JP2020111245A - Vehicular brake force control apparatus - Google Patents

Abstract

To secure travel stability on a low μ road in consideration of the friction coefficient of the surface of a road on which the vehicle travels in deceleration, while appropriately regenerating deceleration energy.SOLUTION: A vehicular brake force control apparatus includes: a regenerative brake device for providing at least either of a front wheel and a rear wheel with regenerative brake force; a hydraulic brake device for providing a wheel with hydraulic brake force; and a control part for controlling the regenerative brake device and the hydraulic brake device. The control part includes: coordination control means for executing control so that at least regenerative brake force is generated as brake force exerted to a wheel, in the case of required deceleration being less than a threshold, and so that the generative brake force and hydraulic brake force are generated and so that a ratio of the hydraulic brake force is increased as the required deceleration increases, in the case of the required deceleration being equal to or higher than the threshold; and variation means for changing a magnitude of the threshold in accordance with the friction coefficient of the road surface on which the vehicle travels. Further, in the case of the friction coefficient of the road surface being lower than a given value, the variation means sets the threshold at lower value than in the case of the friction coefficient being equal to or higher than the given value.SELECTED DRAWING: Figure 5

Description

The present invention relates to a braking force control device for a vehicle.

In Patent Document 1, in a braking force control device for a vehicle including a regenerative braking device and a hydraulic braking device, only a regenerative braking force is generated in a region where a required deceleration is small (a region where a brake pedal operation amount is small), and a required reduction is made. It is disclosed that the regenerative braking force and the hydraulic braking force are generated in a region where the speed is high (a region where the brake pedal operation amount is large).

JP 2012-081917 A

In a vehicle equipped with a regenerative braking device, it is desired to regenerate deceleration energy as much as possible in order to improve electric power consumption and fuel consumption, and therefore, the proportion of regenerative braking force is increased. In the configuration described in Patent Document 1, the regenerative braking force is generated by the regenerative braking device before the hydraulic brake device is actuated for the purpose of improving the brake feeling, but the magnitude of road surface resistance during traveling is reduced. It was not a consideration.

For example, during deceleration while slowly increasing the braking force, when a road surface with a high road surface resistance (dry road surface) enters a road surface with a low road surface resistance (low μ road), the regenerative braking force locks on a low μ road. If it is larger than the limit, the tire will slip. When the tire slips, the control device changes the regenerative braking force to zero and replaces it with the hydraulic braking force.However, since there is a difference in the response of the motor and the response of the hydraulic braking device, the braking force temporarily decreases. I will end up. In addition, some control devices cannot change the distribution of the regenerative braking force and the hydraulic braking force until the tire slip is detected.

On the other hand, if the regenerative braking force is set smaller than the lock limit from the beginning to prevent this, when decelerating while driving on a road surface (dry road surface) with a large road surface resistance, a region with a relatively large required deceleration is reached. Even though the regenerative braking force alone is sufficient, hydraulic braking force is generated. Therefore, the amount of regeneration of deceleration energy is reduced by the amount of the hydraulic braking force, and there is a possibility that electric power consumption and fuel consumption are deteriorated. In this way, there is room for improvement in terms of electric power consumption and fuel consumption, and vehicle stability.

The present invention has been made in view of the above circumstances, and in consideration of road surface resistance during deceleration traveling, it is possible to ensure traveling stability on a low μ road while appropriately regenerating deceleration energy. An object of the present invention is to provide a braking force control device for a vehicle.

The present invention provides a regenerative braking device that applies a regenerative braking force to at least one of a front wheel and a rear wheel, a hydraulic braking device that applies a hydraulic braking force to the front wheel and the rear wheel, and the regenerative braking device. A braking force control device for a vehicle, comprising: a control unit that executes cooperative control with the hydraulic brake device, wherein the control unit is a braking force applied to the wheels when the required deceleration is less than a threshold value. As a result, at least the regenerative braking force is generated, and when the required deceleration is equal to or more than a threshold value, the ratio of the hydraulic braking force is increased as the required deceleration is increased while the regenerative braking force and the hydraulic braking force are generated. When the road surface resistance is lower than a predetermined value, the variable control means has a cooperative control means for controlling the road surface resistance to increase and a variable means for changing the magnitude of the threshold value according to the road surface resistance during traveling. In addition, the threshold value is set to a lower value than when the road surface resistance is equal to or higher than a predetermined value.

Further, the cooperative control means may generate only the regenerative braking force as the braking force applied to the wheels when the required deceleration is less than the threshold value.

According to this configuration, when the required deceleration is less than the threshold value, the braking is performed only by the regenerative braking force, so that the regenerative amount of deceleration energy can be increased, and the fuel consumption and the electricity cost are improved.

Further, the hydraulic brake device has a hydraulic circuit configured such that a distribution ratio between the braking force of the front wheels and the braking force of the rear wheels is constant, and the cooperative control unit controls the required deceleration to be When it is equal to or more than the threshold value, the regenerative braking force may be reduced as compared with the case where the required deceleration is less than the threshold value, and the hydraulic braking force may be increased as compared with when the required deceleration rate is less than the threshold value.

According to this configuration, even when the distribution ratio of the hydraulic braking force between the front wheels and the rear wheels is fixed, the amount of energy regenerated by the operation of the regenerative braking device is ensured while the road resistance is low on the road surface. Driving stability can be secured.

In the present invention, the magnitude of the threshold value used when controlling the distribution of the regenerative braking force and the hydraulic braking force can be changed according to the road surface resistance during traveling. When the road surface resistance is high, the threshold value is increased, so that only the regenerative braking force can be applied to a region where the required deceleration is relatively large, and fuel consumption and electric power consumption are improved. Further, when the road surface resistance is low, the threshold value is made small, so that both the regenerative braking force and the hydraulic braking force are generated even in a region where the required driving force is relatively small, and slip can be suppressed. This makes it possible to regenerate deceleration energy and ensure traveling stability on a low μ road.

FIG. 1 is a skeleton diagram schematically showing the vehicle of the embodiment. FIG. 2 is a functional block diagram for explaining the configuration of the electronic control device. FIG. 3 is a diagram showing a reference map in the brake distribution map. FIG. 4 is a diagram showing a low μ road map in the brake distribution map. FIG. 5 is a flowchart showing a braking force control flow. FIG. 6A is a diagram showing a map set on a low μ road. FIG. 6B is a diagram showing a map set on a road surface having an intermediate μ. FIG. 6C is a diagram showing a map set on a dry road surface. FIG. 7 is a diagram for explaining an example in which the braking force distribution ratio between the front wheels and the rear wheels of the hydraulic brake device is fixed. FIG. 8 is a diagram showing an example of a map used when the hydraulic brake device shown in FIG. 7 is used.

Hereinafter, a braking force control device for a vehicle according to an embodiment of the present invention will be specifically described with reference to the drawings. The present invention is not limited to the embodiments described below.

FIG. 1 is a skeleton diagram schematically showing the vehicle of the embodiment. The vehicle Ve is an electric vehicle including a motor (MG) 1 as a power source. The motor 1 is a motor/generator having a motor function and a power generation function, and is electrically connected to the battery 3 via an inverter 2. The electric power of the battery 3 is supplied to the motor 1 via the inverter 2 to drive the motor 1. Then, the power output from the motor 1 is transmitted to the left and right front wheels 11L, 11R via the differential gear mechanism 4 of the power transmission device. That is, the vehicle Ve is a front wheel drive (FWD) electric vehicle. A power transmission device such as a transmission may be provided in the power transmission path between the motor 1 and the differential gear mechanism 4.

The inverter 2 is a power conversion device that converts DC power from the battery 3 into AC power and supplies the AC power to the motor 1. The motor 1 is controlled by the inverter 2 being controlled by an electronic control unit (hereinafter referred to as ECU) 5. The battery 3 is a power storage device configured by a secondary battery and capable of storing the electric power generated by the motor 1, for example.

The ECU 5 is composed of an electronic control device that drives and controls the motor 1. The ECU 5 includes a CPU, a storage unit that stores data such as various programs, and an arithmetic processing unit that performs various arithmetic operations for driving and controlling the motor 1.

Further, as shown in FIG. 2, signals from various sensors such as a motor rotation speed sensor 31 that detects the rotation speed of the motor 1 and a wheel speed sensor 32 that detects the wheel speed of the wheel are input to the ECU 5. It Wheel speed sensors 32a, 32b, 32c, 32d are provided on the left and right front wheels 11L, 11R and the left and right rear wheels 12L, 12R, respectively. For example, when a resolver signal is input from the motor rotation speed sensor 31 to the ECU 5, the ECU 5 calculates the rotation speed of the motor 1 (motor rotation speed) based on the resolver signal. When the wheel speed is input to the ECU 5 from the wheel speed sensor 32, the ECU 5 calculates the vehicle speed of the vehicle Ve based on the wheel speed. Further, the signals input to the ECU 5 include a shift position from a shift position sensor that detects an operation position of a shift lever, an accelerator opening degree from an accelerator pedal position sensor that detects a depression amount of an accelerator pedal, and a brake pedal. A brake pedal position from a brake pedal position sensor that detects the amount of depression is included.

The vehicle Ve is equipped with a regenerative braking device and a hydraulic braking device. The regenerative braking device is configured to include the motor 1 connected to the left and right front wheels 11L and 11R, and applies braking force (regenerative braking force) generated when the motor 1 functions as a generator to the drive wheels. Is configured. The regenerative braking force is a braking force applied only to the front wheels 11L and 11R. Further, the hydraulic brake device includes a brake disc that rotates integrally with the wheel, and a brake pad that frictionally contacts the brake disc. This hydraulic brake device is configured to apply a braking force (hydraulic braking force) generated by hydraulic pressure to wheels. The hydraulic braking force is a braking force applied to all the wheels 11L, 11R, 12L, 12R.

As shown in FIG. 1, the hydraulic brake device includes a hydraulic brake device 21L that applies a braking force to the left front wheel 11L, a hydraulic brake device 21R that applies a braking force to the right front wheel 11R, and a left rear wheel 12L. A hydraulic brake device 22L that applies a braking force and a hydraulic brake device 22R that applies a braking force to the right rear wheel 12R are included. A brake actuator 6 is connected to each hydraulic brake device 21L, 21R, 22L, 22R. A hydraulic pressure (brake hydraulic pressure) is supplied from the brake actuator 6 to each hydraulic brake device 21L, 21R, 22L, 22R. The brake actuator 6 is controlled by the ECU 5.

As shown in FIG. 2, the ECU 5 includes a road surface μ estimation unit 5a and a brake distribution calculation unit 5b. The road surface μ estimation unit 5a estimates the road surface resistance (μ) during traveling. The brake distribution calculation unit 5b calculates the distribution of the regenerative braking force and the hydraulic braking force according to the road surface resistance (road surface μ).

The road surface μ estimation unit 5a is a processing unit that calculates the slip ratio between the road surface and the wheels and determines the road surface state. For example, the road surface μ estimation unit 5a determines that the wheel is in the slip state based on the rotation speed difference between the wheel speed and the motor rotation speed. Since the vehicle Ve is driven by the front wheels, the braking force when the front wheels 11L and 11R, which are the driving wheels, stop rotating (lock) when there is a braking request during traveling is referred to as a front lock limit (Fr lock limit). That is, the road surface μ estimation unit 5a can calculate the front lock limit according to the road surface μ.

The brake distribution calculation unit 5b calculates the distribution of the braking force applied to the wheels between the hydraulic braking force of the hydraulic braking device and the regenerative braking force of the regenerative braking device based on the front lock limit. For example, the brake distribution calculation unit 5b sets the distribution of the regenerative braking force and the hydraulic braking force by using the map showing the relationship between the required deceleration and the brake distribution. This map consists of a reference map as the first map that is set to the front lock limit in the state where the road surface is normal (dry road surface) and a case where the road surface μ is low and slippery (low μ road). A low μ road map after distribution change as a second map set to the front lock limit of A plurality of these maps are stored in the storage unit of the ECU 5.

FIG. 3 is a diagram showing a reference map in which the front lock limit is set high. As shown in FIG. 3, the reference map is a map used when decelerating on a dry road surface having a high road surface resistance, so that the front lock limit is set high. This front lock limit is set as a threshold for the required deceleration. The ECU 5 is configured to include a variable unit that changes the magnitude of the threshold value (the upper limit value of the regenerative braking force) according to the road surface resistance. Then, when the required deceleration is smaller than the front lock limit, the required deceleration can be satisfied only by the regenerative braking force. The front lock limit is the upper limit value of the regenerative braking force. When decelerating on a dry road surface, the map shown in FIG. 3 is referred to, and it becomes possible to cope with the front lock limit with a relatively large deceleration torque (required deceleration) only by the regenerative braking force. Then, when the required deceleration is larger than the front lock limit, slipping may occur only with the regenerative braking force, so that regenerative braking force and hydraulic braking force are generated. In this description, the required deceleration will be considered as deceleration torque.

FIG. 4 is a diagram showing a low μ road map in which the front lock limit is set low. As shown in FIG. 4, the low μ road map is a map used when decelerating on a low μ road having a low road surface resistance, and therefore the front lock limit is lower than the front lock limit on a dry road surface. It is set to a value. When decelerating on a low μ road, the map shown in FIG. 4 is referred to, and the regenerative braking force and the hydraulic braking force are generated at the front lock limit of a relatively small deceleration torque. That is, even if only the regenerative braking force is generated in the normal reference map, the hydraulic braking force is generated in the low μ road map. Then, as the braking force increases, the hydraulic braking force is controlled to increase with the magnitude of the regenerative braking force kept constant at the front lock limit (upper limit value). That is, when the required braking force exceeds the front lock limit, the ECU 5 executes the braking force control so as to decrease the ratio of the regenerative braking force and increase the ratio of the hydraulic braking force.

Here, the braking force control flow will be described with reference to FIG. FIG. 5 is a flowchart showing an example of the braking force control flow. The control shown in FIG. 5 is executed by the ECU 5.

The ECU 5 acquires the wheel speed and the motor rotation speed (step S1). In step S1, the wheel speed from the wheel speed sensor 32 and the motor rotation speed from the motor rotation speed sensor 31 are input to the ECU 5.

The ECU 5 estimates the road surface μ (step S2). In step S2, the road surface μ estimation unit 5a of the ECU 5 constantly estimates the road surface μ during traveling.

The ECU 5 calculates the front lock limit (Fr lock limit) using the estimated road surface μ (step S3). In step S3, the front lock limit can be calculated by using the rotation speed difference between the motor rotation speed and the vehicle speed. A well-known calculation method may be used as the calculation method of the front lock limit.

The ECU 5 determines whether the front lock limit is smaller than the predetermined value α (step S4). In step S4, the front lock limit calculated in step S3 is compared with the predetermined value α. The predetermined value α is a preset value.

When the front lock limit is equal to or greater than the predetermined value α (step S4: No), the ECU 5 selects the reference map as the regenerative/hydraulic brake distribution map (step S5). In step S5, a map assuming a dry road surface is set, as illustrated in FIG. 3 described above. When step S5 is performed, the control routine proceeds to step S7, which will be described later.

When the front lock limit is smaller than the predetermined value α (step S4: Yes), the ECU 5 selects the low μ road map as the regenerative/hydraulic brake distribution map (step S6). In step S6, a map assuming a low μ road is set, as illustrated in FIG. 4 described above.

Then, the ECU 5 acquires the required deceleration (step S7). In step S7, it is detected that the driver has stepped on the brake pedal during traveling, and the required deceleration corresponding to the brake pedal operation amount is calculated.

Based on the required deceleration calculated in step S7 and the regenerative/hydraulic brake distribution map selected in step S5 or step S6, the ECU 5 regenerates braking force by the regenerative braking device and hydraulic braking force applied to the front wheels 11L, 11R. The hydraulic braking force applied to the rear wheels 12L and 12R is calculated (step S8). In step S8, the brake distribution calculator 5b of the ECU 5 calculates the distribution of the regenerative braking force and the hydraulic braking force.

The ECU 5 executes the cooperative control by the hydraulic braking control by the regenerative braking force and the hydraulic braking control by the hydraulic braking force (step S9). In step S9, the regenerative braking device and the hydraulic braking device are cooperatively controlled based on the distribution of the regenerative braking force and the hydraulic braking force calculated in step S8.

Then, the ECU 5 ends the braking control (step S10). Braking of the vehicle Ve is ended by step S10.

After braking, the ECU 5 returns the regeneration/hydraulic brake distribution map to the reference map (step S11).

As described above, according to the braking force control device for the vehicle Ve in the embodiment, the front lock limit is variably controlled according to the magnitude of the road surface resistance during deceleration traveling, thereby improving the electric power consumption and the fuel consumption. It is possible to secure running stability on low μ roads.

In the control flow shown in FIG. 5 described above, in steps S4 to S6, one of the two maps is selected by comparing the front lock limit and the predetermined value α, but the present invention is not limited to this. .. For example, instead of the processing means corresponding to steps S4 to S6 described above, the ECU 5 has a processing means for selecting the regenerative/hydraulic brake distribution map using the front lock limit as an argument without comparing with the predetermined value α. May be. As an example, as shown in FIG. 6, an appropriate map can be selected from three maps. When the front lock limit is small, the low μ road map is selected as shown in FIG. When the front lock limit has a medium size, a medium size map is selected, as shown in FIG. 6B. When the front lock limit is large, as shown in FIG. 6C, a map that assumes a dry road surface with high road surface resistance is selected.

Further, the hydraulic brake device may be configured to have a hydraulic circuit in which the distribution ratio of the hydraulic braking force between the front wheels 11L and 11R and the rear wheels 12L and 12R is fixed. FIG. 7 is a diagram for explaining an example in which the braking force distribution ratio between the front wheels 11L and 11R and the rear wheels 12L and 12R is fixed in the hydraulic brake device. FIG. 8 is a diagram showing an example of a map used when the hydraulic brake device shown in FIG. 7 is used.

As shown in FIG. 7, the brake actuator 6 has a hydraulic circuit in which the front-rear hydraulic pressure distribution ratio (α:β) is fixed. The oil output from the oil pump 61 is supplied to the hydraulic brake devices 21L and 21R of the front wheels 11L and 11R and the hydraulic brake devices 22L and 22R of the rear wheels 12L and 12R via the pressure adjusting portion 62. The oil pressure adjusted by the pressure adjusting unit 62 is supplied to the wheel cylinders of the respective wheels in a state where the distribution ratio of the oil pressure on the front wheel side and the oil pressure on the rear wheel side is fixed to α:β. Further, the hydraulic pressure from the oil pump 61 is accumulated in the accumulator (ACC) 63.

As shown in FIG. 8, when the front lock limit is reached and the regenerative braking force reaches the upper limit value, both hydraulic braking force and regenerative braking force are generated. At this time, when the hydraulic braking force is applied to the front wheels 11L and 11R, the hydraulic braking force is inevitably applied to the rear wheels 12L and 12R. Control to reduce the braking force. Therefore, when the required braking force is larger than the front lock limit, the regenerative braking force changes so as to be smaller than the upper limit value.

As described above, according to the braking force control device of the embodiment, the regenerative braking device can effectively collect the deceleration energy in the daily range where the vehicle Ve travels in the city, and on the low μ road. It is possible to ensure the running stability of the vehicle.

The present invention is not limited to front wheel drive, and may be rear wheel drive or four-wheel drive. In short, the vehicle to which the present invention is applied may be a vehicle in which the motor functioning as a regenerative brake is provided on at least one of the front wheels 11L, 11R or the rear wheels 12L, 12R. Further, the vehicle to which the present invention can be applied is not limited to the electric vehicle (EV) and may be a hybrid vehicle (HV, PHV).

1 motor (MG)
2 Inverter 3 Battery 5 ECU
6 Brake actuators 11L, 11R Front wheels 12L, 12R Rear wheels 21L, 21R, 22L, 22R Hydraulic brake device 31 Motor rotation speed sensor 32 Wheel speed sensor

Claims (3)

A regenerative braking device that applies a regenerative braking force to at least one of the front wheels and the rear wheels,
A hydraulic brake device for applying a hydraulic braking force to the front wheels and the rear wheels,
A control unit that executes cooperative control between the regenerative braking device and the hydraulic braking device;
A braking force control device for a vehicle, comprising:
The control unit is
When the required deceleration is less than the threshold value, at least the regenerative braking force is generated as the braking force applied to the wheels, and when the required deceleration is not less than the threshold value, the regenerative braking force and the hydraulic braking force are generated. And a cooperative control means for controlling such that the ratio of the hydraulic braking force increases as the required deceleration increases.
Variable means for changing the magnitude of the threshold value according to the road resistance during traveling,
Have
When the road surface resistance is lower than a predetermined value, the variable means sets the threshold value to a lower value than when the road surface resistance is higher than a predetermined value. .. The vehicle braking force control according to claim 1, wherein the cooperative control unit generates only the regenerative braking force as the braking force applied to the wheels when the required deceleration is less than a threshold value. apparatus. The hydraulic brake device has a hydraulic circuit configured such that a distribution ratio between the braking force of the front wheels and the braking force of the rear wheels is constant.
When the required deceleration is equal to or greater than a threshold, the cooperative control means reduces the regenerative braking force as compared to when the required deceleration is less than a threshold, and the hydraulic braking force is when the required deceleration is less than a threshold. The braking force control device for a vehicle according to claim 1 or 2, wherein the braking force control device is increased.

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