JP7664968B2 - Vehicle Control Systems - Google Patents

Description

The present invention relates to a vehicle control system.

In recent years, efforts to provide access to sustainable transport systems that take into consideration vulnerable transport participants such as the elderly, people with disabilities and children have been gaining momentum. To achieve this, we are focusing on research and development to further improve transport safety and convenience through development of vehicle behavior stability.
Conventionally, a vehicle control device is known that determines whether or not to switch from regenerative braking to friction braking based on a wheel speed threshold that determines wheel slippage during braking and a correction amount threshold that determines an increase in the braking force correction amount due to wheel traction control (see, for example, Patent Document 1).

JP 2021-146788 A

In terms of vehicle behavior stability, when wheel slip occurs during deceleration due to regenerative braking, it is important to eliminate the slip state while suppressing a decrease in recovered energy and destabilization of vehicle behavior.
For example, the vehicle control device of the above-mentioned prior art performs allocation from regenerative braking to friction braking by a judgment process using two thresholds (wheel speed threshold and correction amount threshold), so there is a risk that slip cannot be eliminated or vehicle behavior becomes unstable depending on the braking force allocation process or road surface conditions. For example, the regenerative capacity of each wheel changes depending on the state of each motor and battery, or the regenerative braking force is biased between the left and right wheels during regenerative braking on a split friction road, etc., which may result in inappropriate braking force allocation process, resulting in unresolved slip and unstable vehicle behavior.

The present application aims to solve the above problems by suppressing the deterioration of energy recovered by regenerative braking and the instability of vehicle behavior while suppressing the progression of slip conditions. This will ultimately contribute to the development of a sustainable transportation system.

In order to solve the above problems and achieve the above object, the present invention employs the following aspects.
(1): A vehicle control system according to one aspect of the present invention (e.g., vehicle control system 10 in the embodiment) includes a first control unit (e.g., front motor control unit 25a in the embodiment) that controls the operation of a first rotating electric machine (e.g., front rotating electric machine 11a in the embodiment) that transmits and receives torque between a first wheel (e.g., front wheel Fr in the embodiment), a second control unit (e.g., rear motor control unit 25b in the embodiment) that controls the operation of a second rotating electric machine (e.g., rear rotating electric machine 11b in the embodiment) that transmits and receives torque between a second wheel (e.g., rear wheel Rr in the embodiment), and a friction braking control unit that controls friction braking of each of the first wheel and the second wheel. (e.g., an electric braking control unit 21 and a behavior control unit 23 in an embodiment), and a cooperative control unit (e.g., an integrated control unit 27 in an embodiment) that, when regenerative braking is performed by the first control unit and the second control unit, obtains a braking force distribution for the first wheel and the second wheel by the friction braking control unit in a case where the friction braking is virtually prioritized relatively over the regenerative braking depending on the slip state of at least one of the first wheel and the second wheel, and when the braking force distribution is the same as the braking force distribution for the first wheel and the second wheel in the regenerative braking within a predetermined range, prioritizes the regenerative braking relatively over the friction braking.

(2): In the vehicle control system described in (1) above, when regenerative braking is performed by the first control unit and the second control unit, the cooperative control unit may determine whether the slip state will be accelerated if the friction braking is virtually prioritized relatively over the regenerative braking depending on the slip state of at least one of the first wheel and the second wheel, and if it is determined that the slip state will be accelerated, the cooperative control unit may relatively prioritize the regenerative braking over the friction braking.

(3): In the vehicle control system described in (1) or (2) above, the cooperative control unit may determine whether the road is a split friction road or not depending on the slip state of at least one of the first wheel and the second wheel when regenerative braking is performed by the first control unit and the second control unit, and if it is determined that the road is a split friction road, give priority to the friction braking relatively over the regenerative braking.

(4): In the vehicle control system described in (1) or (2) above, when the first control unit and the second control unit perform regenerative braking, the cooperative control unit virtually prioritizes the friction braking relatively over the regenerative braking depending on the slip state of at least one of the first wheel and the second wheel, and when it is determined that the braking force distribution of the friction braking is not the same as the braking force distribution of the regenerative braking within the predetermined range and the slip state is suppressed, the cooperative control unit may relatively prioritize the friction braking over the regenerative braking.

According to (1) above, by providing a cooperative control unit that relatively prioritizes regenerative braking over frictional braking when the braking force distribution between regenerative braking and frictional braking is the same, it is possible to suppress the decrease in energy recovered by regenerative braking while suppressing the instability of vehicle behavior and the progression of slippage.

In the case of (2) above, the destabilization of vehicle behavior and the promotion of slippage caused by braking force distribution in friction braking can be suppressed by prioritizing regenerative braking, and the deterioration of braking performance can be suppressed.

In the above case (3), by giving priority to friction braking over regenerative braking on a split friction road, it is possible to prevent the vehicle behavior from becoming unstable and the slipping state from becoming worse due to continued regenerative braking on a split friction road, and to prevent a decrease in braking performance.

In the case of (4) above, if the braking force distribution of regenerative braking induces a slip state that is not resolved, the slip state can be improved by prioritizing friction braking.

1 is a configuration diagram of a vehicle control system according to an embodiment of the present invention. 1 is a block diagram showing a functional configuration of a vehicle control system according to an embodiment of the present invention. 4 is a flowchart showing a braking operation of the vehicle control system according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of a state in which regenerative braking is relatively prioritized over friction braking in the vehicle control system according to the embodiment of the present invention. FIG. 13 is a diagram showing another example of a state in which regenerative braking is relatively prioritized over friction braking in the vehicle control system according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of a state in which friction braking is relatively prioritized over regenerative braking in the vehicle control system according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle control system according to an embodiment of the present invention will now be described with reference to the accompanying drawings.
Fig. 1 is a configuration diagram of a vehicle control system 10 according to an embodiment. Fig. 2 is a block diagram showing the functional configuration of the vehicle control system 10 according to an embodiment.
The vehicle control system 10 of the embodiment is mounted on an electric vehicle (vehicle) 1, such as an electric vehicle, a hybrid vehicle, or a fuel cell vehicle. An electric vehicle is driven by a battery as a power source. A hybrid vehicle is driven by a battery and an internal combustion engine as a power source. A fuel cell vehicle is driven by a fuel cell as a power source.

As shown in Figures 1 and 2, a vehicle 1 equipped with a vehicle control system 10 includes, for example, a front rotating electric machine 11a and a rear rotating electric machine 11b, a front differential device 13a and a rear differential device 13b, a first front brake mechanism 15a and a second front brake mechanism 15b, a first rear brake mechanism 15c and a second rear brake mechanism 15d, and a processing device 17.

The front rotating electric machine 11a transmits and receives torque between the left and right front wheels Fr, for example, via the front differential 13a. The rear rotating electric machine 11b transmits and receives torque between the left and right rear wheels Rr, for example, via the rear differential 13b. Each rotating electric machine 11a, 11b is, for example, a three-phase AC brushless DC motor. Each rotating electric machine 11a, 11b generates driving torque for each wheel Fr, Rr by performing power running operation using power supplied from a power conversion device or the like. Each rotating electric machine 11a, 11b generates generated power and generates braking torque for each front wheel Fr and each rear wheel Rr by performing regenerative operation using rotational power input from each front wheel Fr and each rear wheel Rr.

The front differential 13a connects, for example, the front rotating electric machine 11a to the left and right front wheels Fr. The rear differential 13b connects, for example, the rear rotating electric machine 11b to the left and right rear wheels Rr. Each of the differentials 13a, 13b is, for example, a bevel gear type differential mechanism, and is an open differential that does not have a so-called differential limiting mechanism.
The first front brake mechanism 15a and the second front brake mechanism 15b are, for example, friction braking mechanisms provided on the left and right front wheels Fr, respectively. The first rear brake mechanism 15c and the second rear brake mechanism 15d are, for example, friction braking mechanisms provided on the left and right rear wheels Rr, respectively. Each of the brake mechanisms 15a, 15b, 15c, and 15d includes, for example, a hydraulic or other fluid-pressure disk brake or drum brake. Each of the brake mechanisms 15a, 15b, 15c, and 15d performs friction braking on each of the front wheels Fr and each of the rear wheels Rr by, for example, fluid pressure generated by an electric motor in response to the operation of a brake operator by an operator.

The processing device 17 includes, for example, an electric braking control unit 21 , a behavior control unit 23 , a front motor control unit 25 a , a rear motor control unit 25 b , and an integrated control unit 27 .
Each of the control units 21, 23, 25a, 25b, and 27 is a software function unit that functions when a processor such as a CPU (Central Processing Unit) executes a predetermined program. The software function unit is an ECU that includes a processor such as a CPU, a ROM (Read Only Memory) that stores programs, a RAM (Random Access Memory) that temporarily stores data, and electronic circuits such as a timer. At least a part of each of the control units 21, 23, 25a, 25b, and 27 may be an integrated circuit such as an LSI (Large Scale Integration).

The vehicle control system 10 of the embodiment includes, for example, a processing device 17 and various sensors mounted on the vehicle 1 .
The processing device 17 acquires detection value signals output from various sensors of the vehicle 1, and performs integrated control of the rotating electric machines 11a, 11b and the brake mechanisms 15a, 15b, 15c, 15d. The various sensors include, for example, a brake switch 31, a rotation sensor 33, a vehicle speed sensor 35, a wheel speed sensor 37, a current sensor 39, a voltage sensor 41, and a temperature sensor 43.
The brake switch 31 detects whether or not an operator has operated a brake operator. The rotation sensor 33 detects the rotation angle of each of the rotating electric machines 11a, 11b. The vehicle speed sensor 35 detects the speed (body speed) of the vehicle 1. The wheel speed sensor 37 detects the rotation speed (wheel speed) of each of the front wheels Fr and each of the rear wheels Rr (each wheel). The current sensor 39, the voltage sensor 41, and the temperature sensor 43 each detect, for example, the current, voltage, and temperature of each of the rotating electric machines 11a, 11b and an electric storage device such as a battery that exchanges electric power between each of the rotating electric machines 11a, 11b.

The electric braking control unit 21 controls the operation of an electric motor, which is a power source for hydraulic cylinders or the like that generate hydraulic pressure for each of the brake mechanisms 15a, 15b, 15c, and 15d, for example.
For example, in order to suppress abrupt changes in the behavior of the vehicle 1 and stabilize its posture, the behavior control unit 23 controls friction braking by the brake mechanisms 15a, 15b, 15c, and 15d based on the hydraulic pressure generated by the control of the electric braking control unit 21. The behavior control unit 23 executes, for example, anti-brake lock control to prevent the wheels from locking during braking, traction control to prevent wheel slip during acceleration, deceleration, etc., and side slip suppression control during cornering.

Each of the front motor control unit 25a and the rear motor control unit 25b includes a power conversion device connected to a power source such as a power storage device mounted on the vehicle 1. Each of the motor control units 25a, 25b controls the exchange of power between the front rotating electric machine 11a and the rear rotating electric machine 11b via a power conversion device composed of, for example, a plurality of switching elements. Each of the motor control units 25a, 25b generates a rotational driving force by sequentially commutating the current to the three phases during the power running operation of each of the rotating electric machines 11a, 11b. Each of the motor control units 25a, 25b generates a rotational braking force by converting the AC power input from the three phases into DC power through the switching operation of each phase synchronized with the rotation during the regenerative operation of each of the rotating electric machines 11a, 11b.

Each of the front motor control unit 25a and the rear motor control unit 25b executes anti-slip control to prevent wheel lock (slip) caused by regenerative braking force during braking caused by the regenerative operation of each of the rotating electric machines 11a and 11b. For example, the control period of the anti-slip control caused by the regenerative braking force is set to be relatively shorter than the control period of the anti-brake lock control caused by friction braking by the behavior control unit 23.
The integrated control unit 27 controls the electric braking control unit 21, the behavior control unit 23, and each of the motor control units 25a, 25b in an integrated manner.

An example of the operation of the vehicle control system 10 according to the embodiment will be described below.
Fig. 3 is a flowchart showing the braking operation of the vehicle control system 10 of the embodiment. Fig. 4 is a diagram showing an example of a state in which regenerative braking is relatively prioritized over friction braking in the vehicle control system 10 of the embodiment. Fig. 5 is a diagram showing another example of a state in which regenerative braking is relatively prioritized over friction braking in the vehicle control system 10 of the embodiment. Fig. 6 is a diagram showing an example of a state in which friction braking is relatively prioritized over regenerative braking in the vehicle control system 10 of the embodiment.

3, for example, when regenerative braking of the vehicle 1 is being performed, the integrated control unit 27 first determines whether or not any of the wheels is slipping based on the vehicle speed of the vehicle 1 and the wheel speeds of the respective wheels (step S01). For example, when a state in which any of the wheel speeds is less than a predetermined threshold value corresponding to the vehicle speed continues for a predetermined period of time, the integrated control unit 27 determines that any of the wheels is slipping.
If the result of this determination is "NO", the integrated control unit 27 advances the process to the end.
On the other hand, if the result of this determination is "YES", the integrated control unit 27 advances the process to step S02.
Next, the integrated control unit 27 determines whether the braking force distribution in regenerative braking and the braking force distribution in friction braking between a predetermined pair of wheels, for example, between the front wheels Fr and the rear wheels Rr, are the same within a predetermined range (step S02).
If the result of this determination is "NO", the integrated control unit 27 advances the process to step S03.
On the other hand, if the result of this determination is "YES", the integrated control unit 27 advances the process to step S04.

The braking force distribution during friction braking is set in advance to a predetermined distribution, for example, depending on the size and friction material of each brake mechanism 15a, 15b, 15c, 15d. The braking force distribution during regenerative braking is set, for example, according to the temperature and other conditions of each rotating electric machine 11a, 11b and the temperature and stored amount of the power source storage device. For example, when the front rotating electric machine 11a generates more heat than the rear rotating electric machine 11b, the amount of regeneration of the front wheels Fr is reduced and the distribution of regenerative braking force to the rear wheels Rr is increased.

Next, when friction braking is virtually prioritized over regenerative braking, for example when regenerative braking that is currently being performed is stopped and friction braking is performed instead of regenerative braking, the integrated control unit 27 determines whether the braking force distribution will leave the wheels unchanged or promote slippage (step S03).
If the result of this determination is "NO", the integrated control unit 27 advances the process to step S06.
On the other hand, if the result of this determination is "YES", the integrated control unit 27 advances the process to step S04.

Next, the integrated control unit 27 judges whether the road on which the vehicle 1 is traveling is a split friction road based on the wheel speeds of the wheels (step S04). A split friction road is a road on which the left and right wheels have different friction coefficients with respect to the road surface. The integrated control unit 27 judges that the road is a split friction road, for example, when a state in which a wheel speed difference between the left and right combination (for example, a wheel speed difference between the left and right front wheels Fr) is greater than a predetermined threshold value continues for a predetermined time.
If the result of this determination is "NO", the integrated control unit 27 advances the process to step S05.
On the other hand, if the result of this determination is "YES", the integrated control unit 27 advances the process to step S06.
Next, the integrated control unit 27 continues the execution of regenerative braking (step S05), and advances the process to the end.
Furthermore, the integrated control unit 27 shifts from execution of regenerative braking to execution of friction braking (step S06), and advances the process to the end.

For example, as shown in FIG. 4, when the braking force BF at the front wheels Fr becomes greater than a threshold braking force BT corresponding to the grip limit of the road during regenerative braking, causing slippage of the front wheels Fr, the integrated control unit 27 acquires the braking force distribution between the front wheels Fr and the rear wheels Rr in a virtual transition from regenerative braking to friction braking. If the braking force distribution during regenerative braking and the braking force distribution during friction braking are the same, for example, and the slippage of the front wheels Fr is not eliminated, the integrated control unit 27 continues the execution of regenerative braking without transitioning to friction braking. In the example shown in FIG. 4, when the transition from regenerative braking to friction braking occurs, the braking force BF of the front wheels Fr and the braking force BR of the rear wheels Rr are unchanged in each of regenerative braking and friction braking, and the slippage of the front wheels Fr is not eliminated.

For example, as shown in Fig. 5, when the braking force BF1 at the front wheels Fr becomes greater than a threshold braking force BT corresponding to the grip limit of the roadway during regenerative braking, causing the front wheels Fr to slip, the integrated control unit 27 acquires the braking force distribution between the front wheels Fr and the rear wheels Rr in a virtual transition from regenerative braking to friction braking. For example, even if the braking force distribution during regenerative braking differs from the braking force distribution during friction braking, if the slip of the front wheels Fr is promoted due to an increase in the distribution of braking force from the rear wheels Rr to the front wheels Fr, the integrated control unit 27 continues to perform regenerative braking without transitioning to friction braking. In the example shown in FIG. 5, when regenerative braking is switched to friction braking, the braking force BR1 of the rear wheels Rr under regenerative braking decreases to the braking force BR2 (<BR1) of the rear wheels Rr under friction braking, while the braking force BF1 of the front wheels Fr under regenerative braking increases to the braking force BF2 (>BF1) of the front wheels Fr under friction braking, promoting slippage of the front wheels Fr.

6, when the front wheels Fr slip during execution of regenerative braking, the integrated control unit 27 acquires the braking force distribution between the front wheels Fr and the rear wheels Rr in a virtual transition from regenerative braking to friction braking. For example, even if the braking force distribution during regenerative braking and the braking force distribution during friction braking are the same, if the left and right front wheels Fr are on a road with different friction coefficients with respect to the road surface (split friction road), the integrated control unit 27 does not continue execution of regenerative braking and transitions to friction braking.
In the example shown in Fig. 6, the split friction road is a low friction road with a relatively small friction coefficient for the left front wheel Fr, and a high friction road with a relatively large friction coefficient for the right front wheel Fr. When regenerative braking is performed, the regenerative braking force is biased to the left front wheel Fr on the low friction road due to the operation of the front differential device 13a, which promotes slipping of the left front wheel Fr and reduces the regenerative braking force transmitted to the right front wheel Fr on the high friction road. Furthermore, when anti-slip control is performed during regenerative braking, the regenerative operation of the front rotating electric machine 11a is controlled for the left and right front wheels Fr, so that the regenerative braking force transmitted to the right front wheel Fr on the high friction road is further reduced.
On the other hand, by transitioning from regenerative braking to friction braking, anti-brake lock control is executed independently for each wheel, so that, for example, slippage is eliminated by anti-brake lock control at the left front wheel Fr on a low friction road, while the desired friction braking force is secured at the right front wheel Fr on a high friction road.

As described above, the vehicle control system 10 of the embodiment is provided with an integrated control unit 27 that relatively prioritizes regenerative braking over frictional braking when the braking force distributions of regenerative braking and frictional braking are the same, thereby making it possible to suppress the decrease in recovered energy due to regenerative braking while suppressing the instability of vehicle behavior and the promotion of a slip state. By prioritizing regenerative braking, it is possible to suppress the instability of vehicle behavior and the promotion of a slip state due to the braking force distribution in frictional braking, and to suppress the decrease in braking performance.
It is possible to suppress the decrease in fuel efficiency and electricity efficiency, and the vehicle behavior can be quickly stabilized by anti-slip control using regenerative braking force, which has a relatively short control cycle.

By giving priority to friction braking relatively over regenerative braking on split friction roads, the integrated control unit 27 can prevent the continued use of regenerative braking on split friction roads from causing instability in vehicle behavior and exacerbating slip conditions, thereby suppressing a decrease in braking performance.
When the braking force distribution of the regenerative braking induces the slip state to remain unresolved, the integrated control unit 27 can improve the slip state by prioritizing the friction braking.

(Modification)
Modifications of the embodiment will be described below. Note that the same parts as those in the above-described embodiment will be denoted by the same reference numerals and descriptions thereof will be omitted or simplified.
In the above embodiment, the braking operation is switched from regenerative braking to friction braking when the slip state is unchanged or not promoted in the determination process of step S03, but is not limited to this. For example, the braking operation may be switched from regenerative braking to friction braking when the slip state is suppressed in the determination process of step S03.

In the above-described embodiment, the vehicle 1 is provided with a front rotating electric machine 11a connected to the left and right front wheels Fr and a rear rotating electric machine 11b connected to the left and right rear wheels Rr, but is not limited to this. For example, each wheel may be provided with an individual rotating electric machine, or each appropriate combination of multiple wheels may be provided with an individual rotating electric machine.

The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

1...vehicle, 10...vehicle control system, 11a...front rotating electric machine (first rotating electric machine), 11b...rear rotating electric machine (second rotating electric machine), 13a...front differential device, 13b...rear differential device, 15a...first front brake mechanism, 15b...second front brake mechanism, 15c...first rear brake mechanism, 15d...second rear brake mechanism, 17...processing device, 21...electric braking control unit (friction braking control unit), 23...behavior control unit (friction braking control unit), 25a...front motor control unit (first control unit), 25b...rear motor control unit (second control unit), 27...integrated control unit (cooperative control unit), 31...brake switch, 33...rotation sensor, 35...vehicle speed sensor, 37...wheel speed sensor, 39...current sensor, 41...voltage sensor, 43...temperature sensor, Fr...front wheel (first wheel), Rr...rear wheel (second wheel).

Claims (4)

a first control unit that controls an operation of a first rotating electric machine that transmits and receives torque between the first wheel and the first rotating electric machine;
a second control unit that controls an operation of a second rotating electric machine that transmits and receives torque between the second wheel and the second rotating electric machine;
a friction braking control unit that controls friction braking of each of the first wheel and the second wheel;
a cooperative control unit that, when regenerative braking is performed by the first control unit and the second control unit, obtains a braking force distribution for the first wheel and the second wheel by the friction braking control unit in a case where the friction braking is virtually prioritized relatively over the regenerative braking depending on the slip state of at least one of the first wheel and the second wheel, and when the braking force distribution is the same within a predetermined range as the braking force distribution for the first wheel and the second wheel in the regenerative braking, prioritizes the regenerative braking relatively over the friction braking. The cooperative control unit includes:
2. The vehicle control system of claim 1, wherein when regenerative braking is performed by the first control unit and the second control unit, a determination is made as to whether the slip state will be accelerated if the friction braking is virtually prioritized relatively over the regenerative braking depending on the slip state of at least one of the first wheel and the second wheel, and if it is determined that the slip state will be accelerated, the regenerative braking is relatively prioritized over the friction braking. The cooperative control unit includes:
3. A vehicle control system as described in claim 1 or claim 2, wherein when regenerative braking is performed by the first control unit and the second control unit, a determination is made as to whether or not the road is a split friction road depending on the slip state of at least one of the first wheel and the second wheel, and if it is determined that the road is a split friction road, the friction braking is relatively prioritized over the regenerative braking. The cooperative control unit includes:
3. The vehicle control system of claim 1 or 2, wherein when regenerative braking is performed by the first control unit and the second control unit, the frictional braking is virtually prioritized relatively over the regenerative braking depending on the slip state of at least one of the first wheel and the second wheel, and when it is determined that the braking force distribution of the frictional braking is not identical to the braking force distribution of the regenerative braking within the specified range and the slip state is suppressed, the frictional braking is relatively prioritized over the regenerative braking.

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