阅读说明：本技术 制动控制装置 (Brake control device ) 是由 河野孝史 于 2020-05-28 设计创作，主要内容包括：本发明提供一种电动车辆的制动控制装置,其实现定速下坡功能中的再生效率的提高。制动控制装置具备：检测道路坡度的坡度传感器；能够将定速下坡功能切换为有效的操作部；对能够从前轮的制动转矩生成再生电力的第一再生部进行控制并且对能够从后轮的制动转矩生成再生电力的第二再生部进行控制的制动控制部；存储表示第一再生部的动作与再生效率之间的关系、以及第二再生部的动作与再生效率之间的关系的效率映射的存储部。制动控制部在定速下坡功能有效的情况下,基于检测到的道路坡度和效率映射,以使综合的再生效率满足第一条件的方式计算前轮及后轮的制动转矩分配(S6),利用计算出的制动转矩分配来控制第一再生部及第二再生部(S8)。(The invention provides a brake control device for an electric vehicle, which improves the regeneration efficiency in a constant speed downhill function. The brake control device is provided with: a gradient sensor for detecting a gradient of a road; an operation unit capable of switching the constant speed downhill function to an effective one; a brake control unit that controls a first regeneration unit that can generate regenerative electric power from the braking torque of the front wheels and controls a second regeneration unit that can generate regenerative electric power from the braking torque of the rear wheels; and a storage unit that stores an efficiency map indicating a relationship between the operation of the first regeneration unit and the regeneration efficiency and a relationship between the operation of the second regeneration unit and the regeneration efficiency. When the constant speed downhill function is enabled, the brake control unit calculates the brake torque distribution of the front and rear wheels so that the integrated regenerative efficiency satisfies the first condition, based on the detected road gradient and the efficiency map (S6), and controls the first and second regeneration units using the calculated brake torque distribution (S8).)

1. A brake control device is characterized by comprising:

a gradient sensor that detects a road gradient;

an operation unit capable of switching the constant speed downhill function to be effective;

a brake control unit that controls a first regeneration unit capable of generating regenerative electric power from the braking torque of the front wheels and controls a second regeneration unit capable of generating regenerative electric power from the braking torque of the rear wheels; and

a storage unit that stores an efficiency map indicating a relationship between an operation and a regeneration efficiency of the first regeneration unit and a relationship between an operation and a regeneration efficiency of the second regeneration unit,

the brake control unit calculates a brake torque distribution of the front wheels and the rear wheels such that a total regenerative efficiency satisfies a first condition based on the detected road gradient and the efficiency map when the constant speed downhill function is enabled, and controls the first regeneration unit and the second regeneration unit using the calculated brake torque distribution.

2. The brake control apparatus according to claim 1,

the brake control unit calculates the brake torque distribution by setting a parameter of a vehicle speed to have a magnitude.

3. The brake control apparatus according to claim 1,

when the road gradient changes while the constant speed downhill function is being executed, the brake control unit may execute the calculation of the brake torque distribution again by setting the vehicle speed as a parameter that provides a magnitude to the vehicle speed at that time, and may execute a first control process of controlling the first and second regeneration units using the calculated brake torque distribution.

4. The brake control apparatus according to claim 2,

when the road gradient changes while the constant speed downhill function is being executed, the brake control unit may execute the calculation of the brake torque distribution again by setting the vehicle speed as a parameter that provides a magnitude to the vehicle speed at that time, and may execute a first control process of controlling the first and second regeneration units using the calculated brake torque distribution.

5. The brake control apparatus according to claim 3,

when the road gradient changes while the constant speed downhill function is being executed, the brake control unit can select whether to execute the first control process or to execute a second control process for maintaining the vehicle speed.

6. The brake control apparatus according to claim 4,

when the road gradient changes while the constant speed downhill function is being executed, the brake control unit can select whether to execute the first control process or to execute a second control process for maintaining the vehicle speed.

7. The brake control apparatus according to claim 5,

the brake control unit selects the first control process to be executed when the regeneration efficiency of the first control process is higher than the regeneration efficiency of the second control process by a threshold value or more.

8. The brake control apparatus according to claim 6,

the brake control unit selects the first control process to be executed when the regeneration efficiency of the first control process is higher than the regeneration efficiency of the second control process by a threshold value or more.

9. The brake control apparatus according to any one of claims 5 to 8,

the brake control device further includes a setting operation unit capable of performing a setting operation,

the brake control unit selects whether to execute the first control process or the second control process based on the setting by the setting operation unit.

Technical Field

The present invention relates to a brake control device for an electric vehicle.

Background

Patent document 1 discloses the following technique: in a hybrid vehicle having a front wheel motor and a rear wheel motor, regenerative braking torques of the front wheel and the rear wheel and a braking force of a hydraulic brake are controlled during a downhill slope, thereby improving energy recovery efficiency.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2004-166363

Disclosure of Invention

Technical problem

In recent years, vehicles having a constant speed downhill function of automatically controlling a braking force in order to maintain a constant vehicle speed when descending a slope have been applied. With the constant speed downhill function, the driver can cause the vehicle to descend downhill at a predetermined vehicle speed without performing a braking operation.

However, even when the constant speed downhill function is enabled, the vehicle speed is less strictly required to be controlled to a predetermined speed, and a slight speed change is often allowed. In addition, regenerative braking is used for the constant speed downhill function, so that the cruising distance of the electric vehicle can be extended by using regenerative energy.

The present invention aims to provide a brake control device for an electric vehicle, which aims to improve the regeneration efficiency in a constant speed downhill function.

Technical scheme

A first aspect of the present invention is a brake control device including:

a gradient sensor that detects a road gradient;

an operation unit capable of switching the constant speed downhill function to be effective;

a brake control unit that controls a first regeneration unit capable of generating regenerative electric power from the braking torque of the front wheels and controls a second regeneration unit capable of generating regenerative electric power from the braking torque of the rear wheels; and

a storage unit that stores an efficiency map indicating a relationship between an operation and a regeneration efficiency of the first regeneration unit and a relationship between an operation and a regeneration efficiency of the second regeneration unit,

the brake control unit calculates a brake torque distribution of the front wheels and the rear wheels such that a total regenerative efficiency satisfies a first condition based on the detected road gradient and the efficiency map when the constant speed downhill function is enabled, and controls the first regeneration unit and the second regeneration unit using the calculated brake torque distribution.

In a second aspect of the invention, in the brake control device according to the first aspect, the brake control unit calculates the brake torque distribution by setting a parameter of a vehicle speed to have a magnitude.

A third aspect of the invention is the brake control device according to the first or second aspect, characterized in that,

when the road gradient changes while the constant speed downhill function is being executed, the brake control unit may execute the calculation of the brake torque distribution again by setting the vehicle speed as a parameter that provides a magnitude to the vehicle speed at that time, and may execute a first control process of controlling the first and second regeneration units using the calculated brake torque distribution.

An invention according to a fourth aspect is the brake control device according to the third aspect, characterized in that,

when the road gradient changes while the constant speed downhill function is being executed, the brake control unit can select whether to execute the first control process or to execute a second control process for maintaining the vehicle speed.

In the brake control device according to the fifth aspect of the present invention, the brake control unit selects the first control process to be executed when the regeneration efficiency of the first control process is higher than the regeneration efficiency of the second control process by a threshold value or more.

An invention according to a sixth aspect is the brake control device according to the fourth or fifth aspect, characterized in that,

the brake control device further includes a setting operation unit capable of performing a setting operation,

the brake control unit selects whether to execute the first control process or the second control process based on the setting by the setting operation unit.

[ Effect of the invention ]

According to the present invention, when the constant speed downhill function is enabled, the braking torque distribution of the regenerative braking of the front wheels and the regenerative braking of the rear wheels is calculated from the efficiency map and the road gradient, and the first regeneration unit and the second regeneration unit are controlled based on the calculated braking torque distribution. Therefore, the regeneration efficiency can be improved when the constant speed downhill function is executed.

Drawings

Fig. 1 is a block diagram showing a configuration of an electric vehicle according to an embodiment of the present invention.

Fig. 2 is a diagram showing an example of an efficiency map for regenerative braking, where fig. 2 (a) is an efficiency map for front wheels, fig. 2 (b) is an efficiency map for rear wheels, and fig. 2 (c) is an efficiency map for front and rear wheels.

Fig. 3 is a flowchart showing an example of constant speed downhill processing executed by the brake control unit.

Fig. 4 is an explanatory diagram illustrating an example of a transition of the running state of the electric vehicle using the constant speed downhill function.

Description of the symbols

1 electric vehicle

2a front wheel

2b rear wheel

3a first traveling motor (first regeneration unit)

3b second traveling motor (second regeneration unit)

4a, 4b converter

5 Battery

10 driving operation part

15 function operating part

16 first function switch (operation part)

17 ECO switch

18 vehicle speed setting switch

19 setting operation part

21 vehicle speed sensor

22 gradient sensor

30 vehicle control unit

31 brake control unit

32 storage part

33 efficiency mapping

50 braking mechanism

52 braking part

53 drive part

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block diagram showing a configuration of an electric vehicle according to an embodiment of the present invention. Fig. 2 is a diagram showing an example of an efficiency map for regenerative braking, where fig. 2 (a) is an efficiency map for front wheels, fig. 2 (b) is an efficiency map for rear wheels, and fig. 2 (c) is an efficiency map for front and rear wheels.

The electric vehicle 1 of the present embodiment includes: front wheels 2a and rear wheels 2 b; a first travel motor 3a that drives the front wheels 2 a; a second travel motor 3b that drives the rear wheel 2 b; an inverter 4a that drives the first travel motor 3 a; an inverter 4b that drives the second travel motor 3 b; a battery 5 for supplying electric power for traveling to the inverters 4a and 4 b; a brake mechanism 50 that generates braking force on the front wheel 2a, the rear wheel 2b, or both of them; a gradient sensor 22 that detects a road gradient; and a vehicle speed sensor 21 that detects a vehicle speed.

The electric vehicle 1 further includes: a driving operation unit 10 including a brake pedal 11, an accelerator pedal 12, and a steering wheel 13; a function operation unit 15 for switching between activation and deactivation of various functions; and a vehicle control unit 30 that controls the electric vehicle 1. The vehicle control unit 30 includes: a brake control unit 31 that performs regenerative control of the first travel motor 3a and the second travel motor 3b and control of the brake mechanism 50; and a storage unit 32 that stores various control data. The storage unit 32 includes an efficiency map 33, and the efficiency map 33 indicates a relationship between the operation (wheel speed and regenerative braking torque) of the first travel motor 3a and the regenerative efficiency, and a relationship between the operation (wheel speed and regenerative braking torque) of the second travel motor 3b and the regenerative efficiency.

In fig. 1, a combination of the brake control unit 31, the storage unit 32, the sensors (the vehicle speed sensor 21, the gradient sensor 22, and the like), and the function operation unit 15 corresponds to an example of the brake control device of the present invention. The first traveling motor 3a corresponds to an example of a first regeneration unit of the present invention, and the second traveling motor 3b corresponds to an example of a second regeneration unit of the present invention.

The first travel motor 3a and the inverter 4a can perform a power operation and a regenerative operation, and generate a driving force by the power operation and a braking force by the regenerative operation. The driving force and the braking force are transmitted to the front wheels 2 a. The first travel motor 3a is an electric motor, and during regenerative operation, delivers regenerative electric power to the battery 5 via the inverter 4 a. As shown in fig. 2 (a), the regenerative efficiency of the first travel motor 3a varies, for example, by 60% to 80% depending on the wheel speed of the front wheels 2a and the regenerative braking torque. The regenerative efficiency represents a ratio of regenerative energy to braking energy.

The second travel motor 3b and the inverter 4b can perform a power operation and a regenerative operation, and generate a driving force by the power operation and a braking force by the regenerative operation. The driving force and the braking force are transmitted to the rear wheels 2 b. The second travel motor 3b is an electric motor, and during regenerative operation, delivers regenerative electric power to the battery 5 via the inverter 4 b. As shown in fig. 2 (b), the regenerative efficiency of the second travel motor 3b varies, for example, from 60% to 80% depending on the wheel speed of the rear wheels 2b and the regenerative braking torque. The specifications of the first travel motor 3a and the specifications of the second travel motor 3b may be different, in which case the efficiency map 33 of the regenerative efficiency of the first travel motor 3a is different from the efficiency map 33 of the regenerative efficiency of the second travel motor 3 b.

The efficiency map 33 stored in the storage unit 32 may be two independent map data of the front wheels 2a and the rear wheels 2b shown in fig. 2 (a) and 2 (b). Alternatively, as shown in fig. 2 (c), the efficiency map 33 may be map data indicating a relationship between the braking torque distribution (the regenerative braking torque of the front wheels 2a and the regenerative braking torque of the rear wheels 2 b), the wheel speed, and the total regenerative efficiency. The braking torque distribution is a combination of the regenerative braking torque of the front wheels 2a and the regenerative braking torque of the rear wheels 2 b. The map data in fig. 2 (c) can be obtained from the map data in fig. 2 (a) and 2 (b).

The battery 5 is, for example, a lithium ion secondary battery or a nickel hydrogen secondary battery. The Electric Vehicle 1 may be an HEV (Hybrid Electric Vehicle) having an internal combustion engine, and in this case, the battery 5 may be a lead storage battery.

The brake mechanism 50 includes: a brake unit 52 such as a caliper brake or a drum brake that applies a braking force to the front wheel 2a, the rear wheel 2b, or both of them; the operation of the brake pedal 11 is transmitted to the master cylinder 51 and the hydraulic circuit of the brake unit 52. The hydraulic circuit is provided with a drive unit 53 that adjusts the hydraulic pressure by the control of the brake control unit 31.

The function operation unit 15 includes: a first function switch (corresponding to an operation unit of the present invention) 16 for switching between the activation and deactivation of the constant speed downhill function; an ECO switch 17 for switching between active and inactive states of the ECO mode; a vehicle speed setting switch 18 for setting a vehicle speed of the constant speed downhill function; and a setting operation unit 19 for setting options. The function operating portion 15 is configured to be operable by the driver. A display element that enables a driver to visually confirm the selection state of each switch by the output of a lamp or a display panel may be provided on an instrument panel or the like.

The constant speed downhill function is a function of automatically controlling the braking force so as to maintain the set vehicle speed without operating the brake pedal 11 when the vehicle is going downhill. The set vehicle speed may be a vehicle speed set in advance by the driver or user via the vehicle speed setting switch 18 within a predetermined range, a default set vehicle speed, or a vehicle speed determined based on the vehicle speed at the time when the function is switched to be effective. However, the vehicle speed controlled by the constant speed downhill function is limited to a low or medium speed (e.g., 5km/h to 40 km/h).

The ECO mode in which switching is performed by the ECO switch 17 is a mode in which the energy efficiency is preferentially improved. The control of the constant speed downhill function is different between when the ECO mode is not active and when the ECO mode is active. For example, in the constant speed downhill function when the ECO mode is not active, constant speed downhill control based mainly on control of the brake mechanism 50 is executed. Under the constant speed downhill function when the ECO mode is active, constant speed downhill control mainly using regenerative braking is performed.

The vehicle control unit 30 receives detection signals from the vehicle speed sensor 21 and the gradient sensor 22 and an operation signal from the driving operation unit 10, and controls the inverters 4a and 4b and the brake mechanism 50 based on these signals. The brake control unit 31 of the vehicle control unit 30 performs regenerative operation of the inverters 4a and 4b and drive control of the brake mechanism 50. The vehicle Control Unit 30 may be constituted by 1 ECU (Electronic Control Unit), or a plurality of ECUs that communicate with each other and operate in cooperation. The vehicle control Unit 30 implements normal travel control by executing a control program by a CPU (Central Processing Unit) of the ECU. The control program includes a program for constant speed downhill processing executed by the brake control unit 31.

< constant velocity downhill treatment >

Fig. 3 is a flowchart showing an example of constant speed downhill processing executed by the brake control unit.

The constant speed downhill process is started by switching the first function switch 16 to be active. If the constant speed downhill process is started, the brake control unit 31 first checks whether the road currently traveling is a downhill road based on the output of the gradient sensor 22 (step S1), and then determines whether the current vehicle speed is a speed (e.g., 40km/h or less) that is allowed by the constant speed downhill function (step S2). If the determination results in steps S1 and S2 indicate that the vehicle is not a downhill road or exceeds the allowable speed, the brake control unit 31 switches the first function switch 16 to off (step S3) and terminates the constant speed downhill process. On the other hand, if the speed is the allowable speed on a downhill road, the brake control unit 31 advances the process downward.

If the vehicle is propelled downward, the brake control unit 31 acquires the set speed of the constant speed downhill function (step S4). Before the first function switch 16 is turned on, if the driver performs the vehicle speed setting operation of the constant speed downhill function, the brake control unit 31 reads the set vehicle speed in step S4. When the vehicle speed at the time when the first function switch 16 is activated is set as the set vehicle speed, the brake control unit 31 acquires the current vehicle speed as the set vehicle speed in step S4.

Next, the brake control unit 31 determines whether the ECO mode is selected according to the operation of the ECO switch 17 (step S5). As a result, if the ECO mode is not selected, the brake control unit 31 shifts the process to the normal constant speed downhill control (step S20), but if the ECO mode is selected, the process proceeds to the constant speed downhill control that gives priority to the regeneration efficiency (steps S6 to S16).

Although the normal constant speed downhill control process of step S20 is not described in detail, the brake control unit 31 controls the brake mechanism 50 to maintain the vehicle speed at the set speed. In the normal constant speed downhill control, the brake control unit 31 may be configured to use the regenerative control at the same time if the chargeable power of the battery 5 is large (if the charging rate is low), and to not perform the regenerative control or reduce the rate of the regenerative control if the chargeable power of the battery 5 is small.

If the shift is made to the constant speed downhill control that gives priority to the regenerative efficiency, first, the brake control unit 31 calculates a brake torque distribution that satisfies a predetermined condition (corresponding to the first condition of the present invention) for improving the regenerative efficiency, based on the efficiency map 33 and the output of the gradient sensor 22 (step S6). As the predetermined condition for improving the regeneration efficiency, for example, a condition that the regeneration efficiency becomes the highest, a condition that the regeneration efficiency is included in a range from the highest regeneration efficiency to several percent, or the like can be used.

In the calculation of step S6, the brake control unit 31 does not fix the vehicle speed at the set speed, but processes the vehicle speed as a parameter having a predetermined width at the set speed. For example, the brake control unit 31 sets the vehicle speed to a parameter v1 having a predetermined width (for example, ± 2[ km/h ]) at a set speed (for example, 15[ km/h ]) (v1 ═ 15 ± 2[ km/h ]). Next, the brake control unit 31 calculates a total braking torque Trbtot that maintains the vehicle speed constant from the road gradient, the vehicle speed, and the known vehicle weight, and sets the regenerative braking torque Trbfr of the front wheels 2a and the regenerative braking torque Trbrr of the rear wheels 2b to parameters that satisfy Trbtot ═ Trbfr + Trbrr. Then, the brake control unit 31 searches the efficiency map 33 for the vehicle speed parameter v1 and the ranges indicated by the parameters Trbfr and Trbrr of the regenerative braking torques of the front wheels 2a and the rear wheels 2b, and obtains the map position where the overall regenerative efficiency is the highest. If the map position is found, the vehicle speed and the brake torque distribution (the regenerative brake torque of the front wheels 2a and the regenerative brake torque of the rear wheels 2 b) corresponding thereto are uniquely found.

If the vehicle speed and the brake torque distribution are calculated, the brake control unit 31 sets these calculation results as target values to be controlled (step S7), and shifts to the loop processing of the constant speed downhill control (steps S8 to S11).

In the loop processing, first, the brake control unit 31 controls the inverters 4a and 4b based on the value of the vehicle speed sensor 21 so that the vehicle speed, the regenerative braking torque of the front wheel 2a, and the regenerative braking torque of the rear wheel 2b match the respective target values, thereby generating the regenerative braking torques of the front wheel 2a and the rear wheel 2b (step S8).

Next, the brake control unit 31 determines whether or not the release condition of the constant speed downhill function is satisfied (step S9). The release condition refers to the end of the road gradient of the downhill or the execution of the release operation. The release operation is, for example, an operation of the brake pedal 11, an operation of the accelerator pedal, or an operation of switching the first function switch 16 to an invalid state. If the cancellation condition is satisfied, the brake control unit 31 switches the first function switch 16 to inactive (step S3), and ends the constant speed downhill processing. On the other hand, if the release condition is not satisfied, the brake control section 31 advances the process downward.

If the vehicle is propelled downward, the brake control unit 31 confirms the state of the battery 5 and determines whether or not the chargeable power of the battery 5 is equal to or less than the threshold (step S10). If the determination result is yes, the brake control unit 31 shifts the process to the normal constant speed downhill control because the regenerative energy cannot be stored (step S20). On the other hand, if the determination result of step S10 is no, the brake control portion 31 advances the process downward.

If the vehicle is propelled downward, the brake control portion 31 determines whether the road gradient is changing based on the output of the gradient sensor 22 (step S11). In step S11, the brake control unit 31 may determine that there is no change in a slight change (for example, a change of a threshold value or less such as 2 degrees or less). If the determination result is that there is no change in the road gradient, the brake control unit 31 returns the process to step S8 and continues the loop processing of steps S8 to S11. On the other hand, if the road gradient changes, the brake control portion 31 temporarily exits the loop processing.

If the loop processing is temporarily exited due to a change in the road gradient, the brake control unit 31 calculates the brake torque distribution again in two ways (steps S12, S13).

In the calculation process a of step S12, the brake control unit 31 sets the vehicle speed as a parameter having a magnitude at the current speed, and calculates the brake torque distribution for improving the regenerative efficiency based on the output of the gradient sensor 22 and the efficiency map 33. If the recalculation of step S12 is compared with the calculation of step S6, the value of the total brake torque Trbtot for maintaining the vehicle speed constant differs due to the gradient change. Further, the vehicle speed parameter v2 is changed to a value (16.5 + -2 [ km/h ]) having a predetermined amplitude (e.g., + -2 [ km/h ]) at the current vehicle speed (the vehicle speed (e.g., + -2 [ km/h ]) as a result of the calculation of step S8). In step S12, the brake control unit 31 searches the efficiency map 33 for the ranges of the above parameters, and obtains the map position where the overall regeneration efficiency is the highest. Then, the brake control unit 31 obtains the vehicle speed (for example, 14.5[ km/h ]) and the brake torque distribution as calculation results from the map position.

In the calculation process B of step S13, the brake control unit 31 sets the vehicle speed at the current speed and sets only the brake torque distribution as a variable parameter to calculate the brake torque distribution that improves the regeneration efficiency. The calculation of step S13 is the same as the calculation of step S12, except that the vehicle speed has no amplitude and is set to a fixed value. As a result of the calculation in step S13, the braking torque distribution for improving the regeneration efficiency is obtained when the vehicle speed is fixed.

If the calculation process a of step S12 and the calculation process B of step S13 are performed, the brake control unit 31 calculates how much the overall regeneration efficiency of the result of the calculation process a is improved over the overall regeneration efficiency of the result of the calculation process B, and determines whether or not the improvement amount of the regeneration efficiency is equal to or greater than a preset second threshold (step S14). If the determination result in step S14 is yes, the brake control unit 31 sets the result of the calculation process a to the target value to be controlled (step S15). On the other hand, if the determination result of step S14 is no, the brake control unit 31 sets the result of the calculation process B to the target value to be controlled (step S16).

That is, in steps S12 to S16, when the road gradient changes, if the overall regeneration efficiency is greatly improved, the constant speed downhill control of the first control process for allowing the vehicle speed to change and preferentially improving the regeneration efficiency is executed, whereas if the overall regeneration efficiency does not change greatly, the constant speed downhill control of the second control process for preferentially maintaining the vehicle speed is executed. The first control process and the second control process may be selected not only based on the amount of improvement in the regeneration efficiency, but also by a user such as a driver selecting the selection of only the first control process, only the second control process, or the amount of improvement in the regeneration efficiency based on the option setting performed using the setting operation unit 19.

If a new target value is set in step S15 or step S16, the brake control unit 31 returns to the loop processing of the constant speed downhill control again (steps S8 to S11). Then, by this loop processing, the regenerative control is performed by the brake control unit 31 so as to realize the vehicle speed and the brake torque distribution of the newly set target value.

In the loop processing of steps S8 to S11, if the downhill slope is finished or the constant speed downhill control is cancelled by the operation of the brake pedal 11 or the accelerator pedal 12, the constant speed downhill slope processing is finished through the processing of step S3.

Fig. 4 is an explanatory diagram illustrating an example of a transition of the running state of the electric vehicle 1 using the constant speed downhill function. Fig. 4 shows a driving example in which the electric vehicle 1 starts a downhill by activating the constant speed downhill function, and the road gradient changes in the middle of the downhill.

If the control process of prioritizing the regeneration efficiency is executed in the constant speed downhill process, the electrically powered vehicle 1 may be driven with the vehicle speed slightly deviating from the set speed V0 at the start of the downhill as shown in the downhill situation J1 of fig. 4. However, the vehicle speed is not fixed, and accordingly, the braking torque distribution that can further improve the regeneration efficiency can be calculated. When the road gradient changes, as shown in the downhill situation J2 in fig. 4, the electrically powered vehicle 1 may be driven with the vehicle speed slightly changing from the speed V1 before the gradient change. However, the vehicle speed is not fixed, and accordingly, the braking torque distribution that can further improve the regeneration efficiency can be calculated. Further, by improving the regeneration efficiency, the charging rate of the battery can be improved, and the cruising distance of the electric vehicle 1 can be extended.

As described above, the electric vehicle 1 and the brake control device thereof according to the present embodiment include: a gradient sensor 22; a first travel motor 3a capable of generating regenerative braking torque at the front wheels 2 a; a second travel motor 3b capable of generating regenerative braking torque at the rear wheel 2 b; a brake control unit 31 capable of controlling a regenerative operation; and a storage unit 32 that stores an efficiency map 33 of regenerative braking. When the constant speed downhill function is enabled, the brake control unit 31 calculates a braking torque distribution (a braking torque distribution by regenerative braking) of the front wheels 2a and the rear wheels 2b that improves the overall regenerative efficiency from the road gradient and the efficiency map, and controls regenerative braking based on the calculation result. Therefore, it is possible to improve the regeneration efficiency and extend the cruising distance of the electric vehicle 1 when the constant speed downhill function is executed.

In addition, according to the electrically powered vehicle 1 and the brake control device thereof of the present embodiment, in the constant speed downhill control that gives priority to the regenerative efficiency, the brake control unit 31 calculates the brake torque distribution with the parameter of the vehicle speed having a width (step S6). Therefore, the vehicle speed may be slightly deviated from the speed set for the constant speed downhill function, and the regenerative braking torque of the front wheels 2a and the rear wheels 2b can be distributed with high regenerative efficiency according to the deviation. This improves the regeneration efficiency when the constant speed downhill function is executed, and can extend the cruising distance of the electric vehicle 1.

Further, according to the electrically powered vehicle 1 and the brake control device thereof of the present embodiment, when the road gradient changes in the constant speed downhill function, the brake control unit 31 calculates the brake torque distribution with a magnitude at the current vehicle speed as a parameter of the vehicle speed (step S12). Therefore, when the road gradient changes during the constant speed downhill function, the vehicle speed may slightly change, and accordingly, the regenerative braking torque of the front wheels 2a and the rear wheels 2b with high regenerative efficiency can be distributed in accordance with the change in the road gradient. Thus, even when the road gradient changes in the constant speed downhill function, the regeneration efficiency can be improved, and the cruising distance of the electric vehicle 1 can be extended.

Further, according to the electrically powered vehicle 1 and the brake control device thereof of the present embodiment, when the road gradient changes in the constant speed downhill function, the first control process (steps S12, S15, S8) that allows the vehicle speed to change and the second control process (steps S13, S16, S8) that maintains the vehicle speed constant are selectively executed. Therefore, the constant speed downhill function can be realized that is suitable for a situation where the vehicle speed is kept constant and a situation where the regeneration efficiency is improved by allowing a slight change in the vehicle speed.

Further, according to the electrically powered vehicle 1 and the brake control device thereof of the present embodiment, when the road gradient changes in the constant speed downhill function, the brake control unit 31 calculates how much the regenerative efficiency of the first control process that allows the vehicle speed to change is improved over the regenerative efficiency of the second control process that maintains the vehicle speed constant. Then, the brake control unit 31 determines whether or not the increase amount of the regenerative efficiency is equal to or greater than a second threshold (step S14), and executes the first control process when the increase amount of the regenerative efficiency is equal to or greater than the second threshold (steps S15 and S8). On the other hand, when the increase amount of the regenerative efficiency is smaller than the second threshold value, the brake control unit 31 executes the second control process (steps S16, S8). Therefore, if the regeneration efficiency changes greatly, the speed change in the constant speed downhill function is permitted, and the regeneration efficiency can be preferentially improved, while if the regeneration efficiency does not change greatly, the vehicle speed can be preferentially maintained.

Further, according to the electrically powered vehicle 1 and the brake control device thereof of the present embodiment, the user can select the control process when the road gradient is changed in the constant speed downhill function, based on the option setting by the setting operation unit 19. Therefore, it is possible to select a control process corresponding to a request from the user with respect to a change in the road gradient in the constant speed downhill function.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. For example, in the above-described embodiment, an example is shown in which the braking torque distribution for improving the regeneration efficiency is obtained by setting the parameter of the vehicle speed to a wide range at the start of constant speed downhill control and at the time of a change in the road gradient. However, the timing at which the braking torque distribution for improving the regenerative efficiency is obtained by setting the parameter of the vehicle speed to a wide range may be various timings such as only the timing when the constant speed downhill control is started, only the road gradient changes, or timings corresponding to other situations in the constant speed downhill control. In addition, the details shown in the embodiments, such as the magnitude of the variation range of the parameter given to the vehicle speed when calculating the braking torque distribution, can be appropriately changed within a range not exceeding the gist of the invention.