Brake control method and brake 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

Technical Field

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

Background Art

[0002] In an electric parking brake that, when a parking brake switch is operated, pulls the left and right brake cables with equal force to operate the left and right rear wheel brakes, detects the inclination of the vehicle body, and increases the braking force of the brake as the inclination increases, the number of operations of the brake is stored for each braking force, and the life of the brake cable is determined based on the stored braking force and the number of operations. An electric parking brake is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above prior art, when parking the vehicle, the brakes of the right and left wheels are operated with the same braking force regardless of the inclination of the vehicle. Therefore, when the inclination is small, the brakes are operated with more braking force than necessary, and there is a problem that the life of the actuator that operates the brakes is shortened.

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

Means for Solving the Problems

[0006] The present invention provides an electric parking brake comprising 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, wherein when the vehicle is parked and it is determined that the tilt of the vehicle is less than a predetermined value, the first actuator and the second actuator are controlled so that one of the first braking force and the second braking force is less than the other, thereby solving the above problem. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the shortening of the lifespan of the actuator that operates the brakes. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view showing one embodiment of a vehicle equipped with an electric parking brake according to the present invention. [Figure 2] Figure 1 is a plan view showing an example of a brake installed on the left rear wheel of the vehicle. [Figure 3] This is a block diagram showing one embodiment of the electric parking brake according to the present invention. [Figure 4] This is a side view showing an example of the vehicle's tilt in Figure 1. [Figure 5] This is a front view showing another example of the vehicle's tilt in Figure 1. [Figure 6] This is an example of a map showing the relationship between brake fluid pressure and vehicle deceleration in this embodiment. [Figure 7] Figure 3 is a flowchart showing an example of the processing procedure for an electric parking brake. [Figure 8] Figure 3 is a flowchart showing another example of the processing procedure for an electric parking brake. [Figure 9] Figure 8 is a flowchart showing an example of a subroutine in step S11. [Figure 10] Figure 8 is a flowchart showing another example of the subroutine in step S11. [Figure 11] Figure 8 shows another example flowchart of the subroutine in step S11. [Figure 12] Another example flowchart of the subroutine in step S11 of Figure 8. [Figure 13] Another example flowchart of the subroutine in step S11 of Figure 8. [Figure 14] Another example flowchart of the subroutine in step S11 of Figure 8. [Figure 15] Another example flowchart of the subroutine in step S11 of Figure 8. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] [Configuration of the electric parking brake] Figure 1 is a plan view showing one embodiment of a vehicle equipped with an electric parking brake according to the present invention. An electric parking brake is a device that stops the movement of a vehicle (specifically, the rotation of the wheels, propeller shaft, etc.) using an electric actuator such as a motor, thereby parking the vehicle. The vehicle is not particularly limited and includes vehicles of any drive system. As shown in Figure 1, vehicle 1 is equipped with 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 braking control device 50, an acceleration sensor 61, a temperature sensor 62, and a parking switch 81. Unless otherwise specified, the rotation of the wheels refers to the rotation of the wheels in the circumferential direction.

[0011] The left front wheel 11, the left rear wheel 12, the right front wheel 21, and the right rear wheel 22 are wheels respectively attached to a suspension (not shown) of the vehicle 1 via hubs, and brakes for restraining circumferential rotation are 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 the present embodiment, the brakes for restraining the rotation of the left front wheel 11 and the left rear wheel 12 of the vehicle 1 are referred to as the first brakes, and the brakes for restraining the rotation of the right front wheel 21 and the right rear wheel 22 are referred to as the second brakes.

[0012] When the brakes are actuated, in order to restrain the rotation of the wheels, a force in the direction opposite to the traveling direction is generated between each wheel and the ground (or road surface) on which the vehicle 1 is grounded. This force is referred to as the braking force, and for example, it is obtained by dividing the braking torque around the vehicle's axle by the radius of the tire. In the present embodiment, the braking force of the first brakes is referred to as the first braking force, and the braking force of the second brakes is referred to as the second braking force.

[0013] The actuators 31, 32, 41, 42 are mechanical elements for actuating the brakes for restraining 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, and are, for example, motors, electromagnetic solenoids, etc. The actuators 31, 32, 41, 42 actuate or stop the brakes according to the control signals output from the braking control device 50. The actuators 31, 32, 41, 42 can be arranged at appropriate positions within the range where the brakes can be actuated. In the present embodiment, the actuators 31, 32 for actuating the first brakes are referred to as the first actuators, and the actuators 41, 42 for actuating the second brakes are referred to as the second actuators.

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

[0015] The braking control device 50 is a device for stopping the movement of the vehicle 1 by controlling and cooperating the devices constituting the electric parking brake. The braking control device 50 is, for example, a computer and includes a CPU (Central Processing Unit) as a processor, a ROM (Read Only Memory) storing a program, and a RAM (Random Access Memory) functioning as an accessible storage device. The CPU executes the program stored in the ROM and is an operation circuit for realizing the functions of the braking control device 50.

[0016] The acceleration sensor 61 is a device for detecting the acceleration applied to the vehicle 1, and a known acceleration sensor such as a capacitive acceleration sensor can be used without particular limitation. The acceleration sensor 61 detects the direction of gravity (vertical direction), the longitudinal direction, the lateral direction, and the vertical direction of the vehicle, and also detects the movement amount, movement speed, and movement direction of the vehicle 1. On the other hand, the temperature sensor 62 is a device for detecting the outside air temperature of the vehicle 1, and a known temperature sensor can be used without particular limitation. The acceleration sensor 61 and the temperature sensor 62 can be arranged at appropriate positions within ranges where they can appropriately detect acceleration and outside air temperature, respectively. Note that 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 operated to activate the electric parking brake and is located around the driver's seat of vehicle 1. The parking switch 81 may be, for example, a switch located on the instrument panel, a pedal located on the left side of the driver's footwell, or a button located on the center console.

[0018] Next, the configuration of the brakes on each wheel will be explained using Figure 2. Figure 2 is a plan view showing an example of a brake provided on the left rear wheel 12 of vehicle 1. As shown in Figure 2, the brake 70 comprises a disc rotor 71, a brake caliper 72, brake pads 73, 74, a piston 75, a cylinder 76, a pressure sensor 77, and a speed sensor 78. In 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 circumferentially with the left rear wheel 12 around an axle (not shown). A brake caliper 72 is provided on the front side of the disc rotor 71 to stop the rotation of the disc rotor 71. The brake caliper 72 comprises a pair of brake pads 73, 74, a piston 75, and a cylinder 76. The pair of brake pads 73, 74 are arranged opposite each other on both sides of the disc rotor 71, sandwiching the disc rotor 71. 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 located inside the brake caliper 72 and houses 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 placed in appropriate positions within a range that allows for proper detection of pressure and rotational speed, respectively.

[0021] When a control signal to activate the brake 70 is input from the braking control device 50, the actuator 32 pushes the piston 75 toward the left side of the vehicle. This push of the piston 75 pressurizes the brake fluid in the cylinder 76, applying a force to the brake pad 74 toward the left side of the vehicle. The brake pad 74, with the force applied by the brake fluid, moves toward the left side of the vehicle and, together with the brake pad 73 held by the brake caliper 72, clamps the disc rotor 71, stopping the rotation of the disc rotor 71.

[0022] In response, when a control signal to stop the brake 70 is input from the braking control device 50, the actuator 32 returns the piston 75 to the right side of the vehicle and releases the pressure of the brake fluid. As the pressure of the brake fluid is released, the brake pad 74 moves to the right side of the vehicle and returns to its original position. Then, the brake pads 73 and 74 separate from the disc rotor 71, and the disc rotor 71 becomes able to rotate freely.

[0023] [Functions of the braking control system] Figure 3 is a block diagram showing one embodiment of the electric parking brake according to the present invention. As shown in Figure 3, the 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 braking control device 50, first actuators 31, 32 and second actuators 41, 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. The ROM of the braking control device 50 stores a program for realizing the braking function, and the CPU executes the program stored in the ROM to realize the braking function. Figure 3 shows, for convenience, 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 explained below using Figure 3.

[0025] The determination unit 51 has the function of determining whether the tilt 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 instruction is output to the braking control device 50 to activate the electric parking brake 80. The braking control device 50 determines whether the parking switch 81 has been operated based on the function of the determination unit 51, and if an operation instruction is received, it determines that the parking switch 81 has been operated. Conversely, if an operation instruction is not received, it determines that the parking switch 81 has not been operated.

[0026] Furthermore, the braking control device 50 may estimate whether the driving scene of vehicle 1 is a parking scene or not. For example, it may obtain the current position of vehicle 1 from a positioning system (not shown) and determine whether vehicle 1 is driving in a parking lot based on map information and the information of vehicle 1's current position. If it is determined that vehicle 1 is driving in a parking lot, it is estimated that the driving scene of vehicle 1 is a parking scene. On the other hand, if it is determined that vehicle 1 is driving on a normal road, it is estimated that the driving scene of vehicle 1 is not a parking scene.

[0027] For example, if the braking control device 50 estimates that the driving scene of vehicle 1 is a parking scene and / or receives an operation instruction from the parking switch 81, it determines that vehicle 1 is parking and, using the function of the determination unit 51, obtains the tilt of vehicle 1 from the acceleration sensor 61, which is a detection means for detecting the tilt of vehicle 1. The acceleration sensor 61 detects the direction of gravity and the longitudinal direction of the vehicle and calculates the tilt of vehicle 1 from the angle formed by the direction of gravity and the longitudinal direction of the vehicle. Alternatively, the braking control device 50 may obtain the direction of gravity and the longitudinal direction of the vehicle from the acceleration sensor 61, which is a detection means for detecting the tilt of vehicle 1, and calculate the tilt of vehicle 1 from the two obtained directions.

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

[0029] Furthermore, the braking 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 Figure 5, if the ground 93 on which the vehicle 1 is in contact with is tilted in the left-right direction of the vehicle 1, and the vehicle 1 is parked with the left side lower than the right side (tilted to the left), the braking 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 ground 93) with respect to the horizontal plane 94, by subtracting 90 from the angle c, which is the inferior angle formed by arrows G and I. Note that the ground includes the road surface.

[0030] The braking control device 50 then determines whether the tilt obtained 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 to an appropriate value within the 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, for example, 10° to 30°. If the braking control device 50 determines that the obtained tilt is less than the predetermined value, it performs a first control to control 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 suppress the shortening of the lifespan of the actuators. On the other hand, if it determines that the obtained tilt is greater than or equal to the predetermined value, it performs a second control to activate the first actuator and the second actuator in order to appropriately stop the movement of the vehicle 1, and to 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 second control is also called parking control.

[0031] Returning to Figure 3, the control unit 52 has the function of executing either 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 brake control device 50 stops either the first actuator or the second actuator. Stopping the first (second) actuator means that when a control signal to stop the actuator is input, the actuator will not be operated any further. In other words, if the brake is not applied, the actuator will not be operated, and if the brake is applied, the actuator will be controlled so that the brake pads do not press against the disc rotor. As another example of the first control, if neither the first nor the second brake is applied, the brake control device 50 will operate only one of the first actuator or the second actuator. When only one of the first or second actuator is operated, the load on the actuator can be further reduced.

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

[0033] In the first control, the braking 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 braking 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, and in the second control, it 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 a 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 as an example, it is a braking force that is a predetermined percentage (for example, 60% to 90%) of the maximum braking force of the first brake and the second brake.

[0034] For example, in the example shown in Figure 4, if it is determined that the angle b indicating the tilt of vehicle 1 is less than a predetermined value, the braking control device 50 performs first control using the functions of the control unit 52. Specifically, it operates only the actuator 32 to stop the rotation of the left rear wheel 12. The first braking force is set to an appropriate value within the range in which vehicle 1 does not move on the ground 91. In contrast, if it is determined that the angle b indicating the tilt of vehicle 1 is greater than or equal to a predetermined value, the braking control device 50 performs second control using the functions of the control unit 52. Specifically, it operates the actuators 32 and 42 to stop the rotation of the left rear wheel 12 and the right rear wheel 22. The braking forces of the first and second brakes are set to appropriate values ​​within the range in which vehicle 1 does not move on the ground 91.

[0035] The memory unit 53 has the function of storing the first braking force and the second braking force in association. When at least one of the first actuator and the second actuator is activated, the braking 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 association with each other in the ROM or the like. Subsequently, when the actuator stops and at least one of the first actuator and the second actuator is to be activated again, if it is determined that the tilt of the vehicle 1 is less than a predetermined value, the control unit 52 uses its function to acquire the previous first braking force and second braking force that were set when at least one of the first actuator and the second actuator was last activated. Then, based on the acquired previous first braking force and second braking force, the current first braking force and second braking force are set.

[0036] Specifically, if the previous first braking force was greater than the previous second braking force, the current first braking force is set to be less than the current second braking force. Conversely, if the previous first braking force was less than the previous second braking force, the current first braking force is set to be greater than the current second braking force. If the previous first and second braking forces were the same value, the first and second braking forces set when the first control was last executed are retrieved, and the current first and second braking forces are set based on the retrieved first and second braking forces.

[0037] The braking control device 50 determines whether vehicle 1 is loaded onto a transport vehicle that is transporting vehicle 1, and if it determines that vehicle 1 is loaded onto a transport vehicle, it may execute the second control. For example, if it is detected from the tilt and acceleration of vehicle 1 obtained from the acceleration sensor 61 that a lateral acceleration has been applied to vehicle 1 which is tilted in the longitudinal direction, it determines that vehicle 1 is loaded onto a transport vehicle and executes the second control. On the other hand, if it determines that vehicle 1 is not loaded onto a transport vehicle, it does not execute the second control. Examples of transport vehicles include car carriers and tow trucks.

[0038] The braking 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 the reduced braking force state). If it is determined that the vehicle 1 is in the reduced braking force state, the control unit 52 may perform a second control 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 brakes 70, the state of the ground (or road surface), etc.

[0039] As an example, the braking control device 50 estimates the temperature of the brake pads of the first and second brakes, determines whether the estimated temperature is above the fade temperature, and executes the second control if it determines that the estimated temperature is above the fade temperature. On the other hand, if it determines that the estimated brake pad temperature is below the fade temperature, it does not execute the second control. The fade temperature is the temperature at which the friction coefficient of the brake pads begins to decrease, for example, between 250°C and 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 braking duration. For example, it pre-determines the relationship between the deceleration of the vehicle 1, the braking duration, and the rise in brake pad temperature. It also pre-determines the relationship between the cooling time when the brakes are not applied and the decrease in brake pad temperature. Then, it calculates the temperature change, which indicates how much the brake pad temperature has risen or fallen between time T1 and time T2, which is a predetermined time after time T1. By adding the calculated temperature change to the brake pad temperature at time T1, it estimates the brake pad temperature at time T2.

[0041] The predetermined time mentioned above is, for example, a time corresponding to the computing power of the CPU of the braking control device 50. The braking control device 50 monitors the brake pad temperature by repeatedly estimating the brake pad temperature at predetermined intervals. The initial brake temperature is, for example, the ambient temperature around the vehicle 1 obtained from the temperature sensor 62, and when a new estimation of the brake pad temperature is started, it may be the last previously estimated brake pad temperature.

[0042] As another example, the braking control device 50 acquires the brake fluid pressure of the first brake and the second brake (hereinafter also referred to as the actual pressure) and the deceleration of the vehicle 1 (hereinafter also referred to as the actual deceleration) when at least one of the first brake and the second brake is activated. It also acquires the deceleration corresponding to the brake fluid pressure at the time of brake activation (hereinafter also referred to as the deceleration corresponding to the pressure) from a preset relationship between the brake fluid pressure and the deceleration of the vehicle 1. It then determines whether the actual deceleration is lower than the deceleration corresponding to the pressure by a predetermined deceleration or more, and if it is determined that the actual deceleration is lower than the deceleration corresponding to the pressure by a predetermined deceleration or more, 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, the second control is executed. On the other hand, if it is determined that the actual deceleration is lower than the deceleration corresponding to the pressure by only less than the predetermined deceleration, the second control is not executed.

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

[0044] Figure 6 is an example of a map showing the relationship between brake fluid pressure and vehicle deceleration. In the map shown in Figure 6, the horizontal axis represents pressure, and the vertical axis represents the deceleration of vehicle 1. The map includes at least the relationship between brake fluid pressure and vehicle deceleration in the initial state (factory state), and thresholds that distinguish between areas where parking control (secondary control) is performed and areas where parking control is not performed. In the map shown in Figure 6, the area to the lower right of the threshold line is the area where secondary control is performed, and the area to the upper left of the threshold line is the area where secondary control is not performed.

[0045] For example, suppose that when at least one of the first and second brakes 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 on the map corresponding to pressure P1 (initial value) is A2, and the difference between the actual deceleration A1 and the deceleration A2 on the map corresponding to pressure P1 is d1. The predetermined deceleration corresponds to the difference d2 between the deceleration A2 on the map corresponding to pressure P1 and the deceleration A3 corresponding to the intersection of pressure P1 and the threshold. Since the difference d1 is smaller than the difference d2, in the case shown in Figure 6, the braking 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, the braking control device 50 may, for example, while executing the first control, obtain the ambient temperature of the vehicle 1 from the temperature sensor 62, determine whether the ambient temperature is below a predetermined temperature, and execute the second control if it determines that the ambient temperature is below the predetermined temperature. The predetermined temperature is, for example, the temperature at which the operating efficiency of the actuator begins to decrease due to low temperatures, specifically -40°C to -10°C. Also, the braking control device 50 may, for example, while executing the first control, obtain the operating status of the vehicle 1's wipers, determine whether the wipers are operating, and execute the second control if it determines that the wipers are operating.

[0047] The braking control device 50 may, for example, while executing the first control, acquire the acceleration of the vehicle 1 from the acceleration sensor 61, determine whether the acceleration of the vehicle 1 is greater than or equal to a predetermined acceleration, and if it determines that the acceleration is greater than or equal to the predetermined acceleration, execute the second control. The predetermined acceleration can be set to an appropriate value within a range in which contact with an object can be detected, for example, 0.5G to 2.0G. The braking control device 50 may also, for example, while executing the first control, determine whether the tilt of the vehicle 1 is greater than or equal to a predetermined value, and if it determines that the tilt of the vehicle 1 is greater than or equal to the predetermined value, execute the second control.

[0048] When at least one of the first brake and the second brake is applied, the braking control device 50 obtains the rotational speed 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 determines 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, it executes the second control. On the other hand, if it determines that none of the wheels are rotating, it does not execute the second control.

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

[0050] [Information processing in electric parking brakes] Referring to Figures 7-15, the procedure for information processing by the braking control device 50 will be explained. Figure 7 is an example of a flowchart showing the information processing performed in the electric parking brake 80 of this embodiment. The processing described below is performed by the processor (CPU) of the braking control device 50.

[0051] First, in step S1, 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. If it is determined that the parking switch 81 has been operated, the process proceeds to step S2. In step S2, the tilt of the vehicle 1 is obtained from the acceleration sensor 61, and in the following step S3, it is determined whether or not the tilt of the vehicle 1 is less than a predetermined value. If it is determined that the tilt of the vehicle 1 is greater than or equal to the predetermined value, the process proceeds to step S8, where the control unit 52 performs the second control (parking control). If it is determined that the tilt of the vehicle 1 is less than a predetermined value, the process proceeds to step S4.

[0052] In step S4, the previously stored first and second braking forces are retrieved from a storage medium (not shown), and in the following step S5, the current first and second braking forces are set based on the retrieved previous first and second braking forces. In the following step S6, the actuator is activated to perform the first control using the set first and second braking forces. After the first control is performed, 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] Next, Figure 8 is another example of a flowchart showing the information processing performed in the electric parking brake 80 of this embodiment. The processing described below is performed by the processor (CPU) of the braking 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 performed.

[0054] First, in step S11, the vehicle's state is detected, and in the following step S12, it is determined whether the vehicle's state is such that the second control is to be executed or continued. If it is determined that the vehicle's state is such that the second control is to be executed or continued, the process proceeds to step S13, and the second control (parking control) is executed or continued. On the other hand, if it is determined that the vehicle's state is not such that the second control is to 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] Figure 9 is a flowchart showing an example of the subroutine for step S11 in Figure 8. First, in step S21, the brake pad temperature is estimated, and in the following step S22, it is determined whether the brake pad temperature is above the fade temperature. If it is determined that the brake pad temperature is above the fade temperature, the process proceeds to step S23, where it is recognized that the second control (parking control) should be executed or continued. On the other hand, if it is determined that the brake pad temperature is below the fade temperature, the process proceeds to step S24, where it is recognized that the second control (parking control) should not be executed or continued. After that, the process proceeds to step S12. Note that the redundant explanations of steps S23 and S24 will be omitted below.

[0056] Figure 10 is a flowchart showing another example of the subroutine for step S11 in Figure 8. First, in step S31, the actual pressure of the brake fluid when the brakes are applied and the actual deceleration of vehicle 1 are obtained. In the following step S32, the deceleration on the map (initial value) 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 a predetermined deceleration or more. If it is determined that the actual deceleration is lower than the deceleration on the map corresponding to the actual deceleration by a predetermined deceleration or more, 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] Figure 11 is a flowchart showing yet another example of the subroutine in step S11 of Figure 8. First, in step S41, the ambient temperature of vehicle 1 is obtained from the temperature sensor 62, and in the following step S42, it is determined whether the ambient temperature is below a predetermined temperature. If it is determined that the ambient temperature is below the predetermined temperature, the process proceeds to step S23; if it is determined that the ambient temperature is above the predetermined temperature, the process proceeds to step S24.

[0058] Figure 12 is a flowchart showing yet another example of the subroutine in step S11 of Figure 8. First, in step S51, the operating status of the wiper is obtained, and in the following step S52, it is determined whether or not the wiper is operating. If it is determined that the wiper is operating, the process proceeds to step S23; if it is determined that the wiper is not operating, the process proceeds to step S24.

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

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

[0061] Figure 15 is a flowchart showing yet another example of the subroutine in step S11 of Figure 8. First, in step S81, the rotational speed of the wheels of vehicle 1 is obtained when the brakes are applied, 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; if it is determined that none of the wheels are rotating, the process proceeds to step S24.

[0062] [Embodiments of the present invention] As described above, according to this embodiment, a braking control method for parking a vehicle 1 is provided, which is performed by a braking control device 50 of an electric parking brake 80 comprising a first actuator that operates a first brake on at least one of the left front wheel 11 and 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 right rear wheel 22 of the vehicle 1 with a second braking force. In this braking control method, the vehicle 1 has a detection means for detecting the tilt of the vehicle 1, and when the vehicle 1 is parked, the braking control device 50 determines whether the tilt detected by the detection means is less than a predetermined value, and when it is determined that the tilt 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 makes it possible to suppress a shortening of the lifespan of the actuators that operate the brakes.

[0063] Furthermore, according to the braking control method of this embodiment, if the braking control device 50 determines that the inclination is less than the predetermined value, it stops one of the first actuator and the second actuator. This further suppresses the shortening of the lifespan of the actuator that operates the brake.

[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 second braking force in association with each other. When it determines that the inclination is less than the predetermined value, it retrieves the previous first braking force and second braking force that were set when at least one of the first actuator and the second actuator was last activated. If the previous first braking force is greater than the previous second braking force, the first braking force is set to be less than the second braking force. If the previous first braking force is less than the previous second braking force, the first braking force is set to be greater than the second braking force. This makes it possible to suppress an increase in the number of times one of the first actuator and the second actuator is activated.

[0065] Furthermore, according to the braking control method of this embodiment, the braking control device 50 determines whether the vehicle 1 is loaded onto a transport vehicle that transports the vehicle 1. If it determines that the vehicle 1 is loaded onto the transport vehicle, it 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 less than or equal to a predetermined braking force. This prevents the vehicle 1 loaded onto the transport vehicle from moving on the transport vehicle.

[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 decreasing. 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 decreasing, the device operates the first actuator and the second actuator and performs parking control by setting 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 stop the movement of the vehicle 1 when the movement of the vehicle 1 cannot be appropriately stopped by the first control.

[0067] Furthermore, according to the braking control method of this embodiment, the braking control device 50 estimates the temperature of the brake pads of the first brake and the second brake, determines whether the estimated temperature is above the fade temperature, and if it determines that the estimated temperature is above the fade temperature, it executes the parking control. As a result, the movement of the vehicle 1 can be appropriately stopped even when the brake pad temperature is relatively high.

[0068] Furthermore, according to the braking control method of this embodiment, the braking control device 50 acquires the pressure of the brake fluid 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. Based on a preset relationship between the pressure and the deceleration, it acquires the deceleration corresponding to the pressure, determines whether the actual deceleration is lower than the deceleration corresponding to the pressure by a predetermined deceleration or more, and if it determines that the actual deceleration is lower than the deceleration corresponding to the pressure by a predetermined deceleration or more, it executes the parking control. As a result, even if the original braking force corresponding to the brake fluid pressure cannot be obtained, the movement of the vehicle 1 can be appropriately stopped.

[0069] Furthermore, according to the braking control method of this embodiment, the braking control device 50 determines whether the ambient temperature of the vehicle 1 is below a predetermined temperature, and if it determines that the ambient temperature is below the predetermined temperature, it executes the parking control. This makes it possible to appropriately stop the movement of the vehicle 1 even if the operating efficiency of the actuator decreases.

[0070] Furthermore, according to the braking control method of this embodiment, the braking control device 50 determines whether or not the wipers of the vehicle 1 are operating, and if it determines that the wipers are operating, it executes the parking control. This makes it possible to appropriately stop the movement of the vehicle 1 even in conditions where the vehicle 1 is prone to slipping, such as in rainy weather or snow.

[0071] Furthermore, according to the braking control method of this 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, it executes the parking control. This makes it possible to appropriately stop the movement of the vehicle 1 even if another object comes into contact with the vehicle 1.

[0072] Furthermore, according to the braking control method of this embodiment, the braking control device 50 determines whether the tilt is greater than or equal to a predetermined value, and if it determines that the tilt is greater than or equal to the predetermined value, it executes the parking control. As a result, even if the tilt of the vehicle 1 changes, the movement of the vehicle 1 can be appropriately stopped.

[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 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, it executes the parking control. As a result, when the parked vehicle 1 starts to move, the second control can be started quickly and the movement of the vehicle 1 can be appropriately stopped.

[0074] Furthermore, according to this embodiment, a braking control device 50 for an electric parking brake 80 is provided, comprising: a first actuator that operates a first brake on at least one of the left front wheel 11 and left rear wheel 12 of a 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 right rear wheel 22 of the vehicle 1 with a second braking force, wherein the vehicle 1 has detection means for detecting the tilt of the vehicle 1, a determination unit 51 that determines whether the tilt 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 tilt is less than the predetermined value. This makes it possible to suppress shortening the lifespan of the actuators that operate the brakes. [Explanation of Symbols]

[0075] 1…Vehicle 11…Left front wheel, 12…Left rear wheel 21...Right front wheel, 22...Right rear wheel 31, 32, 41, 42… Actuators 50... Brake control device, 51... Determination unit, 52... Control unit, 53... Memory unit 61...Accelerometer, 62...Temperature sensor 70...Brake, 71...Disc rotor, 71a...Hub, 72...Brake caliper, 73,74...Brake pad, 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 the first brake of at least one of the left front wheel and left rear wheel of the vehicle with a first braking force, A braking control method for parking a vehicle, which is performed by a braking control device for an electric parking brake, comprising a second actuator that activates the second brake of at least one of the right front wheel and the right rear wheel of the vehicle with a second braking force, The vehicle has a detection means for detecting the tilt of the vehicle, The aforementioned braking control device is When the vehicle is parked, it is determined whether the inclination detected by the detection means is less than a predetermined value. A braking control method that, when it is determined 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.

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

3. The aforementioned braking control device is When at least one of the first actuator and the second actuator is activated, the set first braking force and the second braking force are stored in correspondence. When it is determined that the inclination is less than the predetermined value, the previous first braking force and second braking force, which were set when at least one of the first actuator and the second actuator was last operated, are obtained. If the previous first braking force was greater than the previous second braking force, the first braking force is set to be less than the second braking force. The braking control method according to claim 1 or 2, wherein if the previous first braking force was smaller than the previous second braking force, the first braking force is set to be larger than the second braking force.

4. The aforementioned braking control device is Determine whether the vehicle is loaded onto a transport vehicle that transports the vehicle. The braking control method according to claim 1 or 2, wherein, when it is determined that the vehicle is loaded onto the transport vehicle, the first actuator and the second actuator are activated, and the first braking force and the second braking force are set such that the difference between the first braking force and the second braking force is less than a predetermined braking force.

5. The aforementioned braking control device is The system determines whether the vehicle is in a state where at least one of the first braking force and the second braking force is decreasing. The braking control method according to claim 1 or 2, wherein if the vehicle is determined to be in the state in which at least one of the first braking force and the second braking force is reduced, the first actuator and the second actuator are activated, and parking control is performed to 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.

6. The aforementioned braking control device is The temperatures of the brake pads of the first brake and the second brake are estimated, Determine whether the estimated temperature is above the fade temperature. The braking control method according to claim 5, wherein if it is determined that the estimated temperature is equal to or greater than the fade temperature, the parking control is executed.

7. The aforementioned braking control device is The pressure of the brake fluid in 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 are obtained. From the predetermined relationship between the pressure and the deceleration, the deceleration corresponding to the pressure is obtained. Determine whether the actual deceleration is lower than the deceleration corresponding to the pressure by a predetermined deceleration or more. The braking control method according to claim 5, wherein if it is determined that the actual deceleration is lower than the predetermined deceleration corresponding to the pressure, the parking control is executed.

8. The aforementioned braking control device is Determine whether the outside temperature of the vehicle is below a predetermined temperature. The braking control method according to claim 5, wherein if it is determined that the outside air temperature is below the predetermined temperature, the parking control is executed.

9. The aforementioned braking control device is Determine whether the wipers of the vehicle are operating or not. The braking control method according to claim 5, wherein if it is determined that the wiper is operating, the parking control is executed.

10. The aforementioned braking control device is Determine whether the acceleration of the vehicle is greater than or equal to a predetermined acceleration. The braking control method according to claim 5, wherein if it is determined that the acceleration is greater than or equal to the predetermined acceleration, the parking control is executed.

11. The aforementioned braking control device is Determine whether the slope is greater than or equal to the predetermined value. The braking control method according to claim 5, wherein if it is determined that the inclination is greater than or equal to the predetermined value, the parking control is executed.

12. The aforementioned braking control device is When at least one of the first brake and the second brake is applied, it is determined whether at least one of the left front wheel, the left rear wheel, the right front wheel, and the right rear wheel is rotating. The braking control method according to claim 5, wherein 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, the parking control is executed.

13. A first actuator that activates the first brake of at least one of the left front wheel and left rear wheel of the vehicle with a first braking force, An electric parking brake braking control device comprising: a second actuator that activates the second brake of at least one of the right front wheel and the right rear wheel of the vehicle with a second braking force, The vehicle has a detection means for detecting the tilt of the vehicle, A determination unit that determines whether the inclination detected by the detection means is less than a predetermined value when the vehicle is parked, A braking control device comprising: a determination unit that determines that the inclination is less than a predetermined value, and 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.

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