. The load rate deviation Δμx includes the left front wheel load rate deviation Δμxfl (=μxfl-μxave), the right front wheel load rate deviation Δμxfr (=μxfr-μxave), the left rear wheel load rate deviation Δμxrl (=μxrl-μxave), and the right rear wheel load rate deviation Δμxrr (=μxrr-μxave). The learning control unit 56 calculates the maximum load ratio deviation Δμxmax (=max(|4 wheels Δμx|)), which is the maximum absolute value of the load ratio deviation Δμx at the wheels 12, as the difference in tire load ratio μx at the wheels 12.

[0039] The learning control unit 56 determines whether the vehicle is running in a state where the difference in tire load ratio μx on the wheels 12 is less than or equal to a predetermined load ratio difference Δμxf, based on whether the maximum load ratio deviation Δμxmax is less than or equal to a predetermined load ratio difference Δμxf. The learning control unit 56 determines whether the maximum driving force Fxmax (=max(|4-wheel Fx|)), which is the maximum value among the absolute values ​​of the driving force Fx on the wheels 12, is less than or equal to a predetermined driving force Fxf. The predetermined driving force Fxf is, for example, a predetermined threshold that allows it to be determined that the driving force Fx is in a small range.

[0040] The learning control unit 56 turns on the small load factor deviation determination flag if it determines that the maximum load factor deviation Δμxmax is less than or equal to a predetermined load factor difference Δμxf, or if it determines that the maximum driving force Fxmax is less than or equal to a predetermined driving force Fxf. The learning control unit 56 turns off the small load factor deviation determination flag if it determines that the maximum load factor deviation Δμxmax exceeds a predetermined load factor difference Δμxf, and that the maximum driving force Fxmax exceeds a predetermined driving force Fxf.

[0041] The driving force Fx is used to calculate the tire load ratio μx. Therefore, if the wheel brakes are applied, the learning control CNlrn may not be able to properly determine the learnable area. The learning control unit 56 does not perform the learning control CNlrn if the vehicle state acquisition unit 52 determines that the vehicle 10 is not traveling in a straight line or that the wheel brakes are applied.

[0042] The learning control unit 56 determines whether the vehicle state acquisition unit 52 has determined that the brakes are off. If the learning control unit 56 determines that the brakes are not off, it sets the load factor deviation small determination flag to "off".

[0043] In the nonlinear tire region, where the change in tire slip ratio S is large in response to the change in tire load ratio μx, the change in wheel acceleration dω / dt in response to the change in drive torque Tdrv is large (see equation (1) above). In the nonlinear tire region, the tire slip ratio S at wheel 12 is large. Alternatively, in the nonlinear tire region, the difference in wheel velocity ω at wheel 12 is large. Alternatively, in the nonlinear tire region, the difference in wheel acceleration dω / dt at wheel 12 is large.

[0044] The learning control unit 56 determines that the vehicle is traveling in the linear tire region if the tire slip ratio S of the wheel 12 is less than or equal to a predetermined slip ratio Sf, the difference in wheel speed ω of the wheel 12 is less than or equal to a predetermined speed difference Δωf, and the difference in wheel acceleration dω / dt of the wheel 12 is less than or equal to a predetermined acceleration difference Δdωf. The learning control unit 56 determines that the vehicle is traveling in the nonlinear tire region if the tire slip ratio S of the wheel 12 exceeds the predetermined slip ratio Sf, or the difference in wheel speed ω of the wheel 12 exceeds the predetermined speed difference Δωf, or the difference in wheel acceleration dω / dt of the wheel 12 exceeds the predetermined acceleration difference Δdωf. The predetermined slip ratio Sf, predetermined speed difference Δωf, and predetermined acceleration difference Δdωf are, for example, predetermined thresholds used to distinguish between the linear tire region and the nonlinear tire region.

[0045] The learning control unit 56 determines whether the tire slip ratio S on the wheel 12 is less than or equal to a predetermined slip ratio Sf, based on whether the maximum slip ratio Smax (=max(|4 wheels S|)), which is the maximum value among the absolute values ​​of the tire slip ratio S on the wheel 12, is less than or equal to a predetermined slip ratio Sf.

[0046] The learning control unit 56 calculates the speed difference Δω (=|max(4 wheels ω)-min(4 wheels ω)|), which is the absolute value of the difference between the maximum and minimum values ​​of the wheel speeds ω on the wheels 12, as the difference in wheel speeds ω on the wheels 12. The learning control unit 56 also calculates the acceleration difference Δdω (=|max(4 wheels dω / dt)-min(4 wheels dω / dt)|), which is the absolute value of the difference between the maximum and minimum values ​​of the wheel accelerations dω / dt on the wheels 12, as the difference in wheel accelerations dω / dt on the wheels 12.

[0047] The learning control unit 56 determines whether the velocity difference Δω is less than or equal to a predetermined velocity difference Δωf. The learning control unit 56 also determines whether the acceleration difference Δdω is less than or equal to a predetermined acceleration difference Δdωf.

[0048] The learning control unit 56 turns on the tire linear region determination flag if it determines that the speed difference Δω is less than or equal to a predetermined speed difference Δωf, the acceleration difference Δdω is less than or equal to a predetermined acceleration difference Δdωf, and the maximum slip ratio Smax is less than or equal to a predetermined slip ratio Sf. The learning control unit 56 turns off the tire linear region determination flag if it determines that the speed difference Δω exceeds a predetermined speed difference Δωf, or that the acceleration difference Δdω exceeds a predetermined acceleration difference Δdωf, or that the maximum slip ratio Smax exceeds a predetermined slip ratio Sf.

[0049] Figure 4 is a flowchart illustrating the main part of the control operation of the electronic control device 50, and is a flowchart illustrating a control operation to increase the opportunities to perform learning control CNLrn while suppressing the increase in learning error, and is, for example, executed repeatedly. Figure 5 is a flowchart illustrating a control operation for determining a small load factor deviation, and is a subroutine corresponding to step S10 in the flowchart of Figure 4. Figure 6 is a flowchart illustrating a control operation for determining the tire linear region, and is a subroutine corresponding to step S20 in the flowchart of Figure 4.

[0050] In Figure 4, each step in the flowchart corresponds to a function of the learning control unit 56. First, in step S10 (the step will be omitted hereafter), a load factor deviation small determination is made, and in S20, a tire linear region determination is made.

[0051] In Figure 5, the load factor deviation small determination is made in S10. First, in S110, it is determined whether the vehicle state acquisition unit 52 has determined that the brakes are off. If the determination in S110 is affirmative, in S120, the tire load factor μx (μxfl, μxfr, μxrl, μxrr) and the average load factor μxave are calculated for each of the wheels 12. Next, in S130, the load factor deviation Δμx (Δμxfl, Δμxfr, Δμxrl, Δμxrr) for each of the wheels 12 is calculated. Next, in S140, it is determined whether the maximum driving force Fxmax (=max(|4-wheel Fx|)) is less than or equal to a predetermined driving force Fxf, or whether the maximum load factor deviation Δμxmax (=max(|4-wheel Δμx|)) is less than or equal to a predetermined load factor difference Δμxf. If the judgment in S140 is affirmative, the load factor deviation small judgment flag is turned "on" in S150, and this routine is terminated. If the judgment in S110 is denied, or if the judgment in S140 is denied, the load factor deviation small judgment flag is turned "off" in S160, and this routine is terminated.

[0052] In Figure 6, the tire linear region determination is performed in S20. First, in S210, the vehicle speed Vx estimated by the vehicle state acquisition unit 52 is acquired. Next, in S220, the tire slip ratio S (Sfl, Sfr, Srl, Srr) for each of the wheels 12 is calculated. Next, in S230, the speed difference Δω and acceleration difference Δdω are calculated. Next, in S240, it is determined whether the speed difference Δω is less than or equal to a predetermined speed difference Δωf, the acceleration difference Δdω is less than or equal to a predetermined acceleration difference Δdωf, and the maximum slip ratio Smax (=max(|4 wheels S|)) is less than or equal to a predetermined slip ratio Sf. If the determination in S240 is affirmative, in S250 the tire linear region determination flag is set to "on", and this routine is terminated. If the judgment in S240 is rejected, the tire linear region determination flag is set to "off" in S260, and this routine is terminated.

[0053] Returning to Figure 4, following S10 and S20, in S30, it is determined whether the load ratio deviation small determination flag is "on", the tire linear region determination flag is "on", and the straight-ahead determination flag determined by the vehicle state acquisition unit 52 is "on". If the determination in S30 is affirmative, in S40, the rotation angles θ (θfl, θfr, θrl, θrr) of each wheel 12 and the average rotation angle θave are calculated. If the determination in S30 is negative, in S50, the values ​​of the rotation angle θ and the average rotation angle θave are reset to zero. This effectively prevents the learning control CNlrn from being performed. Following S40 or S50, in S60, it is determined whether the average rotation angle θave is greater than or equal to the learning completion threshold. If the determination in S60 is negative, this routine is terminated. If the judgment in S60 is affirmed, in S70, the correction coefficients K (Kfl, Kfr, Krl, Krr) for each of the wheels 12 are calculated, and this routine is terminated. The correction coefficients K are used to calculate the corrected wheel speed ωc for each of the wheels 12.

[0054] As described above, according to this embodiment, learning control CNLrn is performed when driving with a tire load ratio μx difference of Δμxf or less. This makes it possible to perform learning control CNLrn over a wider range of driving force Fx compared to when learning control CNLrn is performed when driving with a small tire slip ratio S, which is defined as a small range of driving force Fx. Furthermore, even when driving with a tire load ratio μx difference of Δμxf or less, learning control CNLrn is not performed if driving is not in the tire linear region, i.e., if driving is in the tire nonlinear region. This makes it possible to prevent or suppress the increase in learning error due to the increase in the amount of change in tire slip ratio S when driving in the tire nonlinear region where the tire slip ratio S is large. Thus, it is possible to increase the opportunities to perform learning control CNLrn while suppressing the increase in learning error.

[0055] Furthermore, according to this embodiment, the tire slip ratio S is calculated as the increase in wheel speed ω relative to the vehicle speed Vx. It is determined that the vehicle is traveling in the tire linear region when the tire slip ratio S is less than or equal to a predetermined slip ratio Sf, the difference in wheel speed ω is less than or equal to a predetermined speed difference Δωf, and the difference in wheel acceleration dω / dt is less than or equal to a predetermined acceleration difference Δdωf. As a result, even if there is an estimation error in the vehicle speed Vx, the difference in wheel speed ω or the difference in wheel acceleration dω / dt can be used to prevent the learning control CNLrn from being performed while the vehicle is actually traveling in the tire nonlinear region.

[0056] Furthermore, according to this embodiment, the maximum value among the absolute values ​​of the load factor deviation Δμx is calculated as the difference in tire load factor μx. This allows for an appropriate determination of whether or not the vehicle is running in a state where the difference in tire load factor μx is less than or equal to a predetermined load factor difference Δμxf.

[0057] Furthermore, according to this embodiment, if it is determined that the vehicle is not traveling in a straight line, or if it is determined that the wheel brakes are engaged, the learning control CNlrn is not performed. As a result, the learning control CNlrn is not performed during driving, when learning errors tend to increase.

[0058] Furthermore, according to this embodiment, the rotation angle θ is calculated by integrating the wheel speed ω, and the correction coefficient K is calculated by dividing the average rotation angle θave by the rotation angle θ. The wheel speed ω is then multiplied by the correction coefficient K to calculate the corrected wheel speed ωc, and the learning control CNlrn is performed. As a result, the wheel speed ω is appropriately corrected by the learning control CNlrn.

[0059] Although embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is also applicable to other embodiments.

[0060] For example, in the embodiments described above, the vehicle is not limited to a BEV with independent drive for the front, rear, left, and right wheels. For example, it may be a vehicle in which the power of the power source is distributed to each of the four wheels. Alternatively, an engine may be used as the power source in addition to or instead of an electric motor. In short, the present invention can be applied to any all-wheel drive vehicle equipped with front, rear, left, and right wheels and a power source that generates power to drive those wheels.

[0061] It should be noted that the above-described embodiment is merely one example, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. [Explanation of symbols]

[0062] 10: Vehicle 12: Wheels 12fl: Left front wheel 12fr: Right front wheel 12rl: Left rear wheel 12rr: Right rear wheel 50: Electronic control unit (control device) 56: Learning control unit MG: Electric motor (power source)

Claims

1. A control device for a vehicle comprising front and rear wheels and a power source that generates power to drive the wheels, The system includes a learning control unit that performs learning control to correct the difference in wheel speed caused by the difference in tire diameter of the aforementioned wheels through learning, A vehicle control device characterized in that the learning control unit performs the learning control when it determines that the vehicle is running in a state where the difference in tire load ratio, which is the value of the driving force with respect to the ground load on the wheels, is less than or equal to a predetermined load ratio difference, and that the vehicle is running in a tire linear region where the value of the change in tire slip ratio with respect to the change in tire load ratio is small, but does not perform the learning control when it determines that the vehicle is running in a state where the difference in tire load ratio exceeds the predetermined load ratio difference, or when it determines that the vehicle is running in a tire nonlinear region where the value of the change in tire slip ratio with respect to the change in tire load ratio is large.

2. The learning control unit calculates the tire slip ratio as the increase in the wheel speed relative to the estimated vehicle speed. The control device for a vehicle according to claim 1, characterized in that the learning control unit determines that the vehicle is traveling in the tire linear region when the tire slip ratio of the wheel is less than or equal to a predetermined slip ratio, the difference in wheel speeds of the wheel is less than or equal to a predetermined speed difference, and the difference in wheel acceleration of the wheel is less than or equal to a predetermined acceleration difference.

3. The vehicle control device according to claim 1, characterized in that the learning control unit calculates the maximum value among the absolute values ​​of the difference between the average value of the tire load ratio on the wheel and the tire load ratio of each of the wheels as the difference in tire load ratios.

4. The vehicle control device according to claim 1, characterized in that the learning control unit does not perform the learning control when it is determined that the vehicle is not traveling in a straight line or when the wheel brakes are applied.

5. The control device for a vehicle according to any one of claims 1 to 4, characterized in that the learning control unit calculates the rotation angle of each wheel by integrating the wheel speed of each wheel, calculates a correction coefficient for each wheel by dividing the average value of the rotation angles of each wheel by the rotation angle of each wheel, and calculates the corrected wheel speed of each wheel by multiplying the wheel speed of each wheel by the corresponding correction coefficient, thereby performing the learning control.

Images