Braking device

Abstract

To provide a braking device that can suppress electric currents corresponding to back electromotive force generated in an electric motor when reducing load torque and loss torque applied to a pump from flowing into a power supply of the electric motor.SOLUTION: A braking device 10 comprises: a pump device 30 having an electric motor 31 and a pump 41; a first liquid passage 15 through which brake liquid is ejected from the pump 41; a second liquid passage 16 connected to the first liquid passage 15; a check valve 17 provided at a connection part between the first liquid passage 15 and the second liquid passage 16; and a control device 70 that controls the electric motor 31. The control device 70 has a driving circuit 71 including a plurality of switching elements 72a and 72b and a control part 81. The control part 81 starts closed-loop formation processing for forming a closed loop by turning on only some of the plurality of switching elements 72a and 72b when the electric motor 31 is rotating, in order to stop driving of the electric motor 31.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a braking device provided in a vehicle.

Background Art

[0002] Patent Document 1 discloses a braking device including an electric motor having a rotor rotatable in both forward and reverse directions and a pump operated using the electric motor as a power source. In this braking device, when the electric motor is driven so that the rotor rotates in the forward direction, the pump pressurizes the brake fluid sucked from the suction port and discharges it from the discharge port. The braking device includes a first liquid passage connected to the discharge port of the pump, a second liquid passage connected to the first liquid passage, and a check valve disposed at a connection portion between the first liquid passage and the second liquid passage. The check valve restricts only the flow of the brake fluid from the second liquid passage to the first liquid passage among the flows of the brake fluid between the first liquid passage and the second liquid passage.

[0003] The higher the hydraulic pressure in the first liquid passage, the greater the load torque applied externally to the pump and the loss torque depending on the force applied externally. When the load torque and the loss torque are excessive, it is difficult to start the pump. Therefore, when the control unit of the braking device does not request the operation of the pump, it drives the electric motor so that the rotor rotates in the reverse direction. When the electric motor is driven in this way, the pump sucks the brake fluid in the first liquid passage from the discharge port and discharges the brake fluid from the suction port. As a result, the hydraulic pressure in the first liquid passage decreases, so that the load torque and the loss torque can be reduced, and thus it becomes easier to start the pump.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the braking device described above, the hydraulic pressure in the first fluid passage is forcibly reduced by driving an electric motor to rotate the rotor in the opposite direction. In this case, the power consumption of the braking device increases because an electric motor is driven.

[0006] Furthermore, when the hydraulic pressure in the first fluid passage is forcibly reduced by driving an electric motor, it is preferable for the control unit to control the motor speed, which is the rotational speed of the electric motor's rotor, so that the rate of decrease in the hydraulic pressure in the first fluid passage does not become too large. In this case, the control unit will apply a brake to the electric motor to prevent the motor speed from becoming too large. This may cause a back electromotive force to be generated in the electric motor. When a back electromotive force is generated in the electric motor, there is a risk that a current corresponding to the back electromotive force will flow to the power supply through the electric motor's drive circuit.

[0007] Now, consider the case where an electric motor has multiple power supplies. In this case, if current flows through the power supply circuit containing multiple power supplies due to the back electromotive force generated by the electric motor, a potential difference may occur between the multiple power supplies in the power supply circuit. To prevent the occurrence of a potential difference between multiple power supplies, it becomes necessary to add electronic components such as diodes to the power supply circuit, which increases costs. [Means for solving the problem]

[0008] A braking device for solving the above problems comprises a pump device having an electric motor rotatable in both forward and reverse directions and a pump powered by the electric motor; a first fluid passage from which brake fluid is discharged from the pump; a second fluid passage connected to the first fluid passage; a check valve located at the connection point between the first and second fluid passages; and a control device for controlling the electric motor. The check valve allows the passage of brake fluid from the first fluid passage to the second fluid passage, while restricting the passage of brake fluid from the second fluid passage to the first fluid passage. The electric motor is a multiphase motor having multiple coils. When the electric motor rotates in the forward direction, the pump draws brake fluid from a suction port, pressurizes the brake fluid, and discharges it from a discharge port into the first fluid passage. The control device comprises a drive circuit including multiple switching elements and a control unit that drives the electric motor by adjusting the magnitude of the current flowing through the multiple coils by operating the multiple switching elements. When the control unit stops the electric motor from driving, it starts a closed-loop formation process that forms a closed loop including the plurality of coils by turning on only some of the plurality of switching elements while the electric motor is rotating.

[0009] The higher the hydraulic pressure in the first fluid passage when the electric motor is stopped, the greater the load torque applied to the pump from the outside and the torque loss dependent on the external force applied when starting the pump. If the load torque is large, the pump may be moved by the load torque. When the pump is moved in this way, the brake fluid in the first fluid passage is drawn into the pump through the discharge port and discharged from the pump through the suction port. As a result, the amount of brake fluid in the first fluid passage decreases, and the hydraulic pressure in the first fluid passage decreases. Consequently, the load torque and torque loss applied to the pump the next time the pump is started will be smaller. In other words, the power consumption of the braking device can be reduced because the electric motor is not driven in reverse to reduce the load torque and torque loss.

[0010] When the pump is driven by the load torque described above, the electric motor rotates in the reverse direction, which can generate a back electromotive force (EMF) in the electric motor. In the braking device described above, when stopping the electric motor's drive, the closed-loop formation process is initiated while the electric motor is still rotating. Once the closed-loop formation process is executed, a closed loop is formed that includes multiple coils of the electric motor. Therefore, even if a back EMF is generated in the electric motor, this back EMF is consumed within the closed loop. As a result, it is possible to suppress the flow of current corresponding to this back EMF through the drive circuit to the electric motor's power supply.

[0011] Therefore, the above-described braking device can suppress the flow of current corresponding to the back electromotive force generated by the electric motor to the power supply of the electric motor when reducing the load torque and loss torque applied to the pump. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing the configuration of the braking device according to the embodiment. [Figure 2] Figure 2 is a cross-sectional view showing the schematic configuration of the pump included in the braking system. [Figure 3] Figure 3 is a flowchart showing the processing routine executed when the pump is stopped. [Figure 4] Figure 4 is a flowchart showing the processing routine executed when the closed-loop formation process is stopped. [Figure 5] Figure 5 is a flowchart showing the processing routines executed when the electric motor, which is the power source of the pump, is disabled or when the disablement is released. [Figure 6] Figure 6 is a timing chart showing the case when the electric motor rotates in the reverse direction when the pump is stopped. [Figure 7] Figure 7 is a timing chart showing the case where the electric motor does not rotate in the reverse direction when the pump is stopped. [Modes for carrying out the invention]

[0013] An embodiment of the braking system will be described below with reference to Figures 1 to 7. <Configuration of the braking system> As shown in Figure 1, the braking device 10 is a device that adjusts the braking force generated by the wheel by supplying brake fluid to the wheel cylinder 100, which is part of the friction brake of the wheel. The braking device 10 includes a reservoir tank 11, a pump device 30, and a control device 70 that controls the pump device 30. The braking device 10 includes a suction fluid passage 12 that connects the reservoir tank 11 and the pump device 30, and a supply fluid passage 14 that connects the pump device 30 and the wheel cylinder 100. The supply fluid passage 14 has a first fluid passage 15 connected to the pump device 30 and a second fluid passage 16 that connects the first fluid passage 15 and the wheel cylinder 100. A check valve 17 is provided at the connection between the first fluid passage 15 and the second fluid passage 16. The check valve 17 is a valve that allows brake fluid to pass from the first fluid passage 15 to the second fluid passage 16, while restricting the passage of brake fluid from the second fluid passage 16 to the first fluid passage 15.

[0014] The braking system 10 is equipped with a return fluid passage 19 that connects the second fluid passage 16 to the reservoir tank 11. A solenoid valve (not shown) is provided in the return fluid passage 19. When the solenoid valve is open, the brake fluid in the wheel cylinder 100 returns to the reservoir tank 11 via the return fluid passage 19.

[0015] The pump device 30 comprises an electric motor 31 and a pump 41 powered by the electric motor 31. The electric motor 31 is a brushless motor having a rotor (not shown) and a plurality of coils. In this embodiment, the electric motor 31 is a multiphase motor having three coils 32u, 32v, and 32w. The rotor of the electric motor 31 is capable of rotating in both forward and reverse directions.

[0016] Here, an electric motor with a rotor that can rotate in both forward and reverse directions is referred to as an "electric motor capable of rotating in both forward and reverse directions". When the rotor rotates in the forward direction, it is said that "the electric motor 31 rotates in the forward direction", and when the rotor rotates in the reverse direction, which is the opposite direction of the forward direction, it is said that "the electric motor 31 rotates in the reverse direction". The drive of the electric motor 31 to rotate the rotor in the forward direction is called "the forward drive of the electric motor 31", and the drive of the electric motor 31 to rotate the rotor in the reverse direction is called "the reverse drive of the electric motor 31".

[0017] The pump 41 has a suction port 42 and a discharge port 43 as ports. The suction port 42 is connected to the suction liquid passage 12. The discharge port 43 is connected to the first liquid passage 15. When the pump 41 operates due to the forward drive of the electric motor 31, the pump 41 sucks the brake liquid from the suction liquid passage 12 through the suction port 42, pressurizes the brake liquid, and discharges it from the discharge port 43 to the first liquid passage 15. Then, the brake liquid is supplied from the first liquid passage 15 to the wheel cylinder 100 through the second liquid passage 16. As a result, the hydraulic pressure in the wheel cylinder 100 increases, and braking force is generated on the wheel.

[0018] Referring to FIG. 2, the configuration of the pump 41 will be described in detail. The pump 41 is a gear pump. The pump 41 has a cylinder 45, a rotating shaft 46, an inner rotor 47, and an outer rotor 48. The rotating shaft 46 passes through the inside of the cylinder 45. Also, the rotating shaft 46 is connected to the rotor of the electric motor 31. Therefore, when the electric motor 31 is forward-driven, the rotating shaft 46 rotates in a direction according to the forward direction, which is the rotation direction of the rotor. When the rotor rotates in the forward direction, the rotation of the rotating shaft 46 is called "forward rotation", and when the rotor rotates in the reverse direction, the rotation of the rotating shaft 46 is called "reverse rotation".

[0019] The inner rotor 47 and the outer rotor 48 are accommodated in the cylinder 45. The inner rotor 47 is connected to the rotating shaft 46 so as to be integrally rotatable. A plurality of outer teeth 47a protruding outward in the radial direction are arranged along the circumferential direction on the inner rotor 47. The outer rotor 48 is arranged radially outside the inner rotor 47. A plurality of inner teeth 48a protruding inward in the radial direction are arranged along the circumferential direction on the outer rotor 48. A plurality of gaps SP are formed between the inner rotor 47 and the outer rotor 48 in the cylinder 45. By changing the size of the gap SP due to the rotation of the rotating shaft 46, suction of the brake fluid into the cylinder 45, pressurization of the sucked brake fluid, and discharge of the pressurized brake fluid to the outside of the cylinder 45 are performed.

[0020] The relationship of forces when the pump 41 operates will be described. Here, the force that rotates the rotating shaft 46 clockwise or the force that prevents the reverse rotation of the rotating shaft 46 is referred to as the "clockwise rotation force Fa". The force that prevents the clockwise rotation of the rotating shaft 46 or the force that rotates the rotating shaft 46 counterclockwise is referred to as the "counterclockwise rotation force Fb".

[0021] First, consider the case where the electric motor 31 is driven forward. When the rotating shaft 46 is rotating clockwise due to the forward drive of the electric motor 31, the motor torque, which is the torque transmitted from the electric motor 31 to the rotating shaft 46, and the inertia of the pump device 30 act on the rotating shaft 46 as the clockwise rotation force Fa. On the other hand, the lost torque and the theoretical torque of the pump device 30 act on the rotating shaft 46 as the counterclockwise rotation force Fb. The lost torque is the torque corresponding to the first hydraulic pressure and frictional loss in the pump device 30. That is, the lost torque is also referred to as a loss torque that depends on the force applied to the pump 41 from the outside. The theoretical torque is the torque corresponding to the first hydraulic pressure Pa1, which is the hydraulic pressure in the first liquid passage 15. That is, the theoretical torque is also referred to as a load torque applied to the pump 41 from the outside. When the clockwise rotation force Fa is greater than the counterclockwise rotation force Fb, the rotating shaft 46 rotates clockwise as shown by the solid arrow in FIG. 2, and thus the pump 41 operates.

[0022] The magnitude of the lost torque depends on the ambient temperature. When the components of the pump 41 expand or contract due to the ambient temperature, the ease with which the rotating shaft 46 and inner rotor 47 rotate changes. Also, when the temperature of the brake fluid changes due to changes in ambient temperature, the viscosity of the brake fluid changes. The ease with which the pump 41 operates also changes depending on the viscosity of the brake fluid.

[0023] Furthermore, the higher the first hydraulic pressure Pa1, the less the pump 41 can discharge brake fluid into the first fluid passage 15 via the discharge port 43. Therefore, the higher the first hydraulic pressure Pa1, the greater the theoretical torque.

[0024] Next, let's consider the case where the forward drive of the electric motor 31 is stopped and the rotation of the rotating shaft 46 is stopped. In this case as well, the motor torque and the inertia of the pump device 30 act on the rotating shaft 46 as a forward rotation force Fa, while the lost torque and theoretical torque of the pump device 30 act on the rotating shaft 46 as a reverse rotation force Fb. When the forward rotation force Fa is greater than the reverse rotation force Fb, the rotating shaft 46 rotates in the forward direction. However, when the forward rotation force Fa decreases, for example, due to a decrease in motor torque, and the forward rotation force Fa balances the reverse rotation force Fb, the rotation of the rotating shaft 46 stops.

[0025] Let's consider the case where the first hydraulic pressure Pa1 is excessive while the rotating shaft 46 is stopped. In this case, the theoretical torque of the pump device 30 can be said to be relatively large. When the theoretical torque is large, the reverse rotation force Fb becomes large, causing the rotating shaft 46 to try to rotate in the reverse direction. In this case, the inertia and lost torque of the pump device 30 act on the rotating shaft 46 as a forward rotation force Fa. Also, if the electric motor 31 is driven in the forward direction to prevent the reverse rotation of the rotating shaft 46, the motor torque also acts on the rotating shaft 46 as a forward rotation force Fa. If the reverse rotation force Fb is greater than the forward rotation force Fa, the rotating shaft 46 will start to rotate in the reverse direction. Once the rotating shaft 46 starts to rotate in the reverse direction in this way, the inertia of the pump device 30 will act on the rotating shaft 46 as a reverse rotation force Fb. Subsequently, as the theoretical torque decreases in accordance with the decrease in the first hydraulic pressure Pa1, the reverse rotation force Fb will also decrease. Finally, when the reverse rotation force Fb balances the forward rotation force Fa, the rotation of the rotating shaft 46 will stop.

[0026] Here, we consider the case where the rotating shaft 46 is stopped and the electric motor 31 is started under relatively high conditions of the first hydraulic pressure Pa1 to initiate forward rotation of the rotating shaft 46. The higher the first hydraulic pressure, the greater the theoretical torque. A large theoretical torque results in a large reverse rotation force Fb, making it difficult for the rotating shaft 46 to rotate forward. In other words, even if we try to drive the electric motor 31 in the forward direction, we cannot make the rotating shaft 46 rotate forward unless the forward rotation force Fa is greater than the reverse rotation force Fb.

[0027] <Detection system for braking system> As shown in Figure 1, the braking system 10 has multiple sensors as a detection system. For example, the braking system 10 has a hydraulic pressure sensor 61, a motor sensor 62, a brake sensor 63, a vehicle speed sensor 64, and an ambient temperature sensor 65. These sensors 61 to 65 output detection signals to the control device 70 according to the detection results. The hydraulic pressure sensor 61 detects the second hydraulic pressure Pa2, which is the hydraulic pressure of the second fluid passage. The motor sensor 62 detects the motor rotation angle θm, which is the rotation angle of the electric motor 31. The brake sensor 63 detects a state quantity BP (for example, the amount or force of operation of the brake pedal) that changes according to the driver's brake operation. The vehicle speed sensor 64 detects the vehicle speed VS, which is the vehicle's travel speed. The ambient temperature sensor 65 detects the ambient temperature TMP of the vehicle.

[0028] <Control device> The control device 70 adjusts the braking force generated by the wheels by controlling the pump device 30 based on detection signals from multiple sensors 61 to 65. This control device 70 includes a drive circuit 71 for the electric motor 31 and a control unit 81 that controls the drive circuit 71.

[0029] The drive circuit 71 converts the DC voltage output from the power supply circuit 200 of the electric motor 31 into an AC voltage and inputs it to the multiple coils 32u, 32v, and 32w of the electric motor 31. In this embodiment, the power supply circuit 200 includes two power supplies 210 and 220. Of the two power supplies 210 and 220, the power supply that supplies power to the electric motor 31 is selected by the control unit 81.

[0030] The drive circuit 71 includes multiple switching elements. Specifically, the drive circuit 71 provides two switching elements for each coil of the electric motor 31. One of these two switching elements is designated as the "first switching element 72a" and the other as the "second switching element 72b". In this embodiment, since the electric motor 31 has three coils, the drive circuit 71 has three first switching elements 72a and three second switching elements 72b.

[0031] Power MOSFETs are used as the switching elements 72a and 72b. However, other elements besides power MOSFETs, such as IGBTs (insulated-gate bipolar transistors), may be used as the switching elements 72a and 72b, as long as they can be switched on and off quickly.

[0032] The drive circuit 71 includes, as power lines, a first power line 74 connected to the anode of the power supply circuit 200 of the electric motor 31, a second power line 75 connected to the cathode of the power supply circuit 200, and arms 76u, 76v, and 76w in the same number as the number of coils in the electric motor 31. Arms 76u, 76v, and 76w are power lines connecting the first power line 74 and the second power line 75. Of the multiple arms 76u, 76v, and 76w, a U-phase coil 32u is connected to arm 76u. A V-phase coil 32v is connected to arm 76v. A W-phase coil 32w is connected to arm 76w. In arms 76u, 76v, and 76w, a first switching element 72a is arranged in the portion between the connection point with coils 32u, 32v, and 32w and the first power line 74, while a second switching element 72b is arranged in the portion between the connection point and the second power line 75.

[0033] The control unit 81 has a CPU 82 and a memory 83. The memory 83 stores various control programs that are executed by the CPU 82. The control unit 81 controls the electric motor 31 by having the CPU 82 execute the control programs. Specifically, the control unit 81 drives the electric motor 31 by adjusting the magnitude of the current flowing through the multiple coils 32u, 32v, and 32w of the electric motor 31 by operating multiple switching elements 72a and 72b of the drive circuit 71.

[0034] <Processing executed by the control unit> Referring to Figure 3, the processing routine executed by the control unit 81 when stopping the operation of the pump 41 will be described. This processing routine is repeatedly executed at predetermined control cycles from the start of operation of the pump 41 until the start of the closed-loop formation process described later. Here, "operation of the pump 41" refers to the operation of the pump 41 in which the pump 41 discharges brake fluid from the discharge port 43 by the forward drive of the electric motor 31.

[0035] In this processing routine, in step S11, the control unit 81 determines whether or not there is a request to stop the operation of the pump 41. If there is no request to stop (S11: NO), the control unit 81 terminates this processing routine. On the other hand, if there is a request to stop (S11: YES), the control unit 81 proceeds to the processing in step S13. In step S13, the control unit 81 determines whether or not the requested discharge amount DP, which is the requested value of the amount of brake fluid to be discharged from the pump 41, is 0 (zero). If the requested discharge amount DP is 0 (zero), the operation of the pump 41 is considered to have stopped. On the other hand, if the requested discharge amount DP is greater than 0 (zero), the operation of the pump 41 is considered not to have stopped. If the requested discharge amount DP is not 0 (zero) (S13: NO), the control unit 81 proceeds to the processing in step S15.

[0036] In step S15, the control unit 81 performs stop control, which is a control to stop the operation of the pump 41. That is, in stop control, the control unit 81 decreases the requested discharge amount DP toward 0 (zero). For example, the control unit 81 may set the latest value of the requested discharge amount DP to be the larger of the value obtained by subtracting the decrease amount from the previous value of the requested discharge amount DP, and 0 (zero). The previous value of the requested discharge amount DP is the requested discharge amount DP set when this processing routine was executed last time. The control unit 81 drives the electric motor 31 based on the latest value of the requested discharge amount DP. At this time, the control unit 81 drives the electric motor 31 in the positive direction such that the motor speed, which is the rotational speed of the rotor of the electric motor 31, decreases as the requested discharge amount DP decreases. After performing this stop control, the control unit 81 moves on to the processing in step S17.

[0037] In step S17, the control unit 81 determines whether the electric motor 31 is rotating in the reverse direction. For example, the control unit 81 determines whether the electric motor 31 is rotating in the reverse direction based on the change in the motor rotation angle θm detected by the motor sensor 62. If it is determined that the electric motor 31 is rotating in the reverse direction (S17: YES), the control unit 81 proceeds to the process in step S21. On the other hand, if it is determined that the electric motor 31 is not rotating in the reverse direction (S17: NO), the control unit 81 terminates this processing routine.

[0038] On the other hand, if the requested discharge amount DP is 0 (zero) in step S13 (YES), the operation of the electric motor 31 can be considered to have stopped, and the control unit 81 proceeds to the processing of step S19. In step S19, the control unit 81 determines whether or not the electric motor 31 is still rotating. For example, the control unit 81 determines whether or not the electric motor 31 is still rotating based on the change in the motor rotation angle θm detected by the motor sensor 62. If it is determined that the electric motor 31 is rotating (S19: YES), the control unit 81 proceeds to the processing of step S21. On the other hand, if it is determined that the electric motor 31 is not rotating (S19: NO), the operation of the pump 41 can be considered to have stopped, and the control unit 81 terminates this processing routine.

[0039] In step S21, the control unit 81 starts a closed-loop formation process by turning on only some of the multiple switching elements 72a and 72b of the drive circuit 71, thereby forming a closed loop including multiple coils 32u, 32v, and 32w. In this embodiment, the control unit 81 forms a closed loop by turning on all of the second switching elements 72b during the closed-loop formation process. At this time, the control unit 81 turns off all of the first switching elements 72a. Once the closed loop is formed in this way, the control unit 81 terminates this processing routine.

[0040] Next, referring to Figure 4, the processing routine executed by the control unit 81 when terminating the closed-loop formation process will be described. This processing routine is executed at predetermined control cycles when the closed-loop formation process is being performed.

[0041] In this processing routine, in step S31, the control unit 81 determines whether the motor rotation speed Nmt has become 0 (zero). Specifically, the control unit 81 derives the motor rotation speed Nmt based on the detection signal from the motor sensor 62 and determines whether the motor rotation speed Nmt is 0 (zero). If the motor rotation speed Nmt is not 0 (S31: NO), the electric motor 31 can be considered to be still rotating, so the control unit 81 terminates this processing routine. On the other hand, if the motor rotation speed Nmt is 0 (zero) (S31: YES), the rotation of the electric motor 31 can be considered to have stopped, so the control unit 81 proceeds to the processing in step S33.

[0042] In step S33, the control unit 81 determines whether the elapsed time TM from the point of stopping, which is the point in time when the rotation of the electric motor 31 stops, is equal to or greater than a predetermined stop time TMth. If the elapsed time TM is less than the predetermined stop time TMth (S33: NO), the control unit 81 terminates this processing routine. On the other hand, if the elapsed time TM is equal to or greater than the predetermined stop time TMth (S33: YES), the control unit 81 proceeds to the processing in step S35.

[0043] In step S35, the control unit 81 terminates the closed-loop formation process. That is, in this embodiment, the control unit 81 terminates the closed-loop formation process after the rotation of the electric motor 31 stops following the start of the closed-loop formation process. The control unit 81 terminates the closed-loop formation process by turning off all switching elements 72a and 72b that were turned on by the execution of the closed-loop formation process. Once the closed loop is resolved in this way, the control unit 81 terminates this processing routine.

[0044] Next, referring to Figure 5, the processing routine executed by the control unit 81 when prohibiting the driving of the electric motor 31 or releasing the prohibition on the driving of the electric motor 31 will be described. This processing routine is executed at predetermined control cycles.

[0045] In this processing routine, in step S51, the control unit 81 determines whether or not the electric motor 31 has stopped running. The control unit 81 determines that the electric motor 31 has stopped running if the requested discharge amount DP of the pump 41 is 0 (zero). Also, the control unit 81 determines that the electric motor 31 has stopped running if the closed-loop formation process is being executed, even if the requested discharge amount DP is not 0 (zero). If it is determined that the electric motor 31 has stopped running (S51: YES), the control unit 81 proceeds to the process in step S53. On the other hand, if it is determined that the electric motor 31 has not stopped running (S51: NO), the control unit 81 terminates this processing routine.

[0046] In step S53, the control unit 81 derives a first estimated hydraulic pressure value Pa1e, which is an estimated value of the hydraulic pressure in the first liquid passage 15. The process for deriving the first estimated hydraulic pressure value Pa1e will be described later. Once the first estimated hydraulic pressure value Pa1e is derived, the control unit 81 proceeds to the process in step S55.

[0047] In step S55, the control unit 81 determines whether the first estimated hydraulic pressure Pa1e is less than a predetermined hydraulic pressure Pa1th. The predetermined hydraulic pressure Pa1th is the hydraulic pressure used as a reference to determine whether the pump 41 can be started. As described above, if the first hydraulic pressure Pa1 is too high, the theoretical torque will be excessive, which may prevent the pump 41 from starting. Therefore, the predetermined hydraulic pressure Pa1th is set to the upper limit of the first hydraulic pressure at which the pump 41 can be started by the forward drive of the electric motor 31, or a hydraulic pressure lower than that upper limit.

[0048] If the first estimated hydraulic pressure Pa1e is equal to or greater than the predetermined hydraulic pressure Pa1th (S55:NO), the control unit 81 proceeds to step S57. In step S57, the control unit 81 prohibits the driving of the electric motor 31. With the driving prohibited in this way, the control unit 81 does not receive a request to start the pump 41. After that, the control unit 81 terminates this processing routine.

[0049] On the other hand, if the first hydraulic pressure estimate Pa1e is less than a predetermined hydraulic pressure Pa1th in step S55 (YES), the control unit 81 determines that the predetermined release condition for releasing the prohibition on driving the electric motor 31 has been met, and proceeds to the process in step S59. In step S59, the control unit 81 releases the prohibition on driving the electric motor 31. As a result, the control unit 81 can now accept requests to start the pump 41. After that, the control unit 81 terminates this processing routine.

[0050] Next, we will explain the derivation process for the first hydraulic pressure estimate, Pa1e. The braking device 10 has a hydraulic pressure sensor 61 that detects the hydraulic pressure in the second fluid passage 16. Therefore, the control device 70 can obtain the first hydraulic pressure Pa1 at the time the pump 41 is stopped, based on the second hydraulic pressure Pa2 detected by the hydraulic pressure sensor 61. Specifically, the pressure difference ΔP generated between the first fluid passage 15 and the second fluid passage 16 by the check valve 17 is determined from the specifications of the check valve 17, so the control unit 81 knows the pressure difference ΔP. Therefore, the control unit 81 derives the value obtained by subtracting the pressure difference ΔP from the second hydraulic pressure Pa2 at the time the pump 41 is requested to be stopped as the first hydraulic pressure Pa1 at the time the pump 41 is requested to be stopped. The first hydraulic pressure Pa1 at the time the pump 41 is requested to be stopped is defined as the "first hydraulic pressure reference value Pa1b".

[0051] Furthermore, the internal volume of the pump 41, the volume of the discharge port 43 of the pump 41, and the volume of the first fluid passage 15 are known in advance. The sum of the internal volume of the pump 41, the volume of the discharge port 43 of the pump 41, and the volume of the first fluid passage 15 is called the "total volume VLtl". At this time, the control unit 81 derives the total fluid volume Qtl at the time when the operation of the pump 41 is requested to stop, based on the total volume VLtl and the first fluid pressure reference value Pa1b. The total fluid volume Qtl is the sum of the brake fluid volumes present inside the pump 41 and the first fluid passage 15. The total fluid volume Qtl at the time when the operation of the pump 41 is requested to stop is called the "reference total fluid volume Qtlb".

[0052] Furthermore, if the electric motor 31 stops, the brake fluid in the first fluid passage 15 may flow back into the suction fluid passage 12 via the pump 41. In other words, the brake fluid in the first fluid passage 15 may flow back into the suction fluid passage 12 through the gaps in the components of the pump 41. Also, if the hydraulic pressure in the first fluid passage 15 is high and the theoretical torque (i.e., the load torque applied to the pump 41 from the outside) is excessive, the rotating shaft 46 of the pump 41 may rotate in reverse, causing the pump 41 to suck in the brake fluid in the first fluid passage 15 via the discharge port 43 and discharge the brake fluid into the suction fluid passage 12 via the suction port 42.

[0053] The flow velocity of brake fluid flowing back from the first fluid passage 15 to the suction fluid passage 12 due to the reverse rotation of the rotating shaft 46 is defined as the "reverse rotation discharge flow rate DAR of the pump 41". In addition, the flow velocity of brake fluid flowing back from the first fluid passage 15 to the suction fluid passage 12 through the gaps in the components of the pump 41, regardless of the reverse rotation of the rotating shaft 46, is defined as the "leakage flow rate DAL of the pump 41". In this case, since the reverse rotation discharge flow rate DAR and the leakage flow rate DAL are determined by the structure of the pump 41, the reverse rotation discharge flow rate DAR and the leakage flow rate DAL can be known in advance.

[0054] In this embodiment, after deriving the above-mentioned reference total liquid volume Qtlb, the control unit 81 can grasp the trend of the total liquid volume Qtl using the following relational expression (Equation 1). In relational expression (Equation 1), "t" is the elapsed time from the reference time, which is the time when the first liquid pressure reference value Pa1b was derived. "Qtl(t)" is the estimated value of the total liquid volume at the time when elapsed time t has elapsed from the reference time.

[0055]

number

[0056] The control unit 81 then derives a first estimated hydraulic pressure value Pa1e based on the change in the total liquid volume Qtl. That is, since the total volume VLtl does not change, the control unit 81 derives a smaller value as the total liquid volume Qtl decreases as the first estimated hydraulic pressure value Pa1e.

[0057] <Operation and Effects of This Embodiment> Referring to Figure 6, we will now explain the case where the electric motor 31 rotates in the reverse direction when the pump 41 is stopped.

[0058] As shown in Figures 6(A) and (B), at timing t11 while the pump 41 is operating, a request is made to stop the pump 41. The stop control then reduces the requested discharge volume DP toward 0 (zero). As a result, the motor rotation speed Nmt gradually decreases. Finally, at timing t12, the motor rotation speed Nmt becomes 0 (zero).

[0059] In the example shown in Figure 6, the theoretical torque (i.e., the external load torque applied to the pump 41) becomes excessive during the period from timing t11 to timing t12 due to the high first hydraulic pressure Pa1. Therefore, between timing t12 and timing t14, the reverse rotational force Fb shown in Figure 2 is greater than the forward rotational force Fa, causing the electric motor 31 to rotate in the reverse direction. During this period, the motor rotational speed Nmt becomes a negative value.

[0060] When the electric motor 31 stops, brake fluid flows back from the first fluid passage 15 to the suction fluid passage 12 via the pump 41. In the example shown in Figure 6, the theoretical torque is excessive, causing the electric motor 31 to rotate in the reverse direction. Therefore, in addition to the backflow of brake fluid through the gaps in the components of the pump 41, backflow of brake fluid also occurs due to the reverse rotation of the rotating shaft 46 by the pump 41. As a result, the first hydraulic pressure Pa1 is reduced.

[0061] In this embodiment, the change in the total liquid volume Qtl can be obtained using the above relational equation (Equation 1), and therefore the change in the first estimated liquid pressure Pa1e can be obtained. As a result, the control unit 81 can determine that the first estimated liquid pressure Pa1e decreases to a predetermined liquid pressure Pa1th at timing t13.

[0062] At the subsequent timing t14, the first hydraulic pressure Pa1 has also become sufficiently low, meaning the theoretical torque has decreased, and the electric motor 31 also stops rotating in the reverse direction. When the electric motor 31 is rotating in the reverse direction, a back electromotive force may be generated in the electric motor 31. In this embodiment, when it is detected that the electric motor 31 is rotating in the reverse direction after timing t12, the closed-loop formation process is started. That is, when stopping the drive of the electric motor 31, the closed-loop formation process is started while the electric motor 31 is still rotating. When the closed-loop formation process is executed, all the second switching elements 72b in the drive circuit 71 are turned on, so a closed loop is formed that includes the multiple coils 32u, 32v, and 32w of the electric motor 31. Then, even if a back electromotive force is generated in the electric motor 31, the back electromotive force is consumed within the closed loop. Therefore, it is possible to suppress the flow of current corresponding to the back electromotive force into the power supply circuit 200 via the drive circuit 71. That is, when reducing the theoretical torque, which is the load torque applied to the pump 41, it is possible to suppress the flow of current corresponding to the back electromotive force generated in the electric motor 31 into the power supply circuit 200. Therefore, the power supply circuit 200 does not need to take measures to prevent current from flowing in from the drive circuit 71 in accordance with the back electromotive force. In other words, the cost increase of the power supply circuit 200 can be suppressed. Also, since the electric motor 31 is not driven in reverse in order to lower the first hydraulic pressure estimate Pa1e, the increase in power consumption of the braking device 10 can also be suppressed.

[0063] The closed-loop formation process ends at timing t15, when the judgment stop time TMth has elapsed from timing t14, when the motor rotation speed Nmt becomes 0 (zero). In other words, all second switching elements 72b that were turned on by the closed-loop formation process are turned off.

[0064] In the example shown in Figure 6, when the closed-loop formation process begins, the electric motor 31 is disabled. That is, the electric motor 31 is disabled until timing t13 when the first estimated hydraulic pressure Pa1e reaches a predetermined hydraulic pressure Pa1th. Therefore, the control unit 81 will not instruct the pump 41 to start during the period when it may not be possible to start the pump 41 due to the large theoretical torque. Note that the first estimated hydraulic pressure Pa1e continues to decrease even after timing t13, so the disablement of the electric motor 31 is released after timing t13.

[0065] Next, referring to Figure 7, we will explain the case where the closed-loop formation process is not performed when the pump 41 is stopped. As shown in Figures 7(A) and (B), at timing t21 while the pump 41 is operating, a request is made to stop the pump 41. The stop control then reduces the requested discharge rate DP toward 0 (zero). As a result, the motor speed Nmt gradually decreases. Finally, at timing t22, the motor speed Nmt becomes 0 (zero).

[0066] In the example shown in Figure 7, the theoretical torque is relatively small because the first hydraulic pressure Pa1 is not very high even during the period from timing t21 to timing t22. Therefore, the reverse rotational force Fb shown in Figure 2 will not be greater than the forward rotational force Fa. As a result, the electric motor 31 does not rotate in reverse. That is, when the required discharge amount DP becomes 0 (zero), the motor rotational speed Nmt is maintained at 0 (zero). In other words, since the electric motor 31 does not rotate in reverse, the closed-loop formation process is not executed.

[0067] If the electric motor 31 does not rotate in the reverse direction, no back electromotive force is generated in the electric motor 31. In other words, in this embodiment, if it can be inferred that no back electromotive force is generated in the electric motor 31, the closed-loop formation process is not executed. Therefore, it is possible to suppress the excessive number of times the closed-loop formation process is executed.

[0068] In the example shown in Figure 7, the operation of the electric motor 31 is stopped at timing t22, thus prohibiting the operation of the electric motor 31. Even if the electric motor 31 does not rotate in the reverse direction, brake fluid flows back from the first fluid passage 15 to the supply fluid passage 14 through the gaps in the components of the pump 41. As a result, the first fluid pressure Pa1 decreases. In the example shown in Figure 7, the estimated first fluid pressure Pa1e reaches a predetermined fluid pressure Pa1th at timing t23, so the prohibition on driving the electric motor 31 is released after timing t23. Note that if the electric motor 31 does not rotate in the reverse direction as in the example shown in Figure 7, it is advisable to substitute 0 (zero) for "DAR" in the above relational equation (Equation 1) to derive the change in the total fluid volume Qtl.

[0069] Incidentally, when stopping the drive of the electric motor 31, it is possible that the electric motor 31 may still be rotating in the forward direction even if the requested discharge amount DP becomes 0 (zero). In this embodiment, if the electric motor 31 is still rotating in the forward direction even if the requested discharge amount DP becomes 0 (zero), the closed-loop formation process is started while the electric motor 31 is rotating in the forward direction.

[0070] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0071] In the above embodiment, the trend of the first estimated hydraulic pressure Pa1e can be derived. Therefore, the trend of the theoretical torque can be grasped based on the trend of the first estimated hydraulic pressure Pa1e. In addition, the lost torque of the pump 41 can also be estimated. Incidentally, the lost torque varies according to the motor rotation speed Nmt, the ambient temperature TMP, and the first hydraulic pressure Pa1. Furthermore, when the drive of the electric motor 31 is stopped and the electric motor 31 is rotating in the reverse direction, the control unit 81 can derive the motor rotation speed Nmt using the following relational equation (Equation 2). In relational equation (Equation 2), "Tt" is the theoretical torque, and "Tl" is the lost torque. "I" is the inertia of the pump device 30, and "Δt" is the calculation period of the motor rotation speed Nmt.

[0072]

number

[0073] The control unit 81 can estimate the timing at which the electric motor 31 stops rotating in the reverse direction by performing calculations using the above relational equation (Equation 2). The control unit 81 may then terminate the closed-loop formation process at the estimated timing, or it may terminate the closed-loop formation process after a predetermined time has elapsed from that timing.

[0074] In the processing routine shown in Figure 4, the determination in step S33 may be omitted. In this case, the closed-loop formation process will be terminated when the motor rotation speed Nmt becomes 0 (zero), that is, when the rotation of the electric motor 31 stops.

[0075] If a hydraulic pressure sensor for detecting the hydraulic pressure in the first fluid passage 15 is provided in the braking device 10, the control unit 81 may determine the timing for ending the closed-loop formation process based on the value detected by the hydraulic pressure sensor.

[0076] If the closed-loop formation process is executed, the prohibition on driving the electric motor 31 may be released at the time the closed-loop formation process is completed. In the above embodiment, even if the requested discharge amount DP becomes 0 (zero) and the drive of the electric motor 31 stops, if the electric motor 31 is still rotating, the closed-loop formation process is executed. However, if the rotation direction of the electric motor 31 at this time is in the forward direction, the closed-loop formation process does not need to be executed. On the other hand, it is preferable to start the closed-loop formation process when the rotation direction of the electric motor 31 at this time becomes reversed.

[0077] When stopping the drive of the electric motor 31, a closed-loop formation process may be performed. That is, the closed-loop formation process may be started when the requested discharge amount DP is reduced by the stop control.

[0078] When the operation of pump 41 is stopped, the requested discharge rate DP may be suddenly set to 0 (zero). In this case, even if the forward drive of electric motor 31 is stopped, its rotor may still be rotating in the forward direction. Therefore, if the drive of electric motor 31 is stopped by suddenly setting the requested discharge rate DP to 0 (zero), the closed-loop formation process may be started without checking whether the rotor is still rotating or not.

[0079] In the closed-loop formation process, all first switching elements 72a in the drive circuit 71 may be turned on to form a closed loop including multiple coils 32u, 32v, and 32w. In this case, the second switching element 72b does not need to be turned on.

[0080] The pumping device 30 may be a device equipped with a pump other than a gear pump. Examples of pumps other than gear pumps include piston pumps and vane pumps. The electric motor that powers pump 41 can be any multiphase motor having two or more coils. In other words, the electric motor does not have to have three coils.

[0081] The braking system may include a pump device other than the pump device 30 that adjusts the amount of brake fluid supplied to the wheel cylinder 100. For example, the braking system may include a pump device that constitutes a booster device that assists the driver's force in operating the brake pedal.

[0082] The control unit 81 is not limited to one that includes a CPU and ROM and executes software processing. In other words, the control unit 81 may have any of the following configurations (a) to (c). (a) Having one or more processors that perform various processes according to computer programs. A processor includes a CPU and memory such as RAM and ROM. Memory stores program code or instructions configured to cause the CPU to perform processes. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or dedicated computer.

[0083] (b) It must have one or more dedicated hardware circuits to perform various processes. Examples of dedicated hardware circuits include application-specific integrated circuits, i.e., ASICs or FPGAs. ASIC is an abbreviation for "Application Specific Integrated Circuit," and FPGA is an abbreviation for "Field Programmable Gate Array."

[0084] (c) The system includes a processor that performs some of the various processes according to a computer program, and dedicated hardware circuits that perform the remaining processes. [Explanation of Symbols]

[0085] 10...braking device 15...1st liquid path 16…Second liquid path 17… Check valve 30... Pumping device 31… Electric motor 32u, 32v, 32w... coil 41... Pump 42... Suction port 43…Discharge port 45…Cylinder (a component of a pump) 46…Rotating shaft (component of a pump) 47…Inner rotor (a component of a pump) 48…Outer rotor (a component of a pump) 70...Control device 71…Drive circuit 72a, 72b... Switching elements 81... Control Unit SP…Void

Claims

1. The system comprises a pump device having an electric motor rotatable in both forward and reverse directions and a pump powered by the electric motor; a first fluid passage from which brake fluid is discharged from the pump; a second fluid passage connected to the first fluid passage; a check valve located at the connection point between the first and second fluid passages; and a control device for controlling the electric motor. The aforementioned check valve allows brake fluid to pass from the first fluid passage to the second fluid passage, while restricting the passage of brake fluid from the second fluid passage to the first fluid passage. The aforementioned electric motor is a multiphase motor having multiple coils, The pump, when the electric motor rotates in the forward direction, draws brake fluid from the suction port, pressurizes the brake fluid, and discharges it from the discharge port into the first fluid passage. Of the two rotation directions of the electric motor, the direction opposite to the positive direction is the reverse direction. The control device includes a drive circuit that includes a plurality of switching elements, and a control unit that drives the electric motor by adjusting the magnitude of the current flowing through the plurality of coils by operating the plurality of switching elements. When the control unit detects that the electric motor is rotating in the reverse direction when it stops the electric motor, it starts a closed-loop formation process that forms a closed loop including the plurality of coils by turning on only some of the plurality of switching elements while the electric motor is rotating. Braking device.

2. The control unit terminates the closed-loop formation process when the rotation of the electric motor stops after the start of the closed-loop formation process, or at or after that point. The braking device according to claim 1.

3. The control unit, when it stops the operation of the electric motor, is configured to prohibit the operation of the electric motor until a predetermined release condition is met. The control unit, Based on the sum of the brake fluid volume in the first fluid passage, the brake fluid volume in the discharge port, and the brake fluid volume inside the pump, the amount of brake fluid discharged from the suction port by the pump due to the reverse rotation of the electric motor, and the amount of brake fluid leaking from the discharge port to the suction port through the gaps in the components of the pump, an estimated value of the fluid pressure in the first fluid passage is derived. The system is configured to determine that the release condition has been met when the estimated value of the liquid pressure in the first liquid passage falls below a predetermined liquid pressure. The predetermined hydraulic pressure is set to the upper limit of the hydraulic pressure in the first fluid passage that allows the pump to be started by the drive of the electric motor, or a hydraulic pressure lower than that upper limit. A braking device according to claim 1 or claim 2.

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