JP2021030929A - Vehicular brake control apparatus - Google Patents

Abstract

To provide a vehicular brake control apparatus capable of suppressing uneasiness felt by a driver when braking at the time of wheel slipping.SOLUTION: A vehicular brake control apparatus includes a regenerative brake device for applying regenerative brake force to a part of all wheels when braking a vehicle; and a frictional brake device for applying frictional brake force to all wheels. In the apparatus, a controller performs: calculating a slip ratio of the wheel from a wheel speed and a vehicular speed (step S2); and calculating a change speed of the slip ratio in a case where the slip ratio is equal to or lower than a predetermined threshold and switching between regenerative braking by the regenerative brake device and frictional braking by the frictional brake device on the basis of the calculated change speed of slip ratio (steps S4 to S6).SELECTED DRAWING: Figure 3

Description

The present invention relates to a control device for braking a vehicle, and more particularly to a vehicle braking control device including a regenerative braking device for applying a regenerative braking force to wheels and a friction braking device for applying frictional braking force to wheels by flood control. Is.

Patent Document 1 includes a regenerative braking device that applies a regenerative braking force to the front wheels when braking the wheels, and a hydraulic braking device (friction braking device) that applies a hydraulic braking force to all the wheels of the wheels. The braking control device is described. The braking control device described in Patent Document 1 is configured to control regenerative braking and hydraulic braking in a coordinated manner. Specifically, when the slip ratio of the front wheels to which regenerative braking is applied becomes equal to or higher than the first predetermined value (reference value), the braking force in the regenerative braking is reduced by the first rate of change, and at the same time. It is configured to increase the braking force of hydraulic braking. Further, when the slip ratio becomes a second predetermined value smaller than the first predetermined value by the cooperative control, the braking force in the regenerative braking is changed to a second change rate smaller than the first change rate. ing.

Japanese Unexamined Patent Publication No. 2013-043495

Conventionally, it has been known that a regenerative braking device and a hydraulic braking device are coordinated to apply a braking force to wheels. According to the braking control device of Patent Document 1 described above, when the front wheel during regenerative braking slips, the regenerative braking force is stepwise reduced and the braking force due to hydraulic braking is applied to the wheels. Therefore, it is said that the occurrence of a feeling of pulling out (G feeling of pulling out) in which the regenerative braking force suddenly decreases can be suppressed, and the slip of the wheel can be eliminated at an early stage. However, in the control device described in Patent Document 1, the time required for switching or switching between regenerative braking and hydraulic braking is fixed, and the antilock braking system (ABS) may be used depending on the switching time. It operates, and the operation (or intervention) of the ABS may cause discomfort to the driver. Further, since the road surface condition is constantly changing, the μ (friction coefficient) of the road surface is not constant, and the slip ratio also changes depending on the μ of the road surface and the regenerative braking force. Therefore, if the switching time between the regenerative braking and the hydraulic braking is set to be longer than uniform, the wheels may slip and the behavior of the vehicle may become unstable. On the contrary, if the replacement time is set short, a change in acceleration (G fluctuation) may occur, and the shock due to the change in acceleration may increase. In any case, the driver is informed. May cause discomfort. Therefore, there is still room for improvement in coordinating control of regenerative braking and hydraulic braking (friction braking) when the wheels are slipping.

The present invention has been conceived by paying attention to the above technical problems, and an object of the present invention is to provide a vehicle braking control device capable of suppressing discomfort to the driver in braking when the wheels slip. Is to be.

In order to achieve the above object, the present invention provides a regenerative braking device that applies a regenerative braking force to some of the wheels when braking the vehicle, and the regenerative braking device for all the wheels when the vehicle is braked. In a vehicle braking control device provided with a friction braking device that applies frictional braking force, a controller for controlling the vehicle is provided, and the controller is based on the wheel speed of the wheel and the vehicle body speed of the vehicle. The slip rate is calculated, it is determined whether or not the slip rate is below a predetermined threshold, and when it is determined that the slip rate is below the threshold, the rate of change of the slip rate is calculated and It is characterized in that it is configured to switch between regenerative braking by the regenerative braking device and friction braking by the friction braking device based on the calculated change rate of the slip ratio.

According to the vehicle braking control device of the present invention, switching (replacement) between regenerative braking and friction braking, which is executed when the wheel slip ratio reaches a predetermined slip ratio during vehicle braking, is the rate of change of the slip ratio. It is configured to be based on. For example, when the rate of change of the slip ratio is fast (large), switching between regenerative braking and friction braking is performed quickly. In that case, the progress of wheel slippage can be suppressed and the behavior of the vehicle can be stabilized. Further, for example, when the change speed of the slip ratio is slow (small), the switching between the regenerative braking and the friction braking is performed slowly because the slip progresses slowly. In that case, the shock due to the G fluctuation can be suppressed, and the behavior of the vehicle can be stabilized. That is, by switching between regenerative braking and friction braking at an appropriate rate according to the rate of change in the slip rate, it is possible to suppress the discomfort given to the driver at the time of the switching. Further, since the switching control is performed when the predetermined slip ratio is reached as described above, the progress of slip can be suppressed and the operation of ABS can be prevented, and as a result, the operation or intervention of ABS can be performed. This makes it possible to suppress or avoid discomfort given to the driver.

It is a schematic diagram which shows the vehicle which can be the object of this invention. It is a figure for demonstrating the system structure of the ECU. It is a flowchart for demonstrating an example of control in Embodiment of this invention. This is a map for calculating the replacement rate when switching from regenerative braking to friction braking. It is a map when the vehicle speed is added as a parameter to FIG. It is a figure for demonstrating the effect in embodiment of this invention. This is an example for explaining a comparative example when the replacement time is long. This is an example for explaining a comparative example when the replacement time is short.

An embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiments shown below are merely examples of cases where the present invention is embodied, and do not limit the present invention.

The vehicle to be controlled in the embodiment of the present invention is a vehicle whose driving force source is at least one motor. Therefore, it may be an electric vehicle equipped with one or more motors as a driving force source. Alternatively, it may be a so-called hybrid vehicle equipped with an engine and a motor as a driving force source. For example, it may be a hybrid vehicle of a type in which an engine and a motor are connected via a power split mechanism using a planetary gear mechanism. Any type of hybrid vehicle may have a configuration in which the vehicle can be driven (EV traveling) by generating a driving force with the motor torque output by the motor.

FIG. 1 shows an example of a vehicle Ve to be controlled in the embodiment of the present invention. The vehicle Ve shown in FIG. 1 has a front wheel 1 and a rear wheel 2, and includes a motor (MG) 3 as a driving force source. In the example shown in FIG. 1, the vehicle Ve transmits the power output by the motor 3, which is a driving force source, to the front wheels 1 via the power transmission mechanism (TM) 4 and the drive shaft (not shown). It is configured as a front-wheel drive vehicle that generates driving force. The vehicle Ve may be a rear-wheel drive vehicle that generates a driving force by transmitting the power output from the driving force source to the rear wheels 2. Alternatively, it may be a four-wheel drive vehicle that generates driving force by transmitting the power output from the driving force source to the front wheels 1 and the rear wheels 2, respectively.

The motor (MG) 3 is, for example, a permanent magnet type synchronous motor or an electric motor such as an induction motor, and functions as an electric motor that is driven by being supplied with electric power to output motor torque. Further, the motor 3 is a so-called motor generator having both the above-mentioned function as an electric motor and the function as a generator that generates electricity by being driven by receiving torque from the outside. In the motor 3, the output rotation speed and the motor torque are electrically controlled, and the switching between the function as an electric motor and the function as a generator is electrically controlled. At the time of braking, the vehicle Ve converts the kinetic energy of the vehicle Ve into electrical energy by operating the motor 3 as a generator, and recovers the converted energy to the battery.

The power transmission mechanism (TM) 4 is, for example, a conventionally generally known stepped automatic transmission or a belt-type or toroidal-type continuously variable transmission, and sets a speed change (or gear ratio). It is configured to be controllable. Further, in the case of a hybrid vehicle, the power dividing mechanism that synthesizes and divides the power output by the engine and the motor also corresponds to the power transmission mechanism 4.

Further, the vehicle Ve includes the above-mentioned motor 3 and a controller (ECU) 5 for controlling a braking device and the like. The controller 5 is, for example, an electronic control device mainly composed of a microcomputer. The controller 5 is configured to input detection signals, information signals, and the like from sensors and in-vehicle devices of each part of the vehicle Ve.

FIG. 2 is a diagram showing a control system in the vehicle Ve of FIG. 1, and in the example shown in FIG. 2, a plurality of control systems are provided for each device controlled by the controller 5 or for each control content. Specifically, the EVECU 5a that integrates and controls the entire vehicle, the inverter 6 for driving the motor 3, and the motor that controls the drive and regeneration of the motor 3 by controlling the switching elements (not shown) of the inverter 6. It manages the ECU 5b, the brake ECU 5c that controls the brake hydraulic actuator 8 that operates the friction braking device 7 that applies braking force to each of the wheels 1 and 2, and the battery 9 that exchanges power with the motor 3 via the inverter 6. It is equipped with a battery ECU 5d.

As shown in FIG. 2, the depression amount of the accelerator pedal (not shown) detected by the accelerator pedal sensor 10 is input to the EVEC 5a, and the brake pedal (not shown) detected by the brake pedal sensor 11 is input to the brake ECU 5b. The stepping force (not shown) and the wheel speeds of the wheels 1 and 2 detected by the wheel speed sensor 12 are input. Although not shown, other data to be input includes, for example, the vehicle body speed V, the remaining charge of the battery 9, the rotation speed of the motor 3, and the torque. Then, the controller 5 outputs a control command signal to each control target unit such as the brake hydraulic actuator 8, the inverter 6, and the battery 9.

The vehicle Ve configured in this way has a regenerative braking device 13 that applies a regenerative braking force to some of the wheels (driving wheels) during braking, and friction between the wheels 1 and 2 by the brake hydraulic pressure. It is provided with a friction braking device 7 that applies a braking force. The regenerative braking device 13 includes a motor 3, an inverter 6, and a battery 9. Further, the brake control is executed by coordinating the regenerative braking device 13 and the friction braking device 7. In this brake control, the regenerative braking device 13 and the friction braking device 7 are coordinated to generate the required braking force according to the driver's required braking force set according to the operation amount of the brake pedal. For example, the regenerative braking device 13 generates the maximum braking force, and the friction braking device 7 generates a portion insufficient for the required braking force. Further, for example, in the control described in Patent Document 1 described above, when the slip ratio of the wheel becomes a predetermined value or more, the regenerative braking force is reduced and the friction braking force is increased, that is, regenerative braking. It is configured to replace friction braking.

On the other hand, when the regenerative braking and the friction braking are replaced or switched in this way, the driver may be uncomfortable depending on the switching time. For example, as shown in FIG. 7, when the rate (change rate) of switching between regenerative braking and friction braking is small (that is, when the switching time is long), the antilock braking system (ABS) is activated and the ABS is activated. (Or intervention) may cause discomfort to the driver. On the contrary, when the replacement rate (rate of change) is large (that is, when the replacement time is short), the change in acceleration (G fluctuation) becomes large as shown in FIG. Discomfort may increase. Therefore, in the embodiment of the present invention, it is configured to suppress discomfort to the driver when the above-mentioned regenerative braking and friction braking are replaced.

FIG. 3 is a flowchart showing an example of the control. First, information on the wheel speed Vw of each of the wheels 1 and 2 is acquired from the wheel speed sensor 12 (step S1). Further, the vehicle body speed V is calculated (estimated) from the wheel speed Vw of each wheel 1 and 2 acquired in step S1, and the slip ratio S of each wheel 1 and 2 is calculated from the wheel speed Vw and the vehicle body speed V. (Step S2). The vehicle body speed V may be calculated based on the wheel speed Vw, may be calculated by a conventionally known method, or may be calculated using, for example, an acceleration sensor or the like.

Further, the slip ratio S can be obtained by various known methods, for example, by dividing the value obtained by subtracting the vehicle body speed V from the wheel speed Vw by the vehicle body speed V. When this is shown by the calculation formula, it is shown as follows.
S = (Vw-V) / V

When the slip ratio S calculated from this equation is positive, the slip on the acceleration side is indicated. That is, the wheel speed may be faster than the vehicle body speed, and the drive wheels may spin. On the contrary, when the calculated slip ratio S is negative, the slip on the braking side (deceleration side) is indicated. That is, the vehicle body speed may lock the drive wheels faster than the wheel speed. In the embodiment of the present invention, the control is for switching between the regenerative braking and the friction braking, and the control is for braking. Therefore, the slip ratio S described below has a negative value. Further, the slip ratio S is calculated corresponding to each of the wheels 1 and 2 based on each detection value by the wheel speed sensor 12 of each wheel.

Then, it is determined whether or not the slip ratio S calculated in step S2 is equal to or less than the threshold value for switching between regenerative braking and friction braking (step S3). This determines whether or not the slip ratio S of the regenerative wheel (the front wheel 1 if the vehicle Ve in FIG. 1) is lowered and the slip ratio S is equal to or less than a predetermined threshold value. That is, the braking force due to the regenerative braking may be insufficient or insufficient for the braking force required by the driver, and it is determined whether or not it is necessary to replace the regenerative braking with the friction braking. Therefore, if a negative determination is made in step S3, that is, if the slip ratio S is larger than the replacement threshold value, the control example of FIG. 3 is temporarily terminated without executing the subsequent control.

On the other hand, if it is positively determined in step S3, that is, if the slip rate S is equal to or less than the replacement threshold value, the slip rate change rate dS / dt is calculated (step S4). This can be obtained, for example, by calculating the time derivative value of the slip ratio S calculated in step S3. That is, the slip rate change speed dS / dt is obtained based on the slip rate S calculated based on the wheel speed Vw and the vehicle body speed V.

Then, the replacement rate at the time of switching between the regenerative braking and the friction braking is calculated or determined from the slip rate change speed dS / dt and the vehicle body speed V calculated in step S3 (step S5). This is because, as described above, when the time for switching between regenerative braking and friction braking is fast (that is, short), or when the time for switching between regenerative braking and friction braking is slow (that is, long), this is the case. Since there is a risk of causing discomfort to the driver, this is a control for suppressing the discomfort. Therefore, in this step S5, an appropriate replacement rate is calculated.

As shown in FIG. 4, when the slip rate change speed dS / dt is small, the wheel slip progresses slowly, so the replacement rate is set small. On the contrary, when the slip rate change speed dS / dt is large, the wheel slip progresses quickly, so the replacement rate is set large. That is, when the change in the slip ratio S is relatively small, switching between the regenerative braking and the friction braking at an early stage may increase the G fluctuation, so that the replacement rate is reduced (the replacement time is delayed). On the other hand, when the change in the slip ratio S is relatively large, the replacement rate is increased (the replacement time is shortened) in order to suppress the progress of slip. That is, the replacement rate is determined according to the slip rate change rate dS / dt. As shown in FIG. 4, at the initial stage of switching from regenerative braking to friction braking, even if the replacement rate is changed, the responsiveness and the followability are not affected, so the replacement rate is kept constant.

Further, the replacement rate may be calculated by adding the vehicle body speed V as a parameter to the relationship between the replacement rate in FIG. 4 and the slip rate change speed dS / dt. FIG. 5 is a map for determining the replacement rate when the vehicle body speed V is added as a parameter, and when the vehicle body speed V is low, the replacement rate is increased. That is, regenerative braking and friction braking are quickly replaced. That is, in the case of a low vehicle speed, the G fluctuation is small even if the vehicle is switched quickly, so that the vehicle can be replaced faster.

On the other hand, when the vehicle body speed V is high, the replacement rate is reduced. That is, regenerative braking and friction braking are smoothly (slowly) switched. That is, in the case of a high vehicle speed, the slip determination is unlikely to be delayed, so the replacement rate is reduced and the occurrence of G fluctuation is suppressed.

Then, after calculating or determining the replacement rate in this way, replacement between regenerative braking and friction braking is started (step S6). That is, while reducing the regenerative braking force by the regenerative braking device 13 based on the replacement rate calculated in step S5, the friction braking force by the friction braking device 7 is increased to start the replacement between the regenerative braking and the friction braking. The replacement between the regenerative braking and the friction braking may be changed from the front wheel regenerative braking (or the rear wheel regenerative braking) to the all-wheel friction braking, or a part of the front wheel regenerative braking (or the rear wheel regenerative braking) may be replaced. It may be replaced with friction braking.

Next, the operation in the embodiment of the present invention will be described. As described above, in the embodiment of the present invention, when the regenerative braking and the friction braking are switched (switched), the regenerative braking and the friction braking are performed according to the slip rate change speed dS / dt (and the vehicle body speed V). It is configured to determine the rate at which to replace. For example, as shown in FIG. 6, when braking is started at t1 and the slip ratio S reaches a threshold value for switching between regenerative braking and friction braking at t2, the rate according to the calculated slip rate change speed dS / dt. It is configured to start switching between regenerative braking (broken line) and friction braking (single point chain line). Therefore, according to the embodiment of the present invention, it is possible to avoid the ABS from operating when the regenerative braking and the friction braking are replaced. In addition, since it is configured to perform switching between regenerative braking and friction braking at an appropriate rate according to the slip rate change speed dS / dt, the total braking force (solid line) between regenerative braking and friction braking changes. Is suppressed, and the occurrence of shock due to G fluctuation at the time of switching between regenerative braking and friction braking can be suppressed or avoided.

That is, in the embodiment of the present invention, the operation of ABS that occurs by lengthening the replacement time as in the comparative example of FIG. 7 can be avoided. Further, as in the comparative example of FIG. 8, the shock due to the G fluctuation generated by shortening the replacement time can be suppressed or avoided. The point is that it is possible to switch between regenerative braking and friction braking at an appropriate rate of change, so it is possible to suppress or avoid giving the driver discomfort due to this switching, and slip progress and each wheel 1, It is possible to prevent 2 from locking.

1 ... front wheel, 2 ... rear wheel, 3 ... motor (MG), 4 ... power transmission mechanism (TM), 5 ... controller (ECU), 6 ... inverter, 7 ... friction braking device, 8 ... brake hydraulic actuator, 9 ... Battery, 10 ... Accelerator pedal sensor, 11 ... Brake pedal sensor, 12 ... Wheel speed sensor, 13 ... Regenerative braking device, Ve ... Vehicle.

Claims (1)

It is provided with a regenerative braking device that applies a regenerative braking force to some of the wheels when the vehicle is braked, and a friction braking device that applies a friction braking force to all the wheels when the vehicle is braked. In the braking control device of the vehicle
A controller for controlling the vehicle is provided.
The controller
The slip ratio of the wheel is calculated from the wheel speed of the wheel and the vehicle body speed of the vehicle.
It is determined whether or not the slip ratio is below a predetermined threshold value, and the slip ratio is determined.
When it is determined that the slip ratio is equal to or lower than the threshold value, the rate of change of the slip rate is calculated, and the regenerative braking by the regenerative braking device and the friction braking device are based on the calculated speed of change of the slip rate. A vehicle braking control device characterized in that it is configured to switch between friction braking and braking.

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