Braking system

Abstract

A braking system 20 comprises two electric braking devices 22 having a holding function, and two second control devices 63, 64. One of the two second control devices 63, 64 is a main control device, and the other is an auxiliary control device. After both the main control device and the auxiliary control device execute an application process, the operation of the auxiliary control device is stopped. When braking force is increased on a wheel corresponding to the auxiliary control device, the auxiliary control device is activated, and the braking force is controlled by the auxiliary control device.

Description

Brake system

[0001] The present invention relates to a brake system that applies a parking braking force to a vehicle.

[0002] Patent Document 1 discloses a system including a parking actuator that applies a parking braking force to a vehicle and a control unit that controls the parking actuator. After the execution of the apply control for operating the parking actuator to apply the parking braking force, when the normal braking force is applied by the driver's braking operation, the control unit stops its own operation when a predetermined time has elapsed since the end of the application of the normal braking force. Thereby, the power consumption in the system can be reduced.

[0003] International Publication No. 2021 / 181809

[0004] During the running of the vehicle, the normal braking force is applied to the wheels by pressing a friction part against a rotating body that rotates integrally with the wheels. When the normal braking force is applied to the wheels during the running of the vehicle, frictional heat is generated between the rotating body and the friction part, so at least the friction part among the rotating body and the friction part thermally expands. When a parking request occurs when the vehicle has stopped in this state, the parking braking force is applied to the wheels by pressing the thermally expanded friction part against the rotating body.

[0005] After the application of the parking braking force to the wheels has started in this way, if the temperature of the friction part gradually decreases, the friction part gradually contracts. As a result, the pressing force, which is the force pressing the friction part against the rotating body, gradually decreases, so the parking braking force gradually decreases. When the vehicle is parked on a slope, if the amount of decrease in the parking braking force is relatively large, the vehicle may slide down the slope. Therefore, when the parking braking force decreases, it is preferable to operate the parking actuator so that the above pressing force increases. However, in the above system, when the operation of the braking unit has stopped, the parking actuator cannot be operated even if the pressing force, that is, the parking braking force, decreases due to the contraction of the friction part.

[0006] A braking system for solving the above problems comprises: a plurality of electric braking devices that apply braking force to each of a plurality of wheels of a vehicle by the driving force of an electric motor; at least two control devices that control the plurality of electric braking devices; and a holding unit provided in at least two of the plurality of electric braking devices that mechanically prevents the rotation of the electric motor so as to maintain the rotation angle of the electric motor even when the drive of the electric motor is stopped while braking force is applied to the wheels by the driving force of the electric motor. The braking system includes: a main control device which is one of the plurality of control devices and controls a first electric braking device which is part of the electric braking device on which the holding portion is provided; a sub-control device which is one of the plurality of control devices and controls a second electric braking device which is at least one of the remaining parts of the electric braking device on which the holding portion is provided; a stop control device which, while maintaining the operation of the main control device, stops the operation of the sub-control device and transitions the sub-control device to a power-saving state while the braking force from the first electric braking device and the second electric braking device is held by the holding portion; and a start control device which, when increasing the braking force applied to the wheel corresponding to the second electric braking device, releases the power-saving state of the sub-control device and activates the sub-control device, causing the sub-control device to control the braking force from the second electric braking device.

[0007] The above braking system achieves the effect of maintaining the vehicle in a stopped state by suppressing the increase in power consumption of the system during parking braking by transitioning the sub-control device to a power-saving state in the stop control unit, and by activating the sub-control device in the start control unit and controlling the braking force of the second electric brake device.

[0008] Figure 1 is a schematic diagram showing a vehicle equipped with the braking system of the first embodiment. Figure 2 is a schematic diagram showing the configuration of the electric braking device equipped with the braking system of Figure 1. Figure 3 is a block diagram showing the functional configuration of the multiple control devices equipped with the braking system of Figure 1. Figure 4 is a flowchart showing the processing flow for setting the main control device and the sub-control device from among the multiple control devices equipped with the braking system of Figure 1. Figures 5(a) and 5(b) are sequence diagrams showing the processing flow in the main control device and the processing flow in the sub-control device. Figure 6 is a flowchart showing the processing flow executed by the sub-control device when the operation of the sub-control device is started in the braking system of the second embodiment. Figure 7 is a flowchart showing the processing flow executed by the main control device after the apply process is executed in the braking system of the third embodiment.

[0009] (First Embodiment) A first embodiment of the braking system will be described with reference to Figures 1 to 5. Figure 1 shows a vehicle 10 equipped with a braking system 20. The vehicle 10 includes a plurality of wheels and a power supply system 15 that supplies power to the braking system 20. The plurality of wheels include two first wheels 11L and 11R and two second wheels 12L and 12R. For example, the first wheels 11L and 11R are front wheels, and the second wheels 12L and 12R are rear wheels.

[0010] <Braking System> The braking system 20 comprises a plurality of electric braking devices provided for each of the plurality of wheels 11L, 11R, 12L, and 12R, and a plurality of control devices provided for each of the plurality of electric braking devices. The plurality of electric braking devices include two electric braking devices 21 provided for each of the two first wheels 11L and 11R, and two electric braking devices 22 provided for each of the two second wheels 12L and 12R. The plurality of control devices include a control device 61 that controls the electric braking device 21 of the first wheel 11L, a control device 62 that controls the electric braking device 21 of the first wheel 11R, a control device 63 that controls the electric braking device 22 of the second wheel 12L, and a control device 64 that controls the electric braking device 22 of the second wheel 12R.

[0011] <Electric Braking System> The electric braking system 22 will be described with reference to Figures 1 and 2. The electric braking system 22 comprises a friction brake 30, an electric motor 40, a reduction mechanism 42, a linear motion conversion mechanism 43, a piston 44, a braking force holding mechanism 50, and a pressing force sensor 55.

[0012] As shown in Figure 1, the friction brake 30 has a rotating body 31 that rotates integrally with the corresponding second wheels 12L and 12R, and a friction part 32. An example of the friction brake 30 is a disc brake type brake mechanism. In this case, the disc rotor corresponds to the rotating body 31, and the brake pads correspond to the friction part 32. The friction brake 30 applies braking force to the corresponding second wheels 12L and 12R by pressing the friction part 32 against the rotating body 31. The force that presses the friction part 32 against the rotating body 31 is referred to as the "pressing force". The greater this pressing force, the greater the braking force. The pressing force sensor 55 detects this pressing force.

[0013] As shown in Figure 2, the electric motor 40 is driven by power supplied from the power supply system 15. The output shaft 41 of the electric motor 40 is connected to the input section 42a of the reduction mechanism 42. The reduction mechanism 42 reduces the rotational motion of the output shaft 41 and outputs it to the linear motion conversion mechanism 43. An example of the reduction mechanism 42 is a gear mechanism having multiple gears that mesh with each other. The linear motion conversion mechanism 43 converts the rotational motion input from the reduction mechanism 42 into linear motion and outputs it to the piston 44. The linear motion conversion mechanism 43 has a rotating section 43a connected to the output section 42b of the reduction mechanism 42, and a linear motion section 43b arranged coaxially with the rotating section 43a. The linear motion section 43b is engaged with the rotating section 43a, and when the rotating section 43a rotates, the linear motion section 43b moves linearly in a direction corresponding to the rotation direction of the rotating section 43a. An example of the linear motion conversion mechanism 43 is a screw mechanism. The screw mechanism includes a screw shaft and a nut that screws onto the screw shaft. In the example shown in Figure 2, the screw shaft of the screw mechanism corresponds to the rotating part 43a, and the nut of the screw mechanism corresponds to the linear motion part 43b.

[0014] The piston 44 is connected to the linear motion section 43b. Therefore, when the linear motion section 43b moves in a straight line, the piston 44 moves in the same direction as the linear motion section 43b. When the piston 44 approaches the rotating body 31, the friction section 32 is pressed against the rotating body 31, increasing the pressing force. On the other hand, when the piston 44 moves away from the rotating body 31, the pressing force decreases, and the friction section 32 moves relatively away from the rotating body 31.

[0015] The electric motor 40 is configured to allow the output shaft 41 to rotate in both directions. Of the two rotation directions of the output shaft 41, the direction of rotation that increases the pressing force is the increasing direction C1, and the direction of rotation that decreases the pressing force is the decreasing direction C2. When the output shaft 41 rotates in the increasing direction C1 by the drive of the electric motor 40, the piston 44 moves forward. This increases the pressing force. On the other hand, when the output shaft 41 rotates in the decreasing direction C2 by the drive of the electric motor 40, the piston 44 moves backward. This decreases the pressing force. Therefore, the electric braking device 22 can adjust the pressing force, and thus the braking force applied to the corresponding second wheels 12L and 12R, by controlling the rotation angle of the output shaft 41. Hereafter, the rotation angle of the output shaft 41 will be referred to as the "motor rotation angle θmt".

[0016] The braking force holding mechanism 50 is configured to maintain the motor rotation angle θmt by mechanically preventing the output shaft 41 from rotating in the decreasing direction C2, even when the power supply to the electric motor 40 is stopped. In other words, the braking force holding mechanism 50 corresponds to a "holding part" that mechanically prevents the rotation of the output shaft 41 of the electric motor 40 so that the motor rotation angle θmt is maintained even when the drive of the electric motor 40 is stopped while braking force is being applied to the second wheels 12L and 12R by the driving force of the electric motor 40. The electric braking device 22 is an electric braking device equipped with this holding part.

[0017] The braking force retention mechanism 50 includes a ratchet gear 51, a pawl member 52, and a solenoid 53. The ratchet gear 51 is fixed to the output shaft 41 in a state that allows it to rotate integrally with the output shaft 41. The pawl member 52 is displaced between a locked position in which it engages with the ratchet gear 51 and a retracted position in which it retracts from the ratchet gear 51. The pawl member 52 is biased in the direction from the locked position to the retracted position by a coil spring or the like (not shown). When the pawl member 52 is in the locked position, the pawl member 52 restricts the rotation of the output shaft 41 and the ratchet gear 51 in the decreasing direction C2. On the other hand, when the pawl member 52 is in the locked position, the pawl member 52 does not restrict the rotation of the output shaft 41 and the ratchet gear 51 in the increasing direction C1. The solenoid 53 is a power source for displacing the pawl member 52 to the locked position. When the solenoid 53 is energized, the electromagnetic force generated by the solenoid 53 moves the pawl member 52 to the locking position. If the pawl member 52 is locked to the ratchet gear 51 in the locking position, the pawl member 52 will remain in the locking position even if the power supply to the solenoid 53 is stopped. In this way, the braking force retention mechanism 50 retains the braking force applied to the corresponding second wheels 12L and 12R even if the power supply to the electric motor 40 is stopped.

[0018] When the pawl member 52 is in the locked position, if the output shaft 41 and the ratchet gear 51 rotate in the increasing direction C1, the pawl member 52 disengages from the ratchet gear 51. Then, the pawl member 52 is biased by a coil spring (not shown) or the like and displaced to the retracted position. In other words, the state in which the pawl member 52 is locked to the ratchet gear 51 is released.

[0019] The electric braking device 21 includes a friction brake 30, an electric motor 40, a reduction mechanism 42, a linear motion conversion mechanism 43, and a piston 44, but does not include a braking force retention mechanism 50. In other words, although the electric braking device 21 does not have a retention function, it is possible to apply braking force to the first wheels 11L and 11R by pressing the friction part 32 against the rotating body 31 which rotates integrally with the corresponding first wheels 11L and 11R, through the drive of the electric motor 40.

[0020] <Control Devices> Referring to Figures 1, 3, and 4, the multiple control devices 61 to 64 will be described. Hereafter, the control device that controls the electric braking device 21 will be referred to as the "first control device," and the control device that controls the electric braking device 22 will be referred to as the "second control device" to distinguish them.

[0021] As shown in Figure 1, the plurality of control devices 61 to 64 are processing circuits that control the corresponding electric brakes 21 and 22. An example of a processing circuit is an electronic control device. In this case, each of the plurality of control devices 61 to 64 has a CPU 71 and a memory 72 that stores a control program executed by the CPU 71. The first control devices 61 and 62 control the electric motor 40 of the corresponding electric brake 21 by having the CPU 71 execute the control program in the memory 72. The second control devices 63 and 64 control the electric motor 40 and solenoid 53 of the corresponding electric brake 22 by having the CPU 71 execute the control program in the memory 72.

[0022] Multiple control devices 61 to 64 can send and receive various types of information and commands to and from each other via the in-vehicle network 100. An example of the in-vehicle network 100 is a CAN bus. CAN is an abbreviation for "Control Area Network".

[0023] <Functional Configuration of the First Control Device> Referring to Figure 3, the functional configurations of the multiple first control devices 61 and 62 will be described. The first control device 61 functions as multiple functional units when the CPU 71 executes the control program in the memory 72. The multiple functional units include a braking control unit M11.

[0024] The first control device 62 functions as a plurality of functional units when the CPU 71 executes the control program in the memory 72. The plurality of functional units include a braking control unit M11. The braking control unit M11 controls the braking force by driving the electric motor 40 of the electric braking device 21 to control the pressing force.

[0025] When a service braking request occurs, the braking control unit M11 executes a service braking process to apply service braking force to the corresponding first wheels 11L and 11R. A service braking request occurs, for example, when a brake pedal (not shown) is operated, or when another on-board control device requests deceleration of the vehicle 10.

[0026] In the service braking process, the braking control unit M11 derives a target rotation angle θmtTr, which is a target value for the motor rotation angle θmt, based on the required value of the service braking force to be applied to the corresponding first wheels 11L and 11R. Then, the braking control unit M11 drives the electric motor 40 by feedback control that makes the motor rotation angle θmt follow the target rotation angle θmtTr. As a result, the braking control unit M11 can apply the service braking force corresponding to the above required value to the corresponding first wheels 11L and 11R.

[0027] <Functional Configuration of the Second Control Device> Referring to Figures 3 and 4, the functional configurations of the multiple second control devices 63 and 64 will be described. The second control device 63 functions as multiple functional units when the CPU 71 executes the control program in the memory 72. The multiple functional units include a braking control unit M21, a temperature output unit M22, a setting unit M24, a stop control unit M25, and a start control unit M26. In addition, a portion of the memory 72 of the second control device 63 functions as a storage unit M23.

[0028] The second control device 64 functions as a plurality of functional units when the CPU 71 executes the control program in the memory 72. These plurality of functional units include a braking control unit M21, a temperature output unit M22, a setting unit M24, a stop control unit M25, and a start control unit M26. In addition, a portion of the memory 72 of the second control device 64 functions as a storage unit M23.

[0029] <Braking Control Unit> The braking control unit M21 controls the braking force by driving the electric motor 40 of the electric braking device 22 to control the pressing force.

[0030] When a service braking request occurs, the braking control unit M21 executes a service braking process to apply service braking force to the corresponding second wheels 12L and 12R. In the service braking process, the braking control unit M21 derives a target rotation angle θmtTr based on the requested value of the service braking force to be applied to the corresponding second wheels 12L and 12R. The braking control unit M21 then drives the electric motor 40 by feedback control to make the motor rotation angle θmt follow the target rotation angle θmtTr. As a result, the braking control unit M21 can apply the service braking force corresponding to the requested value to the corresponding second wheels 12L and 12R.

[0031] When the vehicle 10 is in motion, the second wheels 12L and 12R and the rotating body 31 are rotating. Therefore, when applying the service braking force to the second wheels 12L and 12R to decelerate the vehicle 10, the friction part 32 is pressed against the rotating body 31. At this time, the greater the pressing force applied to the friction part 32 against the rotating body 31, the greater the frictional force generated. As a result, the rotating body 31 and the friction part 32 generate heat due to the friction between the rotating body 31 and the friction part 32. Consequently, at least the friction part 32 of the rotating body 31 and the friction part 32 undergoes thermal expansion. The greater the pressing force, or the longer the period during which the service braking force is applied to the second wheels 12L and 12R, the greater the amount of thermal expansion of the friction part 32 caused by applying the service braking force to the second wheels 12L and 12R.

[0032] When a parking brake request occurs, the braking control unit M21 performs an apply process to apply parking braking force to the corresponding second wheels 12L and 12R. A parking brake request occurs, for example, when a parking switch (not shown) is turned ON.

[0033] In the apply process, the braking control unit M21 derives a target rotation angle θmtTr based on the required value of the parking braking force to be applied to the corresponding second wheels 12L and 12R. The braking control unit M21 then drives the electric motor 40 by feedback control that makes the motor rotation angle θmt follow the target rotation angle θmtTr. When the braking control unit M21 determines that the motor rotation angle θmt is equal to the target rotation angle θmtTr, it energizes the solenoid 53 to cause the braking force holding mechanism 50 to hold the motor rotation angle θmt. As a result, the braking control unit M21 can apply the parking braking force corresponding to the above required value to the corresponding second wheels 12L and 12R. When the motor rotation angle θmt is held by the braking force holding mechanism 50, the braking control unit M21 stops the power supply to the electric motor 40 and the solenoid 53.

[0034] Under conditions where parking braking force is applied to the second wheels 12L and 12R, the pressing force that presses the friction part 32 against the rotating body 31 may decrease even though the motor rotation angle θmt does not decrease. That is, as time passes, the temperature of the rotating body 31 and the friction part 32 decreases, causing at least the friction part 32 to contract. As a result, the pressing force decreases.

[0035] Therefore, when parking braking force is applied to the second wheels 12L and 12R, the braking control unit M21 performs a reclamping process to increase the parking braking force by activating the electric braking device 22 when the predetermined conditions for executing the reclamping process are met. In the reclamping process, the braking control unit M21 drives the electric motor 40 so that the motor rotation angle θmt increases. After increasing the pressing force by driving the electric motor 40 in this way, the braking control unit M21 energizes the solenoid 53 to cause the braking force holding mechanism 50 to hold the motor rotation angle θmt. Once the motor rotation angle θmt is held by the braking force holding mechanism 50, the braking control unit M21 stops the power supply to the electric motor 40 and the solenoid 53.

[0036] When a request to release the parking brake is received, the braking control unit M21 performs a release process to release the parking brake force applied to the corresponding second wheels 12L and 12R. A request to release the parking brake occurs when, for example, a parking switch (not shown) is turned off while the vehicle 10 is under parking brake force.

[0037] During the release process, the braking control unit M21 drives the electric motor 40 in a direction that increases the motor rotation angle θmt, thereby releasing the holding of the motor rotation angle θmt by the braking force holding mechanism 50. Subsequently, the braking control unit M21 drives the electric motor 40 so that the motor rotation angle θmt decreases until the friction part 32 separates from the rotating body 31.

[0038] <Temperature Derivation Section> The temperature derivation section M22 derives the friction section temperature, which is the temperature of the friction section 32 of the electric braking device 22. The friction section temperature of the friction section 32 for the second wheel 12L is the friction section temperature TPpdL. The friction section temperature of the friction section 32 for the second wheel 12R is the friction section temperature TPpdR. The temperature derivation section M22 of the second control device 63 corresponding to the second wheel 12L derives the friction section temperature TPpdL of the friction section 32 for the second wheel 12L. The temperature derivation section M22 of the second control device 64 corresponding to the second wheel 12R derives the friction section temperature TPpdR of the friction section 32 for the second wheel 12R.

[0039] The temperature output unit M22 derives the friction part temperatures TPpdL and TPpdR based on the operating status of the friction brake 30 of the electric braking device 22 and the ambient temperature. The operating status of the friction brake 30 includes the magnitude of the pressing force, the length of the period during which the normal braking force is applied, and the length of the period during which braking does not occur.

[0040] Furthermore, if the friction brake 30 is equipped with a temperature sensor for detecting the temperature of the friction portion 32, the temperature derivation unit M22 may derive the friction portion temperatures TPpdL and TPpdR based on the detection signal from the temperature sensor.

[0041] The friction part temperatures TPpdL and TPpdR derived by the temperature derivation unit M22 are transmitted to the in-vehicle network 100. Therefore, the second control device 63 can acquire the friction part temperature TPpdR derived by the temperature derivation unit M22 of the second control device 64. The second control device 64 can acquire the friction part temperature TPpdL derived by the temperature derivation unit M22 of the second control device 63.

[0042] <Memory Unit>The memory unit M23 stores thermal expansion amount information, which is information related to the thermal expansion amount of the friction part 32. The thermal expansion amount information is information related to the thermal expansion amount of the friction part 32 when a parking brake request occurs. For example, the memory unit M23 stores the friction part temperatures TPpdL and TPpdR derived by the temperature derivation unit M22 when a parking brake request occurs as the thermal expansion amount information. At this time, each of the memory unit M23 of the second control device 63 corresponding to the second wheel 12L and the memory unit M23 of the second control device 64 corresponding to the second wheel 12L stores the friction part temperature TPpdL of the friction part 32 for the second wheel 12L and the friction part temperature TPpdR of the friction part 32 for the second wheel 12R.

[0043] <Setting Unit>Based on the thermal expansion amount information stored in the memory unit M23, the setting unit M24 sets one of the two second control devices 63 and 64 for the second wheels 12L and 12R as the main control device 60M. For example, the setting unit M24 sets the second control device that controls the electric braking device 22 having the friction part 32 with the largest thermal expansion amount indicated by the thermal expansion amount information as the main control device 60M. The setting unit M24 sets the second control device that is not set as the main control device 60M among the two second control devices 63 and 64 as the sub-control device 60S.

[0044] Among the two electric braking devices 22 provided with the holding unit, the electric braking device 22 controlled by the main control device 60M corresponds to the "first electric braking device". The electric braking device 22 controlled by the sub-control device 60S corresponds to the "second electric braking device".

[0045] Referring to FIG. 4, the setting processes of the main control device 60M and the sub-control device 60S will be described. In step S11, the setting unit M24 acquires from the storage unit M23 the friction part temperature TPpdL of the friction part 32 for the second wheel 12L and the friction part temperature TPpdR of the friction part 32 for the second wheel 12R at the time when the parking brake request occurs.

[0046] In the subsequent step S13, the setting unit M24 sets the main control device 60M based on the comparison result between the friction part temperature TPpdL and the friction part temperature TPpdR. For example, when the friction part temperature TPpdL is equal to or higher than the friction part temperature TPpdR, the setting unit M24 sets the second control device 63 of the electric braking device 22 for the second wheel 12L as the main control device 60M. On the other hand, when the friction part temperature TPpdL is lower than the friction part temperature TPpdR, the setting unit M24 sets the second control device 64 of the electric braking device 22 for the second wheel 12R as the main control device 60M.

[0047] In the next step S15, the setting unit M24 sets the second control device that is not the second control device set as the main control device 60M among the two second control devices 63 and 64 as the sub-control device 60S. After that, the setting unit M24 ends the setting process shown in FIG. 4.

[0048] <Stop control unit> Under the situation where the braking forces applied by the two electric braking devices 22 to the second wheels 12L and 12R are held by the braking force holding mechanism 50, the operation of the main control device 60M is held and then the operation of the sub-control device 60S is stopped to transition the sub-control device 60S to the power saving state. As described above, one of the two second control devices 63 and 64 is set as the main control device 60M, and the remaining second control device is set as the sub-control device 60S. Then, the stop control unit M25 of the second control device set as the main control device 60M functions, while the function of the stop control unit M25 of the second control device set as the sub-control device 60S is stopped. Hereinafter, the stop control unit M25 of the second control device set as the main control device 60M will be simply described as "the stop control unit M25 of the main control device 60M".

[0049] The stop control unit M25 of the main control unit 60M transmits stop permission information to the sub-control unit 60S, which authorizes the cessation of its operation. Upon receiving the stop permission information, the sub-control unit 60S shuts itself down. As a result, the operation of the sub-control unit 60S is stopped, and the state of the sub-control unit 60S transitions to a power-saving state.

[0050] <Start Control Unit> The start control unit M26 of the second control unit set on the main control unit 60M functions, while the function of the start control unit M26 of the second control unit set on the sub-control unit 60S is stopped. Hereafter, the start control unit M26 of the second control unit set on the main control unit 60M will be simply referred to as "the start control unit M26 of the main control unit 60M".

[0051] While the sub-controller 60S is in a power-saving state, the braking control unit M21 of the main control unit 60M may perform a reclamping process. In this case, after the braking control unit M21 of the main control unit 60M performs the reclamping process, the start control unit M26 of the main control unit 60M sends a start command to the sub-controller 60S to start it up. When the sub-controller 60S receives the start command, it starts up. When the sub-controller 60S starts up, the start control unit M26 of the main control unit 60M sends execution command information to the sub-controller 60S indicating that it will perform a reclamping process. When the sub-controller 60S receives the execution command information, the braking control unit M21 of the sub-controller 60S performs the reclamping process. In other words, when the start control unit M26 of the main control unit 60M increases the braking force applied to the wheel corresponding to the electric brake device 22, which is the target of control of the sub-control unit 60S, it releases the power-saving state of the sub-control unit 60S and activates the sub-control unit 60S, allowing the sub-control unit 60S to control the braking force of the electric brake device 22.

[0052] Furthermore, when the braking control unit M21 of the sub-control device 60S completes the reclamping process, it transmits reclamping completion information to the main control device 60M, indicating that the reclamping process has been executed. When the stop control unit M25 of the main control device 60M receives the reclamping completion information from the sub-control device 60S, it transmits stop permission information to the sub-control device 60S, which is information that permits the operation of the control device to be stopped. When the sub-control device 60S receives the stop permission information, it shuts itself down. As a result, the state of the sub-control device 60S transitions back to the power-saving state.

[0053] <Processing flow after applying parking brake force> Referring to Figures 5(a) and 5(b), the processing flow when the power switch of vehicle 10 is turned off while parking brake force is applied to vehicle 10 will be explained.

[0054] When the power switch of the vehicle 10 is turned off, the main control unit 60M functions as a stop control unit M25 and transmits stop permission information to the sub-control unit 60S (ST100). Upon receiving the stop permission information, the sub-control unit 60S notifies the main control unit 60M that it will stop its own operation (ST201). Then, the sub-control unit 60S shuts itself down (ST202). As a result, the power supply from the power system 15 to the sub-control unit 60S is stopped, and the state of the sub-control unit 60S transitions to a power-saving state. Note that the process by which the sub-control unit 60S notifies the main control unit 60M that it will stop its own operation (ST201) may be omitted.

[0055] After the operation of the sub-control device 60S is stopped, the main control device 60M performs a determination process to determine whether or not the reclamping process can be executed (ST101). In this determination process, the main control device 60M determines that the conditions for executing the reclamping process have been met if the detected value of the pressing force sensor 55 of the electric brake device 22, which is the object of its control, falls below a predetermined threshold. This allows the decrease in pressing force to be determined by the actual detected value. In addition, in this determination process, the main control device 60M may also determine that the conditions for executing the reclamping process have been met if the elapsed time since the last parking brake request has exceeded a predetermined determination elapsed time. In this case, the elapsed determination time is a criterion for determining whether the amount of thermal expansion of the friction part 32 has become sufficiently small since the start of the application of parking brake force. If the amount of thermal expansion of the friction part 32 becomes small, the pressing force, i.e., the parking brake force, will decrease even if the motor rotation angle θmt is maintained. The higher the temperature of the friction part 32, the greater the amount of thermal expansion of the friction part 32. Therefore, the higher the temperature of the friction part 32, the longer the determination elapsed time is set. Of course, a predetermined time may be set as the elapsed time for the determination.

[0056] When the main control unit 60M determines that the conditions for executing the reclamping process have been met, the main control unit 60M functions as the braking control unit M21 and executes the reclamping process (ST102). This allows the main control unit 60M to increase the parking braking force. Once the increase in parking braking force due to the reclamping process is complete, the main control unit 60M functions as the start control unit M26 and transmits a start command to the sub-control unit 60S (ST103).

[0057] When the sub-control device 60S receives the startup instruction, the sub-control device 60S executes the startup process (ST203). This releases the power-saving state of the sub-control device 60S, and the operation of the sub-control device 60S resumes. The sub-control device 60S then transmits startup completion information, which indicates that its startup is complete, to the main control device 60M (ST204). Note that the process by which the sub-control device 60S transmits startup completion information to the main control device 60M (ST204) may be omitted.

[0058] Upon receiving startup completion information, the main control unit 60M functions as a start control unit M26 and transmits a reclam command, which is a command to prompt the execution of the reclam process, to the sub-control unit 60S (ST104).

[0059] When the sub-control device 60S receives a reclam command, it functions as the brake control unit M21 and executes the reclam process (ST205). This allows the sub-control device 60S to increase the parking braking force. When the sub-control device 60S finishes executing the reclam process, it transmits reclam completion information to the main control device 60M (ST206).

[0060] When the main control unit 60M receives information that the reclamping is complete, it functions as a stop control unit M25 and transmits stop permission information to the sub-control unit 60S (ST105). When the sub-control unit 60S receives the stop permission information, it notifies the main control unit 60M that it will stop its own operation (ST207). Note that the process by which the sub-control unit 60S notifies the main control unit 60M that it will stop its own operation (ST207) may be omitted. Then, the sub-control unit 60S shuts itself down (ST208). As a result, the power supply from the power supply system 15 to the sub-control unit 60S is stopped again, and the state of the sub-control unit 60S transitions to a power-saving state.

[0061] <Operation and Effects of This Embodiment> (1-1) When a parking brake request occurs, the multiple electric braking devices 22 apply parking braking force to the corresponding second wheels 12L and 12R. In the multiple electric braking devices 22, the motor rotation angle θmt is maintained by the braking force holding mechanism 50.

[0062] Of the two second control devices 63 and 64, one is set to the main control device 60M, while the other is set to the sub-control device 60S. The stop control unit M25 of the main control device 60M maintains the operating state of the main control device 60M and permits the stopping of the operation of the sub-control device 60S. As a result, the sub-control device 60S shuts down, and its state transitions to a power-saving state. When the state of the sub-control device 60S transitions to a power-saving state, the overall power consumption of the system is reduced compared to when the operation of the sub-control device 60S continues.

[0063] While the sub-control device 60S is in a power-saving state, the main control device 60M may perform a reclamping process. When the main control device 60M performs a reclamping process, the start control unit M26 of the main control device 60M activates the sub-control device 60S. After the sub-control device 60S starts operating in this manner, it becomes possible to increase the parking braking force by activating the electric brake device 22, which is the device it controls.

[0064] Therefore, the braking system 20 can maintain the vehicle 10 in a stopped state while suppressing an increase in power consumption in the system during parking braking. (1-2) In the braking system 20 of this embodiment, when the operation of the sub-controller 60S is restarted as a result of the reclamping process being executed by the main control unit 60M, the sub-controller 60S executes the reclamping process. This increases the parking braking force of the vehicle 10. Therefore, the braking system 20 can suppress the continuation of a state in which the parking braking force is reduced due to the contraction of the friction part 32.

[0065] (1-3) In the braking system 20 of this embodiment, when the sub-control device 60S performs a reclamping process, the state of the sub-control device 60S transitions back to the power-saving state. Therefore, the braking system 20 can reduce the power consumption of the system compared to the case where the sub-control device 60S continues to operate after the reclamping process is performed.

[0066] (1-4) After the reclamping process is performed by the sub-controller 60S, the stop control unit M25 of the main control unit 60M transmits stop permission information to the sub-controller 60S. When the sub-controller 60S receives the stop permission information, the operation of the sub-controller 60S is stopped. This prevents either the main control unit 60M or the sub-controller 60S from unintentionally stopping their operation.

[0067] (1-5) The greater the thermal expansion of the friction part 32 at the time a parking brake request is made, the greater the subsequent decrease in parking braking force due to the temperature drop of the friction part 32 tends to be. In order to maintain the vehicle 10 in a stopped state, it is preferable to set the second control device that controls the electric brake device 22 for the second wheel, which has the greatest decrease in parking braking force, to the main control device 60M.

[0068] In the braking system 20 of this embodiment, the main control device 60M is set based on the thermal expansion amount information stored in the memory unit M23. Specifically, the second control device that controls the electric brake device 22 having the hottest friction part 32 is set in the main control device 60M. This prevents the operation of the second control device that controls the electric brake device 22 which is most likely to experience a decrease in parking braking force after a parking braking request is made from stopping. Therefore, the braking system 20 can monitor the state of the electric brake device 22 which is most likely to experience a decrease in parking braking force among the multiple electric brake devices 22 using the pressing force sensor 55 of that electric brake device 22. Based on the state of the electric brake device 22 which is most likely to experience a decrease in parking braking force, the braking system 20 can determine the timing for executing the reclamping process and the timing for starting the operation of the sub-control device 60S.

[0069] (Second Embodiment) A second embodiment of the braking system will be described with reference to Figure 6. In the second embodiment, after the sub-controller 60S is activated in conjunction with the execution of the re-clamping process by the main control device 60M, some of the processing content in the sub-controller 60S differs from that of the first embodiment. In the following description, the parts that differ from the first embodiment will be mainly described, and the same reference numerals will be used for components identical to those in the first embodiment to avoid redundant explanations.

[0070] Figure 6 shows a flowchart illustrating a series of processes executed by the sub-controller 60S when the sub-controller 60S is activated in conjunction with the execution of the reclamping process by the main control unit 60M.

[0071] In step S21, the sub-controller 60S transmits startup completion information to the main control unit 60M, which indicates that it has started up. In the following step S22, the sub-controller 60S determines whether the startup instruction from the main control unit 60M is a normal startup instruction or a reclam startup instruction. A normal startup instruction is a normal startup instruction. A reclam startup instruction is a startup instruction that occurs when the main control unit 60M performs a reclam operation. If the startup instruction from the main control unit 60M is a reclam startup instruction (S22: YES), the sub-controller 60S proceeds to step S23. On the other hand, if the startup instruction from the main control unit 60M is a normal startup instruction (S22: NO), the sub-controller 60S terminates the series of processes shown in Figure 6.

[0072] In step S23, the sub-control device 60S determines whether or not it is necessary to perform a reclamping process. For example, the sub-control device 60S may determine whether or not it is necessary to perform a reclamping process based on the gradient of the road surface on which the vehicle 10 is stopped. In this case, if the sub-control device 60S determines that the road surface is an incline, it determines that it is necessary to perform a reclamping process. On the other hand, if the sub-control device 60S determines that the road surface is not an incline, it determines that it is not necessary to perform a reclamping process. If the sub-control device 60S determines that it is necessary to perform a reclamping process (S23: YES), the sub-control device 60S proceeds to step S25. On the other hand, if the sub-control device 60S determines that it is not necessary to perform a reclamping process (S23: NO), the sub-control device 60S proceeds to step S29.

[0073] In step S25, the sub-control device 60S performs the reclamping process by functioning as the braking control unit M21. When the sub-control device 60S finishes the reclamping process, it moves the process to step S27. In step S27, the sub-control device 60S transmits reclamping completion information to the main control device 60M. Then, the sub-control device 60S moves the process to step S31.

[0074] In step S29, the sub-controller 60S transmits to the main control unit 60M that the reclamping process is not required. The sub-controller 60S then proceeds to step S31.

[0075] Furthermore, when the main control unit 60M receives from the sub-control unit 60S at least one of the following: that the reclamping process is unnecessary and that the reclamping process is complete, it functions as a stop control unit M25 and transmits stop permission information to the sub-control unit 60S.

[0076] In step S31, the sub-controller 60S determines whether or not it has received stop permission information from the main controller 60M. If the sub-controller 60S has not yet received stop permission information (S31: NO), the sub-controller 60S repeatedly performs the determination in step S31 until it receives stop permission information. On the other hand, if the sub-controller 60S has received stop permission information (S31: YES), the sub-controller 60S proceeds to step S33.

[0077] In step S33, the sub-control device 60S stops operating by shutting itself down. <Effects and Effects of this Embodiment> In addition to the effects of the first embodiment described above, the braking system 20 of this embodiment can further obtain the following effects.

[0078] (2-1) When the sub-controller 60S is activated in conjunction with the execution of the reclamping process by the main control unit 60M, if the sub-controller 60S determines that the vehicle 10 can remain stationary without increasing the parking brake force, it stops its own operation without executing the reclamping process. On the other hand, if the sub-controller 60S determines that the reclamping process is necessary, it executes the reclamping process and increases the parking brake force. Therefore, the sub-controller 60S can maintain the stationary state of the vehicle 10 while preventing the reclamping process from being executed excessively.

[0079] (Third Embodiment) A third embodiment of the braking system will be described with reference to Figure 7. The third embodiment differs from the above multiple embodiments in that the main control device 60M does not perform the reclamping process when it is determined that the reclamping process is unnecessary. In the following description, the parts that differ from the above multiple embodiments will be mainly described, and the same reference numerals will be used for components that are the same as in the above multiple embodiments to avoid redundant explanations.

[0080] Figure 7 illustrates a series of processes performed by the main control unit 60M. After the apply process is performed in both the main control unit 60M and the sub-control unit 60S and the operation of the sub-control unit 60S is stopped, the main control unit 60M performs the series of processes.

[0081] In step S51, the main control unit 60M determines whether or not it is unnecessary to perform the reclamping process. For example, if the main control unit 60M determines that the temperature of the friction part 32 of the electric brake device 22 controlled by the main control unit 60M is substantially at room temperature, the main control unit 60M can determine that it is unnecessary to perform the reclamping process. Also, for example, if the main control unit 60M determines that the vehicle 10 is stopped on a level road, the main control unit 60M can determine that it is unnecessary to perform the reclamping process. If the main control unit 60M determines that it is unnecessary to perform the reclamping process (S51: YES), the main control unit 60M proceeds to step S53. On the other hand, if the main control unit 60M determines that it is not unnecessary to perform the reclamping process (S51: NO), the main control unit 60M terminates the series of processes shown in Figure 7. In this case, the main control unit 60M continues to operate.

[0082] In step S53, the main control unit 60M stops operating by shutting itself down. That is, the state of the main control unit 60M transitions to a power-saving state.

[0083] In the braking system 20 of this embodiment, in addition to the effects of the first embodiment described above, the following further effects can be obtained. (3-1) In the braking system 20 of this embodiment, if it is determined that an increase in parking braking force is not necessary after the parking braking force has been applied to the vehicle 10 by the apply process, the main control device 60M will not perform the reclamping process. As a result, the braking system 20 can suppress the excessive execution of the reclamping process.

[0084] Furthermore, if the main control unit 60M does not execute the re-clamping process, the operation of the main control unit 60M is also stopped. As a result, the braking system 20 can further reduce the overall power consumption of the system.

[0085] (Examples of modifications) The above multiple embodiments can be implemented with the following modifications. The above multiple embodiments and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0086] In the third embodiment described above, if the main control unit 60M determines that it is not necessary to perform the reclamping process while the sub-control unit 60S is stopped, the main control unit 60M does not need to perform a shutdown.

[0087] In the above-described embodiments, other control devices besides the main control device 60M and the sub-control device 60S may function as the stop control device M25. The other control device may be one of the multiple first control devices 61, 62, or it may be a control unit.

[0088] In the above-described embodiments, a control device other than the main control device 60M and the sub-control device 60S may function as the start control unit M26. The other control device may be one of the multiple first control devices 61, 62, or it may be a control unit.

[0089] - The thermal expansion amount information stored in the memory unit M23 may be parameters other than the friction temperature of the friction part 32. For example, if the electric braking device 22 is equipped with a detection system that can detect the amount of thermal expansion of the friction part 32, the thermal expansion amount information may be the value of the thermal expansion detected by the detection system.

[0090] The main control device 60M may continue to derive the friction temperature of the friction part 32 of the electric brake device 22 that it controls, even after the apply process has been executed. The main control device 60M may also determine, for example, that the conditions for executing the reclamp process have been met when the amount of decrease in the friction temperature since the execution of the apply process exceeds a predetermined amount.

[0091] - The main control unit 60M and the sub-control unit 60S may be set based on information other than the amount of thermal expansion of the friction part 32 at the time the parking brake request is made. For example, if the second control unit 63 was set to the main control unit 60M during the previous parking brake, the second control unit 64 may be set to the main control unit 60M during the current parking brake.

[0092] - Of the two second control devices 63 and 64, one may be fixed to the main control device 60M and the other to the sub-control device 60S. - An electric braking device equipped with a braking force holding mechanism 50 may be used as the electric braking device 21. In this case, parking braking force can also be applied to the first wheels 11L and 11R. In this case, the main control device 60M and the sub-control device 60S can be selected from the four control devices 61 to 64. In this case, the number of control devices set in the main control device 60M may be two. For example, one of the two first control devices 61 and 62 may be set in the main control device 60M, and one of the two second control devices 63 and 64 may be set in the main control device 60M. In this case, the first control device set in the sub-control device 60S will stop operating. Therefore, when the first control device set in the main control device 60M performs a reclam process, it sends a start command to the first control device set in the sub-control device 60S. As a result, the first control device set in the sub-control device 60S starts up.

[0093] - An electric braking device having a holding function may be an electric braking device equipped with an electric cylinder powered by an electric motor. - The electric braking device 22 drives the electric motor 40 whether it is applying a normal braking force or a parking braking force. However, an electric braking device may have a different configuration from the electric braking device 22, as long as it applies a parking braking force to the wheels by driving an electric motor and has a holding function that maintains the motor rotation angle θmt even when the power supply to the electric motor is stopped. For example, the electric braking device may be a device equipped with a friction brake having a wheel cylinder and a parking braking actuator. The parking braking actuator has a self-locking function that maintains the motor rotation angle θmt. This self-locking function corresponds to the "holding part". For example, an example of such an electric braking device is the device disclosed in "Japanese Patent Application Publication No. 2024-83033".

[0094] The control devices 61 to 64 may be configured as circuits including one or more dedicated hardware circuits, such as one or more processors that operate according to a computer program, and dedicated hardware that performs at least some of the various processes, or a combination thereof. Examples of dedicated hardware include application-specific integrated circuits (ASICs). The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., storage medium, includes any available medium that can be accessed by a general-purpose or dedicated computer.

[0095] (Other technical ideas) The technical ideas that can be understood from the above multiple embodiments and modifications are described below. [Note 1] It is preferable that the setting unit sets the control devices other than the main control device and the control device set as the sub-control devices from among the multiple control devices.

[0096] In this specification, the expression "at least one" means "one or more" of the desired options. For example, if there are two options, the expression "at least one" means "only one option" or "both of the two options." As another example, if there are three or more options, the expression "at least one" means "only one option" or "a combination of two or more arbitrary options."

Claims

1. A braking system comprising: a plurality of electric braking devices that apply braking force to each of a plurality of wheels of a vehicle by the driving force of an electric motor; at least two control devices that control the plurality of electric braking devices; and a holding unit provided in at least two of the plurality of electric braking devices that mechanically prevents the rotation of the electric motor so as to maintain the rotation angle of the electric motor even when the drive of the electric motor is stopped while braking force is applied to the wheels by the driving force of the electric motor, wherein the braking system comprises: a main control device which is a part of the plurality of control devices and controls a first electric braking device which is a part of the electric braking device on which the holding unit is provided; a sub-control device which is a separate control device from the main control device among the plurality of control devices and controls a second electric braking device which is at least one of the remaining parts of the electric braking device on which the holding unit is provided; and a stop control device which, while maintaining the operation of the main control device, stops the operation of the sub-control device and transitions the sub-control device to a power-saving state while the braking force from the first electric braking device and the second electric braking device is maintained by the holding unit. A braking system characterized by comprising: a start control unit that, when increasing the braking force applied to the wheel corresponding to the second electric braking device, releases the power-saving state of the sub-control device and activates the sub-control device, and causes the sub-control device to control the braking force of the second electric braking device.

2. The braking system according to claim 1, wherein each of the plurality of electric braking devices is configured to apply braking force to a wheel by pressing a friction part against a rotating body that rotates integrally with the corresponding wheel when driven by the electric motor, and further comprises: a storage unit for storing information relating to the amount of thermal expansion of the friction part; and a setting unit for setting the main control unit to control the electric braking device having the friction part with the largest amount of thermal expansion indicated by the information stored in the storage unit, among the first electric braking device and the second electric braking device.

3. The braking system according to claim 1, wherein the main control device includes the start control unit and the stop control unit, and when the start control unit activates the sub-control device by releasing the power-saving state in order to increase the braking force of the wheel corresponding to the second electric brake device, the sub-control device performs a reclamping process to increase the braking force by operating the second electric brake device, and transmits reclamping completion information to the stop control unit indicating that the reclamping process has been performed, and when the main control device receives the reclamping completion information from the sub-control device, the stop control unit stops the operation of the sub-control device while maintaining the operation of the main control device, and transitions the sub-control device to the power-saving state.

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