Brake system

Abstract

To suppress noise generated in an electric actuator while suppressing dragging in an electric parking brake operated by the electric actuator.SOLUTION: In a brake system, release control of an electric parking brake is performed in a form that varies on the basis of a brake temperature. Due to this configuration, while dragging is suppressed, a release control amount of a drive member after pressing force becomes smaller than a set value is set to an appropriate amount. As a result, a waste operation of an electric actuator can be suppressed so as to make length of an operating time appropriate, and operating noise generated in the electric actuator can be suppressed.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a brake system including a parking brake.

Background Art

[0002] Patent Document 1 describes a disc brake in which a friction engagement member is shared by a parking brake and a service brake. In this disc brake, when the brake temperature decreases in the operating state of the parking brake, an urging force for pressing the friction engagement member against the brake rotor is added. Thereby, it is possible to suppress a decrease in the urging force caused by a temperature decrease in the operating state of the parking brake.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to suppress squeal and suppress noise generated in an electric actuator in an electric parking brake actuated by an electric actuator.

Means for Solving the Problems

[0005] In this brake system, when releasing the electric parking brake, release control is performed by the operation of the electric actuator. This release control is performed in different modes based on the brake temperature.

[0006] For example, consider a case where first release control and second release control are performed as release controls. The first release control is a control that retracts the drive member by operating the electric actuator until the pressing force in the electric parking brake becomes smaller than the set value. The second release control is a control that further retracts the drive member by operating the electric actuator after the pressing force in the electric parking brake becomes smaller than the set value. When the vehicle travels after the electric parking brake is released and the service brake is actuated, the brake temperature, which is the temperature of the electric parking brake, increases. When the brake temperature increases, the friction engagement member may thermally expand and cause dragging. To avoid this, the second release control is performed to retract the drive member in advance.

[0007] When the brake temperature at the time of releasing the electric parking brake is high, the release control amount of the drive member in the first release control becomes larger than when it is low. This is because the friction engagement member is thermally expanded more when the brake temperature is high than when it is low. The release control amount refers to the retraction amount by which the drive member is retracted in the release control. Also, it is desirable that the release control amount of the drive member in the second release control be larger when the brake temperature is low than when it is high. When the brake temperature at the time of releasing the electric parking brake is low, the brake temperature tends to increase due to the actuation of the service brake during driving, the friction engagement member tends to thermally expand, and dragging is likely to occur.

[0008] In this way, by performing the release control of the electric parking brake in different modes based on the brake temperature, while suppressing dragging, the release control amount of the drive member after the pressing force becomes smaller than the set value can be determined to be an appropriate magnitude. As a result, wasteful operation of the electric actuator can be suppressed, and the operation time can be made an appropriate length. The operation noise generated in the electric actuator can be suppressed, and power consumption can be reduced.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0010] Hereinafter, a braking system according to an embodiment of the present invention will be described in detail with reference to the drawings.

Example

[0011] As shown in FIG. 1, the braking system according to this example is provided in a vehicle and includes disc brakes 10FL, 10FR, 10RL, 10RR, etc. The disc brakes 10FL, 10FR, 10RL, 10RR are provided corresponding to each of the front, rear, left, and right wheels of the vehicle. Hereinafter, the subscripts FL, FR, RL, RR representing the wheel positions are omitted when there is no need to distinguish by wheel position for disc brakes, etc., or when generalizing. The disc brake 10 can operate as both a service brake and a parking brake.

[0012] The disc brake 10 suppresses the rotation of the wheel by pressing a pair of friction pads 14, 15 against the brake rotor 12 and bringing them into frictional engagement. The disc brake 10 includes a pair of friction pads 14, 15, a pressing device 16, and the like. The brake rotor 12 is rotatable integrally with the wheel. The friction pads 14, 15 are located on both sides of the brake rotor 12. The friction pads 14, 15 each include a frictional engagement member 14f, 15f and a back plate 14r, 15r. The pressing device 16 includes a caliper 20, a piston 22, a driving device 24, and the like. In this embodiment, the driving device 24 includes a hydraulic driving device 26 and an electric driving device 28. Also, the friction pads 14, 15 are common to the service brake and the parking brake.

[0013] The caliper 20 is held movably in a direction parallel to the rotation axis of the wheel by a non-rotating member. A piston 22 is held in a cylinder bore provided in the caliper 20 so as to be non-rotatable and relatively movable with respect to the caliper 20. The piston 22 is an example of a pressing member, and a piston seal 29 is provided on the outer peripheral portion of the piston 22. The rear of the piston 22 in the cylinder bore of the caliper 20 is a hydraulic chamber 30.

[0014] The hydraulic driving device 26 includes a hydraulic chamber 30, a hydraulic source 32, a hydraulic control unit 34, and the like. The hydraulic source 32 is connected to the hydraulic chamber 30 via the hydraulic control unit 34. The hydraulic source 32 includes at least one of a manual hydraulic source and a power hydraulic source. The manual hydraulic source generates hydraulic pressure by an operation of a brake operation member by the driver. The power hydraulic source can generate hydraulic pressure even when the brake operation member is not operated by driving a pump or the like. For example, the hydraulic control unit 34 can include one or more solenoid valves or the like. The hydraulic pressure of the hydraulic source 32 is controlled by the hydraulic control unit 34 and supplied to the hydraulic chamber 30. The piston 22 is advanced by the hydraulic pressure in the hydraulic chamber 30, and the service brake is actuated.

[0015] The electric drive device 28 includes an electric actuator 50, a nut member 52, a rotary transmission device 54, a motion conversion device 56, etc. The electric actuator 50 includes an electric motor. The nut member 52 is an example of a drive member. The nut member 52 is provided on the inner peripheral side of the piston 22 so as to be relatively movable and non-rotatable with respect to the piston 22. The rotary transmission device 54 transmits the rotation of the electric actuator 50 to the motion conversion device 56, for example. The rotary transmission device 54 can have a plurality of gears. The motion conversion device 56 can have a screw mechanism, for example. The motion conversion device 56 converts the rotational motion of the electric actuator 50 into a linear motion to linearly move the nut member 52. When the nut member 52 is linearly moved by the electric actuator 50, the piston 22 is advanced and the parking brake is actuated. Therefore, the parking brake can be referred to as an electric parking brake.

[0016] In addition, due to the screw mechanism of the motion conversion device 56, it is difficult for the electric actuator 50 to be rotated by an external force in the operating state of the parking brake. Therefore, in the operating state of the parking brake, the pressing force is maintained even if no power is supplied to the electric actuator 50.

[0017] In this embodiment, the service brake and the parking brake are each driven by a separate drive device.

[0018] The braking system includes a brake ECU (electronic control unit) 80 mainly composed of a computer. A hydraulic control unit 34, an electric actuator 50, etc. are connected to the brake ECU 80, and an electronic parking brake switch (EPBSW) 82, a wheel speed sensor 84, a longitudinal and lateral acceleration sensor 86, a hydraulic pressure sensor 88, a current sensor 90, an outside air temperature sensor 92, etc. are also connected. The EPBSW 82 can be manually operated. An operation in the non-actuated state of the parking brake gives an actuation instruction, and an operation in the actuated state of the parking brake gives a release instruction. The wheel speed sensor 84 is provided for each of the front, rear, left, and right wheels to detect the rotational speed of the wheels. The longitudinal and lateral acceleration sensor 86 detects the longitudinal and lateral acceleration of the vehicle. The hydraulic pressure sensor 88 detects the hydraulic pressure in each hydraulic chamber 30 of the disc brake 10. The current sensor 90 detects the current flowing through each electric actuator 50 of the disc brake 10. The outside air temperature sensor 92 detects the temperature of the atmosphere around the vehicle.

[0019] In the braking system configured as described above, when hydraulic pressure is supplied to the hydraulic chamber 30, the piston 22 is advanced, and the friction pad 15 is pressed against the brake rotor 12. The caliper 20 is moved, and the friction pad 14 is pressed against the brake rotor 12 by the caliper 20. The pair of friction pads 14, 15 are pressed against the brake rotor 12, and the service brake is actuated. When the hydraulic pressure in the hydraulic chamber 30 is released, the piston 22 is retracted by the restoring force of the piston seal 29. The piston 22 may also be retracted by vibrations of the brake rotor 12 or the like during vehicle travel.

[0020] When the service brake is in the actuated state and the vehicle is stopped, if the EPBSW82 is operated, the parking brake is actuated by the operation of the electric actuator 50. The nut member 52 is advanced and abuts against the inner peripheral surface of the piston 22. By the advancement of the piston 22, the friction pads 14, 15 are further pressed against the brake rotor 12. Thereby, the parking brake is actuated. When the EPBSW82 is operated in the actuated state of the parking brake, the nut member 52 is retracted by the operation of the electric actuator 50. The piston 22 is returned by the piston seal 29. The nut member 52 is retracted relative to the piston 22. The nut member 52 is further retracted after the pressing force of the parking brake becomes smaller than the set value.

[0021] In this specification, in the disc brake 10, the pressing force when the pair of friction pads 14, 15 are pressed against the brake rotor 12 may be simply referred to as the pressing force, the pressing force of the disc brake, the pressing force of the parking brake, the pressing force of the service brake, etc.

[0022] Also, the retraction limit of the piston 22 in the disc brake is determined by the nut member 52. As described above, the piston 22 may be retracted by the vibration of the brake rotor 12, but the piston 22 can be retracted until it abuts against the nut member 52.

[0023] In a conventional braking system, first release control and second release control were performed as release control for controlling the release of the parking brake. The first release control is control for retracting the nut member 52 until the pressing force becomes smaller than the set value. The second release control is control for retracting the nut member 52 by a predetermined set release control amount after the pressing force becomes smaller than the set value. The second release control is performed to suppress dragging during vehicle travel. For example, when the temperature of the friction pads 14, 15 is approximately the outside air temperature at the time of releasing the parking brake, if the temperature of the friction pads 14, 15 increases due to the operation of the service brake during travel after releasing the parking brake, the friction pads 14, 15 expand greatly due to heat. In this case, if the set release control amount is small, even if a force in the retracting direction acts on the piston 22 due to the vibration of the brake rotor 12, the retraction of the piston 22 may be restricted by the nut member 52, and dragging may occur.

[0024] Therefore, in the conventional braking system, the set release control amount was set to a large value. As described above, the set release control amount is a value determined based on, for example, the thermal expansion of the friction pads 14, 15 when it is assumed that the temperature of the friction pads 14, 15 becomes high due to the operation of the service brake during travel when the temperature of the friction pads 14, 15 at the time of releasing the parking brake is the outside air temperature. And, regardless of whether the temperature of the friction pads 14, 15 at the time of releasing the parking brake is high or low, the nut member 52 was made to be retracted by the set release control amount.

[0025] Hereinafter, the temperatures of the friction pads 14 and 15 (friction engagement members 14f and 15f) of the disc brake 10 are referred to as the brake temperature. In this embodiment, the brake temperature is classified into a high temperature, a normal temperature, and a cold temperature. The high temperature is the temperature at which the friction engagement members 14f and 15f are in an abnormal overheated state. The high temperature can be, for example, a temperature of 300°C or higher. The normal temperature is the temperature of the friction engagement members 14f and 15f during the normal operation of the service brake. The normal temperature can be, for example, a temperature lower than 300°C and higher than 100°C. The cold temperature can be a temperature approximately equal to the outside air temperature. For example, it can be a temperature lower than 100°C.

[0026] The brake temperature can be estimated based on, for example, the temperatures of the friction pads 14 and 15 in the operating state of the service brake, the operating time of the parking brake, the outside air temperature when the EPBSW 82 is operated, and the like.

[0027] For example, when the operating time of the parking brake is shorter than a first set time which is the set time, it can be estimated that the brake temperature at the time of releasing the parking brake belongs to the same classification as the brake temperature in the operating state of the service brake. When the operating time of the parking brake is longer than a second set time which is the set time, it can be estimated that the brake temperature at the time of releasing the parking brake is a cold temperature.

[0028] When the operating time of the parking brake is equal to or longer than the first set time and equal to or shorter than the second set time, it can be estimated that the brake temperature at the time of releasing the parking brake is a temperature affected by the brake temperature in the operating state of the service brake. For example, when the brake temperature in the operating state of the service brake is a high temperature, it can be estimated that the brake temperature at the time of releasing the parking brake is a normal temperature. When the brake temperature in the operating state of the service brake is a normal temperature, it can be estimated that the brake temperature at the time of releasing the parking brake is a cold temperature.

[0029] Also, the brake temperature in the operating state of the service brake can be estimated based on the wheel rotation speed, longitudinal and lateral accelerations, hydraulic pressure, etc. For example, when the wheel speed is high, the frictional heat is more likely to be high than when it is low, so the brake temperature is estimated to be high. When the hydraulic pressure is high, the pressing force is greater than when it is low, and the frictional force is large, so the brake temperature is estimated to be high. When the longitudinal acceleration, i.e., the deceleration, is large, it can be estimated that the braking force is greater than when it is small, and the brake temperature is estimated to be high.

[0030] Also, when the service brake is actuated while the vehicle is under high-load driving, the brake temperature can be estimated to be high. High-load driving refers to driving in which a high load is applied to the service brake, such as driving on a long downhill slope or high-speed driving on a road with many curves (referred to as circuit driving).

[0031] When the service brake is actuated while the vehicle is under normal driving, the brake temperature can be estimated to be normal temperature.

[0032] Also, the release of the parking brake refers to at least a period from the start to the end of the release control. While the release control is being performed, the brake temperature can be estimated to be substantially constant. Also, the release of the parking brake can be set to the time when the operation of EPBSW82 is performed in the operating state of the service brake.

[0033] On the other hand, when the release control amount of the nut member 52 in the second release control is large, the operating time of the electric actuator 50 becomes long. The release control amount refers to the retraction amount of the nut member 52 in the release control. Also, when the release control amount is large, the lock control amount, which is the forward movement amount of the nut member 52 when locking the parking brake, also becomes large, and the operating time of the electric actuator 50 becomes long. Since a sound is generated when the electric actuator 50 operates, there are problems such as being concerned about the sound. Therefore, it is desirable to set the operating time of the electric actuator 50 to an appropriate length.

[0034] As described above, in the conventional braking system, it was assumed that the brake temperature at the time of parking brake release was at the cold temperature. However, the brake temperature at the time of parking brake release is not necessarily the cold temperature. For example, it is conceivable that the parking brake is actuated in a state where the brake temperature in the operating state of the service brake is high, and the parking brake is released before the first set time elapses. In this case, it is estimated that the brake temperature at the time of parking brake release is high. Therefore, the release control amount of the nut member 52 in the first release control becomes large. On the other hand, it is considered that it is less likely that the brake temperature becomes higher than the brake temperature at the time of parking brake release due to the actuation of the service brake during the running of the vehicle after the parking brake is released. Therefore, even if the release control amount in the second release control is small, it is considered that dragging is less likely to occur.

[0035] From the above circumstances, when the brake temperature at the time of parking brake release is high, it is considered that there is little need to set the release control amount in the second release control to a large value. Therefore, in the present embodiment, the second release control is performed in different modes based on the brake temperature at the time of parking brake release. Specifically, the release control amount of the nut member in the second release control is determined based on the brake temperature.

[0036] Also, in the conventional braking system, it was assumed that the brake temperature would become high due to the actuation of the service brake during the running after the parking brake was released. However, there are cases where the brake temperature does not become high due to the actuation of the service brake during the running. For example, when the service brake is actuated during normal running, it is estimated that the brake temperature is at room temperature. Further, when the braking system is mounted on a front-wheel drive hybrid vehicle or a vehicle in which front-rear braking force distribution control is performed, in general, the pressing force of the disc brake 10 is smaller at the rear wheels than at the front wheels. Therefore, in the disc brake 10 of the rear wheels, it is less likely that the brake temperature becomes high during running.

[0037] From the above circumstances, in this embodiment, the release control amount of the nut member 52 in the second release control is set to a value smaller than the conventional set release control amount. Also, when the brake temperature becomes high during running after the parking brake is released, the nut member 52 is retracted. This release control of the nut member 52 is referred to as the third release control.

[0038] In this embodiment, when the operation of the EPBSW82 is performed in the operating state of the service brake (an example at the time of releasing the parking brake), the brake temperature is acquired.

[0039] In this embodiment, the release control for the parking brake includes, as described above, the first release control, the second release control, the third release control, and the like. When comparing the conventional brake system and the brake system according to this embodiment, the first release control is the same, but the second release control is different. In the conventional brake system, the second release control was performed in the same manner regardless of whether the brake temperature at the time of releasing the parking brake was high or low. In contrast, in this embodiment, the second release control is performed in different manners based on the brake temperature at the time of releasing the parking brake. Also, in the conventional brake system, the third release control is not performed, but in this embodiment, the third release control is performed when the brake temperature becomes high during running. In other words, in the conventional brake system, the third release control was part of the second release control, but in this embodiment, the third release control is separated from the second release control and is performed when the brake temperature becomes high during running.

[0040] In the first release control, for example, when conditions such as the current flowing through the electric actuator 50 being smaller than the set current and the change in the current being small continue for a set time or more are satisfied, it can be obtained that the pressing force is smaller than the set value. The state where the pressing force is smaller than the set value can be estimated as a state where the pressing force is approximately 0. Also, in the first release control, when the brake temperature is high, the release control amount of the nut member 52 is larger than when it is low. This is because the friction pads 14 and 15 are greatly thermally expanded.

[0041] In the second release control, when the brake temperature is high temperature or normal temperature, the release control amount is made smaller than when it is cold temperature. When the brake temperature at the time of parking brake release is high temperature or normal temperature, due to the operation of the service brake during driving, the possibility of dragging occurring because the brake temperature becomes higher than the brake temperature at the time of parking brake release is low. On the other hand, when the brake temperature at the time of parking brake release is cold temperature, when the brake temperature rises to normal temperature due to the operation of the service brake during driving, there is a possibility of dragging occurring due to insufficient release control amount of the nut member 52.

[0042] In this embodiment, the target release control amount in the second release control when the brake temperature at the time of parking brake release is cold temperature is referred to as the cold temperature release control amount. Also, the target release control amount in the second release control when it is normal temperature is referred to as the normal temperature release control amount, and the target release control amount in the second release control when it is high temperature is referred to as the high temperature release control amount. The high temperature release control amount and the normal temperature release control amount are smaller than the cold temperature release control amount.

[0043] For example, the high-temperature release control amount and the normal-temperature release control amount are determined to be a magnitude ΔRb that is considered to be unlikely to cause dragging even if the brake temperature rises due to multiple operations of the service brake during driving. For example, ΔRb can be determined based on the thermal expansion of the friction pads 14 and 15 due to the temperature rise caused by multiple operations of the service brake during driving, the uneven wear of the friction pads 14 and 15, the brake rotating body 12, etc., and a margin value.

[0044] For example, the cold-temperature release control amount is determined to be a magnitude (ΔRa + ΔRb) obtained by adding the above-described ΔRb to a magnitude ΔRa that is considered to be unlikely to cause dragging even if the brake temperature rises until it reaches the normal temperature during driving. ΔRa can be determined based on, for example, the thermal expansion of the friction pads 14 and 15 due to the rise in the temperature of the friction pads 14 and 15 from the cold temperature to the normal temperature.

[0045] In this way, at the start of the second release control, the target release control amount is determined based on the brake temperature, and the electric actuator 50 is operated until the actual release amount of the nut member 52 reaches the target release control amount.

[0046] The target release control amount in the third release control can be, for example, a magnitude ΔRc based on the thermal expansion of the friction pads when the brake temperature rises from the normal temperature to the high temperature. After the end of the second release control in the parking brake, when the vehicle performs high-load driving, etc., the brake temperature becomes high. On the other hand, when the brake temperature at the time of releasing the parking brake is the cold temperature or the normal temperature, in the second release control, the nut member 52 is retracted without considering the thermal expansion when the brake temperature becomes high. Therefore, after the end of the second release control, when the brake temperature becomes high and the friction pads 14 and 15 thermally expand, dragging may occur. Therefore, after the end of the second release control, when the brake temperature becomes high, the nut member 52 is further retracted.

[0047] In this embodiment, the actual retraction amount of the nut member 52 in the second release control and the third release control is obtained based on the operating time of the electric actuator 50. After the pressing force becomes smaller than the set value, since the load applied to the nut member 52 is very small, the retraction speed of the nut member 52 can be estimated based on the rotation speed of the electric actuator 50. Therefore, the target release control time corresponding to the target release control amount is obtained, and when the actual operating time of the electric actuator 50 in the second release control reaches the target release time, it can be considered that the nut member 52 has been retracted by the target release control amount.

[0048] Each of the above-mentioned ΔRa, ΔRb, and ΔRc can be set to a preset set value. Also, these ΔRa, ΔRb, and ΔRc can have the same value whether the brake temperature is high, normal, or cold.

[0049] The first release control and the second release control programs represented by the flowchart of FIG. 2 are executed every preset set time. In step 1 (hereinafter simply abbreviated as S1; the same applies to other steps), it is determined whether the second release control is in progress. In S2, it is determined whether the first release control is in progress. In S3, it is determined whether the operation of the EPBSW82 has been performed in the operating state of the service brake. If the determinations in S1-3 are NO, S1, 2, and 3 are repeatedly executed. If the determination in S3 is YES, the brake temperature is obtained in S4, and the first release control is started in S5. Then, in S6, it is determined whether the pressing force has become smaller than the set value. If the determination in S6 is NO, the first release control continues. When the determination in S2 becomes YES and S6 is executed. When the determination in S6 becomes YES, the second release control is started in S7.

[0050] The second release control is represented by the flowchart in FIG. 3. In S21, it is determined whether the brake temperature obtained in S4 is high temperature, normal temperature, or cold temperature. If it is high temperature, the target release control amount is determined to be the high-temperature release control amount ΔRb in S22. If the brake temperature is normal temperature, the target release control amount is determined to be the normal-temperature release control amount ΔRb in S23. If the brake temperature is cold temperature, it is determined to be the cold-temperature release control amount (ΔRa + ΔRb) in S24. Then, the electric actuator 50 is operated so that the actual release control amount of the nut member 52 reaches the target release control amount.

[0051] If it is during the second release control, the determination in S1 becomes YES, and it is determined in S8 whether the end condition of the second release control is satisfied. It is determined whether the release control amount of the nut member 52 has reached the target release control amount. Specifically, since it is determined whether the actual operation time of the electric actuator 50 in the second release control has reached the target control time corresponding to the target release control amount. If the determination in S8 is NO, the second release control is continued. If the determination in S8 is YES, end processing is performed in S9.

[0052] After that, the vehicle usually starts running. During the running of the vehicle, the brake temperature may rise when the service brake is operated. During the running of the vehicle, the third release control program represented by the flowchart in FIG. 4 is executed at every predetermined set time. In S41, the brake temperature is acquired, and in S42 and S43, it is determined whether the second release control is executed at a cold temperature or at room temperature. In other words, it is determined whether the brake temperature at the time of releasing the parking brake was at a cold temperature or at room temperature. If the determination in either S42 or S43 is YES, then in S44, it is determined whether the brake temperature is high. If the determination is YES, then in S45, the target release control amount is determined to be ΔRc, and in S46, the nut member 52 is retracted until the release control amount of the nut member 52 reaches the target release control amount.

[0053] Note that the third release control can be performed only once after the end of the second release control and before the parking brake is actuated next, or can be performed a plurality of times each time the temperature becomes high. When the third release control is performed a plurality of times, the target release control amount ΔRc can be set to a smaller value compared to the case where it is performed only once.

[0054] As described above, when the release control of the parking brake is performed, changes in current, the release control amount of the nut member 52, the brake temperature, etc. over time are shown in FIGS. 5, 6, and 7. In these FIGS. 5, 6, and 7, as indicated by the dashed line, in the conventional brake system, the target release control amount in the second release control was set to ΔRa + ΔRb + ΔRc regardless of whether the brake temperature was high or low. On the other hand, in the present embodiment, the second release control is performed in different modes based on the brake temperature. Specifically, in the second release control, the target release control amount is set to (ΔRa + ΔRb) when the brake temperature is at a cold temperature, and is set to ΔRb when the temperature is at or above room temperature. Therefore, it is possible to maintain the clearance at an appropriate size and to suppress dragging well. In addition, useless operation of the electric actuator 50 can be suppressed, and the operation time can be determined to be an appropriate length.

[0055] On the one hand, as shown in FIGS. 5 and 6, when the second release control is performed at a cold temperature or normal temperature, if the brake temperature becomes high during running, the third release control is performed, and the nut member 52 is retracted by the target release control amount ΔRc. Thereby, it is possible to satisfactorily suppress the dragging caused by the shortage of the release control amount of the nut member 52 in the second release control. Further, since the nut member 52 is retracted as necessary during the running of the vehicle after the end of the second release control, the target release control amount in the second release control can be set to a small value. As a result, the operation of the unnecessary electric actuator 50 can be further suppressed. The sound generated along with the operation of the electric actuator 50 can be suppressed, and the power consumption can be reduced.

[0056] In addition, in the above embodiment, the third release control is performed when the brake temperature becomes high after the end of the second release control, but the third release control can be performed when the brake temperature is estimated to become high. For example, when the vehicle is running at a high load, the third release control can be started.

[0057] In the above embodiment, the brake control unit is configured by the brake ECU 80 or the like, and the release control unit is configured by a part that stores S1-9, S21-24, S41-46, a part that executes them, and the like.

[0058] In addition, the present invention can be implemented in various forms with various changes and improvements based on the knowledge of those skilled in the art.

Explanation of Reference Numerals

[0059] 10: Disc brake 14, 15: Friction pad 16: Pressing device 20: Caliper 22: Piston 26: Hydraulic drive device 28: Electric drive device 30: Hydraulic chamber 32: Hydraulic source 50: Electric actuator 52: Nut member 56: Motion conversion device 80: Brake ECU 82: EPB SW 84: Wheel speed sensor 86: Longitudinal and lateral acceleration sensor 88: Hydraulic sensor 90: Current sensor 92: Ambient temperature sensor Patentable invention

[0060] (1) In a brake system including a brake control unit that controls an electric parking brake, a brake system including a release control unit in which the brake control unit performs release control for releasing the electric parking brake in different manners based on a brake temperature that is the temperature of the electric parking brake.

[0061] (2) The electric parking brake presses a friction engagement member against a brake rotating body by a drive member, the release control includes first release control for retracting the drive member until the pressing force of the electric parking brake becomes smaller than a set value, and second release control for further retracting the drive member after the pressing force becomes smaller than the set value, the brake system according to item (1), wherein the release control unit includes a portion that determines a release control amount, which is a retraction amount of the drive member in the second release control, based on the brake temperature.

[0062] (3) The brake system according to item (2), wherein the release control unit includes a portion that determines the release control amount in the second release control to be a smaller value when the brake temperature is high than when it is low.

[0063] (4) The brake system according to item (3), wherein the release control unit includes a portion that determines the release control amount in the second release control based on the degree of thermal expansion of the friction engagement member during running of the vehicle after release of the parking brake.

[0064] (5) The release control includes a third release control for further retracting the drive member after the second release control is completed. The release control unit performs the third release control when the brake temperature becomes equal to or higher than the set temperature, or is estimated to become equal to or higher than the set temperature, after the end of the second release control, and does not perform the third release control when the brake temperature is lower than the set temperature, or is not estimated to become equal to or higher than the set temperature. The brake system according to any one of (2) to (4).

[0065] The set temperature can be, for example, a temperature determined based on the temperature of the friction engagement member when the service brake is actuated during high-load driving. For example, it can be a temperature of about 300°C.

[0066] (6) The release control includes a third release control for further retracting the drive member after the second release control is completed. The release control unit performs the third release control when the brake temperature at the start of the release control is lower than the set temperature and the brake temperature becomes equal to or higher than the set temperature after the end of the second release control, and does not perform the third release control when the brake temperature at the start of the release control is equal to or higher than the set temperature, or when the brake temperature does not become equal to or higher than the set temperature after the second release control. The brake system according to any one of (2) to (5).

[0067] (7) The electric parking brake includes a friction engagement member and a pressing device that presses the friction engagement member against a brake rotating body. The friction engagement member is common to the service brake. The brake system according to any one of (1) to (6).

[0068] In an electric parking brake, the friction engagement member is pressed against the brake rotating body by the forward movement of a drive member by an electric actuator.

[0069] (8) The pressing device includes an electric actuator that moves a drive member to press the friction engagement member against the brake rotor. The service brake according to item (7) of the brake system includes a pressing device having a piston that presses the friction engagement member against the brake rotor and a hydraulic pressure source that applies hydraulic pressure to the piston.

Claims

1. In a brake system including a brake control unit that controls an electric parking brake, the brake system including a release control unit in which the brake control unit performs release control for releasing the electric parking brake in different modes based on a brake temperature that is the temperature of the electric parking brake.

2. The electric parking brake presses a friction engagement member against a brake rotating body by a driving member, the release control including first release control that controls the driving member to retreat until a pressing force of the electric parking brake becomes smaller than a set value, and second release control that further controls the driving member to retreat after the pressing force becomes smaller than the set value, the brake system according to claim 1, wherein the release control unit includes a portion that determines a release control amount, which is a retreat amount of the driving member in the second release control, based on the brake temperature.

3. The brake system according to claim 2, wherein the release control unit includes a portion that determines the release control amount in the second release control to be a smaller value when the brake temperature is high than when it is low.

4. The release control includes third release control that further retreats the driving member after the second release control ends, the release control unit performing the third release control when the brake temperature becomes equal to or higher than a set temperature, or is estimated to become equal to or higher than the set temperature, after the end of the second release control, and not performing the third release control when the brake temperature is lower than the set temperature, or is not estimated to become equal to or higher than the set temperature, the brake system according to claim 2 or 3.

5. The electric parking brake includes a friction engagement member and a pressing device that presses the friction engagement member against a brake rotating body, the brake system according to any one of claims 1 to 3, wherein the friction engagement member is common to a service brake.

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