Braking control method and braking control device

Abstract

In an electric parking brake (80) comprising a first actuator which actuates a first brake of at least one of a left front wheel (11) and a left rear wheel (12) of a vehicle (1) at a first braking force and a second actuator which actuates a second brake of at least one of a right front wheel (21) and a right rear wheel (22) of the vehicle (1) at a second braking force. When the vehicle (1) is to be parked and it is determined that the inclination of the vehicle (1) is less than a predetermined value, the first actuator and the second actuator are controlled such that one of the first braking force and the second braking force is smaller than the other one thereof, thereby suppressing a decrease in life of the actuators that actuate the brakes.

Description

Braking control method and braking control device

[0001] The present invention relates to a braking control method and a braking control device.

[0002] When the parking brake switch is operated, an electric parking brake pulls the left and right brake cables with equal force, activates the left and right rear wheel brakes, detects the inclination of the vehicle body, and increases the braking force of the brakes as the inclination increases.One electric parking brake known in the art stores the number of times the brakes have been activated for each braking force and determines the life of the brake cables based on the stored braking force and number of activations (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2007-253790

[0004] In the above-described conventional technology, when parking a vehicle, the brakes on the right and left wheels are activated with the same braking force regardless of the vehicle's inclination, which means that when the vehicle is only slightly inclined, the brakes are activated with more braking force than necessary, resulting in a problem of shortening the life of the actuator that activates the brakes.

[0005] The problem to be solved by the present invention is to provide a braking control method and a braking control device that can prevent the life of an actuator that operates the brake from being shortened.

[0006] The present invention solves the above problem in an electric parking brake that includes a first actuator that activates a first brake on at least one of the left front wheel and left rear wheel of a vehicle with a first braking force, and a second actuator that activates a second brake on at least one of the right front wheel and right rear wheel with a second braking force, by controlling the first actuator and the second actuator so that one of the first braking force and the second braking force is smaller than the other when it is determined that the inclination of the vehicle is smaller than a predetermined value when the vehicle is parking.

[0007] According to the present invention, it is possible to prevent the life of the actuator that operates the brake from being shortened.

[0008] 1 is a plan view showing an embodiment of a vehicle equipped with an electric parking brake according to the present invention. FIG. 2 is a plan view showing an example of a brake provided on the left rear wheel of the vehicle of FIG. 1. FIG. 3 is a block diagram showing an embodiment of the electric parking brake according to the present invention. FIG. 4 is a side view showing an example of inclination of the vehicle of FIG. 1. FIG. 5 is a front view showing another example of inclination of the vehicle of FIG. 1. FIG. 6 is an example of a map showing the relationship between brake fluid pressure and vehicle deceleration in this embodiment. FIG. 7 is a flowchart showing an example of a processing procedure in the electric parking brake of FIG. 3. FIG. 8 is a flowchart showing another example of a processing procedure in the electric parking brake of FIG. 3. FIG. 9 is a flowchart showing an example of a subroutine of step S11 of FIG. 8. FIG. 10 is a flowchart showing another example of the subroutine of step S11 of FIG. 8. FIG. 11 is a flowchart showing yet another example of the subroutine of step S11 of FIG. 8. FIG. 12 is a flowchart showing yet another example of the subroutine of step S11 of FIG. 8.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [Configuration of Electric Parking Brake] FIG. 1 is a plan view showing one embodiment of a vehicle equipped with an electric parking brake (electric parking brake) according to the present invention. The electric parking brake is a device that uses an electric actuator such as a motor to stop the movement of the vehicle (specifically, the rotation of the wheels, propeller shaft, etc.) and park the vehicle. The vehicle is not particularly limited, and includes vehicles of any drive system. As shown in FIG. 1 , the vehicle 1 includes a left front wheel 11, a left rear wheel 12, a right front wheel 21, a right rear wheel 22, actuators 31, 32, 41, 42, a brake control device 50, an acceleration sensor 61, a temperature sensor 62, and a parking switch 81. Note that, unless otherwise specified, wheel rotation refers to rotation in the circumferential direction of the wheel.

[0011] The left front wheel 11, the left rear wheel 12, the right front wheel 21, and the right rear wheel 22 are wheels attached to a suspension (not shown) of the vehicle 1 via hubs, and a brake that prevents rotation in the circumferential direction is provided for each of the left front wheel 11, the left rear wheel 12, the right front wheel 21, and the right rear wheel 22. In this embodiment, the brake that prevents rotation of the left front wheel 11 and the left rear wheel 12 of the vehicle 1 is referred to as a first brake, and the brake that prevents rotation of the right front wheel 21 and the right rear wheel 22 is referred to as a second brake.

[0012] When the brakes are activated, a force in the opposite direction to the direction of travel is generated between each wheel and the ground (or road surface) on which the vehicle 1 is in contact in order to stop the rotation of the wheels. This force is called braking force, and is calculated, for example, by dividing the braking torque around the vehicle axle by the radius of the tire. In this embodiment, the braking force of the first brake is called the first braking force, and the braking force of the second brake is called the second braking force.

[0013] The actuators 31, 32, 41, and 42 are mechanical elements, such as motors or electromagnetic solenoids, that activate brakes to stop the rotation of the left front wheel 11, the left rear wheel 12, the right front wheel 21, and the right rear wheel 22, respectively. The actuators 31, 32, 41, and 42 activate or stop the brakes in accordance with control signals output from the braking control device 50. The actuators 31, 32, 41, and 42 can be disposed in appropriate positions within a range in which the brakes can be activated. In this embodiment, the actuators 31 and 32 that activate the first brake are referred to as first actuators, and the actuators 41 and 42 that activate the second brake are referred to as second actuators.

[0014] The electric parking brake includes a first actuator that operates a first brake on at least one of the left front wheel 11 and the left rear wheel 12 of the vehicle 1 with a first braking force, and a second actuator that operates a second brake on at least one of the right front wheel 21 and the right rear wheel 22 with a second braking force. The brake control device 50 can control the first actuator and the second actuator independently. Note that, although the vehicle 1 shown in FIG. 1 is provided with electric parking brake actuators on all wheels, it is not necessary to provide actuators on all wheels. For example, actuators 31, 41 may be provided only on the left front wheel 11 and the right front wheel 21, and actuators 32, 42 may be provided only on the left rear wheel 12 and the right rear wheel 22.

[0015] The braking control device 50 is a device for controlling and cooperating with devices that constitute an electric parking brake to stop the movement of the vehicle 1. The braking control device 50 is, for example, a computer, and includes a CPU (Central Processing Unit) that is a processor, a ROM (Read Only Memory) that stores programs, and a RAM (Random Access Memory) that functions as an accessible storage device. The CPU is an operating circuit that executes the programs stored in the ROM and realizes the functions of the braking control device 50.

[0016] The acceleration sensor 61 is a device that detects acceleration applied to the vehicle 1, and any known acceleration sensor, such as a capacitance type, can be used without any particular limitation. The acceleration sensor 61 detects the direction of gravity (vertical direction), the front-rear direction, left-right direction, and up-down direction of the vehicle, as well as the amount of movement, speed, and direction of movement of the vehicle 1. On the other hand, the temperature sensor 62 is a device that detects the outside air temperature of the vehicle 1, and any known temperature sensor can be used without any particular limitation. The acceleration sensor 61 and the temperature sensor 62 can be placed in appropriate positions within ranges that allow appropriate detection of acceleration and outside air temperature, respectively. The acceleration sensor 61 corresponds to the detection means for detecting the inclination of the vehicle 1 according to the present invention.

[0017] The parking switch 81 is a switch that is operated to activate the electric parking brake, and is provided around the driver's seat of the vehicle 1. The parking switch 81 is, for example, a switch disposed on the instrument panel, a pedal disposed on the left side of the driver's feet, or a button disposed on the center console.

[0018] Next, the configuration of the brakes for each wheel will be described with reference to Figure 2. Figure 2 is a plan view showing an example of a brake provided on the left rear wheel 12 of the vehicle 1. As shown in Figure 2, the brake 70 includes a disc rotor 71, a brake caliper 72, brake pads 73 and 74, a piston 75, a cylinder 76, a pressure sensor 77, and a speed sensor 78. In the vehicle 1 shown in Figure 1, the left front wheel 11, the right front wheel 21, and the right rear wheel 22 are also provided with brakes similar to the brake 70 shown in Figure 2.

[0019] The disc rotor 71 has a hub 71a to which the left rear wheel 12 is attached, and rotates together with the left rear wheel 12 in the circumferential direction of the left rear wheel 12 around an axle (not shown). A brake caliper 72 that stops the rotation of the disc rotor 71 is provided on the vehicle front side of the disc rotor 71. The brake caliper 72 includes a pair of brake pads 73, 74, a piston 75, and a cylinder 76. The pair of brake pads 73, 74 are arranged facing each other on both sides of the disc rotor 71, sandwiching the disc rotor 71 therebetween. A small gap (e.g., 0.1 mm or less) is provided between the disc rotor 71 and the brake pads 73, 74. The cylinder 76 is provided inside the brake caliper 72 and contains the piston 75 and brake fluid.

[0020] The pressure sensor 77 is a device that detects the pressure (hydraulic pressure) of the brake fluid contained in the cylinder 76, and any known pressure sensor can be used without particular limitation. On the other hand, the speed sensor 78 is a device that detects the rotational speed of the disc rotor 71, and any known speed sensor can be used without particular limitation. The pressure sensor 77 and the speed sensor 78 can be disposed at appropriate positions within ranges that allow appropriate detection of the pressure and rotational speed, respectively.

[0021] When a control signal to operate the brake 70 is input from the brake control device 50, the actuator 32 pushes the piston 75 toward the left side of the vehicle. This pushing of the piston 75 pressurizes the brake fluid in the cylinder 76, applying a force toward the left side of the vehicle to the brake pad 74. The brake pad 74, to which force is applied from the brake fluid, moves toward the left side of the vehicle and, together with the brake pad 73 held by the brake caliper 72, presses against the disc rotor 71, thereby preventing the disc rotor 71 from rotating.

[0022] In response to this, when a control signal to stop the brakes 70 is input from the brake control device 50, the actuator 32 returns the piston 75 to the right side of the vehicle, releasing the brake fluid pressure. As the brake fluid pressure is released, the brake pads 74 move to the right side of the vehicle and return to their original positions. Then, the brake pads 73 and 74 separate from the disc rotor 71, allowing the disc rotor 71 to rotate freely.

[0023] [Function of Brake Control Device] Figure 3 is a block diagram showing one embodiment of an electric parking brake according to the present invention. As shown in Figure 3, an electric parking brake 80 includes a parking switch 81, an acceleration sensor 61, a temperature sensor 62, a pressure sensor 77, a speed sensor 78, a brake control device 50, first actuators 31 and 32, and second actuators 41 and 42. These devices are connected by a CAN (Controller Area Network) or other in-vehicle LAN, and can exchange information with each other.

[0024] The braking control device 50 has a braking function that stops the movement of the vehicle 1. A program for realizing the braking function is stored in the ROM of the braking control device 50, and the braking function is realized by the CPU executing the program stored in the ROM. For convenience, Fig. 3 shows the determination unit 51, the control unit 52, and the storage unit 53 as functional blocks that realize the braking function. The functions of each functional block will be described below with reference to Fig. 3.

[0025] The determination unit 51 has a function of determining whether or not the inclination of the vehicle 1 is less than a predetermined value. When the driver or the like operates the parking switch 81 of the vehicle 1, an operation command to operate the electric parking brake 80 is output to the braking control device 50. The braking control device 50 determines whether or not the parking switch 81 has been operated using the function of the determination unit 51, and if an operation command is acquired, it determines that the parking switch 81 has been operated. On the other hand, if an operation command is not acquired, it determines that the parking switch 81 has not been operated.

[0026] The brake control device 50 may also estimate whether the driving scene of the vehicle 1 is a parking scene. For example, the current position of the vehicle 1 is acquired from a positioning system (not shown), and based on map information and the information on the current position of the vehicle 1, it determines whether the vehicle 1 is driving in a parking lot. If it is determined that the vehicle 1 is driving in a parking lot, it estimates that the driving scene of the vehicle 1 is a parking scene. On the other hand, if it is determined that the vehicle 1 is driving on a normal road, it estimates that the driving scene of the vehicle 1 is not a parking scene.

[0027] For example, when the braking control device 50 estimates that the driving scene of the vehicle 1 is a parking scene and / or receives an activation instruction from the parking switch 81, it determines that the vehicle 1 is parking, and uses the function of the determination unit 51 to acquire the inclination of the vehicle 1 from the acceleration sensor 61, which is a detection means for detecting the inclination of the vehicle 1. The acceleration sensor 61 detects the direction of gravity and the fore-and-aft direction of the vehicle, and calculates the inclination of the vehicle 1 from the angle formed between the direction of gravity and the fore-and-aft direction of the vehicle. Alternatively, the braking control device 50 may acquire the direction of gravity and the fore-and-aft direction of the vehicle from the acceleration sensor 61, which is a detection means for detecting the inclination of the vehicle 1, and calculate the inclination of the vehicle 1 from the two acquired directions.

[0028] Fig. 4 is a side view showing an example of the inclination of the vehicle 1. In the example shown in Fig. 4, the ground 91 on which the vehicle 1 is in contact is inclined in the fore-and-aft direction of the vehicle 1, and the vehicle 1 is parked in a state in which the rear side is lower than the front side (in a state in which the vehicle is tilted backward). In this case, the brake control device 50 acquires the direction of gravity (arrow G) and the fore-and-aft direction of the vehicle (arrow H) from the acceleration sensor 61, and calculates the angle b, which is the inclination of the vehicle 1 (or the ground 91) with respect to a horizontal plane 92, by subtracting 90 from the minor angle a formed by the arrows G and H.

[0029] Furthermore, the brake control device 50 may acquire or calculate the tilt of the vehicle 1 in the left-right direction in addition to the tilt of the vehicle 1 in the front-rear direction. For example, as shown in Fig. 5 , when the ground 93 on which the vehicle 1 is in contact is tilted in the left-right direction of the vehicle 1 and the vehicle 1 is parked in a state where the left side is lower than the right side (a state where the vehicle is tilted to the left), the brake control device 50 acquires the direction of gravity (arrow G) and the left-right direction of the vehicle (arrow I) from the acceleration sensor 61, which is a detection means for detecting the tilt of the vehicle 1, and calculates the angle d, which is the tilt of the vehicle 1 (or the ground 93) with respect to the horizontal plane 94, by subtracting 90 from the minor angle c formed by the arrows G and I. Note that the ground includes the road surface.

[0030] The braking control device 50 then determines whether the tilt acquired from the acceleration sensor 61, which is a means for detecting the tilt of the vehicle 1, is less than a predetermined value. The predetermined value can be set, for example, to an appropriate value within a range in which the movement of the vehicle 1 can be appropriately stopped by either the first brake on the left side of the vehicle or the second brake on the right side of the vehicle, such as 10° to 30°. If the braking control device 50 determines that the acquired tilt is less than the predetermined value, it executes a first control that controls the first actuator and the second actuator so that one of the first braking force and the second braking force is smaller than the other in order to prevent a shortening of the actuator's lifespan. On the other hand, if the braking control device 50 determines that the acquired tilt is equal to or greater than the predetermined value, it executes a second control that operates the first actuator and the second actuator and sets the first braking force and the second braking force so that the difference between the first braking force and the second braking force is less than the predetermined braking force in order to appropriately stop the movement of the vehicle 1. Note that the second control is also referred to as parking control.

[0031] Returning to FIG. 3 , the control unit 52 has a function of executing the first control or the second control when it is determined that the tilt of the vehicle 1 is less than a predetermined value. As an example of the first control, the braking control device 50 stops one of the first actuator and the second actuator. Stopping the first (second) actuator means that the actuator is not operated any further when a control signal to stop the actuator is input. In other words, the actuator is not operated when the brake is not applied, and when the brake is applied, the actuator is controlled so that the brake pads do not press against the disc rotor. As another example of the first control, when the first brake and the second brake are not applied, the braking control device 50 operates only one of the first actuator and the second actuator. Operating only one of the first actuator and the second actuator can further reduce the load on the actuator.

[0032] On the other hand, as an example of the second control, the brake control device 50 sets one of the first braking force or the second braking force set in the first control as the braking force of the first brake and the second brake. As another example of the second control, the brake control device 50 sets a braking force of a predetermined percentage (e.g., 60% to 90%) of the maximum braking force of the first brake and the second brake as the braking force of the first brake and the second brake. As yet another example of the second control, the brake control device 50 sets the first braking force and the second braking force to the same value.

[0033] In the first control, the brake control device 50 may set the first braking force and the second braking force so that the difference between the first braking force and the second braking force is equal to or greater than a predetermined braking force. Alternatively, in the first control, the brake control device 50 may set the first braking force and the second braking force so that the difference between the first braking force and the second braking force is equal to or greater than the predetermined braking force, and in the second control, the brake control device 50 may set the first braking force and the second braking force so that the difference between the first braking force and the second braking force is less than the predetermined braking force. The predetermined braking force can be set to an appropriate value within a range in which the load on the actuator can be suppressed, and is, for example, a braking force that is a predetermined percentage (e.g., 60% to 90%) of the maximum braking force of the first brake and the second brake.

[0034] For example, in the example shown in FIG. 4 , if it is determined that angle b, which indicates the inclination of the vehicle 1, is less than a predetermined value, the brake control device 50 executes the first control using the function of the control unit 52. Specifically, only the actuator 32 is activated to stop the rotation of the left rear wheel 12. The first braking force is set to an appropriate value within a range in which the vehicle 1 does not move on the ground surface 91. On the other hand, if it is determined that angle b, which indicates the inclination of the vehicle 1, is equal to or greater than a predetermined value, the brake control device 50 executes the second control using the function of the control unit 52. Specifically, the actuators 32 and 42 are activated to stop the rotation of the left rear wheel 12 and the right rear wheel 22. The braking forces of the first brake and the second brake are set to appropriate values ​​within a range in which the vehicle 1 does not move on the ground surface 91.

[0035] The memory unit 53 has a function of storing the first braking force and the second braking force in correspondence with each other. When at least one of the first actuator and the second actuator is activated, the brake control device 50 uses the function of the memory unit 53 to store the first braking force and the second braking force set when the actuator was activated in correspondence with each other in a ROM or the like. Thereafter, when the actuator is stopped and at least one of the first actuator and the second actuator is newly activated, if it is determined that the inclination of the vehicle 1 is less than a predetermined value, the function of the control unit 52 acquires the previous first braking force and second braking force set when at least one of the first actuator and the second actuator was last activated. Then, the brake control device 50 sets the current first braking force and second braking force based on the acquired previous first braking force and second braking force.

[0036] Specifically, if the previous first braking force is larger than the previous second braking force, the current first braking force is set smaller than the current second braking force, and if the previous first braking force is smaller than the previous second braking force, the current first braking force is set larger than the current second braking force. Also, if the previous first braking force and the second braking force are the same value, the first braking force and the second braking force set the last time the first control was executed are obtained, and the current first braking force and the second braking force are set based on the obtained first braking force and second braking force.

[0037] The braking control device 50 may determine whether the vehicle 1 is loaded on a transporter that transports the vehicle 1, and may execute the second control if it is determined that the vehicle 1 is loaded on a transporter. For example, if it is detected from the tilt and acceleration of the vehicle 1 acquired from the acceleration sensor 61 that lateral acceleration has been applied to the vehicle 1 that is tilted in the forward / backward direction, it determines that the vehicle 1 is loaded on a transporter, and executes the second control. On the other hand, if it is determined that the vehicle 1 is not loaded on a transporter, it does not execute the second control. Examples of transporters include a vehicle transporter and a tow truck.

[0038] The brake control device 50 may determine, by the function of the determination unit 51, whether or not the vehicle 1 is in a state in which at least one of the first braking force and the second braking force is reduced (hereinafter also referred to as a reduced braking force state). If it is determined that the vehicle 1 is in a reduced braking force state, the brake control device 50 may execute a second control by the function of the control unit 52 in order to appropriately stop the movement of the vehicle 1. The reduced braking force state refers to a state in which the original braking force corresponding to the operation of the actuator cannot be obtained due to the driving environment around the vehicle 1, the state of the brake 70, the state of the ground (or road surface), etc.

[0039] As an example, the braking control device 50 estimates the temperatures of the brake pads of the first and second brakes, determines whether the estimated temperatures are equal to or higher than the fade temperature, and executes the second control if it determines that the estimated temperatures are equal to or higher than the fade temperature. On the other hand, if it determines that the estimated brake pad temperatures are lower than the fade temperature, it does not execute the second control. The fade temperature is the temperature at which the coefficient of friction of the brake pads begins to decrease, and is, for example, 250°C to 350°C.

[0040] The braking control device 50 estimates the temperature of the brake pads based on the deceleration of the vehicle 1 when the brakes are applied and the duration of the brake application. For example, the relationship between the deceleration of the vehicle 1, the duration of the brake application, and the temperature rise of the brake pads is calculated in advance. The relationship between the heat dissipation time when the brakes are not applied and the temperature drop of the brake pads is also calculated in advance. The brake control device 50 then calculates the temperature change amount, which indicates how much the temperature of the brake pads has risen or fallen from time T1 to time T2, a predetermined time after time T1. The temperature of the brake pads at time T2 is estimated by adding the calculated temperature change amount to the temperature of the brake pads at time T1.

[0041] The predetermined time period is, for example, a time period corresponding to the calculation capacity of the CPU of the brake control device 50. The brake control device 50 monitors the temperature of the brake pads by repeatedly estimating the temperature of the brake pads at predetermined time intervals. The initial temperature of the brakes is, for example, the outside air temperature around the vehicle 1 obtained from the temperature sensor 62, and when a new estimation of the brake pad temperature is started, the initial temperature may be the most recently estimated temperature of the brake pads.

[0042] As another example, the braking control device 50 acquires the brake fluid pressures (hereinafter also referred to as actual pressures) of the first brake and the second brake when at least one of the first brake and the second brake is activated, and the deceleration of the vehicle 1 (hereinafter also referred to as actual deceleration). Furthermore, the braking control device 50 acquires the deceleration corresponding to the brake fluid pressure when the brakes are activated (hereinafter also referred to as deceleration corresponding to the pressure) from a preset relationship between the brake fluid pressure and the deceleration of the vehicle 1. Then, the braking control device 50 determines whether the actual deceleration is lower than the deceleration corresponding to the pressure by at least a predetermined deceleration, and if it is determined that the actual deceleration is lower than the deceleration corresponding to the pressure by at least the predetermined deceleration, it executes the second control. In other words, if the difference between the actual deceleration and the deceleration corresponding to the pressure is greater than the predetermined deceleration, it executes the second control. On the other hand, if it is determined that the actual deceleration is lower than the deceleration corresponding to the pressure by less than the predetermined deceleration, it does not execute the second control.

[0043] The relationship between the brake fluid pressure and the deceleration of the vehicle 1 is pre-recorded in the ROM of the brake control device 50, for example, as a map showing the relationship between the brake fluid pressure and the deceleration of the vehicle 1. The predetermined deceleration is, for example, a deceleration at which the second control needs to stop the movement of the vehicle 1, and specifically, is 60% to 80% of the deceleration corresponding to the pressure in the initial state (shipment state). In other words, when the actual deceleration obtained from the acceleration sensor 61 is 20% to 40% of the initial value of the deceleration corresponding to the pressure, the second control is executed.

[0044] Fig. 6 is an example of a map showing the relationship between brake fluid pressure and vehicle deceleration. The horizontal axis of the map shown in Fig. 6 represents pressure, and the vertical axis represents deceleration of the vehicle 1. The map sets at least the relationship between brake fluid pressure and vehicle deceleration in the initial state (shipment state), and a threshold value that separates an area where parking control (second control) is executed from an area where parking control is not executed. In the map shown in Fig. 6, the area to the lower right of the line indicating the threshold value is the area where second control is executed, and the area to the upper left of the line indicating the threshold value is the area where second control is not executed.

[0045] For example, assume that when at least one of the first brake and the second brake is activated, the actual pressure obtained from the pressure sensor 77 is P1 and the actual deceleration obtained from the acceleration sensor 61 is A1. In this case, the deceleration (initial value) on the map corresponding to the pressure P1 is A2, and the difference between the actual deceleration A1 and the deceleration A2 on the map corresponding to the pressure P1 is d1. The predetermined deceleration corresponds to the difference d2 between the deceleration A2 on the map corresponding to the pressure P1 and the deceleration A3 corresponding to the intersection of the pressure P1 and the threshold value. Because the difference d1 is smaller than the difference d2, in the case shown in FIG. 6 , the brake control device 50 determines that the difference between the actual deceleration and the deceleration corresponding to the pressure is less than the predetermined deceleration and does not execute the second control.

[0046] Furthermore, for example, while executing the first control, the brake control device 50 may obtain the outside air temperature of the vehicle 1 from the temperature sensor 62, determine whether the outside air temperature is equal to or lower than a predetermined temperature, and execute the second control if it is determined that the outside air temperature is equal to or lower than the predetermined temperature. The predetermined temperature is, for example, a temperature at which the operating efficiency of the actuator begins to decrease due to low temperatures, specifically, a temperature between −40° C. and −10° C. Furthermore, for example, while executing the first control, the brake control device 50 may obtain the operating status of the wipers of the vehicle 1, determine whether the wipers are operating, and execute the second control if it is determined that the wipers are operating.

[0047] For example, while executing the first control, the brake control device 50 may obtain the acceleration of the vehicle 1 from the acceleration sensor 61, determine whether the acceleration of the vehicle 1 is equal to or greater than a predetermined acceleration, and if it is determined that the acceleration is equal to or greater than the predetermined acceleration, execute the second control. The predetermined acceleration can be set to an appropriate value within a range in which it is possible to detect contact of an object with the vehicle 1, and may be, for example, 0.5 G to 2.0 G. Furthermore, while executing the first control, the brake control device 50 may determine whether the inclination of the vehicle 1 is equal to or greater than a predetermined value, and if it is determined that the inclination of the vehicle 1 is equal to or greater than the predetermined value, execute the second control.

[0048] When at least one of the first brake and the second brake is activated, the braking control device 50 obtains the rotational speeds of the left front wheel 11, left rear wheel 12, right front wheel 21, and right rear wheel 22 from the speed sensor 78 and determines whether at least one of these wheels is rotating. If it is determined that at least one of the left front wheel 11, left rear wheel 12, right front wheel 21, and right rear wheel 22 is rotating, the braking control device 50 executes the second control. On the other hand, if it is determined that none of the wheels are rotating, the braking control device 50 does not execute the second control.

[0049] The braking control device 50 may determine whether the first control is being executed, and if it is determined that the first control is being executed, determine whether the vehicle 1 is in a state of reduced braking force. Alternatively, the braking control device 50 may determine whether the brakes of the vehicle 1 are operating, and if it is determined that the brakes of the vehicle 1 are not operating, determine whether the vehicle 1 is in a state of reduced braking force.

[0050] [Information Processing in Electric Parking Brake] The procedure for information processing by the brake control device 50 will be described with reference to Figures 7 to 15. Figure 7 is an example of a flowchart showing information processing executed in the electric parking brake 80 of this embodiment. The processing described below is executed by a processor (CPU) included in the brake control device 50.

[0051] First, in step S1, the function of the determination unit 51 determines whether or not the parking switch 81 has been operated. If it is determined that the parking switch 81 has not been operated, step S1 is repeated. On the other hand, if it is determined that the parking switch 81 has been operated, the process proceeds to step S2. In step S2, the inclination of the vehicle 1 is acquired from the acceleration sensor 61, and in the subsequent step S3, it is determined whether or not the inclination of the vehicle 1 is less than a predetermined value. If it is determined that the inclination of the vehicle 1 is equal to or greater than the predetermined value, the process proceeds to step S8, where the second control (parking control) is executed by the function of the control unit 52. On the other hand, if it is determined that the inclination of the vehicle 1 is less than the predetermined value, the process proceeds to step S4.

[0052] In step S4, the stored first and second braking forces of the previous braking force are obtained from a storage medium (not shown), and in the subsequent step S5, the current first and second braking forces are set based on the obtained previous first and second braking forces. In the subsequent step S6, the actuator is operated to execute the first control using the set first and second braking forces. After the first control is executed, in step S7, the current first and second braking forces are stored in the storage medium by the function of the storage unit 53.

[0053] 8 is another example of a flowchart showing information processing executed in the electric parking brake 80 of this embodiment. The processing described below is executed by the processor (CPU) included in the brake control device 50 when the vehicle 1 is stopped but the electric parking brake 80 is not activated or when the first control is being executed.

[0054] First, in step S11, the state of the vehicle is detected, and in the following step S12, it is determined whether the state of the vehicle is such that the second control should be executed or continued. If it is determined that the state of the vehicle is such that the second control should be executed or continued, the process proceeds to step S13, where the second control (parking control) is executed or continued. On the other hand, if it is determined that the state of the vehicle is not such that the second control should be executed or continued, the process proceeds to step S14, where the first control is executed or continued, and then the process proceeds to step S11.

[0055] 9 is a flowchart showing an example of a subroutine of step S11 in FIG. 8. First, in step S21, the temperature of the brake pad is estimated, and then in step S22, it is determined whether the temperature of the brake pad is equal to or higher than the fade temperature. If it is determined that the temperature of the brake pad is equal to or higher than the fade temperature, the process proceeds to step S23, where it is determined that the second control (parking control) is in a state to be executed or continued. On the other hand, if it is determined that the temperature of the brake pad is below the fade temperature, the process proceeds to step S24, where it is determined that the second control (parking control) is not in a state to be executed or continued. Then, the process proceeds to step S12. Note that, hereinafter, redundant descriptions of steps S23 and S24 will be omitted.

[0056] 10 is a flowchart showing another example of the subroutine of step S11 in FIG. 8. First, in step S31, the actual pressure of the brake fluid during braking and the actual deceleration of the vehicle 1 are obtained, and then in step S32, the deceleration (initial value) on the map corresponding to the actual pressure is obtained from the map. In step S33, it is determined whether the actual deceleration is lower than the deceleration on the map corresponding to the actual deceleration by at least a predetermined deceleration. If it is determined that the actual deceleration is lower than the deceleration on the map corresponding to the actual deceleration by at least the predetermined deceleration, the process proceeds to step S23. If it is determined that the actual deceleration is lower than the deceleration on the map corresponding to the actual deceleration by less than the predetermined deceleration, the process proceeds to step S24.

[0057] Fig. 11 is a flowchart showing another example of the subroutine of step S11 in Fig. 8. First, in step S41, the outside air temperature of the vehicle 1 is obtained from the temperature sensor 62, and then in step S42, it is determined whether the outside air temperature is equal to or lower than a predetermined temperature. If it is determined that the outside air temperature is equal to or lower than the predetermined temperature, the process proceeds to step S23, and if it is determined that the outside air temperature is higher than the predetermined temperature, the process proceeds to step S24.

[0058] Fig. 12 is a flowchart showing yet another example of the subroutine of step S11 in Fig. 8. First, in step S51, the operation status of the wipers is acquired, and then in step S52, it is determined whether the wipers are operating. If it is determined that the wipers are operating, the process proceeds to step S23, and if it is determined that the wipers are not operating, the process proceeds to step S24.

[0059] Fig. 13 is a flowchart showing yet another example of the subroutine of step S11 in Fig. 8. First, in step S61, the acceleration of the vehicle 1 is obtained from the acceleration sensor 61, and then in step S62, it is determined whether the acceleration is equal to or greater than a predetermined acceleration. If it is determined that the acceleration is equal to or greater than the predetermined acceleration, the process proceeds to step S23, and if it is determined that the acceleration is less than the predetermined acceleration, the process proceeds to step S24.

[0060] Fig. 14 is a flowchart showing yet another example of the subroutine of step S11 in Fig. 8. First, in step S71, the tilt of the vehicle 1 is obtained from the acceleration sensor 61, and then in step S72, it is determined whether the tilt of the vehicle 1 is equal to or greater than a predetermined value. If it is determined that the tilt of the vehicle 1 is equal to or greater than the predetermined value, the process proceeds to step S23, and if it is determined that the tilt of the vehicle 1 is less than the predetermined value, the process proceeds to step S24.

[0061] Fig. 15 is a flowchart showing yet another example of the subroutine of step S11 in Fig. 8. First, in step S81, when the brake is applied, the rotation speed of the wheels of the vehicle 1 is acquired, and in step S82, it is determined whether any of the wheels are rotating. If it is determined that any of the wheels are rotating, the process proceeds to step S23, and if it is determined that none of the wheels are rotating, the process proceeds to step S24.

[0062]

[0023] As described above, according to this embodiment, a braking control method for parking a vehicle (1) is performed by a braking control device (50) of an electric parking brake (80) including a first actuator that activates a first brake on at least one of a left front wheel (11) and a left rear wheel (12) of the vehicle (1) with a first braking force, and a second actuator that activates a second brake on at least one of a right front wheel (21) and a right rear wheel (22) of the vehicle (1) with a second braking force. The braking control method includes: the vehicle (1) having a detection means for detecting an inclination of the vehicle (1); when the vehicle (1) is parking, the braking control device (50) determines whether the inclination detected by the detection means is less than a predetermined value; and, if it determines that the inclination is less than the predetermined value, controls the first actuator and the second actuator so that one of the first braking force and the second braking force is smaller than the other. This prevents a shortened life of the actuators that activate the brakes.

[0063] Furthermore, according to the braking control method of this embodiment, when the braking control device 50 determines that the slope is less than the predetermined value, it stops one of the first actuator and the second actuator, thereby further preventing the life of the actuator that operates the brake from being shortened.

[0064] Furthermore, according to the braking control method of this embodiment, when at least one of the first actuator and the second actuator is activated, the braking control device 50 stores the set first braking force and the set second braking force in correspondence with each other, and when it determines that the slope is less than the predetermined value, it obtains the previous first braking force and the previous second braking force that were set the last time at least one of the first actuator and the second actuator was activated, and if the previous first braking force is greater than the previous second braking force, it sets the first braking force to be smaller than the second braking force, and if the previous first braking force is smaller than the previous second braking force, it sets the first braking force to be greater than the second braking force. This makes it possible to prevent one of the first actuator and the second actuator from being activated too many times.

[0065] Furthermore, according to the braking control method of this embodiment, the braking control device 50 determines whether the vehicle 1 is loaded on a transporter that transports the vehicle 1, and if it determines that the vehicle 1 is loaded on the transporter, activates the first actuator and the second actuator, and sets the first braking force and the second braking force so that the difference between the first braking force and the second braking force is equal to or less than a predetermined braking force. This makes it possible to prevent the vehicle 1 loaded on the transporter from moving on the transporter.

[0066] Furthermore, according to the braking control method of this embodiment, the braking control device 50 determines whether the vehicle 1 is in a state in which at least one of the first braking force and the second braking force is reduced, and if it determines that the vehicle 1 is in the state in which at least one of the first braking force and the second braking force is reduced, executes parking control to operate the first actuator and the second actuator and set the first braking force and the second braking force so that the difference between the first braking force and the second braking force is less than a predetermined braking force. This makes it possible to appropriately restrain the movement of the vehicle 1 when the movement of the vehicle 1 cannot be appropriately restrained by the first control.

[0067] According to the braking control method of this embodiment, the braking control device 50 estimates the temperatures of the brake pads of the first brake and the second brake, determines whether the estimated temperatures are equal to or higher than the fade temperature, and executes the parking control if it determines that the estimated temperatures are equal to or higher than the fade temperature. This allows the vehicle 1 to be appropriately prevented from moving even when the temperature of the brake pad is relatively high.

[0068] According to the braking control method of this embodiment, the braking control device 50 acquires the brake fluid pressures of the first brake and the second brake when at least one of the first brake and the second brake is activated, and the deceleration of the vehicle 1, acquires the deceleration corresponding to the pressure from a preset relationship between the pressure and the deceleration, determines whether the actual deceleration is lower than the deceleration corresponding to the pressure by at least a predetermined deceleration, and executes the parking control if it determines that the actual deceleration is lower than the deceleration corresponding to the pressure by at least the predetermined deceleration. As a result, the movement of the vehicle 1 can be appropriately restrained even when the braking force corresponding to the brake fluid pressure cannot be obtained.

[0069] According to the braking control method of this embodiment, the braking control device 50 determines whether the outside air temperature of the vehicle 1 is equal to or lower than a predetermined temperature, and if it determines that the outside air temperature is equal to or lower than the predetermined temperature, executes the parking control. This makes it possible to appropriately restrain the movement of the vehicle 1 even when the operating efficiency of the actuator is reduced.

[0070] According to the braking control method of this embodiment, the braking control device 50 determines whether the wipers of the vehicle 1 are operating, and if it determines that the wipers are operating, executes the parking control. This allows the vehicle 1 to be appropriately prevented from moving even in slippery conditions such as rainy weather or snowy weather.

[0071] According to the braking control method of the present embodiment, the braking control device 50 determines whether the acceleration of the vehicle 1 is equal to or greater than a predetermined acceleration, and if it determines that the acceleration is equal to or greater than the predetermined acceleration, executes the parking control. This allows the movement of the vehicle 1 to be appropriately stopped even if another object comes into contact with the vehicle 1.

[0072] According to the braking control method of this embodiment, the braking control device 50 determines whether the tilt is equal to or greater than the predetermined value, and if it determines that the tilt is equal to or greater than the predetermined value, executes the parking control, thereby making it possible to appropriately restrain the movement of the vehicle 1 even if the tilt of the vehicle 1 changes.

[0073] Furthermore, according to the braking control method of this embodiment, when at least one of the first brake and the second brake is activated, the braking control device 50 determines whether at least one of the left front wheel 11, the left rear wheel 12, the right front wheel 21, and the right rear wheel 22 is rotating, and executes the parking control when it determines that at least one of the left front wheel 11, the left rear wheel 12, the right front wheel 21, and the right rear wheel 22 is rotating. As a result, when the parked vehicle 1 starts to move, the second control is quickly initiated, and the movement of the vehicle 1 can be appropriately restrained.

[0074] Furthermore, according to this embodiment, there is provided a braking control device 50 for an electric parking brake 80 including a first actuator that activates a first brake on at least one of a left front wheel 11 and a left rear wheel 12 of a vehicle 1 with a first braking force, and a second actuator that activates a second brake on at least one of a right front wheel 21 and a right rear wheel 22 of the vehicle 1 with a second braking force, wherein the vehicle 1 has a detection means for detecting the inclination of the vehicle 1, and the braking control device 50 includes: a determination unit 51 that determines whether the inclination detected by the detection means is less than a predetermined value when the vehicle 1 is parked; and a control unit 52 that controls the first actuator and the second actuator so that one of the first braking force and the second braking force is smaller than the other when the determination unit 51 determines that the inclination is less than the predetermined value. This makes it possible to prevent a shortening of the life of the actuators that activate the brakes.

[0075] 1...Vehicle 11...Left front wheel, 12...Left rear wheel 21...Right front wheel, 22...Right rear wheel 31, 32, 41, 42...Actuator 50...Brake control device, 51...Determination unit, 52...Control unit, 53...Memory unit 61...Acceleration sensor, 62...Temperature sensor 70...Brake, 71...Disc rotor, 71a...Hub, 72...Brake caliper, 73, 74...Brake pads, 75...Piston, 76...Cylinder, 77...Pressure sensor, 78...Speed ​​sensor 80...Electric parking brake, 81...Parking switch 91, 93...Ground, 92, 94...Horizontal surface

Claims

1. a first actuator that activates a first brake for at least one of a left front wheel and a left rear wheel of the vehicle with a first braking force; a second actuator that activates a second brake of at least one of a right front wheel and a right rear wheel of the vehicle with a second braking force, the vehicle has a detection means for detecting an inclination of the vehicle, The braking control device includes: When the vehicle is parked, it is determined whether the tilt detected by the detection means is less than a predetermined value; When it is determined that the inclination is less than the predetermined value, the braking control method controls the first actuator and the second actuator so that one of the first braking force and the second braking force is smaller than the other.

2. The brake control method according to claim 1 , wherein the brake control device stops one of the first actuator and the second actuator when it determines that the inclination is less than the predetermined value.

3. The braking control device includes: When at least one of the first actuator and the second actuator is activated, the set first braking force and the set second braking force are stored in correspondence with each other; When it is determined that the inclination is less than the predetermined value, the previous first braking force and the previous second braking force that were set when at least one of the first actuator and the second actuator was last operated are acquired, and If the previous first braking force is larger than the previous second braking force, the first braking force is set to be smaller than the second braking force; 3. The brake control method according to claim 1, wherein when the previous first braking force is smaller than the previous second braking force, the first braking force is set to be larger than the second braking force.

4. The braking control device includes: determining whether the vehicle is loaded on a transport vehicle that transports the vehicle; 3. The braking control method according to claim 1, wherein, when it is determined that the vehicle is loaded on the transporter, the first actuator and the second actuator are activated, and the first braking force and the second braking force are set so that a difference between the first braking force and the second braking force is less than a predetermined braking force.

5. The braking control device includes: determining whether the vehicle is in a state in which at least one of the first braking force and the second braking force is reduced; 3. The braking control method according to claim 1, further comprising the steps of: when it is determined that the vehicle is in a state in which at least one of the first braking force and the second braking force is reduced, operating the first actuator and the second actuator; and performing parking control to set the first braking force and the second braking force so that a difference between the first braking force and the second braking force is less than a predetermined braking force.

6. The braking control device includes: Estimating temperatures of brake pads of the first brake and the second brake; determining whether the estimated temperature is equal to or greater than a fade temperature; 6. The brake control method according to claim 5, wherein the parking control is executed when it is determined that the estimated temperature is equal to or higher than the fade temperature.

7. The braking control device includes: acquiring brake fluid pressures of the first brake and the second brake when at least one of the first brake and the second brake is activated, and a deceleration of the vehicle; obtaining the deceleration corresponding to the pressure from a predetermined relationship between the pressure and the deceleration; determining whether the actual deceleration is lower than the deceleration corresponding to the pressure by a predetermined deceleration or more; 6. The braking control method according to claim 5, wherein the parking control is executed when it is determined that the actual deceleration is lower than the deceleration corresponding to the pressure by at least the predetermined deceleration.

8. The braking control device includes: determining whether the outside air temperature of the vehicle is equal to or lower than a predetermined temperature; 6. The braking control method according to claim 5, wherein the parking control is executed when it is determined that the outside air temperature is equal to or lower than the predetermined temperature.

9. The braking control device includes: determining whether the wipers of the vehicle are operating; 6. The braking control method according to claim 5, wherein the parking control is executed when it is determined that the wipers are operating.

10. The braking control device includes: determining whether the acceleration of the vehicle is equal to or greater than a predetermined acceleration; 6. The braking control method according to claim 5, wherein the parking control is executed when it is determined that the acceleration is equal to or greater than the predetermined acceleration.

11. The braking control device includes: determining whether the slope is equal to or greater than the predetermined value; 6. The braking control method according to claim 5, wherein the parking control is executed when it is determined that the inclination is equal to or greater than the predetermined value.

12. The braking control device includes: determining whether at least one of the left front wheel, the left rear wheel, the right front wheel, and the right rear wheel is rotating when at least one of the first brake and the second brake is operating; 6. The braking control method according to claim 5, wherein the parking control is executed when it is determined that at least one of the left front wheel, the left rear wheel, the right front wheel, and the right rear wheel is rotating.

13. a first actuator that activates a first brake for at least one of a left front wheel and a left rear wheel of the vehicle with a first braking force; a second actuator that activates a second brake of at least one of a right front wheel and a right rear wheel of the vehicle with a second braking force, the vehicle has a detection means for detecting an inclination of the vehicle, a determination unit that determines whether the tilt detected by the detection means is less than a predetermined value when the vehicle is parked; a control unit that controls the first actuator and the second actuator so that one of the first braking force and the second braking force is smaller than the other when the determination unit determines that the slope is less than the predetermined value.